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NOVEMBER 2024 ISSN 1030-2662 11 9 771030 266001 The VERY BEST DIY Projects! $1300* NZ $1390 INC GST INC GST FlexIIDIce Flex Dice up to 100 Random cards heads or tails 1.5kW Speed Controller for single and three-phase induction motors Surf Sound Simulator siliconchip.com.au Australia's electronics magazine November 2024  1 3D PRINTER HOT OFFERS MARK YOUR CALENDAR: Wed 30th Oct to Tue 31st of Dec, 2024 ONLY 249 $ ONLY 739 $ HOT OFFER HOT OFFER PRINTS UP TO 220 X 220 X 250MM PRINTS UP TO 220 X 220 X 250MM ULTRA FAST PRINTING SPEED UP TO 600MM/S PRINTING SPEED UP TO 250MM/S SUPPORTS CARBON FIBRE FILAMENTS BEGINNER FRIENDLY CHAMPION OF SPEED & SKILLS TL4751 TL4761 K1C Ender V3 SE $ ONLY 389 ONLINE ONLY ONLY 1169 $ HOT OFFER HOT OFFER PRINTS UP TO 220 X 220 X 240MM HUGE PRINTS UP TO 300 X 300 X 300MM FAST PRINTING SPEED UP TO 500MM/S ULTRA FAST PRINTING SPEED UP TO 600MM/S ADVANCED AI-ASSISTED FEATURES Ender V3 KE K1 MAX TL4753 $ FROM 1699 TL4762 ONLINE ONLY HOT OFFER 22W & 40W Falcon 2 Pro Laser Engravers TL4802 / TL4804 $ TL4802 ONLY 219 HOT OFFER UW-03 Wash & Cure Machine TL4417 3D PRINTING? 3D PRINTING HOT OFFERS LOVE SEE ONLINE OR IN-STORE Contents Vol.37, No.11 November 2024 14 Nikola Tesla, Part 2 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 42 Precision Electronics, Part 1 This series covers the basics of precision electronics design, with a range of topics from precision op amps to temperature drift and noise. We aim to cover these from a practical perspective, rather than just the theory. By Andrew Levido Electronic design Precision Electronics Part 1 – Page 42 Nikola Tesla the original ‘mad scientist’ Part 2 Page 14 78 0.91-inch OLED Screen These small monochrome OLED modules have a 128 x 32 pixel display and typically use an SH1106 or SSD1306 drive controller IC. Because they use an I2C serial interface they are easy to drive with a microcontroller. By Jim Rowe Using electronic modules 90 Maxwell’s Equations Michael Faraday and James Maxwell helped to define the most basic equations upon which a lot of electronics theory rests. We give some background, explain what the equations mean and why they’re useful. By Brandon Speedie Electronics theory 2 Editorial Viewpoint 5 Mailbag 41 Subscriptions 59 Jaycar Mini Projects 76 Circuit Notebook 95 Online Shop 96 Serviceman’s Log The FlexiDice can display a 100-sided die, but it’s not just restricted to dice. It can also randomly pick a card face from a standard 52-card deck or even perform a simple coin toss. By Tim Blythman Game project 103 Vintage Radio 108 Ask Silicon Chip 82 3D Printer Filament Dryer, Part 2 111 Market Centre Store up to four 1kg reels of 3D printer filament, while keeping it warm and free of moisture using our Filament Dryer. The filament is drawn straight out of the sealed box making it easy to keep jobs going. By Phil Prosser 3D printer accessory 112 Advertising Index 112 Notes & Errata 24 Variable Speed Drive Mk2, Part 1 Our new Variable Speed Drive is smaller, cooler & more efficient. It can drive single-phase shaded pole or permanent split capacitor (PSC) induction motors, as well as three-phase 230V induction motors, both up to 1.5kW. By Andrew Levido Motor speed control project 48 Surf Sound Simulator Enjoy the sound of the beach from the comfort of your home. The Surf Sound Simulator is a fun project on a colourful surfboard-shaped PCB that is perfect for beginners or experienced constructors, using all through-hole parts. By John Clarke Audio relaxation project 66 FlexiDice 1. Analog pace clock & stopwatch 2. Digital spirit level 1. Tunnel timer using a 555 2. Simple negative rail generation 3. Model train rail blockage detector Revisting the Zenith Royal 500 by Ian Batty SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff 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 The hydraulic analogy is valuable for beginners Recently, I came across someone who was new to electronics, explaining that they were having a lot of trouble understanding how even simple circuits work. It reminded me of how helpful I found the hydraulic analogy when I was first learning electronics. Many readers will be familiar with this, and some will also recognise how all sorts of other physical systems (involving heat transfer, mechanical energy, spring oscillation and more) can be modelled similarly to electronic circuits. This analogy involves thinking about an electronic circuit like a series of water pipes instead of wires. The flow of water is equivalent to the flow of electrons, with the volume of water that flows being equivalent to current and the pressure of water at a given point (or, more accurately, pressure difference between two points) being similar to the voltage in an electronic circuit. The equivalent for resistors are skinny pipes; the smaller the diameter of a pipe, the more it resists the flow of water, the greater the pressure (voltage) drop through that pipe, and the more restrictive it is to current flow. Just like with electrical conductors, the smaller the cross-sectional area of a pipe, the higher its ‘resistance’. A power supply can be considered like a pump, or alternatively, water being delivered by a reservoir at a higher level. In either case, the source provides both water pressure and flow. Capacitors are modelled as rubber bladders. As the pressure (‘voltage’) increases, the bladder expands and stores more water (‘charge’). When the pressure drops, the bladder shrinks and pushes water out, briefly sustaining the pressure as it does so. Inductors are equivalent to a turbine in the water flow, with a higher inductance being equivalent to a turbine with more mass (inertia). As water (‘current’) flows through the turbine, it spins up at a rate determined by the pressure differential across it. If the source pressure (‘voltage’) drops, the turbine continues to spin and force water (‘current’) through the outlet. Diodes are easy to model: they are simply one-way valves. The equivalents to transistors are valves that can open or close partially to restrict (or not) the flow of water. A Mosfet equivalent would be controlled by the pressure in a second pipe; you could imagine this second pipe joining the main one, except that there is a rubber diaphragm between them. As the pressure in this second pipe varies relative to the first, the diaphragm flexes and actuates the valve to control the flow of water. A bipolar transistor would be modelled similarly, except that the second pipe would actually have a one-way valve opening into the main one, allowing a small water current to flow. That current flow would impinge upon a flap that controls the opening of the valve, opening it more as the flow through that small valve increases. There are real hydraulic devices that operate like that, called ‘hydraulic servos’, although they are actually closer in behaviour to op amps (another useful analogy!). Other components can be modelled too (zener diodes, Triacs, logic gates etc). These are not necessarily perfect analogies, although I think a hydraulic system could be built that operated pretty similarly to an electronic circuit. The point, though, is that this analogy makes it a lot easier to visualise what the electrons are doing in a circuit, at least until you have more experience with electronics and the understanding comes more naturally. 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”. PicoMSA doesn’t work with all Picos Thanks for publishing my Pico Mixed-Signal Analyser (PicoMSA) project article in the September 2024 issue (siliconchip.au/Article/16575). It has come to my attention that some Raspberry Pi Pico microcontroller modules don’t run reliably for long periods at 240MHz, resulting in “Capture failed” errors in PulseView even at quite modest capture rates. New firmware is available to download at siliconchip. au/Shop/6/452 which runs the Pico at 200MHz and should ameliorate the problem. Trying to capture data at 240MHz in PulseView will cause a legitimate capture error with this new binary. Also, please see the Notes & Errata in this issue (page 112) regarding a small error on the PCB that can be fixed with a wire link. Richard Palmer, Murrumbeena, Vic Photovoltaic solar panel degradation and more Recently, I gave my home solar array a clean, as I do once in a while. While cleaning, I found a couple of suspect cells, so had the panels replaced. See attached photo of one – it was clearly undergoing temperature stress. Having seen the underside, I decided to go over the panels with a laser thermometer one afternoon. I found a few other cells that measured quite high temperatures (eg, 80°C when the others are more like 50°C), so these are clearly on the way out too. On removing them, some showed signs of stress underneath as well. No damage was visible to any on the front side; there were no marks on the polycarbonate cover sheets. The visible cracks are in the cell itself. I hadn’t noticed any significant drop in generated power; however, it’s difficult to tell since it varies so much, all the time. The moral of the story – check your panels! Concerning Neutral vs Earth in domestic mains wiring, in the USA they use black for Active and white for Neutral. I always do a double-take when I’m mentally tracing out the wiring of an American product; you really need to pay attention to it. The story given is a classic example of why electricians are obliged to upgrade any part they work on to the current standard. Regarding the letter on “Soldering SMDs not as difficult as first thought”, I completely agree. I was a bit apprehensive about it also, but it’s really not as hard as you might expect. The hardest part is that first connection; many parts are so small that if you breathe too heavily, they’re gone! The first connection anchors the part to the board. For inspection, I use a lens I took out of a Holden ‘projector’ car headlight. It works like a charm, and it was free. siliconchip.com.au On smartphones supposedly listening to conversations, I can see why advertisers might like knowing what you’re searching for (and talking about), but I hate it with a passion (big brother and all that). Whenever I get one of those “Allow App to track your history” prompts, I always give them a resounding “no!”. While writing this, I thought there’s probably a phone setting that allows you to stop it tracking entirely, and found one. On my iOS phone, it’s in Settings → Privacy and Security → Tracking. I know this won’t stop my phone listening to me, and in fact may not even stop it tracking, but at least It’s something. I did try DuckDuckGo for searching for a while but found its results pretty useless. Regarding nuclear power, I agree with Phil Denniss. Nuclear power will take too long and cost too much to help Australia’s cause in reducing carbon emissions by 2040. In my opinion, the Liberals want it just to be seen as different from Labor, and if they get in, it won’t be long before it gets canned. 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Portable powerful and easy to use. ArcDroid™ brings CNC plasma to your garage or workshop. ArcDroid™ combined with our custom operating system with Simple Trace™ can accurately reproduce your designs delivering fast, accurate and repeatable parts from your plasma cutte. 4,125 (P8990) $ SAVE $220 NOW OPEN SYDNEY BRISBANE MELBOURNE (03) 9212 4422 (08) 9373 9999 PERTH ADELAIDE 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains 4 Abbotts Rd, Dandenong 11 Valentine St, Kewdale Unit 11/20 Cheltenham Pde Woodville SA 5011 (02) 9890 9111 (07) 3715 2200 (08) 9373 9969 09_SC_281024 Specifications & Prices are subject to change without notification. All prices include GST and valid until 30-11-24 policies presented to send a message of what you want and don’t want. D.T., Sylvania, NSW. Switching Ethernet and the dangers of repairing UPSs The magazine is amazing. I saw the reply to my network query from Brett Neale (Mailbag, September 2024), titled “An easy way to switch Ethernet on and off”. My son tends to forget his cutoff times. When I pull his network connection from the router, he simply waits until I am in bed and plugs it back in. The parental options in the router’s firmware are confusing and don’t seem to control what I want it to. The idea of simply using a plug-in timer to cut the supply to the router is interesting, but my son is smart enough to bypass that! He would also know to find another plugpack with the same voltage and use it if I removed the plugpack and took it to bed. So I had to get sneaky! I found that I don’t have to switch every conductor in the network cable as the network only uses four conductors. If I cut just one, the connection will no longer work. So I did that with a simple relay timer from Jaycar. When the timer switches off the relay, it interrupts the connection to the white/orange striped wire (TX+). The timer is inside a Jiffy box hardwired into its plugpack, both of which are hidden behind the couch. If he goes looking and pulls the plugpack out of the mains socket, nothing changes as the timer needs power to energise the relay. It has been working perfectly now for nearly a month, and he has no idea what I have done. Yes, it is a bit of a pain if I have to reprogram the timer, but at least he is getting offline when he is supposed to. Thanks for the help! On another matter, I recently repaired a UPS (uninterruptible power supply) after a friend gave himself a nasty shock! Please reiterate to all your readers that solar inverters with battery backup, UPS units and many other off-grid generating systems can supply more than enough current and voltage to be lethal. Make sure you isolate the equipment from its mains supply and disconnect any and all batteries connected to the inverter circuitry. Doing that could save your life! Dave Sargent, Maryborough, Qld. Nikola Tesla, magnetic flux density and the ZC1 MkII Regarding the recent article about Nikola Tesla, the SI unit for magnetic flux is not named after Tesla; the SI units of magnetic flux are Webers. It is the unit of flux density that is the Tesla (one Tesla is one Weber per square meter). Also, the article suggested he was not big on mathematics or quantitative theory. There are a couple of reasons I don’t think that is really the case. One is that Tesla’s designs were clearly not the result of cut and try experimentation, more typical of Edison. He demonstrated a much higher level of analysis, specifically AC theory. Then there was a remark he once made about Edison. He said, “an ounce of theory would have saved him a pound of hard work”. I get the impression there is a lot of inaccurate stuff about Mr. Tesla on the web. Before the internet was a thing, I read quite a lot about his inventions and his life. Sometimes I wonder if people try to rewrite history. Note that the Tesla as a unit of flux density is much more 8 Silicon Chip useful than Webers as a unit of magnetic flux. When transformers and other electromagnetic devices are designed with magnetic cores, it is the maximum flux density that is of main interest. The flux density relates to the B magnetic field that represents the result of the magnetising force of the H field. When this field acts on the magnetic material of some permeability μ, the formula is B = μH. The B field (unlike the H field) includes the contribution of the magnetic material. If the magnetising force is too high, the material gets pushed too far up the B-H magnetisation curve and it flattens out. The incremental permeability drops, as does the inductance. When designing line power transformers and similar low-frequency iron core transformers, there is a very useful rule of thumb: keep the maximum flux density of the core below one Tesla. The formula to check the maximum Tesla value applied to the core is very simple. It is the applied RMS voltage of the sinewave to the primary, divided by (4.44 × f × A × N), where f is the frequency, A is the core cross-sectional area in square meters and N is the number of turns on the primary winding. I once had a transformer company make a line power transformer for me. I asked the designer what the maximum core flux density was, and he said, “I don’t know, the design software did it, I’ll look it up in the file”. Things are done differently now, and some people forget the basics; they are used to computer assistance. Also, thanks for publishing my Vintage Radio article on the NZ-made ZC1 MkII Communications Receiver in the October issue. Something amusing happened in the text that I didn’t notice until after it was published. Where I was talking about a brown paper “tube” in the NZ made capacitors and the electrical insulating “tube” I used on the power connector, the word “tube” got changed to “valve” in both cases. I think it must have been some global word replacement selected to change the word “tube” to “valve” because most Australians call them valves, while Americans call them “tubes”. Dr Hugo Holden, Buddina, Qld. Comment: you are right that the search-and-replace of “tube” to “valve” caused some problems. Oops – several people read it but all missed that somehow. The future of TV in Australia & NZ The following table, taken from https://w.wiki/BKtP, shows what Australian television stations are currently transmitting. LCN is the logical channel number, which is what you press on your remote control. 7 Regional has done the best job, with complete conversion to MPEG-4 transmission of all programs, as well as the most HD channels. This is because they have no simulcasts, so all receivers are MPEG-4 compatible. Lowlights include the ABC, which hasn’t changed anything. Also, Imparja and Southern Cross Austereo in remote Australia retransmit metro HD primary program in SD only. It costs more to downgrade the HD programs to SD, which cost the same to distribute and transmit. Southern Cross Austereo have now put their TV networks up for sale. Network 10 programming in Mildura and WA regional have been running at a loss, so the 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. 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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 Mildura transmitter has been switched off and the WA joint venture has been subsidised by the Commonwealth Government. The primary programs of each commercial network in the northern and southern footprints are in standard definition only. There are additional regional commercial news bulletins for eastern states, Aboriginal and religious broadcasters in SD. New Zealand has eight HD network programs from three transmitters per site, which have four SD delayed repeats of HD programs. A visit to retailers will show all large-screen TVs are UHD1 (4K) or, even better, UHD 2 (8K). These receivers are compatible with all older Australian TV standards, but currently no broadcaster has any 4K programs. I have checked the specifications of most of these TVs and they have HEVC decompressors. The recent Paris Olympic Games was transmitted in super-sharp UHD with surround sound in France (covering 70% of the population) and Spain (100%) on free-to-air terrestrial using DVB-T2 with HEVC compression. Netflix uses HEVC video compression and the newest xHE AAC sound compression for their UHD customers in Australia. As a result, nearly all new TVs contain HEVC decompression and xHE AAC sound decompression. A survey of manufacturers’ specifications reveals that many do not specify if their TV can receive DVB-T2 signals. The latest VAST satellite receivers are capable of UHD reception. There are lots of large-screen UHD TVs in retailers, but currently only streaming services can really take advantage of their high image quality. We need upgraded AS4933:2015 and AS4599:2015 standards so we can watch the 2032 Brisbane Olympic Games in UHD with surround sound anywhere in Australia! The broadcasters need to fight back against the streamers by broadcasting UHD programs and HD programs. Current broadcast TV looks blurry on such large screens. The greedy telcos have been pressuring the government to get broadcasters to share fewer TV channels by converting to DVB-T2 so they can make more money streaming TV to phones and tablets. Their screens are too small to LCN HD MPEG4 HE AAC SD Unique MPEG4 HE AAC SD Simulcast MPEG2 MP1 Level 2 SD Unique MPEG2 MP1 Level 2 Paramount Metro 1x 2 3 1 1 Central DTV Rem Est, NT, SA 1x 1 0 0 2 Darwin DTV Darwin 1x 1 0 1 2 ABC National 2x 1 0 1 3 SBS National 3x 4 2 2 0 C44 Adelaide 44 0 0 0 1 C31 Melbourne 44 0 0 0 1 Region Various Darwin 4x 1 2 0 1 Goolarri Broome 4x 1 0 1 1 Juluwarlu Roebourne 4x 0 0 0 1 SCA regional East mainland 5x 1 5 1 2 SG/BH 5x 1 3 1 2 Tas/SG/BH 6x 1 4 or 5 1 1 or 0 Darwin 7x 1 7 1 0 Central 7x 1 0 0 2 SG/BH 8x 1 1 1 2 West DTV Reg/rem WA 5x 1 0 0 3 Tas DTV Tasmania 5x 1 3 1 0 6x, 7x 4 3 0 0 NSW/Vic 6x 3 3 1 1 WA 6x 2 3 0 0 7x 3 3 1 1 8x 3 3 1 0 WA 8x 1 4 1* 0 NBN Newcastle 8x 3 0 3 2 Nine Metro 9x 3 0 3 3 9x 1 0 0 2 7 Regional Qld Seven Metro WIN East & East SA, Tas Imparja Remote East/ Central * unnecessary SD simulcast in MPEG-4 when all receivers are HD capable. 10 Silicon Chip Australia's electronics magazine siliconchip.com.au Do you need an easy way to connect your HDMI sources to a second TV in the house? 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The existing components are freely available for manufacturers to make set-top boxes for those who have not bought a compatible TV. Adding DVB-T2 to new TVs is an insignificant cost because it is used extensively overseas. The announcement of a switchover date is a target for importers, retailers, broadcasters and Standards Australia, which will drive down receiver prices and the import of set-top boxes for incompatible receivers. The Brisbane Olympics in 2032 would be a good target. Alan Hughes, Hamersley, WA. Bad solder joints can be hard to see With the help of his highly intelligent daughter Emily, what they discover will lead them into a web of drama and intrigue, danger and distrust. When the co-workers are charged with their superior’s murder, Time Warp Tommy must explain the science to the judges in order to save their lives. But time is running out. This email was originally going to be asking for help with problems I had with the calibration of a Pico Audio Analyser (November 2023; siliconchip.au/Article/16011) that I built yesterday. I wasn’t getting any output at all while doing the 500mV output calibration. Continuity and component placements checked out OK, but voltage checks showed no 1.65V rail. Before sending a help email, I borrowed a USB microscope and checked all soldered connections. It turns out I had not soldered pin 8 of IC1, but when checking continuity and voltage on pin 8, I was pushing the pin down onto the solder pad, leading to an assumption that all connections were OK. After soldering pin 8, a 497mV AC signal appeared on the output. I have assembled my unit with an external fuse and 18650 cell holder. Dave Cole, Rotorua, New Zealand. Comment: it’s good to hear that you got it going. We have certainly run into the same scenario, where nothing works except when you apply pressure with the test lead, which temporarily fixes the faulty solder joint. In fact, just a few days ago we built a prototype device that wasn’t working, which initially puzzled us. Touching an oscilloscope probe to the top of the ground pin on one of the many ICs, we noticed the trace was noisy and not quite sitting at 0V. Very close inspection of the joint showed that solder had flowed onto the pin but had not adhered to the pad, likely because it was on a ground plane. We had to add flux to that pin and heat it quite a bit before the solder would finally adhere to the pad, and the device suddenly sprang into life! Besides having to fix that joint, the whole device worked on the first attempt. The external 18650 cell holder looks like a simple way to get some extra runtime. Beware! The Loop has many twists and turns, facts and figures that inspires your imagination. Electricity saver scams just won’t go away “Beware! The Loop”, a book by Jim Sinclair on the what-if time travel was possible Tom Marsden, aka “Time Warp Tommy”, is asked to investigate the circumstances surrounding the disappearance of a military scientist experimenting with time travel in a small country in the middle of Asia. What he finds will shock you! Time Warp Tommy is asked to explain how the world’s greatest expert on time travel has built a time machine, climbed into it and disappeared into a grey haze. With only two co-workers left behind and a pile of hand-written notes and diagrams, Time Warp Tommy must devise a way in which the experiment can be safely ended. Purchase it for just $5.50: https://moonglowpublishing. com.au/store/p48/bewarethe-loop-jim-sinclair Beware! The Loop is available as an EPUB, MOBI and PDF RRP $5.50 | available as an EPUB, MOBI and PDF 12 Silicon Chip E-ISBN 9780645945669 It appears that this scam is still going with yet another different energy-saving device that makes a claim that’s too good to be true. I don’t know how they can get away with this sort of advertising: https://blog.nativediscount.com/ smart-energy-ai-usd-2 Bruce Pierson, Dundathu, Qld. Comment: these scam products will likely stay around as long as uninformed people are easily duped into buying them. SC Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine November 2024  13 1856–1943 Nikola Tesla the original ‘mad scientist’ L ast month, our final entry concerned Tesla’s application for multiple radio patents in 1897 and some of the controversy surrounding his claims predating some of Marconi’s, despite Tesla not having demonstrated any real radio communications. Here is what happened after that: Ignition system for gasoline engines 1898 In 1898, Tesla obtained US Patent 690,250 for a spark plug for petrol engines – see Fig.14. Teleautomatics 1898 The first article in this two-part series, published last month, introduced prolific inventor Nikola Tesla and covered his life and developments until 1898 before we ran out of space. This article picks up where that one left off and also covers some overarching topics, like his contributions to AC electricity and some of his misconceptions. Part 2 by Dr David Maddison, VK3DSM 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 14 Silicon Chip Australia's electronics magazine Tesla received US Patent 613,809 for a remote-controlled vehicle in 1898 (Fig.15), titled “Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles”. Based on this, he demonstrated a remote-controlled 1m-long boat at Madison Square Garden in New York City as part of the first annual Electrical Exhibition. The boat was controlled by an operator with a transmitter (see Fig.16). The receiver used a device called a coherer, an early type of radio signal detector containing metal filings that came into contact with each other when a radio signal was received, changing its resistance. Once a signal was received, the device had to be reset by shaking it or using a ‘clapper’ attached to an electromagnet. Such a device could only detect the presence or absence of a signal, like in Morse code; such a binary output was ideal for this application. One of Tesla’s inventions was a coherer that continuously rotated to reset it, although he does not use the term “coherer”. The boat contained a motor for propulsion and one for a servo mechanism. The boat could steer, start, stop, go forwards or backwards or light one of two lamps. To control the boat, there was a mechanism that, upon detecting the radio signal, moved a set of electrical contacts to the next of several positions that would execute the predefined manoeuvre. This represented the state of the rudder, motor and lighting. Radio signals from Mars 1899 Tesla believed that radio signals he received in 1899 in Colorado may have been from Mars (see Fig.17). In 1909, he wrote: To be sure, we have no absolute siliconchip.com.au proof that Mars is inhabited... Personally, I base my faith on the feeble planetary electrical disturbances which I discovered in the summer of 1899, and which, according to my investigations, could not have originated from the sun, the moon, or Venus. Further study since has satisfied me they must have emanated from Mars – siliconchip.au/link/aby4 Some have suggested that the signals Tesla was receiving were, in fact, from Marconi’s (or others’) radio experiments. Fig.14: Tesla’s ignition system for petrol engines. Source: https:// patents.google. com/patent/ US609250A Tesla Experimental Station 1899 to 1900 In 1899, Tesla established the Tesla Experimental Station in Colorado Springs, Colorado, and used it for one year. He moved there because he wanted a high altitude for his experiments in wireless electricity transmission and more space than his Manhattan laboratory. His main focus was on high-frequency, high-voltage experiments. He built the largest Tesla coil to date, with a diameter of 15m, to be configured as a “magnifying transmitter”. This was a variation of the Tesla coil with an antenna (see Fig.18) tuned to the supposed resonant frequency of the Earth to create standing waves of electrical energy. The idea was to harvest them with an appropriate antenna and receiver. The magnifying transmitter was a three-coil, triple-resonant design. This coil reportedly had a 300kW power rating and generated millions of volts at 150kHz. This was to be the prototype for his magnifying transmitter at the Wardenclyffe Tower. Tesla produced electric arc discharges up to 41m long. He had a deal with the local power company to provide large or unlimited amounts of power (he occasionally damaged their generators!). Tesla wrote that he had produced 20MV at 1000-1100A (we assume that was current drawn from the mains supply) and that he had learned how to produce 100MV (see p196, siliconchip.au/aby0). Tesla also wrote that lightning arrestors on buildings within a 19 km radius were “bridged with continuous arcs” and that he lit handheld incandescent lights 15-30m from his laboratory when the oscillator was running at 4MV. Apparently, the light filament often broke due to the resulting vibrations. siliconchip.com.au Fig.15: a remote-controlled boat described by Tesla’s US Patent 613,809 (top: plan view, bottom: the vessel in the water). Fig.16: a model of Tesla’s boat in the Nikola Tesla Museum in Belgrade. The museum website (https://tesla-museum.org/en/ qr-en/exhibit-049) gives no information about when the model was made, but clear acrylic wasn’t invented until the 1930s. Source: https://w.wiki/AbUv Fig.17: a newspaper article titled “Nicola Tesla Promises Communication with Mars” from The Times (Richmond, Virginia, USA) on January 13th, 1901, page 8. Source: The Times, January 13th 1901 – siliconchip.au/link/abyo Australia's electronics magazine November 2024  15 Fig.18: an exterior view of the Colorado Springs laboratory. The antenna mast was telescopic and 43m tall. Source: https://w.wiki/AbUx Fig.19: Tesla’s “magnifying transmitter” at his Colorado Springs facility, around 1899. This photo was a long-exposure photo taken in a darkened room with a double exposure showing Tesla sitting on a chair. Source: https://w.wiki/AbUw 16 Silicon Chip Tesla stated that when he energised the large transmitter coil, butterflies were caught in the field and flew around in circles as if trapped in a hurricane. He also noted sparks in the sand when walking “some distance from the building”, saying: At night a continuous stream of tiny sparks could be seen between the heels and the earth and between the grains of sand. When I operated with undamped waves, the oscillator being perfectly silent (no streamers whatever), a horse at a distance of perhaps one-half a mile, would become scared and gallop away the instant the switch was thrown on... When using damped waves the roar was so strong that it could be plainly heard ten miles away. Fig.19 was a long-exposure photo taken in a darkened room. The arcs are for demonstration purposes, deliberately induced and were not a normal part of the operation of this machine. The discharge was reported to be deafening and that “sparks an inch long can be drawn from a water main at a distance of three hundred feet from the laboratory”. The laboratory was torn down in 1904, and the contents were sold to pay off debts. Energy harvesting 1901 In 1901, Tesla was granted US Patent 685,957 for supposedly harvesting energy from sources such as Australia's electronics magazine “ultra-­violet light, cathodic, Roentgen rays, or the like”. Wardenclyffe Tower 1901 to 1906 Wardenclyffe was Tesla’s last major laboratory (see Figs.20 & 21). It was built in Long Island, New York and was intended for trans-Atlantic wireless communications. Later, he wished to extend it for wireless power transmission in accordance with his theories. Banker JP Morgan was the main financial backer for this project, but he refused to continue funding it. So it was abandoned in 1906, never having become operational. The tower was, to some extent, an extension of Tesla’s Colorado Springs experiments in an attempt to implement the World Wireless System for transmitting electric power. Tesla believed that if he injected current into the Earth at the right frequency, he could get the Earth’s natural charge to resonate and establish standing waves, which could be utilised to harvest electricity remotely. At Wardenclyffe, iron pipes were sunk 37m into the ground, and the tower was 57m tall. The tower was believed to be also intended to have ultraviolet lights on top, possibly to create an ionised pathway to conduct electricity to the upper atmosphere. After JP Morgan’s final refusal to continue to fund the project, Wikipedia siliconchip.com.au notes, “newspapers reported that the Wardenclyffe tower came alive shooting off bright flashes lighting up the night sky. No explanation was forthcoming from Tesla or any of his workers as to the meaning of the display, and Wardenclyffe never seemed to operate again” (also see the website www.teslasociety.com/warden.htm). Even before the tower project’s failure, investors had lost interest in Tesla. They were more interested in Marconi, who transmitted a Morse code wireless signal from England to Newfoundland in 1901. The failure of the Wardenclyffe project led Tesla to have a nervous breakdown in 1905. Apart from the withdrawal of financial support by JP Morgan, Tesla may have had doubts about whether his science was correct. Biographer Bernard Carlson wrote: Tesla faced a serious dilemma... Either he was wrong or nature was wrong. Wireless electricity transmission 1905 In the January 7th 1905 issue of Electrical World and Engineer, Tesla wrote about how he saw wireless transmission of electricity as a means of furthering world peace (p85, siliconchip. au/aby0). Wireless communications 1905 In 1905, he received US Patent 787,412 for the “Art of transmitting electrical energy through the natural mediums”. He described “stationary waves” from lightning at a 25-70km wavelength that “may be propagated in all directions over the globe”. He proposed reproducing this to transmit messages and establish positional data. He anticipated that resonances would occur at greater than 6Hz. Predictions 1911 According to the New York American on the 3rd of September 1911, Tesla’s “World System” (Fig.22) would perform the following tasks. We will comment on the status of each. • Television, making it possible to see any object at any distance. > Yes. • Universal twenty-four-hour daylight by wireless illumination. > No, although there is plenty of night-time lighting. • Instantaneous transmission of typed or hand-written characters all over the world. > Yes. • Operation of flying machines by wireless power. > No, but solar-powered aircraft exist, as do some experimental remotely-­powered drones. For more details, see our article on Aerial Platforms (August 2023; siliconchip.au/ Article/15894). • Navigation of ships through fogs and channels by wireless “tuned” compasses. Yes. • Communication with Mars. > Yes, in the sense that we can send and receive radio signals to and from spacecraft on Mars. • Operation of all manufacturing and transportation machinery. > Yes, if it means remote wireless or autonomous operation of machinery. • Every clock and watch in the world set and regulated by wireless at certain time each day. > Yes, that is certainly possible now. • Universal telephony, making it possible to speak at any distance. > Yes. • A perfect government secret signal service by exclusive wireless waves. > It is essentially possible now by using strong encryption. • Simultaneous operation of all stock tickers throughout the world. > Yes. • Universal system of musical transmission on atmospheric currents. > Not exactly, although radio can transmit music over very long distances. • Irrigation and fertilization of arid lands by wireless power. > No, that amount of wireless power is not practical. • The magnetizing of enemy’s battleships to attract torpedoes. > No, although magnetism is used to detect ships. > Fig.20: a newspaper article about Wardenclyffe Tower from the New-York American, May 22nd, 1904. Source: https://w.wiki/AbUz Fig.21: Wardenclyffe Tower in 1904. The tower was 57m tall but was never finished due to a lack of funding. The top of the tower was meant to be a smooth dome. Source: https://w. wiki/AbU$ siliconchip.com.au Australia's electronics magazine November 2024  17 • Reproduction of drawings and photographs at any distance. > Yes. • Absolutely exclusive telegraphy and telephony. > Yes (encrypted communications). Tesla turbine 1913 In 1913, Tesla received US Patent 1,061,206 for a novel bladeless turbine in which the working fluid impinged tangentially on a stack of discs. The fluid causes the discs to rotate via the laminar flow of the fluid at the disc surface, and thus, it extracts energy from the working fluid, such as steam or water (see Figs.23 & 24). The fluid enters the stack of discs at the edge and is exhausted at the centre. The turbine was said to be more efficient, simpler, could run faster and at higher temperatures than bladed axial turbines of the time. It could also be used as a pump. The turbine has seen little commercial application, probably because its advantages have been difficult to realise in practice. For more on this, see the video titled “The Tesla Turbine & How it Works” at https://youtu.be/mrnul6ixX90 Wireless transmission of electricity 1914 science centre, partly with the aid of Elon Musk. See: https://teslasciencecenter.org/ Finding hidden submarines In 1914, Tesla was granted US Patent 1,119,732, which improved upon his previous power transmission schemes. While the size of the power transmission structure shown in Fig.25 is not specified, we expect it would be a large tower similar to what was (incompletely) built at Wardenclyffe and similar to the modern one pictured in Fig.26. In his proposal to find enemy submarines, he wrote, “I believe this magnetic method of locating or indicating the presence of an iron or steel mass might prove very practical in locating a hidden submarine.” This article was published in The Electric Experimenter in August 1917. It turned out to be a practical idea, used widely during WW2. Speedometer Allis-Chalmers In 1916, Tesla was granted US Patent 1,209,359 for a speedometer. He licensed it to Waltham Watch, which sold 60,000 copies. During this period, Tesla worked with the steam and gas turbine manufacturer Allis-Chalmers, testing 200kW and 500kW steam turbines. The results were unsatisfactory, and Tesla also said the working conditions were poor, so the collaboration soon ended. 