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OCTOBER 2024 ISSN 1030-2662 10 The VERY BEST DIY Projects! 9 771030 266001 $ 00* NZ $1390 13 INC GST INC GST The MG4 XPower Electric Car Review MICROMITE EXPLORE-40 a Micromite in the Raspberry Pi Pico form factor Refresh your workbench with our GREAT RANGE of essentials at the BEST VALUE. Here's just a small selection of our best selling workbench essentials to suit hobbyists and professionals alike. ALL THE REGULAR OSCILLOSCOPE FUNCTIONS IN A SMALL FORM FACTOR 2 CHANNELS SuperPro Gas Soldering Tool Kit SOLDER ANYTHING, ANYWHERE! DURABLE CASE WITH EXTRA TIP STORAGE Ideal for soldering, plastic cutting, heat shrinking, etc. • Includes two double flat tips, hot air blow, hot knife & hot air deflector tips • Up to 580°C temperature range • Up to 120 minutes run time ONLY 209 $ TS1328 GREAT ES. FEATUR GREAT PRICE! 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Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. ONLY www.jaycar.com.au 1800 022 888 Contents Vol.37, No.10 October 2024 12 The life of Nikola Tesla, Part 1 Nikola Tesla was a prolific inventor, engineer, futurist, essayist and the original ‘mad scientist’. In this two part series we will cover his many (significant) contributions to society. By Dr David Maddison, VK3DSM Biographical feature The MIPI I3C Bus Feature: Page 28 Page 44 28 The new MIPI I3C Bus standard I3C (Improved Inter-Integrated Circuit) is one of the more recent serial bus standards supplementing I2C and SPI. This article compares I3C to the older standards, and explains what new functionality has been added. By Andrew Levido Digital interfaces 54 MG4 XPower Electric Car The MG4 XPower is a mid-sized battery-powered electric hatchback. After nine months and 20,000km with the MG4 XPower, is it any good? Review By Julian Edgar Electric vehicles 8-Channel Learning IR Remote Receiver PAGE 82 63 1-24V USB Power Supply The Zk-DP is an inexpensive supply module that converts 5V DC to any voltage from 1 to 24V DC at up to 3W. By Jim Rowe Using electronic modules 20 3D Printer Filament Dryer, Part 1 Store up to four 1kg reels of 3D printer filament in this Drying Chamber. The filament can then be fed straight to your printer from a small hole in its lid. By Phil Prosser 3D printer accessory 44 8Ch Learning Remote Receiver This eight-channel relay board can be controlled by nearly any IR remote control. Each output on the relay board can be set to toggle on/off, be switched on for a fixed period or stay on while the button is held down. By John Clarke Remote control project 66 Jaycar-sponsored Mini Projects This month we have a WiFi relay remote control, and an analog servo gauge which converts an analog voltage to a dial readout. By Tim Blythman Mini projects 72 Dual-Rail Load Protector This project disconnects a load from its power supply if the voltage is reversed or too high or if the current is above the adjustable trip level. It works with audio amplifiers, or other devices rated from ±4-36V DC. By Stefan Keller-Tuberg Power supply project 82 Micromite Explore 40 The Explore 40 (also called the Explore-40) is a Micromite in the same form factor as Raspberry Pi Pico boards. It allows you to build designs intended to use a Pi Pico but program them in Micromite Basic. By Tim Blythman Microcontroller project MICROMITE EXPLORE-40 2 Editorial Viewpoint 5 Mailbag 39 Circuit Notebook 81 Subscriptions 89 Serviceman’s Log 95 Online Shop 96 Vintage Radio 106 Mouser’s Aus Office 109 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata 1. 3-phase sinewave generator 2. Explore 100 Reflow Oven Controller 3. Supercap boost starter for vehicles 4. Caravan clock and power monitor The New Zealand-made ZC1 MkII military transceiver by Dr Hugo Holden SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $130 24 issues (2 years): $245 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint There are still TDM TLAs The phrase “TDM TLAs” (too darn many three-letter acronyms) was coined back around 1990 to describe the ridiculous number of three-letter abbreviations floating around. Since then, the problem has only gotten worse. Sometimes when I’m reading press releases or news articles, I’m forced to use Google to try to decode the gobbledygook presented to me. It isn’t helped by the fact that for any given set of three letters, there are probably a dozen (or more) possible meanings. It isn’t always easy to figure out which one the writer is referring to from context! Take, for example, DRM. If I wrote that DRM was bad (or DRM was good), what would that mean to you? Am I referring to Digital Rights Management? Digital Radio Mondiale? Disaster and Risk Management? Document and Record Management? Design Rules Manual? Design Review Meeting? Department of Resource Management? Data Recovery Module? (I could go on!) Did the folks who decided to call it Digital Radio Mondiale really want it to be confused with something that has negative connotations like Digital Rights Management? They could at least have called it Mondiale Digital Radio; MDR does refer to other things already, but nowhere near as many as DRM. In our articles, we try to spell out any term before we introduce its abbreviation. For example, if we introduce the concept of a digital-to-analog converter (DAC), then later we refer to a DAC, the reader should be able to understand what we mean. It’s when these things come out of the blue, and often in groups, that they can be perplexing. Here’s an example of a real sentence someone apparently wrote that I found online: Our team is using a CI pipeline with a new API to improve our POC for the CRM integration, but we ran into issues with the DNS when configuring the TLS settings. The devs are also considering switching the DB to a more robust SQL solution after some KPI analysis showed lag in the UX. Did you get that? Even if you’re familiar with some IT terms like CRM, TLS and SQL, you probably won’t know all of those terms, and you’ll have to go off searching for a while before you can decode that sentence. It’s really only helpful to experts in the field, so if you’re writing like that, you’d better be sure of who your audience is. It certainly doesn’t help that some of those terms have multiple meanings. For example, POC can be Point of Contact, Proof of Concept, Power Converter and some other, less flattering things (similar to POS). I have a sinking feeling that regardless of what I write here, the overcrowded list of abbreviations is only going to grow with time. Still, perhaps by ‘raising awareness’, we can work together to resist this scourge on our language. Subscription price changes From October 1st, 2024, prices for print subscription in Australia and New Zealand have increased slightly due to increased postage costs. For the new prices, see the adjacent side panel and page 95. The cover price has also increased by 50¢ (to $13.00). by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Collection of SC & EA magazines available in New Zealand My father (John Caudwell), a longtime tinkerer/repairer and subscriber of your magazine, recently passed away. He had accumulated a large collection of magazines from 1983 to 2024, being Electronics Australia up to 2000 and Silicon Chip from then on. The family has donated them to a charity in Whakatāne that can be contacted at: crew<at>pouwhakaaro.co.nz www.crewonline.org.nz Derek Caudwell, Tauranga, New Zealand. Old valve-based test equipment I recall reading about some home-made oscilloscopes in recent pages of Silicon Chip. I recovered Dad’s RF Output Waveform Scope from under the house. Switching it on, the CRT spot appeared on the screen; I don’t know if it had an internal timebase generator. Dad passed in 1994, aged 90. I think the origins of these instruments would date back to the 1950s, to Radio & Hobbies magazine. The L/C Bridge with the Magic Eye certainly would. I wonder if the ‘scope would be of interest to Mr Batty. I also have his Grid Dip Oscillator, with a cast aluminium handle branded VK3MX, in a protective cover. The coil set is somewhere, too. I’m just a little younger than Jamieson ‘Jim’ Rowe, who recently retired. I still have his book, “An Introduction to Digital Electronics”, in pristine condition. Robert Sebire, Emerald, Vic. Neutral vs Earth in domestic mains wiring After reading Mr Pierson’s article on an extension lead repair (Serviceman, August 2024), I have been prompted to mention my unusual experience with installing a GPO in an older house here in Germany. I also came across a projector that had its plug replaced incorrectly due to poorly thought-out colour-­coding of the wires. I was asked to replace a broken power socket in an older house here. The electrical installation regulations are much less stringent than in Australia & NZ, which makes me rather question whether the laws in Australia are perhaps a bit over the top sometimes. Anyway, I was allowed to tackle the task without needing certificates etc, so I set about investigating the situation in more detail. When I opened the wall socket, I noticed something unusual that was the norm here until about 30 years ago. To save wire, the regulations used to allow you to connect the Earth pin of the GPO to the mains Neutral conductor, rather than having a separate Earth conductor. The Neutral conductor is Earthed at the switchboard via various Earthing rods and water pipes etc (as in Australia). As long as that connection is intact (which is naturally a big assumption), it should still work OK. If the Neutral-Earth connection at the switchboard is not intact, the Neutral conductor should still be more-or-less at Earth potential anyway. If a device somewhere else in the house has a short to the ‘Earth’, a fuse should still blow. Otherwise, there is the danger that all the devices in your house are suddenly at 230V potential, which is probably not a good thing. Plenty of assumptions here! Anyway, virtually all houses here built before about 1979 have their GPOs connected this way and I have never heard of a problem. I would be interested in what your readers think about this configuration, which, thankfully, has now been discontinued. So, to get back to my GPO replacement, I cheerfully went about installing a proper Earth wire and noticed that the Photos provided by Robert Sebire showing his father with his home-made radios and test equipment. siliconchip.com.au Australia's electronics magazine October 2024  5 Neutral wire was red. Gasp! Another interesting German anomaly. For some unbelievably stupid reason, the Active wires in these older houses were black and the Neutral & Earth (if it existed) wires were red. The danger lurking here is obvious, as my experience with a slide projector I was given demonstrates. It didn’t seem to work properly and was prone to giving shocks sometimes. So I was asked to give it the once-over and see where and what the concern was. Well, it had a normal power cord with three conductors, as one would expect. My first check concentrated on the new plug that had recently been fitted as a replacement for an old, broken plug. When I opened the plug up, I noticed that, in keeping with the older colour coding, the wires were coloured red, red and black. How would you connect them to a new plug? Perhaps logically, the owner had attached the red & red wires to the power pins, and the black to Earth. What he didn’t know was that one of the red wires was the Earth and was connected to the projector housing! It was quite extraordinary that he was not killed in the middle of a slide show. As the plugs here are not polarised, depending on how he plugged the projector in, its metal housing was either close to Earth or at 230V. Of course, I fitted a new power cord with the correct colour coding. To return to my GPO, I left the red wires in place as they were in conduit in the wall and served other plugs and devices. However, I connected the Earth pin of the new GPO to a separate Earth conductor that I installed from the switchboard to the socket. This was still no remedy for the many other sockets in that house that continue using the (red!) Neutral wire as Earth. The main thing is that the owner is happy with his repaired GPO. Christopher Ross, Tübingen, Germany. Comment: using red for both Neutral & Earth (even if they will sometimes run via the same wire to the GPO) is a baffling decision; especially since in the old Australian scheme, which was probably used elsewhere, red indicated Active! Soldering SMDs not as difficult as first thought Thank you for your recent project of an Automatic LQ meter in the July 2024 edition of Silicon Chip (siliconchip. au/Article/16321). At first, I was reluctant to start a project using SMD components. Being an old-school TV Tech from the 1970s, it looked to be a difficult project. I decided to have a go anyway, and was pleased with the result. Soldering the SMD components was easier than I thought, even though a few expletives were mumbled when the components moved out of position when holding them down ready for soldering. The main problem I found was identifying the writing on the components, even with a magnifying light. I did, however, have success with taking a close up photo with my phone and then zooming in on the photo. Programming the Nano was also easy, and I was thrilled when I switched on the power to the LQ Meter and it worked perfectly first time! A photo of the finished device is shown at the lower left of this page. I urge anybody who is a bit reluctant to use these components to give it a go. It’s well worth it. Neville Bell, Wangaratta, Vic. Smartphones listen to your conversations I just received the June 2024 issue in the mail and have the following comment about privacy phones. While in earshot of an unattended smart phone, a mate and I had a detailed discussion about camel testes for a bit of fun. The resulting targeted marketing was hilarious; however, the phone’s owner was not amused! She was awakened to the ads she was receiving and as to why. After an incident that she described as ‘creepy’, I was asked about improving privacy on her older HTC-brand phone. As a well-known technician, I am expected to know everything about anything technical, but I had been able to avoid modern smartphones, so knew very little. I cherish my tiny Nokia 208 which, combined with the Nokia PC Suite on my Toshiba Tecra A-10, is an amazing device that allows me to do incredible tasks. I am certain that if Nokia produced an updated version, they could dominate the market again. The impending demise of the 3G network will force me to embrace ‘modern’ phone technology, so I took on the task to redeem myself and to learn. After some research, I settled on a Google Pixel 6 Pro phone on which I loaded GrapheneOS via the website. I easily transferred her contact list via a CSV file. The phone is very responsive, with a good battery life and takes excellent photos. I also set up her social media on her laptop with Firefox and Facebook Container to limit prying. She now feels safe, and I have redeemed myself for my initial mischief. I am preparing a replacement for my beloved Nokia; however, I live off-grid in an old shack where the only service is 3G and there has been no discussion of any 4G being provided to the area. With no NBN fixed or wireless services, and my ADSL service being recently discontinued, I anticipate a very quiet lifestyle. Chris Ryan, Dubbo, NSW. Date of TV shop photo and the fate of Stromberg-Carlson The finished LQ Meter assembled by Neville Bell. It was his first project involving SMDs. 6 Silicon Chip In the September issue, on page 74, the caption for the second photo on the left states it is “An HMV radio and television display circa 1969.” The picture depicts some 17-inch E1 or E2 TVs (a disaster for EMI, by the way) that were last produced in 1957. The rest of the TVs are from the F-series, which commenced in 1957. So the photo would presumably have been taken in 1957. Australia's electronics magazine siliconchip.com.au FREE Download Now! Introducing DaVinci Resolve 19 Edit and color correct video with the same software used by Hollywood, for free! DaVinci Resolve is Hollywood’s most popular software! Now it’s easy to create feature film quality videos by using professional color correction, editing, audio and visual effects. Because DaVinci Resolve is free, you’re not locked into a cloud license so you won’t lose your work if you stop paying a monthly fee. There’s no monthly fee, no embedded ads and no user tracking. 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Learn the basics for free then get more creative control with our accessories! so you are learning advanced skills used in TV and film� www.blackmagicdesign.com/au Learn More! NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING Also, in Vintage Radio on page 106, there is a statement that Stromberg-Carlson failed because it was not competitive in the TV market. That is quite untrue. They designed all their TVs in Australia and they were a good-performing, reliable product that incorporated many unique construction innovations and sold well. What killed Stromberg-Carlson was the twin effects of a huge bad debt from a major retailer (HG Palmer), who were actually trading insolvent, and the government-imposed credit squeeze of 1961. You can read about the fall of HG Palmer (apparently also due to the credit squeeze) in the Australian Financial Review at siliconchip.au/link/ac18 Henry Gordon Palmer was later sentenced for issuing a false prospectus, and was a guest of Her Majesty at the Malabar Mansions for a time. There was actually a connection between Stromberg-­ Carlson and Radio, TV & Hobbies magazine. Their early-­ 1960s electronic organ project started as a Stromberg-­ Carlson product for HG Palmer. I think it was made possible by the liquidation of the company. Ian Robertson, Belrose, NSW. Comment: regarding the photo, Kevin Poulter is checking his records to see if he can shed any light on the apparent misdating. It may be that the description for that photo was mixed up with another one. Regarding Stromberg-Carlson, Assoc. Prof. Graham Parslow points out that Admiral also went bust as a result of HG Palmer’s business strategy but AWA survived, so some TV manufacturers fared better than others. Keeping hands safe while using a sharp knife Thank you for another interesting project in the Styloclone musical instrument (August 2024; siliconchip.au/ Article/16415). I am currently getting parts to make it and looking forward to getting it singing. I will add it to my Skill Tester timber base, so there will be a kind of matching pair. One comment regarding your suggestion of a mesh glove for cutting. Another of my interests is bookbinding, which involves using a strong, very sharp blade to cut paper and thick card. After a couple of attempts to sever my left thumb (it’s never been quite the same!), I invested in a couple of safety steel rulers. One is the Maun Metal Safety Ruler, which has an M-shaped profile; your fingers are protected inside the central depression. Another is an anonymous type with a lift-up flap that protects your fingers. That might make it a bit easier to keep the cut straight than using a metal glove. David Coggins, Beachmere, Qld. Single-valve radio has room for improvement Thanks to Ian Batty for the kind words about the single-­ valve radio project (Mailbag, September 2024, page 6). That whole project really taught me a lot about the practical aspects of feedback, positive and negative. However, there is still another drop to squeeze out of the lemon! I wanted to implement ‘reaction’ feedback to the tuning coil as well, but ran out of time and the will to continue. You will note in the photo of the under chassis (July 2024, page 83) the aerial coil has a bunch of odd windings left on it. Some of that is the unused reaction coil. Having used reaction in another project and found out how much the overall gain and selectivity of a tuning stage can be improved, it would have been the ‘cherry on the 8 Silicon Chip Australia's electronics magazine siliconchip.com.au BUILD YOUR OWN MODULAR STORAGE SOLUTION! 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The improvement can be about the same effect as adding another tuned low-gain stage, and that is sorely needed in this one-valve radio. Perhaps one day I may revive the project and give it some more time. On the subject of running out of time, I wonder how many contributors or readers are in my age group. I passed the 80 mark in May this year and still run a workshop covering all sorts of hobbies, mechanical and electrical. Even if you are approaching invalid status, as I am, your brain still needs exercising; you can achieve a lot just shuffling around a workshop, slowly but surely. The lesson here to the guys and girls of this age is that you are never too old to learn and to make stuff. I wonder what the average age of readers and contributors is. Fred Lever, Toongabbie, NSW. Solar/wind vs nuclear power I read Kelvin Jones’ letter in Silicon Chip (page 12, July 2024). Coincidentally, an article from The Conversation by Peter Martin appeared on the ABC site, titled “When it comes to power, solar could leave nuclear and everything else in the shade” (siliconchip.au/link/abyt). A few salient quotes: “Whereas nuclear power is barely growing, and is shrinking as a proportion of global power output, The Economist reported solar power was growing so quickly it was set to become the biggest source of electricity on the planet by the mid-2030s.” “Installed solar capacity is doubling every three years, meaning it has grown tenfold in the past 10 years. The Economist says the next tenfold increase will be the equivalent of multiplying the world’s entire fleet of nuclear reactors by eight, in less time than it usually takes to build one of them.” Perhaps the main reason is cost, and Martin delivers a quote from The Economist to help explain: As the cumulative production of a manufactured good increases, costs go down. As costs go down, demand goes up. As demand goes up, production increases — and costs go down further. The main argument raised against solar is that the sun doesn’t always shine. Martin writes: [T]he efficiency of batteries is soaring and the price is plummeting, meaning that on one estimate the cost of a kilowatt-hour of battery storage has fallen by 99 per cent over the past 30 years. Australia’s energy market operator says record generation from grid-scale renewables and rooftop solar is pushing down wholesale electricity prices. Meanwhile, at The Conversation (and not yet at the ABC site), “Australia’s ‘carbon budget’ may blow out by 40% under the Coalition’s nuclear energy plan – and that’s the best-case scenario” (siliconchip.au/link/abyu). According to various “energy experts”, including the likes of CSIRO and AEMO, The Dutton Plan for seven nuclear reactors will come online too late to make up for the closure of coal plants with the prospect of blowing out our carbon budget by 40%, and will contribute only somewhere in the vicinity of 10% of the country’s energy needs all at enormous cost. The Dutton Plan is not so much a nuclear plan but a gas plan, probably to please some of his party’s donors. Meanwhile, renewables are expanding at a frightening pace and getting cheaper all the time. Martin writes: “In 2023, China 10 Silicon Chip Australia's electronics magazine siliconchip.com.au Despite the completely-broken screen, this laptop still worked using an external display. installed as much solar capacity as the entire world did in 2022.” Furthermore, in The Guardian, Graham Readfearn casts doubt on Dick Smith’s pronouncements, saying, “but CSIRO analysis shows his argument in meltdown” (see siliconchip.au/link/abyv). Backing nuclear power in preference to renewables is simply poor economic policy. Anybody nailing their colours to the mast of nuclear energy will see renewable alternatives overtaking them based mostly on cost, that is, the relative cheapness of renewables compared to nuclear and fossil fuels. After all, sunshine is free. Australia doesn’t even have a nuclear industry to speak of, so all the palaver about costs and projected timelines for completion is not much more than optimistic speculation. Phil Denniss, Darlington, NSW. How much punishment can a laptop take? I just read the July 2024 issue, and one of the first articles I read in each issue is Serviceman’s Log. This time, Dave tells of the trials of bringing equipment back from the dead, which hits a bit too close to home. A few weeks ago, my local Amateur Radio Club had a break-in. There wasn’t a lot of damage, except for how the vandals got in. All of our fire extinguishers had been let off and the powder was spread throughout the club rooms, with food and drink cans left behind as well. Quite a mess, to say the least. One thing that was severely damaged was a little laptop computer. It was used by a few of the members from time to time. It was connected to a television so we could use it for the occasional presentation. The people that broke in decided to take their anger out on this little laptop and damage the screen beyond repair. We all thought it was ready for recycling, but I decided to try and see if it would boot up. Firing up the television (thankfully it was not damaged) and changing over to the correct HDMI input, all of a sudden, the laptop display appeared on the TV screen. Except for the ruined screen, we couldn’t find any other problems. It looks like it will live another day! Stephen Gorin, Bracknell, Tas. SC siliconchip.com.au Australia's electronics magazine October 2024  11 1856–1943 Nikola Tesla the original ‘mad scientist’ B efitting someone who made such contributions, he was said to have been born during a violent lightning storm at midnight between July 9th and 10th, 1856, in Croatia. According to his family, the midwife said the lightning was a “bad omen” and that he would be a “child of darkness”, to which the mother replied, “No. He will be a child of light.” Fortunately, he became a force for good and lived for 87 years. He passed away in 1943, leaving a remarkable and world-changing legacy, which we will now examine. Of his numerous inventions & developments, among the most important were his contributions to threephase AC electricity, the induction motor, the Tesla coil (used in many early radios) and one of the world’s first hydroelectric power plants. The development of three-phase electricity allowed the transmission of electrical power over long distances, one basis of modern industrial civilisation. The electric car company Tesla is named after him. Two museums are dedicated to him, and there are statues of him on Goat Island, USA and Queen Victoria Park, Canada, both near Niagara Falls. There are also several Tesla memorial plaques in Manhattan, New York, USA. Tesla’s thought processes Tesla on the cover of Electrical Inventor magazine, February 1919. The lead image is based on a photo of Tesla from around 1900 demonstrating wireless power transmission. He is holding a partially evacuated glass bulb that’s glowing due to the electric field from a nearby Tesla coil. See https://w.wiki/ AZMz Tesla’s creative genius might be attributable to his unusual thought processes. These facilitated his ability to visualise and create things. He wrote in Electrical Experimenter, February 1919: In my boyhood I suffered from a peculiar affliction due to the appearance of images, often accompanied by strong flashes of light, which marred the sight of real objects and interfered with my thought and action. They were pictures of things and scenes which I had really seen, never of those I imagined... I was quite unable to distinguish whether what I saw was tangible or not. Then I observed to my delight that I could visualize with the greatest facility. I needed no models, drawings or experiments. I could picture them all as real in my mind. Thus I have been led unconsciously to evolve what I consider a new method of materializing inventive concepts and ideas, which is radically opposite to the purely experimental and... so much more expeditious and efficient. Australia's electronics magazine siliconchip.com.au Nikola Tesla was a prolific inventor, engineer, futurist and essayist. He spoke eight languages, had a wide range of interests and has been described as a “Renaissance man”. Despite his ‘mad scientist’ vibe, his contributions to our modern industrial civilisation are significant. Part 1 by Dr David Maddison, VK3DSM 12 Silicon Chip ... My method is different. I do not rush into actual work. When I get an idea I start at once building it up in my imagination. I change the construction, make improvements and operate the device in my mind. It is absolutely immaterial to me whether I run my turbine in thought or test it in my shop. I even note if it is out of balance. There is no difference whatever, the results are the same. In this way I am able to rapidly develop and perfect a conception without touching anything. When I have gone so far as to embody in the invention every possible improvement I can think of and see no fault anywhere, I put into concrete form this final product of my brain. Invariably my device works as I conceived that it should, and the experiment comes out exactly as I planned it. Also, like many creative geniuses, he had various eccentricities. Tesla, mathematics and quantitative theories Tesla was different from most other scientists and engineers. His writings are highly descriptive and contain few equations. He was a visual thinker and performed mathematics ‘visually’ rather than presenting it through formal methods. He also did not accept Maxwell’s equations, which are the basis of electricity, magnetism and optics. (“We can no longer believe in the Maxwellian hypothesis of transversal ether-undulations and the literal truth of its corollaries.” – siliconchip. au/link/aby0). He generally ignored quantitative theories; it has been suggested he may have suffered from “mathematical aphasia”. His work was experimental, usually practical, descriptive and not analytical. In that respect, he was much like Michael Faraday; it was Maxwell who turned Faraday’s intuitive ideas into equations. Separating fact from fiction While Tesla’s contributions to technology were undoubtedly outstanding, it should be recognised that work has been attributed to Tesla that either he did not originate or where he was a partial contributor. Also, during his lifetime, there was fierce commercial competition regarding which electrical supply technology was to be adopted, so there were often siliconchip.com.au An American postage stamp featuring Nikola Tesla. Source: https://postalmuseum.si.edu/ object/npm_2008.2007.74 claims and counterclaims made that didn’t necessarily reflect the reality of who invented what. Tesla had no marketing department; he had to do his own promotion, which is often reflected in his writing style. Not all of Tesla’s inventions or ideas were successful or viable. Tesla’s early work, such as with the induction motor, generators and the Tesla coil was excellent. However, some of his later work, which involved long-­ distance wireless electricity transmission, was not based on sound physical principles. Tesla’s patents Tesla was prolific and obtained around 112 US patents, 29 UK patents and six Canadian patents. He applied for 33 patents that were not granted. He also had patents in other countries for a total of around 300; for a complete list, see https://w.wiki/AZLY Tesla’s life and career We will now take a look at some of Tesla’s milestones in chronological order. This article will end in 1897; the remainder will be covered in the second and final article in this series, to be published next month. University 1875 to 1878 Tesla studied engineering from September 1875 at the Graz University of Technology in Austria but, having started with excellent results, did not finish his degree. He left after the first semester of the third year, apparently losing interest in his studies while spending too much time in a café and associated activities. He sat no exams that year and was excluded. While at university, he saw a Gramme dynamo, which operated either as a generator or motor. He conceived a way to eliminate the commutator, which his professor didn’t believe was possible. This ultimately led to Tesla’s development of the AC induction motor, which contains no commutators. He received an honorary doctorate from Graz in 1937. Prague 1880 Tesla arrived in Prague and spent much of his time reading at the Klementinum Library and Národní Interesting facts about Nikola Tesla ● He had a great sense of humour. ● He was a rival of Edison, not a sworn enemy; they had a mutual respect for each other. ● He had the idea of a ‘smartphone’ type device in 1901. He described to his then-backer J.P. Morgan a handheld device he said would deliver stock quotes and telegram messages. ● For unknown reasons, he hated pearls and would not speak to any lady wearing them. ● He had a photographic memory. ● He had a fear of germs, always wore white gloves and rarely shook hands. ● He asked for large numbers of napkins at meals. ● He never stayed in a room or floor number divisible by three. ● He ran his life according to a strict daily schedule. ● He was very particular about dress and grooming. ● He had a beloved pet pigeon. ● The SI unit for magnetic flux is named after him, the Tesla (T). ● Toward the end of his career, he ran out of profitable ideas, or at least people who were prepared to back him financially. As a result, he passed away in poverty with many unpaid debts. Australia's electronics magazine October 2024  13 Kavárna café. He also attended lectures at the University of Prague but was not enrolled as a student. magnetic field combined to create the AC induction motor. Budapest Telephone Exchange 1883 1881 In 1881, Tesla commenced work with the Budapest Telephone Exchange, a new company that was not yet functional. So he helped set it up, as a draftsman and later chief electrician, making several design improvements. Continental Edison Company 1882 In 1882, Tesla worked for Edison in Europe. He started by installing lighting systems, but his expertise was noted, and he became involved in designing improved dynamos and motors. Rotating magnetic fields 1882 The idea of a rotating magnetic field was conceived as early as 1824 by François Arago but, according to Tesla, he conceived of its use in an AC electric motor while walking through a park in Budapest in 1882 (documented on p198 of the PDF at siliconchip.au/ link/aby0). Although he doesn’t explicitly mention the rotating magnetic field, it was the basis of the motor. His idea of eliminating commutators and the rotating Prototype induction motor In 1883, while working for Edison in Strasbourg, he constructed (on his own time) an induction motor but could not find any interest in it. Emigration to the USA 1884 Tesla’s manager in Europe was recalled back to Edison in the USA and requested Tesla to come to work at the Edison Machine Works in New York City. There, he managed staff involved in installing New York’s electricity utilities. He was also involved in developing an arc lamp street lighting system, but that needed high voltages and was incompatible with the Edison system. Tesla’s designs were not utilised; there had been improvements in incandescent lighting. Tesla only worked there for six months before he left, apparently after a dispute about an alleged promised bonus. Tesla Electric Light & Manufacturing 1885 After leaving Edison, investors asked Tesla to design a system of electric arc lamps for lighting the streets of New York and other cities. This led to the establishment of the Tesla Electric What is polyphase electricity? Many early writings on AC electricity use the term “polyphase”. Polyphase refers to an AC electrical system with two or more AC voltage supplies supplied by separate wires and with the sinewaves of each displaced from each other by a certain amount, usually described in degrees. Early work on polyphase systems was with two phases, but today, three phases is the most common configuration. A three-phase system is twice as efficient at conductor utilisation as a single-phase system. Polyphase power, especially three-phase, is ideal for induction motors, as it can easily generate a rotating magnetic field, eliminating high-maintenance commutators and allowing simple and inexpensive construction. The principle of a rotating magnetic field in a threephase induction motor. The magnetic field sequentially rotates between the various motor poles, causing the rotor to follow it and rotate. 14 Silicon Chip Australia's electronics magazine Light and Manufacturing Company. Tesla continued obtaining patents for motors, generators and other equipment, but the investors showed no interest in those. They decided manufacturing was too competitive and just wanted to run an electric utility. They left the company, which left Tesla penniless; worse, he had assigned his patents to them in return for the now-worthless stock. He described it as “the hardest blow” he ever received. Digging ditches 1886 to 1887 After the failure of his company, he made a living digging ditches. Labs in New York 1887 to 1902 During this period, Tesla maintained a series of laboratories in Manhattan, New York. They were on Liberty Street (1887-1889), Grand Street (1889-92), South Fifth Avenue (1892-95) and East Houston Street(1895-1902). The Tesla Electric Company 1887 In 1887, with new investors, Tesla set up the Tesla Electric Company and the Liberty Street laboratory. In the same year, he invented an induction motor (patented in 1888) that would run on the newly developed AC system. It was becoming popular in Europe because of its advantages of long-distance transmission with little electrical loss. The motor used polyphase current which, at the time, was two-phase (we have three now). The polyphase current generated a rotating magnetic field. The advantage of this motor was that it did not need a commutator, which caused sparks, required high maintenance, and was expensive and complex. Apart from motors, Tesla developed generators and other power system devices. Polyphase induction motor patent 1888 In 1888, Tesla obtained US patent 381,968, the first of a series on electric motors (it continued until 1896). It was for commutator-free polyphase alternating current induction motors (see Fig.1). He envisaged two- and threephase motors in that patent. He also published descriptions of other motors, including a synchronous motor for which the rotation speed is locked to the AC power frequency. Those are ideal for clocks and other motors where precise speed control is essential. siliconchip.com.au induction and other types of electric motors and generators. Independently wealthy 1889 Tesla became independently wealthy due to Westinghouse licensing his patents, so he had the funds from 1889 to pursue his own interests. It has been suggested that Tesla was not a particularly good businessman and was always looking for investors, unlike Edison. Also, Tesla tended to work for himself, while Edison employed many other people and had multiple projects on the go at once. Wireless lighting 1890 Fig.1: a model of Tesla’s first induction motor at the Tesla Museum, Belgrade, Serbia. Source: https://w.wiki/AZM$ Galileo Ferraris independently invented and demonstrated a commutator-free two-phase alternating current induction motor in 1885, but he didn’t patent it because he could see no practical application. royalty clause on the motors and he later purchased the patent. The cancellation of the royalty clause meant that Tesla would get a minute amount of the true value of his motor and generator patents. Westinghouse Polyphase current and generators George Westinghouse of the Westinghouse Electric & Manufacturing Company was already marketing an AC power system and needed a suitable AC motor. He considered using Ferraris’ motor but decided that Tesla’s was superior. Tesla’s investors negotiated with Westinghouse in 1888 to license his AC transformer, dynamo and motor designs for cash and stock plus a royalty per horsepower of AC motor sold. He also hired Tesla as a consultant for a hefty fee. During 1888, there was intense competition between the three main electrical companies: Westinghouse, Edison and the Thomson-Houston Electric Company. There was also the emerging “war of the currents” between the AC system promoted by Westinghouse and the DC system promoted by Edison. Tesla’s motor was not immediately successful, and the adoption of the polyphase AC system was limited. The intense competition meant that Westinghouse did not have the resources to continue to develop Tesla’s induction motor or the polyphase AC system. Westinghouse was then in serious financial trouble. He explained the difficulties to Tesla, and in 1891, Tesla released Westinghouse from the The first of two important patents this year was US patent 390,413 for a “System of Electrical Distribution” for electrical transmission of polyphase power such that “two or more circuits may have a single return path or wire in common”. The second was US patent 390,414 on a “Dynamo Electric machine” concerning adapting existing dynamos easily and cheaply to polyphase alternating current. 