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JUNE 2023 ISSN 1030-2662 06 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST 26 | Basic RF Signal Generator Generate a test signal from 10Hz to 25MHz 38 | The History of ETI Magazine What happened over ETI magazine’s 19-year life 44 | Loudspeaker Testing Jig A convenient way to test and tweak loudspeakers 60 | WiFi Time Source for GPS Clocks Modify your GPS clock to use NTP time over WiFi 70 | The Y2K38 Bug The Year 2000 Problem wasn’t the last ...plus much more inside STARLINK How SpaceX is Providing Global Wireless Internet Printing Perfection: Bold details and large sized models Our Newest 8K 3D Printer Elevate your creations with our cutting-edge Phrozen Sonic Mega 8K Resin 3D Printer. Outperforming the competition with 43µm detail, nearly double the precision of other large scale printers. 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Savings on Original RRP (ORRP). Contents Vol.36, No.06 June 2023 14 Starlink, Swarm and Starshield SpaceX is providing affordable internet anywhere in the world via Starlink! They do this via a cluster of satellites in low Earth orbit (LEO). SpaceX also offers the Swarm and Starshield services, aimed at remote connectivity for IoT devices and government users respectively. By Dr David Maddison Technology feature 38 The History of ETI Magazine This article explains what happened during Electronics Today International (ETI) magazine’s 19 year lifespan. It started on March 23rd, 1971 and lasted until its merger with Electronics Australia (EA) in June 1990. By Peter Ihnat History feature 56 Using Room EQ Wizard (REW) While you don’t need our Loudspeaker Test Jig to use this software, they are an ideal combination. We describe how to set up and use REW or Speaker Workshop for designing and tweaking loudspeakers. By Phil Prosser Software guide The history of: ETI MAGAZINE starting on page 38 Page 26 Basic RF Signal Generator LOUDSPEAKER TESTING JIG 70 The Y2K38 Bug The Y2K bug ended with a fizzle due to diligent preparations; however, it isn’t the only time related bug. We cover what we are doing to make sure our newest project does not succumb to these issues. By Tim Blythman Software feature 26 Basic RF Signal Generator This RF Signal Generator uses an AD9834 IC to generate a test signal from 10Hz to 25MHz. It’s ideal if all you need is a simple piece of test equipment that is also compact and easy to build. By Charles Kosina Test equipment project Page 44 2 Editorial Viewpoint 5 Mailbag 37 Subscriptions 69 Product Showcase 83 Circuit Notebook Our Loudspeaker Test Jig allows you to measure complex impedances via your PC. And as per the name, connecting a microphone to it lets you test loudspeakers. It allows you to measure the speaker or driver frequency, phase response, relative SPL and more. By Phil Prosser Audio / Test equipment project 86 Vintage Radio 60 WiFi Time Source for GPS Clocks 96 Serviceman’s Log 44 Loudspeaker Testing Jig The Raspberry Pi Pico W is the perfect substitute for a GPS module, especially when you cannot get a reliable GPS signal. You can instead source the time from an internet NTP server via WiFi. We show you how to modify our existing GPS clock designs to use the Pico W module instead. By Tim Blythman Timekeeping project 72 Wideband Fuel Mixture Display, Pt3 To finish off our Fuel Mixture Display, we cover the construction details, how you configure, install it in your car and use our Bluetooth app. By John Clarke Automotive project 1. Carbon monoxide (CO) detector 2. DCC block train detector 3. Cupboard light 4. 3D-printed case for SMD Test Tweezers Servicing Vibrators, Pt1 by Dr Hugo Holden 104 Online Shop 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Junk email is out of control We have multiple layers of junk email filtering, starting with an adaptive Bayesian filtering system, followed by hand-written rejection rules, then junk filtering on our email clients. Despite this, we still get hundreds of junk emails per day. Sometimes they come in every few seconds. If I removed all the filtering, it would be thousands per day. This can make it very hard to find legitimate emails among the deluge. It’s also hard to get any work done when we are constantly interrupted by notifications for new emails when most of them are a waste of our time. I just received another one while writing that last sentence. Ugh! It’s getting to the point where we might have to stop paying attention to incoming emails except for checking a few times per day. That way, we can more efficiently delete all the junk. Unfortunately, that will mean readers or customers who want to ask us questions or otherwise get support will have to wait longer. If you tried to contact us lately but didn’t get a reply, that might explain what happened to your email. In that case, please try again; hopefully, the second time will be the charm. There needs to be an internet-wide system for dealing with this type of junk (and scams too). Every email client should have a button to report a message as junk or a scam to a local authority. Once that authority gets more than a couple of reports for the same originating server/IP address, it should be automatically disconnected from the rest of the internet until it can be proven that it is no longer a source of these rubbish messages, eg, by fixing the misconfiguration or remove the virus that was allowing spammers/scammers to use it as a relay. As I wrote that last paragraph, I got another ten junk emails. This is a solvable problem, but a more comprehensive effort is needed to deal with it. We use SPF (sender policy framework) to prevent junk mail from claiming to come from us but that does little to stop us from receiving it unless everyone uses similar technology. One solution I have considered is to use a service like Google’s Gmail, which seems to be very good at dealing with junk mail, but I think it errs on the side of placing legitimate emails in the junk pile to do that, which is not ideal. I also don’t like the idea of having our email hosted by a foreign company, nor do I want to pay extra for a service we can otherwise provide ourselves. Email forwarding concerns While I’m on the topic of email, we sometimes have problems sending emails to readers when they have email forwarding set up improperly. If you forward from address a<at>x.com to address b<at>y.com by simply redirecting the whole email to the y.com server, it will be rejected. That’s because that server sees our from address as <at>siliconchip.com.au, but the originating server from its point of view (x.com) is not one of our mail servers. The solution is for the forwarder to re-write the ‘from address’ so that it is in its domain; in this case, x.com. That way, the receiving server will see that it matches the source and won’t reject it. If you forward your email to another address, please check that it does this correctly. Otherwise, any emails we (and others using SPF) send you will probably be rejected. Cover image: www.pexels.com/photo/white-outer-space-satellite-586056/ by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au Delivering more The widest selection of semiconductors and electronic components in stock and ready to ship™ au.mouser.com australia<at>mouser.com MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Australian underground communications specialists I just read your April 2023 issue article on Underground Communications (siliconchip.au/Article/15729). Having worked in this field for several mines on-site in the recent past, I note that some Australian companies are global leaders in this field. For instance, Mine Site Technologies (https://mstglobal. com) has its global headquarters not far from you in North Ryde, NSW. They design and manufacture an extensive portfolio of products and integrate complete underground systems, including communications, people and machinery tracking, cap lamp, SCADA telemetry, UG (underground) minewide WiFi and PoE networking and CCTV, VLF emergency comms, leaky feeder UHF systems, remote blasting etc. It is amazing what is being done by such local businesses and deployed worldwide. Other significant mining industry comms/automation suppliers/manufacturers based in Australia that I am aware of include Omnitronics (WA), Redarc (SA), Ampcontrol (NSW) and Sage Automation (SA). Peter Guenther, North Haven, SA. What about pumped hydro energy storage? Your April 2023 editorial on electricity generation and storage raised a few points I have been pondering for a considerable time. I am a qualified Mechanical Design Engineer and a member of Engineers Australia (EA) (they will probably disown me after this!). As a student, I was made aware of the losses between the South Island (the “mainland”, according to the locals) and the North Island of New Zealand (“Pig Island”, according to the South Islanders). Hydroelectricity generation was abundant on the South Island but not on the North Island. To get it from the South Island to the North Island required conversion from AC to DC (to get under Cook Strait) and, at the other end, to convert it back from DC to AC. These conversion processes resulted in the loss of 80% of the input energy. Why did they put up with these losses? Desperation? With electronic conversion now available, the losses are much lower. In those early days, the conversion was done using an AC motor to power a DC generator and, at the other end, a DC motor to power an AC alternator. Now, you raise the question of the storage of energy from solar and other sources. I considered this question some time ago, and the most viable option appeared to be in pumped hydro storage. I’ll admit that other (pie-in-thesky) options may work, but they have to be created first! There is also the consideration of using lithium-ion batteries for storage. Still, serious ethical concerns exist over siliconchip.com.au mining the raw materials required to build them, especially in large quantities. EA (Engineers Australia, not Electronics Australia) ran an article recently which stated quite clearly that for the world to change to nearly 100% electric vehicles in 10 years would require the mining of more copper over that period than has ever been mined on this planet previously. As I recall, copper has been mined for about 2000 years! To say that we will mine more than this in a 10-year time frame raises several questions. I am not aware of a sufficient number of mines that could ramp up production so quickly. Even if they exist, it takes time to ramp up production to such a high level, probably three to four years. Is it possible to mine the required amount of copper in such a time frame? I think not. I like the idea of conducting experiments to ‘create green petrol’, as is currently happening in South America. This uses solar energy to acquire hydrogen from water using electrolysis and carbon from carbon dioxide in the atmosphere, also using solar energy, to create a usable form of petrol. As I understand it, this is close to being 100% solar-­ powered and does not add to the pollutants to the atmosphere. Of course, the infrastructure to dispense this product is currently in place worldwide! John, Tewkesbury, UK. Comment: pumped hydro seems like the obvious answer. The problem is that it doesn’t seem possible to store enough energy in our existing dams and we’re unlikely to build more. To give you an idea of the challenge, a dam with a 100m head would go through the entire full water volume of Warragamba dam to provide NSW’s electricity needs for just one day! Pitfalls of Artificial Intelligence were foreseen The ongoing discussion on AI in the magazine has been of some interest to me. I’m over 80. Many years ago, a science fiction writer named Isaac Asimov wrote a series of books about robots before the actuality of robots was achieved. Asimov also wrote into the stories a concept of robots being programmed so they could not harm humans. Very convenient, so it seemed. Then he added a curve; the robots were also required to protect humans from harm. Many other writers followed that regime. Asimov realised a flaw in his “robot laws”. In protecting a human from harm, it could also be interpreted as needing to protect the human from their own actions and thus began an “update” of the law where the robots effectively locked the humans out of any potential to cause harm to themselves. Australia's electronics magazine June 2023  5 We are now facing that same complex situation where AI may well reprogram itself to “protect” us from our own perceived stupidities and thus lock us into a digital prison. Adding to that, Arthur C. Clarke inserted that robotic law into his story 2001, where the robot on the spaceship took over all functions. Again, all these situations were foreseen before the 1960s. Robert Forbes, Forest Hill, Vic. Comment: when OpenAI starts collaborating with Boston Dynamics, we’re all doomed. Look them up if you haven’t heard of them. For example, see this video: https://youtu. be/tF4DML7FIWk Incorrect electrode placement for Heart Rate Sensor The Heart Rate Sensor Module you reviewed in the February 2023 issue (siliconchip.au/Article/15662) is a delightfully simple solution to a significant problem faced by designers for many years. However, the article defines the three locations for the electrodes as Right Arm (RA), Left Arm (LA) and Right Leg (RL). The most common medical practice is to place the electrodes on the RA, LA and the left leg (LL). This is known as “Einthoven’s triangle” after the originator of this monitoring pattern. Dr Stewart Montano, Clontarf, NSW. Success in troubleshooting Micromite LCD BackPack V2 I appreciate your help with my Micromite LCD BackPack V2 (May 2017; siliconchip.au/Article/10652). I had to wait for some new parts to arrive before I could try again with the BackPack v2 and the GPS-synched Frequency Reference. I fixed the problems, but one last question came up during the fix. I tried your suggestion to send a Ctrl-C from the serial console to break out of the running program. For some reason, that program would not stop running-- Ctrl-C didn’t work, nor did any other tips/tricks from the articles on the Frequency Reference, BackPack V2 etc. Still, the May 2017 article on the BackPack V2 mentions a ‘nuclear’ option of pressing the mode switch on the Microbridge for at least two seconds while simultaneously sending a stream of exclamation marks. Yes, it works, but it also completely erases programs and options held in memory. So, I reloaded all the software and tried again. I still had no luck with the screen; it had the same problems as before. I ordered and tried a new touchscreen, which fixed it; I completed the GUI test and calibration procedures with no further problems. All screen items work the way they should. With that out of the way, I tried to figure out what was causing the repeated reset of the Micromite processor, causing the screen to jump between the Status and Main pages for the first few minutes after startup. After doing basic voltage and continuity checks (no problems found), I took a look at the 47µF tantalum/10µF ceramic capacitor, as you recommended. The capacitor was the right type, capacitance, polarity etc, but lacking anything better to try, I just desoldered it and soldered in a new 47µF tantalum polarised capacitor. The new one worked, and the resets have stopped. I have no idea what was wrong with the first capacitor, but at this point, I don’t care. Capacitors are cheap, and the unit is fixed. 6 Silicon Chip Australia's electronics magazine siliconchip.com.au After that, I went through the procedures to mount the unit in a Jiffy box, adjust the temperature settings etc. Per the article’s instructions, the oven temperature set point is at 35°C. With the oven’s bottle cap in place, reaching that temperature is no problem. I adjusted the offset value from 3000 to 1500 to bring the steady state temperature to within 0.1°C of the set point. With that steady state, I checked the status page and found that the status is “TEMP COMP”. The offset’s DAC output is not constant but varies near the 1500 offset I set. What is the “TEMP COMP” status, and do I need to be doing anything about it? Dan Purdy, Enon, Ohio, USA. Comment: We are glad you got it sorted out. TEMP COMP is the status that you want. It is short for ‘temperature compensated’ and means everything is working, with the oven near its temperature setpoint. Comments on welding with medical implant The following is my reaction to the anonymous letter titled “Reader won’t let health problems get in the way of welding!” starting on page 12 of the May 2023 issue (Mailbag). Companies should not prevent someone from earning a living or being denied leisure unnecessarily. Yet they do not test their products for their susceptibility to electromagnetic radiation. Unfortunately, most regulators are only concerned about the health effects of emitting electromagnetic radiation. The Commonwealth Government ARPANSA (Australian Radiation Protection & Nuclear Safety Agency; siliconchip. au/link/abl9) regulates the health effects of electromagnetic waves in Australia. The Australian equivalent of the FCC is ACMA (Australian Communications and Media Authority; siliconchip.au/link/abla). Their regulations are aimed at the sources of electromagnetic radiation. I read Nevro’s manual on their website (siliconchip.au/ link/ablb). Based on page 6, it appears that they have not tested their implantable device under these conditions. They have only given a generic list of electromagnetic radiation sources. There is no mention of the welder’s certification under the United Nations International Electrotechnical Commission standard on arc welders’ radiation (siliconchip. au/link/ablc). Considering that, under ideal conditions, if you double the separation from the source to the person, the received power quarters, it rapidly reduces to a negligible level by moving further away from the source. So where are their minimum separation values? Lawyers have written these manuals to prevent any litigation. I saw this from a US-manufactured machine that said, in the maintenance section, that fault-finding must be done with the power off. This machine was powered by threephase (400V) and contained computers and many small motors. How can an electrician diagnose faults in complex machinery with the power off?! I went to the Nevro’s USA site, and they use Bluetooth to communicate with a remote control. Where is the FCC approval for a radiating device? It is compulsory in that country (see www.fcc.gov/oet/ea/rfdevice). The implantable cardiac pacemaker is a similar device that has been tested near arc welders (https://pubmed. 8 Silicon Chip ncbi.nlm.nih.gov/8800120/). These devices are encased in a metal container that shields them from electromagnetic interference; the only pickup points are the wires to the nerves. The surgeons who implant this nerve stimulator are not experts in electromagnetic radiation either. Assessment of implantable devices should be a job for ARPANSA. In operating theatres, they are much more concerned by leakage currents to Earth because the skin has a high resistance, which is bypassed during an operation. Arc welders have a large current flowing from the transformer through the handpiece, the work and the return lead. The work and the welder must be connected to Earth with a low-­impedance connection. It would be a good idea for an electrician to verify that the Earth connection resistance is low using a very low ohm resistance tester. This letter is to highlight the flaws in the regulatory system for susceptibility to electromagnetic radiation and is not medical advice. Alan Hughes, Hamersley, WA. Serviceman’s Log has always been one of my favourites I was interested to read about the faulty Yamaha home theatre repair that Dave Thompson had to pass on because of a transformer fault in the May 2023 issue (siliconchip. au/Article/15790). I suspect that a simple thermal fuse will be buried inside the primary winding. I have seen several much smaller (and cheaper) consumer devices fail because of these things; some I could fix, others had to be scrapped. Thermal fuses are notorious for failing under even moderate thermal overload. They can even go open-circuit when they age and get a bit tired. They are a pig of a thing to replace (if you can get at them) because they cannot be soldered and are generally fitted using tiny crimp sleeves. The other problem is working out the rated temperature of the fuse used. The fuses only cost a few dollars each (Jaycar has several at ~$6 each), but in most cases, there is simply no way to replace them without stripping the transformer down and possibly even rewinding the whole thing. Not something to contemplate lightly! I always thought that they were one of the least useful protection devices used in the equipment of that era. They are a one-shot, fail-open, inaccessible device which has probably resulted in many expensive devices (like the Yamaha system in question) being scrapped while otherwise perfectly serviceable. Kevin Snelson, Porirua, New Zealand Comment: you are quite right. While he didn’t mention it in the article, Dave did inform the amplifier owner of this possibility. Thanks for the soldering tips (no pun intended) I liked the Serviceman’s Log column with Dave Thompson’s soldering tips in the April 2023 issue (siliconchip.au/ Article/15741). Like Dave, I started soldering DIL packages in the early seventies. As times changed, I went with the flow and started soldering SOIC packages and have become pretty proficient with them. The MSOP & SSOP ICs used in the Automated Test Bench (April 2023; siliconchip.au/Article/15736) are next-level, Australia's electronics magazine siliconchip.com.au ADD MOTION DETECTION TO YOUR PROJECT PIR MOTION DETECTION MODULE ADD OBSTACLE DETECTION OR AVOIDANCE DUAL ULTRASONIC SENSOR MODULE • Adjustable delay times XC4444 $6.95 • 2cm - 450cm 15° range XC4442 $8.95 Expand your projects with our extensive range of Arduino® compatible Modules, Shields & Accessories. OVER 100 TYPES TO CHOOSE FROM AT GREAT PRICES. 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Jaycar reserves the right to change prices if and when required. jaycar.com.au/shieldsmodules 1800 022 888 and I was not looking forward to soldering the little buggers. Thank goodness I read his article about soldering while waiting for the short-form kit to arrive. Your suggestion about using a larger soldering iron tip was a game-changer for me and has made the task relatively easy! Rob Chandler, Clayton, Victoria. Ian Robertson of Engadine, NSW I was sad to read of Ian’s passing, as reported in the February 2023 issue. I worked with Ian for many years at Elevators Pty Ltd (formerly part of Lend Lease, now acquired by Kone Elevators). We both contributed to “Circuit Notebook” over the years. Ian had many published – do you have a count of his items? Colin Fisher, via email. Comment: we count 37 contributions that were published. You can see the complete list at siliconchip.au/link/abld We published two projects by a different Ian Robertson in the August 2017 and March 2018 issues. The above search link omits those. Confusion over transistor neutralisation Thanks to the readers who reported errors in my redrawn diagram for the Astor APN radio, published in May 2023 – the connections of capacitors #35, #36 & #38 and resistors #6 & #10 were incorrect. The circuit has been corrected in the online edition and an erratum will be published. However, I think clarification is still needed regarding how neutralisation works (as implemented by capacitor #35). I previously addressed misconceptions about output-­ input feedback in tuned amplifiers in my article on the Grebe Synchrophase published in the February 2018 issue (siliconchip.au/Article/10977). Collector-base, drain-gate and anode-grid feedback in an untuned circuit (parasitic or intentional) will reduce gain and input impedance, as per Electronic Devices and Circuits, Millman and Halkias, 1967, p512. These factors were also described in the Hazeltine “Neutrodyne” patent (US1489228, 1924). Both neutralisation and (for transistors) unilateralisation apply positive feedback to compensate for this. Because this can lead to confusion, I prefer to describe both neutralisation and unilateralisation as “balancing” circuits that nullify the feedback effect and leave the feedback polarity for a more detailed discussion, such as Hazeltine (above). My erroneous circuit showed capacitor #35 as adding to transistor Q2’s existing collector-base capacitance, which would actually reduce the gain. The corrected circuit now shows it connected to Q2’s collector via the primary of IFT2, which provides the requisite phase shift so that it provides positive feedback instead. It’s a peculiarity of tuned-circuit amplifiers that shunt voltage feedback can provoke oscillation. The Barkhausen Criterion for oscillation requires a loop gain of unity or greater and a loop phase shift of zero. Since tuned circuits can present voltage-current phase shifts, the input and output circuits can create an overall phase shift that counteracts the device’s 180° input-output phase shift and bring the loop phase into the Barkhausen region. This is complicated by transistor feedback not having a phase shift of exactly 180°, proven by its characterisation 10 Silicon Chip in data sheets as both resistive and capacitive, and by fully-­ developed unilateralisation circuits using a combined resistor-­capacitor network. If you need more convincing that neutralisation is positive feedback, dig out a book on valve radio transmitters and find the circuit for a neutralised push-pull power amplifier. You will find a circuit indistinguishable (going by component connections) from a push-pull RF oscillator or an astable multivibrator. All will show cross-coupling from one anode to the grid of its partner valve and vice versa. Amateur Radio readers may recall VHF twin tetrodes with internal cross-coupled neutralising ‘rods’ that provide a low capacitance, removing the need for external neutralising components. Ian Batty, Rosebud, Vic. Praise for contributor and battery caution I would like to compliment your competition contributor, Keith Anderson, on his near-perfect implementation of the Noughts and Crosses game using an Uno with a touchscreen (Circuit Notebook, January 2023; siliconchip.au/ Article/15621). Since I already had the parts in my Arduino kit, I put the innards together and had a good play. No matter what strategy I tried, I could not defeat it, but I am proud that I managed frequent long strings of stalemates. It is probably impossible to beat it. Keith’s packaging of his project is hugely professional, with his case being 3D printed and cut so precisely. I get the feeling that Keith is a programming guru who put the same pedantic precision into both the hardware and software implementation of this simple game: which is not so simple when your aim is for it to win every time. The only negative I can think of with this project is that it is so infallible that interest inevitably wanes as you are denied a win after so many tries. Perhaps a fallibility switch is required. However, after reading in the April Edition of his final polishing of the project with a bespoke rechargeable lithium battery package (siliconchip.au/Article/15745), I wanted to point out a potential problem. My radio-controlled electric model aeroplane club has experienced several extremely destructive lithium-ion battery fires during charging activity. One member even lost his house that way. Once started, these fires are impossible to extinguish fully. The exothermic chemical reaction inside the battery is self-sustaining in that it requires no other fuel or oxygen, and fire retardants have no effect. Even if the residue is stomped into a flat charred mess, the fire may spring back into life spontaneously. Our inevitable and often spectacular model plane crashes are now sometimes graced by an ultra-realistic fuel fire effect as the crushed battery takes off. Our safety rules do not permit us even to collect the wreckage as it is too dangerous to bring near anything flammable. We are encouraged to do all our battery charging outside in the open and even store the batteries safely away from the house. For this reason, I think it is unwise to have the charging going on inside an opaque, sealed plastic box. By the time a fire is noticed, it may be too late to do much about it. AA batteries, although tediously temporary, may be a safer option for this toy. Australia's electronics magazine siliconchip.com.au Many of us are on the lookout for challenging Arduino projects, so I hope Keith will continue to contribute his wonderful designs. Barry Matson, Nicholls, ACT. Variacs are helpful but not safety devices I would like to comment on the letter you published by Evan Bennett of Balga, WA in the May issue. He was asking about mains safety when servicing equipment, especially older gear. I am a moderator on the US “Antique Radio Forum”. America has a vast number of hot chassis radios, ie, sets with no transformer. Europe also has its fair share, some even having what looks like a transformer, which is not; it’s a tapped ballast that provides no isolation from the mains. “Variacs” are autotransformers (as are many step-up/ step-down transformers). In these, the primary is directly coupled to the secondary and offers no protection. The danger here is that when the output voltage of a variac is set below 130V, a 30mA RCD will not trip. That should be of concern if you are the resistance to Earth. To be safe with such equipment, it must be operated with a proper isolation transformer. Where there is a transformer, it will generally be isolating if the primary is above ground and not connected physically to the secondaries, a correctly connected Earth being an exception. Powering old valve radios and other things with exuberance without inspecting them first is a dangerous and often expensive practice. The mains side can be compromised, and often is, requiring repair and insulation testing before powering. You should also inspect and repair the secondary side of the transformer. It is not unusual when ‘tagging & testing’ charitable donations to find 10%+ are not repairable and some are just downright dangerous. Also note that when buying instrumentation, not all of what’s available now can withstand the RF and HT voltages of our old valve radios. Marcus Chick, Wangaratta, Vic. Voltage supervisor needed for reliable ESP32 operation I struggled to get an ESP32 to run on solar power. It wouldn’t start up correctly in the morning but ran OK when the power was disconnected and reconnected. This YouTube video by Andreas Spiess hit the nail on the head: https://youtu.be/cKDv0aN67BY A voltage supervisor (KA75330) soldered directly onto the leads on the ESP32-WROOM unit allows it to work perfectly. It holds the “EN” (enable) pin low, preventing the ESP from starting until the 3V3 terminal reaches close to 3.3V. Before, the slowly increasing solar supply voltage first thing in the morning would prevent it from starting correctly. It also stops the ESP32 from running if the voltage drops below 3.3V (on the removal of power or a reduction in the solar voltage). The data sheet shows a hysteresis of 50mV. While the data sheet indicates the need for a pull-up resistor, it worked perfectly for me just by tacking the three leads of the KA75330 onto the 3V3, EN and GND terminals. It costs about $4 for 20, plus $7 for delivery from AliExpress. They are a must-have addition when using ESP32s in a remote location with solar power and no battery backup. Sid Lonsdale, Whitfield, Cairns. SC siliconchip.com.au Australia's electronics magazine June 2023  11 IDEAL FOR STUDENT OR HOBBYIST ON A BUDGET • DATA HOLD • SQUARE WAVE OUTPUT • BACKLIGHT • AUDIBLE CONTINUITY Don't pay 2-3 times as much for similar brand name models when you don't have to. 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Explore our wide range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide. www.jaycar.com.au/multimeters 1800 022 888 LARGE BACKLIT DISPLAY AND IP67 WATERPROOF RATED • TRUE RMS • CAPACITANCE • FREQUENCY • RELATIVE MEASUREMENT TAKE EASY ENVIRONMENTAL MEASUREMENTS • MULTIMETER FUNCTIONS • SOUND LEVEL • LIGHT LEVEL • INDOOR TEMP • HUMIDITY ONLY 109 $ QM1549 WIRELESS BLUETOOTH® FEATURE FOR DATA LOGGING • AUTORANGING • TRUE RMS • 6000 COUNT • IP67 WATERPROOF ONLY 149 $ QM1594 ONLY 199 $ QM1578 Use this colour coded selection guide to pick the meter that best suits your needs. GREEN labelled product suit hobbyists and those on a budget. BLUE suit makers familiar with multimeters and want more features. For all the bells and whistles and the highest ratings, choose from the ORANGE professional range. ENTRY LEVEL * QM1500 QM1517 QM1527 MID LEVEL QM1529 QM1321 QM1020 QM1446 Display (Count) 2000 2000 2000 2000 4000 Analogue Security Category Cat II 500V Cat III 600V Cat III 500V Cat III 600V Cat III 1000V Cat II 1000V • • Autorange True RMS PROFESSIONAL QM1323 QM1552 2000 4000 2000 4000 4000 2000 4000 6000 4000 Cat III 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat IV 600V Cat III 1000V • • • • • • QM1551 QM1549 • • • • • XC5078 QM1594 QM1578 • Voltage 1000VDC/ 750VAC 500V AC/DC 500V AC/DC 600V AC/DC 1000VDC/ 750VAC 1000V AC/DC 1000VDC/ 700VAC 600V AC/DC 1000VDC/ 750VAC 600V AC/DC 1000V AC/DC 600V AC/DC 600V AC/DC 1000V AC/DC Current 10A DC 10A DC 10A DC 10A AC/DC 10A AC/DC 10A DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 200mA AC/DC 10A AC/DC 10A AC/DC Resistance 2MΩ 2MΩ 2MΩ 20MΩ 40MΩ 20MΩ 20MΩ Capacitance 100mF Frequency 10MHz Temperature Duty Cycle 20MΩ 40MΩ 200MΩ 40MΩ 40MΩ 40MΩ 60MΩ 100μF 100µF 100mF 100µF 100µF 100µF 6000µF 10MHz 10MHz 10MHz 10MHz 10MHz 10MHz 10kHz 1000°C 760°C 1000°C 760°C 750°C 760°C • • • • • • • • • • • • • • • • • • • Continuity • • • • • • Relative Min/Max/Hold • Non Contact Voltage • • • $26.95 $32.95 $49.95 Max Hold • • • $59.95 $74.95 $74.95 IP Rated Price • Max Hold • • $20.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $32.95 $59.95 1000VDC/ 750VAC 4000MΩ • • • IP67 $11.95 QM1493 $109 IP67 $99.95 $149 $199 $289 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Dr David Maddison describes S TARLINK WARM TA SHIELD R Global Wireless Internet from SpaceX Starlink, owned by SpaceX, provides affordable satellite internet anywhere in the world. Remote connectivity for Internet of Things (IoT) devices located just about anywhere can also be via Starlink or another subsidiary, Swarm, while Starshield is aimed at government users. M ost people in developed or even developing countries can now receive mobile, wireless internet data via their smartphones or other devices when near a city or town, or along a major transport route. Internet connectivity outside such areas via satellite tends to be expensive and slow. Starlink is owned by SpaceX and enables regular users to (relatively) affordably get satellite internet anywhere in the world, no matter whether they be at sea on a yacht or ship, on an aircraft, in Antarctica, in a mobile home, a remote area, or on an outback expedition. Low latency Apart from relative affordability, Starlink aims to have low latency, ie, keeping the round trip time for a packet of internet data as low as possible. A finite amount of time is required for a radio wave to travel between transmitter and receiver at the speed of light (about 3 × 108m/s). There are also delays due to signal processing and internet switching time. The realistic round-trip time for a geostationary satellite orbiting at 35,786km is around 600ms or more when including switching overhead, which is excessive for two-way live audio or video, gaming or other interactive applications. Starlink achieves low latency by having satellites in low Earth orbit of about 550km, giving a latency of about 20ms, comparable with wired networks. However, because the satellites are orbiting at such a low altitude, a very large number are required to give global coverage. Another stated objective of Starlink is to provide internet connectivity in developing countries, some of which have little wired or wireless phone or internet infrastructure. According to the UN, about 57% of the world’s population lacks internet access. SpaceX Image source from SpaceX (CC BY-NC 2.0): www.flickr.com/photos/spacex/49422067976/in/photostream/ 14 Silicon Chip Australia's electronics magazine SpaceX, or Space Exploration Technologies Corp, is largely owned by the Elon Musk Trust (47.4% equity, 78.3% voting control). SpaceX builds the Starlink, Swarm and Starshield satellites and their delivery systems, such as the Falcon 9 rocket. As of December 2022, Starlink had one million customers, including in Australia and New Zealand. siliconchip.com.au Satellite constellation & orbit A satellite constellation is a group of satellites working together as an integrated system. A well-known example is the GPS satellite constellation. Starlink, Swarm and Starshield all form satellite constellations too. Due to the low latency requirement of Starlink, the satellites need to be in low Earth orbit. Because of this, the visibility of an individual satellite to any given area on Earth is quite limited. Therefore, a large number of satellites are required for complete Earth coverage. Fig.1 shows the comparative Earth coverage for three common satellite orbital altitudes: geosynchronous orbit (GEO), medium Earth orbit (MEO) and low Earth orbit (LEO). Starlink satellites will be placed in LEO. Fig.2 and Table 1 show further orbital characteristics for GEO, MEO and LEO. GEO MEO LEO Fig.1: a representation of three common orbit types and comparative ground coverage areas: geosynchronous orbit (GEO), medium Earth orbit (MEO) and low Earth orbit (LEO). Land surface visible to a satellite We can calculate the amount of the Earth’s surface visible to a satellite at a certain altitude as follows. If the altitude above the Earth’s surface is d and the radius of the Earth is R (nominally 6378km at the equator), then the fraction of the surface visible to the satellite is given by the formula f = d ÷ 2 × (R + d). We use this formula to calculate the areas visible to a satellite for various orbits in Table 1. For practical reasons, a satellite will not be visible all the way to the horizon due to mountains, trees etc. Also, the signal will be degraded by extensive travel through the atmosphere. So in practice, a certain elevation angle is defined below which no attempt is made to communicate with the satellite from an Earth station, as illustrated in Fig.3. The red disc shows the absolute horizon, while the yellow one represents the minimum coverage at the designed elevation angle, which is smaller than the horizon. Therefore, the coverage a satellite can achieve is less than we calculated with the above formula. Starlink orbital altitude As with any large satellite program, there will be several different versions of satellites. For Starlink, there are presently V1, V1.5 (Figs.4 & 5), V2 and V2 mini satellites. So siliconchip.com.au Fig.2: a not-to-scale representation of features of several orbital altitudes. RTT is the round-trip time for a radio signal. The Van Allen radiation belts are best avoided. The radius listed is from the centre of the Earth, while the height is from the surface of the Earth. Source: https://w.wiki/6H8X Table 1 – Characteristics of various satellite orbits Geosynchronous orbit (GEO) Medium Earth orbit (MEO) Low Earth orbit (LEO) 2000-35,786km (20,500km typical) 160-2000km (500km typical) GPS (20,180km) Starlink (550km) Latency at 600ms typical altitude (round trip) 400ms 20ms Proportion of 42.4% Earth’s surface visible 38.1% 4.0% 10-15; more for redundancy At least 32, but in practice, hundreds Slow; each satellite is visible for 1-3 hours Fast; each satellite is visible for 5-15 minutes Fewer satellites than LEO, lower latency than GEO; smaller antenna systems; better signal strength above 72° latitude Low latency, low signal loss, low power Earth stations, potentially lower cost due to mass production Altitude 35,790km typical Examples GOES, Inmarsat, Intelsat Min. number Three; four for of satellites some overlap. for full Earth coverage Antenna No tracking tracking speed needed required Advantages Few satellites required, no tracking, no handover, always connected, simple management, no complicated orbits Australia's electronics magazine June 2023  15 Table 1 – Characteristics of various satellite orbits (continued) Geosynchronous orbit (GEO) Disadvantages Weak signals, poor coverage above 72° latitude, high latency Typical >15 years satellite life Network Low complexity Medium Earth orbit (MEO) Low Earth orbit (LEO) Antenna tracking required, satellite handover needed, more satellites than GEO, more exposure to Van Allen Belt radiation than GEO or LEO Small service area, antenna tracking needed, frequent satellite handover, large Doppler shifts, short orbital life due to atmospheric drag 10-15 years 3-7 years Medium High far, only V1 and V1.5 satellites have been launched; V1.5 satellites are still being launched. Starlink V1 satellites are inserted into various ‘shells’ in orbits of altitudes between 540km and 570km, shown in Table 2. A satellite orbital shell is a series of satellites sharing the same circular orbit at a certain altitude. Satellite deployment timeline SpaceX is constantly launching Starlink satellites, but the following satellites have been launched at the time of writing. They launched two “Tintin” test satellites in 2018. In 2019, a further series of 60 V0.9 ‘production design’ satellites were launched. SpaceX launched operational v1.0 satellites from November 2019 through to May 2021. Usually, 60 were launched at a time (some launches had fewer), over 29 launches, for a total of 1675. Of those, around 183 are no longer working. Starlink V1.5 satellites started to be launched in June 2021 through to at least January 2023. There have been 40 launches of V1.5 satellites, each launch carrying up to 54 satellites, for a total of 1881 so far, of which 52 are no longer operational. For a complete, up-to-date list of Starlink satellite data, see https:// planet4589.org/space/con/star/stats. html There were also four Starshield V1.5 launches on the 13th of January 2022 and another four on the 19th of June 2022, for unknown US government agencies. Coverage area With the first orbital shell at 53.0°, Starlink initially provided coverage to areas below about 55° latitude, which covers a vast majority of the world’s population. Later launches at other orbital inclinations covered higher latitudes. The 53.2° shell extended the number of customers covered in the mid and low latitudes. The 70.0° shell expanded coverage to Alaska and northern Europe (and presumably equivalent latitudes in the southern hemisphere). These earlier Starlink launches were in ‘equatorial orbits’, so they did not cover polar regions – see Fig.6. Four launches of 46 satellites each for the 97.6° shell occurred in July and August 2022, adding coverage for polar regions. This includes Antarctica plus areas of northern Alaska, northern Canada, Finland, Norway and Sweden not previously covered. High-level Starlink architecture Starlink consists of three main components: satellites, ground stations Fig.3: satellite visibility at zero elevation (red) and designed elevation (yellow), showing the difference between the theoretical and actual coverage. Original source: www. frontiersin.org/articles/10.3389/ frcmn.2021.643095/full and user terminals. The ground stations are the connection to the terrestrial internet and can also act as a means for Starlink satellites to communicate with each other. The number of ground stations needed is minimised by later (V1.5+) satellites that can communicate with each other via inter-satellite laser links. When a user connects to a satellite via their user terminal, the satellite either relays the signal directly to a Starlink ground station connected to the internet, or to another Starlink satellite via laser and then onto a ground station. This inter-satellite relay is necessary for users at higher latitudes where the satellites have access to few or no ground stations. Laser communication between satellites V1.5 satellites can communicate with each other via inter-satellite laser links. This reduces latency, as a signal travelling via laser will travel about 30-40% faster than between switching equipment on the ground connected via coaxial cable or optical fibre. Also, due to the shorter distance between satellites compared to cables on the ground or undersea, overall latency is reduced by up to 50%. Laser connections between satellites are necessary for the Starlink satellites Table 2 – orbital shells and numbers of Starlink V1 and V1.5 satellites (4408 in total) Inclination 16 Orbital altitude Orbital planes Eventual satellites/plane Total satellites Shell 1 53.0° 550km 72 22 1584 Shell 2 70.0° 570km 36 20 720 Shell 3 97.6° 560km 6 (polar) 58 348 Shell 4 53.2° 540km 72 22 1584 Shell 5 97.6° 560km 4 (polar) 43 172 Silicon Chip Australia's electronics magazine Laser comms. All All siliconchip.com.au Fig.4: an artist’s concept of a Starlink V1 satellite. Source: https://w.wiki/6H8Y in polar orbit, as they won’t have access to many or any ground stations. Geographic availability of Starlink Starlink can be used everywhere on the surface of the Earth; however, under International Telecommunication Union (ITU) regulations and international treaties, each country and its telecommunications regulators must grant rights to use satellite communications such as Starlink. This means that Starlink has to set up operations in each country in which it does business. Australia and New Zealand provided rapid regulatory approval for Starlink in April 2021, the 6th and 5th countries to do so after the USA, Canada, the UK and Germany. Fig.7 shows Starlink availability by country. Starlink equipment is programmed only to work at or near your residential address if on a residential plan, or other areas on an RV plan. Fig.5: a rendering of Starlink V1.5 (left) and V1 (right) satellites. V2.0 satellites have five times as much surface area for Earth-facing antennas and are much more capable. Source: www.teslarati.com/ spacex-elon-musknext-gen-starlinksatellite-details/ Number of satellites in orbit To appreciate the enormousness of the Starlink project, it is important to consider the number of satellites already in orbit. According to the United Nations Office for Outer Space Affairs (UNOOSA) searchable index at www. unoosa.org/oosa/osoindex/search-ng. jspx, as of 3rd January 2023, 14281 objects had been launched into space since Sputnik 1 in 1957. Of those, 8734 are classified as still ‘in orbit’ although not necessarily functional. Of the 8734 objects classified as ‘in orbit’, 3568 were labelled Starlink and 5166 were not. This means that nearly 41% of orbiting objects are associated with Starlink. Still, that number will increase dramatically as the entire constellation is rolled out. So, in a few years, a large majority of all artificial satellites could be part of Starlink! According to a web page that keeps a tally of Starlink satellites at https:// planet4589.org/space/con/star/stats. html, as of 20th January 2023, 3389 Starlink satellites are currently operational. Fig.6: the incomplete global coverage provided by earlier Starlink satellite launches in equatorial orbits (left) compared to the complete global coverage after later launches into polar orbit (right). Starlink satellite features Some features of the Starlink satellites not already mentioned include: • a flat design for easier and higher density packing into Falcon 9 rockets • a star tracker for guidance siliconchip.com.au Fig.7: the availability of Starlink services. Green means approved and activated, blue means activated and grey is unknown. Source: https://w.wiki/6H8Z Australia's electronics magazine June 2023  17 • each satellite has four phased-­ array antennas and two parabolic antennas (see www.starlink.com/ technology). The current lineup of Starlink ground station antennas for users is shown in Fig.8. Aviation antennas An aviation application for Starlink with an aerospace-certified antenna, shown in Fig.9, is to be released in 2023. Link speeds will be 350Mbps with no data volume restrictions and latency as low as 20ms. While internet connectivity is already available in some aircraft, it is slow and can be expensive. Starlink will enable high-bandwidth or low-­ latency activities on aircraft, such as video calls, streaming high-definition video, online gaming etc. Devices on the plane will access the Starlink internet via a standard WiFi connection. For those interested in costs, at the time of writing, there is a onetime hardware cost of US$150,000 (~$210,000) and monthly service fees with unlimited data are US$12,50025,000 (~$18,000-$35,000). Initial certification is being obtained for the following business and regional aircraft types: ERJ-135, ERJ-145, G650, G550, Falcon 2000, G450, Challenger 300, Challenger 350, Global Express, Global 5000, Global 6000, and Global 7500, with more applications being developed for larger commercial jets. How Starlink antennas work Unlike an antenna pointed at a geostationary satellite, which needs a clear view in only one direction, Starlink antennas need to be unobstructed from horizon to horizon, as the LEO satellites can be anywhere in the sky. When setting up a Starlink antenna, a phone app will guide your placement to confirm a good signal. Starlink antennas are motorised and Frequencies used by Starlink satellites According to www.elonx.net/starlink-compendium/, the following frequencies are used by Starlink: ● Satellite to user terminals: 10.7–12.7GHz, 37.5–42.5GHz ● Satellite to gateway: 17.8–18.6GHz. 18.8–19.3GHz, 37.5–42.5GHz ● Terminals to satellites: 14.0–14.5GHz, 47.2–50.2GHz, 50.4–51.4GHz ● Gateways to satellites: 27.5–29.1GHz, 29.5–30.0GHz, 47.2–50.2GHz, 50.4–51.4GHz ● Tracking, telemetry and control (downlink): 12.15–12.25GHz, 18.55–18.60GHz, 37.5–37.75GHz ● Tracking, telemetry and control (uplink): 13.85–14.00GHz, 47.2– 47.45GHz self-aligning, but once the antenna is pointed in the optimal direction, it does not need to move much more by itself. That is because, apart from antenna motors used for basic alignment, the antenna can electronically steer its beam using a phased array. New versions of Starlink antennas intended for rooftop RV mounting or aircraft are not mechanically steered at all; they are electronically steered only. Hacking antennas Starlink antennas are not designed to be disassembled by users. An attempt to do so might void the warranty if it causes damage, but some hackers have done so. Various people disassembled their antennas, either to see what was inside or to repurpose stationary antennas for mobile (car) or lightweight expedition (on foot) use. While a mobile antenna is now available, that was not always the case. Antenna teardown There is very little officially published information about the construction of the Starlink ground station antennas. What we know is only what has been discovered by hackers – see Figs.10, 11 & 12. The Starlink antenna is a remarkably complicated device and arguably Fig.8: a standard Starlink antenna for regular residential users (left), with a 100° field of view. The high-performance antenna (middle) is for businesses and enterprises as it can connect to more satellites, is more tolerant of extreme environments and has a 140° field of view. The flat high-performance antenna (right) is intended for mobile applications such as motor homes and boats, also with a 140° field of view. Source: Starlink. 