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MAY 2024 ISSN 1030-2662 05 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST Computerised Traffic Management 10Mhz Frequency Divider DDS Function Generator The Formula 1 Power Unit Three Mini Projects Fan Speed Controller Mk2 RTV&H Oscilloscope Project; Page 33 Starting on page 60 Project; Page 40 Project; Page 70 Feature; Page 56 Vintage Electronics; Page 96 Make amazing projects with our microcontrollers & mini computers. EXPANDABLE WITH SHIELDS, SENSORS & MODULES We have an incredible line-up of micros for beginners, hobbyists and professionals. 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No rain checks. Savings on Original RRP (ORRP). ONLY 139 $ RASPBERRY PI 4B MICROPROCESSOR XC9100 1800 022 888 Contents Vol.37, No.05 May 2024 14 Traffic Management Page 40 Australia is a world leader in computerised traffic management systems, such as variable speed limits, lane direction changes, traffic lights etc. This article explains how they make sure you aren’t stuck in traffic forever! By Dr David Maddison, VK3DSM Computerised systems 56 The 2024 Formula 1 Power Unit Formula 1 (F1) engines are powerhouses despite needing to be very compact. Current F1 engines are hybrid designs that can generate over 750kW from just 1.6 litres of displacement. So how do these engines work? By Brandon Speedie Hybrid engines 96 RTV&H Calibrated Oscilloscope WiFi DDS Function Generator The Formula 1 Power Unit Page 56 This oscilloscope was designed by Jim Rowe and published in the JuneOctober 1963 issues of Radio, TV & Hobbies magazine. It’s a brilliant circuit that needed just one minor adjustment. By Ian Batty Vintage electronics 33 Compact Frequency Divider This project converts a 10MHz frequency reference (such as from an oscilloscope) down to 1MHz or 1Hz square wave signals with a 50Ω or 75Ω output impedance. The 1Hz signal can be used as a 1PPS clock source. By Nicholas Vinen Test equipment project Image Source: Jay Hirano Photography/Shutterstock.com Jaycar Mini Projects 40 WiFi DDS Function Generator, Pt1 This flexible and easy-to-build Function Generator is a staple on test benches. It provides two wide-range, low distortion outputs and can be controlled from its touchscreen or remotely via a WiFi connection. By Richard Palmer Test equipment project 60 Jaycar-sponsored Mini Projects This month’s set of Mini Projects include: a Symbol USB Keyboard for typing special characters; a Thermal Fan Controller; and a Wired Infrared Remote Extender. Each project is designed so that anyone can build it. By Tim Blythman Mini projects 70 Fan Speed Controller Mk2 Our updated, quiet Fan Speed Controller is suited for ceiling, pedestal and box fans (any using a 230V AC shaded-pole motor). It provides full control over the motor speed and is rated up to 80W. By John Clarke Speed controller project 80 Skill Tester 9000, Part 2 This retro game is a fun and educational project based on the “buzz wire” game but with some modern twists. The construction covered here is divided into sections to suit beginners and pros. By Phil Prosser Game project Page 60 2 Editorial Viewpoint 5 Mailbag 55 Subscriptions 86 Serviceman’s Log 92 Circuit Notebook 106 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index 1. DSB/AM phase-shift modulator 2. Replacement supply for BWD scope 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): $70 12 issues (1 year): $127.50 24 issues (2 years): $240 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 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 Our new Mini Projects Starting with this issue, we have a new section for the magazine: Mini Projects, sponsored by Jaycar Electronics. You can think of this as somewhere between Circuit Notebook and our regular projects. The idea is that they will be simple, coming in at 2-3 pages each, with two or three in each issue. They are designs that relative beginners should be able to understand and build, using parts that can be easily obtained at your local Jaycar store and assembled in a few hours at most. Unlike in the Circuit Notebook column, which consists mainly of contributed circuits, we have built and tested these designs. The articles include a full list of parts, some photos, typically a circuit or wiring diagram, plus links to software and source code when required. They won’t need a custom PCB, instead using a breadboard or protoboard if more than a handful of components are involved. Due to the shorter article length, we’ll likely leave some of the finer details to the reader/constructor. Given that the circuits will generally be pretty straightforward, that should not pose any obstacles to building them. We have wanted to present simpler projects for a while now, but there were a few roadblocks. For a start, many of the simple things you can build with a handful of parts have already been presented in the past, either in earlier issues of Silicon Chip or in other magazines like Electronics Australia. We didn’t want to publish too many articles similar to existing ones as it seems lazy. Also, many ideas that start simple (or seem simple initially) increase in complexity by the time they are finished. So even when we have planned to have more basic constructional articles in the past, it hasn’t always panned out that way. This new column should satisfy the demand for more straightforward and educational projects. One of the great things about these new articles is that they all use off-the-shelf parts. You can go from reading the article to buying the parts, assembling and testing one of the designs in a few hours! The Mini Projects will not displace our usual projects, feature articles, and other columns, at least most of the time. We still plan to run four projects in most issues, along with two or three Mini Projects, for a total of 6-7 projects. We see this as a significant benefit to our readers, who will get more content thanks to Jaycar’s support! I can’t rule out the possibility that we will occasionally have to hold over one other article (eg, a smaller project) to be able to fit the extra Mini Projects. I don’t expect that to happen too often, but it may occasionally occur, depending on factors like article lengths. Regardless, we will still have more content than before on average. You will not be surprised to discover that these articles will mainly use parts sold by Jaycar. That doesn’t mean you are locked into shopping there; those products will be available elsewhere, and many readers may already have most of them in their collections. (Obviously, Jaycar would like you to be their customer, but we can’t twist your arm...) Still, Jaycar has indicated that they may start offering discounted packages of the parts required for specific Mini Projects. If that happens (I can’t promise it will), we’ll have the details in those articles. To make it easier to find software and other items relating to the Mini Projects, we are allocating them numbers. However, note that they might not be published in the same order they were produced. For example, in this issue we have three Jaycar/Silicon Chip Mini Projects: JMP001, JMP003 & JMP004. There is a JMP002 but it will appear in a future issue. by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au Ensure your products are 100% authentic Mouser was the first SAE AS6496 accredited distributor Widest selection of electronic components in stock™ au.mouser.com/authentic-products 03 9253 9999 | 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”. More information on vintage disk drives I read with interest the articles on Data Storage Systems in the February & March 2024 issues (siliconchip. au/Series/411). A minor correction: the Model 1316 disk pack for the IBM Model 1311 disk drive has six platters, not five. The top and bottom surfaces were not used but data was stored on the other 10 surfaces. This allowed the use of five identical access arms. Later removable disk packs had 11 platters with 20 recording surfaces. It was mentioned that using helium is a recent practical development. I believe the ICL drum storage model 1964 was helium-filled to 2½ atmospheres. I worked for the Caulfield Institute of Technology in the early 1970s; they had an ICL 1904A computer with drum storage. Computers in those days had regular maintenance and I believe the engineers checked the helium pressure in the drum and added some if needed. However, I have been unable to find documentary evidence of that. Alan Cashin, Islington, NSW. More reports of SSD slowdowns Your editorial on SSDs in the March issue was most timely. I have been using a WD Blue 500GB SSD as the C: drive on my desktop. It has recently been loading apps with inordinately long delays. For example, “Everything” takes 18 seconds to load. Cloning the C: drive to a new SSD has restored things to normal. Thanks for a great magazine. Geoff Champion, Mount Dandenong, Vic. 25-year-old disks are still operational Thanks for publishing my letter on various topics in the March edition (it just arrived today). I hope it was of interest to your readers. I enjoyed Dr David Maddison’s article on disk drives, including SSDs. I still occasionally use 5¼-inch floppy disks (photo attached). Although they must be at least 25 years old by now, so far, I haven’t been caught out with any data loss – quite remarkable! Thanks for a great mag. Christopher Ross, Tuebingen, Germany. siliconchip.com.au Talk about a disk head crash! Thank you for your article on Computer Memory Systems; it brought back some memories. I worked at a large Queensland Brewery (XXXX) and we had a Honeywell 2000 Process computer system with a large hard drive about the size of a small desk, weighing about 500kg. It had a removable 14-inch (355mm) Winchester Disk Pack with five 50MB disks and a large solenoid coil for the head positioning system. This was in the late 1970s or early 1980s. I received a call from Ok Tedi Mine in New Guinea. They had a problem: their system had fallen over, and Honeywell had quoted them about $70,000 to fix it! He was inquiring if we had any backup Disk Packs he could borrow to get his system running again. I was unable to help as the system BIOS and data were different. After further discussion, I found out they had an earthquake, and the whole drive system cabinet fell over. They duly stood it up and inserted the Disk Pack into the machine, but it failed, which you would expect with floating heads and earthquake damage. It would have scored the disks. So they tried the next one, and so on until they had used all backups. They then realized they had a big problem! I think Honeywell quoted low in this instance, considering that a helicopter was required to access the remote site. Philip Tomlinson, New Farm, Qld. Advice on using RCDs with inverters I’ve just finished reading the latest issue of Silicon Chip and would like to add some comments to Dr Hugo Holden’s letter on RCDs and battery inverters (Mailbag, March 2024, page 8). A couple of years ago, I fitted a 12V lithium-ion battery, charger and inverter to supply 230V AC for a laptop and other equipment to my daughter’s enclosed ute for work use. I considered the possibility of faulty equipment posing a shock risk, so I fitted a standard 30mA RCD and a regular twin 10A GPO. I ‘earthed’ one side of the inverter output to the vehicle’s metal canopy and fed it to both the Earth and Neutral terminals of the GPO, with the other output wire to the switched Active terminal of the GPO. The battery and inverter negative terminal connect to the vehicle chassis. The RCD tripped when tested by connecting an 8.2kW resistor from Active to the vehicle body (drawing a nominal 28mA RMS). This setup is similar to the standard domestic mains supply where the Neutral and Earth are bonded at the N-E link in the switchboard before connection to the switchboard RCD. Andrew Fraser, Para Hills, SA. Australia's electronics magazine May 2024  5 Frustration over bad digital TV reception I was reading the comments on TV reception in the latest issue and thought I would mention the problems we have here. A while back, we had all the channels with occasional corruption, but in more recent times, this situation has become a lot worse. A few months ago, Channel 7 was almost always corrupted throughout the day or not even on air at all. It would come back a bit before 7pm and was mostly OK for recording programs from that time until the next day. This situation has been recently resolved, with Channel 7 now giving good reception again. We used to get all the ABC channels. However, starting a few months ago, all the ABC channels have been corrupted all the time. Channel 10’s channels sometimes have corruption during the day but are fine at night. Channel 9’s channels are usually fine during the day but sometimes have corruption at night. SBS’s channels were off air at about the same time as Channel 7’s channels were, or if they were on air, they were severely corrupted. This situation has improved recently. I tried re-tuning the channels several times, but in most cases, it made no difference. We never had any of these problems with the old analog TV transmissions; at worst, the reception was a bit snowy sometimes. We replaced our two TV aerials with digital types when Digital TV started. You’d think that by now, they would know how to transmit digital TV signals correctly. So much for digital TV supposedly being better than analog TV. Bruce Pierson, Dundathu, Qld. Solar panels generate plenty of power We recently moved from Sydney to Queensland to retire. As sometimes happens in this case, we had some spare cash and decided to invest in a medium-sized solar power system to see if we could be mostly self-sufficient. We now have 10kW of solar panels, an 8kW hybrid inverter and a 19kWh LiFePO4 battery stack. I am pleased to say that so far, we have not used any power from the grid in spite of rather cloudy days. There was even a blackout last week that affected more than 50,000 homes for several hours and we did not notice it! We run a pool with salt chlorination for about eight hours a day and charge our electric car. The only change in habits is charging the car mostly during the day rather than overnight. With all the discussions about nuclear power and the truly astronomical cost, one wonders if it would be feasible to pay for ‘micro-grids’ all over the country, and just use the big nuclear fusion thing in the sky at a similar cost. Horst Leykam, Barmaryee, Qld. Suggestions for better TV reception It appears that G.B.’s existing antenna is in very poor condition (Ask Silicon Chip, April 2024, p99). If he types his street address into https://myswitch.­ digitalready.gov.au/, he will see that, if he is in the centre of Wamboin, he is in a good signal area. The profile graph shows few obstructions for that location. The best antenna for strong, vertically polarised signals is a phased array. A phased array mounted for vertical polarisation, shown at siliconchip.au/link/abuc will reject reflected signals from 6 Silicon Chip metal roofs on either side of the antenna, which can otherwise make reception unreliable. For horizontally polarised signals, a horizontally mounted Yagi-Uda antenna will reject signals from the sides similarly. Alan Hughes, Hamersley, WA. Solid-state drives suffer from ‘read disturb’ In reading “Data Storage Systems”, especially the “My experience with the longevity of SD cards” panel, and the editorial in the same (March) issue, I think I can help you understand some of these problems a bit better. NAND flash is subject to a phenomenon called ‘read disturb’. It is caused by bits flipping their state when the block in which these bits live is predominately ‘read-only’. It is explained in detail in the PDF available from: siliconchip.au/link/abub This can occur after as few as 20,000 reads, but that is not a fixed amount. In one test I performed with identical cards, one failed after 60,000 reads, while another did not fail after 600 million reads! At the 2015 Flash Memory Summit, one respected presenter urged that “Read disturb tolerance specifications must be documented in supplier flash component data sheets.” While that may now be the case, these documents are not generally in the public domain, and the information is not echoed in the ‘built up’ memory device documents. I tried getting one manufacturer to admit to a read-­disturb problem. First, I had to escalate several times to get to a support person who even knew what read-disturb was. Then I was abused because, in the support person’s view, “20,000 reads without a write” was an invalid expectation for a consumer-grade product and that we should be using their industrial-grade products. Personally, I think that a failure after 20,000 reads means the device is not fit for purpose. I’m not sure at what point it becomes fit for purpose, but surely one should be able to rely on a ‘backup’ in a defined way. Note that ‘industrial grade’ products do not necessarily include read disturb protection. When you purchase an industrial-grade product, you nominate what features you require and you will be quoted a price for a card with those features. Other features you can get include ECC (error correction code), wear levelling, smart functions, bad block management, pseudo-SLC (single level cell), data duplication, embedded mode, read refresh and more. Some of those features may be present in consumer-grade products; for example, wear levelling must be present in some form on all SSDs, or they would fail in a fairly short period. Still, in general, you only get those features if you pay extra for them. Simply inserting a card periodically will achieve nothing. While some brands of industrial cards do ‘scan refresh’ in the background, most do not. The ones that do have shocking normal ‘performance’, which probably explains why that feature is so rare. We have been able to disturb cards with read-disturb protection. In most cases, the manufacturer puts this down to ‘read patterns’ and, after observing the pattern, releases a new software revision for their industrial cards. We have also been able to disturb SLC cards, which the manufacturer pretty much said was impossible. It would appear that all the mechanisms are still not fully understood. Australia's electronics magazine siliconchip.com.au Introducing ATEM Mini Pro The compact television studio that lets you create presentation videos and live streams! Now you don’t need to use a webcam for important presentations or workshops. ATEM Mini is a tiny video switcher that’s similar to the professional gear broadcasters use to create television shows! Simply plug in multiple cameras and a computer for your slides, then cut between them at the push of a button! It even has a built in streaming engine for live streaming to YouTube! Live Stream to a Global Audience! Easy to Learn and Use! Includes Free ATEM Software Control Panel There’s never been a solution that’s professional but also easy to use. Simply press ATEM Mini is a full broadcast television switcher, so it has hidden power that’s any of the input buttons on the front panel to cut between video sources. You can unlocked using the free ATEM Software Control app. This means if you want to select from exciting transitions such as dissolve, or more dramatic effects such go further, you can start using features such as chroma keying for green screens, as dip to color, DVE squeeze and DVE push. You can even add a DVE for picture media players for graphics and the multiview for monitoring all cameras on a in picture effects with customized graphics. single monitor. There’s even a professional audio mixer! Use Any Software that Supports a USB Webcam! You can use any video software with ATEM Mini Pro because the USB connection will emulate a webcam! That guarantees full compatibility with any video software and in full resolution 1080HD quality. Imagine giving a presentation on your latest research from a laboratory to software such as Zoom, Microsoft Teams, ATEM Mini Pro has a built in hardware streaming engine for live streaming to a global audience! That means you can live stream lectures or educational workshops direct to scientists all over the world in better video quality with smoother motion. Streaming uses the Ethernet connection to the internet, or you can even connect a smartphone to use mobile data! ATEM Mini Pro $495 Skype or WebEx! www.blackmagicdesign.com/au Learn More! You also see multiple posts in various small systems forums about the need to replace microSD boot disks regularly because they’ll wear out in a couple of months. They certainly don’t wear out that quickly, but they can become read-disturbed in a few months. A quick check for a disturbed file, assuming you have isolated it to a single file, is to copy the file onto your hard drive, remove the suspect media and reinsert it (to ensure it is being read from the media and is not a cached copy), then copy it again using a new name. Now perform a binary comparison of the two copies of the file. If you get random bit errors, you are seeing read disturb in action. Mark van der Eynden, Mount Waverley, Vic. How to avoid being locked into subscriptions I note the difficulties mentioned in your January editorial regarding cancelling subscriptions on shonky sites; in particular, your experiences trying to cancel a subscription to a VPN service. I am probably a bit more ‘street-wise’ than you, having run my factory in Shenzhen, China, for seven years and now in Taiwan for over four years. I have seen it all from these characters! I needed a VPN recently and was fully aware of the near impossibility of cancelling such services, so I formulated a plan. I paid for only one month with Proton VPN, as my investigations revealed they could provide the best results for my purpose. Here is how you can be one step ahead of them! I paid using PayPal and then, once I had paid, went into my PayPal account and looked deeply. I found where Proton VPN had automatically inserted a ‘pay this amount every month’ deep in my PayPal account. I cancelled this ‘repeat payment authorisation’, logged out and back into my PayPal account and double-checked that it was gone (it was). I then waited for the end of the month to see what would happen. I received a renewal advice email from Proton about two days after the month expired. About seven days after its expiry, the service stopped working. Success! I had beaten their uncancellable service runaround and saved myself all the associated aggro with credit card companies! This might be of use to you in the future as long as the VPN service doesn’t wise up and stop accepting PayPal! Cheers, and keep up the excellent work. I possibly wouldn’t have renewed my subscription if it was only available as a hard copy, as getting the physical mag to me here in Taiwan is difficult. For your information, we are building pinball machines in Taiwan for export worldwide. All are 100% designed and built in my factory, including all the electronics. Our current machine is “This is Spinal Tap Pinball”. Mike Kalinowski, Homepin Taiwan Company Limited. How about Vintage Computer articles? I thought I would respond to the question you posed in the March 2024 editorial regarding the name of the “Vintage Radio” column. 8 Silicon Chip I turned 50 a year or so ago and have been reading Silicon Chip for over 20 years. In that time, I must confess to pretty much never reading the Vintage Radio section whilst avidly reading almost every other aspect of the magazine. Its presence has never bothered me, but I’ve always viewed its content as ‘before my time’. I grew up in the late 1970s and 1980s, so I was inevitably drawn to the home computers of that period. I suppose 8-bit computers were the radios of my era. So, I would welcome dropping “Radio” from the name of this section and also further broadening the scope of the material presented. I recall you published an article some years back on restoring an Apple Macintosh – I would love to see more articles like that. Also, it would be great to see pieces on modern hardware for vintage machines. For example: The video enhancement for the Commodore 64 to produce pin-sharp component output (https://github.com/ c0pperdragon/C64-Video-Enhancement). The stunning RGBtoHDMI project (https://github.com/ hoglet67/RGBtoHDMI), which uses a Raspberry Pi to convert the video signals of a vast number of vintage computers into perfect HDMI. The Harlequin remake of Sinclair’s ZX Spectrum, based on Chris Smith’s reverse-engineering of this machine’s custom ULA (https://github.com/DonSuperfo/Superfo-­ Harlequin-128). Joe Branton, Umina Beach, NSW. Comment: we suspect many people who read the current Vintage column would not be interested in Vintage Computers, but we could publish separate articles on that subject. It would depend on experts in the field being willing to write such articles. We have published a few Vintage Computer articles over the last few years. For example, Dr Hugo Holden’s articles on the Cromemco Dazzler (September 2021; siliconchip. au/Article/15023), Arcade Pong (June 2021; siliconchip. au/Article/14884) and the Matrox ALT-256/512 video cards (October & November 2020; siliconchip.au/Series/352). He is one of the few people we know who is into both Vintage Radio/TV and Vintage Computers! We also published a CGA to VGA converter project in the February 2015 issue (siliconchip.au/Article/8306). We would welcome more article submissions on the topic, provided they are sufficiently interesting. More on DC supply switches Reading the letter on page 5 of the March 2024 issue titled “The reason DC mains switches were so loud”, I feel the story has only been half told. My experience today is with 12V solar, but it was once with the 32V DC domestic supply as my father’s assistant (in my mind, anyway). DC has a tendency to melt the metal of the switch contracts as they open because the current density involved can reach thousands of amps per square centimetre due to the very small area involved. This molten metal then allows the current to continue to flow even though the contacts have opened. A DC arc will continue until the contacts are far enough apart for the arc to be extinguished (which depends on the voltage), or some other means of extinguishing the arc is used. Most domestic switches intended for 32V DC use have Australia's electronics magazine siliconchip.com.au Discover New Technologies in Electronics and Hi-Tech Manufacturing See, test and compare the latest technology, products and turnkey solutions for your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference features seminars and workshops from international experts on the latest innovations and solutions for design and assembly. Details at www.smcba.asn.au In Association with Supporting Publication Organised by contacts about 10mm apart. The circuit is made or broken by very rapidly dropping a metal bridge across the contacts or removing it to an off position about 15mm clear. That’s the reason for the loud click; the bridge moves rapidly when the switch knob builds up enough spring pressure. Such a mechanism is not necessary with AC since, due to the voltage swinging from negative to positive at 50Hz, there is no voltage across the contacts 100 times per second. Thus, an arc cannot be sustained for more than about 10ms. I had an interesting job once repairing the emergency lights in a theatre. Somewhere along the line, a licensed electrician ‘had a go’ and came across something he had never seen. The system was 24V DC (using two 12V batteries), with a magnet positioned to drag the arc off the contacts, thus allowing the lights to be switched off after the magnetic switch closed if the mains voltage failed. This guy knew he didn’t understand DC, so he took the DC out of the circuit and operated the lights off the battery charger. That was highly illegal because if the power failed, there was no light for people to find their way out of the theatre! I repositioned the magnet and repaired the damage it had done to the 50A battery charger, and all was well. Graeme Burgin, Ararat, Vic. Current transformers can produce high voltages Regarding the Circuits Notebook entry on the Isolated Mains Voltage and Current monitor published in the February issue (siliconchip.au/Article/16123), there should have been a warning that the current transformer (CT) should never have current flowing in its primary without a load on its secondary. Open-circuited CTs are notorious for developing lethally high voltages under these circumstances. For this reason, CTs used in industry are supplied with a shorting bar that is only lifted once the secondary circuit has been thoroughly tested and connected. In most older installations, one end of the shorting bar remains connected so that the other end can be swung back to the connected position as a precursor to work being carried out on the secondary circuit. In more modern installations, there may be a test link arrangement with a sliding shorting bar engaging before the secondary can be opened for testing or servicing. In the circuit described in the article, the secondary voltage is limited by the 100W resistor across the CT output. Still, the CT output is potentially dangerous if this resistor ever fails or is lifted. Therefore, caution should be exercised with the resistor rating, and it must remain solidly connected. Caution should also be exercised when connecting instruments to the secondary socket. Ron, via email. Comment: the designer of that circuit, Mark Hallinan, responds: current transformers do indeed generate dangerously high voltages when disconnected from their burden resistors. However, in industrial installations, the burden resistance is often very remote from the current transformer, with multiple connections in between that may go open-circuit at some stage. As you write, this will present dangerous voltages on otherwise ‘safe’ low-voltage circuits. In the case of the Mains Monitor, the burden resistor and 10 Silicon Chip Australia's electronics magazine siliconchip.com.au A selection of our best selling soldering irons and accessories at great Jaycar value! 25W Soldering Iron TS1465 $22.95 Build, repair or service with our Soldering Solutions. We stock a GREAT RANGE of gas and electric soldering irons, solder, service aids and workbench essentials. 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The burden resistor is soldered directly across the rear terminals of the BNC connector, so an open circuit in the wiring to the transformer cannot present a voltage risk to the monitoring equipment. Even with 10A flowing in the primary circuit, the 100W resistor will only dissipate 10mW, so virtually any resistor should have sufficient ratings. Constructors willing to take on mains projects are likely capable of securely soldering a resistor to a BNC connector. Still, your comments remain valid, and the output should be checked under static and load conditions before pressing the unit into service. The mains waveform is often very distorted I enjoyed the February 2024 issue, particularly the Mains Power-Up Sequencer project (siliconchip.au/Series/412). The scope graphs on page 49 attracted my attention, as they show the same flattened peaks I am seeing on my homebuilt energy meter (the green curve in the screenshot below). I first noticed the flat tops when I commissioned my prototype energy meter with a measuring circuit based on the one published in your August 2016 issue (siliconchip.au/ Series/302). My first thought was that there was a problem with the design, but I eventually measured the mains supply with an oscilloscope to find that the display on my power meter was correct after all. I tried to find a ‘clean’ mains supply to confirm my energy meter was working correctly, so I visited a good friend of mine who is an electronics engineer and lives in an off-grid household, thinking that his inverter supply is not subject to the nasties found in the public grid. The 12 Silicon Chip result had pretty much the same flat tops I saw at my place. My friend and I surmise that the flat-top voltage distortion is due to non-linear loads, which make up the majority of power consumers these days, and seem to be strong enough to distort the grid supply. The screenshot of my energy meter also shows the current curve (blue), confirming the nature of the switch-mode type load. Please ignore the Power Factor reading in the screenshot, as the current is too low for a stable reading, so it is artificially kept at 1.00 on the display. However, the difference between the W and VA readings indicates a low PF. The scope screenshots in the February 2024 issue of Silicon Chip gave me some confidence that I’m not the only one suffering voltage distortion in the supply grid. However, Mark Hallinan in Woolloongabba shows a perfectly sinusoidal supply voltage in his mains monitor on page 44 of the same issue. The Queensland mains supply may not be as easily distorted as in Victoria and NSW. Does Queensland have more large spinning generators and, therefore, a lower supply impedance than here, where we have many large- and small-scale inverters? Erwin Bejsta, Wodonga, Vic. Comment: we think this is due to various factors such as distance from the generators, the type of loads found in the area (motors won’t lead to flat-topping, but switchmode power supplies and transformer/rectifier/capacitor supplies will) and so on. Flat topping seems very common in cities and urban areas but less common in rural areas. On X2 capacitor degradation I would like to comment on the Power-up Mains Sequencer project published in the February and March issues. The 470nF capacitor that supplies power to the electronics needs to be better than a garden-variety X2 capacitor. The problem is that poly caps across the mains degrade over time; the capacitance reduces as a function of their ‘self-healing’. A long time ago, I designed a product using X2 capacitors similarly, although they were functionally more like the 22nF cap in your design, ie, feeding zero-crossing detectors. After about a year or two on the market, the products started giving problems, which were traced to these capacitors having degraded in value. The solution was to use high-stability caps in that position. They had a higher voltage rating and actually consisted of two capacitor elements in series. We encountered no more problems after that. David Timmins, Sylvania Southgate, NSW. Comment: you are right that this is a problem, but we think it is more due to capacitor quality than type. For example, we’ve seen brand-new appliances where the X2 capacitor value has dropped dramatically, causing them to fail. Replacing it with one purchased from Jaycar, we noted that for the same capacitance and voltage rating, the new part was much larger. It has worked fine ever since. Note that we have been using X2 capacitors in this role for many years across many projects, and we haven’t had complaints about failures (although that doesn’t necessarily mean they never failed). Still, components have a limited lifetime; we expect the electrolytic capacitors to cause problems sooner than X2 capacitors, although it depends on the manufacturer and the quality of the parts in both cases. SC Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine May 2024  13 Computerised Traffic Management By Dr David Maddison, VK3DSM If you are frustrated sitting in traffic now, you may take solace in the fact that it could be far worse without computerised traffic management. Australia is a world leader in many of the traffic management systems Image source: https://unsplash.com/photos/aerial-photo-of-vehicles-on-highway-XICpU0Aulr0 described in this article. S treets and intersections with light traffic, such as suburban and country roads, generally do not require automated traffic flow control. They might instead use Give Way signs, Stop signs, or roundabouts to prevent traffic conflicts and keep traffic flowing. However, beyond a certain level of traffic flow, traffic lights are typically installed to control traffic better and prevent blockages. Contrary to popular belief, traffic lights are not always beneficial. Although traffic lights can reduce the likelihood of T-bone collisions, they can increase the likelihood of 14 Silicon Chip rear-end collisions. For example, the city of Philadelphia, USA, found that “… replacing (traffic) signals by multiway stop signs on one-way streets is associated with a reduction in crashes of approximately 24%”. Famous Dutch traffic engineer Hans Monderman said that stripping all traffic controls from a city resulted in safer roads (www.wired.com/2004/12/ traffic). I have also observed that traffic seems to flow more smoothly when a set of traffic lights is out of service. Regardless of the benefits or drawbacks of traffic lights, we are stuck with them. Given that, the best way to keep Australia's electronics magazine traffic moving is to coordinate them so drivers are not forced to stop at every intersection. There are levels of traffic management beyond that, intending to keep traffic flowing as fast and smoothly as possible across an entire road network. Examples of other traffic control strategies are variable speed limits, lane direction changes, ramp entry timings (metering), variable tolling and even changing the traffic direction of entire roads. As an example, some motorway onramps in Sydney’s North Shore change to offramps at certain times of day, depending on demand. siliconchip.com.au CNC - WATERJET CUTTING The world’s first desktop waterjet. standup. desktop. TILES Now cut anything with digital precision using high-pressure water COPPER GLASS STEEL ALUMINIUM WAZER is the first desktop water jet that cuts any hard or soft material with digital precision. 