1888 siliconchip.com.au 1888 A large number of patents 1888 to 1891 This period was enormously productive for Tesla; many patents were granted, including 43 US patents in the area of single and polyphase currents, In 1890, Tesla started experimenting with wireless lighting and performed public demonstrations with power transmitted by inductive or capacitive coupling. This work continued for about another ten years. Tesla coil 1891 In 1891, Tesla patented a type of resonant transformer that is now known as the Tesla coil (US patent 454,622). A resonant transformer uses capacitors across one or more windings, which act as coupled resonant tuned circuits. It produces high-voltage, low-current, pulsed or AC electricity at radio frequencies. Voltages produced can range from 50kV to millions of volts at 50kHz to 1MHz. The essential elements of a Tesla coil are an air-cored ‘oscillation transformer’, a capacitor, a high voltage primary transformer and a spark gap. Tesla used these coils in numerous experiments and built them to very large sizes, such as in Colorado and Wardenclyffe. Experiments Tesla used the coils for included investigating biological effects, high-frequency phenomena, lighting (for which the Fig.2: Tesla giving a demonstration of wireless power transmission in 1891. Source: https://w.wiki/ AZN2 Australia's electronics magazine October 2024  15 original patent was issued), phosphorescence, radio, wireless power transmission and X-rays. Tesla made a radio antenna out of the high-voltage end of the secondary part of the transformer, turning it into a radio transmitter. Such an arrangement was used in most early sparkgap radios for wireless telegraphy applications until the 1920s, when the vacuum tube rendered them obsolete. Lighting power supply 1891 In 1891, he applied for and was granted US Patent 454,622 for a means of generating high-voltage and high-frequency electricity for lighting purposes. Incandescents & power transmission 1891 In this year, he obtained US Patent 455,069 for an incandescent light. On May 20th, Tesla demonstrated wireless power transmission to the American Institute of Engineers in a lecture hall at Columbia University. The lecture was entitled “Experiments with alternate currents of very high frequency and their application to methods of artificial illumination”. In one demonstration, he vertically suspended two large zinc sheets from the ceiling, which were connected to a high-frequency, high-voltage Tesla coil. He held an unconnected gasfilled tube between them, and the tube glowed due to the electrostatic field between the sheets, just as a fluorescent tube glows when near a high-­ voltage power line due to capacitive coupling. Wireless power transmission 1891 to 1898 Tesla’s dream was global wireless electrical transmission. From 1891 to 1898, he performed numerous experiments and demonstrations in wireless Fig.4: in Tesla’s design, two single-phase alternators were magnetically coupled, 90° out-of-phase to provide two-phase AC for the exposition lighting. Note the alternator’s size in relation to the man. Source: https://historicpittsburgh.org/ islandora/object/pitt:20170320-hpichswp-0011 transmission via capacitive or inductive coupling (see Fig.2). In 1899, he commenced larger-scale experiments at Colorado Springs and later Wardenclyffe. AIEE organisation 1892 to 1894 From 1892 to 1894, he was vice president of the American Institute of Electrical Engineers, a forerunner of the IEEE. Visit to Europe 1892 He gave a series of lectures in London and Paris on “Experiments with alternate currents of high potential and high frequency”. Chicago World’s Fair 1893 Also called the World’s Columbian Exposition, was a significant turning point in the “war of the currents”, with Fig.3: nighttime lighting at the 1893 Chicago World’s Fair using Tesla’s patented AC and lighting systems. Source: https://w.wiki/ AZN3 George Westinghouse winning the lighting contract ($399,000) over Edison’s DC system ($554,000) – see Fig.3. Westinghouse used Tesla’s AC power patents to power lighting of their own design (they could not use Edison’s lights). The lighting and other systems at the fair used twelve 745kW 60Hz single-phase AC generators of Tesla’s design. These were mounted in pairs and arranged to provide twophase power (see Fig.4). The Westinghouse Company also had a section showcasing Tesla’s inventions, such as induction motors (Fig.5) and generators. The rotating magnetic field used in induction motors was demonstrated with the “Egg of Columbus” (Fig.7). Tesla demonstrated wireless lighting using neon tubes, although he did not invent neon lighting (see Fig.6). He also demonstrated clocks synchronised to the mains frequency. Talks at Franklin Institute & NELA 1893 His talk was “On light and other high frequency phenomena” and he mentioned the “transmission of intelligible signals and power to any distance without the use of wires” (radio). He also discussed the idea of transferring power over long distances through the Earth. Niagara Falls hydroelectric power 1893 In 1893, Tesla was invited to consult for the Niagara Falls hydroelectric 16 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.5: an exhibition of Tesla’s motors and the “Egg of Columbus” at the 1893 Chicago World’s Fair. Source: https://w.wiki/AZN4 ► Fig.6: Tesla’s wireless lighting demonstration using neon tubes at the Chicago World’s Fair. project. Proposals that had been put forward for the electrical system included two- and three-phase AC and high-voltage DC. Tesla advised that a two-phase AC system from Westinghouse, designed by Tesla and based on his patents, was the best and most reliable option (see Fig.9). Westinghouse was awarded the main contract based on Tesla’s advice and the success of the Tesla and Westinghouse displays and lighting system at the Columbian Exposition. Nine of the twelve patents used for the plant’s machinery were Tesla’s. Electricity from the plant first went to a nearby factory in 1895 and then to Buffalo, New York, in 1896. At a talk about the City of Buffalo receiving power from Niagara on January 12th, 1897, at the Ellicott Club, Tesla said: It is a monument worthy of our scientific age, a true monument of enlightenment and of peace. It signifies the subjugation of natural forces to the service of man, the discontinuance of barbarous methods, the relieving of millions from want and suffering. From “The Age of Electricity” by Nikola Tesla, Cassiers Magazine – London, March 1897, pp378-386. This AC power plant is regarded as the final victory of the “war of the currents”, with Tesla’s AC proving itself superior to Edison’s DC. A low frequency of 25Hz was chosen, as it was expected that much of the Fig.7: a drawing of the “Egg of Columbus” that was designed to demonstrate the rotating magnetic field devised by Tesla. Source: https://w.wiki/AZN5 siliconchip.com.au Australia's electronics magazine power would be converted to DC via rotary converters for uses such as aluminium production. However, it was realised that three-phase power was superior for transmission efficiency, so phase-changing transformers were used to convert the two-phase power to three-phase. These are known as “Scott-T” transformers since they were invented by Charles F. Scott, who worked for Westinghouse in the late 1890s. The configuration of this type of transformer is shown in Fig.12. The first output phase (0°) is a direct transformer-­ coupled copy of the first input phase (0°) via transformer T1. The second phase at 120° is generated by connecting the centre tap of Fig.8: a drawing of Tesla lecturing before the French Physical Society and The International Society of Electricians in the 1880s. October 2024  17 Fig.9: ten 3.7MW 25Hz 2kV Westinghouse generators at Edward Dean Adams Power Plant in Niagara Falls, installed in 1895. The voltage was stepped up to 10kV or 20kV depending upon how far away the destination was. These generators remained in use until 1961. Source: https://w.wiki/AZN6 Fig.10: the “unipolar vacuum tube” comprising a glass bulb (b), a single electrode (e) and a lead-in conductor (c). A second electrode could be added towards the bottom; otherwise, the return circuit was via capacitive coupling through the air. Source: Tesla Universe – siliconchip. au/link/abyf T1’s secondary to the lower (90°) end of T2’s secondary and adding a tap at √3 ÷ 2 or 86.6% of T2’s secondary. The third phase requires no extra connections to generate as the 240° waveform is simply available as 360° − 120° (360° = 0°), so between the start of T1’s secondary and that same 120° tap. This can also work in reverse, to convert three-phase to two-phase, but in that case the load has to be perfectly balanced, as it would be in a motor. Wireless World System 1893 and later In 1893, he established the foundations of what he would call in a 1900 brochure, “The Wireless World System”. It was to be a global wireless communications and wireless power transmission system (see Fig.13). According to Tesla, it would allow “the transmission of electric energy without wires” as well as point-to-point communications. He said that the communications aspects of the system would allow “the instantaneous and precise wireless transmission of any kind of signals, Fig.12: a simple but clever way to convert twophase AC to threephase. messages or characters, to all parts of the world.” and “... an inexpensive receiver, not bigger than a watch, will enable him [the user] to listen anywhere, on land or sea, to a speech delivered, or music played in some other place, however distant”. In 1915, in the New York Times, he added that the system “would enable thousands of persons to talk at once between wireless stations and make it possible for those talking to see one another by wireless, regardless of the distance separating them” (see page 136 of the PDF at siliconchip.au/link/ aby0). All that sounds very familiar today! To implement this system, he convinced banker John Pierpoint Morgan (J.P. Morgan) to invest in this project, which he built at Wardenclyffe on Long Island, New York (more on that next month). Tesla received numerous patents for wireless communications and power transmission, such as transformer design, transmission methods, tuning circuits and signalling methods. Tesla also envisaged a system of thirty telecommunications towers worldwide, linked to telegraph and telephone systems. He proposed transmitting “radiations”, which were not Hertzian waves and would apparently travel through the Earth with little loss. The energy of such waves could be harnessed anywhere on Earth simply by placing a wire in the ground. We now know that radio waves do not travel through the Earth to any significant degree. A reciprocating engine 1894 In 1894, Tesla received US patent 514,169 for a multipurpose reciprocating engine device that used gas or Hand pump The wireless light: place a wire in the ground that is all G = pressure indicator gages Flexible spherical envelope filled with liquid or gas Analogy of Tesla’s Earth Wave Vibration Theory Each pulse of the pump is felt with equal force at all points of he sphere Tesla’s wireless power for properlling ships and aeroplanes Tesla’s Wireless Transmission Theory The oscillating energy surges thru the Earth to every point on the globe. Thus electric light, heat and power can be drawn to any point of the Earth from a universal central station Fig.13: Tesla’s proposed scheme to deliver light and power anywhere on Earth by “ground waves” travelling through the Earth. Illustration by Tesla from Electrical Experimenter, February 1919. Source: https://w.wiki/AZN8 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.11: a colourised photo of the interior of Tesla’s East Houston St lab. It is lit by lights of Tesla’s design. Source: https://teslaresearch. jimdofree.com/ labs-in-newyork-1889-1902/ steam pressure to generate mechanical oscillatory movement to generate electricity or for other purposes. The development of efficient steam turbines rendered its use for electricity generation obsolete. In the New York World-Telegram of July 11th, 1935, Tesla recounted an incident of 1887 or 1888 where he said a little version of this device apparently brought an entire building to resonance, potentially destroying the building had he not stopped the it with a hammer (www.rexresearch. com/teslamos/tmosc.htm). Mythbusters looked at this in their episode on “Nikola Tesla’s Earthquake Machine!” (season 4, episode 20 – https://youtu.be/LHsHiKtjoag). X-rays 1894 In 1894, Tesla worked with Crookes tubes and a “unipolar vacuum tube” of his own design. He noted mysterious damage to photographic plates in his laboratory by some sort of radiant energy. Although X-rays had yet to be discovered or named, Tesla realised the source of the damage was rays from the point where the “cathodic stream” in the devices struck the anode (Crookes tube) or glass wall (his tube) – see Fig.10. It was later discovered that such a process generates X-rays. In 1895, Wilhelm Röntgen discovered and published work about this “new kind of rays” (X-rays). Tesla started to work on X-rays and, in 1896, he reported being able to produce radiographs at a distance of ~12m; see siliconchip.au/link/aby0 (p33). siliconchip.com.au Had Tesla fully recognised the phenomenon causing damage to his photographic plates, he may have been credited with their discovery. Tesla gave Röntgen full credit for his discovery. Later versions of Tesla’s unipolar vacuum tube had a cooling system. Laboratory fire 1895 In March 1895, Tesla’s laboratory at South Fifth Ave, New York (occupied 1892-1895) burned to the ground. Tesla lamented, “I am in too much grief to talk. What can I say? The work of half my lifetime, very nearly all my mechanical instruments and scientific apparatus, that it has taken years to perfect, swept away in a fire that lasted only an hour or two... Everything is gone. I must begin over again.” This is said to have delayed his application for radio patents. Wireless power experiments 1895 In his East Houston Street laboratory (1895-1902), he conducted experiments on the wireless transmission of electricity, setting up large Tesla coils, other types of resonant transformers and other apparatus (see Fig.11). He was producing up to 4MV, the maximum he could safely work with in a city building. The Nikola Tesla Company 1895 In 1895, the Nikola Tesla Company was set up to fund, develop, and market Tesla’s patents, which it did for the next few decades. Transformers/induction coils 1897 In 1897, he was granted US patent 593,138 for a safe high-­voltage, high-frequency electrical transformer/ induction coil. In this patent, he showed single-wire electricity transmission with the return circuit flowing through the Earth. This concept was recently demonstrated in 2023, when Australia's electronics magazine 5kW was transmitted over 5km with 87% efficiency; see https://ieeexplore. ieee.org/­document/10023995 Application for radio patents 1897 In 1897, Tesla applied for US patents 645,576 and 649,621, both granted in 1900. These are considered his first radio patents, which he stated were relevant to “energy of many thousands of horsepower [being] transmitted over vast distances”. In other words, he thought large amounts of electrical power could also be transmitted via this technology. At this stage, wireless power transmission was his main focus, rather than radio communications. Contrary to popular belief, Tesla did not invent radio and, unfortunately, did not have a good or correct understanding of the physics involved. In 1900, Guglielmo Marconi also applied for a US patent for radio, but it and subsequent revisions were rejected based on Tesla’s preexisting patents. However, in 1904, Marconi was granted US Patent 757,559 for radio, which he had applied for in 1901. Marconi had also previously applied for a British patent for radio in 1896, and it was granted in 1897, predating Tesla. The British patent (12,039) was the first for a system of wireless telegraphy using Hertzian waves. Marconi was thus recognised as the inventor of radio; he shared a Nobel prize for it in 1909 with Karl Braun. Of course, there were many other contributors to the invention of radio, such as Reginald Fessenden, Heinrich Hertz, Oliver Lodge and John Stone. There was litigation over early radio patents, and in 1943, the US Supreme Court settled a case involving Tesla’s patents. However, it was not, as is often claimed, a case about who invented radio but who would be compensated by the US Government for using various patents during WW1. The story is too complicated to go into here; see https://earlyradiohistory.us/tesla.htm Next month In the following article, we’ll pick up where we left off and cover the remainder of Tesla’s life, from 1898 until his passing in 1943. We’ll then go over related topics such as Tesla’s mistakes and misconceptions, why the World Wireless System could never work, the ‘war of the currents’ and Tesla’s lost files. SC October 2024  19 3D Printer Filament Drying Chamber This enclosure can store up to four 1kg reels of 3D printer filament, keeping them dry and ready for use at any time. You don’t even need to remove them – the filament can simply be fed to the printer through a small hole in its lid! Part 1 by Phil Prosser T he ability to produce functional 3D parts, either standalone or as part of a larger project, is incredibly useful. Over the last few years, 3D printer prices have fallen remarkably. You can now find some amazingly-priced 3D filament printers on the market. The major Australian electronics stores (Jaycar and Altronics) both stock “Creality” products, which I think are excellent. There are plenty of other good alternatives available online. My grandson, who wanted to buy printed parts, drew me into this. I pointed out that for the price of a handful of ‘bought bits’, we could buy our own 3D printer. So I did. I quickly found that being able to manufacture complex 3D parts was incredibly handy. Like most of these technical things, once you start, there is an amazing range of extras you might want or need. One surprising accessory is a filament dryer. It had not dawned on me that plastic filament can absorb moisture. However, PLA (polylactic Photo 1: the surface of the black boat is not smooth due to moisture in the filament. The white filament was dry, giving a much better result. 20 Silicon Chip acid), probably the most common filament these days, is sufficiently hygroscopic that moisture can become a real problem. 3D printers work by heating the plastic filament to around 200°C (or much hotter for materials like ABS) and extruding it through a small nozzle, typically 0.4mm in diameter. The printer acts like an X-Y plotter and deposits lines of melted filament where required, in layers, thus building the part. It is incredible to consider that a large print may have the printer laying down material in this manner for 12-24 hours, all without error. If that sounds too complicated to be reliable, well, you need to get many things right for the printer to work well. However, when set up correctly, reliable results can be achieved. I would say that most electronics hobbyists would have the inclination, skill and inquisitiveness to learn the tricks and tips required to keep a 3D printer running, but they certainly are not ‘set and forget’. When I first ran the printer, things went swimmingly well. However, I later realised that even a little moisture in the filament can cause problems when it is heated in the extruder. The moisture boils into steam, which pushes filament out of the extruder and causes ‘blobs’ on the print. Photo 1 tries to show the difference between fresh new filament (white) Australia's electronics magazine and some that had been lying around (black). All the printer knows is that it has driven the correct length of filament at the right time, but the ‘blobs’ mean it doesn’t end up exactly where it should be. So surfaces can get ‘blobby’, and you hear small popping noises during printing. While PLA certainly suffers from these problems, other materials, such as Nylon, also have a terrible reputation for being hygroscopic and hard to print with. While the printers themselves are competitively priced, I was not really into spending hundreds more on a fancy filament dryer. Some people use a food dehydrator, which, while cheap, does not handle multiple reels or allow you to feed straight from the dryer to your printer. I was convinced that I could easily make something to do the job with a handful of bits from the spares box, a leftover laptop power supply and maybe a microcontroller. We can even customise the size and shape to suit our workspace and needs. So, while we provide a complete parts list here, you can modify the design to reuse bits you already have, saving a few bucks. There does not seem to be a specific ‘right way’ to dry or, perhaps more correctly, dehydrate filament. All approaches use an elevated temperature and some form of timer. Some add air circulation, while a few incorporate siliconchip.com.au a mechanism to change the air in the box periodically. The idea of heating the filament in a sealed enclosure is that when the air in the enclosure gets hotter, it can hold a lot more moisture, so relatively speaking, the air is dryer. In other words, the relative humidity of the air in the box reduces as it is heated. Fig.1 shows that for a typical room at 20°C and 40% relative humidity (RH), there is about 6g of water per kilogram of air. If the box is sealed, there is always the same amount of water in the box. So, at 42°C, we see the relative humidity will be about 10%. Because the air is now quite dry (for its temperature), it pulls moisture from everything in the box. PLA filament that has absorbed moisture does not dry out quickly; drying times are typically 6-9 hours. By keeping the dryer sealed and including some desiccant, such as silica gel, in the enclosure, we can keep the filament dry and ready for use. If you will not use the dry filament for a while, it remains a good idea to seal it in a vacuum bag. and substantial protection circuitry. The second part is making an enclosure for the filament. There are several possible approaches, ranging from very simple to quite complicated. Choosing your approach to the container is probably the most critical choice, as the controller is not that complicated. We built two enclosures. The first was a custom one optimised for our needs and just a little bit fancy – see Photo 2 and the image above. The second was an 18L plastic tub into which we installed the controller and heater (Photo 3). The latter proved to be quick and simple to assemble and quite effective. It must be said that it looks a lot like a plastic tub, though. We will provide an overview of how to build the custom enclosure but will not go into great detail. If you are not confident in filling in the details yourself, stick to using the off-the-shelf plastic tub. Both enclosures use the exact same controller, but we have arranged the heating plates quite differently to suit the differing enclosure shapes. In both cases, we found that without adding insulation to the enclosure walls, we could achieve about 47°C inside with 50W of heating. Adding a layer of Corflute to the bottom and walls of the enclosures increased the temperature at that power level by well over 5°C, effectively reducing the amount of power needed to keep the enclosure at a given temperature. The unit is powered by either a 24V DC 4A plugpack or an 18-24V 3A+ DC laptop power supply. Is it just me who has a growing collection of these things, which seem to outlast the laptops they powered? Either way, it drives a resistive heater in the box via a control board, much of which is safety circuitry. We put a couple of small bags of silica gel in the box to absorb any The design This project has two distinct parts. The first is a filament dryer controller board. This is a standalone thermostat controller board that could equally be used to control an incubator or curing oven for painted parts. The board is essentially a thermostat with a timer siliconchip.com.au Fig.1: water in the air plotted against temperature for a range of different relative humidity (RH) values, from 10% to 90%. You can see how hotter air can contain a lot more moisture for the same RH figure. Australia's electronics magazine October 2024  21 moisture released by the filament and occasionally change the air in the box to expel excess moisture. Cat litter crystals are simply silica gel, so for $10 at the local supermarket, we got a huge bag of silica gel from which we make our own drying sachets. We just put it in paper envelopes to pop in the dryer. Our filament dryer hangs the reels on a rod and allows you to draw the filament straight from inside the dryer box. We decided to omit a fancy display, which technically is not hard but adds construction constraints and cost. During development, we noted that even with a fan circulating air in the dryer, the temperature throughout the box varied significantly. So, a temperature display may feel important, but it would only be indicative. Leaving out the display also avoids the need for a humidity sensor. This decision was hard but it keeps things simple and cheap. If the box is warm and you have fresh silica gel, after a couple of cycles, your filament will be as dry as it will get. Some really cheap humidity sensors are available online that you can pop in the box if you want to monitor it. Because we are making potentially combustible materials hot, we have taken a very conservative approach to the design to ensure that it is as safe as reasonably possible. Refer to the text box on safety analysis for a discussion of how key design drivers were arrived at. If you are designing your own enclosure, you should consider the hazards we list and satisfy yourself that your approach mitigates all hazards. The design presented here is mostly about implementing the control and safety systems identified in Table 1, which mandate the following inclusions: • A controller that maintains the Dryer in a safe state until the user deliberately starts a cycle. • A thermostat, allowing the temperature to be set from room temperature to 50°C. • A timer that allows a six- or ninehour drying period, then shuts the heater down. Table 1 – Hazard & Risk Assessment Hazard Initial Risk Mitigation Final risk High Implement a temperature control system. Limit the maximum energy available so the ultimate temperature without control is safe (50W gives a maximum of around 60°C). Low Short circuit or critical component failure Low Integrate thermal switches/fuses that disable the system at a safe temperature. Include a fuse in the design, to blow in case of a catastrophic short. Low Excessive heating since the control system does not sense the real temperature Moderate Include a fan to circulate air throughout the enclosure. Low Failure of fan results in loss of thermal control Low Integrate a ‘fan operating’ sensor and shut the heater down if the fan fails. Low Heating element contacts personnel Medium Mount heating resistors inside a plenum or behind sheet aluminium to minimise the likelihood of contact with personnel. Low Personal injury User touches energised part Medium Operate the dryer from an isolated plugpack with a low voltage output. Low Electric Shock Long-term heating results in auto-ignition of material Low A timer shuts the unit down after six or nine hours Low Fire and uncontrolled energy Enclosure operates unexpectedly Medium The system starts in an idle state. Force the user to press a start button to commence drying. Low Inadvertent operation Software fails Low Critical controls (thermal- and energy-related) are to be implemented in hardware. Low Inadvertent operation Heating element touching combustible material Medium Limit the heating power such that the element does not exceed 80°C. Mount the heating element so it is not in permanent contact with timber. Use polypropylene Corflute for insulation, which has an autoignition temperature of 288°C (flash point 260°C). Low Fire Misuse – user fills the enclosure with rags or paper Medium Integrate thermal cutout on heater plates at 90°C (high but safe). Low Fire Misuse – user covers the dryer with a blanket Medium Use a thermostat to control the internal temperature, with a safety shutdown & timer. Low Fire Uncontrolled heating, causing the enclosure to become excessively hot 22 Silicon Chip Australia's electronics magazine Consequence if not mitigated Damage or combustion of filament or enclosure siliconchip.com.au • Onboard fusing. • A thermal cutout on each heater element. • A thermal fuse on the controller board. • The maximum heating power is limited to 50W. • A ventilation fan that is integral to the controller board, ensuring airflow in the box. • An interlock that shuts down the heater if the ventilation fan stops. We have spread the heating across six 25W resistors, which dissipate 8W each into the large aluminium heating element. Even if everything fails, they will never get hot enough to create a hazard. We tested our two boxes with all controls disabled and determined that 50W of heating resulted in a maximum box temperature of no more than 60°C. Looking at what is on the market and having read a lot of tests on commercial filament dryers, most make wild claims as to the temperatures they achieve. We feel that 50-55°C is a good, safe temperature. If you want it to get hotter, you would need to increase the power or reduce the size of the box. The controller will accommodate that, but we advise you approach any changes with appropriate caution. You may have your own spin on how to build this; you could design a box that better suits your needs and use a surplus power supply. You could even reuse some different heating resistors. That will let you build a dryer for a fraction of the cost of a ‘bought one’, but make sure you follow our safety tips so everything goes well for you. We will first describe the controller and then present a couple of way it can be used. Photo 2: this DIY timber box can be sized to suit your needs. It has a rod for hanging the reels and convenient handles. The lid is removable and has a hole for feeding filament through. The controller The controller can operate from 18-24V DC, so you can recycle a laptop supply or similar power brick. It must deliver sufficient current for your resistor bank. The input is fused; select a fuse rating an amp or so above your expected maximum operating current. There is also a polarity protection diode that will dissipate about 2W; we have included heatsinking fills on the PCB, and this ‘extra power’ simply adds to the overall heating in the system. The controller is expected to be siliconchip.com.au Photo 3: this box from Bunnings doesn’t look as elegant and may be a little large for some people, but it’s much less work to prepare and does the job well. Australia's electronics magazine October 2024  23 installed inside the Filament Dryer, as that simplifies the wiring, and the temperature sensor is on the board. This means the controller will be operating at up to 50°C, perhaps a little more. That fine for most electronic components, but you will notice that we have specified high-temperature electrolytic capacitors and allowed for heatsinks on transistors Q1 and Q2. Circuit details The circuit is shown in Fig.2. An 8-bit PIC16F15214 operates as the timer, while an LM336-2.5 voltage reference (REF2) is used to produce a 2.5V reference, which is buffered by half of an LM358 op amp (IC1a). This is used in the temperature measurement circuit. The reason we have chosen the LM336-2.5 is it produces a reference voltage that is very stable over a wide temperature range. The LM336-2.5 has a variation of just 6mV over 0-70°C, so we can expect to see an error of less than a degree in temperature control over our operational range. The temperature sensor itself is a simple 1N4148 silicon diode (D6), using its -2.1mV/°C temperature coefficient. This is stable, reliable and used in many measurement circuits. The controller is a ‘Bang-Bang’ style, which simply turns the heating element on and off rather than implementing fancy control loops. This choice is again to keep things simple and cheap. The controller comprises half of the LM358 (IC1b), which compares the voltage across the sense diode to the temperature set voltage. We use the 2.5V reference voltage to set the current through the sense diode via a 4.7kW resistor. The same reference Fig.2: the circuit of the Filament Dryer Controller. REF2 and IC1a create a 2.5V reference (trimmed by VR1). This biases diode D6, the temperature sensor. The voltage across D6 and the setpoint from VR2/VR3 are compared by op amp IC1b to drive Mosfet Q2 for powering the heating elements. Microcontroller IC3’s timer limits the heating time and powers the fresh air fan periodically. 24 Silicon Chip Australia's electronics magazine siliconchip.com.au voltage generates the set voltage using trimpots VR1 and VR2 plus a couple of padder resistors. By using this very stable 2.5V reference, we can be assured that the current through the sense diode and the set voltage are constant over time and temperature. At room temperature, there is 400μA flowing through the sense diode, giving 0.56V across it. With the 12kW and 2.7kW padders and two 500W potentiometers, we get a temperature set point range of about 20-50°C. The reason we have included two pots is to allow us to use one (VR2) to set the minimum temperature to room temperature, while the other (VR3) is used to choose the temperature setpoint. With trimpot VR2 at the nominal value of 220W, the minimum voltage will be 0.489V (2.5V × 2.90kW ÷ [12kW + 2.92kW]). The maximum voltage will be 0.554V (2.5 × 3.42kW ÷ [18kW + 3.42kW]). The difference is 0.065V, and at 2.1mV/°C, that gives a spread of 31°C. Even using 1% resistors, the errors in the voltage divider are significant. If one is 1% high and the other is 1% low, the setpoint could move as much as 7°C. By adjusting VR2 so the minimum setpoint is room temperature, we can calibrate such errors out. The output of IC1b is low when the sensed temperature is below the setpoint and goes high when the temperature exceeds the setpoint. The 8.2MW resistor adds about 2°C of hysteresis by feeding back the output voltage to slightly shift the setpoint voltage. The ratio of the 8.2MW and 4.7kW resistors results in a shift of just a couple of milivolts, which is what we need. This stops IC1b from oscillating once the setpoint is reached. With the controller being flat out on or off, and the degree or two of hysteresis, the temperature control is not super precise. But for warming the filament to dry it out, that is OK. For the timer, we started by considering simple CMOS timer circuits and the venerable 555. To get a nine-hour period from these is not easy, so the cheapest way to make the timer was to use a PIC. These cost nearly $1.50 in single units, a fraction of the cost of the discrete solution, and can be programmed to do a huge range of jobs. We consider the timer to be an integral part of this design and strongly recommend against omitting it. Parts List – Filament Drying Chamber siliconchip.com.au Australia's electronics magazine 1 double-sided PCB coded 28110241, 126 × 93mm 1 18-24V DC 3A+ power supply (eg, laptop charger) 2 12V DC 40mm fans, 10mm-thick [Altronics F0010A] 1 40mm fan grille [Altronics F0012] 2 PCB-mounting M205 fuse clips (for F1) 1 5A 250V M205 fuse (F1) 1 77°C axial thermal fuse (F2) [Altronics S5631] 5 2-pin vertical polarised headers, 2.54mm pitch (CON1-2, CON4-5, CON7) [Altronics P5492] 5 2-pin polarised header plugs with pins [Altronics P5472 + 2 × P5470A each] 1 5-pin header, 2.54mm pitch (CON6; optional, for programming IC3 in-circuit) 1 PCB-mounting DC socket, 2.1mm ID or to suit power supply plug (CON8) 1 PCB-mounting 90° miniature SPDT toggle switch (S1) [Altronics S1320] 1 PCB-mounting 90° sub-miniature SPST pushbutton switch (S2) [Altronics S1498] 1 10kW side-adjust single-turn trimpot (VR1) 1 500W side-adjust single-turn trimpot (VR2) 1 500W 16mm single-gang linear potentiometer (VR3) 2 TO-220 micro-U heatsinks (optional) [Altronics H0627] 2 90°C normally-closed (NC) thermal switches/breakers (S3, S4) [Altronics S5612] Hardware (common to both versions) 1 3D-printed vent (“Vent Rotor.STL”, “Vent Rotor Base.STL” & “Vent No Fan.STL”) 1 3D-printed fan cover (“Fan Shroud.STL”) 6 M3 × 25mm panhead machine screws 18 M3 hex nuts & 32 M3 flat washers 1 3m length of high-temperature (90°C+) heavy-duty hookup wire 1 250mm length of 6mm diameter heatshrink tubing 1 2m length of 5-10mm wide open-cell foam adhesive tape 1 small tube of thermal paste Hardware (for plastic box version) 1 polypropylene box [Bunnings 0171464] 2 1.5mm-thick aluminium plates, 210 × 180mm Panhead machine screws: 8 M3 × 6mm, 32 M3 × 10mm, 8 M3 × 16mm, 6 M3 × 25mm Tapped spacers: 4 M3 × 15mm, 16 M3 × 25mm male/female hex spacers [Altronics H1243] Other: 58 M3 shakeproof washers, 46 M3 hex nuts Hardware (for timber box version) 2 3D-printed handles (“Filament Dryer Rail Tall.STL”) 1 sheet of 12mm MDF or plywood 1 1.5mm-thick aluminium plate, 330 × 225mm Panhead machine screws: 6 M3 × 6mm (30 if building lid), 16 M3 × 10mm, 4 M3 × 16mm, 24 M3 × 25mm, 1 M4 × 10mm (for attaching handle to lid) Tapped spacers: 12 M3 × 6mm (for lid), 10 M3 × 15mm Other: 42 M3 shakeproof washers, 38 M3 hex nuts Capacitors 1 470μF 35V 105°C electrolytic [Altronics R4865] 2 10μF 50V 105°C electrolytic [Altronics R4767] 7 100nF 50V multi-layer ceramic or MKT Semiconductors 1 LM358 dual single-supply op amp, DIP-8 (IC1) 1 LM336BZ-2.5 voltage reference diode, TO-92 (REF2) [Altronics Z0557] 1 PIC16F15214-I/P 8-bit microcontroller programmed with 2811024A.HEX, DIP-8 (IC3) 1 LM317T adjustable positive linear regulator, TO-220 (REG1) 1 BD139 80V 1.5A NPN transistor, TO-126 (Q1) 1 IRF540(N) 100V 30A N-channel Mosfet or similar, TO-220 (Q2) 2 BC548 30V 100mA NPN transistors, TO-92 (Q3, Q4) 1 BC338 25V 800mA NPN transistor, TO-92 (Q5) 1 BC558 30V 100mA PNP transistor, TO-92 (Q6) 4 1N4004 400V 1A diodes (D1, D3, D11, D13) 1 R250H or 6A10 400V 6A diode (D2) [Altronics Z0120A] 3 1N4148 75V 200mA diodes (D4-D6) 1 12V 0.4W or 1W zener diode (ZD10) 2 5mm red LEDs (LED7, LED8) 1 5mm green LED (LED12) Resistors (all ¼W 1% axial unless noted) 1 8.2MW 1 100kW 1 12kW 12 4.7kW 1 2.7kW 3 1kW 1 330W 1 47W 6 39W (18V), 47W (19-20V) or 68W (24V) 25W aluminium body resistors [Ohmite HS25 series] October 2024  25 Our dryer includes two fans. The first is to circulate air inside the box and it runs full-time. There is also a ventilation fan that runs briefly every 10 minutes. This is intended to draw fresh air into the box and to exhaust the hot (and possibly moist) air. This ventilation fan is driven by the PIC microcontroller. We do not want to continuously change the air in the enclosure, as it would require a lot of power to keep the temperature elevated. So our tiny PIC microcontroller drives the vent fan sparingly. Software The program in the timer is quite simple. At power-up, the PIC goes into an idle state, disabling the heater and ventilation. It stays in this state until the user presses the start button. This requires a deliberate action by the user. Once the start button is pressed, the timer moves into the running state. If IC3’s RA4 digital input is low, the timer drives its RA2 output low and counts nine hours. If RA5 is low instead, the output is low for six hours. After the selected time, the heater is switched off and the system goes back to the 26 Silicon Chip idle state. If the input is invalid, it remains idle. The PIC includes a secondary timer that drives digital output RA1 to switch on the ventilation fan every 10 minutes. The timer output and the output of the temperature sensor comparator are combined using open-collector transistors Q3 and Q4, which disable heater drive transistor Q2 when they are on. When the box is up to temperature, the output of IC1b goes high, switching on Q3, which disables the heater. Green LED12 is in series with this output, and lights showing that the set temperature has been achieved. Switching the load on is implemented using an IRF540 or similar power Mosfet with a gate pullup resistor to 12V. The gate drive pullup is derived from the ventilation fan power supply, which might seem an odd choice. The ventilation fan draws current through D11, D13 and the parallel 47W resistor. The specified fan draws 60mA in operation and develops 1.2V across these diodes. This voltage switches on Q6 on via its 4.7kW base resistor, which forms the Mosfet gate drive. If the fan stalls, its internal controller reduces its supply current to 2mA and attempts to restart it every few seconds. This 2mA current only generates 94mV across the 47W resistor, which is not enough to switch Q6 on, and consequently the Mosfet gate drive is removed. Thus, we disable the heater if the ventilation fan is stalled or not working. For Q2, pretty much any TO-220 package, low-RDS(ON) N-channel Mosfet will work. They virtually all have the same pinout. If you want to use a different Mosfet from our recommended part, look for one with an RDS(ON) under 0.1W. For example, the MTP3055V has an RDS(ON) of 0.18W and for a load current of 3A, it will dissipate 1.6W (3A2 × 0.18W). That would demand the use of a flag heatsink; there is room for this on the PCB. The recommended IRF540 has an RDS(ON) of 0.077W and will dissipate 0.7W at 3A (or 0.4W for the IRF540N version), which will make it warm but it won’t require a heatsink. Photo 4: the top side of the prototype PCB. The fan is mounted to the underside using four M3 x 16mm machine screws with matching hex nuts. Australia's electronics magazine siliconchip.com.au There are two headers for wiring up the heater resistors. This allows you to run separate wiring to two banks of resistors, making the wiring and layout easier in some builds. The current rating of the recommended Altronics P5492 headers is 3A, so you could get away with using just one. We have included a thermal fuse in the power supply to the Mosfet. The specified fuse has a current rating of 10A AC but in our application, we are breaking nominally 2A DC. The fuse does not have a DC rating but that is well within its capacity. This device will fuse at 77°C, and will hold at 55°C continuously. Should your enclosure exceed 55°C for extended periods, you may trigger this protection. The heater We performed a number of tests on the boxes we’re presenting and determined that we need 50W to heat our enclosures to 50°C reliably in a 20°C room. This is also a good maximum, as per the safety considerations we touched on earlier. To allow us to spread the power around the enclosure, we are using six 25W resistors mounted to large heatsinks. We have used 68W devices, which at 24V will dissipate 50W in total. To spread the heat, we used a 330 × 225mm aluminium sheet folded to fit inside our timber box, or two 210 × 180mm panels for the plastic box. If using a 19V supply, the heating resistor values need to be reduced to 47W to keep that 50W target. We recommend the cheapest aluminium case power resistor we could find, mentioned in the parts list. The cost is around $20 for six, so you can save some decent money reusing parts you have. It is important that the devices you select can be bolted to the heat spreader, as this ensures they do not get hot enough to create a hazard. We tried using 10W ceramic resistors each dissipating 5W. While they were operating within their specification, their surface temperature of over 130°C would have the potential to create a hazard if combustible material fell onto them. Safety considerations for the Filament Dryer In designing the controller, we undertook a hazard assessment and developed controls for each hazard we identified, seeking to mitigate these hazards as much as reasonably practicable. This in broader engineering often forms part of a “Safety Engineering Program”. This process involves identifying credible hazards them applying the ‘hierarchy of controls’ which, in order, are: ● Eliminate the hazard ● Substitute to avoid / minimise the hazard ● Apply engineering controls ● Add administrative controls (how it is used) ● Use Personal Protective Equipment (PPE) In safety engineering, there is an important differentiation between a hazard, which is a potential outcome, and the risk this represents, which considers the likelihood of this occurring. The intention of applying the hierarchy of controls is to mitigate and minimise the overall risk of a system. Our hazard assessment was undertaken to inform the design of the project and to shape the solution, both to minimise the underlying hazards in the design and also to apply substitutions, engineering and administrative controls to further mitigate residual risks. By keeping a record of the approaches to managing safety, and building those into the design, we can then test the project to ensure that these controls do what we expect. The hazards and controls we identified for the filament dryer are shown in Table 1 (Hazard & Risk Assessment). Some significant changes in design were implemented. Those practised in the safety art will note that we have picked parts of a larger process to document here, as a full safety program is comprehensive and at times less than fascinating. We have, however, included some important elements for your consideration when making your own version of this. Next month The second and final article next month will have the construction and testing details, including building or adapting and then insulating the container. SC Photo 5: the Filament Dryer in use, showing how filament is drawn from the container. siliconchip.com.au Australia's electronics magazine October 2024  27 The MIPI I3C Bus There is a brand-new serial bus on the block named I3C (Improved InterIntegrated Circuit). It is beginning to appear in mainstream parts; here’s what you need to know about it. By Andrew Levido R ight now, if you want to connect a peripheral like a sensor or an EEPROM to a microcontroller, you would probably use either the SPI (Serial Peripheral Interface) or I2C (Inter-Integrated Circuit) bus. These are tried and tested serial interfaces that date back to the 1980s. The new I3C standard was developed by the MIPI Alliance (www.mipi. org) and incorporates key attributes of the venerable I2C and SPI interfaces, as well as some interesting new features such as dynamic addressing, in-band interrupts, high data rate modes and 28 Silicon Chip hot-join capability. As the name suggests, I3C is closely aligned with I2C. In fact, I2C devices can even be used on an I3C bus. Like SPI and I2C, I3C uses a controller, typically a peripheral within a microcontroller, and one or more targets. Fig.1 shows a comparison between an I2C, SPI and I3C bus, each connecting a controller (master) with three targets (slaves) that can each interrupt the controller. With I2C, the targets are addressed via the bus, whilst SPI requires a separate chip select (CS) signal for each target. I2C uses bidirectional data transfer on the data line (SDA), while SPI requires two unidirectional lines (MISO and MOSI) for bidirectional communication. Both require separate interrupt lines if targets are to interrupt the processor asynchronously. I3C uses device addressing and bidirectional data transfers, just like I2C, but does not require dedicated interrupt signals, since targets can send interrupts to the controller via the bus. The best of both worlds Fig.1: compared with I2C and SPI, I3C requires fewer data lines for bidirectional communication with interrupt capability. Data throughput is similar to SPI, while addressing is managed over the bus. The I2C protocol uses open-drain drivers to achieve bidirectional