1916 Wardenclyffe Tower dismantled 1917 In 1917, the metal tower was demolished for its scrap metal value to help pay Tesla’s debts and the property was foreclosed in 1922. The original brick building remains and has been converted into a museum and educational 1917 1918-1920 Tesla fluid valve 1920 In 1920, Tesla was awarded US Patent 1,329,559 for a “valvular conduit”, Fig.23: a drawing of the Tesla turbine. Source: Open Source Ecology – siliconchip.au/ link/abyp Fig.22: an illustration from the article in the “New York American” of 3rd of September, 1911 on Tesla’s “World Wireless System”, entitled “To Turn Earth into One Gigantic Dynamo”. Source: https://teslauniverse.com/nikola-tesla/ articles/turn-earth-one-gigantic-dynamo 18 Silicon Chip Australia's electronics magazine Fig.24: a Tesla turbine on display at the Nikola Tesla Museum, Belgrade. Source: https://w.wiki/AbV2 siliconchip.com.au which causes the fluid flow to be relatively unimpeded in one direction but highly impeded in the opposite direction. It is the fluid equivalent of a diode (see Fig.27). The device has no moving parts and is scalable from microfluidic applications upward. However, the fluid needs a certain minimum flow speed for it to work effectively. Today, there is renewed interest in the valve and its applications, including its use in microfluidics (see our article on that in the August 2019 issue at siliconchip. au/Article/11762). Xiaomi uses it in its “loop liquidcool technology” for mobile phones (siliconchip.au/link/aby5). It is also used in a steam mop (https://youtu.be/ rYdtf90CcJQ) and a blood viscometer (siliconchip.au/link/aby6). Sulfur processing 1923 In 1923, Tesla was granted two US Patents (645,568 & 645,569) for treating and transporting sulfur, but he failed to pay the fees, and the patents were withdrawn. VTOL aircraft 1928 In 1928, Tesla received his final patent, US Patent 1,655,114 for what he described as “a new type of flying machine, designated ‘helicopter-plane’, which may be raised and lowered vertically and driven horizontally by the same propelling devices” – see Fig.28. Electric car (hoax) 1931 There were claims that in 1931, Tesla made an electric car powered by a “cosmic energy power receiver” without a battery. These are false and no such machine was ever made. Ocean & geothermal energy 1931 Tesla suggested improvements to existing ideas to harvest geothermal energy from within the Earth. His idea was to pump water down a borehole, where the internal heat of the Earth at sufficient depth would turn it into steam, after which it returns and drives a turbine to generate electricity, condenses and is then returned Fig.28: Tesla’s “helicopter-plane” drawing from US Patent 1,655,114. to the borehole to continue the cycle (see Fig.29). He also suggested improvements to existing ideas for energy generation by harvesting heat differentials between the deep and shallow parts of the ocean. A working fluid would be vaporised at a higher temperature, drive a turbine, and then condense at a lower temperature. Breaking up tornadoes 1933 In 1933, Tesla proposed using a radio-controlled plane to carry Fig.25: the terminal structure, coil, capacitor and other components for radiating electrical energy, from Tesla’s 1914 US Patent 1,119,732 regarding wireless power transmission. Fig.26: Tesla’s Wardenclyffe wireless power transmission tower (1901) and Viziv’s tower (2018). Source: Stack Exchange – siliconchip.au/link/abyq Fig.27: at the top, fluid travels from left to right and is blocked because part of the fluid stream is turned around and interferes with the other part. Below that, fluid is travelling from right to left and is unimpeded. Source: https://w.wiki/AbV3 siliconchip.com.au Australia's electronics magazine November 2024  19 Fig.29: Nikola Tesla proposed improvements to existing ideas for geothermal energy (L) and oceanic energy (R) harvesting. Originally published in Everyday Science and Mechanics, December 1931. Source: www.eenewseurope.com/ en/slideshow-the-other-things-tesladiscovered-invented on “Rail Guns and Electromagnetic Launchers” in the December 2017 issue (siliconchip.au/Article/10897). Predictions 1934 explosives into the funnel of a tornado to break it up (p251, siliconchip. au/aby0). Wirelessly powered aircraft 1934 In a 1934 article (p268, siliconchip. au/aby0), Tesla proposed that aircraft would be powered by wirelessly transmitted electricity (Fig.30), among other futuristic proposals. Telegeodynamics 1934-1941 According to the Tesla Science Foundation, from 1934 to 1941, Tesla worked on what he termed “telegeodynamics”. This concerned the transmission of mechanical energy through the Earth via mechanical oscillators. He offered it to various companies, but they were not interested. No practical outcome seems to have arisen from this work. Teleforce 1934 In 1934, Tesla described a proposed defensive “beam” weapon (also called the “Death-Beam”, siliconchip.au/ link/aby7) he called “Teleforce”. The invention was said to be “Powerful Enough to Destroy 10,000 Planes 250 Miles Away”. It comprised an open-ended vacuum tube from which small charged particles of metal or other materials were fired (not subatomic particles). These were accelerated to a high velocity by a large potential difference of perhaps 50MV. For Tesla’s description, see: www.teslaradio.com/pages/ teleforce.htm Similar experimental weapons have now been developed; see our article 20 Silicon Chip In Modern Mechanix and Inventions, July 1934, Tesla wrote: We are on the threshold of a gigantic revolution, based on the commercialization of the wireless transmission of power. Motion pictures will be flashed across limitless spaces... The same energy (wireless transmission of power) will drive airplanes and dirigibles from one central base. In rocket-propelled machines... it will be practicable to attain speeds of nearly a mile a second (3600 m.p.h.) through the rarefied medium above the stratosphere... We will be enabled to illuminate the whole sky at night... Eventually we will flash power in virtually unlimited amounts to planets. Dynamic theory of gravity 1937 For his 81st birthday, he announced he had developed a “Dynamic Theory of Gravity”. He wrote “that it will put an end to idle speculations and false conceptions, as that of curved space”, but no further work on this was published. Tesla passes away 1943 Tesla passed away on the 7th of January 1943, aged 86. US Government takes Tesla’s papers 1943 After Tesla passed away, the US Government came to his room and took many of his papers. While this is the subject of numerous conspiracy theories, bear in mind that this was in the midst of World War 2. The most likely explanation is that they wanted any material related to the proposed Teleforce weapon or anything else that might be useful for the war effort. If a weapon such as Teleforce had been possible, it would have greatly benefitted the Allied war effort. Australia's electronics magazine Dr John G. Trump (the uncle of Donald Trump) of the US National Defense Research Committee examined Tesla’s papers and reported: [Tesla’s] thoughts and efforts during at least the past 15 years were primarily of a speculative, philosophical, and somewhat promotional character often concerned with the production and wireless transmission of power; but did not include new, sound, workable principles or methods for realizing such results. Zenneck surface waves much later in 2018 Tesla’s dream of global wireless power transmission is not over. Jonathan Zenneck proposed ‘surface waves’ in 1907. They represent vertically polarised electromagnetic waves at certain planar boundaries, such as the surface of the Earth. They have been proposed as a means of wireless power transfer. Power delivery with Zenneck waves was demonstrated in 2020, although only along conducting surfaces and only over a distance of up to 15m – see siliconchip.au/link/aby8 We are not suggesting that the idea is technologically or scientifically valid for global power delivery; however, Tesla’s dream of wireless power delivery at a large scale remains alive with others. In 2018, Baylor University in Texas announced a collaboration with Viziv Technologies LLC (siliconchip.au/ link/aby9). A power transmission tower was built in Texas; see Fig.26. Unfortunately, Viziv filed for bankruptcy in 2020. See the related article at siliconchip.au/link/abya and the videos: • “Texzon Utilities - Imagine a world without wires” – (https://youtu. be/7mZErR_ZR3E) • “Texzon Zenneck Wave Wireless Power Transmission” – (https://youtu. be/vQTYaL9jCMo) • “Viziv Technologies sends power without wires” – (https://youtu.be/ jK5XUptZDEs). Tesla’s final decades Arguably, Tesla’s best work was done before about 1900. His final years, until his passing in 1943, involved him living off a small stream of royalties, giving annual press conferences, writing articles about the future of technology and living in seclusion, depression and poverty. siliconchip.com.au There was a revival of interest in his work in the 1970s and beyond, some of it from counterculturalists who believed in “free energy”. Today, most people know Tesla’s name, in part due to Elon Musk’s influence. His legacy also inspires other creative scientists and engineers who are prepared to dream and ‘push the boundaries’. Tesla’s mistakes and misconceptions While he was a genius, Tesla evidently made mistakes and had misconceptions. Among these were: • He did not accept Einstein’s theory of curved spacetime • He did not accept Maxwell’s equations • He believed he had measured faster-­than-light speeds • He did not believe in electrons and thought that atoms were the smallest units of matter • He believed that the ‘aether’ transmitted electric currents • He did not believe the splitting of atoms resulted in the liberation of energy The aether was once thought to fill the universe and be the medium through which light and gravity were transmitted. The existence of the “luminiferous aether”, which transmitted light, was disproven by the Michelson–Morley experiment in 1887, and subsequent experiments. Some of these misconceptions are remarkable, given his highly successful early work with electricity and magnetism. Tesla also said of nuclear energy, “The idea of atomic energy is illusionary but it has taken a powerful hold on the mind and there are still some who believe it to be realizable”. In an article in the Electrical Experimenter of February 1919, he also wrote that the moon does not rotate on its axis (p14 of siliconchip.au/link/abyd). However, it was known at the time that it did. In fact, it rotates in synchrony with the Earth, so we always see the same side of the moon. World Wireless System flaws It is certainly possible to transmit power wirelessly; we see it every day in things like mobile phone wireless chargers. They are based on ‘near field’ effects that occur close to the transmitting device. In the near field, the electric and magnetic field components of an electromagnetic wave can exist independently of each other, while in the ‘far field’, the electric and magnetic fields are perpendicular to each other. Far-field charging techniques are also available, but they require strongly focused beams such as lasers or microwaves. What Tesla demonstrated as wireless power transmission involved Fig.30: an illustration from the July 1934 Modern Mechanix and Inventions magazine of a proposed electric aircraft, to be powered wirelessly. Fig.31: the future of warfare, as envisaged by Tesla and illustrated by Frank R. Paul in 1922. This image ties together some of Tesla’s ideas, such as wireless power transmission, radio and teleautomatons (remotely operated vehicles). Few people would be hurt in this war, as it would be mostly between remote-controlled machines. Source: https://w.wiki/AbV4 siliconchip.com.au Australia's electronics magazine November 2024  21 either capacitive coupling (such as when a fluorescent tube illuminates near a high-voltage power line) or inductive coupling (like in an air-cored transformer). These are near-field phenomena and do not work at extended distances beyond a few tens of metres and certainly not worldwide. Besides, the energy of electromagnetic waves decreases with the distance from the antenna. Tesla also incorrectly believed that the entire Earth could be made to electrically resonate in the manner of an LC circuit. He thought that, by injecting current into the Earth at its resonant frequency from a grounded Tesla coil with a capacitance, standing waves could be established around the Earth that could be received at their nodal points anywhere on Earth with an antenna tuned to resonance. Another idea Tesla had was to hoist both transmitting and receiving power antennas high up into the atmosphere on balloons, to about 9100m, where he thought the rarefied air would be sufficiently electrically conductive to transmit electric power, with the Earth being the return circuit. That idea would not be practical; the ionosphere (not discovered until 1924), where the atmosphere does become electrically conductive, starts about 48km above the surface. Tesla and alternating current Contrary to popular belief, Tesla did not invent the concept of AC electricity. The first AC generator was invented in 1832 by Hippolyte Pixii, as mentioned in our article on the History of Electronics (October 2023, p19; siliconchip.au/Article/15966). However, André-Marie Ampère convinced him to convert it to pulsed DC. According to the book The Electric Light from 1884 (p238, siliconchip.au/ link/abye), around 1856, due to frustration with failed commutators on a generator, they were dispensed with, resulting in the successful use of AC for lighting, such as arc lights. However, Tesla did invent many successful AC machines. Falls hydroelectric project, at which Tesla’s generators were used. This ensured the future of AC. During the war of the currents, and even afterwards, some residences in New York had both DC and AC outlets, which looked the same! The last DC utility service in New York was shut down in 2007, see: www.edisontechcenter.org/NYC.html War of the currents Tesla had studied and was aware of Hertzian radio waves. However, he believed Hertz’s theories were incorrect and that Hertzian waves were not suitable for anything but short-range communications, such as under 2km. He also thought they behaved like light and would go straight into space rather than travel long distances on Earth. Tesla was more interested in wireless long-distance electricity transmission than in communications. However, in 1893, he noted that his proposed wireless electricity transmission system could also be used for communications. Tesla also incorrectly believed, as some others did at the time, that radio behaved much like the familiar telegraph system and that a return circuit was required, with radio waves travelling through the air and a return path of current through the Earth. While the Earth plays an important role in a radio system by providing a reference potential and allowing a small amount of current to flow through it, radio signals do not ‘return’ via that path. He incorrectly believed that radio waves could travel losslessly through the Earth. Tesla also had an idea of producing non-Hertzian “longitudinal electromagnetic waves” in the manner of sound waves, which he called “electromagnetic thrusts”. Radio waves are, in fact, transverse. The war of the currents lasted from the late 1880s to the early 1890s and basically concerned which of the two electrical systems would dominate large-scale electricity distribution. These were AC, represented by George Westinghouse (and Tesla), and DC, represented by Thomas Edison. AC was ideal for long-distance distribution because, at high voltages, it had low transmission losses and it was easy to change the voltage for use by the consumer with a low-cost, reliable transformer. DC systems had high losses at low voltages and would have required vast numbers of local power stations since DC voltage conversion was not practical. Edison promoted the safety of DC compared to the dangers of AC. Edison and Westinghouse’s other rival, Thomson-Houston Electric Company, even colluded to ensure the first electric chair was powered by a Westinghouse AC generator to ‘prove’ how dangerous AC was. In 1893, Westinghouse won the contract for lighting at the Chicago World Fair, at which Tesla’s inventions were demonstrated, and won most of the contract for the Niagara Links and References ● Nikola Tesla and the Planetary Radio Signals: https://radiojove.gsfc.nasa.gov/ education/educationalcd/Books/Tesla.pdf (K. L. Corum & J. F. Corum, 2003). ● Tesla’s autobiography from 1919: www.tfcbooks.com/tesla/my_inventions.pdf ● Plans to make your own Tesla turbine: www.instructables.com/Tesla-Turbine ● The Nikola Tesla Museum in Belgrade: https://tesla-museum.org/en/home/ ● A 301-page collection of some of Tesla’s writings, called “Tesla Said”, is described as “the most comprehensive single volume of Tesla’s writings”: https://archive.org/ details/nikolateslajohnt.ratzlaffteslasaid ● Tesla: Inventor of the Electrical Age, W. Bernard Carlson, Princeton University Press (2015). ● The Tesla Memorial Society of New York: www.teslasociety.com ● The Tesla Science Center at Wardendclyffe: https://teslasciencecenter.org ● The Tesla Collection, a comprehensive compilation of newspaper and periodical material: https://teslacollection.com 22 Silicon Chip Australia's electronics magazine Tesla and radio Tesla’s “lost files” There are many conspiracy theories related to Tesla’s documents, which the US Government took after his passing. After they found nothing of practical use for the war effort (such as the “death ray”), the papers were released to Tesla’s relative, Sava Kosanović. He took them, along with Tesla’s entire estate (packed into 80 trunks) to Belgrade, Serbia in 1952, and they now reside in the Nikola Tesla Museum in Belgrade. 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Dual 12V 10A relay and control board with the ability to switch on and off loads using eWeLink app on your phone via Bluetooth. Z 6422 SAVE 24% 6 $ ea 2 Channel Relay Board 10A relays with 5V DC coil. Can be controlled by R-Pi, Arduino etc. P 1021 Pin to Socket P 1022 Pin to Pin P 1023 Socket to Socket Ribbon Jumper Leads Easy peel apart cables. Your electronics supplier since 1976. Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/11/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. M k 2 Variable Speed Drive For Induction Motors Part 1 by Andrew Levido This new VSD significantly improves on our previous design. It’s more compact, lighter, better cooled, and more efficient. It has better safety margins (making it more robust) and some new features. W e last published an induction motor speed controller more than ten years ago (April & May 2012; siliconchip.au/Series/25), so we thought it was high time to revisit this project and improve it where possible. Some critical components used in the old design, notably the integrated IGBT/driver module, are now obsolete. We can take advantage of some other technological advances to make this unit smaller, more efficient and easier to build. We have used a compact tunnel heatsink, with active cooling via a small DC fan, to significantly decrease the size and weight of the unit compared to its predecessor. Other things contribute to its compactness, like using switch-mode AC/DC converters rather than transformers and active discharge of the HV capacitor bank, rather than bulky power resistors acting as bleeders. Functionally, the speed controller is similar to the previous unit in that it is designed to run single-phase shaded pole or permanent split capacitor (PSC) motors rated up to 1.5kW (2 horsepower) or any three-phase induction motor of a similar rating, as long as it can be configured for 230V operation (most can). 24 Silicon Chip Like all such drives, the Variable Speed Drive (VSD) described here is not generally suitable for use with induction motors with centrifugal switches, since the start windings in these motors are not rated for continuous operation. You can read more about that in the separate article on how induction motors work. An induction motor’s power rating describes the output power at the shaft, not the electrical input required to run it. For example, your average 1.5kW single-phase induction motor draws a full-load current of 8.9A with a power factor of 0.95. That means the real power input is around 2kW, suggesting an efficiency of about 73%. For a three-phase 1.5kW motor, the typical full-load phase current will be about 5.5A at a power factor of 0.82, giving a similar real power input. This VSD can deliver around 9A continuously in single-phase mode and around 5.5A per phase in threephase mode. It can deliver twice this current on a very short-term basis when starting the motor. The output frequency can be varied from 0.5Hz to 50Hz with a set point resolution of 0.25Hz. When ramping between set point frequencies, the frequency steps are even smaller than this. Australia's electronics magazine Features The basic topology of the power electronics is shown in the upper part of Fig.1. Power from the mains is rectified and filtered to create a DC ‘bus’ voltage of around 330V. This DC bus voltage is then pulse-width modulated by an IGBT bridge to produce the desired output voltage. Only two of the output IGBT pairs (the U and V phases) are used in single-­ phase mode. This part of the circuit operates at mains voltages and stores considerable energy. Contact with any part of this can be lethal – so exercise care. Because of this risk, the user controls, shown diagrammatically in the lower part of Fig.1, are isolated from the power circuit and near Earth potential. The board has six DIP switches for setting the operation modes. These are only read at start-up, so changing any of these while the speed controller is powered up has no effect until the next restart. If the first of these switches is closed, it selects three-phase motor operation; otherwise, the controller operates in single-phase mode. The second and third switches are related to pool pump operation. Running a pool pump at a lower speed can siliconchip.com.au Fig.1: a basic overview of how the VSD works. At this ‘zoomed out’ level, it’s similar to the previous IMSC (Induction Motor Speed Controller); the mains is rectified and charges a DC capacitor bank. The voltage from that bank is chopped by three IGBT half-bridges and applied to the motor windings, with the isolated control circuitry shown below. save a considerable amount of energy in cases where the pump has to run for a long time – such as when a saltwater chlorinator is used. These typically must run for four to eight hours daily in summer to produce sufficient chlorine. Under these circumstances, running the pump at 50% or even 75% of full speed can save a lot of energy. Just make sure the pump speed is high enough to keep the chlorinator cells covered and that the whole water volume is turned over at least once during each daily cycle. If you operate a pool pump at reduced speed, it can be a good idea to run the pump for a short time at full speed first, to ensure the pump is primed and to purge any air from the system. That is the purpose of the pool pump mode. If the Pool Mode DIP switch is closed, the VSD will initially ramp the motor up to full speed and hold it there briefly before ramping to whatever operating speed the user has set. The Pool Time DIP switch controls the duration of this full-speed period. If left open, the full-speed period is about 30 seconds; if it is closed, the time is extended to five minutes. The Pool Mode and Pool Time siliconchip.com.au switches are ignored if three-phase mode is selected. The speed control signal can come from either an onboard trimpot or an external potentiometer/control voltage. The latter option is selected by closing the External Speed DIP switch. Alongside the speed input terminal, 5V reference and ground terminals are provided for use with an external pot. The reference can comfortably source 10mA, so any pot with a resistance of 500W or more can be used. You can also feed a 0-5V signal into this terminal to control the motor speed from an external device. The common terminal for the speed control is referenced to the mains Earth. In addition to the internal speed control pot, there is a second trimpot Variable Speed Drive Features & Specifications » Can drive single-phase shaded pole or PSC motors up to 1.5kW » Can drive three-phase 230V induction motors up to 1.5kW » Speed range: 1% to 100% of full speed in 0.5% steps » Runs from a standard 10A GPO » Inbuilt mains EMI/RFI filter » Robust inrush current limiting » Higher efficiency than our previous design » Fan-based cooling for critical components » Uses standard, discrete IGBTs for switching » Compact and lightweight » Over-current and over-temperature shutdown » Pool pump mode » Three-phase motors can be reversed at any time (they will slow down, stop, reverse and speed back up) » Adjustable speed ramp rate » Internal or external controls for speed, on/off and emergency stop » Relay outputs that switch when the motor is up to speed or on a fault Australia's electronics magazine November 2024  25 Fig.2: a somewhat more detailed view of how the VSD works. The soft starter & discharger block limits the inrush current into the capacitor bank when power is first applied and ensures that the bank discharges quickly when mains power is lost. Two similar AC-DC converters supply power to the ‘hot’ and isolated sections, with an eight-channel digital isolator bridging them. to set the ramp rate. This controls how quickly the motor speed changes. The ramp rate can be set between three and 60 seconds for a ramp from zero to full speed. The longer ramp times may be necessary for high-inertia loads. To get the speed controller to start, both the Run and E-Stop circuits must be closed or 12V fed into the relevant terminals from some external source. Opening the emergency stop (E-Stop) terminals immediately switches the IGBTs off, letting the motor freewheel to a stop. Opening the Run circuit causes the motor speed to ramp down to zero before the IGBTs are switched off. The final external input is the Reverse control. This is only relevant in three-phase mode, and it sets the direction of rotation of the motor, effectively changing the phase sequence at the output. If you switch to the opposite direction while the motor is running, it will ramp down to zero, pause for two seconds, then ramp up again in the new direction. Three LEDs indicate the VSD’s operating status. The green LED indicates that the motor is running. It flashes quickly when the motor is ramping up or down and is illuminated steadily when the preset speed is reached. During the pool pump full-speed period, the green LED flashes slowly. The yellow LED indicates that the speed controller is in idle mode. This 26 Silicon Chip means the IGBTs are off, but the VSD is ready to run once the E-Stop and Run switches are closed and a nonzero speed signal is applied. The red LED indicates a fault condition. If just the red LED is illuminated, the fault is either an overcurrent trip or the DC bus voltage has risen too high. If the red and yellow LEDs are both lit, the heatsink temperature has become dangerously high. Either way, the fault can be reset by cycling power or toggling the E-Stop switch (opening then closing it) after the fault has cleared. An output relay (RLY2) provides a set of uncommitted isolated changeover contacts that the user can employ as they see fit. The At-Speed DIP switch configures the relay function. If the DIP switch is open, the relay activates when a fault occurs. If closed, the relay activates when the motor has reached the preset speed. The Boost DIP switch increases the motor voltage at very low speeds. You may need to switch this in to reliably start constant-torque loads such as displacement pumps, conveyers or hoists. Some pool pumps may also require this boost since the pump seals can sometimes become ‘sticky’ if the pump has been stationary for some time. How it works Fig.2 is a block diagram of the VSD showing the two distinct power Australia's electronics magazine domains. The high-voltage section containing the power electronics is shown in red, while the low-voltage part with the control circuitry is shown in green. As we step through the full circuit (Fig.3), it may be helpful to refer to this diagram as well. The mains input first passes through a 10A slow blow fuse, F1 – a last line of defence in case of a catastrophic failure. It then passes through an EMI filter consisting of the common-mode inductor L1 and six capacitors. The EMI filter is there to minimise the high-frequency artefacts (of which there are plenty in a circuit of this type) making their way back to the mains supply. The mains supply is then rectified by a full-bridge rectifier, BR1, and applied to the five parallel DC bus capacitors via a soft start/discharge circuit. Thermistor NTC1, which has a resistance of around 10W when cold, limits the capacitor bank inrush current to about 35A peak. We use a specialised inrush-limiting thermistor here because it would be difficult to guarantee the reliability of a generic power resistor in this application. The thermistor used here is rated for a maximum capacitor inrush energy of 150J. The maximum energy that our capacitor bank can store is 110J (from E = ½CV2) if the mains siliconchip.com.au The third (black) cable gland is for wiring to an optional external controller, which can be as simple as the one shown here. voltage is at its upper limit of 260V. The thermistor’s resistance drops dramatically as it heats up, and it can continuously pass 15A – more than enough for this application. However, unlike the original controller, we have chosen to short it out with relay RLY1, which closes once the capacitors are charged. This simultaneously disconnects the capacitor discharge section when the speed controller is operating. Shorting out the NTC thermistor has a few advantages. Firstly, it increases efficiency and reduces heat dissipation in the case due to the thermistor’s resistance. It also cools down more quickly after the unit is switched on, so it will effectively reduce the inrush current if the unit is switched off and then (almost) immediately on again. The capacitor discharge circuit is also an upgrade from the previous design. There, we used three bulky 5W power resistors, which resulted in a discharge time of about 90 seconds and continuous power dissipation approaching 10W (a complete waste). This time, we have used a constant-­ current discharge circuit based around transistors Q7 and Q8. This discharges the capacitors at a nominal 50mA, taking around 10 seconds, making the unit much safer to work on. Switching it out during operation again improves efficiency and greatly reduces the heating inside the case. siliconchip.com.au Adding RLY1 has eliminated a total of about 20W of continuous power dissipation compared to the previous design. The capacitor bank itself deserves a few words. The input current of any circuit like this, which rectifies and filters the mains, is very ‘spikey’ as the rectifier diodes only conduct at the very peak of the mains. This results in a pretty terrible input power factor and very high levels of ripple current in the capacitors. The current flowing out of the capacitors to the motor also contributes. A simulation (this is very hard to calculate any other way) showed this ripple to be around 10A RMS in total, or 2.0A RMS per capacitor. Therefore, it is essential to use capacitors designed for a 100Hz ripple current of at least 2A, like the Nichicon caps specified in the parts list. After the filter capacitors, there is a 15mW current-sensing resistor (more on this later) and more EMI suppression via another set of three X2/Y2 capacitors. These help to shunt any high-frequency artefacts on the DC bus to ground or Earth. Another big difference between this design and the previous Induction Motor Speed Controller (IMSC) is the use of discrete IGBTs (Q1 through Q6) and a separate driver chip (IC2) instead of an integrated power module. Australia's electronics magazine The DGTD65T15H2TF IGBTs used here are rugged devices rated at 650V/30A and specifically designed for motor drive use. They include an anti-parallel diode with similar ratings, and come in an isolated TO-220 case. The latter is important since we want to use an Earthed heatsink for safety and don’t want to have to fuss with insulating washers and the like. The diode bridge and discharge Mosfet, Q8, are also mounted on the heatsink; all use isolated packages for maximum convenience and safety. Driving the IGBTs The IGBTs are driven by a surprisingly inexpensive, specialised IGBT driver chip, the Infineon 6EDL04I06PT (IC2). The block diagram of this chip is reproduced in Fig.4. For each of the three phases, there are two logic-level inputs, one for the high-side IGBT and one for the low-side. In addition, a global enable pin (EN) must be high for any of the drivers to be active. These inputs pass through a noise filter to some logic that prevents both high-side and low-side IGBTs in the same phase from being switched on at once. The logic also ensures there is a short dead time when switching between high-side and low-side transistors or vice versa. About 310ns in length, this is sufficient to give one November 2024  27 Fig.3: the complete VSD circuit. The red dashed line is the isolation barrier; note how RLY1 also bridges it. Comparator IC5a’s output goes low if the capacitor bank voltage gets too high, while IC2 pulls the same FLT line low if an overcurrent condition is detected. Either way, the drive to the IGBTs shuts down. 28 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine November 2024  29 Fig.4: a colourised and cleaned-up version of the internal block diagram from the 6EDL04I06PTXUMA1 IGBT driver data sheet. It provides all the functions we need to drive the six IGBTs and monitor the current draw in one package. IGBT time to turn off before its opposite number begins to turn on. The microcontroller also inserts dead time into the PWM signals, so this circuit provides some useful ‘belts and braces’ backup should something unexpected happen. From there, the high-side signals go to three high-side IGBT gate drivers via level shifters. This is necessary because these gate drivers are referenced to the high-side IGBT’s emitters via the VS1, VS2 and VS3 pins. In operation, these pins are switching alternatively between the negative side of the DC bus (when the low side IGBT is on) and the positive side of the bus (when the high-side IGBT is on). Most of the circuitry in the high-­ voltage domain, including the IGBT driver’s VSS pin, is referenced to the negative side of the DC bus. The circuit diagram shows this with a triangular ‘ground’ symbol. Do not confuse this with the common in the low voltage 30 Silicon Chip domain (shown with the usual ground symbol having three horizontal lines), which is referenced to mains Earth. You will also notice a ‘chassis Earth’ symbol in a few places. This symbol refers specifically to mains Earth connections. It consists of two thick horizontal bars with a series of diagonal lines coming off the lower one. Returning to IC2, the low-side drive signals are routed to the three low-side gate drivers via a delay block, which is necessary to match the delay introduced by the high-side level shifters. The low-side gate drivers are referenced to the COM pin, which is connected to the low-side IGBT emitters. This COM signal can float a few volts up or down with reference to VSS (HV_COM) since there may be some voltage drop across the 15mW current shunt resistor and the PCB traces. The IGBT driver is powered by a +15V supply applied to the Vcc pin. This supply is used for the logic and Australia's electronics magazine low-side drivers directly, but powers each high-side driver via three bootstrap circuits. These consist of internal bootstrap diodes connected between Vcc and three 2.2μF external capacitors connected to the VB1, VB2 and VB3 pins. When a low-side IGBT is on, the corresponding high-side driver’s bootstrap capacitor charges via its bootstrap diode. When the low-side driver is off, the diode is reverse biased, and the capacitor provides a floating power source for the high-side driver. An undervoltage lockout prevents the high-side driver from operating if its bootstrap voltage is not sufficient. Overcurrent and overvoltage protection The 6EDL04I06PT driver includes a trip circuit to protect the IGBTs from overloads or short circuits. This works by monitoring the voltage at the ITRIP pin and shutting down the drive to all siliconchip.com.au Single-Phase Induction Motors With a 3-phase supply, achieving a rotating magnetic field is easily achieved by spacing the three windings around the rotor. Swap any two of the phases and the field will rotate in the opposite direction. With a single-phase supply, the sole winding can only produce a pulsating field. There is no torque on the rotor when it is stationary, so it cannot start without some impulse to get it going. Once moving, the torque builds up. The motor will rotate equally well in either direction, depending on the sense of this initial kick. There are a few different schemes to give this initial kick-start. Manufacturers have not adopted a common set of terms to describe their various approaches, so the whole topic is potentially confusing. Below, we have summarised a few of the more common starting mechanisms: so usually limited to low power motors such as found in small domestic fans and blowers. These motors can be used with a speed controller such as the one described here but generally that would be an expensive solution for a low-power device. Shaded Pole 4 These are similar to the PSC motor in that a capacitor and start winding create a phase-shifted field for starting. The capacitor is larger and the start winding designed to draw significantly more current and therefore A shorted turn on the corner of the stator poles distorts the magnetic field to create a weak starting torque. Shaded pole motors are inefficient due to the shorted turn and Permanent Split Capacitor 4 A start winding in series with a capacitor produces a second, weaker field slightly out of phase with the main field. It is designed to draw a relatively modest current and rated for continuous operation. Permanent Split Capacitor (PSC) motors have low starting torque and are very reliable since there is no centrifugal switch. Typically used for fans and centrifugal (pool & spa) pumps up to about 2kW, these are suitable for use with a speed controller. Capacitor Start 8 START WINDING RUN WINDING RUN WINDING RUN WINDING START WINDING SHADED POLE CAPACITOR START PERMANENT SPLIT CAPACITOR START WINDING CAPACITOR START/RUN RUN WINDING RUN WINDING START WINDING CENTRIFUGAL START SWITCH provides a much higher starting torque. The start winding and capacitor are not rated for continuous operation and waste a lot of energy so are switched out by a centrifugal switch, typically at about 70% of full speed. They are used for conveyors, large fans, pumps and geared applications requiring high starting torque. Capacitor Start motors are not suitable for speed control use because at lower speeds the centrifugal switch will close and the start winding or capacitor may burn out. Capacitor Start/Run 8 These are the “big guns” of single-­phase motors and are used for machine tools, compressors, brick saws, cement mixers etc. They have a large start capacitor that is switched out by a centrifugal switch and a smaller run capacitor that is permanently connected to the start winding. They have very high starting torque and good overload performance. For the same reason as the capacitor start motors, they cannot be used with variable speed drives. A 3-phase motor is recommended in these applications if speed control is desirable. Centrifugal Start Switch 8 Commonly used on small bench grinders and column drills, these motors arrange a phase-shifted field with a resistive winding. Again, the start winding is only rated for intermittent operation (due to its high resistance) and will burn out if operated continuously. NOTE: in spite of the above warnings, some readers may want to try using the VSD with motors using a centrifugal switch to energise the start winding. The danger is that the start winding may be burnt out if it is energised for too long when operating at low speeds. There is also a risk that the over-current protection in the VSD will prevent normal operation. WARNING: DANGEROUS VOLTAGES This circuit is directly connected to the 230V AC mains. As such, most of the parts and wiring operate at mains potential. Contact with any part of these non-isolated circuit sections could prove fatal. Note also that the circuit can remain potentially lethal even after the 230V AC mains supply has been disconnected! To ensure safety, this circuit MUST NOT be operated unless it is fully enclosed in a plastic case. Do not connect this device to the mains with the lid of the case removed. Do not touch any part of the circuit for at least 30 second after unplugging the power cord from the mains socket. This is not a project for the inexperienced. Do not attempt to build it unless you understand what you are doing and are experienced working with high-voltage circuits. siliconchip.com.au Australia's electronics magazine November 2024  31 IGBTs if the voltage exceeds 0.45V. We use this to monitor the voltage across the 15mW shunt resistor, giving a nominal trip current of 30A. An RC low-pass filter consisting of a 1kW resistor and 470pF capacitor provides some immunity from false triggering due to noise. If an overcurrent condition is detected, the gate drivers are switched off, and a fault signal is asserted on the open-drain FLT pin, pulling the FLT line low. After a short time, dictated by the value of the 10nF capacitor at pin 11, the gate drivers are re-enabled, and the fault output is de-asserted. The 10nF value sets this time to about 20ms, long enough for the microprocessor to detect the fault condition, disable the IGBT driver and latch the fault state. In addition to the overcurrent detection provided by the IGBT driver, there is also an external overvoltage detection circuit on the DC bus. This voltage can increase when a motor is decelerated due to regeneration. The voltage rise can become significant if the load has a lot of inertia. In the worst case, it could exceed the capacitors’ voltage ratings. A voltage divider consisting of four series 100kW resistors and a 5.1kW resistor to HV common reduces the bus voltage by a factor of about 80. If the divider’s output reaches 5V, corresponding to a bus voltage of 400V, comparator IC5a’s open-collector output will pull the FLT line low. The overvoltage and overcurrent faults are therefore wire-ORed together to create a single fault signal that deactivates the IGBT drive of IC2 and is also transmitted across the isolation barrier (via IC4) to the microcontroller. Power supply and isolation The high-voltage domain circuity is powered by a small modular AC-to-DC switch-mode converter that supplies 15V (designated +15VH on the circuit diagram) at 5W from the mains. 