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(07) 3715 2200 PERTH Kewdale ADELAIDEY OPENING JUL 03_SC_290424 Gift SIGN-UP 305mm Y Axis Travel Z Axis Travel Go from design to cutting, fast WAZER’s web-based software WAM is fast and easy. Load your design file into WAM and prepare your cut in minutes. There is no need for a dedicated PC, WAM is compatible with Chrome, Internet Explorer, Safari, Firefox web browsers. TO WIN PRIZES & RECEIVE DISCOUNTS 305 x 460mm X Axis Travel It is important to bear in mind that, no matter how advanced any traffic management system is, if there is insufficient physical road infrastructure to suit the demand, there will still be slowdowns or stoppages. However, the severity of those problems can sometimes be reduced with good management. This doesn’t just apply to cars, motorbikes, trucks and coaches. Bad traffic flow can also impede public transport vehicles such as buses and trams, as well as bicycle riders. Modern electronic traffic management comes within the purview of ‘Intelligent Transport Systems’ (ITS). ITS uses information and communications technologies, traffic sensors and software to manage a road transportation system. Cooperative ITS (C-ITS) involves road users communicating with each other, plus local and central traffic management systems, to improve safety and efficiency. Adaptive traffic control is a means by which traffic signal timing, variable speed limits, entry onto motorways (ramp metering), lane direction changes and other techniques can be varied to optimise traffic flows according to demand. Loosely speaking, a “platoon” of vehicles (or the French version of the word, peleton) is a group of vehicles travelling together. More strictly speaking, it refers to groups of vehicles travelling very closely together as part of an intelligent transportation system, with a controlled distance between them, much like the carriages of a train. If platooning is fully automated, it allows increased capacity on a given road, reduces air resistance (lowers fuel consumption) and reduces collisions, although it may result in lesser driver attention. Adaptive cruise control (where a radar or camera is used to keep a constant distance from the vehicle in front) enables a primitive form of platooning. A major objective of traffic signal coordination or “progression” is to allow a group or platoon of cars travelling along a particular route to get a highly desirable “green wave”, passing through many consecutive intersections without stopping. A motorist’s dream... Important parameters Before covering traffic management 16 Silicon Chip methods, we should explain what traffic flow parameters need monitoring and possibly adjustment. The basic variables to be dealt with and controlled as part of any traffic management strategy are as follows: • Volume or traffic flow – the number of vehicles passing a fixed point, measured in vehicles per hour. • Speed – vehicle speed, instantaneous or average, either individually or as a stream. It is typically measured in kilometres per hour (km/h). • Concentration or density – the number of vehicles occupying a given length of road at an instant in time, measured in vehicles per kilometre or metre. • Headway – the interval between vehicles passing a fixed point, measured in seconds per vehicle. • Spacing or distance headway – the distance between vehicles passing a certain fixed point, typically measured in metres per vehicle. • Occupancy – a measure of the proportion of time vehicles are stationary at a specific point in a lane, such as over a detector loop or other sensor. It is reported as a percentage. As part of any traffic management system, a wide variety of sensors must collect data like the above, to be analysed and acted upon in real time. They can use techniques such as: • A light beam that’s broken when a vehicle passes. • An inductive loop that detects the metal of a vehicle above. • Analysis of radar returns. • Image analysis from a camera. • Observations from within the traffic stream, such as via smartphones. • Active vehicle identification, such as at tolling points. • Other methods, which we will discuss later. Traffic signals (traffic lights) The modern traffic light or signal is the most fundamental form of electronic traffic management. The first traffic signals (for horse-drawn vehicles) were installed in London in 1868. They used semaphore-style indicators; the first electric traffic lights were installed in Cleveland, Ohio in 1912. The first four-way, three-colour traffic lights were installed in Detroit, Michigan in 1920. All of those were manually controlled, but by 1922, traffic lights were Australia's electronics magazine controlled electronically by automatic timers, saving vast amounts of labour. Australia’s first traffic lights were installed in Sydney in 1933 (see siliconchip.au/link/abu2). Additional traffic lights were not installed in Australia until 1937. Computers started to be used to control traffic lights in the 1950s. In 1963, Toronto, Canada implemented a computerised traffic light system that controlled intersections across the city with communication over leased phone lines, using 1000 vehicle detectors. That system was initially responsible for 500 intersections, with the control computer able to handle 1164 intersections. However, Toronto was rapidly expanding, and the computer was running out of capacity, so the system was upgraded in the early 1980s. Also in 1963, SCATS (Sydney Coordinated Adaptive Traffic System) started controlling eight intersections in Sydney’s CBD. We’ll come back to that system later. At the most basic level, traffic signals can be either fixed-time or actuated. Fixed-time or interval-based operation means the signals operate according to a fixed sequence and timing, repeating the same sequence regardless of the number of vehicles on each road. The timing of such signals may change according to a schedule. Such signals are now rarely used in Australia. Traffic-actuated or phase-based signals rely on the input from sensors, such as an inductive loop in the road, to determine timing and sequencing and adjust their operation according to traffic demand. That is for just one set of signals for one isolated, non-­ coordinated intersection. Beyond that, sets of traffic signals at multiple locations can be coordinated to facilitate the green wave. Isolated traffic-actuated and fixedtime controls are now not generally used in Australia since the increased adoption of SCATS Master Isolated (SMI) control. A SCATS controller may be run in its regular mode, linked to a regional computer as part of a wide-area traffic control system, or in an isolated mode for single non-coordinated intersections. When running a non-­ coordinated intersection, SMI still uses SCATSstyle adaptive algorithms. siliconchip.com.au Types of traffic light sequences include: • Fixed sequence that never varies. • Tr a f f i c - a c t u a t e d s k i p p e d sequence, where some sequences are skipped if there is no traffic needing a certain sequence. • Variable sequence that uses near real-time measurement of traffic via detectors to constantly adjust timing and sequences according to demand. • Priority sequence, inserting a sequence to accommodate a train, bus or tram. • Forced sequence, determined by a master controller in a centrally-­ coordinated system. There is also emergency vehicle priority or ‘preemption’ where traffic signal phasing can be adjusted to facilitate the passage of emergency vehicles, using techniques such as: • In-vehicle transponder. • Emergency sequences activated from stations or facilities near traffic signals to clear traffic. • GPS tracking of an emergency vehicle, communicated to a central controller to implement appropriate sequences as the vehicle arrives at each intersection. • A phone call to a central traffic control office to implement appropriate sequencing along the emergency vehicle route. Traffic signal coordination If you ever get a run of green lights (green wave), it is likely the result of traffic signal coordination to time the length & duration of the green phases. This concept is called “traffic signal progression”; it is “the practice of coordinating the operations of two or more signalised intersections” – see Fig.1. The problem gets more complicated the more sets of traffic lights are to be coordinated, and even more complex when considering crosswise traffic flows. Crosswise traffic might experience increased delays in such a system. Pedestrian movements and other road users also have to be considered. Traffic signal terminology Each possible legal trajectory of traffic at an intersection is called a movement. At a basic two-way intersection, there can be 12 movements, with traffic in each approach being able to go left, right or straight ahead. A traffic signal phase is a set of traffic signal indications applying to vehicles or pedestrians, allowing simultaneous non-conflicting legal movements. For example, a phase might Offset reference point is beginning of first co-ordinated phase yellow Fig.1: traffic lights can be synchronised to avoid vehicles having to stop and go constantly, but there are limits to such synchronisation. The purple and blue lines represent the outer limits of a green wave. Original source: www.kittelson. com/ideas/pros-and-cons-of-signal-coordination/ siliconchip.com.au Australia's electronics magazine May 2024  17 Fig.2: an example of an intersection with three phases and parallel pedestrian movement. Original source: https://austroads.com.au/ (Guide to Traffic Management Part 9, page 81). Fig.3: traffic light phases (intervals). Original source: https://austroads.com.au/ (Guide to Traffic Management Part 9, page 222). Fig.4: the desired sequence of operations for a four-way intersection, which can be implemented in a Programmable Logic Controller (PLC), microcontroller or other means, or in earlier times, electromechanically with relays and timers. have north-south traffic seeing green in both directions while also allowing left turns for both sets of traffic. A particular phase in the sequence can be skipped if there is no demand for it; eg, a right turn phase could be skipped if no cars are waiting to turn. Fig.2 illustrates an intersection with three phases. Phase sequence is the order of phases in a signal cycle. These may be fixed or altered according to demand. Signal groups are sets of individual lights that share the same colour and are all activated for a particular phase. They are identified by which phase they belong to, such as the green lights associated with phases A, B or C in Fig.2. A cycle is a complete rotation through all possible phases. The cycle time is the time taken to move through all possible phases (sequences) at an intersection. An interval refers to the change from one phase to another, either the running phase interval (green) or the clearance phase interval (yellow and some red) – see Fig.3. Phase split is the proportional of cycle time a given phase is displayed. Offsets are the time relationships between green phases of successive sets of signals when the system is coordinated. Vehicle detectors may obtain information for either ‘strategic’ or ‘tactical’ purposes. Strategic information is used to compute cycle length, phase splits and signal offsets. Tactical information is used to determine the demand or duration of phases. The traffic controller Original source: https:// instrumentationtools.com/plc-based4-way-traffic-light-control-system/ 18 Silicon Chip Australia's electronics magazine The traffic signal controller is the heart of a set of traffic signals. Older ones contained relays and mechanical timers, while modern types are microprocessor-controlled and receive inputs from various sources. They generate various outputs and communicate with other controllers and central management systems. Typical traffic signal sequencing is shown in Fig.4, while the inputs, outputs and communications for a typical controller are shown in Fig.5. One Australian company making traffic controllers is Aldridge Traffic Controllers, now owned by Siemens Mobility (siliconchip.au/link/abu1). They designed and manufactured the ATSC4 Adaptive Traffic Signal siliconchip.com.au Controller (Fig.6). It can manage up to 32 signal (phase) group displays with up to 64 inputs from vehicles, pedestrians or emergency services. It can operate in standalone mode or as part of an Intelligent Transportation System such as SCATS. It can communicate via Ethernet with a local network or 4G modem, ADSL or PSTN networks, supports VC6 SCATS protocol and DSRC (Dedicated Short Range Communications, see later) and comes with advanced software. Preventing hazardous signal combinations It would be disastrous if all signals at an intersection showed green simultaneously. This can be prevented by interlocked switching and/or conflict monitoring. For example, in relay-­ Fig.5: operation of a modern traffic signal controller. Original source: https:// controlled circuits, if one signal group austroads.com.au/ (Guide to Traffic Management Part 9, page 85). shows green, the conflicting signal ◀ Fig.6: the ATSC4 Adaptive Traffic groups are forced to red. Signal Controller, which is This can be done by methods like SCATS compatible. Source: www. cutting the power to conflicting green aldridgetrafficcontrollers.com.au/ signals when one is activated. In solid-­ products/traffic-signal-controllers/ state relay controlled systems, the outatsc4 puts must be monitored to ensure safe signal groups and avoid unsafe groups, as per Fig.7. Traffic sensors It is necessary to measure the traffic flow to control traffic. There are various ways of doing that. Stationary sensors can measure traffic flow, but in other cases, the data comes from vehicles. The latter example is known as Floating Car Data (FCD). FCD can also be used by Apps like Google Maps and Waze to provide information about road hazards such as accidents, construction works, potholes etc. Automatic Number Plate Recognition (ANPR) ANPR is used for tolling and legal compliance but can also provide traffic flow data. Optical character recognition is used along with algorithms to locate the position of the number plate in an image. Bicycle and pedestrian counters Some traffic management systems include bicycle counters. Bicycles are counted using much the same technology as cars. One example at Veloway 1 in Woolloongabba, Queensland is shown on the Department of Transport’s website (siliconchip.au/link/ abu3). It uses a camera and artificial siliconchip.com.au Fig.7: safe and unsafe combinations of signals. Original source: https:// austroads.com.au/ (Guide to Traffic Management Part 9, page 88). Australia's electronics magazine May 2024  19 Fig.8: a pedestrian counting system in the City of Melbourne. Source: www.pedestrian.melbourne.vic.gov.au/#date=26-022024&sensor=RMIT14_T&time=15 intelligence (AI) to classify traffic as either pedestrians, cyclists or riders of some other device. There is a Pedestrian Counting System in the City of Melbourne (see siliconchip.au/link/abtq). It uses laser or thermal sensors to record pedestrian movements. The sensors are connected to a 4G wireless data transmission system, a central server and a visualisation system. The data can be seen with an online visualisation tool at www.pedestrian.melbourne. vic.gov.au (see Fig.8). People-counting systems are also used for measuring occupancy in places such as shopping centres, entertainment venues, libraries, government buildings and retail stores. Cameras Software can be used to analyse video streams from any source to count and classify vehicle traffic. Such cameras typically use AI and machine learning (ML). An example is shown in Fig.9. Fig.9: analysing a video stream using the Camlytics software (https://camlytics. com/). Some software does offline analysis, like this one, while others do it in real-time. Source: https://camlytics.com/solutions/car-counting Fig.10: how an inductive loop traffic sensor works. Original source: www. researchgate.net/publication/287003681 20 Silicon Chip Australia's electronics magazine Mobile phone data (FCD) Tracking mobile phone signals from car users requires no roadside or other infrastructure, and nearly all cars have at least one mobile phone on board. Privacy concerns aside, no specific permission is required to do this, as mobile phone towers already obtain such data as part of their function. Location and speed data is obtained via triangulation of the phone signal and hand-over data from tower to tower. Collecting such data from large numbers of phones enables traffic flow to be monitored (and, incidentally, pedestrian traffic). Inductive loop sensors Inductive loop traffic sensors have an insulated wire loop or loops embedded in the roadway to detect traffic – see Fig.10. You can often see where they are because the road has been cut and resealed to embed the wire. The loop is energised at 10-200kHz. It acts as a tuned circuit that changes in frequency when a mass of metal, such as a car, is nearby. This change in frequency is detected by the associated electronics and interpreted as the presence of a vehicle. One problem with such loops is that they may not register the presence of a small vehicle such as a motorcycle, scooter or bicycle. We have also seen siliconchip.com.au cases where people stop short of the sensor and never get a green light! Figs.11 & 12: the TIRTL processor (left) and transmitter (below). Source: CEOS Pty Ltd. GPS data (FCD) Some phone apps like Google Maps and Waze (now owned by Google) upload GPS data, which is used for various purposes, such as choosing optimal routes to avoid traffic. In a sense, it is ‘crowdsourced’ traffic data. Infrared sensors An example of an infrared traffic sensor is the Australian-developed TIRTL (The Infra-Red Traffic Logger) – see Figs.11 & 12. It consists of an infrared transmitter and receiver on opposite sides of the road. As vehicles interrupt the beams, it can record the number and type of vehicles, their speed and which lane they are in. The information can be logged for statistical purposes or traffic control. It can also be connected to a red light and/or speed camera to record violations, detect over-height and overlength vehicles, be used for bus lane enforcement and various other applications. Some of its operating modes are shown in Fig.13. It is a product of CEOS (www.ceos. com.au/products/tirtl/) and is used in twenty countries. Commercial sales started in 2002. Fig.13: some of the operating modes of the TIRTL. Original source: www.ceos. com.au/products/tirtl/ Piezoelectric sensors Piezoelectric material converts stress into an electric charge, which can be measured to detect a load such as a vehicle. They can detect the number of vehicles, number of axles, vehicle speed and weight. Pneumatic road tubes These familiar devices, used on a temporary basis for traffic surveys, consist of one or more rubber tubes across a road. They sense vehicles as they drive over and compress air in the tube, activating a switch in the electronics box at the side of the road. Software can determine the number of axles and speed of the vehicle, plus the number of vehicles that pass. With two tubes, the travel direction can be sensed. Radar sensors Radar sensors measure road traffic and perform tasks such as counting and classification, incident detection, wrong-way detection, ramp metering, lane blockage detection and queue siliconchip.com.au Fig.14: lane-specific forward-looking radar detection using a smartmicro device (right) compared to a side-mounted radar device (left). Australia's electronics magazine May 2024  21 Fig.15: the smartmicro-MLR MultiLane Radar detector mounted on a pole. Source: www.yunextraffic.com/ wp-content/uploads/2023/06/YunexTraffic_Smartmicro-MLR_EN.pdf length measurement, among others. Objects such as pedestrians, bicycles, motorbikes, passenger cars, transporters, short trucks and long trucks can be sensed and classified. One such device from smartmicro (www.smartmicro.com) has multiple forward-firing beams, can simultaneously detect 256 vehicles and provide lane-specific detection for up to 12 lanes with a 500m range (see Fig.14). The device (Fig.15) can also be used to trigger speed and/or red light cameras. Detecting emergency vehicles A typical “emergency vehicle preemption” system involves an emitter attached to an emergency vehicle, a detector at a traffic signal and an optical signal processor. As an emergency or other priority vehicle approaches a signal, optical emissions are detected, and the signals switch to green for the emergency vehicle. A typical installation is shown in Fig.16, as per VicRoads specification TCS 055-1-2005. VicRoads uses the Tomar STROBECOM II emitter, detector and optical signal processor (see siliconchip.au/link/abtr). Fig.16: a typical emergency vehicle preemption system. Original source: www. vicroads.vic.gov.au/-/media/files/technical-documents-new/its-specificationstcs/specification-tcs-055--emergency-vehicle-preemption.ashx adjusting speed limits, changing freeway ramp entry timing etc. Products that do this include: Australian Integrated Multimodal EcoSystem (AIMES) AIMES is described as a “worldfirst living laboratory based on the streets of Melbourne, established to test highly integrated transport technology with a goal to deliver safer, cleaner and more sustainable urban transport outcomes”. It is an experimental system by the University of Melbourne, the Victorian Department of Transport and Planning, and industry partners. It uses a mesh of individual smart sensors to track pedestrians, cyclists and traffic within a city’s transport system of intersections, tramways, bus routes and traffic signals. The goal is to achieve more efficient and productive use of transport infrastructure. It is said to be the world’s first and largest ecosystem for testing new transport management technologies, incorporating 100km of roads bounded by Lygon & Hoddle Streets and Victoria & Alexandra Parades in Melbourne. Information from such a system could be used to operate a driverless car or improve pedestrian or cyclist safety. A 2.5km test corridor along Nicholson Street in inner Melbourne with comprehensive monitoring and sensors at every intersection provides improved traffic flow and safety for all types of vehicles and traffic. The Nicholson Street intelligent corridor integrates data from existing sources such as CCTV footage, Bluetooth signals from personal devices, the Sydney Coordinated Adaptive Traffic System (SCATS), General Transit Feed Specification (GTFS) and sensors specifically installed for AIMES – see Fig.17. Vehicle re-identification (FCD) Vehicles can be detected at one location and then at another location. This enables travel time and speed to be calculated between pairs or groups of sensors. A vehicle can be sensed by the MAC address of any Bluetooth device in the car, by reading RFID serial numbers from devices such as toll tags or using number plate recognition. Traffic management systems Once traffic data is collected, it needs to be analysed and appropriate actions taken. Possible actions include altering traffic signal timings, 22 Silicon Chip Fig.17: the “Kapsch Intelligence Corridor”, featuring part of the AIMES Nicholson Street “intelligent corridor” in Melbourne. Australia's electronics magazine siliconchip.com.au Machine learning and analysis are used to process CCTV images, then the EcoTrafiX platform is used to visualise and manage sensor data. Cloudbased AI and predictive models are also used. According to Dr Neema Nassir, the system uses “machine learning models that can optimise – through millions of simulation executions – the best right-of-way allocation, or the best green traffic light time allocation for competing modes and competing volumes”. ARCADY Assessment of Roundabout Capacity and Delay from the Transport Research Laboratory, UK (https://trl.co.uk/) is used to model roundabouts and “... predict capacities, queues, delays and accident risk at roundabouts”. COMPASS This traffic management system in Ontario, Canada, uses in-road traffic sensors to measure the speed and traffic flow on freeways. The data goes to a central computer so operators can view the data and cameras. They use the McMaster algorithm to change message signs and speed limits. Kapsch EcoTrafiX This traffic visualisation and management platform (www.kapsch.net/ en) is from Austria; see Fig.18. It includes traffic signal control, adaptive traffic control, event management, traffic prediction, travel information, data fusion and more. Other Kapsch products used in Australia and NZ are toll collection systems in Melbourne, Sydney, Brisbane and Auckland using Dedicated Short-Range Communications (DSRC), video-­based detection and classification and Automatic Number Plate Recognition (ANPR); the Nicholson Street intelligent corridor and AIMES and the Eastlink tolling system in Melbourne. In Queensland, they demonstrated a Cooperative Intelligent Transport System (C-ITS) to send warning messages about road works to appropriately equipped vehicles. MASSTR Meadowlands Adaptive Signal System for Traffic Reduction (www.njsea. com/transportation/masstr/) is an adaptive traffic control system used in the New Jersey (US) Meadowlands area, coordinating 125 traffic signals. It uses the Australian-designed SCATS software and is its fourth-­ l argest deployment worldwide. McMaster Algorithm This is a widely used traffic congestion detection algorithm based on the mathematical branch known as catastrophe theory. Speed, flow and lane occupancy (density) are analysed. If there is a dramatic loss in speed without a corresponding drop in flow and density, that suggests an incident has occurred. MOVA Microprocessor Optimised Vehicle Actuation from the Transport Research Laboratory (UK) was introduced in the 1980s for controlling isolated sets of traffic signals. NoTraffic NoTraffic (https://notraffic.tech/), founded in 2017 in Israel, is the world’s first AI-powered traffic management platform that fuses data from traffic sensors such as cameras, radar and information from vehicles via V2X (see later) and IoT technology with artificial intelligence. AI is used for NoTraffic’s computer vision neural networks and traffic optimisation algorithms. NoTraffic can be retrofitted at any intersection to connect it ‘to the cloud’. It can run in a fully autonomous mode, communicating with other intersections, road users and managers. Managers establish intersection and corridor policies with NoTraffic (see Fig.19). AI is used to classify and manage traffic according to those policies to maximise road capacity (see Fig.20). NoTraffic also provides information so traffic managers can better understand road networks by “understanding the root cause of traffic issues and applying the most relevant and effective solutions on a case-by-case basis”. NoTraffic can communicate with connected vehicles via V2X to provide alerts and rerouting information for accidents and hazards (see Fig.21). Fig.18: the Kapsch EcoTrafiX software. Source: NYSERDA Department of Transportation siliconchip.au/ link/abu4 siliconchip.com.au Australia's electronics magazine May 2024  23 It operates in Arizona and California, USA, among other places. One recently demonstrated capability of the system is the ability to detect a “red light runner” approaching an intersection and warn drivers with a green light going in other directions to stop to avoid a collision (see https:// youtu.be/aEuyUY28qzc). The NoTraffic video channel can be found at www.youtube.com/<at> NoTraffic Fig.19: NoTraffic allows intersection policies to be set up on its dashboard. OSCADY Optimised Signal Capacity and Delay is modelling software from the Traffic Research Laboratory (UK) that “calculates capacities, queues and delays for isolated (uncoordinated), traffic signal-controlled junctions. It can evaluate a set of known signal timings, and optionally, it can optimise stage (phase) lengths and/or cycle time to minimise delay”. PICADY Priority Intersection Capacity and Delay is modelling software from the Traffic Research Laboratory (UK) for the “prediction of capacities, queues, delays and accidents at isolated priority junctions”. Fig.20: NoTraffic uses AI to classify traffic types. Source: https://youtu.be/O_ Bpyuu_URI Rayven This Australian company offers an IoT platform for a “traffic monitoring and intelligent highway solution” to integrate “infield devices, sensors, third-party systems, and machinery to deliver real-time and predictive insights, as well as all-new capabilities to improve safety, maintenance, and use.” It is primarily for monitoring rather than traffic management – see siliconchip.au/link/abts Fig.21: information that NoTraffic might display in a V2X-connected vehicle. Source: https://youtu.be/O_Bpyuu_URI SCATS Sydney Coordinated Adaptive Traffic System was introduced in 1963 as a pilot controlling eight intersections in the Sydney CBD using valve-based IBM equipment. By 1970, DEC PDP11 computers controlled intersections, followed by microprocessor-based traffic signal controllers in 1974. SCATS is owned and developed by Roads & Maritime Services (RMS) in NSW. It is now used in many countries, controlling 37,000 intersections, and is considered one of the world’s leading adaptive traffic control systems. 4200 intersections in Sydney are controlled by one SCATS system. In Australia's electronics magazine siliconchip.com.au 24 Silicon Chip Victoria, SCATS controls over 4000 intersections in Melbourne, Ballarat, Bendigo, Traralgon, Geelong and Mildura. SCATS is used in another 150 cities in 27 countries, including the USA, Brazil, Singapore, India, Malaysia, Ireland, South Africa, Fiji and China. SCATS runs on Microsoft Windows via one or more regional controllers and a central manager computer. A central manager can control 64 regional controllers (regions). Each regional controller can manage 250 traffic signal controllers (intersections) for a total of 16,000 intersections. There is plenty of redundancy, as each regional controller can continue to operate even if communication with the central manager is lost. If regional controllers fail, there is a fall-back mode to local individual intersection control by the local traffic signal controller. The ATSC4 traffic signal controller is specifically designed to work with SCATS. SCATS controls three principal signal parameters: cycle time, phase split and offset. SCATS works at two levels: strategic and tactical. At the strategic level, regional controllers receive data from vehicle detectors to assess flow and occupancy data and optimise cycle length, phase splits and offsets for an area (groups of intersections). At the tactical level, individual traffic signal controllers use data from local vehicle sensors to omit signal phases if no vehicles are waiting. Even though there is tactical local control, ultimately, the system is coordinated by the regional controllers. SCATS uses a measurement known as the degree of saturation (DS), a measure of road capacity utilisation determined by traffic sensors during green phases. A figure over one means there is insufficient green time to satisfy demand and the road is congested. Cycle length is adjusted to keep DS around 0.9. Phase splits are also adjusted to keep the DS about equal for different approaches to the intersection. When using a SCATS traffic signal controller (eg, the ATSC4) for the first time, the signal controller will provide the initial default timings. Then the SCATS regional controller will start to adjust the timings (self-calibrate) according to the traffic flow at that junction. It will attempt to balance siliconchip.com.au and coordinate flows between neighbouring junctions as demand requires. SCATS can turn off coordination between intersections if necessary, such as during periods of light traffic when traffc at some intersections might flow better without coordination. SCATS can also prioritise the passage of certain vehicles, such as public transport buses and trams. If a pedestrian presses a button to cross the road, the signal phasing will be altered to run the pedestrian phase. SCATS can also be set for special events or other special purposes. VicRoads claims the following benefits from SCATS in Victoria: travel times down by 21%, stops down by 40%, fuel consumption down by 12% and fewer crashes due to smoother traffic flow. Fig.22 shows a SCATS interface window. The pie chart (on the left) shows the length of time for each phase, while a map of the junction is on the right, with the different signal phases shown to its left. SCOOT The Split Cycle Offset Optimisation Technique is an adaptive traffic control system for groups of traffic signals that are close together. It was first introduced by the Traffic Research Laboratory (UK) in 1979. Its purpose is to adjust signal timings based on input from sensors to minimise delays. It is used in 350 towns worldwide. SURTRAC Scalable Urban Traffic Control (https://miovision.com/surtrac/) was developed at Carnegie Mellon University in Pittsburgh, USA. It is an adaptive traffic control system that optimises traffic flows along corridors and complex urban grid networks. It uses artificial intelligence that treats the “intersection control challenge” as a “single machine scheduling problem” to optimise each intersection and share information with neighbouring intersections, to enable coordination and control across the whole network. The operational concept is: 1. Traffic conditions are established from sensor data. 2. The appropriate traffic signal phase schedule is computed for flow optimisation at intersections. 3. The schedule is transmitted to downstream intersections. 4. Rescheduling occurs every few seconds. It is used in Pittsburgh, USA and Peterborough, Canada. TRANSYT (TRAffic Network StudY Tool) This traffic modelling software was introduced in 1967 by the Transport Fig.22: a SCATS interface window. Source: www.aldridgetrafficcontrollers. com.au/ArticleDocuments/230/Introduction_To_New_Generation_Scats_6_5. pdf.aspx Australia's electronics magazine May 2024  25 Research Laboratory (UK) to optimise signal timing and perform simulations for “designing, evaluating and modelling everything from single isolated road junctions to large mixed signal-controlled and priority control traffic networks”. The results from the modelling can be used to optimise signal timing, SCOOT timings, for performance prediction and platoon modelling. UTC Urban Traffic Control, from the Traffic Research Laboratory (UK), takes data from SCOOT to coordinate traffic signal controls over a wide area, such as an urban road network. Veronet This traffic management system uses artificial intelligence to manage traffic and traffic signals, supporting inflows and outflows for a city, and optimising certain directions. It also supports autonomous driving modes for cars that support that mode. See www.veronet.eu/home.html Waze This navigation software (Fig.23) is “free” (because your data is the product). It is now owned by Google. It collects vast amounts of user data for driver navigation and other purposes. However, traffic managers can also feed that data to traffic management software or use it to visualise traffic flows, monitor conditions on key routes and observe changes over time. Heavy vehicle monitoring in Australia The National Heavy Vehicle Regulator operates a network of fixed digital cameras called the National Safety Camera Network to monitor the movement of heavy vehicles by recording number plate data. The network has over 120 cameras covering more than 5800km of road across five jurisdictions with an average of 4.2 million “sightings” per month. According to their website, they “use safety camera, registration, crash, defect, intercept and infringement data to generate profiling reports to identify operators, vehicles, drivers and infrastructure of interest”. There are also five mobile Automatic Number Plate Recognition (ANPR) cameras to detect the number plates of passing heavy vehicles. Their website shows trailer-, vehicle- and dronemounted cameras. According to the website, the mobile cameras are “used to develop policies and programs to increase road safety”. Traffic Management Channel The Traffic Management Channel (TMC) is a worldwide system delivering digital traffic data via commercial FM broadcast stations that can be displayed on a car’s built-in GPS map system (or, in some cases, add-on systems). It is incorporated into the existing Radio Data System (RDS), typically used to transmit station identification and program information. The protocols used for RDS-TMC data are ALERT C or TPEG. Such data can also be delivered via Digital Audio Broadcasting (DAB) or satellite radio. Information that can be delivered relates to traffic events, containing an event code, location code, expected incident duration, affected extent and any other relevant details. Vehicle navigation systems can use this data to generate an optimum route. This system only requires the reception of an FM, DAB or satellite radio signal from a cooperating broadcaster. Intelematics Australia (www. intelematics.com, owned by the RACV) broadcasts encrypted RDSTMC data under the brand SUNA Live Traffic to provide live traffic updates to participating in-car navigation systems and compatible add-on GPS devices. Originally, SUNA was only transmitted via FM radio, but today, it is also delivered over the mobile data network. According to the peak body for advanced transport technology, ITS Australia (https://its-australia.com. au/), SUNA is used by 90% of vehicles in Australia and NZ. According to ITS, their “road traffic data is collected through thousands of probes and sensors located on roads, in vehicles and infrastructure” and “We enrich our data using multiple proprietary sources and machine taught algorithms”. Intelematics has advised us that SUNA will be discontinued. In the past, Intelematics also maintained historical traffic databases that could be used for future road and traffic planning via the discontinued software tool INSIGHT (siliconchip. au/link/abtt). The INSIGHT software tool allowed visualisation of historic and present real-time data of such parameters as traffic volume or turning volume at intersections over periods of 15 minutes, days, months or years. It allowed the impact of various events or infrastructure changes to be determined. VicRoads “Smarter Roads” Fig.23: Waze data being used to manage traffic by the Port Authority of New York and New Jersey. Source: https://support.google.com/waze/partners/ answer/10715145?hl=en The VicRoads Smarter Roads program (see siliconchip.au/link/abu5) includes CCTV, travel time sensors, live travel information signs and pedestrian Australia's electronics magazine siliconchip.com.au 26 Silicon Chip crossing sensors. There are 2500 CCTV cameras covering most suburban traffic signals in Victoria, used by the Traffics Operations Centre to monitor traffic incidents and traffic flows. There are also 400 wireless travel time sensors and 43 live travel time signs. According to VicRoads, these cameras are not used for law enforcement purposes, and the video is not recorded, so it is not available for evidentiary purposes, such as for accident liability. However, that could change. Pedestrian detectors determine the number of pedestrians waiting to cross the road & prevent unnecessary waiting (https://youtu.be/vyyN92qT6OY). They also monitor roadside air quality. Fig.24: Sydney’s WestConnex road and tunnel network use Smart Motorways technologies. Source: www.westconnex.com.au/explore-westconnex/ WestConnex Smart Motorways WestConnex private motorways around Sydney (Fig.24) use “Smart Motorways”, their proprietary name, for technologies such as vehicle detection, CCTV cameras, ramp signalling, lane use management and variable speed limits. Smart Motorways are designed to operate and integrate with the rest of the Sydney (non-WestConnex) road network and the existing SCATS system. WestConnex Motorway operations are controlled from the Motorway Control Centre (MCC) shown in Fig.25. Self-driving vehicles Australia’s laws do not currently support autonomous vehicles on public roads; the National Transport Commission released a policy paper on the subject in 2022. An Automated Vehicle Safety Law (AVSL) is proposed by 2026 (siliconchip.au/link/abtu). In the USA, California allowed driverless taxis in San Francisco, but permission was suspended after an accident with a pedestrian. Similar laws are under development in several countries. V2X V2X or “vehicle-to-everything” refers to communication to and from a vehicle for traffic management and other purposes. V2X incorporates concepts such as those listed below and shown in Fig.26: • V2D (vehicle-to-device): Apple CarPlay or Google Android Auto. • V2G (vehicle-to-grid): connecting an EV to a smart electrical grid. • V2I (vehicle-to-infrastructure): a siliconchip.com.au Fig.25: Australia’s largest Motorway Control Centre (MCC) at St Peters, Sydney, with 60 panels. It provides monitoring and incident response for the M4, M8 and M5 East motorways. Source: www.westconnex.com.au/media-releases/ australia-s-largest-motorway-control-centre-supporting-westconnex-motorists/ Braess’ Paradox Braess’ Paradox is the counter-intuitive idea that adding an extra road can increase the average travel time. Conversely, closing roads can sometimes decrease travel time (of course, that isn’t always true!). The idea is used in traffic planning and management. For example, a section of road could be opened or closed depending on traffic conditions. The basic problem is that drivers don’t know what other drivers are going to do. If a new, high-capacity road is opened, many drivers who would otherwise take different routes might decide to use that road, resulting in their paths intersecting and generating heavy traffic and delays. If a smaller number of the drivers took the new road while others remained on the smaller roads, the average travel time could decrease, but that would require either good luck or coordination. It is also applicable in electrical networks, biological networks and even sports; for example, the addition of a champion player might decrease the team’s overall efficiency if there is an over-reliance on that player. For more information, see the video on “The Spring Paradox” at https:// youtu.be/Cg73j3QYRJc Australia's electronics magazine May 2024  27 vehicle communicating with traffic lights, parking meters etc. • V2N (vehicle-to-network): comms via WiFi or the mobile network for remote diagnostics and monitoring. • V2P (vehicle-to-pedestrian): provide alerts from vehicles to pedestrians’ smartphones, coordination with pedestrian crossings, prediction of pedestrian behaviour, automatic sounding of vehicle horn. • V2V (vehicle-to-vehicle): exchanging data with neighbouring vehicles, such as warning of Fig.26: some examples of V2X communications in a country that drives on the right-hand side of the road. Original source: www.researchgate.net/ publication/279765559 vehicles or pedestrians that cannot be seen directly due to obstacles, or an approaching emergency vehicle. Information for V2X can be obtained from various sensors, as shown in Fig.27. Sensor data management and communication are performed by the V2X OBU (On-Board Unit). An example of a commercial OBU is shown in Fig.28. The original V2X technology was based on WLAN (Wireless LAN) IEEE 802.11p, which is now incorporated into IEEE 802.11. The term used by the SAE (Society of Automotive Engineers) for this technology is DSRC (Dedicated Short Range Communication). In Europe, it is known as ITS G5. DSRC has a range of up to about 1km, supporting V2I and V2X. Unfortunately, the DSRC systems used in Europe, Japan and the USA are incompatible. In Australia, DSRC uses the 5.9GHz band. Australian E-Toll tags use RFID transponders with a DSRC protocol. DSRC can also be used for cooperative cruise control, cooperative collision warning, warning of an approaching emergency vehicle and warning of a railway level crossing. 