signalling on the clock and data lines. High-to-low transitions are actively driven, but low-to-high transitions rely on pull-up resistors, so the signal rise time is limited by the resistor value and bus capacitance. The maximum data rate that can be achieved over I2C is therefore significantly lower than SPI, where the bus is actively driven high and low by push-pull drivers. For I2C, the maximum clock speed is typically 400kHz, or 1MHz with Fast mode+ drivers. There is a standard allowing speeds up to 3.4MHz, but it is not widely supported. The SPI interface does not have standard clock rates but can typically operate at a maximum clock speed of 10-20MHz. I3C uses drivers that can operate in open-drain mode when required, but they switch to push-pull mode whenever possible to maximise the data transfer rate. External pull-ups are not required – these are provided by the controller when necessary. Besides using open-drain drivers when communicating with legacy I2C devices, open-drain drivers are used whenever bus arbitration is required; we’ll cover that in more detail later. Australia's electronics magazine siliconchip.com.au Data transfers generally use the pushpull drivers. As a result, the I3C bus operates at a range of clock speeds. In pushpull mode, the maximum clock speed is 12.5MHz, while in open-drain mode, it is 2.5MHz. The clock speed drops to 400kHz (or 1MHz for Fm+) when communicating with legacy I2C devices. Address arbitration All communications on the I3C bus begin with the bus in the idle state, where the SDA and SCL lines are both high, and with open-drain drivers enabled. The start of a transaction is indicated by a start condition, a highto-low transition on SDA while SCL remains high. A transaction is terminated with a stop condition, a low-tohigh transition on SDA with SCL high. All other SDA transitions occur with SCL low. Repeated start conditions may be issued to allow multiple messages per transaction. A target address header follows each start or repeated start condition. If all this sounds familiar, that’s because, so far, this is identical to how I2C works. One key difference is that, with I3C, it is possible for targets to issue a start condition and/or to emit the address header under certain circumstances. On an I2C bus, only the controller can do that. This can happen when a target wishes to signal an interrupt to the controller, a device wants to ‘hot join’ the bus, or a target wishes to become the controller. It is therefore possible that two or more devices may try to write the address header to the bus at the same time. We need a mechanism to arbitrate this conflict. The open-drain nature of the bus during this phase provides a form of Fig.2: address arbitration occurs if two devices simultaneously attempt to write an address header to the bus. On the fourth clock cycle, device A’s zero overrules device B’s one; device B recognises this and gives up. Because zero-bits are asserted actively on the bus, while ones are passive, the device with the lowest address always wins arbitration. natural arbitration, ensuring that the device with the lowest address always ‘wins’. Consider the example shown in Fig.2. Here, devices A and B, with hexadecimal addresses 0x26 (binary 010 0110) and 0x29 (binary 010 1001), respectively, attempt to write their address headers (7-bit address + read/ write bit) to the bus. On the first clock cycle after the start condition, each emits a logic zero by pulling the bus down with their opendrain driver. Both A and B monitor the bus and check that its level matches the value they emitted. If so, they each continue to deliver the header. Both devices emit a logic one on the second clock cycle, and the passive pull-up pulls the bus high. Again, each device sees that the bus state is as expected and moves on to the next bit. This process continues until the 4th bit, when device A emits a zero and device B emits a one. The bus will be pulled low by device A’s open-drain driver, so device B will see a mismatch between the logic level it emitted and that which appeared on the bus. At this point, device B has ‘lost’ the arbitration and ceases to participate. Meanwhile, device A continues to place its address on the bus unopposed, and the transaction it initiated ensues. Under these circumstances, device B will likely reattempt to assert the header after the transaction concludes and the bus is idle once again. This type of arbitration is zero-­ dominant, so the device with the lowest address always wins. For this reason, most controller-initiated I3C transactions don’t begin with a target address header as they do in I2C. If they did, it would not be possible for the target with the highest address to win an arbitration. Fig.3: controller-initiated read or write transactions on the I3C bus look similar to their I2C counterparts. However, I3C transactions generally begin with the special address 0x7E, allowing targets to assert their addresses if necessary. Each data byte is followed by a T-bit rather than an ... ... acknowledge bit; it is a parity bit for writes and a continuation bit for reads. siliconchip.com.au Australia's electronics magazine October 2024  29 Instead, they generally begin with the special address 7E hexadecimal (111 1110 binary). This address is higher than any valid target address, so it is guaranteed to lose arbitration to any target, should there be a conflict. sending data bytes, depending on the value of the read/write bit. Because the sender is in pushpull mode, it is not possible for the receiving device to ACK each byte, as happens in I2C. Instead, the sending device sends a ‘T-bit’ on the 9th clock cycle. Single data rate transactions For writes, the T-bit sent by the conI3C supports several different trans- troller is a parity bit protecting the preaction types. Let’s first look at a sim- ceding byte. Odd parity is used; The ple example where an I3C controller parity bit is set or cleared such that the wishes to write to or read from a tar- total number of ones in the data and get, as illustrated at the top and centre the parity bit is odd. of Fig.3, respectively. In the case of reads, the target sets SDR transactions begin from the the T-bit to indicate that more bytes of idle state, with the controller issu- data will come. The last byte has its ing a start condition followed by an T-bit cleared. address header containing the special Fig.3 also shows a typical hybrid 7-bit address 0x7E and a write (zero) write-read that might be used to bit. All I3C targets will acknowledge address and then read a specific reg(ACK) this address by pulling SDA low ister in a target. The arbitrable 0x7E on the 9th clock cycle. header is written as before, followed The controller then emits a repeated by a repeated start condition and a start condition followed by a non-­ write of the register address to the tararbitrable address header containing get. Another repeated start condition the target’s dynamic address, along is then issued, followed by a read to with the read or write bit, depend- obtain the register value; in this case, ing on the desired data direction. a single byte. The target with a matching dynamic Apart from the T-bit replacing the address will acknowledge (ACK), and acknowledge bit, and the clock speed, any others will ignore the rest of the this is all very similar to I2C. transaction. Apart from this ACK, the whole In-band interrupts transaction following the repeated One elegant feature of I3C is the start is carried out in push-pull mode in-band interrupt (IBI) capability. A with a nominal 12.5MHz clock. The target may signal an interrupt by placcontroller or the target then begins ing its dynamic address (and the read/ write bit set to one) on the bus following a start condition. It may do this when the controller or another target initiates a start condition, or it may emit the start condition itself. Since a controller message generally begins with the 0x7E address, the interrupting target will win the arbitration. If two or more targets interrupt simultaneously, the lowest addressed one will win. Fig.4 shows the typical IBI process. The controller may accept the interrupt by ACKing the request as shown at the top or decline it by NACKing it as shown below that. If the controller accepts the interrupt, it reads in a “mandatory byte” (MDB) sent by the interrupting target with details of the interrupt source. The target may optionally send additional bytes of data, indicated by the value of the T-bit. Once finished, the controller terminates the transaction with a stop condition. If the controller denies the IBI request, the target may continue to try interrupting until the controller accepts. The controller may prevent a target from interrupting by sending a specific command to the target. Common command codes This introduces another feature of the I3C standard – the ability to send predefined common command codes (CCC) to targets. All targets must support a subset of CCCs, but others are Fig.4: a target may signal an In-band Interrupt (IBI) by asserting its address header after a start condition. The controller accepts or rejects the IBI request by ACKing or NACKing the address. If accepted, the controller reads a Mandatory Byte describing the interrupt reason; the target may send further data after that. Fig.5: common command codes (CCCs) allow the controller to put targets in defined states (eg, by turning IBI on or off) or to query the target (eg, to get device ... ... characteristics). Some CCCs are broadcast to all targets on the bus, while others are directed to one or more specific devices. 30 Silicon Chip Australia's electronics magazine siliconchip.com.au optional or only required when the target has specific features. All CCCs are one byte long, with those in the range 0x00 to 0x7F being broadcast codes that all devices will respond to, and those in the range 0x80 to 0xFF being direct codes intended for only a specific target. The standard defines many CCCs, a selection of which are included in Table 1. Fig.5 shows how broadcast or direct CCCs are used. Broadcast CCC transmissions begin with the special address 0x7E, followed by the command code and any associated data bytes. Direct CCCs begin the same way, with a 0x7E address followed by the CCC. This time, there may be a ‘defining byte’ associated with the CCC. A repeated start condition is then issued, followed by the dynamic address of the target to which the CCC is directed, plus a read/write bit. Additional targets may be addressed by issuing another repeated start condition and target address header. Dynamic addressing So far, we have referred to target addresses as though they are fixed, like I2C device addresses. In I3C, the controller must assign each target a 7-bit dynamic address before any directed transactions can occur. The target retains this address until it is reset or the target receives a Reset Dynamic Address Assignment (RSTDAA) CCC. Dynamic addressing has a couple of advantages over fixed addressing. Firstly, since lower addresses have higher arbitration priority, the controller can assign interrupt priorities by appropriate dynamic address choices. Secondly, it avoids conflicts between devices with identical static addresses, as occurs with I2C. That it can happen is unsurprising since there are only about 120 non-­ reserved 7-bit addresses and many thousands of unique devices. For example, the site https://i2cdevices. org/addresses suggests the address 0x44 is shared by no fewer than 19 devices, ranging from an IR temperature sensor to a high-side current monitor to a resistive touchscreen controller. Dynamic addressing avoids such overlaps. Table 1 – some of the more frequently used I3C Common Control Codes CCC Type ENEC Enable Events Command Broadcast Write 0x00 Direct Write 0x80 Enable Target events such as Hot-Join and In-Band Interrupt RSTDAA Reset Dynamic Address Assignment Broadcast Write 0x06 Direct Write 0x86 Discard current Dynamic Address and wait for new assignment ENTDAA Enter Dynamic Address Assignment Broadcast Write 0x07 Enter Controller initiation of Dynamic Address Assignment Procedure SETDASA Set Dynamic Address from Static Address Direct Write 0x87 Controller assigns a Dynamic Address to a Target with a known Static Address SETNEWDA Set New Dynamic Address Direct Write 0x88 Controller assigns new Dynamic Address to a Target SETMWL Set Maximum Write Length Broadcast Write 0x09 Direct Write 0x89 Controller sets maximum write length SETMRL Set Maximum Read Length Broadcast Write 0x0A Direct Write 0x8A Controller sets maximum read length and IBI payload size GETMWL Get Maximum Write Length Direct Read 0x8B Controller queries Target’s maximum possible write length SETBUSCON Set Bus Context Value Broadcast Write 0x0C Brief Description Controller specifies a higher-level protocol and/or I3C specification version GETMRL Get Maximum Read Length Direct Read 0x8C Controller queries Target’s maximum possible read length and IBI payload size GETPID Get Provisional ID Direct Read 0x8D Controller queries Target’s Provisional ID GETBCR Get Bus Characteristics Register Direct Read 0x8E Controller queries Target’s Bus Characteristics Register GETDCR Get Device Characteristics Register Direct Read 0x8F Controller queries Target’s Device Characteristics Register ENTHDR0 Enter HDR Mode 0 Broadcast Write 0x20 Controller has entered HDR-DDR Mode ENTHDR1 Enter HDR Mode 1 Broadcast Write 0x21 Controller has entered HDR-TSP Mode ENTHDR2 Enter HDR Mode 2 Broadcast Write 0x22 Controller has entered HDR-TSL Mode ENTHDR3 Enter HDR Mode 3 Broadcast Write 0x23 Controller has entered HDR-BT Mode RSTACT Target Reset Action Broadcast Write 0x2A Direct Write & Read 0x9A Controller configures and/or queries Target Reset action and timing GETSTATUS Get Device Status Direct Read 0x90 Controller queries Target’s operating status GETMXDS Direct Read 0x94 Controller queries Target’s maximum read/write data speeds and maximum read turnaround time Get Maximum Data Speed siliconchip.com.au Australia's electronics magazine October 2024  31 Fig.6: dynamic addresses can be assigned by two methods – from a static 7-bit address using the SETDASA CCC, or via the Dynamic Address Assignment process started by the ENTDAA CCC. The latter is preferred; in this case, bus arbitration is used to assign addresses to all devices in sequence. Fig.7: the Provisioned Identifier (PID) is a 48-bit value containing a manufacturer ID, a part ID, an Instance ID and a 12-bit device characteristic descriptor. On some parts, the Instance ID is programmable via pins or other means to allow multiple instances of the same device to be uniquely identified on the bus. There are two different options for assigning dynamic addresses. Some early devices do have a static 7-bit address, which is used to assign a dynamic address using the CCC “Set Dynamic Address from Static Address” (SETDASA), as shown at the top of Fig.6. The static address can’t be used for any other purpose. The controller starts the transaction in the usual way, sending the SETDASA CCC, followed by a restart, then the static address of the target with the read/write bit set. When the target ACKs the static address, the controller sends the dynamic address it wishes to assign. The controller can optionally set further dynamic addresses by repeating the process after issuing a repeated start condition. This approach does not really help with the problem of address duplication, so the preferred option is to assign dynamic addresses based on a 48-bit device identifier known as a ‘Provisioned ID’ (PID), the format of which is shown in Fig.7. The upper 15 bits of this are the manufacturer ID assigned by the MIPI Alliance. The next bit, #32, is usually zero, while the following 16 bits are the part identifier. Bits 12 through 15 32 Silicon Chip are an instance ID. These may be programmed by setting device pin(s) to specific levels, to allow the user to deploy multiple instances of the same device on the same bus. The process for assigning dynamic addresses to these targets relies on the same bus arbitration mechanism we saw earlier. The lower part of Fig.6 shows this in action. The CCC Enter Dynamic Addressing Assignment (ENTDASA) is sent, followed by a repeated start condition and another 0x7E address. Any targets on the bus that do not have a dynamic address assigned will ACK this and begin writing their 48-bit PID, followed by the contents of two 8-bit capability registers, BCA and DCA. This write is arbitrable, so only the device with the lowest PID will complete the process, at which time the controller sends the dynamic address it wishes to assign. If the device acknowledges, the dynamic address is considered assigned. A repeated start condition is issued, and the whole process is repeated for the remaining targets with unassigned dynamic addresses until none are left. At that point, the 0x7E address is passively NACKed, and the assignment process is terminated. Hot-Join mechanism Fig.8: the hot join process is similar to the IBI process, except that the joining device uses the special 0x02 address. If the controller ACKs the request, the target waits for a dynamic address to be assigned by the controller. A target may join an I3C bus once it is up and running (for example, by being plugged in or powered up). It does this using a mechanism similar to the In-Band Interrupt, shown in Fig.8. The hot-joining device emits an address header with the special high-priority address 0x02, guaranteeing it will be heard. The controller may accept the hotjoin request by ACKing it or reject it by NACKing it. If the request is accepted, the joining device waits for the controller to assign a dynamic address via Australia's electronics magazine siliconchip.com.au Fig.9: the I3C controller produces the SCL clock with a duty cycle such that the high period is 40ns or less. I2C devices are required to have a 50ns glitch filter on their SCL and SDA inputs, so the I3C clock should be invisible to them. Fig.10: the HDR exit and restart patterns; the exit pattern is always followed by a stop condition and returns the bus to the idle state. The restart pattern is analogous to the repeated start condition and delineates multiple messages within an HDR transaction. the ENTDAA CCC process described above. If the controller rejects the request, the joining device will likely continue to make requests unless the controller switches off hot-join requests via the DISEC CCC. Note that this process works if more than one device joins simultaneously – the 0x02 address will be emitted by all devices simultaneously, and they will all succeed in the arbitration. The controller ACK will put them all in a state awaiting dynamic address assignment, and the ENTDAA assignment process will assign them all addresses in order of their PIDs. I2C compatibility I mentioned before that I2C targets can co-exist with I3C targets on the same bus. It is important that these devices don’t react to I3C messages and potentially disrupt them. I3C uses a couple of mechanisms to reduce the chance of that happening. Firstly, the special address 0xFE in the header of I3C messages is a reserved address in I2C and should be ignored by all complying devices. On top of this, I3C takes advantage of the 50ns glitch filter that is required by the standard on the SDA and SCL pins of I2C devices. The duty cycle of the SCL signal is managed so that the clock high period is always less than or equal to 40ns, making the I3C clock ‘invisible’ to I2C targets. They should ignore any signal on their SDA line, because they don’t see any clock transitions on SCL. Fig.9 shows how this works. For the 12.5MHz push-pull clock, the high and low pulses are naturally 40ns long at a 50% duty cycle. The 2.5Mhz opendrain clock is emitted at a duty cycle of around 10%, leaving the high pulses 40ns long. This behaviour is only needed if there are legacy devices on the bus. Most controllers allow for a 50% duty cycle to be used on both clocks for ‘pure’ I3C buses. When communicating with I 2C devices, the SCL clock is reduced to 400kHz or 1MHz with a 50% duty cycle and transactions are carried out in open-drain mode with signalling conforming to the I2C standard. However, I3C does not support the I2C features of 10-bit addressing, clock stretching or multi-master operation, so be careful. High data rate modes So far, everything we have covered is occurring in ‘Single Data Rate’ (SDR) mode. The I3C protocol supports several higher data rate (HDR) modes. I am only going to cover the most common one of those in the interests of brevity. Regardless of the HDR mode chosen, the I3C bus is always initialised and configured in SDR mode. Only limited extra functionality is available in the HDR modes – you can’t assign dynamic addresses or receive in-band interrupts, for example. HDR modes are always entered from SDR mode by issuing the appropriate Enter HDR Mode X (ENTHDRx) CCC. Once entered, the HDR mode has a buswide effect until it is exited via an HDR exit pattern. Within an HDR mode transaction, multiple messages can be separated by HDR restart patterns, Fig.11: HDR-DDR transactions begin with an ENTHDR0 CCC, followed by a command and address word. Data is then sent one word at a time to or from the controller, depending on the command. The last data word is followed by a five-bit CRC and an exit or restart pattern. siliconchip.com.au Australia's electronics magazine October 2024  33 analogous to the repeated start condition in SDR mode. The HDR exit and restart patterns are shown in Fig.10. The exit pattern is defined as four consecutive falling edges on SDA while SCL is low. It is always followed by a stop condition. The restart pattern is defined as two successive toggles of SDA (fall, rise, fall, rise) followed by a rising edge on SCL. Fig.12 shows how the command, data and CRC words are constructed. The Command and CRC words begin with the same preamble but are distinguishable by context – the command word only ever comes immediately after entry to the HDR mode or a restart pattern, while the CRC only ever comes after a data word. Only a very limited range of CCCs are supported in HDR-DDR mode. HDR-DDR Other features The common HDR Double Data Rate (HDR-DDR) mode uses the same 12.5MHz clock as SDR mode but allows data bits to be sent on both rising and falling clock edges, effectively doubling the data throughput. Fig.11 shows how a typical HDRDDR transaction works. After sending the ENTHDR0 CCC in SDR mode, the bus switches to HDR-DDR mode. The controller then issues a command and address word indicating the data direction (read or write) and the intended target’s dynamic address, followed by one or more data words written by either the controller or the target, depending on the data direction. When all the data has been sent, the sender concludes with a five-bit CRC. The controller then emits a restart pattern if another DDR message is to be sent, or an exit pattern and stop condition if not. The basic unit of transmission (except for the CRC) is a 16-bit word with a two-bit preamble and two trailing parity bits, for a total of 20 bits. DDR mode can achieve an effective data throughput of 20Mbps, comparable with SPI (but with error checking). Faster HDR modes are possible, including some that allow for two or four data lanes and can achieve effective data rates of up to 96Mbps. However, not all modes are supported by all targets. In addition to those features described here, I3C offers some other interesting capabilities, including the ability to reset targets (individually or in groups) over the bus and to send synchronising ‘ticks’ to targets to coordinate timing. It supports group addressing, where a set of targets share a group address (alongside their individual dynamic addresses), so they can be sent messages simultaneously. It is also possible for one target to communicate directly with another via device-to-device tunnelling. There is a lot to this standard; it will be interesting to see what features receive support from chip vendors. Trying it out I have experimented with I3C over the last couple of weeks, using an NXP LPC865 microcontroller with an integrated I3C controller. For targets, I tried a Bosch BMI323 inertial measurement unit (IMU), an ST Microelectronics LPS22HH humidity sensor and a TDK ICM42688P motion sensor. I was able to test a lot of the SDR functionality, and it works as advertised, but the experience was not as smooth as it could have been. I think these rough edges are due to the relative immaturity of the standard. The device data sheets were a mixed bag regarding the thoroughness of their documentation of I3C features – I did have to resort to a bit of trial and error to get things going. The MCU toolchain and the I3C driver provided in the SDK worked fine for my purposes. Debugging the bus was a challenge, as my logic analysers do not currently have support for the I3C protocol. For this reason, I had to resort to printing out waveforms and marking ones and zeros by hand on a few occasions. I am sure that all of these points will improve as I3C becomes more common. Right now, I3C is available on only a limited number of devices, which are helpfully listed at https:// binho.io/blogs/i3c-reference/i3c-­ devices I believe this list will grow, given that the MIPI Alliance lists almost every silicon vendor as a member, and it has a pretty good track record of establishing standards. Over the next few years, I suspect we will see I3C becoming more and more popular. References Fig.12: data is transmitted on both clock edges in HDR-DDR mode. For data and command words, a two-bit preamble is followed by 16 data bits and two parity bits. The CRC word is slightly different and is always followed by a restart or exit pattern. 34 Silicon Chip Australia's electronics magazine I 2C-Bus Specification and User Manual (2021): NXP, siliconchip.au/ link/abtv I3C and I3C Basic specifications: MIPI, siliconchip.au/link/abgm ICM-42688-P: TDK, siliconchip.au/ link/abtw Bosch Sensortec BMI323 Inertial Measurement Unit (IMU): Bosch, siliconchip.au/link/abtx Arm Cortex-M0+ LPC86x 60MHz 32-Bit Microcontrollers (MCUs): NXP, siliconchip.au/link/abty STMicroelectronics LPS22HH High-Performance MEMS Nano Pressure Sensor: ST, siliconchip.au/link/ abtz SC siliconchip.com.au OCTOBER altronics.com.au TECH BUYS! Goodbye eye strain! Bag-a-bargain this October with these handy tech buys. 79 Why pay $300 for a MaggyLamp? 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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. B 0010 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. Three-phase sinewave generator with TL074s The entry in Circuit Notebook for a three-phase generator using the LM3900 Norton current-feedback op amp caught my eye (“Three-phase sinewave generator”, April 2023 issue; siliconchip.au/Article/15746). I vaguely remember the chip hitting the market around 1973, but I did not have any experience with it then. So I thought this was a good time to catch up. I wanted to build it to demonstrate three-phase systems to first-year engineering students. siliconchip.com.au Unfortunately, I had difficulty maintaining oscillation in the oscillator stage. It seemed that the ratios of both the resistors and capacitors were critical for maintaining oscillation. Having fixed that, the oscillator produced a sinewave with distortion (to be expected) on the negative excursions. But I just could not get the phase-shifting circuitry to work. I built it in isolation on the breadboard, separate from the oscillator, but had no success with it. Australia's electronics magazine So I decided to build the buffered phase-shift oscillator using just a few op amps (the venerable TL071/2/4 types) and RC networks. Next, I devised a section to provide two signals that would be phase-shifted, one leading and the other lagging. Combined with the direct output from the oscillator, they provide three sine waves of roughly equal amplitude, 120° apart. The nominal frequency for the oscillator section is 13.96kHz (1.732 ÷ [2πRC]) with the values used (measured at 13.4kHz). Each stage in the oscillator (IC1a-IC1d) provides a phase shift of 60°. The tangent of 60° is 1.732, hence the formula. Each section attenuates the signal by half (-6dB), so overall, the attenuation factor is 8 (23). Thus, the amplifier needs a gain of eight times. The 39kW/4.7kW divider provides a gain of 8.3 times, which is close enough. The four buffers prevent the RC sections from loading each other. Alternatively, a chip like the XR2206 could be used as the oscillator, with the lead and lag sections based on IC2c & IC2d added to its output. Allan Grant, Tutor, Curtin Uni, Perth, WA ($100). October 2024  39 Micromite Plus Explore 100-based Reflow Oven Controller Phil Prosser presented an excellent Reflow Oven project in the April & May 2020 issues (siliconchip.au/ Series/343). I sourced a small forced convection oven for about $100 and was able to modify it to bring out the fan drive. But getting the cover off proved a real chore, and in retrospect, I would not recommend this approach to any but the most enthusiastic! Anyhow, I was able to neatly fit an IEC socket to the cool rear panel of the oven – and move the fan wires over to it – a very safe installation. Unfortunately, this oven has quartz tubes as elements, which significantly increase the heating time constant of the system. Still, the temperature tracked similarly to what Phil reported in his article, probably due to improved convection provided by the fan. I successfully reflowed numerous boards with it, including some with TSSOP and QFN chips. None required any rework. My motivations for migrating Phil’s design to an Explore 100 included: • I had an Explore 100 on hand and wished to learn GUI controls and explore capabilities. • The colour LCD touchscreen is a superior way to interface with it. • The touchscreen eliminates a rotary encoder, multiple PCBs, ribbon cables and IDC connectors. • MMBasic is likely easier for hobbyists to understand, so they can modify the code if desired. 40 Silicon Chip Fig.1: the temperature compensation scheme. I replicated all of Phil’s controls, but one advantage of my design is that it includes a compensation system that significantly reduces the temperature overshoot. This works using an ‘internal feedback’ model, where the software simulates the reaction of the oven to inputs (Fig.1). With correct tuning – see the screen grab overleaf, this allows the oven temperature to track the desired profile (Fig.2) closely. The wiring is simple, as shown in Fig.3. If you have an Explore 100 on hand, you can load my software to experiment with it from your desktop. You just need to add the thermocouple amplifier to see real temperature readings and add a 4.7kW resistor in place of the solid-state relay (SSR) so that the screen will correctly show when it is trying to switch the heating element on. Firstly, update the Explore 100 firmware to MMBasic Ver 5.05.05 (HEX file available from https://geoffg.net/ micromite.html) if it’s older than that. Next, plug in a USB cable to connect Australia's electronics magazine the Explore-100 to your PC. Once it is detected, connect to its virtual serial port using a terminal emulator at a baud rate of 38,400, 8 bits, no parity, two stop bits, and no flow control. Set the terminal size to 100 × 70 characters and mode to VT100 with CR for send & receive and UTF-8 coding (I use Tera Term, but other emulators should have similar options). Pressing Ctrl-C should now give you a “>” prompt. You can then set some Options, eg, “OPTION DISPLAY 60, 70”. My OPTION LIST is as follows: OPTION AUTORUN ON OPTION BAUDRATE 230400 OPTION COLOURCODE ON OPTION DISPLAY 60, 70 OPTION LCDPANEL SSD1963_5, LANDSCAPE, 48, 6 OPTION TOUCH 1, 40, 39 GUI CALIBRATE 1, 106, 3800, 2063, -1335 OPTION SDCARD 47 OPTION RTC 67, 66 siliconchip.com.au You can enter each option as above – skipping the RTC line if you don’t have one fitted, and ignore the LCDPANEL, TOUCH, and GUI CALIBRATE options if you have already set them. You can enter GUI TEST LCDPANEL to check the operation of the LCD – press the space bar to exit the test. Note that if you change the baud rate (as I have done), you might need to also change it in the terminal software. If all goes well, you can press F11 (or type XMODEM RECEIVE followed by Enter), then, on the top bar of Tera Term, press File/Transfer/XMODEM/ send and select my software file (available for download from siliconchip. com.au/Shop/6/510). After that, pressing F2 (or typing RUN followed by Enter) should start the program. On the first run, it will ask you if it should reset to defaults – press “YES” this first time and the startup page should appear. The system will start controlling the temperature, although the measured temperature will show 0 if no thermocouple amp is fitted. Pressing EDITS will take you to another page showing several editing option buttons while temperature control continues. With the Controller operating, the next step is to power it down and connect it to the oven. I used socket-tosocket jumper leads (Jaycar WC6026), stripping one end bare as necessary. Firstly, as per Phil’s recommendation, you need to set the thermocouple amplifier offset to 0. That involves soldering a link between pins 2 (reference) and 3 (ground) on the AD8495 chip on the amplifier board. I fitted straight pin headers to this board and mounted it with an insulating pillar – at the opposite end of the enclosure from the power plugs etc. The circuit diagram shows the wiring for both the thermocouple amplifier and SSR. All the wiring between the mains input & output sockets and the SSR must be mains-rated, properly colour coded and fully insulated (eg, with heatshrink tubing and/or neutral-­ cure silicone sealant). The next step is to calibrate the gain and offset values for the thermocouple while the Controller is on the startup page. To do that, I dipped the thermocouple tip into a glass of boiling water, then adjusted the gain to match the reading on an industrial glass thermometer. The temperature Fig.3: the wiring diagram for the Reflow Oven Controller to the Explore 100. siliconchip.com.au Australia's electronics magazine October 2024  41 falls rapidly; ideally, the water would be kept boiling on a Bunsen burner or the like for a constant 100°C. If you use a metal container, use a peg or similar to prevent the probe from touching the metal surface. Use a stirred ice bath (0°C) to adjust the offset reading, then re-check the scale again. In my case, the offset was very close to 0, and the gain was 6.08 – these relate to Phil’s figures, except I sum 32 voltage readings, so the values are scaled. The internal photo was taken before the Presspahn cover was fitted. The firmware download includes the BASIC code and a PDF document describing how to tune the oven compensation parameters. Finally, note that if you press and hold down a SpinBox up or down arrow, it will ‘auto-repeat’ at a fast rate – as described in the Micromite Plus Manual – a very useful feature. However, if you slide your finger to the side instead of lifting it (easy to do inadvertently), the icon will stay coloured (although the repeat will cease). This will inhibit the opposing icon. The fix is to tap the icon again. Ian Thompson, Duncraig, WA. ($150) Supercap Boost Starter for Vehicles If your car battery struggles to start the engine, this low-cost project might save replacing it and is a good excuse to play with supercapacitors. The total cost is about $25. Six 120F 2.7V supercapacitors are connected in series to give a bank of 20F <at> 16.2V. The circuit board includes resistors to balance the charges on the capacitors. When the pushbutton switch (S1) is pressed, a DC-DC boost converter is powered by the car battery and charges the capacitor bank to 15.75V (16V maximum), even though the battery voltage will be much less than that. The DC-to-DC converter briefly draws 20A while charging a ‘flat’ capacitor bank. So use the appropriate wire gauge and a heavy-duty momentary switch. The LED voltmeter connected to the capacitor bank displays the charging progress. So, just before starting the car, hold S1 and watch the caps charge. When the caps are charged, start the car. As the key is turned to the ‘start’ position, the connection to the starter motor solenoid or relay now powers the 12V 200A relay and the capacitor bank dumps into and parallels the car battery. The internal resistance of the capacitor bank is much lower than a wellworn car battery and provides the starting current. There is no need to keep the caps charged all the time – only just before starting the engine. If you start the engine without charging the caps first, the car battery will have to charge the capacitors and power the starter motor. A suitable diode (shown as optional on the circuit) in series with the output from the relay will prevent this, but I did not think it was necessary as I like pressing the big red button! If you want to add it, you can use the VS-100BGQ045 (100A, 45V schottky diode) or two in parallel for close to 200A (although they will not share perfectly, so probably more like 150A…). My unit was assembled from modules I got from AliExpress: an Elnabrand supercapacitor bank, a 10A boost converter (Core Electronics 018-DCDC-BOOST-150W; minimum input voltage of 10.4V for a 16V output), a 12V 200A car relay (TN686), a generic fuseholder with a 30A fuse and a two-wire LED digital voltmeter. You might wonder why I did not use a Mosfet instead of a relay. It’s mainly because I don’t have to worry about protecting it from voltage spikes or gate drive voltage requirements. Relays are commonly used for car starter motors, so they should not give any trouble here. You can see a video of my device operating in the video at https://youtu. be/zaLPW-d8fJg John Russull, Kratie, Cambodia. ($100) The DC-DC converter can be purchased from Core Electronics, or on AliExpress. 42 Silicon Chip Australia's electronics magazine siliconchip.com.au GPS caravan clock and power monitor This GPS-based clock will provide the correct time no matter where you are, whether in Australia or overseas. It will also provide local sunrise and sunset times, plus your altitude above sea level. As a further bonus, it will monitor your caravan’s DC voltage and current. It is driven by a Raspberry Pi. Any model Pi will do; the smallest and cheapest Pi currently available is the model 3A+. The code is written in Python, making it easy to customise and extend. The display is a Waveshare RPi LCD High-Speed SPI Touch Screen (Waveshare 15811), and it uses a four-­ channel ADS1015 analog-to-digital converter (ADC; Adafruit 1083) for power monitoring. Many 3.3V TTL GPS modules that would work with this design are available, but I used the u-blox Neo-6M from Altronics (Cat Z6333). The upgraded Neo-7M sold in the Silicon Chip Online Shop (SC6737) should also work. Raspberry Pi scripts are provided with the software (link below) to make installing the driver files for the Waveshare LCD easy. The Python code is also part of that package. Due to the LCD being attached to the Pi’s only GPIO connector, it is necessary to solder wires for the GPS and ADC modules. There are eight wires in total. Fortunately, the LCD uses only a few GPIO pins, leaving sufficient spare ports. Note that the GPS and ADC modules are connected to the underside of the Pi’s GPIO header so that the LCD can plug into the top. Assuming you start with a blank Pi, begin by loading a microSD card (16GB or greater) with the Raspberry Pi OS (32-bit version recommended) using the Raspberry Pi Imager. Details and the download can be found at siliconchip.au/link/absc At the time of writing, the Waveshare LCD does not work with the latest Raspberry Pi OS (Bookworm). If you have problems getting the LCD to work, try the Legacy version (Bullseye). It can be found on the “Raspberry Pi OS (other)” page of the Imager. Next, connect a monitor, keyboard and mouse to the Pi; a wireless combo keyboard/mouse makes it easier if you are using the Model 3A, which only has one USB port. Plug in the SD card and attach the LCD. Connect the Pi power supply and power it on. After it boots up, run the configuration utility (raspi-config) to check the settings. Turn off Screen Blanking on the Display tab to stop the clock from disappearing due to the screen going to sleep. On the Interfaces tab, turn on SSH and VNC. This provides a headless display, so you do not need to plug a monitor into the HDMI port. Enable SPI for the LCD screen and I2C for the ADS1015. Also switch on the Serial Port option for the GPS module. Ensure the Serial Console is off; otherwise, we will not be able to receive messages from the GPS module. Click Save and accept the reboot request, then check your WiFi connection and download the files from siliconchip.au/Shop/6/348 to your Pi’s Home folder, then unzip the package (“unzip Cara.zip”). Enter the command “chmod +x setupLCD” in the terminal to make the file executable, then “./setupLCD” to run the file. The driver files for the LCD will automatically be downloaded and installed and then the Pi will reboot. Watch for the diagnostic messages on the LCD during boot-up to confirm the drivers were correctly installed. Now re-open the terminal and enter “chmod +x installLIBS” to make the file executable, then “./installLIBS”, which will install the necessary Python libraries. To use a VNC session with a different resolution to the LCD, run the supplied “./start script” from an SSH session (eg, via Putty). Make the file executable with “chmod +x start”, then run it. Direct your VNC viewer to the Pi’s IP address (eg, 192.168.1.44). To start the clock automatically on boot, from a terminal, run: sudo nano etc/xdg/lxsession/ LXDE-pi/autostart Then, using the editor, add the following command before the <at>xscreensaver command: <at>/bin/python home/pi/Cara.py The current monitor I used does not have a part number, but it is standard in most vans with an output of 0-4V for a current of 0-50A. An ACS712 30A module could be used; they provide 66mV per amp (0-2V for 0-30A). That requires changes to the code, but it is easy to modify it to cater for any Hall effect current sensor. Dennis Smith, Strahan, Tas. ($110) siliconchip.com.au Australia's electronics magazine October 2024  43 By John Clarke 8-Channel Learning IR Remote Receiver This eight-channel relay board can have its outputs switched on and off using almost any remote control, including universal types. Each output can be set to toggle on or off, switched on for a fixed period, or on while the button is held down. The outputs can be controlled by an onboard reed relay or a transistor; the latter can switch external relays. W ith so many appliances operated using infrared (IR) remote controls, you are bound to have at least one remote that is not used anymore. With our 8-Channel Learning IR Remote Receiver, it can be put back in service to provide control over eight separate relay outputs to control low-voltage DC or AC devices. Many different kinds of remote control can operate the Receiver; you can even use it with multiple remotes. It learns the remote control code to switch each of its eight outputs. You could use a different remote control unit for each output if you wanted to. Most people would use a single remote control, though. Remote controls transmit signals using specific IR protocols. These are usually transmitted using an infrared LED that is modulated on and off at between 36kHz and 40kHz. The modulated signal is switched on and off in a pattern with a start code, followed by address and command codes (visible in Scopes 1 to 4). The address determines what appliance the code is to control, such as a TV, satellite decoder, DVD player, amplifier etc. The command code indicates what function is to operate. This can be power on or off, channel selection, volume up, volume down, mute etc. Our Receiver can be used with remotes that produce signals in the NEC, Sony, RC5 and RC6 remote control protocols. More information about these is in a panel overleaf titled “Infrared Coding”. Many remotes will use one of those protocols. The controller has eight separate outputs, and each one can be switched using a separate code. Each channel can either be controlled by a reed relay (normally open contacts) or an open-collector transistor. Reed relays can be used for all channels, open Fig.1: driving an external LED from an open-collector output. With a 12V supply, the 390W resistor will limit the current to around 25mA. Fig.2: an opto-coupler’s outputs are triggered by an internal LED, so driving them is basically the same as driving LEDs. Fig.3: no series resistor is required if the coil is rated at 12V DC when driving an external relay from an open-collector output. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Features Learns infrared remote control codes from a handheld IR remote Supports four different IR protocols 1-8 output channels controlled by reed relays or open-collector transistors Can be used with external relays (12V DC coil types) Eight LED channel status indicators Momentary or toggle operation on each output Adjustable timer for momentary outputs (125ms to 32s) Timer settings are shown on an 8-LED dot bargraph Specifications IR reception range: typically 10m Power supply: 12V DC at 150mA+ (external relays may require more current) Output switching: up to 24V <at> 500mA IR codes supported: learns NEC, Sony and Philips RC5/RC6 remote protocols Momentary mode: 16 timer values, from 125ms to 32 seconds Output toggle rate: minimum cycle time of 600ms Oscillator frequency adjustment: ±6% in 128 steps Power-on indication: dimmed LED collector outputs for all channels or a mixture of the two. Both output types can switch LEDs or other low-current loads. Alternatively, the transistor outputs can drive relays with 12V DC coils and contacts that can handle higher voltages and/ or currents. You don’t need to build the controller with all eight outputs if you don’t need them; just make it with fewer if that’s all you need. Outputs The reed relays are ideal for switching low voltages (up to 24V maximum) and currents up to 500mA. They can be used to trigger pushbutton switches on equipment by wiring the reed relay contacts across the switch. A reverse-biased diode should be connected across the relay’s contacts if switching inductive loads. Never use the onboard reed relays to switch mains voltages directly. Neither the relays nor the PCB tracks can handle that. If you need to switch higher voltages, use the open-collector transistor outputs to switch appropriately-rated external relays. Any external relays used for mains switching must be built to comply with mains voltage safety standards, including using correctly rated wire of the right colour and adequate insulation. Figs.1-4 show a few different ways you can use the eight outputs when they are driven by open-collector transistors. Fig.1 shows how you can drive an external LED, Fig.2 shows how an external opto-coupler can be switched, Fig.3 shows how to drive an external relay and Fig.4 shows how you can switch off or control the direction of a motor. With the motor, you can use the channels with the outputs set for momentary or toggle operation. In the momentary mode, pressing (and holding) the button for open-collector output X activates RELAY 1 and causes the motor to rotate one way, while pressing the button for output Y activates RELAY 2 and causes the motor to rotate the other way. With both outputs set for toggle operation, the motor will be stopped until one of the outputs is toggled. Its direction of rotation will depend on which output is switched on. The motor can then be reversed by toggling both outputs, or stopped by toggling either output. Scope 2: an oscilloscope capture of the output of IRD1 when receiving a Philips RC5-coded signal. Scope 3: an oscilloscope capture of the output of IRD1 when receiving a Sony-coded signal. Remote control protocols Scope grabs 1-4 show captured waveforms for decoded IR signals transmitted in the RC6, RC5, Sony and Fig.4: a simple method to control the direction of a motor using two external relays, driven from two of the Receiver’s outputs. siliconchip.com.au Scope 1: an oscilloscope capture of the output of IRD1 when receiving a Philips RC6-coded signal. Australia's electronics magazine Scope 4: an oscilloscope capture of the output of IRD1 when receiving an NEC-coded signal. October 2024  45 A panel on Infrared Coding Most infrared controllers switch their LED on and off at a modulation frequency of 36-40kHz in bursts (pulses), with the length of and space between each (pauses) indicating which button was pressed. The series of bursts and pauses is in a specific format (or protocol) and there are several commonly used. This includes the Manchester-encoded RC5 and RC6 protocols originated by Philips. There is also the Pulse Width Protocol used by Sony and Pulse Distance Protocol, originating from NEC. For more details, see application note AN3053 by Freescale Semiconductors (formerly Motorola): siliconchip.com.au/link/aapv NEC protocols, respectively. These waveforms were taken from the output of IRD1. The 36-40kHz modulation was removed by the receiver; its output is low during the modulated burst and high when there is a pause in modulation. Scope 5 shows the repeat pulses for the NEC protocol that follow the initial main code if the remote control button is held down. For the remaining protocols (RC5, RC6 and Sony), holding down the remote control button simply repeats the code that is initially sent. More details are provided in the “Infrared Coding” panel. Momentary & toggle modes Each output can be set for momentary or toggle operation. With the momentary selection, an output and its associated LED switch on when the remote control button is pressed, then off again after a set period from ⅛th of a second (125ms) to 32 seconds. The timer period can be elongated by holding down the remote control button, in which case the timer starts when the button is released. In toggle mode, the output switches on with one press of an IR remote button, and it remains on until the same button is pressed again, whereupon it switches off. During the IR code learning procedure, a pushbutton switch on the controller board selects momentary or toggle operation for each output. For channels set to momentary mode, the on-time period is set at the same time, using a trimpot, with the front panel LEDs indicating the period selected. 46 Silicon Chip Philips RC5 (Manchester-encoded) (36kHz) For this protocol, the 0s and 1s are transmitted using 889µs bursts and pauses at 36kHz. A ‘1’ is an 889µs pause then an 889µs burst, while a ‘0’ is an 889µs burst followed by an 889µs pause. The entire data frame has start bits comprising two 1s followed by a toggle bit that could be a 1 or 0. More about the toggle bit later. The data comprises a 5-bit address followed by a 6-bit command. The most significant address and command bits come first. When a button is held down, the entire sequence is repeated at 114ms intervals. Each repeat frame is identical to the first. However, if transmission stops, then the same button is pressed again, the toggle bit changes. This informs the receiver as to how long the button has been held down. That’s so it can, for example, know when to increase volume at a faster rate after the button has been held down for some time. Sony Pulse Width Protocol (40kHz) This is also known also as SIRC, which is presumably an acronym for Sony Infra Red Code. For this protocol, the 0s and 1s are transmitted with a differing overall length. The pause period is the same at 600µs, but a ‘1’ is sent as a 1200µs burst at 40kHz, followed by a 600µs pause, while a ‘0’ is sent as a 600µs burst at 40kHz followed by a 600µs pause. The entire data frame starts with a 2.4ms burst followed by a 600µs pause. The 7-bit command is then sent with the least significant bits first. The address bits follow, again with least significant bits first. The address can be five bits, eight bits or 13 bits long to make up a total of 12, 15 or 20 bits of data. Repeat frames are the entire above sequence sent at 45ms intervals. NEC Pulse Distance Protocol (PDP) (38kHz) For the NEC infrared remote control protocol, binary bits zero and one both start with a 560µs burst modulated at 38kHz. A logic 1 is followed by a 1690µs pause while a logic 0 has a shorter 560µs pause. The entire signal starts with a 9ms burst and a 4.5ms pause. The data comprises the address bits and command bits. The address identifies the equipment type that the code works with, while the command identifies the button on the remote control which was pressed. The second panel shows the structure of a single transmission. It starts with a 9ms burst and a 4.5ms pause. This is then followed by eight address bits and another eight bits which are the “one’s Australia's electronics magazine siliconchip.com.au complement” of those same eight address bits (ie, the 0s become 1s and the 1s become 0s). An alternative version of this protocol uses the second series of eight bits for extra address bits. The address signal is followed by eight command bits, plus their 1’s complement, indicating which function (eg volume, source etc) should be activated. Then finally comes a 560µs “tail” burst to end the transmission. Note that the address and command data is sent with the least significant bit first. The complementary command bytes are for detecting errors. If the complement data value received is not the complement of the data received then one or the other has been incorrectly detected or decoded. A lack of complementary data could also suggest that the transmitter is not using the PDP protocol. After a button is pressed, if it continues to be held down, it will produce repeat frames. These consist of a 9ms burst, a 2.25ms pause and a 560µs burst. These are repeated at 110ms intervals. The repeat frame informs the receiver that it may repeat that particular function, depending on what it is. For example, volume up and volume down actions are repeated while the repeat frame signal is received but power off or mute would be processed once and not repeated with the repeat frame. Codes learned are stored in non-­ volatile flash memory. This ensures that the IR codes and other settings like momentary/toggle and the timer period are not lost if the power is cycled. All outputs are initially off when power is applied to the Receiver. The 8-Channel Learning IR Remote Receiver fits neatly into a compact instrument enclosure. An acknowledge (ACK) LED and the eight channel status LEDs are mounted on the front, while the power input and channel output connections are at the rear. A 12V DC plugpack or similar supply powers the Receiver. Circuit details Philips RC6 (Manchester-encoded) (36kHz) 0s and 1s are transmitted using 444μs bursts with 444μs pauses at 36kHz. The entire data frame has start bits comprising a 2.666ms burst followed by a pause for 889μs, then a ‘1’ bit. After this, there is a 3-bit mode value, typically 000. The toggle bit comes after that; it uses an 889μs burst and 889μs pause instead of the 444μs used for the Mode, Address and Command bits. The data is an 8-bit address followed by an 8-bit command, with the most significant bits first. The same sequence is repeated at 106ms intervals when a button is held down. If transmission stops and the same button is pressed again, the toggle bit changes state. This lets the receiver determine how long the button was held down. Referring to the circuit diagram, Fig.5, an infrared receiver (IRD1), sends signals to a PIC16F1459 microcontroller (IC1), which drives reed relays, NPN transistors or a combination of both, depending on how you configure the PCB. IRD1 includes an infrared detector, amplifier, bandpass filter (typically centred around 38kHz) and an automatic gain control (AGC). IRD1’s output is normally high (5V) but goes low (near 0V) when it receives a 38kHz IR signal. This means that the infrared receiver removes the 38kHz modulation, with the output staying low for the duration of the frequency burst. The supply for IRD1 is derived via a 100W resistor from the 5V rail and it is decoupled by a 100µF electrolytic capacitor. This is to keep electrical noise out of the supply for IRD1; it requires a steady supply as it contains a sensitive, high-gain amplifier. The infrared signal is modulated so that the detector will ignore other infrared sources, such as halogen lamps, bar radiators and the sun. Bar Scope 5: the repeat code sent by an NEC-style remote control when you hold down a button. siliconchip.com.au Australia's electronics magazine October 2024  47 Fig.5: the main part of the circuit comprises microcontroller IC1, infrared receiver IRD1, a few LEDs and pushbuttons and a simple linear power supply. While there are eight output sections, only two are shown; the other six are identical. Each section can either have a reed relay (as shown in the boxes in the middle) or a transistor and diode (as shown on the right). radiators and halogen lamps produce a modulated signal at 100Hz (for 50Hz mains), while the sun produces a constant level of infrared that can vary slowly over time. These are all removed by the bandpass filter within IRD1. Many general-purpose IR detectors centre the filter at 38kHz, allowing a frequency range from 36kHz to 40kHz to be received without too much attenuation from the bandpass filter. There may be a small amount of attenuation that reduces the reception range slightly, but not to any significant extent. RC5 and RC6 encodings use 36kHz modulation, NEC uses 38kHz and Sony uses 40kHz. These varying frequencies mean we have to compromise with the infrared detector for it to work with all these protocols, with 38kHz being the best bet as it’s in the middle of the range. 48 Silicon Chip IRD1’s output goes to the RA0 digital input of microcontroller IC1 (pin 19), which decodes the demodulated signal pulses and drives the outputs according to the infrared code sent by the handheld remote. Each output channel includes an indicator LED, driven via a 1kW resistor, and either a 100W resistor to drive a reed relay or a 470W resistor going to the base of an NPN transistor. If a reed relay is used, a reverse-­ biased diode (D11-D18) clamps the back-EMF voltage from the relay’s coil as it switches off. If an output transistor is used instead, a diode (D1-D8) clamps the back-EMF produced by any external relay coil it might be driving. Whenever the transistor is turned on, the external relay will be on. The circuit shows one output driven by the RC6 digital output (pin 8) and one driven by the RA5 digital output Australia's electronics magazine (pin 2), but six other outputs are also available, for a total of up to eight. Any output configured as an open-collector type provides a +12V terminal suitable for driving an external 12V DC coil relay. This comes from the power input socket (CON9) via reverse-polarity protection diode D9. The acknowledge (ACK) LED, LED9, is driven from IC1’s RC2 digital output and flashes whenever an infrared signal is received. LED9 doubles up as a power indicator by glowing at about 6% brightness when an IR signal is not being received. The ACK LED also provides indications during the process of learning infrared codes; more on that later. Pushbutton switches S1, S2 and S3, connected to IC1’s RB5, RB6 and RA1 digital inputs, are used during the learning process. Those three inputs are held high (at +5V) unless pulled siliconchip.com.au A bird’s eye view of the Learning Remote Receiver. The CON1-CON4 outputs are driven by transistors in this case, and CON5-CON8 by relays. The board allows either style to be used to drive any of the eight outputs. to 0V when the corresponding button is pressed. The RA1 input is pulled high via a 10kW resistor to the 5V supply, while the RB5 and RB6 inputs are held high by pullup currents provided internally by IC1. Trimpots VR1 and VR2 provide adjustments for the timer and IC1’s oscillator. These connect to the AN5 and AN4 analog inputs, and IC1 converts the voltage at the wiper of each trimpot to a digital value. VR1 allows the timer for each channel to be adjusted from ⅛th of a second to 32 seconds. Frequency adjustment VR2 allows IC1’s internal oscillator to be trimmed. Typically, it is set to its mid position so IC1’s internal oscillator runs at the factory calibration rate (usually within 3% of nominal at 25°C). This oscillator is used as the siliconchip.com.au time base for decoding the IR codes. Having an accurate time base provides reliable IR code detection. While handheld IR remotes should transmit according to timing specifications, the timing can vary between remotes because many use a relatively inaccurate ceramic resonator for timing. These are used since they are cheaper than crystals and also smaller. The accuracy for low-cost versions is typically ±5%. While IC1’s decoding of IR signals does have some tolerance, having the adjustment allows for extra variation. VR2 can be adjusted to accommodate variations in IC1’s oscillator as well as the IR remote control’s. It allows IC1’s frequency to be adjusted by ±6% in 128 steps. The 5V supply for IRD1 and IC1 comes from REG1, a 78L05 regulator. A 100µF electrolytic capacitor bypasses Australia's electronics magazine its input, while a 10µF capacitor filters its output. IC1’s supply is also bypassed by a 100nF capacitor close to its supply pins. Construction All parts are installed on a PCB coded 15108241 that measures 130 × 101.5mm. This can be housed in a 140 × 110 × 35mm plastic case, with optional panel labels affixed to the front and rear panels. Fig.6 shows the layout of the parts on the PCB with all eight reed relays fitted. In contrast, Fig.7 shows the identical layout but with open-­ collector transistor outputs suitable for driving external 12V DC relays or other 12V loads. You can mix and match the two output types, and you don’t have to populate all eight outputs. As shown in the photos of our prototype, we installed open-collector October 2024  49 Fig.6: the PCB populated with eight reed relays. With these relays, the outputs are not polarised. You don’t need to install all eight relays if you need fewer. transistor outputs for the first four channels and relays for the last four channels. Regardless of whether you populate all eight outputs, you should fit LED1 to LED8 and their associated 1kW resistors. As well as showing activated channels, they display the selected timeout period during the learning procedure. Begin assembly by fitting the resistors. The parts list shows the resistor colour codes, but you should also check their values using a DMM before soldering them to the PCB. Be sure to fit the correct values for resistors R1-R8: 100W for reed relays or 470W for open-collector transistor outputs. Keep the lead off-cuts, as you may need them later. The diodes can go in next. D11-D18 are 1N4148 types, while D1-D9 are 1N4004s. Take care that the diodes are all orientated correctly. Next, install the 20-pin DIL socket for IC1 (notched end to the lower edge of the PCB). The capacitors can then be soldered in place, ensuring that the three electrolytics are orientated correctly. The 100nF capacitor can be fitted either way around. Follow by installing the DC socket (CON9) and switches S1, S2 and S3. After that, fit transistors Q1-Q8 and/ or relays RLY1-RLY8 with the notched ends downwards. Be sure to place REG1 (78L05) in the correct position. It has the same TO-92 body as the transistors. Jumper wires JP1-JP8 can now be installed in any channels where a transistor is fitted. These only need to be very short (less than 5mm) and can be fashioned from resistor lead off-cuts bent in a ‘U’ shape. Trimpots VR1 & VR2 can be installed now, along with screw terminals CON1-CON8. Ensure that the terminals sit flush against the PCB and that their wire entry holes are toward the board’s top edge before soldering their pins. LEDs & infrared detector Fig.7: this is like Fig.6 but all eight output sections have been populated with transistors. They can drive external loads directly or be used to control external relays. You can also mix and match relays and transistors. The wire links feed 12V to the left side of the terminals (marked +). 50 Silicon Chip Australia's electronics magazine LED10 can be installed with its body a millimetre or two above the PCB. Be sure to install it with the correct polarity: the longer anode lead goes to the left, as indicated on the overlay diagrams. Mount the remainder of the LEDs, as shown in Fig.8. Their leads must be bent down by 90° 6mm from their bodies. That’s best done using a 6mm-wide cardboard siliconchip.com.au Fig.8: bend LED1-LED9 like this so they will reach the holes in the front panel. Make sure you bend the leads in the right direction so that the longer (anode) leads will be on the left when mounted on the PCB, as shown in Figs.6 & 7. Fig.9: similarly, by bending the IR receiver leads like this, it will reach the associated hole in the front panel. Using Figs.8 & 9, and this photo as a reference, the LEDs and IR receiver need to bent so they fit into the front panel. template. Make sure that each LED’s cathode (K) lead (the shorter of the two) is towards you before bending it as shown. That way, the LEDs go in with the correct polarity, with the anode to the left-most hole in the PCB. Don’t solder the LEDs to the PCB at this stage. We’ll do that later, with the PCB in the case. Having prepared the LEDs, you can now bend the infrared detector’s leads as shown in Fig.9. Solder it in place with the centre of its lens 9.5mm above the PCB. need to drill 6mm diameter holes for the nine LEDs and their bezels, as well as for the infrared receiver, IRD1. The holes in the rear panel are for cable glands and the DC socket. We used two glands, but the total number can be increased if you can’t fit all the output wiring through just two glands. Their holes should be at least 22mm apart in the region shown. The 12mm holes for the glands are best made using a small pilot drill to begin with, carefully enlarged to size using a tapered reamer. Drilling the case Final assembly The next step is to drill the front and rear panels of the enclosure. The drilling template, Fig.10, shows where the holes are located and their sizes. You Once all the holes have been drilled, the PCB can be placed into the case. The nine LEDs can then be adjusted by cutting the leads shorter if they hit the base of the case. Next, insert the LEDs into the front panel holes (without the LED bezels initially) and fit the PCB and front panel into the enclosure. Check that each LED is correctly orientated and that it protrudes through its front panel hole before soldering its leads on the top of the PCB. Once they have all been soldered, remove the board and also solder them on the underside of the PCB, then trim the leads further. Now check that the infrared detector’s lens aligns correctly with its frontpanel hole. If not, bend its leads until it’s centred. Testing Apply power using a 12V DC plugpack and check that the voltage Fig.10: the front and rear panel drilling details. These diagrams can be printed/copied at actual size and used as templates. We drilled two 12mm holes for cable glands, but you can have up to four if needed. Ensure they’re in the specified zone and a minimum of 22mm apart. All dimensions are in millimetres. October 2024  51 between pins 1 and 20 of IC1’s socket is close to 5V (4.85-5.15V). If no voltage is present, check diode D9’s polarity and the polarity of the 12V DC supply (the centre of the plug should be positive). Also ensure that REG1 is correctly orientated and all leads have been correctly soldered to their PCB pads. If the supply checks out, switch off the power and install IC1, ensuring that its notched end faces toward the front and all its pins correctly go into the socket. Set VR2 to its mid position. VR1 can be set fully anti-clockwise initially, for a 125ms timeout, so it is easier to check the momentary and toggle operations for the channel outputs. Learning codes The 8-Channel Learning IR Remote Receiver can learn infrared codes matching NEC, Sony, RC5 and RC6 protocols. These are commonly used in many handheld IR remote controls. Each channel should be programmed using a different button on the handheld remote. You don’t have to use the same remote to operate each channel. You can use different remote controls, provided they produce one of the supported protocols. Once you start the learning mode, you have 20 seconds to finish this procedure before it times out and returns to the normal operating mode. To program each channel, press the Program switch (S1). This will fully Parts List – 8-Channel IR Remote Receiver 1 double-sided PCB coded 15108241, 130 × 101.5mm 1 140 × 110 × 35mm plastic case [Jaycar HB5970, Altronics H0472] 2 panel labels, 131 × 28mm (optional) 1 12V DC plugpack rated at 150mA or more (see text) 3 SPST vertical tactile switches with ~0.7mm actuators (S1-S3) [Jaycar SP0600, Altronics S1122] 8 2-way screw terminals, 5.08mm pitch (CON1-CON8; as required) 1 2.1mm or 2.5mm inner diameter PCB-mount DC socket to suit plugpack (CON9) 2 10kW mini top-adjust trimpots (VR1, VR2) [Jaycar RT4360, Altronics R2480B] 2 cable glands for 3-6.5mm cable [Jaycar HP0720, Altronics H4380] 1 20-pin DIL IC socket 9 5mm LED bezels 4 No.4 self-tapping screws Semiconductors 1 PIC16F1459-I/P microcontroller programmed with 1510824A.HEX (IC1) 1 TSOP4838 or similar 36-38kHz IR receiver (IRD1) [Jaycar ZD1952/ZD1953, Altronics Z1611A] 1 78L05 5V 100mA regulator (REG1) 8 high-brightness 5mm red LEDs (LED1-LED8) 2 high-brightness 5mm green LEDs or other colour (LED9, LED10) 1 1N4004 1A diode (D9) Capacitors 2 100μF 16V PC electrolytic 1 10μF 16V PC electrolytic 1 100nF 50V MKT polyester or MLCC Resistors (all ¼W, 1% axial) 1 10kW 11 1kW 1 100W Extra parts for reed relay outputs (per output, up to 8 total) 1 SPST DIP 5V reed relay (RLY1-RLY8) [Jaycar SY4030, Altronics S4100] 1 1N4148 75V 200mA diode (D11-D18) 1 100W ¼W 1% axial resistor (R1-R8) Extra parts for open-collector transistor outputs (per output, up to 8 total) 1 BC337 65V 100mA NPN transistor (Q1-Q8) 1 1N4004 1A diode (D1-D8) 1 470W ¼W 1% axial resistor (R1-R8) 52 Silicon Chip Australia's electronics magazine light the ACK LED on the front panel. One of the channel LEDs will also be lit, showing the currently selected channel. Initially, this will be channel 1, but other channels can be selected by pressing the Channel switch (S2). Each press will choose the next channel; after 8, it will return to channel 1. The Momentary/Toggle (MOM/ TOG) LED will indicate the current selection for that channel. It lights for 125ms every second to show the momentary selection, or lights solid to show the toggle option is selected. Pressing S3 selects between momentary and toggle action. When momentary is selected, the time the channel is on (once programmed) is set by the timer. The timer value for the selected channel is adjusted using VR1. Timer values range from 125ms to 1s in eight 125ms steps, then options of two, three, four, five, six, eight, 16 and 32 seconds. To set the timer, press and hold the MOM/TOG switch for at least 600ms. This will change the channel LEDs from showing the selected channel to displaying the chosen timer period instead. If VR1 is fully anti-clockwise, none of the channel LEDs will light, but the ACK LED will be fully lit. For other timer periods, the ACK LED will be off, and the 8-channel LEDs will show the timer setting as per Fig.11, like a dot bargraph. Adjust VR1 for the timer period required. When S3 is released, the channel display and ACK LED will siliconchip.com.au return to showing the selected channel and fully lit ACK LED to indicate that it is still in the programming mode. The MOM/TOG LED will flash to show that momentary action is selected. If you decide to change to toggle, press S3 again and the LED will stay lit, indicating toggle mode. In this case, the timer for that channel is inactive. Once the channel has been selected and the timer adjusted (or toggle enabled), press S1. This makes it ready to receive an infrared signal from the handheld remote. The ACK LED will flash in readiness, with the LED lighting for 125ms every two seconds. A lack of flashes indicates that the Receiver hasn’t accepted the code as valid. It will flash at 1Hz with a 50% duty cycle. Point the handheld remote toward the receiver and press a button on the handheld remote. If the IR code is valid, the ACK LED will flash once for an NEC code, twice for a Sony code, three times for an RC5 code and four times for an RC6 code. If you are sure that the code from the remote should be valid, try adjusting the VR2 frequency adjustment trimpot to check if the code becomes valid. You will need to select the learning mode (S1) each time to test this. Use small changes over the full range of VR2 before rejecting the remote as unsuitable. If the code is accepted as valid, the channel LED will light when the programmed button on the handheld remote is pressed again. For toggle mode, the channel will be on with one press of the handheld button and be off on the next press. For momentary operation, the channel will be on for the timer’s duration. In momentary mode, if the handheld Up to four cable glands can be fitted for the wiring to CON1-CON8 although we found two sufficient. remote button is continuously pressed, the channel will remain on until after the button is released, plus the timer period. If you find that the unit doesn’t operate reliably or only works with certain orientations of the remote, it may be due to reception frequency tolerances. In that case, it’s just a matter of altering IC1’s frequency with VR2 to improve the IR code detection. Panel labels Assuming it’s all working correctly, all that remains now is printing out and fitting the front and rear panel labels. They are shown in Fig.12 but are also available as a PDF download from siliconchip.au/Shop/11/468 Information on making front panel details is available on the Silicon Chip website at siliconchip.com.au/Help/ FrontPanels Once you have made the labels, affix them in position and cut out the holes using a sharp hobby knife. For the front panel, insert the LED bezels from the front and insert the LEDs from the rear. The PCB is held in place with No.4 self-tapping screws into the four integral mounting posts at the bottom SC of the case. Fig.11 (left): as you adjust VR1 to set the timing for a momentary output, the LEDs will show the current setting like this. Rotate VR1 while holding S3 until the LEDs show your desired output ontime, then release S3. Fig.12 (right): the front and rear panel labels. These can also be downloaded as a PDF from siliconchip.au/ Shop/11/468 siliconchip.com.au Australia's electronics magazine October 2024  53 The MG4 XPower Electric Car by Julian Edgar No technological change seems to inspire love/hate emotions like electric vehicles (EVs). Many people are either intensely for them or intensely against. The truth is much more nuanced, as Julian Edgar describes after nine months and 20,000km with his MG4 XPower EV. H aving been interested in car tech for over 40 years, I’ve watched the advent of EVs with fascination. I first drove a Tesla 15 years ago and was enormously impressed. However, especially living in a rural area, I couldn’t see the worth of buying an EV until about nine months ago. Then, an EV was released that, for the first time in the modern history of electric vehicles, had a significant advantage over any new internal combustion engine (ICE) car in existence. That advantage was the price for the level of performance! With the release of the Chinese-made MG4 XPower, extraordinary performance became available at a cost that, in round terms, was about half that of an equivalent ICE car. For $60,000, you can now get performance that is the province of ICE cars costing at least $120,000. That is simply incredible; it is the most significant change in cars I have ever seen. Of course, if the car itself were 54 Silicon Chip terrible, that apparent advantage would count for nought. I went to a dealer and drove the MG4 XPower and was very impressed, so I bought it. Now, nine months later, what do I think of the MG4 – and of owning an EV, generally? The MG4 XPower The venerable UK brand MG has been owned by Chinese company SAIC Motor since 2007 (although it was initially acquired from BMW by another Chinese company in 2005). While the company maintains a small UK design base, perhaps 95% of the car is designed and manufactured in China. A mid-sized hatchback (some people say the car is small; it could only be termed that in an era when very large cars have been normalised), most models of the MG4 use a rear-mounted 150kW electric motor and a 64kWh 400V lithium-­ion battery pack. That under-floor battery weighs 409kg. Australia's electronics magazine The sportier XPower uses a 170kW rear electric motor and a 150kW front electric motor, both of which are threephase, permanent magnet synchronous designs. Compared to the standard car, the XPower has larger brakes, revised suspension and different interior and exterior trim. Its claimed 0-100km/h time is just 3.8 seconds. That is phenomenally fast – as fast as a Ferrari from a few years ago. The XPower weighs 1800kg, which is not particularly heavy in today’s terms. As opposed to a hybrid car that uses a combination of an ICE engine, HV battery and electric motor, an EV must be charged from mains power. The time that takes depends on the car itself and the charger to which it is connected. With the MG4, the DC charging power to the battery pack can be up to 140kW, meaning that a normal 10% to 80% charge takes about 30 minutes (charging speed isn’t linear). Of course, that’s only when using siliconchip.com.au The Chinese-built MG4 is one of the new breed of cost-effective electric cars currently available. This is the XPower version, a very fast car priced about half the equivalent car with a petrol engine. The high-voltage battery is mounted under the floor, with clever styling disguising the increased height of the lower edge of the doors. a high-power charger such as those found at highway rest stops, shopping centres and the like. Using the provided AC charger (termed by many a ‘granny’ charger because it is so slow!), it takes more than 20 hours to charge the battery fully. I use an aftermarket 3.6kW charger powered from a dedicated 15A home socket, which will charge the battery to 80% overnight from a starting level of about 20%. Electric power is limited when the battery charge drops below about 25%; as the battery charge decreases below that, the available power continues to decline. This caused us a problem only once, when my wife was driving home with a very low battery level and had to climb a long highway hill. In that case, the car would only achieve 80km/h, which was a bit dangerous on a 110km/h road. The official energy consumption of the XPower is 19kWh per 100km. That has proven accurate in summer conditions, but the consumption is a bit higher in winter – nearer 20kWh per 100km. With a 64kWh battery, and working from 80% to 10% capacity, the range is about 230km. Why only 80% to 10%? The manufacturer suggests using the battery in that way under normal conditions and only tapping into the full capacity siliconchip.com.au when undertaking long trips. Using the full battery capacity gives a range of about 330km, but doing that frequently will degrade the battery prematurely. The displayed battery range is very accurate. Initially, I was fearful of letting the battery level get below about 15%. Judging the remaining range of ICE vehicles based on fuel levels can be hit and miss, so I thought the MG4 display might suddenly drop from 15% to zero, stranding me by the side of the road and requiring a flatbed truck to get me home! However, I now realise there are no problems in running the battery down to, say, 5% as the change in the predicted range corresponds very well with the distance travelled. As with all EVs, the MG4 uses regenerative braking (ie, it returns power to the battery under braking). This is achieved in two ways. The first way is as you lift the accelerator pedal, the car automatically starts to brake regeneratively, a bit like engine braking with an ICE car in gear. The amount of regeneration can be seen on the driver display; it is seamlessly varied with the right foot. The second way regenerative As with many modern cars, instruments and most controls are via LCD screens. The centre is a touch screen; the buttons below it are the only buttons on the car! Australia's electronics magazine October 2024  55 The environmental footprint One reason many people are for or against EVs relates to the environmental footprint. There is so much information (and misinformation) on this topic. However, major peer-reviewed studies show that the total lifecycle environmental footprint (including building the car, running it and disposing of it) is less for an EV than an ICE car. That is the case even when the EV is charged mainly from coal power. However, hybrid cars can be very close depending on the exact power-generating mix. But for me, some of this debate loses the wood for the trees: it’s far better for the environment to ride a bicycle or take public transport. Or even to retain the old ICE car and use it only for short trips. braking occurs is when the brake pedal is pressed. That increases the level of regeneration over that achieved by lifting your foot off the accelerator pedal and, if the brake pedal is applied harder, the friction (conventional) brakes also help to slow the car. Regenerative braking is so effective that the disc brakes become slightly rusty from a lack of use and can squeak a little when applied. One hard braking event then cleans them again. The stand-out feature of the XPower is its amazing drivetrain. With 600Nm of torque, the XPower is extraordinarily strong, linear, refined and responsive. The only ICE car I’ve driven that comes close to its effortless performance is a twin-turbo V-12 Mercedes and, of course, the XPower is much faster. We’re talking about a wave of torque that just hurls the car forward, making driving situations like overtaking on country roads ridiculously easy. The drivetrain is the most impressive I have driven in 35 years of professionally testing cars; it makes my Porsche 981 Cayman engine and transmission look positively agricultural. The ability to ‘play a tune’ on the accelerator pedal, seamlessly moving from immense power to braking, is simply wonderful. It’s a delight I enjoy every time I get into the car, whether in city stop/start traffic or driving down a twisty country road. The design and build quality of the MG4 are excellent. The paint is very good and panel margins (gaps between adjoining panels) are consistent. Even when delving under the plastic covers positioned over so many of the mechanicals, the engineering and build quality look good. You must search hard to find deficiencies, but an example is the stitching on the underside of the head restraints. It looks as if the person operating the machine was looking 56 Silicon Chip the other way at times! The interior of the car is quite minimalistic; some would call it plain. There are the two displays, a short row of buttons, a charging pad for your phone and not much else. To some people, it looks cheap and nasty; to others, it is sleek and modern. I fall midway between the two camps – I’d like to see more control buttons and bigger screens, but otherwise, the interior austerity doesn’t concern me. Regarding the screens, the central unit measures 10.25 inches (26cm), but unfortunately, the screen behind the steering wheel is only 7 inches (18cm). With the small font that’s often used, the latter can be hard to read at a glance, although familiarity has improved this. Nearly all the controls are operated through the central touch screen, with only seven physical buttons provided below it. The central screen can be slow to react, especially when the car is first started, and accessing controls that in other cars would be a simple button-push away can become a clumsy dance of fingers. However, two of the steering buttons are programmable so, for example, some of the heater/air conditioner controls can be accessed through a steering wheel button and then adjusted via a steering wheel toggle. The air conditioner uses a high-­ voltage electric motor to power the compressor and it works extremely well. Heating is by a resistance heater rather than using the air conditioning system as a heat pump. Interestingly, in some overseas markets, the MG4’s heater does use the air conditioner; they must not think it ever gets cold in Australia! The seats and steering wheel are heated; these work very effectively, and I tend to use these functions rather than the cabin heater itself. Where the technology fails – and it Australia's electronics magazine utterly fails – is in some of the driver assistance systems. The Lane Keeping Assistant is the worst. It is so bad that it needs to be switched off; otherwise, it beeps and yanks on the steering wheel at every imagined driving misdemeanour. On unmarked country roads, it is positively dangerous. Frustratingly, it cannot be permanently disabled but must be switched off every time the car is driven. Another technology that is below par is the active (radar) cruise control. It’s almost as if the system was not recalibrated for the greater performance of the XPower, as it tends to be too heavy-handed with both acceleration and braking. Certainly, any competent driver can be much smoother than cruise control – in this regard, even a 15-year-old Holden Commodore is much superior. Other MG4 users have additionally reported autonomous braking for phantom events; however, luckily, I have not experienced that. Hopefully, MG will release software patches to solve these problems. These require a dealer visit as no over-the-air updates are available despite the car having a 4G connection. Editor’s note: given that some vehicles have been remotely ‘bricked’ or had features removed after purchase, I think that is a good thing. The good and the bad of EVs At this stage, and especially in rural and regional Australia, EVs do not make for a persuasive case for many users. More than anything else, the issues are range and charging infrastructure. Basically, for long trips, EVs are terrible. Sure, the web is full of EV discussion groups where people claim that long trips are not only possible in EVs but are, in fact, delightful. Just stop every 2-3 hours for 30 minutes of charging, and since those stops correspond to when you’d want a break anyway, what’s the problem? The reality is different. First, you must find a high-speed charger – and compared to ICE fuel pumps, they are as rare as hens’ teeth, especially off main routes. Then, the charger needs to be available. Many are broken, while others already have EVs plugged in. Imagine how long a fuel fill would take if every ICE car required half an hour at the petrol pump! siliconchip.com.au The XPower uses both front and rear electric motors, giving all-wheel drive. This is the view under the bonnet. Its build quality is excellent overall. The MG4 has a phone app that can remotely check the battery level, lock or unlock the car and turn on the heater or air conditioner. Here, it is at 63% charge, charging at 2.7kW on its way to 80%. The XPower sits a bit higher than a traditional hatchback due to the underfloor battery pack. It helps to keep the centre of gravity low. siliconchip.com.au Australia's electronics magazine October 2024  57 Yes, you can do it, but taking an ICE car with a decent range (these days, all ICE cars) is vastly less stressful. On a long trip, the ICE car is also much quicker. Having tried it a few times, I now rarely take my MG4 on trips over 300km. Next on the downsides is the financial uncertainty. People often quote the meagre ‘fuel’ cost of an EV versus an ICE car. And, especially if charged from a home PV solar system, the running costs will indeed be a lot lower. However, the major cost of buying a new car is depreciation – the amount the car loses in value each year. At this stage, it very much looks like EVs will have fast depreciation – that has been the case in markets that are more mature than Australia in terms of EV penetration. There are several reasons why. First, as technology rapidly improves, people value the older EVs less highly. Second, battery life. While the manufacturer often guarantees EV batteries for a set period (eg, seven years), the fine print shows that the guarantee is typically for 70% charge retention. Multiply the worst range by 0.7, and the real-world range of many EVs is likely to become marginal without any real recourse. And what if the battery degradation is even greater than 70%? The reality of older used EVs in Australia, like the Nissan Leaf and Mitsubishi MiEV, is that these cars often have a range that’s now as little as 70-80km. Yes, they use older battery technology – but they are real examples of older EVs. Most ICE cars still run just fine after 7-10 years (as long as they’re maintained) and don’t lose range. Also, EV proponents often overlook the purchase cost. As the MG4 XPower demonstrates, in the expensive car market, EVs are now more than competitive with ICE cars. But what of those who are less wealthy? A competent second-hand ICE car can be bought for well under $10,000. No such alternatives currently exist for EVs. As for the good aspects of EVs, they require almost no maintenance. I was initially sceptical of this, but my MG4 XPower has not seen the inside of a workshop in its first 20,000km. The first scheduled service interval is 40,000km – for most people, that’s every three years! In terms of convenience, that is a major plus. Driven hard, I don’t think the tyres on my car will last more than about 30,000km, so it will be a tyre shop that I first visit. Another positive is that, depending on your use, an EV is very convenient. Plug it in each night just like your phone, and it’s ready the next morning. No visits to petrol stations; just unplug and go. And, as discussed, the cost of charging an EV can be very low, especially if charging during the day from solar panels or using a low offpeak overnight tariff (where available). I’ve already discussed driveability. Truly, no ICE car can compete with the superb flexibility and throttle control that EVs have. Some people suggest that EVs are rather uninvolving and aren’t fun to drive – I think that is just balderdash. So where does that leave us? I love the MG4 XPower. It’s a car that is practical, a joy to drive and gives me performance unmatched by anything at its price. As for EVs in general, I think that at this stage, they’re perfect for some and quite unsuitable for others. If you’re relatively wealthy, live in a city, have PV panels (and especially a storage battery) and commute daily, they are perfect. However, if you’re not very wealthy, take many long trips and don’t have a home charging facility with at least 3.6kW, steer clear for now. If you’re listening to people discussing EVs and they say, “EVs are fantastic!” or conversely, “EVs are terrible!”, remember that they’re both likely to be wrong. The truth is much SC more nuanced. 