18 Silicon Chip Australia's electronics magazine the most critical part of the ground equipment. If you watch the teardown videos, you will see that it is an engineering masterpiece. It has a lot of electronics in it, including an ARM processor, RAM chips and many custom ICs. Presumably, these are all to drive the phased array. Teardown videos include: ● Starlink Teardown: DISHY DESTROYED! https://youtu.be/iOmdQnIlnRo ● TSP #181 - Starlink Dish Phased Array Design, Architecture & RF In-depth Analysis https://youtu.be/h6MfM8EFkGg ● Starlink Dish TEARDOWN! - Part 1 - SpaceX BugBounty is open during the Starlink Public Beta https://youtu.be/QudtSo5tpLk ● Starlink Dish TEARDOWN! - Part 2 - Serial console and login prompt. Can you guess Dishy’s password? https://youtu.be/38_KTq8j0Nw ● Starlink RECTANGLE Teardown Details - Working on trimming Rectangle dish to make a low-power panel https://youtu.be/AlvIWF0AXI0 There is also a good article on this at siliconchip.au/link/abjf Mobile phone service In August 2022, Starlink partnered with T-mobile in the United States to provide cellular phone service via V2 Starlink satellites, to begin testing in 2023. Unlike other satellite phone systems, this will use standard mobile devices. The service will initially support text messaging and voice calls. The total bandwidth available per satellite will be 2-4Mb/s, which equates to 1000-2000 simultaneous voice calls or millions of text messages across a cell. The intention is to use this service in remote areas with no existing cellular service or in emergencies. It will be initially offered in the USA only, but T-mobile will siliconchip.com.au Fig.9: a rectangular Starlink antenna facing up is visible toward the front of the aircraft. Source: Starlink. Figs.10 & 11: part of a Starlink antenna PCB. The PCB traces are curved to provide constant lengths for all traces (and RF signals don’t like sharp corners). Source: https://youtu.be/AlvIWF0AXI0 eventually partner with providers in other countries. The technological challenges in providing satellite connectivity to a standard mobile phone are significant. Firstly, by the time the phone signal travels around 550km or more, it will be very weak. With the satellite moving at around 27,000km/h, there will be a significant Doppler shift to account for. The phone will be electronically locked onto using a phased array antenna, which can steer the satellite beam to the phone’s location as the satellite moves in its orbit. According to Elon Musk, these are the most advanced phased-array antennas in the world. The satellites used for this service will be very large at 7m long, with a mass of 1.25 tonnes each, and the antenna will be 5 × 5m but folded for launch. They are too big for the SpaceX Falcon 9 rocket, so they will be launched on a SpaceX Starship rocket. SpaceX has also proposed a miniature version of the V2 satellite, which will fit on the Falcon 9. Each V2 satellite will represent one mobile phone cell covering an area of nearly 17,000km2. There will eventually be 30,000 V2 satellites (see Table 3), enough to cover the Earth’s entire surface of around 510 million km2! Until the whole constellation of V2 satellites is up, cell phone connectivity will only be when V2 satellites are visible to the user. Tesla cars will also be able to connect to Starlink cellular service in T-mobile coverage areas or other areas with other providers as they become available. Besides cellular coverage, V2 satellites will also provide internet connectivity through conventional ground or air stations. Collision avoidance and satellite lifespan Starlink satellites, indeed all satellites these days, need to be able to manoeuvre to avoid collisions with other satellites and adjust their orbit. They also need to be able to deorbit at the end of their life to prevent excessive debris from accumulating in orbit. Starlink satellites are equipped with Hall-effect thrusters (HETs), electric ion engines that use krypton gas as the propellant to effect the required manoeuvres. Even if the thruster malfunctions at the end of a satellite’s life, its orbit will decay due to atmospheric drag within about four years, and it will re-enter the Earth’s atmosphere and incinerate. Table 3 – proposed orbital shells & numbers of Starlink V2 satellites (29,988 total) Fig.12: part of the phased array ‘sandwich’ on the non-component side of the antenna PCB. Source: https:// youtu.be/AlvIWF0AXI0 siliconchip.com.au Inclination Altitude Orbital planes Satellites/plane Total satellites 53.0° 340km 48 110 5280 46.0° 345km 48 110 5280 38.0° 350km 48 110 5280 96.9° 360km 30 120 3600 53.0° 525km 28 120 3360 43.0° 530km 28 120 3360 33.0° 535km 28 120 3360 148.0° 604km 12 12 144 115.7° 614km 18 18 324 Australia's electronics magazine June 2023  19 Fig.13: Starlink satellites can lower their profile to avoid collisions. Source: https://astronomy.com/ news/2022/02/spacex-defendsstarlink-over-collision-concerns Avoiding collisions with the large number of satellites now in space is vital to avoid the Kessler syndrome. This is a phenomenon where a satellite collision generates a large amount of debris. That debris creates more collisions and debris, leading to a cascading effect, rendering orbital space unusable. Starlink uses an AI-based autonomous collision avoidance system with tracking data from the US Space Force 18th Space Defense Squadron (see siliconchip.au/link/abjg). Suppose a Starlink satellite is expected to come very close to another object and cannot manoeuvre out of the way. In that case, it can lower its solar panel to present a lower profile and less chance of collision, as shown in Fig.13. A major loss of Starlink satellites Starlink satellites are deployed at a much lower altitude than they operate at. This is for initial testing; if the satellite is entirely non-functional, the orbit will quickly decay at the lower altitude, preventing orbital debris from 20 Silicon Chip Fig.14: a 2019 photo taken at the Cerro Tololo Inter-American Observatory (CTIO) in Chile after the launch of the second batch of Starlink satellites. This 333-second exposure contains 19 streaks from satellites. Source: https://noirlab. edu/public/images/iotw1946a/ accumulating. If the satellite tests OK, its orbit is raised. On the 4th of February 2022, while 49 V1.5 satellites (Group 4-7) were deployed into low orbit, there was a major geomagnetic storm. This caused increased atmospheric drag, and 38 of the satellites deorbited, leaving only 11 to raise their orbits. configuration just after launch is changed to a ‘shark fin’ configuration for the solar panel when on-orbit, with the panel pointing away from Earth (see Fig.15). • They are also testing a roll manoeuvre during orbit raising to minimise reflections (see Fig.16). Interference with astronomy Naturally, Starlink has been a target for hackers. We do not recommend you do this but we present this as a matter of interest. A group has published “Glitched on Earth by Humans: A From the outset of the Starlink project, with its thousands of satellites, astronomers have had concerns about interference with their observations. Fig.14 is a very early example of image interference due to the second batch of Starlink satellites being launched in November 2019. Mitigation strategies include: • A ‘visor’ called VisorSat to cover radio antennas and other parts of the satellite. It is transparent to radio waves but stops light reflections (see Fig.17). • A light-absorbing coating on the satellite (‘DarkSat’); however, this makes the satellite get too hot, so the preference is for the visor. • The high-reflection ‘open book’ Australia's electronics magazine Hacking Starlink! Fig.15: the shark fin configuration reduces the amount of sunlight reflected towards the Earth. Source: https://astronomynow.com/2020/05/05/ spacex-to-debut-satellite-dimmingsunshade-on-next-starlink-launch/ siliconchip.com.au Black-Box Security Evaluation of the SpaceX Starlink User Terminal” at https://github.com/KULeuven-COSIC/ Starlink-FI that enables execution of arbitrary code on a Starlink User Terminal – see Fig.18. This has no stated purpose except for experimentation. We expect by now that the exploited security deficiencies have already been patched. This doesn’t bother Starlink; in fact, they encourage it under the “Bug Bounty Program”. Starlink will pay US$25,000 ($35,500) to anyone who finds a bug in their network. If you want to have a go, see siliconchip.au/ link/abjh Also, a group at The University of Texas at Austin devised a way to use Starlink signals as a GPS alternative. See siliconchip.au/link/abji Swarm Swarm (https://swarm.space/) offers low-bandwidth IoT (Internet of Things) global connectivity via dedicated SpaceBEE satellites (see Fig.19) – BEE stands for ‘basic electronic elements’. Swarm Technologies became a subsidiary of SpaceX in July 2021. Interestingly, the venture capital arm of the US CIA (Central Intelligence Agency), In-Q-Tel, lists Swarm as one of their start-ups (see https://www.iqt.org/ portfolio/). The satellites used for Swarm are thought to be the smallest commercially active satellites at ¼U (11 × 11 × 2.8cm), with a mass of about 400g. ¼U is a Cubesat designation referring to the size relative to a standard 1U cube of 10 × 10 × 10cm, although, strictly speaking, the Swarm satellite slightly exceeds the Cubesat standard. For more information, see our article on Cubesats in the January 2018 issue (siliconchip.au/Article/10930). The Swarm satellites are classed as ‘picosatellites’. They are in a sun-­ synchronous orbit at 450-550km with an intended constellation size of 150. A sun-synchronous orbit is a special kind of polar orbit (travelling roughly north-south) in which a satellite visits the same spot on the Earth’s surface at the same time each day. You can check when the next Swarm satellite comes into your area at https://kube.tools. swarm.space/pass-checker/ Solar panels and batteries power the SpaceBEEs, and the antenna unfolds when the satellite is deployed. siliconchip.com.au ORIENTATIONAL ROLL ARRAY MITIGATION DURING ORBIT RAISE The rolling satellite makes sunlight bounce off the smaller ‘knife edge’ of the array, reducing reflection. Fig.16: detail of the shark fin configuration. Source: same as Fig.14. VISORSAT ANTENNAE MITIGATION ON STATION On station, sun shade blocks sunlight from antennas, preventing reflection. Fig.17: the visor was added to later Starlink satellites to reduce the amount of light reflected at the Earth. Source: same as Fig.15. Fig.18: a “Modchip” board (red) and interface added to a Starlink antenna panel. Source: https:// github.com/KULeuvenCOSIC/Starlink-FI Fig.19: a Swarm SpaceBEE satellite, the tiniest satellite in commercial use. Australia's electronics magazine June 2023  21 IIoT gateway satellite mounted on rear of panel Wind speed & direction sensor Temp, humidity & barometric pressure sensor 12W solar panel Multiple mount points on base & rear Fig.20: an example of a commercial remote ModuSense Weather Station with built-in Swarm connectivity. Source: www.freewave.com/ products/modusense-weather-station/ Fig.21: the Swarm asset tracker fitted to an asset. Source: https://swarm.space/ swarm-announces-new-asset-tracking-product/ All satellites in orbit have to be able to be tracked for collision avoidance and orbital planning purposes. There were concerns about the trackability of these satellites due to their small size, but that was addressed by: • Incorporating a passive ‘Van Atta array’ radar retro-reflector, increasing their radar return strength. • The satellite has a GPS and sends its location when requested. • The 1m-long antenna improves visibility to ground-based tracking radars and other sensors (eg, by the US Space Surveillance Network). One of the main attractions of Swarm, apart from its global accessibility, is its low cost. Swarm devices and data plans are easily within reach of typical hobbyists and are also suitable for professional users. According to the Swarm website, a typical data plan costs US$5 ($7) per month per device and “provides 750 data packets per device per month (up to 192 bytes per packet or 144kB per month), including up to 60 downlink (2-way) data packets, AES256-GCM encryption for secure transmission, annual contract with no setup or hidden fees and data delivered via a REST API or Webhook to any cloud service”. That amount of data should be sufficient for hourly readings from a remote weather station, like the one shown in Fig.20. Devices available to connect to Swarm include an asset tracker (US$99/$140) to globally track assets with “one GPS acquisition every two hours with one transmission per twohour window” and “motion detection enabled”. The data rate is 1kbps (oneway) and the frequencies used are 137138MHz (downlink) and 148-150MHz (uplink). The device weighs 227g and the battery lasts 40+ days on internal power, or it can be connected to external power. Data can be accessed from the Swarm Hive – see Fig.21. Another Swarm device is the M138 Fig.22: a SparkFun M138 modem breakout board. The M138 is the device in the centre with “Swarm” written on it. Source: www. electronics-lab.com/sparkfuns-swarm-m138modem-satellite-transceiver-breakout-board/ 22 Silicon Chip Australia's electronics magazine modem, designed to be embedded in a third-party IoT device with data delivered via a REST API or Webhook to any cloud service. These cost US$89 ($125) with a minimum purchase of 25. For fewer units, the SparkFun M138 Modem breakout board can be purchased for US$149.95 ($215; www. sparkfun.com/products/19236) or a later version for US$199.95 ($285; www.sparkfun.com/products/21287) – see Fig.22. The M138 comes in a Mini PCB Express card form factor weighing 9.6g and includes a GNSS receiver for GPS and other navigational systems. Data is sent to the modem as a hexadecimal ASCII string, and two-letter NMEA-like (National Marine Electronics Association) commands are sent over a 3.3V serial (UART) link. The M138 modem is incorporated in the asset tracker mentioned above. Applications for the M138 modem with the breakout board include reading remote sensors such as for weather monitoring, remote equipment monitoring, asset tracking and environmental monitoring – see Fig.23. Finally, the US$449 ($637) Swarm Eval Kit (Fig.24) “is designed to provide the developer with an easy-to-use platform, with the included FeatherS2 – ESP32 board + OLED, a USB-C port and I2C port for sensors. FeatherWing add-on modules can provide a suite of additional capabilities”. “The Eval Kit includes a tripod, solar panel, batteries, and integrated VHF and GPS antenna. A live readout of RF background noise helps you siliconchip.com.au Fig.23: a mountaintop sensor array connected to Swarm. Source: https://swarm.space/ achieve the best possible link quality”. Devices can be connected via WiFi (AP or STA mode), USB, or serial interfaces, and data can be managed via the Swarm Cloud and REST API. The data rate is 1kbps with a maximum packet size of 192 bytes, and it supports AES256 GCM encryption. The command format is two-letter NMEA. The kit comes with an M138 modem described above and weighs 2.6kg. Starshield Starshield (www.spacex.com/ starshield/) is a derivative of Starlink specifically for US government and military use. According to the SpaceX website, Starshield’s initial focus is on Earth observation, communications and hosted payloads. Earth observation involves launching satellites with sensing payloads and delivering processed data directly to the end user (a government agency). This includes global communication with Starshield equipment, having an even higher level of security than Starlink, which is already end-to-end encrypted. Hosted payloads involve building appropriate satellite buses to suit customer needs. A satellite bus is the basic structural element of a spacecraft with equipment such as command and data handling, comms, power, propulsion, thermal control, attitude control and guidance. There is room to install a customer’s specialised payload, such as a sensor array to suit a specific mission. siliconchip.com.au This is less expensive than building a dedicated satellite from scratch. The spacecraft bus will be based on existing Starlink V1.5 and V2.0 satellites with a much greater solar array area. If desired, Starshield satellites can be made interoperable with Starlink via inter-satellite laser communications. Starlink applications can be rapidly developed because of SpaceX’s delivery systems, their manufacturing of the satellites and their ability to rapidly deploy large numbers of satellites in a single launch. Similar satellite systems AST SpaceMobile ast-science.com AST is launching a cellular broadband service in LEO that will allow the use of standard unmodified smartphones via a satellite with an enormous 64.4m2 phased array antenna. Its prototype BlueWalker 3 satellite launched in November 2022, orbits at 508-527km and has a field of view of 777,000km2. AST SpaceMobile eventually plans to deploy a constellation of 243 BlueBird satellites in orbits between 725740km in late 2023. The BlueBird satellites are similar to the prototype BlueWalker 3; later versions will have an even larger antenna array. Their partners are AT&T, Vodafone, Orange and Rakuten Mobile. BlueWalker 3 was launched as a ‘rideshare’ on a SpaceX Falcon 9 along with Starlink satellites. Globalstar www.globalstar.com/en-ap Globalstar offers a constellation of LEO satellites at 1400km altitude for Fig.24: the Swarm Eval Kit. Documentation can be found at https://swarm. space/documentationswarm/ and www.sparkfun. com/products/19236 under the “documents” tab. Australia's electronics magazine June 2023  23 Notes on accuracy and timeliness We have done our best to provide the most accurate and up-to-date information, but precise information on specific details of Starlink satellites and their numbers in orbit are either not published or are subject to variation as the commercial plans of SpaceX change with time. Remember that Starlink, Swarm and Starshield are systems that are being built even as you read this, and plans are constantly evolving. voice telephony with special phones and low-speed data. There are 24 2nd-generation satellites in the constellation. Users of the iPhone 14 in the USA and Canada can send emergency messages via this satellite system. Hughes Network Systems hughes.com Hughes Network Systems is a US provider of broadband internet services worldwide, mostly in remote areas. They also offer ‘cellular backhaul’ services via geostationary satellites (connections between parts of mobile networks) and internet services on aircraft. Their cellular backhaul services are via satellite because wires or traditional microwave links to a remote site are too expensive. Since geostationary satellites are used, there is the problem of high latency, meaning the system is unsuitable for videoconferencing and gaming, and there is a significant delay in voice communications. Inmarsat www.inmarsat.com Inmarsat uses 14 satellites in GEO orbit and offers a range of services and coverage options, including connectivity for 160,000 ships and 17,000 aircraft, plus government agencies and large businesses. Their services include tracking, high-speed internet, distress and safety services. A special phone or other terminal equipment is required to connect to Inmarsat. Malaysia Airlines Flight 370 that mysteriously disappeared used Inmarsat’s satellite phone service, and the analysis of that data determined it flew into the southern Indian Ocean. Iridium www.iridium.com Iridium uses 66 active satellites in polar LEO with a 100-minute orbital period in six orbital planes, 30° apart at an altitude of 780km. Communication is via dedicated equipment by Iridium or third parties (www.iridium. com/products/) and includes options for text, data, SOS, voice and others. The frequencies used are 1616.0MHz to 1626.5MHz, while gateway uplink is 29.1-29.3GHz, gateway downlink is 24 Silicon Chip 19.1-19.6GHz and inter-satellite links are at 22.55-23.55GHz. Kuiper Systems LLC www.aboutamazon.com/news/tag/project-kuiper Kuiper Systems is a subsidiary of Amazon. Its objective is to provide accessible and affordable satellite broadband internet to “unserved and underserved communities around the world”. It is building a constellation of 3276 satellites in LEO, with the prototype satellites to be launched in early 2023. The satellites will orbit between 590630km. Lynk Global lynk.world Lynk wants to create a “cell tower in space” so standard mobile phones can connect to its satellites in LEO at 500km. It will focus on providing coverage to people in ‘third-world’ countries so they can use cheap, affordable phones. They will also cover areas of the world where there is no mobile signal coverage or coverage is down due to a natural disaster. Lynk is currently in a testing phase and will need 1000 satellites for full broadband coverage, which it expects to achieve by 2025, and ultimately a full constellation of 5000 satellites. O3b www.ses.com O3b uses a constellation of 20 satellites in medium Earth orbit (MEO), 8000km above the surface, for relatively low latency. The idea is to provide internet connectivity to rural and remote areas at altitudes between 50°N and 50°S (covering 96% of Earth’s population) for mobile network operators, telcos, enterprises and government. Examples include telemedicine, electronic banking and virtual classrooms in places like American Samoa, Brazil, Chad, East Timor and Papua New Guinea. 4G+ mobile phone services can be offered in places like the Cook Islands by providing backhaul services. They can also provide internet connectivity at sea, such as on cruise ships. For the next generation of services, O3b is also launching mPower Australia's electronics magazine satellites for government, military and various enterprises and will have 11 satellites in MEO, each of which can produce 5,000 digitally-formed beams directed to various users. OneWeb oneweb.net OneWeb is in the process of launching a 648-­satellite constellation into LEO (1200km) to provide global broadband internet services by the end of 2023. Customers are intended to be government, military, telcos and remote communities, not individuals. Orbcomm orbcomm.com/en/partners/connectivity/satellite Orbcomm offers a constellation of Isat Data Pro satellites in GEO orbit and ORBCOMM OG2 in LEO for satellite IoT (Internet of Things) connectivity. Project Loon is a now-defunct proposal to use high-altitude balloons at 18-25km to create a wide-area wireless network. Manoeuvring to stay on station was by adjusting buoyancy to find winds in the correct direction. Links • Find naked eye visibility of Starlink satellites in your area at https:// findstarlink.com/ Note that Starlink satellites are less visible now than they used to be due to measures taken to minimise the disturbance to astronomers. An App is also available for Android and iOS devices. • See the present location of the Starlink constellation, as well as OneWeb and GPS constellations, at https:// satellitemap.space/ • There is an interactive map to determine availability at your service address at www.starlink.com/map While the availability of the satellite service is global, there still needs to be ground-level national agreements and billing arrangements. • There is a video of an Australian review of the Starlink system for travel in an RV titled “The Truth About Starlink RV! Is It Worth It?” at https:// youtu.be/d29jURzZGe0 • A video of the ‘satellite train’ shortly after launch, before the satellites were put in their final orbits, titled “Starlink Satellites train seen in the sky” at https://youtu.be/ihVuz8uM1qU • A very interesting and simple project to receive Starlink beacon (tracking) signals with a Raspberry Pi computer, a software-defined radio and a satellite antenna receiver (LNB): siliconchip.au/link/abjm SC siliconchip.com.au Create highly detailed prints for less with our bargain priced Resin 3D Printer Perfect for any maker or hobbyist looking to get into the world of resin printing 1 YEAR WARRANTY • MAKE MODELS UP TO 160H x 129W x 80Dmm • FAST 2 SEC LAYER CURE • REPLACEABLE ANTI-SCRATCH FILM • 10-50µm LAYER HEIGHTS • 6.08” 2K MONOCHROME LCD • COMPATIBLE WITH PHOTON MONO FEP SHEETS • 50µm XY RESOLUTION BRINGS VIVID DETAILS • 400:1 CONTRAST RATIO FOR SHARP & CLEAR EDGES • RESIN FILL INDICATOR • UV BLOCKING COVER PRICED TO CLEAR 299 $ TL4650 SAVE $50 WHILST STOCK LASTS • 3.5” TOUCHSCREEN LCD Order yours today! jaycar.com.au/p/TL4650 Phone: 1800 022 888 In-stock at over 110 stores nationwide Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Stock may be limited and offer available only whilst stock lasts. No rain checks. Savings on Original RRP (ORRP). Basic RF Signal Generator My AM/FM/DDS Signal Generator design (May 2022) is a very convenient piece of test equipment, but it’s overkill for many tasks. If you just need a basic test signal from 10Hz to 25MHz, this Generator is it; it’s compact, cheap to build and doesn’t involve many parts. T his design came about because my Q Meter (January 2023; siliconchip.au/Article/15613) needs a 100kHz to 25MHz signal at close to 0dBm to function. Many constructors may already have a suitable signal generator, such as my May 2022 design (siliconchip.au/Article/15306). Still, I decided to create a simpler version that does the job with minimal components and at a lower cost. A DDS design is the most sensible option, and the Analog Devices AD9834 is a good DDS chip, but it costs $27 plus delivery. It makes far more sense to purchase a ready-made module, which costs less and comes with most of the necessary parts already assembled onto a PCB. There are a variety of suitable DDS modules available on AliExpress and similar; I used (and can recommend) the one at siliconchip.au/link/abjo Using a module like this takes a lot of the hard work out of the design. By itself, the module will not do anything; it requires the power and control signals through the 10-pin header. It only took me a little while to design a control module for it. This has a microcontroller with a small display to show the frequency and a knob to set it. I kept the same display and appearance as the Q Meter, the earlier Signal Generator and associated projects. Circuit details The resulting circuit is shown in Fig.1. Microcontroller IC1 is a 28-pin 26 Silicon Chip DIP ATmega168 or ATmega328. Speed is not critical, so I am using the internal 8MHz RC clock source; no external crystal is needed. The display is the same SSD1306-based 128×64 pixel OLED screen as in my other designs, and the frequency is changed by a rotary encoder with a built-in pushbutton switch. IC1 updates the display over a twowire I2C bus with the usual 4.7kW pull-up resistors. The rotary encoder terminals are pulled up by 4.7kW resistors, with 100nF and 470nF debouncing capacitors. The differing time constants make it easier for the micro to detect the encoder rotation reliably. The Generator could run from any standard 5V plugpack, but as the current drain is not high, I decided to use two AA cells and a switch-mode boost converter to generate 4.4V DC. This boost converter is the same MCP1661 or MP1541 chip used in my LC Meter (November 2022 issue; siliconchip.au/ Article/15543). Why 4.4V instead of 5V? The resulting current consumption is lower, extending battery life. The AA cells should operate down to 1V each before the up-converter drops out. This voltage is set by the ratio of the 330kW and 120kW resistors to the feedback (FB) pin of REG1, which is maintained at 1.25V. Since 1.25V × ([330kW ÷ 120kW] + 1) = 4.4V, the voltage at the cathode of D1 will increase until it reaches 4.4V, then REG1 will adjust its duty cycle to maintain that. The switch interrupting power from the battery to REG1 (S1) is Australia's electronics magazine By Charles Kosina onboard, making construction easier. The AD9834 module is powered and controlled by IC1 via 10-pin header CON1. It has an onboard 75MHz oscillator, so the maximum output frequency (the Nyquist limit) is half that, ie, 37.5MHz. But it is best to operate it lower than that, so I chose a maximum of 25MHz. As for the low end, the Q Meter needs a minimum frequency of 100kHz, but the module can go as low as 1Hz. I decided that 10Hz was a reasonable lower limit, spanning the full range of useful audio frequencies. The resolution of the signal generator is 1Hz; pressing the pushbutton on the encoder toggles through step sizes of 1Hz, 10Hz, 100Hz, 1kHz, 10kHz, 100kHz and 1MHz. On power-up, the default step size is 1MHz. CON4 is a standard Atmel six-pin ICSP header that allows you to program IC1 in-circuit if fitted. There’s also an optional serial debug interface at CON3; if you aren’t using that, you can leave off Mosfet Q1 and its 1kW pull-up resistor. However, CON3 should be fitted as it is also used to trigger calibration when S2 is closed or its pins 1 & 3 are shorted. Output frequency response Once the firmware was working, I plotted the output level against frequency, shown as the red trace in Fig.2; two problems are apparent. The output was about -11dBm, which is too low, and it falls off rapidly above 18MHz. The output level is set by one siliconchip.com.au Fig.1: the circuit is simple because the DDS signal generator is a prebuilt module that plugs into CON1. It’s controlled by micro IC1, which monitors rotary encoder RE1 and displays the status on the OLED1 screen. Power comes from a pair of AA cells via boost converter REG1 that generates a steady 4.4V. Fig.2: the output frequency response of the Signal Generator with the original resistor R2 (red) and new value (green). siliconchip.com.au Australia's electronics magazine June 2023  27 resistor, R2, which is 6.8kW on the supplied module. By changing this to 1.2kW, the output increased to near 0dBm over the flat part of the range, shown in green in Fig.2. The resistor on the module is an M1608/0603 size SMD type, but a larger M2012/0805 size resistor will also fit. I measured the output power three ways, and they did not quite agree. The most reliable method is to measure the peak-to-peak voltage on an oscilloscope with an accurate 50W RF load (how I plotted Fig.2). The other methods used the tinySA spectrum analyser and the Analog Devices AD8318 power meter. Those two methods gave values between 1dBm & 4dBm lower. This still leaves the problem of frequencies above 18MHz having a reduced level. If this is sufficient for your needs, no further modifications are needed. However, I decided that it was worthwhile to improve the frequency response. If you look at my photos, you will see that the two outputs on the module each have a low-pass filter (LPF) consisting of three inductors and three capacitors. We can fix the drop-off by replacing L4-L6 & C7-C9 with different value components, giving a cutoff frequency of 35MHz. The inductors are M2012/0805-size, and the capacitors are M1608/0603size SMDs, but again, M2012/0805 size capacitors will fit. The new 5th-order Chebyshev LPF is shown in Fig.3. You will note that C8 is not needed in this topology. The new frequency response is shown in Fig.4. The other output can be left as-is, as it is unused. Despite the 35MHz cutoff frequency, there is still a reduction at 25MHz due to the relatively low Q of the Coilcraft chip inductors I used; their rated Q factors are not high. At 25MHz, the 820nH inductor has a Q of 23, the 1.5µH has a Q of 10 and the 1.8µH has a Q of 15. These are not very impressive figures! Fig.3: this new Chebyshev LPF arrangement provides a much flatter response than the one that comes with the module. I tested some other SMD inductors that supposedly had a higher Q but they actually made the output level slightly lower. So the Coilcraft inductors are good if you can get them; the parts list includes some close alternatives that might be easier to get. Harmonics As with all DDS systems, the output is not pure, with multiple spurs. These are shown in Plots 1-3. Of the five frequencies I tested (5MHz, 10MHz, 15MHz, 20MHz & 25MHz), 15MHz and 25MHz give the purest output as they are one-fifth and one-third of the clock frequency. The only spurs are harmonics of the fundamental. All others had multiple spurs, mostly more than 20dB down compared to the output frequency (the other two not shown are similar in appearance to Plot 2). Housing it I used a 105 × 75 × 40mm ABS enclosure with a clear lid, Altronics Cat H0321. An alternative is the Altronics Cat H0323 which is deeper at 55mm. Using the shallower H3021 case, there is only just enough spare room for the battery holder on the left side. The larger one has more room for the battery holder, allowing it to be attached to the bottom of the case. Another advantage of the larger (H0323) case is that there is enough room to fit a potentiometer to allow you to adjust the output level from around -23dBm to 0dBm, to be detailed at the end of the article. Actually, you can fit a small (9mm or 10mm body size) potentiometer in the smaller (H0321) case, but using the larger case gives you more room and choices for that pot. Apart from the AD9834 module, two circuit boards are used. One contains the control circuitry, and the other is the front panel with a cutout for the display and two holes for the switch and tuning shaft. This panel is a snug fit into the detent on the front panel, and it is held in place by the nut on the switch shaft. Construction The control board is built on a 59 × 65mm double-sided PCB coded CSE221001 that attaches to the clear lid by two screws in opposite corners. Countersunk holes must be drilled 28 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.4: the measured response of the new filter. It isn’t quite as good as estimated in Fig.3 due to the limited inductor Q values, but it’s a vast improvement on the original. We calculate that the response to be significantly flatter than this using the specified components. in the clear panel for these screws – the best way to position the holes is to place the blank PCB inside the top cover hard up against the right side and use it as a template for drilling the holes for the switch, shaft encoder and two diagonal mounting holes. After that, assemble the control board (see Fig.5), starting with the surface-mounting components. The resistors and capacitors are all 2.0 × 1.2mm, so they aren’t too difficult to solder. However, the 5-pin SOT-23 chip (regulator REG1) requires some care due to its close pin spacing. It really helps to have some flux paste to solder REG1. Put a little over the pads, then place the IC over them and tack one of the pins on the side with only two pins by loading a little solder on the clean tip of a soldering iron and touching it to both the pin and pad. Check that all the other pins are correctly located over their pads; if they aren’t, re-heat the joint and gently nudge the regulator into position. Once it’s aligned, put a bit more solder on the iron and, after adding a little more flux paste, touch it to the three pins close to each other so that three good joints are formed. Check for bridges between the pins. If any have formed, add more flux paste and then use some solder wick to remove the excess solder. Finally, solder the last pin on the other side. After that, all the through-hole components on the front side can be mounted. The OLED plugs into a 4-pin socket strip and is attached by 16mm screws through 8mm untapped spacers. Depending on the exact OLED siliconchip.com.au Plot 1 5MHz Plot 2 10MHz Plot 3 25MHz Australia's electronics magazine June 2023  29 Fig.5: fit the components to the control board as shown here; note that there are two 4.7kW resistors under the OLED screen and a 100nF capacitor on the underside of the PCB. screen used, the screws may need to be either 2mm or 2.5mm in diameter; most will accept M2 screws. So the OLED sits at the right height, carefully slide off the plastic strip on the 4-pin header soldered to the OLED and cut the pins to suit the depth of the socket. Use a 28-pin DIL socket for the ATmega168/328. Finally, attach the three connectors on the underside of the board. Transistor Q1 and its associated 1kW resistor can be omitted if you don’t need the serial debug feature. If you’re using the microcontroller purchased from the Silicon Chip Online Shop, it will come pre-­ programmed. In theory, you could solder it straight to the board, but using a socket will make replacing it easier in future, should that be necessary. If you have a blank chip, it is easiest to program it in-circuit using CON4. You will need an Atmel serial programmer; an Arduino can be used in this role. First, use the Arduino IDE to upload the ArduinoISP sample code to the Arduino to be used as a programmer. Next, wire up CON4 to the six-pin programming header on the Arduino, except for the RST signal on pin 5. Assuming you’re using the Uno, pin 5 on CON4 goes to its D10 digital pin instead. After that, you can use the free software AVRDUDE (Linux or Windows command-line) or AVRDUDESS (Windows GUI) to upload the HEX file (available from the Silicon Chip website) using “Arduino” as the programmer and 19,200 as the baud rate. Make sure you select the correct COM port (the one the Arduino programmer 30 Silicon Chip board is using) and the target chip (ATmega168, ATmega328 etc). Modifying the DDS module First, desolder and remove the small SMDs labelled L4-L6 & C7-C9 from the board. You can do this with a standard iron by grabbing one component at a time with some reasonably solid tweezers, then alternately heating one side and the other while pulling up gently until the part lifts off the board. It usually helps to melt a little extra tinlead solder into the pad on each side before doing this. Once the parts are off the board, squirt a small blob of flux paste onto each pad, place some solder wick on top, press down with the iron, and, when it’s hot enough, slide it off the pad. That should remove all but a very thin layer of solder. Clean up the flux residue with some flux cleaner or pure alcohol and a lint-free cloth or cotton bud. You can then install all the new components: L4 = 820nH, L5 = 1.8μH, L6 = 1.5μH, C7 = 33pF & C9 = 30pF. Do not install a new capacitor on the pads for C8. Note that one of the specified inductors has an open side which should face towards the PCB while the other inductors and the capacitors can be fitted in any orientation. Making the cable A short 10-pin flat ribbon cable with IDC connectors at each end joins the two modules. Crimp the IDC connectors as shown in Fig.6; if in doubt, check the photos. You can use a vice to close down the connector on the flat cable, making sure that it is exactly square, although it’s better to use a dedicated IDC crimping tool (eg, Altronics T1540). This photo shows nearly all parts required to build the Basic RF Signal Generator, except for the replacement components for the DDS module (see the text above). Australia's electronics magazine siliconchip.com.au Inductors L4-L6 and capacitors C7-C9 have been replaced on the AD9834 module to provide a 35MHz cutoff frequency. The output level is adjusted by changing R2, which I replaced with a potentiometer. There is no room for the strain relief clips on the connectors, so leave them off if supplied. Testing For initial testing, before assembling it into the case, connect the battery and switch it on. The OLED should come up with an initial message showing the version number. After two seconds, the display will show the frequency, step size and battery voltage. The default frequency on power-up is 10MHz, and the step size is 1MHz. Check the VCC voltage at pin 7 or 20 of IC1; it should be close to 4V. You can use the labelled pad near the bottom edge of the PCB as a GND reference. Rotating the knob should increase or decrease the frequency. Depending on the shaft encoder, it may operate backwards. If so, plug a jumper on the programming header between pins 4 and 6 of CON4. If you haven’t fitted the header, you can do it now or solder a short component lead off-cut between those pins. The firmware reads the level on digital input PORTB.3, which determines the encoder direction sensing. Adding a jumper between pins 4 & 6 of CON4 pulls that pin to GND. If all is well, connect the AD9834 module, being careful with the orientation of the flat cable, ensuring that pin 1 goes to GND at both ends. A green LED on that module should light up when power is applied. Check the output on the two SMA connectors with an RF power meter or oscilloscope. The output of the LPF requires 50W termination; without it, there may be some distortion of the output waveform. Final assembly Attach the control board to the transparent lid by two screws on opposite Fig.6: the ribbon cable is simple to make but ensure that the pins are fully pushed into the plastic housing, or you might end up with bad connections. Fig.7: where to drill the holes in the side of the box for the SMA connectors. siliconchip.com.au Australia's electronics magazine corners with 12mm-long M3 tapped spacers, into the countersunk holes you made earlier. The AD9834 module attaches to the bottom of the case with M2/M2.5 × 12mm CSK screws and nuts plus 5mm untapped spacers. First, two holes need to be drilled in the side for the SMA connectors, as shown in Fig.7. The square wave output connector is not accessible and is not used in this design. Next, slide in the module and use it as a template to mark the position of the two holes in the bottom. Drill these to 2.0mm or 2.5mm to suit your screws and countersink them on the bottom. Calibration The output frequency accuracy depends on the exact frequency of the 75MHz oscillator on the module. I found the error at 10MHz to be about 140Hz. This is of little importance for some applications, such as driving the Q meter. However, there is a calibration procedure built in. Set the frequency to precisely 10MHz and measure the output with a frequency counter. Turn on S2 or plug the jumper across CON3 and rotate the tuning knob until the readout on the counter is 10MHz ±1Hz, then press the knob. This sets a correction factor into an EEPROM which is read on power-up. As there is no temperature compensation in the 75MHz crystal oscillator, you can expect this frequency to drift slightly, but it is likely to remain within ±20Hz at 10MHz. Recalibration may be needed from time to time as the crystal oscillator ages. June 2023  31 Parts List – Basic RF Signal Generator 1 double-sided PCB coded CSE221001, 59 × 65mm 1 black PCB coded CSE220902B, 77.5 × 64mm, 1mm thick (front panel) 1 0.96in OLED screen, SSD1306-compatible controller (OLED1) [SC6176] 1 AD9834-based RF DDS signal generator module (MOD1) [AliExpress siliconchip.au/link/abjo] 1 vertical-mount rotary encoder with integral pushbutton and 20mm-long shaft (RE1) [SC5601] 1 105×75×40mm or 105×75×55mm ABS case [Altronics H0321 or H0323] 1 3.3uH axial RF inductor (L1) 1 820nH SMD inductor, M2012/0805, Q = 100 <at> 25MHz (L4 on MOD1) [Coilcraft 0805HP-821XJRC or Vishay Dale IMC0805ERR82J01] ● 1 1.8μH SMD inductor, M2012/0805, Q ≈ 40 <at> 25MHz (L5 on MOD1) [Coilcraft 0805CS-182XJRC or Murata LQW21HN1R8J00L] ● 1 1.5μH SMD inductor, M2012/0805, Q ≈ 40 <at> 25MHz (L6 on MOD1) [Coilcraft 0805CS-152XJRC or Murata LQW21HN1R5J00L] ● 1 2×AA cell holder with flying leads (BAT1) 2 AA alkaline cells 1 2×5 pin header (CON1) 1 2-pin polarised header with matching plug and pins (CON2) 1 3-pin polarised header with matching plug and pins (CON3) 1 2×3 pin header (CON4; optional; for in-circuit programming of IC1) 1 jumper shunt (optional; to set the direction of RE1) 1 4-pin female header (for OLED1) 2 SPDT chassis-mount toggle switches with solder tags (S1 & S2; S2 is optional, for calibration) 1 28-pin DIL IC socket (for IC1) 2 10-way IDC crimp sockets Cable & hardware 1 knob to suit RE1 2 M3 × 12mm tapped spacers 2 M3 × 6mm panhead machine screws 2 M3 × 6mm countersunk head machine screws 2 M2.5 or M2 × 12mm countersunk head machine screws 2 M2.5 or M2 × 16mm panhead machine screws 4 M2.5 or M2 hex nuts 2 3mm ID, 8mm long untapped spacers 2 3mm ID, 5mm long untapped spacers 1 70mm length of 10-way ribbon cable 1 double-sided foam tape pad or strips (to secure the cell holder) Semiconductors 1 ATmega168P or ATmega328P programmed with CSE22100A.HEX (IC1) 1 MCP1661T-E/OT or MP1541DJ-LF-P integrated high-voltage boost regulator, SOT-23-5 (REG1) 1 2N7002 N-channel signal Mosfet, SOT-23 (Q1; optional, debug interface) 1 MBR0540 50V 500mA schottky diode, SOD-123 (D1) Capacitors (all SMD ceramic, M2012/0805 size, unless noted) 2 10μF 6.3V X5R or X7R 1 33pF 50V C0G/NP0 (C7 on MOD1) ● 1 470nF 6.3V X7R 1 30pF 50V C0G/NP0 (C9 on MOD1) ● 4 100nF 50V X7R Resistors (all 1% SMD M2012/0805 size, unless noted) 1 330kW 1 120kW 5 4.7kW 1 1kW (optional, for debug interface) ● replacement parts for the AD9834 DDS module Additional parts for adjustable output level 1 100nF 50V X7R SMD M2012/0805 size ceramic capacitor 1 1.2kW 1% SMD M2012/0805 size resistor 1 50kW chassis-mounting single-gang linear potentiometer [Altronics R2245 or Jaycar RP8516] 1 short length of light-duty figure-8 wire (eg, stripped from ribbon cable) 32 Silicon Chip Australia's electronics magazine Battery life With fresh AA alkaline cells, the input voltage is about 3.2V. The current drain starts at 80mA and increases as the battery voltage drops (because the boost regulator maintains a constant output voltage). By the time the battery drops to 2.7V, the current is about 95mA. The best alkaline AA cells are 3000mAh, but that rating is for a light load. It has to be derated to 2000mAh or so at the expected current drain. This gives an expected operational life of about 20 hours. Adjusting the output level Depending on component values and settings, the Q meter can be fussy about its input signal level. Sometimes the 0dBm value is too high. We can use external attenuators, but this makes the setup rather complicated. The output level is set by resistor R2 on the DDS module, so I thought why not use a potentiometer in its place? The wires to the potentiometer could pick up noise that would amplitude-­ modulate the output. However, if the wires are short, that might not be a problem. The previous photos shows how I did this on the prototype. I started by replacing R2 with a 100nF M2012/0805 SMD capacitor, providing noise filtering and a firmer base to the connecting wires. Connect a 1.2kW M2012/0805 SMD resistor to one end of this capacitor, then use short wires to connect a 50kW pot between the wiper and the anti-clockwise end of the track. Mount this on the right-hand side of the enclosure so the wires are very short. Take great care in attaching the wires to the module to prevent any damage to the SMD connections. With the maximum resistance, the output becomes about 22mV peak-topeak, corresponding to about -29dBm. At minimum resistance, the output is close to 0dBm. I saw no evidence of noise pickup in the output signal. If adding this output control, using the larger case (H0323) gives you more options; you could use a 16mm, 10mm or 9mm potentiometer. With the smaller case, you’ll have to use a 9mm or 10mm potentiometer to have SC any chance of it fitting. KIT (SC6656) – $100 + P&P Includes everything except case, cells and optional 50kW pot siliconchip.com.au Gear UP! Build It Yourself Electronics Centres® Charge TEN USB devices at once! Ultimate benchtop charging station! Great for families, class rooms & business. Massive 19A charge output across 10 x USB type A outputs. QC3.0 on 2 ports. Includes adjustable dividers & power supply. Size: 238 x 118 x 26mm. All the gear you need to keep building & creating. SAVE $45 130 $ *Devices & charging leads not included th. Sale ends June 30 M 8882A* SAVE $46 99 $ High Output Blow Torch Z 6452 Build & code your own STEM bot STEM bot is an easy to program 2 wheel obstacle avoidance and line tracking robot using Arduino. Wiring and construction has been designed to be as simple as possible. Programmable or Bluetooth controlled. Easy to follow instruction booklet provided. Runs from 6 x AA batteries (or 2 x 18650 lithium). Ages 8+ Super hot 1350°C flame with high output nozzle. Handheld or self standing design for tasks such as heatshrinking, model making, silver soldering! Easy to refill. T 2496 Don’t forget the gas! r can. T 2451 $9.50 pe SAVE 22% 62 $ stocks at this Hurry limitedounted price! sc di ly huge 799 109 SCOOP BUY! 150Ah Lithium Batteries Need longer run time from your remote power system? Upgrade with more capacity from this premium 150Ah LiFePO4 battery, with commercial grade cells & high discharge rating. 