5V linear regulator REG1 produces the +5VH rail for the fault logic and the digital isolators. The previous IMSC used a relatively large and heavy mains power transformer instead of a switch-mode supply. While there is an argument for preferring the simplicity of a transformer, these switch-mode supplies are less expensive, considerably smaller, lighter, and more efficient and allow 32 Silicon Chip Parts List – Variable Speed Drive 1 double-sided PCB coded 11111241, 150 × 205mm, black solder mask 1 Hammond HM1112/RP1455 220 × 165 × 60mm IP65 enclosure [Altronics H0312A] 1 Zettler ZP05S1500WB mains to 15V DC 5W AC/DC converter (MOD1) 1 Zettler ZP05S1200WB mains to 12V DC 5W AC/DC converter (MOD2) 2 M205 PCB-mount fuse clips (for F1) 1 10A M205 slow-blow ceramic fuse (F1) [Bel 5HT 10-R] 1 vinyl M205 fuse cover/insulator (for F1) [Keystone 3527C] 1 SL32 10015 10W 15A NTC thermistor (NTC1) 1 NRG2104F3435B2F 10kW lug-mount NTC thermistor (NTC2) 1 1.2mH 14A toroidal common-mode choke (CMC1) [Kemet SC-14-12J] 2 J107F1CS1212VDC.45 12V DC coil 12A SPDT relays (RLY1, RLY2) 2 10kW mini top-adjust single-turn 3362P-style trimpots (VR1, VR2) 1 6-way DIP switch (S1) [CUI DS01C-254-L-06BE] 7 vertical PCB-mounting 5mm pitch 4.8mm male spade lugs (CON1-CON7) 4 3-way mini terminal blocks, 5.08mm pitch (CON8-CON11) 1 2×5-pin keyed shrouded SMD box header, 1.27mm lead pitch (CON16) [CNC Tech 3220-10-0300-00] 1 3-pin header, 2.54mm pitch (CON17) 1 100mm-long 40 × 40mm tunnel heatsink [AliExpress 1005006064507597 or AliExpress 1005006255161284] 1 40 × 40 × 20mm 12V DC 0.3m3/minute maglev fan [Sunon MF40201VX-1000U-A99] 1 40mm fan guard & filter [Qualtek 09150-F/45] 1 10A mains extension cord 1 150mm length of 10A green/yellow striped wire 2 cable glands to suit the mains extension cord 7 4.8mm female spade crimp lugs to suit 1mm2 wire 2 4.8mm female piggyback spade crimp lugs to suit 1mm2 wire 1 100mm length of 8mm diameter blue heatshrink tubing 1 100mm length of 8mm diameter red heatshrink tubing 1 100mm length of 10mm diameter green/yellow striped heatshrink tubing 1 small cable gland (optional; for external control box) 1 external control box (optional; see separate parts list) 4 M3 × 25mm panhead machine screws 15 M3 × 10mm panhead machine screws 11 M3 spring washers 4 No.4 × 6mm self-tapping screws 1 small tube of thermal paste 1 small tube of superglue small zip-lock cable ties extra cabling required for connection to a 3-phase motor Semiconductors 1 6EDL04I06PTXUMA1 high-voltage three-phase H-bridge gate driver, SOIC-28 (IC2) 1 ISO7760DW six-channel unidirectional digital isolator, wide SOIC-16 (IC3) the unit to operate from a wide range of mains supply voltages. This brings us to another improvement on the earlier controller, which used opto-couplers to transmit the control signals across the isolation barrier. This design uses modern lowcost digital isolators. They work by modulating the input signal, passing it capacitively across an insulating barrier and demodulating it on the other side to reconstruct the original signal. The ones we used here have an isolation voltage of 5000V RMS (somewhat less of a ‘reinforced’ rating, but still plenty for mains work) and support data rates up to 100Mbps. Australia's electronics magazine You can get these digital isolators in all sorts of configurations. We use one with six channels, all going in the same direction (IC3) for the PWM signals, and one with two channels (IC4), one going in each direction, for the enable (EN) and fault (FLT) signals. The supply voltages on each side do not have to be the same. We have used 5V logic on the high-voltage side and 3.3V logic on the isolated (control) side. Control circuitry The STM32G030K6T6 microcontroller (IC7) is the heart of the control circuitry. This has a 32-bit ARM siliconchip.com.au 1 ISO7721FD two-channel bidirectional digital isolator, SOIC-8 (IC4) 1 LM393AD dual differential comparator, SOIC-8 (IC5) 1 LM358AD dual single-supply op amp, SOIC-8 (IC6) 1 STM32G030K6T6 32-bit ARM microcontroller with 32KiB flash, programmed with 1111124A.HEX, LQFP-32 (IC7) 1 LD1117S50 5V low-dropout linear regulator, SOT-223 (REG1) 1 LD1117S33 3.3V low-dropout linear regulator, SOT-223 (REG8) 6 DGTD65T15H2TF 650V 30A IGBTs, TO-220FP (Q1-Q6) 1 AOTF4N60L 600V 4A N-channel Mosfet, TO-220FP (Q7) 1 BC847C 45V 100mA NPN transistor, SOT-23 (Q8) 3 BSS138K 50V 220mA N-channel logic-level Mosfets, SOT-23 (Q9-Q11) 3 M2012/0805 size LEDs; red, yellow & green (LED1-LED3) 1 BZX84-C12 12V 250mV zener diode, SOT-23 (ZD1) 3 BZX84-C5V1 5.1V 250mV zener diodes, SOT-23 (ZD3-ZD5) 1 GBJ2506-F 600V 25A SIL bridge rectifier (BR1) 3 1N4148WT 75V 300mA switching diodes, SOD-523 (D2-D4) Capacitors (all SMD M2012/0805 size 50V X7R unless noted) 5 330μF 400V 105°C snap-in electrolytic, 30mm diameter, 40mm tall [Nichicon LGW2G331MELB40] 2 100μF 35V 105°C SMD electrolytic, 6.3mm diameter [Nichicon UCD1V101MCL6GS] 3 10μF 25V 4 2.2μF 25V 3 220nF X2 capacitors, 15mm lead pitch, 7mm wide [EPCOS/TDK B32922C3224K000] 6 4.7nF Y2 radial ceramic capacitors, 7.5mm lead pitch [Kemet C947U472MZVDBA7317] 12 100nF 1 10nF 1 470pF NP0/C0G 1 100pF NP0/C0G Resistors (all SMD M2012/0805 size ⅛W 1% unless noted) 1 470kW 4 100kW 2 82kW M6332/2512 size 1W [RC2512FK-0782KL] 1 18kW 1 13kW 4 10kW 1 5.1kW 1 4.7kW 3 2.2kW 1 2kW 10 1kW 1 470W 3 220W 7 12W 1 0W 1 15mW 3W M6432/2512 metal element current-sense resistor [Eaton MSMA2512R0150FGN] Optional External Control Box 1 small Jiffy box 1 panel label 3 SPST panel-mount toggle switches 1 1kW 16mm potentiometer 1 knob to suit the potentiometer 2 small cable glands 1 1m length of 9-core shielded data cable (or length to suit) Cortex M0+ core running at 64MHz, 32kiB of flash memory and 8kiB of static RAM (SRAM). It includes all the usual peripherals, including a timer designed specifically for motor control applications and comes in a 32-pin 0.8mm-pitch SMD quad package. CON16 allows IC7 to be reprogrammed in-circuit while CON17 provides a way to power it besides the mains supply. The motor speed can be set by one of two sources: an external 0-5V control signal or an onboard trimpot. The external speed input enters via pin 2 of terminal block CON8. A 1kW series resistor and 100nF capacitor to ground siliconchip.com.au provide noise filtering and protection for the op amp buffer (IC6b). The 470kW resistor prevents this input from floating if it is left unconnected. After buffering, the external speed signal is scaled by the voltage divider formed by the 1kW and 2kW resistors to suit the 0-3.3V range of the microcontroller’s internal analog-to-digital converter (ADC). The other half of the dual op amp (IC6a) creates a 5V signal to drive one end of the external speed pot. The 5V potential is derived from the 12V rail via the 18kW/13kW divider and filtered by a 100nF capacitor. It is then applied to op amp IC6a, which is connected Australia's electronics magazine as a current-limited unity-gain buffer. Suppose the current drawn from the 5V terminal is small. In that case, the voltage drop across the 470W resistor is low enough that the op amp is not in saturation, and the negative feedback (via the 10kW resistor) can maintain the output voltage at 5V. The op amp output will saturate if the current increases beyond about 14mA with these component values. Voltage regulation will be lost, but the current will be limited to a safe level. The three digital switch inputs (E-Stop, Run and Reverse) and their respective 12V sources are likewise protected from modest levels of accidental abuse. Taking the E-Stop input at CON9 as an example, the 220W series resistor limits the current that can be drawn from the 12V supply. The signal from pin 2 of CON9 passes through a voltage divider/pulldown/filter formed by 1kW and 2.2kW resistors plus a 100nF capacitor. Zener diode ZD3 clamps the resulting voltage to a maximum of 5.1V, which is within the safe operating range for the relevant microcontroller I/O pins. In addition to the external speed control, IC7 has three other analog inputs. The wiper voltages of the internal speed pot VR1 and ramp rate pot VR2 are each fed straight to the micro, with 100nF capacitors providing some noise filtering and buffering for the ADC sample-and-hold capacitor. The final analog input comes from NTC thermistor NTC2, which monitors heatsink temperature and is connected via CON12. The thermistor forms the upper leg of a voltage divider, with a 4.7kW fixed resistor forming the lower leg. The resulting voltage, related to temperature by a non-linear relationship, is fed directly to an ADC channel (PA02 pin 9) on the microcontroller. The microcontroller drives the two relays and the heatsink fan via moreor-less identical circuits. All three drivers use logic-level Mosfets (Q9, Q10 and Q11) as low-side switches, along with freewheeling diodes (D2, D3 and D4) and 10kW gate pulldown resistors. The microcontroller also drives the three LEDs via current-­ limiting resistors. The motor control timer inside the MCU uses seven I/O pins – six outputs for the three pairs of PWM signals, plus one input for the fault signal (HOT_ FLT). A separate general-purpose I/O pin is used for the enable (PWM_EN) November 2024  33 Scope 1: this scope grab shows three traces corresponding to the U, V & W outputs (CON4CON6). It shows that each is made up of two distinct pulse widths, corresponding to the two phase legs driving it; the use of centrealigned PWM doubles the effective switching frequency. The vertical scale is 500V/div. signal. Finally, six digital inputs configured with internal pull-up resistors are used to read the DIP switches (S1). Power for the control circuitry is derived from a second AC-to-DC switch-mode converter module (MOD2), this time one with a 12V output to suit the fan and relay coils. A linear regulator (REG8) derives a 3.3V rail for the microcontroller and associated circuitry from the 12V rail. Firmware Of course, a lot of the complexity of a project like this lies in the firmware. Fig.5 shows an overview of the three main blocks of the firmware architecture. As its name suggests, the I/O driver is responsible for managing all of the I/O functions except those related to the motor-control PWM. On initialisation, this driver reads the mode control DIP switches and stores their values for later use. The driver provides interface functions so the higher-level code can query the state of any switch at any time. Much of this driver’s functionality takes place in a low-priority interrupt service routine (ISR), which is called every 20 milliseconds by a hardware timer. This ISR scans the digital inputs corresponding to the E-Stop, Run Fig.5: the firmware’s three principal blocks. An I/O driver manages the digital and analog interfaces, a PWM driver generates the motor control signals, while a state machine controls the overall system logic. 34 Silicon Chip and Reverse switches. The inputs are debounced, and the resulting state is stored. The I/O ISR also starts the sequential analog-to-digital conversion of the four analog inputs (external and internal speed, ramp and heatsink temperature). Direct memory access (DMA) is used to read and store the results when available. This approach means the reading and processing of the inputs takes place more-or-less automatically. The state machine just has to call an interface function to get the most up-to-date analog or digital input data. In the case of the analog inputs, the reading functions scale the raw ADC values into meaningful units. The heatsink temperature read function switches the fan on if the heatsink temperature rises above 45°C and off again if it falls below 40°C. If the heatsink temperature exceeds 95C°, an over-temperature error is signalled, and when it drops below 70°C, the over-temperature error is cleared. Finally, the same ISR manages the flashing of the three LEDs. The state machine code only has to call an interface function once to initiate the flashing of a given LED an arbitrary number of times at a specified rate. PWM generation A separate module looks after the generation of the motor PWM signals. The timer used to generate the PWM includes (among many other things) a 16-bit counter and three comparison Fig.6: centre-aligned PWM is preferred for motor drive applications since the switching edges of each phase are not aligned, doubling the effective switching frequency seen by the motor windings and reducing EMI/RFI. Australia's electronics magazine siliconchip.com.au registers. The counter is clocked at 64MHz and is programmed to count from zero up to 2047, then down again to zero, as shown diagrammatically in Fig.6. On every clock cycle, the counter value is compared to the value in the compare registers to generate a centre-­ aligned PWM signal, as shown in that figure. Centre-aligned PWM is preferred for motor control since the switching edges on each phase are not aligned with each other, as would be the case if edge-aligned PWM was used. This means the phase-to-phase voltage across the motor windings switches twice as often, doubling the effective switching frequency and PWM resolution. The phase (IGBT) switching frequency is 15.625kHz, but the motor phase-to-phase windings see switching at twice this rate, or 31.25kHz, as you can see in Scope 1. This shows the three phase-to-phase voltages at a scale of 500V per division. You can see that each waveform has two different pulse widths, corresponding to the phase legs driving each end of the winding. The result is two transitions each 64µs period. The motor control timer also takes care of generating the complementary output signals to drive the high-side and low-side switches and inserting a dead-time between them, as shown in Fig.6. The timer’s final job is to ensure the outputs are placed in a known state if there is a fault. In our case, the timer is configured to switch them all low, turning off all the IGBTs, although this is fully configurable. This leaves our PWM code with the task of loading an updated pulse width value into each compare register every 64µs PWM cycle. To do this, a 32-bit ‘accumulator’ for each phase is incremented each time by an amount proportional to the desired output frequency. The upper eight bits of the accumulator are used as an index into a look-up table containing 256 samples of one cycle of the output waveform we want to produce. The appropriate sample is extracted, scaled according to the required output voltage, and loaded into the relevant compare register. Two accumulators and two PWM channels are used for a single-phase motor. The accumulators are initialised to values representing 0° and 180° in the table. The table contains siliconchip.com.au Fig.7: if we modulated each phase with a pure sinewave, the phase-to-phase output voltage would only be about 87% of the maximum (at top). Adding third harmonic content to the modulation allows us to achieve the maximum phaseto-phase voltage (around 230V RMS), demonstrated in the lower plot. values representing a sinusoid. For three-phase operation, three accumulators and three PWM channels are used, with the U, V and W accumulators initialised to positions 0°, 120° and 240° into the table for forward rotation or 0°, 240° and 120° for reverse rotation. Unlike the single-phase look-up table, the three-phase table does not contain samples of a pure sinewave. Instead, it contains values representing a sinusoid with about 16% of added third harmonic. Fig.7 shows why this is necessary. Starting at the top, sinusoidal phase voltages with a peak-to-peak value of 330V (shown dotted) produce phaseto-phase voltages (solid lines) with a peak-to-peak value of 570V. This corresponds to an RMS voltage of just 200V RMS, not the 230V we desire. If we modulate the phase voltages with a sinewave with an added third harmonic, as shown below, the peakto-peak phase voltages are the same as before, but the wave shape is very Australia's electronics magazine different. The resulting phase-to-phase voltages are nonetheless sinusoidal, but their peak-to-peak value is now 660V, giving an RMS voltage of 230V. State machine With the I/O and PWM taken care of, all that remains is to implement the motor controller’s application logic. This is done using a simple state machine. A state machine (properly a finite state machine) is a computational model that can be used to implement complex behaviour in a structured manner. The behaviour is modelled by several states, only one of which can be active at any given time; a set of transition rules determines how and when the machine can transition from one state according to external trigger events. Each state can have actions that are executed when it is entered, exited, or when a trigger event occurs. The simple version used here is always triggered by a regular timer ‘tick’, prompting the state machine to November 2024  35 Entry Action Trigger Action (Transition Rules) Exit Action - Initialise internal variables - Start IO Driver (reads mode switches) - Start PWM Driver (specify 1-phase or 3-phase) - Flash red, yellow & green LEDs twice, fast - Start soft start bypass timer (3 seconds) - if soft start bypass timer expired: - if 1-phase & Pool-mode transition to Pool-Pump state - else transition to Idle state - else no transtion - Close soft start bypass relay - Flash green LED slowly - Start pool pump timer (30 or 300 seconds) - Set speed_now to zero - Enable PWM - if fault transition to Fault state - if E-Stop open transition to Idle state - if Run open: - if speed_now > min_speed transition to Ramp state - else transition to Idle state - if pool pump timer expired transtion to Ramp state - if speed_now < pool_pump_speed increment speed_ now - else no transition - Turn green LED off - Disable PWM - Set speed_now to zero - Turn yellow LED on - Start idle dwell timer - if fault transition to Fault state - if idle dwell timer running no transition - if E-Stop open no transition - if speed_req > min_speed transition to ramp state - Turn yellow LED off - Read Reverse pin state - Flash green LED indefinitely fast - Set PWM direction (ignored if 1-Phase) - Set PWM speed to speed_now - Enable PWM (ignored if already enabled) - if fault transition to Fault state - if E-Stop open transition to Idle state - Get speed_req (speed demand, Run & Reverse states) - if speed_now ≤ speed_req – margin: - Increment speed_now (based on ramp, limit to speed_req) - Set PWM speed to speed_now, no transtion - else if speed_now ≥ speed_req + margin: - Decrement speed_now (based on ramp, limit to speed_req) - if speed_now < min_speed transition to Idle_state - Set PWM speed to speed_now, no transition - else transition to At-Speed state - Turn green LED off Fault state At-Speed state Ramp state Idle state Pool Pump state Initalise state Table 1: Software States - Assert At_Speed output (ignored if not enabled) - if fault transition to Fault state - Deassert At_Speed - Turn green LED on - if E-Stop open transition to Idle state output - if speed_now ≤speed_req – margin transition to Ramp - Turn off green LED state - if speed_now ≥ speed_req + margin transition to Ramp state - else no transition - Disable PWM - Set PWM speed to zero - Clear E-stop cycle flag - Assert Fault output (ignored if not enabled) - Set red LED - Set yellow LED if overtemp fault assess the transition rules associated with the current state and initiate a transition if required. If a state change is required, the state machine executes the current state’s exit actions, switches to the new state and executes its entry actions. The following trigger causes the new state’s transition rules to be evaluated. States are defined by three functions: an entry function containing the entry actions; a tick function 36 Silicon Chip - if faults cleared: - if E-Stop cycle flag clear: - if E-Stop open set E-stop cycle flag - no transition - else if E-Stop closed transition to Idle State - else no transition - else no transition containing the state change rules and tick actions; and an exit function containing the exit actions. By partitioning the VSD’s operation in this way, the controller’s logic becomes easier to understand and therefore implement and maintain. You can see this in Table 1, which describes the VSD’s operation in one neat summary. A total of six states are required, including an initialisation state where execution starts. The Australia's electronics magazine - Turn off red & yellow LEDs - Deassert Fault output timers described in the table are software timers driven by a 1ms interrupt provided to the state machine. The ‘tick’ time in the VSD is set to 100ms, meaning the state transition rules are evaluated 10 times per second. Conclusion That’s all we have room for this month. Next month, we will cover the construction, testing and use of the VSD. SC siliconchip.com.au Gear fest! November altronics.com.au 279 $ C 6162 189 $ C 6161 Instant event PA system! Sale prices end November 31st 2024 Super comfy! Bluetooth Boom Box & Wireless PA System Need instant sound for your next big get together? C 9038A S 9017A SAVE $30 SAVE $19 69 $ 60 $ Open Ear BT Earphones Latest design in over ear wireless stereo (OWS) headphones - drivers sit on your ear rather than in your ear canal for all day comfort. Includes charging case for up to 8 hours use per charge. 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Sale Ends November 30th 2024 Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or find a local reseller at: altronics.com.au/storelocations/dealers/ Shop online 24/7 <at> altronics.com.au © Altronics 2024. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0011 Subscribe to OCTOBER 2024 ISSN 1030-2662 10 The VERY BEST DIY Projects ! 9 771030 266001 $13 00* NZ $13 90 INC GST INC GST The MG4 XPower Electric Car Review MICROMIT Australia’s top electronics magazine EXPLORE-40E A slot-in replacement for the Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Raspberry Pi Pico Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $70 $80 $52.50 1 year $130 $150 $100 2 years $245 $280 $190 6 months $82.50 $92.50 1 year $155 $175 2 years $290 $325 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 Prices are valid for month of issue. Try our Online Subscription – now with PDF downloads! Micromite Explore-40; October 2024 8CH Learning IR Remote; October 2024 Compact OLED Clock; September 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 Part 1: Introduction Precision Electronics This is the first article in a series covering the basics of precision electronics design. The practical series will cover a range of topics, including precision op amps, instrumentation amplifiers, signal switching and noise. I will use real examples and real components to demonstrate the concepts. By Andrew Levido W hile I aim to cover this topic from a practical perspective rather than a theoretical one, some theory is unavoidable. Along with explaining the concepts, I hope to give a few tips and tricks along the way. Since most devices built today include a microcontroller, we will also look at analog-­to-digital and digital-to-analog conversion. What is precision? We should start by defining ‘precision’ in the context of precision circuits. We should also distinguish between precision and accuracy, two often confused terms. Both precision and accuracy are ways of looking at the error in the measurement of a physical or electrical quantity. Accuracy describes how closely a measurement or series of measurements matches the ‘true’ value. In practice, that more likely means how closely it matches an accepted proxy for the quantity, probably traceable to some international standard. Precision describes how closely a series of measurements match each other. It relates to the repeatability of a measurement – how confident we can be that another measurement in one minute, tomorrow, or next year will be the same as the one taken now. Alternatively, it could indicate how confident we are that the measurement taken by the second, 100th or 10,000th unit off the production line will perform identically to the first one. Fig.1 illustrates this nicely. It is a histogram of 16 different measurements of a nominal 10.0V source taken over time. The mean of the samples is Fig.1: 16 samples of a nominally 10V source. The measurement accuracy is the difference between the sample mean and the ‘true’ value of 10V, while the precision is the spread of samples about the mean. Here, the precision is ±0.2V (absolute) or ±2% (relative). 42 Silicon Chip Australia's electronics magazine 9.9V, with a spread of ±0.2V around this (from 9.7V to 10.1V). The mean differs from the ‘true’ 10V value by 0.1V. Therefore, we can say that our accuracy is within ±0.1V of 10.0V or ±1%. The precision of our measurement is ±0.2V around the 9.9V mean, so within ±2%. Precision and accuracy are related but independent quantities. We can have precision without accuracy and accuracy without precision (although the latter would be of limited value). Note that in the example above, an accuracy of ±1% does not mean that every measurement will be within ±1% of the actual value since the measurement precision is not good enough to allow that. Accuracy is all about traceability and calibration, whereas precision is all about understanding and controlling the sources of uncertainty or error in our circuits. It is not always about achieving the highest levels of precision – it is about getting ‘good enough’ results for the application, which requires us to know what the precision of our circuit is. From the example above, you will have seen that we talk about precision in both absolute terms, such as ±0.2V, or in relative terms using percentages (±2%). We also use parts per million (ppm) for relative precision when the numbers get very small; for example, 0.01% equals 100ppm. If we have extremely good precision, we might even talk about parts per billion (ppb)! We can always measure the precision of a circuit after it is built, but we have just seen that one sample isn’t enough. Also, we usually want to be sure our design will meet the precision targets before we commit to mass manufacture. Precision circuit design is the process of keeping careful track siliconchip.com.au of errors and uncertainties and how they accumulate to impact the overall precision of the circuit of interest. Sources of uncertainty Before we get into a practical example, it might help to understand where these errors and uncertainties come from. Many errors result from complex interactions of various causes, but it helps to think of them in some broad categories: Limitations of physics Real-world limitations introduce errors. For example, there is no such thing as a perfect insulator, so leakage currents occur. It is impossible to source or sink infinite current, so devices must have some finite output impedance, which means outputs will change with load. Noise Another inescapable result of physics is the electrical noise caused by the random movement of electrical charges in certain materials. This can significantly impact measurements involving small quantities (microvolts and microamps, or even nanovolts and nanoamps!). Noise is a whole topic in itself that we will cover later in this series. Temperature Sadly, almost everything in electronics changes with temperature, and usually not for the better. Resistor values change, noise increases and offsets drift. The wider the temperature range your device will be subject to, the more this will be a problem you must address. Frequency and time Like temperature, frequency changes almost everything. A parameter specified at DC may vary considerably as frequency increases. Some things get worse over time, too. MLCC capacitors lose capacitance with age, and even the frequency of crystals can drift over time. It’s not the biggest problem you will likely encounter, but it is worth being aware of. Manufacturing variation Even a well-designed component, using the best materials and a good manufacturing process, will have some degree of variation between parts. It is impossible to make them all siliconchip.com.au absolutely identical. Common examples include resistor tolerances and op amp input offset voltages. There will be a natural spread of these values around a mean (the nominal resistance for resistors or 0mV for op amp offset voltages). Understanding component limitations There are no perfect components, just as there are no perfect circuits. Optimising for one parameter may have a detrimental effect on another. One example that springs to mind is the common multi-layer ceramic capacitor (MLCC). Many of these use a dielectric material that allows the manufacturers to cram a huge amount of capacitance into a tiny volume for a ridiculously low price. The downside is that the capacitance is highly sensitive to temperature, applied voltage and ageing. The component variation with these conditions can easily be two or three times the nominal tolerance of the capacitance. That is the price you pay for 10¢ 10µF 0402-size capacitors. Sticking with the example of ceramic capacitors, do you know what it means when a capacitor is labelled X7R, X5R, Y5V, C0G, NP0 etc? It is related to the temperature range and how much the capacitance varies over it, but it is actually much more than that. For example, these codes also affect how capacitance changes with voltage. This shows why it pays to do your homework! Manufacturers are not always as forthcoming about a part’s limitations as they are about its features (especially on the front page of the data sheet). Be wary of typical values compared to worst-case values. You must read the data sheets carefully and thoroughly. Don’t just read the data tables – often, the graphs give useful information about how a device will perform that is quite different from the flattering conditions under which the nominal values are derived. A practical example Despite all this, it is, of course, possible to design high-precision circuits, and there are a few handy tricks that can help us get there. To get started, we will use a simple example that we can build upon in subsequent articles. Imagine we are designing a DC power Australia's electronics magazine Fig.2: our first attempt at a current-measuring circuit. The 0-1A current to be measured (Il) flows through Rs and the resulting voltage is amplified by IC1 to produce a 0-2.5V output. It uses regular 1% resistors and a lowcost rail-to-rail op amp. supply to power a microcontroller-­ based circuit. We want to measure the current consumed by our device over the range of 0A to 1A. We would ultimately like to measure currents down to the microamp level (or lower) if possible, since our device may go into sleep mode. This isn’t easy to achieve. We will develop the idea over the next few articles, but let’s start by working out what sort of performance is possible with some very basic components and a straightforward circuit. Fig.2 shows the circuit we will begin with. On the left is a 0.1W resistor used as a current shunt. For the time being, we will assume it is ground-referenced. This shunt will drop 100mV across it at the full 1A load. We need to amplify this signal to get it into the range of an analog-to-digital converter, say to around 2.5V, which means we need an amplifier gain of 25. I have used a low-cost general-­ purpose rail-to-rail input and output (RRIO) op amp, the LM7301, to start with since its inputs and outputs can swing to the rails. We’ll also use standard 1% tolerance resistors to set the gain. Initially, we will power this part of the circuit with a single 5V supply. To estimate the precision that we can expect from this circuit, we need to move through the circuit one element at a time, find its contribution to the overall error and sum them somehow. We will take this very slowly initially to illustrate the process. At node A, we will see a voltage proportional to the load current but with some uncertainty due to the resistor November 2024  43 Parameter Test Conditions TYP MAX Ta = 25°C 0.03mV 6mV Ta = Tj N/A 8mV 2μV/°C Measured Data Error Current Vout Abs. Rel. 0.0 25.0 25.0 1.0% N/A 99.7 251.9 2.7 0.1% Fig.3: this extract from the LM7301 data sheet shows the expected input offset voltage. At 25°C, it is specified to be ±30µV (typical) and ±6mV (maximum) – quite a range! I suggest using the latter in your designs. 199.8 515.2 15.7 0.6% 299.7 769.6 20.4 0.8% 399.9 1021.3 21.6 0.9% 499.9 1272.5 22.8 0.9% 599.9 1523.9 24.2 1.0% 699.9 1777.0 27.3 1.1% 800.0 2030.1 30.1 1.2% 900.0 2282.1 32.1 1.3% 1000.0 2533.3 33.3 1.3% Vos – input offset voltage TCVos – input offset voltage average drift Ta = Tj Adding two quantities with errors: (z + Δz) = (x + Δx) + (y + Δy) = (x + y) + (Δx + Δy) → z = x + y, Δz = Δx + Δy Multiplying two quantities with errors: (z + Δz) = (x + Δx)•(y + Δy) = x•y + x•Δy + y•Δx + Δx•Δy → z = x•y Δz Δx Δy and ≈ + Δz ≈ x•Δy + y•Δx z x y Fig.4: when adding or subtracting quantities with uncertainties, the uncertainty of the result is the sum of the absolute uncertainties, shown at the top. When multiplying or dividing, the uncertainty of the result is approximated by the sum of relative uncertainties, shown below. Table 1 – measured results from the Fig.2 circuit using a single supply (+5V). Units: Current (mA), Vout (mV), Absolute (mV), Relative (%). tolerance. The resistor tolerance is 1%, so it will have an absolute resistance value of 100±1mW. We will therefore see a voltage across it of 100±1mV at full load. We will also see the op amp’s input offset voltage appearing at node A. Fig.3 shows the relevant extract from the LM7301 data sheet. The input offset voltage at 25°C is specified to be ±30µV (typical) and ±6mV (maximum). The maximum offset is more than 100 times the typical figure! We will use the worst-case value for reasons I will discuss below. We now have two quantities (voltage across the resistor and the op amp offset voltage), each with its own uncertainty, that we need to sum. The error in the total value will simply be the sum of the absolute errors of each part. This probably seems obvious, gain-setting resistors will be 25±2%, or 25±0.5 in absolute terms. The total error at the circuit output (Node B) will therefore be the sum of the relative errors of the Node A voltage (±7%) and the gain (±2%), or ±9%. This corresponds to about ±225mV absolute error in the 2.5V full-scale signal. Clearly, that is not acceptable. The op amp offset voltage is the biggest contributor by far and is pretty easy to deal with. But how will this circuit perform in real life? but you can see the maths that proves it in Fig.4. That figure also shows the less obvious result: that the total error when two quantities are multiplied is approximated by the sum of the relative errors of each quantity. The approximation works because we can ignore the Δx•Δy term if the errors are small. This leads to an important rule for precision circuit design: If adding or subtracting quantities, sum the absolute errors; if multiplying or dividing, sum the relative errors. So, back to our circuit. Summing the absolute errors at node A gives a total error of ±7mV. You can probably already see this is a potential problem (no pun intended), but let’s keep going. At node B, we will see the voltage at node A multiplied by the gain of the op amp stage. The gain with two 1% Practical results I built this circuit and measured the results shown in Table 1. You won’t be surprised that they are much better than the worst-case estimate of ±9%. This is because the errors result from statistical variation, and there is a much higher probability that any given Fig.5: at left is a plot of the measured results from the Fig.2 circuit; note the subtle kink in the curve near zero. The closeup on the right clearly shows that the output is too high at 0A due to the op amp’s limited output swing. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Measured Data Error Measured Data Error Current Vout Abs. Rel. Current Vout Abs. Rel. 0.0 -41.5 -41.5 -1.7% 0.0 12.8 12.8 0.5% 97.9 203.7 -41.1 -1.6% 97.9 253.9 9.2 0.4% 198.2 454.6 -41.9 -1.6% 198.2 500.7 5.2 0.2% 298.3 693.3 -52.5 -2.1% 298.3 735.5 -10.3 -0.4% 398.3 944.1 -51.7 -2.1% 398.3 982.1 -13.6 -0.5% 498.3 1197.2 -48.6 -1.9% 498.3 1231.1 -14.7 -0.6% 598.3 1447.5 -48.3 -1.9% 598.3 1477.2 -18.5 -0.7% 698.0 1728.3 -16.7 -0.7% 698.0 1753.4 8.4 0.3% 798.0 1982.2 -212.8 -0.5% 798.0 2003.1 8.1 0.3% 898.0 2235.2 -9.8 -0.4% 898.0 2252.0 7.0 0.3% 998.0 2488.8 -6.2 -0.2% 998.0 2501.4 6.4 0.3% Table 2 – raw results from the Fig.6 circuit with a dual supply (±5V). Table 3 – the Table 2 data after applying a fixed offset and gain corrections. sample will be near the mean or nominal value than an outlier. The full-scale error was 33mV, or 1.3%, and the errors reduce at lower currents except at the bottom of the range, where there seems to be some kind of anomaly. You can see this also in the plot of the results in Fig.5, on the left. The full set of results looks OK except for the zero-current reading, which is slightly off. The first three readings, along with the ideal response, are shown on the ‘zoomed in’ plot on the right of Fig.5. There is clearly a problem at or near zero current. We know the op amp offset voltage is not causing this, because that would appear as a consistent vertical shift of the measurements above or below the ideal line. It is not caused by gain error, because that would appear as a variation in the slope compared to the ideal line. Something else is going on – there is a small but definite ‘bend’ in the measured results at the bottom end. The culprit is the op amp’s output swing. While the LM7301 claims to be a “rail-to-rail” output op amp, a close look at the data reveals that with a 5V supply and a 10kW load, the output typically won’t go below 70mV (and isn’t guaranteed to go below 120mV). We are measuring 25mV, which is better than claimed. This is a very good swing, better than most op amps, but it isn’t rail-to-rail as advertised! We would rather avoid non-linearities like this because they are harder to deal with than purely linear errors such as fixed offsets or gain errors, as we shall see. I refined my circuit by adding a negative supply rail (Fig.6). Running the tests again produced the data shown in Table 2 and plotted in Fig.7. In some ways, this looks worse than our first test! The most significant error is just over -52mV or 2.1% of full scale. This error occurred mid-scale, with the absolute error at zero being -42mV; at full scale, it is only -6mV (0.2%). The good news is that the points are fairly linear. The dotted line in Fig.7 is a line of best fit, using the equation shown on the graph. This line suggests there is a fixed offset error of -54.5mV and a gain error (the difference between the slope of the line and the ideal slope of 2.5) of about 1.7%. The fixed error comes mainly from the op amp’s offset voltage, which must be around -2.2mV (taking the gain of 25 into account). The gain error comes largely from the resistor tolerances. The good news is that there is no longer a bend in the plot. Note that the op amp offset is less than the quoted worst-case figure (±6mV), but by no means does it fall within the typical figure of ±30µV. This is just one sample, but it does illustrate the danger of assuming your results will match the ‘typical’ figures in the data sheet. We will improve this result next time by selecting a ‘better’ op amp and tighter tolerance resistors. But just for a moment, let’s look at another solution. We could compensate for both of these errors (offset & gain) by adding a fixed correction – either through analog trimming or, more likely these days, in software on the microcontroller. Just because we can, let’s look at how much we could improve these readings by applying gain and offset correction using the values from the Fig.6: powering the op amp from dual supply rails (±5V) fixes its output swing problem. Otherwise, this circuit is identical to Fig.2. Fig.7 (right): the measured result of the Fig.6 circuit, along with a calculated line of best fit (dotted). There is now a fixed offset and gain error that can be trimmed out in either the analog or digital domains. siliconchip.com.au Australia's electronics magazine November 2024  45 line of best fit. Table 3 shows the corrected results. Now the absolute error is never worse than about ±20mV, or 0.75% of full scale. Not bad, given the parts we have chosen. This is one of the big secrets of precision design. You can usually trim out fixed offset or gain errors to some significant degree. The emphasis should be on the word “fixed”. It’s way more difficult to trim out non-linearities or errors that change over time, such as temperature drift. Temperature effects To examine the effect of temperature, I want to introduce the idea of the error budget table. This is just a way of capturing the uncertainties we discussed above in a neat tabular form. Table 4 shows an example. You can use any format you like, but this is how I generally do it. Under the “At Nominal 25°C” section, you will see each step we went through in the above example, capturing the nominal value and relative and/or absolute uncertainty. For example, Line 1 is the shunt resistor and Line 3 is the op amp offset. Lines 2 and 4 are calculated values and are shown in bold text. I always show both the absolute and relative errors on calculated lines. At Line 8, we get to the ±225mV and ±9% error figures calculated above. The second part of the table brings the temperature-dependent errors into the picture. We obviously have to know the temperature range of interest to calculate these uncertainties. I have chosen a range of 0°C to 50°C (±25°C either side of the nominal 25°C) in this example. The data sheet for the shunt resistor I used (Stackpole CSR1225) tells me that its temperature coefficient (tempco) is 100ppm/°C. This means we will see a resistance change of up to ±2500ppm or ±0.25% over the range of interest on top of the 1% tolerance. Similarly, the op amp’s offset voltage has a drift of ±2µV/°C, corresponding to ±50µV. This is already more than the ±30µV ‘typical’ offset at 25°C claimed in the data – another reason to take ‘typical’ values with a grain of salt. If we continue with the rest of the analysis in the same way, we arrive at a variation of about ±0.8% over the proposed operating temperature range. Even if we could trim out all of the 25°C error in software, we are left with a temperature-dependent error approaching 1%. We will look at how we can reduce this in further instalments. Optimist or pessimist? One objection that frequently comes up when we are summing worst-case errors in this way is that we are being overly pessimistic in our design. We are assuming that errors will accumulate in the worst possible way. For example, we have assumed that our gain error is 2%, which would only be the case when both gain-setting resistors are at the extremes of their tolerances and in opposite directions. If they were both high or low by the same percentage, this would cancel out, and the gain would be unaffected. Is it reasonable to take this pessimistic view? What if our circuit had 10 gain-setting resistors instead of two? Would it be reasonable to assume they would all be at their tolerance extremes in the worst way? There is no correct answer to the question, but I can suggest some guidelines. Uncertainty is a statistical game – it’s all about probabilities and consequences. If the likelihood of the worst case occurring is low and its consequences are not severe, it is probably OK to make some concessions. But if the probability of an error Table 4: Error Budget Table for our Application occurring is high (eg, if you are making a lot of something), or the consequences of any errors are significant (dangerous, expensive or embarrassing), a cautious approach is better. One concession you might choose to make is to assume that the sources of error are uncorrelated. In such cases, it is possible to add errors (absolute or relative) as the root sum of squares. In our example of 10 gain-setting resistors, each with a 1% tolerance, we would come up with a gain error of ±3.1% instead of 10%. But I urge caution. The root sum of squares is just another statistical tool – it works best when there are a great many samples in a truly random and uncorrelated distribution. We do use this type of summation for noise, which fits these criteria, as we shall see in a later article. Remember that if some resistors have the same value, they will likely come from the same batch. In fact, they will probably have been manufactured sequentially. So they will very likely be off by roughly the same amount and in the same direction. In other words, the errors won’t be uncorrelated at all! In some cases, that can help you; eg, if you’re relying on matched resistor values. Still, you must examine the specific circuit to determine whether correlated errors will help or hurt your precision. Summary At this stage, it has become clear that our simple circuit is probably not up to the job of monitoring the current in our supply if we want anything better than a couple of percent resolution. We can trim out the worst of the ±9% error down to a little better than 1%, but we will have another 1% or so of error over the temperature range. This 2% error means a ±20mA uncertainty. We’ll have to do better next time! SC At Nominal 25°C Error Nominal Value Shunt Resistor: Stackpole CSR1225 (1% 100ppm/°C) 100mW Node A Voltage due to I × R shunt 100mV 1mV Op Amp: LM7301 (Vos ±6mV, 2μV/°C) 0mV 6mV Node A Voltage total (Line 2 + Line 3) 100mV 7mV Op Amp Gain Resistor R1: Yageo RC0805 (1% 100ppm/°C) 1kW 1.00% 0.25% Op Amp Gain Resistor R2: Yageo RC0805 (1% 100ppm/°C) 24kW 1.00% 0.25% Op Amp Gain (R1 + R2) ÷ R1 25 0.5 2.00% 0.125 0.50% Vout (Line 4 × Line 7) 2.5V 0.225V 9.00% 0.02V 0.80% 46 Silicon Chip Abs. Error Rel. Error 0-50°C (Nominal ±25°C) Abs. Error 1.00% Australia's electronics magazine 1.00% Rel. Error 0.25% 0.25mV 0.25% 0.05mV 7.00% 0.3mV 0.30% siliconchip.com.au Amazing value under $100 Q 1073A Q 1089 Q 1068A NEW! SAVE $20 79 $ 79 $ Autoranging True RMS DMM This compact true RMS meter provides in depth functionality for technicians troubleshooting circuits. 