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Buy 1 x GH1642 & 1 x GH1653 for $429. SPECIAL OFFERS: Limit of 2 of each item per customer. Unfortunately, we are being impacted by supply chain hiccups which may result in some of these Special Offers not being available in-store on the date advertised. We are working hard to get them to you as soon as possible and appreciate your patience. 3 Bag a Bargain with Up to 40% Off! MI5736 WITH QUICK CHARGE™ & POWER DELIVERY 2 FOR 50 $ ZM9065 10,000mAh Power Bank SAVE 40% Charge via USB Type-A or Type-C. Up to 3A combined output. MB3810 RRP $44.95EA M ZM9056 NOW FROM 299 $ NOW FROM 79 $ 1995 $ SAVE<at>$100 . 12V Fixed Solar Panels High performance monocrystalline panels. 40W ZM9056 NOW $79 SAVE $40 170W ZM9065 NOW $199 SAVE $100 SAVE<at>$250 ONLY 2 X MAINS OUTLETS USB PORT POWER SENSITIVE EQUIPMENT 12VDC to 230VAC Pure Sine Wave Inverters EA BUY 1 GET 1 HALF PRICE Get 230VAC (mains) from 12VDC (i.e. batteries). 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QM3842 WATERPROOF Insulated Grey or Green Cover GH1652 / GH1653 RRP $139EA 50L 12V Convertible Dual Zone Portable Fridge/Freezer Ultra-versatile with removable divider. GH1642 RRP $499 SALE ENDS SUNDAY 20.10.2024 Scan QR Code for your nearest store & opening hours 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE Rhodes Corporate Park, Building F, Suite 1.01 1 Homebush Bay Drive, Rhodes NSW 2138 Ph: (02) 8832 3100 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Using Electronic Modules with Jim Rowe 1-24V Adjustable USB Power Supply The “Zk-DP” is a surprisingly inexpensive supply module that converts 5V DC from a USB port into any DC voltage between 1V and 24V at up to 3W. It features a three-digit LED display showing the output voltage, plus easy adjustment of the output voltage with a built-in multi-turn potentiometer. A lot of small electronic devices now run from low-voltage DC. Luckily, many can run from a 5V DC supply, so they can be powered from a USB port on your computer, a standard 5V USB mains power supply or a portable battery bank. But things are not so easy if a device needs a supply of 9V, 12V, 15V, or 24V DC (or another ‘oddball’ value). Usually, you must provide a separate power supply or plugpack to deliver the required voltage. In those cases, it would be handy to have a small, low-cost power conversion device that could take the power from a standard 5V USB power source and convert it into one of those other voltages. That’s precisely the function of the module we’re looking at this month. It plugs directly into a USB-A socket providing 5V DC and can then power a device at any voltage between 1V and 24V DC. Despite its small size, it can supply in excess of 3W of power at any of those output voltages, eg, 250mA <at> 12V. Setting the desired output voltage is very easy, using a built-in multiturn potentiometer with an attached knob and a tiny three-digit LED display that indicates the current output voltage. From the legend on the PCB, it is called the Zk-DP Desk Power module, although it would also be correct to call it a DC/DC voltage converter. It’s currently available from several online marketplaces at prices ranging from $4.12 to $15.50 plus delivery. We obtained the unit shown in the photos via AliExpress from a supplier called AGUHAJSU Global Purchase Store for $4.12 plus shipping (a total of just over $6). We noticed that the Fig.1: a block diagram for the Zk-DP power supply module. Note that we have not included values for the resistors and capacitors. siliconchip.com.au Australia's electronics magazine same unit is also available from eBay. The Zk-DP module is 70mm long, 26mm wide and 14mm tall (not including the spindle of the voltage adjustment pot). All the components are mounted on a small PCB that’s 52.5mm long and 21.5mm wide. The USB-A input plug is at one end of the PCB, while the voltage adjustment pot and small 2-way output screw terminal block are at the other. All the electronics are housed in a snap-together clear blue plastic case, which allows the 3-digit output voltage indication to be easily read through the case. How it works Some searching on the internet didn’t reveal any circuit details of the Zk-DP. Still, I was able to remove the PCB from the case and glean enough information to produce the block diagram (Fig.1). I was not able to determine the type of microcontroller used as the ID marking on the top of its 20-pin SSOP package had been removed. The five-pin SIL onboard programming header suggested it might be a Microchip product. However, when we compared numerous AVR and PIC microcontrollers in that package to the pinout used on the board, none matched, so it’s probably something else. Luckily, the SX1308 voltage converter chip still had its ID on top of its 6-pin SOT-23 package. This device, shown just above the centre of Fig.1, is designed as a boost converter. However, it is being used in a slightly different configuration October 2024  63 These photos show the rear end and general view of the module with the supplied blue plastic case. Note that there is not a cut-out for the 3-digit segment display. Both photos are shown enlarged for clarity. here, known as a SEPIC converter (single-ended primary-inductor converter). This has a similar function to a buck-boost converter but requires just one switching element instead of two. The operation is described at https://w.wiki/9DjN An ordinary boost converter (eg, as shown in the SX1308 data sheet) would have a series diode from pin 1 of U2 directly to the output. However, that would mean the output voltage could never go below 5V because there would be a direct path for current to flow from USB +5V through L2 and that diode to the output. Basically, the series capacitor AC couples the switching waveform to diode D1 so that there is no longer a constant path for current to flow, allowing the output voltage to be regulated below the input as well as above it. The other inductor, L1, keeps the load current flowing when the internal switch in U2 is closed and no current flows through the series capacitor to the output. That means the output filter capacitor does not have to supply the entire load current during this time, significantly reducing the output voltage ripple. The SEPIC configuration is related to the Ćuk converter (https://w. wiki/9Db2), except that the positions of the diode and second inductor (L1 here) are swapped. Thus, SEPIC gives a non-inverted output voltage compared to the input. In contrast, the Ćuk converter produces a negative output voltage from a positive input. The SX1308 runs at a fixed switching frequency of 1.2MHz and uses an internal power Mosfet (with its drain connected to pin 1) as a low-loss switch. The output voltage is adjusted by varying the voltage divider ratio to send a proportion of the output voltage back to pin 3 of the SX1308, its FB (feedback) input. U2 varies the Mosfet duty cycle in response to changes in the feedback voltage. With a 50% duty cycle, the output voltage is similar to the input voltage of 5V. Higher duty cycles allow the output voltage to go above 5V, while lower duty cycles result in an output below 5V. The conversion efficiency is quite high because the power Mosfet inside the SX1308 has an on-resistance of only 80mW (80 milliohms). For example, when configured as a boost converter and converting between a 5V input and a 12V output, its efficiency for load currents between 100mA and 400mA is better than 92%. The microcontroller’s main job in the Zk-DP module is to measure the output voltage and show it on the small 3-digit LED display. The LED digits are 6mm high and are quite readable. Trying it out After connecting the Zk-DP module to a bench power supply capable of providing well over 3W, I also fired up my bench DMMs and connected them to the module’s output. I used one to measure the module’s output voltage, while the other measured the current it delivered to a programmable DC load. I used a third DMM to monitor the input voltage to the module. Using this setup, I could test the module’s performance at various output voltages for a range of output currents at each voltage level. The results are summarised in Fig.2. The red horizontal lines show the module’s output current at the nine voltage settings I used for testing: 24V, 18V, 15V, 12V, 9V, 7.5V, 5V, 3.3V and 2.5V. The dashed pink curve shows the module’s rated maximum output power of 3W. An example photo showing what the voltage display looks like when powered on, here it is supplying 15.0V. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au The output voltage at each setting remained essentially constant for current levels beyond that corresponding to 3W of output power; there was no ‘drooping’ on any of the voltage plots. The voltage level at the 24V setting remained within 30mV up to a load of 200mA (4.8W!), while the level at the 18V setting was within 45mV up to 300mA (5.4W). The voltage at the 15V setting remained within 3mV at loads up to 300mA (4.5W); at the 12V setting, it remained within 5mV at loads up to 300mA (3.6W); at the 9V setting, it remained within 5mV at loads up to 400mA (3.6W); and at the 7.5V setting, it remained within 25mV at loads up to 500mA (3.75W). Its output voltage held up similarly well at the 5V and lower voltage settings, so you can see why the plots in Fig.2 are all shown simply as horizontal lines. Although I tested the module’s performance beyond the 3W limit, that was only for brief periods. I would not recommend using the module to deliver more than 3W for more than short periods to prevent it from overheating and possibly being damaged. The next test I ran on the module was to check the accuracy of its LED voltage display at various output voltage settings. Here again, it performed well, as shown in Fig.3. The readout error was highest at 2.5V, at +1.2%, then varied between -0.2% and +0.8% before rising to +0.5% at 12V, then falling to -0.3%, -0.1% at 18V and 20V, and then to -0.6% at 24V. So, using the module’s LED display to set its output voltage gets you pretty close. The error percentages provided are best-case values, an additional error of up to 100mV is possible due to display rounding. Fig.2: this graph shows how the Zk-DP power supply module performed at various voltages for different output currents. Fig.3: this graph shows the difference between the selected output voltage and the voltage displayed on the 3-digit segment display. Conclusion There is little more to say about this tiny low-voltage voltage conversion module. It is nicely made, performs surprisingly well and carries a very small price tag. You could use it to power a small breadboard during development from a conveniently nearby computer, or any other time you need a stable DC voltage at a modest current level. Adding it to a USB power bank makes a handy portable, adjustable DC voltage source. SC siliconchip.com.au There’s nothing of importance on the underside of the module, although this is the only place that the output polarity is clearly indicated. Australia's electronics magazine October 2024  65 SILICON CHIP Mini Projects #012 – by Tim Blythman There are lots of IoT (Internet of Things) gadgets and widgets available, but many require a subscription to work. The WiFi Relay Remote Control could be considered one of the simplest IoT devices. You don’t need to sign up for anything, and you can build it yourself. WiFi Relay Remote Control W e covered Jaycar’s XC3804 WiFi Relay Module in January 2024 (siliconchip.au/Article/16088). As the name suggests, it is a small module containing a relay and a WiFi radio. The Relay Module can be controlled by sending commands over a WiFi network. It doesn’t even need an internet connection to work. While it’s a handy tool, another device is required to operate it. You could use an old mobile phone or similar WiFi-equipped device to control it, but we think there are better ways. So we’ve designed the WiFi Relay Remote Control. As the name suggests, it is a remote controller for the Relay Module. Since the Relay Module uses a dedicated WiFi network for its operation, it’s easy to set up a controller dedicated to that task. WiFi Relay Module There are more details on the WiFi Relay Module in our other article, but the principle of operation is as follows. The Relay Module sets up a WiFi access point, allowing WiFi clients to connect. When it receives particular web page requests, it operates the relay in response. So we just need to create a client that connects to the access point and then sends the appropriate requests depending on user input, like pushing a button. It would be good if it also indicated if the request has worked or not. That’s basically how the WiFi Relay Remote works. It has two pushbuttons connected to a WiFi Mini Main Board that connects to the access point provided by the Relay Module. When the buttons are pressed, it sends commands to open or close the relay. We’ve used illuminated pushbuttons, so the LEDs light up to show what is happening. You can see a video showing the WiFi Relay Remote in operation at siliconchip.au/link/abx4 Circuit details Fig.1 shows the circuit diagram. The pushbutton contacts are each connected between a digital I/O pin and ground. Internally, the processor on the WiFi Mini applies a weak pullup Fig.1: you could easily rig it up on a breadboard if you wanted to test it before building it. We recommend using the same pins on the D1 Mini as we did, as some other pins have special functions that might cause a conflict. Fig.2: how we placed parts on the underside of the shield (also refer to the adjacent photo). The shield’s top side is bare, apart from the switches. The wiring is hidden on the underside of the shield. We originally planned to use the D8 pin instead of D1, which would have made the layout neater. However, that is impractical, as D8 has a pulldown instead of a pullup. for those pins, so it can sense when the switch is closed and the I/O pin is pulled to ground. Two status LEDs are also provided that are internal to the illuminated pushbuttons. Each has a 220W series resistor to limit the current flow to an appropriate level for the LEDs. The WiFi Mini also has an onboard LED that lights up when pin D4 is driven low, so we can also use that as an indicator. Construction We intended the Remote to be a compact and self-contained unit, so the hardware has been assembled onto a small prototyping shield that can plug into a WiFi Mini. Fig.2 and the photos show how it has been laid out. Start by fitting the switches. Straighten the leads so that they will slot straight into the prototyping shield. To get the orientation correct, note the longer (LED anode) pins and place them as shown. Solder them after making sure the switches are flat against the shield. Solder the two resistors as shown, from the longer anode pin to the pads for D6 and D7. We use the inside row of pads so the outer rows are free for attaching the headers later. Keep the wire lead offcuts for the next steps. Next, solder a wire from the D5 pad to the corner lead of the switch as shown. All three leads on the other side of both switches connect to ground, so run a wire from each group of three back to the ground (G) pin. Then run a piece of insulated wire from the switch with the red LED back to D1. Slot the header pins onto the WiFi Mini (to align them) and then solder them to the prototyping shield. That’s it, the hardware is finished! Software operation The software consists of an Arduino sketch that uses the ESP8266 board profile. The sketch attempts to connect to the ‘Duinotech WiFi Relay’ access The assembled shield slots onto the top of the WiFi Mini, making for a compact unit. We used a small breadboard and jumper wires to power the WiFi Relay Module from the same supply for testing. The switch with the red ‘off’ LED is at the top, while the green ‘on’ LED is at the bottom. Unfortunately, there is no way to tell them apart when unlit, so our software lights both LEDs dimly so you can tell which is which. point created by the Relay Module, flashing the onboard (D4) LED until it does. Both switch LEDs are made to light dimly by driving them with a low duty cycle PWM (pulse width modulated) waveform so you can see which is on (green) and off (red). The software then waits until one of the buttons is pressed and sends the corresponding request to the Relay Module. Simultaneously, both LEDs switch off to indicate that a request is pending. If there is a successful response, the corresponding LED is switched on at full brightness, and the Relay Module will have its state set accordingly. If the request fails, both LEDs will return to a dim state after a while. The request can be tried again by pushing one of the buttons. Firmware installation Open the Arduino IDE and check that you have https://arduino.esp8266. com/stable/package_esp8266com_ index.json in your list of Board Manager URLs. Next, install the ESP8266 board profile from the Boards Manager Parts List – WiFi Relay Remote Control (JMP012) 1 Smart WiFi Relay Main Board [Jaycar XC3804] 1 WiFi Mini Main Board [Jaycar XC3802] 1 WiFi Mini Prototyping Shield [Jaycar XC3850] 1 PCB-mounting tactile switch with integrated red LED [Jaycar SP0620] 1 PCB-mounting tactile switch with integrated green LED [Jaycar SP0621] 2 220W ½W 1% axial resistors [Jaycar RR0556] 1 25mm length of insulated wire 2 5V DC power supplies siliconchip.com.au Australia's electronics magazine window. We used version 3.1.2 of the board profile, but later versions should work too. Download the software package for this project from siliconchip.com.au/ Shop/6/460 and then choose the ‘D1 R2 & Mini’ board type and its corresponding serial port in the IDE. Upload the sketch; no changes need to be made as the Relay Module uses a fixed WiFi network. Operation The LEDs on both buttons should light up dimly and the small blue LED on the WiFi Mini should start flashing. Power on the Relay Module. As you can see from our video and photo above, we just used a pair of jumper wires connected to the WiFi Mini’s 5V & GND (G) pins to get power for testing. After a few seconds, the blue LED will light solidly and you can control the Relay Module by pressing the buttons. If the blue LED goes out at any point, the Remote has lost its connection. In that case, check that the Relay Module is powered correctly. Note that other devices (such as a mobile phone or another Remote) can control the Relay Module. In this case, the LEDs might not show the correct status. There is no way to get the Relay Module’s status without triggering it, so there is no workaround for that without reprogramming the WiFi Relay Module with altered firmware. Now you can set up the Relay Module to run off its own power source and also control something. SC October 2024  67 Mini Projects #015 – by Tim Blythman SILICON CHIP Analog Servo Gauge A gauge with a needle is often the simplest way of communicating a reading. This project lets you convert an analog voltage to a gauge readout. Because it uses a servo motor, you can make it really big! › Only needs a 5V DC supply › Span and offset adjustment trimpots › Converts a 0-5V signal into a PWM signal to drive a servo motor › Uses just one comparator IC and a voltage regulator, plus some passives. T his project displays a voltage from 0-5V using a moving needle. While simple analog voltmeter movements can do this, they are delicate, somewhat expensive, and limited in size due to the movement’s strength. Our servo motor allows a much larger pointer to be used. That means some extra circuitry is needed, but our circuit uses just a few inexpensive parts and can be built on a prototyping board in under an hour. The servo we are using (intended for use in remote-controlled [RC] vehicles and such) comes with mounting screws and plastic arms (‘horns’), so it is easy to attach it to a dial to suit your application. Making a suitable needle that can be affixed to the horn is also straightforward. This sounds like the perfect application for a small microcontroller board like an Arduino; it would need just a single analog input and one digital output pin. However, servo motors similar to those we are using were invented before microcontrollers. So we can drive the servo motor using some old-fashioned analog electronics. You can see a video of the Servo Gauge working at siliconchip.au/ Videos/Analog+Servo+Gauge How an RC servo works The term ‘servo motor’ has a broader scope than just the type we are using in this project. In general, any motor that uses a feedback system to attain accurate positioning can be considered a servo motor. Specifically, we use a standard three-wire servo, as used for radio control (RC) and robotics. Apart from 5V power and ground, this type of servo has a digital input that accepts a pulse train. The pulses are sent around 50 times per second; the exact rate is unimportant but the pulse width is. Pulses around 1-2ms are commonly used. These servos have a shaft connected to a potentiometer. When the servo receives a pulse, it generates its own pulse, the length of which depends on the potentiometer position. By comparing the pulse lengths, the Some components are packed quite closely around IC1 (as can be seen in the lead photo), but you should be able to squeeze them all in with some care. Note the blue wire and two bridged pads on the back of the PCB (circled in white). Australia's electronics magazine siliconchip.com.au servo knows whether it needs to turn clockwise, anti-clockwise or stay still (when it has reached the desired position). Bob Young’s article in the March 1991 issue explains this in more depth (siliconchip.au/Article/7102). Unsurprisingly, modern servos contain a microcontroller, but they are still compatible with the same protocol that dates back to the 1960s. So we can easily interface with modern servo motors using electronics of a similar age. Circuit details Our circuit (shown in Fig.1) consists of several simple sections with distinct purposes. The section around REG1 at upper right generates a stable 3.3V for the rest of the circuit from the 5V DC input. Since the servo can draw relatively high current pulses that might affect the 5V rail, this is necessary to ensure the rest of the circuit does not change its behaviour. We are using an LM2936-3.3 regulator with the two capacitors it requires at its input and output. The other two parts of the circuit each use half of an LM393 dual comparator IC. As the name suggests, this IC compares the voltages of its two input pins. If the + (non-inverting) input (pin 3 or 5) is higher than the – (inverting) input (pin 2 or 6), the corresponding output pin (pin 1 or 7) is not driven. If the inverting input is higher than the non-inverting input, the output is pulled to ground (0V). This is known as an ‘open collector’ or ‘open drain’ since it is usually implemented with a transistor where the collector (or drain) is only connected to the output pin. The circuit around IC1a is a sawtooth waveform generator. Initially, the 2.2µF capacitor is discharged and the V_SAW level (and thus pin 2) is at 0V. Around 2.2V is on pin 3, so the output at pin 1 is not driven and thus pulled up by the 1kW resistor. The 2.2µF capacitor charges up via the 1kW and 4.7kW resistors until it reaches 2.2V, at which point the comparator output goes low. This causes the capacitor to start discharging via the 4.7kW resistor, into the comparator’s low output pin. At the same time, the voltage at pin 3 goes to around 1V. When the capacitor (V_SAW) reaches 1V, the comparator output changes again and the cycle siliconchip.com.au Fig.1: 3.3V regulator REG1 ensures variations in the supply voltage don’t affect the pulse timing. One half of the comparator (IC1a) provides a sawtooth waveform, while the other half (IC1b) uses that to generate pulses suitable for driving the servo motor. 5.0 4.0 3.0 2.0 1.0 0.0 -1.0V -20.0ms 0.0 20.0 40.0 60.0 80.0 100.0 Scope 1: the blue trace is V_SAW (pin 5 of IC1b), green is pin 6 of IC1b, yellow/ brown is the servo control signal from pin 7 of IC1b and red is output pin 1 of oscillator IC1a. 5.0 4.0 3.0 2.0 1.0 0.0 -1.0V -20.0ms 0.0 20.0 40.0 60.0 80.0 100.0 Scope 2: this is the same as Scope 1 except that the green trace voltage has changed slightly due to varying the control signal voltage, resulting in a change in the pulse width of the yellow/brown trace that goes to the servo motor. Australia's electronics magazine October 2024  69 We created this simple design, printed it out and glued it to some cardboard to suit a 5V scale over about 90°. The needle is simply a piece of dark-coloured cardboard glued to one of the servo horns. All the necessary screws should come bundled with the motor. Watch the polarity of the electrolytic capacitors; their negative leads all connect to the ground rail. continues around 40 times per second. Scope 1 shows the V_SAW voltage (the blue trace) and the pin 2 comparator non-inverting input (red trace). The arrangement of resistors and potentiometers connected to the second comparator translates the input voltage (from the Control input) to a voltage suitable for feeding to comparator IC1b. The modified voltage fed into IC1’s pin 6 is the green trace in Scope 1, while the output to drive the servo (from pin 7) is the yellow trace. The stack comprising the 4.7kW resistor, 1kW potentiometer and 10kW resistor puts the green trace just below 2.2V, near V_SAW’s peak, so we get the brief pulses needed to drive the servo. The 10kW potentiometer allows us to set how much of the Control input signal is passed on to the rest of the circuitry, while the 100kW resistor ensures that the Control input only has a small effect on the green trace level. The 2.2µF capacitor in this part of the circuit ensures that the control voltage doesn’t change too rapidly. If the voltage here jumped around too fast, it could cause glitches that would make the motor behave erratically or even damage it. Scope 1 was captured with the control input at 0V, while Scope 2 has the control input at 5V; otherwise, the circumstances are identical. You can see that the green trace has lifted slightly, causing the pulse width to nearly halve. That gives the required 1-2ms pulse range to control the servo over a roughly 90° range of rotation. Construction The first step is to build the circuit, which can be done on a small prototyping board with a similar layout to a breadboard (except that the power rails are down the middle). You don’t have to follow our layout strictly, but we know it works, so you might find it easier to match it. Check our photos and the layout diagram, Fig.2, while you solder the components to the board and add the Fig.2: here is how we have laid out the components on a prototyping board. Note that there is a single wire link under the IC, between pins 2 and 5, shown in cyan. The ground and 5V supplies for the IC are also connected by bridging pins 4 and 8 to their power rails with solder blobs. 70 Silicon Chip wires. While most features are visible from the top of the board, a wire and a couple of solder links are on the underside (see the photo on the opening spread). Start by fitting the IC socket; this will make it easier to run some tests with the IC out of circuit. Note the direction of the notch (to the left). Install the parts as shown, paying attention to the orientation of the electrolytic capacitors. After fitting all the components except IC1, add the wires shown. Three are on the copper side of the board, under the IC1 socket. In addition to those, there are two dark grey ground wires, two orange 3.3V power wires and one cyan/blue signal wire; don’t forget to add any of them. After that, connect a 5V DC power supply and run some tests. We used cut-off jumper wires so that we could plug into an Arduino board for power but you might have a different idea. Apply 5V and check that you get 3.3V at pin 1 of the regulator (towards Fig.3: use this guide to help cut a hole to suit the servo motor. It can be copied (or downloaded and printed) for use as a template. Australia's electronics magazine siliconchip.com.au the bottom in Fig.2); you should be able to measure different voltages of around 2-3V at pins 1, 2 and 3 of IC1’s socket. Pin 6 of the IC socket should be about 2.0-2.2V. Disconnect the power and plug IC1 into its socket, being careful not to fold up any of the pins under its body. Power on the circuit and connect the servo motor to the three-way header. It will probably run to one of its end stops and stall. Adjust the 1kW trimpot so that it is near the middle of its travel. It should work backwards; that is, turning the trimpot clockwise will cause the servo to turn anti-clockwise. If it is not responding, disconnect the power to avoid damaging the servo’s mechanism and motor, then check your wiring. If all is well, connect a jumper wire from the signal input (where the blue wire is shown in Fig.2) to 5V. You should then be able to move the servo by adjusting the 10kW trimpot. Again, be careful not to allow the servo to run against its end stops excessively. Parts List – Servo Gauge (JMP015) 1 micro servo motor [Jaycar YM2758] 1 25-row prototyping board [Jaycar HP9570] 1 8-pin IC socket [Jaycar PI6500] 1 3-way header, 2.54mm pitch [cut from Jaycar HM3212] 2 2-way headers, 2.54mm pitch [cut from Jaycar HM3212] 1 10kW side-adjust mini trimpot [Jaycar RT4016] 1 1kW side-adjust mini trimpot [Jaycar RT4010] 1 10cm length of insulated wire 1 5V power supply (see text) 1 gauge face and needle to suit (see photos) Semiconductors 1 LM393 dual comparator, DIP-8 (IC1) [Jaycar ZL3393] 1 LM2936-3.3 3.3V LDO voltage regulator, TO-92 (REG1) [Jaycar ZV1650] Capacitors 1 10μF 16V radial electrolytic [Jaycar RE6066] 2 2.2μF 63V radial electrolytic [Jaycar RE6042] 1 100nF 50V multi-layer ceramic or MKT [Jaycar RM7125] Resistors (all ¼W or ½W 1% axial) 1 100kW [Jaycar RR0620] 1 10kW [Jaycar RR0596] 2 4.7kW [Jaycar RR0588] 2 2.2kW [Jaycar RR0580] 3 1kW [Jaycar RR0572] Turning it into a gauge You have a bit of flexibility in choosing your gauge face and pointer. The servo should be supplied with screws and plastic horns for mounting. The photos show the basic gauge we created, with a printed piece of paper glued to some cardboard, to show readings from 0V to 5V. The servo will have a usable span of just over 180°, but we’ve gone for a more traditional analog gauge range of about 90°. Fig.3 shows the dimensions of the holes for the servo, which should help you to cut out your gauge face to suit. There is one rectangular cutout to make plus two small holes for self-tapping screws to retain the servo motor. The grey-shaded circle shows the servo shaft, which serves as the pivot point for the Gauge. Fig.4 shows the image we printed to make the gauge face; it is available as a PDF download from siliconchip. au/Shop/11/488 For the needle, we screwed one of the horns to the servo shaft, then glued a pointer to it so that it pointed at the 0V marker. Using it To calibrate the Gauge once the glue has set, power the circuit and connect the voltage input to 0V (eg, ground on the protoboard). Then adjust the 1kW siliconchip.com.au Fig.4: the gauge panel artwork we created shown at 90% of actual size. You can download it as a PDF from siliconchip.au/Shop/11/488 trimpot until it points at the 0V point on the gauge. Next, connect the input to 5V (or whatever your maximum will be). The 3.3V rail is another well-defined and accurate level. Adjust the 10kW trimpot so that it points accurately for the higher input. Australia's electronics magazine The two inputs interact slightly, so switch back and forth between them a couple of times to make minor adjustments until the Gauge is operating accurately. Remember that the 10kW trimpot will slightly load the source of the control voltage. SC October 2024  71 Project by Stefan Keller -Tuberg This device will disconnect a load from its power supply if the voltage is reversed or too high. It also disconnects the load if it draws current above the adjustable trip level. Its dual-rail support means it can work with devices like audio amplifiers with a split (positive and negative) supply. I Dual-Rail Load Protector n June 2024, we published three DC Supply Protectors that guard against reversed or excessive supply voltages, but they could only handle a single-rail supply (siliconchip.au/Article/16292). This design provides even more functions, extends the reverse/overvoltage protection to split rails and adds adjustable current limits with automatic or manual resetting. If you’ve built something that uses flying power leads, you may already have had a close call mixing up polarities. Or have you ever forgotten to check that you’re using the right supply to power a device? If any of these ring true, this design might help avoid a catastrophe by introducing power supply protection. It’s so versatile that you’ll think of many applications for it. The overvoltage cut-out levels can be set between ±5V and ±19V (or 5-38V for the single-rail version). If the supply overshoots the protection level, this device will rapidly interrupt it. The overcurrent thresholds are set by a current sense resistor and trimpot. The sense resistance is chosen so the voltage drop is approximately 50mV at the nominal protection level. The trimpot range permits adjustment from zero up to twice the nominal current level. When the current limit is reached, it interrupts the offending power rail 72 Silicon Chip by turning it off completely, similar to a fuse blowing. This minimises the chance of damage due to a fault compared to simply holding the current at the threshold by reducing the voltage, as a current-limited bench supply would do. Also, if the device is unattended when it fails, interrupting rather than limiting the power delivered could help avoid an even larger disaster. It can be set so that when the overcurrent circuit trips, it will automatically reconnect after a two-second delay or require manual intervention (a button press). If your dual-rail application is asymmetric, you can set different overvoltage and overcurrent thresholds for each rail. Depending on the Mosfets used, it can handle up to 4-7A per rail without heatsinking. Adding heatsinks to the Mosfets will allow them to handle more, up to 10A for the higher-current Mosfets specified. Due to the design’s modularity, you only need to populate the required features. To start with, you can equip it to suit single or dual supply rails. Configuring it for a single rail saves a few components and doubles the single supply maximum voltage to 36V. If your device to be protected has more than one positive or more than Fig.1: some of the different ways the Supply Protector can be used. If the maximum voltage of ±18V for the dualrail version is not enough for your application, you can stack two boards to double that, as shown on the far right. Australia's electronics magazine siliconchip.com.au Features & Specifications ● Voltage range: 4-36V DC or ±4-18V DC (±4-36V DC with two boards) ● Over-voltage cut-out: 5-38V DC or ±5-19V DC (±5-38V DC with two boards) ● Voltage withstand: up to ±60V at either input or across both inputs ● Current capability: 7A+ without heatsinking (more with heatsinks) ● Voltage insertion loss: typically <300mV <at> 10A ● Over-current protection: disconnects rails independently if current draw exceeds a set threshold ● Over-current reset: automatically after two seconds or manually via pushbutton 🔹 🔹 🔹 🔹 exact values depend on parts used one negative rail, you can common the grounds and use two or more of these boards to protect them all, including dual-rail applications operating up to ±36V, as shown in Fig.1. You can leave some components off if you don’t need overcurrent protection. You can also leave off the overvoltage sections if you don’t want that feature. The circuit is arranged in three sections, each supporting one or two power rails. Reverse polarity protection The first section of the circuit, shown in Fig.2, uses Mosfets Q1 & Q2 like ‘ideal diodes’. They have a very low voltage drop when forward-biased but a high impedance when reverse-­biased. If you accidentally connect the input voltages with the wrong polarity, the internal body diodes of Mosfets Q1 and Q2 will be reverse-biased, and no current can flow. Q1 and Q2 remain off, protecting all the downstream components from the abnormal condition. The specified Mosfets have reverse voltage ratings up to 60V, offering plenty of protection against accidental power supply reversal. However, without protection, the Mosfets could be damaged by gate-tosource voltages exceeding 20V. Zener diodes ZD1 and ZD2 ensure that the voltage between the gate and source of each Mosfet cannot exceed 15V. Other Mosfets in the design have similar protections. When the input voltage polarities are correct, the internal diodes of Q1 & Q2 are forward-biased. As current starts to flow, 47kW resistors pull the Mosfet gates to ground, so they switch on. As the gate bias exceeds 2-4V and the Mosfet channel resistance drops, the internal protection diodes will be shunted, so very little voltage will be lost across the Mosfets. The Supply Protector’s minimum voltage rating of 4V is because that is the minimum voltage at which the Mosfets used are guaranteed to switch on and conduct sufficient current. Over-voltage protection The following section deals with over-voltages. Zener diodes ZD3 and ZD6 set a fixed value for each rail’s protection threshold. The knee voltage for 1W zener diodes rated above 5.6V occurs around 3.5-5% below the nominal zener voltage. As the supply voltage reaches this level, they will start to break down. Lower voltage zener diodes have a more rounded knee, so the difference from nominal can be larger. When enough current flows to develop 0.6V at the gate of the associated SCR, it will trigger and switch off either Mosfet Q4, in series with the positive rail, or Mosfet Q5 in the negative rail, disconnecting and protecting the downstream circuitry and the load. The SCR will remain latched until the supply voltage is removed. Providing the applied voltage remains below the Mosfet specification (55V or 60V), the unit will tolerate the condition indefinitely, and the device you’re protecting will stay safe. Most applications won’t require fine overvoltage threshold adjustment, so you can simply set it by selecting the nearest zener. Two extra diodes labelled D4 and D5, in series with the zeners, allow the threshold to be tweaked. Usually, they are replaced with wire links, but if required, regular or schottky diodes can be fitted to increase the overvoltage trip thresholds by 0.3V (SB140/1N5819) or 0.6V (1N4004). Op amp IC1 has an absolute maximum limit of 40V, the highest overvoltage threshold supported. In practice, the trip points should be no more than ±19V for one dual-rail device or 38V for a single-rail version, giving a small safety margin. The 220μF and 3300μF electrolytic capacitors are to counteract the effects of power source inductance. At switch-on, many devices cause a momentary current surge as the supply Dual-Rail Load Protector hard-to-get parts (SC7366, $35): includes the PCB and all semis except the optional/varying diodes. siliconchip.com.au Australia's electronics magazine October 2024  73 Fig.2: the Supply Protector circuit has mostly independent positive and negative sections with three stages each. The first is reverse polarity protection (using Mosfets Q1 & Q2), followed by overvoltage protection (Mosfets Q4 & Q5), then overcurrent protection (Mosfets Q10 & Q11). The only sections shared between the positive and negative rails are the half-supply generator (IC1d), reset oscillator (IC1c) and reset switch. bypass capacitors charge. This high current pulse can interact with inductances in the wiring etc, causing ‘ringing’ (oscillation), which causes an overshoot voltage to appear on the affected power rail, sometimes a significant one. One of my test supplies caused damped oscillations with a frequency of around 2MHz, resulting in a peak overshoot voltage of around 50% above the nominal supply. This persistently tripped the overvoltage protection at power-on. The electrolytic capacitors dampen power-on overshoot to avoid false overvoltage trips. In severe cases, you may need to increase the value of the 220μF parts, although they should be sufficient for most cases. It is usually more severe with a longer input power cable. Overcurrent protection The third section of the circuit 74 Silicon Chip provides overcurrent protection. The load current is monitored by the voltage drop across the ‘+sense’ and ‘-sense’ resistors. For the positive rail, LED15, VR1 and one ‘+bias’ resistor set an adjustable reference voltage at pin 3 of IC1a that is a couple of volts below the +ve rail voltage. LED17 and the other ‘+bias’ resistor create another voltage at IC1’s pin 2 that varies with the ‘+sense’ voltage drop. IC1a compares these voltages; its output is low when the sensed current is below the setpoint, so Mosfet Q10 is usually on. If the current setpoint is exceeded, IC1a’s output goes high, switching off Q10 and disconnecting the load, while also lighting overcurrent indicator LED21. Op amp IC1b, Mosfet Q11 and LED22 function similarly for the negative rail. The purposes of LED15 and LED17 aren’t to emit light; they provide consistent voltage drops so the op Australia's electronics magazine amp inputs remain within the chip’s common-­ mode range, which does not go up to the positive rail. The fact that LEDs have a higher voltage drop than a regular silicon diode (around 1.8V rather than 0.7V) is useful in this application. The voltage across the ‘+sense’ resistors is approximately 50mV at the nominal overcurrent trip point. VR1 is for fine-tuning; its 100W value means that with 1mA flowing through it, a full trimpot rotation will cover twice the nominal voltage range expected across ‘+sense’. Note that the ‘+set’ LED (LED15) usually goes out when the overcurrent LED (LED21) lights. However, there are cases where the current is near the overcurrent set point where both could light. So if you notice that, it’s normal. The overcurrent protection only interrupts the rail experiencing the overload. When that happens for the siliconchip.com.au positive