12.8V output. M8/F12 terminals. Iroda® Mini Jet Blowtorch Produces a powerful jet like flame - up to 1300°C! Refillable design is great for hobbyists. BARGAIN! T 2488 21.95 $ Precision Knife Set Includes to handles and a variety of blades (13) to suit different cutting jobs. Includes plastic carry case. 15 $ Utilises a microprocessor to ensure your battery is maintained in tip-top condition whenever you need it. Helps to extend battery service life. Suitable for permanent connection for battery maintenance. 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Perfect for 4WDs, campers, caravans & trade vans. 299 $ M 8057 1500W The same top notch quality and safety features as our popular Black Max inverter series (left), with a modified sine wave design to bring 240V power to any vehicle at a fantastic price. Models up to 600W have USB and auxiliary 3A 12V DC output. 240V outlet runs most simple appliances such as power tools, pumps, lights, fans and heater elements. All inverter models fully isolated for safety and certified to AS/NZS 4763.2011. GREAT VALUE 175 N 2019B N 2087 20A Powerhouse® Solar DC-DC Battery Chargers 275 $ N 2089 40A This dual input design connects to a solar panel and your cars alternator (12 or 24V) to provide charging for secondary batteries such as those used in campers, caravans and trades service vans/ trailers. Suitable for Lead Acid, AGM and Lithium Fe PO4 batteries. Suitable for 12/24V systems with either lead acid or lithium chemistry batteries. Supports Li-NiCoMn & LiFePO4. 30A max charge current. LCD provides easy to read system status. SB50 Anderson Chassis Mount Housing P 7865 39 P 0697 29 $ Handy Power Panels For Cars & Camper Vans These panels can be easily surface mounted to custom panels to provide power to your devices & portable appliances. 15A DC breaker. P 0697: 50x130x70mm. P 0698: 50x187x70mm. A combined chassis mount housing for 7 pin trailer socket and 50A anderson style connector. Anderson A comprehensive power monitor panel for solar and remote power systems. Huge selection of on screen power stats. Supplied with a 200A shunt for easy connection. Cut out size: 87 x 47mm. P 7866 42.50 $ connector not included. Includes QC3.0 3A output, plus 18W USB C PD. 29mm mounting hole. SAVE 16% SAVE 23% 14 Anderson Style Panel Socket W 4100 Red W 4102 Black P 7810 Easy connection for solar panels and auxiliary batteries. Cutout: 40x21mm. High Current OFC Power Cable 5 $ /m Rated up to 61A this handy 8AWG cable is ideal for automotive power cabling. 39 $ P 0696A .95 SAVE $10 Handy Digital Power & Solar Meter USB 18W PD Panel Socket & Voltmeter $ Q 0592 connector not included. Trailer Connector SB50 Style & 7 Pin Socket SAVE 20% P 0698 The Ultimate Battery Fuel Gauge. Accurately measures battery voltage, current, power, real capacity and remaining run time of your connected battery (suitable for any type of chemistry and voltages between 8V to 120V). Includes 50A shunt with 2m cable. 1% accuracy. Cut out dimensions: 53.5 x 37.5mm. Mount an SB50 connector on your tow hitch with this handy housing. Anderson 18.95 $ NEW! 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Table Lamp With Wireless Charger Self standing lantern or hand torch Ultra-bright long life LED for fantastic clarity (plus no need to change a globe - EVER!). Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. Great for collectors, model makers, jewellers etc. A stylish glossy white table lamp with adjustable dimming, colour temperature & wireless charging. Great for the desk or bedside table. Powered by any USB wall charger - 2A minimum (M 8862B $13.95). SAVE 19% 16 $ X 0209B A great bedside or study lamp SAVE $10 29 Rechargeable 2 In 1 Lantern Torch $ Powerful 300 lumen, 3W LED torch with aluminium body, adjustable beam & USB recharging. Includes battery. 109 $ X 4221 X 4201 5 Dioptre 15ea Part RRP NOW UV X 3300 $125 W/White X 3301 $109 Nat. 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Works with X 4101 controller which is powered by 2xAA batteries. n X 4105 Green 3m Roll n X 4106 Blue n X 4107 Red n X 4108 White 5 $ .75 X 4101 Controller $11.50 Sale Ends June 30th 2023 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au SAVE 33% X 3270 Warm White X 3271 Natural White 500mm Aluminium 12V LED Strips 300mm Aluminium 12V LED Strips • Stylish LED strips for workspaces, cabinets, cars etc • Easy to mount & power. • 25Wx10Hx500Lmm. • 4 strips can be daisychained using X 3255 joiner ($2.95) • Suggest M 8936D 2A plugpack for mains iuse ($24.75). Perfect for lighting inside cabinets, under shelves, wardrobes etc. Utilises high efficiency SMD LEDs - 4W per strip. Use at home or in cars, caravans & 4WDs. 39Wx8Hx300Lmm. Join up to 5 strips together using joiners (sold separately). 12V input, 500mA per strip. Genlamp® PIR Security Lights Get quality motion activated security lighting at your place for less! Fully adjustable sensitivity, on time and dusk settings. Fitted with 240V 3 pin mains plug. Fully approved. Natural white. Rust free stainless steel brackets and hardware. IP65 rated. SAVE $19.95 40 $ X 2340C 10W SAVE $24.95 55 $ X 2315C 20W SAVE $30 69 $ X 2317C 50W Western Australia Build It Yourself Electronics Centres SAVE $20 » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2023. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0006 Find a local reseller at: altronics.com.au/storelocations/dealers/ Subscribe to MAY 2023 ISSN 1030-2662 05 The VERY BEST DIY Projects! Melbourne Exhibition Centre, 9 771030 266001 $1150* NZ $1290 INC GST INC GST May 10-11 Australia’s International Airsho All Australia’s top electronics magazine w the newest tech in Avalon Airpor t Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! Australian International Airshow; May 2023 The Songbird; May 2023 500W Class-D Amplifier; April 2023 Silicon Chirp; April 2023 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe siliconchip.com.au Australia's electronics magazine June 2023  37 The History of ETI Magazine The voyage of the good ship “etty” by Peter Ihnat Electronics – the final frontier. This describes the voyage of the good ship “etty”. Its 19-year mission: to explore the brave, new world; to seek out new technologies and to innovate; to boldly go where no journal had gone before! The first cover of Electronics Today magazine from April 1971, and the last cover of ETI magazine from April 1990; before it merged with Electronics Australia. R eading the articles by Leo Simpson about the history of Silicon Chip magazine (August & September 2022; siliconchip.au/Series/385) made me put a finger to the keyboard to describe the other side of our electronics magazines at the time, Electronics Today International or the good ship “etty” as it was known. April 2023 marks 52 years since ETI was first published. While my employment with the magazine was short (about 16 months), it overlapped with the upheavals in the electronics magazine scene described by Leo Simpson. 38 Silicon Chip By going through my back issues of the magazine, editorials, staff listings, various online references and my recollections, I was able to piece together a brief history of ETI magazine. According to an editorial by Roger Harrison in ETI, August 1984, “Electronics Today” was conceived by 15-year-old schoolboy Kim Ryrie in 1968. Kim tried to convince his publisher father, Colin, that there was a market for an alternative electronics magazine. It was a market dominated by the then-long-established Electronics Australia magazine (EA). Australia's electronics magazine Collyn Rivers responded to an advert for an “electronics journalist” with sound practical experience placed in, of course, Electronics Australia. He joined Modern Magazines in 1970, and Electronics Today was born on March 23rd, 1971. Editor’s note: we previously published a brief memoir about ETI by ex-editor Collyn Rivers (April 2011; siliconchip.au/Article/960). Surely, a publisher starting a competing electronics magazine wouldn’t advertise in what would be the magazine’s competitor. Looking through siliconchip.com.au back issues of Electronics Australia from about November 1968 to December 1970, the only advert that even remotely looked plausible was on page 49 of the October 1970 issue (reproduced below). Some of the details look about right: the production of a new publication, requiring a complete and thorough knowledge of electronics and being fully conversant with the Australian electronics industry. Could this have been the advert? Electronics Today’s first issue then came out in April 1971 with minimal staff: Collyn Rivers as editor-in-chiefsub-layout-secretary-cleaner and Barry Wilkinson doing the projects and drawings. A subscription to the magazine cost $6 for 12 issues (EA’s cover price at the time was 50¢). Kim Ryrie was the Projects Advisor, and I noticed that Roger Harrison’s name appeared in the staff list from around July of that year as Editorial Assistant. Going international Collyn’s initial research indicated that the publication would be financially viable if it could be published in at least two countries. So twelve months later, in April 1972, a British edition was launched, followed six months later by a French edition. In 1977, German and Dutch versions were released, Canadian in 1978 and Indonesian in 1980. There was also a pirated Indian version that he decided “not to know about”. The word “International” was added to the title with the launch of the British edition, and ever since, the magazine has been known as Electronics Today International or simply “ETI”. The August 1972 editorial by Collyn covered the sudden death of Colin Stirling Ryrie on July 7 in a boating accident. In the late 1970s, Kim Ryrie and school friend Peter Vogel went on to invent the Fairlight CMI synthesiser and achieved a good deal of international fame – see https://w.wiki/6Lz4 and https://w.wiki/6Lz5 This article, written by Collyn Rivers and Roger Harrison, was featured in the July 1979 issue of ETI magazine and gave some background information on those two early staff members in their usual cheeky manner. This advert was taken from the October 1970 issue of Electronics Australia. It presumably served as Collyn Rivers’ introduction to Modern Magazines, upon where Electronics Today was created. Topics covered in ETI To appeal to a wide range of readers, the magazine not only covered the design and construction of electronic projects but also featured many general topics of interest, from cable TV to the latest space missions. siliconchip.com.au Australia's electronics magazine June 2023  39 Left: this cartoon (December 1979), drawn by Brendan Akhurst, was used for the regular column called “Dregs”. It was a column that mostly described ‘interesting’ queries people would make to ETI by phone or letter. Below: ETI were not immune to the odd joke here and there, with this FM Tuna project from the April 1979 issue, the result of their “Synergistic Beer Drinking” sessions they had with readers. The magazine had the following regular columns: ■ Amateur Radio (written by Roger Harrison, starting October 1972) ■ Book Reviews ■ Classical Recordings (reviews of classical music LPs until September 1974) ■ Component News ■ Equipment News ■ News Digest ■ Readers’ Letters ■ Ideas for Experimenters (circuits and ideas submitted by readers) ■ From June 1979, “Dregs” (the name says it all) There were many multi-part series to help those just starting out in electronics and those wanting to brush up on their theory, such as a 14-part series called “Radio Astronomy for Amateurs”, written by Roger Harrison that started in December 1971. A series called “ELECTRONICS – it’s easy!” started in November 1973 and wound up having 36 parts. It introduced many aspects of electronics, describing the different devices, what they did and how to use them. “CMOS – a practical guide” had six parts and started in July 1976. Some of the names of staff and contributors to the magazine would certainly ring a bell with those who read ETI: Louis A Challis and Associates, David Tilbrook, Phil Wait, Ron Koenig, Graeme Teesdale, Tom Moffat, Ian 40 Silicon Chip Thomas, Ian Bishop, S.K. Hui, Peter Phillips, Neale Hancock, Terry Kee, Jane McKenzie and Mary Rennie to name just a few. I’m sure they each have a great story to tell about their association with the magazine. continuous stream of enquiries from those still wishing to build the ETI480. It was intended as an upgrade in the same spirit as the ETI480 (it used much the same components). The SC200 followed in January-March 2017, which delivers more power using more modern parts; it is still quite popular. Notable projects Due to the popularity of the different There were close to 700 projects topics covered by the magazine, and published in the magazine over its maybe also to generate an extra income run, some of them quite involved. For stream, ETI released separate publiexample: cations (sometimes known as “one■ The ETI3600 and ETI4600 music shots”). They included titles such as: synthesisers, starting in the Octo■ 30 Audio Projects ber 1973 issue. ■ Electronics – It’s Easy! (volumes ■ The ETI477 series 5000 stereo 1 and 2) amplifier (January to March 1981) ■ ETI Circuits (1 to 6) and its ETI478 preamplifier (July ■ Circuit Techniques (1 to 4) to October 1981). ■ Lab Notes and Data ■ The ETI414 8-channel master-­ ■ How to build Gold and Treasure mixer (February to May 1973). Detectors ■ The ETI166 function generator ■ Test Gear (1 to 4) (July to October 1983) ■ Top Projects (volumes 1 to 11) A very popular amplifier was the ■ International 3600 and 4600 SynETI480 100W amplifier, published in thesisers December 1976. Many up-and-coming ■ Electronic Projects for Cars bands used it at the time. I lost track Collyn Rivers remained Editor, of how many mixers and amplifiers with Steve Braidwood as Assistant I helped build for friends playing in Editor, until November 1976. Around bands. For the band I played in, I built then, Steve became Editor and Collyn a couple of ETI480s and an expanded moved to the role of Publisher. Les Bell 12-channel mixer based on the ETI414, took over as Editor from June 1977 till which I still have. March 1979. Editor’s note – we published the SC480 amplifier in the January & Social events February 2003 issues in response to a In October 1978, the magazine Australia's electronics magazine siliconchip.com.au Above: “Synergistic Beer Drinking” was a monthly event held by ETI at the Bayswater Hotel in Rushcutters Bay, Sydney. It was a way for readers to provide feedback to the staff. It was held from October 1978 till December 1979. Right: from September 1979, Roger Harrison (pictured) took over from Collyn Rivers as the Editor. This continued until the end of 1984, which was not long after ETI had been sold to Federal Publishing (the owners of EA). launched a new event: “Synergistic Beer Drinking”. On the evening of the first Wednesday of each month, ETI staff could be found at the Bayswater Hotel, Rushcutters Bay, having a few beers. Readers were invited to turn up to have some fun, share stories, have a drink or two, provide feedback on the magazine, and of course, provide ideas for projects. A couple of months later, it was changed to the second Wednesday of the month to better coincide with the release of each issue of the magzine. This continued until Friday, December 7th, 1979, when “The last great wild SYNERGISTIC beer-­ drinking bash!” was held (see above). In March 1979, another feature of the magazine was introduced. Readers could phone ETI after 4pm and speak to staff about their projects. The April 1979 issue listed the staff as Collyn Rivers (Managing Editor), Roger Harrison (Acting Editor), Phil Wait (Project Manager), Les Bell (Special Assignment) and three names under siliconchip.com.au Editorial Staff: Phil Cohen, Jonathan Scott and Jan Verdon. From September 1979, Roger Harrison became Editor, a position he held until about December 1984 or January 1985. A significant change occurred in March 1983, when Roger announced in his editorial that ETI had been sold and was now owned and published by The Federal Publishing Company Pty Ltd at 140 Joynton Ave, Rosebery NSW. It ended up staying under Federal Publishing until its demise in 1990 (the end for EA came just 11 years later). The upheaval in the Australian electronics magazine industry started around mid-1985. Leo Simpson covered what happened from the EA and Silicon Chip point of view in the article I mentioned earlier. 1984/85 was when I was involved with ETI, so I saw events from the ETI perspective. My background I studied Electrical Engineering at the University of Wollongong and, in Australia's electronics magazine the last year of the course, I scored a part-time job in their Physics Department, designing and building electronic equipment. While finishing the BE, I enrolled in a BSc and eventually completed my studies in 1983. At the time, I was reading Electronics Australia occasionally but buying ETI just about every month. I saw an advert for a Project Engineer at ETI and decided to apply. They looked at my credentials and, despite that, I got the job and started in December. Finally, I was working alongside Roger Harrison (Editor), Jennifer Whyte (Assistant Editor), Geoff Nicholls (Project Engineer), David Currie (Draughtsman) and several other staff who looked after production, advertising, art and reader services. What an interesting and vibrant team! Working for ETI The offices and workshop were in an area of Federal Publishing in Rosebery, Federal Publishing being the magazine arm of Eastern Suburbs June 2023  41 Aug 1922 – Mar 1939 Wireless Weekly Apr 1939 – Jan 1955 Radio & Hobbies A Timeline of Electronics Magazines in Australia The Masterplay was one of the projects I worked on with Geoff Nicholls. It was published in the September 1984 issue of ETI. Newspapers group. Out the back, in a separate building, were the presses. What a sight to see - kilometres of paper streaming through the machines printing papers and magazines in full colour at high speed! With flexible working hours, I was able to drive up from Wollongong after the peak each day, missing all the traffic, then return home after the rush. It helped that Rosebery is on the southern side of Sydney, so I had to do minimal driving through the Sydney traffic. Not long after I started at ETI, there were more additions to the staff: Rob Irwin as a Project Engineer in January 1984, Jim Rowe as Managing Editor in April 1984, followed closely by Jon Fairall as Technical Writer in May 1984. It was a dynamic place. We spent many hours coming up with ideas for projects, designing them, building them, having lunch at the Rosebery Hotel just down the road, having lunch at the Sri Lanka Room above the Agincourt on Broadway and so on. Geoff, Rob and I had a small, cramped workshop where we designed and constructed our projects. The component drawers were well-stocked, and we could always order what was needed for any project we were working on. There were two rooms outside the workshop with a UV light box, a sink for wet work (etching PCBs) and a high-speed drill press for drilling PCBs and enclosures. Basically, we laid out our circuit boards by sticking DIP and circle patterns onto clear sheets. These were joined using stick-on tapes of different widths. We exposed the sheet onto Scotchcal 8007 orange film using the UV light box to produce a negative and developed the sheet by wiping it with cotton wool soaked in Scotchcal 8500 developer. We then exposed the film onto negative-­ acting Riston-coated PCB material using the UV light box again, developed the Riston using another special developer, etched the PCB in hot ammonium persulfate solution, removed the Riston with acetone and then drilled the holes using the drill press. Finally, we could solder parts onto the board. The idea was to get the board design right on the first go; otherwise, it would take too long to re-do it. It’s interesting to note that, as far back as October 1977, ETI started printing the PCB artwork for its projects on a separate page with the reverse side of that page printed in blue. This was to allow constructors to expose directly through the paper onto Scotchcal film. They continued this until ETI moved to Federal Publishing. I recall having frequent team meetings, usually at the Sri Lanka room, with the late Gary Johnston, who was in the early stages of running Jaycar Electronics. At one lunch, he mentioned that he had acquired multiple turntables and asked if we could design a project around them. Geoff and I got stuck straight into it. We designed the electronics; I cut up some pineboard at home and made a box to house the electronics with the turntable dropping into the top. I covered it with iron-on timber veneer, and it came up looking quite good. It needed a name, so after a bit of to-ing and fro-ing, we came up with David Kelly, Rosalind Bromwich and Kim Bucknole were just some of the people who acted in the role as Editor for ETI. 42 Silicon Chip Australia's electronics magazine siliconchip.com.au Feb 1955 – Mar 1965 Radio, Television & Hobbies (RTV&H) April 1965 – May 1990 Electronics Australia (EA) Apr 1971 – Mar 1972 April 1972 – April 1990 Electronics Today Electronics Today International (ETI) June 1990 – September 1995 EA with ETI combined magazine October 1995 – December 1999 EA with Professional Electronics & ETI January 2000 – March 2000 Electronics Australia name brought back April 2000 – April 2001 – January 2001 October 2001 Electronics Renamed again to Australia Electronics Australia renamed to “ea” Today (“eat”) Note: December 2000 & January 2001 was a combined issue of “ea”, with Jul 1985 – Dec 1988 Australian Electronics no February & March 2001 issues. “eat” magazine had a combined issue for September & October 2001, but had no issue in August 2001. Monthly (AEM) November 1987 – Present Silicon Chip magazine one. EA had the “Playmaster” series of amplifiers and such, so we named this one “Masterplay” (ETI442). Most of the projects we tackled fitted in with the different interests of staff and feedback from readers. So Rob designed many of the audio projects, Geoff worked on Microbee/microprocessor and audio projects and I did photography and microprocessor-­ based projects. Photography was one of my hobbies. Besides taking photos, I also did darkroom work developing monochrome & slide film and making B&W, Cibachrome and Ektacolour prints. As soon as it was known I could take photos, it wasn’t long before I was photographing the project prototypes for inclusion in the magazine. Things start to change It was either December 1984 or January 1985 that I came into work and saw Roger Harrison being escorted out. My memory is a bit hazy; I still don’t know what had happened, but a new Editor, David Kelly, had been appointed. Around that time, a new extension to the building was completed, and ETI moved into new offices and workshop. Unknown to us, Federal Publishing had purchased Electronics Australia magazine in November 1984, and their whole team was moving into the same area! What a strange situation – two competing magazines owned by the same company and sharing the same space. At least the new electronics workshop was roomy and square. EA project engineers worked at benches against one wall with component shelves/ drawers in the centre separating them from our benches, which were against the opposite wall. I left around March 1985. By December, both Geoff and Rob had also left, and Jon Fairall moved up to become Editor around June 1986. siliconchip.com.au Only a few years later, in his March 1989 editorial, Jon announced that it was his last one. He commented, “The number of pages devoted to electronics in one form or another must have jumped tenfold in the last two decades. Unfortunately, the audience hasn’t increased by anything like that amount”. With several competing electronics magazines being produced locally, maybe he saw the writing on the wall. Rosalind Bromwich took over as Editor in April, and in her May 1989 editorial, she announced the return of Roger Harrison. With his son Jamye and others from the Apogee Group, they would be contributing regularly to the magazine. Rosalind left in October, and Kim Bucknole took over as Editor and manager in November. But alas, all that was short-lived, and the final issue of ETI came out in April 1990, ending a 19-year run. An unsuccessful merger Was there still hope? Jim Rowe had been Editor of Electronics Australia since July 1987 after Leo Simpson, Greg Swain and John Clarke had left. In his June 1990 editorial, he announced that Federal Publishing “decided to merge the two titles together”, combining the best elements of both publications. So EA and ETI became “Electronics Australia with ETI”, the first issue under that name being June 1990. The timeline above shows the history of Australian electronics magazines from 1922 to the present. It is apparent that after a stable period from August 1922 to about 1990, not long after Federal Publishing had purchased both ETI and EA, things started to go haywire. Combining ETI with EA lasted less than 10 years, and by the 1990s, Silicon Chip was becoming more established as the electronics magazine of choice. Then, in the space Australia's electronics magazine of 22 months, with three more name changes and a new Editor (Graham Cattley from September 1999), the Federal Publishing idea of what an electronics magazine should be had failed. The final issue of Electronics Australia Today (eat) appeared as the September/October 2001 double-issue. This ended a record run for an electronics magazine in Australia, starting in 1922 and finishing in 2001. I believe the last few years of that run emphasised that electronics enthusiasts weren’t interested in a glossy magazine describing the latest tech gear; they wanted ‘real’ electronics, ie, circuits, software and hardware. That is the market that Silicon Chip has been catering for and continues to support. After I left ETI, I lost contact (for a while) with the other ETI staff I had worked with. Roger Harrison went on to create a new magazine called Australian Electronics Monthly (AEM), which continued for just over three years. I remember receiving a call from Rob Irwin sometime after he left ETI. He was working for Choice Magazine and was looking for ideas on how to set up stepper motors to automate a test rig. I hadn’t heard from Geoff Nicholls for nearly two decades until one day he phoned, from Germany, of all places! He was living there and had come across my contact details in a box of electronic parts he was sorting through. We stayed in contact and exchanged many circuit designs, software and ideas until his unexpected death at the end of 2021. It was a great experience working for the good ship “etty”, a short period I’ll never forget. I enjoyed the projects, comradery, jokes and brainstorming sessions over drinks and great meals. Those times have passed, and “etty’s” voyage is now over, but it’s great to see the spirit of electronics in Australia continue through the surviving magazine, Silicon Chip. SC June 2023  43 Author & Designer: Phil Prosser LOUDSPEAKER TEST JIG Use your computer’s sound card to measure loudspeaker performance, inductors, capacitors and complex impedances. With this Jig and appropriate software, measuring and tweaking crossovers, cabinets and speakers is easy. W hen designing and building loudspeakers, you need a good microphone and test setup and the ability to measure the impedance of the loudspeaker driver and crossover parts. You can do this at home with our Loudspeaker Test Jig, without breaking the bank. It is an interface to your PC, allowing you to measure complex impedances, which is important when building crossovers. This is one job where even the best multimeter doesn’t help, as impedance is frequency dependent, with real and imaginary components. The Test Jig also connects to a microphone for analysing loudspeakers. Fig.1 is the impedance and phase plot of a 12-inch (305mm) driver, a PA bass-mid with a resonant frequency of 60Hz. The dotted phase line goes through an inflection at this frequency, from about +55° degrees to -55°. It is possible to make this sort of plot using an oscilloscope and graph paper, but your PC and sound card can make this sort of measurement in seconds with our test jig. Eric Wallin is credited with originating the basic concept of the “Wallin Jig”, shown in Fig.2. It is the de facto standard for PC-based speaker testing. It uses the left output channel of the sound card output to drive a signal through a reference resistor and the — Common-mode rejection ratio (CMRR): >60dB on prototype (20Hz to device under test (DUT). The left input channel measures the voltage across both the reference and DUT, while the right input channel measures the voltage across the DUT alone. For a complete test setup, you need: ● A PC or Mac with a sound card ● Test software. We recommend “Room EQ Wizard” (REW, Windows/ Mac) or the old but good “Speaker Workshop” (Windows only). Both are available for free. ● A measurement microphone ● The Loudspeaker Test Jig, which includes: – An audio power amplifier of a few watts – A microphone preamplifier – A reference resistor of a few watts capacity that is ‘calibrated’ – A switching arrangement It is also very useful to have: ● A monitor output for the audio input to the Test Jig, allowing both monitoring and regular use of the sound card when not testing ● An oscilloscope to monitor the microphone signal on the front panel Two handy features this design provides are floating power for the Test Jig to avoid Earth loop induced hum and switchable gain on the input and microphone to allow for ‘near field’ and ‘far field’ tests. — THD+N: <0.01% across the audio range Software support Features & Specifications — Measures loudspeaker driver frequency and phase responses — Measures loudspeaker relative SPL (absolute SPL possible with external calibration sources) — Time alignment of loudspeaker drivers in combination with an oscilloscope — Measures the impedance of loudspeakers, crossover networks etc — Measures the value of capacitors, inductors (μH to mH range) and resistors — Incorporates a microphone preamplifier and small power amp — Frequency range: 10Hz to 20kHz (depending on your sound card) — Power output; about 5W peak into 8Ω (not continuous due to power supply limitations) — Amplifier gain: switchable between +14dB & +34dB 20kHz) — 50/100Hz hum: more than 100dB below full-scale — Microphone phantom power: 48V, selectable via header on PCB — Power supply: 15V AC <at> 1.2A from a plugpack (no mains wiring) 44 Silicon Chip Australia's electronics magazine The software does the heavy lifting in this design. The most current program that can be used is “Room EQ Wizard” (REW), currently in siliconchip.com.au Fig.1: the magnitude and phase of the impedance of a loudspeaker bass driver in free air. You can see the high impedance peak close to 80W at 60Hz and the rapid change in phase around there. Fig.2: the basic arrangement for measuring impedance. Conventionally, the power amplifier and microphone preamplifier are standalone devices, wired to the “Wallin Jig”. Our new design incorporates everything you need into a handy, compact unit. development and available at www. roomeqwizard.com – we tested V5.20.13. For Mac users, this is a good option. We will focus on this program as it is the most actively supported. A surprising but excellent option for Windows users is “Speaker Workshop”, which has been around for over 20 years. It is dedicated to designing and building loudspeakers and, among other things, can measure Thiele-Small parameters accurately and simply. siliconchip.com.au Sadly, it hasn’t been upgraded since about 2001. Even though it gives a warning message on startup, this remains a brilliant tool and is worth checking out. The last version is V1.06 and is available from the download page at www.claudionegro.com These programs perform measurements in slightly different ways but ultimately deliver similar results. REW uses a swept sinewave to make measurements, while Speaker Workshop uses a noise pulse. Both programs Australia's electronics magazine perform Fourier transforms and compare the reference to the measured signals to calculate either the speaker frequency response or the impedance of the DUT. Our Loudspeaker Test Jig provides the amplification and switching to allow these programs to work. We have kept it as simple as practical. It would be possible to add more switching for attenuators and reference resistors, but as we will show in the “how to use this” article, they would be gilding June 2023  45 46 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.3: the complete circuit diagram of the Test Jig with shaded boxes showing the separate sections. The Power Amplifier drives a loudspeaker while the Microphone Preamplifier picks up the resulting sound and amplifies it to send it to the sound card. The Speaker Measurement section is essentially a buffer, while the Switching section lets you perform various tests without disconnecting and reconnecting many leads. siliconchip.com.au Australia's electronics magazine June 2023  47 the lily and make it harder to use than necessary. You could easily add more switching externally if you wish. Microphone selection As for the microphone, you need a measurement microphone. The Shure SM58 has a shaped frequency response and is unsuitable for this job. At the low end, you can buy a Behringer ECM8000 for about $65 or a Dayton Audio EMM6 with calibration data for about $140. Alternatively, it is easy to build an excellent measurement mic very cheaply indeed, which will be the subject of an upcoming project. Circuit description The full circuit is shown in Fig.3, and it has five main sections: the power amplifier, microphone preamplifier, input buffer, switching and power supply, shown as shaded areas. While some of these sections connect to each other, besides the power supply, they primarily operate as independent blocks. The power amplifier is used to drive the loudspeaker being tested while the microphone preamplifier picks up the radiated sound and converts it to a signal that can be analysed. The input buffer allows the sound card’s outputs to be monitored while one is fed to the power amplifier. The switching section determines whether the output of the mic preamp or sense input is fed to the computer sound card’s inputs. It also provides switchable attenuation for the sense input and switchable gain for the amplifier. Power amplifier We do not need a substantial power amplifier; the LM1875 IC is commonly available (eg, from Jaycar) and requires minimal parts to work. It needs to be able to drive a loudspeaker at a modest volume and be tolerant of abuse, which can happen with this sort of equipment. You would never short the amplifier, would you? We run it from dual half-wave rectified 15V AC to get positive and negative rails of about ±20V from the 15V AC plugpack. This is cheeky, but we only need a couple of watts at most. Note that only half the diodes in bridge rectifier BR1 are used since we don’t have a centre-tapped transformer (few plugpacks have a centre tap as it requires a 3-pin connector). This power amplifier will provide 48 Silicon Chip sufficient output to allow you to wire your speaker to the output binding posts to perform listening tests as you develop it. We have set the gain to about 10 (set by the ratios of the 9.1kW & 1kW resistors), which is low but enough for our purposes. The signal is AC-coupled to IC3’s input via a pair of back-to-back 22µF electrolytic capacitors to remove any DC bias. The output goes straight to CON4, which is wired to a pair of binding posts. The 1W/220nF Zobel network ensures stability. We mount the LM1875 on a heatsink to ensure that the IC has adequate cooling if you do extended testing. This heatsink is available from Altronics, but if you can’t find that, a folded piece of aluminium would work just fine. Interestingly, the Altronics heatsink we bought had one hole in the middle, but their specification has two holes, and our design accommodates that. If yours only comes with one hole as well, you will need to drill a 3mm hole 10mm to the left of the centre. Microphone preamp This basic design is pretty standard across the audio industry. It includes a tweak by Douglas Self, described in his books, whereby the input transistors are included in the operational amplifier feedback loop. This significantly reduces the resulting distortion. The microphone preamplifier is simply an AC-coupled balanced amplifier with switchable gain. If you switch off the phantom power, this becomes a simple balanced input. That is handy to remember if you want to probe a circuit using the Loudspeaker Test Jig. RF is filtered out of the input signals by series ferrite beads and an RC low-pass filter comprising 10W resistors and 680pF & 1nF capacitors. 