3GPP C-V2X uses mobile networks for V2X communications. C-V2X also uses the 5.9GHz band, like DSRC, for short-range communications and has about 25% better range than DSRC. There is no restriction on range as long as a mobile tower is nearby. It supports V2I, V2V and V2N. It was originally based on 3G but now uses 5G. DSRC and C-2VX are competing technologies. Variable tolling Fig.27: vehicle sensors that might be used for V2X communications and other purposes. OBU stands for On-Board Unit. Original source: www.researchgate. net/publication/279765559 Some authorities advocate variable tolling, supposedly to reduce congestion, as a form of traffic management. Such a scheme operates on the Sydney Harbour Bridge. According to Wikipedia, it has been minimally effective, only reducing traffic by 0.19%. Other management systems Fig.28: a Commsignia ITS-OB4 V2X on-board unit (OBU). An equivalent roadside unit can receive data from units like this for traffic management purposes. Source: www.itsinternational.com/its2/products/ commsignia-gets-green-light-c-v2x-units 28 Silicon Chip Australia's electronics magazine Traffic management systems aren’t just restricted to roads. Systems are needed for air traffic management, space traffic management (to ensure satellites do not collide), rail traffic management, sea and harbour traffic management and even underwater traffic management! Similar schemes and approaches apply, but generally with different sensors. SC siliconchip.com.au Project Build It Yourself Electronics Centres® DEALS Get prepared for a big Winter of project building with these savings. Only until May 31st. 195 $ Raspberry Pi 5 The latest generation Pi is here! With 2-3x the speed of the previous generation Pi. 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See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0005 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. Project by Nicholas Vinen This small board converts a standard 10MHz frequency reference (eg, from an oscilloscope) to 1MHz and 1Hz square wave signals. The latter can emulate the 1PPS output of a GPS receiver and has options for a 10% or 50% duty cycle. Build your own compact Frequency Divider 10MHz – 1MHz | 10MHz – 1Hz T his straightforward circuit accurately divides a 10MHz signal to 1Hz with extremely low jitter. It has various applications, such as testing clocks and other devices that are time-locked to GPS signals. It could also be used to drive several clocks from a single accurate time source or to derive a very accurate 1Hz signal from a low-cost 10MHz temperature-­c ompensated crystal oscillator (TXCO). The divider uses just four logic ICs, including the somewhat unusual 74HC4059, plus an ultra-high-speed comparator and a buffer for driving the outputs. It can be powered at 5V DC from a USB supply or 6.6-12V DC, drawing only about 10mA. It has supply reverse polarity protection and input overload protection and won’t generate an output unless it’s being actively fed a signal. A jumper selects between the 10% and 50% duty cycle options for the 1Hz output. The output jitter is extremely low as long as the input signal is relatively clean. Many pieces of test equipment will have a suitable 10MHz output, or you could use one of our GPS-­Disciplined Oscillators: • GPS-Disciplined Oscillator (May 2023; siliconchip.au/Article/15781) • GPS-synched Frequency Reference (October and November 2021; siliconchip.au/Series/326) • GPS-based Frequency Reference (March-May 2007 & September 2011; siliconchip.au/Series/57) Circuit details Its circuit is shown in Fig.1. We have tried to keep it simple and inexpensive without sacrificing performance. The 10MHz signal is fed into SMA connector CON1 and goes into the first stage, based on ultra-high-speed comparator IC6 (TLV3501). The TLV3501 is an interesting device as it runs from 2.7 to 5.5V, drawing just 3.2mA and yet has extremely low input bias currents at ±2pA (typical), a low input offset voltage of ±1mV (typical) and very high-speed operation with a maximum toggle frequency of 80MHz. That makes it suitable for many applications. Here, its job is to convert what might be a relatively low-level, sinusoidal input signal into a 5V peak-to-peak square wave. That means the circuit is not too sensitive about what drives it, as long as it is a 10MHz waveform of at least 10mV RMS or 35mV peakto-peak; it will most likely be a sine or square wave. The circuit is designed with 75W impedances in mind, although you could change that if necessary (eg, using 49.9W or 51W resistors instead of 75W). So the input is terminated with a 75W resistor, then coupled to comparator IC6 by a 1nF DC-­blocking capacitor and 220W series resistor. Dual schottky diode D1 protects IC6 from over-voltage or having a signal applied while the circuit is powered Frequency Divider Features & Specifications » Divides the nominally 10MHz input frequency by 10 (to 1MHz) and 107 (to 1Hz) » 10% or 50% duty cycle option for 1Hz output (5V peak-to-peak unloaded) » Operating input signal level: 10mV to 3.2V RMS (28mV to 9V peak-to-peak) » Recommended input signal: 35mV to 2V RMS (100mV to 5.6V peak-to-peak) » Jitter: estimated at 0.1ns with a clean clock source (see Scope 1) » Propagation delay: approximately 100ns » High noise immunity with 23.5mV built-in hysteresis » Outputs are in phase with inputs » No output signals if the input is not driven » SMA connectors for input and outputs » Choice of 50Ω or 75Ω input/output impedances » Power supply: 5-12V DC <at> 10mA » Power connectors: USB Type-C, 2.1mm/2.5mm inner diameter barrel plug, (polarised) pin header » 3mm mounting holes: 4 (the board can be made smaller by cutting them off) siliconchip.com.au Australia's electronics magazine The prototype board is very similar to the final version; it just lacks the power LED and used a Type-B mini USB socket instead of the now more standard Type-C. May 2024  33 Scope 1: the yellow waveform is the 1Hz output (reduced in amplitude due to a lower than normal supply voltage and 50W termination) while the blue waveform is the 10MHz reference signal from the oscilloscope. The grey areas around them show the previous 50 or so traces, indicating extremely low variation in timing between them (ie, low jitter). The output edge seems to come first because the propagation delay is just under the input signal period (100ns); it was triggered by the previous edge. down by clamping the input signal to within 0.3V of the supply rails. The 220W resistor primarily exists to limit the current through these diodes, protecting them and the rest of the circuit from excessive ‘bus pumping’ of the 5V rail. As the signal is AC-coupled to IC6, it is DC-biased to half of the 5V supply using a pair of 10kW resistors and a 47kW bias resistor. The 100nF capacitor prevents supply ripple from coupling back into the signal, which could cause jitter. A 10MW resistor from output pin 6 of IC6 back to its non-inverting input, pin 3, provides around 23.5mV of hysteresis for noise rejection. This forms a voltage divider with the 47kW bias resistor for pin 3. With around 2.5V across the hysteresis resistor (regardless of whether IC6’s output is at 5V or 0V), 2.5μV flows through it and subsequently the 47kW resistor, causing an offset of around 11.75mV. That offset switches polarity as IC6’s output switches, meaning that any noise on the input signal would have to exceed 23.5mV to cause an unwanted edge at IC6’s output. It also means that there needs to be at least a 23.5mV peak-to-peak signal applied to IC6 before its output will start to toggle. Thus, it won’t oscillate without a signal at CON1. With the 75W termination resistor, 34 Silicon Chip Scope 2: to check the frequency ratio was correct, we captured the unit’s output on the scope for two seconds and then measured the time between edges. Here three of the captured edges are overlaid, in yellow (-500ms), red (0ms) and green (+500ms). The yellow and green traces overlap, indicating they are exactly one second apart as per the scope’s timebase (and hence 10MHz reference oscillator). As we captured two full seconds of data, the time resolution is more coarse than in Scope 1. plus the low-pass filter formed by the 220W resistor and IC6’s input capacitance (plus that of both diodes in D1), the minimum signal the circuit will respond to is about 30mV peak-topeak at CON1. However, a higher level is recommended to ensure jitter-free operation. 30mV at CON1 implies a higher voltage at the signal source, probably closer to 60mV peak-to-peak. Frequency divider Now that we have a clean 10MHz square wave signal from IC6, it’s fed to the first divider, IC1. This is a 74HC4017 Johnson decade counter, a lower-­voltage, higher-speed version of the good old 4017 counter IC. These are inexpensive, run from 2-6V, operate at up to 77MHz with a 5V supply and provide ten 10% duty cycle outputs with different phase angles, plus a single 50% duty cycle output that’s phase-aligned with the input (and Q0 output). For IC1, we feed the 10MHz signal into the pin 14 clock input and get a nice 1MHz square wave from the Q5-Q9 output. The MR (master reset) line is tied low for constant operation, while the inverting clock input at pin 13 is also tied low as we are using the non-inverting clock input. The ten phase outputs, Q0-Q9, are not used in this case. The 1MHz output from pin 12 is fed Australia's electronics magazine to two places: firstly, to three of the six buffers in IC5 connected in parallel, then to the 1MHz SMA output (CON2) via a 75W impedance-matching resistor. The MC74VHCT50A is similar to a 74HC04 hex inverter IC except that it does not invert the signals but merely buffers them. That keeps the outputs in phase with the 10MHz input. Secondly, the pin 12 1MHz output of IC1 goes to another 74HC4017 counter, IC2, configured identically to IC1. It produces a 100kHz square wave at its pin 12 output, which is fed to the clock (CP) input, pin 1, of IC3. This is the ‘main event’, configured to divide its input frequency by a factor of 10,000. It is a larger IC than the others, with 24 pins rather than 16, and somewhat more expensive (but still pretty reasonable). It takes up less space than four more 74HC4017s and has a much lower propagation delay. It can be configured for thousands of different frequency division ratios in various ways based on the logic states of its KA-KC and J1-J16 pins. The accompanying panel explains how this particular configuration achieves the 10,000:1 division ratio. We could have added a microcontroller to this board, driving all those pins, and provided a few different ratios. However, we decided it was better to keep this simple and avoid programming any chips. siliconchip.com.au Fig.1: the circuit uses three divideby-ten ICs (74HC4017) and one divide-by-10,000 IC (74HC4059) to reduce the 10MHz input at CON1 to 1Hz at CON3. High-speed comparator IC6 converts whatever waveform is fed in to a 5V peak-topeak square wave for driving IC1. IC3 has an output latch that we do not use, so the latch enable (LE) input, pin 2, is tied to ground. The 10Hz signal appears at pin 23 (Q). Note, though, that this pin will only be high for one input pulse, and with a 100kHz input, the output pulses are 10μs wide. That is why we divided the 10MHz signal siliconchip.com.au by a factor of 100 first; otherwise, the output pulses would be a mere 100ns wide. To make this short pulse useful, we feed it to the final counter, IC4, another 74HC4017 configured much like the others. It performs the final division to get a 1Hz signal and converts the short Australia's electronics magazine pulses into a 50% duty cycle square wave at its pin 12 output. We feed that, plus the similar but shorter 10% duty cycle pulse from output Q0, to a three-way pin header. That allows you to select the desired duty cycle using a jumper shunt. The resulting signal is fed to another triple May 2024  35 parallel buffer (IC5d-IC5f) and then the final SMA output, CON3, via another 75W impedance-matching resistor. The 10% duty cycle output more closely simulates a GPS 1PPS output, while the 50% duty cycle signal is nice and symmetrical for driving something like a clock. Power supply There are three power supply inputs. The USB Type C connector (CON4) is the simplest as it feeds the USB 5V directly into the circuit. However, note that its ground connection goes via the internal switch in barrel socket CON5. This way, if you plug both in simultaneously, you won’t be feeding power into the device connected to the USB socket. Unlike USB Type-B sockets, the Type-C socket needs two 5.1kW pulldown resistors connected to signal the power source to deliver 5V. You can leave those resistors off the board if you aren’t fitting the Type-C socket. This particular socket only has the six pins needed for USB power delivery, without the data signals. By the way, we’re switching from Type-B to Type-C because it is now the universal standard, so expect to see more of this in future. After passing through CON5’s internal switch, the GND connection from CON4 also passes through Mosfet Q1 before reaching circuit ground. This provides reverse supply polarity protection, although that should not be necessary for the USB socket as the socket itself should guarantee the correct polarity. However, it is helpful if powering the circuit via barrel connector CON5 or header CON6. In those cases, as Q1’s gate is connected to the +5V rail and incoming DC supplies via two 10kW resistors, it will only conduct if the incoming supply polarity is positive. If it is negative, Q1’s gate will be pulled negative, Q1 will be off, and the whole circuit will be unpowered, floating at the positive DC supply voltage (that was erroneously connected to the negative input). There are two 10kW pull-up resistors for the gate so that Q1 will switch on regardless of whether the USB connector is used (feeding 5V directly) or one of the other inputs, which feed 5V low-dropout regulator REG1. Zener diode ZD1 prevents damage to Q1 as its gate is only rated to handle ±12V. This method has a much lower voltage loss than using a series diode (a few millivolts instead of 300mV+), allowing you to use a supply barely above 5V while still getting a regulated 5V at the output of REG1 to power the rest of the circuit. Construction This counter is quite complicated as it includes a prescaler plus a three or four digit ‘decimal’ main counter that varies in how you can use it. The prescaler can divide by between 1 and 10 in five different modes. However, which prescaler mode you choose affects what values you can have in the main counter’s top (thousands) digit. For example, if you have a divide-by-10 prescaler, the main counter only has three digits (up to 999). If you use one of the other prescaler values, the main counter has four digits, with more options as the prescaler division ratio becomes smaller. The lower three decimal digits of the main counter can always be preset with a value from 0 to 9. Depending on the mode, the overall maximum division ratio is either 9999 (eg, with the prescaler in divide-by-10 mode) or 15999 (with the prescaler dividing by a power of two). It is actually possible to divide by a much higher number than that because the ‘BCD’ or ‘binary coded decimal’ counter stages that it initially seems can only count up to 10 are actually full binary counters that can count up to 16. So, while programming it is trickier, it can be set to divide by up to 21,327. Luckily, our desired division ratio of 10,000 is relatively easy to set up. We could have used a prescaler value of 10, leaving a three-digit main counter. While dividing by 1000 with three digits seems impossible, we could have set the top ‘digit’ to 10 (because the actual limit is 15), which would have given the desired result. In the final design, we use a prescaler ratio of 8, leaving us with four digits for our main counter, although the top digit can only be 0 or 1. That’s fine because we set the main counter to divide by 1250, as 1250 × 8 = 10,000. The prescaler value of 8 is selected with KA low, KB low and KC high as per Table 1. We then program the top digit of the counter using J4, which we set high, to 1. The remaining three digits are set to 2, 5 & 0, as shown in Table 2. One ‘gotcha’ when setting up this counter is that, while the thousands digit for the counter is set using low-numbered inputs (J2-J4), the hundreds digit is set using the highest-numbered inputs (J13-J16). So the digits do not appear at the inputs in order, except in the mode when the prescaler can divide by up to 10. While it uses mainly SMD parts, the board is relatively easy to assemble as they are all fairly large. Experienced constructors can gather the parts and solder them to the board as shown in overlay diagrams Figs.2 & 3. We suggest fitting all the SMD parts to one side of the board, followed by the other, then the through-hole parts. It’s best to start with the top, as more parts are on that side. The Frequency Divider is built on a double-sided PCB coded 04112231 that measures 64 × 37.5mm. We recommend soldering IC1-IC5 in numerical order, then ZD1, Q1, REG1, the USB socket (if fitting it), then the top-side capacitors and resistors. With the ICs, check very carefully that each one is the right way around before soldering them; most will have a pin 1 dot or bar. Use a magnifier to find them if necessary. As shown in Fig.2 and on the PCB, in each case, pin 1 faces towards the top of the board or to the left (for IC5). There is one 1μF capacitor on this side; the rest are 100nF. As mentioned earlier, you can leave off the 5.1kW resistors if you aren’t using the USB socket. Also note that unlike the Type-B USB sockets we’ve been using for a while, these Type-C sockets have no locating posts that slot into holes in the PCB, so you will have to be careful to align all its pins and tabs with the pads before soldering more than one. There are various ways to solder these parts: with solder paste and hot air, solder paste and a reflow oven, solder paste and a hot plate or regular solder and a regular iron (which is how we did it). If using a standard iron, we strongly recommend having a good quality flux paste on hand, plus some solder wick, as they make it much easier. There is no ‘right’ way to hand solder SMD ICs, but here is how we did it, starting with the ICs. We placed a Australia's electronics magazine siliconchip.com.au Programming the CD74HC4059 counter 36 Silicon Chip Figs.2 & 3: we recommend fitting all the SMDs on the top side first. Ensure all the ICs are orientated correctly and leave the SMA connectors, DC socket and headers until after you’ve populated the underside of the board. There are not as many components on the underside; just the comparator IC, passives and the dual diode. little solder on one of their pads, then slid them into place while heating that solder (to keep it molten). Removing the iron, we checked that all the leads were centred on their pads. If not, we reheated that solder joint and gently nudged the IC towards the correct position, rechecking each time. Once the IC was positioned correctly, we soldered a couple more pins, then spread a thin layer of flux paste along both rows of pins, loaded the soldering iron tip with some solder and dragged it along the pins. Each one took up the right amount of solder, making quick work of all the joints. Only a few joints got too much solder, resulting in a bridge to an adjacent pin. We removed the bridges using a bit more flux paste and an application of clean solder wick. You could use a slightly different technique, where you clamp the device in the correct location using a clothes peg, haemostat clamp or similar, tack it down, then solder the remaining pins. That technique involves more set-up time but less trial-­and-error. Once the ICs are in place, you can solder the remaining three-lead and two-lead components with a similar technique. Just make sure you let one joint solidify (which can take a few seconds) before making the other, or you could end up pushing the parts out of position. With all the parts in place, clean the board with some flux cleaner (or pure alcohol if you don’t have a specific flux cleaner), let it dry and inspect all the solder joints to ensure you haven’t missed any imperfect/incomplete joints or bridges. Then flip the board over and solder the parts on the other side using a similar technique. There is just one chip (IC6) on the underside, plus one dual diode in a three-pin SOT-23 package and 10 passives (resistors & capacitors). Take care with the orientation of IC6; its pin 1 goes towards the nearest PCB edge. Some parts are close to IC6, so it’s best to solder IC6 first, then the components right next to it, followed by those further away. Again, when finished, clean off the flux residue and inspect your work. Finally, flip the board back over and solder the SMA connectors, the threepin header for LK1, plus whichever of CON5 and CON6 you will be using. If leaving CON5 off, you will need to solder the short wire link shown in red in Fig.2 and the PCB silkscreen, or the board won’t get power. Note that you could leave SMA connector CON2 off if you don’t need or want the 1MHz output. Testing The board should draw under 20mA when powered up. If you have a current-­limited bench supply, set it to 6V and at least 30mA and connect it to CON5 or CON6. If it goes into current limiting, switch it off and check for faults. If you don’t have a bench supply, use a regular DC supply fed through a DMM set to measure milliamps and switch off if the current shoots up when you power it up. Lacking such a supply, you just have to YOLO it: plug a suitable power supply in and check if LED1 lights. If it doesn’t, unplug the cable and try to figure out why. If it does, proceed with the following checks. Assuming the current draw is OK, check the voltage between the shell of one of the SMA connectors (ground) and the large tab of REG1. It should be close to 5V. If it is below 4.75V or above 5.25V, check the soldering on REG1 and its adjacent bypass/filter capacitors. If it isn’t drawing any current and the LED is off, that probably means that Q1 is not conducting. You can Table 1 – 74HC4059 modes (● must be set up with Master Preset mode first) KA KB KC Prescaler ratio Preset inputs Counter thousands digit Preset inputs Maximum count 1 1 1 2:1 to 1:1 J1 0-7 J2-J4 15,999 (17,331 extended) 0 1 1 4:1 to 1:1 J1, J2 0-3 J3, J4 15,999 (18,663 extended) 1 0 1 5:1 to 1:1 ● J1-J3 0-1 J4 9,999 (13,329 extended) 0 0 1 8:1 to 1:1 J1-J3 0-1 J4 15,999 (21,327 extended) 1 1 0 10:1 to 1:1 J1-J4 0 - 9,999 (16,659 extended) Table 2 – our 74HC4059 configuration KA KB KC Prescaler preset (J1-J3) Thousands (J4) Hundreds (J13-J15) Tens (J9-J12) Units (J5-J8) 0 0 1 000 (0) 1 (1) 0101 (5) 0000 (0) siliconchip.com.au 0010 (2) Australia's electronics magazine May 2024  37 verify that by measuring the voltage between your supply negative and the shells of the SMA connectors. There should be very little difference. If you measure the full supply voltage, check that you’ve applied power with the correct polarity. If you have, there is a fault around Q1/ZD1. Finally, assuming the current draw is OK and the 5V rail is close to 5V, feed a signal with a known frequency into CON1 and check for 1/10th that frequency at CON2 (if you didn’t fit CON2, you can probe its centre pin). If that checks out, apply 10MHz to CON1 and look for a 1Hz output at CON3. If it’s missing, make sure JP1 is inserted in one of the two possible positions. Remember that, depending on your test instrument, it could take several seconds to register a reading of such a low frequency. If the board isn’t behaving, common problems to look for are solder bridges, pins where the solder hasn’t adhered to the PCB pad below, or incorrectly orientated ICs (we did warn you!). Usage There isn’t much to it: connect your reference signal source to CON1 and feed the output at CON3 to your GPS clock(s) or other devices needing 1Hz pulses. Move JP1 if necessary to get the desired duty cycle, although almost any device expecting a 1PPS signal should work in either position. We suggest housing the board in a small diecast aluminium box with the case connected to circuit ground to minimise EMI pickup. However, we tested it as a ‘bare board’ and it performed well in our lab. The SMA connectors are arranged along one edge, so you can mount the board such that they project through holes in the case, then add a chassis-mounting DC socket wired to CON6. The four corner mounting holes will provide a convenient way to attach the board to the inside of such a box. If you need to make the board as small as possible, the tabs those holes are on can be cut off with a hacksaw or similar (but don’t breathe the resulting Parts List – 10MHz Frequency Divider 1 double-sided PCB coded 04112231, 64 × 37.5mm 3 right-angle or vertical through-hole SMA connectors (CON1-CON3) 1 SMD USB Type-C power-only socket with six pins (CON4) ● 1 PCB-mount DC barrel socket (CON5) ● 1 2-way polarised header, 2.54mm pitch (CON6) ● 1 3-pin header, 2.54mm pitch (JP1) 1 jumper shunt (JP1) ● omit any of these power input connectors that are not needed Semiconductors 3 (CD)74HC4017(M96) high-speed CMOS Johnson decade counters, narrow body SOIC-16 (IC1, IC2, IC4) 1 (CD)74HC4059 high-speed CMOS programmable divide-by-N counter, wide body SOIC-24 (IC3) 1 MC74VHCT50A hex CMOS non-inverting buffer, SOIC-14 (IC5) 1 TLV3501AID rail-to-rail high-speed comparator, SOIC-8 (IC6) 1 AMS1117-5.0 or compatible 5V 1A low-dropout regulator, SOT-223 (REG1) 1 AO3400 30V 5.8A N-channel logic-level Mosfet or equivalent, SOT-23 (Q1) 1 SMD LED, SMA/M3216/1206 size, any colour (LED1) 1 BZX84C5V6 5.6V 1% tolerance zener diode, SOT-23 (ZD1) 1 BAT54S dual series schottky diode, SOT-23 (D1) Capacitors (all SMD M3216/1206 size 50V X7R) 1 1μF 8 100nF 1 1nF Resistors (all SMD M3216/1206 size 1%) 1 10MW 1 47kW 4 10kW 2 5.1kW (only needed if USB socket is fitted) 1 1kW 1 220W 3 49.9W, 51W or 75W (to suit desired input/output impedance) 10MHz Frequency Divider kit (SC6881, $40): includes everything in the parts list. 38 Silicon Chip Australia's electronics magazine dust and cut them outdoors or in a well-ventilated area). Most oscilloscopes, spectrum analysers, high-end frequency counters etc will have a pretty accurate 10MHz output; it’s usually specified as something like ±1ppm. That isn’t as good as a GPS-disciplined oscillator but it’s still very precise. You will likely need a BNC-to-SMA cable to make this connection. You may need a second similar cable for the 1Hz output, depending on where it’s going. Lacking that, some newer DSOs have a waveform generator output that can generate a 10MHz sinewave or square wave (either is suitable). They tend to have quite a bit less stability and more jitter than a 10MHz reference output. However, an actual GPS 1PPS signal has jitter, so if you are using this board to emulate such a signal, you generally needn’t worry too much about it. You can also get connectors that break a BNC connection out to screw terminals if you’re going to feed the 1PPS signal to pin headers or similar. If you want to feed the 1Hz output of this board to multiple clocks or other devices, given its low frequency and the fact that most 1PPS inputs will have a high impedance, you will probably just need to ‘fan it out’. You could even omit CON3 and solder wires directly to its pads. We mainly provided the SMA connector for convenience in hooking it up to prebuilt test equipment. If you need to split the 10MHz output of your test equipment to go to multiple locations, consider building our Frequency Reference Signal Distributor (April 2020; siliconchip. au/Article/13810). But note that the design won’t work on the 1Hz output without modification as it is AC-­ coupled at the input and outputs. SC We used rightangle SMA connectors. siliconchip.com.au Stay connected with our 4G Antennas & adaptors Compatible with 2.4GHz & 4/5G networks for cross-compatibility 1 5dBi Antenna • Magnetic mount • Suitable for LTE, AMPS, GSM, PCS, UMTS and Wi-Fi • 2m lead with FME connector • 337mm long AR3340 ONLY $64.95 3 5m SMA Extension Lead 4 SMA to Induction 3G Plug 5 SMA to Modem Leads • Low loss • 50Ω coax • Flexible lead WC7824 ONLY $59.95 7dBi Antenna • Magnetic mount • 3m lead with FME connector • 435mm long AR3344 ONLY $89.95 2 • Adhesive backing AR3330 ONLY $32.95 7dBi Spring Mount Antenna • ½ wavelength design • 5m lead with FME connector • 740mm long AR3342 ONLY $169 Range of leads that plug into the antenna socket on your USB modem. AR3332-AR3336 ONLY $32.95 EA SMA to Huawei E160/618 Plug AR3332 1 2 SMA to Sierra TS9 Plug AR3334 Telstra 4G USB Modem AR3336 We stock a great selection of Networking Antennas, Leads, Plugs, Sockets and Adaptors to improve the range and reliability of your wireless network. Explore our wide range of wireless networking products, in stock on our website, or at over 115 stores or 130 resellers nationwide. jaycar.com.au 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. Part 1 by Richard Palmer WiFi DDS Function Generator A signal generator is one of the most useful instruments on the test bench. This flexible and easy-to-build generator provides two wide-range, low-distortion outputs. It can be controlled from its LCD touch screen or remotely by a computer, tablet or smartphone using a WiFi connection. W hile sinewave signals are commonly used for testing audio circuits, triangle, square, pulse and ramp signals have many test applications in the power, digital and linear arenas. Some commercial function generators include many rarely-used waveforms, such as Lorenz pulses and even heartbeats, but we have chosen to avoid excessive complexity in this project. Subwoofers and their crossovers pose challenges for many audio tools that can only generate signals from 20Hz to 20kHz. This unit’s outputs are DC-coupled, so it can produce very low (sub 1Hz) frequencies with very low distortion. Out-of-band frequency testing can be important in other aspects of audio design, as signals beyond the audio range may impact signals at audible frequencies through intermodulation and other effects. We have extended sinewave generation up to 70kHz to support such testing and included an intermodulation distortion (IMD) test signal. 40 Silicon Chip Tone burst and pulse testing can help identify ringing and other circuit misbehaviour. Both frequency and amplitude sweeps are supported for sine, square, and triangle waves. Additionally, duty cycle sweeps are provided for square and triangle waves, plus amplitude sweeps for pulse and step waveforms. Bursts are available for all waveforms. For sine, triangle and square waves, channel B can mirror channel A with a phase shift of 0-360°. For most other waveforms, channel B can mirror channel A, either in phase or 180° out of phase. The output terminals are floating with respect to mains Earth to avoid hum-inducing Earth loops. Like my previous lab projects, it can be remotely controlled via a web browser, see: • Programmable Hybrid Lab Supply (May & June 2021; siliconchip. au/Series/364) • WiFi Programmable DC Load (September-October 2022; siliconchip. au/Series/388) Australia's electronics magazine • Automated Test Bench/Swiss Army Knife (April 2023; siliconchip. au/Article/15736) Also like those other projects, it has a set of SCPI commands that allows it to be part of an automated test setup controlled by a program such as TestController (siliconchip.au/link/abev). I described how to use that software in an article in April 2023 (siliconchip. au/Article/15740). Automatic testing of a vast range of equipment is possible using combinations of the four instruments in this series! Performance Noise and distortion are important performance measures for sinewave signals. As shown in Figs.1 & 2, for a 2V peak-to-peak signal from 20Hz to 2kHz, distortion was below 0.0025%, rising to only 0.0055% at 10kHz. Accurate measurement beyond 25kHz was not possible due to the predominant 3rd harmonic moving beyond the Nyquist limit of my audio analyser, which samples at 192kHz. siliconchip.com.au Features & Specifications » Seven waveform options: sine, square, pulse, triangle, stepped, IM (intermodulation) & white noise » Two independent or linked channels with adjustable phase difference » Maximum output level: 11.5V peakto-peak » Sine frequency range: 0.01Hz to 70kHz » Sine frequency response: ±0.1dB, 1Hz to 50kHz (see Fig.3) » Sine distortion: <0.003% to 5kHz, <0.007% to 20kHz (see Fig.2) » Signal-to-noise ratio: >80dB » Square, triangle and pulse frequency range: 0.01Hz to 20kHz » Intermodulation (IM), white noise and step functions » Comprehensive sweeps and tone bursts » Control via 3.5in LCD touchscreen and WiFi (web browser or SCPI) » TestController definitions for automation » Optional laser-cut bench stand The number of sample points at 10kHz is only nineteen, reducing as the frequency rises. At 50kHz, there are only four sample points per cycle, with the DAC’s interpolation filter raising the number to eight. It is no wonder that it is impossible to maintain extremely low distortion with very few samples per cycle. Measured distortion below 20Hz rises to 0.0055% at 7Hz. The actual distortion could be lower, as my test equipment is AC-coupled and the input filter’s drop-off degrades measurements below 20Hz. The background noise is -89dB (unweighted) below a 2V peak-to-peak output level in the 5Hz-20kHz band, mainly comprising 50Hz mains hum and its harmonics. That figure should be better at higher output levels as the signal will be greater but the noise/hum level will remain similar. The sinewave frequency response varies by less than ±0.1dB across the entire range (see Fig.3). Further exercising the DAC and filter with an SMTE/DIN standard intermodulation signal, a 4:1 mix of 60Hz and 7kHz, the artefacts are 100dB below the 60Hz peak and 88dB below the 7kHz component, as shown in Fig.4. siliconchip.com.au Fig.1: distortion at 1kHz measures 0.0026%, with noise nearly 90dB below the fundamental. Fig.2: distortion remains below 0.003% between 10Hz and 2.5kHz, rising to 0.006% at 25kHz, the limit of our testing capability. Fig.3: the DDS frequency response is flat within 0.1dB across the whole range. Australia's electronics magazine May 2024  41 Fig.4: in the intermodulation distortion (IMD) test, the sidebands, separated from the fundamental by 60Hz, are more than 100dB below the -3.18dBV 60Hz signal, which is off-screen for clarity. The sinewave frequency is very accurate and stable, being locked to the Pico’s crystal oscillator. As the phase accumulator has a finite number of bits, there will always be a small positive frequency error due to truncation from floating point to integer values when the per-sample phase increment is calculated. However, this frequency error is less than 0.012% across the audio band. Pulse waveforms have a resolution of 5µs due to the 192kHz DAC sampling rate. The maximum square wave frequency has been limited to 20kHz. While it is possible to create pulses with a shorter duration, the filtered output becomes increasingly rounded beyond that point (Scope 1). This is due to the DAC’s internal digital filter and the analog filter’s 100kHz corner frequency. The maximum slew time of rising and falling edges is 5µs (Scope 2), largely independent of voltage. This is mainly due to the DAC’s digital filtering and interpolation. For square, triangle and pulse waveforms, the available frequencies become more granular as the frequency Scope 1: by 16kHz, the square wave output starts to become rounded. 42 Silicon Chip increases, as each phase of the waveform – rise, high, fall and low – is limited to an integral number of samples. At 1kHz, the total number of samples in a cycle will be 192; the next available step, at 191 cycles, will give a frequency of 1.0052kHz. A 10kHz square wave will have 20 samples, slightly higher than the perfect value of 19.2, resulting in a frequency of 9.6kHz. The next available step, with 18 samples, is 10.66kHz. The step from 19.2kHz to 21.33kHz is twice as large. Sinewave generation is not greatly affected by the small number of samples at high frequencies due to the DAC’s oversampling at 384kHz, which fills in the missing samples quite effectively up to 60kHz, as seen in Scope 3. Closer to the Nyquist limit of 96kHz, artefacts from the DAC’s digital filter start destabilising the waveform (Scope 4). Signal generation Traditional analog sinewave generators, such as the Wien bridge, can produce excellent noise and distortion figures but lack flexibility. Generating more complex waveforms, such as tone bursts, frequency sweeps, triangular waves and dual-tone intermodulation (IMD) signals rapidly increases analog circuit complexity. Direct digital synthesis (DDS) provides the required flexibility and can be implemented with simple circuitry at the expense of somewhat more complex software. Generating a high-quality sinewave Scope 2: interposing a single sample midway between the high and low levels largely cures signal overshoot. Australia's electronics magazine siliconchip.com.au Most of the components and connectors, including the two main modules, mount on the side of the PCB shown at right. Sockets are recommended for the microcontroller and DAC modules, while IC sockets are optional. Either of the two commonly available PCM5102A modules can be accommodated on the PCB. The photo on the left shows the LCD screen, function LEDs and user controls, which are mounted on the rear of the main PCB. poses a significant CPU speed challenge. Calculating a separate sin(x) value for each sample is relatively time-consuming, requiring several double-precision floating-point calculations. At a 192kHz sampling rate, two new samples (for both channels) are needed every 5µs. Calculating a pair of values using sin(x) on the Pico, which lacks floating point hardware, takes 16µs, making direct calculation impractical. The calculations must take less than 1µs, leaving sufficient time for other processing and housekeeping tasks such as triggering, burst and sweep management. To achieve this, a 4096-entry sine lookup table (LUT) is pre-calculated. It contains one whole cycle of a sinewave in integer format. The code steps through the table, selecting the correct value for each sample. So that any frequency can be selected, not just those that correspond to exact entries in the table, the required location in the table is calculated using a 20-bit phase accumulator with a 12-bit upper part to index into the lookup table and an 8-bit lower part used to interpolate between the two nearest table entries. While there are many ways to calculate a value partway between two points on a curved line, the quickest is a linear approximation, which treats each segment as a straight line. While it might seem that this would lead to significant inaccuracies, the substantial size of the lookup table ensures that the error, which is greatest at the point of maximum curvature on Scope 3: the raw 20kHz sinewave output of the DAC (orange trace) has steps at 384kHz due to the DAC oversampling rate. The output of the filter circuit (green trace) smooths the steps out. siliconchip.com.au the sinewave, remains below 0.0005%. That is four times lower than the 0.002% distortion figure specified for the DAC. As the Pico does not have integer division arithmetic hardware, we have avoided using division during the calculation of individual samples by the simple expedient of precalculating the inverse of any required divisors using fixed point (with 10 bits for the fractional part) and multiplying instead. That is around 23 times faster than using actual division. The intermodulation mode sums the A and B channel sinewave calculations, sending them to the channel A output. Channel B may still be used for other waveforms while this is happening. White noise is implemented as a Scope 4: by 70kHz, the DAC output has become quite ragged, and the filtered output shows visible distortion near the peaks. The scalloping of the raw signal is due to the DAC’s internal digital filter. Australia's electronics magazine May 2024  43 sequence of pseudorandom values calculated to be within the desired voltage range. The square, triangle, pulse and step waveforms all use the same pulse-­ generating algorithm internally. Pulse signals are straightforward to generate, being a sequence of linear ramps between set points. For steep slopes, the value increments by an appropriate value for each sample, while for shallower slopes, the value is incremented after several cycles. When the slope approaches one increment per sample, the range of slopes becomes very limited. In this case, increments are calculated for blocks of 50 samples, increasing both slope granularity and accuracy. Channel A provides sweep and burst capability across a range of waveforms. For burst waveforms, the output alternates between the idle value and active signal, each with the desired 44 Silicon Chip number of cycles. For sinewaves, the idle value is the DC offset, while it is the low voltage set point for square, triangle, pulse and step waveforms. For IMD and white noise, it is 0V. For IM and white noise, the on and off periods are calculated in milliseconds, and the changes are made immediately after a zero-crossing to minimise transients. For all waveforms, the output is switched on or off immediately after a zero crossing to minimise transients. Sweeps are generated as a series of stepped values between two end points. Amplitude, frequency or duty cycle can be swept as appropriate to the waveform. Sweeps may be linear or logarithmic. At each sweep step, the new waveform value starts from the last output value (see Scope 5) to minimise transients. Negative values are problematic for logarithmic sweeps, as the logarithm of negative numbers is undefined. Australia's electronics magazine Where this is detected, a value of 0.01 is substituted for the offending setting. Circuit operation As shown in the full circuit diagram, Fig.5, we use an audio DAC (digital-to-analog converter, MOD1) driven by a microprocessor to generate the signals. Following the DAC is a filtering buffer amplifier (IC1), which reduces out-of-band frequencies and increases the available output voltage. The Raspberry Pi Pico W microcontroller at the heart of this project features two CPU cores and comprehensive WiFi and Bluetooth capabilities. In this application, one core is dedicated to signal generation while the other manages WiFi, the LCD screen, EEPROM, switches, the rotary encoder and housekeeping tasks. While the ESP32 used in previous instruments in this series has sub- siliconchip.com.au stantially faster arithmetic hardware that would be useful for DDS signal generation, the simplicity of uploading programs and the low cost of the Pico W made it a better choice for this project. A PCM5102A 24-bit stereo DAC chip translates the values calculated by the Pico into voltages, with a maximum output of 2.1V RMS (5.9V peakto-peak). Thanks to a charge pump that’s internal to the PCM5102 chip, it can produce negative and positive voltages from a single supply, allowing the design to be direct-coupled, which is critical for low-frequency signal generation. Modules containing the PCM5102A are readily available online, premounted with support components on a small PCB, avoiding the need to solder an SMD component with finely spaced pins. The circuit of our recommended module is shown in Fig.6. The top of the Function Generator has four RCA sockets for the two output channels plus the trigger input and output, as well as the coaxial power connector. It is shown here on the optional stand. A key design consideration was the DDS sampling rate. At 96kHz, two sinewaves can be comfortably synthesised on the Pico. However, the practical sinewave frequencies would be limited to around 35kHz and square waves to 10kHz before significant distortion. Simultaneously synthesising two sinewaves with a 192kHz sampling rate is difficult with the Pico running at its standard 133MHz clock speed. However, stable synthesis is achieved with mild over-clocking to 240MHz. That might seem extreme, but the maximum supported clock rate is Fig.5: the Pico W microcontroller module streams serial digital audio data to the PCM5102 DAC module. Its analog outputs are filtered and amplified by dual op amp IC1 and fed to the outputs at CON4 & CON5. The Pico W also manages the LCD touchscreen, control switches and LEDs. It provides web services via WiFi for remote control as well. siliconchip.com.au Australia's electronics magazine May 2024  45 The WiFi DDS Function Generator resting in the optional acrylic stand. 