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SEPTEMBER 2021 ISSN 1030-2662 09 The VERY BEST DIY Projects! 9 771030 266001 $ 95* NZ $1290 9 INC GST INC GST Digital Preamp with Tone Controls Plus Touchscreen and IR Remote Advanced Imaging Non-Medical Uses – Security, Archaeology & Biometrics Cromemco’s Dazzler Tapped Horn Subwoofer One of the first colour Using a single 8-inch graphics siliconchip.com.au cards Australia’s electronics magazine driver September 2021  1 Build your own Ultrasonic Radar Build your own old-school radar and watch objects slide across your computer screen like the old war-time movies! The ultrasonic sensor measures distance in a rotating fashion across your workbench, while Arduino and the easy-to-use “Processing” software provide the display on your PC. Note: Accuracy of detecting helicopters not guaranteed. SKILL LEVEL: Beginner TOOLS: Drill, Soldering Iron CLUB OFFER BUNDLE DEAL 4995 $ For step-by-step instructions scan the QR code. SAVE 35% www.jaycar.com.au/ultrasonic-radar See other projects at KIT VALUED AT $78.10 www.jaycar.com.au/arduino ONLY 14 $ FROM ONLY 3 $ FROM 495 95 $ EA Grey Vented ABS Enclosures Prototyping Boards Protect your project from unwanted fingers or objects. Satin textured finish, snap-fit assembly. 3 sizes. HB6114-HB6118 100 $ gift card Awesome projects by On Sale 24 August to 23 September, 2021 Transfer your breadboard design without having to rework it. Small 25 Rows/400 Holes HP9570 $4.95 Large 59 Rows/862 Holes HP9572 $9.95 ONLY 2195 95 $ 100 PIECES Jumper Lead Mixed Pack A mixed pack of jumper leads for your Arduino®, breadboarding and prototyping projects. WC6027 Got a great project or kit idea? If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Solderless Breadboard with Power Supply Power from USB or 12V plugpack. Includes 64 mixed jumper wires of different length and colour. PB8819 Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.34, No.9 September 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 Advanced Imaging – Part 2 Imaging technologies aren’t just used for medical purposes; they can also be used in airports for X-ray inspections, reconstructing ancient or damaged objects via a CT scan and more – by Dr David Maddison 27 The Cromemco Dazzler The Dazzler board by Cromemco could be considered one of the first ‘reasonable’ computer graphics devices capable of producing a colour image. It generates an NTSC signal which can be fed to a TV – by Dr Hugo Holden 48 Review: IOT Cricket WiFi Module The IOT Cricket is a small, low-power WiFi module by Things On Edge. It incorporates an ESP8266 and could potentially be powered for years(!) from a pair of AA cells – by Tim Blythman 86 Review: the tinySA Spectrum Analyser For just $80, this spectrum analyser works over 0.1MHz-350MHz and 240960MHz ranges with selectable resolution bandwidth. It has a colour display and separate signal generator mode – by Allan Linton-Smith The Cromemco Dazzler was the first colour graphics card for the S-100 bus computer. It was released in 1976, and came as two separate S-100 boards which had a total of 72 ICs – Page 27 Constructional Projects 38 Touchscreen Digital Preamp with Tone Control – Part 1 This preamp has four external stereo inputs plus two stereo outputs. It uses a colour touchscreen and has IR remote control functionality. Bass, mid and treble presets are provided, plus volume control – by Nicholas Vinen & Tim Blythman 61 Second Generation Colour Maximite 2 – Part 2 Finishing off our shiny new 2nd Gen Colour Maximite 2, we cover construction details and running your first program – by Geoff Graham & Peter Mather 66 Tapped Horn Subwoofer Using just a single 8-inch driver, this subwoofer’s response extends below 30Hz and can deliver over 100dB SPL (sound pressure level) – by Phil Prosser 82 Micromite to a Smartphone via Bluetooth Even a Micromite can be used as the heart of an Internet of Things (IoT) project! Building this simple project on a breadboard provides you with an easy way to control a Micromite using your Android smartphone – by Tom Hartley Your Favourite Columns Our new Digital Preamp uses a classical Baxandall style volume and tone control circuitry to achieve the low noise and distortion expected of an analog design. It can be controlled via a colour touchscreen or an infrared remote – Page 38 The IOT Cricket is a tiny, ultra low-power ESP8266-based WiFi module – Page 48 75 Serviceman’s Log ‘Playing’ with fire – by Dave Thompson 90 Circuit Notebook (1) Multiple RAM banks for the IR Remote Control Assistant (2) Solar garden light using a supercap (3) 1-2-5 switching arrangments (4) Simple tripwire alarm (5) Letterbox counter 96 Vintage Radio Sanyo 8-P2 TV (1962) – by Dr Hugo Holden Everything Else 2 4 94 106 Editorial Viewpoint Mailbag – Your Feedback Silicon Chip Online Shop Product Showcase 107 111 112 112 Ask Silicon Chip Market Centre Notes and Errata Advertising Index This Tapped Horn Subwoofer is built into a modestly-sized cabinet which measures 50 x 90cm with a width of 28.2cm. You don’t need much more than a hand-held circular saw, drill and clamps to assemble it – Page 66 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. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Reader Services Rhonda Blythman, BSc, LLB, GDLP Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Editorial Viewpoint Upcoming price changes As discussed previously in the magazine, the Silicon Chip cover and subscription prices have not changed since mid-2013. I have been holding off increasing what we charge as long as possible, despite most issues of Silicon Chip now having 112 pages rather than 96 or 104 (and considerably more content as a consequence). To keep up with inflation, the magazine cover price will change to $11.50, starting with the next issue (October). The New Zealand cover price will not change. Domestic and online subscription rates will increase by roughly the same amount (15%) – see below. You can extend your subscription now for up to two years to lock in the current rate. Unfortunately, we must increase international subscription costs by an even higher percentage because the cost of mailing magazines overseas has increased so much. The company we were using before went out of business due to the impacts of COVID-19. This has resulted in our international mailing costs roughly doubling. Affected customers could consider switching to an online subscription if they cannot afford the new rates, at least until international mailing goes back to normal. These changes should mean that we can afford to stay in business for a while yet, and continue to produce a world-class magazine with a considerable amount of exclusive content. Our new pricing in Australian dollars as of October 31st 2021 will be: Subscription Type 6 Months 12 Months 24 Months Online Subscription (Worldwide) $50 $95 $185 Printed Magazine Only $65 $120 $230 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. Print + Online (Combined) $75 $140 $265 Printed Magazine Only $80 $145 $275 Print + Online (Combined) $90 $165 $310 Subscription rates (Australia only): 12 issues (1 year): $105, post paid 24 issues (2 years): $202, post paid For overseas rates, see our website or email silicon<at>siliconchip.com.au Printed Magazine Only $100 $195 $380 Print + Online (Combined) $110 $215 $415 Founding Editor (retired) Leo Simpson, B.Bus., FAICD Staff (retired) Ross Tester Ann Morris Greg Swain, B. Sc. (Hons.) Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. ISSN 1030-2662 Printing and Distribution: Australia New Zealand Rest of World A note about cheques Due to COVID-19 related restrictions, it is becoming difficult to deposit cheques and money orders. We will continue to accept them, but there could be delays in processing orders paid by these methods. We recommend making payments via EFT, credit card or PayPal as those payments can be processed without leaving our premises, and such orders are typically processed within one business day. ElectroneX 2021 delayed The ElectroneX 2021 trade show and associated SMCBA conference has been pushed back to the 10th & 11th of November – see the ad on p7 for more details. by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine September 2021  3 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 had 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”. Video of Harold S. Black Since you published my article on Harold S. Black (the inventor of negative feedback) in the August 2021 issue, I came across an excellent documentary on his invention on YouTube, which you can view at https://youtu. be/iFrxyJAtJ7U This video has Harold Black himself describing his discovery of the negative feedback amplifier while on a ferry going to work. Roderick Wall, Mount Eliza, Vic. It seemed like a good idea at the time I have a coffee table made on a 1960s Yamaha “Elephant Ear” 33 x 24in (85 x 60cm) speaker frame. The speakers were reviewed in Electronics Australia, April 1969. Electronics is littered with hundreds of ‘good ideas’ from the last hundred years. Most disappeared quickly, but a few survived, while others reemerged years later when technology caught up to the idea. In science and technology, often the ‘good idea’ is years ahead of the means to implement it. Two examples are mechanical fuel injection for cars in the 1970s and early “portable” computers. Some great ideas are washed away by the competition through no fault of their own. Cassette tapes were inferior to open-reel and eight-track tapes, but Dolby and the Walkman turned them into a brilliant success. In the late sixties, Yamaha, who made quality musical instruments, including audio equipment such as amps, speakers and electronic organs, made these enormous speakers for some organs. The “good idea” was that being 4 Silicon Chip asymmetrical, it would have less resonance and gain some of the audio ‘personality’ of grand pianos that are a similar shape. The accompanying extract from EA shows a speaker in one such organ. The article reviewed two smaller “Natural Sound” Yamaha ear-shaped speakers at ‘just’ 17 x 13 inches (43 x 33cm). The reviewer was sceptical of the concept of a speaker adding to the sound, rather than just reproducing it, almost in defiance of the path taken by other top speaker manufacturers. My elephant ear speaker is from a thrown-away electronic organ and, with long leg bolts, makes a fantastic coffee table. The matching curved glass top reinforces the ear shape. The frame is cast aluminium, and the diaphragm is heavy moulded styrofoam with deep reinforcing ribs. I have not assessed the sound quality; I don’t think it would fare well against my JBL 250Tis. The Yamaha engineers obviously thought that the earshaped “Natural Sound” speakers were a good idea at the time; unfortunately, history does not agree. Dave Dobeson, Berowra Heights, NSW. Motorised pots can be finicky I read with interest the correspondence from D.M.C., regarding shunt resistor values to use for audio pots in the June 2021 issue (pages 109 & 110). I also built the Ultra Low Noise Remote Controlled Stereo Preamplifier (MarchApril 2019; siliconchip.com.au/Series/333) and mounted this, plus the 6-input selector board, in a 3RU rack case. Like D. M. C., I felt that the bass and treble control knobs are mounted too close together, and as such, I took them Australia’s electronics magazine siliconchip.com.au off the board, together with the volume control, mounting them with more aesthetically pleasing spacing on the 3RU front panel. During testing, I had very similar experiences with the 5kW motorised volume control potentiometer and actually had to ask for replacement pots around August 2020. They all worked correctly for about one week, then the volume control of the left-hand channel started to become unreliable. The sound was still OK, but the volume could not be controlled. There was no problem with the right channel, where the volume control still worked. I tracked the fault to an open-circuit connection on the pot. Upon replacing it, it worked correctly for about five days, then gave the same fault, only this time on the right channel. This happened with several pots until I came across a good one. It seems to me that there was a manufacturing fault with these motorised pots. Since then, it all has worked very well, except for the intermittent problem with the six-channel input selector randomly changing channels. This was fixed by revised firmware that was supplied to me by John Clarke. By the way, I also built the SC200 Amplifier (January & February 2017; siliconchip.com.au/Series/308) and combined them with speakers I built from a kit. They really sound excellent and work very well on the SC200 power amp, and were fun to build. The sound quality is great, with lots of volume and deep, full bass and very clear vocals. Allan Metcalf, Alexandra Hills, Qld. Nicholas responds: I built an Ultra-LD Mk1 amplifier from an Altronics kit some years ago, and it came with a motorised pot for the remote control. My young kids frequently abuse that pot but surprisingly, it still works fine. So they can be reliable; as you say, there must have been a poorly manufactured batch of the 5kW dual gang log motorised pots we specified for the later preamp. Still, mechanical devices can fail; even non-motorised pots can wear out and go scratchy. Our new Digital Remote Controlled Preamp, starting on page 38 of this issue, is an excellent way to avoid those problems. SILICON CHIP magazines to give away I have around 250 issues of Silicon Chip (including the complete set 2003 onwards but starting from 1988) that I would like to give away rather than dump them in the recycling. I also have around 200 issues of EA that I want to dispose of similarly (note: e-mail silicon<at>siliconchip. com.au if you are interested). Mark Patterson, Northern Beaches, NSW. Also sick of so many updates I can only whole-heartedly agree with the Editorial Viewpoint on software updates in the July 2021 issue. I left Adelaide around 35 years ago when our company was attempting to run security and lifts from a program installed on a 51/2 inch floppy disk. IT people, as we now call them, were so aloof they could keep you waiting for hours. I had my reservations back then, so I pulled the pin. I did some opal mining in an outback town and kept their current technology going for nearly 10 years. No computers in sight! 6 Silicon Chip Australia’s electronics magazine siliconchip.com.au When my partner became sick of the desert, we moved to a small town on the Yorke Peninsula, where I kept their technology going for around 25 years. Of course, I had to embrace computers once again; they had improved and formed a good deal of my business in later years. I still felt the IT people had too much control, though. When I retired, I set myself up with a new laptop and other tech with Windows 10. I persevered for quite a while and eventually gave up for the very same reasons as Nicholas. I now run Linux Mint, which I can update at my leisure, and Android on my phone and tablet. Life is good. Of course, some programs will only run on Windows, so the IT people still have control! Rick Boston, Warooka, SA. Comment: Linux does handle updates a lot better than Windows. It doesn’t force them down your throat or force reboots, and now it can even perform kernel updates without needing to reboot. Parts mixup in HF Preamp For the Tunable HF preamp (January 2020; siliconchip. com.au/Article/12219), I ordered the BF1105 Mosfet from element14, and I had to purchase 10. I was unaware of the differences in the Mosfets in regards to the letter after the type number. The components I received were BF1105R. The type required is the BF1105S. This difference was not mentioned in the parts list. I have since attempted to purchase the correct Mosfet, but to no avail. The BF1105 is no longer in production and I am unable to determine a substitute. The major difference between the two Mosfets listed above is that they are a mirror image of each other. Do you know of a suitable substitute Mosfet and where I can purchase one, preferably in Australia? Paul McKendry, Kedron, Qld. Comment: BF1105 is the correct part code. You can verify this by checking the manufacturers’ data sheet at www. nxp.com/docs/en/data-sheet/BF1105_R_WR.pdf We were not aware that there was an R suffix version. We have also been bitten by this ill-conceived practice of incompatible devices differing only by an optional suffix. Perhaps the creation of the BF1105S part code was due to their realisation that it is a problem. You are correct that the BF1105 is no longer being manufactured and there is no direct equivalent (as is the case with so many of these discontinued dual-gate Mosfets), but new old stock (NOS) parts are available at reasonable prices on eBay. However, be careful because, according to the designer, Charles Kosina, sometimes if you order a BF1105 from eBay, you might get a BF1105R. It would be a good idea to order a couple from different sellers to ‘hedge your bets’. Caution when testing using variacs After reading your article on Variac-based Mains Voltage Regulation in the May 2021 issue (siliconchip.com. au/Article/14856), I’d like to make some comments about variacs (slide regulators). It must be remembered that they are not isolation transformers. The fuse is merely to protect it and not you. These are auto-transformers. They are directly connected to the mains; therefore, you are not protected from it. The only thing that will isolate you from the mains is an isolation transformer. This would cover pretty much any transformer that has no physical conductive connection between the primary and secondary. Often, variacs are used in conjunction with an isolation transformer for radio & other work. The danger with slide regulators comes mainly on the output side. RCDs trip based on current. To illustrate this, I put a 30mA RCD tester on the output of a variac and wound the volts up from zero. The RCD did not trip until it got to 130V; therein lies risk. One should be aware that safety devices are not failsafe; there are limitations. As an example, with transformers. I have seen a stick welder at a Men’s Shed and two others elsewhere, plus a couple of radios, where there has been a malfunction on the secondary incinerating the Earth connections. In one case, it took out all the Earth wiring in the building! The circuit breakers, RCDs and fuses in this scenario did not activate as, in most cases, the primary load did not exceed the ratings, leaving the secondary to melt down. There was no Earth leakage on the primary side, as the secondary is isolated from the primary; the RCDs, where fitted, had no cause to activate. It all comes down to risk management and understanding what you are dealing with. That applies to everything. My isolation transformer for radio work has circuit breakers on the primary and secondary and run lights to indicate if both are alive, plus a kill switch. 10% OFF YOUR NEXT SEPTEMBER ORDER WITH DISCOUNT CODE SCSEP10 THE TOOLS TO BUILD THE FUTURE w w w. p h i p p s e l e c t r o n i c s . co m 8 Silicon Chip Australia’s electronics magazine siliconchip.com.au “Setting the standard for Quality & Value” Established 1930 ’ CHOICE! 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It now has a mains thermal fuse to deal with any recurrence. Marc Chick, Wangaratta, Vic. Comment: many low-cost UPSs have the problem you describe, and when (not if) the batteries fail, they become fire hazards. It doesn’t help that the low-cost gel cells frequently supplied with them are lucky to last two years on standby. You’re 20 years too late I have built many shortwave radios and all have similar problems with noise levels. Emerging trends in the radio spectrum make most, if not all, shortwave radio listening and VHF/UHF scanners obsolete. Metropolitan interference noise levels and digital modes make most radio an exclusive communications service, off-limits to anyone with only a traditional analog shortwave radio or VHF/ UHF scanner. If you have to use the internet to listen, it is no longer truly radio listening; it’s just another web service. Traditional analog radio listening requiring a good antenna and radio receiver. In 2021, the VHF aircraft band and UHF citizens’ band are just about the only activity on a radio scanner. Most, if not all, other communications are now digital. Even amateur radio operators are slowly moving to digital. Model trains are another hobby that’s dying out. Today, metropolitan passenger trains are as interesting as an elevator ride for most of us. Long gone is the age of steam trains and busy shunting yards, with many men working on the line. Try to set up a traditional tabletop model train; it needs the same room space as a pool table. Most of us, if under 40 years old, will settle for playing a train simulator video game. Digital wins again. Your DIY projects are still good, even if fewer and fewer of us will build them as life is so so busy. John Crowhurst, Mitchell Park, SA. Comments on the last few issues I have enjoyed reading the last few issues of Silicon Chip. Not every article is to my liking, but that is life. Regarding your January editorial, if you need to raise the price of the magazine, do so. Silicon Chip must make a profit to survive, and please do not listen to those who want everything for nothing. I have to express some embarrassment over the publication of my Points Controller in the December 2020 issue (siliconchip.com.au/Article/14682). If you remember, after I submitted the circuit, I notified you that MERG in Britain had produced an almost identical unit. Consequently, I never expected you to publish it. For some years, I have been hoping that Silicon Chip would publish a robot project of some substance but, of course, that has not happened. I have been searching through old magazines and have noticed that almost all the robot projects of any substance Australia’s electronics magazine siliconchip.com.au Development tools in one location Thousands of tools from hundreds of trusted manufacturers Choose from our extensive selection mouser.in/dev-tools 080-4265-0000 india<at>mouser.com have been from individuals or businesses. The only magazine produced robots have been simple line followers or simple Braitenberg type vehicles. I suppose that makes sense considering the immense effort that is required for such a complex machine. I have considered submitting a robot project, but there is always the question of whether it is worth the effort. While thinking about the type of robot, I searched the internet for images of what was already available. It is absolutely amazing what is available. There is a huge range of robots, either fully assembled or as kits, ranging from very simple to very complex. That made me have second thoughts. I haven’t dismissed the idea entirely, but it needs to be thought out very carefully and particularly as to the mechanical capabilities of anyone wanting to build the project. I have machining equipment; others do not. Mechanical parts need to be relatively easy to obtain or easily made with standard hand tools. In my November 2020 letter, I referred to the poor efficiency of charging Li-ion cells, and I wanted a switchmode type charger instead of a linear. In the meantime, I have been asked about available balancing modules for several cells in series. I remembered that the TL431 could be used to make a shunt regulator. There was even an example circuit in the Texas instruments data book. However, the original TL431 required a minimum cathode current of 5mA, and later versions required 1mA. This is too much for a circuit that would be permanently connected to a cell. A search for a better equivalent returned the ZR431, manufactured by Diodes Incorporated. It has a minimum cathode current of 50μA, and Digi-Key stocks the ZR431, selling them for around 80¢ in one-off quantities. The ZR431 now makes it feasible to make high powered shunt regulators to limit the cell voltage to 3.7V, provided the charging is via a current limited supply. With minimal electronics, a suitable solar panel can be directly connected to a Li-ion battery without worrying about overheating. Once all the battery cells are charged to 3.7V, the shunt regulators will divert the excess power into a heatsink. George Ramsay Holland Park, Qld. Comment: the existence of another similar points controller design does not detract from the usefulness of yours; you developed it, and we can’t see any reason why others would not want to build it. So it deserved publication. You have struck on most of the reasons why we do not publish many robot projects. They are difficult and time-consuming to develop, require constructors to have skills beyond electronics assembly, and it’s hard to think of one which is more than just a novelty. Of course, we would be happy to publish a good robotics project should someone happen to contribute it. We are working on a simple, shunt regulator based cell balancer along the lines of what you suggest. There are some subtleties that mean that you need a bit of extra circuitry. But it isn’t too complex. Hopefully, this will come to fruition in the next couSC ple of months. Silvertone Electronics sells a range of Signal Hound spectrum analysers from 4.4GHz up to 24GHz. There's even a 43GHz analyser coming soon! « This 4.4GHz spectrum analyser is yours from just $1567.50 This product and even more can be purchased from Silvertone's Online Store https://silvertoneelectronics.com/shop/ ► UAV & Communications Specialists 1/21 Nagle Street Wagga Wagga NSW 2650 Phone: (02) 6931 8252 https://silvertoneelectronics.com/ contact<at>silvertone.com.au Spike RF analysis software included for FREE with every Signal Hound analyser Silvertone is a reseller of these brands BitScope 12 Silicon Chip Australia’s electronics magazine siliconchip.com.au Ready for Tomorrow Meet our new international distribution centre At 360,000sq.ft., the new distribution centre in Leeds, United Kingdom is the biggest warehouse in the element14 global supply chain 3.2 times bigger 30% more products stocked Over 30 supplier lines added Contact us now Phone: 1300 361 005 Sales: au-sales<at>element14.com Quotes: au-quotes<at>element14.com au.element14.com/ready4tomorrow Advanced medical & Biometric Imaging Part 2: By Dr David Maddison – Non-Medical Uses Now that we’ve covered many medical imaging techniques like X-ray, CT, PET, MRI and ultrasound, it’s time to cover other uses for these (and similar) technologies. There are surprisingly many applications outside the realm of healthcare. Image source © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons – https://w.wiki/3XDf) Y ou will be aware that X-rays are used for security purposes, such as at airports to check baggage and passengers for contraband and weapons. But these days, it isn’t just X-rays being used, and many of these imaging techniques are being used for other purposes, like archaeology, as we shall now describe. X-ray inspection When Röntgen discovered X-rays in 1895, he mentioned one possible use as detecting flaws in materials such as steam pressure vessels. They are still used for that purpose to this day – see Fig.49. One important electronics-related use of X-rays is the inspection of PCBs and solder joints, especially when solder joints are hidden, such as with BGA and LGA packages. X-ray inspection is a critical part of quality control for advanced electronics which make extensive use of BGA/LGA package devices – see Fig.50. Defects that can be detected by X-ray include breaks in tracks, voids in solder joints and missing or incorrectly-sized solder balls. Airport baggage and cargo Airport passenger luggage (and indeed all aircraft cargo) is always X-rayed to detect explosives or weapons (see Fig.51). X-ray machines have traditionally been of the planar type, with a single X-ray beam passing through the luggage. To give you some idea of the advances in security X-ray technology, the machine shown in Fig.51 offers optional proprietary iCMORE software algorithms to detect lithium batteries, as well as other hazardous or dangerous cargo such as flammable liquids or solids, and liquefied or compressed gases. We have probably all noticed the images on the security screener monitors as we have gone through X-ray security checkpoints at airports. But Fig.50: an X-ray of an assembled printed circuit board (PCB) with a ball-grid array (BGA) package IC at the centre, and vias and passive devices surrounding it. Not only can you see the PCB tracks, IC bond wires and BGA solder balls adhering to the lands and pads, but also the copper plating in the vias and the internal structure of the components to the left, which appear to be a resistor and possibly a fuse. Fig.49: X-ray inspection of a weld showing defects. Source: NTB (https://ntbxray.com). 14 Silicon Chip what do the colours mean? X-rays do not yield colour information, but they do provide information about the average atomic weight and thickness of the materials they pass through. Most X-rays will pass through materials with a low average atomic weight, such as plastics which include some combination of two or more atoms of carbon, hydrogen, nitrogen and oxygen. Materials that have much higher atomic weight metals such as steel and aluminium will comparatively absorb many X-rays. Similarly, the thicker or more dense something is, the more X-rays are absorbed and the lower the X-ray count through the material. With security X-ray machines, the X-ray image is artificially coloured according to a material’s overall atomic weight average (and density), which initially appears as grey levels. The software colourises the greyscale X-ray image, as the human eye can more readily distinguish colours Australia’s electronics magazine siliconchip.com.au than shades of grey. This aids the job of the security screener, providing a rough indication of what materials are present. A certain amount of interpretation is required, as a very thick layer of a low atomic weight organic material like a block of photocopy paper may appear the same as a thinner layer of a more dense metallic material. Typically, materials can be identified according to whether they are organic, metallic or a mixture of both, and some further distinctions within those categories. Within organic materials, it is usually possible to distinguish between harmless inert materials like clothing according to the substance’s mean atomic number and density. So it might be possible to distinguish between materials like plastics, explosives and illicit drugs. Lighter atomic number metals like aluminium can be distinguished from heavier atomic numbers like steel. Similarly, gunpowder can usually be identified. Gold and silver, which might be the subject of smuggling, can also be distinguished because of the very high atomic number of these metals. Human intuition, common sense and observation of a suspicious person are also parts of the detection process. Teledyne ICM (www.teledyneicm. com) is one company that makes various security products. They produce a system and software known as Flatscan for portable X-ray screening. Fig.52 shows a monochrome X-ray image produced with Teledyne’s Flatscan software, with no colour coding. Firearms, bullets and a laptop computer are clearly visible. Lighter areas represent substances of high atomic weight like metals, where few X-rays penetrate. Darker areas are lower atomic weight materials such as plastics, where many X-rays penetrate. In Fig.53, the image of Fig.52 has been colourised. The firearms are blue, suggesting they are very dense metal, not fake plastic toys. The green/blue square object indicates an item made of dense plastics and metal, like a laptop computer. In Fig.54, an image of a similar bag has been processed using Teledyne’s Flatscan software to reveal different materials according to their atomic weight. The non-organic materials or dense organic plastics are green, with siliconchip.com.au Fig.51: the Smiths Detection Group Ltd HI-SCAN 10080 XCT advanced CT explosives detection system for checked baggage and air cargo. The manufacturer states that it “features a dual-view dualenergy X-ray line scanner with full 3D volumetric computed tomography (CT) imaging and reconstruction”. 53 52 Fig.52 (above left): a ‘standard’ greyscale X-ray image of a bag that an airplane passenger might carry. Source: Teledyne ICM. Fig.53 (above right): a colourised version of Fig.52, showing different details. Source: Teledyne ICM. 54 Fig.54 (lower right): this false-colour X-ray image shows organic materials in orange and inorganic in green, with the inorganic materials mostly removed. Source: Teledyne ICM. Z-Number Material Type 3 Color 6 Color Examples Possible Threats 0-8 Organic Orange Brown Wood, Oil C-4, TNT, Semtex 8-10 Low Inorganic Orange Orange Paper Cocaine, Heroin 10-12 High Inorganic Green Yellow Glass Propellants 12-17 Light Metals Green Green Aluminium, Silicon Gunpowder, Trigger Devices 17-29 Heavy Metals Blue Blue Iron, Steel Guns, Bullets, Knives 29+ Dense Metals Blue Violet Gold, Silver High Value Contraband – Impenetrable Black Black Lead Shielding for above threats Fig.55: an X-ray colour-coding scheme from Totalpost Mailing Ltd, showing the atomic number range (Z) in the left column and examples of possible threats that might be represented. Different software manufacturers may use different colour coding. These colours do not apply to Figs.52-54. Australia’s electronics magazine September 2021  15 lighter organic materials represented by orange. Note the orange object (a light organic material) at the bottom with what appears to be green nails in it, suggestive of a bomb; this might not be readily visible without this sort of high-contrast colouring scheme. Fig.55 shows one possible colour coding scheme for this type of false-colour image. This is not necessarily consistent between X-ray devices or manufacturers. Backscatter X-rays for airport screening Fig.56: typical backscattered X-ray images from an airport security scanner showing no weapons detected. Some systems have software that covers private body parts. Source: US Transportation Security Administration (TSA). Fig.57: the Tek 84 Defender airport body scanner. It uses software to provide automated threat detection (ATD). When threats are detected, they are placed on a cartoon figure representation of the body. It uses backscattered X-rays and detects both metallic and non-metallic threats. Source: Tek 84. Fig.58: the Z Portal from Rapiscan AS&E (www.rapiscan-ase. com) for trucks and cargo. It provides high-throughput backscattered X-ray imaging of large trucks, buses and shipping containers. It can process up to 250 trucks per hour. The X-ray systems discussed above operate in transmission mode. The X-rays have to penetrate the target and be detected by a sensor of some kind. With backscattered X-rays, some of the X-rays directed at the target are instead reflected back toward the X-ray source by a process called Compton scattering. One of the main applications for backscattered X-rays is full-body scanning in airport security systems to detect weapons (see Figs.56 & 57). Very low doses of X-rays are used, about one-thousandth that of a chest X-ray. These are not considered harmful, although not all agree with that claim. A controversial aspect of backscattered X-ray imaging is that it can produce high-resolution imagery of a person’s body beneath their clothes. Therefore, software often covers or distorts a person’s private parts, and the screening agent looking at the image may be physically separate from the person being scanned. X-rays of shipping containers and trucks X-rays of shipping containers and trucks have become routine for security purposes and the unavoidable: taxation! See Figs.58, 59 & 60. These scanners provide high-resolution images. The X-rays are generated with the aid of a linear accelerator. Either regular transmission or backscattered X-rays can be used – backscattered X-rays have the advantage of being less harmful to people, and can be used if only one side of the object is available for inspection. Handheld backscattered X-ray imaging system These devices are suitable for 16 Silicon Chip Australia’s electronics magazine siliconchip.com.au inspection applications like vehicles, house walls, aircraft interiors, packages etc. They are handy when away from stationary inspection systems (see Figs.61 & 62). CT scanning of the Antikythera Mechanism The Antikythera Mechanism is an extraordinarily complicated 2000+ year-old mechanism (Fig.63), recovered from a shipwreck by fishermen around 1900. It had become a heavily corroded, calcified mass that has been intensively studied. It was too fragile and corroded to disassemble, so it was originally X-rayed and has most recently has been subjected to CT scanning, to try to understand how it was made and what it did. This revealed some hereto unknown or undecipherable engravings (see Figs.64 & 65). All the evidence points to it being a type of mechanical orrery for predicting orbital positions and eclipses. See the video titled “Scientists Have Just Fully Recreated The Design Of The Antikythera Mechanism For The First Time” at https://youtu.be/ E8YUxuz1uZQ An Australian YouTuber called Chris has reconstructed the tools the Ancient Greeks would have had, then used those tools and techniques to reproduce the mechanism. See his videos playlist at siliconchip.com. au/link/ab98 The industrial CT machine used to scan the Antikythera Mechanism was a prototype by X-Tek Systems called Bladerunner (Fig.66), operating at 450kV. X-Tek is now Nikon Fig.63: the mass of one of the fragments of the Antikythera Mechanism. It can’t be prised apart without destruction, so it is investigated via non-destructive means. Source: Wikimedia user Marsyas. siliconchip.com.au Fig.59: a backscatter X-ray image of a truck showing a dummy ‘hiding’ inside. This was taken by a ZBV system manufactured by Rapiscan AS&E (www. rapiscan-ase.com). Source: www.proammo.cz/x-rays/ Rifle Propane Tank Drugs Fig.60: an image from the Z Backscatter system from Rapiscan Systems AS&E. The backscatter X-ray of the suspect vehicle on the left reveals organic items like drugs, while the transmission X-ray on the right reveals metallic objects. Source: Rapiscan. Fig.61: the handheld MINI Z backscattered X-ray inspection system from