48V phantom power, if selected, is applied via 6.8kW resistors with a 1kW/100µF low-pass filter before them to remove any supply noise. Pairs of back-toback zener diodes protect the rest of the circuitry from any voltage spikes that might be picked up. The two balanced signals are then fed to the bases of PNP transistors Q1 and Q2 which are within the feedback loop of low-noise op amps IC1a & IC1b, providing the amplification as follows. Pins 2 and 3 of IC1a must be at essentially the same voltage, enforced by negative feedback from this op amp. Australia's electronics magazine The current through transistors Q1 and Q2 will be essentially the same, and within the tolerance of transistor matching, their emitter voltages will be the same. From a DC perspective, the output will be close to 0V as IC1b inverts the signal from IC1a, creating differential feedback to the transistors. The transistor bases are AC-coupled to the input and DC-biased to ground, so their emitters will be pulled up to about 0.6V by the 10kW emitter resistors and the 2.7kW op amp feedback resistors. Q1 and Q2 will each pass about 1mA, which will primarily flow through the 4.7kW collector resistors, resulting in pins 2 and 3 of IC1a being about 4V above the negative rail. The AC input is a differential voltage between the bases of Q1 and Q2. The emitters of Q1 and Q2 are the feedback point, via the 2.7kW resistors. As the input is differential, the 100W resistor (and 1.2kW if the contacts of relay RLY3 are not shorting it out) see the total differential voltage; the midpoint of these can be seen as a ‘virtual zero point’. So the gain is defined by the 2.7kW feedback resistors with the parallel combination of half of (100W + 1.2kW) and (10kW + 10kW) forming the voltage divider for gain. Gain is controlled by the 2.7kW resistors in series with the NE5532 outputs, combined with the 10kW resistors to the positive rail and the 1.2kW and 100W resistors. A 20dB gain step is implemented by switching RLY3 across the 1.2kW resistor. The gain on the low setting can be calculated as: 1 + 2.7kΩ ÷ (10kΩ || [(1.2kΩ + 100Ω) ÷ 2]) = 1 + 2700Ω ÷ 610Ω = 5.42 times gain (+14.7dB) On the high setting, it is: 1 + 2.7kΩ ÷ (10kΩ || [100Ω ÷ 2]) = 1 + 2700Ω ÷ 49.8Ω = 55.2 times gain (+34.8dB) The input buffer The Loudspeaker Test Jig includes a simple op amp based buffer to ensure that your sound card output is presented with a high impedance, while also providing a monitor output to drive an amplifier or other equipment. You can even use this output to drive an active crossover for testing active speakers. The input includes protection siliconchip.com.au against RF noise with ferrite beads and 100pF capacitors to ground, while schottky clamp diodes protect the op amp from voltage spikes on the input. The signals are AC-coupled to the op amp inputs via 22µF non-polarised capacitors with 47kW DC bias resistors, forming a high-pass filter with a -3dB point of 0.15Hz. So there will be no detectable roll-off at 20Hz. The outputs are also AC-coupled and have 100W series resistors for stability and safety. A jumper on JP1 can feed either the left or right channel to the input of the power amplifier. Switching section This section does two main things in Loudspeaker Test Jig. It switches one of the sound card’s input channels between the output of the microphone preamplifier and a “DUT Sense” input. It also allows you to select a gain of 1× or 0.1× for both the “DUT Sense” signal and “Amp Out Sense” signal. When “DUT Sense” is selected as the signal source, the power amplifier gain is automatically cut from 10× to 1× by switching in a 910W/100W resistive attenuator in its input signal path. This is so that, when testing components, a signal of only a few hundred millivolts is applied to them. That allows you to measure the impedance of tweeters without over-driving them. Despite this, if you are testing tweeter responses, always put a 20-100µF capacitor in series with the tweeter to avoid over-driving it at low frequencies. When testing loudspeaker frequency responses, though, you need more volume. Therefore, with the 10× gain provided in the amplifier, it delivers a couple of volts RMS (depending on where you set your sound card volume). This will be loud enough to get good frequency response plots. resultant ripple challenges. So we have doubled down on the filter capacitors and used two 2200µF capacitors per rail, which in a standard application, would be overkill. In this case, a couple of dollars worth of extra capacitors saves on using a dual-winding transformer. With 4400µF per rail, there will only be a couple of volts ripple on the rails during higher-power tests. The small signal circuitry needs clean power, so we have added LM317/337 regulators generating regulated rails at nominally ±12V. These are textbook circuits. Generating the 48V phantom power rail for the measurement microphone is a little more interesting. We use a voltage doubler circuit that steals energy from the positive unfiltered rail via diode D3 charging the 220µF capacitor at its cathode on negative voltage swings at the plugpack tip, then dumping its charge into the other 220µF capacitor via D2 on positive swings. The second 220µF capacitor ‘sits on top of’ the main unfiltered rail, resulting in close to 70V DC at the cathode of D2 when it is unloaded. This is dropped to 48V by an LM317HV adjustable regulator. You could use a normal LM317, provided you never short its output to ground. In typical operation, its output goes via a 1kW resistor, so there is no chance of that happening in daily use. The current drawn from the 48V rail is never more than 14mA, so the 220µF capacitors are more than sufficient to keep ripple below 1V. We have included heatsinks on all regulators. In our tests, we did not notice them getting that warm, so if you want to save a couple of dollars, you might get away without them. Construction Construction is fairly easy, although, for designs like this, we like to load the power supply section first and check the voltage rails. Once that checks out, you can power it down and fit all the remaining parts with the confidence that a power supply fault won’t fry them at switch-on! The Loudspeaker Test Jig is built on a 99.5 × 189.5mm double-sided PCB coded 04106231. To build the power supply section, fit all the resistors and diodes in that section, as shown in Fig.4. Be careful with the orientation of the diodes as they vary. Follow with the MKT and electrolytic capacitors in this section (watching the polarity of the electros), then the rectifier, fuse holder and connectors. Install a 2A fuse. Finally, attach the regulators to the heatsinks with a TO-220 insulator kit on each. Don’t tighten the screws until Power supply The power supply for the Loudspeaker Test Jig is minimalist to keep cost, complexity and size down. We use a single 15V AC plugpack to power the unit. As mentioned earlier, dual half-wave rectification via BR1 provides the split rails to drive the power amplifier. This avoids the need for any fancy voltage inverting IC or the use of a single-rail topology for the whole Test Jig. It does mean that our supply rails are 50Hz half-wave rectified, with siliconchip.com.au Fig.4: it’s best to fit the power supply components as shown here, then power it up and verify that all the supply rails are correct before installing the remaining parts. That way, if there is a fault, it likely won’t blow anything up. Australia's electronics magazine June 2023  49 Photo 1: an exterior view of the completed front panel assembly. Dymo labels will help you to remember what each switch and terminal does down the track! Fig.5: once you’ve tested the power supply, you can fit all the components as shown here. Ensure all the TO-220 devices are insulated from their heatsinks and watch the polarity of the ICs, diodes and electrolytic capacitors. Two of the 22µF electrolytics are nonpolarised types (near the lower-left corner), so no polarity markings are shown. 50 Australia's electronics magazine you have inserted the regulators with their heatsinks into the PCB. Then you can solder the heatsink mounting pins along with the regulator pins. Testing the power supply Plug in the 15V AC plugpack and check the unregulated rails by measuring the voltages on pins 3 and 5 of the LM1875 IC relative to GND (there is a GND test point at upper left in the Audio Input Buffer section). These voltages ought to be 18-24V DC. If they measure low, check the AC voltage and verify that the bridge rectifier has been installed the right way around. Also check the capacitor orientations. Assuming that’s OK, measure the ±12V rails at pin 2 of the LM317 (REG3) and pin 3 of the LM337 (REG4). These ought to be within 1V. If not, verify that the regulators are in the right spots, the correct resistors have been used and the diodes are orientated properly. There should always be 1.25V between the ADJ and OUT pins of the LM3X7s. Next, check that the 48V rail is within 3V (ie, 45-51V). This is accessible on pin 2 of the LM317HV. If it is off, verify that the input voltage on its pin 3 is well above 48V. Also check the resistor values around this regulator and that the capacitors and diodes are the right way around. Finishing off the PCB Now that we know the power supply is working, remove power and fit all the remaining parts, as shown in Fig.5. As usual, start with the lower-profile components by mounting the resistors, diodes, relays, NE5532 ICs and right-angle headers first. Then move on to the larger parts, including the capacitors and RCA sockets. As with the regulators, loosely attach the LM1875 to the large heatsink and use an insulating kit. Insert the IC into its pads and solder the heatsink to the board. The solder pins will require some effort to get hot enough, but they do work (it is not screwed to the PCB). Once it is held in place securely, tighten up the IC mounting screw and solder its leads. Note that there are two bipolar (non-polarised) electrolytic capacitors right next to CON2, as we don’t know if an input will have a DC offset. They have polarity marks on the PCB, but you can ignore them as the parts are not polarised. siliconchip.com.au The two 47µF capacitors all the way on the left side of the Mic Preamp section can operate with 48V DC phantom power applied, so we must use minimum 50V rated electrolytic devices and orientate them with their longer positive lead to the right as shown. If you will never use phantom power, you could instead use polarised electrolytics with a much lower voltage rating. With the PCB assembled, we can move on to wiring it up so it can go in the case. Case preparation The PCB slides into the second slot up from the bottom in the recommended extruded aluminium case. Use the provided drilling drawings, Figs.6 & 7, to cut the required holes in the front and rear panels. Once prepared, they fit perfectly, allowing you to secure the board using 4G screws through the rear panel into the RCA sockets. Our recommended case is very tidy, but it is not the cheapest. If you want a more cost-effective solution, any case over about 220mm wide, 130mm deep and more than 60mm high will work. You could consider using plastic instrument cases like Altronics H0476 or H0482; however, you will need to adapt Figs.6 & 7 to fit the differently-sized panels. The PCB can be secured via spacers and screws through the provided mounting holes if you are not using the recommended case. Mark and drill the front and rear panels. Be careful to choose the right side of the panel, as the pre-drilled screw holes are countersunk on the outside. All the holes have been kept circular for easy construction, except the power connector hole, which will require a little filing. If you choose one of the larger ABS plastic cases, you could spread things out a bit and run flying leads from the power, input and output connectors to the rear panel. However, since the front panel connectors are all wired, you could still mount the PCB right up against the rear panel to avoid extra wiring. We labelled our panel using Dymo stickers, as shown in Photo 1. We printed labels in small text on 10mm wide tape and used tweezers to place the labels on the panel. Most of the switches are self-explanatory, but our siliconchip.com.au Fig.6: drill the front panel supplied with the recommended case as shown here, making sure the pre-drilled countersunk screw holes face outwards. Fig.7: drill the rear panel as shown here, again paying attention to which side has the holes countersunk. For the rectangular hole, you can drill an 11mm hole and then file the corners out. Otherwise, you can drill out the dotted hole marked in red which only leaves enough room for the plug sleeve. Australia's electronics magazine June 2023  51 Fig.8: use this diagram and Photos to wire up the front panel. By using polarised header plugs, the whole assembly can be disconnected from the main board, making assembly and disassembly easier. experience is that we will have forgotten what does what in a year or two. So labelling is a good idea and makes the box look better. With the case panels prepared, mount the front panel hardware. We used dual binding posts for the speaker connections, although you could save a little money by using captive-head binding posts. Whatever you choose, make sure they can act as both binding posts and banana sockets, as that is really handy in use. After mounting the binding posts, follow with the three switches, then the XLR microphone socket. Watch your selection, as some XLR connectors are pretty deep and the mounting hole locations vary. The last ‘fiddly bit’ is the microphone monitor output. We had very little space and wanted a test output for hooking an oscilloscope probe, similar to the calibration post on many oscilloscopes. We made ours from a 25mm M3 screw by cutting the head off with a hacksaw, filing each end flat, then drilling a 1.5mm hole through the flat parts using a PCB drill. That worked a treat, as shown. Fig.9 shows the details. We soldered to this using plenty of flux. It is used for measuring the time alignment of speaker drivers. Wiring it up Cabling for the Loudspeaker Test Jig is made easy by using plugs on the end of the leads connected to the front panel as shown in Fig.8. You need to make up the following flying leads, all using wires stripped from ribbon cable or light-duty figure-8, except the ground lead: ● Four 150mm-long leads with two wires for: – The Mic output monitor post (CON3) Photo 2: heatshrink tubing and cable ties keep the front panel wiring manageable. Note the 10W reference resistor soldered across the binding post terminals. Fig.9: filing and drilling an M3 stud makes a convenient place to attach a test probe. However, you could devise your own scheme if you prefer; a loop of tinned copper wire would be sufficient. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au The assembled PCB, ready to be wired up to the front panel via eight right-angle polarised headers. That makes plugging and unplugging easier when it is mounted in the instrument case. – The Output Attenuation switch (CON5) – The Mode switch (CON6) – The sense wires for the Amp Output and DUT (CON8) ● One lead from medium-duty hookup wire for the ground connection (CON9). ● Two 200mm-long leads with two wires for: – The amplifier output (CON4). Ideally, use two lengths of light-duty hookup wire. – The Mic Gain switch (CON7) ● One 150mm-long lead with three wires for the Microphone input (CON2). Label these at the plug end so you will know what header they plug onto later. Also make sure you mark pin 1 on each lead; we used pieces of leftover heatshrink to mark pin 1. You could use a marker pen, but be aware that the marking could become less distinct with time and handling. Wire up the board to the front panel connectors and controls as shown in Fig.8. The best way to do this is: ● Solder the CON9 ground wires to the black pins on the banana sockets/ binding posts. Jumper across them at the banana socket to ‘double up’ the ground wiring. ● Measure your 10W reference resistor with the best precision you can. Mark the reading on the resistor, so you don’t forget the resistance. Securely bend the leads around the red posts of the “Amp” and “DUT” headers and solder them. ● Solder pin 1 of CON4 to the red terminal of the AMP banana socket. Pin 2 goes to ground. ● Solder pin 1 of CON8 to the red terminal of the DUT banana socket and pin 2 to the red terminal of the AMP banana socket. ● Solder the CON5 wires across the top two pins of the Atten switch on the front panel. ● Solder the CON6 wires across the top two pins of the Mode switch on the front panel. ● Solder the CON7 wires across the top two pins of the Mic Gain switch on the front panel. ● Solder pin 1 of CON3 to the Mic Monitor post. Fold the ground wire back and insulate it. ● Solder pin 1 of CON2 to the ground pin of your XLR, pin 2 to hot (+) and pin 3 to cold (−). These should all now plug in neatly to the PCB. Use a couple of tie wraps/ cable ties to secure the wiring after checking that it all works. You are now ready to test it properly! Once wired up, the front panel will look something like Photos 2 & 3. Assembly to the rear panel just involves sliding the board into the case and using two 4G screws to secure the RCA connectors to the rear panel, as shown in Photo 4. Operational testing Photo 3: label the plugs and wire so that you don’t get them mixed up when plugging them into the PCB headers. This photo also more clearly shows how the reference resistor is connected. siliconchip.com.au Australia's electronics magazine It’s best to plug the front panel into the PCB before inserting the PCB into the case for testing, as you can’t probe the test points on the PCB once it is in June 2023  53 Photo 4: the rear panel is held to the case by the four corner screws, while the PCB is held to the rear panel by the two screws that go into the RCA socket plastic housings. the case. Once you’ve verified it’s all working correctly, you can slide the PCB in and then attach the front panel. Set the jumper for the input you expect to use for testing on JP1. Without this, the power amp will not get a signal, although most programs seem to drive both outputs with the test signal. Apply a signal to the input (CON3a left and right) of 200mV RMS at about 1kHz. A buffered version of this signal should appear at CON3b. Toggle each switch and check that you hear the relays click. If not, check that you have used the correct relays and that the diodes are the right way around. Set the “Speaker/Comp” switch to Speaker. Monitor the Amp Out at pin 1 of CON4 and check that you see an amplified version of the input signal at about 2V RMS. Switch the “Speaker/ Comp” switch at CON6 and check that the output is attenuated in the “Comp” position. This should be close to the amplitude of your test signal (about 200mV RMS). Next, ensure you have the phantom power enabled by putting a shorting block on LK1 and check that you have 48V ±3V on the hot and cold pins of CON2. Plug in your test microphone and check for a signal on pin 1 of CON3 and your Mic test point on the front panel. If you have trouble, check that: ● There is about 10.3V across the 10kW resistors connected to the emitters of Q1 & Q2 (both above and to the left of Q1). ● There is about 3.7V across the 4.7kW resistors at the collectors of Q1 & Q2 (next to D7 & D8), and that these 54 Silicon Chip voltages are the same. ● Pin 1 of IC2 is close to 0V. If any of these are wildly off, verify the component values and orientations in these areas; check for short circuits and that you have used the right transistors. Testing, calibration & usage With the unit now assembled and working, the next step will be to install the software, set it up and verify that it’s working as expected. As the “REW” software is not tied to this hardware, we have those instructions in a small separate article starting on page 56. You will need a computer with a reasonably good sound card that has stereo analog inputs & outputs to hook up to the Speaker Test Jig. If your computer lacks those, consider building our very high-quality external USB SuperCodec, described in the August to October 2020 issues (siliconchip. au/Series/349). That unit is capable of simultaneous 192kHz, 24-bit recording and playback and has a rated THD figure of just 0.0001% (-120dB) and a THD+N figure of 0.0005% (-106dB) for playback and 0.00063% (-105dB) for recording. You don’t need a sound card with such high quality for speaker testing, but it certainly doesn’t hurt! Whatever sound card you use, go into your operating system’s settings and ensure it is the active device for recording and playback. In recent versions of Windows, you can do that by right-clicking the speaker icon in the screen’s lower right-hand corner and selecting “Open Sound settings”. If your sound card’s sockets are 3.5mm jack sockets, you can use 3.5mm jack plug to twin RCA plug cables to connect them to the Input & Output sockets on the Loudspeaker Testing Jig. If the sound card has RCA sockets, like the SuperCodec, use twin RCA to RCA leads instead. Then, connect the Monitor outputs to your amplifier inputs with a twin RCA to RCA lead. When ready, turn to page 56 for the SC final testing procedure. A real-world application of the Jig: measuring the frequency response of a bookshelf speaker. Australia's electronics magazine siliconchip.com.au Parts List – Loudspeaker Test Jig 1 double-sided PCB coded 04106231, 99.5 × 189.5mm 1 Hammond 220×103×53mm black aluminium instrument case [element14 9287892, Mouser 546-1455N2201BK, Digi-Key HM1732-ND] 1 15V AC plugpack (rated at least 1.2A) [Jaycar MP3021] 3 2A 5V DC coil DPDT PCB-mounting telecom relays (RLY1-RLY3) [Altronics S4128B] 4 5mm-long, 2mm inner diameter ferrite beads (FB1-FB4) 2 PCB-mounting M205 fuse clips (F1) 1 2.1mm or 2.5mm inner diameter PCB-mounting DC barrel socket, to suit plugpack (CON1) 1 stereo right-angle PCB-mounting RCA socket, above/ below (CON2) [Altronics P0210] 1 dual stereo vertical PCB-mounting RCA socket (CON3) [Altronics P0214] 7 2-way 2.54mm right-angle polarised headers with matching plugs (CON4-CON9, CON12) [Altronics P5512 + P5472 + P5470A × 2] 1 3-way 2.54mm right-angle polarised header with matching plug (CON11) [Altronics P5513 + P5473 + P5470A × 2] 1 2-pin header with jumper shunt (LK1) 1 3-pin header with jumper shunt (JP1) 2 8-pin DIL sockets (optional; for IC1 & IC2) 2 dual panel-mount red/black binding posts with banana sockets [Altronics P9257A] 3 SPDT solder tail panel-mount toggle switches with locking mechanism [Altronics S1311] 1 panel-mount 3-pin XLR socket for microphone (CON10) [Altronics P0903] Hardware & wire 1 2A 250V M205 fast-blow fuse (F1) 1 84×24×28mm low-profile PCB-mounting heatsink [Altronics H0668] 3 16×22mm TO-220 PCB-mounting heatsinks [Altronics H0650] 5 TO-220 insulating kits (washers + bushes) [Altronics H7210, set of four] 1 M3 × 25mm panhead machine screw 6 M3 × 16mm panhead machine screws 6 M3 shakeproof washers 6 M3 flat washers 4 M3 hex nuts 2 fibre or Nylon washer, 3mm inner diameter [Jaycar HP0148] 2 4G × 12mm countersunk head machine screws [Bunnings 2420062] 1 150mm length of 3-wire jumper cable 1 300mm length of green light-duty hookup wire 1 1m length of light-duty figure-8 twin lead or ribbon cable 1 200mm length of 3mm diameter black heatshrink tubing Semiconductors 2 NE5532 dual low-noise op amps, DIP-8 (IC1, IC2) 1 LM1875T 20W audio amplifier, TO-220-5 (IC3) [Jaycar ZL3755] 1 LM317HV high-voltage adjustable linear regulator, TO-220 (REG1) [Altronics Z0545] siliconchip.com.au 1 LM317 adjustable positive linear regulator, TO-220 (REG3) 1 LM337 adj. negative linear regulator, TO-220 (REG4) 2 BC559 100mA 30V PNP transistors, TO-92 (Q1, Q2) 4 6.8V 1W zener diodes (ZD1-ZD4) 1 400V 4A SIL bridge rectifier (BR1) [eg, KBL404; Altronics Z0076A] 8 1N4004 400V 1A diodes (D2, D3, D22, D23, D26-D29) 7 1N4148 75V 200mA signal diodes (D4, D6-D9, D11, D12) 4 BAT85 30V 200mA schottky diodes (D5, D10, D15, D16) Capacitors 4 2200μF 25V low-ESR radial electro, 7.5mm pitch [Altronics R6204; Jaycar RE6330] 3 470μF 25V radial electrolytic, 5mm pitch [Altronics R5164; Jaycar RE6326] 2 220μF 63V radial electrolytic, 5mm pitch [Altronics R5148; Jaycar RE6348] 1 220μF 16V radial electrolytic, 3.5mm pitch [Altronics R5143; Jaycar RE6312] 3 100μF 50V radial electrolytic, 5mm pitch [Altronics R6127; Jaycar RE6346] 9 47μF 50V low-ESR radial electrolytic, 3.5mm pitch [Altronics R6107; Jaycar RE6344] 2 22μF 50V low-ESR radial electrolytic, 2.5mm pitch [Altronics R6077; Jaycar RE6342] 2 22μF 50V non-polarised radial electrolytic, 3.5mm pitch [Altronics R6570A; Jaycar RY6816] 5 10μF 50V low-ESR radial electrolytic, 2.5mm pitch [Altronics R6067; Jaycar RE6075] 1 220nF 63V MKT polyester 12 100nF 63V MKT polyester 2 1nF 63V MKT polyester 1 680pF 50V NP0/C0G or YSP radial ceramic 2 100pF 50V NP0/C0G or SL radial ceramic 2 22pF 50V NP0/C0G radial ceramic Resistors (all ¼W 1% axial unless otherwise stated) 4 47kW 6 22kW 1 12kW 2 10kW 3 9.1kW 2 6.8kW 0.5W or 0.6W 1% 2 4.7kW 2 3.3kW 2 2.7kW 1 2.2kW 1 1.2kW 6 1kW 1 910W 2 390W 1 330W 3 240W 9 100W 2 10W 1 10W 5W 5% non-inductive [Altronics R0323; Jaycar RR3250] 1 1W 1W 5% Australia's electronics magazine June 2023  55 Setting up and Using Room EQ Wizard This accompanying article for the Speaker Test Jig explains how to set up and use the freely-available Room EQ Wizard (REW) or Speaker Workshop software to help you design and tweak loudspeakers. Y ou don’t need the Loudspeaker Test Jig described in this issue to use Room EQ Wizard or Speaker Workshop to design and test loudspeakers and drivers, but it makes it a lot easier. This article will describe setting up and using REW (and later, Speaker Workshop) assuming you have built the Loudspeaker Test Jig. If you haven’t, you can still follow these procedures; you just need to rig up a microphone preamp, power amplifier, test resistor and some other bits and pieces to perform similar functions. Essentially, what you need (and the Jig provides) for measuring driver By Phil Prosser impedance is to have your computer’s sound card feeding a power amplifier that drives the device under test (DUT) via a well-characterised 10W or similar power resistor. Both ends of that resistor then connect to the two sound card inputs. For driver and speaker frequency response plots, you instead need a calibrated microphone and microphone preamp combination that gives a flat response feeding into one of your sound card’s inputs while the output(s) drive the DUT via a small power amplifier. The Jig also does that if you have a calibrated microphone (we’ll describe an inexpensive one in an upcoming issue). Final testing & setting up REW We assume you have your computer set up and your sound card properly installed. Importantly, make sure you have the sample rate set and no effects turned on. Also check that you do not have ‘monitor recordings’ set. The critical steps to getting the Test Jig operational with the REW software are provided here. There are many resources on the internet for this program, and its full details are well beyond the scope of this article. Screen 1: the REW Preferences dialog. Check that the input and output devices and sampling rate settings are set correctly. 56 Silicon Chip Australia's electronics magazine siliconchip.com.au Still, let’s get it up and running. After installing and launching REW, to set it up, open the preferences pulldown and then the preferences tab – see Screen 1. Select your input and output here; usually, you would use the default sound input and output devices. To calibrate your sound card: 1. Set the Loudspeaker Test Jig to “component test” and make sure there is nothing connected to the Speaker and DUT connectors. 2. Make sure the Loudspeaker Test Jig attenuator is switched out. 3. In REW, open the preferences pulldown and open the preferences tab. 4. Click on “Calibrate soundcard”. Note that by using the “Component” test mode, the 10W reference resistor acts as the loopback mentioned in the text box that will pop up. 5. Click Next, and a text box will appear providing instructions. Follow them. 6. Click Next and check that you have levels that are about right. You should find that with about 200mV RMS output, you see a measured signal in the region of -10dB on the loopback test. Sound cards vary in sensitivity, so your voltages may vary somewhat from ours. 7. Then click Next until the measurement sweep is made. You will get a graph similar to that in Screen 2. 8. On the tab for the measurement you just made, add any notes you need. Then click the disk symbol on the measurement and save this file somewhere sensible. 9. Now press Alt+Tab to switch back to the preferences screen and click on “Make Cal File”, which is below the “Calibrate Sound Card” button. 10. Navigate to where you saved the previous measurement. Select “all files” from the pulldown “files of type” and then select your calibration measurement. Click “Save”. 11. Your sound card is now calibrated. To calibrate the Test Jig: 1. Set your Loudspeaker Test Jig to “component” test and ensure there is nothing connected to the Speaker and DUT connectors and that the Attenuator is out. 2. You only need to do this on the first measurement you make. Click “Measure” in the top left corner of siliconchip.com.au Screen 2: this shows the frequency response REW has calculated for the measurement system, including the computer sound card. Screen 3: you make impedance and frequency response measurements using this screen in the REW software. Screen 4: calibration with our 10W test resistor is complete, and the result almost exactly matches what our Low Ohms Meter reads. Australia's electronics magazine June 2023  57 Screen 5: a measurement of the impedance of a subwoofer taken using REW and our Test Jig. It gives a nice smooth plot that shows resonance peaks at about 31Hz & 72Hz (driver/box) plus 850Hz & 2.5kHz (cone breakup etc). Screen 6: a frequency response plot of a wide-range driver made using REW. This sort of information is invaluable in speaker design and tweaking. the main REW screen (Screen 3). If you have not calibrated the SPL, you will get a message box; you can ignore it for now. 3. Enter your sense resistor value in the Rsense box at the right of this window. 4. Click on “Open Circuit Cal” and follow the instructions. Save the file along with your others. Do the same for “Short Circuit Cal” and use a known resistor value for “Reference Cal”. 5. You can now measure an impedance. A window similar to that shown in Screen 4 will pop up. Screen 5 shows the measured impedance of a subwoofer. Using it To measure an impedance: 1. Set your Loudspeaker Test Jig to “component” test and make sure there is nothing connected to the Speaker and DUT connectors and that the Attenuator is out. 2. Click “Measure” in the top left corner of the main REW screen. 3. Click “Impedance” in the top left of the screen, as shown in Screen 3. 4. Click Start once you have connected your unknown impedance across the DUT terminals. To measure speaker frequency response: 1. If you are testing a tweeter, put a high-value non-polarised capacitor in Screen 8: an impedance plot of the 10W calibration resistor in Speaker Workshop. It’s a bit noisier than the equivalent REW plot, but it demonstrates that the measurement system is accurate from about 5Hz to over 20kHz. Note that this plot was made as part of the verification process of the Speaker Test Jig. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au series to protect it from low frequencies, and consider running the sweep from, say, 500Hz up. 2. Set your Loudspeaker Test Jig to “speaker” test. 3. Connect your speaker across the Speaker terminals. 4. Plug your microphone in and set the microphone gain as required. 5. Set the attenuator on or off depending on the level you intend to test at. 6. Click Measurement again, and this time select “SPL”. 7. The system will run a sweep and you will hear the chirp. 8. Check that the levels are reasonable. If necessary, adjust the sound card output level, the microphone gain switch and the output Attenuator for the Loudspeaker Test Jig. You will find that once you are set up for testing, these don’t change often. 9. Watch the levels; if the outputs or inputs clip, you will get odd results. If this happens, investigate the cause and correct it. 10. You will see the result pop up in a window similar to that in Screen 6, a very rough plot of a speaker done on our workbench. 11. You can change the smoothing setting, show a waterfall plot, show distortion and a range of other plots from this measurement, which is pretty cool. Tips ● The room will play havoc with far-field measurements. If you do this in a room, you will never get a 20Hz to 20kHz plot without all sorts of peaks and dips. Just accept this. ● You will need to apply smoothing to get a plot anything like what you see in hifi magazines, as that is what they do. ● Testing outside is good; the ground is always there, though. This will generate ‘ground bounce’, which is perfectly natural, and you need to work around this unless you point your speaker up and hang your microphone from a ladder. Yes, we have done this! From here, we recommend that you explore some of the resources on the web for these programs. REW is more active, but Speaker Workshop has a strong community. The DIY audio community has several quite active groups. “DIY Audio” is a good place to find like-minded people. SC siliconchip.com.au Getting Speaker Workshop up and running If you want to try out Speaker Workshop, read relevant parts of the “unofficial manual” on the download page at www.claudionegro.com Ignore the “failed to update system registry” warning on startup. You must set up a project: 1. Create a new file by clicking on “File” then “New”. 2. This program works by adding resources to the “system”. Resources might be an enclosure, driver or network etc. 3. You need to add a driver at minimum. To do this, open the “Resource” menu and select “New” then “Driver”. You need to select this to make measurements – see Screen 7. To calibrate the system: 1. From the “Options” menu, select “Calibrate”. 2. Make sure there are no leads connected to the Amp and DUT jumpers on the Test Jig. 3. Switch the Jig to “Comp” and switch the measurement attenuator out. In this position, both sound card channels measure the amplified output. 4. Click “Test” on the channel difference box. Follow the instructions to run the calibration, finishing with “OK” to accept it. After calibration, look at the bottom left of the screen. This shows the digital values read in the calibration. The maximum must always be less than ±32768 and ideally in the 10,000-20,000 region. Adjust your PC’s output level and Jig attenuator setting until you get sensible readings. We generally find that an output level in the region of 40% works well. To set the Reference, open the “Options” menu, then the “Preferences” tab. Click on the “Impedance” tab and type the exact resistance of your reference resistor in the Impedance Jig definition box. To make an impedance test: 1. Connect your DUT between the DUT and ground terminals. 2. Select the driver we created earlier. It will become highlighted in blue. 3. Open the “Measure” menu and click on “Impedance”. 4. Once the measurement is complete, check that the values at the lower left of the screen are reasonable. You should see a window pop up with the measurement, as shown in Screen 8. Our Low Ohms Meter measured this resistor as 10.09W. 5. If the impedance plot is very fuzzy, check that you are not clipping the sound card or amplifier. To make a speaker frequency response test: 1. Switch the jig to SPKR. 2. Switch the attenuator next to the DUT connector in. 3. Connect a driver to the AMP output, not the DUT output. 4. Plug in your test microphone and place it close to your speaker. 5. Click on the driver icon you created and then select the “Measure” pulldown, select the “Frequency response” tab, then “Nearfield”. 6. You should get a reasonably clean frequency response. It will have more noise than one from REW and may need smoothing. If the frequency response graph is very fuzzy, check that you are not clipping the sound card or amplifier. Screen 7: to use Speaker Workshop with the Test Jig, you must create a “driver” instance and set some critical parameters. Australia's electronics magazine June 2023  59 WiFi Time Source for GPS Clocks The Raspberry Pi Pico W can be used as a substitute for GPS modules in existing time keeping designs, for when you can’t get a reliable GPS signal. It gets the time from an internet NTP server via WiFi and is accurate to a fraction of a second. Project by Tim Blythman S ince GPS modules have been affordable for the hobbyist, we have used them as accurate time sources. While GPS (and other similar satellite systems) has revolutionised navigation and mapping, it also provides easy global access to highly accurate time sources. Each GPS satellite is equipped with two atomic clocks and they transmit a very accurate time signal every second. We have used that signal for many projects to date, including the recent, very popular GPS Analog Clock Driver from September 2022 (siliconchip.au/ Series/391). While GPS was the first GNSS (global navigation satellite system), there are now several more, including the Russian GLONASS, European Galileo and Chinese Beidou systems. The Indian Regional Navigation Satellite System (IRNSS) and Japanese Quasi-Zenith Satellite System (QZSS) are designed to improve positioning on a national scale, with the QZSS also benefiting Australia as the satellites’ orbits bring them over us. While they use subtly differing technologies (even GPS has evolved over its 50-year existence), a common external interface has been established. In fact, the VK2828U7G5LF GPS module that we use for many projects can receive signals from GPS, GLONASS and Galileo satellites. For the purposes of this article, we’ll use GPS as an encompassing term for all the different navigation satellite systems. However, note that some of these systems are not truly global, as the satellites do not usually provide coverage at high latitudes (close to the poles). Previous GPS Time Source In the April 2018 issue, we published the Clayton’s GPS Time Source (siliconchip.au/Article/11039). As the name suggests, it doesn’t use any GPS What projects does it work with? New GPS-Synchronised Analog Clock, September 2022; siliconchip.au/Article/15466 GPS-Synchronised Analog Clock, February 2017; siliconchip.au/Article/10527 High-Visibility 6-Digit LED GPS Clock, December 2015 – January 2016; siliconchip. au/Series/294 6-Digit Retro Nixie Clock Mk2, February – March 2005; siliconchip.au/Series/282 6-Digit GPS-Locked Clock, May – June 2009; siliconchip.com.au/Series/37 60 Silicon Chip Australia's electronics magazine technology, but rather it can be used as a source of GPS-like time signals when an actual GPS signal is unavailable. It’s often recommended as a replacement for a GPS module in clock projects. The motivation for this concept was driven by many clocks being used indoors, where very weak GPS signals are hard to receive. On the other hand, WiFi signals are usually available indoors. The actual hardware of the 2018 unit is simply a D1 Mini WiFi ESP8266 microcontroller module. The module is programmed with firmware to connect to a WiFi network and update an internal clock from the internet using NTP (network time protocol). This time is then used to generate ‘sentences’ to communicate that time. A 1PPS signal is also generated, although this signal will not have the precision of an actual GPS module. Pico W update This project is an update of the original Clayton’s GPS but using a Raspberry Pi Pico W instead of a D1 Mini. While we could have refactored the same code for the Pico W GPS, there are several reasons why we did not. We have had many suggestions for improvements over the last five years, siliconchip.com.au WiFi Time Source Features Delivers NMEA 0183 data simulating a GPS time source Adjustable baud rate 3.3V logic levels work with 3.3V and 5V systems Synthesised 1PPS signal Gets the time from NTP servers via WiFi Generates estimated latitude and longitude based on IP address Can also output fixed dummy coordinates Can scan for up to eight WiFi networks (SSIDs) Configurable via virtual USB serial port, independent of data stream Uses a compact & low-cost Raspberry Pi Pico W module Integrated buck/boost converter runs efficiently from 1.8-5.5V Crystal oscillator offers better than 30ppm accuracy between updates Draws 50mA, or up to 100mA during WiFi transmissions (3.0V supply) so it made sense to incorporate them where possible. We’ve chosen to use the C SDK as we found it gave us better access to low-level functions and programs run more quickly. Some of the new features were possible (and much easier to implement) due to aspects of the C SDK and its software libraries. There is no doubt that the Pico W is very well priced, making it an attractive option when the module is all or most of the hardware required. Indeed, it is cheaper than the GPS module it can replace. But particular features of its RP2040 microcontroller helped us to create the WiFi Time Source. For example, it can implement a virtual USB serial port, meaning that the configuration menu is separate from the NMEA data stream (National Marine Electronics Association). Due to the nature of the serial port on the D1 Mini, these were shared on the Clayton’s GPS, so using the configuration menu interrupted the data stream. The Pico W also implements a virtual USB drive for flash memory programming. Some people had difficulty uploading to the flash memory to the D1 Mini for various reasons. For example, it requires either a dedicated siliconchip.com.au programming application or the Arduino IDE for programming. On the other hand, the Pico W can be flashed by just about any computer with a USB port. The process is as simple as copying the file to the virtual USB drive. The RP2040 processor on the Pico W has two cores, so one can be dedicated to sending out the NMEA data and not be blocked by activity on the other core, which handles the configuration and WiFi connections. The Pico W also has an onboard switchmode regulator that’s more efficient than the linear regulator found on the D1 Mini. Some readers reported problems powering the D1 Mini, so it is a welcome upgrade. It not only reduces the current requirement at higher supply voltages but also enables operation from supplies as low as 1.8V. Like the earlier time source, the WiFi Time Source emits three NMEA sentences: “RMC” (recommended minimum data for GPS), “GGA” (Fix information) and “GSA” (satellite data). Most of our GPS clock designs only use the RMC sentence, with some also using GGA. So this data is entirely adequate for driving those clocks. NMEA sentences Practically all GPS modules deliver data generally in accordance with the NMEA 0183 standard. The standard actually specifies 4800 baud serial data using a balanced signal complying with the RS-422 electrical standard. The newer NMEA 2000 standard uses a CAN bus network at 250kiB per second. The full contents of this standard are not publicly available, so the simpler NMEA 0183 is still widely used, as it is well understood. Most receivers nowadays use single-­ ended logic level signals (typically 3.3V) with baud rates of 9600 or even higher. Many modules also offer a 1PPS (pulse per second) signal that is synchronised to the satellite atomic clocks. The serial data consists of lines of ASCII characters called sentences. For our purposes, each sentence is marked at the start by a “$” character, followed by two characters that identify the ‘talker’. This is typically “GP” for GPS systems, although we have seen some modules that use “GN” where data from multiple satellite systems are combined. Australia's electronics magazine The next three characters identify the type of message, followed by sentence-­specific data and a checksum code to provide a degree of protection against corrupted data. The most common sentences that encode the time also contain location data, so the WiFi Time Source can produce dummy location data or even use an IP address geolocation data service to generate an approximate location. In any case, it’s a good idea to generate such data in case the receiving device expects there to be valid data in this location, even if it is not used. This approximation will never be good enough for navigation purposes. Still, it is usually sufficient to determine a timezone, which is ideal for those clocks that use GPS location data for this purpose. For example, the High Visibility 6-Digit LED GPS Clock from December 2015 and January 2016 (siliconchip. au/Series/294) uses location data to set the time zone and daylight savings rules automatically. With most of our GPS projects using the GPS signal for clock timekeeping, the WiFi Time Source is well-suited for use with indoor clocks, where they may not have a view of the sky and thus to a GPS signal, but can easily be connected to a WiFi network. Hardware The WiFi Time Source hardware is minimal. The dashed box in Fig.1 shows the pinout of the Pico W after it has been programmed. The remainder of Fig.1 shows the full map of all the pins with their features. As you can see, we’ve kept all the useful pins at one end. It would have been nice to be able to shorten the board by cutting off unnecessary section. Unfortunately, the entire board is needed and it can’t be made much smaller, especially as the WiFi antenna is at the end opposite the USB connector. The power pins are fixed on the right-hand side, near the USB connector. These are pin 40 (VBUS), pin 39 (VSYS) and pin 38 (GND). There are actually several GND pins (see Fig.1), but pins 3 and 38 are closest to the other important pins. Pin 37 (3V3_EN) is an input to the regulator on the Pico W; this is kept high by a 100kW resistor but can be pulled low to shut down the regulator and thus power off the Pico W. June 2023  61 Pins used for the WiFi Time Source Fig.1: the pins on the Pico W that can be used for the WiFi Time Source are shown in the dashed red box. Pin 1 (GP0) is the closest UART TX pin to the USB end of its PCB and is also near the relevant power pins. You probably won’t need all the connections shown here for most clock projects (see Figs.3-6); three or four connections are often sufficient. Pin 1: serial NMEA data; pin 2: 1PPS signal; pin 3: ground; pin 36: 3.3V; pin 37: 3.3V enable (active high); pin 38: ground; pin 39: 1.8V to 5.5V in; pin 40: USB supply. Pin 1 (GP0) is the source of the generated NMEA serial data, which idles at a 3.3V logic high level. The Pico W’s hardware UART (universal asynchronous receiver/transmitter) peripherals are only available on specific pins. This pin was chosen as it is the UART TX pin closest to the USB connector and the power pins. We selected the adjacent pin 2 (GP1) for the 1PPS output; it could have been any of the remaining GPIO pins. We’ve shown the 3.3V output only because it might be handy if you need a regulated 3.3V supply for your project. The regulator on the Pico W can deliver up to 2A, although some of that is used by the Pico W. Fig.2 shows the power circuitry of the Pico W and will help you decide how to connect the WiFi Time Source in your circuit. Most people will simply need to connect a supply between the VSYS and GND pins. But note that there is a diode between VUSB and VSYS, so if a USB cable is connected, it might feed into VSYS, particularly if VSYS is less than the 5V from USB. Unless you can be sure you won’t connect anything to VSYS while power is applied to VUSB (for example, via 62 Silicon Chip the USB socket), the safest option will be to connect the incoming supply to VSYS via a schottky diode, which will prevent current from passing from VBUS into your supply. Given that most people will use the USB port to program, configure and test the Pico W, the easiest solution is to disconnect the USB cable before connecting to the target circuit. In that case, direct connections to the Pico W pins will be fine. Later on, we’ll also show you how to connect the WiFi Time Source to some of our recent clocks. Software development The Raspberry Pi C SDK is still evolving, especially the parts of it that deal with the WiFi features of the Pico W. But it is well documented, and interest is sufficient that the online community is also very helpful. So, we ran into some minor difficulties during development, but we managed to work around them. We used version 1.5.0 of the SDK; versions before 1.4.0 did not support the Pico W and later versions might differ. As we noted, the Pico W has two processor cores. One of these (the second core) is programmed to do nothing Australia's electronics magazine more than generate the NMEA data and 1PPS pulses. This is crucial as we found that the D1 Mini (as used in the 2018 time source) would occasionally block (be busy and not be able to run other parts of its program) during WiFi operations. By setting up one core to do the critical activity, the WiFi Time Source can continue to operate, even in the extreme event that one processor core crashes entirely. This core can even reset the Time Source under some conditions. When a reset happens, some data is stored in RAM to preserve the current time across the reset. This is possible as RAM remains powered during the soft reset process. We saw very occasional crashes (and reset recovery) when the Time Source had been active for long periods, but this should not be an issue for operation with the recent GPS clocks, as the Time Source should only be powered long enough to set the time, after which it is powered off. This second processor core looks at the current time and calculates what the time will be when the next second rolls over. It then prepares all its data to suit this next second. As soon as the siliconchip.com.au Fig.2: the power supply circuit of the Pico W, shown here in case you wish to adapt the WiFi Time Source to a different application. For example, consider adding a diode feeding into VSYS to prevent VBUS power from feeding into your power supply if a USB cable is connected. second rolls over, the data is sent, and the 1PPS signal is pulsed. This means that the NMEA data and 1PPS pulses are delivered with minimal jitter. Providing the output as the second rolls over means that the fractional data can be ignored, simplifying the code slightly, both for us and potentially for any device receiving that data. The other core has the vital role of periodically getting an accurate value for the time and collecting the other data that is needed. One of these is a ‘validity’ flag, equivalent to the GPS ‘satellite lock’ that should always be checked to ensure valid data is being received. The Pico W implements an internal 64-bit counter with microsecond resolution. This counts up from zero when the processor starts or is reset. The documentation jokes that (in the vein of the Y2K or Millennium Bug) this will eventually cause a year 5851444 bug. Such bugs typically occur when a counter rolls over beyond its maximum value. While we are not too concerned about this particular counter, we need to be aware of a few other such bugs. We have a separate small article starting on page 70 that explains these ‘gotchas’. The main role of the software running on the first core is to fetch an accurate timestamp from the NTP servers. This timestamp is compared with the current value of the 64-bit counter, and an offset is used to calculate the actual siliconchip.com.au time (at any time) by simply adding the current value of the 64-bit counter. The RP2040 processor in the Pico W has an internal real-time clock peripheral, but this only has a resolution of one second, so we can’t really use this to keep time accurately. However, we set it and use it in places where it is accurate enough, such as reporting time in human-readable form on the configuration interface. The first core also provides a virtual USB serial port that is used to print an interactive menu with the help of a serial terminal program. This can be seen in Screen 1; we’ll look more closely at the options later. The menu allows up to eight SSIDs (WiFi networks) to be set. The software will automatically cycle through these networks until it successfully connects to one. It will attempt to reconnect if the connection is lost. Since many applications of the Time Source depend on it only being turned on briefly (to save battery power), the initial behaviour is to perform a network scan to ensure that the first attempted connection is to an available network. The virtual serial port also produces status information, mainly concerning the WiFi status and time since the last NTP update. One of the menu Time is 22:43:01 on 14/02/2023. NTP OK. Last updated 0 minutes ago. WiFi Status: Connected with IP: 192.168.130.140 Menu: 1 : Scan networks 2 : Show saved 3n : Delete SSID (n from saved list) 4n : Set SSID (n from scan list) 5 : Manual SSID 6n : Set Password (n from saved list) 7 : Test saved 8 : Save to flash 9 : Set Country Code (currently XX) A : Set IPAPI URL (ip-api.com/line?fields=lat,lon) B : Set Latitude (−27.467899 = 27°28’4”S) C : Set Longitude (153.032501 = 153°1’57”E) D : Set baudrate (9600 baud) E : Set Talker (currently GP) F : Set NTP validity timeout (200 min) G : Set NTP server (pool.ntp.org [139.99.222.72]) H : Set default year (2022) I : Turn debug on (currently off) J : Reboot Clayton’s Pico W GPS Time Source Screen 1: many options are available to configure the WiFi Time Source. At a minimum, you will probably need to use commands 1, 4, 7, 8 and 9 to set the country code and connect to your WiFi networks to operate it with our GPS clocks. Other commands could come in handy depending on your application. Australia's electronics magazine June 2023  63 Table 1 – WiFi Time Source configuration commands Comm. Function Notes 1 Scan networks and display a list in order of decreasing RSSI Channel and authentication are also listed. The number shown in column n is used for Command 4. 