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Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/11/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. Surf Sound Simulator By John Clarke Relax and enjoy the sound of the beach from the comfort of your home. Forget the scorching heat in summer, the cold winds of winter or your bathing suit being full of sand! Ideal for beginners and experienced constructors alike, it’s a fun-filled project. Image Source: https://unsplash.com/photos/birds-eyeview-of-seashore-3P3NHLZGCp8 O ur new Surf Sound Simulator uses standard through-hole components that mount on a blue PCB shaped like a surfboard. It produces a sound that imitates the ebb and flow of the surf rolling up on the beach, including the occasional big wave. It can be used to augment the sound of surf if you live near the beach, or allow you to experience the beach even if you live in Alice Springs. The sound is ideal for masking background noises so that you remain relaxed or for a peaceful sleep. The project uses all standard parts and has a fun surfboard shape that includes graphics depicting waves. It includes an onboard loudspeaker, or you can use the RCA socket to feed the sound to a stereo system or powered speaker for an even more realistic effect. Using large speakers with extra bass will reproduce the deep thumps as the waves crash onto the beach. It’s powered by a 12V DC plugpack, so you don’t have to worry about batteries going flat. It requires no adjustments to work. All you do is switch it on, set the volume and you’re instantly drifting off, imagining a day at the beach. Producing the surf sound The sound of the surf is very similar to white noise, a randomly produced sound that covers the audio 48 Silicon Chip spectrum from 20Hz-20kHz (for humans). White noise has the same intensity level at every frequency. It is similar to the sound coming from an AM radio when it is not tuned to a radio station, or the noise produced by heavy rainfall. Pure white noise needs some changes to sound like the surf. The volume needs to change over time and there needs to be some tailoring of the frequency response to sound realistic. There also must be some randomness to the waves since there is considerable variation in the surf noise as waves come into and crash onto the beach, then withdraw. The volume levels of the surf have a triangular shape over time with some extra details. As a wave comes in, the sound steadily increases, hits its peak and then dies away. To simulate surf sound, we use a white noise source that has its volume varied by triangular ‘envelopes’. By having two such envelopes, we can obtain a degree of randomness to the sound level. With one generator, you only get the same wave crashing at a constant rate, but with two, you get two sets of waves rolling in at more unpredictable intervals. With further shaping of the triangular envelope, we can obtain extra surf sound realism. This design is based on a circuit from October 1990 by Darren Yates Australia's electronics magazine (siliconchip.au/Article/6622). We have kept it based around two lowcost LM324 quad op amps; while we could have reduced the component count using a microcontroller, that would have been less interesting and harder to modify. This version features some improvements to the circuit and it is considerably more compact and appealing on the surfboard-shaped PCB rather than in a plastic box. Block diagram Fig.1 shows the block diagram of the Surf Sound Simulator circuitry. The preamplifier, IC2c, provides the main sound output. It is fed white noise to its non-inverting (+) input, while the volume (or amplifier gain) is altered over time using two triangle wave generators and three modulators, designated MOD1, MOD2 and MOD3. The modulators change the shape of the triangular envelopes. The output of triangle wave generator MOD1 is also fed to a peak amplifier, IC2d. This amplifies just the peak of the triangular waveform, where it increases the triangle wave output level. After feeding this voltage into another modulator (MOD3), it is used to produce a large wave crash simulation for when the wave hits the beach. All three modulators vary the impedance from IC2c’s inverting siliconchip.com.au input to ground, changing the gain and therefore the sound level of the white noise. The output of preamplifier IC2c is fed to a low-pass filter stage comprising IC2b and some passive components. This changes the frequency response of the white noise so that the higher frequencies are reduced, more like water sounds. From there, the signal is available at the CON2 line output for connection to an external amplifier and loudspeaker. This signal is also fed to the volume control (VR1) for the power amplifier, IC2a, that drives the onboard loudspeaker. Circuit details Refer now to Fig.2, which shows all the circuit details. It is similar to the October 1990 version, with some variations. Some changes are simply because DC mains plugpacks these days are switch-mode types that provide a stable voltage under load, so we don’t need a separate regulator. In the 1990s, plugpacks generally comprised a mains transformer, bridge rectifier and filter capacitors. They provided a higher voltage with no load that dropped as current was drawn from the supply. The ripple also increased under load. For a voltage sensitive circuit, regulation was required. Other changes were to isolate the supply between the sensitive circuitry used to produce the surf sound from the amplifier that drives the loudspeaker. This allows a higher volume level, as the 1990 version was a little too quiet. Without the isolation and with higher volume levels, the circuit would oscillate, producing a squealing noise as well as ‘motor boating’. While ‘motor boating’ might seem like a reasonable thing to include in a surf sound simulator, it is actually an electronic term to describe a low-­ frequency circuit oscillation malfunction. This is where a circuit produces its output in bursts, a bit like the putput sound of a single-cylinder motor in a boat. Another change was to prevent click and pop noises when parts of the circuitry suddenly change voltage level, from near 0V to near 12V or vice versa. We will describe those changes as we come to them in the following circuit description. The main part of the circuit is the noise source. This is based on NPN transistor Q1. Its base-emitter junction is connected as a reverse-biased diode. This junction breaks down when the supply is in the reverse direction, allowing current to flow when the voltage across it reaches about 5V. The breakdown is a random process that produces considerable white noise. To avoid damage, the current through the transistor junction is limited to around 200μA using the 33kW resistor to the +12V supply. This noise is capacitively coupled to the non-inverting input (pin 10) of op amp stage IC2c. Two 100kW resistors connected in series across the 12V supply provide a 6V bias for IC2c so that its output can swing symmetrically within the 12V supply range. Triangle wave generators IC1d & IC1c together form the first triangle wave generator, while IC1a & IC1b form the second. The first generator is responsible for a wave that sounds very close (louder), while the second produces a wave that crashes in the distance (lower in volume). Because the two are nearly identical, we’ll just describe how one of them works, then mention the slight differences between the two. IC1d acts a Schmitt-trigger gate, while IC1c is connected as an integrator. IC1d’s output will be either high (around 10.5V) or low (near 0V). It charges or discharges the 33μF capacitor at different rates depending on whether it is high or low. When the output is low, the capacitor charges via the 680kW resistor and series diode (D1) plus the parallel 330kW resistor. When IC1d’s output is high, the capacitor charges only via the 330kW resistor. The 33μF capacitor charge increases in a linear fashion toward the positive supply when the pin 8 output of IC1c is low, while it discharges linearly toward the 0V supply when that output goes high. If you are interested in a more detailed (and complicated) description of how this works, see the panel titled “Triangle wave generation”. The only difference in the second triangle generator based on IC1a & IC1b is that the second generator has some lower-value resistors (100kW & Fig.1: two triangular waveform envelope generators with different periods control the preamplifier gain applied to the white noise source. Three modulators and one peak amplifier tweak the sound to make it more like waves crashing on the shore. The resulting audio is filtered and fed to the line output (CON2) plus a volume control (VR1) and power amplifier to drive the onboard loudspeaker. siliconchip.com.au Australia's electronics magazine November 2024  49 Fig.2: it helps to refer to the block diagram, Fig.1, when trying to understand how this circuit works. Transistors Q2 & Q4, diode-connected in series, produce a bias voltage for current buffer transistors Q3 & Q5 that tracks over temperature, to avoid thermal runaway. 150kW instead of 120kW & 680kW). It helps to make the two waves more random because the two generators run at different speeds. It also provides the second wave with a faster ‘travel rate’ towards the shore. One of the problems with the triangle generators is that the Schmitt trigger outputs (pins 1 & 14) produce a clicking sound whenever the voltage from their output swings between 0V and 10.5V. The 1990 circuit used 100nF capacitors from the outputs to ground to suppress this, but on building the circuit in 2024, we found it wasn’t that effective. Without any capacitors, the rise time of those outputs was 25μs; with the capacitors, it was reduced to 18μs, worsening it! We found that placing the 100nF capacitors at the non-­ inverting inputs of the op amps, at pin 50 Silicon Chip 12 for IC1d and pin 3 for IC1a, significantly increased the output rise time to 75μs. The clicks and pops went away. There are still two clicks that occur when the Surf Sound Simulator is initially switched on, but no more are evident after that. Diode modulators The outputs of the two triangle wave generators drive the diode modulator circuits as shown in the block diagram (Fig.1). These rely on the fact that the conductivity of a diode varies with the voltage across it, ie, a diode with 0.6V across it will conduct more current than one with only 0.2V across it. There are three modulators in the circuit, based on diodes D3 to D6. Diodes D3 & D4 connect to the same IC1c output, so are counted as one Australia's electronics magazine modulator. The first triangle generator drives D3 & D4, the second drives D6, while the third (D5) modulator is driven by the peak amplifier, IC2d. At the cathodes of these diodes is a voltage divider. In the case of D6, for example, there is a pair of 100kW resistors. These set the offset voltage for this modulator to 6V. Different resistance values are used in the voltage dividers of the other modulators. These set the offset levels to different values to ensure the correct switch-on sequence. For diode D6, this means that the output of its triangle wave generator must rise above 6V before the diode has enough forward bias to conduct. This output is coupled to the anode of D6 via a 47kW resistor and also to the inverting input of preamplifier IC2c via a 120nF capacitor. siliconchip.com.au While the voltage from IC1b remains below 6V, D6 is reverse-biased and the 120nF capacitor sees a high-­ impedance to ground. However, when the voltage rises above 6V, the diode begins to conduct, which decreases its AC impedance. The 120nF capacitor thus sees a progressively lower impedance to ground as the voltage across the diode increases. Since op amp IC2c is connected as a non-inverting amplifier, these impedance variations directly control its gain. If the impedance goes down, the gain goes up and vice versa. Thus, the diode modulators control the gain of the preamplifier stage to vary the sound level. When the voltage across D6 reaches 0.6V, the diode appears as a short-­ circuit to the capacitor and the impedance to ground is then set by the 8.2kW resistor connected to D6’s cathode. The 100μF capacitor and 8.2kW resistor form a high-pass filter that rolls off the response below 0.2Hz. D3 and D4 work similarly but have offset voltages of 7.2V and 5.45V, respectively. Note also that D4 controls another high-pass filter, consisting of a 4.7kW resistor and 100nF capacitor, with a -3dB point of 340Hz. Because of their different offset voltages, D4 comes into operation before D3 (which controls lower frequencies), so we get a realistic “whooosshhh” sound as the wave breaks. Peak amplifier The gain of IC2c is also controlled by diode modulator D5, which is driven by peak amplifier IC2d. Its input comes from the output of IC1c. The bias for IC2d’s inverting input (pin 13) is set to about 7V by the 33kW resistor and the two 100kW resistors. Thus, the output of IC2d remains low until pin 8 of IC1c reaches this threshold level. At that point, IC2d amplifies the signal to produce a faster, steeper waveform. This produces the big ‘dumper’ sound of a wave that crashes onto the beach. Triangle wave generation For the first triangle wave generator, IC1d forms a Schmitt trigger gate, while IC1c is connected as an integrator. IC1d’s output will be either high (around 10.5V) or low (near 0V) with different charge and discharge rates for the 33μF capacitor. The capacitor charges when IC1d’s output is low via the 680kW resistor and series diode, plus the parallel 330kW resistor, but only discharges via the 330kW resistor when IC1d’s output is high. The IC1d Schmitt trigger receives the voltage from IC1c’s pin 8 via a 47kW resistor to the non-inverting input (pin 12). Hysteresis is provided by the 120kW resistor from pin 12 to IC1d’s output. When IC1d’s output is low, pin 12 input is pulled lower via the 120kW resistor and the voltage divider formed with the 47kW resistor that monitors the IC1c output. The inverting input at pin 13 is at 6V. IC1d’s output will go low when pin 12 rises above the pin 13 voltage. Knowing that pin 14 of IC1d is low (0V) and that pin 8 is rising, we can find the voltage where pin 8 causes pin 12 to be at 6V. When there is 6V across the 120kW resistor, 50μA flows through it. The voltage at pin 8 must be sufficient to produce a 50μA flow through the 47kW resistor that has its pin 12 end at 6V. The voltage across the 47kW resistor will be 2.35V (47kW x 50μA). So pin 8 would be 8.35V (6V + 2.35V). This means that the 33μF capacitor charges to 8.35V at pin 8. The pin 9 side remains at 6V as IC1c adjusts its output to maintain this 6V. With pin 12 of IC1d just above 6V, its output goes high to around 10.5V. Now the capacitor (and pin 8 of IC1c) begins to discharge toward 0V via the 330kW resistor. Diode D1 is reversed-biased in this case. We can calculate what the pin 8 voltage will be when pin 12 just falls to 6V again. Since IC1d’s output is at 10.5V and pin 12 will be at 6V, the voltage across the 120kW resistor will be 4.5V (10.5 – 6V). So the current through the 120kW resistor will be 37.5μA. This same current flow is through the 47kW resistor, so it will have 1.76V across it, below 6V, giving 4.23V. Once this voltage is reached, the output of IC1d drops again to recharge the capacitor in the positive direction. We ignore any current to the non-inverting input of the op amp, as that will be just 100nA at most. As the two switching levels are 4.5V and 8.3V, that means there is a 3.8V hysteresis provided by the 120kW resistor. Without this, there would be no controlled oscillation. The resulting waveform at pin 8 of IC1c will be a sawtooth, a triangular shape rising faster than it falls. Partly this is because the LM324’s output can pull down to nearly 0V but can only go up to about 10.5V when powered from 12V. The other reason is that there is an extra current path via D1 when IC1d’s output is low. Scope 1 shows oscilloscope traces of IC1d’s output (pin 8) in the top yellow waveform and the triangle waveform output from pin 8 of IC1c in cyan. The triangle wave swings between 4.2V and 8.4V, close to the values calculated above. The faster charge and slower fall time for the triangle wave has the overall effect matches the sound of ocean waves, which come up to shore faster than they run back to the sea. Scope 1: the triangular sawtooth waveform generated at pin 8 of IC1c is shown in the lower (cyan) trace. On the right, the ‘scope indicates that the voltage difference between the peak and trough is 4.16V. The voltage at pin 8 of IC1d that dictates whether the capacitor is being charged (low) or discharged (high) is shown above in yellow. Low-pass filtering As IC2c amplifies the white noise generated by Q1, a 1.2nF capacitor in the feedback loop of IC2c rolls off the response above 130Hz. The 2.2μF capacitor in the feedback network of IC2b also rolls off the low frequency response of this stage below 7Hz. IC2b is a non-inverting amplifier siliconchip.com.au Australia's electronics magazine November 2024  51 Fig.3: assembly of the PCB is straightforward; simply fit the parts as shown here. Make sure the ICs, diodes and electrolytic capacitors (except the non-polarised ones) are orientated correctly. For the polarised electros, the longer lead goes on the side marked +. The speaker goes on the rear of the PCB; it is wired to the CON3 terminals and sound passes through the holes in the PCB. with a gain of 28. The original 1990 circuit used a gain of 11 for this amplifier, but with supply routing changes (described later), a higher gain is possible. It is a significant increase in the maximum volume at just over 8dB. Indicator LED1 is driven from the IC2b amplifier output via a 4.7kW resistor. The LED will light with varying brightness and, to some extent, mimic the sound level. Following IC2b is another low-pass filter stage comprising a 4.7kW resistor, a 10μF coupling capacitor and an 18nF filter capacitor. The 18nF capacitor rolls off the response above 1.88kHz to reduce higher frequencies further, adding realism to the sound. After that, the signal goes to the CON2 RCA socket and also to the 10kW volume control pot (VR1), which feeds the signal to the power amplifier, based on op amp IC2a and transistors Q2 to Q5. Q3 and Q5 buffer the output of the op amp to provide current gain; they are within IC2a’s feedback loop to reduce crossover distortion. Transistors Q2 and Q4 produce a bias voltage for the output transistors (Q3 & Q5). Only the base (B) and emitter (E) terminals of these transistors are connected, using them as diodes to produce a nominal 0.6V bias. These diode junctions match the voltage across the output transistor (Q3 and Q5) base-emitter junctions. The bias voltage ensures the output transistors are always conducting 52 Silicon Chip current and this reduces crossover distortion as signal swing passes the mid (6V) level where the output drive switches between Q3 and Q5. This type of amplifier is called Class-AB. Class-B means that one output transistor conducts for positive excursions and the other conducts for negative excursions. It also has some amount of Class-A operation at low signal levels, where both Q3 and Q5 are conducting, due to a small standing current through both transistors at these low levels. The 1W emitter resistors provide a degree of bias current stability. A higher bias current will cause extra voltage across the 1W resistors that effectively raises the bias required for Q3 and Q5 to conduct, reducing the current through them. The bias voltages from Q2 and Q4 remain more-orless constant unless the temperature changes. The bias current is kept steady with temperature because Q2 is physically touching Q3 and Q4 is touching Q5, so the transistor pairs maintain a similar temperature. This prevents thermal runaway should the output transistors heat up when driving a load like a loudspeaker. Without the thermal matching and with a fixed bias, as Q3 and Q5 heat up and their base-emitter voltages drop, the current through them would increase, causing more heating and thus thermal runaway. In our circuit, Q2 and Q4 will reduce the bias voltage Australia's electronics magazine as they heat up, preventing that. Q3 and Q5 drive the loudspeaker via the 1W resistors and the 470μF coupling capacitor. This capacitor removes the 6V DC offset of the amplifier so that the loudspeaker is driven purely by an AC voltage. Power for the circuit is from a 12V DC plugpack connected to CON1. Switch S1 connects this supply via two paths. One is via the 100W resistor to power the op amps. This supply is bypassed using two 470μF capacitors. The second path is via diode D8 to the loudspeaker amplifier circuitry, bypassed by one 470μF capacitor. Note that apart from the two wires for the loudspeaker, the other components that you can see fitted to this side are not required, and were only needed for our prototype. We have installed a plastic end cap on the back of the loudspeaker to improve its bass response. siliconchip.com.au clamps the reverse voltage applied to the circuit to -0.6V; the current through it is limited to 114mA by the 100W resistor. D8 provides reverse polarity protection for the 470μF capacitor that bypasses the loudspeaker driver supply. It prevents any current from flowing if the supply polarity is wrong. Construction The 100W isolation resistor prevents the circuit from oscillating and motor boating, as mentioned previously. This resistor, along with the two 470μF capacitors, maintains a stable voltage for the op amp circuitry that is separate from the loudspeaker driver supply. Without this isolation, any supply voltage change due to current drawn to drive the loudspeaker would reduce the op amp supply voltage, causing the surf sound generator voltages to vary, leading to motor boating. Reverse supply polarity protection is provided by diodes D7 and D8. D7 siliconchip.com.au All components for the Surf Sound Simulator mount on a double-sided blue PCB coded 01111241 that measures 236 × 80mm. As shown on the overlay diagram, Fig.3, most parts are on the top of the PCB. Only the loudspeaker is on the other side. An end cap is attached to the rear of the loudspeaker to improve its bass response. Begin by fitting the resistors. The colour codes for these are shown in the parts list but it is best also to check the values using a multimeter. Some of the colours can be difficult to discern against the blue background body colour of the resistor. Install the diodes next. D1-D6 are the smaller 1N4148 types, while D7 and D8 are 1N4004s. Take care to fit each with the correct orientation. The two IC sockets can be mounted next. Again, these need to be orientated correctly, with the notched section at the end with pins 1 & 14 as shown. The MKT polyester capacitors can now go in. These are not polarised, so they can go either way around. They will likely be marked with a code Australia's electronics magazine rather than the actual value; the likely codes are shown in the parts list. The transistors can go in next. There are three types: a BC549C for Q1, BC337s for Q2 & Q3 and BC327s for Q4 & Q5. Take care to install each in the correct position. Q2/Q3 and Q4/Q5 have their flat sides facing each other. Ideally, they should touch each other (perhaps with a smear of thermal paste between) so their temperatures track. Install CON1 (the PCB-mounting DC barrel socket) and switch S1 now. S1 can be an Altronics toggle switch or a Jaycar slider switch as specified in the parts list. LED1 can also be fitted now; ensure it goes in with the anode (longer lead) in the hole marked “A”. It can sit close to the PCB. The electrolytic capacitors are next. Most of these are polarised, so they must be orientated with the correct polarity. The plus sign (+) on the PCB shows the positive side, which corresponds to the longer capacitor lead. The striped side of the can is the opposite (negative) side. The two 33μF capacitors are non-polarised (NP) types, so they can be mounted either way. Now install CON2 (the PCB-­ mounting RCA socket) and potentiometer VR1. Insert and solder two PC stakes (PCB pins) at the CON3 speaker connection points. The loudspeaker mounts on the back of the PCB and is connected to those stakes/pins with two short lengths of hookup wire. For the moment, the loudspeaker can be left November 2024  53 Parts List – Surf Sound Simulator off the PCB and connected with wire leads for testing. 1 double-sided plated-through blue PCB coded 01111241, 236 × 80mm 1 76mm 8W 1W loudspeaker (SPK1) [Jaycar AS3006] 1 12V DC 150mA+ plugpack 1 PCB-mount DC barrel socket to suit plugpack (CON1) [Altronics P0621, Jaycar PS0520] 1 vertical PCB-mounting RCA socket (CON2) [Altronics P0131] 1 10kW logarithmic vertical 9mm PCB-mounting potentiometer (VR1) [Altronics R1988] 1 PCB-mounting 90° SPDT toggle or vertical slide switch (S1) [Altronics S1421, Jaycar SS0834] 2 14-pin DIL IC sockets 2 1mm diameter PC stakes (for CON3) 1 65mm uPVC DWV end cap (Iplex D105.65, Holman DWVF0194 or equivalent) [Bunnings 4770359] 2 M3-tapped 25-30mm Nylon standoffs or spacers (25mm for Holman end cap, 30mm for Iplex; use 10+15mm or 15+15mm if you can’t get the required lengths) 2 M3 × 25mm panhead machine screws Semiconductors 2 LM324 quad single-supply op amps (IC1, IC2) 1 BC549 (ideally BC549C) 30V 100mA NPN transistor (Q1) 2 BC337 45V 800mA NPN transistors (Q2, Q3) 2 BC327 45V 800mA PNP transistors (Q4, Q5) 6 1N4148 75V 200mA diodes (D1-D6) 2 1N4004 400V 1A diodes (D7, D8) 1 5mm white LED (LED1) Capacitors (all 63/100V MKT polyester unless noted) 4 470μF 16V PC electrolytic 1 330μF 16V PC electrolytic 3 100μF 16V PC electrolytic 2 33μF 50V NP (non-polarised) PC electrolytic 2 10μF 16V PC electrolytic 1 2.2μF 63V PC electrolytic 1 470nF (code 474) 2 120nF (code 124) 4 100nF (code 104) 1 56nF (code 563) 1 18nF (code 183) 1 1.2nF (code 122) Resistors (all axial ¼W 1%) 1 1MW 2 150kW 3 47kW 3 4.7kW 1 680kW 2 120kW 2 33kW 1 1kW 2 330kW 14 100kW 3 10kW 1 100W 1 270kW 4 68kW 1 8.2kW 2 1W 5% Testing Insert the two LM324 ICs into their sockets with the pin 1 and notched end orientated correctly. Make sure that when you push them down, the pins go into the socket and don’t get folded up under them. When you power the unit up with a 12V DC supply and S1 on, you should see LED1 light and hear the surf sound coming from the loudspeaker. If not, check the setting of the volume potentiometer, VR1. If there is still no sound, check the supplies to IC1 and IC2. There should be around 11.75V between their pins 11 and 4. Also check your construction for correct component locations and orientations. Once you are satisfied with the operation, the loudspeaker can be secured to the rear of the PCB using neutral-cure silicone sealant (roof & gutter sealant), contact adhesive or any other suitable glue. A 76mm-­diameter screen-printed circle is provided on the back of the PCB to show the ideal position. We attached a PVC plumbing end cap (a 65mm DWV [Drain Waste and Vent] type) to the rear of the loudspeaker to provide a baffle for it, giving extra bass. A small notch will need to be made with a round file to allow the speaker wires to enter the bottom edge of the end cap. The end cap can then be secured to the rear of the loudspeaker with the same glue used for the speaker M3 screws and spacers can be attached at the PCB mounting hole near CON1 and switch S1 so that the Surf Sound Simulator can sit horizontally or lean back vertically on the plumbing fitting at the rear of the loudspeaker SC and the lower standoff. The finished Surf Sound Simulator can rest on a shelf, desk or other flat surface. 54 Silicon Chip siliconchip.com.au TECH TO POWER UP YOUR SUMMER FUN? MARK YOUR CALENDAR: Wed 30th Oct to Sun 10th of Nov, 2024 NOW ONLY $ 199 EASY DIGITAL CONTROLS SAVE $100 FOR SUMMER COLDIES 29 95 RUNS ON 12V OR 24V MORE MODELS IN STORE $ ONLY 32 In-Car Handsfree Kit Take calls, stream music from a Smartphone via Bluetooth® to your car’s FM radio. AR3146 Get 230VAC (mains) from 12VDC (i.e. batteries). 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TL4762 RRP $1499 SALE ENDS SUNDAY 10.11.2024 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 Mini Projects #014 – by Tim Blythman SILICON CHIP Analog Pace Clock & Stopwatch Despite the commonality of digital clocks, analog Pace Clocks are still prevalent, being used for purposes like timing swimming laps. This version is driven by a microcontroller, so it can be started and stopped and even used as a stopwatch. As well as the mounting and wiring arrangements, you can also see the jumper wire connected between D8 and ground to force the Pace Clock to operate when it is powered on. If wiring up the switches, they connect to D8-D12 and GND. P ace Clocks are used by swimmers for training and practice. It is claimed they were invented on Sydney’s Northern Beaches, just up the road from the Silicon Chip office. A pace clock has a solitary hand, and the face is marked out in seconds, making it easy and quick to check lap times. It is usually marked with a 60 (or zero) at the top and a 30 at the bottom. The hand sweeps one revolution per minute, allowing times to be measured by simply glancing at the clock at the end of each lap. It would be easy to make a Pace Clock using just the second hand of a standard quartz analog wall clock, but using a stepper motor and a microcontroller gives us several advantages. Firstly, the stepper motor is much more powerful than the motor in a quartz clock, so the Pace Clock can be built with a bigger face and longer hand, making it more visible. Secondly, adding a microcontroller means it is possible to turn the Pace Clock into a stopwatch. Our Pace Clock can be started, stopped and reset. Since this can be done using digital inputs on the microcontroller, you could even Parts List – Pace Clock (JMP014) 1 5V Stepper Motor with Controller [Jaycar XC4458] 1 Arduino Leonardo main board [Jaycar XC4430] 6 male-female jumper wires [Jaycar WC6028] 1 male-male jumper wire [Jaycar WC6024] power supply for the Leonardo (eg, a USB power supply & micro-USB cable) 2 M4 × 15mm panhead machine screws [Jaycar HP0453] 4 M4 flat washers [Jaycar HP0465] 2 M4 hex nuts [Jaycar HP0462] Nylon M3 screws, nuts and washers to mount the Leonardo & stepper driver 5 SPST momentary pushbutton switches (optional) wire to connect switches to Leonardo board (optional) 1 sheet of cardboard, Corflute or thin ply 1 printed clock face (see text) 1 clock hand (eg, cut from cardboard or 3D-printed) space-filling glue such as epoxy, hot melt glue or neutral-cure silicone sealant siliconchip.com.au Australia's electronics magazine use it for automated race timing with the right accessory hardware. You can see a short video of the Clock in operation at siliconchip.au/ Videos/Pace+Clock The Leonardo board we are using (like many Arduino-compatible boards) has a crystal oscillator, so it will be pretty accurate, typically within 50ppm; that’s certainly accurate enough for an analog clock that is meant to be read by eye. We’ll detail the construction of our prototype, which is based on a clock face around 20cm across (allowing it to be printed on A4 paper). But you should have no trouble scaling up your version to be larger if needed. Circuit details Fig.1 shows the circuit. The stepper motor and its controller are on the right and are connected by a harness terminated with a polarised plug, so it can only plug in one way. The boxed area shows the parts on the stepper motor control module. Note how they connect to the motor and the Arduino Leonardo microcontroller board. This stepper motor has four windings, each of which is positioned in conjunction with an arrangement of fixed metal teeth. When energised November 2024  59 ALL DIMENSIONS ARE IN MILLIMETRES sequentially, they attract the corresponding teeth on the rotor. Because the teeth are positioned at intervals, the motor’s position can be set quite accurately. The motor we are using has 32 teeth and is also connected to a 1:64 reduction gearbox. That is equivalent to a simple stepper motor with 2048 teeth, which is more than enough to count out seconds with precision. The driver IC is a ULN2003 chip with open-collector Darlington transistor outputs; only four of its seven channels are used. The ULN2003 pulls its outputs to ground when the corresponding input is driven high. In addition to the connections to the motor windings, there are four LEDs with series resistors. Their anodes are connected to 5V and the cathodes to the outputs, so the LEDs light up as each winding is activated. Since the stepper motor is a unipolar type, this simple control system works well. A bipolar stepper motor type would require a more complex circuit, such as an H-bridge, that can drive positive and negative voltages. 60 Silicon Chip Six jumper wires provide power and control signals from the Leonardo to the stepper motor controller. For more information on stepper motors, see our primer article (January 2019 issue; siliconchip.au/Article/11370). To build a functioning circuit, you need only the first five items in the parts list. You might like to test and assemble them first to get a feel for the stepper motor’s operation. Assembly We tested our prototype with an Arduino Leonardo, so we know that it works, but just about any Arduino board with enough pins should also work. The functions of the pins are set by #defines in the sketch so that they can be changed if needed. The motor draws around 100mA, which any Arduino board can supply from its 5V pin. Connect the six jumper wires between the Leonardo and driver board as shown in Fig.1. For testing, connect an extra jumper wire between D8 and ground; that will start the clock when it is powered on (you can see this Australia's electronics magazine in our lead photo showing the back of the Clock). Software You’ll need the Arduino IDE software to upload the sketch to the board. It can be downloaded from: siliconchip.au/link/aatq Once it is installed and running, choose the Leonardo board and its corresponding serial port in its menus. Download the PACE_CLOCK sketch from our website (siliconchip. au/Shop/6/486), open it in the IDE and upload it to the Leonardo board (Ctrl-U). The default sketch scans all the switches shown in Fig.1; they are simply ignored if they are unconnected. You should see the LEDs on the driver board start to move in a quick sequence. Connect the motor and it should start to rotate at 1 RPM. If the motor buzzes or hums without turning, check that all the wires are connected and in the correct sequence. You can test the other switch functions by disconnecting the jumper wire from D8 and touching it to each siliconchip.com.au Fig.1: the driver module and pluggable wiring harness make this a very easy project to build, at least electronically. Take care with the wiring between the Leonardo and the driver module and you should have no trouble getting this circuit up and running. Fig.2: the dimensions for mounting the stepper motor. The larger 9mm hole accommodates the boss that protrudes from the body of the motor; the shaft is only 5mm in diameter and 3mm across the flats. The centre of the 9mm hole also marks the centre of the clock face. of D9-D12. The function pins are set out in the sketch. When the Start switch is pressed, the clock begins delivering the sequence to the control board needed to advance the clock hand. When the Stop switch is closed, the sequence is paused. Pressing Reset causes a faster sequence to be generated in reverse order, which rewinds the hand to the zero position. All we need to do this accurately is to keep count of the steps that the hand has moved. The Trim+ and Trim- buttons only work when the hand is stopped. They move the hand forwards and backwards at a moderate pace, to allow it to move to a new zero position, such as when first powered on. This also resets the step number. Clock face An online image search for “pace clock face” gave us many samples that could be printed out for use on the Pace Clock. We simply printed ours on a sheet of A4 copy paper and glued it to a piece of cardboard. siliconchip.com.au Our clock face was printed on a sheet of A4 paper and glued to a piece of cardboard. The metal screws retain the stepper motor while the plastic screw heads are for the Leonardo and driver module; the positions of the latter are not critical. If you want something a bit more polished, Bunnings has sheets of white Corflute (corrugated plastic sheet) that would also work quite well as a baseboard. We used Fig.2 to mark out the holes we would need and carefully cut them out with a sharp hobby knife. Wad punches would work quite well if you have them. Use M4 machine screws to mount the stepper motor to the board, with just the shaft poking out the front. The driver board and Leonardo have 3mm mounting holes, so they can be mounted with the Nylon M3 hardware. The positions are not critical; we recommend placing the Leonardo near the bottom of the clock so its power lead can hang down. We also designed a 3D-printed hand and a bracket to help mount a custom-­ built hand to the stepper motor’s shaft. These are available as part of the software download. We printed ours on a resin printer, and you can see them in our finished clock in the photos. A simpler approach would be to use a cardboard cutout for the hand. When Australia's electronics magazine The hand on the right has a socket on its underside, like the bracket at lower left, that makes it a friction fit to the stepper motor shaft. You might like to add some glue to help secure it. November 2024  61 gluing the parts, apply the glue and then rest the clock face-down. That will prevent the glue from running back up the shaft and into the workings of the motor. Customisation Our Pace Clock is not waterproof at all, so you will need to install it in a waterproof enclosure for use around the pool or at the beach. For simplicity, we left the control switches off our prototype. You could mount the Trim switches on the back since they won’t be used often. You could mount the Stop, Start and Reset buttons remotely, so that they can be controlled from a convenient location. If you want to make your Pace Clock more robust, something like the XC4482 prototyping shield could be used to mount the wires and switches. A few #defines in the sketch can be used to customise the Pace Clock. The PERIOD #define sets the time for one revolution and could be changed if you wanted a different period (eg, 30 seconds or two minutes). We have seen some Pace Clocks at swimming pools with dual opposing hands of different colours, so you The Palm Beach Scientific Training Group poses with the world’s first swimming pace clock at the Palm Beach rock pool north of Sydney, Australia. Source: https://swimswam.com/history-swimming-pace-clock/ Songbird don’t have to wait as long for one to reach the zero. If you need the clock to operate anti-clockwise, use the ANTICLOCKWISE #define in the code. An easy-to-build project Unfortunately, this will not make time run backwards. As noted earlier, the nine I/O pins that are used are also set by #defines, so you can change them SC too if you wish. that is perfect as a gift. SC6633 ($30 plus postage): Songbird Kit Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 62 Silicon Chip Australia's electronics magazine siliconchip.com.au Mini Projects #013 – by Tim Blythman SILICON CHIP Digital Spirit Level Here’s an easy project that’s really on the level! Using a digital accelerometer module and a bright LED display, it indicates its tilt in either degrees or percent. It’s powered via a USB cable (eg, from a USB battery bank). › Tilt angle display: -99° to +99° (1° resolution) › Gradient display: -99% to +99% (1% resolution; equivalent to -44.5° to +44.5°) › Power: 5V DC via micro-USB socket › Other features: an error message is shown if the Level is not aligned correctly A device like a spirit level is a handy tool for knowing whether things are level or not. It can also tell you how far something is from being level. For example, we recently had to install shelves on a sloping floor. We used a spirit level to adjust the height of each foot so that they were stable and round items wouldn’t roll off them. We thought a Duinotech Arduino Compatible 8×16 LED Matrix display (Jaycar XC3746) would make a great base for attaching a few other parts to build a Digital Spirit Level. It has mounting holes in the corners, so you attach this Level to a piece of equipment to check if it’s level or not (or screw it to a long piece of straight timber to make it more accurate). If you’re driving off-road, it’s important to know that your vehicle isn’t tilting beyond its abilities. You could mount this Level on the dash or near the rear-view mirror to make it easy to tell. Knowing that your caravan is parked on level ground will help you sleep at night, since you’re less likely to fall out of bed! In a vehicle, you could power it from a car phone charger, while if you want to make it portable, it can easily run off a USB battery bank. You can see a video of the Level in operation at siliconchip.au/Videos/Digital+Level Circuit details The Level is made from three modules and one pushbutton, wired Parts List – Digital Level (JMP013) 1 Leonardo Tiny main board [Jaycar XC4431] 1 I2C Tilt Sensor module [Jaycar XC3732] 1 16 × 8 LED Display module [Jaycar XC3746] 1 2-pin through-hole tactile pushbutton switch [Jaycar SP0611] 1 5cm length of double-sided foam tape [Jaycar NM2821] 1 micro-USB cable to suit Leonardo Tiny [Jaycar WC7724] 30cm of wire in various colours (display module wiring harness can be cut up if required) siliconchip.com.au Australia's electronics magazine together as shown in Fig.1. The Leonardo Tiny main board connects to a tilt sensor module, which incorporates an MMA8452Q three-axis accelerometer. By sensing the acceleration due to gravity, it can tell which way is down and thus how far from level the module is. The accelerometer is a digital IC that is controlled by and sends data over an I2C serial bus. An I2C bus requires two lines plus ground, so it connects to the SDA (serial data) and SCL (serial clock) pins of the Leonardo Tiny. There is also a tactile switch connected between the A1 pin and ground. The main board applies a pullup to the pin to sense when the button is pressed, which shorts that pin to ground. The LED matrix display module is also marked with SDA and SCL, but it doesn’t actually use the I2C protocol. Thus, we have connected it to different pins, which we can directly drive to produce its somewhat peculiar protocol. This sort of strategy is often called ‘bit-banging’, where I/O pins are driven manually high and low as needed to generate the required sequences. November 2024  63 Fig.1: follow this wiring diagram to connect the modules and switch. The SDA and SCL wires for the tilt sensor must be soldered to the underside of the Leonardo, while the remaining wires can be attached from above. In short, the AIP1640 chip in the LED module expects 8-bit bytes with their least significant bit first, while I2C uses 9-bit bytes (as it adds an acknowledgment bit) and sends them with their most significant bit first. The first byte that is expected by the AIP1640 chip is a command, while I2C devices expect to see an address first (allowing multiple devices to coexist on the same bus). Using the same pair of pins to communicate with both devices thus risks triggering unwanted actions, so we have kept them separate. Luckily, we had enough spare pins on the Leonardo Tiny to do that. Construction We’ve used the large back surface of the LED module as a convenient place to mount the other modules. It’s a bit fiddly to put together, but it makes for a tidy final package. Start by removing the header pins from the tilt sensor module, if it came with them fitted. We found it easiest to start by bending the pins straight. Apply heat to the underside of each pin and pull it upwards; it should slide right out of the plastic shroud. Use some solder-wicking braid (with a bit of extra flux, if you have some) to remove any stray blobs or lumps of solder. For wiring, we used some coloured solid-core wire we had on hand, but the LED module also comes with a harness we do not need, so you could scavenge some wire from that. Solder the tactile switch between the GND (−) pad and the A1 pad of the Tiny. Trim any excess lead length so they do not protrude below the bottom of the PCB. Then solder some insulated wires to the SDA and SCL pins on the underside of the Leonardo Tiny. These are the white (SCL) and light blue (SDA) wires in our photos. Attach the Leonardo Tiny and tilt sensor to the back of the LED Module using some lengths of double-sided tape, being sure to keep the tilt sensor’s edge parallel to the LED Module’s edge. We placed them in the corners of the module, but you might like to move them down slightly to make the top mounting holes more accessible. Be sure to use foam-backed tape so there is no chance of the boards shorting together where they touch, particularly the wires on the back of the Leonardo Tiny. Solder the other ends of the white (SCL) and light blue (SDA) wires to the corresponding pads on the tilt sensor. Next, run the red wires seen in the photo. They connect the Leonardo Tiny + pad to the Vcc pad on both modules. Similarly, the black wire in the photos connects the Leonardo Tiny – pad to GND on both modules. Now solder a wire (yellow in our photos) from D11 on the Leonardo Tiny to SCL on the LED module. A dark blue wire then goes from D10 on the Leonardo Tiny to SDA on the LED module. Software The software is simple enough. A library is used to communicate with the tilt sensor and gather data from it. It is processed to display a reading in degrees, or a percentage gradient, on the LED module. When the pushbutton is pressed, the display blanks and changes modes. The software is compiled and uploaded using the Arduino IDE, We found it best to lay it out in this fashion, with the switch and the white and light blue wires attached to the Leonardo Tiny before it is stuck to the LED Module. The remaining wires can then be soldered to complete the circuit. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P The display will show a percent symbol when a gradient is being shown. A 100% gradient is the same as a 45° angle. An arrow is shown to the left of the numerical display to show whether the slope is upwards or downwards. It is not shown when the displayed value is 0° or 0%. which can be downloaded from www. arduino.cc/en/software You will also need the SparkFun MMA8452Q library, which can be installed by searching for “SparkFun MMA8452Q” in the IDE’s Library Manager. We’ve also included a copy of version 1.4.0 of the library in the software downloads (siliconchip.au/ Shop/6/462). The library file for the LED module (XC3746.h) is included in the sketch folder. You can use this for your own projects by simply copying it to another sketch folder. Connect the Leonardo Tiny to your computer using a USB cable, then choose the Leonardo board profile in the IDE and set its serial port. After that, you can upload the sketch. The LED module should light up with a splash screen and then display an angle in degrees. If you want to change the default startup mode to percentage gradient, change the code to initialise the dispMode variable as ‘true’ instead of ‘false’ and reupload the sketch. If you see the message ERR flashing on the LED display, the sketch cannot communicate with the tilt sensor. Pressing the tactile switch (attached siliconchip.com.au to A1) when the message is flashing should reset the Leonardo Tiny so that it tries again. If the ERR message is shown but not flashing, ensure the Level is strictly vertical. If that is not the case, errors can creep into the calculations, so the Level presents a warning instead of producing erroneous values. During regular use, pressing the button will cause the display mode to change between degrees and gradient. The up or down arrow indicates whether the left-hand end of the Level is higher or lower than the right. Completion Place the Level on a horizontal surface and carefully adjust the tilt sensor until the Level reads 0°. If you like, cut a piece of card the same size as the LED module and use double-sided tape to stick it to the back of the Level. Remember to cut out a hole for the switch. You could also use some tape to stick the Level to a vehicle or a length of straight timber. Be sure the vehicle or timber is level and place the Level so it reads 0° or 0% before securing it. SC Australia's electronics magazine Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. November 2024  65 FlexIIDIce Flex Project by Tim Blythman We’ve published several dice projects over the years but all have been traditional six-sided affairs. Other types of dice are used for various games and activities. This dice project can emulate dice with up to 100 faces, coin tossing and other random events. N ot long after publishing our Dual Mini LED Dice project (August 2024 issue, siliconchip.au/Article/16418), we thought it'd be nice to have a more configurable ‘digital dice’ design. While some Circuit Notebook dice-rolling entries have used a microcontroller, most of our electronic dice designs, including the latest iteration from August, have used straightforward digital logic to implement the throw and display of the dice. One thing these designs all have in common is that they only emulate dice with six faces. The FlexiDice uses a microcontroller and an OLED display, so it can emulate just about any number of faces. We have chosen to allow up to 100, as that is the highest number of faces we have found on a real-life die. The FlexiDice is compact and handheld, running from a coin cell. The board uses surface-mounting components, but they are M3216 (3.2 × 1.6mm) passives, SOIC ICs and several larger parts, so it is not too difficult to build. Some games need only one or two six-sided dice, but many games use other types of dice or larger numbers. For example, the Dungeons and Dragons role-playing game (like many other role-playing games) uses dice with four, eight, 10, 12 and 20 sides. That includes 10-sided dice marked in tens so that its result can be combined with a regular 10-sided die to produce one of 100 different values. Dice with 100 sides exist, although their near-spherical shape makes them impractical to use because they do not stop rolling as quickly as smaller dice. One such example is shown below. Most of the other dice mentioned (with four, six, eight, 12 and 20 sides) are regular polyhedrons, so they are symmetrical with regard to their faces, while the 100-sided dice are not. Asymmetrical dice like the D100 may not show each face with equal probability. Those familiar with Dungeons and Dragons will also know the abbreviations used for various combinations of dice rolls. A roll of a single six-sided die would be abbreviated as “D6”, while the roll of two six-sided dice (as in games like Monopoly) is “2D6”. Dice with 100 sides exist but can be impractical. Our FlexiDice can give rolls up to 100 but won’t roll off the table. Source: https://w.wiki/AjL4 66 Silicon Chip Australia's electronics magazine We also use this terminology with the FlexiDice. Other games of chance use playing cards or coins to give a random result. The FlexiDice can emulate flipping two coins and shows images that resemble those found on an Australian penny, as is traditional in the historic Australian game Two-Up. The FlexiDice can also display playing cards and imitate decks with between zero and six Jokers. While most people will be familiar with decks with two Jokers (and thus 54 cards), the German game Zwickern has six Jokers in a 58-card deck. The Jokers are removed for many games (hence the zero option). The odds A microcontroller is designed to provide a deterministic outcome; the same input should result in the same output, so we need a way to inject some randomness into its behaviour. Of course, having a truly random outcome is the essence of dice, so we must ensure our means of generating random numbers is fair and not predictable. That the result is fair means that each outcome has a reasonably equal chance. For a result to be not predictable, results must be independent of each other. The most common method of generating randomness in our earlier siliconchip.com.au Features & Specifications ● Compact, handheld device ● Runs from one 3V lithium coin cell ● Operates down to 2.4V ● Auto power-down with <1μA sleep current ● Fun mini-game console form factor ● Graphic display for easy viewing ● Shake-to-roll vibration sensor ● Hardware-based random number generator ● Ten configurable roll presets plus numerous user presets Roll Types Dice with two to nine pips Numeric dice from two to 100 Random card pick with 0-6 Jokers Coin toss (heads or tails) dice projects is to use the variability in user input to randomise the result. That usually involves the user pressing a button or switch to activate the roll. The exact time the button is held down is used as the random element. As long as the hardware can cycle through the states fast enough, the user cannot influence the outcome, and the result is random. As we found during the development of the Dual Mini LED Dice, that is not always sufficient. In that case, we found that if the values of two critical timing capacitors were similar, the two halves of the circuit would interact and synchronise, resulting in the two dice often having the same result. The result could still be fair, but it was also predictable, which is undesirable. Fortunately, using two different values of timing capacitor was enough to overcome this with the Dual Mini LED Dice. The FlexiDice measures user input, but that is not the only source of randomness. We investigated several different noise (true random data) sources to see what would be suitable for this project. implemented such a circuit in the Personal Noise Source from September 2001 (siliconchip.au/Article/4151). A high enough voltage applied to the junction reaches a critical point that causes a rapid and unpredictable increase in current; an avalanche. In situations where the current is sustained, this can cause heating and damage. When avalanche breakdown is used for noise generation, a series resistor limits the current to avoid damage to the junction and allows it to recover and experience further random events. Many such noise sources (including the 2001 project) use the emitter-base junction of a transistor, with the collector being left unconnected. The necessary breakdown behaviour requires at least 6V, and the noise level is quite low, so substantial amplification is needed. These factors conspire to make such a noise source difficult to operate from a coin cell; hence, we looked at other options. Pseudo-random (LFSR) A later noise source project, the White Noise Generator (September 2018; siliconchip.au/Article/11225), uses a different noise generation method. In this case, the output is known as ‘pseudo-random’ since it is not truly random but generated by a deterministic process. Since they are deterministic, many pseudo-random processes can be proven to be fair and uncorrelated, but as the name suggests, they are not truly random. There are many types of pseudo-­ random noise sources, but one of the simplest to implement is the linear feedback shift register (LFSR). This is a shift register with its input being a linear combination of some of its outputs, usually by XORing some carefully chosen register bits. The FlexiDice implements a 31-bit LFSR that works in much the same fashion as that in the Digital White Noise Generator from 2018, although we do not use it as the primary source of randomness. This 31-bit LFSR cycles through nearly all 31-bit states (and thus over two billion 31-bit numbers) and so takes very many cycles to repeat. The all-zero state is the only state that is avoided since it results in the LFSR being stuck in that state. Since the LFSR's future state can be known from its current state, it can be very predictable. For example, we tested the FlexiDice using the LFSR as its only input and, unsurprisingly, the dice rolls were identical every time it was powered on. Noise multiplier The circuit we have implemented is known by various names, but “noise multiplier” seems the most appropriate. As the name suggests, the circuit amplifies noise from all sources, so even power supply noise enhances its operation. Unlike an avalanche diode, only modest amplification is needed, and one of the outputs is digital in nature, allowing it to be easily fed to a microcontroller. Consider the sub-circuit shown in Fig.1. The left-hand op amp is wired as a comparator, with its inverting input connected to a half-rail reference generated by a divider. A signal is applied at Vin; if it is more than half of the supply voltage, BIT_OUT is high; otherwise, it is low. The right-hand op amp is configured to have a gain of two, with the inverting input referenced to BIT_OUT. In other words, Vout will be double Vin minus BIT_OUT. Scope 1 shows these values as Vin is simulated being swept from 0V to Vcc. Avalanche diodes One of the better-known random noise sources is the breakdown behaviour of a reverse-biased PN junction (avalanche breakdown). We Fig.1: this circuit snippet has various uses, including as an analog-to-digital converter, but we are using it as a noise source. By sampling and holding the output and feeding it back to the input, repeated cycles amplify the noise to a measurable level. siliconchip.com.au Australia's electronics magazine November 2024  67 Scope 1: these traces are from a simulation of the Fig.1 circuit, with Vin being the input and Vout and BIT_OUT being the outputs. If you add the green trace to the cyan trace, the result is double the pink trace. Scope 2: the voltages around IC2 and IC3. The blue trace is one of the phase outputs from IC1, while the yellow trace is the mid-rail reference. The red trace is Vin and the green trace is Vout downstream of the 1kW resistor. Note the settling time and that for each phase, the red trace follows the previous phase’s green trace as the capacitors alternate. Scope 3: this is much the same as Scope 1, except it is measured on the actual hardware. Vin (red) ramps up as current is applied to one of the 100nF capacitors. The transition on BIT_OUT (blue trace) is clear. The grey trace shows the sum of BIT_OUT and Vout (green trace), which is double Vin apart from the brief glitch at the transition. 68 Silicon Chip Australia's electronics magazine What the circuit is doing is doubling the voltage (including any noise present); hence the term noise multiplier. By maintaining its output between the supply rails, the circuit avoids saturating, which would cause noise information to be ‘lost’. The extra information is available at BIT_OUT. Another name we have seen for this circuit is “modular entropy multiplier”. Consider a division operation, with the dividend being Vin × 2 and the divisor being Vcc. The outputs (BIT_OUT and Vout, respectively) are the quotient and modulus (or remainder) of the operation. Another way of viewing the circuit is as a one-bit analog-to-digital converter. The circuit can iterate over multiple bits by taking the output voltage and feeding it back to the input. To do that, we need a sample-and-hold circuit to allow the intermediate states to stabilise and not immediately feed back. At each stage, the value of the BIT_ OUT line state would be noted, then the voltage on Vout would be fed back to Vin. In this case, it turns out that the BIT_OUT values will form a binary value representing the initial voltage. Table 1 shows the progression with a starting voltage of 0.333 (for Vcc = 1V). The binary value formed from the BIT_OUT column is 01010101, or 85 in decimal, which is one-third of 256, as expected. Note that the Vin values do not return exactly to the 0.333 starting value but quickly diverge from it. That is what makes this circuit useful as a random source. For example, take a 100nF capacitor at 3V, for which the formula Q = CV gives a charge of 3 × 10-7 coulombs or around 1.8 × 1012 electrons. That many electrons can be represented by a binary number with 41 bits. If we run the noise multiplier for more than 41 cycles, we are apparently counting fractions of electrons. Those familiar with electrons will know that they do not divide easily! What we are measuring at this stage (and probably for many stages before) is just the noise present in the system. That is the essence of the noise multiplier’s operation. Firmware The program on the microcontroller is responsible for driving the display in siliconchip.com.au The top (right) and bottom (left) side of the main PCB. The OLED module mounts to the top side and sits with a small gap between it and the components below. Note the hole for a screw to help secure the coin cell in place. response to user input. The main task is to emulate a random event, such as rolling dice or picking a playing card at random. The firmware requests multiple bits from the noise multiplier by toggling PH1 and PH2 and reading BIT_OUT a few times (more on this later). It performs an XOR operation on those bits. We substantially reduce the correlation between successive bits by combining multiple bits to output one bit. We need to request multiple bits to represent an event with more than two outcomes. In practice, every roll uses 24 bits from the noise generator. A 24-bit number is large enough that any rounding that might cause one number to appear more often than another is minimal. The result is converted to a coin flip, dice pips, card selection or numerical display and then shown on the OLED screen. Each ‘roll’ can be configured to show one or two results, and they can be any of the alternatives; you could request a coin and a playing card, for example. Two dice would be a common option. Note that the choice is done ‘with replacement’. For playing cards, it is equivalent to picking a card from a deck and then returning that card before choosing the second card. Thus, the same card can be selected twice in the same draw. Another way to consider this is drawing a single card from each of two decks. When starting up, the analog voltage on pin 19 (which is not connected to anything) is converted to a value from 0 to 1023. The noise multiplier is run siliconchip.com.au for that many cycles plus another 40, which ensures it is not in a state that can not be predicted by the initial conditions. When a roll is requested, bits are taken from the noise amplifier while the button is held down, further randomising the outcome. An animation is played with random results from the LFSR before the final roll is displayed using results from the noise multiplier. We use the LFSR for the animation since the noise multiplier takes some time to generate a result. It’s also possible to use the LFSR as the main random data source for rolls. When the results are displayed, the microcontroller starts a timer. When the timer expires, all peripherals are shut down, and the microcontroller enters a low-power sleep mode that it can be left in for extended periods without flattening the cell. We tested this with our Coin Cell Emulator from the December 2023 issue (siliconchip.au/Article/16046). Table 1 – analog-to-digital conversion one bit at a time It registered 0.0μA during sleep, so we are confident that the current consumption when not in use is well below 1μA. When it is not sleeping, like many such projects, the OLED is the main current draw; how much it draws depends on the brightness setting. We saw up to 10mA total current with the default brightness settings, so it pays to keep the OLED brightness as low as possible. The rest of the circuitry uses about 1.5mA when it is not sleeping, jumping to 2.5mA while a roll is occurring or SETTINGS is active, since the processor has more to do. The remainder of the firmware is responsible for configuring the Flexi­ Dice, including choosing what combinations of rolls are available. We’ll delve into these once construction is complete. Much of the microcontroller’s flash memory (which also holds the program instructions) is used to store the graphics and fonts used to create the various displays. Circuit details VIN BIT_OUT VOUT 0.333 0 0.666 0.666 1 0.332 0.332 0 0.664 0.664 1 0.328 0.328 0 0.656 0.656 1 0.312 0.312 0 0.624 0.624 1 0.248 Fig.2 shows the final FlexiDice circuit. IC2 and IC3 form the noise multiplier, each with a 100nF capacitor bypassing their supplies. IC3 is a dual low-power rail-to-rail op amp configured nearly the same circuit as in Fig.1. The main exceptions are that the feedback resistor is only 82kW and that there is a 1kW resistor on Vout to limit peak currents from the op amp. The Vin and Vout voltages connect Australia's electronics magazine November 2024  69 to quad analog switch IC2, which is arranged to allow either of two 100nF capacitors to be connected to Vin and Vout. This is the sample-and-hold buffer mentioned before in practice. The PH1 and PH2 lines from microcontroller IC1 control it. If both PH1 & PH2 are low, the capacitors are disconnected. When PH1 is high and PH2 low, one capacitor is connected to Vin and the other to Vout. The connections are reversed if PH1 is low and PH2 is high. The situation with both PH1 and PH2 high is avoided. Alternating PH1 and PH2 allows us to step bits out of the noise multiplier circuit, which you can see in Scope 2. Note the settling time (about 1ms) needed to ensure the capacitor fully charges to the Vout value. Even with a rail-to-rail op amp, component tolerances and op amp input offsets could conspire to saturate Vout to one of the power rails, which would result in the same data being continually delivered. The feedback resistor value has been reduced from 100kW to 82kW in order to exclude the possibility of the multiplier getting stuck in this state. This value means that Vout is limited to between about 10% and 90% of Vcc, which makes it more likely for BIT_OUT to change states on each cycle. Thus, the output is not entirely random. Using the terms we mentioned earlier, the outcome is fair but slightly predictable. We handle this by requesting extra random bits in the microcontroller firmware. Microcontroller IC1 is a PIC16F18146 8-bit microcontroller; it also has a 100nF supply bypass capacitor. A 22μF bulk bypass capacitor helps reduce the peak current loads on 3V coin cell BAT1. IC1’s pin 4 MCLR input is pulled up to 3V by a 10kW resistor; this, the power pins (1 and 20) and programming pins (18 and 19) are taken to Coin Cell Precautions The FlexiDice requires a coin cell; even though we have added protections such as the locking screw, care should be taken so that children are not left unattended with it. ICSP connector CON1. This can be used to program the microcontroller; we also used it for debugging during development. The microcontroller drives the PH1 and PH2 lines from pins 6 and 7, ensuring that both are never high simultaneously. When it switches them, they are both briefly set low to ensure that the circuitry around IC2 is not closed in a loop. Seven of the micro’s I/O pins (9, 10, 14, 13, 12, 11 and 15) are configured as inputs with pullups, and these connect to switches S1-S7. S1-S6 are tactile switches, while S7 is a vibration switch that can be triggered by shaking or bumping the FlexiDice. The other ends of all the switches connect to ground so that their closure changes the state of the connected I/O pin to low. MOD1 is an I2C OLED display module powered by IC1’s pin 3 (RA4). This allows the display to be completely powered down for minimum power consumption when not needed. Pins 2 and 16 of IC1 provide the I2C data interface for updating the display. Fig.2: apart from the noise amplifier section, which is similar to Fig.1, the FlexiDice circuit is a fairly simple microcontroller application. IC3 is the op amp in Fig.1, while quad analog switch IC2 and the two 100nF capacitors provide the sample-and-hold feature. The microcontroller can power down everything except itself, allowing the lowest possible sleep current. 70 Silicon Chip Australia's electronics magazine siliconchip.com.au Similarly, the noise multiplier is powered from IC1’s pin 5 and can be shut down as needed. We have connected one of the noise multiplier capacitors to pin 17, allowing us to monitor the noise multiplier state or inject a voltage if required. Using a weak pullup current from pin 17, we created the plot shown in Scope 3. This is similar to Scope 1 but measured on real hardware instead of a simulation. All ICs are rated for operation down to 2V or lower, but from experience, we have found that the OLED display modules will falter around 2.4V; this is what sets our lower operating limit. A lithium cell reaching that voltage under a light load has exhausted almost all its stored energy. Construction The FlexiDice is built on a double-­ sided PCB coded 08107241 that measures 34 × 62mm. It includes surface-­ mounting components, so you will need the standard SMT gear. A finetipped soldering iron, flux paste and tweezers are recommended. A magnifier, some solder-wicking braid and fume extraction will also help. Start with the three ICs. They are all different sizes, so it should be easy to tell them apart, although you will have to take care with their orientations. Note the location of the pin 1 dot in each case and check it against the PCB silkscreen and Fig.3 overlay diagram. Start by applying flux to the PCB pads for the ICs and sit each in place. Tack one lead and check that the others are aligned. If not, remelt the solder and nudge them into place. Also make sure that the parts are flat against the PCB. Solder the remaining leads, cleaning the iron’s tip as needed. If you get a bridge between pins, you can remove that by adding more flux and pressing the braid against the bridge with the iron. Carefully drag both away Parts List – FlexiDice 1 double-sided main PCB coded 08107241, 34 × 62mm 1 double-sided panel PCB coded 08107242, 34 × 62mm 1 SMD 2025/2032 coin cell holder (BAT1) 1 5-way right-angled header strip (CON1, optional, for ICSP) 1 1.3in 128×64 I2C OLED module (MOD1) [Silicon Chip SC6511 or SC5026] 1 4-way pin header (for MOD1, may be included) 6 SMD 2-pin tactile switches (S1-S6) 1 SW18010 vibration-triggered switch or similar (S7) 1 M2 × 6mm Nylon panhead machine screw 2 M2 Nylon hex nuts 1 2 × 2cm piece of double-sided foam-core tape 2 1cm piece of wire (eg axial lead offcut or pin header) to secure MOD1 Semiconductors 1 PIC16F18146-I/SO microcontroller programmed with 0810724A.HEX, SOIC-20 (IC1) 1 74HC4066 quad analog mux IC, SOIC-14 (IC2) 1 MCP6L2 dual low power rail-to-rail op amp, SOIC-8 (IC3) Capacitors (all SMD M3216/1206 X5R/X7R) 1 22μF 16V 1 1μF 35V 5 100nF 50V Resistors (all SMD M3216/1206, 1%, ⅛W) 3 100kW [104/1003] 1 10kW [103/1002] 1 82kW [823/8202] 1 1kW [102/1001] FlexiDice Kit (SC7361, $30 + P&P): contains all parts in the parts list except the ICSP header, which is not required because IC1 comes pre-programmed. together once the excess solder has been taken up. Five 100nF capacitors and one 1μF capacitor mount on the top of the PCB. Do not mix them up, as they will not be marked. Solder them using a similar strategy to the ICs: add flux, tack one lead, check and then solder the other lead. The six resistors will have codes marked on their tops, making them less likely to be mixed up. Solder them to the PCB similarly, according to the silkscreen markings. Flip the PCB over and solder the 22μF capacitor, followed by cell holder BAT1, as shown in Fig.3. Ensure that the cell holder opening faces towards the edge of the PCB. Add a good amount of solder to help secure it firmly. Now is a good time to clean flux residue from the PCB. Use a solvent such as isopropyl alcohol, a general flux cleaner or whatever is recommended for your flux. Allow the PCB to dry and inspect it closely for dry joints, bridges and other issues. These will be hard to fix once the OLED screen is fitted to the PCB. One of the more insidious problems occurs when the solder does not adhere to the pad on the PCB. The lead may appear to have a glossy, well-formed solder bead, but it is not connected to the pad below. That can be caused by the part not being flat against the board. If you find this has happened, add more flux and press down gently on the pin with your soldering iron. Solder the six tactile switches next, being sure to align them with their Fig.3: assembly of the FlexiDice is easy with even modest SMD skills. Ensure the ICs are orientated correctly and do not mix up the capacitors. The OLED module sits over the top of the PCB (see the black outline). Once you have tested everything, we recommend carefully glueing the body of the vibration switch to the PCB. siliconchip.com.au Australia's electronics magazine November 2024  71 Screen 1: when first powered on, the FlexiDice shows this screen, indicating it is ready to roll a D4 (four-sided die). The coin cell voltage is at upper left, while the sleep countdown timer is at top right. Screen 2: pressing the UP button will run a brief random animation and then show the result of the roll. Pressing DOWN will return to Screen 1. Any button press will also reset the countdown timer. Screen 3: pressing LEFT and RIGHT will cycle between numerous roll options. Shown here is a draw of two playing cards, each from a standard 52-card deck (without Jokers). Screen 7: in case you find the vibration sensor too sensitive, you can turn off S7's ability to wake the FlexiDice from low-power sleep. By default, ‘shake to wake’ is on. Screen 8: if you wish to test the MEM (modular entropy multiplier), press UP from this screen. Screen 11 shows the testing screen that can be used to check its fairness and correlation. Screen 9: if you prefer to use the LFSR (linear feedback shift register) as the random noise source, this screen can be used to turn the hardware noise source off, saving a small amount of power. silkscreen markings. Any excess flux can be cleaned up with a cotton tip dipped in solvent, which avoids getting solvent into the switch mechanisms (that can cause them to fail). Solder vibration switch S7 next. Bend the leads 90°, being mindful of the orientation of the leads. Make sure its body is flat against the PCB. If the 4-way header is not already attached to MOD1, the OLED module, fit it now. Then use a piece of card or thin plastic to temporarily space the module away from the components below it on the PCB. Solder its leads, adjusting if needed to make the display align neatly with the PCB. Trim the excess lead lengths and remove the card or plastic. Next, solder some short pieces of wire (such as lead offcuts or single header pins) from the PCB to the two pads in the bottom corners of the display, adding some mounting rigidity. part of the MPLAB X IDE from: siliconchip.au/link/abzy The Snap cannot supply power, so you will need to provide some; fitting a coin cell is the easiest way. Choose the PIC16F18146 as the Part, open the 0810724A.HEX file (available to download from our website) and connect the programmer to CON1, aligning the pins marked with the arrow. If you only plan to use this connection once, you can insert a five-way pin header into the first five pins of the programmer’s header and hold the FlexiDice PCB against the pins to ensure good contact. Press the Program button and check that the programming completes and is verified successfully. The OLED should also light up (see Screen 1), indicating that the program is working. Using it Fit a coin cell if you have not already done so. Check that the polarity is correct; there should be a small + sign on the top part of the cell holder. The default program allows the FlexiDice Programming IC1 If you have bought the PIC or a kit from the Silicon Chip Shop, IC1 will be programmed already and you can skip to the next section. Otherwise, use a PICkit 4, PICkit 5 or Snap programmer and the MPLAB IPE (integrated programming environment). The IPE can be downloaded as The main board should look like this before you fit the OLED. Make sure all the solder joints are good before doing that! 72 Australia's electronics magazine Silicon Chip siliconchip.com.au Screen 4: Pressing BACK and OK together will enter SETTINGS. This screen sets the display timeout, which can be changed in five-second steps with the UP and DOWN buttons. Screen 5: pressing RIGHT cycles to the next setting screen, which changes the display OLED module’s brightness. The display will dim slightly during the last two seconds before sleep. Screen 6: some OLED modules have a horizontal offset, which can be trimmed on this screen with UP and DOWN. Both arrows are showing fully, meaning the display is correctly aligned. Screen 10: this and nine other screens like it configure your custom rolls. Pressing UP will take you to Screen 12, where you can change the graphics, colour and number of outcomes. Screen 11: here, UP starts the test, taking 100 single-bit samples from the noise generator. The results are shown at the bottom. If you consistently see low % results, the noise generator may not be working. Screen 12: from each page here, use LEFT and RIGHT to view each option and UP and DOWN to edit it. If the right die is set to NONE, only a single outcome (the left die) will be displayed. to work immediately, and the OLED should show a sensible display as soon as it is powered on (see Screen 1). You can initiate a roll by pressing S3 (the UP button) or activating the S7 vibration switch. Screen 2 shows the result of a roll. S4 and S5 (LEFT and RIGHT) cycle between the different roll options. Screen 3 shows one of the other options before a roll is performed. Pressing S6, the DOWN button, will reset the screen; the other two buttons are associated with SETTINGS. If the display times out and the FlexiDice enters sleep mode, pressing any button will wake it up again. Perform a few rolls and confirm that the results appear random. If you get the same result on every roll (especially if it is 1), the noise multiplier may not be working. There is a utility within SETTINGS to check the noise multiplier’s output (see Screen 11). mode. In this mode, the LEFT and RIGHT buttons cycle between the available parameters, while UP and DOWN will change them. Pressing BACK will exit SETTINGS. There are a handful of display and operation preferences, plus configuration for ten roll combinations that can be set up as you choose. They (and the other settings) are kept in EEPROM, so they take effect immediately and will be retained even if the battery is removed. Screens 4-12 and their accompanying captions explain Configuration Pressing S1 and S2 (BACK and OK) together will enter the SETTINGS The PCB shown at left is only used as a ‘panel’ to protect the back of the main PCB, it has no components to solder to it. siliconchip.com.au Australia's electronics magazine November 2024  73 Screen 13: dice with pips can show rolls up to nine. You’ll note some nice touches, like the orientation of the two and three roll is not fixed but can vary, just like actual dice. Screen 14: rolls (draws?) using the card options show the standard playing card symbols as seen here. Up to six Jokers can be added to the deck by selecting the 58-card option. Screen 15: the coin toss shows its outcomes as images of an Australian penny, so it’s well-suited for a traditional game of Two-Up. each of the settings screens available on the FlexiDice. notable bias towards one result. Our tests would put the fairness and correlation of those real-life coin toss results at around 97%. and card picks and those that are configurable from SETTINGS. Whenever the FlexiDice enters sleep mode, all settings are retained. Pressing any button apart from UP (or the vibration switch) will reinstate the previous display so that you can, for example, see what the last roll was. Pressing UP (or shaking) will always start a new roll, so there is no delay in getting a result after exiting sleep mode. This means it is less distracting when you are playing a game. Because settings are saved in EEPROM, all the settings and presets will be retained even if you change the cell. The LFSR state is also saved every time the Dice goes to sleep, so there is less chance of the same result occurring repeatedly if you are using the LFSR. Diagnostics Screen 11 shows the noise multiplier diagnostic screen. It performs several rolls and reports on their fairness and correlation. Scores of 100% mean that the rolls are fair (equal number of 0s and 1s) and uncorrelated (any roll has an equal chance of following any other roll). The result of all rolls is also delivered as serial (UART) data at 115,200 baud through pin 18 (RA1) of IC1, which is also pin 5 of the CON1 ICSP header (furthest from the > pin 1 marker). Pin 3 of CON1 is circuit ground. You could connect a USB-­ serial converter to these pins to dump this data into a computer for analysis. All rolls from the main screens are also dumped via the serial port in this fashion. You can run repeated rolls on the main screen (for example, to accumulate numerous results on the serial port) by holding the DOWN button after pressing the UP button for a roll. On Screen 11, values above 90% are typical and expected, although any one test might show a lower result. This is because any truly random phenomenon will occasionally show long runs of one particular value. Running multiple tests will accumulate the results, and you should see the long-term results, which will be more representative. If you see values near 0%, the noise multiplier is not working and is probably stuck at a specific value. In that case, check the circuitry around IC2 and IC3, plus their connections to IC1. During our research for this project, we came across an experiment (see siliconchip.au/link/abzz) where coins were tossed 40,000 times. It found that even a real coin shows a 74 Silicon Chip Completion Once you are confident the Flexi­ Dice is working as expected, you can secure the coin cell by using the M2 screw and nuts. Attach them to the hole near the cell to prevent it from being accidentally removed. Add a dab of glue between the PCB and the vibration switch. This will reduce the strain on the leads. Stick the double-sided foam tape to the back of the battery holder and use it to attach the panel PCB, aligning it with the main PCB. Some pads on the back of the panel PCB align to CON1, so you can solder some wires between the two for some extra stability if you want. Play Screens 13-15 show some of the different graphics the FlexiDice can display. They include dice ‘pip’ faces, playing cards and coin faces. For numbers higher than nine, numeric displays like those seen in Screen 2 must be used; they are also available for lower rolls. Use the LEFT and RIGHT buttons to cycle between the various options, which include several single dice rolls Conclusion The FlexiDice is a compact and handy substitute for all sorts of dice and can also be used to simulate coin tosses and card draws. You could even set it up to pick your numbers for Lotto draws. It runs from a single coin cell and the cell voltage display should give you plenty of warning before it goes flat. It also looks like a tiny games console, so we hope some of our readers think of other playful applications for SC this hardware. Double-sided foam tape is used to attach the protective panel PCB to the battery holder, although it isn’t strictly required. Australia's electronics magazine siliconchip.com.au No more eye strain! Ultra-bright long life LED for fantastic clarity (plus no need to change a globe - EVER!). Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. 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SAVE 33% 15 $ $ each • 4 strips can be daisychained using X3255 joiner ($2.95) • Buy M 8936D 2A plugpack for mains use ($24.75). each X 3270 Warm White X 3271 Natural White X 3250 Warm White X 3251 Natural White Your electronics supplier since 1976. Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/11/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. 