Rapiscan Systems / AS&E. Fig.62: concealed items inside a car tyre are revealed with a MINI Z scanner. Fig.64: a computer reconstruction and exploded view of the Antikythera Mechanism. Source: Nikon Australia’s electronics magazine September 2021  17 Metrology, and they offer a 450kV machine called XT H 450 X-ray and CT system with a unique 450kV microfocus X-ray source. This gives 25 micron (0.025mm) repeatability and accuracy. The Dead Sea Scrolls Fig.65: a CT reconstruction of the engravings on the Antikythera Mechanism from within the encrusted, corroded mass. PTM stands for polynomial texture mapping. CT imaging enabled unambiguous interpretation of previous results (A vs B and C vs D, unknowns in squares). Source: Plos One (siliconchip.com. au/link/ab9e) Fig.66: the X-Tek, now Nikon Metrology XT H 450 X-ray and CT machine for high-resolution non-medical X-ray imaging and CT scanning. A similar device was used to scan the Antikythera Mechanism. The Dead Sea Scrolls were one of the world’s most spectacular archeological finds. They were found in Israel in the later 1940s and early 1950s, consisting primarily of ancient biblical scrolls about 2000 years old. They were mostly written on parchment; some had become illegible due to age and damage, while others were so damaged and brittle they could not be unwrapped. Advanced methods were required to read both some of the parchment, papyrus and even copper scrolls. Some otherwise unreadable parchment was read using the process of multispectral imaging (see Fig.67). This relies on the fact that the reflectance of ink and paper are much different with non-visible wavelengths of light such as infrared. The remarkable difference between the visible light image and the infrared image can be clearly seen in the figure. The so-called En-Gedi scroll was very badly damaged, brittle and very little more than a chunk of burned charcoal. It could not be unwrapped as it would disintegrate. Archeologists therefore ‘shelved’ it for many years, waiting until technology could help view its contents. In 2016, it was imaged with a micro-CT scanner by a team at the University of Kentucky, Hebrew University of Jerusalem and the Israel Antiquities Authority – see Fig.68. Also see the video titled “Virtually Unwrapping the En-Gedi Scroll (English)” at https:// youtu.be/GduCExxB0vw The ink was iron- or lead-based and so gave a contrast difference in the imagery. After scanning, clever mathematical techniques were applied to ‘virtually unwrap’ the scroll and read the text – see siliconchip.com. au/link/ab99 The team that deciphered the En-Gedi scroll is now looking at using radiation from a synchrotron to read certain scrolls at an even higher resolution than these CT scans. A giant CT scanner The Fraunhofer Institute for 18 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.67: a fragment of Biblical text on parchment, invisible to the naked eye, is clearly revealed under infrared light. Source: Israel Antiquities Authority. Integrated Circuits IIS in Germany (www.iis.fraunhofer.de/en.html) has developed a giant CT scanner for scanning objects such as cars, shipping containers or aircraft parts. The system is known as high-energy CT or XXL-CT (see Fig.69). The X-ray beams used are up to 9MeV to provide high penetration levels and suitable imaging density and resolution in the sub-millimetre range (Fig.70). The main components are a linear accelerator to produce X-rays, a 4m wide X-ray detector for line-by-line scanning, and a turntable to rotate the object being scanned. A scan can take up to 100 hours and produce terabytes of data to analyse. Applications include: • material analysis such as the detection of defects in castings or composite layups down to 0.2mm • checking the assembly of various components to make sure all parts have been assembled correctly (including the location of welds and adhesives, cable layouts and that no parts have been omitted) • analysis of failed components • examination of crashed vehicles and comparison with simulations • examination of objects for hidden contraband • digitisation of objects of significant cultural heritage (eg, so that a destroyed statue could be reproduced) Other uses for CT scanners Apart from archeological investigations and engineering inspections, industrial CT has a multitude of other uses. Among these are looking at the distribution of crystals or cavities inside rock samples, examining embedded or exposed fossils (Fig.71), studying meteorites etc. CT scanners are also siliconchip.com.au Fig.68: the En-Gedi scroll was extremely damaged, almost a lump of charcoal (see the image on the right). It was scanned using a micro-CT scanner and “unwrapped” with software, as shown on the left. Source: University of Kentucky. Fig.69: the Fraunhofer XXL-CT system. The main components are a linear accelerator on the left to produce X-rays, a four-metre-wide X-ray detector on the right for line-by-line scanning, and a turntable to rotate the object being scanned. The object in the middle at the back is an alternative detector and specimen manipulation system. Source: Fraunhofer IIS. Fig.70: a CT image of a car made with the Fraunhofer XXL-CT machine. Fig.71: an unusual patient. This is a 3D CT reconstruction of the skull of a Herrerasaurus dinosaur with a cutaway showing the braincase. The sample is 32cm long. Source: Carleton University. Australia’s electronics magazine September 2021  19 Fig.72: the Rapiscan 920CT airport CT hand baggage scanner. Fig.73: the primary sequence of an iris recognition scheme. used for airport hand-luggage security screening (Fig.72). See the Youtube video titled “920CT - SEE INSIDE THE FUTURE - Checkpoint CT” at https://youtu.be/ PFOEQKqNOFE Eye scans for biometric security Biometric imaging of the eye is increasingly important for security purposes. The iris or pattern of blood vessels of the retina or sclera can be scanned. The retina is the lightsensitive part at the back part of the eye, while the iris is the coloured part, the sclera is the white part of the eye. Like a fingerprint, the eye has many unique characteristics for each individual, even identical twins. The retina has a unique pattern of veins that remain stable throughout life and are not prone to damage like fingerprints (although they can change somewhat due to various diseases). These can be harmlessly imaged 20 Silicon Chip using infrared light. Once an image is acquired, the software checks whether the scan matches the stored image of an authorised person. One disadvantage of the technology is the relative difficulty of quickly acquiring a sufficiently high-quality image, and cataracts or glaucoma can render the technology unusable for an affected individual. Retinal scanning is currently not the preferred method of eye scanning due to these difficulties. The pattern of the iris is highly individual. While a fingerprint has 60-70 points of comparison, an iris has about 260. It is currently the preferred eyebased biometric security measure over retinal scanning (see Fig.73). Iris recognition works by first taking a snapshot of the iris with a camera 10-100cm away, using infrared light, which copes better with all iris colours. Once an eye image is acquired, the image is processed, with concentric circles around the iris forming a polar Australia’s electronics magazine Fig.74: this is the optical fingerprint scanner module that we used in our November 2015 access control project. More advanced (and complicated) schemes can be used for higher security. coordinate system. These coordinates are then transformed into a rectangular coordinates to create a strip image which is then analysed. The computer converts this image to an “iris code”, which is a 512-digit number used to compare with reference images. As for fooling the system with cosmetic contact lenses, these can be detected because they have different reflective characteristics. Systems are also in place to detect a living person’s natural, involuntary eye movements, plus the pupil expansion is checked. However, some commercial scanners without these precautions have been fooled using high-resolution pictures of a person’s eye. Iris scanning is often confused with retinal scanning, but iris scanning is much more common. Another method under development is scanning the blood vessels of the sclera. It has the advantages of rapid image acquisition with standard cameras, without needing infrared light. Facial recognition Facial recognition is used by smartphones, social media, governments, militaries and police agencies. This was the subject of an article in Silicon Chip, April 2019: “Big Brother IS watching you: Facial Recognition!” (siliconchip.com.au/Article/11519). See that article for further information on this topic. Fingerprint scanning Many phones and other systems use siliconchip.com.au Fig.75: how two radiation sources would appear if stored in an enclosed container and imaged with an NGET machine. fingerprint scanning for access control. These can be based on optical, capacitive, ultrasound or thermal technology. The fingerprint is first scanned by one of these methods, then the distinguishing features of the fingerprint are extracted and matched to a database. We published a DIY project to build a fingerprint-based door access controller in the November 2015 issue (siliconchip.com.au/Article/9393). That design used an optical fingerprint scanning module – see Fig.74. Neutron-Gamma Emission Tomography (NGET) NGET is a technology under development at the KTH Royal Institute of Technology in Sweden to pinpoint the source of nuclear materials that could be used for terrorism, such as weapons-grade plutonium or materials that could be used to make a “dirty bomb”. It is a form of tomography for nuclear materials – see Fig.75. Fig.76: the Leidos ProVision 2 is a millimetre-wave scanner for aviation security use. It features automatic target detection, and only shows a cartoon-style image of the location of any detected items. It is designed to process 200-300 people per hour. Source: Leidos (www.leidos.com). Millimeter-wave imaging Millimetre waves are radio waves with a frequency around 30-300GHz. Millimetre-wave whole-body imaging scanners illuminate the body with low-power millimetre RF waves and detect the reflected radiation – see Fig.76. Unlike X-rays, millimetre waves are a form of non-ionising radiation, and are claimed to be safer than backscattered X-ray scanning. Millimetre-wave scanners may be active or passive. Active systems generate the radio waves themselves and measure the reflected radiation, while passive systems produce images from siliconchip.com.au Fig.77: the operating principle of ultrasonic material testing. An extra reflection corresponding to a hidden defect results in an addition to the expected reflections from the front and back surfaces. Ep relates to the depth of the piece, while D relates to the defect depth. Source: Romary. Australia’s electronics magazine September 2021  21 Fig.78: the general scheme of an acoustic emission system. With multiple transducers, the location of the crack or other defect can be determined. Source: Khodadadi and Khodaii, 2018. the millimetre waves naturally found in the environment. As with X-ray backscatter scanners, many such machines use software to disguise the body image and produce only a generic cartoon-like outline of the body showing the location of suspicious objects. See the video titled “ProVision 2 - Compact Advanced Personnel Screening” at https://youtu.be/ O6HxV807f5A Ultrasonic flaw detection Ultrasonics can be used to detect flaws in mission-critical components such as aircraft parts. An ultrasonic wave is sent into one side of the test piece, and if an internal flaw is present, there is a reflection from it as well as the far side of the piece. If no flaw is present, there is only the expected reflection from the far side – see Fig.77. Acoustic emission Acoustic emission is the phenomenon whereby crack growth processes in a material generate acoustic energy. This typically occurs in response to mechanical loading of the material. By instrumenting an item under test, the location of a propagating crack can be determined, or the overall structural health of an object under continuous monitoring can be determined (see Fig.78). Acoustic waves generated by the cracking process are typically in the range of 100kHz to 1MHz. A computer can process signals from multiple acoustic sensors to determine the location of a growing defect such as a 22 Silicon Chip crack, eg, by triangulation. This process cannot detect defects that aren’t growing. Acoustic emission testing is typically used on: • concrete structures like bridges • metallic structures like pressure vessels, pipelines, aircraft structures and steel cables • composite structures such as used in aircraft and racing cars, and structural composite beams • rotating machines, to detect bearing wear in machinery • electrical machinery like transformers, to establish if there are unwanted electrical discharges taking place • leak detection in pipes Borescopes Borescopes are the non-medical equivalent of endoscopes and are used to inspect inside engines, machinery, walls or ceilings, pipes, security inspections, inside gun barrels, or anywhere else where disassembly of an item is impractical, expensive or impossible – see Fig.79. They may be rigid or flexible. Low-cost borescopes can be purchased on eBay or from some retailers, and many of them connect to the USB port of a computer or a phone. We have even seen some for sale that suit Android phones for less than $10, while some more expensive modules work over WiFi. We have tried some slightly more expensive models (around $30) and found them to work very well for tasks like checking inside ceiling cavities through downlight openings. Australia’s electronics magazine Other Silicon Chip articles Apart from those articles already mentioned above, you might be interested to read the following sections of past articles which touch on this topic: • The Range-R through-wall scanner described in the article “History of Cyber Espionage... Part 2” (October 2019; siliconchip.com. au/Article/12013). • Ground-penetrating radar from the article “Underground mapping... & pipe inspection” (February 2020; siliconchip.com.au/ Article/12334). • Seismic surveys in the article “Directional Drilling: How It Works” (July 2016; siliconchip. SC com.au/Article/9997). Fig.79: the PCE-VE 270HR industrial-grade borescope from PCE Instruments (www.pce-instruments. com/english). It has a two-metre-long flexible cable, 2.8mm in diameter. siliconchip.com.au Build It Yourself Electronics Centres® ED T N A W T S O M Electronics SALE everyone loves! Top deals on tech ember 30th. prices end Sept Hurry, discounted 1080p HD! 49 $ ADD ON DEAL: USB QC 3.0 wall charger for $10 (M 8863) D 2320 Wireless Charger Alarm Clock A stylish USB powered clock with in-built 10W wireless charging for your phone & 8 colour night light. Clock auto dims at night time. Dual alarms so you’ll always wake up on time! USB output also lets you charge your watch. A complete computer the size of a keyboard! A neat new portable design ideal for education environments. With all the same features as the Raspberry Pi 4, it’s a powerful computing platform for work, education and play! Rear panel provides access to all ports including the GPIO header. 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Western Australia Build It Yourself Electronics Centres Sale Ends September 30th 2021 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2021. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ THE CROMEMCO DAZZLER The Cromemco Dazzler was probably the first ‘reasonable’ computer graphics device capable of producing a colour image. It generated an NTSC composite video signal that could be fed to a monitor or TV. As they are now quite rare, I built a copy of the By Dr Hugo Holden device and in doing so, discovered some quirks. C omputer graphics were coming of age in the mid-to-late 1970s, and efforts were being made to provide home computer enthusiasts with graphics accessory cards. These were typically designed to be used in early S-100 computers such as the Altair and others. Matrox was on the front line then, with monochrome graphics cards such as the ALT-256 and the ALT-512 (as described in our October and November 2020 issues; see siliconchip.com. au/Series/352). Three Matrox monochrome cards could be deployed to make an RGB colour system, but it was a very expensive purchase. Other companies such as Godbout Electronics offered the “Spectrum” board by 1980, which was advanced enough to support colour and have onboard video RAM. But before that, the Cromemco company offered the “Dazzler” board set in 1976. graphics cards. It was the first colour graphics card for S-100 bus computers, having an NTSC colour composite video output. The idea behind it was born in 1975 when Roger Melon and Harry Garland created the first solid-state video camera. Their idea was to use a 1k x 1 bit MOS dynamic RAM IC with its top cut off, acting as an optical sensor (transistors are photosensitive). This led to the creation of the “Cyclops” solid-state video camera (Fig.1), and the founding of Cromemco. The camera controller board put the camera’s pixel data into general RAM in the host computer. The Dazzler board could read that RAM and create a standard (or close to standard) NTSC composite video signal to feed a colour video monitor or a domestic TV set via an RF modulator. But the Dazzler board set became an entity of its own. It was presented as a Fig.1: the Cromemco “Cyclops” video camera was innovative in that its sensor was an SRAM chip with the lid removed! That’s a similar principle to the one used by CCD and CMOS sensors today. Dazzler history The Cromemco Dazzler was pivotal in the development of computer siliconchip.com.au Australia’s electronics magazine September 2021  27 project to build in Popular Electronics magazine, February 1976. It became so popular that Cromemco started making it, both in kit form and fully assembled and tested. It found its way into the television industry, being used to produce colour graphics for weather forecasts. Unlike other graphics cards of the time, which had non-interlaced scanning, the composite video signal generated by the Dazzler was an interlaced scan, compatible with the NTSC colour television system. The Dazzler has no onboard video RAM; instead, it hijacks the host computer’s system RAM for the job by using direct memory access (DMA). This required the computer’s RAM to be fast static RAM with an access time of 1µs or less. Dynamic RAM did not work because the refresh activities interrupt the proceedings. The Dazzler came as two separate S-100 boards, linked by a 16-way ribbon cable, as shown in the photo. The two boards contain a total of 72 ICs, most of which are common 74 or 74LS series TTL types. The exception is one extremely rare IC, the TMS3417 quad 64-bit shift register, which was rare even in the 1970s. Dazzler board sets are very hard to come by these days, so I realised that if I wanted to try one out, I would have to make replica PCBs and obtain the parts to populate them. Making the boards Cromemco provided the PCB foil patterns in their manual, but the old photocopies I could find were not very clear in places. After some months tracing over them in a drawing program, I managed to make clear copies of each board’s top and bottom track patterns. Then I checked them against the schematic to correct errors, which took a few late nights. I then sent the image files to LD Electronics (see Market Centre on p111), and they made very high-quality PCBs for me, with an exact track pattern Figs.2 & 3: the reconstructed Dazzler boards, packed with discrete logic ICs. Note the blue socket in a similar position on both boards, which allowed them to be connected via a ribbon cable with IDC connectors at each end with the same footprint as a DIP chip. 28 Silicon Chip Australia’s electronics magazine siliconchip.com.au replica to my drawings and with gold plating. George from LD Electronics did a terrific job; they are likely better than the originals. Figs.2 & 3 are the overlay diagrams for the two PCBs, showing both copper layers and where the components go. I acquired all of the components required as per the parts list in the Cromemco manual. As part of this, I imported NOS Augat gold machined pin sockets for all the ICs. It became apparent right away that the TMS3417NC 5MHz 64-bit shift register would be a problem. The closest modern part I could find was the 74HCT7731, but it has a different pinout, and I was not 100% sure if it was a suitable substitute. Another possible candidate is the Fairchild F3342DC, which is pincompatible, but only rated at 2MHz. Initially, that put me off. However, a Practical Electronics article from 1976 showed an F3342DC IC being used in a Dazzler. After much searching I found a small number of TMS3417 IC in Germany and a few F3342DCs in the USA, so I am well stocked for these now. Once I got the Dazzler operating, I found that the clock frequency for this shift register is close to 1.8MHz, explaining why both the 2MHz and 5MHz rated shift registers work. Once the Dazzler was assembled, I fitted it to my SOL-20 computer. Much to my surprise, considering all the steps involved in the PCB artwork and the large number of mainly vintage ICs, it worked immediately. By that, I mean that it responded normally to manipulating its registers and testing its modes and running a software package. Testing it out My SOL-20 computer has external 5.25in disk drives which allow me to run the CP/M operating system. This has an assembler, so I was able to assemble the Kaleidoscope program. This was one of the most famous programs that ran with the Dazzler. It puts the Dazzler cards into a 2KB 64 x 64 pixel display mode (4096 pixels total). Fig.4 shows the space occupied on a monitor by the Dazzler’s image in this mode. Four bits of each byte control a pixel; three bits code the RGB combination and one bit the intensity, as shown in Fig.5. The Kaleidoscope program places siliconchip.com.au Australia’s electronics magazine September 2021  29 Screens 1-6: these still images don’t really do the Kaleidoscope software justice. Check out https://youtu.be/2tDbn1N8EWI to see it in action. the image in the computer’s RAM starting at address 0200 hex and ending at 09FF hex. The image is divided into four 512 pixel blocks, as shown in Fig.6. The program only alters one 512 pixel block, and the data is rotated and copied into the other three blocks to provide the Kaleidoscope-like symmetrical effect. When the Kaleidoscope program is running, it is quite something to observe. You can see a video of the resulting display at https://youtu. be/2tDbn1N8EWI It is hypnotic and mesmerising. The images shown in Screens 1-6 only indicate how it looks. These stills were photographed directly from the face of the CRT. If the program is terminated (with a CPU reset), this resets the Dazzler hardware and switches the Dazzler off. The last image values remain in RAM, so if the Dazzler board is switched back on and set into the same mode, the last image is seen there as a still frame. This short machine language program switches the Dazzler on: 3E 81 D3 0E 3E 30 D3 0F C3 04 C0 Fig.4: the image from the Dazzler doesn’t fill the screen; instead, it is a rectangle about 68% of the scan width and 77% of the height. The black borders around the edges would be smaller on a TV screen due to overscan. It could produce a 64 x 64 pixel image with 4-bit colour, or a 128 x 128 pixel monochrome image. 30 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.5: the 15 colours available in 4-bit colour mode. The I bit controls the intensity while the R, G and B bits determine the colour. They could have added a 16th colour (dark grey) by using the intensity bit in combination with black, but that probably would have complicated the circuitry. This is equivalent to the short assembly language program: MVI A,81H OUT 0EH ; sends 81H to port 0E on Dazzler card (starts image at 0200H) MVI A,30H OUT 0FH ; sends 30H to port 0F on Dazzler card (colour mode 2k picture) JMP 0C004H ; returns to the Sol’s operating system without a reset These are easily entered to memory say (at 0100 hex) in the Sol with the EN command, and executed with the EX 0100 command. Video signal details The output is an interlaced scan format (as is NTSC); however, there are no equalising pulses around the vertical sync pulse. So the interlace is not perfect, and examination shows there is a slight line pairing of the scan lines of consecutive even and odd fields. This is only detectable with a monochrome image on a monochrome monitor; it is much harder to see on a colour monitor/TV. The Dazzler also has a non-standard horizontal line scan period. For NTSC, this is usually around 63.5µs, while for the Dazzler, it is around 62.6µs. In addition, the Dazzler uses a very siliconchip.com.au Fig.6: the addresses where pixel data appears in the computer’s memory in 4-bit (64 x 64 pixel) mode with a starting address of 200 hex, compared to the physical layout. Note how the data jumps from the upper left quadrant to the upper right, then to the lower left and lower right, complicating how the computer needs to write video data. wide burst gate pulse of around 4.7µs. This lets through a wider-than-normal colour burst, which starts immediately after the horizontal sync pulse, so there are more cycles of the colour burst. The colour burst also appears on the vertical sync pulse when it is low, due to the way the pulses are combined. None of this usually bothers the NTSC colour decoders in TV sets. Only a percentage of the active line and active field time scan is used, so there is quite a lot of space on the screen around the actual displayed pixel area. This helps to allow for overscan on domestic TV sets. About 77% of the vertical active scan time is used, and about 68% of the active horizontal scanning time. So the image on the monitor’s 4 x 3 screen (1.33 ratio) adopts a 1.17 ratio, with the overall image (and each pixel) not being perfectly square. Screen 7: the colour test bars as produced by the Dazzler on a standard NTSC-compatible CRT screen. Screen 8: the same bars as in Screen 7, shown on a monochrome display. They don’t decrease in intensity leftto-right as expected. Australia’s electronics magazine September 2021  31 Scope 1: this scope grab shows how the NTSC DC signal level jumps around as the CRT beam sweeps across the test bars. With a standard NTSC signal, you would expect a series of evenly decreasing ‘stair steps’ instead. Screen 9: the rearranged colour test bars should allow the Dazzler to produce the expected result on a monochrome display... The colour encoder To check the Dazzler’s operation and correctly set its red and green colour carrier phase adjustments, I wrote a short assembly language program to generate an output that resembled a standard NTSC colour test pattern. This enabled the best setting of these controls for the most accurate colour rendition and white balance. I used Figs.5 & 6 to help me do this. Note how the memory addresses are not continuous due to being broken up into four quadrants. I wrote a standard NTSC test pattern into the memory, and Screen 7 shows the result (with optimum adjustments of the R & G phase presets on board 1) with high-intensity colours selected. If the usual NTSC luminance (Y signal) weighting was used, when switched to monochrome (on the TV or monochrome mode on the Dazzler card), it should give a descending order of luminance from left to right. However, it did not as Cromemco chose a different arrangement. Scope 1 shows the monochrome mode levels (also notice the wide burst is still there in monochrome mode), while Screen 8 shows the image on a monochrome monitor. In the Cromemco system, the next step down in luminance from white is cyan, then magenta, blue, yellow, green and finally, red. For comparison, the standard NTSC luminance steps are shown in Fig.7. This anomaly comes about because of the relative proportions of R, G & B to create white in the Cromemco luminance resistor matrix differ from the standard. For NTSC, the weighting is generally 30% red, 59% green and 11% blue but the Dazzler uses weights of 14% red, 29% green and 57% blue. Despite this, it is hard to see the effect of it on a colour image. This is because the colours are heavily saturated. The problem is only apparent Fig.7: for a standard NTSC signal, the test pattern contains coloured bars in this order. On a monochrome monitor, they appear as bars of decreasing intensity leftto-right. 32 Silicon Chip when the card is switched to monochrome mode. I programmed another test pattern to investigate this, putting the colours in the luminance order that Cromemco did. This is shown in Screen 9, and it includes the memory byte values (for two consecutive pixels) that correspond to the colour and intensity selection. Notice how the byte values correspond directly to the brightness level, and also that blue looks a tad purple (for reasons explained below). When switched to monochrome mode, the greyscale is very respectable for this colour order (Screen 10). The magnitude of the grey level being proportional to the nibble value that codes the pixel is convenient for programming monochrome images. If the three RGB resistor mixing assignments are switched around to make them conform to an NTSC scheme, the result is as shown in Screens 11 & 12. Fig.8: the general colour mixing scheme used by the Dazzler, similar to how audio data is typically mixed, with a virtual-Earth inverting amplifier. The resistor values determine the relative intensities of red, green and blue, as shown at the bottom of the figure. Australia’s electronics magazine siliconchip.com.au Screen 10: ...and here’s confirmation that they do so. Screen 11: back to the standard colour test bars, but this time with tweaked R, G & B intensities to give a more correct result. Screen 12: the same display at left on a monochrome monitor, confirms that changing the relative intensities produces the expected result. It became clear after some investigation why this was the case. The colour system which interprets the memory byte (or nibble for a single pixel) used in this mode is MSB…LSB (MSB is the most significant bit, LSB the least significant bit) where the four bits code I, B, G, R where I is intensity, high (1) or low (0). Changing that to I, G, R, B would give the Dazzler a colour order that matched NTSC. Also, an RGB image (if that were to be provided directly from the board) would match up exactly with a composite video image in all respects (except perhaps having superior resolution). Why Cromemco did not make it like this is a mystery; however, in the field of computer graphics, things like this often crop up. Most early computer systems used monochrome or RGBI systems (like CGA), and there was less compatibility with domestic television systems. As another example of this sort of thing, in IBM’s early computers from the 1980s, the output from IBM’s CGA card had both composite and RGBI outputs. But the image seen on a composite monitor did not match up with that seen on a CGA monitor. Fig.8 shows how to calculate the relative contributions of the red, green, and blue channels to the output’s luminance level based on the resistor values in the circuit. In Cromemco’s original scheme, to use the host computer’s memory byte to represent two pixels, they assigned them as shown at the top of Fig.9. In the NTSC system, where the relative luminance intensities were assigned to the three colours G > R > B, (59% > 30% > 11%), if this is normalised to make blue = 1 then the proportions are 5.4 green, 2.7 red and 1.0 blue. Therefore, if the colours are also represented by three binary bits per pixel, the intensity weighting is not too far off the bit magnitudes of 4, 2 and 1. This is why in a digital system attempting to replicate NTSC video, it is better to have blue as the LSB and green as the MSB, as shown at the bottom of Fig.9. This way, when the bits are mixed in magnitude to form a greyscale, it better matches the NTSC system. Presumably, Cromemco did it this way so that the greyscale intensities corresponded to the binary values stored in memory. However, if the colour image in memory was derived from NTSC originally, then the picture would not have the correct shades of grey in monochrome mode. It is simple to modify the Dazzler card to fix this by swapping the three resistors around and switching the three connections feeding the luminance adder as shown in Fig.10. However, I do not propose to modify my card, because that would be like trying to change history, and I want to keep the Dazzler the way it was designed. Fig.10 (right): the Dazzler’s mixer circuitry could be modified like this to produce a more standard signal, but the author built his card with the original design for authenticity. siliconchip.com.au Australia’s electronics magazine ► ► Fig.9 (below): how the RGB pixel data is stored in memory interacts with the circuitry to determine the ratios they are mixed in. If changed from the existing order at the top to the new order at the bottom, the NTSC signal produced would be more standard, producing the expected test pattern on a monochrome monitor. September 2021  33 Fig.11: more details of the circuitry surrounding the output stage, showing the phase shift circuitry used to generate the colour subcarriers. Colour encoder details Fig.12 (right): a standard NTSC phasor diagram. As described in the text, the phase shifts produced by the Dazzler are slightly different (as well as the amplitudes), producing less pure colours. Circuit complexity would have to increase to produce more accurate results. Fig.13 (above): in monochrome mode, even the pixel order within a single byte is not straightforward! The bits control pixels spread across two lines, in a nonobvious order, complicating the code to drive the display. 