2 Show the current network list The list is active but may not reflect the contents in flash memory unless a save has been completed. 3n Delete item n from the list shown by Command 2 4n Add network n from Command 1 Also prompts for a password. If all slots are full, an error is printed and you will need to use Command 3 to free a slot. 5 Enter a network name manually 6n Enter the password Shouldn’t need to be used unless you need to for a network, using change a password. n from the list shown by Command 2 7 Test networks in the list Scans through the list and attempts to connect to each network in turn. This can take a while and success is only reported if an IP address is obtained. 8 Save all settings to flash memory It’s a good idea to reboot after this to ensure that all settings are reloaded correctly. 9 Set two-letter country code Only loaded on boot, so reboot after setting this and using Command 8 to save. A Set IP to lat/lon API URL This should return two lines of text with decimal latitude on one line and longitude on the next. Set URL to blank to disable. B Set default latitude Enter in the decimal format. C Set default longitude Enter in the decimal format. D Set NMEA baud rate The default is 9600, but any rate between 300 and 921600 can be used. E Set Talker code The default is “GP”, but it can be any two characters. “GP” works for all our clocks. F Set NTP validity timeout in minutes The longest period for which the time can be considered valid without a (typically hourly) NTP update, from 60min to 50000min (about a month). G Set NTP server URL The default is “pool.ntp.org”, which automatically redirects to a geographically nearby server. Others can be used, such as “time.nist.gov”. The IP address may not be correct until a network is connected. H Set default year The year used at boot when no other time data is available, from 1970 to 4095. See the separate article on the Y2K38 bug for why this is important. I Toggle debugging Can be used to check and debug the NMEA NMEA data output to data. This setting is saved in case you need USB serial port this data to always be available on the USB serial port. J Reboot Pico W 64 Silicon Chip It’s recommended to reboot after saving settings to ensure that all settings are reloaded at boot time. If you hold the BOOTSEL button while rebooting, you can use electronicsmode. magazine this methodAustralia's to enter bootloader options allows the NMEA data to be dumped to the virtual serial port for easy debugging. The first core is also responsible for controlling the Pico W’s inbuilt LED, which is used to flash a status indication. The LED is switched on solid when power is applied, indicating that the Time Source is powering up correctly. It can also flash once, twice or three times per second. One flash means it is connected to a WiFi network, while two flashes indicate that the time is considered to be correct. Three flashes occur when both those conditions are true. In general, the time is correct if an NTP update has been received in the last few hours, although this limit can be adjusted. The crystal oscillator used on the Pico W has a 30ppm tolerance, meaning it could drift by up to one second every eight hours. In practice, we saw NTP adjustments up to 200ms, so we’re confident that the time will be accurate within half a second with the default settings. Programming the Pico W It makes sense first to program the Pico W and check that it is working as expected. Hold the BOOTSEL button on the Pico W and plug it into your computer. A USB drive named “RPI-RP2” should appear. Copy the NEW_CLAYTONS_1.UF2 file to it; after a second or so, the LED should come on. You can then use a serial monitor program to access the menu. We use TeraTerm on Windows, while minicom can be used on Linux systems. Open the Pico W’s virtual serial port to access the interactive menu. Ensure that your terminal program uses CR or CR+LF as its line ending. Since it is a virtual serial port, the baud rate is unimportant, and any baud rate setting should work. Basic setup All commands should be followed by Enter. The Pico W implements country codes to ensure that the correct (legal) WiFi channels are used for communication. The default “XX” setting is a subset that is safe worldwide but does not allow the use of some WiFi channels. So it should work but might not be optimal. siliconchip.com.au It’s a good idea to set this to your country. Use command 9 (followed by Enter) and enter a two-letter country code (AU, NZ, US, UK etc), then save the settings with command 8 and reboot the Pico W with the J command. Editor’s note: the codes should be in the alpha-2 format, see: https://w. wiki/4kP Reconnect to the Pico W if necessary; TeraTerm usually does this automatically. Now use menu option 1 to run a WiFi scan; this should complete within a second or so. The networks are listed in order of RSSI (signal strength), so you should find your SSID near the top. Note that commands listed with an n suffix take a second numeric argument. For example, if your network appears first (next to number 0), enter command 40. You will then be prompted for the password for this network; type it in and press Enter. You can enter multiple networks without rescanning. If your network doesn’t appear, use command 5 to enter the name manually, and you will be prompted for the password too. Command 6 on its own is used to change or set a password if, for example, you have entered it incorrectly. Then try command 7 to test the saved networks. You should see a message saying “Connected with IP”, followed by an IP address for each SSID. If not, try again. If you get an “Auth failed (password?)” message, the password entered may not be correct; you can use command 6 to re-enter it. The serial port will print updates around every 15 seconds if nothing has been entered on the serial port; this is to prevent updates from interfering with your configuration process. If all is well, use command 8 to save the settings to flash and reboot again to ensure that the settings are loaded. This is necessary as some parameters can only be set once, and the easiest way around this is to reboot the device. This should be the minimal amount needed to set up the WiFi Time Source to work with most of our clocks. A detailed list of commands, along with their use and purpose, is shown in Table 1. Screen 2 shows the typical responses to the more common and complex commands. Most other commands require a simple response and will report a message if there is a problem. siliconchip.com.au Screen 3 shows the typical progression at startup, although events may not occur in this order. You might also see a much larger NTP adjustment; that is normal. You can toggle the printing of GPS sentences over the USB serial port by using the I command. Screen 4 shows this; naturally, your data might be different. If you have a PC program that can process GPS data, you can use it to verify the data. Connecting it to a clock The WiFi Time Source could feasibly connect to just about any system that expects logic level NMEA 0183 data; however, its lack of accurate speed and location data means it is not the best choice in some cases. We don’t recommend using it as the source for any of our GPS-based frequency references; the 1PPS signal provided by this time source is not intended to have the necessary precision. And since it only ever gives a speed of 0 knots, it won’t be much use in the GPS Finesaver (siliconchip.au/ Article/11673). Screen 2 (right): this edited screen dump shows the output of some of the more complex commands. Note that these commands have been issued in the order shown, to add and then remove an SSID. Commands 3 and 4 require a second parameter which is a number printed by commands 2 and 1 (respectively) issued prior. ----------------------------------Command 1 ----------------------------------1 Scanning Scan complete Scanned network list: n SSID RSSI Chan Auth 0 AndroidAP4AA0 −44 1 PASS 1 APV Admin Only −65 3 PASS 2 APHV Conference −66 3 PASS 3 TPW4G_ZeB426 −82 11 PASS 4 WiFi-5E5EE1 −84 8 PASS 5 NTGR_4E0C −93 11 PASS ----------------------------------Command 43 ----------------------------------43 2 TPW4G_ZeB426 Added OK Enter password. PASSWORD password saved. ----------------------------------Command 2 ----------------------------------2 Saved network list: 0 AndroidAP4AA0 1 Tim 2 TPW4G_ZeB426 ----------------------------------Command 32 ----------------------------------32 SSID deleted. Saved network list: 0 AndroidAP44A0 1 Tim ----------------------------------Command 7 ----------------------------------7 Testing networks. 0 AndroidAP4AA0 >connected with IP:192.168.208.140 1 Tim >SSID not found 2 Networks tested, 1 OK Time is 04:01:30 on 13/02/2023. NO NTP. Connect failed Connecting to 0 AndroidAP4AA0 Skip IPAPI fetch, no WiFi. **** NTP adjustment: 11953 **** Connected with IP: 192.168.130.138 Time is 04:01:45 on 13/02/2023. NTP OK. IPAPI start. Headers of 170 bytes report 18 bytes of Received 18 bytes. HTTP finished:200 OK Lat/Lon=−27.467899,153.032501 Time is 04:02:00 on 13/02/2023. NTP OK. Time is 04:02:15 on 13/02/2023. NTP OK. Time is 04:02:30 on 13/02/2023. NTP OK. Time is 04:02:45 on 13/02/2023. NTP OK. Time is 04:03:00 on 13/02/2023. NTP OK. Time is 04:03:15 on 13/02/2023. NTP OK. Time is 04:03:30 on 13/02/2023. NTP OK. Time is 04:03:45 on 13/02/2023. NTP OK. Time is 04:04:01 on 13/02/2023. NTP OK. Last updated 0 minutes ago. content. Last Last Last Last Last Last Last Last Last updated updated updated updated updated updated updated updated updated 0 0 0 1 1 1 1 2 2 minutes minutes minutes minutes minutes minutes minutes minutes minutes ago. ago. ago. ago. ago. ago. ago. ago. ago. Screen 3: the last few lines on this screen (using the TeraTerm serial terminal program) show that the WiFi Time Source has connected to WiFi and updated its time from NTP servers. The previous lines are typical of what might be seen on a normal startup. Australia's electronics magazine June 2023  65 $GPRMC,050215.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*3F $GPGGA,050215.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*78 $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050216.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*3C $GPGGA,050216.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*7B $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050217.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*3D $GPGGA,050217.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*7A $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050218.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*32 $GPGGA,050218.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*75 $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050219.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*33 $GPGGA,050219.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*74 $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050220.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*39 $GPGGA,050220.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*7E $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050221.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*38 $GPGGA,050221.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*7F $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F $GPRMC,050222.000,A,2728.0004,S,15301.0057,E,0.00,000.00,130223,,,*3B $GPGGA,050222.000,2728.0004,S,15301.0057,E,1,04,1.0,0.0,M,0.0,M,,*7C $GPGSA,A,3,,,,,,,,,,,,,1.00,1.00,1.00,*2F Screen 4: the I command sends GPS sentences to the virtual serial terminal so that you can confirm the data being produced. This setting can be saved to flash, so the GPS data continues to be sent to the USB virtual serial port even after it reboots. It’s not going to be much use as a navigational aid either, ruling out the Advanced GPS Computer from 2021 (siliconchip.au/Series/366), so we’ll assume you are using the WiFi Time Source with one of our GPS clocks. We have instructions below on using the Time Source with some GPS clock projects we have published over the last ten years. Table 2 also summarises how this Time Source can replace some common GPS modules. Note that these connections may not be optimal, especially for clocks that run on batteries. You might want to experiment with alternative configurations. The suggested wiring for the recent battery-powered clocks is different to Table 2 for that reason. The problem is that the WiFi Time Source has a higher current demand than most GPS modules, and the circuitry sometimes cannot provide enough current to drive it. New GPS-Synchronised Analog Clock – September 2022 The most recent GPS-synchronised clock was published in September 2022 (siliconchip.au/Series/391) and was followed by an update describing how to connect the original Clayton’s GPS Time Source in the November 2022 issue. Like many of our recent GPS projects, it uses the VK2828U7G5LF GPS module. In fact, we recommend this module as a replacement for all the previous GPS modules we have used in clock projects. The VK2828U7G5LF has six connections, but you only need four for the Time Source. The connections are all fairly straightforward, although they don’t all connect to the GPS module header – see Fig.3. The black and blue wires are connected to the obvious points on the GPS module header. The red wire feeds power directly from the battery to the Pico W’s VSYS pin; one of the pins of the ICSP header is ideal for this purpose. Note that we’ve used a header pin for this connection, so power can be disconnected when we connect to the USB socket for programming. This prevents 5V from the USB cable being fed into the battery. With just these three wires, the Pico W would run continuously. So the green wire connects the 3V3_EN pin to pin 7 of IC1 on the Clock PCB. This pin is usually used to control the Clock’s boost regulator. This connects underneath the PCB, as shown in the photo, since it is easier to connect to the corresponding pad. Fig.3: connecting to the New GPS-Synchronised Analog Clock using the 3V3_EN pin on the Pico W makes the most efficient use of the Pico W’s onboard boost regulator, bypassing the Clock’s own boost regulator (the Pico W is shown larger than life size in Figs.3-6 for clarity). In this case, you could omit IC3, L1 and the two 10μF capacitors. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au The WiFi Time Source wired to the New GPS-Synchronised Analog Clock from 2022. To save battery power, the boost regulator on the clock PCB is bypassed; in fact, those onboard components could be left off entirely. The photo at upper left shows the green wire connecting directly to pin 7 of IC1 on the reverse of the PCB. This scheme bypasses the boost regulator on the New GPS-Synchronised Analog Clock, which is possible as the Pico W has its own buck/boost regulator. That also means that if you are building the Clock board from scratch, you can leave off the boost regulator IC and its associated components. With this arrangement, the Pico W will power up even when the battery is down to 2V, the lower limit of the Clock. By that stage, there wasn’t enough voltage to power the blue LED on the Clock, but everything else worked as expected. The photos show the Time Source connected via short lengths of wire and then mounted on the ICs using a pad of double-sided tape. Note how the Pico W’s WiFi antenna is clear of the PCB below. The WiFi Time Source typically takes about 25 seconds to ‘get a fix’, often faster and occasionally longer if it does not connect to the WiFi network immediately. This should be the same with most Clocks that use the Time Source. After powering on the Clock with the Time Source connected, the Clock would flash its LED once or twice, after which the Time Source’s LED would come on and start flashing at the same rate as the Clock LED. After a few more seconds, the LED on the Time Source would turn off, showing that the Clock has obtained the correct time and powered down the Time Source. Generally, the Clock LED should also turn off after half an hour at most (and the clock should start ticking), so if it continues flashing for longer than that, you should investigate. In general, we found that if the data displayed on the USB serial terminal appeared correct, the Time Source would work correctly when connected to the Clock. GPS-synchronised Analog Clock Driver – February 2017 The GPS-synchronised Analog Clock Driver from February 2017 (siliconchip.au/Article/10527) also recommended the VK2828U7G5LF GPS module. Note that we have not tested this arrangement or any of the following arrangements with clocks before 2022. Here we propose a variation that will avoid a small amount of inefficiency by also bypassing the Clock Driver’s boost regulator. Since the Pico W can work from voltages down to 1.8V at VSYS, we take 3V directly from the input of the boost regulator, as shown in Fig.4. GPS clocks from 2015 All the earlier GPS clocks we published used external power supplies, so they should not have any problems due to the limitations of a battery supply. Figs.5 & 6 show how to connect the WiFi Time Source to the 6-Digit Retro Nixie Clock Mk.2 and High Visibility 6-Digit LED GPS Clock, respectively. Note that both use the same header pinout for connections to their respective GPS modules, corresponding to the connections shown in Table 2. For efficiency reasons, the GPS power supply voltage link for these Fig.4: how to connect the Time Source to the GPS-synchronised Analog Clock Driver from 2017. This also bypasses the Clock’s onboard regulator to power the Pico W. Note that we have not tested this configuration. siliconchip.com.au Australia's electronics magazine June 2023  67 Fig.5: connections to the 2015 Nixie Clock. LK1 (which chooses between a 3.3V and 5V supply for the connected module) should be set to the 5V position. Still, this design is not powered by a battery, so efficiency is less critical. Fig.6: the High Visibility 6-Digit LED GPS Clock uses the same header pinout as the Nixie Clock, so the wiring is much the same, as is the choice to set LK1 to the 5V position. projects (LK1 for both projects) should be set to the 5V position, since the Pico W will happily work with 5V at its VSYS input. If you have any problems after connecting the Time Source to one of the other clocks, it is most likely a power problem. Check that the 3V3_OUT pin is near 3.3V. If not, the circuit may not be able to supply enough current for the Pico W. Conclusion The Pico W board provides helpful features in roles like this, such as its integrated buck-boost power supply, dedicated USB peripheral allowing a separate configuration console and good software support. The WiFi Time Source is a natural progression of the original Clayton’s GPS Time Source from 2018 and is 68 Silicon Chip similarly simple and well-priced. The Pico W variant adds extra features, particularly the ability to connect automatically to one of several WiFi networks. At the time of writing, Bluetooth support is in its early (beta) stages, so we will investigate if it is possible to add a Bluetooth interface for configuration. This would be very handy for updating settings as it would remove the need to connect a USB cable. SC Table 2 – Time Source pin mapping compared to GPS modules Pico W VK2828 EM408 Pin 1 GP0 (NMEA data) TxD(4, blue) Tx(4) Pin 2 GP1 (1PPS) 1PPS (6, white) Not connected Pin 3/38 GND GND (2, black) GND(2) Pin 39 VSYS VCC (5, red) V+(5) Pin 40 VBUS Not connected Not connected Not needed EN (1, yellow) EN (1) Not needed RxD (3, green) RX(3) Australia's electronics magazine Notes Not needed for most applications Or another source of 1.8V to 5.5V siliconchip.com.au PRODUCT SHOWCASE Nordic Semiconductor announces the nRF54 series The nRF54H20 is the first SoC (System on a Chip) in the nRF54 Series. It is ideal for IoT applications demanding high processing power, excellent energy efficiency and state-of-the-art security. It is capable of supporting Bluetooth 5.4 and future specifications, plus LE Audio, Bluetooth mesh, Thread, Matter and more. The nRF54H20 boasts multiple ARM Cortex-M33 processors and multiple RISC-V co-processors. The processors are clocked at up to 320MHz, and each processor is optimised for specific workloads. The nRF54H20’s integrated memory is comprised of 2MB of non-volatile memory and 1MB of RAM. The SoC’s high level of integration enables developers to shrink their designs by replacing multiple components with a single device. In addition to wearables, smart homes, medical and LE Audio applications, the nRF54H20 SoC is an ideal solution for machine learning and sensor fusion. The nRF54H20 features several new digital and analog interfaces, including a high-performance external memory interface (400MBps), high-speed USB (480Mbps), two I3C peripherals, a CAN FD controller and a 14-bit ADC. A 2.4GHz radio ensures the nRF54H20 SoC is the first in the world to offer -100dBm receive (RX) sensitivity when receiving a 1Mbps Bluetooth LE signal. Combined with up to 10dBm transmit (TX) power, the nRF54H20 offers an ample link budget for enhanced robustness and longer range. The nRF54H20 SoC is now available to selected customers for sampling. Contact your local Nordic sales representative or visit www.nordicsemi. com/Products/nRF54H20 Nordic Semiconductors www.nordicsemi.com Microchip expands its secure authentication IC portfolio These six devices enable developers to implement trusted authentication to prevent counterfeiting, improve quality control and safeguard the user experience. As counterfeits become prevalent across many industries, implementing embedded trust in many designs is critical. The devices are supported by the Trust Platform Design Suite, a dedicated software tool used to onboard these ICs with Microchip’s secure key provisioning service. The scalable service enables cryptographic assets to be provisioned for projects of virtually any size across applications like consumer and medical disposables, automotive and industrial accessory ecosystems, wireless charging and data centres. Five of the ICs are hardware-based secure storage intended to keep keys hidden from unauthorised attackers: 1. ECC204: ECC-P256 signature and Hash-based Message Authentication Code (HMAC) 2. ECC206: Two-pin parasitic power, ECC-P256 signature and HMAC 3. SHA104: Client SHA256 MAC 4. SHA105: Host SHA256 CheckMAC 5. SHA106: Two-pin parasitic power and client SHA256 MAC The last device (TA010) is an AECQ100 grade 1-qualified CryptoAutomotive IC with an ECC signature and HMAC. It enables OEMs to implement secure authentication into their design without costly modifications. Microchip’s security products are compatible with any MPU or MCU and can be used as companion devices to Microchip’s PIC & AVR MCUs and ARM core-based MPUs and MCUs. The new secure authentication ICs are supported by Microchip’s Trust Platform Design Suite, MPLAB X IDE, product-specific evaluation boards and CryptoAuthLib library support. Microchip Technology Australia Suite 32, 41 Rawson Street, Epping NSW 2121 Phone: (02) 9868 6733 www.microchip.com New at Mouser: AVR64EA 8-Bit AVR microcontrollers Mouser Electronics is now shipping AVR64EA 8-Bit AVR microcontrollers from Microchip Technology. The AVR64EA microcontrollers have an AVR CPU with a hardware multiplier and run at up to 20MHz. They have 64KB of Flash, 6KB of SRAM and 512B of EEPROM, and feature a 12-bit differential ADC with a programmable gain amplifier with up to 16× gain. The AVR64EA 8-Bit AVR micro enables measurement of smaller siliconchip.com.au amplitude signals, reclaims signals from noisy environments and performs fast conversions for quick and accurate signals in harsh environments, all with low-power efficiency. The devices are offered in SPDIP, SSOP, TQFP and VQFN packages ranging from 28 to 48 pins, with an operating temperature range of -40°C to +85°C. They are supported by the AVR64EA48 Curiosity Nano evaluation kit (EV66E56A), available to Australia's electronics magazine order at Mouser. No external tools are necessary to program or debug the AVR64EA48 in this kit. To learn more, visit: siliconchip.au/link/ablh siliconchip.au/link/abli Mouser Electronics (HK) Ltd. Unit 1901-1906, 19/F LU Plaza, 2 Wing Yip Street, Kowloon, Hong Kong Phone: +852 3756 4700 www.mouser.com June 2023  69 Feature by Tim Blythman The Y2K38 Bug and other time gremlins After much promised chaos, the Y2K bug turned out to be a fizzle, partially due to diligent actions taken by many to correct it before it happened. But other less obvious date- and time-related bugs are coming up, especially in 2036 and 2038. S etting aside the year 5851444 bug mentioned in the WiFi Time Source article – I think we probably have time to deal with that one – there are three well-known bugs potentially affecting time-handling protocols that are expected to occur much sooner, in the 2030s. While that might sound like a while away, it is now nearly 15 years since we first published a GPS clock project. There is a good chance that the WiFi Time Source will be obsolete in 15 years, although some will no doubt still be in use. So we had to ensure it would not be affected by any of these potential pitfalls. The following discussion might seem excessively cautious, but many people will recall some of the strange things that happened (or were predicted as happening) around the time of the “Millennium Bug” (Y2K). All these bugs are tied to dates in the future, but like the Millennium Bug, symptoms have already occurred before their relevant dates, primarily due to references to future dates. It’s probably due to these previous occurrences of these bugs that we are now suitably prepared to handle their arrival. 2036 The original NTP protocol uses a 32-bit timestamp (number representing a time) for the number of seconds since the 1st of January, 1900. Another 32-bit number is used to represent fractions of a second, giving a resolution of 232 picoseconds. This means that the counter used for NTP timestamps will roll over on the 7th of February, 2036. Fortunately, the NTP designers considered this possibility and the rollover, on its own, will not be a problem. While NTP transmits absolute timestamps, the main use of NTP is to set and maintain clocks that are capable of keeping time themselves. Checks are performed to validate clock sources 70 Silicon Chip and even prioritise which should be used in case many are available. The NTP protocol is designed to reckon its updates based on the current time (and date). In the worst case, the ‘true’ NTP time must be within 34 years of the system’s current time to perform these calculations correctly. 34 years is one-quarter of the 136year span that the 32-bit timestamp can represent. This allows enough spare bits to perform the correct binary arithmetic. As early as 2004, it was reported that some systems with default dates of 1970 (which is common as the beginning of the UTC epoch, see below) were unable to correctly update their time since the necessary adjustment was more than 34 years. The WiFi Time Source project uses a default date in 2022, and thus should have no trouble with NTP until at least 2056. We’ve made the default year adjustable, and even when it was set more than 34 years away from the present, it was able to synchronise correctly. So we expect that as long as this is updated every decade or so, there should be no problems with its NTP implementation. Interestingly, the timestamp represented by all 64 bits being zero (including the fractional part) is considered invalid. This timestamp will occur for 232 picoseconds on the 7th of February, 2036. The worst that might happen in this case is that the timestamp is discarded as invalid and an update is missed. The internal clock will continue to keep time and should be updated later. 2038 bug one (Unix time bug) The subsequent expected bug will manifest on the 19th of January, 2038, at 3:14:07 UTC (Coordinated Universal Time). UTC is roughly the modern equivalent of GMT (Greenwich Mean Time), based on solar time at the 0° (prime) meridian of longitude. Australia's electronics magazine Unix time measures the number of seconds since the start of the 1st of January, 1970. Like NTP, Unix time is often encoded as a 32-bit timestamp. Unlike NTP, this number is often interpreted as being signed, allowing dates back to the 13th of December 1901 to be represented. As you might guess, the signed 32-bit counter rolls over in 2038, and some systems will interpret these dates as being out by around 136 years. This bug is most like the Millennium Bug in its cause and possible effects. However, many computer systems are now switching to 64-bit processors (or have already switched), and using a 64-bit counter will prevent bugs on such systems. It will most likely be older, unmaintained computers and embedded systems that will be affected by this, as they will be less likely (or unable) to receive updates to correct this problem. Thankfully, the Pico W’s C SDK uses a 64-bit counter to keep track of time, even though it is only a 32-bit device. This has a resolution of microseconds and is what we use to primarily keep track of time in the WiFi Time Source. So as far as that design is concerned, this bug is not an issue. The NTP library actually passes a 32-bit Unix timestamp to set the time, as an unsigned value. This is reasonable as negative values map to times before 1970 and are thus not expected to occur. Thus, the Unix time bug is not expected to affect the WiFi Time Source until the 32-bit counter hits its unsigned limit in February 2106. We’ve set a reminder in our calendar to deal with it in mid-2099; that should be enough time to sort it out. 2038 bug two (GPS rollover) A time bug related to GPS is also expected to occur in 2038. This will not affect the WiFi Time Source as it’s related to technology used in the GPS satellites, and we don’t take any siliconchip.com.au ► 0.8 0.6 Left: a plot of UTC vs mean solar time (UT1); the vertical sections show leap seconds while the slope of the graph shows the relative drift speed and how it has changed over time. Source: https://w.wiki/6S8w 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 1976 1982 1988 1994 2000 2006 2012 2018 2024 Right: this is the time shown at the US official time.gov website at the time the most recent leap second occurred in 2016. Since most clocks can't even display a 61st second, we think that being one second off during a leap second is not such a big deal. Source: https://w.wiki/6T6X information from the GPS satellites (that’s the point of the project). The bug will occur around November 20th and 21st in 2038 and has actually already occurred twice (in 1999 and 2019), so its behaviour is well known. It’s known as the GPS rollover bug, and our feature about satellite navigation in November 2019 (siliconchip. au/Article/12083) mentioned it. In short, a 10-bit counter (allowing values from zero to 1023) is used to count the number of elapsed weeks in the GPS satellites. This counter rolls over every 19 or so years. A newer satellite protocol uses a 13-bit counter, so the updated hardware will not be affected by a rollover until 2137. Since the problematic counter affects the weeks, things such as the time of day will still be correct. So even if this bug were an issue, it would not cause problems for simple analog clocks. The worst that could happen is that the wrong daylight savings rules may be applied due to the bug. 2100 The NMEA sentences used by GPS only include the year as a two-digit number, in a pattern reminiscent of the original Millennium Bug. Naturally, this shouldn’t cause any problems until much closer to 2100. The New WiFi Time Source will produce accurate data, at least according to the NMEA standards. It will be up to the receiving circuitry to interpret siliconchip.com.au the year field as being in the correct century. Like with the GPS rollover bug, simple analog clocks do not need to know the year, so they will probably not be affected. Because 2100 is not a leap year, but 2000 is, the worst that could happen is that daylight savings changes might be applied a day early or a day late. Dealing with leap seconds UTC (which is derived from atomic clocks) is also subject to leap seconds. This is an attempt to align the time with so-called mean solar time. Mean solar time ties its noon time to when the sun is directly overhead, and can drift due to geological phenomena. The difference is due to the subtle changes in the Earth’s rotational speed. When these variations build up, leap seconds are effectively a jump in the value of UTC. When a leap second occurs, a clock might be out by up to one second until its time is adjusted. Leap seconds are not applied in a standard fashion, especially with NTP. Some servers freeze the time for a second, while others smear the time change over a longer period. Some might not apply the change at the correct time. There are proposals to eliminate leap seconds. At the moment, the equivalence between mean solar time and UTC is very close; there has not been a leap second since 2016, compared to the 1970s and 1980s when one occurred in most years. Australia's electronics magazine So, for this reason, we cannot guarantee exactly what will happen with the WiFi Time Source around the time a leap second occurs, and for around a day on either side. The time could be out by up to a second. Still, that will only be a problem if and when a leap second is required. As an aside, the reasons why the need for leap seconds comes and goes are complex but are partially due to the interaction of the Earth, Moon, Sun and other planets and bodies in the solar system. Those bodies affect the orbit of the Earth and Moon and thus influence the amount of angular momentum transferred from the Earth to the Moon due to the tides. Conclusion We think our WiFi Time Source will be a robust time source well into the future and will work correctly up until at least 2056. With some minor settings updates, it should work until at least 2100. However, be aware that other systems, especially embedded systems, might run into trouble around 2036 or, more likely, in 2038. Many small embedded devices run Linux or other systems derived from Unix and thus will potentially be affected by the 2038 bug, especially if they are no longer being supported with software updates. Keep in mind that before these bugs occur, it’s possible that WiFi or NTP might become obsolete and disappear, possibly ‘solving’ these problems in another way. SC June 2023  71 Switch between displaying air/fuel ratios for two different fuels ◀ Accurate air/fuel ratio and lambda measurement and display ◀ Wideband and narrowband O2 sensor compatible outputs ◀ Several display options, including wireless via Bluetooth ◀ Optional exhaust pressure correction for readings ◀ Correct sensor heat-up procedure implemented ◀ Compact size, fitting in a 120 x 70mm case ◀ Factory-calibrated oxygen sensor ◀ Part 3 of John Clarke’s WIDEBAND Fuel Mixture Display Our Wideband Fuel Mixture Display (WFMD) includes Bluetooth support, fits in a compact case and can compensate for higher exhaust gas pressures. This month, we give the complete construction, setting up and installation details. W hile the Wideband Fuel Mixture Display (WFMD) uses multiple surface-mount components, it’s pretty straightforward to assemble. Most parts are mounted on a double-sided, plated-through PCB coded 05104231 that measures 103.5 × 63.5mm (not 160 × 98.5mm as stated in the parts list in the April issue). It is housed within a 120 × 70 × 30mm plastic enclosure. An 8-pin circular multi-pole panel plug connector provides the interface to the external wideband sensor. This sensor is mounted in the exhaust stream (either directly or via an adaptor pipe) and connects to the controller via a 7-way extension cable. The enclosure also hosts cable glands for the power input, pressure sensor and volt/amp panel meter (or external multimeter) leads. The WFMD provides a simulated narrowband sensor output. This enables a vehicle’s existing narrowband sensor to be replaced with the 72 Silicon Chip Bosch LSU4.9 and still provide for normal engine operation by connecting the narrowband signal to the ECU. If your engine already uses a wideband oxygen sensor instead, the simulated narrowband output will not be a suitable replacement signal source. In that case, you can add the Bosch wideband oxygen sensor to the exhaust pipe as a standalone unit driven by the Wideband Fuel Mixture Display to observe the Air/Fuel mixture, leaving the ECU’s oxygen sensor(s) alone. PCB assembly Fig.13 shows the parts layout on the PCB. While there are components on both sides, we recommend fitting all the top-side SMDs before you solder any to the underside. That way, the board will still sit flat until you have mounted all the top-side SMDs. Begin by fitting the ICs. These are not overly difficult to solder, provided Australia's electronics magazine you have magnification of the work area and a fine-tipped soldering iron. Be sure to install the correct IC in each place and, in particular, double-check the orientation of each before soldering. Do not mix up IC2 and IC3. While IC2 is an OPA2171AID, IC3 can be either the OPA2171AID or an LMC6482AIM. Our kits will likely be supplied with two OPA2171AIDs; in that case, IC2 and IC3 will be the same type. To solder each IC, align the pins with the pads on the PCB, ensure pin 1 is in the correct position and then solder a corner pin. Check the IC alignment and, if necessary, remelt the solder and adjust the alignment until the pins are all centred over their pads. Solder the diagonally opposite pin of the IC before soldering the remaining pins; applying a little flux paste before soldering them will make that easier. siliconchip.com.au That takes care of all the SMDs on the top side. Now flip the board over and fit the SMDs on the underside, which include eight resistors, five capacitors, one zener diode, three regular diodes and two transistors: Q2 (BC817, NPN) and Q3 (BC807, PNP). Use the same techniques as before to mount all those components. Through-hole parts Fig.13: the overlay diagram for the Wideband Fuel Mixture Display (WFMD); we recommend fitting the components on the underside last. Any solder bridges that form can be cleared using a bit of extra flux paste and some solder wick. The resistors can be mounted next; all are surface-mount types that will be printed with a coded resistance value. For the 1% resistors, this is usually a four-digit code where the first three digits are the resistance value and the fourth value is the zeros multiplier. A code of 1003 means 100 with three zeros for 100kW. If it’s a three-digit code instead, it will be 104 (10 with four more zeros). For lower resistance values, the label could be just the resistance, eg, a 10W resistor might read 10 or 10R. A 100W resistor may be printed with 1000; the last zero indicates there are no zeros added to the value of 100. If present, R represents a decimal point, so a 0.1W resistor may read R100 or 0R10, although that resistor should be obvious as it is larger than the others. If you are unsure, check the resistor’s value with a multimeter set to siliconchip.com.au read ohms, but be careful not to press so hard on it with the probes that it goes flying off, never to be seen again. Next, install the SMD diodes and zener diodes. Most will have the type number on the top of the diode body, although you might need a magnifier to read the markings. Take care to orientate each with the anode and cathode (the end with a stripe) positioned as shown on the overlay diagram. We also placed a + near the cathode end on the PCB screen printing for clarity. Transistors Q4 and Q5 can go in next. Be sure to use the correct transistor in each place; Q4 is a BC847, while Q5 is a BC817. These are threepin SOT-23 surface-mount types, both NPN transistors. Follow with the surface-mount capacitors. These are unmarked, so you will need to rely on the packaging markings (or, in a pinch, a capacitance meter) to find their value. They are not polarised and can be installed either way on the PCB. Australia's electronics magazine Now we can move on to the throughhole parts, starting with the sole through-hole diode, D1 (1N4004), with its cathode stripe facing as shown in Fig.13. The through-hole capacitors are either MKT polyester or electrolytic types. The electrolytic capacitors need to be oriented with the polarity indicated, with the longer (positive) leads into the pads marked with a + and the negative stripes on the opposite side. All the electros are 100μF except for one 10μF type, so watch out for that. The MKT polyester capacitors can be mounted either way. Similar to the SMD resistors, they may have a coded value in picofarads instead of a direct value. The 470nF capacitor’s marking could be 474; 220nF could be marked as 224, and 100nF could be 104. Once those are soldered in and the leads cut short on the underside of the PCB, REG1, REG2 and Q1 can be installed. These parts are all in TO-220 packages that mount vertically, as far down as the device leads allow. Make sure that each device goes in the correct location and orientation, with the metal tabs toward the edge of the PCB. Once they are in, install the twoway pin headers for JP1, JP2 and JP3. Orientate LED1 as shown in Fig.13, locate its lens about 6mm above the board surface and then solder and trim the leads. The 13 trimpots (VR1-VR13) can now go in. Check that the correct value is installed at each location, and orientate each one with its adjusting screw as shown on the overlay. Using the correct orientation ensures that the voltages (or required resistance) at their wipers increase with clockwise rotation. Once again, these trimpots may be marked with a code other than the actual resistance value in ohms. So the 500W trimpot may be coded 501 (50 plus one zero), the 1kW trimpot may June 2023  73 be coded as 102 (10 plus two zeroes), the 10kW trimpots may be 103, and the 500kW trimpot may be 504. Bluetooth module The HC-05 Bluetooth Module can come with a right-angle or straight 6-way header strip. If you have a right-angle header, a 6-way header can be installed on the PCB so that the HC-05 right-angle header can be soldered to it, as shown in the overlay diagram. If your HC-05 has a straight header, it is easily installed by inserting the 6-way pin header into the holes allocated and soldering it. Switch S1 is also installed at this stage. If you intend to program microcontroller IC1 yourself instead of using the pre-programmed IC from the Silicon Chip Online Shop (the one supplied in kits is also programmed), a 6-way in-circuit serial programming (ICSP) header will need to be installed (CON1). Boxing it up With the PCB finished, it can be installed in the enclosure. The PCB rests inside the case on the integral mounting bushes. Four screws and nuts secure it; however, the screws do not pass through the bushes but off to the side. Drill the holes for these screws by placing the PCB into the case and drilling four 3mm holes through the PCB mounting holes. The ends of the enclosure can then be drilled and filed for the circular connector and cable glands. You only need to drill holes for the glands you are using. The corresponding holes are not required if you are not using the volt/amp meter or pressure sensor. Fig.14 shows the drilling details for two cable gland sizes that will fit within the designated enclosure; use the correct size hole for each gland you are using. Once the holes are drilled and shaped, mount the glands and the connector in position. Then run the A modified volt/amp LED panel meter in a Jiffy box makes for a convenient way to get a live readout of the air/fuel ratio and lambda. wiring as shown in Fig.15. Use minimum 7.5A-rated wire for the 12V supply, ground and heater wires. For the 8-pin circular panel connector, first connect the sensor leads to the PCB, with the heater and ground leads at the other end. Then cover each soldered pin on the connector with heatshrink tubing to avoid shorts and prevent the leads from breaking. That means you have to slide a length of heatshrink over each lead before soldering it to the connector. After soldering, push the heatshrink over the connection and shrink it using a hot-air gun. The power supply leads must be fed through the cable gland before connecting them to the PCB. The negative lead connects to the vehicle chassis near the battery negative wire, while the +12V lead goes to the vehicle’s switched ignition circuit via an inline fuse holder. Alternatively, for temporary use, the cigarette lighter or 12V DC socket can be used via a plug connector. Finally, secure the board using four M3 × 15mm screws and nuts. Tighten up the cable glands and circular connector to the sides of the enclosure. Sensor extension cable The sensor extension cable is made using a 6-way sheathed and shielded lead from TechEdge (see the parts list). It’s wired as shown in Fig.16. Ensure the wiring is done correctly and use heavy-duty (7.5A minimum) leads in the cable for the H+ and H− leads. The wiring is shown from each connector’s back (wiring side). The 6-pin connector includes rubber sealing glands to be placed over each lead before it is attached to the 2.8mm female crimp spade terminals. Before Fig.14: the drilling diagram for both sides of the bulkhead case. 74 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.15: the overall wiring diagram for the WFMD. Note the use of 7.5A-rated wire where required. attaching the oxygen sensor plug, you must remove the purple locking clip from the socket. Setting it up Power must not be applied at this stage since the 5V supply is not set. Also, leave the oxygen sensor unplugged from the WFMD and ensure there are no jumpers on JP1, JP2 or JP3. It’s then simply a matter of following this step-by-step procedure. With the sensor unplugged and no power connected: 1. Connect a multimeter between TP10 and Rcal, set the meter to read ohms and adjust trimpot VR3 for a reading of 311W. 2. Measure the resistance between TP1 and GND and adjust VR1 for a reading of less than 341W. This ensures a maximum of 5V at TP1 when power is switched on. Apply power (12V) to the circuit, monitor the voltage between TP1 and TP GND and adjust VR1 for a reading of 5.00V. 3. Connect the multimeter between TP GND and TP17 and adjust VR13 for 4V. This initially sets the enginestart battery voltage threshold to 12V. 4. Monitor the voltage between TP6 and TP GND and adjust VR2 for a reading of 3.3V. 5. Monitor the voltage between TP15 and TP GND and adjust VR4 for a reading of 3.92V. 6. Check that TP2 is at about 12V (it will be slightly lower than 12V if the supply is only 12V). 