300MHz, and RP2040 processors have been clocked to 436MHz and beyond without damage. I ran some tests and after several hours of operation at 240MHz, the RP2040 chip was only a few degrees hotter than it was running at 133MHz. The DAC’s output signals are amplified and filtered to reduce out-ofband components using a dual lownoise NE5532 op amp IC, increasing the available output to 4.1V RMS (11.5V peak-to-peak), which should be sufficient for most applications. The DC-coupled filter allows voltage offsets to be applied to the signals, which is particularly useful for square, pulse, stepped and triangle waveforms. For the LCD screen, 3.5in touchscreens are only slightly more expensive than the 2.8in variety and provide 50% more screen area with 100% more pixels. While creating all sorts of waveform options in software is relatively straightforward, every option requires an on-screen parameter. To keep the Fig.6: the circuit of the PCM5102-based DAC module. Using it means we don’t have to solder the SMD IC. It provides two regulators and some other necessary components, including numerous bypass and filter capacitors. 46 Silicon Chip Australia's electronics magazine siliconchip.com.au size and separation of the on-screen buttons and text reasonable, we have limited the main elements of the touchscreen layout to seven lines of editable parameters and a row of buttons across the top and bottom of the screen. A 24C256 I2C EEPROM chip stores parameters when the circuit is powered off. While the Pico has onboard flash memory that could be used to store the values, it has a write endurance measured in tens of thousands of cycles, rather than the millions of a true EEPROM. With parameters saved every 30 seconds, the flash memory could wear out after less than 100 hours of use. The four pushbutton switches are debounced in software and use the Pico’s internal pull-up resistors to sense contact closure. The rotary encoder creates significant switching noise, so it requires additional components to function correctly; two RC low-pass filters remove most of the noise while passing up to 100 pulses per second. Power supply Powering the unit posed several challenges. The Pico generates significant noise in the 2-12kHz band from its onboard switch-mode voltage regulator. This is reflected back into the 5V supply if there is any significant resistance in the path between the supply and the unit, for instance, when powering it via a USB cable. A 5V supply is required for the Pico, LCD screen and PCM5102A module, while 3.3V is needed for the trigger input protection and rotary encoder circuitry. The op amp runs from a ±9V split supply; the supply rails for the buffer amplifier must be several volts greater than the desired maximum output and referenced to the analog rather than digital ground plane. Mixed-mode circuits should have separate ground planes for the analog and digital sections. These should be joined at only one point, preferably under the DAC chip. The PCM5102A module provides this feature, while a 10W resistor between the two ground planes ensures they remain closely coupled if the unit is tested without the DAC module in place. The device is powered from an external 12V DC source, with 9V linear regulator REG1 stabilising the supply for the linear electronics, plus 5V siliconchip.com.au Parts List – WiFi DDS Function Generator 1 double-sided PCB coded 04104241, 149 × 108mm 1 Raspberry Pi Pico W microcontroller programmed with 04104241A.uf2 (MOD1) 1 micro Type-B to Type-A USB cable (for programming the Pico W) 1 PCM5102A DAC module (MOD2) 1 200 × 114 × 40mm plastic instrument case [Altronics H0378] 1 12V 500mA+ plugpack (tip positive) 1 3.5in SPI TFT LCD touch screen (LCD1) [Silicon Chip SC5062] 4 PCB-mount RCA sockets (CON1, CON2, CON4 & CON5) [Altronics P0208C/P0145A, Multicomp Pro PSG01547, Keystone 97x series, Cliff FC68371] 1 PCB-mount coaxial power socket (CON3; size to suit plugpack) [Altronics P0620, Jaycar PS0519] 1 rotary encoder (S1) [Jaycar SR1230 (D shaft) or Silicon Chip SC5601] 1 ‘scrubber’ knob [Adafruit ADA-2055 (D shaft), Multicomp Pro MP716XX (splined or D shaft)] 2 white momentary PCB-mount pushbutton switches (S2 & S3) [Altronics S1099, Jaycar SP0723, C&K D6R (no LED) series] 2 red momentary PCB-mount pushbutton switches (S4 & S5) [Altronics S1095, Jaycar SP0720, C&K D6R (no LED) series] 2 20-pin headers, 2.54mm pitch (for mounting the Pico W) 2 20-pin header sockets, 2.54mm pitch (for mounting the Pico W) 1 9-pin header, 2.54mm pitch (for mounting the PCM5102 module) 1 9-pin header socket, 2.54mm pitch (for mounting the PCM5102 module; eg, cut from a longer strip) 1 6-pin header, 2.54mm pitch (for mounting the PCM5102 module) 1 6-pin header socket, 2.54mm pitch (for mounting the PCM5102 module) 3 8-pin DIL IC sockets (optional; for IC1, IC2 & REG3) 2 A5 laminating pouches for top and rear decals, 120 microns preferred Hardware 4 10mm M3-tapped spacers 4 6mm M3-tapped spacers 2 M3 × 8mm panhead machine screws 4 M3 × 16-25mm countersunk head machine screws 4 M3 × 12-16mm countersunk head machine screws 10 M3 hex nuts 4 small self-adhesive rubber furniture bumpers [Bunnings 0262216] 1 small tube of thermal paste OR 2 TO-220 thermal washers Semiconductors 1 NE5532 dual low-noise op amp, DIP-8 (IC1) 1 24C256 256kb serial CMOS EEPROM, DIP-8 (IC2) [Jaycar ZZ8485] 1 7809 9V 1A linear regulator, TO-220 (REG1) 1 7805 5V 1A linear regulator, TO-220 (REG2) 1 MAX1044 switched capacitor voltage converter, DIP-8 (REG3) [element14, DigiKey, Mouser] 1 BAT54S 25V 200mA dual series schottky diode, SOT-23 (D1) 1 1N5819 40V 1A schottky diode, DO-41 (D2) 1 red 3mm LED (LED1) 1 blue 3mm LED (LED2) 2 white 3mm LEDs (LED3, LED4) Capacitors 3 220µF 16V electrolytic 2 10µF 16V electrolytic 11 100nF 50V X7R ceramic 4 220pF ±5% polystyrene, MKP, MKT or NP0/C0G ceramic 1 100pF 50V ceramic Resistors (all 1/4W 1% axial leaded) 4 10kW 2 5.6kW 4 4.7kW 10 2.2kW 1 1kW 4 10W Parts for optional stand 4 3mm acrylic laser-cut pieces [Silicon Chip SC6932] 4 small self-adhesive rubber furniture bumpers [Bunnings 0262216] 1 small tube of superglue WiFi DDS Function Generator Short-Form Kit (SC6942, $95): includes everything except the case, USB cable, power supply, labels and optional stand. The Pico W is supplied unprogrammed. linear regulator REG2 to supply the Pico, LCD screen and DAC module. The DAC module has an onboard 3.3V regulator to supply its needs, providing adequate filtering of any noise fed back into the 5V supply from the digital circuitry. The 3.3V rail that provides clamping protection for the trigger input and the rotary encoder debouncing is taken from the Pico’s 3.3V output pin. To reduce the 5V regulator’s heat dissipation, its input is supplied by REG1’s output (9V) rather than directly from the 12V supply. The unit draws around 210mA when driving two 10V peak-to-peak sinewaves into 600W loads, so REG1 typically dissipates no more than 630mW ([12V – 9V] x 210mA). The -9V rail for the analog electronics (primarily the op amps) is generated by a MAX1044 switched capacitor voltage inverter chip (REG3) running at its boosted frequency to avoid in-band noise. The two 10µF electrolytic capacitors set the MAX1044’s oscillator frequency to around 100kHz, well above the maximum sinewave frequency. Schottky diode D2 ensures the output voltage never rises above 0V, which could otherwise occur when operating the unit without the DAC module in place, as the +9V rail is established before the MAX1044 starts oscillating. Without D2, the rise in AGND’s voltage relative to GND is enough to exceed the limit of allowable voltage on the MAX1044’s output pin, causing it to fail. The optional laser-cut acrylic stand. The lettering on the sides has been removed from the final version. Further attention has been paid to limiting the coupling of digital signal noise to the linear elements of the project. The high-speed digital signals supplied to the DAC module have 22W series resistors to reduce noise induction due to spikes and ringing generated from any trace capacitance and impedance mismatch. The ±9V supplies pass through RC low-pass filters comprising 10W resistors and 220µF electrolytic capacitors in parallel with 100nF ceramic capacitors before being applied to the op amp. These components decouple the supplies from the digital ground plane while keeping the voltage drop Scope 5: the signal level change is minimised at sweep step boundaries to avoid generating transients. 48 Silicon Chip manageable. This allows full-scale output into 600W before any increase in distortion. Filtering DACs produce wideband high-­ frequency noise as output level changes are in discrete steps. In the unfiltered blue and orange trace waveforms seen in Scopes 3 & 4, the output is not a pure sinewave, and signal changes occur at closer intervals than the sampling rate would suggest. This is because the DAC is oversampling, smoothing out changes by producing intermediate values at 384kHz. Second harmonic sinewave dis- Scope 6: a 10kHz square wave at the DAC output (blue trace) and after filtering (green trace). Both show significant overshoot compared to the improved version (see Scope 2). Australia's electronics magazine siliconchip.com.au extremes in each half-cycle improves this (Scope 2). The waveform becomes quite rounded once the frequency rises past 16kHz (see Scope 1). The green trace in Scope 7 shows smoothing of the slope of a 5kHz triangle wave by the analog filter. Note that the filter doesn’t noticeably increase the rounding at the top of the triangle wave, which is an artefact of the DAC’s digital filter. Triggers Fig.7: the two-pole Sallen-Key low-pass filter is designed to attenuate the signal by less than 0.1dB at 70kHz but more than 20dB by 384kHz. tortion is significantly decreased by oversampling, particularly at higher frequencies. A digital filter in the DAC chip provides a 60dB reduction in artefacts above the Nyquist limit, which is half the sampling frequency. The digital filter also restricts the signal slew rate. Analog filtering is provided to further reduce unwanted high-frequency signal components. The two-pole Sallen-Key filter built around IC1 is designed to be maximally flat within the passband and just a fraction of a dB down at 70kHz (see Fig.7). The filter has a gain of two. The values of the 2.2kW resistors connecting from the DAC outputs to the input of the op amp based filters are lower than might be expected. That is because the DAC module has 470W series output resistors. The result of this filter can be seen in the substantially smoother green traces in Scope 3 & 4. Square waves are the most impacted by both the digital and analog filters. Scope 6 shows the DAC and filtered outputs of a 10kHz square wave. The DAC’s digital filter generates some overshoot at the top of the cycle and some ringing at the bottom. Setting the last sample halfway between the two Scope 7: the filtered output of a 5kHz triangle wave doesn’t have noticeably more rounding at the top than the unfiltered signal. siliconchip.com.au A short 3.3V trigger pulse is produced at the start of burst, step and sweep waveforms on channel A. In sweep mode, the trigger output is set at the start of the sweep and reset at the end of the first step. For step mode, the trigger signal alternates at the end of each up/down staircase. To enable more reliable oscilloscope triggering at very low frequencies, a trigger output pulse is also produced for the midpoints of channel A sine, square and triangle signals. The trigger pulse is synchronised to signal calculations rather than the DAC output. As Scope 8 shows, the trigger can be seen to lead the DAC output signal change by several milliseconds. This is because the calculated values are passed to the DAC using five 512 sample DMA buffers, which allow accurate timing for the transfer of samples to the DAC by the Pico’s hardware. The time lag can vary between four and five buffer times (10-13ms), Scope 8: the trigger output pulse comes 10-13ms before the generated signal since the signal is buffered before transmission by the DAC. Australia's electronics magazine May 2024  49 depending on where the DAC and CPU are up to emptying and filling buffers. At frequencies of 10Hz and below, this jitter becomes a small fraction of the waveform and triggering is relatively stable. Channel A sweep, burst and step waveforms may be triggered using an external signal or an SCPI command. When enabled, a rising or falling edge will trigger the function. Two 4.7kW series resistors, a 100pF parallel capacitor and two schottky diodes clamping the signal within the 0V & 3.3V supply rails protect the Pico’s trigger input pin from ESD or accidental application of the wrong voltage. Schmitt triggers are configured on the Pico’s GPIO inputs, reducing false triggering from noisy sources, such as switches and relays. Component selection PCM5102A DAC modules are available from many online suppliers. The PCB accommodates either of the two most common module layouts (see the photos below). The one with L-shaped pinouts is preferred, as it has separate 3.3V regulators for the analog and digital supplies to the PCM5102A IC. I tested an OPA2134 op amp, but the NE5532 is preferred as it is significantly cheaper and has slightly lower 2nd harmonic distortion across the 5-30kHz range. Some components related to the NE5532 filters need close tolerances and linear dielectrics for good performance, so make sure the parts you These are the two PCM5102 modules that can be used in this design. We recommend the one on the left; we expect it to have lower output noise as it has separate 3.3V regulators for the analog and digital functions. use meet the specifications in the parts list. If suitable leaded capacitors are unavailable, SMD capacitors with an M3216/1206 or M2012/0805 footprint can be soldered across the pads on the PCB, assuming they meet the minimum specifications. 1% tolerance resistors are adequate throughout the design. The 3.5” LCD SPI touchscreen is commonly available and is the same as used in the Micromite LCD BackPack V3. It is available from the Silicon Chip Online Shop, along with the PCB for this project and some other parts. The footprints for PCB-­ mounting RCA sockets are unfortunately anything but standard. The two most common footprints can be accommodated on the PCB and are available from multiple suppliers, eg, Altronics has P0208C or P0144A, while other major parts suppliers stock at least one of Cliff FC68371, Keystone 970 series, Lumberg 1553-02 or Multicomp Pro PSG01547. Switched or unswitched varieties can be used. The centre height of the RCA connector barrel varies between types, which will affect the case drilling. We recommend using headers to mount the PCM5102A and Pico modules to facilitate commissioning and debugging. Sockets for the three 8-pin DIP ICs are optional. Rotary encoders come with either splined or D-shaped shafts; either can be used. I prefer ‘scrubber’ knobs with a small dimple on the top. The most commonly available is the Adafruit 35mm Scrubber Knob, which fits a flatted shaft. Whichever knob you select, make sure that the shaft fitting of the encoder matches the knob’s. Next month Part two of our series on building the WiFi DDS Function Generator next month will have all the construction details, programming instructions, testing procedures and usage instrucSC tions. U Cable Tester S B Test just about any USB cable! USB-A (2.0/3.2) USB-B (2.0/3.2) USB-C Mini-B Micro-B (2.0/3.2) Reports faults with individual cable ends, short circuits, open circuits, voltage drops and cable resistance etc November & December 2021 issue siliconchip.com.au/Series/374 DIY kit for $110 SC5966 – siliconchip.com.au/Shop/20/5966 Everything included except the case and batteries, see our website for postage rates 50 Silicon Chip Australia's electronics magazine siliconchip.com.au A must have reference for your projects in the year ahead. Did you miss out on a copy of our latest catalogue? Register today and we will send you a complimentary copy in the post. www.altronics.com.au/catalogue/ Your electronics supplier since 1976. 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Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 31/5/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. Subscribe to APRIL 2024 ISSN 1030-2662 04 The VERY BEST DIY Projects ! 9 771030 266001 $12 50* NZ $13 90 INC GST INC GST Pico Gamer A RETRO GAME CONSOLE WITH NINE GAMES INCLUDED Amateur Radio Operators and how to become a “ham” ROCK Model 4C+ SBC Review; Page 58 Australia’s top electronics magazine Skill Tester 9000 Project; Page 62 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. Free entry to the Altium Roadshow 2024 Thursday April 4 , 12:00 – 5:00PM AEDT Pullman Sydney Olympic Park, NSW 2127 <at> NEXUS ROOM th see page 7 ESP-32CAM LCD BackPack Project; Page 72 Reference MEMS Mics Project; Page 79 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 $70 $80 $52.50 1 year $127.50 $147.50 $100 2 years $240 $275 $190 6 months $82.50 $92.50 1 year $150 $170 2 years $285 $320 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 Prices are valid for month of issue. Try our Online Subscription – now with PDF downloads! Computer Storage Systems; February & March 2024 Raspberry Pi Pico Digital Video Terminal; March & April 2024 The Pico Gamer; April 2024 Becoming a Radio Amateur; April 2024 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 The Formula 1 Power Unit By Brandon Speedie Modern Formula 1 engines have incredible performance despite their modest size. They owe their high power and astonishing efficiency to the clever use of two electric motors and some smart electronics. Image Source: Jay Hirano Photography/Shutterstock.com T he current specification for Formula 1 race car engines was introduced in 2014. It was a major shift for the sport from the previous V8 petrol engines, given its much higher reliance on electrical power and a strong emphasis on efficiency. These hybrid engines can generate over 750kW, a remarkable feat considering its compact design—a turbocharged 1.6-litre V6 weighing only 145kg. Even more astonishing is its efficiency, peaking above 50%, nearly twice as efficient as most other petrol engines and approaching the theoretical maximum efficiency of a heat engine (54% for the 18:1 compression ratio per FIA regulations). This exceptional efficiency allows a Formula 1 car to cover an entire Grand Prix (300km) circuit at race speeds using just 100kg of fuel despite the constant acceleration and braking inherent in motor racing. Internal combustion engine To explain how the electrical system works, we first need to understand the internal combustion engine (ICE). Similar to the engines in most road-going cars, air enters the intake manifold 56 Silicon Chip and is mixed with a hydrocarbon fuel similar to petrol (with 10% ethanol). It is ignited inside the engine cylinders, producing heat. This increased heat, and therefore pressure, pushes down on a piston, which attaches to a crankshaft and ultimately to the rear wheels for propulsion. Assuming perfect combustion and a 9:1 mixture by weight of octane (the closest single hydrocarbon to regular petrol) and ethanol, the chemical reaction is: 58 C8H18 + 16 CH3CH2OH + 773 O2 → 496 CO2 + 570 H2O The turbocharger After passing through the engine, the combustion byproducts are expelled as hot exhaust gas (a mixture of CO2 and steam). While they are considered waste to the piston engine, they still contain heat, which can do useful work. Some of that ‘waste’ energy is used to spin a shaft by attaching a turbine to the exhaust manifold. The shaft is connected to a compressor assembly on the intake manifold, which increases the intake fuel and air Australia's electronics magazine mixture density, allowing more molecules to enter the fixed volume of the engine. Burning this greater air/fuel volume produces higher cylinder pressures and therefore more power. This increased intake pressure is referred to as ‘boost’. The hybrid system The electrical system operates together with the ICE to increase power and efficiency. It consists of two electric motors, which can also work as generators: the Motor Generator Unit – Kinetic (MGU-K) and the Motor Generator Unit – Heat (MGU-H). There is also a small (4MJ or 1.1kWh) Energy Store (ES) unit, which can be used to keep power from these generators for later use. Some participating F1 teams initially experimented with a mechanical flywheel-style ES, or capacitors, but all have now adopted a lithium-ion battery. The type of motor used for the MGU-K and MGU-H is a closely guarded secret but they are almost certainly permanent-magnet synchronous reluctance (PMSynRM) types. The PMSynRM is a hybrid motor siliconchip.com.au An exploded view showing the components of the energy recovery system in an F1 engine. Source: Renault combining technology from permanent magnet motors and synchronous reluctance motors. Its theory of operation is similar to that of a hybrid stepper motor, which we previously covered in some detail (January 2019 issue; siliconchip.au/Article/11370). The rotor in a PMSynRM motor is designed to have a very low reluctance in one axis and a high reluctance in another axis offset by 45°. When the stator windings apply a rotating magnetic field, a reluctance torque is generated that rotates the rotor with very little power loss. Pure SynRM motors do not need permanent magnets; the PMSynRM motor is a hybrid type that includes some permanent magnets in the flux barriers for increased torque and power at a given motor size – see Fig.1. Recently, the PMSynRM motors have begun to gain widespread use. They have slightly higher efficiency than an equivalent induction motor, as there are lower resistive losses in the rotor (no squirrel cage with induced currents and therefore resistive heating). However, PMSynRM motors have high torque ripple, which makes them difficult to control. It has only been recent advances in power electronics and control algorithms that have made them attractive for general use. Tesla Motors has begun using PMSynRM in their newer vehicles, moving away from the induction motor their company siliconchip.com.au namesake, Nicola Tesla, so famously invented. The Motor Generator Unit – Kinetic (MGU-K) The MGU-K is a 120kW motor connected to the crankshaft of the ICE. Regulations limit the rotational speed to ‘just’ 50,000 RPM. By coupling the MGU-K to the engine crankshaft, the motor has a direct path to the wheels. When operated as a motor, the driver has 120kW of extra power available. When operated as a generator, electrical energy can be harvested and stored in the ES as the car is slowing for a corner, ie, regenerative braking. This also means the rear disc brakes can be much smaller and lighter than they would otherwise need to be; the MGU-K provides much of the stopping force, so the mechanical brakes have much less power and heat to dissipate. The Motor Generator Unit – Heat (MGU-H) Fig.1: PMSynRM motors use a combination of radially variable reluctance and permanent magnets to provide very high power and efficiency in a compact package. Flux lines are obstructed along the q-axis but not along the d-axis. Note that the flux guides/barriers don’t have to line up with the motor poles, and they are usually more gracefully curved in a real motor. Australia's electronics magazine The MGU-H is similar to the MGUK, except it is coupled to the turbocharger shaft rather than the engine crankshaft. The F1 rules allow a higher rotary speed limit of 125,000 RPM to better suit the typical operating speed of a turbo. Unlike the MGU-K, it has no mandated power limit. The MGU-H has two primary functions. One is to operate as a generator, harvesting electricity from the turbine. On a traditional engine, a turbo’s operating speed is controlled by a wastegate, which opens to bypass exhaust around the turbine as it approaches maximum speed. This gas is effectively wasted (although many people like the whooshing sound it generates on accelerator lift-off!). On a Formula 1 engine, the MGU-H May 2024  57 controls the turbine speed. Once the engine has enough boost, the motor begins generating electricity, which has the side benefit of acting as a turbo boost controller. In this way, no exhaust gas is wasted and the engine’s overall efficiency is drastically improved. This is known as “cogeneration”. It is worth noting that the engine also has a wastegate, as in a traditional turbocharged engine. However, it only opens in specific scenarios that will be described later. The MGU-H can also operate as a motor to help spool up the turbo when there is insufficient exhaust gas for the turbine to do it alone. This is most often done exiting a corner, where the driver is beginning to accelerate, but the turbo is not yet spinning fast enough to provide adequate boost. The MGU-H is thus used to eliminate ‘turbo lag’, a common complaint from drivers of turbocharged cars who suffer degraded throttle response and driveability. It’s less of a problem on a racetrack because you can anticipate needing to accelerate, but it’s still something that would otherwise need to be managed by the driver. Turbos suffer two related problems: turbo lag refers to the time the turbine takes to spin up from a sufficient exhaust flow, while the ‘boost threshold’ is the amount of exhaust required before the turbine can produce maximum boost. Both cause a delay in full power availability, and both are mitigated by the MGU-H being able to spin the turbine up on demand, regardless of exhaust flow. Energy flows The MGU-K, MGU-H, and ES all work together to optimise the racecar’s performance. This orchestration is performed by the control electronics, which can quickly redistribute power between each component. The control electronics can control when the MGU-K and MGU-H act as a motor or generator, the amount of power delivered or extracted, and where that energy goes. Regulations limit some power flows, while others are left unbounded – see Fig.2. The ES is capped at 4MJ of deployment each lap, which gives the driver 33 seconds of additional power through the 120kW MGU-K. Of this 4MJ, up to half can be provided by the MGU-K through regenerative braking. The rest of the ES charge comes from the MGU-H, which has no harvesting limit. Power can also flow directly from the MGU-H to the MGU-K, which bypasses the ES and is therefore not counted in the 4MJ limit. This ends up being a large proportion of the overall deployment energy in a typical race lap. Control algorithms Teams spend considerable resources modelling the system’s behaviour to develop optimum control algorithms. These ‘maps’ change to suit every track and will have different options depending on the driver’s needs at any given time. Let’s consider how the hybrid system might respond to one corner of a race track, with reference to Fig.3. As the car approaches the corner, the driver applies the brakes. During the stopping phase, the MGU-K operates as a generator, sending power to the ES to charge it up. The driver is neither braking nor accelerating through the corner apex, so the system is idle. Upon exiting the corner, the driver begins to open the throttle. Power is deployed from the ES to the MGU-H to spool up the turbocharger. As more throttle is applied, the exhaust gas begins to take over from the MGU-H in spinning up the turbo, so less and less power flows from the ES. Once the car has straightened out, the driver has the throttle fully open. Power flows from the ES to the MGU-K to give the driver maximum acceleration. The turbocharger is now fully spooled up, so the MGU-H crosses over from being a motor to a generator and starts supplying the MGU-K directly, rather than discharging the ES. The MGU-H continues to supply the MGU-K for much of the straight. On approach to the next corner, energy from the MGU-H is diverted from the MGU-K to charge up the ES. The driver will feel this as a sudden loss of power, as the MGU-K is no longer deploying. The drivers call this a ‘derate’, and it is a common source of complaint over the radio. While it may feel unnerving to a driver to suddenly lose power under the pressure of a race, it is the overall best choice as the ES needs to be recharged for deployment on the next corner exit, which is much more critical to overall lap time than corner entry. Once the driver applies the brakes, the entire cycle repeats. The driver can use different modes to help them execute their race strategy. For example, if a driver is approaching a slower car, they might opt for a charging mode, which will harvest slightly more power than usual, and the ES will charge up to its maximum of 4MJ. When the driver is ready to attempt an overtake, they can swap to a more Fig.2: a block diagram of a current, standard Formula 1 power unit. The ICE is combined with a turbocharger, two electric motors (MGU-K and MGU-H) and an energy storage system (Li-ion batteries), forming a hybrid power source. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au aggressive mode (via the buttons and flaps on the steering wheel), which will discharge the ES and give the driver extra power to complete the overtake. The car in front can also use its battery defensively to try to retain track position against the faster car approaching from behind. The hybrid system thus allows an element of catand-mouse between drivers. For this reason, overtakes can be many laps in the making; the attacking driver may need to mount multiple attempts to deplete the battery pack of the car in front before the move can be made. Qualifying mode An interesting configuration of the hybrid system occurs during qualifying, where the cars are timed over a single lap. During this session, it is all about power; there is less need to optimise efficiency. When in ‘quali mode’, there are periods where the wastegate is purposefully opened, venting otherwise usable energy. This reduces the back pressure on the engine, allowing it to make marginally more power. To retain boost, the MGU-H constantly takes power from the ES to spool the turbo. This can be thought of as an electric supercharger system. As the energy stored in the ES only needs to last a single lap during qualifying, this unusual mode actually provides peak performance. Fig.3: an example of how the MGU-H, MGU-K and energy storage system can recover kinetic energy during the entry to a corner and increase acceleration out of the corner. The exact profiles will vary depending on the corner speed, radius, what follows it etc. Formula 1 teams and drivers work to optimise the precise scheme used for each corner of every track. Road-going versions The technology behind the MGU-H and MGU-K has filtered down to production vehicles. The Mercedes-Benz SL 43 AMG features an “electrically assisted turbocharger” from Garrett (which they call an E-Turbo). It functions similarly to the MGU-H, eliminating turbo lag. The Mercedes-Benz AMG ONE is a sports car featuring a modified version of the Formula 1 engine, with the addition of two electric motors driving the front wheels. This system provides up to 360kW of electric propulsion, in addition to the 422kW from the ICE directly, for a total of 782kW. This vehicle has achieved numerous lap records for a road-going production car, including at the famed Nürburgring Nordschleife, beating the previous record by a staggering 13 seconds. SC siliconchip.com.au Fig.4: a top-down schematic view of the Mercedes-Benz power unit. Note the elongated turbocharger shaft, allowing the compressor and turbine to be positioned at either end of the engine. This is unusual as the turbine and compressor are normally next to each other, in the same housing. Intake air and fuel are in blue, while exhaust is in red/orange. The MGU-H is coupled to the turbocharger shaft and is in the engine V to save space, while the MGU-K connects to the engine crankshaft. Australia's electronics magazine May 2024  59 Mini Projects #001 – by Tim Blythman SILICON CHIP Symbol Keyboard We are already using this Mini Project every day. It’s easy to build and requires only a Leonardo board and a display shield. It’s a Symbol Keyboard, allowing you to easily type symbols and other characters that don’t appear on regular keyboards. M any of the articles that we write include scientific, mathematical or typographic symbols that aren’t easily entered with a keyboard. In Windows, for example, some symbols can be entered from the so-called Emoji Panel; previously, tools like Character Map allowed symbols to be copied to the clipboard for pasting into a document. However, those methods are slow and awkward. Windows also supports ‘Alt codes’, which allow a code (corresponding to a specific symbol or character) to be entered on the numeric keypad. Many of the available characters come from what is known as Code Page 1252. Since a Leonardo board can emulate a USB keyboard, it can generate these key sequences as needed. While a series of pushbuttons could be used for input, we have decided to use an LCD touch panel, as it allows us to customise the available symbols. By using a display shield, assembly is simple: just plug the shield into the Leonardo board. Of course, it needs to be programmed; we have used the Arduino IDE for this, so it is easy to modify or customise. The photo shows a complete Symbol Keyboard populated with our choice of symbols. We often use these symbols when writing our articles, but there are many other useful ones in the Windows Code Page 1252 set. Many are accented letters used in languages other than English. Note that the Alt codes scheme only works on Windows computers, so this keyboard will not work on other operating systems. Alt codes should also work in Linux, but for macOS, you would have to modify the software to use either Option codes or text replacements. Assembly and programming Plug the display shield into the Leonardo and use the USB cable to connect it to a computer. That completes the physical assembly! Next, download the sketch (siliconchip.au/ Shop/6/378), extract the ZIP file, open the sketch with the Arduino IDE and upload the sketch. You shouldn’t need any external libraries. While the sketch is compiling, open a text editor window (eg, Notepad) to test the Symbol Keyboard. This will also help to catch any stray keystrokes if there is a problem. You should see the LCD screen initialise with the graphics seen in our Parts List – Symbol Keyboard (JMP001) 1 Arduino Leonardo [Jaycar XC4430] 1 2.8in Colour LCD Touch Screen Shield [Jaycar XC4630] 1 USB Micro-B to Type-A cable [Jaycar WC7723 or similar] 60 Silicon Chip Australia's electronics magazine photos. Pressing any of the symbols on the display panel should cause the corresponding symbol to be typed into the text editor. In that case, all is well. If your display is not correct, try pressing the touch panel to see if that triggers keystrokes. That should still work even if the display is wrong. If the touch panel isn’t responding, try reprogramming the Leonardo. Software details The software is relatively straightforward. It displays a series of symbol buttons on the LCD and waits for a touch to be registered on one of them, after which it sends the appropriate key sequence to the attached computer. The Arduino AVR board profile (which supports the Leonardo) includes the keyboard library. We have written a function that wraps the sequence needed to send the Alt code. The XC4630d.c file is customised for the specific display shield we’re using; you might need to set the shield version near the top of this file. We’re using the XC4630_v4 #define, which works well with a recently obtained shield sample. The bitmaps.c file contains the data for displaying the symbol images on the screen. We created them as 64×64 pixel files in Microsoft Paint by entering the necessary Alt codes to create matching text characters at a 48-point size. siliconchip.com.au The Symbol Keyboard is a simple and compact project based on an Arduino Leonardo and 2.8in LCD touchscreen module. It is usable without an enclosure, although it’s a good idea to add some rubber feet to protect your desk. We then used the online converter at siliconchip.au/link/abu6 to generate the data used in the program. You can use similar steps to create your own custom symbol images. You