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. Tunnel timer uses 555 instead of a microcontroller As an alternative to Les Kerr’s PIC12F617-based tunnel timer design (August 2024; siliconchip.au/Article/ 16424), here is one that does a similar job using a 555 timer IC. It is designed to stop a model train inside a tunnel briefly to give the impression that the tunnel is longer than it is. A small rare-earth magnet is mounted on the train engine. When it passes over a reed switch on the track inside the tunnel, the switch momentarily closes, and the timer is triggered to open a relay contact that cuts power to the train. After the delay period, the relay switches off, closing the contacts to resupply supply power to the train. The train resumes its journey and exits the tunnel. The timer circuit is shown with the 555 timer configured as a monostable, where the pin 3 output goes high (near 12V) for a period when the trigger input at pin 2 momentarily goes below 1/3 of the supply voltage. When the 555 is not triggered, the 100μF capacitor is discharged by the pin 7 discharge output (which is pulled low) via the 1kW resistor. Pin 2 is held high via the 10kW resistor connecting to 12V. The other side of the 10nF capacitor (also at pin 2) is held high via a 10kW resistor connecting to 12V. The 555 is triggered via the action of the reed switch. When it closes as the train passes, the 10nF capacitor momentarily pulls pin 2 toward 0V to trigger the timer. The timing then starts with the discharge pin going open circuit, and the 100μF capacitor at pin 6 starts charging via the 10kW resistor and VR1. Simultaneously, pin 3 goes high to drive the relay, opening the relay contacts and disconnecting power to the train, stopping it. When the capacitor charges to 2/3 of the supply voltage, pin 3 goes low and the relay contacts close, restarting the train. The 1N4004 diode quenches the back-EMF the relay coil generates at switch-off. The timing period is adjusted using VR1, which sets the train stop duration between about one second and 12 seconds. LED1 lights during this period. John Clarke, Silicon Chip. Using a common IC to generate a negative rail I needed a simple circuit to generate an unregulated negative supply. I have been playing with buck (step-down) chips to generate fully regulated positive and negative supplies capable of reasonable currents. However, I didn’t need much in this case, just an arbitrary, unsmoothed negative voltage. There are various ways to do it, such as using a flip-flop, a 555 timer or an op amp based oscillator, but this circuit uses a standard 76 Silicon Chip buck chip with a capacitor charge pump to generate the negative supply. They are ubiquitous, cheap and easily recovered from defunct circuit boards. Buck chips typically contain an oscillator, PWM logic, a reference generator (1.25V in this case), a comparator and a high-current driver or drivers. They can operate from a wide input voltage range. The 470pF capacitor slows the internal oscillator, although the Australia's electronics magazine chip will generate a suitable output without it. The over-current sensing is disabled by joining the Vcc, Ips (current sense), Drc (driver transistor collector) and Swc (switching transistor collector) pins to the incoming supply. The internal voltage reference and PWM generator are disabled by connecting Cin- (comparator negative input) to GND. Swe is an open-emitter output, so a 100W pull-down resistor is required siliconchip.com.au Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Model train rail blockage detector This circuit was developed to avoid a problem in the operation of the Traverser published in the Circuit Notebook column of the December 2022 issue (“Traverser for photography or model railway” – siliconchip.au/­ Article/15592). If the Traverser is out of sight in a model railway layout, it is possible that a train could be stopped across the junction between the Traverser and the rest of the model. If the Traverser operates in this condition, damage could occur to both the rails and the train. This circuit detects the presence of a train across the junction, warning the operator against using the the Traverser. It produces an infrared (IR) beam modulated at 38kHz directed at a detector taken from a remote control receiver. This beam is positioned so that it will be blocked if a train lies across the rail junction. I decided to base it on a remote control receiver to simplify the detection of the beam. The first prototype was surprisingly insensitive, so I modified it to use two IR diodes. That worked initially, but I found it less sensitive occasionally, and the receiver would not change state permanently. Yet it could reliably detect the signals from a TV remote control. The solution was to put a 100nF capacitor across the supply rails next to the detector. The transmitter is a basic 555-based circuit oscillating at around 38kHz. When this is received, the output of IRD1 goes low and inhibits the oscillator based on IC2. The green LED (LED1) then switches on. IRD1’s output is high when the beam is interrupted and IC2 oscillates. This leads to a flashing signal between the green and red LEDs. An audible signal could have been used, but I was concerned it could have been annoying. Graham P. Jackman, Melbourne, Vic. ($60) Editor’s note: it’s always a good idea to place a bypass capacitor between the supply pins of an IC, especially one with a high-gain amplifier like an infrared receiver/detector. to generate a square wave at that pin. This square wave drives the charge pump formed by the two 10μF capacitors and two diodes, inverting the incoming supply from CON1 and making it available at CON2. The values of the capacitors are not critical and can be low due to the high switching frequency. For a higher output current, the value of the 100W resistor can be lowered, but much lower than 100W will make the circuit wastefully inefficient. The absolute value of the output voltage will be ~0.6V lower than the input due to the diode forward voltages, with the voltage drop increas- ing as the load current goes up. Michael Harvey, Albury, NSW ($75). siliconchip.com.au Australia's electronics magazine November 2024  77 Using Electronic Modules with Jim Rowe 0.91-inch monochrome OLED screen Small monochrome OLED display modules have become widely available at a low cost in the last few years. This one is just 37.5 × 11.5 × 4.5mm but has a 128 × 32 pixel display that’s either white or blue. With its I2C serial interface it can be easily driven by a microcontroller. I n the October 2023 issue, we reviewed the ‘big brother’ of this OLED module, with a display measuring 1.3 inches or 33mm diagonally. It had 128 × 64 pixels – twice that of this module – along with an I2C serial interface. We have used the 1.3inch module in several projects, like the Multi-Stage Buck/Boost Charger Adaptor (October 2022; siliconchip. au/Article/15510). We have also used smaller OLED displays in various projects. For example, a 0.96in module with 128 × 64 pixels was used in these projects: » LC Meter Mk3, November 2022: siliconchip.au/Article/15543 » Q Meter, January 2023: siliconchip.au/Article/15613 » Advanced Test Tweezers, February & March 2023: siliconchip.au/Series/396 And there’s an even smaller 0.49in OLED display with 64 × 32 pixels that we used in the: » SMD Test Tweezers, October 2021/April 2022: siliconchip. au/Article/15276 » Pocket Audio Oscillator, September 2020: siliconchip.au/ Article/14563 The main difference between the current module and all of those others is that the ‘active area’ of its display is wider but shorter: 22.4mm wide by 5.6mm high. Since it has 128 × 32 pixels, that means that it provides a display basically equivalent to the top or bottom half of the 1.3in OLED module. We obtained the module shown in the photos from a supplier on AliExpress for ~$2. Another supplier 78 Silicon Chip on AliExpress had it for ~$3, while it was on eBay for ~$12. Closer to home, Tempero Systems offer it for ~$7, while Core Electronics had a very similar module available for ~$17 (siliconchip.au/link/abw3). All the prices listed above are exclusive of postage costs. Inside these OLED modules The 0.91in (23mm) OLED modules all use a single interface/controller and OLED driver IC, usually either the SH1106 device from Sino Wealth or the SSD1306 device from Solomon Systech. The same controllers are also used in many of the larger modules. Fig.1 is a block diagram of the SH1106 and the SSD1306 interface/ controllers. At upper left is the microcontroller (MCU) interface, which can be configured to interface with an MCU via an 8-bit 6800/8080 parallel interface, a 3- or 4-wire SPI interface or an I2C serial interface. Most of the OLED modules currently available use the I2C interface, including the one we’re looking at here. Display data from the MCU is stored in the Data RAM just to the right of the interface block. The SH1106 and SSD1306 controllers both have around 1024 bytes of Data RAM, enough for a 128 × 64 pixel display. Since the 0.91in OLED only has 32 rows, only half of the Data RAM is used in this module. The Display Controller block to the right of the Data RAM takes data from the RAM and displays it on the OLEDs via the page and segment drivers at the right-hand end of Fig.1. The MCU can also send commands to the controller, which pass from the MCU interface to the Command Decoder block below it in Fig.1. The commands can be used to update the display, turn it on or off, set its addressing mode, set the column starting address and adjust the display Fig.1: the block diagram of the SH1106 and SSD1306 OLED driver controller ICs. The SSD1306 has a slightly bigger internal RAM, letting it store 132 x 64 pixels (four more pixels horizontally than the SH1106). Australia's electronics magazine siliconchip.com.au Fig.2: a common circuit diagram for the 0.91in OLED modules using an SSD1306 controller. contrast and brightness (the latter also determining its operating current). The SH1106 and SSD1306 devices both come in very thin (0.3mm) SMD packages with over 260 contact pads. In the modules, they are mounted directly on the rear of the OLED screen. The module’s circuit Fig.2 shows the circuit of a typical 0.91in monochrome OLED module based on the SSD1306 device. As you can see, it’s very similar to that of the 1.3in OLED module we looked at in the October 2023 issue, although a little simpler. The circuitry to the left of the OLED provides the power supply and assists with the I2C interface. These components are all mounted on the rear of the module’s PCB. Four-pin SIL header CON1 at far left handles both the power input and the I2C interface. REG1 takes the incoming Vcc and steps it down to +3.3V to run the OLED and its controller. The +3.3V line is also used to drive the controller’s reset circuit (it needs to be reset as soon as power is applied) and provides the reference for the 4.7kW pull-up resistors used on the I2C interface lines, SCL and SDA. Before we move on to more practical things like driving one of the modules from an MCU, Fig.3 shows how the SH1106 and SSD1306 controllers save the display data in their Data RAM, and how it is shown on the OLED screen. This is achieved by setting them to what is described as Page Addressing Mode. In this mode, the OLED screen is divided into eight horizontal ‘pages’, where each page consists of 128 vertical segments eight pixels high. The siliconchip.com.au Fig.3: the SH1106 and SSD1306 controllers save their display data into RAM using column-major order. The OLED module’s PCB measures just 37.5mm wide, 11.5mm tall and the module is only 4.5mm deep, making it ideal for compact designs. You can see it at actual size in the adjacent image. Australia's electronics magazine November 2024  79 Fig.4: how to connect the 0.9in OLED module to an Arduino Uno or similar. Fig.5: connecting the OLED module to a Micromite Plus Explore 64 are just as simple as an Arduino. If instead you’re operating the module with a Micromite Mk2 or BackPack, then the SCL pin of the module connects to pin 17 of the Micromite, and the SDA pin connects to pin 18. An example photo of the OLED module connected to a Micromite via a breadboard. The underside of the OLED module shown enlarged for clarity. All components except for the screen are mounted to this side. 80 Silicon Chip Australia's electronics magazine pages are themselves arranged vertically, with page 0 along the top of the screen, page 1 immediately below it and the remaining pages descending. With the 0.91in OLED module, though, the pages and segments are used rather differently. In this case, only every second segment byte of each page is used (segments 0, 2, 4 and so on), and only four bits are used in each segment byte (bit 0, bit 2, bit 4 and bit 6). These four data bits are then used to display the four upper pixels in that segment of the OLED. The data for the lower four pixels of that OLED segment come from the next page in the controller’s RAM, which is organised in the same way: only every second segment is used, and only the four bits are used in each segment byte. I think you’ll agree that this all seems a bit weird, but that’s the way data is organised in the 0.91in OLED modules. Now we can turn our attention to what is involved in driving one of these modules from an MCU like an Arduino Uno or a Micromite. Connecting it to an Arduino Connecting the OLED module to an Arduino Uno (or compatible) is quite straightforward, as you can see from Fig.4. The GND and Vcc pins connect to the GND and 3.3V pins om the Arduino, while the SCL and SDA pins connect to the Arduino’s A5 (SCL) and A4 (SDA) pins, respectively. You can also connect the OLED module to an Arduino Uno R4 Minima, simply by connecting the module’s SCL pin to pin 17 of the Minima and the SDA pin to the Minima’s pin 16. As for software to drive the OLED module, if you go to www.arduino. cc and look at the library listings for ‘Display’ applications (siliconchip.au/ link/abw5), you will find quite a few libraries intended to do this job. The first one I found was Adafruit’s SSD1306 library, with the latest version (V2.5.9) able to handle OLED displays with either 128 × 64 or 128 × 32 pixels. It also relies on using their GFX library. The Adafruit library comes with five example sketches, including one called SSD1306_128x32_i2c.ino – which is the one most suitable for use with the 128 × 32 pixel OLED module. siliconchip.com.au When you run this sketch, it gives you a series of graphics and text displays, including those shown in the article lead and at left. As you can see, the 128 × 32 OLED’s display is quite small, but can display a useful amount of information. Connecting it to a Micromite It’s also quite easy to connect the OLED module to a Micromite MCU. Fig.5 shows the connections needed for a Micromite Plus Explore 64 and, as you can see, they are just as straightforward as driving the module from an Arduino. Connecting the module to a Micromite Mk2 or LCD Backpack V1/V2/V3 would be almost the same, except the module’s SCL pin would be connected to pin 17 of the Micromite and the SDA pin to pin 18. As with an Arduino, you also need some software. It turns out that this isn’t quite as easy as with the Arduinos, as it’s much harder to find any Micromite OLED driver software. As I related in the October 2023 article, I could write an MMBasic program to display text and simple graphics on the 1.3in OLED module, with some much appreciated help from fellow Silicon Chip staff member Tim Blythman. Since the 0.91in OLED modules use the same SSD1306 controller, I decided to try adapting that program to work with them. But that approach didn’t work with the 0.91in module, even when I tried quite a few modifications to the program – the OLED’s display remained stubbornly dark. So once again, I asked Tim for help (sorry, Tim). And as before, he provided a lot of help. Tim searched around The Back Shed (www.thebackshed.­ com/forum) and found some valuable information I had missed concerning MMBasic programming of the various OLED modules. He found a driver written by MM­Basic programming guru Peter Mather and soon came up with his own working program by combining elements of Peter Mather’s driver with a few ideas taken from my program for testing the 1.3in OLED module. Tim sent me his new program by email, and when I tried it out, I found it worked very well. So I added a few comments, plus code to display a full four lines of text instead of the single line that Tim had provided. You can see the display produced by this program at lower right. The program is called “091in OLED TB version.bas” and you can download it from siliconchip.au/Shop/6/454 As before, it’s a fairly simple program, and as it stands it only demonstrates how to drive the OLED module to display text and very simple graphic symbols. It doesn’t let you type text in via the Micromite console and display it directly on the OLED, as that would involve a fair bit of additional code. Hopefully it will make it easy for those who want to display up to four lines of text and basic symbols on the screen of one of the 0.91in OLED modules from a Micromite to do so. I’d like to thank Tim Blythman for help in producing this MMBasic program for the Micromite. Useful links • Interfacing the 0.91in OLED with an Arduino Uno: siliconchip.au/link/abw6 • OLED breakouts: siliconchip.au/link/abw7 • LCDwiki MC091GX user manual: siliconchip.au/link/ abw8 SC siliconchip.com.au Australia's electronics magazine November 2024  81 3D Printer Filament Drying Chamber This device uses relatively simple hardware to keep 3D printer plastic filament warm, driving moisture out and keeping it out. That’s important for consistent printing results, especially with PLA or Nylon filament. Your printer can draw the filament directly out of the sealed box. Part 2 by Phil Prosser T here are two main versions of our Filament Dryer design: one that uses an off-the-shelf plastic box to store the filament, plus a custom timber box made from plywood. While making the timber box isn’t all that difficult, it is a bit involved, so we won’t go into great detail on how to build it. We think most people will prefer the convenience of simply buying and modifying a pre-made box. Both solutions perform similarly, although the timber box is, in some ways, a little bit neater. We suggest you read through most of this article before deciding which approach is best for you. Before we get to the boxes, let’s build and test the controller electronics. Controller construction The controller is built on a PCB coded 28110241 that measures 126 × 93mm. During assembly, refer to its overlay diagram, Fig.3, which shows which parts go where, as well as Photo 4 (note there are some differences between the prototype and final version of the PCB). It is not hard to put together; we have stuck to throughhole parts and easy-to-get bits. The board layout puts all the controls and adjustments along one edge, which we mounted to face the user. Start by fitting all the resistors. Make sure you use 1% tolerance 12kW and 2.7kW resistors. The others are 82 Silicon Chip not so critical, although we tend to just use all 1% resistors these days as they don’t cost that much more than 5% resistors. Follow by mounting the diodes, ensuring that they are orientated correctly, as shown in Fig.3, and that you don’t mix up the four different diode types (again, refer to the overlay). Mount D6 on longer leads so you can bend it to sit in the fan’s airflow channel, as shown. Now install the LEDs. We bent LED7 (red, heater running) and LED12 (green, temperature achieved) over so they are visible from the control side of the PCB once it’s installed in the enclosure. LED8 doesn’t matter as it’s used for its forward voltage, not because it lights up. Next, fit the 100nF ceramic/MKT capacitors, which are not polarised, then the three electrolytic capacitors, which are. The latter must be inserted with the longer (positive) lead into the pad on the + side. The negative stripe on the can indicates the opposite, negative side. You can then solder the PIC microcontroller and LM358 operational amplifier. If you bought your PIC from the Silicon Chip store, it will already be programmed. Otherwise, you will need to install CON6 and use a PICkit or similar to program it yourself. The firmware can be downloaded from: siliconchip.au/Shop/6/484 Australia's electronics magazine Next, fit the five components in TO-92 packages: four transistors and the LM336BZ voltage reference. Ensure they go in the locations shown and the flat face is orientated as per Fig.3 and the PCB silkscreening. Follow with the headers and trimpots. While heatsinks are shown for transistors Q1 and Q2, they are not necessary unless you are using a Mosfet with a higher RDSon than the one we specified (for Q2) or your fan draws more current than the one suggested (for Q1). However, you need to make sure the metal tab side of each device faces to the left, as shown in Fig.3. Now is also a good time to mount REG1. Like Q1 and Q2, its metal tab must face to the left. Then you can solder the fuse clips in place; it’s easier to get them positioned correctly by inserting a fuse before soldering them, but be careful not to overheat it. On the top side of the board, that just leaves CON1, S1, S2, VR3 and F2, all of which can now be mounted, with the exception of F2. The thermal fuse warrants some care in soldering, as it will ‘blow’ at 77°C, which is not hot at all when soldering. We blew the first one we soldered, so be warned! We dealt with the thermal fuse by using quite long leads and being very fast in soldering. To draw away some of the heat, you could clamp something like pliers (with a rubber band on siliconchip.com.au Photo 4: the top side of the early prototype PCB, repeated from last month’s issue. the handle), a haemostat (self-closing pliers), or perhaps a clip-on heatsink on the lead between the fuse and pad during soldering. The fan is installed on the back of the PCB and is intended to push air into the enclosure. If you look at the side of the fan, you will typically see two arrows, one indicating the rotation direction and the other the airflow direction. If you are using a fan different from the one we got from Altronics, check that yours draws more than 50mA when running and less than 10mA when stalled. This will ensure that the protection system operates as intended. Secure the fan and its 40mm grille on the underside of the PCB using 16mm-long M3 machine screws, hex nuts and shakeproof washers. You can use a polarised header plug to connect this fan to CON4 or solder its leads directly to the PCB, as it should not usually need to be removed. At this point, the board should be fully loaded and ready to test. Testing can be done without the heater plates and before the controller is installed in the enclosure. Testing procedure Start by applying power and checking for excess heat or smoke. The fan on the PCB should be running all the time; that is normal. Check that the 5V rail is OK; there are GND and 5V test points in the lower right-hand corner of the PCB. If the voltage between those is not in the range of 4.75-5.25V, check around the LM317 regulator. Are the resistors the correct values? Is there a short on the regulator, PIC or op amp? Use a DVM to monitor the voltage on the 2.5V test point at upper right and adjust VR1 to get 2.5V on that test point. If you can’t do that, check that the LM336-2.5 is the correct part and the right way around. If the onboard fan is not running, check for about 12V on the “+” pin of CON4, the fan header. If it is present, check that the fan is plugged in the right way around and that the wiring is OK. Also verify that the BD139 transistor (Q1) and 12V zener diode are both the right way around. Now set the temperature control (VR3) fully anti-clockwise and adjust trimpot VR2 up and down. You should see the green “Set Temp Achieved” light (LED12) switch on and off. If that does not happen, check the voltage on pin 6 of IC1, the LM358. This is the forward voltage of the temperature sense diode and should be about 0.55V. Also check the voltage on pin 5 of IC1, which is adjusted by VR2. It should vary above and below 0.55V as you rotate VR2. Fig.3: use this overlay diagram to help you assemble the controller board. All parts mount on the top, except the 40mm fan, which goes on the underside. Its power wires come around to the top side of the board to plug into CON4. Watch the orientations of the ICs, Q1. Mount LED7 & LED12 on long leads bent over to face the left. siliconchip.com.au Australia's electronics magazine November 2024  83 Fig.4: the wiring to the heater resistors is straightforward. If using low-value resistors, you might want to connect them in series rather than parallel. Either way, the thermal cutout must be wired to disconnect all the resistors if it gets too hot. • Do not place the heat plate in continuous contact with timber; it can auto-ignite. Use standoffs for any heater plate at the bottom of the enclosure. • Ensure that the circulation fan can circulate air throughout the enclosure. • Ensure that the air around the temperature sense diode will be representative of the overall enclosure air temperature (good circulation should provide that). • Ensure that the user can easily access the controls, especially S2. • Ensure that the 90°C thermal cutout switches are installed and located near the heating resistors. • Ensure the resistors are securely connected to the plate and will not run excessively hot. There are two primary considerations for resistor selection. Firstly, they must be able to be affixed to the heatsink securely. Secondly, you must be able to safely dissipate about 50W into your case. Our experiments showed that in a normal room, 50W is adequate to achieve 50°C. You can use resistors in series or parallel. We had a bunch of 7W 25W resistors lying around that we used in one prototype, wired in series. Do your sums and select the resistance you need, then search out the cheapest option. The resistors specified in the parts list (visible in the photos) are pretty close to optimal in terms of ratings, size and cost. Once you have made the heater plates, it is worth plugging them into the controller on the bench and checking that they work as expected. Once you set the system running, the heater plates should get hot after a few minutes. You should be able to feel that each resistor is dissipating power by touching its case while running; it will be noticeably warmer than the heatsink. If any resistors are extremely hot, check that they are correctly mounted. If they’re all reaching about the same temperature, the heater is ready to go. Wire up the plate using medium/ heavy-duty hookup wire rated to a minimum of 90°C; Altronics carries suitable wire, as stated in the parts list last month. Make the flying leads long enough that you can assemble the box easily. The required connections are shown in Fig.4. On the controller end of the wires, we recommend crimping them into Australia's electronics magazine siliconchip.com.au Photo 6: this shows how the resistors & thermal cutout mount onto the heat plate shown in Fig.5, along with the wiring (with the resistors in parallel, as per Fig.4). Also note the 50mm standoffs made from pairs of 25mm male-female spacers. Check the voltage on pin 7 of the LM358. It should switch between low (0V) and high (a couple of volts below the supply) as VR2 is adjusted. If it does, but LED12 is not lighting, that points to a problem with diode D12, transistor Q3, LED12 or its series resistor. Now it’s time to use VR2 to calibrate the temperature setting. Do this at room temperature (20-25°C). Turn VR3 up a little bit. Yes, that is a technical term; aim for around 1/3 to 1/4 of its travel, which corresponds to around 10°C. Adjust VR2 until green LED12 is off, then slowly rotate it anti-clockwise until LED12 comes on. Once you’ve done that, VR3 will let you adjust the set point from room temperature to about 30°C above that. Now if you turn VR3 fully anti-­ clockwise, LED12 should come on. If it does not, repeat the prior step with the control up a ‘little bit more’ (another technical term). Turn VR3 up, and LED12 should go off. Now press the Start button, S2. The red “Heater On” LED, LED12, should light. That means the PIC and Mosfet Q3 are working, as is the thermostat. If not, check that there is about 12V on the left-hand side of the 4.7kW resistor between Q3/Q4 and Q2. This is the Mosfet gate drive. If not, verify that you have used a PNP device for Q6. The PIC output at pin 5 should start high (5V) and go low (near 0V) when you press the Start button, S2. You can check this by monitoring the upper pin of CON5, nearer Q2. If this does not go from high to low when you press S2, check the PIC. 84 Silicon Chip With this all OK, the controller should be working and ready to test and install. The fact that the Mosfet switches the LED indicates it is working. You are ready to assemble and wire the heater plates, which we will describe in the next section. The approach to use will depend on how you are packaging the Dryer. Making the heater plates We are presenting two approaches to the heat plates. These aim to dissipate 50W in the enclosure while keeping surface temperatures to a safe level. With a 50°C enclosure temperature, these plates reach about 70°C. Any aluminium sheet more than 1.2mm thick will work, depending on what you have available. In deciding how you want to make your heater plates, here are the safety controls you need to consider: Fig.5: this plate for the Bunnings plastic box holds just three power resistors and the thermal cutout. All dimensions are in millimetres. pluggable header pins and inserting them into the blocks so you can easily plug in and remove the heater boards to the controller. You can use any matching pair of 2.54mm pitch headers and plugs for this, just make sure that the connector is rated for 3A or more (the Altronics ones in the parts list are rated at 3A). We like to flow a little solder into the crimped joint to ensure it can’t come loose, but if you do that, be careful not to add excessive solder or get it on the outside of the pin, or it may no longer fit in the block. The pins often need to be straightened before they will slide into the blocks and click into place. They can be released by pressing the tab with a tiny flat-bladed jeweller’s screwdriver. We recommend against soldering the wires straight to the PCB, as this will make the whole thing very fiddly to handle and assemble. Making the enclosure As mentioned previously, you have two options: modify a plastic box or make your own timber box. We won’t go into a lot of details for the latter case; we recommend you only take that route if you are confident in sorting out the details yourself. For the simpler plastic enclosure, the secondary heat plate is just three resistors and a 90°C thermal cutout switch mounted to a 180 × 210mm sheet of 1.5mm-thick aluminium, as shown in Photo 6. The recommended drilling pattern and mounting locations are in Fig.5. We used 50mm metal threaded standoffs (two 25mm male/female spacers joined) to fix this to the end of our plastic box. The controller mounts on the primary heat plate, shown in Fig.6 and Photo 7. This uses the same size sheet, but holds the heating resistors, thermal switch and also the control board. We cut a 40mm hole in the plate and mounted the controller on 15mm standoffs so that the fan forces air through this hole. This plate also uses 50mm standoffs and mounts to the end of the plastic enclosure. In both cases, secure the resistors to the plates using 10mm-long M3 machine screws, shakeproof washers and nuts. Add a little thermal paste under each resistor for good heat transfer. siliconchip.com.au Photo 7: this plate is similar to the one shown in Photo 6, except it’s rearranged to allow the controller board to mount on it. There’s a hole under the fan that you can’t see from this angle. Australia's electronics magazine November 2024  85 Fig.6: the second plate for the Bunnings plastic box is similar to the first, except that the controller board also mounts on it, with a hole for the fan’s airflow to pass through. We use a single large heat plate measuring 330 × 225mm for the timber enclosure, as shown in Fig.7 and Photo 8. This sits in the base of the enclosure. To ensure there is good ventilation around this, we bent the outer 60mm of each side up at about 45° and screwed six 10mm standoffs on the underside of the flat part to act as feet. This creates a plenum under the entire plate and larger triangular plenums down the sides. The ends of the plenum are cut off at 45° to create openings at the opposite end to the controller. We have mounted the controller so that it draws air through this plenum. The six resistors are mounted three on each side of the plate, on the underside, so they are protected from peoples’ fingers and stray material. We also mount 90°C thermal switches on either side of the plate to protect against overheating. In all our testing, we did not manage to trigger these switches, but they are an important failsafe. Do not omit them. Fig.7: the heater plate for the custom box has all six power resistors mounted on it, three on each side, with each triplet having its own over-temperature cutout. The six holes in the middle are for standoffs to space it off the bottom of the box. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au We made a lid for the timber enclosure from two sheets of acrylic (not included in the parts list). One is cut to the full size of the box, and a second is cut so it fits neatly inside the box. By mounting these to one another with 10mm spacers (we drilled straight through both sheets, ensuring an exact alignment of holes), we achieve a poor person’s ‘double-glazed’ lid, which self-aligns itself when you put it on (see Photo 9). Photo 8: the all-in-one heater plate for the custom timber box, shown from the underside so you can see the mounting and wiring of the components, along with the feet made from tapped spacers. The box Your approach to the box will depend on how handy you are in the workshop and how much time you want to spend. We will show two examples of how it can be made, one from 12mm plywood and the other using an 18L storage box from our local hardware shop. To reduce heat loss, you need to install Corflute insulation in both versions. If you chose a smaller plastic box, you would have less heat loss and be able to achieve a higher temperature and/or reduce the power consumption. We will leave this to your creativity. We certainly would not go any larger than the 18L box we used. We used some offcuts of 12mm plywood for our timber box and made a rod to hang four 200mm diameter filament reels inside. While there is no standard, most manufacturers seem to be settling on this as the size of a 1kg reel. We added a baffle inside the box that allows us to force air circulation through it. It also ensures that our controller is protected from any rough handling of the reels. Because we used timber, which is not moisture-proof, we gave the box two coats of varnish. We used “Estapol”, but any paint will do, so you can make it any colour you like. Check the paint you’re going to use to see if you need to seal and/or prime the timber before applying it. Our design includes provision for a rail on which you can hang up to four reels of filament. We 3D-printed the hanger hooks; the STL files for these and the other 3D-printed parts used can be downloaded from: siliconchip.au/shop/6/484 These suit 22mm diameter or smaller timber dowel; ours was pinched from an old broom handle. siliconchip.com.au Photo 9: we made a lid for the custom timber box from two sheets of acrylic, making it ‘double glazed’. The sheets are held together with short tapped spacers and machine screws. Note the filament exit hole in the foreground. Australia's electronics magazine November 2024  87 Photos 10 & 11: these photos show the locations of the two heat plates and controller in the plastic case. Note how the dowel is held in place by two red 3D-printed brackets to make it easy to add and remove reels. We also made ventilation covers, one for the exit and one for the ventilation fan (the ventilation fan should be installed in a hole in the outside of the box). Both of these allow you to close the vent. The STL files for these are in the same download package. We used long screws to secure the vent fan cover to the case; you could use superglue instead. We have included some simple drawings of our timber box in the download package, but we expect readers to have their own spin on it. Again we note that the box we built is right at the upper limit of what we would suggest you build; making it shorter would reduce heat loss. Insulation For the Bunnings plastic box, we cut ‘insulation panels’ from polypropylene Corflute material. We chose this as it is easily cut, includes air pockets for insulation and does not present a fire hazard at the temperatures we are working with. The sidewall insulation pieces are 270mm wide at the base, 290mm wide at the top and 235mm high. The end wall insulation pieces are 200mm wide at the top, 180mm wide at the base and 235mm high. The side flaps are 10mm wide at the base and 35mm wide at the top. The bottom layer insulation sheet is 280 × 170mm. Foam tape must be applied around the top lip of the box to improve the seal on this enclosure. It makes a huge difference to the system’s performance. We found it increased the temperature inside the box by 4°C for the same power input (tested at 34W). To justify the need for insulation, we tested the performance with and without insulation. With 50W continuous dissipation in the insulated box, it reached 50°C (22°C ambient), while Photos 13 & 14: here you can see the finished custom timber box, with 3D-printed parts holding up the dowel from which the filament reels hang. This box can handle four 1kg reels. The Corflute insulation on the sides and the foam tape to seal the lid are essential for good performance. The controller is mounted in the section, behind the baffle panel, with a hole for the fan to push air through. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au Silicon Chip PDFs on USB Photo 12: the finished Filament Dryer in the custom timber case connected to a Creality 3D printer. without insulation, it only reached 41°C at the same power level. The Corflute insulation and foam seal for the lid together save around 20W during operation. You should insulate the timber box similarly, but the dimensions of the pieces will depend on the exact size of your box. Once insulated with Corflute, the timber box’s performance was pretty much identical to that of the Bunnings plastic one, reaching 50°C with 50W of dissipation or 41°C at 32W. Using the Dryer Using the Dryer is really simple. You thread the reels you want to dry onto the rail and hang them in the Dryer. Secure the lid and press the Start button with your selected temperature (set with VR3) and time (set with S1; up [away from the PCB] is six hours and down [towards it] is nine). We prefer to turn the temperature up to 50°C and allow the controller to take over from there, but almost all our printing is done with PLA. We hope that the discussion of safety & implementing controls in the design has led to some consideration of where and how safety in design plays SC a role in your hobby. ¯ 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). EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OR PAY $500 FOR ALL SIX (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS siliconchip.com.au Australia's electronics magazine November 2024  89 The derivation of Maxwell’s Equations ∇.E ∇×B ∇×E ∇.B by Brandon Speedie Our recent feature on the history of electronics covered many prominent contributors to the field. Two names stand out above others; their work is commonly referred to as the ‘second great unification in physics’. D avid Maddison’s History of Electronics series was published in the October, November and December 2023 issues (siliconchip.au/ Series/404). It mentioned hundreds of people who laid the foundations for modern electronics. Englishman Michael Faraday was one of the standouts in that list, with significant contributions to the understanding of electromagnetics. Faraday was born in 1791 to a poor family. He had an early interest in chemistry, but his family lacked the means to formally educate him. Instead, he became self-taught through books and an unbounded curiosity for experimentation. This practical approach continued throughout his career and set the blueprint for his breakthroughs in electromagnetics, despite having no formal training. Faraday was responsible for many notable discoveries, including the concept of shielding (the Faraday Cage), the effect of a magnetic field on the polarisation of light (the Faraday Effect), the electric motor (an early homopolar type, see Fig.1), the Faraday’s coil and ring experiment demonstrated electromagnetic induction. Source: Ri – siliconchip.au/link/abv3 electric generator (an early dynamo, see Fig.2), and the fact that electricity is a force rather than a ‘fluid’ (as was the understanding at the time). He also theorised that this electromagnetic force extended into the space around current-carrying wires, although his colleagues considered that idea too far-fetched. Faraday didn’t live long enough to see his concept accepted by the scientific community. It was an experiment with an iron ring and two coils of wire in 1831 that proved a defining moment for the vocation we now call electrical engineering. By passing a current through one coil, Faraday observed a temporary current flowing in the second coil, despite the lack of a galvanic connection between them. We now refer to this phenomenon as electromagnetic induction, the property behind many common products such as transformers, electric motors, speakers, dynamic microphones, guitar pickups, RFID cards etc. Most notably, this principle is involved in generating the bulk of our electricity. It was a remarkable achievement, later earning Faraday the moniker, “the father of electricity”. James Clerk Maxwell Maxwell was born in 1831 in Scotland. His comfortable upbringing and access to education contrasted with Faraday. Recognising his academic potential, his family sent him to technical academies and University to foster his curiosity about the world around him. Maxwell had long admired Faraday’s work but understood that he was fundamentally a tinkerer with only a basic understanding of mathematics. Maxwell recognised that his own strengths in mathematics were needed to unify Faraday’s experimental results, along with the work of other notable contributors such as Carl Friedrich Gauss and Hans Christian Ørsted. In 1860, Maxwell’s employment moved to King’s College, where he came into regular contact with Faraday. During this period, he published a four-part paper, “On Physical Lines of Force”, using concepts Faraday had Figs.1 & 2: Faraday’s homopolar motor (left) and Faraday’s disc generator (right). 