34 Silicon Chip Australia’s electronics magazine The output amplifier is in an inverting configuration, so its input has a virtual Earth. Therefore, the currents fed in via the resistors shown in Fig.11 are mixed without interfering with each other. The standard NTSC colour subcarrier phasors are shown in Fig.12, with respect to the colour burst (reference) at 180°. Note how the blue phasor’s amplitude is slightly lower than the red and green, which explains why they used a 15kW resistor rather than 10kW on the blue colour carrier gate’s output. The blue carrier phase is nearly 180° delayed from the burst. To attain this phase, Cromemco simply inverted the burst signal using a NAND gate wired as an inverter. This explains why the blue bar (on the test pattern) looks just a little purple, because there is a small phase shift toward magenta. With optimum settings of the red and green phase controls (VR27 & siliconchip.com.au 1000 siliconchip.com.au CHEA3.BIN CHEB3.BIN COMPF.COM COMPF.COM 4096 byte file CMPF2.COM CMPF2.COM Vertical address flip CMPF3.COM CMPFB.COM NNNN.BIN = 12880 byte image file 512 byte Dazzler compatible file 13FF 11FF 1600 1400 The 4x resolution mode CHEC.BIN CHED.BIN COMPF.COM COMPF.COM CMPF2.COM CMPF2.COM CMPFC.COM CMPFD.COM 15FF 17FF DAZZLER MEMORY MAP FOR A 2K BYTE IMAGE Address example starts at 1000h, register 0Eh, programmed with byte value 88h Fig.14: due to the pixel ordering shown in Fig.13, and the way the image was broken up into quadrants, it took three stages to convert the contents of a .BMP file into data suitable for display in the Dazzler’s monochrome mode. ► In this mode, each byte of the image memory file in RAM controls eight pixels, with the bits turning the pixel either on or off (ie, monochrome). The lower four bits of output port 0Fh are used to control the intensity and the selected R, G & B colours for all pixels, in any combination. With 2048 memory bytes, there are 16,384 pixels accounted for in a 128 x 128 pixel array, and the pixels are three CRT beam scanning lines tall. Compare this to colour mode, where each pixel covers six scan lines; three even and three odd. I tried out the 4x resolution mode with a still image. One complication is that the image is divided at the hardware level into four 512 byte blocks, where the addresses are not sequential. So this required processing the image in four blocks. The other complication is the way Cromemco organised one byte to represent four pixels vertically stacked, not as a linear sequence customary in other systems – see Fig.13. I started with a 128 x 128 pixel .BMP monochrome high-contrast image file and cropped it into four separate 64 x 64 pixel files. I then stripped out the 54-byte leader of the .BMP file in a hex editor. The .BMP has three bytes to represent R, G & B, so the actual file size is 12,288 bytes or 12kB (3 × 64 × 64 bytes). This was a manageable size to send to the SOL-20 computer using the serial port, from TeraTerm on the PC to a CP/M program running on the SOL called PCGET, then saved to the SOL’s floppy disk drive. I had previously written software to move disk files to address 4000h in RAM in the SOL, so I modified that. I then wrote custom 8080 software to 1200 Fig.15: output port 0Eh is used to turn the Dazzler’s output on and off, and tell it where in the computer’s memory to find the video data. Because the top 7 bits of the 16-bit address field are stored in the lower 7 bits of this register, setting the base address is a bit confusing. ► VR28), looking at the test pattern on the colour monitor, I measured the red phase delay as 292° (180° + 112°). Fig.12 shows that red should be at 283° (180° + 103°), so it was fairly close. I measured the total delay for the green carrier as 59° (180° + 112° + 127° - 360°), which is pretty close to the 61° (241° - 180°) shown in Fig.12. So the red colour is slightly shifted (9°) towards yellow. Green is very close, and blue (not adjustable) is shifted approximately 13° (360° - 347°) toward magenta. Screen 13 (right): the Dazzler certainly was ‘revolutionary’, Comrade! This is my monochrome test image shown on an amber VDU, which started as a .BMP file. Fig.16: to expand on how the base address is set, in this example, a value of 81h written to port 0Eh sets the base address to 200h (1 × 200), while a value of 82h sets it to 400h (2 × 200). strip out two out of every three bytes, giving a 4096-byte image. It also had to reorder the pixel order, as .BMP starts at lower left and moves to the right then up, while the Dazzler needs data that begins at upper left and ends at lower right. I also had to ‘swizzle’ the image blocks to get them into the right addresses. Fig.14 shows where the Australia’s electronics magazine data needed to be placed in memory, and the three separate pieces of code I used to achieve this from the .BMP file data. Initially, I was perplexed by the instructions to set the starting address of the image in memory using the register (output port) assignments shown in the manual. This is because the bits they refer to in their output port have a September 2021  35 The Dazzler mounted into a SOL-20 computer with external 5.25in drives, and running the CP/M (Control Program/ Monitor) operating system. one-bit offset with respect to the computer’s actual address lines. The best way to explain this is by looking at Fig.15, reproduced from the manual. The MSB here has no counterpart as part of a memory address; it is purely to turn the Dazzler on and off. This means that if you load say 81h into this location, that turns the Dazzler on and tells us that the video data starts at address 200h, not 100h. That’s because the lowest bit in this register is A9, not A8 as you might expect (as elaborated in Fig.16). So this short machine language program: 3E 88 D3 0E 3E 6F D3 0F C3 04 C0 ... loads 88h into output port 0Eh, 36 Silicon Chip setting the image start address to 1000h. The 6F value loaded into output port 0Fh sets the Dazzler to the monochrome resolution 4x mode. The image I had stored in RAM appeared at the Dazzler’s output, as shown in Screen 13 (on an amber monochrome computer VDU). Since the Dazzler was ‘revolutionary’ when it came out, I thought the image was an appropriate choice. The 4x resolution mode can also be a colour mode, with the proviso that all pixels switched on are the same colour (any of the 14 available, not including black). Summary The Dazzler was an astonishing Australia’s electronics magazine creation at the time, and in my opinion, still is. It was designed to bring colour graphics into the world of home computer users who had S-100 computers in the mid-1970s. The Dazzler also found use generating NTSC colour graphics for the television industry, and provided a way to display images derived from early solid-state digital cameras like the Cyclops. The boards’ cost was kept down due to them not having onboard video RAM, instead using the RAM already present in the host computer. You can find some more detail on the Dazzler at: siliconchip.com.au/link/abar https://w.wiki/3nac SC siliconchip.com.au Price Changes For Silicon Chip Magazine From October 31st 2021, the price of Silicon Chip Subscriptions will change as follows: Online (Worldwide) These two Dazzler boards have been almost completely assembled. The jumper wires between the J1-J7 points still need to be run. Once both boards are installed in the computer, they are joined by the ribbon cable with IDC connectors shown at upper right. Current Price New Price 6 Months $45 $50 12 Months $85 $95 24 Months $164 $185 Print Only (AUS) Current Price New Price 6 Months $57 $65 12 Months $105 $120 24 Months $202 $230 Print + Online (AUS) Current Price New Price 6 Months $69 $75 12 Months $125 $140 24 Months $240 $265 Print Only (NZ) Current Price New Price 6 Months $61 $80 12 Months $109 $145 24 Months $215 $275 Print + Online (NZ) Current Price New Price 6 Months $73 $90 12 Months $129 $165 24 Months $253 $310 Print Only (RoW) Current Price New Price 6 Months $90 $100 12 Months $160 $195 24 Months $300 $380 Print + Online (RoW) Current Price New Price 6 Months $100 $110 12 Months $180 $215 24 Months $330 $415 All prices are in Australian Dollars The cover price of the October issue onwards will be $11.50 in Australia. The New Zealand cover price will remain the same at $12.90. The blank boards. Creating these was a lot of work, as the scanned images from the Dazzler manual needed much cleaning up before they could be used for manufacturing. siliconchip.com.au Australia’s electronics magazine SILICON CHIP September 2021  37 Part 1: by Nicholas Vinen & Tim Blythman Touchscreen & Remote Digital Preamp with Tone Controls This preamp has the best of both worlds: the benefits of digital control such as an intuitive touchscreen interface, presets and remote control, along with the low noise and distortion of an analog design. It achieves that by using classic Baxandall style volume and tone control circuitry with op amps, incorporating high-quality digital potentiometers to provide the adjustments. M ost of our remote-controlled preamplifiers to date have used motorised potentiometers. While these have many benefits, such as low noise and distortion, and the ability to simply turn the knob if you are close to the preamp, they are quite expensive and can be hard to obtain. They also can fail and wear out. Digital volume control ICs are an attractive alternative, but there have only been a few of these with performance that we would call hifi, and most of those have been discontinued. They also can be pretty expensive and difficult to obtain. And since they only adjust the audio level, we need separate arrangements for input switching (as any self-respecting preamp needs at least a few pairs of inputs) and tone controls. Those are a frequently requested feature for preamps, and we agree that they can be handy. For example, they can compensate for loudspeaker shortcomings, such as a lack of bass or treble, or too much treble. So any digital preamp we came up with would have to tick the following boxes: 1) Decently low distortion and noise (at least CD quality, and ideally better) 2) Tone controls (ideally with at least three bands for flexibility) 38 Silicon Chip 3) A wide volume control range operating in a logarithmic manner 4) Adjustable gain to suit a wide range of signal sources 5) Infrared remote control 6) Input switching 7) Ideally, an intuitive and attractive colour touchscreen interface for direct control We achieved 1) through 4) by using two quad Analog Devices AD8403ARZ10 digital potentiometer ICs. While these are not especially cheap at around $10 each, they are still quite reasonably priced compared to hifi-quality volume control chips. The eight potentiometers they include let us adjust the volume, bass, mid and treble levels in both channels using just two chips. These devices have impressive specifications, borne out by our testing, with a rated THD+N figure of 0.003% at 1V RMS/1kHz (they tested considerably better than that), a -3dB bandwidth of 600kHz and an impressively low noise level of 9nV per √Hz. So they are well suited to audio signal processing tasks. Because each chip has all four potentiometers needed for a channel, the digital pot and its associated op amps are laid out all in one area, simplifying the PCB design and minimising crosstalk between channels. Australia’s electronics magazine The input switching is handled by three telecom style relays, which has worked well for us in the past, as these mechanical devices have minimal impact on signal quality. Finally, the control interface is handled by a Micromite LCD BackPack with either a 2.8-inch, 320x240 or 3.5-inch, 480x320 colour touchscreen. This provides many benefits such as a nice clear volume readout when you adjust it via the remote, the ability to show the actual frequency response for any given tone control setting, loading/ saving presets – the whole nine yards. It’s just the go for a modern preamplifier or amplifier, without compromising the sound quality. Besides the BackPack, which would generally mount on the unit’s front panel (along with the IR receiver), all this circuitry is packed onto a modestly-sized PCB at 206 x 53mm. It has four pairs of onboard RCA inputs, so that it can be mounted at the back of the unit. It can be powered from a separate AC or split DC supply or an internal transformer with suitable windings. That includes transformers with high-voltage windings to power amplifier modules, and low-voltage secondaries for preamps like this one. For standalone use, the power input can be an onboard socket on the siliconchip.com.au back, near the inputs, along with the optional rear panel pre-outs. These are in parallel with a pair of internal RCA sockets, which can feed the preamp’s output signals to a couple of internal amplifier modules, making a complete preamp/amplifier combination. Performance The performance of the preamp is summarised in Figs.1-4. Fig.1 shows a plot of total harmonic distortion plus noise (THD+N) against frequency for an input signal level of 1.5V RMS and an output level of 3V RMS. As the final stage has a gain of two times, this means that the volume control section is set for unity gain. The 20Hz-22kHz bandwidth plot (in cyan) gives the best indication of audible performance. This shows a total harmonic distortion level of less than 0.001% from around 35Hz up to 2.3kHz. The distortion level rises above 1kHz, with the dashed line showing how the curve would look if the harmonics weren’t rolled off at the upper end by the bandpass filter. As a good CD player is generally expected to have a THD+N figure of less than 0.0018% at 1kHz, we’d say that this preamp exceeds CD quality. That’s also indicated by its signal-tonoise ratio of over 100dB, with CDs being limited to 96dB by their 16-bit sampling resolution. Fig.2 shows how THD+N varies with signal level for some typical gain settings. The rise in distortion at the low end is due to noise being a larger component of the signal for small signals, while the rapid rise at the upper end is where the preamp has run out of headroom and has started clipping. The best performance is around 2V RMS, a typical level for many playback systems such as CD, DVD & Bluray players. Fig.3 shows how the channel separation varies with frequency. We consider this an excellent result, with worst-case crosstalk of -75dB at 20kHz. Fig.4 shows the preamp’s frequency response with the controls set flat, which only varies by about 0.5dB across the whole audio spectrum, rolling off slightly towards the 20Hz end. It also shows plots with the bass/ mid/treble controls set to their extremes individually. This should give you an idea of the adjustment range that the preamp permits. Of course, you would usually not use the siliconchip.com.au Features • • • • • • Four input stereo preamp with a colour touchscreen and remote control Bass, mid & treble adjustments with presets, plus volume control Better than CD quality Four external stereo inputs (one active at any time) Two stereo outputs, one internal and one external Optional loudness control automatically adjusts tone with volume Specifications • • • • • • • • • • • • • THD+N: typically less than 0.001%; see Fig.1 Signal-to-noise ratio: typically around 104dB with respect to 2V RMS input Frequency response: 20Hz-20kHz +0,-0.5dB Channel separation: >75dB, 20Hz-20kHz Signal handling: 0.1-2.5V RMS Volume control range: approximately 78dB Gain range: -50dB to +27.6dB (0.003 times to 24 times) Input impedance: 100kW || 470pF Bass tone control: ±12.5dB centred around 20Hz (±11.5dB <at> 50Hz, ±8.5dB <at> 100Hz) Midrange tone control: ±11dB centred around 440Hz (±7.5dB <at> 200Hz & 1kHz) Treble tone control: ±11.5dB centred around about 20kHz (±10.5dB <at> 10kHz, ±9dB <at> 5kHz) Power supply: 12-15V AC, 24-30V AC CT or ±15V DC Current draw: typically around 200mA with touchscreen on and <50mA with it off Fig.1: harmonic distortion plus noise plotted against frequency for two different analyser bandwidths. The blue plot with the dashed line is the most realistic representation of the performance, which we think is meritable. 1.5V RMS gives the best performance, but it’s still pretty good at around 1V RMS full-scale, and the unit can handle over 2.5V RMS at its inputs before clipping. Fig.2: a plot of distortion versus signal level for a 1kHz tone, confirming that distortion rises at lower signal levels due to noise. This also shows the onset of clipping for high signal levels, but note that there are two reasons for clipping; either the input signal rises above 2.5V RMS (as is the case with lower gain settings), or the output runs into clipping at about 4V RMS (higher gain settings). Australia’s electronics magazine September 2021  39 Fig.3: the channel separation of the preamp is excellent, with very little of one channel leaking into the other channel, especially below 5kHz. The input separation is even better, exceeding 100dB in most cases. Fig.4: with all the tone settings at 0, the preamp’s frequency response is very flat, dropping by only about 0.5dB at 20Hz. The other curves show the result of each tone control being individually set to maximum boost or cut. They indicate how much adjustment you can make and over what frequency range each band operates. Fig.5: there is a bit of unavoidable interaction between the controls if you make large adjustments in more than one band. The cyan, red and green curves demonstrate this. The other three curves show the results of much subtler simultaneous bass and treble boost settings of various magnitudes. You can see from those curves that there is essentially no interaction at those levels. controls at their extremes, as shown in that plot. Fig.5 shows some more realistic tone control settings (mauve, orange & blue) along with some examples of what happens if you set multiple controls to their maximum extents (red, green & cyan). Note how there is some interaction between the controls. For example, the treble boost is reduced when a lot of 40 Silicon Chip bass or mid boost is introduced. These are somewhat odd situations, though, since you would typically be better off with bass cut instead of using a lot of mid/treble boost, and mid cut instead of a lot of bass/treble boost. Circuit details The Digital Preamp circuit is shown in Fig.6. Signals are fed into one of four pairs of RCA sockets, CON1A-D Australia’s electronics magazine and CON2A-D. These have individual 100kW termination resistors to prevent signals from deselected devices from floating and causing a thump when switching inputs. These go to the contacts of a pair of DPDT relays which narrow the signals down to two pairs, and these then go to a third DPDT relay which makes the final selection of which stereo signal reaches the RF filter. The RF filter comprises a 100W series resistor, a ferrite bead and a 470pF capacitor to ground for each channel. This RC low-pass filter has a -3dB point of 3.4MHz, while the ferrite bead helps to eliminate much higher frequency signals which could otherwise be rectified by the following buffer stage, inducing unwanted signals into the audio. 1kW stopper resistors further help eliminate RF coupling and also protect op amp IC1 from damage in case a high amplitude signal (or static discharge) is fed into one of the input connectors. Op amp IC1 buffers the selected stereo signal, and its outputs are ACcoupled to the gain control section via 10µF capacitors. Note that the input side of IC1 is not AC-coupled; it is expected that signals applied to the preamp are reasonably close to 0V DC bias. The signals from the outputs of IC1 are DC-biased to +2.75V and clamped to be within the range -0.3V to +5.8V. This is done by a pair of schottky small-signal diodes for each channel, connected to ground and a +5.5V rail. This +5.5V rail is also used to power the quad digital pot ICs, IC6 & IC7. This is their maximum recommended supply voltage (the absolute maximum is +8V). We have done this so it can handle the maximum expected RMS signal voltage from a signal source like a Bluray player, which is usually around 2.2-2.3V RMS. To achieve this, we’ve had to slightly attenuate the signals being fed to the digital pots, using 2.2kW fixed series resistors connected to pin 3 of the two digital pot ICs. These combine with the digital pots’ 10kW track resistance to reduce the input signals by 18%. So a 2.3V RMS signal is diminished to 1.89V RMS, just within the 1.94V RMS capabilities of the digital pots running from 5.5V. This is easily compensated for by adding extra gain in the volume control stage. Those 2.2kW resistors also limit siliconchip.com.au the current that op amp IC1a needs to deliver if the signal is clipped by diodes D1-D4. IC1a runs from ±12V regulated rails for best performance, so its maximum output swing is about ±10.5V, enough to damage the digital pots without current limiting and clamping. Volume control The Baxandall volume control for the left channel consists of dual op amp IC2 plus digital potentiometer #2 within IC6. Similarly, for the right channel, it is op amp IC4 and digital pot #2 in IC7. Op amps IC2a & IC4a are buffers, while IC2b & IC4b are configured as inverting amplifiers with fixed gains of 14.7 times. The digital pots are then connected within the feedback loop between the output of IC2b/ IC4b and the input of IC2a/IC4a. As a result, IC2a/IC4a are fed a signal voltage between that of the input signal and the inverted and amplified output signal. The net result of this is, with the digital pot ‘wiper’ (pin 4) all the way at the input (A) end of the ‘track’, the full input signal is applied to the pair of op amps, so the maximum gain of 14.7 times occurs (actually about 12 times or +21.6dB when you consider the attenuation due to the 2.2kW resistors). As the ‘wiper’ moves towards the output (B) end of the ‘track’, the gain reduces logarithmically, eventually to almost zero. The minimum gain (actually attenuation) is limited only by the digital pots’ wiper resistances of around 50-100W. Our tests show that the lowest gain setting gives about 1.5% of the input signal at the outputs of the volume control section, equivalent to -56dB. This means that with the volume control at zero, you will still get a little sound out of the preamp, but it will be very quiet. To fully mute the audio, the digital pots have a shutdown feature that disconnects each pot’s ‘A’ terminal entirely. This is where our input signal connects; hence, we can fully mute the outputs if desired. The output signals from IC2b and IC4b are again clamped to the supply rails by pairs of schottky smallsignal diodes, protecting the digital pots from damage if you set the gain too high. The op amps limit the current to around 50mA, so neither the diodes nor the op amp will be damaged during clipping. As the signal siliconchip.com.au Parts List – Touchscreen Digital Preamp 1 Micromite LCD BackPack programmed with 0110319A.HEX (2.8in display) or 0110319B.HEX (3.5in display) [SC3321, SC4237 or SC5082] 1 double-sided PCB coded 01103191, 206 x 53mm 2 double-sided PCBs coded 01103192, 12.5 x 45.5mm 1 universal IR remote control (optional) [Jaycar XC3718 / Altronics A1012A] 3 EA2-12 DPDT 12V DC coil telecom relays (RLY1-RLY3) 2 500W mini horizontal trimpots (VR1,VR2) 2 small slip-on ferrite beads (FB1, FB2) 3 2-pin headers with shorting blocks (LK1-LK3) 2 quad right-angle RCA socket assemblies (CON1, CON2) [Altronics P0214] 1 dual vertical right-angle RCA socket pair (CON3) [Altronics P0212] 1 white vertical PCB-mount RCA socket (CON4) [Altronics P0131] 1 red vertical PCB-mount RCA socket (CON5) [Altronics P0132] 1 3-way mini screw terminal block, 5.08mm pitch (CON6) 1 PCB-mount barrel socket (optional) (CON7) 1 18-pin header (CON8) 2 18-pin socket strips 2 16-pin box headers 2 16-pin IDC sockets 1 length of 16-way ribbon cable to suit installation 1 3-pin infrared receiver (IRR1) 1 12-15V AC plugpack/transformer or 24-30V AC centre-tapped transformer with associated wiring, fuse, mains plug etc (to power preamp board) 1 M3 x 6mm machine screw, washer and nut (for mounting REG4) 3 tapped spacers plus 6 machine screws (length to suit installation) Semiconductors 5 LM833 low-noise dual op amps (IC1-IC5) 2 AD8403ARZ10 quad digital potentiometer chips, SOIC-24 (IC6, IC7) [SC5912, Digi-Key, Mouser, RS] 1 78L12 +12V 100mA linear regulator, TO-92 (REG1) 1 79L12 -12V 100mA linear regulator, TO-92 (REG2) 1 LM317L 100mA adjustable linear regulator, TO-92 (REG3) 1 7805 +5V 1A linear regulator, TO-220 (REG4) 3 PN200 or equivalent PNP transistors (Q1-Q3) 3 PN100 or equivalent NPN transistors (Q5-Q7) 1 through-hole LED (LED1; 3mm or 5mm, any colour) 1 5.6V 1W zener diode (ZD1) 1 W04M bridge rectifier (BR1) 12 BAT42 schottky small-signal diodes (D1-D12) 3 1N4148 silicon small-signal diodes (D13-D15) Capacitors 2 1000μF 25V electrolytic 3 220μF 16V electrolytic 3 100μF 16V electrolytic 2 47μF 16V electrolytic 2 22μF 16V electrolytic 3 10μF 16V electrolytic 2 1μF 63V MKT 2 220nF 63V MKT 4 150nF 63V MKT 5 100nF 63V MKT 2 33nF 63V MKT 2 470pF ceramic disc 4 100pF C0G/NP0 ceramic disc Resistors (all 1% ¼W axial metal film unless otherwise stated) 11 100kW 6 2.2kW 1 110W 6 47kW 13 1kW 5 100W 2 22kW 1 910W 2 10W 1W 5% resistors OR 2 10kW 11 680W 4 4.7W 1W 5% (see text) 2 4.7kW 1 560W Australia’s electronics magazine September 2021  41 Fig.6: the Digital Remote Controlled Preamp circuit, plus its attached infrared receiver. Besides those components, everything is mounted on one board, which mounts on a small board that plugs into the Micromite LCD BackPack. The components shown in red could be installed but we recommend you leave them off, as our testing shows that they don’t provide any benefits. 42 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine September 2021  43 This photo shows the completed preamp board without the LCD BackPack. We have fitted RLY4 and associated components as it is a prototype; we expect most constructors will leave these off and link out RLY4, as explained next month in the Construction section. A small adaptor board (shown inset) converts the SIL header to a DIL type more easily connected to a ribbon cable, and this same board at the other end also provides somewhere to mount the IR receiver and its supply filter components (shown adjacent). is AC-coupled, this will only ever be intermittent anyway. Tone control This output signal is AC-coupled to the tone control section via a pair of 47µF capacitors. The tone control section is the classic Baxandall feedback-based tone control using op amp IC3a for the left channel and IC5a for the right channel. Digital pots #1, #3 and #4 are connected in the negative feedback loops of these op amps, with capacitors connected such that each controls the amount of feedback over a particular range of frequencies. With these pots all centred, the tone control section has virtually no effect on the signal, basically just acting as an amplifier with a gain of -1. When the pot wipers move off-centre in one direction, signal components in that frequency range are amplified, producing bass, midrange or treble boost. When they move in the opposite direction, signals in those frequency ranges are attenuated (cut) instead. As the tone control stage is inverting, and the volume control stage is too, the phase of signals fed through the preamp is maintained. Since the outputs of op amps IC3a and IC5a are fed back to the digital pot ICs, they once again are clamped to the supply rails using schottky diodes. The 44 Silicon Chip 100pF capacitors directly connecting the outputs to the inverting inputs ensure stability. Relay RLY4 is the bypass relay. When it is energised, the inverting inputs of op amps IC3a & IC5a are no longer connected to the digital pots. They are instead connected to the centre taps of pairs of 4.7kW resistors connecting from the output of the volume control stage to the output of the tone control stage. This configures these two op amps as fixed signal inverters. The idea behind this is to eliminate any distortion or noise that might be introduced by the digital pots or the associated passive components when a flat response is desired. In practice, the performance of the tone control stage is good enough that this is not necessary. While we have left provision for RLY4 and its associated components on the board (there would be no real benefit to modifying it to remove them), we don’t think the extra cost and complexity is justified. So our parts list and construction details (to come next month) will omit these components. The output signals from the tone control stages are AC-coupled again, to remove the DC bias, then amplified by a factor of two by op amps IC3b & IC5b. This allows the output amplitude to be above 1.9V RMS if desired, up to about Australia’s electronics magazine 3.8V RMS before clipping. The 100W series resistors prevent cable capacitance from affecting those gain stages. The two outputs are connected in parallel; one is available at the rear panel (if those connectors are installed). The other pair consists of vertical connectors on the board, more suited for internal connections to amplifier modules. It should be possible to use both at once, given that the output impedance is relatively low. This could be the case in an integrated amplifier that provides pre-out signals. Control by Micromite The digital pots are controlled using an SPI serial bus, with one CS (chip select) line each, plus active-low common reset (RS) and shutdown (SHDN) lines. That’s a total of seven digital lines required to control both ICs. We also have four relays to control. An NPN transistor drives each relay coil with a back-EMF clamping diode. These relays have 12V DC coils, and somewhat unusually, are powered from the -12V rail. This is because the +5.5V rail is derived from the +12V rail, so we are driving the relays from the negative rail to better balance out the current draw. This means that all the relay coil positives are connected to GND, and the negative ends are switched to -12V. Some clamp diodes connect to GND siliconchip.com.au and some to +12V depending on PCB routing convenience; either way, they will still absorb back-EMF spikes and prevent damage to the transistors on switch-off. PNP transistors Q1-Q4 level shift the 0-3.3V digital relay control signals to allow the NPN transistors with their emitters connected to the -12V rails to be switched normally. So the relays activate when the associated control line is pulled down to 0V, and are off if that control line is at +3.3V or floating (high-impedance). These 11 total control lines are wired back to SIL header CON8, in positions suitable for being directly wired to the I/O header on a Micromite LCD BackPack module. There are two additional connections: one to allow the BackPack to illuminate or flash the onboard LED (LED1) in response to remote control commands and to indicate that power is on etc. This LED could also be duplicated on the front panel, if desired, along with a series current-limiting resistor. The other connection is for infrared reception, at pin 8 of the I/O header. While the IR receiver and its supply RC filter are shown on the circuit diagram, they are mounted on a small board attached to the BackPack, as the receiver needs to be mounted behind a hole on the front panel of the unit. Power supply The power supply is pretty basic; AC is applied to either barrel socket CON7 or terminal block CON6. If a centre-tapped transformer is used, this siliconchip.com.au would typically be wired to CON6, with the tap to the middle terminal. DC split rails can also be fed to CON6. If AC is applied, this is rectified by bridge rectifier BR1 and filtered by a pair of 1000µF capacitors. The pulsating DC across these capacitors is then regulated to smooth ±12V DC rails by REG1 and REG2. We have chosen 12V rather than the commonly-seen 15V because the performance is much the same, and we don’t need the extra signal swing given the 5.5V limitation of the digital pots. This also provides more headroom for regulation. The +12V rail is dropped to +5.5V using adjustable regulator REG3. This is adjustable so that it can be set to precisely +5.5V; to be safe, we don’t want to exceed the maximum recommended supply voltage for IC6 or IC7 (even though the absolute maximum rating is much higher). A series fixed resistor is provided to limit the adjustment range. Zener diode ZD1 acts as a safety so that if the output of REG3 is much too high for some reason, it should conduct and prevent damage to IC6 & IC7. The +2.75V mid-supply rail is derived from the +5.5V rail using a resistive divider and trimmed using VR2 so that signal clipping to the supply rails is symmetrical. It’s filtered using a 220µF capacitor so that the source impedance seen by the rest of the circuit is low, preventing unwanted crosstalk etc. Links LK1-LK3 are provided for testing because IC6 and IC7 are SMDs. Australia’s electronics magazine They can be left out while the supply voltages are checked, and IC6, IC7 and the op amps will not receive power. Once the supply voltages have been verified as correct, they can be inserted, and the unit powered back up. Finally, regulator REG4 provides a 5V DC supply to run the BackPack control circuitry. Two series 10W 1W resistors have been provided to prevent this regulator from overheating due to the relatively high current required by the BackPack, and the large difference in the input (12V) and output (5V) voltages. This works, although these resistors run fairly hot if you have the BackPack LCD backlight turned up to a high brightness setting. If you find this to be a problem, there isn’t room to fit a heatsink to REG4, but you could add more dropper resistors. For example, four 4.7W 1W resistors mounted vertically instead of horizontally would spread out the heat load. Software As the control module is a Micromite, the software is written in BASIC (MMBasic, to be exact). The control program for the Digital Preamp is quite small compared to other Micromite-based projects. This is mainly due to the relatively simple functions it provides, with the hardware doing most of the work. The Micromite processor controls the four relays and the two digital potentiometer ICs, which have four potentiometers each, for a total of eight. The Micromite also commands the LED and receives signals from the infrared receiver. While the MMBasic code provides an interrupt that is triggered when an IR code is received, we simply use this to set a flag, as other operations could be occurring when the interrupt is triggered. The received command is processed later, when the Micromite would otherwise be idle. We think that many constructors will want to use the 2.8-inch touchscreen (eg, as used in the original BackPack or BackPack V2) because it will be a better fit on the front panel of many cases suitable for a preamp. However, you can use the Micromite LCD BackPack V3 with its higherresolution, larger 3.5-inch touchscreen if you have room. The software has been designed so that it can use either September 2021  45 Screen 1: the main screen has buttons to quickly load one of six presets, change the volume, mute the output or go to one of two settings screens (presets and tone/EQ adjustments). Screen 2: the tone control/ equaliser (EQ) adjustment screen. Here you can set the bass/mid/treble boost/cut values as well as a volume adjustment (PRE+/-), and it shows you an approximation of the resulting frequency response below. You can also switch between the inputs, adjust the loudness control, reset the settings or store them to the current preset. Screen 3: in the preset screen, you can switch between the six presets, give them names, view their settings and adjust the backlight brightnesses and timeout. Screen 4: if you decide to name one of the presets, you will be presented with this basic QWERTY keyboard so you can enter a new name or change the existing one. 46 Silicon Chip Australia’s electronics magazine screen with just minor changes to the code, and we will provide both versions (BASIC code and HEX files) in the download package for this project. User interface As with other projects using the Micromite BackPacks, several different screens are provided for various features. The MAIN screen offers the features that will be used most often, while two other screens allow the settings to be customised. The MAIN screen (Screen 1) has six buttons corresponding to six presets. While there are only four inputs, some readers might have these connected to other devices with more inputs, so multiple presets can use the same input to provide various custom tone profiles for each input. You might also want different sound profiles for the same device (eg, to suit movies or music playback). If one of the presets is selected, its button is highlighted; the MUTE button is also highlighted when active. Three more buttons provide MUTE, VOLUME UP and VOLUME DOWN functions. These nine buttons correspond one-to-one to the functions that are available via the IR remote control. The volume level is also displayed numerically. At the top right is a much smaller button marked SAVE. Pressing this will cause the current settings to be saved to flash memory if they have changed. There is also an automatic timed save feature. To help conserve flash memory longevity, this defaults to 10 minutes (of unsaved changes), but you can alter that. The SAVE button is red if there are any unsaved changes; otherwise, it is grey. Below the SAVE button is a timer showing the number of seconds before the screen changes to a low-brightness idle mode. Two more buttons provide access to the settings. The EQ SETTINGS screen (Screen 2) is used to set the tone controls and input selection. This screen also shows an approximate frequency response graph of the current settings. The graph is based on tests conducted with our prototype, so it will not reflect variances due to component tolerances. The response calculation assumes that the frequency response of each stage is linear, which does not apply at the extreme ends of the potentiometer travel. siliconchip.com.au Screen 5: once you press the Enter (Ent) key, it confirms the new name you have typed for the preset. The graph is characterised by arrays of values which provide a value for the midpoint response and another value for the difference per potentiometer step at ten different frequencies. These are the values you would need to change if you wanted to characterise your device precisely. The default values should be acceptable for most users. The SETTINGS (Screen 3) screen allows the currently set tone controls to be allocated to a preset and for these presets to be renamed. The parameters for each preset are displayed next to their buttons. These are shown in raw digital potentiometer steps from -127 to +127, with zero denoting the midpoint. Each of the six presets can be renamed by pressing the corresponding RENAME button. This brings up a keypad allowing capital letters and numbers to be entered (Screen 4). To make good use of the available space, only a limited set of keys is provided. Backspace, Enter and Cancel buttons are also provided. Upon pressing Enter, the new name is displayed briefly (Screen 5). Finally, there are buttons to allow for numeric entry of three backlight settings (normal intensity, idle intensity and idle timeout) and the save timeout setting. Pressing the corresponding button displays a numeric keypad for entering a new value, with the prompt containing a range for valid values (Screen 6). Entering a value also displays a brief popup indicating the entered value (Screen 7) or noting an error if an entered number is out of range (Screen 8). For simplicity, only positive integer values are supported. The normal backlight values range from 1-100%, while the idle backlight extends the lower limit to 0%, blanking the display completely. This is handy if you don’t wish the display to interfere with, for example, viewing a movie in a dark room. The idle backlight is only activated on the MAIN screen, so it does not interfere with changing the settings. A touch anywhere on the screen will awaken it; you can use the title area at the top of the screen to be sure of not changing any parameters. We’ll explain the particulars of setup and operation next month after going over the construction and testing details. SC siliconchip.com.au Screen 6: this simpler numeric keypad is used to enter backlight brightness percentage values. There’s one setting for when you are actively using the touchscreen, and another dimmer setting after the timeout. For best audio performance, we suggest using 0% (backlight off) as the timeout value. Screen 7: the confirmation message that appears when you have adjusted one of the brightness settings. Screen 8: if you enter an invalid value, an error message will be displayed. Australia’s electronics magazine September 2021  47 The IOT Cricket is a small, ultra-low-power WiFi module designed for makers, scientists and hobbyists. It can run for years from a pair of AA cells. We were sent a sample to test and review. Review: IOT Cricket by Tim Blythman T he IOT Cricket was created by a UK company, Things On Edge, based in Cambridge. The IOT Cricket (IOT stands for ‘internet of things’) appears to be their only product at this stage, but, as they suggest, it is a versatile module. Things On Edge also provides an online platform for the IOT Cricket to connect to. At the time of writing, it is listed at £16, which equates to about AU$29. Free shipping is offered when purchasing three or more modules. What makes the IOT Cricket different? The IOT Cricket is different to other WiFi modules we’ve seen. It’s designed to be used with sensors to report their state but it requires virtually no programming. Most other devices (typically) need to be programmed with high-level software such as Python. However, with this one there’s not much more to it than plugging it in and away it goes. This makes it an ideal add-on to a wide variety of applications and especially suits the “maker” market – though we believe it will also find ready acceptance amongst designers and manufacturers, due to its simplicity. It’s housed on a small PCB module measuring 37.2mm by 16.4mm, and most of its top surface is covered by a folded metal shield, meaning the unit is around 4mm thick. According to the Things On Edge website, it includes an ESP8266 processor running at 160MHz. 48 Silicon Chip A notch in one corner of the shield provides access to a minuscule tactile switch and LED. At one edge is a 6-way set of full (through-hole) and castellated pads. The reverse has 13 surface test pads, six of which are arranged in a 2x3 grid, which