also need to set correct Alt codes to ‘type’ them. We found them on the Wikipedia page at https://w. wiki/9SGq We knew they would type the corresponding characters later since we used the Alt codes to generate the corresponding bitmaps. Customisation To customise the symbols, you must change the Alt code in the codes[] array. The appropriate code can be found in the Windows 1252 Code Page (link above). You will also need to add a matching monochrome bitmap to the bitmaps.c file and add a reference to that in the bitmaps[] array. Apart from creating custom bitmaps to display different symbols, The 64×64 pixel bitmaps were created with a 48-point font in Microsoft Paint. We made them by typing the same Alt codes that we set the program to produce when they are selected. siliconchip.com.au the orientation of the buttons on the display can be changed too. The XC4630_rotate() command in setup() determines the orientation. Values 2 and 4 are landscape mode, while values 1 and 3 give portrait orientation. ROWS and COLUMNS should be changed to 4 and 3 to make the portrait orientation work correctly. The BUTTON_WIDTH and BUTTON_HEIGHT #defines determine the spacing between the buttons. Using a spacing of 80 pixels with bitmaps measuring 64 pixels means that there is a comfortable amount of room between them. If you are confident with the Arduino IDE, you can change these values to fit more buttons and thus symbols on the display. You could create smaller bitmaps too. The colours can also be changed by modifying the FGC and BGC #defines. The available colour names are listed in the XC4630d.c file. Other 16-bit (RGB565) colour values can be used here instead. Note that you must re-upload the sketch for any changes to take effect. Conclusion It’s a simple build, but the Symbol Keyboard has already become a handy tool for us while we write our articles. We can’t believe we didn’t think of it SC earlier! These characters in the Windows 1252 Code Page can all be typed by the Symbol Keyboard. Alt codes for Unicode characters exist but require the Windows Registry to be modified to enter them. Australia's electronics magazine May 2024  61 SILICON CHIP Mini Projects #003 – by Tim Blythman Thermal Fan Control This project demonstrates how two modules can be combined with a bit of extra circuitry to do a useful job. The result is a circuit that will power a load, like a fan, when the ambient temperature exceeds a set threshold. T he fans in practically all modern desktop PCs are thermally controlled. This means that they are only turned on when needed, usually when the PC’s internal temperature gets too high. The fans can turn on when the temperature rises, moving hot air and replacing it with cooler air. Some PCs can even run the fans at different speeds, depending on the temperature. Older PCs always had their fans running at full speed. Being able to control them means that noise is kept down and the wear and tear on the fans is minimised. This project has a similar function; it provides automatic control of a fan based on temperature and can be adjusted to work at different temperatures, but it doesn’t require a microcontroller. It could be useful, for example, to power a ventilation fan in a room if the temperature inside that room gets too high. We use the Jaycar XC4494 Temperature Sensor Module to sense the ambient temperature and the Jaycar XC4488 Mosfet Module to switch the fan (or other low-voltage DC load) on and off. The Temperature Sensor Module produces an analog voltage that depends on the temperature. We apply that voltage to a simple comparator chip that produces a high or low level output, depending on whether the analog voltage is above or below a set level. Circuit details Fig.1 shows the resulting circuit. Note the two boxes that correspond to the two modules. The circuitry Parts List – Thermal Fan Control (JMP003) 1 Temperature Sensor Module [Jaycar XC4494] 1 Mosfet Module [Jaycar XC4488] 1 12V DC fan [Jaycar YX2512 or similar] 1 12V 500mA plug pack or other 12V power source [Jaycar MP3011] 1 17-row breadboard or protoboard [Jaycar PB8820 or HP9570] 1 2.1mm DC socket [Jaycar PS0526 or PA3713] 1 10kW potentiometer (VR1) [Jaycar RP7510] 1 LM311 comparator IC, DIP-8 (IC1) [Jaycar ZL3311] 1 100nF 100V MKT capacitor (C1) [Jaycar RM7125] 1 100μF 25V electrolytic capacitor (C2) [Jaycar RE6140] 1 220W 1/2W axial resistor (R1) [Jaycar RR0556] 1 1MW 1/2W axial resistor (R2) [Jaycar RR0644] 1 8-pin DIL IC socket (optional, for IC1) [Jaycar PI6500 or PI6452] Assorted breadboard wire/jumper wires [Jaycar PB8850 or WC6027] 62 Silicon Chip Australia's electronics magazine and components in those boxes come pre-soldered to the module when you buy it. One advantage of this analog approach is that we can run all the circuitry from 12V DC rather than needing to generate a lower voltage to run a microcontroller. That reduces the necessary parts and simplifies the design. The parts we’re using will happily run from 5V up to 18V. IC1 is a comparator. In simple terms, when the voltage at + pin (pin 2) is higher than the – pin (pin 3), output pin 7 ‘floats’ and is pulled up to 12V by current from the 220W resistor. The rest of the time, when the + voltage is lower than the – voltage, IC1 internally connects pin 7 to pin 1, where pin 1 is at 0V (ground). That means the output is 12V when the + voltage is higher than the other, or at 0V when the + voltage is lower. By connecting the pin 7 output to the SIG line of the Mosfet Module, the Mosfet switches on when the voltage at pin 7 is 12V, and when the Mosfet is on, it powers the fan. VR1 is a potentiometer that provides our voltage/temperature setpoint; the wiper voltage can be adjusted between 0V and 12V by rotating the shaft on top. This adjustable voltage is applied to pin 2 of IC1. Thus, IC1 compares the VR1 setting to the voltage from the Temperature Sensor Module, so siliconchip.com.au have delayed the hysteresis, making it much less effective, as we found in one of our early prototypes! By reversing the connections to the trimpot and Temperature Sensor module and swapping those inputs, the output of IC1 behaves the same. However, the hysteresis problem is solved, as no capacitor is connected to the trimpot wiper. The remaining components are 100nF and 100μF supply bypass capacitors that stabilise the circuit by smoothing out any changes to the incoming supply voltage. Top left: the small component with the black bead is a 10kW negative temperature coefficient (NTC) thermistor. That means its resistance is close to 10kW at 25°C, decreasing as the temperature rises. Jaycar’s RN3440 is an NTC thermistor similar to the module’s onboard one. Top centre: the Mosfet Module consists of the components shown in the right-hand box in Fig.1 and can be replaced by their equivalents if you want to build a version without modules. Jaycar’s ZT2468 (IRF1405 Mosfet) is similar to the IRF520. Right: any 12V brushless DC fan will do for this project. We have used the Jaycar YX2512. adjusting VR1’s screw lets you set the temperature at which the output will switch. Hang on – isn’t it backwards? While the S pin of the Temperature Sensor Module connects to pin 3 of IC1, its V pin is connected to ground (0V), and the G pin is connected to the 12V supply. That might seem backwards, but the Temperature Sensor module is just a group of passive components, none of which care about polarity, so we’re free to connect it this way. When wired this way, an increasing temperature causes a decreasing voltage at the S pin. VR1 is also wired ‘backwards’, so that turning the screw clockwise reduces the wiper voltage, to match the behaviour of the Temperature Sensor Module. The reason for doing it this way is to allow us to provide predictable hysteresis. That is the purpose of the 1MW resistor. When IC1’s pin 7 is high, some current flows through the 1MW resistor, raising the potentiometer wiper voltage slightly. Since VR1 is wired backwards, this is the same as reducing the setpoint slightly, meaning that the temperature has to drop a little after the fan switches on before it switches off. That stops it from ‘juddering’ on and off rapidly when the ambient temperature is hovering near the switching setpoint. If we had wired the circuit up the ‘normal’ way, the hysteresis current would have to be applied to the input connecting to the S terminal of the Temperature Sensor Module. The filter capacitor in that module would Construction We built our prototype on a PB8820 solderless breadboard. Still, the design is well-suited to the HP9570 prototyping board, which has an identical layout and will provide a more robust and permanent result. We soldered short lengths of wire to the modules to make for a neat layout. If you prefer not to solder, the circuit will work with jumper wires but may not be as tidy. In our photos, all red wires connect to the 12V supply and all black wires go to 0V. Use the photos and circuit diagram to wire yours up like ours. We placed the 1MW resistor on top of IC1, as it connects between pins 2 & 7. Also, the 220W resistor has had its lead bent by 180° so that it can be wired to two adjacent rows, connecting to both pins 7 and 8 of IC1. We used a soldered DC socket to supply power, but you could use the Jaycar PA3713 screw terminal version if you prefer. Leave the fan off for testing, since the Mosfet Module has an indicator LED that shows whether it is on or off. We used a 12V DC plugpack for Fig.1: this simple circuit uses a comparator (IC1) to compare a setpoint (from VR1) with the voltage from a Temperature Sensor Module (on the left). The 1MW resistor feeds some voltage back from the comparator’s output, providing hysteresis that stops the fan from turning on and off rapidly if the temperature is near the setpoint. siliconchip.com.au Australia's electronics magazine May 2024  63 Silicon Chip Binders REAL VALUE AT Pin 1 $21.50* PLUS P&P Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. 64 Silicon Chip The potentiometer at upper left sets a voltage that is compared to the voltage from the Temperature Sensor Module. If the temperature is higher than that set by the potentiometer, the fan is switched on by activating the Mosfet Module to supply 12V. We have included some close-ups of the wiring. power, but a 9V battery (connected using a PH9251 battery snap to 2.1mm plug) should be fine for initial testing. If you start with VR1 fully anti-­ clockwise, the LED should be on initially. It should go off at some point as you rotate VR1 clockwise. If the LED works in reverse or isn’t switching on and off as VR1 is adjusted, check your wiring before connecting the fan. Turn VR1 anti-clockwise until the LED is on, then turn it back until it just goes off. If you now touch the Temperature Sensor Module’s thermistor, the LED should switch on as the thermistor registers a higher temperature (assuming the ambient temperature is lower than your body temperature!). After a while (depending on the settings and ambient temperature), the LED will switch off. In that case, all is well, and you can connect the fan and adjust VR1 for a suitable switch-on threshold. Australia's electronics magazine That would be easiest to do if the thermistor were exposed to a temperature close to your desired threshold, eg, by heating a bit of metal and then holding it against the thermistor. Let it stabilise, then adjust VR1 until the fan just switches on at that temperature. If a DC motor is connected to the output (rather than a BLDC fan), a back-EMF quenching diode needs to be connected across it to avoid damaging the Mosfet at switch-off. Summary The comparator was one of the first integrated circuits, appearing around 60 years ago. Even modern microcontrollers often include one or more among their internal peripherals. This project is a great example of how a simple chip like a comparator can interface to analog and digital modules, and perform a role often delegated to more complex devices. SC siliconchip.com.au Mini Projects #004 – by Tim Blythman SILICON CHIP Wired Infrared Remote Extender IR (infrared) remote controls have been around for about 50 years, with TV being one of the first major applications. They are used in many fields, so components and modules for IR remote control systems are widely available. Here’s how to use them to build an IR remote control extender. S ometimes an IR remote doesn’t have enough ‘reach’, especially if the receiving device is in another room, around a corner or blocked by furniture. The Wired IR Extender is a simple fix for that problem; it can easily be built with just a few components. Rather than transmitting the binary ones and zeroes of IR codes as the presence or lack of an IR signal, the IR beam is modulated (turned on and off) at around 38kHz and further encoded to simplify reception and error checking. The modulation helps to make IR signals immune to interference from things like sunlight and fluorescent tubes, since they do not modulate their IR output near 38kHz. A simple design Thanks to the technology packed into modern electronics modules, we can create the Wired IR Extender with a couple of simple modules and a few other bits and pieces. The main components are the IR Receiver Module and an IR LED Module. While it might appear that we could simply connect one to the other, the IR Receiver Module demodulates the 38kHz IR carrier, but the IR LED Module has no internal means of reapplying the modulation. So we need some extra circuitry to add back the necessary modulation. Fig.1 shows the resulting circuit. The 100μF and 100nF bypass capacitors help to reject noise on the 5V supply rail and keep its voltage stable. The IR Receiver Module contains the parts in the box on the left. The part labelled IR1 could be substituted by a separate component like Jaycar’s ZD1952 IR receiver. The output (at the S pin) usually sits near 5V, but when an IR signal around 38kHz is detected, this pin goes low, lighting up the LED on the The Wired IR Extender is built on a small prototyping board, which can easily be put into a small Jiffy box for permanent use. You can run two wires (eg, a figure-8 cable) to situate the Transmitter Module wherever it needs to be. siliconchip.com.au May 2024  65 220Ω 10kΩ The lines drawn on top of the board 2 x 1kΩ module. That is called an activelow output. The 555 timer based circuit turns the active low signal from the IR Receiver Module into a 38kHz modulated active-high signal that can drive the Infrared Transmitter Module, which consists of nothing more than an IR LED (similar to Jaycar ZD1945) on a PCB. NPN transistor Q1 and its two resistors (1kW & 10kW) form an inverter that turns the active low signal into an active high signal. With no IR signal falling on the IR Receiver Module, current flows into Q1’s base, turning it on. When Q1 is on, it conducts current into its collector (C) and out of its emitter (E). The voltage at the collector is therefore low. If an IR signal is received, the S pin goes to 0V and no current flows into the base of Q1, so Q1’s collector voltage can rise to 5V due to current flowing through the 10kW resistor. That allows the 555 to oscillate and deliver a 38kHz-­ modulated signal to the IR LED. The inverted signal from Q1’s collector goes to IC1’s RESET pin (RS, pin 4), so IC1’s output (O, pin 3) is low whenever there is no IR signal. However, when RESET is high, the 555 timer can operate. Its output will be mirror the copper tracks on the underside. 10nF output producing a 38kHz square wave. This signal is applied to the IR LED as long as the IR Receiver 100nF Module receives a signal. Note that when there is no sig100μ 100 μF nal, current through LED1 must flow through both 1kW resistors. When a signal is detected and the S pin is near ground, current only needs to flow through one of the resistors. So you will see the LED’s brightness increase as a signal is received. high after the TRIGGER (Tr) pin goes below 1/3 of the supply voltage, then Construction switches low when the THRESHOLD We built our prototype on a bread(Th) pin goes above 2/3 of the supply board pattern prototyping PCB and voltage. recommend you do the same, as we The TRIGGER (pin 2) and THRESH- found that using a breadboard added OLD (pin 6) inputs are joined, and stray capacitance. Some of this stray the 10nF capacitor is kept discharged capacitance appears in parallel with when RESET is low by the 1kW resis- the 10nF capacitor, slowing down tor. So the 555’s output goes high as the oscillator. That means it may not soon as RESET goes high. work, although we found that many The 10nF capacitor charges up from devices were not too fussy about the the OUTPUT through the 1kW resis- exact frequency. tor until the voltage on it (and thus To help you place and wire up the the TRIGGER and THRESHOLD pins) components, closely examine the reaches 2/3 of the 5V supply. The out- prototype photos; solder the compoput goes low and the 10nF capacitor nents and wires in place as shown. To discharges until the 1/3 supply voltage make it easier to see where the coppoint is reached. per tracks go on the underside of the The cycle continues, with the 555’s PCB, we have drawn lines on the top Pin 1 Fig.1: the two boxes correspond to the modules; they could be replaced by the separate parts in each box. The Receiver Module demodulates the incoming IR signal. Q1 and IC1 add back the modulation before resending the signal via the Transmitter Module. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au Silicon Chip PDFs on USB Scope 1: the blue trace is the voltage at the Receiver’s S pin, while the green trace is the voltage at IC1’s pins 2 and 6 (across the 10nF timing capacitor). The red trace is the voltage across the Transmitter LED, while the yellow trace is the signal from another Receiver Module that is not connected to the circuit. and + and – symbols on the two supply rails. Note that pin 1 of the 555 is near the 100nF capacitor (towards the bottom in both photos). We used stiff wire to join the modules to the PCB. You can use longer wires (or jumper wires) to place the Transmitter further from the Receiver. We recommend using short wires for the Receiver and longer wires for the Transmitter, especially since there are only two wires to the Transmitter. You could use a socket for the IC rather than soldering it directly to the board. Take care with the orientation of the transistor. Its pin 1 (collector) is connected on the same row as IC1’s pin 4, with the Q1’s flat edge facing away from the middle. The white wire in the photo loops over the top of IC1, from its pin 6 to pin 2; add it last. Testing Solder the Transmitter and Receiver modules, but leave off the S wire for the Receiver (yellow in the photos). This allows IC1 to run and the Transmitter will produce a signal continuously, so you can aim the Transmitter at the Receiver to test them both. Apply 5V to the + rail and connect supply GND (0V) to the – rail. The LED on the Receiver module should light up. If you wave your hand between the Transmitter and Receiver, the LED should flicker as the signal changes. If you don’t see this, use an oscilloscope, multimeter or frequency counter to check the frequency at either end of the 220W resistor. Scope 1 shows some of the waveforms you should see. Once the circuit is working, hook up the last wire and deploy the Extender. Don’t aim the Transmitter at the Receiver in use; otherwise, it will be SC confused by its own signal! ¯ 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. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 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). Parts List – Wired IR Remote Extender (JMP004) 1 breadboard-pattern prototyping circuit board [Jaycar HP9570] 1 555 timer IC, DIP-8 (IC1) [Jaycar ZL3555] 1 8-pin DIL IC socket (optional; for IC1) [Jaycar PI6500] 1 IR Transmitter Module [Jaycar XC4426] 1 IR Receiver Module [Jaycar XC4427] 1 BC548 NPN transistor, TO-92 [Jaycar ZT2154] Assorted solid-core wire [Jaycar PB8850] 1 5V DC supply 1 100μF 16V electrolytic capacitor [Jaycar RE6130] 1 100nF 100V MKT capacitor [Jaycar RM7125] 1 10nF 100V MKT capacitor [Jaycar RM7065] 1 10kW 1/2W 1% metal film resistor [Jaycar RR0596] 2 1kW 1/2W 1% metal film resistor [Jaycar RR0572] 1 220W 1/2W 1% metal film resistor [Jaycar RR0556] siliconchip.com.au Australia's electronics magazine EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OR PAY $500 FOR ALL SIX (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS May 2024  67 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. ONLY 2895 $ QM1517 HANDY FOR THE HOME TOOLBOX AUTORANGING FOR EASE OF USE • TEMPERATURE • DUTY CYCLE • NON-CONTACT VOLTAGE ONLY 6495 $ QM1323 FOR THE TECH'S TOOLBOX FOR A STUDENT OR APPRENTICE ONLY 59 $ 95 QM1321 ACCURACY OF TRUE RMS MEASUREMENT • CAPACITANCE & FREQUENCY • TRANSISTOR HFE TEST • DIODE & AUDIBLE CONTINUITY • NON-CONTACT VOLTAGE ONLY 3595 $ QM1020 EASY TO READ MEASUREMENTS • MIRROR BACKED SCALE • TRANSISTOR LEAKAGE TEST • AUDIBLE CONTINUITY Test & Measure with our GREAT RANGE of multimeters at the BEST VALUE, to suit hobbyists and professionals alike. Explore our wide range of multimeters, in stock on our website, or at over 115 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 119 $ QM1549 WIRELESS BLUETOOTH® FEATURE FOR DATA LOGGING • AUTORANGING • TRUE RMS • 6000 COUNT • IP67 WATERPROOF ONLY 179 $ QM1594 ONLY 219 $ 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 • • • $33.95 $39.95 $59.95 Max Hold • • • $64.95 $87.95 $87.95 IP Rated Price • Max Hold • • $28.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $35.95 $65.95 1000VDC/ 750VAC 4000MΩ • • • IP67 $16.95 QM1493 $119 IP67 $109 $179 $219 $329 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. John Clarke’s Mk2 Fan Speed Controller On a hot night, a gentle cooling breeze from a fan can keep you cool and help you to sleep. This new Fan Speed Controller is an effective, noise-free, low-speed fan controller. It works with ceiling, pedestal and box fans. M ost fans include speed control, but many run too fast, even on their slowest setting, and can be pretty noisy. If you want to use the fan to keep cool while sleeping, you don’t need a fast breeze but just gentle air movement. You also don’t want the fan blades or the motor to make any noise that will keep you awake. Whether a fan makes noise at a slow speed depends upon the type of speed control. Of the methods used for controlling fan speed, phase control causes the most motor noise. This type of control is where just a portion of the full mains sinewave is applied to the fan motor. Because just a part of the mains waveform is applied, it produces a rapid change in voltage as the waveform is switched on and off. That can produce vibration in the motor windings and bearings, causing a buzzing sound. Other fan speed controllers use a switch that selects from one of several different capacitors or inductors. While they don’t generally make the fan motor noisy, they only provide a few fixed speeds and the lowest speed is usually not that slow. Our Fan Speed Controller does not use phase control; instead, it introduces resistance in series with the fan motor to adjust the fan speed. The mains sinewave is simply reduced in voltage without changing the wave shape. Applying a sinusoidal voltage to the motor ensures the fan makes minimal noise. It also provides continuous adjustment from stopped to full speed or anywhere in between. This does have the disadvantage that power is dissipated as heat. But Fig.1: AC is applied to the motor but the diode bridge ensures that Mosfet Q1 only sees DC. 70 Silicon Chip Australia's electronics magazine considering that most fans will draw a maximum of 60W at full speed and less as speed is reduced, the heat produced is modest and can be dissipated by the aluminium diecast box, which acts as a heatsink. We don’t need to dissipate anywhere near 60W because, at full speed, the dissipation in the controller is relatively low since the resistance of the controller is low. At lower speeds, where the controller resistance is higher, dissipation increases. But because the motor is running slower, the overall power drawn by the fan is much less than at full speed. An over-temperature thermostat will switch the power off should there be excess heat buildup. This precaution prevents the speed controller from overheating and possibly causing skin burns if touched. For the resistance element, we use a Mosfet with a drain-to-source resistance that can be controlled by adjusting the gate voltage. The Mosfet can behave like a very low resistance for full-speed operation or a higher resistance under partial conduction for slower speeds. A single Mosfet cannot directly control the mains AC voltage. While it operates as a resistance element when the current flows in one direction, in the other direction, it is shunted by an intrinsic diode that’s part of the Mosfet structure. To prevent reverse current flow siliconchip.com.au Fan Speed Controller, Mk2 Features & Specifications » Quiet fan speed control » Suitable for 230V AC shadedpole fan motors » Full control of motor speed from stopped to maximum » Over-current limiting » Over-temperature cutout » Fuse protection against faults » Rugged aluminium case » Fan power: 80W maximum » Fuse: 1A, 230V AC » Current limiting: 235mA at low speed, up to 940mA at high speed » Over-temperature cutout: triggers with case at 50°C (resumes at 45°C) This photo shows the completed Fan Speed Controller PCB mounted in the case without any of the wiring. through the Mosfet, the Mosfet is placed within a full wave bridge rectifier. That way, it only handles current in one direction, but an alternating current (and voltage) is still applied to the fan. Fig.1 shows the general arrangement. The Mosfet (Q1) is between the positive and negative terminals of the bridge rectifier. When the mains Active voltage is more positive than the Neutral, current (i1) flows from Active through the motor, diode Da, Mosfet Q1, then diode Dc to Neutral. When the Active is more negative than Neutral, current (i2) flows from Neutral through diode Dd, Mosfet Q1, diode Db and the fan motor to Active. In both cases, the current through Mosfet Q1 is always from its drain to its source and never in the reverse direction, so the current never flows through the body diode. Full circuit description The circuit for the Fan Speed Controller is shown in Fig.2. It comprises just one IC, several diodes, the high voltage Mosfet, Q1, plus some resistors and capacitors. Power for the circuit is derived directly from the 230V AC mains. The entire circuit floats at mains potential, including circuit ground, which is not connected to mains Earth. The critical part of the circuit comprises potentiometer VR1b, op amp IC1a and Mosfet Q1. This part of the siliconchip.com.au circuit allows the user to adjust the average voltage across Mosfet Q1 using potentiometer VR1b. As VR1b is rotated clockwise, the voltage applied to pin 2 of IC1a reduces. IC1a reacts by increasing the gate voltage of Mosfet Q1 to reduce the average voltage across its channel. That might seem backward, rotating clockwise to reduce the voltage. However, Q1 is in series with the fan motor, so the fan gets more voltage when the voltage between Q1’s drain and source is lower. So when VR1b is fully anticlockwise, the average voltage across Q1 is at a maximum, and the applied voltage to the fan is at a minimum. As VR1b is rotated clockwise, the voltage across Q1 decreases, and the voltage applied to the fan increases, allowing it to speed up. At the same time, IC1b monitors the current through Q1 and provides current limiting to prevent excessive current flow that could overheat and damage Q1. That usually should not happen, but it depends on what is plugged into the outlet. Perhaps someone will plug in a fan that’s too large or a different load, in which case IC1b will activate to protect Q1. In more detail Op amp IC1a, which drives the gate of Mosfet Q1, is connected in a feedback control loop that monitors a divided version of the voltage across Australia's electronics magazine Q1’s channel (drain to source) and the voltage from the wiper of speed potentiometer VR1b. IC1a adjusts its output voltage so the divided Mosfet channel voltage matches that set by the speed potentiometer. The divider is formed by a 220kW 1W resistor and a 5.1kW 1/4W resistor. The voltage from this divider is filtered with a 10μF capacitor, providing a DC voltage proportional to the average of the full-wave rectified voltage. The resistive divider is there to produce a voltage suitable for monitoring by IC1a. When monitoring up to 230V AC (325V DC peak), the divider output is around 7.4V peak that averages to 4.7VDC after filtering. This average voltage is 63.7% of the waveform peak voltage and well within the input range for IC1a when powered from a 15V supply. As the resistance of Q1 decreases and the fan speeds up, there is more voltage across the fan motor and less voltage across the Mosfet. The voltage from the divider therefore also reduces. The Mosfet source also has a 1W series resistor that connects it to circuit ground for current monitoring. This increases the voltage applied to the divider by about 1V, depending on the fan motor current, but this does not affect the output from the voltage divider much. That’s because 1V is a small fraction of the hundreds of volts that can be across the Mosfet. May 2024  71 Fig.2: the circuit diagram for the Fan Speed Controller Mk2. Op amp IC1a controls the resistance of Mosfet Q1 to regulate the fan speed while op amp IC1b prevents the fan from drawing too much current. Potentiometer VR1b is used to set the fan speed. It connects in series between a 22kW resistor from the +15V supply and a 150W resistor to the 0V supply. With this resistor string, the voltage range for VR1a’s wiper is 5V to 0.07V. The lower voltage for VR1b is deliberately made to be slightly above 0V as IC1b would oscillate if it were set to 0V. Another reason for keeping the lower limit at 70mV is to avoid the Mosfet operating outside its safe operating area, but more about that later. If VR1b is set to produce 2V DC at its wiper, IC1a adjusts its drive to the gate of Q1 so that the voltage monitored at the resistive divider junction is also 2V DC. 2V on the divider means that there is 88V average across Q1, equivalent to 97.5V RMS. If the mains voltage is 230V AC, the voltage across the fan is 230V minus 97.5V or 132.5V RMS. 72 Silicon Chip The feedback control ensures that the voltage across the Mosfet is strictly maintained to prevent changes in the motor speed. Without the feedback control, just applying a fixed voltage to the gate of Q1, the fan would slow quite markedly as the Mosfet heats up. That’s because the Mosfet drainto-source resistance increases with temperature. Apart from adjusting the speed control (VR1b), the only other factor that can alter the fan speed is if the mains voltage changes. Typically, the mains voltage is reasonably constant, fluctuating by less than 5%. Current limiting Current limiting for this circuit is necessary since we are operating the Mosfet in a linear mode for speed control. Linear operation has the Mosfet operating in a region of Australia's electronics magazine partial conduction where it is neither fully conducting (with minimal on-­ resistance) nor fully off. This differs from a switching circuit where the Mosfet is either fully on or off. Linear operation sees the Mosfet dissipating significant amounts of power, so the Mosfet must be kept within the safe region of its drain current (Id) versus drain to source voltage (Vds) over the entire voltage range. The manufacturer’s safe operating area (SOA) graph for the Mosfet shows the region of operation. Fig.3 shows the DC SOA curves for three different Mosfets that can be used in this circuit. SOA graphs also show the pulsed region of operation, but since we are not switching the Mosfet on and off, we have only included the DC SOA curves. These keep the Mosfet semiconductor junction below 150°C. For each Mosfet to be used safely, we siliconchip.com.au need to keep the curve in the operating region below the DC SOA curve. If the Mosfet is operated above the curve, it will likely fail due to melting (maybe not immediately, but eventually). The red line indicates our circuit’s current limit to safeguard the Mosfet. We restrict the maximum current to around 1A up to about 20V Vds. Up to 20V, the fan will run fast. The Vds will be higher at lower fan speed settings, so we reduce the current limit to prevent it from encroaching on the SOA curve. For the slowest speeds and highest Vds, the current is limited to around 230mA. That does not mean the Mosfet will be operating near this curve. It is just an overload threshold where the Mosfet is protected from damage, should conditions cause the Mosfet operating point to otherwise go above the current limit curve. IC1b monitors the voltage across the 1W 5W resistor in series with Q1 for current limiting. This resistor converts the fan current to a voltage; eg, at 1A, it has 1V across it. IC1b is connected as an amplifier with a level shift due to VR1a. As the voltage across the 1W resistor exceeds the voltage at the wiper of VR1a, IC1b’s output goes high and drives the pin 2 input of IC1a high via diode D2 and the 1kW series resistor. This overrides the motor speed setting of VR1b, slowing the fan speed to reduce the current. If the voltage across the 1W resistor is less than the voltage set at the wiper of VR1a, IC1b’s output is low and has no effect on IC1a, as D2 is reverse-biased. VR1a is connected across the 15V supply similarly to VR1b, but the padder resistors have different values. The 200kW and 3.3kW resistors set VR1a’s wiper range to 235-940mV. VR1a and VR1b share the same shaft, so adjusting the fan speed will automatically adjust the current limit. Note that VR1b’s wiper produces a lower voltage as the potentiometer is rotated clockwise, while VR1a’s wiper voltage increases as it is rotated clockwise. That’s so that the current limit is higher for faster fan speeds. Power supply Mains power is applied to the controller via fuse F1, which is within the IEC input connector. This protects the circuit against excessive current flow should a fault occur, such as a broken wire short-circuiting against the siliconchip.com.au Fig.3: the DC SOA (safe operating area) for three different Mosfets. The current limiting curve is well within all three. Two of the curves are limited by the minimum Mosfet on-resistance at lower voltages, so even if the red line was extended to lower Vds values, it couldn’t cross them. enclosure. Both power switch S1 and over-temperature switch TH1 must be closed for the Active mains conductor to be connected. Switch S1 includes a Neon indicator that lights when the unit is switched on. TH1 monitors the temperature of the fan speed controller enclosure and switches off power if it reaches 50°C. It will reconnect power once the temperature drops to 45°C. This 5°C temperature hysteresis prevents the controller from switching on and off rapidly since it will take some time to cool by 5°C. The Neon indicator within S1 will be unlit whenever TH1 is open. The AC terminals of bridge rectifier BR1 connect between the Neutral of the incoming mains supply and the Neutral of the general purpose outlet (GPO) for the fan motor. When the fan is connected, it is connected to mains Active via the GPO from switch S1. BR1 is a 6A, 400V bridge rectifier. As mentioned earlier, the bridge keeps the polarity of the voltage applied to the Mosfet consistent while the fan motor receives AC. A 15V supply to power the remainder of the circuit is obtained using a 22kW dropping resistor via diode D1 directly from the 230V AC mains switched Active. A 470μF capacitor filters the rectified waveform to produce a smoothed DC voltage clamped to 15V by zener diode ZD1. This 15V supply powers dual op amp IC1, Mosfet Q1 and the associated diodes, resistors and capacitors. Using an X2 capacitor instead of a 22kW resistor would be slightly more efficient, like the previous design from the May 2014 issue (siliconchip.au/ Article/7595). However, the capacitor Make sure to use plenty of cable ties to secure the wiring, and heatshrink at the ends. Australia's electronics magazine May 2024  73 Fig.4: the overlay diagram for the Fan Speed Controller. is somewhat expensive and bulky, and requires other support components like a second bridge rectifier. We decided it was not worth the size, expense or complexity for a slight increase in efficiency. Enclosure & mounting options Fig.5: the cutting and drilling guide for the diecast aluminium case. Depending on the application, the potentiometer can project from the side of the case or the lid, so read the text before making any holes. The red circle shows the hole for the shaft when mounting the pot on the lid (which is only possible if the GPO is not used). Three different diecast aluminium enclosures can be used to house the Fan Speed Controller: an IP65 diecast box measuring 115 × 90 × 55mm (Jaycar HB5042), an IP66 diecast box measuring 114 × 90 × 55mm (Altronics H0423) or an economy diecast box measuring 119 × 94 × 57mm (Jaycar HB5064). The PCB is shaped so that it fits within the contours of the Jaycar HB5042, allowing it to be mounted horizontally on the enclosure’s integral lands. For the other two enclosures, there are minimal internal contours to avoid but also no integral PCB-mounting lands, so the PCB needs to mount using four 9mm Nylon standoffs, attached via holes drilled in the base. The Fan Speed Controller can be built as a standalone controller that plugs into a mains socket for power and has a general purpose outlet (GPO) that the fan plugs into. This version is suitable for pedestal and box fans. For ceiling fans, the Fan Speed Controller can be built to intercept the fan wiring at the wall switch. In this case, it will need to be installed by a licensed electrician. The speed control adjustment potentiometer can be placed at one end of the enclosure, like the standalone version, or on the lid, which may be more convenient if the enclosure is wall-mounted. Construction The Fan Speed Controller is built on a PCB coded 10104241 that measures 94 × 79mm. To assemble it, follow the overlay diagram, Fig.4. Begin by soldering in the resistors, using the table for the colour codes in the parts list, but leave the 5W resistors off for the moment. Diodes D1, D2 and ZD1 can be fitted next, taking care to orientate them correctly (and don’t get the three different types mixed up). You can use an IC socket for IC1, or it can be directly soldered in. The latter should give better long-term reliability. Either way, be sure to install the socket and the IC correctly, with the notch facing the direction shown 74 Silicon Chip Australia's electronics magazine siliconchip.com.au on the overlay. Then mount the two 5W resistors, slightly raised from the PCB surface, to aid in cooling. Install the capacitors next. The 100nF capacitor may be labelled as 104. The electrolytic capacitors have their value directly marked and must be orientated correctly, with the longer leads through the holes marked with a + symbol. However, the larger 10μF capacitor is non-polarised (NP) and can be mounted either way around. Fit diode bridge BR1 now, taking care that the cut corner is towards the top left of the board and placed adjacent to the + symbol. Before installing VR1, its shaft may need to be cut to length to suit its knob. Do not install the potentiometer on the board if it is to be mounted on the lid. The six-way screw terminal strip (CON1) can be fitted now. Q1 is mounted by kinking the outer two leads outward so that they will fit into the more widely spaced holes in the PCB. This wider spacing provides a 2.54mm clearance between the Q1 mounting pads and prevents possible arcing between the leads with peak voltages approaching 400V. Keep the Mosfet as high as possible above the PCB, with about 1mm of the leads protruding below the PCB. Final assembly The cutting and drilling guide (Fig.5) should help you to make the required cutouts in the case. You can download that as a PDF, along with the panel label artwork, from our website at siliconchip.au/Shop/19/6928 Fig.5 shows the locations, sizes and shapes of the IEC connector and GPO cutouts, which are suitable for all three enclosure options. For the version that mounts on a wall for controlling ceiling fans, you don’t need to make the IEC connector hole or the one for the lid-mounted GPO. Just fashion the cutouts for the switch, potentiometer and Earthing points. As mentioned earlier, in the wallmount application, the potentiometer can be mounted either on the PCB