rail, D19 provides a feedback path to latch the state even after Q10 interrupts the current and the ‘+sense’ voltage drop falls back to zero. It will remain off until the condition is reset by NPN transistor Q8 switching on and pulling pin 3 of IC1a below the pin 2 level. When the output of IC1a goes high, another NPN transistor (Q9) inverts the transition to create a falling edge. This is combined with any falling edge from IC1b by diode D24. These are AC-coupled to IC1c by a 1nF capacitor and diode D29, which works as an overcurrent reset monostable. A two-second delay is provided by the 1μF capacitor and 2.2MW resistor. The 100kΩ resistor at pin 9 of IC1c prevents damaging input currents when pins 9 and 10 differ by more than 5.5V. When the monostable times out (if enabled) or the reset pushbutton is pressed, Q6, Q7 and Q8 temporarily siliconchip.com.au shift the voltage levels at the inputs of IC1a and IC1b. This forces them out of their latched states, re-enabling Mosfets Q10 and Q11. If the auto-reset feature is enabled, voltage to the load will be restored two seconds after it trips. If the overcurrent condition persists, the trigger-­ delay-restore process will repeat indefinitely every two seconds (or until the fault clears). This monostable arrangement requires a reference voltage at the midpoint of the IC’s power supply. We could have used the GND line for this reference, but that would mean the circuit would only work with symmetrical dual rails, reducing its flexibility. So IC1d synthesises a mid-rail voltage (halfway between +ve and -ve) that self-adjusts without needing different configurations. The 100nF capacitor and 1MW resistor connected to header CON3 ensure Australia's electronics magazine that resets are only momentary, even if the pushbutton is held down. This quickly rearms the overcurrent protection while preventing the output from being held on continuously if excessive current continues to flow. The 100nF capacitor at IC1c’s output works similarly for monostable-­ initiated resets. We don’t care about the brightness of LED15-LED18 since, as mentioned, they are not indicators. However, it does matter for LED7, LED8, LED21 and LED22. The circuit shows 22kW current limiting resistors for them, suiting high-brightness LEDs. If using regular LEDs, reduce the values to around 5.6kW for more current. Alternatively, if they’re too bright (which may happen with higher-­ voltage single-rail applications), increase the series resistances. Diodes D26 and D27 across the output terminals are normally October 2024  75 reverse-­biased. These protect the circuit from inductive loads or long output power leads. Any inductance in these can cause a reverse voltage spike when the load current is interrupted (as can certain capacitor configurations in the load). These diodes will safely dissipate that energy. Component selection The PCB is designed for miniature 1/8W resistors, 3.5mm long. You can get them from element14, DigiKey or Mouser. You can use more common 1/4W resistors, but you will need to stand them up (at least partially). The current sense resistors will typically be below 0.1W. element14, DigiKey and Mouser have wide ranges of low-value ‘current sense’ resistors, many of which will be suitable, even if their power ratings are higher than necessary. Alternatively, parallel two or more resistors to create a lower resistance. The PCB holes are large enough for the leads of current-sense resistors or multiple regular resistors. The parts list gives information on supported capacitor lead pitches (although you can bend them if you have to) and suggested Mosfet types. However, many more suitable ones will be available. If substituting other Mosfets, pay particular attention to their maximum on-resistance, Vgs threshold voltage and reverse breakdown voltage. Particularly for P-channel Mosfets, cost-effective options with a low on-­ resistance aren’t common. The higher the maximum on-resistance, the hotter the Mosfets will run. Heatsinking Using, say, IRF1018E and IRF4905 Mosfets, at 4A current draw and 10V or higher, they will dissipate 135mW and 320mW each, respectively. The temperature of a TO-220 package in free air rises by around 70°C/W, so without heatsinking, they will rise to 9°C and 22°C above ambient. Note that the ambient temperature is the air temperature within the enclosure, which could be significantly higher than room temperature. The Mosfet on-resistances could be a little higher when using rail voltages significantly below 10V, so for lower operating voltages, pay close attention to the Mosfet temperatures during testing. If they become too warm to touch comfortably, they require heatsinks. If you know or suspect you’ll need heatsinks in advance, it will be easiest to fabricate and mount the transistors onto them before soldering the transistors to the PCB. You can fashion heatsinks from 3mm aluminium using three separate bars or angles for the three rows of Mosfets. Cut the material to fit comfortably within the component footprint. For a dual rail application, mount two Mosfets per angle with their centre holes spaced 18mm apart. Use insulators and Nylon bushes and/or screws; insulating each Mosfet from its heatsink is the best practice. You won’t necessarily require large heatsinks; it depends on how much power needs to be dissipated. For maximum heat dissipation, bridge the tops of the three aluminium angles with a commercial heatsink. Construction Figs.3 & 4: the dual-rail version of the Supply Protector uses all the parts on the PCB, although some sections can be omitted. Parts that can be left off if you don’t need over-current protection are shown, in Figs.7 & 8. Soldering heavyduty 1mm2 wires to the underside of the board, as shown here, will reduce the resistance of the current-carrying tracks. That will lower the voltage drop between the input and output and allow the PCB to handle more than 5A. 76 Silicon Chip Australia's electronics magazine Start by selecting the values of the current sense and bias resistors, and over-voltage threshold zeners, using either the panel or Tables 1 & 2 overleaf. The Supply Protector is built on a double-sided 96 × 69mm PCB coded 18109241. If you’re building the full dual-rail version, fit all the components shown in Fig.3, while if you want to make the single-rail version, fit just the components shown in Fig.5 or Fig.6. Figs.7 & 8 show further variations, which experienced constructors siliconchip.com.au could combine with one of the single-­ rail variants if desired. The two adjustment diodes, D4 and D5, are generally not required and can be replaced with wire links. If you need to fine-tune the trip voltage, you can fit diodes instead, as explained earlier. We suggest constructing in two stages: build and test the reverse-­ polarity and overvoltage protection sections before adding the remaining components. Roughly speaking, the reverse and overvoltage protection components are below and to the left of the 3300μF electrolytic capacitor in the middle of the board, not including the two 3300μF capacitors (use Fig.7 as a guide). Pay close attention to the orientation of the transistors, diodes, LEDs and electrolytic capacitors. The two SCRs should face in opposite direc- The fully assembled Dual Rail Supply Protector PCB with all features available. tions. Start by fitting the lower-profile Note the use of smaller-than-usual resistors to keep it compact. components like the diodes and resistors that will lie flat on the board (see Figs.5 & 6: Table 3), then the capacitors, then the these overlay taller components like the Mosfets. diagrams shows the If you want to minimise the voltboard fitted age drop across the device, or will be with just the using it at high currents, you can solder components extra wires to the underside as shown needed for in Fig.4. That should not be necessary a single for applications up to around 5A per rail Supply rail, though. Protector. You need to add wire links where shown in red. When building any of these versions, watch the orientation of the IC, diodes and Mosfets, as they must all be correct. Initial testing The easiest way to verify the correct operation of the reverse polarity protection is with a variable power supply. Apply power to the input connector in reverse but starting at 0V. Ramp the voltage slowly up to -1V and monitor the “+rail” and “–rail” test points with a multimeter to verify the absence of any voltage. It is working if the supply reaches -1V and there is no voltage on those test points. You could use one AA or AAA cell if you don’t have a variable power supply. Note that if you previously applied power in the correct direction, your multimeter may read the residual charge on the 220μF capacitors. Next, verify the overvoltage protection threshold by switching off the variable power supply and reconnecting the supply with the correct polarity. As you ramp the variable power supply up, by the time it reaches 1V, a voltage will be detectable on both test points. siliconchip.com.au Australia's electronics magazine October 2024  77 Pluggable terminal blocks for the inputs and outputs make connecting the wires easy. The board can be mounted using a tapped spacer in each corner. Figs.7 & 8: these overlays shows which components you can leave off (or link out) if you don’t want either the overcurrent or over-voltage protection feature. If building a single-rail version, you will need to refer to Figs.5 & 6 as well, and figure out which components to leave off or link out. 78 Silicon Chip Australia's electronics magazine The readings will initially be around 0.7V below the variable power supply level. Once you reach 3-4V, the test point voltages should rise to the input voltage. There are two additional test points labelled “+rail prot” and “–rail prot”, which you can now monitor. Continue increasing the variable supply towards the protection threshold. As you pass the threshold, each overvoltage protection LED should illuminate and then, at a fractionally higher input voltage, the “+rail prot” and “-rail prot” test points should start falling back to zero. The actual tripping thresholds may differ from the calculated value due to component tolerances and the zener knees. Remember not to ramp the input voltage past the ratings of the 220μF capacitors, and be very careful not to ramp your variable supply past 40V (or ±20V) until you are sure the overvoltage protection in both rails is working correctly, or you risk damaging IC1 (if fitted). If either rail’s protection hasn’t kicked in by 1V beyond the calculated trip point, it’s either not working, or the zeners are wrong. To reset after the overvoltage protection has tripped, return the variable supply to 0V or temporarily disconnect it. With the overvoltage protection section working, you can finish fitting components to the PCB, starting with IC1; ensure its pin 1 indicator goes at upper right as shown in the overlay diagram. Don’t mount the two trimpots yet. If your board needs cleaning because it’s covered in flux residue, submerge it under isopropyl alcohol or methylated spirits and gently rub it with an old toothbrush. Wait for it to dry, then mount and solder the trimpots. Check that Mosfets are electrically isolated from any heatsink metal. To verify the overcurrent trip circuit, connect the power rail (or rails) to a variable supply but don’t yet connect a load. Adjust the power supply to the same voltage you used to calculate the bias resistances. If either overcurrent trip LED is already illuminated, slowly wind the trimpots clockwise until they extinguish automatically, use the pushbutton reset or short the upper two pins of CON3. If either of the overcurrent trip LEDs fails to extinguish, there is a problem siliconchip.com.au with the reset or overcurrent circuit. If you’re using auto-reset, check the output of IC1d at the “VG” (virtual ground) test point is near ground level for a symmetrical dual-rail version, or otherwise approximately midway between the power rails. Assuming both overcurrent LEDs are off and the set LEDs are on, wind each trimpot anti-clockwise until either the trimpot is fully anti-­ clockwise or the corresponding set LED switches off and the overcurrent LED comes on. When you’ve reached this point, nudge the trimpot clockwise (and press the reset button if equipped) so both the overcurrent LEDs are again off. The overcurrent protection circuits will now be armed at a very small current threshold. Use a low-value resistor (say 100W or less) between ground and each output rail to verify that the overcurrent protection triggers. The corresponding overcurrent LED should illuminate instantaneously, and the associated set LED should extinguish. If your overcurrent trip point exceeds the normal operating current by an amp or more, connect a dummy load that will draw current just below the overcurrent tripping point and adjust VR1 and VR2 so the load remains turned on. Otherwise, use your intended load to set the overcurrent trip point. Finally, run the device for ten minutes while monitoring the temperature of the Mosfets. If the Mosfets become too warm to touch comfortably, turn off the power and fit heatsinks before using it. Wire it up, and you can sit back and relax, knowing your load device is protected! Parts List – DC Supply Protectors (all features) 1 double-sided PCB coded 18109241, 96 × 69mm 2 100W miniature top-adjust trimpots (VR1, VR2) 2 3-way 5.08mm pitch pluggable terminal blocks (CON1, CON2) [Jaycar HM3113+HM3123, Altronics P2873+P2813] 1 3-way pin header and jumper shunt (CON3) 1 NO momentary pushbutton (optional) 4 M3 × 6mm panhead machine screws and matching spacers Semiconductors 1 NCS20074 quad rail-to-rail output op amp, SOIC-14 (IC1) 3 high-current P-channel Mosfets, TO-220 (Q1, Q4, Q10) ★ 3 high-current N-channel Mosfets, TO-220 (Q2, Q5, Q11) ★ 2 BC556 45V 100mA PNP transistors, TO-92 (Q3, Q7) 3 BC546 45V 100mA NPN transistors, TO-92 (Q6, Q8, Q9) 2 C106 SCRs, TO-126 (Q12, Q13) 8 high-brightness 3mm LEDs (LED7-8, LED15-18, LED21-22) [Vishay TLLK4401] 6 15V 1A zener diodes, DO-41 (ZD1, ZD2, ZD11, ZD12, ZD23, ZD25) 2 1A zener diodes, DO-41, values to suit application – see Table 1 (ZD3, ZD6) 2 1N5819 or SB140 40V 1A schottky diodes (D13 & D14) 6 1N4148 75V 200mA diodes, DO-35 (D19-D20, D24, D28-D30) 2 1N4004 400V 1A diodes, DO-41 (D26, D27) 2 extra diodes to fine-tune over-voltage thresholds (D4, D5; optional, see text) ★ suitable types include IRF4905 (up to ±55V & 4A), IPP80P03P4L-07 (±30V & 7A) and SUP90P06-09L-E3 (±60V & 7A) ★ suitable types include IRF1018E (7A), CSD18534KCS (7A), DIT050N06 (4A), STP60NF06 (5A) & IPP80N06S4L (8A; all can handle up to ±60V, ratings are without heatsinks and are only a guide) Capacitors 2 3300μF 50V electrolytic (5mm or 7.5mm lead pitch) [Altronics R5217] 2 220μF 63V low-ESR electrolytic (3.5mm or 5mm lead pitch) 1 1μF 50V ceramic or MKT 9 100nF 50V ceramic or MKT 2 10nF 50V ceramic or MKT 1 1nF 50V ceramic or MKT Resistors (all ⅛W 5% miniature axial unless noted) ♦ 1 2.2MW 9 47kW 4 3.3kW 1W 5% 3 1MW 9 22kW 2 910W 1 330kW 1 15kW 4 Rbias resistors – see Table 1 2 150kW 6 10kW 2 Rsense resistors – see Table 2 3 100kW ♦ regular ¼W resistors can be used but they won’t sit flat on the PCB Table 1 – zener diode values Table 2 – current sense resistors Trip ZD3/ZD6 Bias resistors Adjustment range Sense resistor ~5V 5.1V 3.0kW 0-1A 100mW 1/8W ~5.5V 5.6V 3.3kW 0-2A 50mW 1/4W ~7.25V 6.8V 5.1kW 0-3A 33mW 1/4W ~10.3V 10V 8.2kW 0-4A 25mW 1/2W ~13V 13V 11kW 0-6A 16mW 1/2W ~15.1V 15V 13kW 0-8A 12mW 2/3W ~18V 18V 16kW 0-10A 10mW 1W ~20V 20V 18kW ~23.8V 24V 22kW ~29.5V 30V 27kW Tables 1, 2 and the panel on the next page are used to determine the best values of various components to suit your needs. ~38V 39V 36kW siliconchip.com.au Australia's electronics magazine Table 3 – resistor colour codes October 2024  79 Silicon Chip PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). Calculating component values Several component values should be selected to suit your application as follows. Overvoltage trip point First, you must determine the highest voltage that’s safe to apply to the load. If unsure, measure the output of the existing power supply and add a safety margin. Zener diodes ZD3 (‘+OVtrip’) and ZD6 (-OVtrip’) set the overvoltage trip point for each rail in combination with the 3.3kW resistors. The SCRs will trip when their trigger input reaches approximately 0.6V. Allowing for a voltage drop of about 100mV across the resistors, the required zener voltage is (Trip – 0.7V) × 1.05. As mentioned earlier, low-voltage zeners may trigger at lower voltages than expected. Also, typical zeners diodes have 5% tolerances. In the middle of the voltage range (eg, around ±15V), you can generally get away with a zener diode that has a voltage rating close to the desired trip point, as the 0.7V and 5% factors cancel out. Because the expected overvoltage trip point lies within a range, and zeners are only available in certain preferred values, you may need to use adjustment diodes if you require high precision. Adding a schottky diode for D4 or D5 (like a BAT85, SB140 or 1N5819) will increase that rail’s trip point by around 0.3V, while adding a silicon diode (like a 1N4148 or 1N4004) will increase it by around 0.6V. Don’t use zeners below 4.3V or above 19V (for a dual-rail configuration) or 39V (for single-rail operation). You can use different values for the two zeners for asymmetric applications. Ensure that the 3300μF output capacitors have voltage ratings above the trip points. For example, if you have ±18.1V overvoltage protection thresholds, select 25V capacitors. Because the 220μF capacitors after Mosfets Q1 & Q2 are on the unprotected side of the overvoltage protection circuit, they will experience any overvoltage, so their voltage ratings should exceed the highest expected input voltage. We recommend using 50V or 63V rated capacitors there, although you might get away with 35V caps in some cases. Overcurrent trip point The ‘+sense’ and ‘-sense’ resistors are used to monitor the current in each rail. The overcurrent trip is calculated for a sense resistor voltage drop of about 50mV, although the trimpots let you set it up to 100mV. Use Ohm’s law, R = V/I, and the power formula, P = VI, to calculate the required resistances and power ratings. Let’s use 2A as an example. For a 50mV drop, the formulas give R = 25mW (0.05V ÷ 2A). If you can’t find a resistor with the calculated value, round the resistance to the closest available value. A 0.022W, 0.025W or 0.033W resistor would be suitable in this case. We calculate the power at 100mV as we don’t want the resistor to overheat if the trimpot is set to maximum, so P = 200mW (0.1V × 2A). Ideally, the resistor should have close to twice the power rating (to account for elevated ambient temperatures etc), so in this case, use a ½W or 0.6W resistor. If your application has asymmetric current requirements, you can choose different values for the two resistors. WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS Bias resistances Four resistors are labelled ‘+bias’ or ‘-bias’. The bias resistors are selected so that about 1mA flows through them when the supply is at its nominal (not overvoltage trip) level. The series LEDs have a forward voltage drop of around 1.8-2V, so consider that when calculating the resistor values. The exact drop doesn’t matter as long as the four LEDs (LED15-LED18) are the same type, so the voltage drops are similar. Red, orange or yellow LEDs with a forward voltage drop below 2.3V will work. You can measure the LED’s forward-biased drop using a digital multimeter’s diode testing function. Say the nominal power supply is ±12V and you have red LEDs with a 1.6V forward voltage. The required resistance will be R = (12V – 1.6V) ÷ 0.001A = 10.4kW. Choose the nearest available resistance, 10kW in this case. If you have an application with asymmetric voltage rails, the ‘+bias’ and ‘-bias’ SC resistances may differ. 80 Australia's electronics magazine EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OR PAY $500 FOR ALL SIX (+ POST) Silicon Chip siliconchip.com.au Subscribe to SEPTEMBER 2024 ISSN 1030-2662 09 9 771030 266001 $12 50* NZ $13 90 INC GST INC GST OLED CLOCK/TIMER MULTIPLE TIMEZONES, WIFI How Mains Earthing Systems Work Australia’s top electronics magazine TIMEKEEPING AND MORE Raspberry Pi Pico Mixed-Signal Logic Analy Silicon Chip is one of the best DIY electronics magazines in the world. 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Compact OLED Clock; September 2024 Discrete Ideal Bridge Rectifiers; Sept 2024 The Styloclone Musical Instrument; Aug 2024 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe MICROMITE EXPLORE-40 A wealth of software has been written for the Micromite; The Back Shed online forum is a great place to find much of it. This compact Explore-40 board is a Micromite in the same form factor as the popular Pico boards, allowing a Micromite to be used with hardware designed for the Pico. PROJECT BY TIM BLYTHMAN T HE RASPBERRY PI PICO has taken a well-deserved place as one of the most popular microcontroller boards. It is cheap, easy to use and can be programmed in C, BASIC, Micro­ Python & even with the Arduino IDE. Our Pico BackPack (March 2022; siliconchip.au/Article/15236) capitalised on those features, providing stereo audio and a microSD card interface with the 3.5in LCD panel that we had previously used with the Micromite V3 BackPack. These new features can now be accessed from Micromite BASIC, since the Explore-40 board allows a Micromite processor to be plugged into the Pico BackPack. Thanks in part to the ongoing work of The Back Shed forum members, software is available to use these new features. The Micromite Explore-40 is not just a Micromite/PIC32 breakout board. It has been designed to include niceties like an inbuilt USB-serial converter, plus some LEDs and pushbuttons. It can even plug into a Pico Digital Video Terminal (March & April 2024 issues; siliconchip.au/Series/413). Since this board is patterned after the Raspberry Pi Pico and thus a bit larger than the Explore-28, we have taken the opportunity to add some extra features. Circuit details Fig.1 shows the circuit of the Explore-40. IC1 is a PIC32MX170F256B in a relatively large 28-pin SOIC package. This is the familiar 28-pin part The Explore-40 we have used for many Micromite The Explore-40 is typical of min- projects. imal Micromite implementations Its I/O pins are connected to pins on that include the Microbridge USB-­ the pair of 20-way headers that match serial converter. The circuit resem- the pinout of the Pico. We’ll explain bles earlier Micromite boards like the our choices for this specific mapping a Explore-28 from the September 2019 bit later. As the Pico has more pins than issue (siliconchip.au/Article/11914). the 28-pin PIC32, there are some empty positions on those 20-way headers. IC2 is a PIC16F1455 programmed Micromite Explore-40 Features & Specifications with the Microbridge firmware. The » Allows a PIC32 Micromite processor to be plugged into a Pico socket Microbridge was originally published » All 28-pin Micromite I/O pins are available as a separate board (see May 2017; » Onboard Microbridge serial interface/programmer siliconchip.au/Article/10648); it has » USB-C socket for power and data since been incorporated into many Micromite designs. It can function as » Micromite BASIC software examples for all Pico BackPack features a USB-serial converter, allowing com» Supports LCD touch panel with backlight control munication between a computer and » Supports IR receiver the Micromite chip. » Stereo audio output The Microbridge can also act as a » microSD card interface programmer, allowing new firmware » Realtime clock interface (such as a new version of Micromite » Add-on 3.5mm board provides 3.5mm stereo audio socket with Pico BackPack BASIC) to be easily installed on the Micromite chip. » Power and status LEDs As such, it connects to the data lines » Reset and Mode pushbuttons on USB-C connector CON1, as well » In-circuit serial programming (ICSP) header for the PIC32 Micromite chip as the serial and programming pins 82 Silicon Chip Australia's electronics magazine siliconchip.com.au of IC1. IC2 also drives LED1, which indicates its mode (USB-serial or programming) and shows serial traffic. Onboard pushbutton S2 selects IC2’s mode. CON1, the USB-C socket, has connections to power via the VBUS pins. The CC1 and CC2 pins are connected to ground via 5.1kW resistors, signalling to the USB source (eg, a computer) that it should supply 5V on the VBUS pins. The VBUS voltage goes via schottky diode D1 to REG1, an MCP1700 3.3V low-dropout regulator. The diode also connects to pins 40 and 39 of the Pico headers, emulating that handy feature of the Pico boards. It means that an alternative source of 5V power can be fed into pin 39 (possibly via another diode) without any risk of back-­feeding the USB power supply. REG1 and its capacitors provide a 3.3V rail that powers IC1, IC2 and power indicator LED2 (the latter via a 1kW resistor). The 3.3V output is also available on pins 35 and 36 of the headers, as it is on the Pico boards. IC1’s pin 1 (the MCLR reset input) has also been taken to pin 30 (RUN on the Pico). Pins 3, 8, 13, 18, 23, 28, 33 and 38 of the headers are connected to ground, like the Pico, and we have connected as many of the PIC32’s I/O pins as we can to the remaining I/O pins on the headers. Because of this compatibility, we’re sure readers will find the Explore-40 handy in other situations where a Pico might be used. IC1’s MCLR reset pin, 3.3V, ground and the two ICSP programming pins are also available at the CON2 ICSP header, allowing the chip to be programmed by an external programmer. IC1 can also be reset by pressing S1, which pulls MCLR to ground. A 10kW resistor pulls this up otherwise. A reset button is one feature that the real Pico lacks! Micromite Explore-40 Kit (SC6991, $35) A complete kit is available for the Micromite Explore-40 with all the parts listed in the parts list on page 87 (not including the Audio Breakout Board or Pico BackPack). Pin mapping The mapping of the 40-pin header has been mostly chosen to match the functions of the Pico BackPack to that of the Micromite. For example, the Micromite has fixed SPI and I2C pins, so the mapping matches the wiring of these two peripherals on the Pico BackPack. Similarly, the pins for interfacing with the LCD on the V3 BackPack have been arranged identically on the Explore-40. This allows identical siliconchip.com.au Fig.1: the Explore-40 has much in common with the Micromite V2 BackPack and the Explore-28, although we’ve added a USB-C socket, power indicator LED and a reset button. The I/O pin mapping to the two 20-pin headers is designed to allow the Micromite processor to work with the Pico BackPack and retain some compatibility with software designed for the V3 BackPack. Australia's electronics magazine October 2024  83 Micromite OPTIONs to be used. The IR pin (Micromite pin 16) has also been connected to the IR receiver on the Pico BackPack. Pins 21 and 22 on the Micromite have been connected to pins 11 and 12 of the Pico header; these are used for audio on the Pico BackPack and are a convenient pair for this purpose. If not used for audio, they can be used as the Micromite’s COM1 serial port. The serial console pins have been allocated to pins 1 and 2, allowing the console to be connected to the Pico Digital Video Terminal. That doesn’t leave many pins spare to be allocated. We have connected pins with analog functions where possible, although the Pico has fewer than the Micromite. We’ll detail the OPTIONs and pins that should be used with the Pico BackPack later, when we explain the software features in more detail. A small add-on While putting together this design, A 3.5mm jack socket breakout board for the Pico BackPack Building this board is simple, as you can see from our photos. As long as you connect the R, G and L pins to the matching pins on CON3 of the Pico BackPack, the board can be installed in a few different ways. It can be mounted on either side of the board, giving four main configurations. We think the method shown in our photos is the simplest, gives a compact result and does not put the audio socket awkwardly close to the microSD card socket. The Audio Breakout extends slightly beyond the Pico BackPack and is intended to sit just inside a UB3 Jiffy box so that the socket can be accessed through a small hole in the side. We suggest fitting the audio socket to the PCB first. That will allow you to easily check that your chosen positioning does not foul any other components. The photo shows the assembly of the listed parts that can then be fitted to the Pico BackPack. Once fitted, you can simply plug in headphones or an aux cord to hear audio from CON3 on the Pico BackPack. This is the recommended placement of the 3.5mm jack socket breakout board on the Pico BackPack, sitting above some passive components in the audio section. Although it’s designed to work with the Pico BackPack, you can also use it for breadboarding or prototyping. Silicon Chip Programming the chips IC1 can easily be programmed via IC2 once you have built the board, but IC2 is best programmed before it is soldered to the board, especially as there is no ICSP header for it. It is possible to use a Micromite to program a Microbridge; there are notes on how to do that included with the Microbridge firmware at siliconchip. au/Shop/6/4269 Still, it is easier to program IC2 with something like a PICkit or SNAP if you have an appropriate SMD adaptor, so we recommend doing that if possible. If you buy a kit from us, both ICs will be programmed already; there is also the option to buy programmed chips separately. Construction The Explore-40 uses mainly SMD parts, including SOIC ICs, M2012 (0805 imperial) passive components measuring 2.0 × 1.2mm, and a somewhat fine-pitch USB-C socket. It is not super difficult, but neither is it extremely easy; it would be ideal to have some SMD soldering experience before assembling it. There are also components on both sides of the PCB. You will need the usual SMD tools and consumables. A fine- or medium-­ tipped soldering iron, solder, flux paste, tweezers and good ventilation are essential. Some solder-wicking braid and a means of securing the PCB are also advised. Blu-Tack will do the job if you don’t have a PCB vice. You should also have a suitable solvent for cleaning up flux, such as one recommended by your flux supplier. Fig.2 (below): when assembling the breakout board, ensure the socket is pushed firmly against the PCB. We used straight headers, but you could use rightangled headers. 84 we realised adding a 3.5mm audio output jack socket to the Pico BackPack would be a nice touch. We initially omitted this from the Pico BackPack because the board is quite tight for space. To solve this, we’ve designed a very small daughterboard that can be connected to the Pico BackPack, breaking out the CON3 audio connector into a 3.5mm stereo socket. It is shown in Fig.2. You don’t need to use the Explore-40 to use the daughterboard; it can also be used with a Pico or Pico W. You can see it in our photos, mounted above the Pico BackPack PCB. We have a panel showing how to build this board and add it to the Pico BackPack. Australia's electronics magazine siliconchip.com.au Alternatively, isopropyl alcohol or methylated spirits will be effective for most fluxes. Fig.3 shows the PCB overlays, which you should refer to during assembly. Start by soldering CON1, the USB-C socket, since it has the closest pin pitch. It will also be difficult to get to once other components are installed. Apply flux to the pads and slot the socket into its holes on the top of the PCB. Clean the iron’s tip and add a small amount of fresh solder. The end-most leads are a bit wider, so tack one of those in place, then check that the other leads are aligned to their pads and that the part is flat against the PCB. Adjust it until you are satisfied. The locating posts should help here. You can then solder the mounting pins from the reverse of the PCB. It might help to add some flux to the bottom and top of those pins to help the solder take. Try not to add too much solder to the mounting pins, as it might get in the way later. Next, solder the remaining pins of CON1 on the top of the PCB. Use the braid and extra flux to remove any bridges that have formed. Place the braid on the solder, apply the iron and gently move both away together once the solder has been taken up. Fit the two ICs next, being sure to get the correct orientation. IC2 faces the opposite direction to IC1 and is on the opposite side of the PCB. Add flux to the PCB, rest the ICs in place and tack one lead before soldering the others. Adding flux to the pins before soldering will help it flow. Check for bridges after soldering and remove any with more flux paste and the solder wick. Regulator REG1 mounts on the same side as IC2. It’s easy enough to solder but small enough to lose sight of easily. Add some flux and place it as shown. Tack one lead, then check the alignment of the others before soldering. The diode mounts on the opposite side of the board from the USB-C socket. Ensure that the PCB’s cathode mark matches the diode orientation and avoid bridging its pads to the socket’s mounting pins. Now solder the remaining parts on the underside of the PCB methodically. The resistors will have small codes printed on top (per the parts list) but the capacitors will be unmarked. You may be able to tell them apart by siliconchip.com.au Fig.3: we’ve placed components on both sides of the PCB to best use the available space. The CON1 USB-C socket and the two microcontrollers have the tightest pin pitches, so they should be fitted first. Avoid using too much solder for CON1 through-hole mounting pins in case it bridges to D1 or the nearby resistors. This diagram is shown at 150% of actual size for clarity. their thickness if you manage to get them mixed up. In each case, add flux to the pads, rest the part in place, tack one lead, then check and solder the other. Next come the two LEDs on the top side of the board. We recommend using red for LED1 (MODE) and green for LED2 (POWER), although you could choose your own scheme. You can test the colour and polarity of the LEDs with a multimeter set to diode mode. The cathode will be the end connected to the black multimeter lead when the LED lights up. Fit the LEDs with the cathodes towards the COM2 silkscreen marking (the overlay also shows a K near each cathode). Solder the last 1kW resistor and 100nF capacitor. Clean both sides of the PCB thoroughly with your chosen flux solvent and allow the PCB to dry. It’s then a good time to inspect the soldering for any bridges or dry joints you might have missed. If you find any, fix them before proceeding. Fit the two tactile switches next. They have much larger pads, making them easier to solder than the other parts. Your board should look like the photos now. If something is not right, check for 5V at the USB pin, at upper right, and around 4.7V (due to the diode) at the SYS pin below it. Check the USB-C socket and 5.1kW resistors if the USB voltage is absent. An absence of voltage at the SYS pin suggests the diode is reversed or not connected, while a lack of 3.3V could point to a problem with the regulator or a short circuit on the 3.3V rail. If you need to fit the CON2 ICSP header to program IC1, do that now. Be aware that you may not be able to leave CON2 attached afterwards since it might be too tall to fit between the Pico BackPack PCB and the LCD Testing There are still some parts to fit, but now is a good time to do some initial tests. Connecting USB power to CON1 should cause LED2 to light up. The 3.3V pin should measure between 3.2V and 3.4V relative to ground. Pressing S2 should cause LED1 to light up, assuming IC2 is programmed correctly. The Explore-40 is a compact board (51 × 21mm) that allows the Micromite to substitute for a Raspberry Pi Pico in some circumstances. IC1 and the two LEDs are the polarised components on the top of the PCB. We recommend using red for LED1 and green for LED2. Australia's electronics magazine 85 fitting the Explore-40 to a Pico BackPack with an LCD panel above. If you just plan to use it on a breadboard, for example, you just need to be sure that the pins align with the sockets in the breadboard. using socket headers fitted to the top of the Explore-40 that will mate with pin headers mounted on the underside of the Pico BackPack. Software support Combining the Explore-40 with the Pico BackPack (and 3.5in LCD panel) For our prototype, we used low-­ brings two new features that were profile header sockets and removed the not present on the V3 Micromite LCD plastic shroud from the pin headers to BackPack. These are the microSD card allow the board to be swapped (eg, for and audio output. a Pico) if needed. However, we found First we’ll recap the features that are that quite fiddly to achieve. shared with the Micromite V3 BackAs you can see in the photo below, Pack and how they are configured there is very little clearance above the and used. This will be a quick way to Explore-40, even though we removed check that the Explore-40 is working the SD card socket from the LCD panel as expected. above. Still, that is an option to conThese features should all behave sider since there is no connection to identically to a Micromite V3 Backthe SD socket on the LCD panel from Pack. Note, though, that the Explore-40 the Pico BackPack. and Pico BackPack lack the RAM or If you want to do that, use a pair of FLASH IC and temperature sensors flush nippers to gently cut and detach that the V3 BackPack includes. each pin from the SD card socket, then The Micromite firmware does not use a soldering iron to remove the rem- have a built-in driver for the 3.5in nants of each pin. Follow with some LCDs, but there is a loadable driver solder-wicking braid and flux paste to developed by Peter Mather. We have remove any solder residue. customised this to suit the configIf you are happy to permanently sol- uration of the Explore-40 and Pico der the Explore-40 to the Pico Back- BackPack hardware; it is the “3.5IN Pack, the height of the plastic spacers DRIVER.BAS” file in the software on standard pin headers will prevent downloads package. the underside components from touchThe code is much the same as that ing the PCB below. To do this, sand- found in the Display Drivers folder of wich the headers between the Pico the Micromite firmware download. BackPack and Explore-40 PCBs, then We have just changed the line in the tack a few pins in place before solder- MM.STARTUP subroutine to suit our ing the remainder and trimming the pin allocation. The “3” at the end indiexcess lengths away. cates a landscape configuration, with If you are doing something differ- the microSD card socket near the top ent, we recommend test-fitting the of the screen. parts first to be sure they will fit and Load this file onto the Micromite (for not cause any fouling with the LCD example, using the AUTOSAVE companel above. It’s also possible to fit mand), then perform a LIBRARY SAVE the Explore-40 to the underside of the and restart the Micromite by pressPico BackPack PCB, although that will ing S1 or entering the CPU RESTART make it difficult to access the buttons command. You should see the screen or see the LEDs. clear and you can run the GUI TEST If you want to do that, we suggest LCDPANEL command to confirm it is working. To configure, calibrate and test the touch panel, use these commands: Fitting it to a Pico BackPack The underside of the Explore-40 shown at actual size; note the orientations of IC2 and D1. REG1 is also polarised, but its correct orientation should be obvious. panel. You can use IC2 to program IC1, after all. If you connect the Explore-40 to a computer and open a serial terminal program such as TeraTerm, you should be able to communicate with the Micromite firmware. The default baud rate is 38,400. You can press S1 and check that the Micromite’s boot message is printed via the terminal. The Explore-40 is now complete enough to plan how you will fit it to the Pico BackPack. The most significant difference is that the Explore-40 has components on its underside, so it will not mount flush like a Pico could. The following assumes that you are OPTION TOUCH 7,15 GUI CALIBRATE GUI TEST TOUCH We used low-profile header sockets to mount our prototype Explore-40, but if you solder it directly to the BackPack PCB using standard header pins, you will gain clearance since the Explore-40 will sit lower. With some care, the unused SD card socket on the underside of the 3.5in LCD panels can be removed, giving extra clearance below. Use solder-wicking braid to clean off any excess solder left behind. 