we suspect is a programming header. At the opposite end of the board is a PCB antenna, similar to the antenna seen on other ESP8266 modules. Probably the most interesting aspect of the IOT Cricket is the fact that it can run for long periods on battery power; the website claims years on a pair of AA cells. We haven’t had the time to test that statement, but it certainly appears feasible with aggressive power saving features. Those who have worked with the ESP8266 would know that it is not a very battery-friendly chip. So they have used some tricks to achieve low power consumption. Although Things On Edge did not share the schematics with us, the general operating concept is straightforward. The six-way edge header provides connections for a battery, the negative of which is also circuit ground. One terminal provides a nominal 3.3V output when the device is ‘awake’, while the remaining pins are digital inputs, with one capable of measuring analog voltages. With the typical supply being a pair of AA cells, the regulator is of the boost variety. The IOT Cricket claims an input of 1V to 3.5V. Most of the The IOT Cricket is small and incorporates an ESP8266 WiFi microcontroller, a boost power regulator and a temperature sensor. Three I/O pins provide digital and analog input options, and it can wake from an external input or onboard real-time clock. Australia’s electronics magazine siliconchip.com.au Screen1: the captive web portal provides the ability to set up the WiFi network. Once connected to the internet, the IOT Cricket can upload data and receive configuration and firmware updates. Screen2: the Info tab indicates that the WiFi has been correctly configured, and lists the unique serial number and password needed to make use of the Things On Edge MQTT (Message Queuing Telemetry Transport) broker. Screen3: the I/O port status can also be monitored via the web portal; this is handy for prototyping and troubleshooting. time, the ESP8266 on the IOT Cricket is powered off. An RTC chip can be configured to wake up the boost regulator at set intervals. One of the I/O pins can also be configured to wake up the IOT Cricket, and it also includes a temperature sensor. This scheme is probably the best way to get the most battery life out of a circuit utilising an ESP8266, with the proviso that it won’t be operating most of the time. It has a web configurator which can be used to change WiFi settings. Unlike many other ESP8266-based devices, this one is not intended to be programmed by the end-user in a lowlevel or high-level language. Instead, the web configuration is used to set how often the IOT Cricket wakes up, what information it reports and how it reports it. It’s a very different philosophy from other ESP8266-based products. Still, Things On Edge also provides a web portal which can work with MQTT (Message Queuing Telemetry Transport) data, which means that it is straightforward to set up something that ‘just works’, without having to worry about programming specifics. As such, it’s well-suited as a sensor node, reporting data, status or user inputs back to another device as part of a larger system. to configure is the IOT Cricket’s connection to your WiFi network, using the Binding tab as seen in Screen1, which shows ‘CONNECTED’ if this is successful. The Info tab shows WiFi and device information (seen in Screen2). In particular, you will need to note down the serial number and password (SN and PWD) to configure other things to work with the IOT Cricket. The Dashboard tab (Screen3) shows the current sensor status. This could be handy during the testing phase, to check that your sensors are working correctly. The Config tab (Screen4) is used to set up what inputs are monitored and siliconchip.com.au Setup process The small button is used to enter the configuration modes; a five second press is used for initial configuration. After holding the button for five seconds, the LED flashes at around 5Hz and a ‘toe_device’ WiFi network appears. Connecting to this WiFi network takes you to the captive portal webpage (at IP address 192.168.4.1) to enter the necessary information. The first thing Features & specifications Connectivity: Supply voltage: Protocols: Configuration: Inputs: Processor: Wake-up: WiFi (b/g/n) 1-3.5V (boost regulator onboard) HTTP and MQTT (free MQTT broker provided) web portal two digital, one analog (shared with digital pin), one wake-up, temperature sensor ESP8266 running at 160MHz real-time clock (RTC) or digital input Australia’s electronics magazine September 2021  49 where they are reported. These settings will also be most critical to getting the best battery life from the IOT Cricket. We enabled most of the reports to run some tests, and set the connectivity to MQTT_TOE, which is Things On Edge’s MQTT broker. There are also options for a custom MQTT broker (which could be on the internet or a local network) or communicating using HTTP GET or POST methods, again connecting to either a remote or local HTTP server. Clicking the power icon at top right exits configuration and starts the IOT Cricket running with its current application settings. We enabled all sensors for our initial tests and set the RTC to wake the IOT Cricket up every 10 seconds. These settings are certainly not optimal for power consumption, but made it easy to check that everything was working correctly. MQTT MQTT stands for Message Queuing Telemetry Transport and is a protocol that is well-suited to allowing small IoT-type devices to communicate. Devices publish messages to so-called Screen5: this command, issued after installing the ‘mosquitto’ software, allows the IOT Cricket’s messages to be checked and monitored. The ‘batt’ topic name can be replaced with any of the others that are supported, or the ‘#’ MQTT wildcard to see all messages. ‘topics’ to a broker, and other devices can subscribe to specific topics. The broker sends these messages when they are received. It is a fairly simple and lightweight protocol, but supports authentication via username/password combinations and security using TLS encryption. The client and broker model also means that many small devices can share information via a single broker. Something like a PC or even a singleboard computer like a Raspberry Pi is typically used as a broker, meaning that a microcontroller can implement the lightweight clients. Since one broker can manage many clients, this is not hard to set up and allows many clients to send, receive and share data. Several open-source home automation projects can use MQTT, and there are also mobile phone apps that can be configured with custom dashboards to send and receive messages. So MQTT is a good choice for integrating with these sort of home-made projects. We set up mosquitto (https:// mosquitto.org/), an open-source, cross-platform MQTT broker and client to test out the setup on our Windows computer, although this should also work for Mac and Linux (including Raspberry Pi). Running the command shown in Screen5, we were able to monitor the status updates from the IOT Cricket. Note that the Things On Edge broker (at mqtt.thingsonedge.com) uses the IOT Cricket’s serial number as its username and password, and passes all messages to a topic named for that Screen4: configuring what and when the IOT Cricket reports data is critical to how it will operate and how much power it will use. 50 Silicon Chip serial number and the property (after the -t option). Table1 is a good summary of what sort of information the IOT Cricket can capture and report. Note that the configuration will need to be set to allow the necessary topics to be reported, and those not used should be switched off to minimise power consumption. Using Things On Edge’s MQTT broker and an MQTT dashboard app could be a simple way to monitor a remote sensor using not much more hardware than the IOT Cricket itself. HTTP The IOT Cricket can also communicate with a web server via HTTP POST or GET methods. In either case, the data is passed by tags which correspond to the topics listed above, but preceded by a ‘#’. The IOT Cricket then replaces the tag (eg, ‘#batt’) with its value when the data is sent. In the case of a POST, the payload can be set to a specific string, which can contain a combination of text and tags. A GET method includes these at the end of a URL, typically in the form of parameters like “?battery=#batt”. This allows custom content to be created and passed to an existing server. When the HTTP server receives a request, it can process the payload or URL to decode the data. The HTTP protocol is quite simple, but it is limited to one endpoint (the HTTP server). Testing We tried a few things out to put Same-size illustration of the Cricket (from above) showing its I/O pins along with the main features. Australia’s electronics magazine siliconchip.com.au temp ...................... batt ....................... io2 ........................ io3 ........................ io1_wake_up ............ rtc_wake_up ............. hwc_wake_up ........... hwc_wifi_enabled....... device_sn ................ device_name ............ Temperature in °C to one decimal place Battery voltage as raw ADC value (up to 8 bits) Pin state as digital (0-1) or analog (0-255) value Pin state as digital (0-1) value Digital value (0-1) if IOT Cricket was woken by pin Digital value (0-1) if IOT Cricket was woken by RTC Count of wake-up events Count of WiFi connections Device serial number (string) Device custom name (string) Table1: these topics are available, and all MQTT data is communicated as strings of ASCII characters. the IOT Cricket through its paces. We found that running it from breadboard wiring was not always successful, especially from a single 1.5V cell, but we had no problem after we had soldered it directly to the battery holder. The hardware notes for the IOT Cricket indicate that the power supply should be able to supply bursts up to 0.5A with a 3.3V supply, and 100mA continuously. We ran some tests with a small 0.1Ω current shunt resistor and an oscilloscope. With a pair of AAA cells providing around 3V, we noted a current spike of 600mA at start-up, causing the battery voltage to sag near 2.5V; see Scope1. The nature of the boost module means that a lower supply voltage will necessarily require a higher current; a 1V supply might need to supply peaks of around 2A at start-up, possibly causing the battery voltage to sag even further. So while the specifications indicate that the IOT Cricket should be able to run from a 1V supply, users should be aware that this would be measured at the unit itself and they should leave some headroom for sagging due to high current bursts. One option could be to fit an external capacitor to help with this. Despite this, we found operation on a pair of AAA cells to be flawless. Given that two AAA cells are not much larger than a single AA cell, we would be inclined to power the unit in this fashion. Average current consumption while active was around 40mA, and the typical uptime was six seconds. This means that each update consumes around 67µAh and a 1000mAh capacity battery (at 3V nominal) can provide about 15,000 updates, assuming the quiescent power consumption is negligible. With this in mind, it is clear that the siliconchip.com.au IOT Cricket’s ability to operate for long periods on battery power is dependent on spending most of its time in the low-power state, where presumably, only the RTC is running. Current in this state was under 1µA, according to our multimeter. The boost regulator inherently limits the upper voltage that can be supplied to the IOT Cricket, since it cannot regulate down. The notes clearly state that 3.5V is the upper battery voltage, which aligns with the 3.6V upper limit for the ESP8266. This rules out rechargeable options such as LiPo or even LiFePO cells without an external regulator, as they can peak up to 4.2V when fully charged. A pair of NiMH cells would be the logical alternative (giving around 2.4V to 2.8V), although we haven’t tested that. We found that the temperature reported by the IOT Cricket was slightly higher than expected, although we were testing with a fairly frequent update rate, so the unit may have been suffering from self-heating. We expect that less frequent updates would ameliorate this issue. Power saving Apart from enabling and disabling individual inputs, there’s also the option only to report changes if the input changes; this is the “force update” option seen in Screen3. When this option is switched off, the input states are only reported when a change occurs. If no data needs to be reported, then the IOT Cricket can skip the power-hungry process of connecting to a WiFi network and sending that data, saving even more power. Of course, this means that it’s more difficult to tell when the IOT Cricket is working correctly. Resources An online brochure, quick-start guide and in-depth IOT Developer Guide are available at www.thingsonedge.com/ documentation, while sample projects and other articles are referenced from the blog page at www.thingsonedge. com/blog The IOT Developer Guide also lists several compatible sensors, including buttons, light sensors, motion sensors and even a microphone. A minimal implementation of the IOT Cricket requires no more than a battery to power the unit. It can be configured to report temperature (using the integrated temperature sensor) and battery status as frequently or infrequently as needed, down to once per day. Australia’s electronics magazine September 2021  51 Scope1: the green trace shows battery voltage while the yellow trace is the voltage across a 0.1Ω Ω current shunt when the IOT Cricket is powering up. The 61mV spike on the yellow trace is notable; it corresponds to 610mA of current draw, while the battery voltage sags to 2.54V. With the 3.3V output, it’s possible to power external sensors only when needed. However, they will need to have modest current consumption to allow the boost regulator to work correctly and prolong battery life. We suggest reading the IOT Developer Guide to get the most out of the IOT Cricket. The IOT Cricket can also upgrade its own firmware from the Things On Edge server. These options are available from the captive web portal under the Upgrade tab. There is also an option to load configuration settings from the Things On Edge server. Enabling this feature could be a good idea for a unit that has been remotely deployed. Conclusion The IOT Cricket has a very different philosophy to many other similar devices we have seen, requiring practically no programming and only some minimal setup, at the expense of the greater options available with a more programmable alternative. It appears to be well thought out and provides an interesting addition to the spectrum of IoT and remote-sensing modules on the market. The ESP8266 is a power-hungry part, and as expected, the way the IOT Cricket gets around this is by shutting down for long periods, although the option of RTC and I/O pins for wake-up should cover most uses for this device. It requires fairly high currents when it is starting and awake, so careful design is needed to ensure that there are no high-resistance paths in the battery circuit, as these will be a major point of inefficiency. A supply closer to 3.5V will provide headway above the minimum operating voltage, reducing the current needed for operation. The provision of an internet connected MQTT broker to complement the IOT Cricket is a handy feature, meaning that its data can be accessed from just about anywhere by multiple clients. 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XC9001 SAVE 10% ON COMPUTER MODULES NOW 44 $ $ 10% OFF 10% OFF Long Range LoRa Shield Transmit and receive data over long distance without a GSM network. The perfect solution to your remote sensor and control projects. External antenna included. XC4392 NOW 34 $ NOW 1795 95 USB to Serial Adaptor Module A mini-USB to 6-pin serial port module used to communicate with Arduino boards and modules. Uses the original FT232 chip with power, sending and receive indicators. XC4464 NOW 1295 95 $ 10% OFF 10% OFF Ethernet Expansion Module A network shield that enables you to set your Arduino® up as web server, control your project over your network or even connect your Arduino® to world wide web. XC4412 ISP Programmer for Arduino® and AVR Unbrick, install or update your Arduino®- compatible boards. XC4627 EVERYDAY GREAT JAYCAR VALUE FROM 3 $ 37 Piece Deluxe Module Package BOARD $ XC4410 micro:bit V2 GO Development Board $ BOARD 45 Jiffy Boxes Manufactured from ABS plastic. Various sizes from 83x54x31mm to 197x113x63mm available. HB6005-HB6025 FROM 4 $ 95 Prototyping Mini Breadboards 170 Tie Points PB8817 $4.95 400 Tie Points PB8820 $7.95 FROM 550 $ PC Boards Vero Type Strip Alphanumeric grid, pre-drilled 0.9mm, 2.5mm spacing. 95mm wide. 75mm, 152mm & 305mm lengths available. HP9540-HP9544 Not sure what to build next? Here's some inspiration: jaycar.com.au/projects Double Up and Save on Modules 2 FOR 7 $ 2 FOR 16 90 $ SAVE 20% Logic Level Converter Module 2.4GHz Wireless Transceiver Module JUST 795 BUY 2 AND SAVE Connect directly to an Arduino® board. 3.5V-6V. Torque 1.6kg.cm <at> 4.8V. Arduino® compatible. YM2758 $11.95EA For projects that don’t require full colour. Wide viewing angle to eliminate eye strain. Arduino® compatible. XC3728 $24.95EA Motor & Servo Controller Module 5V Stepper Motor with Controller JUST 9 95 A small, versatile motor and driver set that can be used with any Arduino® compatible boards via jumper leads. XC4458 JUST 5 95 EA. Connect a legacy device (or computer) to your Arduino® board to directly communicate to a variety of serial peripherals. Support TX and RX signals. XC3724 Breadboard Power Module Adds a compact power supply to your breadboard. Power from a USB socket or DC. 3.3V or 5V switchable. XC4606 ONLY 25m ROLLS Flexible Light Duty Hook-Up Wire Quality 13 x 0.12 tinned hookup wire on plastic spools. 8 different colours available. 25m roll. WH3000-WH3007 ARDUINO® COMPATIBLE This icon indicates that the product will work in your Arduino® based project. FROM 2 $ JUST 995 $ RS-232 to TTL UART Converter Module 95 ONLY $ JUST 795 $ 9 $ BEST SELLER Accepts voltage from 4.5- 35VDC, and outputs from 3-34VDC. Output is adjusted via a multi-turn potentiometer. 2.5A max output current. XC4514 Control up to four DC motors or two stepper motors. 5-16VDC. XC4472 $ 1.3” 128 x 64 OLED Monochrome Display Module DC Voltage Regulator Module ONLY Dual Ultrasonic Sensor Module Measure distances up to 4.5m. Great for obstacle avoidance robotics project. XC4442 SAVE 20% BUY 2 AND SAVE 1295 $ $ 9G Micro Servo Motor This module allows communication on the license free ISM band. Supports on-air data rates of up to 2Mbps. Arduino® compatible. XC4508 $9.95EA 2 FOR 3990 90 SAVE 15% BUY 2 AND SAVE Provides two bi-directional channels to safely marry 3.3V with 5.0V. Drops straight into solder-less breadboard. 12-pin DIL package. Arduino® compatible. XC4486 $4.95EA $ $ SAVE 15% BUY 2 AND SAVE 2 FOR 19 90 95 215 $ ONLY 225 $ SPDT Miniature Toggle Switch Solder tag with threaded bush. ST0335 NE555 Timer IC ZL3555 12-Way Terminal Strips Sturdy retention hole. 6A, 10A, 15A, & 30A available. HM3194-HM3200 RASPBERRY PI COMPATIBLE This icon indicates that the product will work in your Raspberry Pi project. s ' t a Wh w? Ne Swann 4 Channel Wi-Fi NVR Kit Features True Detect™ PIR Motion Sensing Technology, facial recognition, record and playback simultaneously. Includes Network Video Recorder, 4 x 1080p cameras, power cable, mouse, network and HDMI cables. QV9107 THIS IS A HIGH QUALITY SURVEILLANCE SYSTEM COMPLETE WITH REMOTE VIEWING VIA YOUR SMARTPHONE KJ9051 BUILT-IN FACIAL RECOGNITION 1080P FULL HD QUALITY VIDEO ILLUMINATED SWITCHES ONLY 199 $ DC Control Box for External Battery with Voltage Display Feature packed control box with 2 x 50A Anderson sockets, 6 x switches, 3 x cigarette sockets, dual USB socket and fuse block in a sturdy plastic package. Mounting hardware supplied. HB8520 168 PIECES FROM 5995 STYLISH FABRIC KJ9050 Fun to assemble and will make a magnificent art piece on your desk or table. 1 x AA Battery required. Zodiac Wall Clock KJ9050 $69.95 Time Engine Calendar KJ9051 $59.95 2 x AA Batteries SB2424 $1.95 BUILT-IN SPEAKER TURN A 12V BATTERY INTO A POWER STATION DIY Wooden Puzzle Kits QUALITY SOUND ONLY 4495 $ ONLY 129 $ 4K Extends 4K HDMI signal using Cat6 cable up to 40m. Supports 4K up to 40m & 1080p up to 70m. 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Backwards compatible. 1.5m WQ7920 $34.95 3.0m WQ7922 $44.95 ONLY ONLY 3995 $ 95 Concord 8K HDMI Leads 2495 $ SUPER BRIGHT PROJECTION LAMP DETACHABLE FLEXIBLE MIC Fast Battery Charger with Batteries ONLY $ USB Headphones with Microphone 4K HDMI Cat6 Extender with IR Extender AAA Rechargeable Batteries Pk4 ONLY 699 $ WI-FI TECHNOLOGY - EASY INSTALLATION 250 PIECES $ 1TB HDD Concord USB Type-C with Power Delivery High quality Type-C to Type-C, metal shell connector & braided cable. USB 3.1 Gen 2 capable of data speeds up to 10GBs, rated 100W Max for Type-C PD. 2m. WC5100 Your Club, Your Perks. KEEP UP TO DATE WITH THE LATEST OFFERS & WHAT’S ON! JOIN NOW! 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24.08.2021 - 23.09.2021. Second-Generation Colour Maximite 2 This new CMM2 computer is compatible with the original described in mid-2020 and adds several great new features. These include more memory, higher-resolution video modes, 24-bit ‘true colour’, more controller inputs, better keyboard and mouse support and some new optional components like a super-accurate realtime clock. Part 2: assembly & use D itching the use of a microcontroller module like in the original CMM2 means there are more SMDs onboard, but overall it has simplified the design. Since many vendors are now supplying boards with the vast majority of the SMDs already soldered, the cost has been kept low and assembly is quick and easy. So we’ll get stuck into that before we describe some ways you can use it. Construction Fig.4 shows the PCB overlay for the CMM2 Gen2 board. You can use this as a guide during construction, but it is also helpful for debugging, testing or planning hardware expansion (eg, developing an add-on board for the computer). If you’re building your CMM2 Gen2 from scratch (including soldering all the SMDs), we’ll assume that you know what you are doing and just give some general pointers. Firstly, make sure that you have IC3 & IC4 orientated correctly before you solder more than a few pins. Even experienced constructors can sometimes mount ICs with pin 1 in the wrong location, and fixing it is a lot of work! siliconchip.com.au Words and MMBasic by Geoff Graham Design and firmware by Peter Mather After soldering IC3 and IC4, clean up the board and scrutinise the solder joints to ensure they’re all good and there are no bridges. You can mount the remaining SMDs in pretty much any order. Do check the orientation of the remaining ICs and oscillator modules before and after tacking them down. Once you have all the ICs, resistors, capacitors, oscillators and reset switch in place, give the board another clean, and you’re at the same point as someone who is starting assembly from one of the partially pre-assembled kits. Finishing your computer Even if you have a partially assembled second-generation Colour Maximite 2, you still need to complete it by soldering the connectors and larger components, a few of which are surface-mounted. This is reasonably straightforward; only a couple of items need to be treated with care. The first is the SD card socket, which should be soldered first so that you have easy access with the soldering iron. This is a surface-mounting connector, and it has two small pins on its underside which match two holes in the PCB. These help locate the Australia’s electronics magazine connector in the correct position while you solder the pins. The best approach in soldering this socket is to apply plenty of liquid flux on the pins and carry the solder to the joint on a fine-tipped, temperature-controlled soldering iron. You could also use fine-gauge rosin cored soldering wire and solder the joints directly, but this has the risk of adding too much solder causing shorts etc. Note that the socket must be held firm to the PCB while soldering, as any gap between it and the PCB will prevent an inserted SD card from making reliable contact with the connector pins. To start, solder the two tabs on the right-hand side of the socket (viewed from the front) and the five on the lefthand side. Some are close to the socket shield, so take care not to cause a solder bridge there. You can then solder the nine pins at the rear. If you get a solder bridge, don’t worry and carry on with the other pins. Finally, examine your soldering carefully and clean up any solder bridges using solder wick. Be careful here as solder wick can suck up all the solder (although generally, it will September 2021  61 Fig.4 (above): the overlay diagram for the Colour Maximite 2 Gen2. Shown below is the PCB with all the connectors, the SD card socket and the battery holder soldered in place. The large central IC is the ARM Cortex-M7 processor, which does most of the work. Above the processor is the 32MB RAM used for holding VGA images and providing extra memory for BASIC programs. leave enough behind). You should go back over the pins and resolder any that look like they don’t have enough solder. When you have finished, inspect each joint with a x10 or x20 magnifier. Also count the pins on the SD card socket; you should have soldered a total of 16 pins. We have found that most construction faults in this area have been missed pins and blobs of solder shorting to the shield of the SD card socket. The real-time clock cell holder is also surface mounted, but it is easy, and it also has two small pins on the underside which ensure the correct positioning. The locations of the remaining connectors are clearly marked by the silkscreen on the PCB, as well as being shown on Fig.4 and in the accompanying photograph, so they should drop in easily. Usually, the case is supplied by the vendor but, if not, you can purchase it as a standard item from Jaycar (Cat HB5970), Altronics (Cat H0472) or element14 (Cat 1526699). When mounting the PCB in the case, it needs 5mm spacers to be placed between the PCB and the four mounting posts. These raise the PCB and the connectors to match the cut-outs in the front and rear panels. Most vendors will also sell pre-cut and labelled front and rear panels to finish off the computer with a professional appearance. You can make the required cut-outs in the blank panels supplied with the case, but it is much easier to use the machine-cut panels. Getting started With the Colour Maximite 2 Gen2 built, you then need to load the firmware, which includes the MMBasic interpreter and the drivers for the hardware components (video, keyboard etc). You can download the firmware from the Silicon Chip website or the author’s website. There is only one version of this. It will automatically detect the hardware that it is running on (ie, the first- or second-generation designs) and configure itself accordingly. To load the firmware, you will need a desktop or laptop PC running Windows, Linux or macOS. There are two methods of loading the firmware using either a USB Type-A to Type-A cable or a Type-A to Type-B cable. Both methods do not require any additional 62 Silicon Chip Australia's Australia’s electronics magazine siliconchip.com.au hardware and are fully documented in the Colour Maximite 2 User’s Manual, which should be in the firmware download package. Here is a quick rundown of the steps involved in programming the STM32 chip. 01 Install the STM32 Cube programmer software from www. st.com/en/development-tools/ stm32cubeprog.html 02 Move the jumper on BOOT0 from RUN to PRG. 03 Plug the CMM2 Gen2 board into your PC using a USB cable. 04 Launch the STM32 Cube app. 05 Select USB at top right, refresh and connect. 06 Click the download button at left. 07 Browse to the firmware BIN file. 08 Tick Verify. 09 Start Programming. 10 Wait about five seconds for the write/verify process to complete. 11 Check that you get the ‘File Download Complete’ OK message. 12 Check that you get the ‘Verify OK’ message. 13 Unplug the CMM2 Gen2 from your computer 14 Move the BOOT0 jumper back to RUN. 15 Plug it back into your computer. With the firmware loaded, you should see the boot-up screen as shown in Screen 1. At this point, you can try typing in a command at the command prompt. For example, try this simple calculation: > PRINT 1/7 0.1428571429 See how much memory you have: > MEMORY Flash: 0K ( 0%) Program (0 lines) 516K (100%) Free RAM: 0K ( 0%) 0 Variables 0K ( 0%) General 24800K (100%) Free Count to 10: > FOR a = 1 to 10 : PRINT a; : NEXT a 1 2 3 4 5 6 7 8 9 10 Bubbles The next step is to try an actual program, such as the following. This will cover the screen in animated, overlapping coloured bubbles: siliconchip.com.au Oscillator Upgrade for the Colour Maximite 2 As described last month, the clock oscillator design in the first generation Colour Maximite 2 was adequate for the default 800x600 pixel VGA video resolution. However, with firmware upgrades, it is now possible to generate much higher resolutions. Still, they generally require the fitting of an external clock oscillator to eliminate jitter and instability in the video. If you have an original CMM2 and do not plan on using these high resolutions, you don’t need to perform this upgrade. Also, note that the second generation design described here already has this external oscillator fitted by default, so if you build the new version, nothing extra needs to be done. To perform the upgrade, you will need an 8MHz crystal oscillator in a 5x7mm SMD package (QX7 XO ≤ 25ppm) such as the Abracon ASV-8.000MHZ-EJ-T, and possibly a 100nF SMD ceramic capacitor in a 3.2x1.6mm (M3216 or imperial 1206) package. We sell these two parts through our website: siliconchip. com.au/Shop/7/5654 The PCB used in the first generation computer has provision for these parts. The solder pads are located under the Waveshare board near the left-hand 80-pin connector. Installing these parts can be tricky, so if you have not had any experience with soldering SMD parts, you should practice on something unimportant and take extra care. Also note that the solder pads are close to the 80-pin connector, so care also needs to be taken to avoid damaging this by accidentally touching it with the soldering iron. The oscillator has a dot identifying pin 1, and this needs to be aligned with the dot on the PCB silkscreen (it is tiny). With the oscillator correctly aligned, you can solder it with flux paste, a fine-tipped soldering iron and the minimum of solder. Be careful not to overheat the joint, and do not let the solder touch the case of the oscillator (which will short the connection to ground). The capacitor should be fitted after the oscillator. It is easier to solder and is not polarised. It is not necessary to remove the 8MHz crystal from the Waveshare board. The signal from the oscillator is strong enough to swamp the crystal, so it will have no effect. This strong signal might also damage the crystal, but this is not a problem as it is now surplus to requirements. DO CIRCLE RND*799, RND*599, RND*100, 1, 1, 0, RND*16777215 PAUSE 4 LOOP You can see the result of running this program in Screen 2. What the photo does not show is that the screen is quite lively, with bubbles of all sizes popping into existence, then being covered by subsequent bubbles. To enter this program, type the command below at the command prompt: EDIT “bubbles.bas” This will start the built-in editor where you can enter the above program. Once you have done this, press F2 (to save and run it), and you should see the screen fill with coloured bubbles. It will carry on forever; to interrupt it, press CTRL-C on your keyboard and you will be returned to the command prompt. Australia’s electronics magazine If you made an error when entering the program, MMBasic will stop the program and display an error message. You can then press the F4 key and that will take you back into the editor, with the cursor positioned on the line that caused the error. Correct the error and press F2 to save this new version and run it again. How does this program work? The DO and LOOP commands set up a loop that will continuously execute the commands inside the loop until interrupted. The CIRCLE command looks complicated, but it simply draws a circle at a random position with a random size and random colour. In MMBasic, the function RND generates a different random number from zero to 0.999999 every time it is used. We multiply this random number by 799 to give a number between zero and 799. This is the X-axis of the centre of the circle, and it will fit on the screen as the default video resolution is 800x600 pixels. Similarly, September 2021  63 Screen 1: when you have soldered the connectors in place, loaded the firmware and applied power, this is what you will be greeted with. You can see that we entered a few simple commands to prove that we have a working computer. multiplying RND by 599 will give us the Y-axis position. Next, multiplying RND by 100 gives a number between zero and 100, which is the radius in pixels. The following three parameters specify the line width (1 pixel), the aspect ratio (circular) and the colour of the circle’s border (black). The final parameter uses the RND function to generate a random colour from the 16 million-odd colours that the Colour Maximite 2 can display (16777215 is 224 − 1), and that colour is used to fill in the circle. The PAUSE 4 command on the next line pauses the program for 4ms after each circle is drawn. This slows down the creation of bubbles enough for you to admire the display. If you delete that line, you can appreciate the computer’s full speed – it is very fast, and the bubbles merge into a blur. Entering a program Screen 2: the result of running the “bubbles.bas” program described in the text. The screen is animated, with bubbles of all sizes popping into existence, then being covered by subsequent bubbles. Screen 3: the Welcome Tape is a collection of introductory programs accessible via an easy-to-use menu system designed for users new to the Colour Maximite 2. You can download it from https:// github.com/ thwill1000/ cmm2-welcome 64 Silicon Chip Australia’s electronics magazine This was briefly mentioned above in the “Getting started” section, but it deserves to be explained in more detail, as it is central to how the CMM2 is used. A program is a sequence of BASIC commands extending over many lines, so except for the most trivial programs, you won’t be typing commands in one at a time at the command prompt. You need a program editor, and the Colour Maximite 2 has such an editor built in. The editor includes colour-coded text (commands in cyan, comments in yellow etc), advanced search and replace, a clipboard for cutting and pasting and many more handy features. To invoke the editor, you must have an SD card inserted in the front panel slot, as the editor will save the edited file to this card. The command is: EDIT "filename" Where filename is the name of your program (it must be surrounded by double quotes). So, for example, type the following at the command prompt: EDIT "test.bas" This will start the editor, allowing you to edit the file “test.bas” on the SD card. If you have used a text editor before (or even a word processor), you will find that this one operates similarly. The arrow keys move the cursor around the text, the delete key deletes siliconchip.com.au the character under the cursor and the backspace key deletes the character before the cursor. At the bottom of the screen, the status line displays common functions such as F6 for save, ^F (hold CTRL and press the F key) for find and so on. At this point, you can try entering the standard program that most programmers typically use to test a new computer and programming language: “Hello World”. This might not sound like much, but in some cases, this involves installing software, getting to grips with complicated compiler requirements, reading lots of manuals etc. With the Colour Maximite 2, it is easy. Just start up the editor (as described above) and enter the line: PRINT "Hello World" Then press the F2 function key, and the editor will save and run your program with the result that the words “Hello World” should display on your screen. If you have made a mistake, an informative message will be displayed by MMBasic. You can then press the F4 function key, and you will be returned to the editor with the cursor placed on the line that caused the problem. The error can be corrected and by pressing F2 again, your modified program will be saved and run for another test. This ease-of-use is part of why the Maximite series of computers, first published by Silicon Chip ten years ago (starting in March 2011), has become so popular. Colour Maximite 2 Resources Since the introduction of the Colour Maximite 2, many people have had fun creating programs for this great little computer and others have gathered them into libraries that you can access. These are some of them: Colour Maximite 2 Welcome Tape: The Welcome Tape (Screen 3) is a downloadable collection of programs written by the user community that includes games, demonstrations and utilities. It is designed for firsttime users and is intended as an easy introduction to the Colour Maximite 2. See https://github.com/thwill1000/ cmm2-welcome The CMM2 Library: https://cmm2.fun is a wonderful collection of games, utilities and fun stuff written specifically for the Colour Maximite 2. It is presented as an easyto-browse list with screenshots, so you can easily select and download something that could cause you to waste a whole afternoon or evening of playing around. Even better, if you have written something useful, you can upload it to this library. The Fruit of the Shed: A huge catalog of information, code fragments, programming techniques for the Colour Maximite 2 and other devices that run MMBasic. For the Colour Maximite 2 content, go to http:// siliconchip.com.au/link/ab8u 101 BASIC Computer Games: If you were around in the late 1970s and playing with the computers of that era, you may know the book “101 BASIC Computer Games”, edited by David H. Ahl. This