for end-mounted speed adjustment or on the lid. Regardless, the box must be Earthed. Access holes to fit grommets for the wiring can be made in the base of the box so that the fan wiring can be concealed in the wall. For the standalone controller, first mark the hole position for the IEC siliconchip.com.au Parts List – Fan Speed Controller Mk2 1 double-sided PCB coded 10104241, 94 × 79mm 1 115 × 90 × 55mm IP65 diecast box [Jaycar HB5042] OR 1 114 × 90 × 55mm IP66 diecast box [Altronics H0423] OR 1 119 × 94 × 57mm economy diecast box [Jaycar HB5064] 1 panel label (see text) 1 10kW dual-gang 24mm PCB-mount linear potentiometer (VR1) [Jaycar RP3510] 1 plastic knob to suit VR1 1 6-way 15A 300V terminal barrier strip, 8.25mm pin spacing (CON1) [Altronics P2106] 1 SPST 10A 250V AC rocker switch with integrated neon lamp (S1) [Altronics S3228] 1 normally-closed 10A 50°C thermal switch (TH1) [element14 1006842] 1 1A 250V AC M205 fuse (F1) 1 8-pin DIL IC socket (optional) Semiconductors 1 LM358 dual single-supply op amp, DIP-8 (IC1) 1 400V 10A N-channel Mosfet, TO-220 (Q1) [FQP11N40C (element14 2453436), AOT10N60 (SC4571) or IRF740 (Altronics Z1539)] 1 15V 1W zener diode (ZD1) [1N4744] 1 400V 6A PW04 diode bridge rectifier (BR1) [Altronics Z0082] 1 1N4004 1A 400V diode (D1) 1 1N4148 200mA 75V signal diode (D2) Capacitors 1 470μF 25V 105°C PC electrolytic 2 10μF 16V 105°C PC electrolytic 1 10μF 50V 105°C non-polarised (NP) PC electrolytic 2 100nF 63V or 100V MKT polyester Resistors (all ¼W, 1% axial unless specified) 2 1MW 1 22kW 5W [element14 1306258] 1 220kW 1W 5% 1 10kW 1 200kW 2 5.1kW 1 22kW 1 3.3kW 3 1kW 1 150W 1 1W 5W 5% Hardware & cable 1 TO-220 mica insulating washer 1 TO-220 3mm screw hole insulating bush 4 5.3mm ID insulated quick connect crimp eyelets with 4-6mm wire diameter entry [Altronics H1825A, Jaycar PT4714] 1 200mm length of green/yellow striped 7.5A mains-rated wire 1 200mm length of brown 7.5A main-rated wire 1 200mm length of blue 7.5A mains-rated wire 1 160mm length of 5mm diameter heatshrink tubing 1 20mm length of 20mm diameter heatshrink tubing 2 M4 × 10mm panhead machine screws and hex nuts 2 4mm shakeproof (toothed) washers 3 M3 × 10mm panhead machine screws and hex nuts 3 extra 24mm potentiometer washers [Jaycar RP3500] 10 100mm cable ties 2 M3.5 × 6mm screws (only for Jaycar HB5042 case) 4 M3 × 9mm Nylon spacers ● 4 M3 × 6mm panhead machine screws ● 4 M3 × 6mm countersunk head machine screws ● 1 small tube of thermal compound 1 2mm-thick piece of scrap aluminium sheet (if required; see text) ● only for Altronics H0423 or Jaycar HB5064 case Extra parts for the standalone version, for pedestal and box fans 1 surface-mount GPO side-entry mains socket (GPO1) [Altronics P8241, Jaycar PS4094] 1 fused IEC mains input connector [Altronics P8324, Jaycar PP4004] 1 7.5A IEC mains plug lead 2 M3 × 10mm countersunk machine screws and hex nuts 4 small stick-on rubber or felt feet Extra parts for the wall-mounted version, for ceiling fans 1 M205 10A 250VAC panel-mount safety fuse holder [Altronics S5992, Jaycar SZ2028] 1-2 grommets or cable glands for input and output wires 1 600mm length of brown 7.5A mains wire (if VR1 is mounted on the lid) 1 120mm length of 5mm diameter heatshrink tubing (if VR1 is mounted on the lid) Australia's electronics magazine May 2024  75 Fig.6: the wiring diagram for the Fan Speed Controller with the potentiometer mounted on the PCB and its shaft projecting out the side of the case. connector and Earth screw in the end wall of the case. The IEC connector mounts with a gap of about 4mm from the base of the case to the bottom of the IEC connector. The hole is made by drilling a series of small holes around the perimeter of the desired shape, knocking out the piece and filing it to shape. Alternatively, use a Speedbore drill 76 Silicon Chip to make a larger round hole to remove most of the required area, then file that hole to the required shape. The Earth screw hole is 4mm in diameter. A hole is required for the potentiometer at the opposite end of the box. Measure the height of the potentiometer shaft above the base of the enclosure and mark out the drilling position at the end of the enclosure. Australia's electronics magazine Alternatively, for the potentiometer mounted on the lid, drill the hole in the centre of the GPO cutout. Note that the potentiometer can only be installed on the lid for the ceiling fan version that doesn’t require the GPO socket. Insert the PCB into the case and note that the leads for Q1 must be kinked outward from the PCB a little so the siliconchip.com.au Fig.7: here’s how to wire up the Fan Speed Controller if you’re mounting the potentiometer on the lid. This is only practical for hardwired installations. metal flange of the Mosfet sits in intimate contact with the side of the case. You can then mark the mounting hole position for Q1’s tab and drill it to 3mm in diameter. Deburr this hole on the inside of the case with a countersinking tool or larger drill to round off the sharp edge of the hole. This is to prevent punch-through of the insulating washer. siliconchip.com.au TH1 also mounts on the side of the box adjacent to Q1. There is room in the Jaycar HB5042 enclosure to mount TH1 against the side of the enclosure between two sets of protruding slots intended for mounting PCBs vertically. The Jaycar HB5064 enclosure does not have such slots, so there is plenty of room for mounting TH1. Australia's electronics magazine For the Altronics case, there is insufficient room for TH1 to mount flat against the side of the enclosure. One solution is to grind away sufficient protruding slot material so the thermostat’s body can sit flat. The alternative is to make up an aluminium packing piece that’s 19 × 45 × 2mm. This can sit between the protruding slots, and the thermostat May 2024  77 Fig.8: how to mount Mosfet Q1 to the case. The finished PCB for the Fan Speed Controller. can be mounted against that. In this case, the top mounting hole should be about 8mm down from the top edge of the box. Note that you will find it easier to install TH1 if the M3 nuts are tack-­ soldered to the thermostat mounting bracket. To do this, place the screws into the thermostat mounting bracket (when it is out of the case) and screw on the nuts, then solder them in place and remove the screws. For the standalone version, holes are also required in the lid for the general purpose outlet (GPO) mains socket, the power switch and the Earth terminal. Four PCB mounting holes are also needed if you are not using the Jaycar HB5042 enclosure. The PCB is positioned so the speed potentiometer can protrude through the hole at the end of the enclosure. Labels Panel labels (see Fig.9) can be downloaded as a PDF from our website using the earlier link. Details on making a front panel label can be found at: siliconchip.au/Help/FrontPanels The download includes two versions of the front panel. Which one you use depends on whether the control pot is mounted on the lid or is at the end of the enclosure. If the potentiometer is PCB-mounted, its locating lug must be bent backward or snapped off, as we have not made a hole for it. Then slip three washers over the potentiometer shaft, insert it 78 Silicon Chip into the hole in the case by angling the board and drop the PCB onto the mounting points. For the Jaycar HB5042 enclosure, secure the PCB to the case with the two screws supplied with the case plus two extra M3.5 × 6mm screws. For the other enclosures, the PCB is mounted using M3 × 6mm screws into M3-tapped standoffs. Secure the PCB-mounted potentiometer by placing another washer over the shaft on the outside of the case and doing up the nut on top. Attach Q1 to the case with an M3 machine screw and nut, with the mica insulating washer and insulating bush as per Fig.8. Apply a thin smear of heatsink compound on all mating surfaces before assembly. We use the mica washer in preference to silicone since mica has a higher thermal conductivity (lower °C per watt value), and the mounting screw can be tightened more. That keeps the Mosfet cooler compared to using a silicone washer. After mounting Q1, check that the metal tab of the device is isolated from the case by measuring the resistance between them with a multimeter. The meter should show a very high resistance measurement (several megohms or possibly “0L”) between the enclosure and Mosfet tab or the enclosure and any of Q1’s leads. Check that it also reads close to 0W between the enclosure and the mounting screw. The complete wiring diagrams for the two versions are shown in Figs.6 & 7. The Earthing details of the case are most important since Q1 and the potentiometer are all at mains potential, yet they are attached to the case. If the insulating washer or the insulation of the potentiometer were to break down, the case would be live (at 230V AC) if it was not properly Earthed. The case lid must be independently Earthed rather than relying on the lid making contact with the base of the enclosure. All mains wiring must be done using 7.5A minimum mains-rated (230V AC) wire. The IEC connector must be wired using the correct wire colours: We used an aluminium packing piece between the thermal cutout and the case rather than grinding the rails down. Note the soldered nut highlighted in yellow. Australia's electronics magazine siliconchip.com.au brown for Active, blue for Neutral and green/yellow striped for the Earth. Active and Neutral wires soldered to the IEC connector must be insulated with heatshrink tubing covering all exposed metal. Solder the Earth wire to the IEC connector Earth pin, ensuring the Earth terminal is heated sufficiently so that the solder wets and adheres properly to both the Earth terminal and wire. After that, use a crimping tool to secure the Earth wire into the crimp eyelet. The Earth wires from the Earth point to the lid and the GPO are also terminated with crimped eyelets. Secure the Earthing eyelets with M4 machine screws, star washers and nuts. A second nut should be tightened on top of the first as a lock nut. The IEC connector is secured to the case by 10mm M3 countersunk head screws and nuts. Finally, attach cable ties to hold the wire bundles together as shown in the wiring diagrams and the earlier photo of the fully assembled unit. Remember to place the four rubber feet on the bottom of the case. Testing As the whole circuit floats at mains potential, everything on the board should be considered unsafe to touch whenever the circuit is connected to the mains. That means the IEC mains power lead must be unplugged every time before opening the lid. Do not be tempted to operate the fan speed controller without the lid in place and screwed in position. Before you power up the device, set VR1 fully anticlockwise. Also check all of your wiring very carefully against the overlay and wiring diagram. Verify that the case, lid and potentiometer are connected to the Earth pin of the power socket using a multimeter on its low ohms range. If you are satisfied that all is correct, you are ready to screw the lid onto the case. Note that the IP65 and IP66 enclosures are supplied with a rubber seal that goes between the enclosure base and lid. We did not use that seal so that heat from the case can transfer to the lid more efficiently for better dissipation. The easiest way to test the circuit operation is to connect a fan. Apply power and check that you can vary its speed with VR1. Note that the fan controller box will begin to run quite warm with extended use when driving the fan at intermediate speeds. This Fig.9: this label is for the Speed Controller with potentiometer on the lid. The other smaller label is only used if mounting the pot to the end of the case. All labels (including the alternative lid label) are available to download from siliconchip.au/ Shop/19/6928 siliconchip.com.au Australia's electronics magazine temperature rise is normal. The temperature rise should be lower if the fan is set to a low speed. Troubleshooting If the speed controller does not work when you apply power, it’s time to do some troubleshooting. First, a reminder: all of the circuitry is at 230V AC mains potential and can be lethal. That includes any exposed metal parts on components, except those tied to the Earthed case. Do not touch any part of the circuit when it is plugged into a mains outlet. Before going any further, give your PCB another thorough check. Check for incorrectly placed components, incorrect component orientation or bad solder joints (dry joints, missed joints or bridges). Optional heatsink If the Fan Speed Controller works but cycles on and off due to the thermal cutout activating, a fan heatsink can be attached to the side of the enclosure where Q1 is mounted using M3 screws and nuts. The recommended 105 × 25.5 × 55mm fan-type heatsink is available from Altronics (Cat H0520) or Jaycar (Cat HH8570). The mounting holes are placed along the centre line of the heatsink. The lower hole should be positioned high enough not to foul the PCB when the nut is on. The heatsink is positioned with its lower edge at the same level as the bottom edge of the box. The heatsink should be counter-­ bored at the Q1 and TH1 mounting screw positions. You can find where these screws are located by temporarily securing the heatsink onto the side of the case with the two M4 screws, with a thin layer of Blu-tack pressed onto the heatsink in each screw area. When the heatsink is removed, there will be an impression of the screw heads. Drill out those two locations to a shallow depth using a larger drill to allow for the screw heads to sit inside the heatsink. Mount it with a smear of heatsink compound over the mating surfaces. As an alternative, if countersunk screws are used for TH1 and Q1, there will be less counter-boring required on the heatsink. SC May 2024  79 Background image: https://unsplash.com/photos/gaming-room-with-arcade-machines-m3hn2Kn5Bns Skill Tester 9000 Part 2 – by Phil Prosser This retro game is a fun and educational project to create a dexterity-based game with nine difficulty levels, a health bar graph, a timer and four different sound effects. It is based mainly on 4000-series logic and all through-hole parts on a single circuit board. T here are some sections of this game that advanced constructors can customise, such as changing the winning and losing tunes, but we will describe the assembly process for the standard version. There is definitely scope for customisation when you make the wire ‘obstacle course’, as you can make it as easy or as hard as you want! The assembly instructions will be given in seven discrete steps. After adding the parts for each step, you will have new functions to test, so you can pick up any problems early on and fix them before tracking them down will be more difficult. You shouldn’t need any special tools; a soldering iron, solder, fume extractor and a multimeter for testing should be all that’s required. Construction We will build the Skill Tester 9000 section by section and test each as we go along. This allows people to work with young constructors or students in simple sessions, achieving visible progress in each. Even as an experienced constructor, I build projects in 80 Silicon Chip bite-sized chunks as it makes debugging simpler and there are built-in coffee breaks. The Skill Tester is built on a double-­ sided PCB coded 08101241 that measures 174 × 177mm. During construction, refer to the PCB overlay diagram (Fig.5) and Photo 1 to see which components go where and how they are orientated. Here are general cautions and instructions you should keep in mind during the construction process: • Ensure all diodes are fitted the right way around (stripe to the right or down on this PCB). • All LED cathodes are upwards; LEDs have a chamfer (flat edge) on the cathode side. • All ICs are installed with pin 1 to the right. If you get one backwards and are not using sockets, you will have to cut all pins off using side cutters and pull individual pins out (unless you have a hot air rework station). • Check the supply rail voltage every time you power it up after adding parts. We have included a ground test point, with a 9V test point close by Australia's electronics magazine (below IC1). You should measure more than 8V between the two with a fresh battery. If not, something is wrong. • If something is wrong and, while you are investigating, the noise from the speaker is slowly driving you insane, put a 1kW resistor in series with the speaker to tone things down a bit. • Standard checks as you solder: are there any solder blobs shorting pins? Is each solder joint shiny with the right shape? Has the solder adhered to both the component lead and the PCB pad? • For each polarised part, check before and after soldering that it is the right way around. Also check the part numbers of ICs and double-check the orientation before you solder them. • If you need to check clock signals and don’t have an oscilloscope, put your DVM on its AC setting and probe the test point. You should measure a few volts AC or see pulses in the reading for very slow clocks. Touch, Win & Reset sections 1. Let’s start construction with the siliconchip.com.au D51 5819 1kW 100nF 47nF 10kW D18 4148 D21 4148 D44 4148 D47 4148 D48 4148 D46 470kW 10kW 4148 D43 680kW 10kW 680kW 220kW 220kW 120kW 120kW 120kW 220kW 220kW 220kW 270kW 270kW 10mF 100nF 470kW D45 4148 D29 4148 D32 4148 D33 4148 D35 D34 4148 4148 D37 D36 4148 D38 4148 4148 D41 100nF 10nF 100nF 10kW 4148 10kW D42 4148 4148 270kW IC14 NE555 1kW 4148 D23 4148 100nF 100nF 100nF 10mF IC15 4093B 100nF 100nF 24kW 10kW 22kW 27kW 24kW 24kW 24kW 27kW 18kW 18kW 18kW IC13 4017B D53 270kW 100nF 1kW 56kW 330nF 1mF 100nF IC9 NE555 10mF 10kW 1kW 100kW 10mF 100nF 10kW D17 D16 4148 4148 D19 D20 4148 4148 D22 D24 4148 D25 4148 4148 D26 10kW D27 4148 4148 D10 IC88 44001177BB IC 4148 4148 4148 1kW D11 D28 4148 IC11 LM386N 100nF 4148 D14 10kW D39 D40 D52 4148 D30 4148 4148 D31 4148 10kW D13 IC12 4013B 330nF D8 + 1kW 1kW 1kW 1kW 1kW 1kW 1kW 100nF 10kW D55 4148 220mF 56kW CON4 56kW 470mF 10W 100nF 4148 10kW 4148 SPEAKER CON6 GROUND + 1kW 4148 10kW 100kW IC7 4013B 100nF 4148 D3 CON1 9V BATTERY HOLDER 100nF IC4 4013B 56kW 4148 CON3 D5 100nF IC6 NE555 IC1 CD4026B + 470nF D1 DP 100nF 100nF LED11 RESET 4148 D49 1mF D 56 Reduce to make harder 4148 4148 56kW D50 4148 270kW D4 10mF 10mF 22mF 9V IC5 4081B 10kW 4148 IC17 4093B 1kW D6 100nF 4148 D2 D15 D12 8 S1 S2 COMMON CATHODE 1kW D54 4148 10kW 100kW 4148 D9 D7 100nF 10kW 4148 4148 4148 56kW IC2 NE555 IC3 4017B 100nF 1kW CON2 1kW 1kW Health Time LED16 LED17 LED15 LED15 LED12 TOUCH LED13 WIN WIN 1kW 1kW 1mF LED14 SEQ. 470nF 33nF LED1 1kW 1kW LED2 LED3 1kW 1kW 1kW LED4 LED5 LED6 1kW LED7 1kW 1kW LED8 LED9 1kW LOSE DS1 7-SEGMENT LED – LED10 1kW S3 4.7nF 08101241 Fig.5: this overlay diagram shows which components go where. It also shows the correct orientations of all polarised components like ICs, diodes and electrolytic capacitors. It is divided into 11 sections and can be assembled all in one go if you are confident and experienced, or in the seven steps outlined in the article text. Touch, Win and Reset circuits. Fit all the parts in the Win, Reset and Touch areas of the PCB, plus LEDs LED11LED14 and the four associated 1kW series resistors. Also install IC17 (4093B), the 100nF capacitor next to it, power switch S1, 1N5819 diode D51, the battery holder and the 470μF capacitor just below the holder. When inserting the DIP ICs into the board, you may have to bend their leads inward a bit as they will come splayed outwards. siliconchip.com.au Put a battery in the holder and check that the 9V rail is OK. If not, is D51 the right way around? Is S1 switched on? Now short the terminals of CON3 (eg, using a short length of wire). You should see the Reset LED (LED11) turn on. Repeat this for the Win and Touch inputs at CON4 (with LED13 lighting) and CON2 (with LED12 lighting). If that does not work, are IC17 and the diodes the right way around? Measure the voltages on the input Australia's electronics magazine connectors; one terminal should be at 0V, while the other should be pulled up to 9V. If only one input does not work, look for solder bridges, especially on the pins of the 4093 chip, IC17. Check that its pin 2 goes low when you short the Reset pads and pin 3 goes high. Verify that its pin 9 goes low when you short the Touch pads and that pin 10 goes high. Also test that its pin 6 goes low when you short the Win pads and pin 4 goes high. May 2024  81 Photos 1 & 2: the fully assembled Skill Tester shown with the game wand (which is just a looped wire fitted into a pen case). The design is intended to be assembled in sections as marked on the silkscreen. During construction, you can test each section as its completed. At this point, you should be able to trigger Reset and exercise the Touch and Win inputs and see the corresponding debug LEDs light. Health section 2. Now let’s build the Health Clock and LEDs. Fit all the parts in the PCB section labelled HEALTH. Do not miss the 10kW resistor just below IC3. Get the selection of your coloured LEDs for LED1-LED10 right! We used low-cost LEDs with similar brightness. Make sure the switch you use for S3 is a centre-off type, so you have three difficulty levels. Apply power to the board and check that the 9V rail is OK. You should see LED17 come on. Short the pads of the Touch input (CON2), and you should see LED1-LED10 cycle continuously. Short the RESET pads (CON1), and LED17 should relight. If the above works, great, let’s move on. If it does not work, check that there is a clock signal at pin 14 of IC3. If the 82 Silicon Chip clock signal is missing, check around IC2. Short the Touch pads and check that pin 4 of IC2 goes high. If it still isn’t working, Check that IC3’s CP0 (clock enable) pin (pin 14) is low. If not, is there a short, or did you forget to fit the 10kW resistor? Are your LEDs the right way around? Check the Out Of Health signal on pin 12 of IC3 (4017); it should produce a square wave once per LED cycle. Check that the debug LEDs for Touch and Reset still work; if not, retest the input circuitry. At this point, LED1LED10 should be cycling continuously. 7-segment display should count from 0 to 9 continuously. If there are any problems, use a similar testing procedure to the section above, but with IC6 and IC1. The 555 (IC6) clock output is at pin 3, and the 4026 (IC1) clock input is at pin 1. The clock inhibit pin on the 4026 (pin 2) should be low, and Reset pin 15 on the 4026 (IC1) should be low. Shorting the reset pads (CON3) should reset the counter to 0. The pin 5 carry output of IC1 should cycle high and low once per 0-9 count. The Time counter should be running continuously unless you trigger Reset. Time section Siren and Tick section 3. Next comes the Time section and its 7-segment LED display. Fit all the parts in that area. Ensure that all parts in the Time and Health areas are on the board now. Verify that S2 is a centre-off type so we get three difficulty levels. Apply power to the board and check that the 9V supply is OK. The Australia's electronics magazine 4. Fit all the parts in the Siren and Tick area of the PCB. Watch out, as the 1μF capacitor may look the same as the 10μF capacitors. Also solder IC5, the 4081B in the Game Controller section and the parts immediately around it: the 100nF capacitor next to it, two 10kW resistors (one to the right siliconchip.com.au and one below IC5) and the six diodes immediately below IC5. Mount the speaker by gluing it in place with a few small dabs of super glue, silicone sealant or Araldite. Keep it tidy (ie, avoid getting glue where it shouldn’t go). Wire the speaker to the pads for CON6; you can omit the actual screw terminal or mount it on the underside of the board. Apply power and check the 9V rail. You should hear a warbling ‘ping’ from the speaker; that is the Time Clock tick. Switch the Time switch between Slug, Cheetah and Nightmare. You should hear the ticks change pace from very slow to very fast. If there is no sound, probe pins 10 and 11 of IC15 with an oscilloscope or multimeter reading AC volts. There should be AC signals on both. If so, short out diode D43, and you should get a lot of noise from the speaker. In that case, there is something wrong with C44, D47, C46 and the associated parts. Are those capacitors the right way around? Now short out the Touch pads (CON2). You ought to hear a racket from the speaker (the Touch tone). If not, check for an AC signal on pins 3 and 4 of IC15. The signal at pin 3 will have a low frequency, so you will be able to detect the individual pulses. Check that the Touch LED (LED12) lights when you short the Touch pads. If it still isn’t working, check for shorts on the board and parts missing or the wrong way around. At this point, the ticking sound should be running non-stop, and the Touch tone should be generated if you short the Touch input pads (CON2). Win Song section 5. Now fit all the parts in the Win Song section. There are a lot of different value resistors in the tune section; double-check the value of each before you solder it in. Getting resistors off a double-sided board is possible but not easy. If you are not 100% sure, measure each resistance with your multimeter. Remember to avoid touching the meter probes when doing this, as that will affect the measurement of high resistances. The 1μF capacitor and 270kW resistor just below IC17 should also be fitted to the PCB now. They set the period of the tune sequencers. siliconchip.com.au Apply power to the board and check the 9V rail. You should hear the ticking timer noise and the Win Song playing repeatedly. If there is no sound or only a single tone, check IC8 and IC9 for solder bridges. Also check around IC17, as it generates the clock for the tunes. Probe pin 14 of IC9 with an oscilloscope (or multimeter on AC volts). You should find a signal at about 2Hz. Check pin 3 of IC9 (555 timer). It should have an audio-frequency AC signal on it. Are those capacitors and diodes the right way around? At this point, you should have the Win Song running continuously on top of the ticking sound. Lose Song section 6. Fit all the parts in the Lose Song section, then apply power and check the 9V rail. You should hear the time ‘ping’ with a crazy noise in the background, which is the Win Song and Lose Song playing on top of each other, Short pins 1 and 4 of IC9 (555) to stop the Win Song so you can hear the Lose Song by itself. Be careful not to touch any other pins or parts, while doing this. If that makes no difference, probe pin 14 of IC13 with an oscilloscope or multimeter on AC volts. You should see a signal at about 2Hz. Pin 3 of IC14 (555) should have an audio-frequency AC signal on it. Are those capacitors and diodes the right way around? You can stop the Win and Lose tunes independently by connecting a wire to the ground point, then touching the other end to pin 4 of IC5 or IC14, resetting that 555 and stopping that tune generator. At this point, you should have some crazy noises happening while power is applied. The Game Controller 7. We have built and tested each part individually, and you should understand how each section operates. Let’s bring them all together by adding the control components. Fit all the remaining bits, with the usual cautions on getting ICs in the right way around and choosing the right one for each spot. Apply power and check that supply voltage again. The game will start straight off the bat. You should hear ticking, and if you short the Touch pads (CON2), you should hear the Touch noise. Australia's electronics magazine You should hear the Lose Song after the Time counter gets to 9. Try shorting the Reset pads (CON3), which should restart the game. If you short the Win pads (CON4) immediately after starting a game, you should hear the Win Song. If that is not happening, verify that all polarised parts are fitted the right way around, especially the diodes. Check for bad solder joints or bridges (shorts) between adjacent pads, or components that have been mixed up or misplaced. The diagnostic LEDs (LED11LED17) show the state of every latch and input. Our earlier tests showed that the inputs were working, so check everything around IC4 and IC7, as the latches are there. Are any pins shorted? Mounting the PCB Our baseboard was about 500mm long and just deeper than the PCB. How you go about this part of the construction process should reflect the space you have and what you want this game to be. We marked the holes for drilling by putting the completed PCB on the board and drawing through the holes with a marker, then drilling 4mm holes at those points. We had shorter screws on hand, so we countersunk the holes on the back of the game board to get a bit of extra length so our screws reached the standoffs on the top side of the board. Once you have successfully mounted the PCB, remove it to work on the game wire, including the Reset and Win parts at each end. We routed the edges of our board and painted it with clear lacquer to make it tidy. The charm of this project is its nostalgic design and concept, which relies in no small part on a tidy appearance. You need to put some rubber feet on the board, in the corners of the underside. Otherwise, the screw heads will scratch everything you put it on, and it will slip around. Stick-on rubber feet work well. The game wire We used some fencing wire from the shed for this. It is about 2mm thick and pretty solid; it can be bent with pliers or your hands for smoother curves but is tough enough to take a hiding. You want to use steel wire as copper May 2024  83 Photo 3 (left): this photo shows how we secured the game wire to the baseboard. It also shows the wire wrapped around it to form the Win contact (with heatshrink tubing underneath) and how that copper wire connects back to the terminal on the PCB. To attach it to the baseboard, the main wire was bent into a loop just larger than the bolt diameter using sharpnosed pliers. Photo 4 (right): a view of the Reset end of the maze wire, showing how the start contact is bare copper wire from domestic mains cable, wrapped around the heatshrink insulation and soldered in place. Tinned copper wire would also work here. This is also the point that the main game wire is electrically connected to the Touch terminal on the PCB. won’t spring back. It doesn’t need to be fancy or new. If you are scratching your head, look in your wardrobe for a metal coathanger. I reckon that would work just fine. The shape of the maze is up to you. The tighter the kickbacks and the more changes in direction, the harder the game will be. A loop makes the game super hard as the wand has to be rolled to the back of the game to achieve this; that might be for more advanced gamers. Photo 3 shows how we bent the wire to go through the screws on the game board. We drilled holes for 30mm “gutter bolts” about 30mm apart, allowing space for a bolt to hold the game wire and a spot for a second bolt to connect to the Win and Reset wires at each end of the maze. We did this to make the whole thing robust, and so we could pull the wire maze off and put in an easier or harder one later. Our first maze had loops, tight corners, and all sorts of complex curves, making it nearly impossible to play. We suggest you instead start simple and work from there. Once you have your maze bent up, but before you bend the loops for the bolts, insulate about 50mm at each end with a couple of layers of heatshrink tubing. That will allow us to wrap 10-20mm of bare copper or tinned copper wire around the outside to form ‘pads’ that we will connect to the Reset and Win inputs on the game board. These inputs have a pullup on the game board, so if we touch these pads with a grounded wire, we will trigger 84 Silicon Chip Reset or Win, respectively. Our wand will connect to ground, making a neat arrangement for these inputs to the game. The required wiring is shown in Fig.6, although it does not show the physical layout, just what connects where. After you have applied the heatshrink tubing, tightly wrap your copper wire around it. Use pliers to ensure it is tightly in place, then solder the top and bottom of the loops together. Don’t worry; the heatshrink will survive; we put two layers just to be sure. This is shown in Photos 3 & 4. We left enough wire to run to a bolt where we connect Reset and Win to flying leads from the game board. The wand For the wand, we want something that is comfortable to hold and to which we can fix the wire loop that goes around the maze wire, connected to our circuit ground. By connecting the loop on the wand to ground, we can tap this on the Reset wire to start the game. If the loop touches the maze wire, it connects to Touch and, at the end of the game, tapping on the Win wire wins the game; all parts of the maze wire. We used a ballpoint pen case for the wand (Photo 5). The loop was made from the same wire, reclaimed from house mains wiring, that we used to make the Reset and Win pads. Fig.6: this diagram shows how the Touch, Reset and Win terminals (CON2CON4) connect to the wand, game wire and start and finish pads. Refer to the photos to see how we made the required electrical connections, and note that the ground wire going to the wand can connect to the upper screw of any of the three terminals. Australia's electronics magazine siliconchip.com.au Photo 5: we made the wand from an old biro case, some reclaimed wire (tinned copper wire could be used) and enough layers of heatshrink tubing added to make it a snug fit to the case. Some super glue holds the whole thing together. Assembly is a simple matter of screwing everything together. Make sure that the wand’s loop is ultimately wired to a ground pin on one of the Reset, Touch or Win connectors (CON2, CON3 or CON4). In each case, the ground side is closer to the top of the board. By now, you will realise there is a bit of work in making this project and doing so tidily. Still, the basics of a stable base, something to screw the wire to and wide enough to hold the PCB are the essence (see Photo 6 for our completed version). Finishing it off Connect the pad at the start of the wire to the Reset line (not the ground side, so the bottom terminal of CON3) so that tapping the wand here will start the game. Connect the main wire to the Touch connector (bottom of CON2), so touching the wand to the wire will short the Touch pin and reduce the Health counter. Connect the pad at the end of the wire to the Win connector (bottom of CON4). This way, everything you need to run a game is at your fingertips. Tips on playing There are three settings each for speed and difficulty. Noob + Slug makes the game the easiest, while Veteran + Nightmare makes it the most difficult (perhaps impossible)! So start with Noob + Slug and work your way up from there. To win, you must move the want from the start to the end of the wire with time and health left. To play a one-on-one game, choose a difficulty setting and play one game each. If one player wins and one loses, the winner is obvious, but if both win, whoever has the most health left wins. If both have full health left, the fastest time wins. To run a tournament, start with the easiest settings and give each player one attempt at the game. Anyone who loses (whether by running out of time or health) is eliminated. If more than one person is left, play again on a higher difficulty setting. Repeat this until all but one has been eliminated, or you reach the highest difficulty setting. In the latter case, use the rules above to determine the winner. When increasing the difficulty, we suggest going from Noob to Veteran for Health first, then when you reach Veteran, start speeding up the time from Slug to Nightmare. Also, remember that the way you bend, fold and make loops and kickbacks in that wire plays a big part. Is your wire tough enough? Have fun! If you come up with better tunes than we have, send in your resistor values so we can try them SC ourselves! Photo 6: the finished and assembled Skill Tester game. It is an updated version of the old wire loop (also called buzz wire) game. We’ve used an MDF offcut, but you can use whatever timber you have available as long as the size is adequate. siliconchip.com.au May 2024  85 SERVICEMAN’S LOG Cheap fixes for the working Serviceman Dave Thompson is currently on a pilgrimage to Eden Park, home of the All Blacks – an arduous journey undertaken by every good New Zealander at least once in their lives. While he fends off feral kiwi bird attacks and practices his haka, we have a selection of reader-contributed stories for this month’s column. R. W., of Hadspen, Tas was asked if he could put a new fuse in his friend’s Bose subwoofer... I queried why and was told that it stopped working; the LED no longer lit up, and the last time this happened, the warranty repair just involved replacing the fuse. I said I’d be happy to take a look, but fuses blow for a reason, and if the cause was not determined, they would continue to blow. I collected the unit, a “Bose Acoustimass 300”. It is a solidly-­made and very heavy subwoofer that connects wirelessly to a TV soundbar. Its sole LED did not light when power was applied, so I assumed it was a simple power supply fault. The base of the unit houses the electronics in a diecast assembly that forms the base of the enclosure, the lower acoustic port and also acts as a heatsink for the amplifier. Only a couple of screws were visible and, on removing them, the plastic cover wouldn’t budge. Checking under the adhesive felt feet revealed another four screws, but the cover was still fixed after removing them. I located another two screws under the adhesive label and had to cut holes in the label to remove them. Clearly, this was the first time it had been opened, so how had the fuse been replaced? Eventually, the circuit board was revealed and, from below, I could see the HV delineation on the circuit board and took care to handle it from the edges in case some capacitors held charge. It was a wise decision, as a whopping HV electrolytic capacitor occupied the centre of the board. A small multi-conductor ribbon cable needed to be pulled from its socket (what it connected to, I cannot imagine), and after the heavy-duty speaker connector was unplugged, the board was free. About half of the board is occupied by switch-mode power supplies (SMPS), about a quarter is what appears to be a Class-D amplifier and filters, and the remainder looked as if it was microprocessor or wireless related (there was a PCB antenna in the corner). I don’t know how that antenna worked, as it was almost entirely within the diecast enclosure. There was a plastic-encapsulated fuse on the board (covered in white in the photo below) rated at 4A, but it was intact, and there was no evidence that it was not original. Following tracks from the mains cable with an ohmmeter revealed nothing unusual, so I applied power. I measured around 340V DC in several places around the switch-mode supply and main electrolytic. A feed from this cap went via an inductor to another smaller HV cap hidden under masses of what looked like hot melt glue. I was unable to find any low-voltage rails. From here, I was in the dark, and tracing was difficult as the board was a multi-layer type. I desperately needed a schematic. After hours of trawling the internet, I had no useful leads and had ignored all the YouTube fix-it videos. I don’t waste time looking at them as they are generally unhelpful. Eventually, with no other way forward, I watched a video from “Jonny Fix” about an Acoustimass 500, one of several that he has fixed, and they all had the same problem as mine. He had my full attention. It appears that one diode is the culprit, and it’s involved with the smaller SMPS right where I had been looking. Why it fails with such regularity is a mystery. Nearby is a 16-pin DIL IC marked ALTAIR05T N02671, which I determined is a switching regulator. The diode in question was a 3A 100V schottky type in an SMD package, located under a glue river (see the photo at lower left). It measured short-circuit. I removed the diode, and it still measured as shorted. The fault in the Bose Acoustimass 300 power supply was hidden under a big blob of glue. Replacing the shorted schottky diode returned it to a functional state. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au Items Covered This Month • A $3 subwoofer fix • Finding replacements in unexpected places • Repairing an Esseti TIG welder • Revitalising a Miniscamp Computer from EA • Fixing an MTM 4400i inverter generator 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 I could not believe I had found the culprit so quickly with no schematic. Thank you, Jonny Fix! Now to find a replacement. Some people in the comments section said that a 1N5408 had worked for them, but I wanted to replace it with an equivalent schottky type. I found a dual 100V 20A diode in a TO220 package (MBR20100CT) at Jaycar for under $3. 