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JUNE 2022 ISSN 1030-2662 06 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST Spectral Sound MIDI Synthesiser with timbre morphing and 18-note polyphony Buck-Boost LED Driver drive 12V LED panels, charge batteries and convert 12V ↔ 24V Arduino Programmable Load a clever shield to test power supplies Metal Oxide Air Quality Sensors for detecting CO2, NOx and VOCs Integrated Circuit Fabrication Build your own Dew Heater This project brings together a few Arduino-compatible modules and some other parts to create a versatile tool. Inspired by the Dew Heaters used on telescopes, it senses ambient temperature and humidity to control a small heater. Use this on anything that needs to avoid condensation and on your telecscope too (if you have one). SKILL LEVEL: ADVANCED For step-by-step instructions & materials scan the QR code. CLUB OFFER BUNDLE DEAL 5995 $ SAVE 30% For step-by-step instructions & materials www.jaycar.com.au/diy-telescope-dew-heater KIT VALUED AT $91.83 1MM TRACK TRACE WIDTH FROM 595 12 95 $ Blank Fibreglass PCB $ Pure copper bonded to quality fibreglass base. Single or double sided. 150x75mm to 300x300mm available. HP9510-HP9515 100 $ gift card Awesome projects by On Sale 24 May 2022 to 23 June 2022 ONLY Polymorph Pellets Commercial grade thermoplastic that softens to be formed into any shape at around 62 - 65°C. 100g bag of 3mm pellets. NP4260 ONLY 2995 $ Silver Conductive Pen Apply instant traces on most surfaces e.g glass, plastic, metal, epoxy etc. NS3033 PCB Etching Kit Complete with assortment of double-sided copper boards, etchant, working bath and tweezers. HG9990 Got a great project or kit idea? If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com ONLY 3995 $ Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.35, No.6 June 2022 12 IC Fabrication, Part 1 0,', 63(&75$/6281' We take an in-depth look at how silicon chips, also known as integrated circuits, are made. ICs form the lifeblood of most modern technology, from computers to medical devices. By Dr David Maddison Semiconductors 6<17+(6,6(5 SDJH 38 Radar Coach Speed Detector The Radar Coach is ideal for measuring the speed of cricket, baseball and footballs. It can also be used to measure your own sprint, or even a car! By Allan Linton-Smith Speed detector review page 40 72 MOS Air Quality Sensors MOS (metal oxide semiconductor) modules are air quality sensors that rely on the behaviour of metal oxide in the presence of air to measure gas levels. By Jim Rowe Low-cost electronic modules 84 Altium Designer 22 We use Altium Designer for all our project PCBs and so with the release of AD22, we wanted to see what new features are available. By Tim Blythman Software review 24 Spectral Sound MIDI Synthesiser The Spectral Sound MIDI Synth is easy to build and can be connected to any MIDI compatible device. It can play up to 18 different notes simultaneously, providing you with a device that can create rich and detailed sounds. By Jeremy Leach Musical instrument project 40 Buck-Boost LED Driver This high-power project drives ridiculously bright 12V LED panels. It delivers up to 8A with adjustable current and voltage. You can even use it to charge batteries from a DC source, or as a 12 ↔ 24V DC converter. By Tim Blythman LED/regulator project 48 Arduino Programmable Load A variable load is indispensible when testing power supplies, driver circuits and the like. Our Arduino shield can handle up to 70W continuous at 15V and 4.7A, with a load resistance between 3.1W and 47W in 15 steps. By Tim Blythman Arduino project 61 500W Power Amplifier, Part 3 Follow these assembly, testing and calibration instructions to finish building the 500W Power Amplifier. By John Clarke Audio project 81 Revised Battery Charge Controller Due to the unavailability of the Si8751 Mosfet driver, we have redesigned our 2019 Universal Battery Charge Controller to use alternative parts. By John Clarke Project update Buck-Boost LED Driver Altium Designer 22 review on page 84 2 Editorial Viewpoint 4 Mailbag 88 Circuit Notebook 92 Serviceman’s Log 98 Vintage Television 1. RF burst power meter 2. Artificial candle using a “real” flame 3. Digital volume control with discrete logic 4. An easy way to measure SMDs Admiral 19A11S TV by Dr Hugo Holden 106 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Nicolas Hannekum – Dip.Elec.Tech. Advertising Enquiries Glyn Smith Mobile 0431 792 293 glyn<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 Former Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 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 139, Collaroy Beach, NSW 2097. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Shutting down our old website From around 2000 to 2012, our website was run by a third party and not under our direct control. When I started working at Silicon Chip, it was apparent that we needed to build our own website for various reasons. For example, our subscription system was completely separate from the website, so there was no good way for people to renew their subscriptions online (or change their address etc). There were a lot of other reasons to take control, such as being able to sell items like PCBs from the website, which is now a critical service that we provide, along with other parts. It would also give us better control over how our articles were presented online. It just made so much more sense to handle it ourselves. When we set up the new website, we had to decide what to do about people who had paid for access to articles or magazine issues through the old one. We realised that we had to provide continuity, so everyone who had access to a magazine through the old method was given perpetual access to the same issue on the new website. We also kept the old website going as-is to provide the best transition possible for our readers, allowing them to decide when they wanted to switch over. But as time goes on, there seems to be less point in keeping that old website (http://archive.siliconchip.com.au) going. By early 2020, we finished adding all the back issues on our current website, back to the very first issue (November 1987). That’s all the content that was on our old website, and much more. Our main website – www.siliconchip.com.au (or www.siliconchip.au if you prefer a slightly shorter URL), does everything the old site did and so much more. So I think the time is approaching to shut the archive server down. With PDFs now being available for the latest issues to subscribers, and even older issues for those who’ve purchased the PDFs on USB collection (or paid for separate back issues), there is even less reason to keep the archive site up. The