provides simple games that you could type in yourself and inspired a whole generation of budding programmers. Most will run on the Colour Maximite 2 with minor modifications. If you are into nostalgia, the book and its programs are available from this website: www.vintage-basic.net/ games.html The Back Shed: An online forum, where many users gather to discuss the Colour Maximite 2 and swap programs they have written. It is also a great place to get help, as many experienced people regularly contribute, including the designers of the Colour Maximite 2. You can find the forum at: www.thebackshed.com/ forum/Microcontrollers More information If you would like to know more about the Colour Maximite 2, browse the comprehensive User’s Manual, which is available in the download package from the Silicon Chip website and on the author’s website at http:// geoffg.net/maximite.html Also available from both sources is the free PDF “Introduction to Programming with the Colour Maximite 2”, which guides you through using the Colour Maximite 2, including a tutorial SC on programming in MMBasic. Enthusiastic users from around the world have written many programs, including games, for the Colour Maximite 2. Two of them include a modern representation of the Atari game Gauntlet and a version of the classic arcade game Pac-Man. siliconchip.com.au Australia’s electronics magazine September 2021  65 BY PHIL PROSSER Tapped Horn subwoofer This subwoofer uses just one 8-inch (200mm) driver, yet its response extends below 30Hz and it’s capable of delivering over 100dB SPL! That’s despite a modestly-sized cabinet that’s less than 30cm wide, making it relatively easy to hide. So how does it achieve this? Read on to find out. T his subwoofer is relatively inexpensive to build and not all that hard either, thanks to its clever design. If you already have most of the tools, it will probably end up costing around $200 in total (depending on where you get your hardware). You can get away with using a relatively small amplifier to drive it too, given its high efficiency, although you will need an active bandpass filter (to be described next month). Being a “Tapped horn” subwoofer means that its sole driver is placed inside a horn. This type of subwoofer was made famous by Thomas Danley of Danley Sound Labs. They are often used in sound reinforcement; visit siliconchip.com.au/link/ab9q for a few examples. If you want to see the ultimate manifestation of the tapped horn subwoofer, check out the video at https://youtu.be/ Zbf3bzpgml8 The term “tapped horn” does not sit easily with the engineer in me, as 66 Silicon Chip it is not actually horn-loaded. Instead, it would probably be more accurate to call the alignment a re-entrant resonant pipe. But let’s set semantics aside and use the common name. After reading a few articles on this approach to making a sub, I decided to see how they work. The aim was to present a tapped horn design that fits into a domestic setting, allowing readers to explore this concept in an approachable manner. So, if you have ever wondered about this sort of sub, here is your chance to spend a weekend and find out for yourself how they work! This subwoofer is more than enough for a living room, study or bedroom – it has been kept to a modest scale and cost. The design presented has been simplified to avoid odd cut angles, and I have taken out non-essential corner fillets to keep the assembly as simple as possible. I have even sized the box so that you can use standard sheets of MDF with minimal cuts. Australia’s electronics magazine In loudspeaker design, the designer needs to juggle several parameters, notably: the size of the box, how loud it will go (SPL), its low- and highfrequency extension (bandwidth), and its efficiency (how much power it takes to drive to a particular sound level). A tapped horn can push the efficiency, low frequency extension and SPL well beyond that offered by a conventional sealed or vented enclosure. It achieves this by placing the driver inside the acoustic path and folding that path around, so that the output from the back of the driver adds to the output of the front of the driver. But there ain’t no such thing as a free lunch, so you pay the price in complexity. As shown in Fig.1, one side of a loudspeaker drives the horn close to its end, and the other side of a loudspeaker drives it close to its output. If the two drivers are fed with the same signal, they deliver out-of-phase siliconchip.com.au signals into the horn since they face opposite directions. This gives the simulated response shown in Fig.2; note the extended bass response. But the same driver can’t exist in two different places, so to get the driver to fire into both the front and back ends of the horn, the enclosure is folded over on itself – see Fig.3. This single-fold design is still really long and not that convenient. It is possible to fold these up further in several ways. The configuration we have chosen is shown in Fig.4. Ideally, it would be made from conically expanding sections, but those are really fiddly to cut. You will note that we have cheated on this and made the sections straight. Our tests show that the impact is not enough to worry about. Remember that a conventional sealed enclosure is there to absorb the rearward output from a driver. By juggling the length and area of the path from the back of the driver to the mouth, we achieve constructive interference of the sound over a set bandwidth. This increases the efficiency and allows us to push the low-frequency extension further down. Of course, this comes with compromises. A tapped horn only works over a limited bandwidth, after which the output becomes a series of peaks and dips. Therefore, we need to set the crossover frequency low enough to cut out all the unwanted frequencies. Also, below the low-frequency cutoff, cone excursion becomes uncontrolled, similar to a vented enclosure. The solution is to drive the subwoofer with an active crossover that filters out high frequencies and provides a subsonic filter to remove unwanted low frequencies. Every professional sound system includes subsonic filtering for their subs. This protects the drivers from over-excursion and avoids the amplifiers wasting power by driving the speakers with signals they cannot generate. This article presents only the subwoofer. It should be driven with a signal that’s been through a 20Hz subsonic filter (high-pass) of 24dB/octave and a low-pass filter of -24dB/octave with a -3dB point of 80Hz. We will present an active crossover design to provide this next month. Still, you can probably drive it from the subwoofer output on many home siliconchip.com.au Fig.1: the basic concept of a tapped horn subwoofer. The two drivers are supplied with the same signal. As they are mounted rotated 180° compared to each other, the signals they generate within the horn are out-of-phase. But it takes time for sound to travel down the horn, so over a certain range of frequencies, the sound reaching the outer driver is in-phase, resulting in constructive interference and reinforcement. Fig.2: the simulated response of a folded horn. It gives a nice broad plateau over the range from just below 30Hz up to about 100Hz plus a series of peaks and troughs at higher frequencies, as the sound waves constructively or destructively interfere depending on the specific frequency. So we need a lowpass filter to eliminate signals above 100Hz for it to sound good. Fig.3: this rearrangement of the tapped horn shown in Fig.1 is more practical to build since it is both shorter and uses just one driver instead of two, but it achieves the same result. Fig.4: more folding of the horn (and a bit of creativity regarding how it tapers) allows us to create an even more compact enclosure without sacrificing much in the way of performance. Australia’s electronics magazine September 2021  67 9 00 TOP 884 EXIT OF HORN THIS SOUND PATH IS ABOUT 2.54m LONG 153 762 41 6 PANEL C – STEP #3 315 649 FRONT - STEP #1 PANEL B – STEP #2 20 2 635 PANEL A – STEP #6 500 468 200 BACK - STEP #8 START OF HORN PANEL D – STEP #5 PANEL E – STEP #4 18 4 72 346 Fig.5: this diagram shows the order in which we suggest you attach the internal panels to the side and show the two acoustic paths as dashed lines. It also includes most of the important dimensions, so you can check that you’re building it right, but as you’re unlikely to cut the panels to exactly the right sizes, don’t expect a perfect match. Also note that the top and bottom panels sit above and below the side panel, not on it. 868 BOTTOM - STEP #7 theatre systems, noting that these rarely include a subsonic filter. Design This subwoofer was designed using a program called “Hornresp”, written by David McBean. This is freely available from www.hornresp.net and supported on several DIY Audio forums. It would be fair to say that this program is not super-easy to use, but it does allow us to model what various lengths and diameters of horn sections will do. If you try this program out, we recommend using the “Loudspeaker wizard” via the Tools menu. This lets you change the lengths and diameters of each horn section while watching the power response of the horn. The horn we present juggles the following requirements: • A -3dB point below 30Hz. • A passband ripple of no more than 4dB; in the real world, rooms have all sorts of resonances. • Using a readily available, lowcost driver. • Material able to be transported in a small car; say, a VW Golf. • Only small sheets of material required to make the enclosure, ideally with minimum cuts. • An enclosure that can be hidden under a desk or behind a couch. For the driver, the Altronics C3088 is a good balance of size, power handling and cost while providing pretty decent cone excursion compared to its peers. Cone excursion is really important in subwoofers and is often overlooked. At a given SPL, the lower you want to go in frequency demands rapidly increasing cone excursion. 68 Silicon Chip Consideration of this is essential in designing a sub. Ultimately, a driver with a ‘good Xmax’ is essential. The C3088 has a 4.5mm voice coil overhang, and in our tests, more than 5mm effective Xmax, which is pretty good. Folding the horn as shown in Fig.4, to achieve the above, we need the following: • 200mm from the start of the horn to the back of the driver. • 2.54m from the back of the driver to the front. • ~420mm (416mm actual) from the front of the driver to the exit of the horn. This defines our overall enclosure as having the following dimensions: • Internal width (z-axis in Fig.5): 250mm, external 282mm • Internal depth: 868mm, external 900mm • External height: 500mm Performance The resulting tapped horn subwoofer is shown in Fig.5. Measuring the performance of subwoofers is much harder than full-range speakers due to reflections and resonances in the room. I made the measurements shown in Fig.6 at one metre, but not in the corner of a room. Placing the subwoofer facing the corner of a room, with about 20cm between the sub and the walls, will give better performance (ie, more bass!). The sound level is shown by the black line (axis in dB on the left), while the fainter line is the phase (axis in degrees on the right). Note the peak in Fig.6: the measured response of the prototype subwoofer without the bandpass filter in place. The dark line is the amplitude, while the lighter dashed grey line is the phase. This agrees pretty well with the simulation, although the response actually extends to over 200Hz before the severe peaks and dips start to appear. Australia’s electronics magazine siliconchip.com.au The subwoofer was tested in my workshop setting as shown here, and in a spacious church hall shown adjacent. the response at 200Hz. You really need a crossover that provides a minimum of 18dB attenuation by this point, or you will be able to hear the resonance of the tapped horn. The response is somewhat smoother than predicted but does present the predicted ripple above 100Hz, the peak at 200Hz and a deep dip at about 250Hz. There is no question that this subwoofer needs a steep crossover. I carried out further tests in my workshop, a 60m2 converted shed, where this sub generated very solid bass and rattled the tin exterior (see above). It integrated very neatly with some small monitor speakers using five-inch Vifa bass-mid drivers. I set the tapped horn to main speaker crossover at 80Hz, and I applied no attenuation to either the sub or midrange. The next test was to challenge the sub. After painting, I took it to a rather large church hall and integrated it with some old but extremely efficient 10-inch bass-mid driver based speakers. These have an efficiency well above 90dB at 1W & 1m. I kept the crossover at 80Hz but turned up the sub quite a lot to match the level of the bass-mids. In this 110m2 metre hall (shown at upper right), which is 10 metres tall, the tapped horn made a good showing of itself. While you would not run a disco with it, it handled pop and blues music to ‘enthusiastic’, but short of ‘extreme’, levels. The author does, however, have a fairly high tolerance for noise. Being in a church, I tried some very sub laden Gregorian chant music, and Parts List – Tapped Horn Subwoofer 1 Altronics C3088 8-inch 70W woofer [or Wagner SB20PFC30-8] 3 1200 x 900mm 16mm MDF sheets 134 50mm-long 8-10G countersunk wood screws (get a box of 250) 8 16mm 8G screws (for mounting the driver) 1 1m length of 10mm-wide adhesive-backed foam tape (can be cut from a wider strip). 1 pair of speaker terminals (we used a Speakon connector, but you can use any type) 1 1m length of speaker cable (twin-lead, 17AWG) [Altronics W1936] 1 bottle of PVA glue, at least 200mL 1 tub of “builder’s bog”, at least 200mL 1 can of primer paint suitable for timber 1 square of 120 grit sandpaper (buy more than one so you have spares) 1 square of 240 grit sandpaper (buy more than one so you have spares) 1 litre of DuraTex textured paint (bed liner paint would probably work too) [www.cannonsound.com] 1 tube of acrylic gap filler (in case you have unexpected gaps in your joints) 4 feet (we used four 38mm Surface Gard Round Side Glide feet from Bunnings) siliconchip.com.au Australia’s electronics magazine was quite impressed at being able to feel the bass. Construction See the parts list to see what material you need to buy. You will also need the following tools: • A simple hand-held circular saw; you do not need a fancy table saw. Alternatively, get your local hardware store person to make the long cuts and use a hand saw for the remaining, shorter cuts. • A hand-held drill with 3mm and 4mm drill bits, a countersinking bit and a Philips-head screwdriver bit. • A long metal ruler or straight edge. • Either G-clamps or sash clamps, to hold the MDF while cutting. • A router with a 12mm radius bit, for finishing the edges. • A 10mm diameter, 100mm-long nap roller. • A spatula and scraper, for mixing and applying filler over the screw holes. • A tub of water and a dishcloth, to clean up glue spills and the excess squeezed from joints. Cutting the sheets We have laid the panels out on three sheets of timber that you can transport in a VW Golf or larger, per the earlier requirements. Review the drawings (Figs.7-9) before you start cutting. The majority of pieces needed are either 250mm or 282mm wide. After making these main cuts, you can cut the sides from the offcuts, plus a series of lengths from these 250mm and 282mm wide panels. September 2021  69 Figs.7-9: here are the panels that need to be cut from the three 1200 x 900mm sheets. You might be able to cut them all from a single 1200 x 2400mm sheet if you have a way to transport it (or get it delivered), although we haven’t verified that. It’s also a bit easier to work with smaller sheets. Even better, get the hardware store to make the initial cuts for you, yielding three 292mm wide strips, three 250mm wide strips and two 468mm wide strips. You will then just need to make a few extra cuts to get all the pieces you need. Measure carefully and double-check that the side panels are not too tall or deep, as an error in this dimension will result in an overhang of the top or rear panels. Some hints: • Check that all parts are within ±2mm, although you will need to do better than this for ‘living room furniture’. • Mark the hole locations (see photo below). Use a pencil to mark the panels on the inside. Do not be afraid to measure and mark liberally, as once the box is assembled, these will be hidden. • Take your time and check that all the markings are in the right place. Once you are assembling this speaker, it will be a real nuisance if you need to move things! • There are many screw holes through the side panels. Make sure these are marked within 2mm or so. These measurements are essential to the screws going into the internal panels. • Panel C has the speaker driver cut-out, which you should make after the panel has been cut but before the cabinet is assembled. Use a compass to mark the hole in pencil, then use a jigsaw to cut it out. If you’re lucky enough to have a suitable hole saw, that’s even better. You can use a small handsaw if you don’t have either, although it does take a little perseverance! Now make any assembly markings you feel will help you get the panels aligned. Refer to the photos; placing “V” marks will assist you in getting the panels in the proper alignment. The screw holes define the centres along which of the 16mm-thick panels will be attached, so the edges of these To figure out where the panels are going to lie and where to drill holes, you will need to temporarily arrange the cut panels as shown in Fig.5, then use a pencil or other marker to trace their outlines. You can then use a ruler to draw lines down the centre of each panel location and the locations to drill holes will be along these lines. You can see from my photos how I did this (although I didn't mark the panel edges, only the centres, as I have the experience to do that). 70 Silicon Chip Australia’s electronics magazine siliconchip.com.au panels will be 8mm on either side of the row of holes. Once the screw holes have been marked, mark the panel edge locations and add Vs on either side of the panel lines so that you can see how well centred the panel is along the screw hole line when you are installing the panels. Once everything checks out, drill 4mm diameter holes for the screws. Drill from the inside. There will be some chipping of the MDF where the drill exits, but this will be dealt with in the next step. Then countersink all holes from the outside so that the panels are neat and tidy. Countersink the holes deep enough that the screw heads will sit flush with the panels (as shown below). Assembly Refer now to Fig.5 for the order in which you should attach the panels. We’ll go through these steps one at a time. Step 1 is to attach the front panel that sits in the cut-out in the corner of the side panel. If necessary, file the cut-out on the side panel so that the front panel is well-aligned at the top edge of the side panel. Take time to get this right, as all the following panels align to this. Check that the markups on the insides of the front and side panels line up well, then put a modest amount of glue on the joint. The 3mm drill bit is for pre-drilling holes into the sides of the MDF panels where the screws will enter. This is important to keep the panels from splitting. When you have everything aligned, pre-drill one hole (3mm) to a minimum depth of 50mm into the side of the panel, then put that screw in. siliconchip.com.au Australia’s electronics magazine September 2021  71 1 2 When gluing the panels together, you will want to make sure to use a set of clamps and/or weights while it sets. Titebond wood glue is quite good for these types of jobs. Note that these panels are also kept together via screws and not just glue. Take the opportunity now to nudge the panel so that it is straight and well-aligned. Do this before you predrill the remaining holes. Be sure you are happy, as everything that follows hangs off this panel! Once you are satisfied everything is good, pre-drill the remaining holes and then screw the panels together. Steps 2 & 3 are internal baffles B & C. Run glue along the bottom and front edges of panels 2 and 3, but do so one at a time. Push the panel into alignment and use the marks you made to get everything aligned. The V-marks will help you get each panel square over the drill holes. While pushing the panel in place, pre-drill then screw the bottom hole in the front panel (from step 1). Note that by starting with a screw in the bottom hole first, you will pull Panels B and C tight into the front panel with a minimum of error. 3b Continue pre-drilling and screwing all the remaining holes. Clean up any glue that has seeped out of the joints. Step 4 is to fit internal baffle E. Push it down between Panels B and C. This will be tight. Try to get some glue in there, but assuming you have a good fit, this should not be critical. If you have a gap here and there, run a bead of acrylic filler over the gap(s). Pre-drill and screw this in place from both panels B and C, and through the side panel. Step 5 is to fit internal baffle D. Line up panel D with panel C. Again, use those V marks on the panel to get the panel A end of panel D in the right spot. The trick here is to get a good alignment at the corner of panels C and D. Start again with the screw at the bottom of the junction of Panels C and D. Once it is in place, pre-drill and screw in all screws, checking alignments as you go. 5 For step 6, fit panel A similarly to panel D. Steps 7 & 8 are to fit the top and rear panels. Start with the top panel, ensuring a clean edge is presented at the juncture of the front and the top panel. Get this clean and screw along the front and side panel. Pre-drill and screw all screws for this panel. Then screw the rear panel on with two screws only – don’t glue it yet. Check the fit of the bottom panel, trying to get good alignment with the rear panel and front edge of the side panel. Jiggle this around to get the best fit you can. If there is a slight misalignment, it’s much better for it to turn up now. Remember that before painting, you will be filling and sanding – so minor indiscretions will disappear. If you need to slightly shift the rear panel, remove the two screws and predrill new holes to fix this panel where you want it. Once you are sure it is OK, 6 This is a close-up view of the panel in Step 3 showing the gap between Panel B & C. 72 Silicon Chip Australia’s electronics magazine siliconchip.com.au 3a 4 Once the glue has been applied and the joints clamped, they should be left clamped for at least one hour, then left to cure for approximately a day. pre-drill, glue and screw the remaining holes in the rear panel. Do not drill, glue or screw the bottom panel yet! Step 9 is to fit the other side panel. I used acrylic filler rather than PVA to glue the side panel on, but this is not essential, especially if you cut your panels accurately. After applying the adhesive, slide the side panel into place, then drop it onto the internal baffles. Push the side panel in place so that there is a flush fit along the top panel, then pre-drill and screw along this edge. Next, push the front and rear edges of the side panel to get good alignment with the front and rear panels, and again, pre-drill and screw. Now pre-drill and screw all the holes on the side panel. If your measurements were good, all the screws will go into the internal baffles. If the drill falls through the holes and misses the internal baffle, drill at an angle 7 siliconchip.com.au that does catch the internal baffle (this should not be necessary!). Mounting the driver The driver needs to be mounted before the bottom panel is installed. With everything in place, jiggle the C3088 speaker to ensure that it sits neatly in the hole you have cut. If the hole is a touch undersized, the speaker will not sit snugly. If that is the case, now is the time to fix it! Carpenters may shake their finger at us, but you can use a rasp to enlarge the hole slightly, given this is hidden inside. Then stick foam tape around the edge of the driver hole. This will ensure that a good seal is achieved between the driver and Panel C. Then install speaker wire as shown in the photo overleaf, ensuring there is sufficient length to pull through the driver hole and solder to the driver. Make sure you can identify the “+” wire to the driver as this needs to connect to the “+” pin of the speaker connector. Run the speaker wire through to the speaker connector. We used a Speakon connector as many of our speakers use these, although you might prefer to use banana sockets and/or binding posts on your sub. We drilled a 25mm hole on the rear panel to mount the connectors we used. We haven’t shown a location or size for this hole on the cutting diagrams because its size and shape will depend on your connector, and it can go pretty much anywhere you like on the rear panel. It will probably look best if it’s somewhere along the vertical centreline, though. Now seat the speaker in the hole and mount it using 16mm 8G screws that do not pull through the hole in the speaker frame (ie, with large enough heads, or washers if necessary). Predrill the holes to 2mm, then insert the 8 Australia’s electronics magazine September 2021  73 9 Make sure to seal the speaker wires when finished. eight screws. Progressively tighten screws on opposite sides of the driver until all are tight. Do not overtighten these as the foam tape will ensure a good seal. With the driver in place, attach the bottom panel. Do not glue it; simply screw it down with the generous number of fixings. This will allow you to access the driver later if it needs to be replaced. Finishing the box I routed all external edges with a 12mm radius bit. If you do not have a router, that doesn’t matter. Use 80 and then 120 grit sandpaper to round the edges until they look and feel smooth. I then used “builder’s bog” to fill all the countersunk screw holes. Once this dried, I sanded those areas and then applied a second coat of bog to get those areas really smooth. Do not fill the holes in the bottom panel, though! You need to be able to remove it. Once I was satisfied that the enclosure was smooth enough and all screw holes – except those in the bottom panel – were now flush with the MDF, I coated the box in DuraTex. I first applied a thin coat, then after one hour, a second, thicker coat using a 10mm nap roller. DuraTex is a textured paint sold for use on professional speakers. It is tough and textured so that it takes life’s bumps without showing too much. It also helps to hide any imperfections in our work. Finally, I screwed on the feet and the sub was complete. As promised earlier, next month I’ll describe an active crossover that’s perfect for use with this subwoofer (or any two-way SC or three-way speaker system). A router makes finishing the edges much easier, but it can also be done with sandpaper. Any gaps and cracks can be filled by using a mix of wood glue and sawdust, or wood filler. The finished subwoofer had primer applied and was then painted black. You could also just apply a lacquer or polish depending on how you want it to look. 74 Silicon Chip Australia’s electronics magazine siliconchip.com.au SERVICEMAN'S LOG ‘Playing’ with fire Dave Thompson I always hesitate to ‘help’ repairers or installers do work in my home. While I presume that my talents would come in handy (even if I’m just acting as a third hand), I know how frustrating it can be when someone who is not an expert is hovering over you. Sometimes, a ‘helper’ is actually a hindrance. In this case, I think the guy appreciated assistance from someone with decent electronics knowledge. A little while ago, I was sitting in my workshop doing somethingor-other when suddenly there was a huge boom! The earth shook, dust fell from the light fittings, and everything on the bench was rearranged slightly. This didn’t overly disturb me, as earthquakes are a dime a dozen here these days. I’ll admit that my heart did race a little, as it always does with quakes, though I did think it a bit unusual at the time. Most ‘quakes don’t have the sharp shock and loud audio soundtrack this one had, tending instead to be rolling, rumbling affairs lasting perhaps 30 seconds or more. This one was very short and sharp, and quite loud, but I thought nothing more of it at the time. I know, great story, right? However, this will all become relevant later, I promise! Keeping the ‘cave’ comfortable Increasingly, our news reports seem to be chock full of extreme weather events. If it isn’t droughts, it’s floods, and if it isn’t wildfires, it is plunging temperatures from seemingly endless polar blasts. Sometimes both of these will happen in the same place, just a few months apart. While being so far away from the hottest places on the planet does help us here in New Zealand a little, being so close to very cold places does have its drawbacks. Anyone who has visited Christchurch (or anywhere further south of here) in the middle of winter will know what I’m talking about. This year, we have record-breaking ‘cold snaps’, which sound vaguely appealing, like something my grandma siliconchip.com.au would have baked. But to those of us living here, they are anything but. When the mercury drops to -7°C of a morning, for example, one really appreciates having a well-insulated, well-heated double-glazed home. The rub is that most homes built here before, say, the 1980s are mainly uninsulated (apart from some having fibreglass insulating batts retrofitted into the roof over the living areas if you were posh). They typically have single-glazed windows, making them increasingly inappropriate for the temperature extremes we are now seeing in the summer and winter months. My parents’ ex-home, which we have just sold due to them not being here any longer, is a classic example. Mum and dad added insulation and better windows to their 1959-built house, where practical, while they lived there. But with no wall insulation, minimal roof insulation and originally just two back-to-back fireplaces to heat the whole house (eventually replaced with stand-alone electric heaters, then heat pumps), the home was very susceptible to heat and cold. It was sweltering in the summer and impossible to warm up in the winter. These days, it is increasingly important that houses be properly built and well-insulated. Not only is it a nicer place to be, but it is also a lot less expensive to heat or cool, especially given that costs of energy – whether electricity, gas or wood – are all going through the roof (pun intended!). Time for an upgrade Recently, the 35-plus-year-old Australia’s electronics magazine Items Covered This Month • ‘Playing’ with fire • TV remote control repair • Surround sound system repair • RS-485 network with • • intermittent faults Philips AE5230 radio repair Repairing two laptops that wouldn’t POST *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Masport LPG gas fire we inherited when we bought this house five years ago started playing up. The Masport range is well-known and seems to include pretty decent products. However, the model in our lounge was deprecated years ago and finding information on it turned out to be a challenge. The ‘modern’ Masport company has nothing relating to it on their website, not even giving it a listing in its ‘old bangers’ section. I eventually found, through a helpful forum post, a PDF service manual for it. With that, I could finally plumb the depths of what is still available for it parts-wise, which, as you can probably guess, is 5/8ths of less than nothing. So, the weather was getting colder, and our gas fire often wouldn’t start properly (which entails opening a valve to the ‘light’ position and pushing a piezo striker button repeatedly until it decides to work). When it did light, it performed poorly. September 2021  75 When we first moved in, one push would ignite it, and the valve was infinitely adjustable (according to the equally-spaced markings painted on the top of the dial) from a tiny flame to a roaring fire. It suited us perfectly, especially after moving from a pellet stove/fire in our old house which, while efficient and easy to manage, entailed lugging 20kg bags of wood pellets around. That increasingly became a downside for me over time [people pay good money to gyms so they can get exercise like that! – Editor]. However, lately, the fire’s gas valve had to be set to full before the fire would even start, and even then, we often gave up because it just wouldn’t go at all. With research (as is the serviceman’s way), I found the valve’s manufacturer, as that is where I suspected the problem lay. I then discovered that even if we could get one, it would cost around $600-700. I wasn’t keen on throwing too much money at this old fire, but probably would if it was likely to get it back into full working order. Calling in the experts In the end, I bit the bullet and called in a gas serviceman. I’d need a licensed gas guy regardless, and if nothing else, he could ensure our bottled LPG gas system (with two 45kg cylinders) was delivering the right amount of juice to the fire. We also have a gas cooking hob on the same line, and while that seemed OK, for troubleshooting purposes, one has to start somewhere... He had all manner of cool tools to do his work, especially the electronic stuff like digital manometers 76 Silicon Chip and differential pressure meters, all of which looked like something I could use! Now, I’m quite aware of people looking over my shoulder when I’m doing my thing, so I made sure to ask this guy if it was OK if I had a look at what he was doing and how he did it, purely out of professional interest. This wasn’t so I could try to do it myself in the future – working with gas is fraught with potentially lethal pitfalls for the amateur. And here I refer back to my opening statement; a few years ago, a house a couple of kilometres from here (as the crow flies) literally exploded because a gas fitting job wasn’t done properly, which created the colossal boom I’d heard and shook the ground. It was a miracle nobody was killed, but there were some serious injuries and a ton of collateral property damage, so I made a pact that I would never mess with such things. I merely wanted to look on and understand the system used in this house for myself. The guy did some typical pressure and flow tests and determined our bottle regulator, an ancient switchable gas valve that I thought could only be manually switched between bottles, was working but a bit iffy. For the relatively low cost of 150 kiwi bucks, it was well worth upgrading to a newer (and presumably more efficient) model. It also seamlessly auto-switches between bottles when one runs out, something the older one apparently should have done but never did, at least in my experience. That meant the old fire itself was the problem, and though he serviced it, it still sooted up and gave below-normal heat output. It was obvious we needed a new one. Australia’s electronics magazine The astute reader will realise there isn’t much electronics-related material in this column so far; here is where that all changes! It’s a gas, gas, gas Long story short (thank goodness!), we decided on a new gas fire. Though a different brand, the new version is essentially the same physical size but has a higher efficiency rating and overall heat output, so that’s a couple of boxes ticked already. It also bristles with electronics, and there is even an app and optional add-on that allows users to control it from anywhere with mobile phone coverage. I like it very much already! Another feature is the remote controller; this enables instant, singlebutton starting, fan speed control, on/off timer settings and even thermostatic control of the room temperature. A thermocouple that picks up the room temperature is clearly visible through a 1mm-round opening in the side of the remote controller. This is a double-edged sword, though; surely it would depend on where in the room the controller was sitting as to what temperature it picks up. The remote comes with a wall mount, which they recommend putting somewhere handy to the fire. However, common sense tells me that if I put it on the wall right behind the stove, it will be a lot warmer there than across the room, so it won’t have a good indication of the overall room temperature. I’ll have to think about this feature for a while... Installation was the next step for the serviceman. This also interested me, as it became evident as the process went on that I could have easily done this job, except for the ‘gas’ side of things, obviously. The practical side could be done by anyone reasonably competent with manual tools such as drills, concrete screws, wall plugs and the like. In fact, many of the fittings looked very similar to the hydraulic lines and fittings I would have used back in my airline days, and many of the flanging and sealing processes were very familiar. While I was reasonably confident I could have done all this, there was the nagging doubt that the house could explode if I messed it up, and I’m pretty sure the insurance assessor wouldn’t be overly impressed! Fair play! siliconchip.com.au I didn’t want that on my conscience anyway. Lending a helping hand (or 2) The serviceman who installed the fire was an older-school type, and while very adept at the mechanical side of the task, he seemed to be struggling a bit with the electrical/electronic side of things. It turns out he’d installed dozens of this type of fire, but none with the electronic modules fitted, and this obviously perturbed him a little. I offered to help where I could, and he was grateful, even naming me his ‘wingman’ in several telephone conversations he had with his colleagues. I doubted I’d be of much use, but helped out initially holding torches and keeping things steady in cases where a second pair of hands is most welcome. When it came to wiring it all up, I could see he was not that comfortable with the wiring diagrams and sparse instructions printed in the installation manual. The first problem I could see, and something I foresaw the day before as the guy was drilling holes in the concrete hearth for the fire mounting fasteners, was access to the electronics. While there is a manual ‘control panel’ in the bottom