7. Check that the voltage at TP3 is close to -3V, although it could be as low as -2.5V. If this voltage is positive, check the orientation of diodes D2-D4, the placement of Q2 & Q3 and the orientation of the 100μF capacitors. 8. Check that the voltage at TP4 is near +33V. If incorrect, check the orientation of diodes D5-D9 and ZD2. Also check that Q4 is the correct type. 9. With the sensor still unplugged, check that the status LED is initially at low brightness when power is applied. It should then flash at 1Hz, indicating an error with the sensor connection. Fig.16: the wiring diagram for the extension cable, which connects to the Bosch LSU4.9 wideband sensor. siliconchip.com.au Australia's electronics magazine June 2023  75 For more information on making labels, see: siliconchip.au/Help/FrontPanels Calibration Fig.17: the drilling diagram for the external panel meter, which fits inside a UB5 enclosure. The wiring is shown in Fig.15 and the photo opposite. 10. If using the pressure sensor, connect it now and measure its output voltage at the connection to the PCB with both air inputs open to the atmosphere. Adjust VR11 until TP11 is at half the sensor output voltage. This sets pressure calibration to 25mV/kPa. If using a different sensor, you should be able to adjust VR11 so that the calibration is the same. 11. Adjust VR12 until there is no voltage between TP11 and TP12. If adjusting at an altitude above sea level, reduce the value at TP12 by 27.5mV for each 100m above sea level. This is valid up to about 900m. Above that altitude, the adjustment becomes non-linear and will need to be set when at a lower altitude. Leave the adjustment at the 900m level initially, with TP12, 247mV below TP11, until you can redo this at an altitude below 900m. 12. Once step 11 is fully completed, plug the smaller pressure sensor port with silicone sealant to prevent pressure changes at this port. Air/fuel ratio and lambda metering The three methods of displaying the air/fuel ratio and/or lambda include using a multimeter, a volt/amp panel meter or via Bluetooth to a computer or Android-based phone or tablet. When using a multimeter, connect it between MV+ and GND and set it to measure volts to monitor the air/fuel ratio, or between MM and GND for the lambda value. If using a panel meter, connect it as shown in Fig.15 and the photo opposite. It would be a good idea to use a long cable between the WFMD unit and the meter. The wire colours shown 76 Silicon Chip in Fig.15 match the meter wires supplied with the specified meter – yellow and red for current, red and black for voltage and thinner red/black wires for power. The meter needs to be modified by removing its onboard current shunt. A 1W resistor on the WFMD PCB replaces this. To do this, remove the meter’s internal PCB from its surround by levering the side clips and prising it out. The meter shunt is a U-shaped piece of stiff wire between the current measuring wires. It can be desoldered one end at a time and levered out, or simply cut a section out of it. The meter can also be installed in a small UB5 enclosure with the wiring via a cable gland on one side. We made the cutout in the base rather than the lid, as shown in Fig.17. Drill a series of holes around the inside perimeter of the cutout, knock out the inside piece and file it to the correct shape. The meter surround must be installed first before inserting the meter PCB into it. The existing V (Volt) and A (Amps) labels on the meter display can be covered over with lambda and air/ fuel labels, as seen in our photos. These labels are included in the front panel artwork download on the Silicon Chip website (Fig.18). Print them onto suitable sticky labels and attach them to the meter front screen. The front panel label can also be printed out and attached similarly. The air/fuel ratio can be shown for two different fuels, such as petrol and LPG, or E10 and standard 91 octane petrol, designated AF1 and AF2. For example, you could set AF1 for petrol (14.7:1 stoichiometric) and AF2 for LPG (15.5:1). The two readings are selected using jumper shunt JP3. When a jumper is in, the selection is AF1; when the jumper is out, it is AF2. The JP3 contacts can be wired to a toggle switch or other latching type to easily switch between the two options. VR5 and VR6 set the stoichometric air/fuel ratios for AF1 and AF2 for the meter display, respectively, while VR7 and VR8 set the equivalent values for the remote Bluetooth display. The adjustments can be made by inserting a jumper shunt on JP2. This sets the WFMD to produce a lambda 1 output. For the multimeter (MM) output, adjust VR9 for a 1.00V reading in this condition. The narrowband output does not require calibration and should already be at 450mV ±5mV. If using the panel meter, adjust VR10 to show 1.00 on the current (A) display. For the voltage display or to calibrate the MV+ output, adjust VR5 for the desired stoichiometric AFR reading with JP3 in and similarly adjust VR6 with JP3 out. The maximum AFR that can be set for lambda = 1 is 17.9. This results in an output of 33V (AFR 33:1) for a lambda of 1.84. To calibrate the Bluetooth display, switch off the power to the WFMD unit and then switch it on with a jumper shunt at JP2. Then open the GUI and connect it to the WFMD (details on doing that are in the panels). For AF1, adjust VR7 for a reading at TP7 that is one-tenth the desired stoichiometric AFR (eg, 1.47V for 14.7:1). Make the same adjustment at TP8 using VR8 for AF2. The trimpots may require a slight re-adjustment when viewed on the Fig.18: the labels for the WFMD and its panel meter. The main label would look best printed on a transparent label (you can download a PDF from our website). Australia's electronics magazine siliconchip.com.au GUI display. The JP3 setting can be changed to switch between calibrating AF1 and AF2. Note that removing JP2 will not stop the Bluetooth display from showing the lambda of 1 immediately. You will need to switch the power off and then on again with JP2 out before the Bluetooth display will show other values. Testing with the O2 sensor The next step is to check the controller’s operation with the oxygen sensor connected. Switch off power to the WFMD and connect the sensor lead to the controller. Now check that there is resistance between the sensor’s H+ and H− heater terminals, measured at the PCB H+ and H− terminals. You should get a reading of about 3.2W at 20°C. When power is applied, the sensor will become hot, so first remove the plastic protective cap. Place the sensor on a surface that can withstand rapid temperature changes and temperatures up to 200°C. Glass cookware (eg, Pyrex) is ideal, but do not hit the sensor against the glass or its ceramic element could crack. You could also use a clean brick, flat stone, or ceramic tile. Remember that the sensor tip can become hot enough to burn skin when power is applied. You will need a 12V supply that can deliver about 2A. Apply power and check that LED1 lights dimly for around 10s before flashing rapidly. Any display connected should show near full lean readings, such as a lambda of 1.84. If nothing happens, check that the VR13 adjustment gives a voltage reading of 4V at TP17. If your supply is just under 12V, you will need to readjust VR13 so that TP17 has a lower supply voltage threshold setting for the WFMD to start. The panel meter can be wired up in a UB5 case as shown. If the controller still doesn’t appear to be operating correctly, check for assembly or wiring errors. You can also test the sensor temperature control by installing JP1. The voltage across the sensor cell is then echoed at the narrowband output. Typically, this should be around 684mV ±10mV. Having completed the above tests, adjust VR13 so that TP17 is at 4.33V. This sets the controller to wait until the supply voltage reaches 13V (4.33V × 3), meaning the engine must start before it begins heating the sensor. Additional tests can also be carried out after the oxygen sensor is fitted to a vehicle. The Bosch LSU4.9 wideband sensor can be installed in the exhaust pipe by screwing it into the existing threaded boss of the original narrowband sensor or by adding a suitable threaded boss. This should be as close to the engine as possible. However, the exhaust gas temperature at the sensor must be under 780°C under all engine operating conditions, Fig.19: the Bosch sensor must be mounted perpendicular to the exhaust stream, and it must always be inclined 10° or more horizontally. siliconchip.com.au Australia's electronics magazine or the sensor might overheat. In general, installing the wideband sensor in the same position or near the existing narrowband sensor will be OK. You can check for sensor overheating by monitoring the heater impedance with jumper JP1 shorted. In this case, the narrowband output shows the sensor cell impedance. A reading much lower than 680mV DC indicates overheating. In that case, relocate the sensor to a cooler section of the exhaust manifold, further from the engine. The following points should also be taken into consideration: 1. If the sensor is to be used in a turbocharged engine, it must be installed after the turbocharger. 2. The exhaust pipe section before the sensor should not contain any pockets, projections, protrusions, edges or flex-tubes etc, to avoid the accumulation of condensation water. It is recommended to locate the sensor on a downward-sloping section of the pipe. 3. The sensor must be mounted perpendicular to the exhaust stream so it can constantly monitor fresh exhaust gas. It must always be inclined at least 10° from horizontal – see Fig.19. This inclination limit must account for the vehicle being on sloping ground. This is necessary to prevent condensation from collecting between the sensor housing and the element. 4. The recommended material for the threaded boss in the exhaust pipe is temperature-resistant stainless steel to the following standards: DIN 174401.4301 or 1.4303, SAE 30304 or 30305 (USA). Fig.20 shows the threaded boss dimensions. The sensor June 2023  77 The O2 sensor is shown above, with it attached to the extension cable at right. thread must be covered completely when the sensor is installed. 5. Applying high-temperature grease on the boss screw threads is recommended. The tightening torque is 40-60Nm (30-45ft-lbs). 6. The sensor must be protected if an under-sealant such as wax, tar or spray oil is applied to the vehicle. 7. The sensor must not be exposed to strong mechanical shocks (eg, installation or removal using an impact driver). If it is, the sensor element could crack and destroy the sensor without visible damage to the housing. 8. The sensor and its connecting cable should be positioned to avoid damage due to stones or other debris thrown up by the wheels. 9. Do not expose the sensor to water drips from the air conditioner or sources such as windscreen run-off during rain or when using the windscreen washer. The resulting thermal stress could damage the sensor. 10. The sensor heater must remain off until the engine starts. This means that VR13 must be correctly adjusted to ensure heating does not begin until after the engine has started and the battery voltage rises. Using the S-curve (narrowband) output As mentioned earlier, the S-curve narrowband output from the WFMD can replace the signal from a narrowband sensor. That is only possible if the vehicle originally uses a zirconia-­ type narrowband oxygen sensor. If the vehicle already has a wideband sensor, its output should not be replaced with the S-curve signal from the WFMD. A less common type of narrowband lambda sensor has a ceramic element made of titanium dioxide. This type does not generate a voltage but instead changes its resistance according to the oxygen concentration. This type of sensor cannot be simulated using the S-curve signal from the WFMD. Identifying the sensor leads To replace the existing sensor with the S-curve output, you must first identify the leads running from the sensor to the ECU. If you have a vehicle wiring diagram, that will make it much easier. Typically, there are four narrowband sensor variations: 1. If the sensor has one lead, this will be the signal wire, and the sensor body will be ground. 2. If the sensor has two leads, one will be the signal lead, and the other will either be the signal common or, in the case of a heated sensor, a +12V heater lead. For a heated sensor, the body forms a common ground for both the signal and heater circuits. 3. A three-wire sensor usually has Heater+ (H+), Heater− (H−) and a sensor signal lead, with the body as the signal ground. Alternatively, it could have a sensor signal lead, a sensor ground lead and a heater H+ lead, with the sensor body as heater H−. 4. A four-wire sensor is similar to a three-wire sensor but with ground leads for both the signal ground and H−. Screen 1 (left): the export settings for the Windows version of the GUI application. Screen 2 (below): to run the Windows application, you need to run the “air_display_3_pde” executable file by double-clicking it or similar. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Making a Bluetooth connection with a PC Fig.20: the dimensions required for the threaded boss which goes into the exhaust pipe. The thread on the sensor must be completely covered when installed. Having more than four leads suggests that the sensor is probably a wideband type. In each case, the leads are quite easy to identify, but first, a word of warning. Do not measure the narrowband sensor impedance with a multimeter set to read ohms. The current produced by the meter when measuring resistance could damage the sensor. Note also that the maximum loading for the sensor is 1μA. This means that to measure the voltage produced by a narrowband sensor, the meter must have an input impedance higher than 1MW. Digital multimeters (DMMs) generally have an input impedance much higher than 1MW, but an analog meter may not have the required high impedance. The first step in identifying the leads is to set your DMM to read DC volts, then connect the negative lead of the DMM to the chassis. Next, start the engine and probe the sensor leads with the DMM’s positive lead. A sewing pin can be used to pierce the wire Several graphical user interface (GUI) applications allow you to view the air/ fuel ratio and lambda values via Bluetooth. For a computer running Windows, we use an application based on ‘Processing’ (https://processing.org/) written by Tim Blythman. The download includes the Processing source code (“air_display_3_pde. pde”) plus a standalone version that will run in Windows. For macOS computers, the Processing file can be loaded into the Processing software for macOS (available from https://processing.org/) and then run or exported to a standalone app using the File → Export Application option. Screen 1 shows the export settings for the Windows version. When using Processing on a Mac, the macOS options for the platform will be available instead of the Windows and Linux options. By ticking the Embed Java box, the program will run without having Java installed on the computer. The Windows standalone application folder contains 268 files totalling 258MB. To run it, double-click the “air_display_3_pde.exe” file (see Screen 2). The GUI allows the COM port for the HC-05 to be selected using the < and > keys on your keyboard. Note that you don’t need to press shift or caps lock; just press the keys with those labels. Once the correct COM port has been selected, press Enter/Return. Help is available by pressing the H key. Pairing Before the display can show values, you must pair the HC-05 Bluetooth module with the computer. To do this on a Windows machine, click Start → Settings → Bluetooth & Devices, then power up the WFMD unit with a jumper shunt in JP2. This is so the WFMD will show lambda=1 values. The HC-05 Bluetooth module will be powered, and its LED should blink at 4Hz. Click “Add Device” on the computer to find the HC-05 Bluetooth Module. When found, enter the password (1234 or 0000). If the Bluetooth connection does not occur, try pressing and holding button S1 next to the Bluetooth module when power is applied to the WFMD. Hold it until pairing occurs. The computer will automatically pair with the HC-05 module when both are subsequently powered up and the computer’s Bluetooth is on. You will then need to know the COM port it has been allocated. To do this, under Bluetooth and Devices, select Devices, then scroll down to More Bluetooth Settings. Open Settings, select the COM Ports button, and the connected COM ports will be shown, similar to Screen 3. Make a note of the COM port that the HC-05 connects to. When you select the correct COM port on the GUI and press Enter/Return, the HC-05 module should change its onboard LED flash rate. It should give two flashes per 1.5 seconds, indicating that communication has been established. The display should then show a lambda value of 1.00 and the stoichiometric AFR set by JP3 and trimpot VR7 (JP3 closed) or VR8 (JP3 open) – see Screen 4. You can now make the final adjustments to VR7 and VR8 for the required air/fuel ratio readings. Remove the shunt from JP2 after switching the power off, and the WFMD is ready for use. Screen 3: you need to make a note of which COM port the HC-05 module is connected to. In this example, it’s connected to COM4. Screen 4: when the application is up and running it should initially show you the stoichiometric air/fuel ratio (AFR) and lambda value. siliconchip.com.au Australia's electronics magazine June 2023  79 Setting up the Android app There are two ways to install the Android app: via the Google Play store or a downloaded APK file. For the Play Store, open Google Play and search for “Silicon Chip WFMD”. You should find the “Silicon Chip WFMD BT interface” app. Clicking the Install button should be all you need to do. Otherwise, you can go directly to the page via this link: siliconchip.au/link/abl6 To install the APK file, first, you need to enable the “Install apps from external sources” option. Unfortunately, this appears in different places on different devices. In some cases, it will be under Settings → Apps → Special app access or Settings → Apps → Advanced → Special app access. We have also seen it under Settings → Security → More settings → Install apps from external sources. If your Settings has a search option, as many do now, you can try searching for “unknown” (Install unknown apps) or “special” (Special app access). That method can be a lot faster than trawling through the settings. Once enabled, download or copy the APK file (available from the Silicon Chip website) onto your device and launch it. Some devices may prompt for granting the above permission when you do this, if you haven’t already. After installing the APK file, we recommend turning that setting back off to avoid unwanted, malicious apps from being installed. Next, you need to pair the Bluetooth device. Put a shunt on JP2 and prepare the WFMD for being powered up. Remember that it might need a supply voltage above 13V to be enabled, in which case you will have to start the engine. Go to Settings → Bluetooth on your device, then power up the WFMD. A new Bluetooth device should appear shortly after – see Screen 5. Click on it, then enter the password (1234 in most cases, although some modules may use 0000). If the Bluetooth connection does not occur, try pressing and holding button S1 next to the Bluetooth module when power is applied to the WFMD. Hold it until pairing occurs. Once paired, launch the app. There are three buttons on the main screen, visible in Screen 6, and pressing the one marked “Connect Bluetooth Device” should allow you to select from a list of Bluetooth devices, choose the one for the WFMD. The lambda and AFR displays should starting show data, with lambda = 1 (due to JP2 being shorted) and your stoichiometric AFR. You can now fine-tune the value(s) using VR7, VR8 and JP3. Once it’s all working, power the WFMD down, remove the shorting block from JP2, power it back up and check that the values are displayed correctly. If the app complains about Bluetooth Permissions or does not show any devices to connect to, ensure that Bluetooth is turned on and also check that the Nearby Devices permission is allowed under permissions for the Silicon Chip WFMD BT interface app. We found that the app would occasionally say that the permission had been denied, even when it was allowed, but that did not actually prevent it from working. Screen 5: the Bluetooth connection should appear shortly after starting the WFMD. If it doesn’t, press and hold S1 next to the Bluetooth module while power is applied to the WFMD. Keep holding it until pairing occurs. 80 Silicon Chip Australia's electronics magazine insulation, but make sure you seal any holes you make with neutral-cure silicone sealant afterwards, to prevent corrosion. The sensor’s H+ lead will be at +12V, while its signal voltage lead will vary, cycling about an average of 450mV once the sensor has finished heating. Once these two leads have been identified, switch off the engine and unplug the sensor. The H− terminal can now be identified – it’s the one that gives a low resistance reading (typically 5W and usually less than 10W) to the previously identified H+ terminal. If there is no such wire, the H− connection is via the chassis. But ensure you do not connect the meter probe to the previously identified signal terminal when the meter is set to read ohms! The signal ground wire will be the one remaining wire (or the chassis connection, if there are none remaining). Error codes In some cars, the ECU will check that the sensor is connected and produce an error code if it detects anything is amiss. In most cases, the S-curve narrowband signal from the WFMD unit will be accepted as valid, but there can be exceptions. First, the ECU may check the sensor’s impedance to determine if it is sufficiently heated (ie, when its impedance falls below a particular value). The impedance the ECU will measure at the WFMD’s narrowband output will be 100kW, which might be out of range for some sensors. If this happens, you will need to change the value of that 100kW output resistor to stop the ECU from generating an error code. Check the sensor data from the manufacturer to determine the expected impedance. Failing that, experiment with different values. It could be above or below 100kW. Heater fault indications Some ECUs will also indicate a fault if the heater leads to the oxygen sensor are disconnected. In that case, you will have to keep those wires connected to the old sensor and mount it away from parts that could melt, such as rubber and plastics. Ideally, mount it against the metal chassis. If doing this, ensure the heated sensor cannot be accidentally touched as it can run very hot. You could place a metal cover over it for protection. siliconchip.com.au Alternatively, you could make up a resistance box with the same nominal resistance as the sensor’s heater element when it is hot. The hot resistance will be higher than the cold resistance. It can be measured by disconnecting the sensor lead after the engine has reached operating temperature and then measuring the heater resistance using a DMM. The resistors should be installed in a diecast case and must be rated to handle the expected power dissipation, assuming a 14.8V maximum supply and a 50% power derating. For example, if the heater’s hot resistance is 12W, it will dissipate up to 18.25W (14.8V2 ÷ 12W). In practice, given the derating requirement, a 40W resistor would be needed. In this case, the heater could be simulated by connecting four 47W 10W resistors in parallel. Make sure the resistors are secured, and all wiring is prevented from shorting to the enclosure and supported from breakage due to movement. Using the narrowband output If feeding the WFMD’s narrowband output to the ECU, connect the S-curve output to the sensor+ signal input of the ECU. Do not make a direct connection to the sensor’s negative input to GND on the WFMD unit, as that could cause a ground loop. Usually, the ground connection will not be required, but if necessary, add a 10W ¼W resistor in series to minimise the ground current. Check that there is at least 4.33V at TP17 (adjusted using VR13) to ensure the engine is started before the sensor is heated. Ideally, you should use an enginecode reader to check for and clear any resulting fault codes. However, without access to this, fault codes can usually be cleared by disconnecting the vehicle’s battery for a minute or so. This method of clearing faults does have its drawbacks. Disconnecting the battery may affect a security-coded sound system, meaning that the security code will have to be re-entered. Any clocks will be reset, and also it could reset some of the learned parameters stored in the car’s ECU or transmission controller. Learned parameters include engine timing (to prevent pinging), fuel injector trims and transmission shift rates. These are tabled values made by the ECU and/or TCU during normal siliconchip.com.au Tips on removing or replacing an oxygen sensor To remove an existing oxygen sensor, first make sure you remove the correct sensor. The required sensor is the one that’s between the exhaust manifold and the catalytic converter. A second oxygen sensor may be located downstream from the catalytic converter to monitor its operation. Removing the narrowband sensor may be difficult if you do not have the correct tools. The required tool depends on the sensor’s placement. With limited access, you may have to resort to using an open-ended 22mm (or ⅞-inch) spanner. In most cases, though, you should be able to use a special oxygen sensor removal tool. This is a 22mm socket with a slit along one side so that you can slip it over the oxygen sensor wiring. It’s common for the original oxygen sensor to seize in the threaded boss in the exhaust manifold pipe, in which case the hexagonal section will refuse to budge. If using an open-ended spanner, it will tend to spread open under tension and slip, rounding off the hexagonal edges of the sensor nut. Removing a seized oxygen sensor can be tricky, even with the correct tool. We used a thread-penetrating lubricant such as “Loctite Freeze & Release Lubricant” (FAR IDH1024403) to help free it. We have also heard good things about Cre-Oil for this job. Other ‘penetrating oils’ are available from SCA, Chemtools, Protech, Master etc. Due to the risk of rounding, it’s generally a good idea to spray the junction of the O2 sensor and threaded boss with one of these penetrating oils and wait a little while (eg, half an hour or more) before attempting removal. Suppose it proves impossible to remove, and you are not concerned about damaging the original sensor. In that case, you can use a hacksaw or grinder to cut the sensor apart just above the 22mm hexagon nut section. Then you can use a 22mm hexagonal socket and breaker bar for added leverage to remove the remaining section. If you refit the existing sensor, apply high-temperature grease to the screw threads. That will make it easier to remove next time. A new sensor (such as the Bosch LSU4.9 sensor) will probably be supplied with this grease already applied to the thread, or supplied in a small sealed plastic bag along with the sensor. The factory oxygen sensor on a Volkswagen Golf Mk.7. Typically, oxygen sensors are generally installed in a similar position a short distance from the exhaust manifold. Access is not too bad in this case. Note the heat shielding over the exhaust manifold, with a hole for the sensor (and on the firewall behind it). Australia's electronics magazine June 2023  81 SC6721 Kit ($120 + postage) Includes the PCB and all the parts that mount directly on it; the microcontroller comes pre-programmed (the Bluetooth module is also included). You need to separately purchase the oxygen sensor, case, wiring, fuse holder, off-board connectors (including those for the O2 sensor) and optional parts like the pressure sensor and LED display. operation to improve engine running and fuel economy based on oxygen sensor readings and knock sensing, and optimise shift speeds while preventing hard shifts. If they are cleared, the engine and transmission may take a while to restore these parameters. Some automatic transmissions also ‘learn’ and adapt to driving style and can take some time to retrain after a power cut. If, despite everything you do, the engine still runs poorly or the ECU logs a fault code, the original narrowband sensor will need to be reinstalled. In that case, the wideband sensor can still be installed separately. Pressure sensor connections If you wish to use the pressure sensor, which will give more accurate readings, it is necessary to drill a small hole through the exhaust pipe and then braze a short length of metal tubing (steel or brass) to the pipe near the sensor. This should be located downstream from the sensor, so it doesn’t provide a condensation point above the sensor. The tube length should be such that the exhaust pipe heat is dissipated sufficiently for the rubber pressure tubing to attach without softening or burning. If you don’t wish to monitor the pressure, leave the pressure sensor disconnected from the WFMD unit. The WFMD will then operate assuming standard atmosphere pressure within the exhaust at the sensor location. The resulting error will depend on how much back-pressure the exhaust system generates at a given throttle setting. Screen 6: the Android app looks like this when data is being received from the WFMD. Tailpipe mounting If you do not wish to install the wideband oxygen sensor permanently, an alternative is to mount it in a tailpipe extension. This tailpipe extension can then be slid over the end of the tailpipe and clamped in position, as shown in Fig.21. However, readings obtained using this method will be affected by the catalytic converter, so they won’t be as accurate. That’s because the catalytic converter alters the exhaust gas oxygen content. Some catalytic converters also include an air bleed to feed oxygen into the exhaust, allowing full catalytic operation with rich gases and minimising unburnt fuel. This won’t be a problem in older vehicles that don’t have a catalytic converter. Also, consider the effect of exhaust dilution, where air mixes with the exhaust near the tailpipe. This can cause a slightly leaner than actual reading. When the sensor is fitted to a tailpipe extension, TP17 in the Wideband Fuel Mixture Display unit can be set for less than 4.33V. This will allow the sensor heating to start immediately when the WFMD unit is powered, instead of having to wait until the battery voltage rises when the engine is started. This is acceptable, provided the sensor is stored upright in a dry environment, to prevent moisture condensing in the sensor. Follow Fig.21 closely if you intend to mount the sensor in a tailpipe extension. Using the dimensions shown, the sampled exhaust gas is taken sufficiently upstream from the end of the tailpipe to prevent dilution with outside air. The pipe and clamp can be steel or brass, but use a stainless steel SC boss to mount the sensor. Fig.21: the Bosch sensor can also be mounted in the tailpipe. It should be mounted as shown in this diagram to minimise exhaust gas dilution. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Minimalist Carbon Monoxide (CO) detector After reading the “Carbon Monoxide Alert” project by John Clarke (August 2005 issue; siliconchip.au/ Article/3147), I thought that this piece of equipment should be installed in every car, but also in houses; anywhere that CO gas (the ‘silent killer’) is a concern. In the case of houses, a CO gas detector should ideally be installed in the kitchen and the garage. The cheaper we can build the alarm, the easier it is to install it in multiple places. So I set out to come up with the simplest possible version of this design while still keeping the multilevel alerts. The circuit uses a widely-available CO sensor driven by a tiny 6-pin microcontroller (a PIC10F320). Mosfet Q1 (a logic-level P-Channel type) powers the CO module on and off. When IC1 drives its RA1 digital output (pin 3) Circuit Ideas Wanted siliconchip.com.au low, the gate of Q1 is pulled to GND, so Q1 switches on and supplies 5V power to the MQ-7 for 60 seconds. We then need to set the MQ-7’s heater voltage to an average of 1.4V for 90 seconds. This is done by switching the RA1 output with a PWM signal generated by the PIC, with a 28% duty cycle. We can then read the CO level as an analog level at IC1’s AN0 analog input. Unless we want to go into calibration considerations, we may simply split the full ADC voltage measuring range (0 to 5V) into four parts, using the following thresholds (that can be easily modified in the code): • above 1.25V, trigger the CO level 1 alarm (one beep every 20s) • above 2.50V, trigger the CO level 2 alarm (two beeps every 10s) • above 3.75V, trigger the CO level 3 alarm (three beeps every 5s) To produce a beep, the self-­ oscillating piezo buzzer is driven directly from the RA2 digital output (pin 4). The piezo sounds when this pin is brought low and is silent when it is high or high-impedance. RA3 (which can only be a digital input on this PIC) is connected to a pushbutton that’s used to test the operation of the piezo. The D0 output pin of the MQ-7 module can be used to trigger external alarms (to open a window electrically, close a gas valve, power an electric fan etc). The firmware is written in assembly code, and can be downloaded from: siliconchip.com.au/Shop/6/182 The code is fully commented, optimised in size, uses macros to ease reading, and takes only 177 program words and 11 data bytes. Hichem Benabadji, Oran, Algeria ($80). Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine June 2023  83 DCC Block Train Detector Digital Command Control (DCC) is a method of powering and controlling multiple locomotives independently on the same track of a model railway. We described how it works in the February 2012 issue (siliconchip.au/ Article/769). Many, if not most, full-sized railways use the block system of signalling, where the track is divided into lengths called blocks, and the signals are arranged to prevent a train from entering a block already occupied by another train. If this simple fact can be guaranteed, then the chances of a collision are minuscule. Such things are usually not necessary on a model railway, but they can be used to add realism and even automation. At the extreme, the model railway can be completely automated. The automation system would track the location of each train, control signals and points and even send commands to the locomotives. Each train's speed and direction can be controlled by sending commands to the DCC base station. Our DCC controller from the January 2020 issue (siliconchip.au/Article/12220) uses the JMRI program, which can perform some of these tasks when connected to appropriate hardware. Simpler applications of a Detector might be used to activate a level crossing when a train is in the vicinity or sound a horn as a train departs a station. The Detector could be used to set signals to stop if the track ahead of it were occupied, although it would be up to the driver to respect those signals. 84 Silicon Chip One modern Block Detection system used on rails is called axle counting. All ends of a block (blocks around junctions might have more than two ends) have sensors that count the number and direction of axles passing a given point. These typically use a pair of sensors to detect the flange of a wheel passing by, behaving similarly to the two contacts of a quadrature encoder, so it can be determined if the axle is passing in or out. If the number of axles in a block is zero, the block is considered empty. The Automatic Train Controller from October 2022 (siliconchip.au/ Article/15511) could be considered a basic form of axle counter, although it uses a magnet to trigger a reed switch once every time the train passes. Another common system is the so-called track circuit. A low voltage is applied between the two rails, and if this is shunted (short-circuited) by a train axle, the block is detected as having a train present. This requires that each block is electrically isolated from adjacent blocks. That adds complexity for systems that use the rails as a return for the traction power circuit (such as with an overhead wire system). In a DC traction power system, the detection voltage is usually AC applied by a transformer across the rails at one of the block and detected by a second transformer at the other end. Such a system can also detect broken rails, another good reason to stop the train! This DCC Block Train Detector works on a block system, but the detection needs to occur slightly differently Australia's electronics magazine due to the 12V AC or higher DCC supply that is a square wave typically around 6kHz. The circuit shows two detectors wired to adjacent blocks. One wire from the DCC supply passes through the centre of a 5A:5mA current transformer. For extra sensitivity, the wire can pass through the centre multiple times; I used two passes in my prototypes. When a loco is present, it draws current from the track, even if it is not moving. The DCC decoder on a DCC loco will always draw a few milliamps and may also source current to power lights on the loco. The current is detected by the current transformer and rectified by the bridge, converted to a voltage by the 1MW burden resistor and smoothed by the 100nF capacitor. The time constant of this arrangement is around 0.1s, so it is not affected by the pulsating DCC signal. This voltage passes through the 10kW resistor to be available at SIG+/ SIG−. In my applications, the SIG+ terminals connect to the digital inputs of a 5V microcontroller, which has internal diodes to shunt any excess voltage, and SIG− connects to circuit ground. Other arrangements might require a zener diode or similar to clamp the voltage from rising above safe levels. The current transformer has a high turns ratio, so it can generate a high voltage at its output if there is no load. Despite the track breaks shown, the rails are connected by the wiring to the booster, so the loco can move over the breaks fine as long as they are small enough. The diagram shows the breaks in both rails, as this is a common siliconchip.com.au arrangement on model railways that use multiple DC controllers. The railway is divided into blocks, and each block has a switch that can be turned to select one of two or more controllers. If you are transitioning such a railway to DCC, the block arrangement lends itself to this wiring system. Note that this signal is not fail-safe! A train is indicated by the presence of a signal, while no signal implies no train. No signal will be present if the DCC supply fails (eg, the Booster trips). Depending on your application, you might need to detect this condition. The 4.7kW resistor provides a quiescent load and can be tweaked to provide a suitable threshold; in practice, it is enough to approximately overcome the voltage drop due to the bridge rectifier. The values chosen allowed loads as high as 10kW to be easily detected. This means that rolling stock (such as carriages and wagons) can be fitted with resistors across their axles to allow them to be detected too. It’s just as important to know where the back of the train is as the loco at the front! Of course, you will need carriages with metal (not plastic) wheels. I have successfully used SMD resistors mounted on the axles and connected to the wheels by conductive paint. One thing that sets this system apart is that the DCC voltage is always present, even when locomotives are stopped. On a typical ‘analog DC’ system, where the track voltage drives the motor directly, the voltage will drop to zero when the loco is stopped, which means nothing can be detected. Of course, a pure DC waveform will also fail to be detected by the transformer. To use this Detector on a DC system, there must be AC (or at least pulsed) current flowing at all times. So you will need some form of PWM drive. I tested a PWM motor driver module, and with a low duty cycle of around 5%, the loco drew enough current to trigger the Detector but did not move. The current transformers were found inexpensively on eBay by searching for “HMCT103” or “ZMCT103”. Look for values around 5A:5mA (1000:1). Other types may work with component value adjustments. Since the purpose is to sense current rather than accurately measure, even transformers not designed for the specific frequency (5kHz-10kHz) may work well enough. Tim Blythman, Silicon Chip. siliconchip.com.au Cupboard light This simple circuit can temporarily illuminate your cupboard or other usually dark place where a mains connection is not possible or not worthwhile. It is a battery-­ operated light with an inbuilt auto shut-off, designed around a single CMOS hex inverter IC (4049). Two of the inverters, IC1a and IC1b, along with 10MW and 1MW resistors, form a Schmitt-trigger inverter. When switch S1 is momentarily pressed, the voltage across the capacitor rises to 6V almost instantaneously. The Schmitt-trigger output at pin 4 of IC1b goes high, so the outputs of the four other paralleled inverters (IC1c-IC1f) go low, switching on the light. The capacitor then discharges through its parallel 10MW resistor. Eventually, the voltage drops low enough that the Schmitt-trigger inverter output goes low and stays low due to positive feedback. The light then switches off, and the circuit returns to a very low power state, drawing just the static IC current that’s typically 30nA. The lamp remains on for about two minutes with the given components values, calculated as 47μF × 10MW ÷ 4. The four parallel inverters can handle a lamp load of around 50mA, although 20mA is safer (hence the suggested 150W current-­ limiting resistor for the white LED). A transistor can be used in place of parallel-connected inverters for a higher lamp current. Raj. K. Gorkhali, Hetauda, Nepal. ($50) 3D-printed case for Advanced Test Tweezers I like the Advanced SMD Test Tweezers (February & March 2023 issues; siliconchip.au/Series/396), but the exposed metal cell holder on the bottom is just inviting short circuits if you inadvertently touch the wrong spot. As I spend a lot of my time designing 3D-printed stuff, I decided to make a simple case for the Tweezers, and here’s the result. I couldn’t figure out an easy way to 3D-print the text for pushbuttons S1-S3, so I made the three extender buttons in colours based on the resistor colour codes (no brown filament, so that’s texta!). The side view shows how it all fits together; the bottom snaps into place. The STL files are available for download in a zip package from: siliconchip.com.au/Shop/6/184 Geoff Cohen, Nelson Bay, NSW. ($60) Australia's electronics magazine June 2023  85 servicing, repairing and replacing While this article is primarily concerned with servicing a V6295-type vibrator, the general advice would apply to many mechanical vibrator units found in vintage radios and other contemporary equipment, mainly those with three sets of contacts. I will also present a straightforward Mosfet-based circuit that acts as a solid-state replacement for a vibrator. It even fits in an original-looking can! Part 1: by Dr Hugo Holden T he inspiration for this article was my NZ-made ZC1 Mk2 military communications radio, designed to run from a 12V battery. Like many battery-powered radios, the HT supply was provided by an electromechanical switching device with a vibrating reed and contacts known as a split-reed synchronous vibrator (or just ‘vibrator’). In this case, it is a 7-pin unit, type V6295. The circuit of the “vibratorpack” power supply is shown in Fig.1. The vibrator is within the circle; the other components are external to it. The V6295 has a pair of contacts to switch the primary winding of transformer T3 and another pair to switch the secondary winding for synchronous full-wave rectification. One extra contact in the unit is used to switch the magnet coil on and off, to sustain mechanical oscillations of the vibrating reed at around 100Hz. This system was quite efficient, as the coil in the unit only consumed about 2W, and the contacts, when closed, had very low resistance. However, in common with all mechanical contacts which switch an inductive load, the contacts wear and burn, degrading after tens to perhaps 100 hours of use. Another significant problem is due to the latex rubber inside the unit, described later. There are numerous articles on how to repair the V6295. It involves cleaning the contacts of all oxides, ensuring their surfaces mate in perfect opposition when they close, and adjusting the contact gaps. The small contact for the vibrating reed is usually adjusted for maximum oscillation amplitude, consistent with good starting; however, it also has a role in very fine adjustment and contact switching symmetry. If the primary side contact gap is too Fig.1: the ZC1 Mk2 radio power pack with the V6295 vibrator in the centre. The 12V DC supply from the battery at lower right is converted to a 200V+ HT output on the left, mainly due to the interaction of the vibrator and transformer T3. 