86 Silicon Chip Australia's electronics magazine If the required components and jumpers are fitted to the Pico BackPack, the backlight is also driven from IC1’s pin 26, just like the V3 BackPack. This can be controlled using PWM channel 2A. The following will set siliconchip.com.au the duty cycle and backlight brightness to 50%: PWM 2,250,50 IR receiver & realtime clock The IR receiver on the Pico BackPack is routed to the dedicated Micromite IR pin, pin 16, so the IR receiver can be used by simply setting up the IR interrupt with the IR command. The command would be something like: IR DevCode, KeyCode, IR_Int A basic interrupt subroutine to test this could be: SUB IR_Int PRINT “DEVICE:” DevCode “KEY:” KeyCode END SUB The RTC commands support the realtime clock chip: RTC GETTIME RTC SETTIME year, month, day, hour, minute, second You can then retrieve the current time and date from the TIME$ and DATE$ variables. MicroSD card support The Micromite lacks a native driver for interacting with SD cards. Peter Mather has again done some excellent work in creating a CSUB driver to do that. However, there are a few provisos to using this software. Since the Micromite does not have an interface for file handling (unlike the Micromite Plus), everything is done via calls to the CSUB. The driver is quite simple and cannot do things like create or append to files. So, if you wish to write to a file, the recommendation is to create a large file on the card, which the driver can then overwrite. Even with these restrictions, the driver takes up about one-sixth of the flash memory available for programs. More background information on this and suitable code can be found at siliconchip.au/link/abxr We have configured pin 4 as the CS (chip select) pin for the microSD card socket. This is the same pin that is wired to the SD card socket on the LCD panel for the Micromite V3 BackPack. So you could try this on a V3 BackPack, although we haven’t tested it. siliconchip.com.au Parts List – Micromite Explore-40 1 51 × 21mm double-sided PCB coded 07106241 1 16-pin USB-C data and power socket (CON1) [GCT USB4105] 1 5-way pin header, 2.54mm pitch (CON2; optional, for ICSP) 2 20-way pin headers, 2.54mm pitch 2 SMD 2-pin tactile switches (S1, S2) Semiconductors 1 SS14 40V 1A schottky diode, DO-214AC/SMA (D1) 1 PIC32MX170F256B-50I/SO 32-bit microcontroller programmed with the Micromite firmware, wide SOIC-28 (IC1) 1 PIC16F1455-I/SL 8-bit microcontroller programmed with the Microbridge firmware, SOIC-14 (IC2) 1 MCP1700-3.3 3.3V low-dropout voltage regulator, SOT-23 (REG1) 1 red M3216/1206/SMA SMD LED (LED1) 1 green M3216/1206/SMA SMD LED (LED2) Capacitors (all SMD M2012/0805, X7R) 1 22μF 10V X5R/X7R 2 1μF 16V 3 100nF 50V Resistors (all SMD M2012/0805, ⅛W) 1 10kW (code 1002 or 103) 2 5.1kW (code 5101 or 512) 5 1kW (code 1001 or 102) Optional extras 1 Pico BackPack (without Raspberry Pi Pico) plus 3.5in LCD (March 2022) 1 3.5mm jack socket breakout board (see panel and parts below) Audio Breakout Board 1 double-sided PCB coded 07101222, 20 × 15mm 1 stereo 3.5mm PCB-mounting jack socket (CON3A) [Altronics P0094] 1 3-way pin header (CON3) The Explore-40 module is a drop-in replacement for a Pico on the Pico BackPack (described separately). Kit (SC6991, $35): a complete kit is available for the Micromite Explore-40 with all the parts listed (does not include the Audio Breakout Board or Pico BackPack). Australia's electronics magazine October 2024  87 The driver file is named “SDCARD_ SPI1.BAS”. It is installed similarly to the LCD panel driver, using the AUTOSAVE and LIBRARY SAVE commands. We’ve also created a HEX file that contains these two libraries loaded into a working copy of Micromite BASIC version 5.05.05, named “MM BASIC SD ILI9488.HEX”. You can load this with the onboard Microbridge or a PICkit programmer. Audio support The audio driver is another CFUNCTION that is controlled via calls with various parameters. This is based on a similar driver we created for the Advanced GPS Computer (June & July 2021; siliconchip.au/Series/366). This uses a pulse-width modulation (PWM) output to synthesise an analog voltage signal, with the PWM switching frequency being filtered out by a low-pass filter attached to that pin. The analog voltage is varied using a timer interrupt to update the PWM duty cycle for each sample to be played. The big difference is that this driver is capable of stereo output, although it is limited to eight bits of resolution and an 8kHz sampling rate. Given that the Micromite has enough flash memory to play only seven seconds of audio, or enough RAM for about six seconds, we think it is a fair compromise. The AUDIO folder in the software downloads contains several files, including the CFUNCTION driver, some encoded audio samples and BASIC code to demonstrate how to use the driver. The samples are created as CFUNCTIONs, although they do not contain executable code. They consist of a 32-bit header that indicates how many bytes are in the sample, followed by that many bytes. Stereo samples are stored with the left channel data first. A mono sample played in stereo mode will play twice as fast since two bytes are used every sample period. The driver is installed by loading the “CFUN_LIBS.BAS” file onto the Micromite, then using the LIBRARY SAVE command. Since the CFUNCTION returns a value, we need to do something with that value, like print it. Use this to start the driver: PRINT AUDIO(0) A sample is used by loading its BASIC file, then performing a LIBRARY SAVE. Tell the driver where the sample is located like this: PRINT AUDIO(1, PEEK(CFUNADDR SAMPLE_NAME)) Then start playback with: PRINT AUDIO(2) ‘mono PRINT AUDIO(12) ‘stereo The sound will play in the background and stop automatically. Using values 6 (mono) or 13 (stereo) as parameters will cause the playback to loop endlessly. Playback can be forced to stop with: PRINT AUDIO(3) You can also wait for playback to finish with: DO WHILE AUDIO(4)<>0:LOOP The “BASIC_SUBS.BAS” file has some more sample code and variables that can be used to make it easier to see what each parameter does. The file named “AUDIO MMBASIC. HEX” contains the libraries, samples and BASIC code, alongside a working copy of Micromite BASIC version 5.05.05. Notes The 28-pin Micromite has somewhat limited peripherals, so there are some limitations. For example, the timer that provides the interrupt to fetch new audio samples is the same one used for the IR decoder. So we don’t think it is possible to use the IR and audio features at the same time, although it should be possible to switch between them. The audio output uses two of the remappable PWM channels, so the PWM feature on pins 4 and 5 cannot be used at the same time as the audio. Pin 4 is mapped to the microSD card socket, so we expect it will be used for that feature instead. In any case, the CFUNCTION libraries take up quite a bit of program memory, as do audio samples, if kept in flash memory. Remember also that the PIC32MX170F256B microcontroller can be programmed in the C language using the MPLAB X IDE. We did that for the Digital Lighting Controller (October-December 2020; siliconchip. au/Series/351). That older project can play stereo audio from an SD card, so you might find it helpful if you are thinking of doing something similar using the C language and the MPLAB X IDE. Summary The 3.5mm jack socket breakout board is a neat fit under the LCD panel, even when mounted on header pins. Like the Explore-40, you should trim any excess pin length with flush nippers or sidecutters. 88 Silicon Chip Australia's electronics magazine If you are a Micromite fan and yearning for the features of the Pico BackPack, the Explore-40 is the perfect way to bridge that gap. It adds microSD card support and stereo audio features that were missing from earlier Micromite BackPacks. There are some limitations to what the Micromite can achieve, but it is still a handy platform for learning the BASIC language. The Explore-40 also adds nice touches, like the modern USB-C socket and reset button. These features can be handy regardless of whether the Explore-40 is used by itself, on a breadboard or as part of a BackPack. SC siliconchip.com.au SERVICEMAN’S LOG I got the power Dave Thompson The other day, something relatively unusual happened around here, which revealed a flaw in our system. For the first time in a very long time, we experienced a power cut. It wasn’t just one of those ‘oh, the power has gone off and has come back on in minutes’ cuts – it was off for many hours. I assumed some contractor somewhere had dug a little too deeply, or perhaps in the wrong place, and had put the bucket through the cable to our part of town. I fully expected things to come back online pretty quickly. After 15 minutes, I leaned across the fence to my neighbours and asked if they’d also lost power, just in case it was something in our household that had given way. Fortunately, they’d lost power too. Oh wait, that came out wrong; I mean that it wasn’t a fault specific to me that I would have to get someone to fix. Perhaps it was one of those substation explosions you hear about. I could imagine the control room at the power station, with a map of the city and bits of it going dark in sequence as the system fails. Sadly, I think that’s just movie mayhem. Either way, something had obviously happened to our supply and we could do nothing but ride it out and wait. This obviously left us dead in the water regarding our computers, my workshop, our local area network internet connectivity – pretty well everything. Fortunately, we have mobile phones, so we could at least maintain some kind of connectivity. siliconchip.com.au After 30 minutes, I bit the bullet and called our power supplier. I soon discovered that I was gazillionth in the queue for fault reporting and support, so I wasn’t going to waste much time on that. It was obviously being reported already; my whinging about it wouldn’t make much difference in the bigger picture. I also didn’t want to burn up the remaining charge in my phone battery, even though since the quakes here, I have maintained several different USB battery packs so we can charge phones. I was really caught short when the quakes hit in 2011 and we lost power for a week. Back then, my phone had only 24% charge to begin with. With no way of charging it, it soon went flat. The bad old days Not that it was much good in the early days anyway, because all the cell towers lost mains power and the backup batteries only lasted two hours. Plus, they were so overloaded that the whole system crashed. If we were lucky, the odd text might go through, but voice calls were mostly impossible. Australia's electronics magazine October 2024  89 Items Covered This Month • Unlit ruminations • Workzone MIG (metal inert gas) welder repair • Bando Technic 5D transceiver repair Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com Of course, nothing worked once the towers’ backup batteries went flat. Landlines had been severed, and while some users in some suburbs had communications, the rest of us did not. I vowed never to be caught out again. I have at least a week’s worth of battery power here now for charging phones or any other tech. As a bonus, and again, as a result of the quakes, we have gas heating and cooking, so at least we could make a cup of tea while we watch the house fall apart in the aftershocks. However, our newest gas fire, installed recently, requires electric power to run. Given that this recent power cut happened in the middle of winter, my concern was that we’d soon get very cold. We also have several heat pumps around the house to provide basic warmth in the winter and cooling in the summer but, of course, they were offline as well due to the outage. Yes, I know this is a very first-world problem and that many people, including those in so-called first-world countries, experience power loss regularly for various reasons. However, it brought back a lot of bad memories for me, to those times when we and others had no power for weeks on end, in the darkest days of our post-quakes, semi-­dystopian society where, let’s not forget, almost 300 people died. No traffic lights, no streetlights, no mobile phones, no landlines. It was a strange time. The problem was that the earth under everything in many parts of the city turned to a liquid-like quicksand (a phenomenon known as liquefaction). All the pipes and conduits and anything else under the tarmac on the roads just floated to the surface of the street. The earthquake’s strength was such that it just lifted the asphalt, circuit junctions and access covers and ruined the roads. That’s aside from breaking all the pipes, cables and whatever else was nestled inside those conduits. This, of course, plunged entire suburbs into darkness. Luckily – if there was a lucky side to it – it was February and summer, so we didn’t really have to worry about heating. But, with all the sewers broken, there were no toilets, no water, no power, no phone lines. We were cut off. I realise that many other countries had things worse. At around the same time, Haiti experienced a huge quake, which killed thousands, as did Japan, with wider-­reaching consequences. Not having power back then was a real problem. Everything in our home relied on power. My serviceman’s mind sprung into action and, as soon as the shops were open, I vowed to buy a generator. In the meantime, I had an old gas cooker and an old gas heater that used the ubiquitous 9kg bottle of LPG. One company was giving away gas (many companies did this in an effort to help, whether it was free milk, bread 90 Silicon Chip or gas), and I took my old bottle down to have it filled. Of course, it was out of date, so they wouldn’t touch it, let alone fill it. I bought two new ones from a nearby big box store and had them filled for free. I did have to queue for hours at each place, as milk, bread, petrol and gas were being strictly rationed. It really was an eye-opener as to how people behaved under duress. At least our stove and (if we needed it) heating would work. Anyway, back to our recent power outage. As I mentioned, power outages are rare here. The last one we had was seven years ago, when we moved into this place. We’d had the power off as we renovated the house, and when we put it back on, it suddenly failed. Thinking it was something we’d done, I did as much troubleshooting as possible. I could tell power was coming in from the wires, but it died at the old ceramic pole fuse mounted on the house’s bargeboards. I had to call the power company, and the guy climbed the ladder and touched the wire and it simply fell off. Easy job, I thought. But no, new pole fuses actually have to go on poles. But the pole on our back section was apparently an old pole (60 years) and not high enough. So, the pole had to be replaced and the new fuse put on top of it. Red tape holds the nation together, or so they say. It was a completely ridiculous chain of events. Anyway, that’s the last time the power went out, so it’s a rare occurrence, which is why I thought some contractor must have dug up the cable or a substation had failed somewhere. Time for the generator to shine Whatever the cause, our house was dark and dead in the water in the middle of winter. After three, I decided it was time to dig out the generator I had queued to buy 13 years ago, and fire it up. If the power was not going to be back on for hours, we’d need to get something sorted. I knew we had hours before the freezers started thawing, but I wanted to hedge my bets. Even with the generator, we’d have to be pretty careful what we plugged in; it isn’t one of those huge Detroit diesel powered ones I worked on at the airline back in the day. Two of those could power a city! Australia's electronics magazine siliconchip.com.au This one might do some phone chargers, the fridge/ freezer and maybe the TV, at a stretch. The first challenge was getting the thing out of storage in my garage. You’d think a ‘prepper’ like me would have it set up and ready to go in a purpose-­built enclosure next to the house, but no. And it is such an awkward thing to move. It isn’t overly heavy, but it is a two-person lift because there’s nowhere one person can pick it up and carry it from. It has a frame around it, but no finger or hand holds. You also cannot get a sack-barrow underneath it because it seems like something would get bent or damaged if I tried. So, it needs two people. I could drag it from under all the rubbish I’d piled on it to the garage door, but from there to the house is quite a way, so I had to involve my wife. That, of course, is a whole other column. We managed to get it onto the porch, where we could run it out of the weather and add a cable through a cracked window to power what we needed. The next challenge was firing it up. In the interest of being prepared, I have started it periodically over the years, ensuring I had enough petrol in it and even a spare can next to it should the you-knowwhat hit the fan again. The problem is, of course, that petrol loses its punch over time and this lot had been in there for a while now. I didn’t want to just tip it out, but as the tank in the generator seems to have allowed what was in there to evaporate, even with the fuel tap off and the cap tightly applied, I had to refill it with the can I had. With the tank full, it should be good for about seven hours if my calculations are correct. Mind you, I failed maths so many times at school I can’t even count! All joking aside, I was hoping this thing would start. It has a 7HP (5.2kW) motor and electronic ignition, according to the label, so I was expecting it to fire up easily. It didn’t. In the usual design stupidity that many machines seem to have these days, the pull cord has to be pulled at a weird angle off-centre from the pull starter, adding drag on the line and making it harder to start. Whoever designed these things must have been part of the company Bastards Inc. from that TV show, “The Fall and Rise of Reginald Perrin”. Saltshakers with no holes in them, gloves with just three fingers. Surely they’d look at it and think, how can we make this work better? But it appears not. I pulled on the cord a dozen times but nothing happened. With lots of blue language and gnashing of teeth, I realised I hadn’t turned the fuel tap on. I know, I know. It’s the little things that get to you. Anyway, once I opened that, with a few pulls on the cord, it sputtered into life. Boy, these things are loud! It was now sitting right outside the window, and I was rueing the fact I hadn’t built a soundproofed box for it elsewhere and ran some cabling. We might have power now, but the price to pay was the noise. A comedy of errors I still had to connect it up, which meant breaking out the extension cords. Fortunately, I know how to roll these up properly, given my years on the road in the music business. Unfortunately, the last time I used the longest of my siliconchip.com.au cables, which of course was the one I needed now, I was lazy and just gathered it up and chucked it on the garage floor. Now it was a rat’s nest, caught in everything possible on the concrete. Great, there’s 30 minutes of my life I’ll never get back. Note to self: roll the cables properly next time! I plugged everything in and fired the generator again, this time hitting the ‘power on’ button, a standard-­looking panel switch like you see on lots of equipment, similar to those on the rear of a computer power supply. This should liven up the two mains sockets provided. However, I got nothing. No power output. Hrmm, I must be doing something wrong. It’s not unusual (Tom Jones Syndrome). I haven’t used this generator other than to test it in the past, and I might need to (shock, horror) read the instruction manual. Though quite where that manual is, I don’t know. I could always hit the internet to find it. Oh, wait... The control panel has two olde-worlde moving coil meters that showed I should have 230V available from the mains socket and 12V DC from the red and black banana sockets beneath them. So the generator itself appeared to be generating. I broke out my multimeter and tested both; I got no reading from either socket. Great; I’m glad this wasn’t a dire emergency because I was really behind the eight ball here. There must be another switch or something I was overlooking. I just couldn’t see one on the fascia, so I had to go down on my hands and knees, in the noise and smoke, to try to see what was going on. Finally, I found a circuit breaker, stuck around the back, on the motor assembly. I threw caution to the wind and pressed it, and was rewarded with beeps and lights through the open window. The governor on the genny kicked in too, so it sensed there was some load on it. Why they didn’t put that breaker on the front panel is Australia's electronics magazine October 2024  91 another one of the design ‘features’ that people who never have to use these things come up with. At least I know it is there now. So we sat down and thought: what was most important? My wife works remotely and so getting our computers and internet up and running was most pressing. The fridge and freezer would stay cold for a while at least, so we decided to prioritise getting our network up and the internet back online. That wasn’t much load for the generator; it was revving like mad right outside our office window. On reflection, that was not the wisest place to put it. Just as I was reconfiguring the plugs to get everything up and running, the office light came on. I’d switched it on so I’d know when the power came back. Excellent! All that mucking around for nothing. At least I’d wrung out the generator and had shown up some flaws in my systems. Next time, hopefully I won’t be caught as short! 92 Silicon Chip Editor’s note: I wrote an article in the January 2020 issue titled “What to do before the lights go out” about preparing for blackouts and emergencies. Since then, I have purchased another inverter, a generator, extension cords, power meters, jerry cans, propane cylinders and numerous battery-­powered lights and torches. While I haven’t needed them much yet, as Dave implies, it pays to be prepared. Always put fuel stabiliser in the petrol you’re keeping for emergencies. After a year, pour it into your car’s tank and refill the can with fresh petrol (not E10; it’s hygroscopic and corrosive). If testing a generator, switch the fuel supply off and let it die so you don’t have old fuel sitting around in it for years. Workzone Inverter MIG Welder repair Several years ago, I purchased a Workzone gasless MIG welder from ALDI Special Buys. I’ve done a lot of work with this welder, which was reliable until recently. I was building a bike rack for our bikes and all was going well until I got to a particular section. The welder started running erratically, making it difficult to make a decent weld. It was a hot day, so I thought it might be overheating. However, the welder worked well again when I turned the job over. I went on to the next section of the project. It was fine as I was welding one end, but it would not weld at all when I went to the other end. I went back to the initial end, and it worked fine there, but once again, when I went to the other end, it did not weld. Then it stopped welding completely. I no longer thought it was overheating as the overheat light was not on and the welder felt cool. I hadn’t done much continuous welding on this job; had I pushed the welder much harder on other jobs, so it should have been all right. Returning from lunch, I found that the welder still did not work. It did nothing when I pressed the trigger, even though the welder was obviously running, as I could hear the fan and the power light was on. I started troubleshooting it by dismantling the handpiece. This is easy to do as there is a nut on each end. I got my multimeter and tested the microswitch and found it was working. So it was time to take the lid off and look further. The front panel is held on with three screws, one on top and two underneath. Another seven screws hold the cover on. With the cover removed, I found where the thin cable from the microswitch connects to the control board behind the front panel. I pulled the plug out, connected my multimeter to it (on continuity mode) and pressed the trigger again. Nothing happened, indicating a break in the cable between the handpiece and the welder. I then shorted the two pins on the control board and the wire feed motor ran. I laid that wire on the ground clamp, shorted the pins again, and the welder sprang to life. To replace the cable, I had to remove the clamp that holds the outer welding cable to the welder and disconnect the ground cable from the circuit board. I removed the screws from one end of the board and loosened the screws at the other end so I could raise the board to access the nut underneath it. I found some heavier twin-flex, soldered it to the end of the original cable and pulled it through the outer cable. I reconnected both ends by splicing and soldering, then Australia's electronics magazine siliconchip.com.au applied heat-shrink tubing insulation. I reassembled the welder and got back to the job at hand. B. P., Dundathu, Qld Bando Technic 5D repair I may also suffer from Dave Thompson’s “Serviceman’s Curse”. Sometimes repair jobs take far more time than was bargained for or is reasonable. I recently bought a non-working HF amateur band transceiver, as it looked worthy of restoration. It’s a brand I had never heard of, Bando from South Korea, dating to the late 1980s. I found the service manual, all in Korean, but fortunately, the schematics were all readable. As with most transceivers of that era, valves produce the output, in this case, two 6146Bs driven by a 12BY7. The remainder is all solid state. As the final valves operate with an 800V plate supply, any service work must be done carefully. This high voltage is derived from an iron core transformer via a bridge rectifier and filtered by two series 47µF/450V capacitors with 470kW balancing resistors. On inspection, one capacitor was a dead short, which put the entire 800V on the other, which had obviously blown! I decided to concentrate on the receiver side first. After removing the capacitors, I temporarily disconnected and insulated the high-voltage winding from the transformer to the rectifier. Some cosmetic problems needed to be fixed first. A power connector on the back panel was missing, and an ugly heavy power cable passed through the rectangular siliconchip.com.au hole with a home-made cable clamp. In addition, a large toggle switch had been added, which I found was used to turn off the filament supply to the 6146s. In addition, the wires to the microphone gain control were damaged. I removed the switch and associated wiring and drilled out the hole to take a proper cable clamp with a new power cable. I covered the rectangular hole with a small plate. The top and bottom covers needed a good clean-up; a repaint may be a good idea at some stage. A couple of knobs were not original, but a friend reckons he could make some to match using a 3D printer. Now I could safely turn it on to check the receiver operation. The display came up, and the tuning knob changed the frequency correctly on all bands. Connecting a signal generator, some bands appeared to work, but several were completely deaf. The band switch is of the wafer type; using contact cleaner, I managed to get all bands working except for the 28-30MHz ones. A 1µV input signal gave an excellent SNR on all but the top band in that range, which needed at least 20dB more. I ordered some replacement high-voltage electrolytics, but being impatient, I robbed three 350V capacitors from discarded computer power supplies and made up a capacitor that could handle 1050V, together with 270kW balancing resistors. That enabled me to get the transmitter working. I connected a 50W 100W dummy load to the antenna terminal and switched to Tune on the 7MHz band. Immediate success; I had a power output that I could peak with the two variable capacitors of the pi-coupler. There is also Australia's electronics magazine October 2024  93 a Drive control that tunes the plate circuit of the 12BY7, but it did absolutely nothing! The circuit diagram shows a section of a three-gang variable capacitor. The other two sections are used for peaking the receiver’s tuned circuits on either side of a low-noise dual-gate Mosfet preamplifier (Q1). The drive control operates the variable capacitor via a couple of plastic gears. On close inspection, the gears were moving, but the one attached to the capacitor shaft via a friction fit was not rotating the shaft. For some reason, it was jammed completely. It was purely fortuitous that it was stuck in a position that had the receiver working reasonably well. But to achieve maximum output power, it did have to operate. I tried all sorts of ways to move it, such as sliding the gear off and trying to rotate it with pliers, all to no avail. How about removing the capacitor and sorting out its problem? About three hours later, having used all my solder-­removing tools, including a hot air pencil, I had to admit defeat. There are many connections to the capacitor on the circuit board, and even though it is single-sided, it was tightly connected, mainly via the solid end plates. Any further attempts could have damaged the PCB, so I had to develop a Plan B. Looking at the circuit diagram, there is a 10nF capacitor (C60) from the plate of the 12BY7 to the variable capacitor. How about disconnecting it and adding an external capacitor? I had several suitable variable capacitors accumulated over the decades that I had fortunately never thrown away. Doing a quick lash-up of the connections, it looked workable, and sure enough, I could peak the drive voltage to the 6146 valves. I made a bracket from 1.6mm aluminium and bolted it to the top of the original variable capacitor which, by luck, had 2.5mm tapped holes on top. Adding a knob was a workaround solution but not a satisfactory one. It meant that the top of the transceiver had to be left off, exposing what turned out to be 170V peak-topeak at RF on the stator. That could cause a nasty RF burn! But how could I connect to the original drive shaft? One suggestion was to make up a 3D-printed gear to mesh with the one already there, but it just would not fit. Another alternative would be a couple of pulleys and a belt drive, which also looked impractical. Then, I came up with the idea of using two universal couplings. Looking at where they would fit and the angle between the shafts, it seemed a likely solution. Off to AliExpress, and not surprisingly, there are heaps of them from different suppliers for different shaft diameters. The ones in the transceiver are 6mm in diameter, so I ordered a couple for a grand total of $14. They arrived within two weeks, just after I also received a length of 6mm-diameter tubing. As you can see from the photo, it all came together quite easily. The only gotcha was having to carefully drill out one end of the 6mm coupling to 6.35mm (1/4in), as that was the shaft diameter of the 100pF variable capacitor. Tuning with the front knob is now quite smooth and the drive can be peaked accurately. Remember the two extra gangs on the capacitor? The receiver sensitivity and noise figure were quite good on all but the top band, so I decided just to peak the slugs on the coils slightly on either side of the middle of each usable band. For example, on the 40m band, I peaked L9 at 7.1MHz and L16 at 7.2MHz. That applied to all the other bands. I now have a workable transceiver with a clean 100W SSB output on all but the 10m band. After many hours of work, I decided to leave that for another day. Once the proper high-voltage electrolytics arrive, I will replace the temporary arrangement. Yes, it took a long time, but the satisfaction of getting it to work more than made up for it. SC C. K., Mooroolbark, Vic. Above: the Korean-made Bando transceiver and a close-up of its RF section. Left: the universal coupling (with the connectors unplugged). 94 Silicon Chip Australia's electronics magazine siliconchip.com.au ONLINESHOP SILICON CHIP .com.au/shop PCBs, CASE PIECES AND PANELS WII NUNCHUK RGB LIGHT DRIVER (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB SKILL TESTER 9000 PICO GAMER ESP32-CAM BACKPACK WIFI DDS FUNCTION GENERATOR 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (BLUE) FAN SPEED CONTROLLER MK2 ESR TEST TWEEZERS (SET OF FOUR, WHITE) DC SUPPLY PROTECTOR (ADJUSTABLE SMD) ↳ ADJUSTABLE THROUGH-HOLE ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER MAR24 MAR24 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 16103241 SC6903 SC6904 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 08106241 08106242 08106243 24106241 CSE240203A CSE240204A 11104241 Subscribers get a 10% discount on all orders for parts $20.00 $20.00 $7.50 $15.00 $10.00 $5.00 $10.00 $2.50 $5.00 $10.00 $2.50 $2.50 $2.50 $2.50 $5.00 $5.00 $15.00 STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR AUG24 AUG24 AUG24 AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 OCT24 OCT24 OCT24 OCT24 OCT24 23106241 23106242 08103241 08103242 23109241 23109242 23109243 23109244 19101231 04109241 18108241 18108242 07106241 07101222 15108241 28110241 18109241 $10.00 $12.50 $2.50 $2.50 $10.00 $10.00 $10.00 $5.00 $5.00 $7.50 $5.00 $2.50 $2.50 $2.50 $7.50 $7.50 $5.00 PRE-PROGRAMMED MICROS As a service to readers, Silicon Chip Online Shop stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. $10 MICROS $15 MICROS ATmega328P ATtiny45-20PU PIC12F617-I/P PIC12F675-I/P PIC16F1455-I/P PIC16F1455-I/SL PIC16LF1455-I/P PIC16F1459-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) 2m VHF CW/FM Test Generator (Oct23) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Train Chuff Sound Generator (Oct22) Railway Points Controller Transmitter / Receiver (2 versions; Feb24) Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) New GPS-Synchronised Analog Clock (Sep22) Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) 8-Channel Learning IR Remote (Oct24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Digital Volume Control Pot (SMD; Mar23), Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (TH; Mar23), Filament Dryer (Oct24) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) Compact OLED Clock & Timer (Sep24) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) PIC16F18877-I/P PIC16F18877-I/PT PIC16F88-I/P PIC24FJ256GA702-I/SS PIC32MX170F256B-I/SO USB Cable Tester (Nov21) Wideband Fuel Mixture Display (WFMD; Apr23) Battery Charge Controller (Jun22), Railway Semaphore (Apr22) ESR Test Tweezers (Jun24) Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) ATmega32U4 ATmega644PA-AU Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) $20 MICROS $25 MICROS PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS & SPECIALISED COMPONENTS MICROMITE EXPLORE-40 KIT (SC6991) (OCT 24) DUAL-RAIL LOAD PROTECTOR (SC7366) (OCT 24) PicoMSA PARTS (SC7323) (SEP 24) Includes all required parts (see p83, Oct24) Hard-to-get parts: PCB & all semis except ZD3, ZD6, D4 & D5 (see p79, Oct24) Hard-to-get parts: includes the PCB, Raspberry Pi Pico (unprogrammed), plus all semiconductors, capacitors and resistors (see p63, Sep24) $35.00 $50.00 COMPACT OLED CLOCK & TIMER KIT (SC6979) (SEP 24) DISCRETE IDEAL BRIDGE RECTIFIER (SEP 24) Includes everything except the case & Li-ion cell (see p34, Sep24) $35.00 $45.00 Both kits include the PCB and everything that mounts to it (see page 83, Sep24) - All through-hole (TH) kit (SC6987) $30.00 - SMD kit (SC6988) $27.50 DUAL MINI LED DICE (AUG 24) Complete kit: choice of white or black PCB solder mask (see page 50, August 2024) - Through-hole LEDs kit (SC6849) $17.50 - SMD LEDs kit (SC6961) $17.50 AUTOMATIC LQ METER KIT (SC6939) (JUL 24) Includes everything except the case & debugging interface (see p33, July24) $100.00 ESR TEST TWEEZERS COMPLETE KIT (SC6952) (JUN 24) USB-C SERIAL ADAPTOR COMPLETE KIT (SC6652) (JUN 24) DC SUPPLY PROTECTOR (JUN 24) Includes all parts and OLED, except the coin cell and optional header Includes the PCB, programmed micro and all other required parts All kits come with the PCB and all onboard components (see page 81, June24) - Adjustable SMD kit (SC6948) - Adjustable TH kit (SC6949) - Fixed TH kit – ZD3 & R1-R7 vary so are not included (SC6950) WIFI DDS FUNCTION GENERATOR $50.00 $20.00 $17.50 $22.50 $20.00 (MAY 24) Short-form kit: includes everything except the case, USB cable, power supply, labels and optional stand. The included Pico W is not programmed (SC6942) - Optional laser-cut acrylic stand pieces (SC6932) COMPACT FREQUENCY DIVIDER KIT (SC6881) (MAY 24) PICO GAMER KITS (APR 24) Includes the PCB and all other required parts (see page 38, May24) - SC6911: everything except the case & battery; RP2040+ is pre-programmed - SC6912: the SC6911 kit, plus the LEDO 6060 resin case - SC6913: the SC6911 kit, plus a dark grey/black resin case $95.00 $7.50 $40.00 $85.00 $125.00 $140.00 $12 flat rate for postage within Australia. Overseas? Place an order via our website for a quote. All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars & include GST where applicable. HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 10/24 Vintage Radio The amazing NZ-made ZC1 MkII military transceiver In the early phases of WWII, the New Zealand Government decided that their troops required a better standard of field communications radio than what they had. They wanted a transceiver that suited the conditions in New Zealand (bushland) and the tropics (jungles). By Dr Hugo Holden T he task was given to Collier and Beale of Wellington, NZ. They designed the first model, the ZC1 MkI and, by April 1942, they had amassed enough resources to build 750 units. By December 1942, the first production batch was shipped. There were a few minor variations of the MkI model that are not discussed here, as this article is primarily about the MkII. The subsequent re-design was handled by R. J. Orbell of Radio Limited (Radio Corporation of NZ). At least 5000 MkI units were manufactured, and around 10,000 units of the MkII, although estimates vary. I have seen one estimate that 30,000 total units may have been made, but that figure could have been a target. The exact numbers may never be known. The serial numbers were somewhat non-specific and not helpful due to secrecy. The ZC1 radio project was not a cheap undertaking for the NZ Government. Accounting for a total number of around 14,000 to 15,000 units, the cost was $3,000,000 NZ Pounds in the 96 Silicon Chip 1940s, equivalent to about $2,660,000 AU Pounds at the time. Translated on the RBA’s pre-decimal inflation calculator, that is equivalent to AU$234 million today. If the estimates of the ZC1 units made are correct, the cost per set was around $15,600 in today’s currency. 56 factories and 900 workers produced parts and sub-assemblies for the radios. It took about 60 man-hours to build one set; about 20 sets per week could be made initially. Production must have sped up as time passed to at least 100 sets per week to complete around 15,000 units by the end of WWII. I have been unable to determine if many sets were made after 1945. It is possible that some new ZC1s were manufactured to support the NZ and British occupation forces in Japan (J-Force) during 1945-1948. The ZC1s saw service in the Pacific war campaign, and many were sold to the Middle East; however, it was too late for them to see any significant use. After the war, ZC1s were deployed Australia's electronics magazine by NZ Government agencies for various mobile and fixed applications until the 1960s. They then started turning up in Army Surplus stores in good numbers, many being cannibalised for components. They were typically used by radio hams on the 40m and 80m bands (7.5MHz and 3.75MHz, respectively). A ZC1 radio was installed in the Radio Room of the Grammar School that I attended in Auckland in the 1970s; I cannot recall if it was the MkI or MkII model. By then, I had already seen ZC1 radios and many components that had been removed from them in Army Surplus stores. In the early 1970s, my brother used an open-frame relay taken from a ZC1, in conjunction with a capacitor, to build a mains light bulb flasher. Marine conversions ZC1 radios also found their way into fishing boats and other marine applications. Many were modified to be marine band radios; one of my MkII radios had its transmit VFO siliconchip.com.au Photo 1: this crystal module allowed a ZC1 radio to be easily converted to operate on marine frequencies. Photo 2: the red and blue screws on the tuning dial, plus the two small windows at the top, allow the operator to set it up to flick between two specific frequencies instantly. The radio’s front panel has a space for a pocket watch. replaced by a Pierce crystal oscillator circuit running at 2128kHz, a marine frequency. I converted it back to the original spec. Collier and Beale supplied a conversion kit for marine use in the post-war era. Photo 1 shows the modification I found in one radio; it may well be by Collier & Beale. Many ZC1 radios acquired all kinds of modifications; unmodified ones became very hard to find. These days, due to the historical significance of these radios, most owners want them restored to their original condition. Unusual features As seen in the photos, one of the attractive features of the radio’s front panel is a pocket watch holder. Finding a period-correct military-grade pocket watch to fit in that holder is a challenge, but I did. Also note the red and blue rods on the main receive and transmit tuning knobs, called “Flick Set Screws”, shown in Photo 2. These allow mechanical storage, if you like, of two frequencies; the tuning knob returns (flicks) to the position and frequency where the screws were tightened when the Flick knob is deployed. One thing that characterised both models of the ZC1 was the ability to siliconchip.com.au transmit and receive on two different frequencies. Design and specifications The radio is a very solid affair, built into a steel enclosure, the inside of which is heavily copper plated. The front cover (Photo 3) fits tightly with a rubber seal. No harm would occur if the unit were dropped in water with the front cover on. The main assembly is ejected from the housing by two large front panel screws and slides out for easy servicing. The vibrator transformer (at lower right on a sub-chassis, see Photo 6) is encased in a shielded container; all measures were taken to prevent RFI from leaking out of the vibrator power unit and creating radio interference. There is minimal background interference with the original V6295 mechanical synchronous vibrator. When using an electronic vibrator replacement (as I described in the June-August 2023 issues; siliconchip. au/Series/400), no interference of any significance occurs. Those articles described several different suitable designs. Besides no contact wear, some of those designs have the additional advantages of higher efficiency and a higher HT output. The ZC1 was specifically designed for easy servicing (unlike much modern equipment). It was very well documented, not just with a comprehensive working instruction manual for the operator but also circuit diagrams and Photo 3: the front cover is a tight fit to protect the radio from mud, water etc during transportation. Australia's electronics magazine October 2024  97 Photos 4 & 5: a photo of a suggested ground station setup from the radio’s manual, and how the radio could be mounted in a truck. a parts list with extraordinary detail. The two manuals were labelled with “New Zealand Wireless Sets & Stations No. ZC.1, MK.II.”. Photo 4, taken from the working instructions manual, shows a typical setup of a ZC1 MkII radio in the field with a vertical whip antenna. Photo 5 depicts a mobile application in the back of a truck. As well as parts lists, the manufacturers supplied the Army’s Signal Engineers with comprehensive details about the radio that were never generally supplied for domestic radios. For example, they include detailed descriptions of each of the coils and transformers, including things like the exact number of turns used, the size of the former, the type of wire, the SWG wire size, the inductance value with the % tolerance, whether the coil was wound bifilar and the coil base diagrams. The DC resistances of the inductors were also documented. This is by far the most detailed information available for any radio I own. If any of these parts fail in the future, it would be an easy task to replicate them. The voltage on every valve electrode is also well documented in the manuals. Power supply The radio is powered by a 12V storage battery, typically two 6V units in series for the ground stations, or the 12V battery in a jeep or truck for Differences between the ZC1 MkI and MkII The MkI model was a single-band 2-6.5MHz transmitter and receiver (transceiver). The MkII version was split into two bands: 2-4MHz and 4-8MHz. Other differences include that the MkI model did not have an MCW (Morse code) transmit mode. The other major difference between the MkI and MkII units is that the MkI used a non-synchronous vibrator supply and two 6X5 valves as HT rectifiers, as shown in Fig.a. Also, in the MkI unit, there was a switch to select between a higher or lower HT voltage. In the MkII, however, the switch was dispensed with, and a synchroFigs.a & b: the ZC1 nous vibrator, the model V6295, was MkI power supply deployed. The 6X5 valves were dis(above) differs pensed with too – see Fig.b. significantly from the The negative output of the MkII MkII (left) as it uses a non-synchronous supply is connected via resistors to vibrator and HT ground and a voltage of around -50V rectifier valves to -60V is developed across them. (6X5). The ZC1 MkII This is used to cut off the valves in the power supply used a transmitter section when the radio is synchronous vibrator, in Receive mode. In Transmit mode, dispensing with the the resistors are shorted out, boosting two 6X5s. the HT voltage by an additional 50V. 98 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 6: a top view of the ZC1 MkII chassis. Note the large brown tapped antenna tuning coil at top middle. mobile use. Although the unit was said to be “portable”, it weighed 27kg, and somebody had to carry the batteries too. For this reason, many units were fitted into jeeps and trucks. Two people could carry the ZC1 easily as it had handles on each side of the cabinet. For one person to carry the unit long distances by themselves, they would have to be fit and quite strong. The MkII radio’s current consumption is quoted at 2.8A in Receive mode with Sender off and 3.8A with Sender on. In send RT mode, it is 4.9A; close to 2A of that is for the valve’s heaters. The 6.3V heater valves are strung in series pairs across the 12V power supply; since there are 11 valves in the radio, one valve requires a series heater ballast resistor. With an 80Ah battery, the usable life is in the vicinity of 20 hours, with the transmitter used 25% of the total time. Transmission power & modes The ZC1 MkII RF output power is in the order of 2W. A near-perfect impedance match into a 50W load can be made with an impedance-matching transformer and slightly modified coupling, giving 3W output on 80m and easily 2W on 40m. The transmission modes are CW (carrier wave), RT (carrier wave amplitude modulated by the microphone) and MCW (Morse code telegraphy, where an audio tone modulates the carrier wave). siliconchip.com.au The 800Hz tone oscillator was enabled in both CW and MCW mode (even though the modulator is not used in CW mode). The oscillator output was cleverly coupled to the audio stage and headphones so the operator could hear a ‘sidetone’ or beep when the Morse key was pressed. In RT mode, the sidetone was instead the sound picked up by the microphone, helping the operator to ‘hear himself talking’ in the headphones (similar to analog telephones). Antenna The ZC1 was generally used with a vertical 34-foot (10.4m) rod antenna, supplied in several sections. The transmission range was 25-35 miles (40-55km) in CW mode and around 10-20 miles (15-30km) in vehicles with 8-to-12-foot (2.5-3.5m) whip antennas. Wire antennas were also an option, such as an inverted-L or T-shaped wire. The ZC1 has a large two-inch (51mm) diameter antenna tuning coil with many taps, allowing a significant range of antennas to be used. This large coil with the brown former can be seen in Photo 6, sitting above the chassis and behind the front panel and switches that select the coil taps. Component selection The components in the ZC1, like knobs, potentiometers, switches, dials, valves, sockets, coils, shielding cans, variable capacitors, resistors and fixed capacitors were all of outstanding Australia's electronics magazine quality. These radios made for an extremely attractive and economical source of parts for many projects. These were especially good for young people interested in learning radio and electronics but short on cash. The solid black phenolic knobs and other parts, even today (80 years later), look good as new. There was a shortage of components in the early 1940s, especially capacitors. Many of the capacitors, including the mica types used in this radio, were made in New Zealand. The mica came from local mines. Many of the wax-paper capacitors were also made in NZ, although some were imported (see notes on the “Dwarf Tiger” capacitor found inside the metal housing of one capacitor below). The electronic components in the ZC1 were heavily ‘tropicalised’ with wax impregnation. Even the usual wax-paper capacitors in the unit were double-sealed inside additional metal housings with a waxy oil to prevent moisture ingress. All the other transformers were impregnated and sealed in metal containers as well. Even the hook-up wire was said to have been treated with a “non-­ vegetable lacquer”. This was all in aid of reliability in moist bush or jungle environments. Transmitter circuitry The circuit diagram is shown in Fig.1. The modulation source for the MCW mode is acquired by creating a positive feedback pathway so the October 2024  99 Fig.1: the ZC1 MkII transceiver circuit. The signal inputs (mic, line & key) are towards lower right, while the earphone outputs are just above those. The top half of the circuit forms the transmitter, while the lower half is the receiver. They share the antenna at lower left. 100 Silicon Chip Australia's electronics magazine microphone amplifier stage based around valve V1G (6U7G) oscillates. This is easily achieved because the microphone, being a dynamic type, requires a microphone-matching transformer to drive the grid of valve V1G. A feedback capacitor is switched in to make the preamp stage oscillate at 800Hz. The 6U7G valve was used extensively in both the transmitter and receiver sections. It made sense to use the same valve type for as many applications as possible in the one radio to save on carrying different spare parts. Valve V1G drives the 6V6GT Class-A modulator valve, V4B. The transmit VFO (V1F) is another 6U7G, followed by a 6U7G buffer stage, V1E, and a 6V6GT RF output stage, V4A. Generally, a 6V6 can generate around 2-4W of RF (or audio) output power in a single-ended application. These valves were also popular in domestic radio audio output stages and as guitar amplifiers. 