front of the unit, it isn’t very large. It appeared to me by reading through the manual that we’d eventually have to take the various electronic enclosures inside the fire out to work on them. With the fire bolted down, there was very limited room out back to remove this stuff. Surely, they could have printed the manual so that installers could do all this electronics-related work before the thing was installed. I suppose this is where experience comes in; the guy will know for next time, I guess. So mechanically, the fire was securely attached to the floor (a requirement now with quakes being what they are here), but we needed to tweak a few things before we could (ahem) fire it up. The first thing he had to do was convert the stove to run on bottled LPG gas rather than the natural (reticulated) gas it is initially configured for. That entails swapping several internal jets over with the supplied kit. It also had to be changed in the electronic controller, which by now was very difficult to get to. It just wouldn’t come out the siliconchip.com.au front, so we had to try to get it out via the back access panel. I eventually managed to finagle it out. After removing three screws, which doubled as cable clamps at one end of the industrial-looking plastic controller box, I could remove the top. Apparently, there was a ‘jumper’ in there that had to be set for LPG use, but the photos in the Xeroxed installation manual were woeful, making it very difficult to locate. As the installer guy admitted that he had never seen one and didn’t know what to look for, I volunteered for the job. With the usual holding of torches, twisting of bodies and lots of blue air, I finally found the jumper buried in the shadow of a heatsink of some semiconductor or other. Fortunately, it was identical to the typical computer motherboard or hard drive jumpers I’ve grown old with, so I recognised it as soon as I saw it. A set of curved long-nose pliers (supplied by me) enabled me to flip it around, and I set it on one pin only. I could have removed it altogether, but this allows any future owner (however unlikely that scenario is) to revert it to natural gas operation more easily. With the correct sticker applied to the lid of the enclosure (to show it had been converted for LPG use), I remounted the top, finding that in the meantime, all the cabling had expanded, so I needed longer screws. Once again, I went to my workshop to look in my parts bins; luckily, I have literally thousands of screws of all types saved over the years, and soon found three that were suitable. Once buttoned up, I could stuff the controller box back into the cavity. I tried to position it as far from anything hot as possible, and routed all the cabling into place as best I could, tying it back with cable ties (again supplied by me) where necessary. While the front panel was still open, the last thing was to put a digital manometer onto a tap by the main jet and adjust the low- and high-pressure settings for the flame. Then the acid test: with a single tap of the remote controller button, the electronic lighter crackled, and the fire lit up immediately. Flame up and down is just as smooth, and with thermostatic control, our gas usage should be much more manageable. What luxuries modern electronics give us! Australia’s electronics magazine Overall, I think the serviceman/ installer guy was pleased to have my help, but it is hard to know sometimes. We haven’t had the bill yet, so we’ll soon see how much he appreciated it! TV remote control repair B. P., of Dundathu, Qld came up with an unorthodox repair for a wornout TV remote control. You might not expect it to work, but it did, solving a common problem that plagues many old remotes... Several years ago, we picked up a 27-inch TCL TV at a charity shop. This fitted perfectly in our entertainment unit in the lounge room, replacing a more than 20-year-old CRT TV. This TV only has an analog tuner, but we were using it with a PVR that has a digital tuner anyway. The TV performed well for several years, but recently I noticed that it was getting hard to turn on. I had to hold down the power button on the remote hard for several seconds. This fault was at its worst during winter, so whatever was causing it was apparently temperature-sensitive. The remote control for the PVR has a mode where it can operate the TV, but it only provides limited controls. But at least it lets you switch the TV on and adjust the sound and picture. I tried this and found that the TV turned on straight away, so the fault was with the TCL remote control. I dismantled the TCL remote to diagnose it. Care needs to be taken when dismantling remote controls, as it’s quite common for the clips to break. In this case, though, it was quite easy to get it apart without any damage; I was able to use my thumbnail to prise the case apart. I inspected the circuit board and found it to be quite dirty from many years of use. I cleaned the circuit board and the rubber pad button contacts, and then I laid the rubber pads on the September 2021  77 circuit board and fitted the batteries to test it. Unfortunately, it still didn’t work correctly, suggesting that the conductive material on the pads had worn out. I decided to try putting some conductive grease on the pads to see if that would solve the issue. Being a retired motorcycle mechanic, I was fairly sure I would have some sort of conductive grease on hand, such as graphite grease or similar. I checked my workshop and found some copper-based grease, so I tried that. I smeared the circuit board contacts with that grease, then overlaid the rubber pad and worked the buttons to ensure that each button’s contact had a light covering of grease. After lightly wiping down both the circuit board and the pads, I reassembled the remote control and tested it. It was now as good as new, with just a light touch switching on the TV. Several months later, it’s still working well, so this was another successful fix using a simple solution. Surround sound system repair B. C., of Dungog, NSW is the type to help out friends by fixing their gear when it acts up. In this case, the receiver had already been ‘professionally’ repaired, but it still needed a lot of work to put right... It started as a simple request to reconnect all the surround speakers to Trevor’s LG DVD/VCR combo receiver (model LH-CX640W), a device with more accoutrements than your average house. Apparently, it had been repaired by a service centre in a larger town some time ago. After its return, it had only been reconnected to the television using an AV cable; the handful of speaker cables had been left unconnected at the back of the cabinet. When the cabinet was moved out away from the wall, a rat’s nest of very light gauge speaker cables was revealed. I decided to run all-new heavier gauge speaker cables and also to clip them up on to the floor joists (the old ones were dangling). The old cables were used as draw wires, and apart from two of the runs, there was enough crawl space to fit most of the cables without too much bother. I then connected all six speakers to the LG receiver and powered it up. Upon playing a DVD, the centre speaker and one rear speaker were silent. Tapping the top of the LG Combi Receiver would intermittently restore audio to these two channels. I disconnected everything again, took it to the kitchen table and removed the main PCB. I resoldered all the terminals on the speaker output block; some had obvious dry joints. After refitting the PCB, the machine was reconnected to the speakers. It now worked correctly on all six speakers, and I was confident that this would be the end to the sound problems. About a fortnight later, Trevor mentioned that when the receiver had been in use for a while, it would just stop working and the power indicator (red LED) would flash. If the machine was turned off at the power point and allowed to cool down, it would then recover and go back to normal operation. The day eventually arrived that the flashing red LED (signalling that the unit had gone into a self-protection mode) was a permanent feature. I went around to his place and removed the malfunctioning machine and took it back to my workshop. The machine was manufactured in 2005 and has two switch-mode power supplies on the PSU module (6870R8300AA). The main one supplies +12V, +5V and some other minor voltages, while the other supplies the +35V rail for the surround sound amplifier section. In common with most SMPSs, heat and time affect their reliability. I tested all the electrolytic capacitors with an ESR meter, getting a mixture of readings from high to none, particularly on the smaller value electros. These included C173, C175 & C176 (all 4.7µF/50V) and C115 & C125 (10µF/50V).There were also some high-ESR electros on the main PCB: C121, C137 & C138 (all 47µF/50V), all near voltage regulator IC’s. Having replaced those, I also replaced the following resistors with 2W metal film types: R104, R105 and R108 (the 220kW start-up resistors), R121 & R130 (both 100kW bleed resistors) and R138 (the 180W bleed resistor for the +5V rail). The PSU module was refitted into the machine and then powered up. The problem was still there! I downloaded a data sheet for the STRW6753 (power supply IC 104) and looked at the sample circuit diagram. I decided to order this IC on eBay as the next move. The IC arrived in the mail, and I fitted it, but it still did not fix the problem! There was still something not quite right. On a hunch, I decided to desolder one leg on every fast rectifier diode in the main power supply section. I then tested these for reverse leakage set on the multimeter’s highest ohms range. When I tested D129 on the +5V rail, it had some reverse leakage. It was a B10A45V fast diode, so I substituted one MURF1060 (10A 60V fast diode). It then worked correctly and did not miss a beat! After another two days of soak testing, I was confident that the power supply problem was finally fixed. Trevor was so pleased with the result that he bought me a carton of ginger beer and shouted the missus and I lunch at a nearby pub. RS-485 network with intermittent faults N. L. of Taylors Lakes, Vic, had to fix an RS-485 network which was having some odd problems. It turned 78 Silicon Chip Australia’s electronics magazine siliconchip.com.au out to be a part that you wouldn’t expect to be at fault... I was called to a network using an RS-485 physical layer (cable and interface cards in each machine) with 25 machines per segment and two segments. The two segments were connected by a network controller which polled each machine by their assigned network number, one at a time, up to the last machine numbered 25. The network controller was connected by USB to the PC, and then connected to the internet. The initial fault was that random nodes were not responding to the network controller at various times. This occurred on and off for months, and could not be isolated to a specific machine. Then the faults became permanent on one node in both segments. The cable was a 300W shielded pair, but the shielding was not connected continuously from one length of cable to the next or terminated on the network controller Earth either. One blessing the installer bestowed on the system was the 120W termination resistors were attached at the last machine on each segment. Swapping network boards, it was found that the network boards (two boards) on one machine in each segment were faulty. Back at the workshop, testing showed the boards to be working perfectly. I decided to change the line interface chip as they probably get a hiding from the cable. But the fault was still present with the boards reinstalled; luckily, I only changed it on one board. Back at the ranch, I hooked up the Silicon Chip Digital Audio Signal Generator (March-May 2010; siliconchip. com.au/Series/1) to deliver a square wave and noted that at the output of the line interface IC I had changed, it worked properly. Still, the digital receive signal was not present at the network board output. Between the MAX3062E line transceiver chip and the digital output to the machine microcontroller was an HCPL-2200 high-speed opto-coupler with a TTL output which was failing as the switching rate increased. Of course, replacing the opto-couplers solved the problem on both segments. I also re-cabled the longest segment with the correct 120W RS-485 cable with a continuous shield, using the original cable for the recommended reference point connections. Being differential, I am not sure what the reference point connection does. My theory is that it protects the line transceiver IC when one node powers down; any line over-voltages can dissipate into the powered nodes supply instead of through the unpowered transceiver’s internals. I welcome comments on that. I am now waiting to see how long the incorrect cable lasts before it gives errors. The customer (and the installer, whom I know) insists that I am wasting time and money replacing the cable since the existing one “works OK”. POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support Philips radio repair G. McD., of Jindalee, Qld got angry at his radio when it began resetting intermittently. Thankfully, he managed to calm himself down long enough to find the dodgy connection and fix it... My patience was pushed to the limit recently when my trusty Philips portable FM/DAB radio, an AE5230 model, shut down on me for the umpteenth time early one morning. siliconchip.com.au SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au Australia’s electronics magazine September 2021  79 All I was doing at the time was trying to increase the volume. The LCD screen died immediately, then after what seemed like a full thirty seconds, it lit up once more as details of the pre-tuned station began flickering across the screen. I barely avoided flinging the radio across the room in frustration. It had been acting like a temperamental teenager for months. Later that morning, I decided that enough was enough; it was time to see if I could fix the pesky thing. The first suspect was the DC jack at the back of the radio. Close inspection with a headband magnifier showed nothing obvious. So I had to open the radio up and delve a little deeper. I removed five retaining screws from the rear of the radio’s enclosure, allowing me to take off the back panel. I then identified the screws that held the main PCB in place. I removed these and unclipped the main power lead. The on/off switch was now clearly visible. I removed the two small securing screws holding the PCB upon which it was mounted. With the aid of a strong lamp and my headband magnifier, I inspected the condition of the three wires soldered to traces on the PCB. What I saw wasn’t pretty. The solder joints looked as though they had seen better days, and the wires were coated with some kind of dried goo. After desoldering the three wires (red, white and yellow), I cleaned up the through holes on the board with the aid of a solder sucker and refurbished the ends of the wires. I then cleaned up everything and soldered the wires back into place, and returned everything to its original position. I plugged in power and hit the on/off switch. All appeared to be working as it should, so I set it up once more on my bedside table. But the next morning, around 4:00AM, the radio spat the proverbial dummy once more. It was up to its old tricks, I thought, as I began pondering my next step. The problem had to lie with the power supply; I had been trying to adjust the volume at the time and in so doing, had moved the radio slightly to see the dial better. The DC jack was now my prime suspect. I placed the radio back on my workbench early the next morning and opened it up again. The DC jack is 80 Silicon Chip held in position in much the same way as the on/off switch, on its own PCB that is held in place by two small screws. Once I had removed them, it was an easy task to slide the PCB out for inspection. Under a strong light and with the aid of my headband magnifier, I noticed one of the soldered mounting pins had a hairline crack around its base. It was immediately evident that this was a result of stress from the slight sideways movements caused every time the plug is inserted or removed. All I had to do was re-solder the connections and put everything back together again — a simple fix to a problem that was not so simple to find. The radio has behaved itself ever since. Repairing two laptops that would not POST K. D., of Chermside, Qld, writes: in a previous Serviceman column (August 2014, page 61), I stated that I don’t believe in coincidences. Following some recent incidents, I might have to change my mind. A friend at a university biochemistry laboratory told me that two large ultrahigh-speed centrifuges in her laboratory both failed at switch on, within minutes of each other. Both emitted smoke and would need repair by the manufacturer’s technicians. The next day, at my workplace, two identical and quite critical refrigerators failed within 24 hours of each other, having not missed a beat in over five years. The third coincidence involved me, the same friend, and both of our home computers. It happened only a week after the coincidental failures at work. One night, my ageing Dell Vostro PC simply shut off mid-use. When I attempted to restart it, the fans all spun up, but that was it. The computer could not even generate a beep code from the power-on self-test (POST). As I was working at the time, I decided to leave any further investigation until I had a few days off. Before I could look at my PC, my friend called to say that her equally old Dell Inspiron PC wouldn’t switch on. This was worrying as she didn’t even remember when the computer was last backed up, or where the backup was stored. When she brought it to me, the symptoms were identical to mine – the power indicators were on, and the fans were spinning, but the PC wouldn’t even get to the POST. Australia’s electronics magazine I decided to tackle her Inspiron first. I checked the voltages from the power supply, and all were within specification. As the fans ran and responded to the power button, the motherboard couldn’t be completely dead. I disconnected everything possible from the motherboard and removed the memory modules and graphics card. The machine could still not get to the POST. On the off-chance that the BIOS had been corrupted, I removed the CMOS battery and turned on the power. At last, the machine gave four beeps, indicating that there was no memory. I fitted a new CR2032 cell and reconnected everything I had disconnected. The computer told me the BIOS had been changed and that the date and time were invalid. I was prompted to press ‘F1 for defaults’ or ‘F2 to setup’. I pressed F2, and the PC hung with an “ME unconfiguration in progress” message. ME means the management engine for the BIOS. This behaviour was reproducible when turning the computer on and off – pressing F2 wouldn’t get me into the BIOS. After the first power cycle, though, I had an option of pressing F12 for boot devices. Pressing F12 got me into the BIOS. All the settings looked usable except for the date and time. After setting those details and a ‘save & exit’, Windows started normally, and the computer was fixed. It was sent back along with some unparliamentary language about the need for regular backups. My Vostro has had a hard life, but it had the same symptoms as the Inspiron and I hoped it also had the same easily-fixed problem. So, I removed the CMOS battery and applied power, and that is where the similarity with the Inspiron ended. The computer still would not reach the POST. I progressively removed parts and applied power each time. When I removed the four 2GB memory modules, the POST test ran and indicated that the memory was missing. I fitted four replacement modules from a defunct Vostro obtained from a friend and reconnected everything. Pressing F2 at startup allowed me to reset the date and time in the BIOS and check that 8GB of memory was being detected. Windows then started normally, and another veteran computer was returned to service. SC siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s siliconchip.com.au Australia’s electronics electronics magazine magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au eptember2021 2021  81 FSEBRUARY 37 Micromite to Smartphone Connector via Bluetooth By Tom Hartley This project demonstrates how to use a Micromite as the heart of an IoT (Internet of Things) device. But there are many other reasons you might wish to connect a Micromite to your Android smartphone, such as making it easy to monitor what your device is doing without going to the trouble or expense of fitting it with an LCD screen. It also makes it really Phone Image Source: easy to control the software running on the Micromite. Android Open Source project T he Micromite Mk2 (January 2015; siliconchip.com.au/Article/8243) is a great way to get into programming microcontrollers, because you need so little to get it up and running, and the BASIC language it uses is easy to learn. But to make the most of it, you really need some sort of screen. That’s why the Micromite LCD BackPack series (starting in February 2016) has been so popular. It combines the Micromite with a colour touchscreen, giving you an easy way to interact with the device and display information. But that arrangement is considerably more expensive and complex, and a separate screen isn’t always required. The Circuit Notebook section of the May 2015 issue (siliconchip.com.au/ Article/8395) showed how low-cost Bluetooth modules could be used to allow two Micromites to communicate without wires. But what about using such a module to interface with a smartphone? That way, the phone becomes the user interface to the Micromite, so you can get away with a much simpler and cheaper arrangement – assuming you already have a suitable phone. And since smartphones generally have a connection to the internet, the Micromite can become an IoT (internet of things) device and easily share data with other devices. This article explains how to connect a bare Micromite chip to an Android mobile phone to communicate and 82 Silicon Chip display data without using a screen. You can even communicate with the Micromite’s terminal output data stream using an Android app, sending it BASIC commands and so on. Basic arrangement After programming a 28-pin Micromite chip via the conventional PC USB connection, I was able to disconnect it from the PC and transmit the Micromite’s terminal output data stream over Bluetooth to an Android App, running on an inexpensive mobile phone. The design requires very few components: 1) A smartphone running some version of the Android operating system. 2) A 28-pin Micromite PIC chip loaded with MMBasic, and a tantalum or ceramic capacitor for the Vcap pin, as recommended by Geoff Graham. 3) An HC-05 Bluetooth module, preferably one with an Enable pushbutton key. 4) A USB to TTL converter (eg, one based on the ubiquitous CP2102 chip). 5) A short USB extension cable. 6) A BMP180 atmospheric pressure sensor (for this particular demonstration application). 7) A four-AA battery holder modified by tapping the output voltages at 3V and 4.5V. The fourth cell is not needed, so that position can be left empty. 8) A small piece of Veroboard. 9) Some hook-up wire. Bluetooth module setup The first job is to configure the Bluetooth module as required by this Fig.1: the HC-05 Bluetooth transceiver module is wired up to a USB-UART bridge and battery pack so that the Bluetooth module can be set up using a PC. Australia’s electronics magazine siliconchip.com.au project. The HC-05 Bluetooth module has many similarities to a modem, and the procedure to set it up will be familiar if you have ever set up serial communications to a modem. Before you can do this, you will need to install a serial terminal program on your computer. For Windows users, Tera Term appears to be the most favoured. For Linux users, the PuTTY SSH Client is recommended. Download and install this software. Now we need to send the Bluetooth module the appropriate commands to set up the baud rate etc. These are sent as ‘AT’ commands. To do this, you have to connect the module to your computer as per Fig.2. Connect the USB-serial adaptor, HC-05 Bluetooth module and battery pack as shown in Fig.2. Start the terminal program on your PC and plug the USB to TTL converter into a convenient USB port. This will power up the USB to TTL converter but will not power up the HC-05 module. The terminal software will require information about which USB port it should connect to. You can find this in Windows using the Device Manager. In Linux, when there are no other USB devices plugged into the computer, then the usual USB port is /dev/ttyUSB0. Once you have set that, hold down the button on the HC-05 module and turn the switch on the battery box to the ‘ON’ position. Wait a couple of seconds before releasing the button. The red LED on the HC-05 module should flash slowly. Now type “AT” on your computer terminal program and press Enter, the module should respond with “OK”. If it does not, there is probably a baud rate mismatch so check that the terminal is communicating with the HC-05 at 9600 baud, 8 bits, no parity, one stop bit, no flow control (often described as “8-N-1”). Also, the Enter key on your PC must be mapped as a carriage return plus line feed, usually signified in the terminal software as CR/LF. The other baud rate to try is 38,400. Different manufacturers have different default baud rates on first use. Once you get the OK, you can proceed to enter these two commands: AT+UART=38400,1,0 AT+NAME=MMITE01 You should get an OK after each one. siliconchip.com.au Fig.2: you need to change some settings in the HC-05 Bluetooth module before using it, via serial commands from a computer. This is how you can connect it up in order to do that. The suggested wiring is in Fig.1. Fig.3: this minimal circuit is all you need to load the MMBasic firmware onto a PIC32, turning it into a Micromite. You can save yourself the hassle by getting a pre-programmed chip from our Online Shop. If you don’t, you might have a different version of the HC-05 Bluetooth module; see the panel below. Next, check that the settings have been recorded by typing “AT+UART” and pressing enter, which should provide the response “38400,1,0”. Then type “AT+NAME” and press enter; you should give the response “MMITE01”. Power off the circuit and install the HC-05 in the test rig described in the next section. Next, install the Bluetooth Terminal app by Kai Morich on the smartphone. You can download it from siliconchip. com.au/link/ab8y Building the circuit Fig.3 shows how to load the firmware onto the PIC32 chip using a PICkit if it is not already loaded (or you can purchase a pre-programmed microcontroller). Fig.4 is the minimal circuit to build so that you can interface with the Alternative versions of the Bluetooth module We have seen online sellers listing various versions of the HC-05 including the “original” version (likely the one described in this article), a “new” or “revised” version and the HC-06. We ordered some of the new/revised HC-05 modules to try out. They look much the same as the original HC-05, and if you order one from a seller who doesn’t make the distinction, that may well be the one you receive. The new/revised version worked as described in this article, except that it did not respond to the “AT” commands listed in this article at all. However, it seemed to default to 38,400 baud, so we were able to communicate with a Micromite simply by wiring it up and setting that as the baud rate. We haven’t tried the HC-06, but chances are it works much the same way. You might just need to experiment with the baud rate if you cannot communicate with it after selecting 38,400 baud. Australia’s electronics magazine September 2021  83 Fig.4: the minimal circuit to communicate with the Micromite over USB, using a USB/Serial adaptor. Fig.5: by adding a BMP180-based temperature/pressure sensor module as well as the HC-05 Bluetooth module to the Micromite, we can turn it into something useful. It now reports atmospheric data on the smartphone screen via a terminal App. The test rig connected to a Micromite Explore-28 which was built on a breadboard. This setup should easily work with the Micromite BackPacks and Explore-28, assuming the requisite pins are free. 84 Silicon Chip Australia’s electronics magazine Micromite running MMBasic. However, you won’t be able to do much with such a basic configuration, so we will describe how to get the circuit shown in Fig.5 up and running. This includes a BMP180 temperature/ atmospheric pressure sensor so it can actually do something useful. Note that with the Tx/TxD lines of the two serial modules in parallel, you can only have one active at a time. That's assuming that the inactive module is not driving its Tx line actively, which is the case with the HC-05 and USB-serial modules I used, but might not be true for all such devices. If both Tx lines are active at the same time, it's unlikely anything will be damaged (although not impossible), but it certainly isn't going to work as they will fight each other. While Fig.4 shows both a USBserial and Bluetooth adaptor, you don't need both; the USB-Serial module is intended mainly for testing and can be left off once you're confident that the HC-05 is working. Also, you don't need to connect the BMP180 module; it's simply there to demonstrate what you can do. Modify the circuit to suit your requirements. The BMP180 sensor communicates using an I2C serial bus, so it is connected to pins 17 and 18 as shown in Fig.5. It also needs a ground connection and a +3V connection. As before, the 4.5V tap on the battery pack is only required to run the HC-05 module. Connect the test rig setup to your PC and terminal program via the USBTTL converter. We have based the software for this demonstration project on the program written by Jim Rowe for the December 2017 article on the GY-68 module with the BMP180 chip. It can be found at siliconchip.com.au/Shop/6/4521 The revised version is named “BMP180 barometer check prog console only.bas” and is available for download from the Silicon Chip website associated with this article. The only real change is that all lines which pertain to formatting and/or displaying information on the LCD screen have been removed. Instead, it simply prints the data obtained from the BMP180 chip on the console using PRINT commands. Run the program and confirm that it all performs correctly in the usual PC terminal mode. Then shut down the PC terminal and unplug your test rig from siliconchip.com.au the PC’s USB port. Install the Bluetooth Terminal App on your mobile phone (if you haven’t already). Power up the test rig. Notice that the red LED on the HC-05 module is flashing rapidly. Follow the instructions for connecting a Bluetooth device to the Bluetooth Terminal App on your phone. The steps involve registering the HC-05 in your phone’s Bluetooth devices list. It will first show up as an alphanumeric address similar to an IP address but segmented into several pairs of hexadecimal characters. Once you provide the password of 0000 or 1234, your HC-05 should then appear on the list as MMITE01. Now return to the Bluetooth Serial App on the phone and connect to the MMITE01 adaptor. Successful connection to the HC-05 will be detectable by the flashing LED having slowed down considerably. The App should also display precisely what you have previously seen on your PC’s terminal program. If not, turn the test rig off and on again. When you turn off the test rig, the Bluetooth Terminal App will report it has lost the connection. Just tap on the connect icon in the App, and it should reconnect without any further need for your inputs or adjustments. Screen 1 shows a typical display on the mobile phone when connected to the Micromite via Bluetooth. This particular App can log received text, so data coming across from the test rig can be saved. Another advantage of using this particular Bluetooth Terminal App is that it adds the current date and time to every line of data received, making it unnecessary to build an RTC module into your circuit. In fact, now that the data is in your phone, you can exploit the fact that your phone is, in reality, a very sophisticated computer and display resource. For example, you can now write your own Android Phone Apps using MIT App Inventor (ai2.appinventor. mit.edu) because that tool has a Bluetooth connectivity module as a standard built-in item. See our article explaining how to use App Inventor in the February 2021 issue (siliconchip. com.au/Article/14750). Python programs run well on mobile phones, so that provides another opportunity for enhancing the usefulness of your data collected by the Micromite. Another possibility is to install a web server on your Android phone, such as KickWeb (siliconchip.com. au/link/ab8z). That way, you can use PHP scripts or continuously looping Python programs to forward sensor derived data to services such as Thingspeak (www.thingspeak.com) where your data can be displayed graphically and made available across the SC whole internet. That time of year is nearly here... CHRISTMAS Spice up your festive season with eight LED decorations! Tiny LED Xmas Tree 54 x 41mm PCB SC5181 – $2.50 Tiny LED Cap 55 x 57mm PCB SC5687 – $3.00 Tiny LED Stocking 41 x 83mm PCB SC5688 – $3.00 Tiny LED Reindeer 91 x 98mm PCB SC5689 – $3.00 Tiny LED Bauble 52.5 x 45.5mm SC5690 – $3.00 Tiny LED Sleigh 80 x 92mm PCB SC5691 – $3.00 Tiny LED Star 57 x 54mm PCB SC5692 – $3.00 If possible you should try to purchase a HC-05 module which has an “Enable pushbutton” key, as shown at the upper left of this photo. This specific HC-05 is a HiLetgo branded version. siliconchip.com.au Screen 1: a very basic display of local barometric pressure (in hectopascals [hPa]) in the smartphone terminal app, delivered by the Micromite. By changing the Micromite BASIC code and hardware, you can get it to report just about anything you want! Australia’s electronics magazine Tiny LED Cane 84 x 60mm PCB SC5693 – $3.00 We also sell a kit containing all required components for just $14 per board ➟ SC5579 September 2021  85 Allan Linton-Smith reviews an $80 ebay “bargain” tinySA: a 0.1MHz to 960MHz Spectrum Analyser I bought this “tinySA” spectrum analyser/signal generator on ebay for just $80 including delivery! It is a standalone device which can be connected to a computer for recharging and reprogramming. W hile oscilloscopes are used to measure and view signal amplitude (voltage) vs time, a spectrum analyser is used to measure and view a signal amplitude vs frequency. Like oscilloscopes, over time, cheaper and smaller spectrum analysers are becoming available. When I spotted the tinySA for sale, I had to get one as I use spectrum analysers often, and I wanted to know if a device this cheap was any good. It is a standalone device and is connected to a computer or USB charger. It can be programmed using tinySA software from www.tinysa.org/wiki/ It arrived neatly packed in a cardboard box with a lid and included two SMA cables, an SMA female-female converter, a small 10-30cm telescopic antenna and a USB Type-C charging cable. It comes in a nice little pocket-sized black enclosure and has two SMA connectors; one is the high-frequency input 86 Silicon Chip or output (260-960MHz), while the other is the input or output for lower frequency signals, down to 100kHz. It does not have a tracking generator; it is merely switched between analysis mode or generator mode. However, it can be used for plotting RF frequency response using the “max hold” setting and an external sweep generator. It worked straight out of the box. It’s remarkably accurate too, and we didn’t even have to charge it straight away. RF Spectrum Analysers are usually very expensive devices, often costing thousands of dollars (even old preloved ones). Australia’s electronics magazine So for $80, this seems like an excellent deal. And while some cheap modules we’ve tried either didn’t work at all or instantly self-destructed, this one gave useful readings immediately. Using it If you have ever used a “real” benchtop spectrum analyser, you will know that they may need a significant warm-up time and a lot of setting up. But this one required almost no adjustment. The resolution bandwidth (RBW) and reference level were set automatically, and the instrument discovered a signal immediately! Spectrum analysers definitely require a bit more ‘tuning’ than an Oscilloscope, but this little device makes life easy. Except for RF enthusiasts, most of us don’t really need an RF spectrum analyser all that often. But when you need one, you need it. So it makes sense to not spend heaps on a benchtop unit which will just be gathering dust for 99.9% of the time. siliconchip.com.au So if you are an experienced spectrum analyser operator, you will be able to use this device straight away. If you are a beginner, we will get you started with a few easy examples and practical applications. It sounds simple to use a spectrum analyser, but you need to set up some basic settings such as the frequency range you wish to examine and the resolution you require to analyse signals which may be close together. For example, if you wish to view an AM signal modulated with a 10kHz signal, you must use an RBW (resolution bandwidth) less than 10kHz. Otherwise, you will only see the carrier frequency and not the sidebands. Many readers will be familiar with modern oscilloscopes which can automatically set and display a trace. But with spectrum analysers, you have to tell it which signal or band (amongst many) you wish to examine. If you know your signal is around 10MHz, then you just set the centre frequency at 10MHz and the span for say 2MHz. Features & specifications • Low-cost, compact device. • Spectrum analyser and signal generator modes (cannot be used at the same time). • Two spectrum analyser inputs: MF/HF/VHF (0.1MHZ-350MHz) and UHF (240-960MHz). • Selectable resolution bandwidth (RBW) for both inputs, 2.6-640kHz. • Colour display showing 290 scan points up to the full low or high frequency range. • Input step attenuator of 0-31dB for the MF/HF/VHF input. • Two signal generator outputs: MF/HF/VHF sinewave output 100kHz to 350MHz; UHF square wave output 240-960MHz. • Automatic self-test and low-frequency input calibration. • USB socket allows it to act as a PC-controlled spectrum analyser. • Rechargeable battery lasts at least two hours. A marker will appear, telling you the exact frequency of the strongest detected signal in that range, and its amplitude. This particular instrument has a specified range of 100kHz to 960MHz, which will meet most hobbyists’ needs. But it has some limitations that you need to be aware of. Limitations For a start, you must be careful what you hook up to its inputs. The signal level cannot exceed 10dBm or 700mV AC (10mW into 50Ω), or you could damage it. Importantly, you also need to avoid applying any DC voltage to the inputs. Spectrum analysers are really sensitive devices, so it’s a good idea to always use it with an external attenuator until you are sure the signal is safe for a direct connection. SMA 20dB attenuators are available Here the “Tiny SA” is measuring a -30 dBm signal from an RF generator at 300.1MHz. The centre frequency was set at 300MHz and the resolution bandwidth set at 362KHz. The scan took 132 milliseconds to complete. siliconchip.com.au Australia’s electronics magazine September 2021  87 The tinySA’s display when fed with a 25MHz -30dBm carrier with 10kHz, 50% amplitude modulation. RBW was automatically set to 3.1kHz, its best resolution. The delta reading is 10.047kHz, and the carrier is shown as -28.7dBm, which is pretty good accuracy. We used this low-cost, low-noise RF preamplifier in combination with the tinySA analyser to detect signals down to -125dbm. That is about the minimum signal which expensive benchtop analysers can detect. for around $20 on ebay and similar sites. The displayed average noise level (DANL) is -105dBm, and that is the lowest detectable signal level. This changes depending on the resolution bandwidth. A lower bandwidth setting gives a lower noise level. More expensive spectrum analysers can often digitise a broad frequency range at once using an FFT (fast Fourier transform) technique. But the tinySA uses a resolution filter which is swept across the desired frequency range (just like tuning a radio). The oscillator that does the sweeping, together with the power detector that measures the signal power, require some settling time, and the scanning speed of the tinySA is limited. The narrower the filter, the more time it needs to settle. The fastest scanning speed occurs with RBW set to 300kHz or wider, and is about two scans per second. But with increased frequency span and/or decreased RBW, the scanning speed decreases. For example, a scan from 0-350MHz with RBW set to 10kHz takes about two minutes. Also, due to the low cost and very small form factor, you will find that the analyser sometimes develops spurious peaks called ‘spurs’ which can be attenuated by various settings, such as “spur reduction”. Other limitations are the lack of resolution bandwidth settings below 3.1kHz, and that signals in close proximity are impossible to resolve. The same signal as above, but fed to a more expensive spectrum analyser with ten times better resolution. The result is smoother and more accurate. This instrument weights 28kg, though, so it isn’t easy to hold in one hand! The tinySA’s start and stop frequencies were set to 88MHz and 108MHz, and the supplied 30cm aerial connected to capture FM radio stations in Sydney. In waterfall mode, each peak is recorded, and you can see the regular intervals between stations. The marker sits on the most powerful radio signal, 104.12MHz (2DAY FM). 