86 Silicon Chip large, the power pack output voltage drops off as the duty cycle is reduced. If too narrow, the contacts arc over. In addition, if the contact gap is too large, there is an excessive voltage overshoot on the leading edges of the transformer’s primary winding connections. The primary contacts must also have a slightly longer duty cycle than the secondary contacts and overlap when the secondary contacts are closed – see Fig.2. Thus, there is a brief time when no contacts are closed, and the transformer’s field is collapsing. The transformer’s tuning capacitors are chosen so that the voltage overshoot is as low as possible, thereby minimising the contact arcing and voltage spikes. Restoring an original V6295 vibrator (or a similar type) involves four main steps. The first is checking its mechanical integrity and, if necessary, performing any repairs. The second is Fig.2: the secondary contacts are closed for a shorter duration than the primary contacts, and there is a gap between one set of primary contacts opening and the other set closing. Correct timings and symmetry are essential for reliability and low output ripple. Australia's electronics magazine siliconchip.com.au Photo 1: an extension socket like this is invaluable for checking and adjusting vibrators. The loops in the wire make it easy to attach oscilloscope probes. Photo 2: the vibration-dampening natural rubber parts of the V6295 are its downfall. They degrade over time, fouling the contacts. static contact adjustment, while the third is dynamic contact adjustment. The final step is using an oscilloscope to check that it works perfectly. Let’s take these one by one. metal surfaces of the contacts oxidise from being exposed to air, and metal oxides are insulators. Also, any contact arcing produces very corrosive gasses, which are trapped inside the housing. #1 mechanical considerations Restoration Suppose you don’t have an extension plug/socket to support the unit while out of its housing and making adjustments, simultaneously giving you access to the electrical connections. In that case, you will need to make one. Mine is shown in Photo 1. The V6295 needs to be in a condition where it can be disassembled and reassembled without damage. Surprisingly, the main reason a V6295 will not run after a period of storage is due to the latex rubber inside the housing, not contact oxidation. However, the latter is also a factor over longer time frames. As latex (natural rubber) ages, it melts and turns into a tacky brown liquid, then a vapour – see Photo 2. In a closed container such as the metal housing, the liquid goes into equilibrium with the vapour. The vapour is deposited as a sticky brown liquid on the contacts as months and years pass. High storage temperatures speed up this process. For example, an immaculately cleaned and adjusted V6295 was put into storage. Two years later, it would not run. Taking it out of its housing again, brown deposits had appeared on all the contact surfaces, insulating them and causing them to stick together. This material is identical to the areas of melted latex. Therefore, all this old latex needs to be replaced. Even without this latex problem, the The best way to remove a V6295 or similar vibrator from its housing is by gently prising up the zinc material, working around the can very slowly until the lip is unfolded. Next, carefully smooth it to remove any marks. You can replace the rubber inside the unit with various soft, rubber-like products that do not break down as quickly. One example of a very stable, soft material that can withstand high temperatures without breaking down is silicone. It isn’t rubber (which comes from a tree), even though people often refer to anything with similar properties as ‘rubber’. One thing to note is that the zinc canister is a little short, and there is only a minimal amount of room between the mechanism’s top surface and the inside of the zinc case top area. A 1-1.5mm thick silicone rubber sheet is suitable for this top area. For the remainder, the material from an ordinary 4mm-thick soft Yoga mat (usually PVC foam) is suitable and easy to get. When the old latex is removed around the base area, it frees up a siliconchip.com.au metal washer that can be separated from the base by a new felt washer (green) shown in Photo 3. When the unit is reassembled, it is important that you can feel the mechanism shaking back and forth in the housing when held upright. Excessive mechanical coupling of the mechanism to its housing results in mechanical vibrations being coupled to the entire radio, making it noisy. #2 contact cleaning and static adjustments First, clean any latex deposits off with contact cleaner, passing paper strips between the contacts. Clean them further with a fresh piece of 15mm-wide 800 grit abrasive paper folded in half, with a sharp fold, placed between the contacts. With gentle pressure closing the contacts, both faces are cleaned simultaneously. A final wash with contact cleaner is required to remove any fine debris. Never file the contacts under any circumstances, as this ruins their flat faces, and it will not be possible to have a unit with good output and any longevity after that. It is essential that the mechanical alignment of the contacts is such that when their faces meet, their entire surface areas are touching, and the faces are parallel, as shown in Photo 4. Felt washer between metal washer and base Australia's electronics magazine Photo 3: a silicone rubber disc and pieces cut from a PVC yoga mat replace the natural rubber and are much more stable over time. June 2023  87 Photo 4: before adjusting the contact gaps, ensure the contacts are clean and close to perfectly parallel. Photo 5: here I am operating the vibrator in the radio (in this case, a ZC1 Mk2 communications receiver) to test it before replacing it in its metal can. You can now make the static adjustments. A first approximation of contact settings is achieved by setting their gaps to 0.1-0.15mm for the primaries and 0.22-0.28mm for the secondaries. #3 dynamic contact adjustments The best results can only be obtained from the V6295 after a dynamic contact adjustment. This involves running the unit out of its housing while monitoring three things with an oscilloscope and voltmeter. The points to monitor are the primary connections on the transformer, the DC output voltage and the ripple voltage at the filter output (the left end of filter inductor L9B in the case of the ZC1; see Fig.1). Photo 5 shows a V6295 running via the extension, taken at a moment when the vibrating arm was deflected. A pair of secondary contacts can be seen to be closed, with the other pair wide open. When the primary contacts are correctly set, each contact is closed for a nearly identical period. You can place a slight bias pressure on the contact (with a plastic tool, be mindful of the voltages) to check the effect while viewing the scope. It is important to only deflect them close to their bases, to keep the contacts as parallel as possible. If both the primary contacts are too closely or too widely spaced, arcing will be seen between them. If there is asymmetry, one will have a slight arc and the other not. A minor adjustment on the vibrating reed contact can correct the centring of the mechanical motion. More significant corrections must be made by moving both contacts. There are the contact gaps to consider, plus the symmetry of opening and closing comparing one contact to another. Scope 1 shows the waveforms with correct primary contact adjustments, with the scope probes connected to pins 6 & 1 on the V6295, effectively across the transformer primary. The time that each contact is closed, t1 & t2, is in the order of 4ms. When the primary contacts are closed, the voltage on the corresponding trace is 0V. You can see that the periods are very close to equal in this case (t1 = t2). Scope 2: if the secondary contacts are not adjusted correctly, the ripple on the DC output will vary on every second pulse like this. Scope 3: when the secondary contacts are correctly adjusted, the DC output ripple will be reduced in amplitude and more consistent, as shown here. Secondary adjustments The secondary contact spacing and symmetry profoundly affect the ripple voltage superimposed on the DC output (as well as the DC value itself). If the secondary contacts are too closely spaced, arcing and flash-over occur. Again, the effect on the ripple voltage can be seen by placing a slight bias on the contact with a plastic tool while the unit is running. Scope 2 shows when the secondary contacts are out of adjustment, resulting in a very asymmetrical ripple voltage. That is with 11.6V DC into the vibratorpack’s input, the sender switched on and the ZC1 in receive mode RT. Scope 3 shows the t1 t2 Scope 1: probing the two primary contacts in the vibrator (which connect directly to either end of the transformer primary) should reveal a symmetrical waveform. If it’s asymmetric, adjust the contact gaps. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au Scope 4: with the two transformer primary waveforms (middle and bottom) along with the DC output (top), we can see that the secondary contacts close for shorter periods than the primary contacts. correct adjustment of the secondary contacts, resulting in a symmetrical ripple voltage. Scope 4 is a triple trace, showing both the primary voltages and the output ripple with a well-adjusted V6295. Note how the time that the primary contacts are closed is a little longer than the secondary contacts due to the wider secondary contact gaps. The multiple overlaid traces is an artefact of the photographic timing. Scope 5 shows an electronic V6295 replacement plugged in place of the mechanical V6295. This unit runs at 60Hz rather than 100Hz and makes for an interesting comparison. Notice the absence of spikes and transients in the electronic unit and the differently shaped ripple voltage, which is still about 2V peak-to-peak. Scope 5: with a Mosfet-based vibrator replacement instead of the mechanical V6295, the waveforms are somewhat cleaner (at 66Hz rather than 100Hz), but the DC ripple on the output is similar in magnitude. two Mosfets, is among the easiest to build, works exceptionally well and is quite efficient, being slightly more efficient even than the mechanical type (which has a standing power draw of around 2W). If you don’t have an existing housing suitable for this device (eg, taken from a failed mechanical vibrator), you can use a readily-available round aluminium housing. This commercial air intake pipe joiner, 75-76.2mm (3in) long and 38mm (1.5in) in diameter, is available on eBay – see Photo 7. It uses a standard Amphenol 7-pin base, also usually available on eBay, shown in Photo 8. This unit produces very clean switching waveforms and will start from voltages as low as 8V, even when the supply is loaded. Unlike units driven by independent oscillators, it does not require a tuning capacitor on the transformer primary. Also, it is intrinsically short-circuit protected because if the supply is overloaded and oscillations stop, both Mosfets turn off. The circuit is shown in Fig.3. Two Mosfets replace the primary contacts of the vibrator, while pairs of series-connected BY448 1500V diodes replace the secondary contacts. This might seem like overkill, but it #4 reinstallation You can solder a brass wire ring into position to re-fit the unit to the housing, as shown in Photo 6. This way, it can easily be removed later for more repairs/adjustments. Do not re-crimp the zinc can, or it can only be cleaned and repaired once, as the zinc casing will fracture. Solid-state vibrator replacement I have built several different solid-­ state circuits to replace a mechanical vibrator, including two using Mosfets, one using Darlingtons and one using bipolar transistors. The one presented here, using little more than siliconchip.com.au Photo 6: the vibrator can be held in its can using a C-shaped piece of brass wire. This makes it much easier to open again later. Photo 7: the vibrator replacement looks very similar to an actual vibrator, but is made from all-new parts. If you have a defunct vibrator in a suitably-sized can, you could possibly reuse it (and maybe its base). Australia's electronics magazine June 2023  89 OD = 35.3mm ID = 29.4mm Height = 8mm Photo 8: the spacer is held in the centre of the base/plug with a 10mm CSK M3 screw, and the PCBs are, in turn, held to the spacer using two M2 machine screws through holes drilled in it. The cylindrical spacer is used to attach the can to the base. Scope 6: the Mosfet-based vibrator replacement generates waveforms with rounded edges, as they do not switch super fast (to avoid RFI). is necessary to have a very high PIV (peak inverse voltage) diode rating. If the unit is unplugged while running (or there’s a bad connection to one of its socket pins), the undamped collapsing field of the main vibrator transformer can produce a peak voltage high enough to break down and destroy a single 1N4007 rated at 1000V. Each Mosfet is switched on by a positive spike coupled from the opposite end of the transformer when the opposite Mosfet switches off. This pulse is coupled via a 470nF capacitor with a 1.6kW series resistor. The Mosfets switch off after a defined time due to the gate discharge resistors; the result is alternating oscillation. 10nF gate-drain capacitors and 300W gate resistors slow the switch-on and switch-off times of the Mosfets to prevent RFI, while 18V zener diodes prevent the gates from exceeding their ±20V Vgs ratings. When one Mosfet switches on, the rapid drop in its drain voltage will couple through to the gate of the other Mosfets switch more-or-less simultaneously. The fact that the coupling capacitor values are relatively low (under 1µF) assists in making a unit that will slide easily inside the pre-made 38mm aluminium tube, a similar size to a standard vibrator can. Mosfet via the 470nF capacitor and 1.6kW resistor, ensuring it switches off simultaneously. The exact oscillation frequency will depend on the transformer characteristics. Scope 6 shows the drain voltages with the unit in operation in the ZC1 in receive mode, while Scope 7 shows the gate voltage of one of the Mosfets when conducting. The 470nF capacitor charges via the fellow Mosfet’s drain voltage (24V) and 10kW gate resistor until the charge current drops off and the gate voltage approaches the threshold Mosfet’s voltage. By that time, some transformer core saturation is beginning, so the feedback rapidly falls away, the Mosfet turns off, and the fellow Mosfet is driven into conduction. The unit runs at 66Hz in my set. Looking closely at the switching transitions on the transformer primary (drain connections) at 10V/div (Scope 8), they are free from radio frequencies and excessive voltage overshoot with this circuit. You can see how the Construction Various Mosfets will work in this circuit. While I used TO-3 case versions, TO-220 case versions could be used with some lead bending, such as the ubiquitous IRF540N, available from Jaycar and Altronics. Suitable TO-3 case Mosfets include the IRF130, IRF230, IRF350, 2N6756 and 2N6758. The 2N6758s made by Harris, available on eBay, are particularly good quality. It is based on two small, simple PCBs that sit back-to-back, as shown in Fig.4. They are not identical but very similar, with the only difference being the routing of one track. The holes for the components all fall on a Fig.3: this self-oscillating Mosfet-based replacement for the vibrator is nice and simple, needing just two Mosfets, four regular diodes, two zener diodes and 10 passive components. The properties of the external transformer set the oscillation frequency to around 66Hz. Note that the 18V zeners were 20V types in the original design but the voltages have been lowered slightly to allow for part tolerances. Photo 9: the base with the tapped spacer, BY448 diodes (note that the other two diodes are hidden inside the holes in the plug pins) and tinned copper wires already attached. 90 Silicon Chip Australia's electronics magazine siliconchip.com.au Scope 7: a Mosfet drain waveform (top) and its corresponding gate waveform (bottom). You can see how the gate voltage decays during each cycle until the Mosfet switches off and the opposite Mosfet switches on. 2.54mm grid, except for the TO-3 transistor holes, which do not land exactly on the grid due to the geometry of a TO-3 package. Assembly of each PCB is straightforward, with just six components on each board. Use Fig.4 as a guide to mounting the components on both, including the TO-3 Mosfets, which should be bolted down before soldering and trimming the leads. Solder the BY448 diodes directly to the base, as shown in Photo 9, with the second diode in each pair down in the appropriate pin recess. You will also need to cut and drill a metal hexagonal tapped spacer, as seen in Photo 8, plus a 3mm countersunk hole in the centre of the base to attach this spacer later. To ensure the 3mm diameter hole in the plug is drilled on-centre, a temporary 3mm spacer can be placed in the ¼in recess to guide the drill. The hole is then countersunk from the pin side of the plug. The hole for the 3mm countersunk Scope 8: a close-up of the Mosfet drain waveforms, showing how one Mosfet switches on (rising gate voltage) just after the other (with a falling gate voltage) switches off. screw needs to be centred in the well in the plug where the hex brass spacer fits and it is easiest to drill it from that side (opposite side to the pins). With the temporary spacer in the well to act as a guide, run the 3mm drill down the centre of that spacer to make the hole. Then once that hole is made, flip the plug over and use a countersinking tool on the material for the head of the screw. A larger sized drill should not be used as the drill could pass through by accident. The spacer’s end needs to be rounded off a little to fit into the deep hole in the UX7 plug. Additionally, a cylindrical spacer is needed to help fit the finished unit into the aluminium tube. This has an outer diameter of 35.3mm, an inner diameter of 29.4mm and can be 8-10mm tall. I cut the one shown in Photo 8 out of a piece of phenolic plate with two hole saws, then trimmed it to size. This spacer can also be made of metal, like aluminium. Attach the drilled, tapped spacer to the base as in Photo 9, and solder three solid-core wires to pins 1, 6 & 7 to connect to the PCBs later. You can use 0.7mm diameter tinned copper wire with insulating tubing slipped over the wires. Glue the cylindrical spacer to the Amphenol base using 24-hour epoxy (eg, Araldite). The two PCBs are mounted with a 5.4mm gap between them. The wire for the Earth connections passes between the PCBs. Two other ‘crossing’ wires are required, visible in Photo 10. These Fig.4: the two PCBs are similar but with some parts rotated or swapped as they mount back-to-back. Points X & Y on the two boards are joined (X to X and Y to Y), while both GND points are wired to pin 7 on the socket. Pins 1 & 6 are wired to the metal cases of the two TO-3 package Mosfets (not shown here). Photo 10: the vibrator replacement is now operational, with the two PCBs assembled, wired up and attached to the base via the vertical spacer. Australia's electronics magazine June 2023  91 Pin 7 (Earth) Pin 1 Pin 6 Photo 11: a short spacer over the top screw that holds down the two TO-3 Mosfets (insulated from their cases) keeps the PCBs apart. Photos 13 & 14: views of the finished vibrator replacement sans can. are Teflon-covered wire wrap types; however, any light-duty hookup wire would work. Ideally, the PCBs should have plated through holes. In the absence of those, for this hand-made prototype, I used small brass eyelets for the connections between the PCBs. Use a screw and nut to secure the Drain connections from pins 6 and 1 of the Amphenol base to the lower TO-3 transistor mounting holes. Rotate the PCB assembly so that the gap between the PCBs is over pin 7. This allows the wires from the base to pass in a very direct and orderly way to the Earth and two drain connections. Secure the upper mounting holes between the transistors with a spacer and some insulators, as shown in Photo 11. The two boards are joined at the top by using two transistor insulators, a 5.4mm high and 3.5mm diameter spacer, a wave washer and M3 nut plus a 4-40 UNC by 3/4-in (or M3 20mm) binder head screw (shown at the end of the article); Photo 12 shows the result. Photos 13 & 14 show the finished assembly. The final procedure is to fit the completed unit into the pre-made aluminium tube (it might be a good idea to check that it works first!). The top of the tube can be sealed with a 35.3mm diameter, 6mm-thick disc glued into place. This is a firm press fit. I made the disc shown in the photos from Bramite, a fibreglass-like insulator; however, it could be made from aluminium, Paxolin or any other material. The base is a firm fit into the tube. You could glue it in, assuming you have already tested it, because it is unlikely ever to require repairs. However, it can be retained with a 1.21.4mm spring clip made from spring 1.4mm spring wire clip Photo 12: the assembly is a relatively tight fit in the can, but it does fit. If you’re having trouble inserting it, try slightly filing the edges of the PCBs, careful that you don’t encroach on the copper tracks. 92 Silicon Chip Photo 15: like the real vibrator, the best way to retain the vibrator replacement in the can is with a C-shaped spring wire clip. It can be made by bending a piece of spring wire around a cylindrical former (the outside of the can, if necessary). Australia's electronics magazine Photo 16: the replacement (right) doesn’t look exactly like the original (left), but a casual observer probably wouldn’t notice the substitution. siliconchip.com.au steel wire. The clip engages the existing groove in the aluminium housing, then varnish is applied. This allows disassembly if required one day (see Photo 15). Photo 16 shows the finished replacement unit next to an original V6295. The air intake coupler is about 1.5mm longer than the original housing, so I trimmed 1.5mm off the lower edge (at the base end), but this is not necessary; it still fits well in the socket without doing that. Efficiency I measured the output voltages and efficiencies of the original V6295, this design and several other replacements (some of which will be described in upcoming issues). I made these measurements with a 12V DC supply, a 3.75kW load and a 47µF capacitor across the load resistor. The original unit delivered 267V DC at an efficiency of 66.6%, while the Mosfet replacement unit described here managed 276V DC at 67% efficiency. The most efficient unit with the highest output voltage is the somewhat more complicated oscillator-driven Mosfet version, at 72.7%. That is to be expected because of the low power drive requirements for the Mosfet gates and the low RDS(on) figure of the Mosfets used in that design. That is one of the designs to be described in a future issue, likely later this year. Positive-ground radios For positive ground radios, it’s possible to use the same design by using complementary devices (ie, P-channel Mosfets instead of N-channel Mosfets) and reversing both zener diodes. No other components in this design are polarity-sensitive. That is a great advantage of circuits using discrete parts rather than ICs; they are easily flipped to the opposite polarity if SC necessary. Some of the hardware used to assemble the vibrator replacement. siliconchip.com.au Parts List – V6295 Vibrator Replacement 1 Amphenol 7-pin base [eBay 115461595962] 1 76.2mm-long, 38mm diameter air intake pipe joiner [eBay 261366805060] 1 35.3mm diameter, 6mm-thick disc (eg, made from aluminium or FR4) 1 35.3mm OD, 29.4mm ID, 8-10mm high spacer (see text and Photo 8) 1 100mm length of 1.4mm diameter spring wire 1 double-sided PCB coded 18105231, 34 × 53mm 1 double-sided PCB coded 18105232, 34 × 53mm 2 TO-3 package N-channel Mosfets (eg, IRF350, IRF130, IRF230, IRF350, 2N6756, 2N6758) [eBay, AliExpress etc] 2 18V 1W axial zener diodes 4 BY448 1.5kV 2A axial diodes 2 470nF 63V axial plastic film capacitors 2 10nF 400V axial plastic film capacitors 2 10kW miniature ¼W axial resistors 2 1.6kW miniature ¼W axial resistors 2 300W miniature ¼W axial resistors 1 24mm+ M3-tapped metal hexagonal spacer (cut to 23mm long) 1 M3 × 20mm panhead machine screw 1 M3 × 10mm countersunk head screw 2 M3 × 5-6mm panhead machine screws 3 M3 hex nuts 1 M3 copper crinkle washer 2 transistor insulating bushes (the type used for TO-220 package tabs) 2 M2 × 10mm panhead machine screws 2 M2 hex nuts 2 solder lugs 1 5.4mm untapped spacer, 3.2mm inner diameter 1 300mm length of 0.7mm diameter tinned copper wire 1 200mm length of 1.5mm diameter heatshrink or insulating tubing 1 100mm length of light-duty hookup wire 1 small tube of 24-hour epoxy The NZ-made ZC1 Communications Radio The photo below shows the New Zealand-made ZC1 Mk2 Military Communications Radio. This radio was a masterpiece of electronics and mechanical engineering. The ZC1 Mk1 was created by the Collier & Beale Company of New Zealand, while the Mk2 upgraded design is attributed to J. Orbell of Radio Ltd. I’m very proud that this extraordinary radio was created in New Zealand, my original home. Practically every person in New Zealand learning the art of electronics & radio in the post-WWII period would have come across this radio, because they turned up in great numbers in the 1950s, ‘60s and ‘70s in surplus stores throughout New Zealand. They formed a structure on which the radio enthusiast could experiment and modify and, at the same time, learn about radio reception and radio transmitting. As a result, many of these sets were subjected to extreme modifications. It got to a point where unmodified and original units became quite rare. Many of the parts from them formed the cores of other electronics projects. The 6.3V tube heaters were connected in series pairs. As there are 11 valves in the set, one required a series resistor for its heater ballast. A photo of the front panel of the ZC1 Mk2 from the Author’s collection. For more photos of the ZC1, visit: www.radiomuseum. co.uk/zc1inside. html Australia's electronics magazine June 2023  93 Soldering Irons We stock a WIDE RANGE of gas and electric soldering irons at GREAT VALUE to suit your needs and budget. 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Jaycar reserves the right to change prices if and when required. SERVICEMAN’S LOG Off on spring break Our resident Serviceman is taking a deserved break this month from his regular column, and is enjoying himself on a beach far away. This month will be all from contributors, with a return to normal schedule next month. Converting from one problem to another P. M., of Christchurch, NZ used to repair monitors and power supplies for an arcade machine manufacturer, so he has a fair bit of experience. In this case, the equipment to be repaired was very complicated, but the fault turned out to be pretty simple... While I repaired monitors and power supplies, two other technicians repaired the game logic boards. Having little digital experience at the time, I was in awe of them being able to find faults on boards full of digital chips. Sometimes, I would see them with their hands spread over the boards. When I asked, they explained that they could find chips getting too hot or not getting warm, which could lead them to the fault. Now you can use an infrared thermometer to do the same job. 96 Silicon Chip Recently, I was asked to go to my friend’s recording studio to sort out some gremlins. About 15 years ago, he retired the ageing 24-track analog tape recorder in favour of a digital equivalent. This came in the form of a potent computer with expansion cards to connect to three external 8-channel analog-to-digital (ADC) and digital-to-­analog converters (DACs). After some diagnosis, it appeared one of the converters had output signals that were very low in level and distorted. The converters are housed in 1RU rack-mount cases in their own rack, with spaces between them for ventilation. When I put my hand on each of the first two, they were warm, but the third was considerably cooler. My friend was a little sceptical, but I insisted I had located the problem. I figured that a power supply rail had failed, leading to the distortion. My guess was it would be one of the ±15V rails feeding the audio op amps. Back in my workshop, I plugged the unit in but could not get the power LED to come on. A look inside revealed a small relay next to the power jack. An external 9V AC power pack powers these units; it appears that the host computer powers the relay to turn the units on and off. So I removed the board and shorted the relay contacts to get things going. The board had four regulators on it: one +15V, one -15V and two +5V. I checked the 15V regulators first, but both were working correctly. The first +5V regulator was OK, but the second had no volts on its output or its input. I checked the circuit diagram, which showed a diode in series with the regulator input. The diode tested fine with a meter, but my scope showed 9V AC on one end and nothing coming out on the other. A replacement diode brought it all back to life. Further investigation revealed that this regulator powered the Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • • • Recording studio 8-channel DAC repair Beyonwiz DP-S1 PVR repair The electric oven also took a break Repairing a Daikin air conditioner Range Rover excessive battery drain Smoothing out problems on a dot matrix printer Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com digital-­to-analog converters driving the outputs, hence the distortion and low levels. Beyonwiz DP-S1 PVR repair B. P., of Dundathu, Qld is becoming an old hand at repairing PVRs as he has written in several times now with such repairs... Back in 2014, I bought a Beyonwiz DP-S1 on eBay. Unlike my later Beyonwiz purchases, the DP-S1 was in good working order and served as my main personal video recorder (PVR) for some time. After that, it became my secondary PVR as these PVRs will only record two channels at once, so if there was a third or fourth program that I wanted to record, I used the DP-S1. In 2022, the DP-S1 started getting a bit flaky, flashing the screen on and off a few times when it was first turned on. However, it settled down each time and continued to work for a few more months. Then I turned it on and got a message that the HDD was not initialised. I suspected that the HDD might be on its way out, so I formatted it. As I no longer had any files on the HDD, I turned it off. The next time I tried to turn it on, it would not turn on at all. It seemed more like a power supply problem now, so I would need to take the lid off and look to see what the problem was. These PVRs (like any other appliance) are subject to electrolytic capacitor failures, and I have repaired several Beyonwiz PVRs with such faults. The lids are usually removed by undoing four screws on the back and one on each side. However, the DP-S1 is different to the other Beyonwiz models as it has ‘wings’ on the side. After removing the back screws, the lid would not come off, and I had no idea how to remove the wings to remove the two screws on the sides. A check on YouTube proved fruitless, as this model is now at least 15 years old, but I found the answer on the Beyonwiz forum. It’s simply a matter of turning the DP-S1 over, pressing the clip and sliding the wing forward; very easy when you know how. With the wings removed, I could undo the two side screws and take off the lid. I could see the problem straight away. There were three bad electrolytic capacitors on the power supply board. This is typical of how these units fail, often coming up with an ERROR 0000 message. Removing the power supply board was slightly more difficult than later models due to the DP-S1 having a DVD drive, as the power plug for the DVD drive is under the drive and a bit hard to remove. After undoing the five siliconchip.com.au screws holding the PSU in, I was able to reach under the DVD drive and pull out the power plug. With the DVD power cable unplugged, I then removed the IDE cable from the hard drive so that I could unplug the power plug to the hard drive at the splitter. The next step was to desolder the three bad capacitors from the power supply board and look through my reclaimed capacitors and find suitable replacements. It’s important to note the orientation of electrolytic capacitors, as they are polarised and tend to explode if fitted backwards. Ask me how I know that! It’s standard convention to mark the negative side of the capacitor on the PCB, but on rare occasions, the positive side will be marked instead, so you have to pay attention. Having found suitable replacement capacitors, I first tested them with my ESR meter, then soldered them onto the power supply board and put everything back together. I only repair my own gear, so I don’t have any problem using reclaimed components. I’ve even had times when a new capacitor failed after just a few months; I then replaced it with a good used one, in the next voltage range up, and that capacitor has been working for several years. Just make sure to test reclaimed components to verify they are OK before reusing them. Now it was time to test the DP-S1. I turned it on, and it started up with no problems, indicating that the previous screen flashing and the HDD problems had been caused by the bad electrolytic capacitors. I then checked the program guide, and that loaded correctly also. While the DP-S1 only has a 180GB hard drive, it serves the purpose of occasionally recording when there are several programs on at the same time. I also sometimes use it to play DVDs. As far as I know, this is the only Beyonwiz model with a DVD drive. As it was working again, I decided to address another problem that had existed for many years; it had no front panel display. When I first got the DP-S1, the front panel display was a bit on the dim side, and over time, it faded out completely. This is a known problem for this model. It is caused by, if you haven’t guessed already, bad electrolytic capacitors. One post from Warkus (Mark) indicated that the failure of four particular capacitors caused this. Mark has posted a lot of very useful Beyonwiz repair information on the forum. There were bad electrolytic capacitors on the power supply board, shown above. The repaired PVR system is shown at right. Australia's electronics magazine June 2023  97 As I had already replaced the three large bad electrolytic capacitors, it was time to test the rest of the small capacitors to see which ones were bad. Here’s where my trusty ESR meter comes into play. Often, bad capacitors stand out with their blown tops or the bottom seal pushed out. Still, in some cases, they go bad without any visible sign. I checked over the board and found that C7, C31, C35, C37, C44 and C45 were bad. The majority of these capacitors read open-circuit on my ESR meter, while the others had very high readings. As I found each bad capacitor, I marked it with a felt-tipped pen. Then I drew a sketch of the PCB, removed the capacitors one at a time and marked on the sketch the value and the voltage of each one. I have most of my salvaged capacitors sorted into voltage and size ranges, so I located the correct replacements without too much trouble, soldered them onto the PCB and reinstalled it. I connected the power and turned it on, and I was greeted with a working front display. There is a saying that electronic equipment’s reliability is inversely proportional to the number of electrolytic capacitors it contains. This often proves to be the case, and I’ve repaired many devices with just bad capacitors. I’ve lost count of the number of devices I’ve repaired with this fault, including PC power supplies, older computer motherboards, two digital clocks, several PVRs, several monitors and two touch lamps, to name a few. Next to my multimeter, my ESR meter is one of my most valuable tools, along with my transistor and diode tester, both being Electronics Australia designed kits from Jaycar. If my ESR meter ever fails, I have a Silicon Chip ESR meter kit on standby that I can assemble if I need another. The unconventional oven? R. W., of Mount Eliza, Vic had a bit of a shock when his oven quit just before guests were due to arrive for lunch. Could he fix it in time? Sometimes the solution is not what you expect... Our ILVE electric oven was not working on Australia Day, not long before our lunch guests were due to arrive. Earlier that day, the light in our room went out. Upon examining the switchboard, I found that the safety switch had tripped. Switching it back on, the TV started working again, and the lights came back on, but the oven clock was not working. I checked the oven circuit breaker in the switchboard; it had not tripped. To ensure the oven circuit breaker was on, I switched it off and then on again. But the oven clock was still not working. I got my trusty old Fluke multimeter out to see if power was getting to the oven, which is hardwired. So the only way to measure the voltage was at the bottom connection of the oven circuit breaker. But the Fluke multimeter was reading just over 100V AC, not around 230-240V AC as I expected. It also indicated that the supply voltage from the street was just over 100V AC. The TV and lights were working, so I thought the Fluke multimeter battery might need replacing. However, its battery monitor indicated that the battery was OK. So, maybe the 50-year-old multimeter was faulty. I remembered that our SolarEdge inverter also indicated what the grid voltage is. On going into the garage to check it, I noticed that only one of the two lights worked. I found that the SolarEdge inverter was not functioning. That made 98 Silicon Chip me think that perhaps the TV was working because it supported an input voltage range of 110-240V AC, as much equipment does these days. It used to be that mains-powered devices had a switch or link to choose between 110-120V AC and 220-240V AC operation, but that’s far less common these days as most devices use switch-mode supplies with a wide input range. So I phoned United Energy, the company that owns the poles and wires in the street. After a few button presses, the answering robot indicated there was a problem with the electricity supply, but it did not say that the electricity supply was off. It also said it should be fixed by 11am today. Presumably, the computer knows your location from your phone number. So this pretty much confirmed that the TV and lights were working with the supply voltage down to around 100V AC. I decided to determine what else was also working at 100V AC. The WiFi modem was working; the electric kettle display was working, but it took a lot longer for the water to boil; the microwave oven display was working, but it only made food warm and not hot. The display on the LG fridge was working and indicated that the fridge and freezer temperatures were OK, but that does not mean it would have been able to maintain these temperatures all day. It was also good to know that the trusty 50-year-old Fluke multimeter was still working. Later that morning, an SMS from United Energy said, “We’ve restored power from the outage that was caused by a wildfire.” I found that both lights in the garage were now working, and the oven was too, just in time to have lunch ready before our guests arrived. All had a good Australia Day lunch. Component-level repair of a Daikin aircon B. C., of Dungog, NSW spent quite a bit of time investigating why his Daikin air conditioner was no longer working. It turned out to be a reasonably simple fault to repair, once he had pinned down the component that was on the fritz... One cold winter’s morning, we switched the kitchen air conditioner on to get some heat, but no air came out Australia's electronics magazine siliconchip.com.au IPX R ATEX D Keep your electronics operating in Harsh Conditions WATER RESISTANT SWITCH PANELS FOR BOATS OR RVS FROM 7995 $ Marine Switch Panels LOCKING LATCHES FOR EASY ACCESS • IP66 water resistant • Integrated 6-20A circuit breakers • LED illuminated switches • Pre-wired - easy install 4 Way SZ1906 | 6 Way SZ1907 Sealed Diecast Aluminium Boxes • IP65 dust and hoseproof • Internal guide slots • 6 sizes from 64Wx58Dx35Hmm to 222Wx146Dx55Hmm • Flanged versions available HB5030-HB5050 Industrial ABS Enclosures • IP66 weatherproof • Stainless steel hardware • Supports DIN rail components • 2 sizes HB6404-HB6412 FROM 1595 $ Switches for wet & dusty conditions 21 $ FROM 3995 $ STRONG, SAFE & SEALED 95 EA Durable Metal Pushbuttons • IP67 dust & waterproof • 12V LED illuminated (red, green or blue) • DPDT momentary action • SPDT with blue power symbol SP0800-SP0810 FROM 16 $ 95 Illuminated Pushbuttons • IP65 dust & water resistant • Momentary or On/Off • DPDT SP0741-SP0749 Explore our wide range of harsh environment products, in stock on our website, or at over 110 stores or 130 resellers nationwide. Other harsh environment products include: • 15 x Sealed IP65 Polycarbonate Enclosures • 14 x Sealed IP65 ABS Enclosures • 9 x ABS Instrument Cases with Purge Valves • Range of Waterproof Multi-pin Connectors, including Deutsch-type • Range of Sealed Rocker & Toggle Switches • 10 Waterproof Cable Glands jaycar.com.au/iprated 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. The control PCB for the Daikin aircon. of the head unit at the end of the start-up cycle. The Daikin RY60GAV1A A/C was a fixture in the house when we moved in about eight years ago. Holding the CANCEL push button on the remote control for more than five seconds allowed me to enter the FAULT CODE MODE. Then repeatedly pressing the CANCEL pushbutton allowed me to go through all the codes listed and finish at 00 (normal operation). All of the fault codes and their meanings are on a label under the hinged filter cover of the head unit. For example, if there was a long beep after pressing the CANCEL push button with C4 displayed, there could be a problem with the indoor thermistor. However, when I went through the list, there were no long beeps. It appeared that there could be a fault in the outdoor unit, which might not be one of the listed codes. I isolated the power and removed the top cover of the outdoor unit. I checked all the wiring in the outdoor unit but found no broken or loose connections. After powering it up again, I found that the outdoor fan would start up after about two and a half minutes, and I heard a solenoid valve operate at about four minutes. However, the compressor did not start. At the right-hand end of the outdoor unit, in its own compartment, is a large control PCB labelled EX304-3. This PCB is populated mainly with leaded components. Of interest were the Fujitsu MB88515B microprocessor IC, Toshiba TD62004 7-channel Darlington array and seven magnetic relays MRn (see the photo above). I noted that the green LED (near the microprocessor) was flashing at about 1Hz, indicating that it was running OK. I isolated the power again, removed the control PCB and took it to the test bench. I tested all the electrolytic capacitors (ELNA brand) with an ESR meter and found them all to be within specifications. 