6U7s are a very capable RF pentode, described by RCA as a “Triple Grid Super Control Amplifier”. This means they are suited to applications involving AGC circuits and gain control. They were also a common valve type in the 1940s era. It was said that the 6U7 was the most common valve to find in junk sales in NZ. The 6U7 is very similar to the 6K7 found in domestic radios of the time. The 6U7 was abundant in Australasia and had many manufacturers besides the usual RCA, Kenrad and National Union brands. Australian Philips made them, too, for the Department of Defence, and supplied them in very attractive boxes with Art Deco artwork (see Photos 7 & 8). The logo engraved on the 6U7G valve base in my set indicates it was made for the Australian Department of Defence. Receiver section The receiver in the ZC1 is a single conversion AM superhet radio with a BFO (beat frequency oscillator) added, based on a 6U7G pentode, V1D. The valve lineup is a 6U7G RF stage (V1A), a 6K8G triode-hexode converter (V2A), a 6U7G 465kHz IF stage (V1B); a 6Q7 detector, and first audio preamp stage V3A. The receiver’s sensitivity was quoted as 1.5μV at 8MHz, varying above and below that over the bands a little, being 3μV at 2MHz. However, the output siliconchip.com.au Photo 7: the Philips valves for this set came in decorative cardboard boxes. Photo 8: the original 6U7 variable-mu pentode. level was not stated; it probably was around 50mW into the headphones or a 100W dummy load. The audio output stage is only designed to drive headphones, so the designers deployed yet another 6U7G RF pentode, V1C, in a triode-­ connected configuration to act as the audio output valve. The audio output power of a ZC1 is a mere 50mW with low distortion, although it will deliver 150mW with significant distortion, pushing the 6U7G RF valve to its limits in this application. This result is satisfactory for the 100W headphones used and for speech but is not good enough to drive an extension speaker or music. Some historical articles mentioned distortion in the audio. The main cause for it, aside from the non-linearity of the grid voltage versus anode current transfer function, is that even by 100150mW, the 6U7G’s G1 grid is drawing current due to the high drive level exceeding its bias voltage. Restoration I had replaced the electrolytic capacitors in my ZC1 radios over 30 years ago. The other capacitors, which included wax-paper types and moulded mica types, were still in good condition when the radio was 50 years old, but that was 30 years ago. Now those capacitors are about 80 years old. On re-testing them, I found that all the capacitors had deteriorated, including the mica types; nearly all had developed measurable leakage. While the wax-paper types fared better than most due to being immersed in oil inside steel canisters, over time, the rubber seals failed where the canister and the phenolic end disc mated together, and the lower molecular weight part of the oil or wax started to leak out. Many of the mica caps in the ZC1 were custom-made by Radio Corporation, while others were American types made by El-Menco. These were also amazingly good for their age. The ZC1 MkII also used three 1in (25.4mm) diameter twist-lock electrolytic capacitors. In vintage radio restorations, people often replace the original chassis-­ mounted capacitors with radial or axial types under the chassis. I don’t subscribe to that, as it looks non-­ original and messy. New twist-lock capacitors are sometimes available in that size. Of late, though, they have been more difficult to acquire, so now I re-build them instead. I start by machining out the base of the capacitor using a lathe. If I find any latex rubber, I discard it and clean the inside of the canister, as latex can contain halides, which attack aluminium. I machine a 10mm-thick plug from phenolic material to fit the hole I created in the capacitor’s base. I then cut two M2 threads in it for screws and lugs. I also drilled 1mm holes beside those screw holes to pass the wires through from the replacement electrolytic capacitors – see Photos 9 & 10. I glue the plug in place with 24-hour epoxy resin. Don’t forget to label the polarity of the pins before gluing! To do that, I drill a small countersink and fill it with a dot of red paint. When a multi-section part is required, I stack the capacitors on top of each other in the canister and add more terminals. Replacing the wax-paper capacitors There are many wax-paper and mica capacitors in the ZC1. I replaced the mica capacitors with new resin-­dipped 18.7mm diameter hole 10mm thick Phenolic plate (18.6mm diam.) Panasonic 47μF 450V (18.1mm diam.) Photos 9 & 10: after replacing the electrolytic capacitor within the can, I glued the end back on. The new eyelet tags are soldered to the capacitor leads. siliconchip.com.au Australia's electronics magazine Photo 11: soldering the end onto one of the wax-paper capacitor cans. October 2024  101 ◀ Photos 12 & 13: end caps for the waxpaper capacitors made from PCB material and the finished capacitors. Fig.2: an easy way to add an extension speaker to the ZC1 MkII. 500V silver mica types and the wax-­ paper types with polypropylene film capacitors, fitted inside the original metal canisters. When replacing the wax-paper capacitors, I found the best method was to first desolder the internal capacitor wire from the eyelet/tag at the end with the phenolic insulator. Then, holding the capacitor (with protective tape around its body) in the lathe chuck, I carefully go around the circumference near the far end with a junior saw to create an initial groove. After that, I cut the end off with the saw and slide the capacitor contents out of the canister. Next, I drill out the rivet and tag in the phenolic insulator and discard them. These tags were in poor condition; the brass was quite brittle where it was sharply folded, and prone to cracking. After that, I smooth the end with a file while rotating in the chuck, then smooth it further with 400-grade sandpaper. Once ready, I fit 1/8in (3.175mm) diameter silver-plated brass eyelets to the phenolic end. I use fibreglass PCB material to replace the end that was cut off. It is easily cut into discs using a 22mm diameter hole saw in a drill press. I then make a 1/8in central hole and attach a screw and nut to secure it. I then used the lathe to machine the perimeter down to 16.8mm, to be a close fit inside the end of the metal canister. I fit the same eyelet type to this end cap, visible in Photo 12. The replacement capacitor is prepared with a phenolic spacer and some Scotch 27 fibreglass tape, so it is a firm fit in the original canister. I then recess the discs about 0.5-0.8mm into the end of the metal canister before soldering it. This way, a small well for the solder is created between the canister’s edge and the eyelet projecting from the copper side of the PCB material. Polyimide tape must be wrapped around the capacitor body, right up to the edge being soldered, or the solder will track down the outside of the canister, spoiling the appearance of the capacitor body. I use a soldering iron set at 400°C to heat the edge of the canister all the way around initially to create a strong bond, then fill the well with more solder. The same principles apply to re-building the 200nF capacitors, except I initially used a 25mm hole saw to make a larger disc. I decided that having flying leads on the capacitors was a better way to mount them than the tags they once had. An interesting finding while restoring these capacitors: the 20nF types were custom-made by Radio Corporation with a brown paper valve over them inside the canister, also filled with wax. They must have been running low on their own production because one of these four capacitors had an American-­ made 20nF 600V “Dwarf Tiger” capacitor hiding inside. Replacing the mica capacitors Most of the mica capacitors that had become leaky were American-made El-Menco parts. One was made by Radio Corporation in NZ. Photo 14 shows the underside of the Photo 15: the custom 12V DC power connector used by the ZC1 radios is now hard to obtain. Photo 14: the underside of the chassis is pretty neat; it was made to be easily serviced. Most resistors have already been replaced, as the old ones were way out of spec. 102 Silicon Chip Australia's electronics magazine Photo 16: my newly manufactured replacement 12V DC power cord for the radio. siliconchip.com.au ZC1 after re-capping it. In the past, I had replaced nearly every carbon resistor, except just a few, as they measured way out of spec. As well as many resistors having gone high in value, one 50kW power resistor was open-circuit. I carefully removed the paint to inspect it to find out why it happened. It turned out that there was a discontinuity in the carbon film. Optimising transmission on the 40m and 80m bands The RF output impedance of the ZC1 best suits long wire antennas. I found that by using an impedance-matching transformer (an ‘unun’) with modified coupling to the output coil, the output could be optimised for a 50W load. This also makes measuring the output power with standard equipment very easy. It requires the addition of two capacitors inside the unit and the unun outside. The capacitors are selected with positions 10 & 9 on the switch, as shown in Fig.c. The unun matches the resulting ~12.5W output impedance to 50W (Fig.d). The Amidon core and wire (see photo at the bottom of the panel) come as a kit (AB200-10). With this arrangement, 2W is easily delivered to a 50W load on 40m and around 3W on 80m. The 12V power cord One of the tricky parts to get for the ZC1 these days is its polarised 12V DC power cord and plug. The original type was a substantial black phenolic connector with two large-diameter rubber-­ covered wires – see Photo 15. I used my lathe to hand-make a compatible 12V plug from some phenolic plate, machined brass inserts, electrical insulating valves and brass rod – see Photo 16. A friend in the USA also made a CAD file to 3D print this connector. Making an extension speaker As noted, the ZC1 uses a 6U7G radio frequency valve (triode connected) as the audio output amplifier. The designers pushed this valve to near its maximum ratings: a plate dissipation of up to 2.25W and a screen dissipation of 0.25W. The 2kW cathode resistor for the 6U7 can be reduced to 1.8kW to gain a little more power, which is in the range for the specification of the original carbon resistor. If the valve is exchanged for a 6K7G, which has higher plate dissipation but is otherwise similar to a 6U7, the cathode resistor can be lowered to 1.2kW, which gives a good improvement. I wanted to keep the set original but add an extension speaker. It is best to match the speaker with a small autotransformer, the design of which is shown in Fig.2. The taps can be selected to suit any speaker impedance (the impedance ratio is the square of the turns ratio). At this low power level, the laminated iron core transformer I used has a flat, undistorted response from 50Hz to 20kHz. I mounted the matching transformer inside a speaker box with a spare 32W speaker – see Photo 18 (shown overleaf). Other options to increase the audio output power include moving to a higher power rated valve such as a 6V6 siliconchip.com.au Fig.c: this simple modification to the coil switching arrangement can be used with an external impedance-matching transformer to obtain good performance into a 50Ω load. Fig.d: this ‘unun’ matches the 12.5Ω output impedance of the modified radio to a standard 50W antenna. Right: the autotransformer that adapts the modified set’s 12.5Ω antenna impedance to 50Ω is housed in a small diecast box. Silicon Chip kcaBBack Issues $10.00 + post January 1995 to October 2021 $11.50 + post November 2021 to September 2023 $12.50 + post October 2023 to September 2024 All back issues after February 2015 are in stock, while most from January 1995 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com.au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 Australia's electronics magazine October 2024  103 or 6K6. However, that requires modifying the radio’s circuitry, and the small output transformer’s primary current can only be pushed so far. According to the data sheets, transformer T1A’s primary has 3000 turns of 43 SWG wire, which has a current rating of only 18mA. Another option is an active external speaker. Adding a frequency counter Photo 17: the frequency counter connects via the lamp socket on the front, modified to pass enough of an RF signal for this to work. Accessories My ZC1 headset and microphone. The headphones’ cord is a little frayed but both still work fine. The ZC1 came with several accessories, many of which supported its use as a ground station – see Fig.e. The minimum requirements, aside from the batteries and the antenna, were the headphones, microphone and Morse key. The headphones and microphone (see Fig.f and photos) are both dynamic types. They use the same dynamic inserts with a DC resistance of around 40-45W. The ones in the headphones are wired in series and have a total resistance of around 95W and an impedance close to 100W at 1kHz. Other items included a remote control box for the radio (Fig.g), the whip antenna kit, the battery pack and a spare valve kit containing every valve plus a spare V6295 vibrator. There were also two 6V lead-acid 80Ah batteries in wooden boxes. The remote control allows the ZC1 to be operated 100m away via a connecting cable. Two remote control units could be used, and the operators could talk to each other like a telephone link. The remote control units came with a satchel to carry the microphone and headphones. An add-on power amplifier, type ZA-1, was an option. It incorporated type 807 power valves to boost the RF power. Not nearly as many booster amplifier units were made as the ZC1 radios. 104 Silicon Chip There is a connector on the front panel of the ZC1 to power a reading light. One of its connections is via a resistor. Adding some coaxial cable and small coupling capacitors into the radio allows the signal from the Transmit and Receive VFOs to be exported via that connector – see Fig.3 & Photo 17. This modification does not alter the original function of the front panel lamp socket. The dynamic microphone insert (at upper left) is easily removed from the handpiece. Two of the same inserts are used in the headphones. Australia's electronics magazine siliconchip.com.au Fig.3: adding a couple of small capacitors and some coax allows the front panel light socket to be used for monitoring the LO or transmitter frequency with an external frequency counter. Due to the low values required for the coupling capacitors (1.1-2.2pF), the set barely requires retuning after adding them. The C7G and C7H trimmers can be adjusted on the transmit side and C7C and C7B on the receive side (L/O) to fractionally reduce their capacity if required, but I found it unnecessary. The capacitance of the coax forms an Fig.e (above): some of the available ZC1 accessories. Fig.f (right): the microphones, headphones and Morse code key available with the set. The microphones and headphones used the same type of dynamic insert. AC voltage divider and transforms the impedance. The presence or absence of the external frequency counter results in a negligible effect on receive or transmit frequencies. Since one of the connections on the lamp circuit is to positive and not ground, it is a good idea to put two DC isolating capacitors in the banana plugs in case the chassis of the frequency counter and the ZC1 chassis come in contact. In receive mode, the peak voltage is only 30mV; not all counters could work with that low a level and might need a buffer amplifier. My counter has an internal buffer/amp. In transmit mode, the output level is higher at just over 200mV peak. The frequency counter can be modified to switch out its 465kHz offset in transmit mode to automatically show the correct receive and transmit frequencies without manually switching the offset on the counter. Conclusion Fig.g (left): up to two remote control units could be used with a ZC1 radio. They could be located 100m or more away from the radio, connected by wires. siliconchip.com.au Photo 18: the completed extension speaker. The impedance-matching transformer is also inside the box. Australia's electronics magazine The ZC1 MkII radio is a masterpiece of high-quality radio engineering and a very impressive feat for New Zealand’s wartime radio engineers. It is so well built that many are still functional 80 years on. As expected, the capacitors and resistors deteriorated over that time frame. In my ZC1 radios, all the coils, transformers and original valves remain in good order. The radio is an excellent, sensitive receiver for shortwave listening. It remains one of my favourite radios. Unfortunately, many that were deployed for Marine use rusted significantly, but with enough work, that can also be remedied. SC October 2024  105 Mouser Electronics’ new Melbourne office by Tim Blythman Mouser recently opened a new Australian Customer Service Centre. The launch event was held at Hotel Chadstone while the office is located in the Melbourne suburb of Notting Hill. We attended the launch event to see what this means for their customers (including us!). Y ou might have seen Mouser’s announcement about their new Melbourne Customer Service Centre in the Product Showcase section of the March issue (siliconchip. au/Article/16169). It is the first Mouser Electronics location in Australia or New Zealand. Before that, the nearest location was in Singapore! To celebrate this occasion, an event was held in the Altus East Room at the nearby hotel. Mouser representatives present included staff from the Melbourne Customer Service Centre, as well as other staff responsible for the Asia-Pacific region. Mark Burr-Lonnon, Mouser’s Senior Vice President of Global Service and EMEA (Europe, Middle East and Africa) and APAC (Asia-Pacific) Business was there. Other attendees included representatives from local electronics and engineering firms. We caught up with the folks from Microchip Technology, who are always enthusiastic about their new and upcoming products. One sentiment that was discussed at the event is that we should expect more innovation over the next few years. Engineers now need to spend less time chasing parts and alternatives, as was common over the last few years. That’s certainly a relief! This artist’s impression, based on an aerial photo, shows the past and future expansions of Mouser Electronics’ headquarters and distribution centre in Mansfield, Texas. The new distribution centre nearly doubles the warehouse size; the three-storey building uses the latest robot pickers to pick orders (1000ft2 is 92.9m2). 106 Silicon Chip Australia's electronics magazine siliconchip.com.au A rendering of the robotic storage/ picking system inside Mouser’s expanded Global Distribution Center. Source: https:// youtu.be/ FDCS9qSLVpY We have also noticed a lot more products in stock these days; it’s almost back to the pre-COVID situation. We met several of the Mouser customer service staff who work at the Melbourne Customer Service Centre. Their general message is that they are now able to provide a local presence in the same time zone, language and currency. Previously, the alternative would have been to contact someone in Asia, a few hours behind our time zone. There was no mention that any local stock would be held, but Mouser’s shipping options are generally quite fast, even with most products coming from the USA. Mouser Electronics was founded (as Western Components) 60 years ago, in 1964, by Jerry Mouser. He sold electronic equipment and parts to students in California before moving the company to Mansfield, Texas in 1986. Mark was keen to point out that Mouser is still supplying parts at small-to-medium volume for design, research and development. Mouser continues to focus on engaging with students, makers and engineers. Much of the presentation included the typical slideshows and spreadsheets, but there were some interesting insights. Nearly half of Mouser’s sales in Australia and New Zealand for the last few years has consisted of semiconductors, including devices like embedded hardware and sensors. Facility expansions Mouser Electronics has greatly grown their inventory in the last few The presentation The main presentation at the event was from Senior Vice President Mark Burr-Lonnon. He is originally from the UK, but has spent over 20 years in Texas in the USA, where Mouser Electronics is based. His accent is remarkably like that of an Australian. Mark provided some background on Mouser and its sister and parent companies. Mouser Electronics is a subsidiary of the Berkshire Hathaway group, and Mark joked that he is only a few rungs down the ladder from Warren Buffett! Mouser’s sister company, Braemac, is an Australian-based components distributor. It also has offices in the same location in Notting Hill. siliconchip.com.au A slide showing the hierarchy of staff in Mouser’s new Melbourne office. Australia's electronics magazine October 2024  107 Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Mouser’s part inventory peaked in late 2023 at over two billion items (blue bars). The red bars indicate products they had on order at the time. years; that is good evidence that the parts shortages of recent times have mostly subsided. Mark noted that they will continue to increase their inventory, anticipating that the demand for electronic components will continue to increase in the near future. Another slide highlighted just how many unique products Mouser has in stock from many well-known suppliers. We counted over thirty suppliers in this list, including names like Microchip Technology, Texas Instruments, Analog Devices, Vishay and Renesas Electronics. Mouser states that they currently have nearly 1.1 million different parts in stock. Mark also discussed Mouser’s ongoing expansion of its headquarters and distribution centre with modern automation technology, including the AutoStore robotic picking system. The distribution centre has nearly doubled in size. It can be seen at in the video at https://youtu.be/ FDCS9qSLVpY The Mouser AutoStore installation has 225,000 bin locations served by 119 robots, and the robots can do both restocking and picking. You can see a YouTube video of the AutoStore robots and system at https://youtu.be/ mQU2BVrnuH4 Another point that was mentioned was their measures against counterfeit components. Mouser wants to ensure that they only sell authentic parts. 108 Silicon Chip Our interview with Mark BurrLonnon in the October 2022 issue (https://siliconchip.au/Article/15514) also covered the accreditation and certifications that Mouser has earned to fulfil those requirements. Networking One of the reasons we had heard for choosing Melbourne for Mouser’s Australian office was the thriving tech community and manufacturing base, including manufacturers and related services. After the main presentation, there was another opportunity to network with other attendees. We spoke to representatives of a few different companies. It was interesting to hear of the diverse engineering and manufacturing companies operating in Melbourne that use Mouser products. Conclusion We are finally seeing a return of in-person events in place of the virtual events that have been occurring over the last few years. We were glad to meet the Australian Mouser team in Melbourne, as well as catch up with some other familiar faces. It’s promising for the electronics industry that Mouser Electronics is taking the opportunity to expand its inventory, operations and distribution centre. We look forward to see what they plan to do next. SC Australia's electronics magazine Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 siliconchip.com.au 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 Is it OK to use a higher voltage capacitor? This is probably a dumb question, but can I use a 10μF 50V non-­polarised capacitor in place of a 10μF 16V capacitor for the Mk2 Bench Supply? (B. P., Scottsdale, Tas) ● Yes, that will work. You can almost always safely use a capacitor with a higher voltage rating than the one specified. The voltage rating is simply the highest voltage that the capacitor can be safely charged up to. You can also use a non-polarised capacitor when a polarised capacitor is specified, although they are usually larger and more expensive. Query on Australian manufacturing On page 42 of the August 2024 issue, at the top of the page, there is a photo of two men next to a panel van. The bloke in white overalls is named as Ian Hyde. Would he be the same Ian Hyde that designed and built the Tara Systems Australia telephone and radio access equipment for two-way radios in the 1980s? I used and installed the Tara 2020 unit in the local fleet of taxis in Gunnedah, NSW. It was a brilliant and very reliable unit that was in service for 18 years non-stop. I believe Ian Hyde is now retired and living in Bateau Bay, on the NSW Central Coast. (P. H., Gunnedah, NSW) ● Kevin Poulter replies: I believe you are correct. Ian’s email address is in one of my mothballed old computers, so I would need to resuscitate it to confirm. He certainly was a leading identity at Pye and it’s great that the system lasted so long. Another well-known person from Pye Telecommunications is Angus Dawes, from the Export department. He wrote a significant amount about Pye in the 1950s onward and worked together with Ian Hyde at the 1956 Olympics, providing services like radio-telephone connection between siliconchip.com.au the Royal Yacht Britannia and Prince Philip. They worked from a ‘dream’ location in the MCG, a tech room with the best view of the Olympics, plus the essential bar fridge! ESP32 board profile changes break code I have purchased an ESP32-CAM module (February 2024; siliconchip. au/Article/16129) and also the WiFi BackPack kit (April 2024; siliconchip. au/Article/16212). I am trying to get the camera module to function first with your software that I have downloaded from the website. I opened the sketch in the Arduino IDE and downloaded the ESP32 board profile from Espressif for the AI Thinker. I have confirmed connection with COM4 and the correct baud rate for the CP2102 serial device as described in the article. The buttons are set up as Fig.2 in the article. I tried to upload the sketch several times and keep getting these error codes: app_httpd.cpp: In function ‘void setupLedFlash(int)’: error: ‘ledcSetup’ was not declared in this scope; did you mean ‘ledc_stop’? error: ‘ledcAttachPin’ was not declared in this scope; did you mean ‘ledcAttach’? It doesn’t seem to be able to complete the upload to get the camera to a point where I can log in to it. Maybe there is a simple step between this and doing that I am missing. Can you offer any assistance to get me back on track with this project? (G. W., Wellington, New Zealand) ● This is almost certainly due to a ‘breaking’ version change of the ESP32 board profile. We used version 2.0.13 of the board profile (as noted on p66 of the review article), while the latest version (at the time of writing this) is 3.0.4. According to the Releases page Australia's electronics magazine (https://github.com/espressif/arduino-­ esp32/releases), there are several changes between V2 and V3 that will break existing code; see siliconchip. au/link/ac0x That page notes that the ledcSetup API has been removed, which would explain the errors you got. The quickest and simplest fix is to change to using version 2.0.13 of the ESP32 board profile in the Arduino IDE. The Arduino Boards Manager has an option to install a specific version. There should be a drop-down menu with a list of available versions. While you try that, we will see if it is possible to update the ESP32-CAM BackPack software to suit the latest board profile. Miniature oscilloscope wanted I have been reading through old copies of R&H, RTV&H and EA. I came across a pen-sized oscilloscope (the OsziFOX) on page 84 of Electronics Australia, August 1999. Has Silicon Chip ever designed something like that? While I accept the limitations, it seems a really handy tool. (J. R., Wellington, New Zealand) ● We have published a few handheld Test Tweezer type tools, but our Advanced Test Tweezers design from February & March 2023 (siliconchip. au/Series/396) is probably the closest to the OsziFOX as it has an oscilloscope mode. The Advanced Test Tweezers have a 128×64 pixel OLED screen and run from a 3V coin cell, making them considerably more capable than the OsziFOX. Having said that, the OsziFOX would have been incredible to have in 1999! Replacing a motorised pot with the Digital Pot I would like to retrofit the Ultra Low Noise Stereo Preamp (March & April 2019; siliconchip.au/Series/333) with the Digital Potentiometer (March October 2024  109 2023; siliconchip.au/Article/15693). I plan to: 1. Remove the motorised pot. 2. Remove the H-bridge and associated parts. 3. Omit the IR receiver from the digital pot board. 4. Supply the digital pot from the power connector on the preamp. 5. Wire the digital pot input, output and GND in place of the motorised pot. 6. Link the IR receiver on the preamp to pin 1 of JP1 on the digital pot. 7. Tie AN3 of IC5 on the preamp board high to ‘trick’ the PIC into thinking the motorised pot is at the end of its travel (for an ‘instant’ mute). Does this approach make sense? Should I use a resistor rather than a link to tie AN3 high? Do I need to feed it with a voltage lower than 5V, since it typically expects to see 0.4-0.5V depending on the current through the pot motor? I think the ACK and MUTE LEDs on the preamp will still make sense to the user since the two PICs will be decoding and responding to the same signal. The digital pot has 10dB gain. Do I need to somehow attenuate the signal to compensate? If so, where in the signal chain would be best to do this? It occurs to me that the PIC on the low noise preamp could be reprogrammed to drive the digital pot IC directly by repurposing the GPIO used to drive the H-bridge. But that would be considerable more work. (L. S., Kambah, ACT) ● What you propose seems good. It would be wise to connect AN3 of IC5 via a 1-10kW resistor to 5V rather than directly to limit the current and prevent the input going more than 0.3V above Vdd. It does not matter that the voltage is above the 0.4V expected from the motor current detection circuitry. The ACK and Mute LEDs would act as normal. We suggest you change the first op amp on the preamp board to be unity gain by removing the 2.2kW resistor to ground and replacing the feedback components with a wire link, given that the digital pot can provide gain. Your remark about rewriting the code for microcontroller IC5 makes sense. However, that would be a lot more work and code would also need to be converted from the newer PIC used in the Digital Pot, which can be a troublesome process. Given the 110 Silicon Chip relatively low cost of the chips, and the fact that the two projects have been tested separately, we think you should keep the two chips. How to program RPi without an OS I want to develop software that needs the exclusive use of a microcomputer like the Raspberry Pi; in other words, I would like to program it at the ‘bare metal’ level. My understanding of bare-metal development is that it demands much low-level groundwork to use a machine’s devices and peripherals. I was fortunate to stumble on Ultibo (https://ultibo.org), which provides a platform where much of the low-level foundation is provided. It allows the developer to relatively easily build a single, machine-dedicated application on top of that. However, I’m not sure how much support Ultibo receives. I suspect it has received no attention for the last two years. This is a concern if wanting to start a long-term development using the tool. Are you perhaps aware of any similar development platforms? (A. J., Mindarie, WA) ● We hadn’t heard of Ultibo but it is an interesting idea. According to its GitHub repository, there was activity as of two months ago (https://github. com/ultibohub/Core), although a lack of recent releases means the more recent (eg, Pi 5) boards may not be supported. It certainly would be a lot of work to program a Raspberry Pi from scratch. Still, underneath it is just an ARM processor, like so many microcontroller boards. We found one example showing a Pi 3 being used to run a ‘blink’ program on the bare metal (https://github.com/ dwelch67/raspberrypi). Of course, any microcontroller should be able to do that. It will really come down to what peripherals/features you need to use and why it needs exclusive access (eg, for security or real-time requirements). If we had such a need, we would investigate running the software on a ‘lite OS’, such as a console-only Linux distribution. Many operating systems provide a so-called ‘kiosk mode’ to allow single applications to run without allowing user access to the underlying system. Australia's electronics magazine Distributions like RetroPi (which turns the Pi into a dedicated game console emulator) could be another good starting point. For both of these, access to the peripherals would be much like that available on standard high level operating systems. You could also consider using an x86-based single-board computer, as there is plenty of x86 support available. We have published two projects using a Raspberry Pi with a dedicated application: the Raspberry Pi Tide Chart (July 2018; siliconchip.au/ Article/11142) and the Speech Synthesiser (July 2019; siliconchip.au/ Article/11703). Both are fairly secure in that the user inputs do not provide an easy way to access the underlying operating system. Is the Analog Clock beginner friendly? I haven’t really done any soldering before but I have invested in a decent soldering iron and I have a basic oscilloscope and DVM. As more-or-less a beginner to soldering, would I likely be successful in making the new GPS Analog Clock Driver using your SC6472 kit? (E. M., Hawthorn, Vic) ● As a beginner, you may find soldering IC3 and the USB socket (CON4) difficult. We strongly suggest you acquire a syringe of flux paste if you don’t have one, as it makes soldering those parts much easier. A fine-tipped soldering iron would help, along with some solder wick, to remove solder bridges. You could practice soldering the other components first before tackling those. So long as you are careful and can see the area for soldering well enough (a magnifying lens would help), it should be possible. Having said that, it is a bit difficult to predict whether this project is achievable for you. You could consider building the SMD Trainer kit (SC5260) first. Trying to compile older PIC C code I have used MPLAB X assembly language extensively but not the C language. I downloaded the source code for your High Visibility 6-Digit LED GPS continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR Lazer Security LEDsales DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz For Quality That Counts... WE OFFER KITS, LEDs, LED assemblies and all sorts of quality electronic components, through-hole and SMD, at very competitive prices. Check out the latest deals at www.lazer.com.au LEDS, BRAND NAME AND GENERIC LEDs, filament LEDs, LED drivers, heatsinks, power supplies, kits and modules, components, breadboards, hardware, magnets. Please visit www.ledsales.com.au Silicon Chip Kits (Oct24) Micromite Explore-40 Kit (SC6991, $35.00) Includes all required parts Dual Rail Load Protector hard-toget parts (SC7366, $35.00) Includes the PCB and all semiconductors; does not include the optional/variable components ZD3, ZD6, D4 and D5 Silicon Chip Binders H Each binder holds up to 12 issues Price: $21.50 plus postage For postage prices, see our website PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com WANTED PCB PRODUCTION Transistor Driver Transformer: Ferguson TRD223, Special Transformers ST4953 or A&R TD19. To repair an old 1960s amplifier. Call Andrew 0418-170-500 PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine October 2024  111 Advertising Index Altronics.................................35-38 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar............................. IFC, 59-62 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 PMD Way................................... 111 SC Ideal Bridge Rectifiers......... 108 Silicon Chip Back Issues......... 103 Silicon Chip Binders................ 111 Silicon Chip PDFs on USB......... 80 Silicon Chip Shop...................... 95 Silicon Chip Subscriptions........ 81 TME............................................. 11 The Loudspeaker Kit.com.......... 10 Wagner Electronics....................... 8 Notes and Errata Automatic LQ Meter, July 2024: a few constructors had problems with IC1 (OPA2677) oscillating, making it hot and causing excessive current to be drawn from the battery. Some have solved it by replacing diodes D1 & D2 with some from a different batch or by adding a 220Ω resistor in series with diode D1 (see Mailbag, September 2024, page 10). A better solution is to replace IC1 with an OPA2890 op amp. If you bought a kit and have this problem, contact us to request an OPA2890. Next Issue: the November 2024 issue is due on sale in newsagents by Monday, October 28th. Expect postal delivery of subscription copies in Australia between October 25th and November 13th. 112 Silicon Chip Clock (December 2015 & January 2016; siliconchip.au/Series/294) and set up MPLAB X v5.50 and the current XC32 compiler. It appears that Microchip no longer includes the plib.h, math.h and string.h headers with the compiler. Can you tell me what version of MPLAB and the XC32 compiler you used when you developed the clock? The code is in a folder called LED Clock.X, which suggests that the IDE was some version of MPLAB X. Starting with v5.35, it wanted to upgrade the file, so I worked backwards to v4.20 which didn’t. Having found those headers, I got a heap of other errors when I tried to compile the code. I think it might be better if I use the same version of the software you did originally. Some lines in the code that are particular problems are calls to assembler instructions such as: asm volatile (“eret”); There is a similar line with the “wait” instruction. Do I have to do something in Project Properties to get these lines to compile/assemble? The error message is: “C:\Program Files (x86)\ Microchip\xc32\v1.31\bin\ xc32-gcc.exe” -x c -c -mprocessor=32MX170F256B -ffunction-sections -mips16 -Os -fomit-frame-pointer -DSHOW_UTC_FEATURE=1 -MMD -MF build/default/production/ sleep.o.d -o build/default/ production/sleep.o sleep.c -DXPRJ_default=default -legacy-libc -mno-float -G2048 C:\Users\Gjc\AppData\Local\ Temp\cciHwjKm.s:133: Error: unrecognised opcode `wait’ (G. C., Mount Dandenong, Vic) ● You are right that they are no longer packaging those older libraries with XC32. This page on the Microchip website explains where to get plib.h and the other headers: siliconchip.au/ link/abyw It is now a separate download on the same page where you get the compiler. “math.h” and “string.h” are part of the standard C library, so we are surprised they are not included with the compiler. The above download may include them as well. The build logs in the software download package show that the Australia's electronics magazine compiler used was XC32 v1.31. It should be possible to get it to compile with the latest XC32 with some fiddling (basically downloading and installing headers), but you are right that it might be easier to go back to that earlier version. We wonder if the “unrecognised opcode” error is related to the -mips16 option. We suggest you try switching off the MIPS16 option for that file; you can do it in the IDE on a file-byfile basis. MIPS16 is a more compact instruction set, and we used it because the code wouldn’t fit into the available flash memory otherwise. However, it doesn’t seem to include the wait or eret instructions; those appear to be part of MIPS32 only. We suspect the compiler used to detect that and switch to MIPS32 mode to execute those instructions, but it may no longer do that. The strange thing is that the code obviously compiled for us back in 2015, even though we were using the same version of XC32 (v1.31) as you. Perhaps it has something to do with the IDE providing the compiler with a different set of option flags. Without the MIPS16 flag, the compiled objects will likely be a little larger, but we don’t think they all need to be MIPS16 for the software to fit in the chip. So you might be able to get away with switching just those problem files back to MIPS32 mode. Information wanted on EA project I am looking for the original article for the Xenon Strobe Timing Light project that used a Dolphin torch for the reflector and housing. I built one when I was younger. It was published approximately between 1980 and 1982; I seem to remember it was either in the Electronics Australia or ETI magazine. Looking through EA issues between 1979 and 1982, I found the Digital Tacho/Dwell meter and the Transistor-­ Assisted Ignition projects that I built around the same time, but not the Strobe. (S. R., via email) ● The only project we can find in EA or ETI that used a Xenon flash tube in a Dolphin torch reflector is the Digital Strobe project in EA, March 1986 (starting on page 42). However, it is a strobe and not a timing light, as it isn’t triggered by an ignition system. 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