88 Silicon Chip Conclusion While the tinySA is a handy little instrument, it is a bit limited compared to a bigger, more expensive spectrum analyser. As they say, there ain’t no such thing as a free lunch! Still, if you don’t have a spectrum analyser and don’t want to spend lots on buying one, it would be a great choice to start in the field of frequency domain analysis. SC Australia’s electronics magazine siliconchip.com.au The tinySA was fed with a 1MHz signal from a function generator, and a THD (total harmonic distortion) measurement was made. This shows the THD for the oscillator as 0.2%. This measurement was made by averaging 16 traces. The display is difficult to read because the other measurements partly obscure it, but it is handy all the same. Silicon Chip Binders REA VALU L E AT $19.50 * 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? A 1MHz signal from a function generator was analysed using the “harmonic” measurement setting, rather than the THD setting, and the results are a bit more revealing. The first harmonic is shown as -60.5dB and the second harmonic as -57dB below the fundamental. Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover The tinySA’s signal generator was set to 10MHz -15dBm and fed to a benchtop spectrum analyser, and here is the resulting plot. The first harmonic is -56.2dB, and the second harmonic is -46dB relative to the fundamental. That’s almost as good as our benchtop function generator! siliconchip.com.au Silicon Chip Publications PO Box 139 Collaroy Beach 2097 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. Australia’s electronics magazine September 2021  89 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. Multiple RAM banks for the IR Remote Control Assistant 90 Silicon Chip Australia’s electronics magazine siliconchip.com.au I liked the idea of recording macros using your IR Remote Control Assistant (July 2020; siliconchip.com.au/ Article/14505), but I wanted more than eight buttons so that I could merge several remote controls into one. As I could not change the firmware to add extra buttons, I decided to switch the RAM chip instead. Each chip holds IR code sequences for up to eight pushbutton switches. To do this, I added a small PCB (34 x 31mm) which sits over the existing PCB and holds the extra RAM chips, plus a switch to select which one is in use at any given time. There is a choice to expand the Remote to 16 buttons, using a DPDT switch (S2) and one more RAM chip (IC3), or 24 buttons, using a 3PST switch (S1) and two extra RAM chips (IC3 & IC4). The PCB has provision for either switch, as shown on the circuit diagram. The 100kW resistors pull the unused RAM chip CS lines high, disabling the unused chips and maintaining the low current drain on the battery. Switch S1 or S2 pulls one CS line low at a time, enabling the selected chip. The Gerber files for the add-on board can be download from siliconchip. com.au/Shop/10/5913 Robbie Adams, Tauranga, New Zealand. ($100) The IR Remote Assistant PCB needs the track cut between pin 10 of IC1 and pin 1 of IC2. This location can be seen in the diagram at right. The addon PCB is then seated on top of this main PCB, as shown above. Solar garden light uses supercapacitor We purchased quite a few solar garden lights which each have a small solar panel and a battery to store the energy collected during the day, powering a small LED for 5-6 hours at night. These worked well for one year, then the battery started deteriorating, and finally it stopped working altogether. So I thought, why not replace the battery with a supercapacitor? From a good supercapacitor, you can expect a lifetime of 20 years, irrespective of the number of charge cycles while a storage battery has a maximum life of 2000-5000 cycles. I built this circuit with three LEDs, and it runs for a whole night without totally discharging the capacitor. The supercap is charged from the cell via schottky diode D1, which was chosen due to its low forward voltage drop. While there is voltage across the cell, siliconchip.com.au PNP transistor Q1 is held off as its base is pulled up close to its emitter. At night, current can flow in reverse through the cell. D1 stops the supercap from discharging through this path, but the base current for Q1 flows through the 5.6kW resistor and the cell, powering the LEDs. The 470W resistor limits their current to around 4mA ([5V – 3V] ÷ 470W). All the components cost me less than $4. Editor’s note: keep in mind that the energy storage of the supercap is considerably lower than even a relatively small rechargeable battery. While the LEDs probably will produce light for many hours, they will be quite dim after about one hour, with the current dropping from about 4mA initially down to around 1mA after 60 minutes. Bera Somnath, Vindhyanagar, India. ($80) Australia’s electronics magazine September 2021  91 1-2-5 switching arrangements Many instruments offer adjustment in period or frequency range in 1-2-5 steps across a single decade as a knob or switch is changed. It is usually followed by a 10-20-50 in the next decade and so on through subsequent decades. The 1-2-5 relationship makes sense as it approximates a geometrical progression across the decade with just three steps, with the step multipliers being 2x, 2.5x and then 2x. As the period for monostable and astable circuitry is determined as a product of some factor times a resistance, it would be helpful to have a simple way to create resistance values inversely proportional to these steps. This can be done efficiently with either a centre-off single-pole toggle switch or a 3-pin header with a single jumper/shorting block. With the switch set to centre off (or the link removed), the only component connected between IN and OUT is the 5kW resistance. With the switch in the up (or link 1-to-2) position, the 5kW resistance is in parallel with the 3.333kW resistance, giving 2kW. With the switch in the down position (or link 3-to-1), the 5kW is in parallel with 1.25kW for an equivalent value of 1kW. Sourcing accurate 5kW, 3.333kW and 1.25kW resistors is not easy. But if we use a total of 13 resistors of the same value, we can get theoretically 13 100kW resistors soldered to a toggle switch, giving 1-2-5 resistance steps. Simple tripwire alarm I wanted an alarm that was so simple that (almost) anyone could use it without instructions. The result is a simple yet versatile circuit that stopped an intrusion into my car in its first week of use. It activates a powerful siren (the load, between C and D) for 70 seconds if someone disturbs a wire, ie, if the circuit is broken between points A and B. This can be multi-strand wire with bared ends twisted together, making it easy to separate. Alternatively, a piece of string may be tensioned such that it separates the wire when flexed. With the tripwire intact, the charge Circuit Ideas Wanted 92 Silicon Chip across the 3300μF capacitor is limited to less than 1V by the current flowing through diode D1. This is insufficient to switch Mosfet Q1 on, and Mosfet Q2 is held off by the tripwire keeping its gate voltage low, so the siren is not powered. Once the circuit is broken between A and B, the gate of Mosfet Q2 is immediately pulled up by the 100kW resistor and the siren switches on. The 3300μF capacitor can then charge, and eventually the gate voltage of Mosfet Q1 rises high enough to switch it on, pulling the gate of Q2 low and silencing the siren after about 70 seconds. Connect points A and B again, and perfect values by arranging them in parallel sets. We can create the 5kW value with two 10kW resistors in parallel, the 3.333kW value by putting three 10kW resistors in parallel and the 1.25kW value by putting eight 10kW resistors in parallel. As 1% resistors are cheap, the only real disadvantage of this method is the space required. If a single-pole centre-off switch is used, all these resistors can be soldered to the appropriate terminals of the switch on a front panel, and this makes it a simple way to change the period (or frequency) by a factor of 1, 2 or 5 with just one switch. Fewer resistors can also be used if you’re willing to accept slight errors. For 3.333kW, you can use 3.9kW in parallel with a 22kW (an error of just 0.6%). For 1.25kW, we can use 1.5kW in parallel with two 15kW resistors, which is an exact match. You can also scale all the resistor values by the same amount, eg, use sets of 1kW or 100kW resistors instead of 10kW. The accompanying photo shows 13 100kW resistors soldered to a toggle switch as suggested above. Barry Moore, Minto, NSW. ($80) without a squeak, the circuit is ready for another round. In the interests of simplicity, I wanted an alarm without an on/off switch or reset switch. If desired, one may simply clip the circuit onto a 12V battery, and it is ready to go. Three possible scenarios are shown below the circuit diagram. In the first, the alarm is powered up, the tripwire broken and the siren sounds for the full 70 seconds, then times out. The second is identical except that the tripwire is reconnected before the timeout, and the siren is immediately silenced. In the third case, points A & B are never connected, and power to the circuit is simply switched on to power the siren for a fixed period. 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 Letterbox counter This circuit starts counting when someone inserts a letter in the letterbox at your home or office. It is designed to save you time from going to the letterbox to check if there are letters inside. The number of letters present in the box is indicated on a seven-segment display. It uses a white LED (LED1), an LDR, a 555 timer (IC1) in monostable mode, a 4033 seven-segment driver chip (IC2) and a few other components. LED1 and LDR1 together work as a sensor. The resistance of LDR1 changes in accordance with the intensity of incident light on it. When light from LED1 falls on LDR1, its resistance is low. So when the light beam is broken, the voltage at pin 2 of IC1 is low; otherwise, it is high. When a letter is inserted into the letterbox, it passes between LED1 and LDR1. This change in resistance provides a triggering pulse to pin 2 of IC1, generating a short-duration pulse at its output pin 3. This pulse acts as the clock input for the 4033 counter and display driver, IC2. The output pins of IC2 are connected to various segments a, b, c, d, e, f and g pins of the seven-segment display, with the common pin of the display connected to ground. Each segment has its own current-limiting resistor for consistent brightness. When a letter is delivered to the letterbox, LED2 momentarily glows, which indicates that a letter is received, and the displayed count increases by one. When the counter reaches nine, it resets to zero and the cycle repeats. Switch S1 is used to reset the counter when you fetch the letters. Raj. K. Gorkhali, Hetauda, Nepal. ($60) The gate threshold voltages of Mosfets Q1 and Q2 are fairly critical. To avoid complications, I chose identical transistors. Even so, component tolerances may vary. If the alarm does not decisively turn off, or if current consumption does not fall to about 0.25mA when A and B are closed, insert another diode in series with D1 to raise the voltage at Q1’s gate. Almost any 12V battery may be used as long as it supports the load. Q2 can handle loads up to 74W. But note that a heatsink will be required for heavier loads. For driving a standard piezo siren, it will require no heatsink, as they only draw a few watts. One could also switch on a 12V lamp if desired. This circuit will remain on standby for about eight months using a small 12V 1.4Ah gel battery. A battery pack of alkaline AA cells may be used for a similar period of service. Thomas Scarborough, Cape Town, South Africa. ($75) siliconchip.com.au Australia’s electronics magazine September 2021  93 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 139, COLLAROY, NSW 2097 (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. 9/21 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 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F675-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) LED Christmas Ornaments (Nov20; specify variant) Nano TV Pong (Aug21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) Tiny LED Xmas Tree (Nov19) Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) 20A DC Motor Speed Controller (Jul21) Flexible Digital Lighting Controller Slave (Oct20) Automotive Sensor Modifier (Dec16) Remote-controlled Preamp with Tone Control (Mar19) UHF Repeater (May19), Six Input Audio Selector (Sep19) Universal Battery Charge Controller (Dec19) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) 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) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21) Touchscreen Digital Preamp [2.8in/3.5in version] (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sep12), Touchscreen Audio Recorder (Jun14) $20 MICROS dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT dsPIC33FJ128GP802-I/SP PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) PIC32MX695F512L-80I/PF PIC32MZ2048EFH064-I/PT Colour MaxiMite (Sep12) DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20) $30 MICROS KITS, SPECIALISED COMPONENTS ETC TOUCHSCREEN DIGITAL PREAMP (SEP 21) $75.00 $70.00 $40.00 - Micromite LCD BackPack V3 kit (SC5082) - Micromite LCD BackPack V2 kit (SC4237) - pair of AD8403ARZ10 (SC5912) NANO TV PONG SHORT FORM KIT (CAT SC5885) (AUG 21) $17.50 PCB and all onboard parts only (does not include controllers) MODEL RAILWAY LEVEL CROSSING (JUL 21) $15.00 $5.00 - Pair of programmed PIC12F617-I/Ps - ISD1820P-based audio recording and playback module ADVANCED GPS COMPUTER (JUN 21) $75.00 $25.00 $3.00 - Micromite LCD BackPack V3 kit (SC5082) - VK2828U7G5LF GPS module (SC5135) - MCP4251-502E/P IC (SC5052) ARCADE PONG (CAT SC5834) (JUN 21) $12.50 Pair of Signetics-branded NE555Ns, for critical A9/B9 paddle ICs MINI ISOLATED SERIAL LINK COMPLETE KIT (CAT SC5750) (MAR 21) $10.00 All parts required to build the project including the PCB AM/FM/SW RADIO (JAN 21) $2.50 $3.00 $7.50 - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) Complete kit including micro but no coin cell (specify PCB shape & colour) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) $38.50 Complete kit including PCB, micro, diffused RGB LEDs and other parts FLEXIBLE DIGITAL LIGHTING CONTROLLER PARTS $14.00 (NOV 20) (OCT 20) 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 siliconchip.com.au/Shop/ Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) - DHT22 temp/humidity sensor (Cat SC4150) - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor - BME280 temperature/pressure/humidity sensor (Cat SC4608) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) - 10µF 16V X7R through-hole capacitor (Cat SC5106) $30.00 $7.50 $5.00 $10.00 $3.00 $5.00 $1.50 $2.00 VARIOUS MODULES & PARTS - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) $7.50 - EA2-5NU relay (PIC Programming Helper, Jun21) $3.00 - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) $25.00 - MCP4251-502E/P (PIC Programming Helper, Jun21) $3.00 - 2.8-inch touchscreen LCD module (Lab Supply, May21) $22.50 - Spin FV-1 digital effects IC (Digital FX Unit, Apr21) $40.00 - 15mW 3W SMD resistor (Battery Multi Logger / Arduino PSU, Feb21) $2.50 - DS3231(M) real-time clock SMD IC (Battery Multi Logger, Feb21) $3.00 - Pair of CSD18534 transistors (Electronic Wind Chimes, Feb21) $6.00 - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $5.00 - 16x2 LCD module (Digital RF Power Meter, Aug20) $7.50 - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) $15.00 - MAX038 function generator IC (H-Field Transanalyser, May20) $25.00 - MC1496P double-balanced mixer IC (H-Field Transanalyser, May20) $2.50 - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) $10.00 - Si8751AB 2.5kV isolated Mosfet driver IC (Charge Controller, Dec19) $5.00 - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 - SMD 1206 LEDs, packets of 10 unless stated otherwise (Xmas Ornaments, Nov20): yellow – $0.70 ¦ amber – $0.70 ¦ blue – $0.70 ¦ cyan – $1.00 ¦ pink (1 only) – $0.20 - ISD1820-based voice recorder / playback module (Junk Mail, Aug19) $4.00 - 23LCV1024-I/P SRAM & MCP73831T (UHF Repeater, May19) $11.50 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 - ESP-01 WiFi Module (El Cheapo Modules, Apr18) $5.00 - VS1053 Geeetech Arduino MP3 shield (Arduino Music Player, Jul17) $20.00 - DS3231 real-time clock module with mounting hardware (El Cheapo, Oct16) $5.00 - CP2102 USB-UART bridge $5.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT DOOR ALARM STEAM WHISTLE / DIESEL HORN DCC PROGRAMMER (INC. HEADERS) ↳ WITHOUT HEADERS OPTO-ISOLATED RELAY (INC. EXT. BOARDS) GPS-SYNCHED FREQUENCY REFERENCE LED CHRISTMAS TREE DIGITAL INTERFACE MODULE TINNITUS/INSOMNIA KILLER (JAYCAR VERSION) ↳ ALTRONICS VERSION HIGH-SENSITIVITY MAGNETOMETER USELESS BOX FOUR-CHANNEL DC FAN & PUMP CONTROLLER ATtiny816 DEVELOPMENT/BREAKOUT PCB ISOLATED SERIAL LINK DAB+/FM/AM RADIO ↳ CASE PIECES (CLEAR) REMOTE CONTROL DIMMER MAIN PCB ↳ MOUNTING PLATE ↳ EXTENSION PCB MOTION SENSING SWITCH (SMD) PCB USB MOUSE AND KEYBOARD ADAPTOR PCB LOW-NOISE STEREO PREAMP MAIN PCB ↳ INPUT SELECTOR PCB ↳ PUSHBUTTON PCB DIODE CURVE PLOTTER ↳ UB3 LID (MATTE BLACK) FLIP-DOT (SET OF ALL FOUR PCBs) ↳ COIL PCB ↳ PIXEL PCB (16 PIXELS) ↳ FRAME PCB (8 FRAMES) ↳ DRIVER PCB iCESTICK VGA ADAPTOR UHF DATA REPEATER AMPLIFIER BRIDGE ADAPTOR 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER DATE AUG18 SEP18 OCT18 OCT18 OCT18 NOV18 NOV18 NOV18 NOV18 NOV18 DEC18 DEC18 DEC18 JAN19 JAN19 JAN19 JAN19 FEB19 FEB19 FEB19 FEB19 FEB19 MAR19 MAR19 MAR19 MAR19 MAR19 APR19 APR19 APR19 APR19 APR19 APR19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 PCB CODE 03107181 09106181 SC4716 09107181 10107181/2 04107181 16107181 16107182 01110181 01110182 04101011 08111181 05108181 24110181 24107181 06112181 SC4849 10111191 10111192 10111193 05102191 24311181 01111119 01111112 01111113 04112181 SC4927 SC4950 19111181 19111182 19111183 19111184 02103191 15004191 01105191 24111181 SC5023 01106191 01106192 01106193 01106194 01106195 01106196 05105191 01104191 SC4987 04106191 01106191 05106191 05106192 07106191 05107191 16106191 11109191 11109192 07108191 01110191 01110192 16109191 04108191 04107191 06109181-5 SC5166 16111191 18111181 SC5168 18111182 SC5167 14107191 01101201 01101202 09207181 01112191 Price $5.00 $5.00 $7.50 $5.00 $7.50 $7.50 $5.00 $2.50 $5.00 $5.00 $12.50 $7.50 $5.00 $5.00 $5.00 $15.00 $.00 $10.00 $10.00 $10.00 $2.50 $5.00 $25.00 $15.00 $5.00 $7.50 $5.00 $17.50 $5.00 $5.00 $5.00 $5.00 $2.50 $10.00 $5.00 $5.00 $40.00 $7.50 $7.50 $5.00 $7.50 $5.00 $2.50 $5.00 $7.50 $10.00 $15.00 $5.00 $7.50 $10.00 $7.50 $5.00 $5.00 $7.50 $2.50 $5.00 $7.50 $5.00 $2.50 $10.00 $5.00 $25.00 $25.00 $2.50 $10.00 $5.00 $2.50 $2.50 $10.00 $10.00 $7.50 $5.00 $10.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) DATE JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 PCB CODE 06110191 27111191 01106192-6 01102201 21109181 21109182 01106193/5/6 01104201 01104202 CSE200103 06102201 05105201 04104201 04104202 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 01106201 01106202 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 Price $2.50 $5.00 $20.00 $7.50 $5.00 $5.00 $12.50 $7.50 $7.50 $7.50 $10.00 $5.00 $7.50 $7.50 $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 SEP21 SEP21 01103191 01103192 $12.50 $2.50 NEW PCBs TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 Vintage Television Sanyo’s Sanyo’s 8-P2 8-P2 TV TV (1962) (1962) and and horizontal horizontal linearity linearity By Dr Hugo Holden O The early 1960s was a boom time in the television industry, as semiconductor-based compact and portable TV sets were gaining in popularity. Many of these could be powered by either onboard batteries or an external 12V supply. Valve TVs were rapidly becoming obsolete, and transistors started to fill the role of valves in demanding applications. 96 Silicon Chip Australia’s electronics magazine ne of the most demanding roles in a semiconductor-based TV set is that of the horizontal scan transistor. It must have a very low saturation voltage drop during the horizontal scan time, be able to withstand very high peak collector voltages during flyback and have a short storage time, so it can switch off rapidly to allow a fast flyback. Some of these features were difficult to achieve for a germanium device in the early 1960s. In the Sony Micro 5-303E TV, also released in 1962 (to be described in an upcoming article), they were well ahead of the game in transistor design. Sony had already moved to silicon transistors for the horizontal and vertical scan and video output stages. Not all companies were this advanced, but the germanium transistor technology was still up to the task. One of the most acclaimed early transistor-based TVs was Sony’s 8-301W, said to be one of the world’s first nearly all transistor-based miniature TV sets (it had valve EHT rectifiers). However, it was just beaten to the market by the Philco Safari in the USA. But there is little talk of the Sanyo 8-P2 of the same vintage. Despite it being the same size as the Sony 8-301W and the same age as the Sony 5-303E, it does not contain a single silicon transistor. The Sanyo 8-P2 TV educated me on transistor television design. It was given to me by an elderly retired TV technician in 1975 or thereabouts, when I was around 17. He was valve TV trained and never warmed to the notion of transistors, even though he was very smart and had built a number of his own valve TV sets. Faults This particular set was faulty. The horizontal output transistor, which had been replaced, just sat there heating up with no EHT and no horizontal siliconchip.com.au deflection. The assumption was that the line output transformer had failed. The original physically gigantic damper diode (energy recovery diode) was missing, and a silicon rectifier had been substituted. After some research at the time, I worked out that the original PNP germanium transistor had special properties, including low capacitances, a high transition frequency, a fast recovery time and the ability to withstand very high collector voltages, and worked well as a saturated switch. There was no internet back then, so it sometimes took a while to acquire transistor data. The TO-3 cased transistor which had been substituted for the original type was unsuitable, as it was only intended for use at audio frequencies. Eventually, I was able to source a 2N3731 and get the set ‘working’ again. The 2N3731 is a PNP germanium power transistor designed by RCA specifically for TV horizontal deflection applications. It has astonishing specifications for a germanium device: a peak collector-to-base voltage of -320V, a 10A maximum collector current, a turn-off time of 1.2µs and a high maximum junction temperature, for germanium, The original repair (now 45 years old!) did not need many changes initially before testing. of 185°C which is very unusual. This transistor could support 114° deflection and switched off more than fast enough for the approximately 12µs retrace or ‘flyback’ time. RCA also manufactured a companion germanium damper diode, the 1N4785. Remedies At the time, I knew of no source for a replacement germanium damper diode, except for the RCA 1N4785, which I did not have (and of course, there was no eBay back then either). Later, I learned about the DG14TV diode, which was used in Australianmade AWA portable TV sets and also the AY102, either of which would have worked. It is likely that the DG14TV is merely a re-labelled 1N4785. Finally, from a wrecked Sanyo 8-P2 set a year or two later, I found one of the original gigantic germanium damper diodes. I installed the 2N3731 in the set, recapped it (except for the large mains power supply filter capacitors), and that is when the fun began. After a while, the phenolic plate that supported the two valve EHT rectifiers became conductive, with arcing on its surface. To fix that, I hand-crafted a new plate out of acrylic. This repair is around 45 years old now, and it still looks OK (see adjacent). There appears to be a Mitsubishi logo on the line output transformer core in this set; Sanyo must have acquired it from them. It is the only place inside this set where such a logo is found. The rubber-covered EHT cable, which I replaced in the 1970s, has now started to crack. So I replaced it again, this time with very high-quality white silicone-covered wire (see below). As a teenager, I did not have access to good wire like this. Hand-made acrylic panel from 45 years ago 2N3731 installed to replace a 2SB231 Custom germanium damper diode Newly installed white silicone EHT wire Apart from the replacement EHT wire, the rest of the marked items were replaced during the original repair 45 years ago. siliconchip.com.au Australia’s electronics magazine September 2021  97 Audio driver transformer tipped on its side and rotated for minimum pickup of the magnetic field from the vertical yoke’s coils Once the horizontal scan and EHT systems were up and running, I was able to sort out some other problems in the set. It was working on this TV set that I learned the art of sweeping the video and audio IFs with a sweep generator and scope. After aligning the set, I was generally pleased with its performance. But there was an annoying vertical buzz in the audio caused (after much investigation) by the audio driver transformer core picking up radiated magnetic fields from the vertical yoke’s coils. This was due to the audio amplifier and audio IF board being mounted fairly close to the yoke. 98 Silicon Chip The designers must have been aware of this, as they had the transformer at an odd angle on the PCB (see above). I found that by tipping it on its side and rotating it to a particular angle, I could reduce or null the interference to a very low level. So I fitted a small brass hoop on the old bracket mounting and soldered the transformer to the better angle. Of course later, when inter-stage transformers were abandoned in audio amplifiers, this sort of problem vanished too. But, there was still something that troubled me: the horizontal scan linearity was stretched (expanded) at the beginning of scan (on the left) but Australia’s electronics magazine looked reasonable elsewhere. It was much worse with the replacement silicon damper diode, and improved to a fair degree when the original type of germanium damper diode was fitted. It took me some years to understand the cause of this problem. This set has an S-correction cap in series with the yoke H coils, but no width control inductor and no magnetic linearity coil. The width can be altered to a degree by tightening or loosening the clamp screws on the H output transformer; however, better linearity is acquired with them tightened up. The S-correction capacitor in this set is a high-quality, low-ESR, 7µF siliconchip.com.au oil-filled type. There was nothing I could adjust that affected the horizontal scanning linearity. I held on to the set for many years and recently powered it up again, after about a 40-year interval. The set ‘almost worked’ on repowering it recently. One of the five or so 2000µF clamp-mounted electrolytic capacitors (which I had not originally replaced) promptly failed by heating and outgassing. Interestingly, on a low-voltage test, the ESR, capacitance and leakage of all these old 25mm (one-inch) diameter capacitors read OK on my meters. However, when the applied voltage got over about 10-11V, they abruptly started to draw current and heat up. It just goes to show that apart from the usual tests we do on electrolytic capacitors to verify their performance, they should always be checked for leakage just under their rated voltage. I therefore replaced all of the clampmounted capacitors in the set, and also the vertical yoke coil’s coupling capacitor. The original Sanyo capacitors are shown at upper right; they were fairly generous with the number they used. The set requires good power supply filtering as there is no electronic regulator for the 12V rail; merely a transformer and bridge rectifier when running from mains power. The larger 500µF axial electrolytic in the photo is the vertical yoke’s coils coupling capacitor. These capacitors are huge for their ratings compared to modern equivalents, which have about 20% the volume or less. I had to remove the CRT from the set to replace the 500µF 12V-rated vertical yoke coupling cap. I replaced this one with a 125°C, 40V-rated 1000µF Rifa automotive-grade capacitor that will never likely need replacing. I replaced the 2000µF 15V units with 4700µF 80V Nichicon types. This was the closest I could find with a large enough diameter canister size to approximate the original appearance. The extra capacity is not unhelpful when running from line power; it improved the noise rejection when running the TV from a 12V switchmode power supply too. The replacement capacitors on the rear chassis are shown adjacent. This is the view into the battery compartment. This compartment once held, of siliconchip.com.au The original Sanyo capacitors (shown approximately half size) used for power supply filtering etc, had failed when the set was powered on. The 500µF capacitor at right is the coupling capacitor for the vertical yoke’s coils. The rest of the 2000µF capacitors were replaced with 4700µF Nichicon types shown below (actual size), as they were the closest in terms of appearance and size. The Nichicon electrolytic capacitor, which has a diameter of approximately one inch (25mm). The yoke coupling capacitor was replaced with this Rifa 1000µF automotive capacitor. Four replacement Nichicon capacitors are shown installed here instead of the original 2000µF Sanyo ones. The original S-correction capacitor is also shown at the lower centre in a silver can marked with a cross. Australia’s electronics magazine September 2021  99 The Sanyo 8-P2 TV being tested; the 3.8MHz bars are just visible (second set of lines from the right) which is OK given that the screen is eight inches diagonally. all things, a 12V wet lead-acid battery, much like a small motorcycle battery. The set is powered from this 12V battery, or by an external 230V AC mains supply. The manual states “when the voltage is below 10.5V, charge the battery immediately”. There is a selector switch on the top of the chassis. This switch has four modes which are viewed via a small clear window, which is illuminated by a neon bulb. The four modes are: CH – battery charged by mains voltage, said to take 10 hours. DC – powered from the internal 12V battery. AC – powered from 230V AC mains. FL – charge battery while playing the TV from mains power. Performance and linearity The high-frequency video performance of this set is reasonable. The display is shown above; when it is tuned in properly, the 3.8MHz bars are just visible, which is an adequate resolution for the 8-inch (20cm) diagonal screen. Turning now to the horizontal linearity problem I mentioned earlier, compressed linearity is when the horizontal picture elements are cramped together along some part of a horizontal scan line. This is due to a slower-moving electron beam, ie, a yoke scanning current that has a lower rate of change with time than the areas around it on the horizontal scanning lines. Expanded linearity is when picture elements are seen stretched apart due to a faster-moving electron beam, with a higher rate of change of yoke current with time than the areas around it. Note that in a TV or any other electronic apparatus which runs from a low-voltage supply, circuit currents must be higher at lower supply voltages for the same power level. This makes any effects of circuit resistances more significant. The magnetic fields generated by the TV’s deflection yoke’s ampere-turns must be about the same for a given amount of deflection of the CRT’s beam in either a valve or transistor-based set. Therefore, an interesting design challenge crops up. The peak yoke currents in a 12V-powered set need to be much higher than in a higher-voltage operated set for the same deflection power, yet the yoke winding ampere-turns must be similar. This means that the yoke’s winding wire (especially for the horizontal yoke coils) must be made of thick low-resistance wire, yet thin enough to physically wind into a formed yoke coil to get enough ampere-turns. In 12V-operated sets, resistance in the horizontal yoke coils degrades the horizontal linearity, causing compressed linearity of the scan on the right side of the raster and stretching on the left. It took me some time to realise exactly why this was the case. In transistorised TVs, the horizontal scan output stage acts as a switch, and the rate of current increase is dependent on the inductance and resistance properties of the horizontal yoke coil and horizontal output transformer. The horizontal scan linearity is not modifiable by altering the drive waveform to the horizontal output transistor. By contrast, the vertical scan stages act more-or-less like their audio amplifier counterparts, with the waveform Fig.1: the change in current when a fixed DC voltage is applied across an RL circuit. The current will initially rise linearly with time before flattening off exponentially. 