100 Silicon Chip At this point, I decided to download a PDF of “Manual ED01-214A Daikin Room Air Conditioners GA (old)-­Series”. I printed out the wiring diagrams for the RY60GAV1A model on pages 7 and 8 and the piping diagram on page 10. These are a bit basic as to what is on the PCBs, but they were a good starting point for me to reverse-engineer things. When I went to download a data sheet for the TD62004 IC, it turned out to be equivalent to the common ULN2004 IC. I refitted the Control PCB back into the outdoor unit to perform further diagnosis, so I could determine why the compressor would not start up. I dismantled the Main Power Relay (K1Main) near the compressor and found that the contacts only needed a light dressing with a points file. This was despite many cycles of usage. The relay coil measured OK, and when mechanically operated, there was continuity through the double-pole contact set. After powering up and then waiting for the correct part of the cycle (compressor start-up), I found no voltage present across the coil of K1Main. Mains voltage should come through the MRcompressor PCB-mounting relay on the control board. So I once again isolated the power, removed the control board and swapped the MR1 and MRc magnetic relays. This was to no avail; after refitting the control PCB and powering it back up, it still wasn’t working. It was now time to go down to the component level and make some voltage measurements directly on the control PCB. The TD62004 IC measured +12V on pin 9 (Vcc), and each channel input should be at +5V when driven high from the microprocessor IC. Each magnetic relay (MRn) coil is fed from the +12V supply and then grounded through its own Darlington transistor when activated by the microprocessor. The outdoor fan input was on pin 5, the solenoid valve input on pin 1 and the compressor input on pin 3. Even though there was +5V present on pin 3 (from the output of the microprocessor), there was still about +9.5V on that channel output at pin 14. There would need to be close to 0V if the 12V coil of the magnetic relay MRc was going to pull in! Obviously, this channel was faulty, and the IC would have to be replaced. While I had previously found that the ULN2004 was equivalent to the IC used, I could only find a ULN2003 in my collection. However, after perusing the data sheet, the ULN2003 appeared to be a better choice. The ULN2004 required a minimum drive voltage of +6.2V and, in this application, the ULN2003 would work better with the +5V signals from the microprocessor. I duly fitted the ULN2003 and put the control PCB back into the Daikin outdoor unit. After powering it up, it was a great relief to hear the compressor starting at the correct time in the cycle and to have warm air coming out of the indoor head unit. The air conditioner has run faultlessly ever since. Sourcing parts for a Range Rover TD4 J. N., of Mt Maunganui, New Zealand recently had a strange problem with his 2005 Range Rover Freelander TD4, which he has named “Polly”. Getting parts for older vehicles has become a problem, so it’s good he was able to fix the faulty component… My wife needed to attend a doctor’s appointment, so we Australia's electronics magazine siliconchip.com.au Huge Range of Project Enclosures A hand-picked selection of our plastic and metal type enclosures for projects big or small. SAME GREAT RANGE AT SAME GREAT PRICE. SEALED PLASTIC ENCLOSURES • IP65 Rated • ABS & Polycarbonate types • Flanged & Clear Lid options DIECAST ALUMINIUM • Standard, IP65 Rated & Flanged Options Easy to mount with cable entry Protects against dust and moisture General purpose and easy to cut or drill HANDY JIFFY BOXES BULKHEAD BOXES Ideal for harsh, hot or outdoor conditions IP65 RATE D • ABS IP65 RATE D • ABS FROM 3 $ FROM 3 75 HB6006-HB6082 10 sizes available $ Clear lid option FROM 7 75 HB6004-HB6025 11 sizes available $ Flange options 95 HB6120-HB6251 29 sizes available Flange options FROM 12 95 $ HB5029-HB5064 15 sizes available Flange options Shop at Jaycar for: • Over 100 types of plastic & metal enclosures • Enclosure cooling fans • Great range of rubber feet, cable glands & grommets • Huge range of panel mount plugs & sockets • Special selection of fasteners, spacers & standoffs Explore our wide range of enclosures, in stock on our website, or at over 110 stores or 130 resellers nationwide. Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. jaycar.com.au/enclosures 1800 022 888 jumped into Polly at the right time, only for me to find that she would not start. I tried to jump-start her with a small 12V battery, only to find that she was completely drained and would not even respond to my charger. Fortunately, my very reliable battery shop was on call. I dealt with them for many years when I used to repair electric golf carts, so they came and replaced our battery, and we were still able to meet my wife’s appointment. You guessed it; the same thing happened two weeks later. There was no way both batteries were faulty. I put my clamp meter on the negative battery cable and discovered that, in standby, it showed a little over a 1A drain. No wonder the battery was flat! As it happened, Polly was due for service, so I went to the same Range Rover garage I have used for many years. I approached Service Coordinator and booked Polly in, with a request to find and fix the problem of the excessive standby battery drain. A manager listening in said, “I am not sure about helping you with such an old model, as we do not have the records or parts we may need”. I was amazed at this and replied, “if your techies cannot find a fault without the onboard computer or your old manuals, which you should have, may I suggest that they simply rig up an ammeter in series with the battery and start removing fuses until the fault is located”. There was a bit of silence, then a grunt of approval. When I returned to pick up Polly, the serviceman went through the itemised invoice before payment. There was a charge for the service, plus a separate charge stating the battery had been tested, and the technician had found that the battery terminals were loose. He had tightened them and tested the battery, noting that the drain had dropped to the normal standby drain of 20mA. I expressed disbelief at this, as I knew my battery people would not be so remiss. However, I paid up and said, “let us see what happens”. On arrival at home, I tested the standby battery drain again, and sure enough, it was still reading just over 1A! Now very annoyed, I set out to do what I had suggested to the manager. It turned out that the main interior light unit had blown the passenger side bulb, which had somehow caused a permanent tracking to Earth (probably part of an electronic switching circuit). This unit is made not to be repaired and, like all European car parts in New Zealand, is very expensive. The garage refunded the cost of the repair that did not work, and I have ordered a second-hand replacement light unit from the UK. As I had a ‘new’ one on order, I decided to open up the old one to see what had happened and whether I could fix it. I could see some discolouration on the PCB that might have been due to excessive heat. I re-soldered all the joints, and it came right, but I will still replace it. The whole board looks like it was never soldered very well in the first place! Smoothing out problems on a dot matrix printer The main interior light enclosure for the Land Rover. 102 Silicon Chip A. L. S., of Turramurra, NSW uses a dot matrix printer because he has old but helpful equipment that will only work with such devices. Not being able to buy a new one, he had no choice but to fix it when it started acting up... My ten-year-old dot matrix printer began to stop halfway through a print run, leaving only half an image. Repeating the print command occasionally produced a complete Australia's electronics magazine siliconchip.com.au image, but things slowly worsened. It began to produce a very annoying partial document, then nothing at all! My first theory was that the printing ribbon was spent because the print head was tapping away, but nothing much appeared, and when it did, the ink was slightly undercooked. I also thought the ribbon might have jammed. I ordered a couple of spares online, and when they arrived, I fitted up a new one only to be confronted by the same fault. In fact, it was worse because the printer failed to take up the ribbon’s slack and left a horrible length of floppy ink ribbon. I had to question myself: was a dot matrix printer the best option in this day and age of fancy laser and inkjet printers? Well, I use it with an Audio Precision ATS-1 audio analyser that only has a parallel printer port. I tried connecting it to various newer printers, such as an Epson laser printer with a Centronics port, but it just printed noise! Back when I first got the ATS-1 and couldn’t get it to print, I asked a friend who was very clever with these things. He immediately grabbed a brand new Epson LX300+ dot matrix printer out of his archive room, and bingo! Perfect prints! He explained that such an old analyser deserved only an old (but new-old-stock) printer and charged me only $100. Today, these dot matrix printers are still in high demand because they can handle continuous lengths of paper and carbon paper for invoices, delivery dockets etc. I was shocked to find that new ones today sometimes go for $2000 or more! So a new pre-owned printer was out of the question, and all of the pre-loved ones on eBay looked like the love affair was well and truly over. Therefore, I would have to repair mine. I did have a parallel-to-USB converter from avwidgets. com but unfortunately, it failed after I plugged it into a faulty oscilloscope (I subsequently got rid of the oscilloscope!). The converter worked but required 20 keystrokes just to print a graph, whereas the dot matrix printer required two button presses, and the hardcopy could then be scanned or photographed for storage. To give you an example, when I need to do a plot of, say, impedance vs frequency for a loudspeaker, I just attach the analyser to the speaker and then press two buttons, and it produces the graph. With another button press, a beautiful graph is printed together with the impedance value for up to 150 frequencies. This is an enormous time-saver when I need to test many different speakers. A previous contribution in the November 2021 issue documented my repair of an Epson V100 scanner. The fault seemed mechanical, but turned out to be faulty electrolytic Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. siliconchip.com.au capacitors concealed beneath a panel, so I immediately theorised the same fault could have occurred here. The electronic control panels in the printer were also hidden from sight, so I began to split the case to get to the inner workings. The whole thing is held together with four screws, then all the panels interlock and come apart like a puzzle. Deep inside, there are two PCBs full of electrolytics. None showed any signs of leakage or swelling, and a quick test with an ohmmeter did not indicate anything drastic. My next step was to go to YouTube to see if anyone else had a similar problem. I found one guy who had a sticking Epson dot-matrix printer and described his repair in excellent step-by-step detail, but in the Telugu language, an ancient language spoken in India. He still used many English words such as “computer” and “printer ribbon” (I guess they weren’t around in ancient times), so it was still worth listening to. I could glean the rough meaning of what he was saying & doing. You can see the video for yourself at https://youtu.be/CqXDd8mAyTI Basically, he lubricated the track (which carries the printer head) with a silicone lubricant and ran it up and down by hand to ensure it ran freely. There were several other motions, like checking for problems with the cog and belt mechanisms, so I decided to check these out on my printer. Surprise surprise! The printer head was sticking ever so slightly; it felt like a mild brake was being applied at about halfway. I cleaned it up with a rag and tissues, and noticed that the lubricant had become black and sticky from dust and ink. I then used some alcohol to clean it and also cleaned the roller to remove any grease so the paper would not slip. I applied a little lubricant and decided to give it a go without replacing any electrolytics after all. Was this just a mechanical fault? Had I been influenced by my previous Epson electrolytic experience? Well, thanks to the Indian guy, it proved to be a mechanical fault. Now the printer never stops and never slips, and I vowed to treat it with loving care! SC Australia's electronics magazine June 2023  103 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 06/23 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) Basic RF Signal Generator (Jun23) ATmega328P-AUR RGB Stackable LED Christmas Star (Nov20) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10F202-E/OT Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) PIC12F617-I/P Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22), Active Mains Soft Starter (Feb23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) GPS Disciplined Oscillator (May23) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Digital Boost Regulator (Dec22) PIC16LF15323-I/SL Remote Mains Switch Transmitter (Jul22) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC BASIC RF SIGNAL GENERATOR (JUN 23) Kit: includes everything but the case, battery and optional pot (Cat SC6656) - 0.96in SSD1306-based yellow/blue OLED (Cat SC6421) CHAMPION + PRE-CHAMPION COMPLETE KIT (JAN 13) GPS DISCIPLINED OSCILLATOR (MAY 23) Includes everything required to build the Amplifier and Pre-Amp (Cat SC6373) - CH340G-based USB/serial module with panel-mount USB ext. (Cat SC6736) - NEO-7M GPS module with SMA connector (Cat SC6737) - GPS antenna with 3m cable and SMA connector (Cat SC6738) - DD4012SA 12V to 7.5V buck-converter module (Cat SC6339) SONGBIRD KIT (CAT SC6633) (MAY 23) DUAL RF AMPLIFIER KIT (CAT SC6592) (MAY 23) WIDEBAND FUEL MIXTURE DISPLAY (CAT SC6721) (APR 23) Includes all parts required, except the base/stand (see page 86, May 2023) Includes the PCB and all onboard parts (see page 34, May 2023) $100.00 $10.00 (APR 23) DIGITAL VOLUME CONTROL POTENTIOMETER (MAR 23) SMD version kit: includes all relevant parts except the universal remote control and activity LED (Cat SC6623) Through-hole version kit: includes all relevant parts (with SMD PGA2311) except the universal remote control and activity LED (Cat SC6624) ACTIVE MAINS SOFT STARTER (FEB 23) Q METER SHORT-FORM KIT (CAT SC6585) (JAN 23) RASPBERRY PI PICO W BACKPACK (JAN 23) $45.00 $15.00 $20.00 $10.00 $5.00 Complete kit: includes all parts in the parts list, except the DS3231 real-time clock IC (Cat SC6625; see page 56, January 2023) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - DS3231MZ real-time clock SOIC-8 IC (Cat SC5779) $30.00 Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, December 2022) Display Adaptor kit: complete kit (Cat SC6572; see page 45, December 2022) $25.00 (APR 23) Complete kit: includes all parts required, except the coin cell & ICSP header (FEB 23) Includes all parts (except coin cell and CON1) (see page 51, February 2023) Includes the PCB, all required onboard parts (excluding optional debug interface) and the front panel. Just add a signal source, case, power supply and wiring $100.00 Short-form kit: includes PCB, all onboard SMDs, boost module, SIP reed relay & UB1 lid. Does not include ESP32 module, case, 10A relay or connectors (Cat SC6589) $50.00 - ESP32 DevKitC module with WiFi and Bluetooth (Cat SC4447) $10.00 - 3mm black laser-cut UB1 Jiffy box lid (Cat SC6337) $10.00 SILICON CHIRP CRICKET (CAT SC6620) ADVANCED SMD TEST TWEEZERS KIT (CAT SC6631) $30.00 Short-form kit: includes the PCB and all onboard parts. Does not include the case, O2 sensor, wiring, connectors etc (see page 47, April 2023) $120.00 TEST BENCH SWISS ARMY KNIFE siliconchip.com.au/Shop/ $25.00 $60.00 $70.00 Hard-to-get parts: includes the PCB, transformer, relay, thermistor, programmed micro and all other semiconductors (Cat SC6575; see page 41, February 2023) $100.00 DUAL-CHANNEL BREADBOARD PSU $85.00 $7.50 $10.00 (DEC 22) $40.00 $50.00 DIGITAL BOOST REGULATOR KIT (CAT SC6597) (DEC 22) LC METER MK3 (NOV 22) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK (SEP & NOV 22) BUCK/BOOST CHARGER ADAPTOR KIT (CAT SC6512) (OCT 22) VGA PICOMITE KIT (CAT SC6417) (JUL 22) MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) Complete kit that also includes all optional components (see page 87, Dec22) Short Form Kit: includes the PCB and all non-optional onboard parts, except the case, front panel label and power supply (Cat SC6544) $30.00 $65.00 GPS-version kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see September 2022 p63) $55.00 WiFi-version kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see November 2022 p76) $55.00 Includes everything in the parts list (see page 64, October 2022) except the Buck/Boost LED Driver (Cat SC6292) $40.00 Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. $45.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR DATE JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 PCB CODE 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 01106201 01106202 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 Price $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) DATE JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 PCB CODE 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A Price $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET JUN23 JUN23 JUN23 JUN23 04106231 CSE221001 CSE220902B 18105231/2 $12.50 $5.00 $5.00 $5.00 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Identifying SMD resistors and capacitors I so wish we had something like Silicon Chip magazine in the USA. I mean, we do, and yet we don’t. Your magazine is one of the best I have ever had the privilege of discovering. Your feature stories are so in-depth; there are lots of detailed projects, and to do it every month is an incredible accomplishment. On to the question... I am not necessarily a newbie, but 23 years of being a Microsoft Windows Infrastructure Engineer has only made me fall in love with the electronics engineering side while not really preparing me for it. Can you point me in the direction of proper charts or diagrams of SMT/ SMD resistors and capacitors and how to tell what is what? I have found some great resources, but when I look up the SMD resistors that came with the Pico W Backpack kit, the numbers are not matching those on the resistors. Is this an imperial vs metric thing? (N. V., Breckenridge, MO, USA) ● SMD resistor codes are similar to scientific notation. In scientific notation, 7000 might be written as 7 × 103. The resistor codes are shortened; usually, the last digit is the tens exponent, while the remaining digits are the number to put before it. So 223 = 22W × 103 = 22,000W or 22kW and 1504 = 150W × 104 = 1,500,000W = 1.5MW. Alternatively, you might see a resistor code with an R in it. In this case, the R substitutes for the decimal point. So 10R = 10.0W, 1R5 = 1.5W and R100 = 0.1W. While SMD electrolytic capacitors (including aluminium and tantalum types) usually have values printed on them, there’s no easy way to tell SMD ceramic capacitors apart without measuring their values. For our kits, we typically rely on the number of each capacitor supplied to make it obvious which is which. For example, if there are supposed to be three 100nF capacitors in the kit, and you get a strip of three capacitors, 106 Silicon Chip you can infer that those are 100nF. You can see what parts are in the Pico W BackPack kit at: siliconchip. au/Shop/20/6625?show_parts_list=1 It shows two 1nF, four 100nF and four 10µF. So the strip of two should contain both 1nF capacitors. As there is ambiguity between the 100nF and 10µF, sometimes we tape the capacitors to a piece of paper that identifies them. However, we might not have done that in this case because the 10µF capacitors should be noticeably larger and thicker than the 100nF types. SMD ceramic capacitors (like SMD resistors) can be supplied in paper tape, but only if they are pretty thin. So if one of the strips of four parts is in paper tape, it most likely holds the 100nF capacitors. The 10µF capacitors would probably be in plastic tape due to their greater thickness. Hopefully, that lets you identify them. If you are still unsure, try using a multimeter or similar test instrument to measure capacitance. Carefully hold the probes on either end of one capacitor to get an idea of its value. You only need a rough idea of the value to distinguish between 100nF (0.1µF) and 10µF. Don’t press too hard, or the part might go flying! P. S. there was an attempt to start a US version of Silicon Chip magazine about 20 years ago, but it didn’t work out. That was described on pages 66 & 67 of the September 2022 issue, in Leo’s second article on the History of Silicon Chip (siliconchip.au/ Series/385). GPS-Synchronised Clock running too fast I built the GPS Synchronised Analog Clock project from the September 2022 issue (siliconchip.au/Article/15466) and the minute hand runs very fast. My clock has only hour and minute hands. The minute hand is traversing about one minute on the clock face every four seconds. What do you think is the problem? (F. C., Maroubra, NSW) Australia's electronics magazine ● It sounds like you have configured the firmware for a sweep movement but the clock has a stepping movement. Go back into the setup routine, and this time, select a stepping clock. A stepping clock will step one second for every input pulse, but the sweep clock setting will generate 16 pulses per second. If you do the maths, the stepping movement would advance by one minute every 3.75 seconds, which is very close to what you reported. Solar lighting system for a shed Have you considered doing a project for a solar lighting system for a shed that can encompass everything, from a small garden shed to a very large rural shed? I have used a Victron MPPT solar charger to run low-cost strip lights in a tool trailer with a big automotive-type AGM battery that also can be used to jump-start vehicles. So maybe there are enough commercial parts that a project might not be viable. The shed in my yard is about 3 × 4m footprint but has no provision for power coming from the house, so a solar setup with some LED strips could be workable. (K. C., via email) ● While it might be worthwhile to publish an article on this subject, plenty of commercial off-the-shelf components can be used to build such a system, and it need not be complex. Finding suitable lighting is the hardest part if you plan to run low-voltage DC lighting. One approach would be to ask a staff member at your local Altronics or Jaycar store for advice. They both sell many of the components you would need. For example, Jaycar has: • Solar panels: ZM9065 (many others available) • MPPT charger/battery protector: MP3741 (many others available) • Battery: SB2560 (many others available) • Lights: ST3930 (others available) siliconchip.com.au Wiring those together with a few other small parts, like switches, should give you a working solar lighting system. Altronics have some good solar panels and MPPT chargers but not as much in the way of lighting. A specialised battery shop would have a wider range of batteries. Another option would be to use a solar charger/inverter (like the Altronics M8133) with mains-powered lighting, giving you a much wider choice of lights, but then an electrician would need to do the wiring. Probably the trickiest bit would be figuring out what wattage of solar panels is appropriate and the battery capacity. It depends on how often you’ll use the shed lights and for how long, plus your local solar and weather conditions. Too much reliance on Mosfet gate threshold I built the AM-FM DDS Signal Generator (May 2022 issue; siliconchip.au/ Article/15306) and despite everything looking good and it powering up with the correct display, I couldn’t get any RF output from it. I suspected a faulty AD9851, but replacing that chip didn’t help. I checked everything thoroughly and found no faults. All the voltages were correct, as were the component values, and the crystal oscillator was producing a 30MHz output. The only problem I could find was with Mosfet Q1. The drain pin going to pin 12 (Rset) on the AD9851 chip was at 1.26V and the source was at 0V, indicating that Q1 was off. The gate was at 1.5V with no modulation. According to the data sheet, pin 12 should have a 3.9kW resistor to ground to set the output to 10mA full scale. I placed a 3.9kW resistor from Rset to GND and the output sprang to life with a 1.2V peak-to-peak sinewave! I had some VN10KM Mosfets, which are similar to the 2N7002. After replacing Q1 with one of them, it then worked normally, with the correct output level (0dBm) with the output unterminated, and adjustable AM/FM modulation. Do you know why the 2N7002s I bought from eBay, two lots from different suppliers, did not work? I have now ordered some more, which are supposed to be made by ON Semiconductor from a dealer with 100% feedback. By the way, the output level is sensitive to the DC input level. For stability, it could probably benefit from using REG1 in place of the link. (J. S., Avondale, Qld) ● We suspect the 2N7002 you used initially was fine; the circuit unfortunately places too much reliance on the gate threshold of the device used – something we should have picked up before publishing it. The circuit uses a 1.5V DC bias for the gate of Q1, while the 2N7002 data sheet says the gate threshold can vary from 1.0V to 2.5V. Yours must have been at the upper end of that range. It would have been better to place a resistor between Q1’s source and ground and use an op amp to drive the gate via a resistor with a slow response, using a relatively high-value capacitor between the output and inverting input. It would be configured to use feedback to adjust the gate voltage so the drain sinks the required 300μA average from the Rset pin. Such a circuit would automatically compensate for any variation in the Mosfet’s gate threshold voltage. The TEST MANY COMPONENTS ITH OUR ADVANCED TEST T EEZERS The Advanced Test Tweezers have 10 different modes, so you can measure ❎ Resistance: 1Ω to 40MΩ, ±1% ❎ Capacitance: 10pF to 150μF, ±5% ❎ Diode forward voltage: 0-2.4V, ±2% ❎ Combined resistance/ capacitance/diode display ❎ Voltmeter: 0 to ±30V ±2% ❎ Oscilloscope: ranges ±30V at up to 25kSa/s ❎ Serial UART decoder ❎ I/V curve plotter ❎ Logic probe ❎ Audio tone/square wave generator It runs from a single CR2032 coin cell, ~five years of standby life Has an adjustable sleep timeout Adjustable display brightness The display can be rotated for leftand right-handed use Components can be measured in-circuit under some circumstances Complete kit for $45 (SC6631; siliconchip.com.au/Shop/20/6631) The kit includes everything pictured, except the lithium coin cell and optional programming header. See the series of articles in the February & March 2023 issues for more details (siliconchip.com.au/Series/396). siliconchip.com.au Australia's electronics magazine June 2023  107 published circuit was tested with multiple 2N7002 devices, but they were all from the same batch. Rather than replacing Q1, if anyone else runs into this problem, we recommend simply changing the bias resistor values. If, like in your case, there is no output and the drain voltage of Q1 is higher than expected, the 3.3kW resistor can be increased in value, to say 4.7kW (giving a gate bias of 1.8V) or 5.6kW (gate bias of 2.0V). Similarly, if the gate bias is too high, resulting in reduced modulation depth, the 3.3kW resistor can be reduced in value or shunted by another resistor with a similar value. Determining exact hole positions on our PCBs Using vernier calipers to measure PCBs and discover the spacing for mounting holes can be very frustrating. I have just built the Multimeter Calibrator (July 2022; siliconchip. au/Article/15377) and want to put it in an enclosure. The mounting holes on this PCB are offset and difficult to measure. If you provided some simple measurements of board size and mounting hole locations, that would greatly assist your readers. This is easily obtained from the PCB layout program, and it could sit 108 Silicon Chip on the board overlay you show (Fig.3 in the multimeter calibrator project). That would be a simple but radical change to how we prepare enclosures for your wonderful projects. (S. H., Glen Iris, Vic) ● While that is a good idea, we are concerned about diagrams becoming cluttered. You can get the exact locations of holes from the PCB pattern downloads on our website using Inkscape (https://inkscape.org). The screen grab below shows the PDF file of the Multimeter Calibrator opened in Inkscape. Using the select tool (upper left), choosing millimetres (upper right) and then clicking on a hole gives the X & Y coordinates of the hole (top middle) in millimetres. You can then use a calculator to subtract the X/Y coordinates and determine the horizontal and vertical distances between the holes. There’s also the simpler method of using the blank PCB as a template to mark and then drill the holes in the case before populating it. Note that the hole centres are generally (not always) on a 0.025-inch/0.635mm grid. Using switchmode supplies for power amp Is it possible to construct a dual-rail DC power supply for the Hummingbird Australia's electronics magazine power amplifiers (December 2021 issue; siliconchip.au/Article/15126) from two switch-mode power bricks, the kind used for laptops, LEDs and Class-D amplifiers? I envisage two 32V 5A power supplies external to the case. Is it possible to have two reasonably large capacitors to provide additional smoothing and energy storage? The switch mode power supplies are pre-built, seemingly very well regulated, highly efficient, run cool, very small and amazingly cheap. I am currently experimenting with active speakers using a DSP (a Raspberry PI 400 running Brutefir FIR filter software) feeding small Fosi Class-D amplifiers powered by these switchmode power supplies. I would eventually like to replace these cheap Class-D amps with much higher-quality Hummingbird amps. However, the construction of a large linear power supply is off-putting. (P. T., Casula, NSW) ● In principle, yes, that should be possible. You should check a few things, most notably that the outputs are isolated from mains Earth. If you had two 32V supplies forming ±32V rails, you would achieve output power not significantly less than using a dual 25V AC mains transformer. We used 24V DC switch-mode power supplies in our Easy-to-Build Bookshelf speakers (January-March 2020; siliconchip.au/Series/341). We have a bit of a bias toward a good linear power supply with many capacitors. Having a lot of capacity in the power supply ensures that you do not suffer supply droop for peak output demand. Switch-mode power supplies can be much less forgiving and can shut down when you don’t want them to, so you need to size the supply carefully. A 5A power supply can put 40V across an 8W load or 20V across a 4W load. So if you are driving the amplifier very hard, you might run into trouble with low-frequency signals into 4W. Of course, real-world music is not usually sinewaves and has a significant crest-to-average ratio, so these supplies would happily run several channels of midrange and treble amplifiers. We suggest you build a Hummingbird amplifier and try it with the brick supplies. Remember that you will still need proper heatsinking and to ensure things are safely mounted. We suggest testing the amplifier into a 4W dummy load with the signal from siliconchip.com.au the subwoofer output of your Active Crossover. Run it flat out and see how it copes. SuperCodec lacks resistors on op amp I’m finally preparing to build the SuperCodec (August-October 2020; siliconchip.au/Series/349), and I noticed that are no resistors between the op amp outputs (IC10) to the main output connectors. These are typically needed to isolate op amps from destabilising cable and input filter capacitance. I’m concerned that this could well cause problems in some situations. I can add these resistors to my build (say 100W) between the PCB and wires to the output connectors. But it still seems like quite an oversight. Have you had any problems with this, or other feedback/comments? (I. B., Armidale, NSW) ● Phil Prosser responds: I agree it would be better to have 100W resistors in series with the outputs. The NE5532 is a very tolerant op amp and has given no hassles with any of its applications. Still, it would be better with the aforementioned resistors. So yes, if you have any concerns, add 100W resistors at the output socket. If I ever modify the PCB, I will add them there. Freetronics relay shield is impossible to get Is there an alternative to the Free­ tronics 8-channel relay driver shield (Core electronics CE04549) used in your 800W+ DIY UPS project (MayJuly 2018; siliconchip.au/Series/323)? These shields are currently hard to find. (W. F., Atherton, Qld) ● Unfortunately, we can’t find any direct replacements. However, there are ways to make it work with other shields or modules. It seems that the specified Freetronics shield is still a current product, but they are out of stock. One retailer’s website stated they were getting more soon. If you know how to modify the Arduino code, you could use the Free­ tronics N-Drive Shield instead, which is in stock: siliconchip.au/link/ablj There are a few things you’d need to modify in the software and wiring to make it work: 1) Change the I2C commands controlling the relays to instead set up and update the states of the digital pins used by that board: D3, D5, D6, D9, D10 & D11. Luckily, most of those are unused in our design. 2) Move the Piezo Buzzer to a different pin, as D9 will be occupied; we suggest D7. The code would have to be changed accordingly. 3) The specified relay driver board had two terminals per relay; this one has one per relay plus separate VIN & GND pins. That means all six red wires would need to go to the single VIN terminal (or something that splits that out six ways), while the black wires would go to the “FET Drain Connections” on the Mosfet shield. After making those changes, you would need to test it thoroughly to ensure all the relay switching works before connecting the inverter and mains wires to the relays. Theremin transistor base voltage is too low I am building your Theremin Synthesiser Mk3 (January 2018 issue; siliconchip.au/Article/10931) from Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed siliconchip.com.au Australia's electronics magazine June 2023  109 a Jaycar kit (KC5537), but have hit a stumbling block. All the voltages check out bar TP8 – I’m getting 0V instead of the 0.6V specified. No sound is coming from the speaker, even though I can hear a click when power is applied to the board. I checked the connections of Q3 (BC547) and the polarity of the 220μF capacitor is correct. Do you have any suggestions? Could it be a faulty transistor? The base and collector have correct voltage readings. (N. W., Motueka, New Zealand) ● The biasing for Q3 is set by the 100kW and 560kW resistors at the base, connected across the 9V supply. The voltage at Q3’s base should be about 1.36V. Then, with the voltage drop across the base-emitter junction, the emitter (TP8) voltage should be around 0.6V. You have stated that Q3 is the correct type, orientated correctly, and with the right base and collector voltages, so we can rule out a mistake there or problems with its base biasing arrangement. Check the value of the resistor at Q3’s emitter (1kW) and the collector (10kW) and for connections through to the PCB. If the problem persists, remove the 220μF capacitor. If the voltage then is correct, the capacitor is acting as a short circuit. Otherwise, the transistor could be faulty. Recalibrating a nonlinear vehicle fuel gauge Like many others heading towards or arriving at retirement, I purchased a 4×4 vehicle so that I could travel to remote and isolated parts of Australia, specifically the Northern Goldfields and Pilbara parts of WA. I had a long-range tank installed to increase its range, taking the total fuel capacity from 75L to 145L. The replacement tank fits into the same location as the original tank and reuses the original fuel tank sender. The new tank more ‘efficiently’ uses the space under the vehicle to store substantially more fuel. One annoying drawback is that the fuel tank gauge is no longer very useful. It still reads full when the tank is full and empty when the tank is empty. However, the journey between the two is not the same as with the original tank, as the two tanks are substantially different shapes. 110 Silicon Chip I understand that the sender unit in the tank is a simple variable resistor and that, as the tank empties, the fuel float attached to the sender falls, altering the sender’s resistance. The fuel tank gauge (or sender) is calibrated so that X Ohms represents Y% of capacity. This is unlikely to be a linear relationship. Can an Arduino (or similar) be used to sense the sender’s resistance and then, depending on that resistance, set a resistance on a digital potentiometer to ‘correct’ the fuel gauge? It would need to be connected inline between the car’s existing sender and its wiring loom. The biggest hassle is probably emptying the tank completely so I can refill it in steps to calculate the required function to give a linear fuel gauge. Thanks for a terrific magazine. (W. H., Mount Pleasant, WA) ● It is possible to calibrate a fuel sender by intercepting the signal and producing a corrected value. The engine management computer or instrument computer typically receives a voltage between 0V and 5V from the fuel sender. While a resistance, the sender usually acts as a potentiometer across a regulated 5V supply to produce this signal. The voltage indicates the fuel level. It is still necessary to adjust the float to cover the entire fuel level range, but as you say that your gauge correctly reads empty and full, it seems that is already the case. The full voltage range may not be 0-5V but could be something like 0.45-4.5V from full to empty. Our Automotive Sensor Modifier (December 2017 issue; siliconchip.au/ Article/10451) could be used to recalibrate your gauge as long as we are correct that it provides a voltage signal to the cluster. We can supply the PCB and programmed PIC for that project. You could instead use an Arduino to receive the fuel sender voltage and produce a compensated output. You would feed the signal from the sender to one of its analog inputs and then use a PWM output to produce the compensated output, passing it through an RC low-pass filter with a long time constant (seconds) to generate a voltage between 0V and 5V. You would need to write the software to make the readings, produce the PWM output and provide the mapping function. Using our pre-existing Australia's electronics magazine Automotive Sensor Modifier design would avoid the need to do that. Are Super Clock parts available? Can I still get all the parts for the Super Clock (July 2016 & July 2018; siliconchip.au/Article/11137), including the box and DS3231 clock/calendar IC? (R. M., Melville, WA) ● Yes, you can still get all the parts to build it. The Super Clock hardware is basically just the Micromite LCD BackPack, and all the BackPack kits (V1, V2 & V3) are still available. The V2 kit is suggested for this project: siliconchip.au/Shop/20/4237 (if you choose the right option, we’ll supply it pre-programmed for the Super Clock). The DS3231 modules are also still available: siliconchip.au/ Shop/7/3491 Jacob’s Ladder Mk3 queries I am building the Mk3 Jacob’s Ladder (February 2013; siliconchip. au/Article/2369) from a Jaycar kit (KC5520). Page 65 describes mounting a Commodore ignition coil to the metal lid of the kit’s enclosure using two metal M3 bolts that pass through the metal lid, soft drink bottle caps and then the coil itself. It also states not to use metal caps. Why are the plastic caps there? As there is a metal bolt going through them, between the coil and metal lid, they don’t provide any more electrical isolation than if the coil was bolted to the lid directly. That would be a much neater solution, as the box lid could have holes drilled to mount the coil and separate holes drilled for the coil connections, which would be kept internal along with the fuse. Also, you would only need two wires going into the metal box, +12V and GND, giving a much cleaner final appearance! The mounting bolts are still at ground potential, so the result shouldn’t be any different from the PET plastic cap solution. What is the risk of running it from a mains 12V power supply? I’m guessing there’s a remote possibility of the HT coil output getting back into the PSU and breaching the isolation in the PSU, thus ending up with mains on the HT output as well. continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com Lazer Security PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au For Quality That Counts... QUALITY COMPONENTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au FOR SALE OATLEY ELECTRONICS www.oatleyelectronics.com MAY SPECIALS, search for "ITXX" on our website: * MEAN WELL Power Supply 15-20V, 7.5A for $39 (IT134) * 12V-10W Lamp Package Four 12V-10W pure white LED lamps, four sockets with ceramic inlays plus two driver kits for $56 (IT152) * Geiger Counter Kit Military case plus a Geiger module for $90 (IT163) We will quote you a low shipping rate, address and potential order required. www.oatleyelectronics.com branko<at>oatleyelectronics.com Phone: 0428600036 ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have been sold. See photos (recently updated): siliconchip.au/link/abl3 Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine June 2023  111 Thanks for your time. I really enjoyed making this kit some 30 years after I built my first Jacob’s ladder from Oatley Electronics (it used a blue CRT flyback transformer). I am still having fun to this day. (M. A., via email) ● We think Leo specified raising the coil from the metal lid using plastic drink bottle tops to provide distance from the case, preventing the high voltage from the high tension output from arcing back to the case. However, you have a point that the mounting screw contacts the case and is quite close to the output terminals. Ideally, that screw should be plastic or at least shorter. You could run the coil wiring up through holes in the lid instead of being looped around from the side of the box. Suitable cable glands or grommets would be required for the cable to pass through the enclosure lid. As for operating from a mains power supply, the 12V supply will have a lot of high voltage spikes imposed upon the DC level that will likely damage your power supply. Also, any arcing from the Jacobs ladder to the supply can severely damage the power supply circuitry, which is why we do not recommend powering the Jacob’s ladder with anything except a 12V battery. Building the original Wideband unit kit I noticed that Jaycar still has Wideband Fuel Mixture Controller Kits (KC5486), but only via their website. The actual sensor can be picked up for around $40. I believe I would need the other kit, KC5485, to use the KC5486 kit. KC5485 is the display part of the system that gives you the information used to adjust the mixture in the carburettor to get the correct air:fuel ratio. I want to build both kits and connect the sensor in a tuning scenario for my 1960s, 1970s and 1980s A and A+ engines. Are all the bits to build the KC5485 kit still available, or can I get anything else to plug into the KC5486 to make it all work? Back in the day, I built many of your kits. I also once worked for George Brown and Co selling electronics at Parramatta Rd, Camperdown in Sydney. (S. C., Glenwood, Qld) Advertising Index Altronics.................................33-36 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar................... IFC, 9, 12-13, 25, Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 7 Mouser Electronics....................... 4 Oatley Electronics..................... 111 Silicon Chip PDFs on USB....... 109 Silicon Chip Shop............ 104-105 Silicon Chip Subscriptions........ 37 Silicon Chip Test Tweezers..... 107 The Loudspeaker Kit.com............ 6 Tronixlabs.................................. 111 Wagner Electronics..................... 11 112 Silicon Chip Notes and Errata ..................................94-95, 99, 101 ● You can still build the original Wideband unit we designed in 2009 (siliconchip.au/Series/41), which the Jaycar kit is based on. It uses the older (but still available) Bosch LSU 4.2 wideband sensor. However, you might want to look at our new Wideband Fuel Mixture Display (WFMD) that uses the newer LSU 4.9 sensor, that started in the April 2023 issue (siliconchip.au/ Series/398), and finishes in this issue. It has other advantages: the controller is more compact, with extra features like Bluetooth connectivity. The Hand Controller is not required for the new design. We also have a short-form kit for building it. If you still want to build the 2009 design, you need the PCB and programmed microcontroller for the Display Unit. While this display PCB is from a later article, it is compatible with the 2009 design: siliconchip.au/ Shop/8/666 The programmed microcontroller is here: siliconchip.au/Shop/9/1161 Jaycar still sells the 7-segment displays (ZD1857), and you should be able to source the most of the other SC parts from Jaycar. Automated Test Bench Swiss Army Knife, April 2023: 1. the lid cutting diagram, Fig.2 on p64, has the vertical location of the rectangular cut-out too low. The top of the cut-out should be in line with the centres of the upper holes marked “A”, not 5mm below that line. While not critical, it could also be moved 1mm to the right. 2. In the production of the original (Rev A) PCBs, one row of pins (20 to 38) on the ESP32 socket was reversed. Rev B boards are not affected. Rewiring pins 20-38 of the socket is the most straightforward means of rectifying the problem. Please contact us for instructions if you have one of the original PCBs Advanced SMD Test Tweezers, February & March 2023: the Fig.1 circuit diagram (p46, February) labels pins 24 and 25 of IC1 as AN11 and AN10 instead of AN7 and AN6. AM-FM DDS Signal Generator, May 2022: the gate bias for Mosfet Q1 is fixed at 1.5V. Since the threshold of Q1 can range from 1.0V to 2.5V, that might not suit all 2N7002 devices. If there is no output from IC3, the bias might be too low, in which case the 3.3kW resistor can be changed to 4.7kW (1.8V) or 6.2kW (2.0V). If there is output from IC3, but the modulation is weak, the bias might be too high, in which case the 3.3kW resistor can be changed to 1.8kW (1.05V). Advanced GPS Computer, June and July 2021: the circuit diagram (Fig.1, p27, June) and overlay diagram (Fig.2, p78, July) label the data line from the GPS module as RX. It was not mentioned explicitly in the text that this should connect to the TX wire of the GPS module. For the suggested module, the pins/wires labelled E (yellow), G (black), T (blue) and V (red) go to the GPS1 pads EN, G, RX and 5V on the PCB, respectively. The other two are not needed and can be soldered to the remaining GPS1 pads. Next Issue: the July 2023 issue is due on sale in newsagents by Thursday, June 29th. Expect postal delivery of subscription copies in Australia between June 28th and July 14th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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