20A is overkill, but it was the closest 100V schottky I could find. I used only one of the diodes within, and had to use some hot-melt glue to affix the body to a nearby capacitor for rigidity. I left the metal tab open to the air. On powering the unit, nothing happened, and the LED remained dark. I was about to utter a comment when the LED started flashing orange to indicate that pairing was in progress. When I re-introduced it to the soundbar, it performed faultlessly. As for the mystery of the fuse replacement, it appears the retailer simply replaced the whole subwoofer, and the fuse excuse was a furphy. Lucking into replacement parts T. B., of Kogarah, NSW found a rare part he needed in the most unlikely of places... I began my aircraft electronics career as an apprentice with The Flying Kangaroo in the early 1960s. We had the best electronics test equipment, including beautifully made (hand-wired, I assume) Tektronix scopes. They were valve-powered, unlike the Boeing 707’s all-solid-state electronics. So I did not see much valve technology for repair. Fast forward 40 or so years, and in retirement, I was persuaded to join the HARS Aviation Museum at Albion Park, south of Sydney, resuming my trade as a volunteer. Early on, I spotted one of the aforementioned Tektronix ‘scopes gathering dust in the back of the hangar. I couldn’t let it go unused, so I set it up on the workbench and removed the cover. It looked so good, but a valve was missing, with “6DQ6A” helpfully stencilled next to the socket. My valve experience was limited to building a Radio, TV & Hobbies “Playmaster” amplifier, and it had none of those types! Nearby, there was a lead with a top-cap fitting, so I needed to do more research and start looking for one. Where, though? Fast forward to the following Saturday, ie, two days later. I needed to buy a desk for my home computer; a second-hand one would be good enough, so I called into siliconchip.com.au a nearby used furniture store. They showed me to their desks, but none were suitable. As closing time was near, I headed for the exit. My eye caught a glass-fronted display case at the end of an aisle with some interesting bits and pieces piled up. Worth a peep, I thought. Right on top of the pile was a Mullard valve box, with the end visible, reading 6DQ6A! Surely, it wasn’t possible, but it was. I couldn’t believe it; I picked it up and headed for the checkout. “Price for one valve, please?” “$5 for you.” Done deal. “Probably from a deceased estate,” I was told. Next Saturday could not come fast enough. I fitted it to the ‘scope and was greeted by a nice sharp trace on the screen. A joy to my eyes! It was truly a chance in a million to find such a prize in a used furniture shop five minutes before closing time. Scratching the itch to service a welder R. H., of Waverton, NSW discovered, as many others do, that a seemingly serious fault can result from a single failed component. That’s why it’s often worth trying to fix failed equipment... It was about 1998 when I purchased my Esseti Inverter TIG welder. The cost was then $1700; quite expensive! Although I did not realise it then, this welder was quite advanced; it featured hot start, arc force and anti-sticking, but no high-frequency ignition (HFI) – that would have been an optional extra at $450, too expensive! The arc is initiated by ‘scratch start’, requiring constant practice to gain confidence to achieve this method. It also contaminates the tungsten. I constantly toyed with the idea of adding HFI, as lately, many HFI boards and simmer coils have become cheaply available on the internet. Many YouTube sites explain this but leave out essential details of exactly how to connect these items to the welder. I tried, but the result was that my welder failed. What to do? Buy a new TIG welder, with HFI now considerably cheaper, or have a go at repairing it? After some thought, I decided to take a shot! Australia's electronics magazine May 2024  87 The manual that came with the welder was in Italian, with some attempt at English translation and, of course, no circuit diagram. All seemed good at the front panel. The readouts and the gas solenoid worked. But no 90V at the TIG torch. The main board had two spade terminals, marked with a plus sign, adjacent to two L7912CV 12V regulators. Both measured 12V. I next tested the four RURG8060 rectifier diodes and found that one had failed. All the other components looked OK! I hadn’t tested the two G4ON60B3 N-channel IGBTs yet, but I placed orders for four RURG8060 diodes and two G4ON60B3 IGBTs to be on the safe side. Once received, I replaced all four RURG8060 diodes, checked it over and powered it up. With the welder switched to stick, up came the 90V DC. Wonderful! However, when I switched to TIG, the output terminals only measured 12V. Why? I rechecked everything and could not find a reason. Then, when I was lying awake at night, the idea came to me that the 12V was a sensing voltage, and when the arc was struck, up would come the 90V and many amps. So I tried that, and it all went well. As for the HFI addition, I will leave it until I find out more about how it’s supposed to be installed. The moral of this story is: don’t throw it on the scrap heap – have a go. You never know your luck. Miniscamp Microcomputer rejuvenation J. W., of Hillarys, WA decided to try out a computer he built around 46 years ago. Computers were pretty simple back then, so there wasn’t much to go wrong... A few weeks ago, I decided it was time to clean out the workshop. I came across the first computer I ever owned in the back of a cupboard: a Miniscamp microcomputer. The Miniscamp was a project published in Electronics Australia in April 1977. I built it around 1978 and modified it over the next few years to include a serial interface and more memory (ROM & RAM). I decided it would be worth the effort to get it running again after over 40 years of gathering dust. The Miniscamp used a National Semiconductor SC/MP microprocessor and, in its original form, had 256 bytes (that’s right, bytes) of RAM, using two 2112 RAM ICs. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au Input and output were in the form of eight LEDs, eight data switches and 10 address switches. Programs were entered by switching to DMA (direct memory access) mode, setting the address switches to the required address, say 0000h, and setting the data switches to an instruction, say 08h (no operation/NOP). The deposit switch was then pressed, and the instruction would be saved at the selected address. So the first address would now hold the NOP instruction. Entering a large program was a lot of work and concentration. The Miniscamp was basic, but a good learning tool for microprocessors. The first thing to do was to get some information about the design and instruction set. I found an archived copy of the original article and many of the following articles, so I had the circuit diagram and some sample code. I then located the National Semiconductor SC/MP programming and assembly manual, so I was ready to go. I removed the cover and was surprised to find the circuit board in perfect condition, just like it was in 1978. After connecting power, I found the +5V and -12V supplies to be good. Now was the time to see if the hardware was working. I had upgraded the original kit with a ROM containing National Semiconductor’s KitBug ROM (512 bytes), more RAM and a serial interface. I checked the original circuit to find the serial output pin, connected my CRO and pressed the reset button. I was greeted with a stream of pulses from the Flag 0 pin. I had a USB-to-serial interface on hand, so I used a few transistors to isolate the PC and Miniscamp from each other. I ran PuTTY (a serial terminal program) but had to set the baud rate; I thought I had set it to 500 baud all those years ago. I was spot on, and after pressing the reset button, I was greeted with a hyphen as a prompt. The manual indicated that there were only three commands recognised: T for displaying memory, M for modifying memory and G for running a program. I remembered upgrading the original KitBug ROM to add the ability to save (S) and load (L) programs from cassette tape and set breakpoints (B) in a program. I could now enter a program by typing commands instead of setting switches. The original article had a sample program that displayed a binary counter on the LEDs but, upon siliconchip.com.au Australia's electronics magazine May 2024  89 running it, the LEDs did not flash. After some investigating, I realised that to add the extended the RAM, I had to disconnect the LEDs as they took up a 256-byte bank of memory. After a bit more investigation, I disconnected one bank of RAM and got the LEDs working again. I then tried to use the breakpoint command, but it did not work. After printing out the program listing of the ROM, which I had extended to 1kB, I saw what I had done to get the breakpoint feature working. I then set about writing some code of my own. Assembling the code by hand was a bit of a job, so I investigated and found an assembler on the internet to do the job. I was then satisfied that it was all working correctly. Now I just need some tasks for my 40-year-old computer! MTM 4400i inverter generator repair G. C., of Toormina, NSW has an MTM 4400i inverter generator that has served him well during blackouts and remote work over a 10-year period... For those readers not familiar with an inverter-type generator, they have the advantage of producing a pure sinewave output with the correct voltage and a stable frequency. An alternator in this machine supplies three-phase power at varying frequencies depending on the engine RPM. This three-phase supply is rectified into DC and fed to the inverter, where it is converted to the required 50Hz AC output. Another advantage of this system is that the engine can idle slowly on light loads and rev up to meet the demand if the load increases. That is achieved by a stepper motor, which operates the throttle based on the detected load. 90 Silicon Chip Standard generators are hopeless in this regard, as their frequency and voltage can vary all over the shop, and they need to run at approximately 3000 RPM for a two-pole machine to get a 50Hz output. That means a lot more noise. This generator is rated at 4.4kVA and was made in China. I purchased it on eBay for about $500. We recently had a blackout, and the generator ran for about three hours when it stopped producing power. I checked the generator; it was still running but no LEDs were lit on the front panel. There was no output voltage coming from the machine. I stopped the generator to let it cool down so I could look at it the next day. I then began disassembling it to access the internal workings. The machine looked pristine inside. I was impressed by how well-made everything was and how easy it was to take apart. It used all regular Phillips screws, standard metric bolts and no breakable plastic clips. I had to pinch myself to see if I was dreaming! I began by looking for any burnt connections or loose/broken connections. Nothing showed up in that regard. Thankfully, I have a wiring diagram (shown opposite). I disconnected all the plugs from the inverter board to avoid getting false readings or damaging any electronics while testing. I measured the resistance of the three-phase star-­ connected winding labelled “Main windings” in the diagram. All three windings measured 0.7W to the common star point of the windings. All resistance readings should be equal when testing three-phase machines. Sometimes, this information is available from the manufacturer’s website, but I was on my own in this case. I used a Megger set on 500V to test between these Australia's electronics magazine siliconchip.com.au windings and the machine’s frame. It showed above 100MW, so the windings were OK. Next, I measured the resistance of the exciter winding labelled “Control winding” in the diagram. This showed a reading of only 0.2W, which concerned me, but I also checked with an inductance meter and measured about 16µH. That wasn’t totally convincing but at least it proved that the winding wasn’t shorted. This winding was also over 100MW to the frame on the Megger test. At this stage, it looked like the inverter board was the culprit. Unfortunately, it is potted in epoxy resin and seems quite complicated. I may try to de-pot it at a later date. I jumped on the web and was horrified to find no leads about MTM generators or where to get parts. Thoroughly disgusted, I gave up for the day. The next day, I tried another web search and stumbled on a company called Generator Guru (www.generatorguru. com). This was my saviour. They specialise in saving Chinese generators from being thrown away. I got onto their site and searched for my brand and model number. Up came the inverter board and all the other spares they have for this generator. I was impressed. The sad news was that the inverter board would cost $525 with free shipping. That was more than the cost of the generator itself! I thought about it and remembered that I bought it 10 years ago, so considering inflation, it wasn’t all that bad. I searched the web for other generators of similar capacity, which cost at least $1200. I was also loathe to write this machine off. I decided to bite the bullet and ordered the inverter board, plus the ignition controller board, as a spare. Their service was brilliant, with regular tracking updates about the shipping from Sussex in the UK. The parcel arrived in about five days, which was also impressive. When I had a spare moment, I fitted the board, which has six connectors that are all different, so you can’t muck it up. I left some covers off and fired up the generator. All was well with a 10A kettle plugged in as a test load. I refitted the covers and gave it another test run to be sure. I am pleased to have saved the generator from scrap and highly recommend Generator Guru if you are chasing parts. They also have some repair videos and advice SC columns. The wiring diagram for the MTM 4400i inverter generator. siliconchip.com.au Australia's electronics magazine May 2024  91 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. Double-sideband (DSB) / AM phase-shift modulator This circuit produces an AM or a DSB signal at 27MHz by combining two phase-shifted signals of that frequency. Although the idea of amplitude modulation by phase-shifting is not new, I could not find any circuits on the internet for a transmitter using that concept. I implemented this circuit to verify the feasibility of employing that technique to transmit a low-power AM or DSB signal in the citizens’ band. Per the circuit diagram, my design employs digital ICs of the 74HC family. IC1 is a dual flip-flop, with IC1a used as a 6MHz crystal oscillator, as I previously described in the Circuit Notebook section of the March 2021 issue (siliconchip.au/Article/14779). IC1b halves that frequency. The block comprising IC1 to IC3 produces two square waves at the same frequency with a phase difference that can continuously range from nearly -180° to +180°. The phase difference obtained depends on the difference in the delays produced by timers IC2a (upper half) and IC2b. This block uses the 6MHz signal and the 3MHz square wave generated by IC1 to generate two 3MHz square waves with a variable phase difference. The 6MHz signal is applied to the rising edge-triggered clock input of IC1b as well as the rising edge-­ triggered inputs of both timers in IC2. The latter produce very narrow negative pulses at their outputs (pins 7 & 9). So, after short delays, the rising edges at the clock inputs of flip-flops IC3a and IC3b take the logic level present at that instant at the Q output of IC1b. That happens for each rising edge of the 6MHz signal; that is, for each rising and falling edge of the 3MHz square wave produced by IC1b. So IC3a and IC3b Circuit Ideas Wanted 92 Silicon Chip follow IC1b’s Q output, but with delays that depend on the two timers in IC2. Usually, the delays of the 74HC4538 timers are determined by a resistor and a capacitor for each timer (330W and 22pF in this case). However, I added circuitry to inject audio signals into each timer so those audio signals modulate the delays of both timers. NPN transistor Q1 is configured as an amplifier with a gain of about 10. The amplified audio signal at its collector is applied to Q2 and its associated components, which produce two audio signals of opposite polarity at the emitters of Q2 and Q3 (a phase difference of 180°). Q3, connected as an emitter-follower, presents a lower impedance than the collector of Q2. In the DSB position of S1, the two anti-phase audio signals are coupled to pins 2 and 14 of timer IC2 via 470nF capacitors. The two 1kW resistors and trimpot VR1 provide DC biasing, and VR1 allows it to be balanced for both signals. Thus, the two timer delays are modulated by the applied audio signals. By adjusting VR1, the carrier is nullified when there is no audio input, while VR2 is used to balance the modulation effect of both 180°-out-of-phase audio signals. In the AM position of S1, only the first timer receives an audio signal at pin 2, while the second timer produces a constant delay, which can be adjusted by VR3 for minimum distortion. The outputs of IC3a and IC3b (the Q outputs in this case, although the Q outputs could also be used) produce two 3MHz square waves with a phase difference that follows the audio input. IC4 and its associated components extract and amplify the 9th harmonic of IC3a’s output. Similarly, IC5 and its associated components convert the 3MHz signal from IC3b to a 27MHz signal. Push-pull complementary emitter-­ follower pairs Q4/Q5 and Q6/Q7 increase the current delivery capability of this part of the circuit. Both 27MHz signals are applied to a toroidal RF transformer; as their phase difference varies from -180° to +180°, the amplitude at the secondary decreases as the phase shift increases from -180°, being null for 0°, and then reverses its phase and increases its amplitude again, up to its maximum for 180°. For AM transmission, the phase difference varies between 0° and 180°, sitting at 90° without audio input. Since the 3MHz signals have their frequencies multiplied by nine, the angular phase difference between them before the multiplication must be nine times smaller, ie, -20° to +20° for DSB and 0° to 20° for AM. L5 and the 22pF capacitor filter the resulting signal, reducing its harmonic content. L1-L4 are standard moulded chokes; I made L5 by winding 16 turns of plastic-­ covered telephone wire (0.5mm diameter) on a 10mm former, with approximately 0.5mm between the turns. For the toroidal transformer, I used the same wire and a green-blue core salvaged from a PC motherboard, with an outer diameter of 12.8mm, an inner diameter of 7.6mm and a strip length of 6.4mm. I wound it by interleaving each primary turn with two secondary turns, giving six turns for the primary and 12 for the secondary. I used a 1m wire antenna, with the receiver 30m away, with a wall in between. I obtained a strong signal with good audio quality. Ariel G. Benvenuto, Parana, Argentina. ($120) 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 siliconchip.com.au siliconchip.com.au Australia's electronics magazine May 2024  93 Replacement switchmode power supply for an oscilloscope Around 1986, an organisation was offloading their used BWD oscilloscopes. I was very keen to get my own CRO, but being on a tight budget (17% home loans!), I opted to buy one that had been used as a source for spare parts. It only cost about $100 and I figured I could rebuild it. Apart from some sub-boards, the power supply was also missing. I discovered that BWD was closing down and no spare parts were available. Undeterred, I designed a power supply to provide the necessary outputs. The TL494 IC looked like a suitable control device, so I used it as the basis for the design. Winding the transformer was the hardest part! Fortunately, I had been teaching power transformer design at Swinburne University, so I saw it as a challenge. I used an iterative method (repeated manual calculations) to handle the multitude of variables and constraints. I chose an E50 ferrite core made from N27 material for high-­ frequency operation. 94 Silicon Chip At this time, I was doing part-time tutoring at RMIT Electrical Engineering Department (courtesy of SEC), so I had access to their coil winding equipment. The power supply looks a bit crude now, but it produced all the required output voltages. The incoming mains goes to a small transformer that directly produces the low-current 6.9V AC and 2V AC rails for the ‘scope, as well as around 12V AC that is rectified and filtered to feed the 7812 regulator. The mains is also fed through an EMI filter straight into a bridge rectifier that charges a pair of parallel 47μF capacitors to around 340V DC. That voltage is applied to the centre tap of the high-frequency main transformer’s primary, with the ends of the windings alternately connected to the 0V rail by a pair of BUZ50A Mosfets. The high-frequency transformer secondaries produce eight different outputs, with some fed to the ‘scope as AC, while others are rectified and filtered to produce DC rails. None are Australia's electronics magazine regulated; they’re all set by the transformer properties. The five zener diodes and two ultrafast rectifiers connected between the main transformer’s primary winding taps clamp back-EMF spikes to protect the driving Mosfets. An MMH0026 dual low-side Mosfet driver feeds the Mosfet gates since the TL494 is not suitable for directly driving Mosfet gates at fast switching speeds. That IC is also powered by the regulated 12V rail. The TL494 monitors the current through the transformer primary, which is converted to a voltage by the 3.3W shunt resistor between the Mosfet source pins and the 0V rail. That voltage is then fed to pin 15 of the TL494 via a 680W resistor, which is the inverting input of the second error amplifier. Thus, the TL494 adjusts the duty cycle of the Mosfets to achieve the desired current in the transformer primary. The switching frequency is set to around 80kHz by the 15kW resistor at pin 6 and the 1nF capacitor at pin 5. siliconchip.com.au Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Photos of the finished power supply board for the BWD oscilloscope. As that frequency is used to switch the power Mosfets alternately, the drive frequency of the transformer primary is close to 40kHz. Pin 3 of IC1 is the compensation input; the resistors and capacitors connected there slow its response to changes in the primary current, so the duty cycle stabilises. As this circuit involves chopping rectified mains voltages, it requires a correctly designed PCB that adheres to proper clearance requirements, along with thorough insulation and other safety measures. I am not presenting it here expecting others to make one, but as more of an educational exercise. Only attempt to build the circuit if you are familiar with all the required safety paradigms. Mauri Lampi, Glenroy, Vic. ($100) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 siliconchip.com.au Australia's electronics magazine May 2024  95 Vintage OSCILLOSCOPE Valve-based Calibrated Oscilloscope from Radio, TV & Hobbies magazine I was pretty surprised when a fellow Historical Radio Society of Australia (HRSA) member turned up at one of our meetings with not one but two examples of Jamieson (“Jim”) Rowe’s outstanding oscilloscope design. It’s a fully-calibrated oscilloscope based on a three-inch (~75mm) diameter round CRT screen. With no exotic components or tricky construction, it was a well-designed and highly practical instrument that any enthusiast could build. The oscilloscope is effectively an X/Y plotter, plotting an input signal (Y-axis) against a time base (X-axis). That might sound simple, but the Y-axis amplifier must be able to reproduce the input waveform accurately, demanding a broad frequency response. Another challenge is that the timebase generator must be linear and 96 Silicon Chip adjustable over a wide range of speeds to suit signals of different frequencies. As for the Y-axis amplifier, let’s consider low-frequency inputs. While audio frequencies rarely extend below 20Hz, what about electrocardiograph signals, or signals from seismic monitors? What if we need to determine the DC component of a complex signal, such as a television waveform? Ideally, the low-frequency response should go all the way to DC. Early designs did not do this, either for cost-saving reasons, lack of perceived demand, or lack of design experience. Once such designs escaped the laboratory, designers implemented direct coupling and other improvements. What about the high-frequency end? There must be a practical limit to the highest frequency that a wideband amplifier can reproduce without loss. Australia's electronics magazine Common radio valves can easily work above 30MHz in tuned amplifiers, as their internal capacitances can mostly be incorporated into tuned circuits. A wideband amplifier usually has a resistive load, meaning that valve capacitances become a limiting factor. You will find a detailed description of how the circuit works in Jim’s original Radio, Television and Hobbies articles from June to August 1963. The circuit is shown in Fig.1, with some added voltage readings (green, peak-to-peak) and valve designators (yellow) to aid in troubleshooting and restoration. The overall sensitivity is governed by the required bandwidth and the high output voltage demanded by the cathode ray tube (CRT) screen. For conventional tetrode types with the deflection plates as the next-to-final siliconchip.com.au Radio and Hobbies (R&H), later Radio, Television and Hobbies (RTV&H), was Australia’s premier hobby and radio/electronics magazine from April 1939 until it was renamed Electronics Australia in March 1965. This clever oscilloscope, designed by Jim Rowe, was published in RTV&H’s June to August 1963 issues. It’s a brilliant circuit with one small flaw that I decided to address. By Ian Batty electrodes in the electron stream, sensitivities of some 20V/cm demand voltages approaching 150V peak-topeak for full deflection. As Jim noted, advanced post-­ deflection acceleration designs can bring full-screen deflection voltages down to tens of volts. The necessary expense and extra high-voltage power supplies were not judged appropriate for this design. This design settled for a -3dB bandwidth of 3.75MHz and an input sensitivity of 100mV/cm for fullscreen deflection. The vertical amplifier Vertical amplifiers have evolved logically. The first single-stage, AC-­ coupled amplifiers were developed into multi-stage versions. These commonly had limited bandwidths and provided up to 200V peak-to-peak siliconchip.com.au output to drive the CRT to full deflection. Adding a push-pull output stage halved the output voltage needed for full-scale deflection. By about this point, design theories that would extend amplifier bandwidths were being considered and implemented. Research in radar and pulse techniques during WWII had established techniques for wideband amplification, and RTV&H’s design team readily adopted them. The New Wide Band Oscilloscope in RTV&H, February 1957, p70, is the canonical design, with a bandwidth exceeding 3MHz. With a push-pull output and high-frequency peaking, the final step would be direct coupling throughout. Jim’s design is nicely tailored to give all the desirable features in an Australia's electronics magazine economical design. The cleverest part is the connection of the preamplifier and output stages in DC series, allowing a main HT supply of just 270V compared to the 400V found in Hewlett-­Packard’s model 150 from around the same time. With a -3dB bandwidth of 3.75MHz, it’s certainly good enough for most work, including black-and-white television. While the 3.75MHz limit is less than the full 5MHz bandwidth of PAL colour, the ‘scope usefully resolves the colour bar waveforms and displays the colour burst. This instrument is certainly good enough for most repair and alignment work. Previous RTV&H designs, using ex-disposals CRTs such as the venerable 5BP1, needed some 100-plus volts peak-to-peak for full-screen May 2024  97 98 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.1: the complete circuit of the Calibrated Oscilloscope from Radio, Television & Hobbies, June to August 1963. It uses just eight valves, six triode/pentodes, one twin triode (V5) and one pentode (V7), with the latter acting as a timebase oscillator. The red circle (at upper left) indicates the area where the changes noted in Fig.8 were applied. deflection. Jim chose the DG7-32/01; with its high deflection sensitivity, it only needs some 30V peak-to-peak, supplied in antiphase to its vertical deflection plates. This permits the clever design of the preamplifier and output amplifier in DC series from the HT supply noted above. The timebase, extending from 1s/ cm to 1μs/cm, is certainly suited to domestic electronics, including analog colour television. I could easily display the colour bar output from my Arlunya PG100 and observe the duration and positioning of the colour subcarrier burst with its 4.7μs duration. This showed that the Arlunya’s output, while adequate for testing, does not fully conform to the CCIR/PAL timing standard. The timebase While all vertical amplifiers look vaguely similar, timebase design is a bit of a zoo. Apart from special applications, the timebase waveform is a sawtooth wave with a linear ramp during the active display time and a rapid ‘snap’ back to zero during the blanked-out retrace period. The repetition rate must be adjustable, and it needs to offer synchronisation to either the signal being displayed or an external reference. Otherwise, the displayed waveform will not be steady on the screen. A neon lamp will go into conduction once the applied voltage reaches a particular value, typically 70V. It’s simple to take a power supply of perhaps 100V, string a series resistor to the lamp and pop the neon in parallel with a capacitor. On applying power, the capacitor will charge up until the neon strikes. It will then discharge the capacitor until the capacitor voltage drops below the neon’s extinction threshold. Once the neon extinguishes, the capacitor will begin to charge again, repeating the cycle. While this does give a continuous waveform (with frequency adjustable by changing either the capacitor or resistor), the waveform is exponential rather than a true linear ramp. This gives a less-than-­ linear time base, ‘crowded’ towards the right-hand end. The neon has finite ionisation and deionisation times, so the maximum operating frequency is limited to around 50kHz. This simple circuit siliconchip.com.au is difficult to synchronise, so it was reworked to use a gas-filled triode thyratron. The thyratron has strike and extinction characteristics similar to a neon and responds to synchronising signals on its grid. This makes it a practical circuit, but still with the limitations of non-linearity and only a moderate maximum operating frequency. R&H used such designs up to March 1950 (p52). These ‘soft’ timebases could be improved by replacing the timing resistor with an adjustable constant current source, giving a linear output waveform (R&H, April 1950, p64). The added complexity pushed designers to new circuits that were inherently linear. Various forms of multivibrator, bootstrap, and other switching circuits were used in high-performance instruments, but the circuit of choice became the Miller Integrator/Transitron, also known as the Phantastron. The Miller effect describes how a voltage amplifier effectively amplifies its own anode-grid (or collector-base or drain-gate) capacitance. The Miller effect can be used to create a repetitive linear waveform. There’s a complete description of how it works in R&H, September 1956, p32. Jim’s description (with the added detail of the synchronising circuitry) is in a separate RTV&H article in September 1962, starting on p44. The Phantastron exploits what is otherwise a serious problem inherent to tetrode valves. If the screen voltage is held constant and the anode voltage is reduced, there is a critical point below which the screen current skyrockets and the anode current falls. Fig.2 shows the effect, with the transition beginning around 100V on the anode. We need to add one more characteristic that is not commonly considered. The suppressor grid, invented to counteract the tetrode’s undesirable characteristics, can be used to control anode current. Its authority is much less than the control grid, needing some -50V for cutoff in the EF50. Now, let’s consider the basic circuit: a high-gain valve with the timing capacitor connected from the anode to the control grid and the timing resistor from the grid to a positive bias supply, shown in Fig.3. When power is applied, the valve will draw anode current through RL, and the anode voltage will begin to fall. But that will drive the grid negative via timing capacitor CT, which will tend to reduce the anode current. The circuit settles into a balance, where the tendency for the anode voltage to fall almost instantaneously to zero is balanced by the fact that such a fall would cut the valve off. The circuit will produce a ramp with a slope determined by timing capacitor CT and timing resistor RT. Varying the DC bias via the Time Cal potentiometer varies the waveform period. A simplified Phantastron If we left the circuit there, we would have a linear ramp but not the repetitive waveform we need for a timebase. Repetition is provided by the screen-suppressor circuit. As the anode voltage gets close to zero, the screen suddenly takes up the valve’s cathode current, the voltage drop across screen resistor RSG increases, and the screen voltage drops to zero. Fig.2: the sudden change in plate and screen currents at lower anode voltages is usually a problem, but it is taken advantage of in the ‘Phantastron’ oscillator. Fig.3: the basic configuration of the Phantastron oscillator. It generates a linear voltage ramp at its anode that’s periodically reset to a lower voltage over a short duration, thanks to the property shown in Fig.2. Australia's electronics magazine May 2024  99 The underside of the busbar version (one of two I received). It was the hardest to work on. This rapid drop is conveyed to the suppressor by CG3, forcing the suppressor sufficiently negative to cut off all current to the anode. When cut off, the anode circuit will rapidly rise to the full supply voltage. Once the screen comes out of its ‘bottomed’ state, the circuit resets, anode current rises, and a new downward ramp commences. The free-running circuit can be synchronised easily by applying synchronising pulses to cut off the control grid before the end of the active period. So, we have everything we need for an adjustable, synchronisable horizontal timebase waveform for the CRT from a single valve and a handful of other components. Restoration As mentioned earlier, I got my hands on two oscilloscopes built from the Scope 1: after calibrating the vertical amplifier it still had a poor high-frequency response. Scopes 1 & 2 are from my Parameters 5506 bench oscilloscope. I took them during testing to get a better idea of the exact waveform shapes than I could get from the smaller RTV&H ‘scope screen. 100 Silicon Chip Australia's electronics magazine articles. One used impressive busbar construction with solid wire insulated with sleeving, while the other had ‘just put it down and solder it in’ construction. I started with the busbar version as it had the full set of valves, but ran into a few problems. First, the main filter capacitors were drawing excessive current and would not reform. I popped in a pair of substitutes and started to test the rest of the circuitry. There was an extra voltage doubler stacked on top of the existing -300V supply for the CRT (it’s visible on a tag strip at the extreme right of the chassis underside). I have no idea why, and it was messing up the CRT voltages, so I removed it. Next, the main HT was low everywhere. I seemed to have some current drains that I couldn’t locate. I was struggling with the whole instrument – while the busbar construction looked neat, it was pretty near impossible to trace the circuit or get test probes past the wiring and onto actual valve socket connections. So I moved on to the other version, which was much easier to work on. siliconchip.com.au The other oscilloscope was messier, but easier to work on. However, it didn’t have a full set of working valves. Better yet, its electrolytic capacitors all tested OK. I ‘liberated’ the valves from the busbar instrument, tested them all, plugged them into the other unit and got into testing proper. Apart from the usual noisy switches and pots, the restoration was going well until I hit the timebase. The coarse time selector (1 sec, 100ms, 10ms etc) checked out OK, as did the fine time selector (×1, ×2, ×5). However, the variable time selector did nothing. The variable control works by pulling down the voltage divider reference, but it was having no effect. Checking both ends of the variable pot showed identical voltages, around 42V. The wiring is obscured behind a metal shield plate, but I was able to make out a green wire going from the bottom end of the variable pot. Instead of going to a grounded tag on a tag strip, it went to one with no other connection. Connecting the green lead to ground fixed what had been an original wiring fault. gain calibration, then adjusting the five frequency-­compensation trimmers. With a 1kHz square wave input, I found a conflict of settings, so I substituted a stair-step. The stair-step display showed sharp transitions without significant overshoot on all ranges except 100mV/cm. It showed much slower rise times on this range, as seen in Scope 1, so this setting (and just this one) was suffering from a poor high-frequency response. Given that the 100mV/cm range connects the input signal directly to the vertical amp’s input grid, what was causing this loss of bandwidth? Now for the vertical amp. It was working OK, so I went ahead with calibration. This required setting the Fig.4: without compensation, parasitic capacitances will cause a resistive divider to slow down rapid voltage transitions (Cin is the unavoidable grid/input/wiring capacitance). siliconchip.com.au Australia's electronics magazine Vertical amplifier A simple resistive attenuator works fine for DC measurements. Still, circuit capacitances will cause AC voltage measurement errors even at the higher end of audio frequencies and slow down the rise and fall times of square waves and other pulse waveforms. The 6BL8 pentode has an input capacitance of 5.5pF. Circuit wiring will add to that, but let’s stick with a known value. While this capacitance would have a negligible effect at audio frequencies, its capacitive reactance at 1MHz is only 30W. That will give slow rise/fall times, as shown in Fig.4. Fig.5: adding a compensation capacitor across the input resistor forms a capacitive divider with the parasitic capacitance, Cin, flattening the frequency response and speeding up transitions. May 2024  101 Fig.6: in the original Oscilloscope circuit, the compensation capacitor was over-compensating to account for the pure resistance of the calibration potentiometer. Fig.7: however, on its most sensitive setting, the compensation capacitor was shorted out, so we were back to an uncompensated divider and the resulting signal rounding. Fig.8: by adding another compensation capacitor across the calibration resistance, we no longer need the first capacitor to overcompensate, and it compensates on all sensitivity settings. The solution is to modify the attenuator to make it a capacitive divider, as well as a resistive one, as shown in Fig.5. The added capacitance in the ‘top half’ of the divider compensates for the inherent capacitance in the bottom, giving a division ratio that is (theoretically) flat with frequency. Valve input impedance falls significantly at frequencies above about 20MHz, which can add loading to the attenuator. More complex attenuator/input stage designs will be accurate over wider bandwidths, but the RTV&H circuit gives accurate attenuation for audio and video frequencies of its time. Given that the input attenuator in the ‘scope has such compensation, what was wrong, and why on only one range? The calibration potentiometer is not compensated, so it will degrade waveform rise and fall times. The 3~30pF master compensation trimmer was used to compensate for this and therefore null out the under-compensation in the calibration pot, as shown in Fig.6. On the 100mV/cm range, though, the 3~30pF compensation capacitor was shorted out by the range selection switch, and could no longer apply the overcompensation that was masking the calibration pot’s under-­ compensation, as shown in Fig.7. I dislike ‘fixing’ other peoples’ designs, but I decided to add a compensating trimmer across the pot, from its top connection to the wiper, as shown in Fig.8. After adjusting that, Scope 3: the stair-step on its own CRT. Scope 4: a colour bar waveform. Scope 2: after adding a calibration resistor and compensation capacitor, the oscilloscope was finally producing a proper stair-step display on all ranges. Scopes 1 & 2 also confirm, being from a much better-performing instrument, that (i) the asbuilt RTV&H scope did not fully resolve the issue of the input circuit’s design regarding frequency response, and (ii) when corrected, the input circuit - and the entire instrument - did work correctly. The final screenshots from the RTV&H screen (Scopes 3 & 4) confirm the RTV&H’s correct operation as a complete instrument. 