100 Silicon Chip Australia’s electronics magazine siliconchip.com.au shape driving the output stages controlling the vertical scan linearity. This horizontal scan linearity problem was primarily solved or ameliorated in the early solid-state TVs with horizontal yoke windings that were ‘quadra-filar’ wound. Sometimes, up to six strands of wire were paralleled to help keep the DC resistance of the horizontal yoke coils low, while still being able to wind and form them. Later, the horizontal scan linearity in transistor TV sets and computer monitors was manipulated with a combination of ‘S-correction’ capacitors and magnetically saturable inductors (with a permanent magnet) in series with the horizontal yoke coils. Close inspection though will show that most 12V-operated TVs of the very early 1960s have expanded scan linearity on the lefthand side, with no adjustment inside the TV set which can alter it. The technical explanation for this is as follows. When a fixed DC voltage is applied across an RL circuit, the current initially rises linearly with time and flattens off in the usual inverted exponential manner (see Fig.1). Initially at least, when a de-energised inductor is switched across a power supply, the rate of current increase is linear. It rises at V/L amps per second, where V is the power supply voltage and L the circuit inductance. Notice that this initial linear rate of current increase does not contain the variable R for resistance. The yoke’s coils and the power supply are not free from resistance, so as time passes, the rate of current increase flattens off and settles to a value of V/R amps. The variable L has now vanished. In a TV set’s horizontal deflection system, the proportions of yoke inductance, resistance and power supply voltage are chosen so that mainly the first near-linear part of the current ramp is used to scan the CRT’s beam from the centre toward the right-hand side of the CRT’s face. On the righthand side of the scan (with no other corrections), compressed linearity is sometimes seen as the rate of current increase with time is tapering off. However, a small amount of this righthand compression is helpful, as the sensitivity of the yoke (ie, the change in beam deflection for a change in yoke current) is greater for higher angles of beam deflection. Therefore, the tapering rate of current increases with time towards the extreme righthand side of the scan, due to the L & R properties of the yoke, which tends to cancel this sensitivity effect. It is often not wholly cancelled, though; as explained below, S-correction capacitors are usually still required. So it is fairly easy to achieve reasonable horizontal scan linearity in a 12V-operated transistor set, especially for small screen sizes and low range deflection angles, even without a magnetic linearity coil or S-correction capacitor, at least for the righthand half of the screen. That is, provided that the yoke’s L and R values are suitable. However, good linearity is much more difficult to achieve on the lefthand side of the scan. Horizontal deflection operation Fig.2 shows a simplified horizontal deflection system with a switching transistor, damper diode, an inductance L (representing the horizontal yoke coils) and a tuning capacitor C, which tunes the flyback frequency. The transistor’s current ramps up as the CRT scans toward the righthand side of the raster. The damper diode carries the current during lefthand side scanning; the peak horizontal yoke currents Ipk and -Ipk are indicated. The idea is very old and is the basis of some modern SMPS power supplies. At the end of each horizontal scan line (after scanning the righthand side), the energy stored in the magnetic field of the yoke and the horizontal output transformer is transferred into the electric field of the tuning capacitor. This is initiated by the switching transistor cutting off, and this energy transfer period is known as ‘flyback’. Fig.2: a simplified horizontal deflection system with a DC supply (V), switching transistor (Q), damper diode (D), an inductive load (L), and a tuning capacitor (C). siliconchip.com.au Australia’s electronics magazine September 2021  101 102 Silicon Chip The circuit diagram for the Sanyo 8-P2. This was scanned from a photocopy and then cleaned up. The circuit and block diagram (shown overleaf) can also be downloaded from the Silicon Chip website: siliconchip.com.au/Shop/6/5788 siliconchip.com.au Australia’s electronics magazine September 2021  103 Fig.3 (left): how linearity correcting components affect the rate of change of current in the damper diode Fig.4: the red line shows how the S-correction capacitor alters the linear yoke current (black). All the energy has moved into the capacitor’s electric field halfway through the flyback period, when the voltage on the capacitor reaches a peak. At this point, the yoke current is zero, and the beam is horizontally centred on the CRT. The flyback voltage pulse is seen as a half-cycle of high voltage oscillation on the transistor’s collector terminal, over the flyback time of typically around about 12µs. The peak voltages can be in the range of 100V for a small monochrome TV and over 1kV in a large colour TV. The end of the flyback period is just before the flyback diode conducts and after the capacitor’s energy has been returned to the magnetic field. The capacitor’s voltage is zero, and both the yoke current and the polarity of the magnetic field have reversed. The CRT’s beam is at the lefthand side of the raster, ready to scan the next line. The initial line scanning current after flyback on the lefthand side is achieved when the damper (or flyback/freewheeling) diode is pushed into conduction, and the magnetic energy of the inductances are returned to the power supply in a controlled and again, inverted exponential manner. However, on the lefthand side, the damper diode’s current tapers off with time toward the scan centre. Its rate is initially high, rather than having a tapered or lower rate of change at the start of the scan on the lefthand side (which would mirror the shape of the current wave on the righthand side). This effect aggravates, rather than cancels, the yoke’s sensitivity for high deflection angles. The result is expanded linearity on the lefthand side of the CRT (see Fig.3). Therefore, without any linearity correcting components, the horizontal scan will always have expanded linearity on the left. The horizontal linearity on my Sony 104 Silicon Chip Micro 5-303E TV is shown below. This set is an excellent case for studying horizontal scan linearity problems, because it is devoid of any linearity correcting components (it has neither an S-correction capacitor nor a magnetic linearity coil). Its horizontal scan linearity properties show the intrinsic asymmetry of the linearity beautifully at the end of the line scan on either side. It also demonstrates the deflection sensitivity issue with the yoke, showing the central compression compared to the sides. The traditional method which is used to correct the centre horizontal scan linearity, with respect to the sides, is the ‘S-correction capacitor’. It is placed in series with the horizontal yoke coils. The Sanyo 8-P2 has this capacitor (even though the Sony Micro TV of the same year did not). S-correction capacitors are used to effectively expand the linearity near the screen centre area and compress it toward the edges. This happens because the S-correction capacitor forms a resonant circuit with the inductance of the yoke coils to produce a partially sinusoidal current. The red line in Fig.4 shows the effect of the S-correction capacitor. It alters the linear yoke current (the black line), which was closest to a linear sawtooth current beforehand. The S-correction capacitor increases the current rate of change with time near the centre of the scan, expanding the linearity there and compressing it at either side. An advantage of an S-correction (or The horizontal linearity test performed on a Sony Micro 5-303E TV, this acts as a reference to a set without any linearity correcting components. Australia’s electronics magazine siliconchip.com.au The block diagram for the Sanyo 8-P2 scanned from the service manual. another coupling capacitor) in series with the yoke’s coils is that it isolates any DC voltage present. This means that the return point of the yoke connections can either be to the 12V supply or ground. The linearity of the image on the Sanyo 8-P2 is shown below, which has an S-correction capacitor. Unlike the Sony Micro TV, the horizontal linearity of the central area of the screen (B) is very similar to that near the righthand A side (C), thanks to S-correction. But it is still expanded in the region A on the lefthand side, due to the magnetic field reversal and the current waveform shape. As explained earlier, this is because the shape of the current waveform after flyback aggravates the linearity problem, rather than helping it. But there is another factor related to the circuit resistances. It was noted before that any B C The horizontal linearity of the Sanyo 8-P2 is not as good as the adjacent Sony TV (for example region “A”) despite it having an S-correction capacitor. siliconchip.com.au Australia’s electronics magazine resistance in the yoke degrades the horizontal linearity. When the righthand side of the raster is scanned, the current pathway to the power supply has the very low dynamic resistance of a saturated switching transistor. On the other hand, the lefthand side is scanned by the current passing through the damper diode back to the power supply. In many horizontal output stage designs, the damper diode is not connected to the same point as the collector of the output transistor, as shown in Fig.2. A small tap, a few turns away on the output transformer, helps to bring the damper diode into conduction a little earlier and ensures that the transistor’s collector is prevented from going negative (in the case of an NPN output transistor) with respect to its emitter. Regardless of the presence or absence of an S-correction capacitor, due to high-range horizontal yoke currents in TVs running from lower power supply voltages and the high peak horizontal yoke coil currents associated with that, horizontal scan linearity in early 1960s vintage TV’s was always a problem. It depended very much on the yoke design and its DC resistance, until later when magnetically saturable inductors were added in series with the yoke coils. These allowed asymmetric adjustment of the scan linearity. In the case of the Sanyo 8-P2, the horizontal scanning linearity defect on the left side could be eliminated with the addition of a magnetic linearity coil; however, I decided to leave it as it was designed. In the case of the Sony Micro 5-303E TV, I can see why they did not add an S-correction capacitor. While it would have reduced the relative linearity errors from the screen centre area to the righthand side of the scan, it would have made the linearity defect on the lefthand side more obvious. As it stands with that set, the horizontal scan errors overall look better averaged out. SC September 2021  105 PRODUCT SHOWCASE ElectroneX returns to Sydney this year on November 10th Following the delay of ElectroneX this year – The Electronics Design & Assembly Expo and Conference will be hosted in Sydney on the 10-11th of November 2021 at Rosehill Gardens (10am-6pm on the 10th, and 9am-4pm on the 11th). Reflecting the growth of high-tech niche manufacturing in Australia, at the 2019 Expo more than 87% of visitors said that they had met new companies and 81% discovered new products and technology they were not aware of, reinforcing the important role of exhibitions in showcasing new technology. The 33rd Surface Mount & Circuit Board Association (SMCBA) Electronics Design & Manufacture Conference will also be held over the 9-11th of November at Rydges Parramatta. The speaker program for the conference is currently being finalised; visit www.smcba.asn.au for further information. Registration for ElectroneX is free, as is on-site parking. To register online, go to the following link: siliconchip. com.au/link/abae You can also call (03) 9676 2133 or email info<at>auexhibitions.com.au for more information. Australasian Exhibitions and Events Pty Ltd Suite 11, Pier 35, 263 Lorimer St Port Melbourne VIC 3207 Tel: (03) 9676 2133 email: ngray<at>auexhibitions.com.au Web: www.auexhibitions.com.au Electrolube launch new range of versatile thermal gap fillers Electrolube has launched the GF400, a two-part, liquid-silicone-based gap filler. It can either be cured at room temperature or accelerated with heat. Once cured, GF400 forms a low modulus elastomer that prevents the ‘pumpout phenomenon’, ensuring minimal degradation of effective heat dissipation. Thermal gap fillers are widely used for mobile and touchscreen applications. However, the GF400 range is extremely adaptable and can be used in a multitude of applications from PCB assembly and housing automotive electronics discretely, including HEV, NEV and batteries, power electronics, LEDs and fibre optic telecoms equipment. GF400 is soft and compliant, making it ideal for low stress applications, and provides a wide operating temperature range between -50 to +200°C. It’s also low viscosity, enabling easier dispensing, and provides high thermal conductivity of 4W/mK. The GF400 has a straightforward mix ratio of 1:1 and a fast cure time of 20 minutes at 100°C, vastly increasing throughput. Alternatively, the gap filler can be cured at 25°C for 12 hours or 90 minutes at 60°C. The new thermal gap filler is UL94 V-O approved and has an excellent dielectric strength of 9kV/mm. There’s also a 50mL version of the GF400 in development. We will officially pre-launch the GF400 at ElectroneX on the 10-11th November in Sydney, alongside our new range of UV Cure conformal coatings. Electrolube would like to extend a warm welcome to all visitors at their booth A20 during the two day event. For further information, please visit www.electrolube.com Electrolube 3/98 Old Pittwater Road Brookvale NSW 2100 Tel: (02) 9938 1566 email: sales<at>hkwentworth.com.au Web: www.electrolube.com.au/ MPLAB tools – now on the Cloud Microcontroller (MCU) design is easier than ever with the new MPLAB cloud tools ecosystem available now for PIC and AVR devices from Microchip Technology. The enhanced MPLAB Xpress IDE delivers a powerful, scalable cloud infrastructure for development and debugging along with community collaboration tools using secure GitHub repository interface controls. 106 Silicon Chip The free, all-in-one cloud platform combines easy, integrated search and discovery of example code, graphical configuration of projects and code debugging in a collaborative environment. This environment enables enterprise-scale rapid development while simplifying software design for users at all skill levels with an intuitive browser-based interface and cloud connectivity. Australia’s electronics magazine Developing, debugging and deploying project applications directly from any web browser can be completed without any software installation. For more information, visit: www. microchip.com/MPLABCloudTools Microchip Technology Inc. Unit 32, 41 Rawson Street Epping NSW 2121 Web: www.microchip.com/ siliconchip.com.au 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 20A DC motor controller lacks a current limit I enjoyed reading your article on the 20A DC Motor Speed Controller in the July 2021 issue (siliconchip. com.au/Article/14918). It certainly has many useful features. One feature that I couldn’t find mention of is a current limit. If there is a brake on the machine that has been inadvertently left applied or if the mechanism is seized or sticky, the motor current could go sky-high at start-up. Fuse F1 would blow, but would that happen fast enough to safeguard Mosfets Q1 and Q2 and the copper track on the PCB? A current limit, adjustable up to a maximum of 1.5 times the full motor load current would give the user enough time to realise that there is a problem and react. It should be possible to derive a current limit in IC1 using the current feedback signal at pin 9. The formula given for motor impedance on page 30 needs a bit of amendment. Impedance = √R2 + (2π × f × L). (R. H., Bronte, NSW) • We haven’t included a current limit and instead rely on the fuse to blow. The Mosfets are rated up to 60A each and so are rugged enough to handle a high current until the fuse blows. Short circuits would cause the fuse to blow well before any feedback control would come into effect. The PCB tracks have sufficient area to remain intact. Reducing HT (high tension) voltage I have a transformer that produces 370 AC which, when rectified and filtered, gives 515V DC. I need a B+ voltage for my amplifier of 390-400V DC. How can I achieve this? (S. K., Singapore) • To get 400V DC after rectification and filtering, you would typically use a transformer with a secondary of about 280V AC. You could rewind the transformer to get a more suitable 280V AC output from it. siliconchip.com.au If the load current is constant, you could drop about 120V using a highpower resistor, but that would generate much heat. It could also cause catastrophic damage if the load current were suddenly reduced, resulting in a much higher than expected applied voltage. So overall, it is not a good solution. It’s much better to start with an appropriate AC voltage from the transformer. Advanced GPS Computer query I built the Advanced GPS Computer (June & July 2021; siliconchip.com.au/ Series/366), but one thing I have found annoying is having to switch the unit off before I switch off the ignition to prevent the unit from continuing to run on battery. I don’t understand why the battery is there; it only has a usable life down to about 3.6V, so it does not last long. A button cell could run the RTC. Also, would it be possible to include an overspeed alarm, mainly to be used in urban areas where the speed limit is 50/60 and cruise control is not really usable? I thought maybe the displayed speed could change colour to red and sound a warning. The screen is already a bit cluttered, but it should fit somewhere. (P. C., Balgal Beach, Qld) • The battery is intended to allow the GPS Computer to run when not connected to USB power, ie, as a portable device. The easiest way to have it shut off when the ignition shuts off is to set the battery low voltage (LO) to a higher value, which will cause it to shut down sooner. For example, if HI is set to 4.4V, you can set LO to 4.3V, which should cause the GPS Computer to trigger its shutdown timer practically as soon as USB power is removed, and shut down the unit after the TO timer has expired. An overspeed warning is possible, and perhaps it can be added to the large speedometer display tile, with the numbers changing colour as the speed increases. But the program Australia’s electronics magazine already comes very close to filling the available flash space, so it means that other features will need to be cut. We might leave this one for a while and see what other readers suggest. We can do an update once we have an idea of what other features people want. Bench Supply transistor installed backwards I have ordered enough parts to build two of your 45V Linear Bench Supplies (October-November 2019; siliconchip. com.au/Series/339). I have completed the first, but I’ve come across a problem – the 68W 1W resistor across the B-E junction of the BD140 and the input to the LM317HV gets extremely hot with modest loads (1A). This is also reducing the available output voltage due to the voltage across it. Current adjustment via VR4 is functioning as expected (up to 2A), as is voltage adjustment via VR3. With 50V at the collectors of Q4-Q7, and a selected voltage of 20V, even a small load of 500mA results in the 68W resistor overheating. (B. N., Fremantle, WA) • It sounds like you have transistor Q3 (BD140) installed the wrong way around. Note that in Fig.6 on page 70 of the November 2019 issue, it is shown mounted with its metal tab facing away from the surface of the heatsink, not towards it as you would usually expect. This was done to provide electrical isolation from Q3 but perhaps was not explained clearly enough (although it was mentioned in the third-last paragraph on p75). Rotate Q3 by 180° and your supply should work normally. Two audio queries Regarding the Ultra-Low Distortion Preamplifier with Tone Controls (March & April 2019; siliconchip.com. au/Series/333), the component layout diagram on page 38 of the March issue shows two 10W resistors with an asterisk and a note “see text”. They are also shown on the circuit diagram. September 2021  107 I assume they should be fitted to the main board, as they are shown in both pictures, but I can’t find any reference to them in the accompanying article. Am I missing something? Also, I have a Redback A2691A AM/FM 100W Stereo Receiver Amplifier to which I would like to connect a Bose Companion 3 Series II Multimedia Speaker. The Redback has a line out socket with a volume that can’t be controlled. The Bose has a control pod with a 3.5mm stereo plug line input. Can you provide any advice on connecting the Bose line input to the speaker terminals of the Redback? I realise that this could create distortion problems, but the usual listeners are both over 70 years old. If this is possible, I can control the Bose volume from the Redback. Apart from the speaker terminals and the line out socket, there are no other outputs available on the Redback. (D. H., Mapleton, Qld) • The two 10W resistors are to minimise Earth currents in the supply and signal Earths so that hum is minimised. They can be shorted out if there is no hum heard when doing so, but it’s generally safer to leave them in the circuit. Connecting the speaker terminals to the 3.5mm jack socket would require reducing the speaker terminal voltage to that suitable for the Bose line input. To prevent problems with hum, especially if the speakers are driven with a complementary output, it is important to use the audio isolation transformers (eg, Altronics Cat M0706). Connect 22kW/1kW resistive dividers across the speaker terminals, with the 1kW resistors towards the black terminals, then connect the yellow/ blue wires of the isolating transformers across the 1kW resistors. Join the transformers’ green wires together, then connect these to the TRS jack plug ring terminal, with the two red wires going to the tip and the sleeve. You can then safely plug this into the Bose line input socket. Using Keyboard/Mouse Adaptor with Micromite Can the USB Keyboard and Mouse Adaptor for Micros (February 2019; siliconchip.com.au/Article/11414) be used with the original Colour Maximite from the September & October 2012 issues (siliconchip.com.au/Series/22)? (R. M., Melville, WA) • If you want to interface to the Maximite console then, unfortunately, the answer is no. That is because the Colour Maximite does not have a TTL UART interface for the console, just the virtual USB-serial interface and the PS/2 keyboard interface. You could use the Serial I/O to receive keyboard events via the Maximite’s COM2 from inside an MMBasic program (see page six of the Maximite manual), but we suspect that is not what you want. We are considering designing a device similar to the USB Keyboard and Mouse Adaptor but with a PS/2 interface instead of a UART. Such a device would be suitable for the Maximites. Help identifying failed 8-pin LED driver IC Trying to repair an LED driver, I found the 8-pin DIL control IC on the PCB to have bad dry joints. But even after resoldering it, it still would not function. The only markings on its body are “BXUBTA”. I have been unable to find any information on the internet about this IC. Can you help me? (B. C., Dungog, NSW) Radio, Television & Hobbies: the COMPLETE archive on DVD YES! NA MORE THA URY T N E C QUARTER ICS N O R OF ELECT ! Y R HISTO This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to EA. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you’re an old timer (or even young timer!) into vintage radio, it doesn’t get much more vintage than this. If you’re a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you’re just an electronics dabbler, there’s something here to interest you. • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics Exclusive to: SILICON CHIP 108 Silicon Chip ONLY 62 $ 00 +$10.00 P&P Order now from www.siliconchip.com.au/Shop/3 or call (02) 9939 3295 and quote your credit card number. Australia’s electronics magazine siliconchip.com.au • The BX prefix indicates that it is a Sony part. See the list at siliconchip. com.au/link/abac Unfortunately, we can’t find a master list of Sony IC codes, and we don’t usually see Sony ICs for sale at the usual resellers. You probably need to contact a Sony authorised repair agent or spare parts distributor to find out whether they can identify that chip and supply a replacement. Given how inexpensive LED drivers are these days, we suspect it will be easier and cheaper to buy a new one. Prewound transformer is no longer available In the parts list for the New Marine Ultrasonic Anti-Fouling Unit (May & June 2017; siliconchip.com.au/ Series/312) on p81 of the May issue, it lists a pre-wound transformer, Jaycar Cat EM2791. But this is no longer available. Is there an alternative that I could use, or details of how to wind it myself? (C. L., Beaumaris, Vic) • Details for winding the transformer can be found on page 39 of our September 2010 issue (siliconchip.com. au/Article/281), in the article describing the construction of the original Anti-Fouling Unit. The transformer cores, former and clips are available from element14 (https://au.element14. com), among others. You will need two of their Cat 3056375 3C90 ferrite cores, one Cat 178506 former and two Cat 178507 clips. Using DC Motor Speed Controllers for AWD I want to use two of your DC Motor Speed Controllers (January & February 2017; siliconchip.com.au/Series/309) for all-wheel-drive control of my eBike using a twist throttle and possibly crank sensor. I’m assuming I would need two separate controllers, ie, one per 1500W 48V wheel motor. What is the best way to interface the signal from the twist throttle/crank sensor to both DC controllers? For the batteries, I want to make up a battery pack using Ozito 5Ah 18V batteries (three in series, five in parallel to get 52V, 20Ah). These appear to have an inbuilt battery management system (BMS). Is it OK to parallel and series connect intact power tool packs like this? Is fusing advisable between packs? siliconchip.com.au My other option is using four Altronics 12.8V LiFePO4 cells in series, paralleled to give 51.2V at 24Ah. In this case, is it advisable to connect fuses between battery packs? In both battery situations, the cell packs have inbuilt management systems; is an external overall low-voltage cut-out circuit still needed? You should do a feature on eBike circuits, controllers, BMS for Li-ion and LiFePO4 cells. There are many eBay type kits available, but who knows how well they work. (P. B., Cooloongup, WA) • Separate resistors from the twist throttle control to each DC motor controller would isolate the controls. 100W should be suitable. You can parallel the batteries, but before doing so, they must be charged to equal voltages. That will prevent a massive current flow between them when connected. Get each battery to within about 100mV of each other before joining them. Once connected, they can be charged as usual. Paralleled batteries must each be the same type regarding age, brand and capacity and, of course, voltage. Fuses between the paralleled batteries should not be necessary. They would likely blow anyway unless you use very high amperage fuses that would defeat the purpose of paralleling for extra current. Running Motor Speed Controller from Li-ion I have purchased one of the few remaining 12-48V 40A DC Motor Speed Controller kits from Jaycar. Do I need to make any modifications to run the controller from a Li-ion battery with a voltage of 29.4V fully charged? (I. B., Laidley South, Qld) • Assuming you are referring to our January & February 2017 DC Motor Speed Controller (siliconchip.com. au/Series/309), Jaycar kit Cat KC5534. Based on the supply voltage of 29.4V, use the component values given for a nominal supply voltage of 24V, ie, 27kW for R1 & R2, no jumper in JP1 and a 10V 1W zener diode for ZD4. Bridged amps not suitable for headphones I purchased the Champion Amplifier with Pre-Amplifier (January 2013; Australia’s electronics magazine siliconchip.com.au/Article/1301) kit from Jaycar (Cat KC5519). My plan is to adjust the gain to allow me to connect an electric guitar to one input and my iPhone to the other, so that I can play along with music tracks. That shouldn’t present any problems, but I also want to connect headphones to the output of the Champion amp. To do that, I will need to fit an attenuator. I have plans for a simple impedance-matching attenuator designed for this exact purpose. However, that design can’t be used on amps with bridged outputs. Can I just use one of the outputs of the AN7511 referenced to ground, between pins 6 & 7? I’ve read the data sheet, and there’s no guidance on this. (C. C., via email) • You can’t really drive headphones/ earphones with a bridged output amplifier as headphones usually have a common ground connection between the two ears. There’s no good way to do it. In theory, you could use just one of each pair of outputs to drive headphones, as you are suggesting. It will work, but it’s likely to result in significantly higher distortion, so we don’t recommend it. A better solution for driving headphones is our Studio Series Stereo Headphone Amplifier from the November 2005 issue. It isn’t overly complicated or too expensive to build; see siliconchip.com.au/Article/3231 It can be powered from a low-voltage AC plugpack using the 4-Output Universal Voltage Regulator (May 2015; siliconchip.com.au/Article/8562) Fuel pump cut-out project wanted I’d very much like to see more low-to-moderate difficulty projects back in the magazine. For example, in modern vehicles, the Fuel Pump Relay (FPR) has mostly reverted to a standard style relay as the ECU controls it. It might be different colour, but generally, it is a four-terminal standard relay. When Fuel injection was being introduced, the FPR had its own circuitry to detect the RPM from the ignition system and cut off if it wasn’t present for a short period, as well as a starter connection to override this auto-cut-off when the engine was being cranked by the starter (low RPM). September 2021  109 If the engine still used a coil (with/ without mechanical points), it often had an auxiliary output for that as well, usually just a parallel tag to the fuel pump tag on the relay. When restoring older vehicles, it is often difficult to get parts. I don’t just mean the fuel pump relay; this also includes mechanical fuel pumps, overhaul kits etc. So often, an electric fuel pump is used instead. For example, the cheap Goss pumps are ideal for carburetted engines. I find myself in that position and have fitted a Goss pump near the fuel tank to push fuel to the carburettor. I have blanked off the mechanical pump opening in the engine block. Its easy to just wire it from a fuse and relay, but what I’d like to do is have a fuel pump relay set up so that if the ignition is turned on, but the engine does start for some reason, the pump will stop after a short period. This is mandatory in case of an accident; the electric pump should stop pumping fuel if the engine stops. Additionally, it would be good to wire the ignition coil with its ballast resistor to the FPR so that if the ignition is on, but the engine has not started, the coil and ballast won’t heat up if the points are closed. On my car, the ballast is overridden by a standard relay; perhaps this facility could be incorporated as well. This all needs to be in a small package. It could be a standard Bosch relay with another relay case glued to the top of it. I would prefer not to use SMD components so that anyone can make it, but I realise that is contra to needing it to be a small package. If you have a past project incorporating circuitry similar to this, please let me know. I searched through your articles but didn’t come up with anything fitting the description. (S. S., Manly Vale, NSW) • Many of our electronic ignition systems (that can run using points, reluctor, Hall Effect etc triggers) switch off the coil if the engine does not start within a set period and the coil is not energised until the engine is rotated. However, we have not published a fuel pump cut off when the engine stops. Typically, the oil pressure switch would be used as the fuel cut off signal to drive a relay when there is sufficient oil pressure and switch off power to the pump when pressure is low (also when the engine stops). The reserve in the carburettor’s float bowl should be sufficient to get the engine started without the pump until the engine runs. A temporary bypass pushbutton switch could be added to power the pump and refill the float bowl should more fuel be needed to start the engine during stubborn starts or in very cold weather. Also, it does not seem especially worthwhile to design such a device since commercial versions are available at a reasonable price. They are even Australian-made! Search for “PEEL CP30F Fuel Pump Safety Switch” (available on eBay etc). Solar panel voltage should match batteries Your MPPT solar controllers (and many other similar devices) can charge a 24V battery from a ‘24V solar panel’ (approximately 40V open circuit) or charge a 12V battery from a ‘12V solar panel’ (approximately 20V open circuit). Can your controller be modified to charge a 12V battery from a 24V solar continued on page 112 110 Silicon Chip Australia’s electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. SILICON CHIP ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au DAVE THOMPSON (the Serviceman from S ilicon C hip ) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com 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 Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia’s electronics magazine September 2021  111 panel? I realise the efficiency might be lower, but maybe other people, like me, have obtained a second-hand 24V solar panel cheaply and wish to charge a 12V system. I have researched 36-12 DC/DC inverters and 24V solar controllers online, but none of them can do the job. With the 24V controllers, the protection circuit kicks in, and a typical inverter has only 12V DC output, insufficient to charge a 12V battery. Any suggestions please? (B. M., East Hills, NSW) • The power conversion circuit in our MPPT chargers isn’t designed to handle such a large voltage step-down ratio (nearly 3:1). That is possible, although not with the existing design, and the efficiency is likely to be poor. Reduced power version of the Studio 350 Can the Studio 350 Amplifier (January & February 2004; siliconchip. com.au/Series/97) be outfitted with two power transistors per rail instead of the four and powered from a lower supply voltage? I was thinking of building a tri-amp system and using different powers for each frequency; for the low frequencies, I would use the 350W version with four transistors per rail, but for the medium frequencies, I would use the lower-power version. Is it possible to do this, or will I have a problem? Also, I am having trouble getting some of the transistors for this design. Is it possible to replace the BF470 and BF469 with MJE350 and MJE340? And what replacements can I use for the 2SA1084? (R. C., Quito, Ecuador) • Yes, it would be possible to build a lower-power version of the Studio 350 Amplifier, although there are better options. You would be better off building the SC200 (January-March 2017; siliconchip.com.au/Series/308) for the outputs that don’t need the full 350W. If you decide to run the Studio 350 with a lower supply rail voltage, some resistor values need to be changed to ensure the amplifier is operating correctly. For example, the 18kW resistor at the collector of Q1 and the 6.8kW resistor at the collector of Q4 would need to be reduced to keep the transistors conducting with the lower supply. Also, the amplifier gain will probably need to be reduced by reducing the 22kW resistor value at the base of Q3. But you have to be careful doing that since lowering the gain of an amplifier can cause it to become unstable! As for the transistors, our recommended substitutes for BF469 and BF470 are 2SC4793 and 2SA1837, respectively – see page 38 of the July 2011 issue. However, note that the pinout is reversed; ECB for the BF469/470 and BCE for the replacements, so the transistors need to be placed in the opposite orientation. The board should accommodate that. The recommended substitute for the 2SA1084 or 2SA970 is the KSA992. This is a direct replacement with an identical pinout. The collector current rating is 50mA vs 100mA, but that shouldn’t be a problem in any audio amplifier as the front-end current is rarely more than 20mA. SC Advertising Index AEEE ElectroneX........................ 7 Altronics...............................23-26 Ampec Technologies................. 81 Dave Thompson...................... 111 Digi-Key Electronics.................... 3 element14................................. 13 Emona Instruments................. IBC Hare & Forbes............................. 9 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology......... 5,OBC Mouser Electronics.................... 11 Ocean Controls......................... 10 PHIPPS Electronics.................... 8 PMD Way................................ 111 SC Vintage Collection DVD..... 110 SC Xmas Ornaments................ 85 Silicon Chip Binders................. 89 Silicon Chip RTV&H DVD...... 108 Silicon Chip Shop.................... 94 Silicon Chip Subscriptions....... 37 Silvertone.................................. 12 Switchmode Power Supplies..... 79 The Loudspeaker Kit.com......... 52 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics..................... 6 Notes & Errata Programmable Hybrid Lab Supply with WiFi, May & June 2021: the footprints for transistors Q3 and Q4 on the PCB are incorrect, with the base & emitter pins (pins 1 & 2) swapped. There are two possible solutions to this: either gently bend the pins of these transistors up so that they can be soldered in place upside-down, or trim the leads of two NPN TO-92 package transistors to reach the appropriate pads. Also, there is an error in the parts list; the 150W axial resistor should be 68W, and the 68W SMD resistor should be 150W 0.5W (M2012/0805 size). This error also affects Fig.6 in the June 2021 issue; the 150W through-hole resistor below REG2 should be 68W, and the 68W SMD resistor to the right of REG1 should be 150W 0.5W. High-Current Four Battery/Cell Balancer, March & April 2021: The UM6K34N and UM6K31N transistor types have been swapped throughout both parts of this article. Q7 should have been specified as UM6K34N, while Q8, Q13, Q18, Q19 and Q24 should have been UM6K31N. This is not critical unless the total battery 'stack' voltage can exceed 50V. In that case, you should replace Q8 and Q18 with the 60V-tolerant UM6K34N. Finally, in the second article (April), at the start of page 82 where it refers to dividing a reading by 3.3V, it should instead be divided by 1.65V (ie, half the 3.3V rail, which is the ADC reference voltage). Speedo Corrector Mk.3, September 2013: the BC857 is incorrectly listed for Q3 & Q6 in the parts list, it should be for Q4 & Q6. The circuit and overlay diagram are correct. The October 2021 issue is due on sale in newsagents by Monday, September 27th. Expect postal delivery of subscription copies in Australia between September 27th and October 13th. 112 Silicon Chip Australia’s electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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