90 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.3: an application of the cross product. The torque of an axle can be calculated from the cross product of the radius and force vectors. the two vectors together, then multiplying that by the cosine of the angle between them. The cosine is at a maximum if the two vectors point in the same direction and zero if they are orthogonal. If the vectors this is applied to are unit vectors (vectors of length one), the result is simply the cosine of the angle between them. Divergence (∇●) introduced many decades earlier. It contained the four expressions we now know as Maxwell’s equations that tie together electricity, magnetism and light as a single phenomenon: the electromagnetic force. This is called the ‘second great unification in physics’ because Sir Isaac Newton’s trailblazing work with motion and gravity is considered the first. Vector calculus To understand the notation of Maxwell’s equations, a quick primer on vector calculus is in order. Electromagnetism works in three-dimensional space, which can make mathematical representations confusing. We will cover the basics here, using figures to help visualise the equations. The formulas will follow the differential form derived by Oliver Heaviside from Maxwell’s original paper. Combining Del and the dot product is commonly referred to as the divergence operator. When used on a vector field, it returns a scalar field representing its source at any particular point. For example, calculating the divergence on atmospheric wind speed would give a view of pressure differences. Cross product (×) The cross product is a vector operation to calculate the ‘normal’ of two vectors, resulting in a new vector perpendicular to the two input vectors. Curl (∇×) Combining Del and the cross product yields the curl operator. When applied to a vector field, its result is a vector field that shows the rotation or circulation. Returning to the Meteorology example, calculating the curl of wind speeds in the atmosphere will return vorticity, a measure of cyclone or anticyclone rotation. Negative vorticity usually correlates with low pressure and unstable weather (cyclonic rotation), and positive vorticity with high pressure and fine weather (see Figs.4 & 5). #1) Gauss’ law of magnetism ∇●B=0 Maxwell’s first equation is named after German physicist Henrich Gauss. Fig.4 (top): a wind speed plot showing rotational winds off the east coast of Australia and in the southern ocean. Source: BoM, siliconchip. au/link/abv4 Derivative (d/dt) Fig.5 (bottom): calculating the curl of the wind speed yields the vorticity, which more clearly shows the cyclonic rotation off the east coast (blue) and the anticyclone in the southern ocean (red). Negative vorticity (blue) is associated with atmospheric instability, positive (red) usually means fine weather. The same operation can be used on a 3D electric or magnetic field to derive its source. Source: BoM, siliconchip.au/ link/abv5 The derivative operator, d, is shorthand for the Greek letter delta (Δ), which in mathematics refers to a change or difference. ‘t’ refers to time, so d/dt therefore means the change in a parameter over time or more commonly, ‘rate of change’. The symbol ‘∂’ instead of ‘d’ indicates a partial derivative, which is used when differentiating a function of two or more variables. Nabla / Del (∇) Del is the vector differential operator. It is equivalent to the derivative operator above but can be applied to more than one dimension. In our examples, it will be applied to a 3D field. Dot product (●) A dot product is an operation between two vectors that gives a scalar (numeric) result. The result is equivalent to multiplying the magnitudes of siliconchip.com.au A common example is to derive an axle’s torque from its radius and force vectors. The resulting torque vector is orthogonal to both vectors and points in the direction of its angular force (see Fig.3). Australia's electronics magazine November 2024  91 Fig.6: Gauss’ law of magnetism with reference to a permanent magnet. Any field lines exiting ‘north’ wrap around the magnet and enter at the ‘south’ end. The net magnetic field source is zero for any surface cutting through this field (eg, the square), or for the whole magnet in total. Fig.7: Gauss’ law in an air-gapped capacitor (eg, a tuning gang). A voltage source forces a positive charge to build up on the top plate & a negative charge on the bottom plate. An electric field forms between the charged regions. Fig.8: similar to Fig.7 but with a plastic film dielectric, which has a higher permittivity than air. Electric dipoles in the dielectric orientate themselves to cancel some of the electric field strength, increasing the effective capacitance. Here, B is the magnetic field. Simply stated, the sum of all magnetic fields emanating from an interface will always add to zero. This is most obvious when looking at the magnetic field lines surrounding a bar magnet (see Fig.6). Any field lines exiting ‘north’ wrap around the magnet and enter at the ‘south’ end. Considering any isolated area, or the entire magnet as a whole, there is no magnetic field source. #2) Gauss’ law ∇●E=ρ÷ε Also called Gauss’ flux theorem. Here, E is the electric field, ρ is the charge density (the amount of electric charge per volume) and ε is the permittivity of the material or medium (calculated as ε0εr, where ε0 is the vacuum permittivity and εr is the relative permittivity; in a vacuum εr = 1). This law states that electric charge is the source of an electric field. The strength of that field is proportional to the amount of charge and inversely proportional to the permittivity of the supporting material. This phenomenon is most apparent in a capacitor, where an accumulation of negative charge (electrons) builds up on one plate, and a positive charge (protons or holes) on the other (Fig.7). A dielectric between the plates supports the electric field. Its electric dipoles will be orientated opposite to the direction of the electric field and therefore store some of that electric field strength. Film capacitors use a plastic dielectric such as polypropylene or polystyrene, materials which have a relatively low permittivity, meaning they have few electric dipoles to orientate themselves against the field, leaving it mostly intact (Fig.8). In contrast, ceramic capacitors typically use a much higher permittivity dielectric, such as barium titanate, which will orientate many dipoles in response to the applied field and cancel much of the electric field strength (Fig.9). These dipoles provide a higher capacitance per unit area for ceramic capacitors compared to film caps. #3) Faraday’s law of induction ∇ × E = -∂B/∂t Fig.9: this is like Figs.7 & 8 but with a ceramic dielectric. The high permittivity allows many dipoles to cancel a large proportion of the electric field. This arrangement has very high capacitance per area. 92 Silicon Chip Here, E is the electric field and B is the magnetic field, so ∂B/∂t is the change in magnetic field over time. This equation mathematically formalises Faraday’s coil and ring Australia's electronics magazine experiment. It is the notable law of electromagnetic induction, where a time-varying magnetic field induces an orthogonal electric field. The stronger the magnetic field, or the faster its rate of change, the stronger the resulting electric field. This law is most familiar in rotating generators such as hydroelectric, gas, coal and wind-powered electricity production. As the alternator spins, its rotor produces a changing magnetic field for the stator, inducing an electric field that supplies the grid (see Figs.10 & 11). Similarly, the strings on an electric guitar vibrate when plucked. As they oscillate, they cut through the magnetic field produced by the pickups. This changing magnetic field induces a voltage in the pickup windings, which is amplified by a circuit to drive the speaker(s). #4) Ampere’s law ∇ × B = μJ Here, B is the magnetic field, J is the electric current density in amperes per square metre (A/m2) and μ is the magnetic permeability of the material or medium. The original form of Ampere’s law states that the flow of electric current produces an orthogonal magnetic field. The strength of this field is proportional to the current flow and the magnetic permeability of the material (Fig.12). Ampere’s law is the magnetic equivalent of Gauss’ law. We know that electric charge is the source of the electric field but Ampere’s law shows that the movement of electric charge is the source of a magnetic field. This phenomenon is most apparent in an electromagnet, where a wire is wrapped into a coil. As electric current flows, a magnetic field is produced orthogonal to the wire (Fig.13). Suppose a high permeability material such as iron or ferrite is placed in the coil’s core (Fig.14). In that case, magnetic dipoles orientate themselves in the direction of the magnetic field, increasing its strength. Using an iron-based core to increase magnetic field strength is very common in many magnetically-driven devices. For example, silicon steel is widely used in transformers and the field windings of most electric motors or generators. It is also used in hair clippers, where the 50Hz mains siliconchip.com.au Fig.10 (left): Faraday’s law of induction on a simplified three-phase alternator. The permanent magnet rotor spins, providing a changing magnetic field. An electric field is induced in the top coil, as shown by the voltmeter. Fig.11 (right): the same arrangement as Fig.10 but the rotor has rotated 90°, so the top coil sees no change in the magnetic field. The voltmeter shows no deflection. If the rotor continues to spin, the south side of the magnet will soon be near the coil, inducing an electric field with opposite polarity. Through a full 360° rotation, a sinusoidal waveform is generated, ie, AC voltage. waveform is used to induce a changing magnetic field in cutting teeth, providing an oscillatory motion to trim the hair. Ferrite is another common ironbased material widely used in magnetic products. It is favoured for its unique properties as a poor electrical conductor but a good magnetic conductor (high permeability). That is why it is widely used as a former for high-frequency inductors, in permanent magnets for hobby DC motors and as a source of magnetic fields in loudspeakers. This magazine also commonly features AM ‘loopstick’ antennas in its vintage electronics section, which often have an adjustable ferrite core. By rotating the screw, the ferrite can be moved in or out of the coil, providing an inductance adjustment to ‘slug tune’ the receiver. μ is the permeability of the material or medium, ε is the permittivity of the material or medium and E is the electric field (so ∂E/∂t is the change in electric field over time). The additional term includes the property that a time-varying electric field produces an orthogonal magnetic field. Put simply, the strength of the magnetic field is proportional to the permeability and permittivity of the material, as well as the electric field’s strength and rate of change. When considering this relation, together with Faraday’s law of induction, it can be seen that a time-­varying electric field produces a magnetic field Fig.12: an example of Ampere’s law. Current flowing in a wire produces an orthogonal magnetic field. Maxwell’s addition to Ampere’s law Figs.13 & 14: if the length of wire from Fig.12 is coiled, the magnetic fields constructively interfere, producing a stronger field (left). If a high permeability material is used in the core, magnetic dipoles orientate themselves in the direction of the field, increasing the field strength (right). The original form of Ampere’s law only relates electric current to magnetic field strength. Significantly, Maxwell added a term that relates electric and magnetic fields, termed “Maxwell’s addition”: ∇ × B = μ(J + ε∂E/∂t) Here, B is the magnetic field, J is electric current density in amps (A), siliconchip.com.au and a time-varying magnetic field produces an electric field (see Fig.15). It is a remarkable property; as Faraday so eloquently phrased, “nothing is too good to be true if it be consistent with the laws of nature”. A common example is in the transmission of radio waves by an antenna. Alternating current in the antenna produces a time-varying magnetic field around the conductors, which in turn produces a time-varying electric field that continues to propagate in free space. Some distance away, these fields induce a current in a receiving antenna, allowing the wireless transfer of information. Australia's electronics magazine November 2024  93 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) 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) Fig.15: Maxwell’s addition to Ampere’s law models the propagation of an electromagnetic wave. A changing electric field induces an orthogonal magnetic field, which in turn induces an electric field. The wave propagates in a direction normal to both the electric & magnetic fields, at the speed of light. Source: https://tikz.net/files/electromagnetic_wave-001.png This is also how our sun can power the Earth’s biosphere. As tiny atoms such as helium and hydrogen undergo nuclear fusion inside the sun, they emit electromagnetic waves. These waves propagate through free space as time-varying electric & magnetic fields, eventually reaching Earth, where they are used as an energy source by the flora & fauna on this planet. Theory of relativity Years after Maxwell’s publication, a young Albert Einstein expanded these equations in his own papers. Einstein was fascinated by the concept of light as an electromagnetic wave. The significance of this for him was the notion that the speed of the wave depends only on the permittivity and permeability of the medium it travels through and is therefore invariant of the rela- tive speed of the source (Fig.16). This understanding led Einstein to publish his groundbreaking theory of special relativity in 1905, as well as the well-known mass/energy equivalence formula, E = mc2, where E is energy, m is mass and c is the speed of electromagnetic waves (light). This work was further expanded by Einstein’s theory of general relativity in 1915, which included the force of gravitation in addition to the electromagnetic concepts introduced in special relativity. Maxwell’s equations are so central to this theory that they can be derived from Einstein’s general relativity formulas. Einstein paid tribute to Maxwell later in his career when asked whether he “stands on the shoulders of Newton”, to which he replied, “no, on the SC shoulders of Maxwell”. 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 94 Silicon Chip Fig.16: the speed of electromagnetic waves is proportional only to the permittivity and permeability of the material they pass through. In this prism, red light travels at a different speed than blue (because their wavelengths differ), so they are refracted at different angles. This inspired Albert Einstein to derive his groundbreaking theories of relativity. Source: www.vectorstock.com/35129206 Australia's electronics magazine siliconchip.com.au ONLINESHOP SILICON CHIP .com.au/shop PCBs, CASE PIECES AND PANELS 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 STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 AUG24 AUG24 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 08106241 08106242 08106243 24106241 CSE240203A CSE240204A 11104241 23106241 23106242 08103241 Subscribers get a 10% discount on all orders for parts $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 $10.00 $12.50 $2.50 ↳ 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 VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 OCT24 OCT24 OCT24 OCT24 OCT24 NOV24 NOV24 NOV24 08103242 23109241 23109242 23109243 23109244 19101231 04109241 18108241 18108242 07106241 07101222 15108241 28110241 18109241 11111241 08107241/2 01111241 $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 $15.00 $5.00 $10.00 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 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) 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), Flexidice (Nov24) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) 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 FLEXIDICE COMPLETE KIT (SC7361) (NOV 24) MICROMITE EXPLORE-40 KIT (SC6991) (OCT 24) DUAL-RAIL LOAD PROTECTOR (SC7366) (OCT 24) PicoMSA PARTS (SC7323) (SEP 24) DISCRETE IDEAL BRIDGE RECTIFIER (SEP 24) Includes all required parts except the coin cell (see p71, Nov24) 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) $30.00 $35.00 $35.00 $50.00 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. 11/24 SERVICEMAN’S LOG The show must go on Dave Thompson The servicing gods must have some kind of influence in our lives; otherwise, how would it be that very similar jobs end up in the workshop at the same time? Kismet? Synchronicity? Pure coincidence? Dumb luck? It happened that I received two large TVs, a turntable and a DVD player to repair, all arriving within days of each other. Now, I have repaired TVs before and found them to be challenging. In fact, I recall helping out my uncle in Melbourne with simple jobs when he ran a thriving TV hire and repair business back in the 1980s. I was on holiday there and loved his workshops, with the mirrors on the back wall so he could watch what the TV was doing as he poked and prodded around in the back of it. I cannot tell a lie, those high-tension leads scared me, and I remember both Dad and him somehow creating huge fat arcs of electricity to the end of screwdrivers just for fun! Not for me, thank you! Of course, those TVs were very different, being huge, heavy things with CRTs and large transformers and discrete circuitry – some even still used valves, which were always fun to work with, in a shocking sort of way. I’ve built dozens of guitar amplifiers, both solid-state and valve-based, but they don’t scare me as much as those old things did. 96 Silicon Chip I have had people ask me if I can look at their old sets – they are into the retro thing but use set-top boxes of some sort to get ‘modern’ signals. I just politely decline; I don’t really know what I’m doing with them, and would likely end up cooking myself on the flyback transformer output. The very model of a modern modular monitor Modern TVs, however, are a different story. Most are now modular, with several circuit boards inside, all performing their separate functions. That makes any repair a lot easier, as long as you can get the boards. The power supply is obvious. It powers any LED backlighting (on older sets) and of course provides power to all the other boards. There is usually a main board that controls video and audio feeds and sends them to the right place (amongst other things like storing settings and personal channel choices). There is also sometimes a T-Con board, short for “timing controller”, which ensures the signals go to the right place at the right time. Some TVs don’t have these T-Con boards as a separate module; it is all incorporated into the main board. So, there is lots going on inside modern TV. Of course, OLED TVs are very similar to LCDs, just with a different type of screen at the front and suitable circuitry to drive it. The rest is pretty much the same. I ended up with two LED (backlit LCD) TVs in the workshop. Anyone who has seen my workshop knows that it is quite small and that it looks like a grenade has gone off inside. So having two rather large TVs in there makes it difficult to move around, which is why I usually don’t take on big jobs (both figuratively and literally). The first TV is one of several models sold by a local big-box store that are priced quite reasonably for their size and specifications. However, there is often a price to pay when buying cheap. This one had no video output, although there was audio, and the remote control seemed to operate all the settings, if the volume was anything to go by. With this type of display, it always pays to have a good look at it from the Australia's electronics magazine siliconchip.com.au Items Covered This Month • The show must go on • Fixing two broken laptops • The danger of high-impedance measurements • Hickok TV-7 valve tester repair • Repairing a Seiko wall clock 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 side, especially if you’re in poor light. If you can see shadows moving from that angle, it indicates that the panel is doing its thing and the fault is with the backlight. However, in this case, I could see nothing; not good, then. It could be a power supply failure, a screen failure or a mainboard failure. Or even a T-Con board failure. That really narrows it down (not)! It is difficult to get the parts you need to repair these at a component level because these things are all modular now. If something fails, you’re supposed to pull the board, replace it and off you go. However, new boards can be pricey! The evils of a throw-away society I suspect that if these things are returned under warranty, they just give the customer a new one and throw the old one in a skip, which is criminal. The amount of e-waste we generate for such a small country is embarrassing. I know of a printer repair shop that has a literal mountain of old printers, most of which could be repaired with a $10 part (if that). However, because these parts are not available, they just get dumped; the pile is cleared twice a year! Yes, some printer companies have a returns policy where you can take your old one in and they’ll dispose of it. However, that usually means filling containers with this branded waste and sending it to somewhere like Malaysia, Indonesia or (less likely these days) China. The people there either burn it in big piles or smelt it down in crude village furnaces to get any precious metals out of it. The problem is that all the toxins from these basic processes leach into the soil and cause all manner of birth defects and pollution. It certainly makes me think when I am getting rid of an old printer. Anyway, back to the TVs. The other difficulty with finding spares is that parts for these big-box specials are not readily available to the public. The boards have identification numbers on them, so that is where I started, with internet searches. AliExpress had some similar boards listed, but I found more information on forums and in the comments on YouTube videos. It seems these same boards are used in several other brands. Searching for those gave me a lot more information and leads on a spare from eBay. I bought a whole new control board, and after a few weeks, it duly arrived. It certainly looked the same; while the revision number was slightly different, I threw caution to the wind, installed it and pressed the button. This time, after a few flickers, the screen came up with a settings menu. I then went through it with the remote and set it up as best I could. siliconchip.com.au I don’t have an aerial lead out in my workshop, so it was just internal stuff. I connected it up to the internet, and it worked fine, loading the YouTube app and other free ones. I assumed it would load their Netflix and Prime accounts once they re-entered their details and registered the new hardware ID. It was simply then a matter of buttoning it all back up. One job out of the way, then, but it would still very much be in the way in my small workshop until they picked it up! Enter contestant #2 The second TV was slightly smaller, like a rumpus room set that had been demoted from the main lounge for use with the games consoles because the owners bought a new, bigger and shinier one for the lounge. It was older, clunkier and just as dead as the first one. This one was altogether more solid and harder to get apart, with a few hidden – or at least obfuscated – screws. Plus one safety screw, just to make life that little bit more difficult for me. Fortunately, I had a long screwdriver that could reach down the deep plastic tunnel and access the screw. What really rots my togs is that some designer at the company sat in a meeting with the brass and put this idea forward, and it was accepted. They must know it won’t stop people opening the thing up, but they do it anyway, no doubt incurring more expense as yet another step in the assembly process. I eventually managed to get the back off the set, breaking several of the now brittle-from-heat clips that also held the shell together. Once the back was off, which also included undoing the VESA mounted bracket, I could see the three boards inside. This TV is a house-brand device from another big-box store here. This time, there were no identifying part numbers on the boards, and some of the IC’s had scraped off numbers (thanks!). Australia's electronics magazine November 2024  97 I suppose that someone used to repairing these or dealing with them would know where to source parts, but even after I took pictures and tried several search-engine image searches and Chinese site searches, I could not find anything even remotely similar. My usual forums were also of no use; nobody seemed to know who made these things. I’d taken it as far as I could, so I called the client and said sorry that I was unable to do anything with it. Perhaps they could go back through the vendor and hope for a repair there? I heard weeks later that they did just that and were told it was obsolete and non-repairable, which is increasingly the mantra for electronics and appliance vendors these days. The amount of e-waste this terrible policy creates... Don’t get me started on that again! The next job on the list was a turntable, a now-vintage Sansui that back in the day would have cost the owner a pretty penny. This one had been sitting in a container beside the sea for over 20 years, unused, and the other components in the stereo system fared about as well as the turntable did. The speaker cones were rotten through, the metal baskets supporting what was left of them corroded beyond repair. Lord knows what the insides looked like; I envisaged the crossovers looking like something you’d recover from a shipwreck! The amp looked as if it had its own ecosystem growing on it and the tuner looked about as dire as the amp. All this gear was top-of-theline back in the 1980s, but now it looked as if it had been at the bottom of the sea. I flatly told the guy I couldn’t take that kind of restoration on. Not only would i t c o s t a fortune to replace all the rotted parts, there would be no guarantee it 98 Silicon Chip would even be as good as it once was. That’s assuming we managed to find new-old stock parts (he wanted to keep it vintage) and could actually get it working. I just wasn’t prepared to embark upon that sort of quest. He asked if I could look at the turntable at least, and I reluctantly agreed to check it over. He said it worked but made a grinding noise while running. Oh, great. I could just imagine what the bushings and all the motor bearings were going to be like inside, not to mention the state of PCBs or belts (if any) that might be in there. The only thing I could do was to remove the Plexiglas lid and open the thing up to have a look. The platen wouldn’t just lift out, like many I’ve repaired, so it was likely held with a clip underneath. Like most devices of this era, chunky screws held everything together and it’s just a matter of elbow grease to remove them all. Most came out cleanly, but a few were stubborn and needed a little help to let go. Corrosion really does get everywhere. Once the timber base was off (which could actually be easily restored, even though it is only veneered Weet-Bix wood), it was evident this was a project too far, for me at least. The inside reflected the outside. Everything had a powdered layer of corrosion. It would require complete – and I mean complete – disassembly, cleaning and restoration, and reassembly before it would work again. I am not set up for this sort of work, and even if I was, I doubt I would take on such a time-­ consuming task these days. I am sure if this customer set up an alert on the local auction sites he could pick up a good one for a fraction of the price I would have to charge to repair this one. This is where repairs truly make no sense. Unless someone has a deep sentimental attachment to any given appliance, there is a point where we just have to say, that’s it, and pull the pin. Even though this thing was in storage for 20 years, the owner kept hassling me to get it done for some party he was having in a week. He wanted to play records on it, which had been in the same storage container. As if this would ever be a seven-day repair anyway! Oh well, such is the life of a serviceman. Australia's electronics magazine The last job My last related job is a DVD player a client brought in. The whole DVD thing is a bit like watching the slow but sure decline of vinyl and CDs all over again. The problem is, of course, that most of us still siliconchip.com.au have shelves packed with CDs and DVDs. Letting all that go is just as bad as those people who have thousands of records in their collections and can’t let them go either. Keeping the machines that play these media alive is a big job now because, aside from ultra-high-end players or bigbox store cheapies, there’s not a lot in between to choose from. At least, not here in New Zealand. So, the customer brought in a brand-name player to see if I could get it going. It powers up but cannot detect a disc in the player. I’ve seen this before in many a computer CD-ROM or DVD-ROM. It is usually because the laser has simply gotten tired from use and cannot focus on the disc sector that tells the player it is loaded, so it just keeps hunting for one. Many people say their drive doesn’t get much use. However, every time you access This PC or My Computer, or turn a DVD player on, the laser fires to see if there’s a disc in there. So it does some work even when not needed, even if there is no disc present. Over time, the laser just wears out, for lack of a better or more technical term. I have done laser diode swaps in the past in expensive units, but they are an absolute pain to get out of the heatsink/caddy the diode is pressed into. That’s once you drill down to that level to get to it, which in a DVD player is a mission in itself. So I wasn’t about to consider doing anything like that with this one, if that’s indeed what the problem was. The rub is there’s no way of knowing until you swap it out and try it. Once again, I had to do a hard pass on this one. Good quality Blu-ray and DVD home-theatre type players are out there, and often not expensive, so I suggested the customer looked into something like that. The reality is that with high-definition streaming and relatively inexpensive services, physical media is quickly becoming superseded. In our household, I cannot recall the last time I used my DVD player. Perhaps I’ll gift it to this guy to replace his dead one. Editor’s note: many people are going back to physical media due to the fragmentation of streaming services and the ongoing cost of subscribing. Many classic TV shows and movies are no longer available, some even being removed after people had “bought” them! Others have been doctored or censored. So don’t throw away those CDs, DVDs and Blu-rays just yet! For example, see siliconchip.au/ link/ac1k Saving two broken laptops I wanted to send my mate a laptop, so I looked through some I’d had for some time. I decided to repair an Intel Core i5 based laptop we’d previously given to a friend, which had come back broken. The bottom shell was badly damaged, but the rest was in good condition. I was able to salvage an almost identical shell from a similar laptop with lower specifications. The only difference was that this older laptop didn’t have an HDMI port, so I had to cut a hole where the HDMI port was located on the original motherboard. This repair went well and the laptop was shipped off. I also noticed an Acer Aspire laptop among the ‘junk’ that looked like an easy repair. It was missing the keyboard, but otherwise, it was in good order and also had an i5 processor. It wasn’t high-tech any more, but it was good enough for web browsing and emailing. siliconchip.com.au Australia's electronics magazine November 2024  99 I fitted some RAM, plugged in a USB keyboard and a charger and pressed the power button. An initial test confirmed that it worked, so I fitted a 500GB hard drive, but something was wrong. The hard drive went in way too easily. I removed it, looked closer, and found that the SATA port was broken, basically writing off the laptop. How could this laptop be salvaged? I had a thought. I got a 32GB microSD card, put it in an adaptor, and inserted that into the SD card slot. I booted the laptop from a Linux disc and installed Linux on the SD card. I rebooted the computer and it was up and running. The entire installation used only 9GB, so there was plenty of room left to install other programs. That was an easy way to fix and give this broken laptop a new life. Still, I wondered if I could replace the broken SATA hard drive socket so I could fit a 500GB hard drive to install Windows 10 on. I’ve junked a lot of old laptops over time, most of which no longer worked or were really old and in such poor condition that they were unrepairable. However, I’d kept the motherboards, screens and other useful parts for future repairs. I’ve previously been able to salvage USB ports and mouse micro-switches for other repairs, but could I replace a serial ATA socket? I looked through the old motherboards and was surprised at the variety of different SATA sockets. I only managed to find two that looked like they were the same as the one I wanted to replace. After dismantling the laptop, I found that only one was precisely the same, the other one being slightly different, as it sat closer to the motherboard, so it was unsuitable. I considered how to remove the SATA socket from the scrap motherboard. I could either use my heat gun or my 80W soldering iron. I decided to try the heat gun on the socket I didn’t need as a test. While I was able to remove the socket in one piece, it did suffer some slight damage; not bad enough to make it unusable. Still, I decided to use the 80W soldering iron on the socket I needed instead. I successfully removed the socket without damaging it, so it was time to desolder the socket from the good motherboard. I got the socket off successfully with the same iron, but it was quite tricky to remove, as it broke into many small pieces in the process. Now I had to work out how to clean out the tiny holes. I got my desoldering iron, which uses suction to remove the solder. This process was very tedious, but with 100 Silicon Chip perseverance, I got all the holes cleaned out. I fitted the new socket and soldered it in place with my 20W soldering iron. It was time to reassemble the laptop and check if the repair was successful. With the laptop reassembled, I fitted a 500GB hard drive, connected the charger and USB keyboard and pressed the power button. I then pressed the F2 key and waited for the BIOS screen to load. The repair was successful, as the BIOS screen showed that the laptop detected the hard drive. I was unsure if this repair would be successful, with the delicate nature of removing the SATA sockets and fitting the new socket to the motherboard. It seems that I had good luck this time. Now that I knew this repair was successful, it was time to install Windows 10. I used the Windows 7 product key on the back of the laptop, as I had done many times before, but it said I did not have a valid key. What was going on? I looked online and found that Microsoft had just closed this upgrade path. I found a website selling genuine Windows keys at a reasonable price, so I paid for one and it worked. Now the laptop was all good again, so I ordered a new keyboard and fitted it. The repair was complete, and the laptop was saved. B. P., Dundathu, Qld. An impediment to learning Recently, I was behind a car in traffic and noticed that every time the driver applied the brake, one tail light went out. I have some experience with this simple fault, but it can cause frustration for those who happen upon it for the first time. Back in the 1960s, I did my time as an electrical apprentice with what was then the South Australian Railways, mainly at the Islington Railway Workshop. During my training, I was exposed to repairing, maintaining or installing various equipment ranging from low voltage DC (automotive electrics), higher voltage DC (32V, 64V and 110V on rail cars and locomotives), batteries, 240/415V AC industrial machinery, power tools and domestic appliances as well as switchboards for equipment control circuits, lighting and air conditioning within carriages. It was during my stint looking after the battery shop and vehicle electrics that I encountered the brake/tail light fault and learned an enduring lesson. Several years later, I was working in an Army workshop in Hobart as the resident electrician when one of the tradesmen from the vehicle service station begged my help with a Land Rover that had a tail light problem. On arriving at the service station, I was confronted with a vehicle with all the covers off and switches and wiring exposed. The mechanics had spent the best part of five hours trying to find the source of the fault and were not amused when I showed them a high-resistance chassis ground connection on the offending tail light. My input took about three minutes, leaving them with several hours of work putting everything else back together. Back in my apprentice days, the standard multimeter we used was the AVO 8, a reliable device but rather hard to carry and use compared to modern meters. The AVO was a relatively low-impedance meter compared to today’s devices. Late one afternoon, a carriage traverser stopped working, which was needed in service the next morning. Australia's electronics magazine siliconchip.com.au A carriage traverser is a section of rail on a platform that can move sideways to transfer rolling stock from one track to another parallel one. The traverser had a threephase motor to drive the axles to effect the track changes, but there was no power to it. It came via an underground mains feed to a pit, then up a pole via contactor to overhead catenary cables to pickups on the traverser. Being the youngest, I was sent into the pit to test for power to the catenary feed and had the AVO 8 in hand. One of the engineers who had come to see what was happening had a brand-new high-impedance “Sanwa” meter that had arrived only a day or so previous, and passed that meter to me to use instead of the AVO. Using the Sanwa to measure between phases, I got readings of 360V AC and 730V AC instead of the expected 415V AC. That had us all scratching our heads. Swapping back to the AVO, the readings were all zero; another puzzle. Looking upwards, I noticed that the high-tension overhead power line ran parallel to the underground feed. I then realised that the high-impedance meter was reading an induced voltage from the overhead supply. A failed supply fuse to the three-phase contactor was the cause of the fault, and that was easily fixed. Twenty years later, I was working as a supervisor in an electrical workshop at Puckapunyal when a trainee attempting to diagnose a fault on a water cooler was confounded when the wires to a small terminal strip, including switch wires, were all showing 240V to Neutral. He was using the standard issue Fluke multimeter. Sensing déjà vu, I took the Fluke away, handed him the Army “Aust Mk II” multimeter, a low impedance meter, and asked him to repeat the measurements. It was his turn to learn about induced voltages and high-impedance measuring devices. Some lessons learned early never fade. G. D., Mill Park, Vic. Hickok TV-7 valve tester repair My TV-7 D/U valve tester failed the other day. The meter was stuck and moving erratically and the “line set” could not be completed at switch-on. I immediately thought that the meter had failed (which it had), but the mode of failure was what surprised me. I have had this tester for about 12 years. I bought it on eBay when I was living in Tokyo; it’s ex-USAF and has a colourful history. It is in remarkable condition (my alltime favourite). At the time (2012), our dollar was close to parity with the USD, so this tester ended up costing me about $450. I bought about 20 pieces of equipment and had them shipped straight to Australia before the “Harvey Norman” tax on imports; times were good! Anyway, I pulled the meter and removed the Perspex lens, and then suddenly the meter worked perfectly again. I figured I’d put it back in and try it out. I got the same problem; in fact, just wiping my finger across the front caused the meter to move and get stuck in weird positions. These meters were made by Phaostron. They are great because there is a knurled knob inside that you can adjust to change the full-scale deflection (FSD). It works as a magnetic shunt, allowing more or less magnetic intensity through the moving coil (even HP didn’t have this). However, apart from this chestnut, the meters are jewel-­ pivot, not taut-band like HP. Still, I have never had a single siliconchip.com.au Australia's electronics magazine November 2024  101 one get stuck, and I have played with hundreds (another story)... The problem was that the plastic lens on the front was retaining a static charge, causing the needle to misbehave. Most Phaostron meters had an anti-static coating on the inside of the Perspex to prevent that, but perhaps the coating has broken down over the last half-century. I was very surprised as this meter never had any static issues like you expect to see in cheaper plastic meters. Again, this is where the big old HP meters triumph, as they were constructed with anti-static Bakelite and glass lenses. The resolution was to pull the guts out of the meter and transplant them into another Phaostron housing that was made much later (circa 1980s). This had a glass lens; obviously they realised the problem with plastic, or ruggedness was no longer a USAF requirement. In any case, the meter now works perfectly again. Happy days! D. V., Hervey Bay, Qld. Seiko wall clock repair I am sending this in case someone has the same trouble. I probably would not have bothered to fix it because I have too many clocks around the place as it is, but this one has been with me for around 50 years and has a lot of sentimental value. The clock used to keep good time, but over the last couple of years, it was out by up to 20 minutes a month. Try as I may to adjust it, I always failed to get any sort of accuracy. At the beginning of this year, it kept stopping but always started OK. I overhauled the mechanism, which seemed to fix it, but only for a while. Eventually, it stopped and would not start, so I opened it up again and tested some of the components. All tested good except for what I would call the driver coil. I could never get the same resistance reading twice. It varied from 3kW to 3.5kW. The driver transistor was a germanium PNP type. It was easy to remove, so I took it out and tested it, and it was good. To see if a silicon transistor would work, I replaced it with one of those with the closest characteristics. I set the clock up on the bench and it started, but it only ran for a couple of days before stopping, and it would not start again. That meant the driver coil was faulty; I suspect it had intermittently shorted turns. I removed the tape from the coil and found that all the connections were good. I then put the coil on a spindle and unwound all the wire; there were no breaks. I tried to rewind it with some wire off another coil but did not have any success. If the bobbin hadn’t had mounting feet on it, I may have got away with it. But my 77-year-old eyes were watering just trying to see the 0.076mm diameter wire, and when it broke, I gave up. I looked in my relay box but could not find a coil with a big enough hole up the centre for the pendulum rod, so I left it on the bench in case an idea came to mind. I later had a thought that a washing machine water solenoid coil might do the job. I had some in a box and found a few that measured 3.6kW, so I removed the coil. The centre hole was smaller than the original in the clock but large enough to fit over the pendulum rod. By drilling a 29mm hole in a piece of timber 20mm thick, cutting it in half and drilling some holes for mounting bolts, I could set it up to see if the clock worked. It did not. The pendulum in this clock actually drives the gears via a ratchet and pawl system, and the coil did not have enough pull. I shorted out the 1kW series resistor, and although there was an improvement, the clock still did not run. I had been wanting to run the clock from a rechargeable battery in a holder at the bottom of the case to save me having to take the clock down from the wall every time it needed a battery change, so I tried two Eneloop NiMH batteries in series, taking the voltage from 1.5V to 2.4V. The modified clock runs fine with this arrangement, even with the 1kW resistor back in the circuit, and has been doing so for four months. Not only that, but once I got it adjusted, it kept perfect time. I slotted the holes for the coil mount and made a brass plate with tapped holes for the screws. Now I can adjust the position of the coil to suit where the pendulum rod ends up, after changing its length to make it keep the correct time, without having to take it down from the wall. I painted the coil and wood clamp black so they were not visible with the glass door closed. I left the original transistor and coil former in the bottom of the case. The curved rod that enters the coils has a magnet on both ends. It induces a current in the coil large enough to switch on the transistor at the right time. SC R. G., Cooloola Cove, Qld. The internals of the Seiko clock, showing the curved rod and coils (left), and the modified circuit diagram (right). 