102 Silicon Chip Australia's electronics magazine siliconchip.com.au Table 1 – Test point readings Test point Peak-to-peak I got a proper stair-step display on all ranges, shown in Scope 2. In hindsight, it would have been possible to accept the input signal directly to V1A’s grid and perform gain calibration by adjusting the cathode-­ to-cathode coupling of the long-tailed pair input stage. That is how the companion horizontal amplifier is calibrated. The CRT on the working set showed a strangely shaped ‘black hole’ around the middle of the screen. Being irregular, I wasn’t sure if it was screen burn-in, so I’ll leave it with the screen filled by an unsynchronised display to see if it self-heals somehow. The restored ‘scope also lacked a proper engraved graticule and dial illumination lamps (despite having the pot installed), so I pinched them from the busbar version. I’ve previously covered the hazards of unsecured mains cords, and both of these units were offenders. Putting a cord anchor into the chassis may demand enlarging the cord hole in the chassis. Using an ordinary drill or a file can risk damaging under-chassis components. In this case, using a stepped drill bit with a cordless driver gives you complete control over your work – mains-powered drills can take too long to spin down if anything goes wrong. A few other bits and bobs How good is it? We have a saying in the restoration world: “Buy two, get one working”. After my ‘tweak’, I was now able to display a PAL stair-step (greyscale) V1A G1 100mV V1A anode 1.2V V2A anode 30V V2B cathode 30V V5A G1 4.5V V5A anode 25V V7 G1 150mV V7 G2 15V V7 G3 5V V7 anode 13V waveform easily (Scope 2), the colour bar waveform (Scope 4), and the horizontal sync period. These three are complex, high-­ frequency waveforms with a lot of high-frequency content, multiple voltage steps from 0V to 1V and narrow pulse widths. As such, they are good tests of vertical amplifier bandwidth, linearity, and timebase synchronisation and stability. The blurriness of Scope 3 & Scope 4 is more due to my photography than the instrument itself; in use, the display is much more crisp. Voltage readings If you are lucky enough to acquire one of these instruments, I have added my DC analysis to the circuit diagram, Fig.1. The test point readings in Table 1 should also help with checking and calibration. Purchasing advice I already have a complete test bench, but if you see one of these, why not grab it? You’ll have an example of classic Aussie design that’s still highly usable. And it’ll fit just about any service bench! A top view of the oscilloscope chassis. Different units will vary somewhat depending on how the individual constructor has gone about doing things. siliconchip.com.au Australia's electronics magazine May 2024  103 More details on valve-based oscilloscopes by Ian Batty A basic thyratron-based timebase circuit is shown in Fig.9. HT is applied to the circuit via two resistors, VR2 & R3. Together with the selected timing capacitor (C3C5), these form the timing circuit. Note the small circle inside the valve’s symbol, denoting a gas-filled valve. The bias voltage (applied to the grid via R1) sets the thyratron’s strike voltage, restricting the maximum charging voltage of C3-C5. This uses the most linear part of the exponential charging curve, giving an acceptably linear sweep on the oscilloscope screen. More on that later. With no synchronising input, the circuit oscillates at a frequency determined by the selected ‘coarse’ timing capacitor (C3-C5) and the ‘fine’ variable resistor (VR2) in the anode supply circuit. The displayed waveform will drift across the oscilloscope screen in the absence of synchronising pulses. The thyratron is cut off during the positive-­going sweep period as the timing capacitor is charging, and only conducts during the negative-going “flyback” period. Applying synchronising pulses will force the thyratron to go into conduction early. As a result, the sweep frequency will match the incoming synchronising pulses, as long as it is set to run a bit too slow in the ‘free running’ mode. The displayed waveform will appear stationary on the screen. Thyratron behaviour The thyratron (‘door valve’) is a thermionic triode filled with low-pressure gas; hydrogen is commonly used in low-power tubes. When power is applied to the heater, we get the usual space charge cloud of electrons surrounding the cathode. If the grid is made negative to the point of cutoff, the space charge will be confined between the grid and the cathode. No current flows if voltage is applied to the anode as the valve is held in cutoff. So far, the thyratron is no different from any other vacuum triode. If the grid becomes less negative and voltage is applied to the anode, some electrons will pass through the grid and travel to the anode. This is also what we expect, but in doing so, they collide with hydrogen atoms. If the collisions are sufficiently energetic, some hydrogen atoms will become ionised, splitting into negative ions (electrons) and positive ions (the nuclei of the atoms). We now have a stream of electrons heading for the anode: the original electrons emitted from the cathode, augmented by the negative ions liberated from the hydrogen atoms. There is also a corresponding stream of positive ions heading for the cathode. As the positive ions enter the cathode’s space charge, they absorb space charge electrons and become neutral atoms. This ion-electron absorption destroys the space charge. Remember that it’s the space charge that limits the maximum current in any vacuum triode; it creates a high internal resistance between the cathode and the anode. Removing that space charge means that the valve’s internal resistance falls dramatically. The conducting thyratron can pass very high currents with a voltage drop as low as 15V. Large versions, used in high-power radar sets, could switch up to 40MW! Once conducting, the thyratron cannot be switched off by grid voltage. This can only be achieved by reversing the anode voltage polarity or taking it below the ‘keepalive’ (sustaining) voltage. Readers may recognise a similar action in the Thyristor/ SCR (silicon-controlled rectifier). Linearisation The charging curve for a series RC circuit (Fig.10) is clearly exponential over five time constants. The grid bias voltage controls a thyratron’s striking voltage as the anode goes positive. Setting the grid bias to, say, -30V allows a small amount of the space charge Fig.9: how a thyratron can be made to generate an almost linear ramp waveform with an adjustable frequency. 104 Silicon Chip Australia's electronics magazine to penetrate the grid wires and stream towards the anode. This electron stream must be highly energetic to cause ionisation, so such a grid voltage would prevent a type 884 (as used in R&H designs) from striking until its anode voltage reached some 300V. Dropping the grid bias to around -11V allows the type 884 to strike at just 100V. Now we can use a 400V supply and set the grid bias to -11V. This sets the anode strike voltage to 100V, and the valve will extinguish when the anode voltage falls to +15V, using just 85V of the potential 400V of charge. The resulting RC curve looks like Fig.11; it appears to show a linear ramp. Close examination reveals some non-linearity, but such a timebase waveform would be adequate for servicing audio and other common equipment. The thyratron has a particular deionisation period. It must expire before the valve can be made active again; typical times are in the low to high tens of microseconds. The type 884, used in R&H’s designs, could oscillate up to around 100kHz. While its lowest frequency could be set to a period of seconds, oscilloscope timebases worked fine with a minimum frequency of 20Hz. The R&H timebases were modelled on the RCA data sheet for the type 884. This design offered a continuously variable frequency ratio of 3:1. This demanded seven switched ranges (with some overlap) to cover 20Hz to 114kHz – see https://frank. pocnet.net/sheets/049/8/884.pdf Wideband amplifiers A wideband amplifier’s high-frequency response is mainly limited by circuit capacitances. The capacitances we can be certain of are the stage’s own output capacitance and the input capacitance of the following stage. For the 6BL8 pentode driving its triode, we get 3.8pF + 2.5pF = 6.3pF. That doesn’t sound like much, but that is a reactance of only about 7kΩ at the oscilloscope’s top end of 3.5MHz. With the 6BL8 pentode 10kΩ load resistor, the gain will be reduced by about 60% by 3.5MHz (about -8dB). Such a circuit would have a -3dB point of only about 1MHz. The simplest fix is to increase the stage’s load resistance with frequency. Since XL=2π × f × L, a suitable ‘peaking’ inductor (560μH in series with the 10kΩ anode load) will work just fine, as shown in siliconchip.com.au Fig.10: a standard capacitor charging curve with a resistor limiting the current. Fig.12. This is the most common method used. The simplified circuit omits all biasing. V1’s anode load comprises the usual load resistor (R2) and the peaking/compensating inductor, L1. V1’s output capacitance and V2’s input capacitance are lumped together. It’s also possible to use a cathode resistor bypassed by a low-value capacitor. Let’s say the cathode resistor is 470Ω and we shunt it with a 330pF capacitor. At low frequencies, the cathode circuit will appear purely resistive, applying degenerative feedback to reduce the stage’s potential gain. At around 1MHz, the capacitive reactance will be about equal to the cathode resistor’s resistance, and the stage gain will be increased to counteract the effect of valve capacitances. Fig.11: the thyratron charges a capacitor over a smaller portion of the curve, with the result being almost linear. Fig.13 shows a nominal amplifier’s high-frequency response from zero compensation (Lp = 0, no inductance) to an inductor with a reactance equal to the circuit capacitance (Lp = C1 × Rp2), where Rp is the total plate (anode) resistance. The circuit can become resonant, as the pronounced peak for the Lp = C1 × Rp2 curve shows. However, the stage’s load resistor strongly damps the circuit. Such a level of compensation is rarely used, as the excessive high-frequency response causes ringing on rising and falling transitions and creates undesirable phase errors. Notice that an inductor value of Lp = 0.5 × C1 × Rp2 gives an acceptably flat response and triples the upper -3dB point frequency (a gain of 0.7071; from f ÷ f1 = 1.0 to f ÷ f1 > 3). Conclusion & further reading Wideband amplifier design is complicated, but many texts on Radar and Television treat the matter thoroughly. The most authoritative source is the MIT RadLabs series, compiled at the end of WWII, to ensure their groundbreaking wartime work would be preserved. I was going to state, “they wrote the book”, but they actually wrote 27 books, available as PDFs from www.febo.com/ pages/docs/RadLab/ An extensive mathematical treatment of wideband amplifiers appears in Volume 18 of Vacuum Tube Amplifiers. For a basic description, consider reading Zworykin, V. K. & Morton, G. (1954) Television (2nd edition), John Wiley & Sons/ SC Chapman & Hall. Fig.12 (above): the roll-off in response due to unwanted capacitance in a wideband amplifier can be compensated for by a choke in series with the anode resistor. Fig.13 (right): a nominal wideband amplifier’s frequency response with no choke (green) and three chokes of different values. The red curve is as close to flat as can reasonably be achieved. siliconchip.com.au Australia's electronics magazine May 2024  105 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. 05/24 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) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) PIC12F617-I/P Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Auto Train Controller (Oct22), GPS Disciplined Oscillator (May23) Railway Points Controller Transmitter / Receiver (2 versions; Feb24) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch (RX, Jul22) K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) Mains Power-Up Sequencer (Feb24) 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) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC16F1705-I/P Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) 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 ATmega32U4 ATmega644PA-AU Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) $25 MICROS dsPIC33FJ64MC802-E/SP 1.5kW Induction Motor Speed Controller (Aug13) PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $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 WIFI DDS FUNCTION GENERATOR (MAY 24) Short-form kit: includes everything except the case, USB cable, power supply, labels and optional stand. The included Pico W is not programmed (SC6942) - Optional laser-cut acrylic stand pieces (SC6932) - 3.5in LCD touchscreen: also available separately (SC5062) 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (SC6881) (MAY 24) PICO GAMER KITS (APR 24) ESP-32CAM BACKPACK KIT (SC6886) (APR 24) PICO DIGITAL VIDEO TERMINAL (SC6917) (MAR 24) MAINS POWER-UP SEQUENCER (FEB 24) Complete kit: Includes the PCB and everything that mounts to it, including the 49.9Ω and 75Ω resistors (see page 38, May24) $95.00 $7.50 $35.00 $40.00 - SC6911: everything except the case & battery; RP2040+ is pre-programmed - SC6912: the SC6911 kit, plus the LEDO 6060 resin case - SC6913: the SC6911 kit, plus a dark grey/black resin case - 3.2in LCD touchscreen: also available separately (SC6910) Includes everything to build the BackPack, except the ESP32-CAM module - 3.5in LCD touchscreen: also available separately (SC5062) $85.00 $125.00 $140.00 $30.00 $42.50 $35.00 Short-form kit: includes everything except the case; choice of front panel PCB for Altronics H0190 or H0191. Picos are not programmed (see page 46, Mar24) $65.00 Hard-to-get parts: includes the PCB, programmed micro, all other semiconductors and the Fresnel lens bezels (SC6871) $95.00 Current detection add-on: includes the AC-1010 current transformer, (P)4KE15CA TVS and MCP6272-E/P op amp (SC6902) $20.00 MICROPHONE PREAMPLIFIER KIT (SC6784) (FEB 24) Includes the standard PCB (01110231) plus all onboard parts, as well as the switches and mounting hardware. All that’s needed is a case, XLR connectors, bezel LED and wiring (see page 35, Feb24) USB TO PS/2 KEYBOARD & MOUSE ADAPTOR - VGA PicoMite Version Kit: see page 52, January 2024 (SC6861) - ps2x2pico Version Kit: see page 52, January 2024 (SC6864) - 6-pin mini-DIN to mini-DIN cable, ~1m long. Two cables are required if adapting both the keyboard and mouse (SC6869) (JAN 24) $70.00 $30.00 $32.50 $10.00 siliconchip.com.au/Shop/ COIN CELL EMULATOR (SC6823) (DEC 23) MULTI-CHANNEL VOLUME CONTROL (DEC 23) SECURE REMOTE SWITCH (DEC 23) IDEAL DIODE BRIDGE RECTIFIER (DEC 23) MODEM / ROUTER WATCHDOG (SC6827) (NOV 23) PICO AUDIO ANALYSER SHORT-FORM KIT (SC6772) (NOV 23) PIC PROGRAMMING ADAPTOR KIT (SC6774) (SEP 23) CALIBRATED MEASUREMENT MICROPHONE (AUG 23) - Kit: Contains all parts and the optional 5-pin header (see page 77, Dec23) - 1.3in blue OLED (SC5026) - Control Module kit: see page 68, December 2023 (SC6793) - Volume Module kit: see page 69, December 2023 (SC6794) - OLED Module kit: see page 69, December 2023 (SC6795) - 0.96in SSD1306 cyan OLED (SC6176) - Receiver short-form kit: see page 43, December 2023 (SC6835) - Discrete transmitter complete kit: see page 43, December 2023 (SC6836) - Module transmitter short-form kit: see page 43, December 2023 (SC6837) - 28mm square spade: see page 35, December 2023 (SC6850) - 21mm square pin: see page 35, December 2023 (SC6851) - 5mm pitch SIL: see page 35, December 2023 (SC6852) - Mini SOT-23: see page 35, December 2023 (SC6853) - D2PAK SMD: see page 35, December 2023 (SC6854) - TO-220 through-hole: see page 35, December 2023 (SC6855) $30.00 $15.00 $50.00 $55.00 $25.00 $10.00 $35.00 $20.00 $15.00 $30.00 $30.00 $30.00 $25.00 $35.00 $45.00 Short-form kit: includes all non-optional parts, plus a 12V relay and unprogrammed Pi Pico. Does not include a case (see page 71, Nov23) $35.00 Includes most parts, unprogrammed Pi Pico and OLED screen. The case, battery, chassis connectors and wires are not included (see page 41, Nov23) $50.00 Includes all parts, except the optional USB supply (see page 71, Sept23) SMD version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (SC6755) Through-hole version kit: same as the SMD kit (SC6756) Calibrated ECM set: includes the mic capsule and compensation components; see pages 71 & 73, August 2023 issue, for the ECM options (SC6760-5) *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. $55.00 $22.50 $25.00 $12.50 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT TELE-COM INTERCOM 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 ↳ 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 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) DATE OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 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 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 PCB CODE 12110121 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 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 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 Price $30.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $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 $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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) PICO AUDIO ANALYSER (BLACK) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION MAINS POWER-UP SEQUENCER MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) WII NUNCHUK RGB LIGHT DRIVER (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION SKILL TESTER 9000 PICO GAMER ESP32-CAM BACKPACK DATE APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 FEB24 FEB24 FEB24 FEB24 FEB24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 AUG23 AUG23 APR24 APR24 APR24 PCB CODE 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 04106181 04106182 15110231 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 04107231 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 10108231 01110231 01110232 09101241 09101242 16102241 16102242 07112231 07112232 07112233 16103241 SC6903 SC6904 01108231 01108232 08101241 08104241 07102241 Price $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $5.00 $7.50 $12.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 $10.00 $5.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 $12.50 $7.50 $2.50 $2.50 $12.50 $7.50 $7.50 $5.00 $2.50 $5.00 $2.50 $5.00 $2.50 $2.50 $20.00 $20.00 $7.50 $2.50 $2.50 $15.00 $10.00 $5.00 WIFI DDS FUNCTION GENERATOR 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (BLUE) FAN SPEED CONTROLLER MK2 MAY24 MAY24 MAY24 04104241 04112231 10104241 $10.00 $2.50 $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 How to locate pin 1 of an IC I just started to assemble my kit and fell at the first hurdle. I can’t decipher where pin 1 is located on the MAX31855. I am used to a more defined indent for pin 1. There is a + sign printed on one corner and a minuscule dot printed on the other corner. The data sheet says that the + is pin 1, but it seems to be in the ‘wrong’ corner. Can you please enlighten me? (D. C., Beachmere, Qld) ● If you look at the IC end-on, you should see thaat one edge is bevelled. For SOIC and TSSOP packages, pin 1 is on the side with the bevelled edge. For the MAX31855, the leftmost pin on that row is pin 1. See the accompanying image for more details. could use them if they had a red light instead of a relay. I don’t need all the switching gear, just a light to indicate if the exhaust gas is too hot. Would there be much involved in changing the circuit to do that? It looks as if all that is needed is a rewire around the transistor that operates the relay. Based on the article, I should be able to use the existing software to illuminate LEDs to give me a mixture indication. (P. A., Yinnar, Vic) ● Yes, if the relay coil is replaced by one LED with a series resistor to limit the current, it would light when the relay transistor is switched on. That way, you can observe the over- or under-temperature threshold, depending on the setup. Alternatively, if the relay is left on the PCB, the NO and COM contacts can switch power to the LED and series resistor. Typically, with a 12V supply, the LED series resistor would be 1kW. Digital Potentiometer remote control codes K-type Thermostats for tuning motorbikes I have just finished reading the article in the November 2023 issue on the K-type Thermocouple/Thermostat (siliconchip.au/Article/16013). I run a small business tuning two-stroke motorcycles. It is much easier to tune these bikes when you have an idea of the exhaust gas temperature. Have you, or could you, publish a similar design with two or more channels that can log the results against the throttle position measured by a potentiometer? It would not be too hard to rig up a pot to do that, or perhaps you have a better idea. If I buy a couple of your kits and stack them above the tachometer, I 108 Silicon Chip I have built three SMD versions of the Digital Potentiometer project by Phil Prosser (March 2023; siliconchip. au/Article/15693). Two replaced motorised volume controls that developed flakey rivet tabs, as others have experienced, while the third replaced a manual (ugh) volume pot. Two are now in sufficient proximity to require different infrared remote settings. According to the article, the option to reset the default RC5 code from “Philips TV” to “Philips Receiver” is performed by grounding the CS pin at power on and then powering off. So far, so good. My problem is that the recommended Universal Remote Control’s code lists do not offer an equipment type called “Philips Receiver”. There are codes for Philips SAT, DVD, AUX, CD, and DVR – dozens of them! I tried a few and gave up since there were so many. So, I decided to seek clarification. Can you provide me with some hints Australia's electronics magazine for selecting the correct equipment category or remote control codes that will work with both Altronics (Dynalink) A1012 Universal remotes, either the newer 4-digit code or the older 3-digit one? I have both. Many thanks for a great magazine. (R. M., Ivanhoe, Vic) ● Phil Prosser responds: I used several remotes in development, including an Altronics A1012A. I programmed it with the following codes: “TV”: 0088, 0154, 0169 and others “AUX”: 0734, 0846, 0727 and others I also tested a “one for all” remote on “TV” code 0556 and “RCVR/AMP” code 1269. The easiest way to find valid codes is to plug the IR Activity header into the programming port and watch for the LED to light up when you press buttons on the remote. Flashing will indicate that valid IR codes are being received. For the A1012A to produce the “Receiver” codes, select AUX (the lower right blue button on the remote). Remember that if you change between a TV code and an AUX code, you need to press the blue TV or blue AUX button on the remote so it sends the TV or AUX codes, respectively. I have used this a fair bit, so I expect it will work for you. I tried those three codes in the article before I got bored of reprogramming the remote, hence my comment “and others”. How are circuit ground connections made? I have recently been reading some old Silicon Chip magazines and have a question. For the components in a circuit diagram connected to a ground symbol, do you have to wire it so that all the ground symbols in the circuit go back to the negative side of the battery, or do you connect all the grounds together first, then to the battery? (Danny, via email) ● The ground symbols are just a way of showing that all these points are ultimately joined. Without them, siliconchip.com.au lines would run all over the circuit, connecting all those points, making it difficult to follow. These points are joined on the PCB, so you don’t need to connect each separately. Designing the ground connections on a circuit board can be an art, but it really depends on the circuit. In some cases, such as with low-speed digital circuits, it doesn’t matter how you join them. You could, as you say, bring them all back to the battery or power supply negative separately, or you could connect them all together first, or you could take a mix of those approaches. However, it does matter how you connect analog or high-speed digital circuits. The main reason for that is that when the ground current from one device joints the ground current from another device on the same track, it shifts the ground point that those parts ‘see’ or are referenced to. That can cause undesirable things to happen, like digital noise becoming audible in analog audio signals or even errors in digital data communication due to spikes from one or many gates switching simultaneously being superimposed on signals from other gates. Various approaches are used to handle these cases: a single large copper ground plane, multiple ground planes joined in various ways, star grounding, separate analog and digital grounds joined at specific points and so on. Unfortunately, this is a case where the circuit diagram tends to oversimplify the situation; we can’t easily explain all the nuances here! SC200 vs Hummingbird based audio amplifier I want to build a stereo Class-AB amplifier, and I am interested in both your 200W SC200 Amplifier modules (January-March 2017; siliconchip.au/ Series/308) and Hummingbird 100W modules (December 2021; siliconchip. au/Article/15126). This is probably a tricky question to answer, but do you consider one better than the other for audio use? I realise they have different power outputs, frequency responses and distortion figures, but I am still unsure which would be best. The speakers I want to use with the chosen modules are 4W types that require around 75-100W. If you don’t think there is much difference in sound/quality between the two different modules, I will probably go with the SC200s. (S. W., via email) ● They are both good amplifiers; there are a few considerations when deciding between them. 1. The power required. Both amplifiers should deliver enough power for you, although the Hummingbird will be operating at its limit (which is fine, as long as you don’t run into clipping). 2. Cost and effort. The Hummingbird modules cost a little less and are a little easier to build (mainly because of less heatsink drilling etc). 3. Distortion. It depends on what output devices you use for the Hummingbird. Unfortunately, we didn’t give 4W performance for the Hummingbird in the article. Both are good amplifiers, but the SC200 performs better at higher power levels. For example, at 40W into 8W, it’s well below 0.001% THD+N at 10kHz, while the Hummingbird graph shows 0.006% THD at 10kHz for 36W. It isn’t easy to make a direct comparison, but we feel that the SC200 is generally superior. It will be nowhere near its limits when delivering 100W Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus postage): Songbird Kit Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 siliconchip.com.au Australia's electronics magazine May 2024  109 into 4W and it also will be well within the distortion sweet spot. However, the SC200 module is quite a bit bigger and a little more time-­ consuming to build than the Hummingbird. The SC200 is also slightly more expensive to build, needing larger heatsinks etc. The compact size of the Hummingbird does compromise its performance somewhat, mainly at higher frequencies and higher power levels. It will perform well, but not as well as the SC200. So, if you’re willing to put the money and effort into building the SC200-based amplifier, it will be worthwhile. Altronics sells kits for the SC200 (K5157) and Hummingbird (K5158) modules. We have a pack of parts to help build the SC200 available from siliconchip.au/Shop/20/4140 We can also supply the PCBs: siliconchip.au/Shop/8/4135 siliconchip.au/Shop/8/716 Preamp with tape and phono inputs wanted I intend to build an audio system based on the Hummingbird amplifier modules (December 2021; siliconchip. au/Article/15126). The only preamp I can find with the older phono, cassette, tuner and aux style inputs is the Low-Noise Universal Stereo Preamplifier from April 1994 (siliconchip.au/ Article/5284). What feedback values would I use for aux and tuner inputs? I would appreciate any alternative preamp options that you may offer. (I. T., Blacktown, NSW) ● The April 1994 Universal Preamplifier is probably your best choice for a preamp with phono, cassette, tuner and auxiliary inputs. We don’t have anything more recent that would suit all those different sources. A gain of around 3.3 times should be suitable for the auxiliary and tuner inputs. R3 and C3 should be left off. R1 would be a 0W wire link, with C2 as 1nF. Use a 470W resistor for R4 and a 1kW resistor for R2. If more gain is needed, use a lower value for R4, down to a minimum of 200W. You could also use the Ultra Low Noise Stereo Preamp (March & April 2019; siliconchip.au/Series/333) with the Six-way Stereo Audio Input Selector (September 2019; siliconchip.au/ Article/11917). You could then add the RIAA, cassette, tuner and aux input 110 Silicon Chip Multimeter burden voltage is affecting readings You previously suggested I use a 1kW 0.1% resistor instead of 100W to convert the accurate 1V AC source to a 1mA alternating current for calibrating my multimeter, although I forget why you said to do that rather than using the 100W 0.1% resistor mentioned in the original Multimeter Calibrator article (July 2022; siliconchip.au/ Article/15377). I got a 1kW 0.1% resistor, which measured 999.5W. I tested this idea using my Keysight U1282A with the 1V source and 1kW resistor and got a reading of 0.89mA but it should be 1mA according to Ohm’s Law (I = V ÷ R). Other meters gave a similar reading. So I decided to use a 10kW 0.1% resistor instead, which measured 10.004kW, and got a reading of 100.3μA (it should be 100μA according to Ohm’s Law). I have tested this on three meters and got similar readings, although they varied over time. Finally, my meter’s ohms range accuracy is specified as 0.5% + 2 digits. What does that mean? (R. M., Melville, WA) ● We suggested you use a 1kW resistor instead of 100W because there was some question about whether the op amp in the Multimeter Calibrator could supply the 14mA peak current required to calibrate your multimeter with 10mA AC. The 1kW resistor demands a much lower peak current of 1.4mA. According to the Keysight U1282A data sheet, it has a burden resistance of 50W on the ranges you would use for that 1mA measurement. Adding that to the nominal 1kW and 10kW values goes a long way to explaining the difference between your measurements and your calculated currents, since the burden resistance is effectively in series with the shunt resistor. If you repeat the calculations, adding the 50W burden resistance to the precision resistor value, then calibrate the DMM for the expected values, it should be accurate. You might want to verify the actual burden resistance using another accurate multimeter in resistance measurement mode. The 0.5% plus two digits accuracy figure means that the error in the multimeter reading could be 0.5% of the value being read, plus an error amount that depends on its current range. For example, if you measure ohms with a single decimal place (33.0W), the maximum error is 33W × 0.5% + 0.2W = ±0.365W. If you were measuring instead with two decimal places (33.00W), the error would be 33W × 0.5% + 0.02W = ±0.185W. In other words, the percentage error is relative to the resistance being measured, while the digits error figure is relative to the display itself. preamplifiers from the April 1994 design to the Input Selector inputs. Sound generator for tinnitus sufferers Recently there has been some discussion on the benefits of going to sleep and sleeping with different ‘colours’ of sound, especially for those who suffer from tinnitus (as I do). I have heard that such noises are available through Alexa on your phone etc. Has there ever been an article or project in your magazine about building a sound machine to duplicate the frequencies associated with the different ‘colours’, eg, white, pink, green, brown, and various others? (J. D., Mt Barker, SA) ● Our November 2018 project, the “Insomnia and Tinnitus Killer”, can produce white or pink noise and should help with tinnitus: siliconchip. au/Article/11308 Australia's electronics magazine Which amplifier to build? I want to build a stereo amplifier. I’ve been looking at the Ultra-LD Mk.4 (August & September 2015 issues; siliconchip.au/Series/289), but I am not sure about the availability of the output transistors. Would you still recommend building that circuit/project, or is there a better option? (D. A., Mooroopna, Vic) ● If you want the best amplifier, you should build either the Ultra-LD Mk.3 or Mk.4. The Mk.4 is marginally better if you are comfortable working with SMDs. The NJL3281D and NJL1302D output transistors have been replaced with the equivalent lead-free NJL3281DG and NJL1302DG. However, Jaycar still has stock of the original transistors in some of their stores, so that is probably your best option. If your local store doesn’t 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 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 SALE LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware. For a full list of the parts we sell, please visit www.ledsales.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. Lazer Security SILICON CHIP For Quality That Counts... QUALITY COMPONENTS AT GREAT PRICES. Check out the latest deals this month. SMD parts and more. Go to www.lazer.com.au Silicon Chip Binders H Each binder holds up to 12 issues Price: $21.50 plus postage Available in Australia only. ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Most of the remaining books are data sheets. Some of the books may already have been sold. See the photos (updated once again 31/01/2024): siliconchip.au/link/ absm 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. 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 May 2024  111 have them in stock, they may be able to transfer them from another one. At the time of writing, Mouser has the NJL3281DG transistors but DigiKey and element14 do not. The complementary NJL1302DG transistors are not in stock with any of those sellers, but they can be ordered, with delivery expected in May. If you aren’t so fussy about sound quality, the SC200 (January-March 2017; siliconchip.au/Series/308) is easier to build, has basically the same power and should still sound good. We can supply the PCBs and transistors for the SC200, although Altronics has a complete module kit available (Cat K5157). Advertising Index Altronics..................... 29-32, 51-54 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Electronex..................................... 9 Emona Instruments.................. IBC Hare & Forbes............................. 15 Jaycar..................IFC, 11, 39, 68-69 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 PCBWay....................................... 13 PMD Way................................... 111 SC Ideal Bridge Rectifiers........... 95 SC PDFs on USB......................... 67 SC USB Cable Tester.................. 50 Silicon Chip Binders.......... 64, 111 Silicon Chip Shop............ 106-107 Silicon Chip Songbird.............. 109 Silicon Chip Subscriptions........ 55 The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 89 Next Issue: the June 2024 issue is due on sale in newsagents by Monday, May 27th. Expect postal delivery of subscription copies in Australia between May 22nd and June 14th. 112 Silicon Chip It would be possible to build an SC200-based amplifier and swap the modules for Ultra-LD Mk.3/4 modules later. The Ultra-LD modules are slightly smaller than the SC200 module and use the same heatsink pattern. The power supply requirements are identical. If you don’t need a lot of power, consider building an amplifier based on the Hummingbird modules from December 2021, although their performance is not quite as good as the SC200. The Hummingbird uses a lower voltage transformer; Altronics has a complete module kit (Cat K5158). 10kW ½W resistor attached to diodes D2 and D3 is changed to 15kW ½W. For resistors R1 and R2, use the values shown in the table accompanying the circuit diagram according to the DC supply the Loudspeaker Protector is connected to. RF preamplifier for oscilloscopes wanted I want to build the SiDRADIO (October & November 2013; siliconchip.au/ Series/130), but I can’t find the MMC capacitors. (T. R., Southgate, NSW) ● There has been a lot of confusion about the terminology regarding multilayer ceramic capacitors. The term most commonly used to refer to them these days is “multi-layer ceramic capacitor” or MLCC, but other terms have been used in the past, including “monolithic capacitor” and “monolithic multi-layer capacitor” (MMC). They are all essentially the same. All electronics retailers should have them, including Jaycar, Altronics and element14. The Jaycar and Altronics part codes for the values used in the SiDRADIO project are: • 1μF MMC: Jaycar RC5499 Altronics R2950A • 220nF MMC: Jaycar RC5494 Altronics R2935A • 100nF MMC: Jaycar RC5490 Altronics R2931 • 10nF MMC: Jaycar RC5480 Altronics R2910A Thank you for producing a great magazine. I have been a subscriber and buyer since almost the start. I want to build a detachable RF probe similar to the unit in the June 1988 issue (pages 72 to 74) and can source the 2SC3358 transistors. My requirement is probably 0.5-30MHz, mainly for checking oscillators in valve radios. Is there a later circuit that would be better, or using more modern transistors? I prefer through-hole components as they are much easier to handle. I am currently using a dip/wave meter built from an Electronics Australia circuit from the 1970s, but I want a more accurate frequency reading. (J. M., Wellington, New Zealand) ● You could consider building the RF Preamplifier circuit from Circuit Notebook, July 2009 by Dayle Edwards (siliconchip.au/Article/1507). The tuned circuit using L1, VC1 and VC2 can be deleted, and a 1MW resistor can be added to bias gate 1 of the Mosfet to ground. Apply the signal via a 10nF capacitor to gate 1. Alternately, the somewhat similar January 2004 Antenna & RF Preamp For Weather Satellites by Jim Rowe (siliconchip.au/Article/3326) might be of interest. Both circuits use some SMDs as dual-gate Mosfets are not readily available in through-hole packages. Loudspeaker Protector used at higher voltages Charging a Li-ion cell from USB I built your Loudspeaker Protector (October 2011; siliconchip.au/ Article/1178) from an Altronics kit (K5167). The instructions mention that 50V AC is the maximum voltage recommended for the AC Sense input; however, my transformer delivers about 54.5V AC. Is it safe to use the AC Sense feature with the slightly higher voltage? (M. K., via email) ● You can connect your transformer to the AC Sense input provided the I am looking for a kit to charge a 3.7V Li-ion battery from a 5V USB source. Thanks for your help. (R. J., Nambucca Heads, NSW) ● Modules are available to do that so inexpensively that we could not produce a design or kit to compete with them. For example, we sell TP4056 1A Li-ion charger modules in our shop for $2.50 each (SC4305 with a mini Type-B USB socket or SC4306 with a micro Type-B). 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