102 Silicon Chip Australia's electronics magazine siliconchip.com.au Vintage Radio Revisting the Zenith Royal 500 AM Transistor Radio By Ian Batty One year after the release of the groundbreaking Regency TR-1 (shown on the left), a major manufacturer entered the market with a new set: Zenith’s Royal 500 – the ‘peak of technology’. Z enith was co-founded in 1918 by two amateur radio operators, Ralph Matthews and Karl Hassel. They adopted their 9ZN call sign, transforming it to “ZN’th”. Joined in 1923 by Eugene F. McDonald, they formalised the name as Zenith, the astronomical term for the highest point overhead. It was a bold move, but the company became famous for high-quality radios and innovation. Zenith offered their first portable radio in 1924, their first mass-produced AC radio in 1926 siliconchip.com.au and pushbutton tuning in 1927. Their self-contained car radios in the 1930s needed no external batteries or generators. Zenith’s purchase of the Heath electronics company in 1979 saw them enter the computer market as Zenith Data Systems. This was a transition from their declining radio business, which they finally left in 1982. Zenith’s slogan, “The quality goes in before the name goes on”, was well-justified. After around 1995, they Australia's electronics magazine were taken over by Korean manufacturer LG and finally filed for bankruptcy in 1999. Design The Royal 500 is larger than the first “trannie”, Regency’s TR-1. However, the TR-1 was forced to be a simplified design due to being first to market and over cost considerations. Released for sale in November 1954, the TR-1 announced a new era in personal radios. November 2024  103 Table 1 – Zenith Royal 500 differences between models Model Date Construction Transistors Types Unilateralisation AGC 7XT40 cct 1 ‘55/56 Handwired All NPN 2N94, 2N94, 2N94, 2N94, 2N35, 2 x 2N35 IF1, IF2 IF1 only 7XT40 cct 2 ‘55/56 Handwired All NPN 2N193, 2N194, 2N216, 2N216, 2N35, 2 x 2N35 IF1, IF2 IF1 only 7XT40Z ‘55/56 Handwired All PNP 121-9, 121-14, 121-10, 121-10, 121-11, 2 x 121-12 IF1, IF2 IF1 only 7XT40Z1 ‘56/57 Handwired NPN, PNP 121-15, 121-16, 121-17, 121-17, 121-18, 2 x 121-19 IF1 only IF1 only 7ZT40 ‘56/57 PCB All NPN 2N193, 2N194, 2N216, 2N216, 2N35, 2 x 2N35 IF1, IF2 IF1 only 7ZT40Z1 ‘56/57 PCB NPN, PNP 121-15, 121-16, 121-17, 121-17, 121-18, 2 x 121-19 IF1 only IF1, IF2 7Z40Z ‘57/58 PCB All PNP 121-9, 121-14, 121-10, 121-10, 121-11, 2 x 121-12 IF1, IF2 IF1 only 7ZT40 revised ‘57/58 PCB All NPN 2N193, 2N194, 2N216, 2N216, 2N35, 2 x 2N35 IF1, IF2 IF1 only By the time the Royal 500 hit the market, we’d had a year to get used to the miniature marvel of the transistor radio. The Royal 500 benefited from that acceptance, and Zenith was a well-known and respected brand at the time. The Royal 500, using the full five stages we now accept as necessary for good performance, was always going to be larger than the TR-1. The use of standard ‘penlight’ (AA) cells also increased its final size. At about 480cc in volume, the Royal 500 is considerably larger than the 305cc TR-1. However, considering the extra components Zenith used, the Royal 500 is genuinely compact. The TR-1’s ergonomic design is sound, with the large tuning dial easily operated by fingertip. The Royal 500, in contrast, demands that you use your finger and thumb to grasp the direct-drive tuning knob – it is doable, but nowhere near as easy, accurate or elegant as the TR-1’s dial. Dr Hugo Holden described a later version of the Royal 500 in May 2018 (siliconchip.au/Article/11076). His version has the tuning knob supplemented by a small coaxial ‘button’ knob. This operates an epicyclic reduction drive, making accurate tuning easier. Device Engineering Council (JEDEC). The review version is built on a metal chassis with point-to-point wiring and a few terminal points. While there’s better access to components than on the PCB-based versions, the assembly is tight, with six capacitors mounted above the chassis, connecting to the underside circuit via small holes in the metal chassis plate. Such an assembly would have been more time-consuming than (for example) the 1957/58 7ZT40 PCB version that followed. PCB construction was retained for all subsequent models. These have resistors mounted on end, with one end lead exposed to help with testing. Hopefully, they’re the ‘active’ ends, not supply or ground. Transistor types The Royal 500 RF/IF section uses grown-junction NPN transistors, while this 7ZT40Z1 version uses PNP transistors in the audio section. They would also be grown-junction types, based on the early release date of this radio. The TO-22 (Transistor Outline 22) style can, shown in Photo 1, was necessitated by the long ‘sliver’ construction of grown-junction devices. This is a clue to the type of construction, as alloyed-junction types are commonly enclosed in cylindrical cases, Releases RadioMuseum lists eight 7X/7Z models in the original case, manufactured from 1955 to 1958. The product line continued until 1965, using the same “Owl Eye” form. There were four initial releases for the Royal 500: 7ZT40 and 7ZT40Z1, and the second production 7ZT40/7ZT40Z1 – see Table 1. The set I’m reviewing is a 7ZT40Z1. The 121-series transistors used are Zenith’s own part numbers; 2N-­series codes were registered with the electronics industry’s Joint Electron 104 Silicon Chip Photo 1 (inset, highlighted in yellow): one of the TO-22 PNP transistors used in the 7ZT40Z1 version of the Zenith Royal 500. Photo 2: the complete set for the Zenith Royal 500 with the radio, case, instruction manuals and listening earbud. Australia's electronics magazine siliconchip.com.au such as the OC44/45 and the improved AF116/117 series. The transistors are socketed, so they are easily removed for testing or replacement. The sockets do not conform precisely to TO-22 spacings, as shown by the bending of the transistor leads to fit the socket in Photo 1. The 7ZT40-R2 version of the Royal 500 uses NPN types throughout, with the audio section’s 2N35s also using grown-junction technology. Circuit details The original circuit diagram is well laid out, with one oddity: while capacitors are numbered (C1, C2 etc), resistors are not. In Fig.1, I have kept Zenith’s capacitor numbering to prevent confusion and have added resistor and transistor numbering for clarity. Signal pickup is via a rectangular ferrite rod antenna. It’s tuned by C1a, the antenna section of the gang, with a separate secondary winding on the rod supplying the signal to the converter. There are no external antenna/Earth connections. The converter stage uses separate excitation. NPN local oscillator (LO) transistor Q2 injects the LO signal to the base of NPN converter transistor Q1. Separate excitation allows the designers to apply automatic gain control (AGC) to the converter. Circuit measurements show that the converter has just 0.03V (30mV) of standing bias, so this transistor is very much in class-B operation. With full AGC, Q1’s base voltage goes to zero. While it might seem that this would cut the transistor off completely, its emitter voltage in these conditions is about +0.12V, showing that it is still drawing current. This is explained by the applied LO signal of about 700mV peak-to-peak. This means that, even with the base bias at zero, Q2 still swings between being in cutoff and conduction by the alternating negative- and positive-­ going parts of the LO signal. The LO itself also works with a slight DC bias of only about 0.1V. This measurement obscures the oscillator’s action; the base signal is some 0.5V peak-to-peak, confirming it operates mainly in class B. The oscillator’s collector connects to pin 6 of LO autotransformer T6. Its pin 4 ‘cold’ tap goes to the positive supply. This allows the transformer to provide phase reversal, making this a modified Hartley circuit. It was here that I discovered an error in the original circuit diagram. Their diagram shows pin 1 of T6 going to the end of the winding, while pin 2 connects to the next tap along. However, on testing my set, I found more signal (700mV peak-to-peak) at pin 2 than at pin 1 (500mV peak-to-peak). That means that pin 2 actually connects to the end of the winding and pin 1 to the tap, as shown on my corrected circuit diagram. If you need to test the LO section of one of these sets, you should carefully check whether Fig.1: the redrawn circuit diagram for the Zenith Royal 500 (version 7XT40Z1). The circled numbers are voltage readings taken at various points in the circuit. your set is like mine or matches the original circuit, with the internal connections to pins 1 & 2 of T6 swapped compared to mine. The LO circuit is tuned by the tuning gang’s C1d connection to T6’s pin 3. The Royal 500 uses a cut plate design, so there is no padder capacitor. Both the incoming signal and the LO signal are applied to the converter base. I found that this prevented direct measurements at Q1’s base at any frequency other than the IF. There is a workaround, which I will describe in the performance section below. The converter feeds the untapped, tuned primary of the first intermediate frequency (IF) transformer, T1. T1’s untuned secondary feeds the 455kHz IF signal to the first IF amplifier transistor, Q3 (NPN). This transistor is stabilised by unilateralisation network R10/C7, which compensates for the high collector-base feedback of early devices. Emitter resistor R11, bypassed by capacitor C5, provides DC stabilisation. Q3’s collector feeds second IF transformer T2’s untapped, tuned primary. T2’s untuned secondary feeds second IF amplifier transistor Q4 (NPN), which lacks unilateralisation. This stage is biased from the emitter circuit of Q3. DC stabilisation is provided by emitter resistor R15, bypassed by capacitor C9. Q4’s collector feeds the untapped, tuned primary of third IF transformer T3 and T3’s secondary feeds demodulator/AGC diode D1. The original diagrams for all versions except the initial 7XT40Z have D1’s anode and cathode reversed. This error is confirmed by theory, inspection and circuit action. As they showed it, it would have reverse bias applied rather than the weak forward bias universally applied in such circuits. It would not demodulate, nor would it generate a suitable AGC voltage. D1 is loaded by 5kW volume control potentiometer VR1, while 50nF capacitor C11 forms a low-pass filter with its resistance to remove the IF component of the signal. D1’s output also feeds 4.7kW resistor R17, which conveys D1’s DC output to the AGC line. The AGC line is biased weakly positive by 47kW resistor R9. This provides a slight forward bias for D1, improving its sensitivity, plus a standing bias for the converter and the first IF amplifier transistor. Automatic gain control (AGC) The review set is labelled as 7XT40Z1. According to the circuit diagram, that version applies AGC to the Volume Control 2nd IF Oscillator 1st IF Audio output stage 3rd IFT 2nd IFT 1st Audio Osc. Coil 1st IFT Output Converter Output Demod Driver Transformer Output Transformer Photos 3 & 4: annotated top and underside views of the Zenith Royal 500’s chassis. 106 Silicon Chip first IF stage alone. However, this set’s AGC circuit applies control to both IF stages. It appears to be an undocumented factory variation. The AGC line is bypassed for audio by 3μF capacitor C16. This is generally frowned on, as electrolytics perform poorly at intermediate and radio frequencies. The Regency TR-1 I tested in April 2013 showed RF instability due to such a capacitor having aged (siliconchip.au/Article/3761). The AGC voltage is applied to the converter stage via 1kW series resistor R6, which also isolates the LO signal from the AGC circuit. The first IF transistor (Q3) has the AGC voltage applied via 2.2kW decoupling resistor R7. Recall that the second IF transistor (Q4) is biased from Q3’s 470W emitter resistor (R11) via 2.2kW resistor R13. As the AGC circuit reduces the bias on Q3 (also reducing its emitter current), the voltage across Q3’s emitter resistor, R11, will fall. Full AGC action brings Q3’s bias close to cutoff, with a bias of about 0.22V, so its emitter voltage will fall to only about 0.05V (50mV), implying a collector current of 100μA. A drop of only 0.05V across R11 would reduce Q4’s available bias to zero, but 47kW resistor R14 from the positive supply rail ensures that Q4’s bias never goes below the cutoff threshold. In effect, AGC is applied to the converter and both IF amplifiers in this radio. See the voltage annotations on the circuit for the actual operating values. Australia's electronics magazine The audio section follows the design that had become standard at about this time. Like many other circuits, it uses PNP transistors with a positive battery supply. This sees the emitters fed from the positive supply and collectors going (via their loads) to ground. PNP driver transistor Q5 uses fixed combination bias: R18 & R19 form the divider, while R20 is the emitter resistor, bypassed by 50μF capacitor C13. Q5 feeds driver transformer T4, which has a split secondary that provides anti-phase drive to the Class-B PNP output transistor pair, Q6/Q7. 1nF capacitor C14 is wired across T4’s primary. This looks like it would provide a top-cut function, but its low value means it will have no effect until about 15kHz. It’s most likely there to siliconchip.com.au filter out any remaining IF signal that C11 did not remove. The output pair gets about 150mV of forward bias from divider R22/R23. This bias network is not compensated for temperature or changing battery voltage. The lack of temperature compensation makes it inadvisable to run the output stage at full sinewave power for any length of time. The two emitters share a common 10W resistor, R24, which provides some local feedback and helps compensate for mismatches in Q6/Q7. They drive output transformer T5 which, in turn, drives the 15W internal speaker. 100nF capacitor C15 does have a top-cut effect. Photo 5: a close-up of the front panel controls on the Zenith Royal 500. The left control handles volume and power, while the right is for tuning, audio stages (preamplifier, driver, output). The Royal 500 uses the more familiar two IF stages and two audio Cleaning up the set stages (driver and output). I was offered this set at the HRSA’s As noted earlier, designs applying RadioFest in September 2023. It was both the LO and signal to the converter complete, including the original ear- base do not allow a signal generator, phone, leather and cloth carry cases, with its low output impedance, to the original handbook, and even a spe- inject a signal directly into the base. I cial (unused) label allowing the owner was able to measure its sensitivity for to ‘personalise’ the set. a direct 455kHz input but not for anyCollectors will appreciate the rarity thing in the broadcast band. I solved of getting any old radio complete with this problem by adding a 470W series all accessories, so thank you to the own- resistor between my generator and the ers who kept this set complete as pur- converter base. chased! It also had a receipt for repair Comparing my direct 455kHz injecwork at Truscott’s, dated 14/11/2001. tion at 8μV and the modified input at The set was pretty much undisturbed, 110μV, I have an attenuation of 13.75 apart from a professional recap. times. Assuming that ratio holds, senThe case showed signs of wear, sitivity at the converter base is about mostly affecting the front gold-­ 135μV/13.75, ie, 10μV at 455kHz, and coloured ZENITH branding, the rear about 6μV at 1260kHz. These values set name and the “tubeless – 7 transis- are roughly comparable to the sensitivtors” moulding. It came with batteries ities of other five-stage sets I’ve tested. and worked at first switch-on. Its sensitivity is superior to the The volume control and tuning were T-2500; 3WV Horsham rocked in noisy, so I applied contact cleaner with pretty much at local station volume. good results. The alignment seemed I tried getting some Hobart and SydOK but I went over it to be sure. I ney stations during the day, but either found that Zenith’s suggestion of using it could not pick them up or adjacent 535kHz for the low end did not give the Melbourne stations blanked them best results, so I aligned it at 600kHz. out. I did manage to pick up 3BT BalZenith also specified aligning the top larat and 3EL Maryborough, while end at only 1260kHz, and I followed 3CS Colac treated me to some vintage their recommendation. Fleetwood Mac! With the set working well, I put it The Royal 500’s service sheets on the test bench for evaluation. give a sensitivity of “approximately 500μV/m for 50 milliwatts output”. How good is it? On test, sensitivity at 600kHz was For sensitivity, it’s up there with the 120μV/m at 600kHz and 115μV/m best of the day. It’s much smaller than at 1260kHz. The signal-plus-noiseRaytheon’s ‘picnic set’ T-2500, which to-noise (S+N:N) ratios were 11dB in it rivals in all but sound quality. both cases. These were for a modulaBoth sets use five active stages and tion frequency of 1kHz; sensitivities a separately-excited converter stage. for 400Hz were, unusually, worse by The T-2500 uses only one IF amplifier some 2dB. but makes up for that by having three For the standard 20dB S+N:N siliconchip.com.au Australia's electronics magazine ratio, sensitivities were 325μV/m and 400μV/m, confirming Zenith’s original specifications. RF bandwidth was ±2.5kHz at -3dB and ±30.5kHz at -60dB. The AGC was effective, with a +40dB change of input needed to give a +6dB output change. I was not able to force it into overload. The audio response was perhaps adequate, given the small speaker. From the volume control to the speaker, it reached -3dB at about 320Hz and 3.9kHz; from antenna to speaker, it was around 260~2700Hz. Distortion at 50mW was 6.4% and the output started to clip at 100mW. The output sinewave was visibly asymmetric at low volume, indicating a mismatch between the two output transistors. With no feedback in the audio section, this radio does depend on output transistor matching for best performance. Special handling It’s well-built, but be aware that the ferrite antenna bar is fixed to the chassis by a semi-flexible clamp. Mine was still intact, but I’d be careful about applying too much stress. Purchasing advice The Royal 500 was released in several colours. For me, the ‘black brick’ design is most appealing. It’s striking, but not as ‘shouty’ as the cherry red version. If you don’t have one, consider this fine example of radio technology. It’s a ‘proper trannie’ with all the design features and performance you’d expect, and it runs on ordinary AA cells. For more information, see: • https://w.wiki/8$Z4 • Search www.radiomuseum.org/ for Zenith Royal 500 SC November 2024  107 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 Dud battery used with Compact OLED Clock I have just finished building the Compact OLED Clock/Timer and it’s working well (September 2024; siliconchip.au/Article/16570). However, the battery life seems very limited. Even when left in sleep mode, it barely lasts a day. Is that normal, or did I get a dud battery? ● We measured our prototype as drawing 5mA while sleeping and up to 20mA when the screen is on (except for the brief times when the Time Source is running, when it draws more). 600mAh is about the lowest capacity we have seen for that size of cell, and that should mean 120 hours (600mAh ÷ 5mA) or five days in sleep mode before the battery goes flat. One test we did with the prototype was to leave it sleeping for around four days without being charged, then we woke it up, and it was still powered. So our testing bears out our calculations. Your unit might have a current draw higher than expected. We suggest you use something like a DMM on milliamps mode to measure the current draw from the battery and verify that your build is consistent with our numbers. Our cell was the LiFePO4 type, since they are better at handling being deeply discharged. A Li-ion type that has been fully discharged may have suffered a loss of capacity. Or, as you propose, you could have a dud. Unfortunately, many batteries and cells available on sites like eBay, Amazon and AliExpress fall far short of their capacity claims! Making Compact OLED Clock alarm louder I am interested in building the Compact OLED Clock/Timer from the September 2024 issue. I have a high-­ frequency hearing deficit and cannot hear the beeps of our kitchen timer. Therefore, I’m concerned about the pitch of the alarm beeps it produces. 108 Silicon Chip On a more trivial subject, can the location field on the timer be edited to read “Melbourne”? I realise the time zone is the same, but I would feel more comfortable if that change was possible. (T. V., Ivanhoe East, Vic) ● Both the changes you want can be made by altering the source code and recompiling the software. To achieve that, you will need the MPLAB X IDE and the XC8 compiler, plus the PIC16F1xxxx device family pack (DFP); all are free downloads. We used version 2.41 of the compiler and version 1.18.352 of the DFP. If you load the project (TIMER_ REVD_13.X) in the MPLAB X IDE, it should prompt you to install the matching versions if they are not present. We used the free version of the compiler, so you will not need a paid license to recompile the code. You will, however, need a suitable device programmer to transfer the modified firmware to the microcontroller (eg, a PICkit 4). The beep frequency is determined by the code in the initTone() function in the io.c file. It defaults to a square wave around 900Hz (with a good amount of higher harmonic content too). The period SFR (special function register) PWM1PR sets the period and is the inverse of the frequency, which is derived from the 32768Hz clock crystal. The frequency can be reduced by increasing the period. The duty cycle can also be changed with the PWM1S1P1 SFR; we made it half of the period value to maintain a 50% duty cycle. The text strings for the time zones are set in the timeZoneNames array in the timezones.c file and should be 13 characters long, so you can change “SYDNEY” to “MELBOURNE” there. Just be sure to pad the strings with spaces so that they are all the same length. Replacement for RURG3060 diode I have just started ordering the parts I need for the 180-230V DC motor Australia's electronics magazine speed controller (July & August 2024; siliconchip.au/Series/418). Apparently, the RURG3060 fast diode is no longer manufactured by Onsemi, and there is no stock at element14. Also, the element14 part number in the parts list is incorrect. Any help with this part would be appreciated. (E. M., Blaxland, NSW) ● It seems that they have stopped making the RURG3060 is because it has been replaced by the RURG3060-F085, which has slightly higher ratings (90A peak vs 70A). Otherwise, it looks very similar. You can get the RURG3060-F085 from DigiKey or Mouser: • DigiKey RURG3060-F085OS-ND • Mouser 512-RURG3060_F085 We are not sure why, when element14 ran out of RURG3060s, they didn’t switch to selling the RURG3060-F085. Perhaps it was just not popular enough to be worth their while. Strange bug in firmware for Automatic LQ Meter I was initially unable to get the rotary encoder to work in the Automatic LQ Meter I built (July 2024; siliconchip.au/Article/16321). I confirmed that the rotary encoder is OK by removing it and testing it with a Micromite. I also confirmed that when installed back in the LQ Meter, I get signals at pins D2, D3 and D21 of the Nano when the encoder is rotated or the switch activated. The switch works as it should but, unfortunately, there is no response from the Nano for shaft rotation. I had already desoldered the LCD screen because I thought maybe there was not enough clearance between protruding lugs on the back of the screen and the row of soldered pins of the Nano. I was down to thinking the problem was either software or a faulty Nano. I couldn’t do much about the software and I didn’t look forward to desoldering the Nano. Having run siliconchip.com.au out of ideas, I tried to implement the procedure outlined in the article whereby if the rotary encoder was operating in reverse, the software could be changed to make it run normally. My encoder was not operating at all, but I had nothing to lose but to try the procedure. And that was it. The rotary encoder burst into life and the whole instrument behaved exactly as it was designed to do. I would like to express my appreciation to Charles for such an interesting project. It was well-thought-out and implemented. I would like to see more projects of this calibre. (J. H., Nathan, Qld) ● We’re glad you figured it out. We think there must have been unexpected data in the Nano’s EEPROM; that procedure would have reset it. Charles has provided a revised version of the firmware for this project (v3.5) that addresses this problem and provides a few other improvements, such as remembering the last top frequency when the power is cycled (siliconchip. au/Shop/6/416). responded: Philco is an American Company with a wide variety of models made in the USA for that market. In Australia, the Philco radios were badge-engineered by local manufacturers who repurposed existing designs. The beautiful radiogram in question would have been made in the period from 1946 to 1948. Radiomuseum has some information on it here: siliconchip.au/link/ ac1l Changing WiFi SSID on Pico W Time Source I have some basic questions regarding the Pico W-based WiFi Time Source board (June 2023; siliconchip. au/Article/15823). I want to connect it to the New GPS-Synchronised Analog Clock board (September 2022 issue; siliconchip.au/Article/15466) as per page 66 of the June 2023 issue. I hope you can assist me. The SSID I’ve been using with the Pico W needs to be updated. I understand I need to disconnect the red power wire when the Pico W is connected to the computer via the USB cable. However, I want to check that the other three wires to the Pico W do not need to be disconnected when connecting the Pico W to the computer. Should the batteries be fitted to the clock board while changing the SSID? Should the Pico W switch be held pressed whenever the USB cable connection is made between the Pico W and the computer, then released? (G. D., Bunyip, Vic) ● The safest option is to completely disconnect the Time Source from the Clock. The Clock can keep working (for a while) without the Time Source, and you can confirm the Time Source is working correctly before reconnecting it. The red and green wires need to be disconnected to prevent USB power feeding back into the clock; the other wires do not matter. It should not matter whether the batteries are fitted or not. You could leave them in so that the clock keeps its state. Identifying Mosfets in Supply Protector kits I bought your SC6949 kit for the DC Supply Protector kit (adjustable TH version, June 2024; siliconchip.au/ Article/16292). It contains two transistors, marked 4N06L07 and 4P03L07. Evidently, these are transistors Q1 and Q2. Could you please tell me which is which? (M. S., Wellington, New Zealand) ● The one marked 4N06L07 is an N-channel type (full code IPP80N06S4L-07), while 4P03L07 is a P-channel type (full code IPP80P03P4L-07). So the one marked 4P03L07 is Q1 and the one marked 4N06L07 is Q2. Help identifying a Philco radiogram I came across this magnificent radiogram on display (shown in the photo). It is a Philco brand and has a Garrard record changer. From the radio dial showing all states, it seems to have been made in Australia. Can anyone give me any further information on it? (E. M., Capel, WA) ● We asked Associate Professor Graham Parslow about this and he siliconchip.com.au Australia's electronics magazine November 2024  109 You do not need to hold in the BOOT­SEL switch, since the firmware does not need to change. Adding an SSID is managed by the existing firmware on Time Source. Once the Time Source is connected to a computer and terminal program, you can follow the instructions starting from the Basic Setup section on page 64 of the article. Questions on Capacitor Discharge Welder I am in the process of building the CD Welder project from March & April 2022 (siliconchip.au/Series/379) and I have some questions about it. 1. Is a 31V 2.42A DC power supply OK? The testing section says up to 35V, but is that for working as well, or is heat a problem? 2. Are 35V low-ESR capacitors sufficient, or is a 50V rating mandatory considering Q1? Or does the 7815 take care of that? 3. I have 14 ESM modules, is there an enclosure big enough for that configuration, or should I keep four as spares and use the recommended enclosure? 4. Would Nylon bolts & nuts be better for the Presspahn, or even cable ties? 5. Should it be noted that the footswitch must be momentary? I was sold a DPDT switch as a substitute and only discovered that prior to testing. How much of a problem could it have caused? I love the magazine; keep up the good work. I was keen to learn more about electronics in school, but was not encouraged and busy enough with other things anyway. Now that I’m retired I have the time, but so much has changed in the interim, it’s an uphill battle to catch up. (G. M., Kettering, Tas) ● Phil Prosser replies: a 31V 2.4A power supply will be fine. Use 2.2kW and 10kW resistors to set a 2A charging current. That will mean the capacitors take longer to charge, but if you don’t need to make hundreds of welds at a time, it will be fine. The voltage limit is the linear voltage regulator’s voltage rating, so 31V is OK. Nothing will get hot. The high-­current part is dealt with by the MC34167 switching regulator, and that will run reasonably cool at 2A. On the capacitor voltage ratings, if you look at places like Altronics and Mouser, you will see that 50V is a 110 Silicon Chip common rating for may of the capacitors. For example, Altronics’ 10μF types start at 50V. Their 1000μF capacitors are available in 25V and 50V; 25V is too little a margin for comfort. If you can get 35V low-ESR capacitors, they would be fine. My general approach with electrolytic capacitors is to try to keep a good margin on their voltage and ripple current ratings. I would never operate a 25V rated capacitor at 25V as that would have a negative impact on their lifespan. A 10V margin is much more comfortable. If you look at the part of the circuit the capacitor is in, you should quickly be able to choose a rating. For example, the caps on the DC input from your plugpack, the 220μF and 2.2μF parts, will see 31V, and really need to be rated well above 35V, so for those, I would always pick 50V parts. The capacitors on the output of the 7815 should have a 25V rating or greater. If I had 14 ESM modules, I would make a point of finding a box that fit them, but I do have a little flair for the extravagant when it comes to things like that. The welder works fine with 10. If you ever need that little extra oomph, you will have it ready to rock and roll! I have done silly things to the ESMs and they have not broken, so I strongly suspect that if you have them as spares they will never be used. Thus, you might as well put them to work. I do not know what case would fit them – you will have to do a bit of research. I included the Presspahn (or other insulator) between those busbars as a safety measure. While the output is not enabled without the footswitch being pressed, if someone did lay a screwdriver across the busbars and hit the footswitch, the result of 1F charged to 25V being shorted on busbars like that would be both spectacular and dangerous. I was more than happy to use steel bolts, as they are not going to short anything. The voltage itself does not present a meaningful hazard. So using Nylon bolts or cable ties is not necessary. On the footswitch, I think it worth clarifying it should be momentary. A latching DPDT footswitch would work, but would be horrible to use. The circuit will not do anything odd, it would fire when the switch was Australia's electronics magazine closed, then you’d have to press it again to open it before another weld. That would likely lead to unintentional firing of the circuit due to the user losing track of what state the circuit is in. While the capacitors are charging, the firing circuit is inhibited by the signal on pin 7 of the headers. Also, the 555-based timer is triggered by a pulse from the 100nF capacitor between Q2 and the first timer, IC4. So if you hold the momentary switch down (or it latches on), nothing strange will happen. Battery Management System needed I am making a headlamp battery replacement. The lamp requires four 18650 Li-ion cells wired in a series/ parallel combination with a fully charged terminal voltage of 8.4V. From disassembling other cell packs, I see they include some extra cell management circuitry, for cell balancing or overcharging protection. Is there any propriety battery protection/charging management/cell balancing PCB, that can be wrapped up in the cell pack, that I should include? Otherwise, the headlamp functions OK with switching/charge indication all housed in the lamp body. (R. S., Emerald, Vic) ● It is always a good idea to include a Battery Management System (BMS) in any battery pack using Li-ion cells, especially if those cells don’t have their own protection circuits, or they are connected in series. A good BMS will protect against overcharging, overdischarging and will keep the cells balanced. There are many BMSs to suit different battery configurations available on sites like eBay and AliExpress. As your battery has two cells in series (2S), try searching for “2S BMS” on those sits and you will find several options. Just make sure they are designed for your particular configuration and can handle the maximum discharge current. While we have not published complete BMS designs, we have published cell balancers and also ‘battery lifesavers’ to protect from overdischarge. For cell balancers, see: • Battery-Pack Cell Balancer (March 2016; siliconchip.au/Article/9852) – suits 2S, 3S & 4S. continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au Compact OLED Clock & Timer 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 September 2024 PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. Short-Form Kit SC6979: $45 siliconchip.au/Article/16570 This kit includes all parts except for the UB5 Jiffy box and Li-ion cell. USB-C Serial Adaptor Complete Kit SC6652: $20.00 June 2024 siliconchip.au/Article/16291 Includes the PCB, programmed microcontroller and all other parts required to build the Adaptor. 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 November 2024  111 High-Energy Ignition with individual coils I would like to use your Multi-Spark CDI design (December 2014 & January 2015; siliconchip.au/Series/279) on distributorless systems, primarily with aftermarket standalone ECUs. I was wondering if I could wind the transformer to support two or more Advertising Index Altronics......... 11, 23, 37-40, 47, 75 Beware! The Loop....................... 12 Blackmagic Design....................... 9 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................ 6-7 Jaycar............................. IFC, 55-58 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 PCBWay....................................... 13 PMD Way................................... 111 SC Bridge Rectifiers.................... 94 Silicon Chip Binders.................. 65 Silicon Chip OLED Clock......... 111 Silicon Chip PDFs on USB......... 89 Silicon Chip Shop...................... 95 Silicon Chip Songbird................ 62 Silicon Chip Subscriptions........ 41 Silicon Chip USB-C Adaptor.... 111 TME............................................. 99 The Loudspeaker Kit.com........ 101 Wagner Electronics..................... 81 112 Silicon Chip cylinders at a time and then use one multi-spark section/IGBT per cylinder to switch the high voltage. I don’t foresee needing to fire more than six cylinders in sequential ignition mode. Please let me know what you think. (M. N., Bangalore, India) ● You can use the CDI with multiple cylinders and separate ignition coils by duplicating the trigger section for each cylinder and connecting them all to the high voltage generator. Only one of the transformer section that produces the 300V is needed. Checking if ultrasonic tweeters are functioning I would like to build a simple go/ no-go indicator to determine the operation of a tweeter at ultrasonic frequencies, around 20-25kHz. I had in mind perhaps a bat detector or a modified microwave oven detector to suit that frequency range. Have you published anything suitable in the past? (C. O., Adelaide, SA) ● The Ultrasonic Eavesdropper project (August 2006; siliconchip. au/Article/2744) could be used as it down-converts high frequencies to something you can hear. A microwave oven detector would not be suitable as microwave energy is at a much higher frequency and is not sound but electromagnetic waves. Soldering iron power control My wife has expressed an interest in Pyrography (burning patterns into timber and similar) and has a couple of suitable soldering type tools with appropriate tips. She wants a basic heat controller for better results; my mind went back to the ‘simmerstats’ and Triacs/Diacs of my earlier days. I assume there are much better Errata & Sale Date for the Next Issue • High-Current Four Battery/Cell Balancer (March & April 2021 issues; siliconchip.au/Series/358) – also suits 2S, 3S & 4S at higher currents and with better efficiency. For battery lifesavers, see: • Lifesaver For Lithium & SLA Batteries (September 2013; siliconchip. au/Article/4360) – up to 20A. • Dual Battery Lifesaver (December 2020; siliconchip.au/Article/14673) – up to 5A per output. alternatives these days, such as Mosfet control. The irons are quite low power, 30-40W. Could you refer me to a suitable circuit or kit in an earlier publication that I could build? (D. C., Beachmere, Qld) ● Using a Triac for phase control of mains power is still a valid approach. Mosfets can be used for mains switching, especially for dimming LED lighting where trailing-edge phase control is needed. The most relevant project is the Heat Controller (July 1998; siliconchip.au/ Article/4687). The PCB for that project is still available (siliconchip.au/ Shop/8/873). Alternatively, you could use a standard light dimmer housed in an Earthed metal enclosure with suitable mains wiring (similar to the July 1998 Heat Controller wiring). That concept was described in the article on Power Control With a Light Dimmer (October 1996; siliconchip.au/Article/4946). Alternatively, a phase-control based motor controller could be used, such as our Full Wave Universal Motor Speed Controller (March 2018; siliconchip. au/Article/10998). Substitute for old toroidal core I have been unable to find an equivalent for the RCC32.6/10.7, 2P30 ring core (Philips 4330 030 6035) used in the 40V 3A Power Supply (January & February 1994; siliconchip.au/ Series/167). Can you help me find a suitable substitute, preferably available from element14? (M. B., Parkes, NSW) ● The cores available from element14 appear to be for higher frequencies than are suited for the 40V 3A Power Supply. Jaycar’s LO1238 should be a suitable replacement. Their LO1244 would also be suitable. SC Pico Mixed-Signal Analyser (PicoMSA), September 2024: an error in the PCB means that the 10Ω through-hole resistor that powers the +5VA rail (just to the left of LED1) does not connect to the +5V rail. This is most easily fixed by running a short wire on the underside of the PCB from the pad of that resistor that’s closest to the Pico, to the Pico’s pin 40. Alternatively, scrape off the solder mask from the top-layer track that runs under the resistor and solder a short jumper across to it. Also see the Mailbag column of this issue for a letter regarding new firmware that runs the Pico at 200MHz for better reliability. Next Issue: the December 2024 issue is due on sale in newsagents by Thursday, November 28th. Expect postal delivery of subscription copies in Australia between November 25th and December 13th. 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