presentation of articles in our PDFs is so much better than on the archive website, where the articles were converted to HTML format and diagrams were rasterised, often making them blurry or pixelated. So I am writing this to give anyone who objects to that an opportunity to contact us and explain why they think we should keep the archive server up. As the saying goes, “speak now or forever hold your peace”. If you’re wondering why I want to shut it down, part of the reason is that we didn’t develop any of the code, and it is now on a very old platform that sees few updates. I’m concerned about the security implications of keeping such old software running. It is isolated from the rest of our infrastructure, but a breach could still reveal some customer information such as names and e-mail addresses. There are also costs associated with keeping it going, including some of our time and hosting expenses that I would rather spend on our current website and producing new content. I hope that, by now, all our readers have switched over to using the new website. If not, please give it a go as we believe it is a significant improvement over the old one. Unless we are given good reasons to keep it going, we plan to shut the archive site down by the end of July 2022. 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”. The early years of radio and TV I am writing regarding the Vintage Radio article on the Phenix Ultradyne L-2 by Dennis Jackson (March 2022; siliconchip.au/Article/15248). Dad made a “Neutrodyne” Receiver some years back, shown in the photos. He also made the “Queen Anne” legs on the cabinet. He was born in 1904 and died in 1994. I saw in “Percy’s” Log Book that he had still been active on the radio a week or so before he passed. The receiver remains for (public) inspection at the Historic Homestead of “Mont DeLancey” at Wandin in the Dandenong Ranges. You can lift the lid with the speaker trumpet out of the way! Mum used the battery compartment for glassware and various other table items. He built his own amateur radio rig and wound all the various transformers. He made a reel-to-reel tape recorder, LCR Bridge with magic-eye tuning and the beam rotator transmission propagation indicator, driven from a pulley with thin stainless rope on a drum. The display was backlit, with Melbourne at its centre point. His longest-lasting communications receiver was a Hammarlund Super Pro. When he got around to making a new transmission tower in his retirement, he had to make an arc welder first. When the tower was finished, he had to dig a hole about eight feet deep to meet the council regulations. An inspector from Moorabbin council came and measured the depth for compliance. When he was transmitting, the dimmed shack flickered with the blue light of the mercury arc rectifiers, conducting with his voice modulation. He earned a certificate for making contact with one amateur operator in each of the 50 United States plus Washington DC and Puerto Rico. As a boy, I watched Casey Jones, Seahunt and Mickey 4 Silicon Chip Mouse Club on the TV he made; it had a war-surplus round green-phosphor screen. He made a fridge in the 1930s, when most still had ice cabinets. He went to a lot of trouble getting the cabinetry all vitreous enamelled. In Melbourne, before Farnell and Radio Spares moved in, we had a local supplier as well as Radio Parts. It was called “Stewart’s Electronics”. Stewart Day would call in at the Moorabbin Radio Club for the old timers’ morning tea; not bad for business! Stewart was talking to Dad and said we must get some of this down for the record, and took a few notes. During the WW2, dad had to parcel all his gear up and surrender it to the post office until the war ended. Robert Sebire, Emerald, Vic. Comment: we have reproduced some of the photos provided to us by Robert Sebire of his father on this page and overleaf. More on Noughts & Crosses design Thanks for publishing a brief description of my entry in the Dick Smith Noughts & Crosses competition (April 2022, page 84). Regarding the “impractical to build it” comment you added at the end, I’m not sure why that was necessary, but I understand the editor is entitled to their opinion. Yes, it would be a beast to build the entire system using TTL logic-gate ICs. But remember that Dick Smith made such a machine out of disused telephone exchange switching gear. As Dick explains in his autobiography, building such a beast has great benefits from a pedagogical and self-confidence perspective. The ICs are organised into modules so that each module can be built and tested separately, then integrated into a complete system in a step-wise manner. A teacher could Australia's electronics magazine siliconchip.com.au even organise a class of students to work in teams, each team working on one of the modules and learning how the systems integration process works. The full design is intended to adjudicate a game between competing automated players. That is why there are 12 PCBs of TTL ICs. The design deliberately avoids the use of a synchronising clock so that the only limit to how fast the system can adjudicate a game between two players is the propagation delay of the TTLs. It is possible to build a cut-down version of the design with only two PCBs, a bit like your runner-up #1. Since the design uses a common bus interface between the modules, a minimal system would be the human-­interface module plugged into the Arduino module. I would suggest that as a good starting point for a school or classroom-based project. For anyone interested in such a project, I have uploaded the article describing the full system (https://moonbounce. com.au/tictactoe.html). That page also includes a Java­ Script version of the suggested logic that can be played in most web browsers. If anyone has questions regarding the design or PCBs, I can be reached by e-mailing Silicon Chip with a request to forward the query. Dr George Galanis, Emerald, Vic. Power supply one-upmanship I read with interest the comment by Greig Sheridan in the October 2021 issue (Mailbag, page 12). It referred to an Electronics Australia May 1987 lab power supply he had built. I built a switchmode 50V/5A laboratory power supply based on the design by Jeff Skeen published in Electronics 6 Silicon Chip Australia, May 1983. To reduce the cost, I used parts I had on hand. This called for some changes in the output specification and circuit design. I replaced the nominated transformer with a 31V, 4A toroidal type, effectively giving me a 44V/4A power supply. I replaced the main MJ15004 switching transistor with a BDX62A Darlington and the volt and amp panel meters with a single, switchable digital meter to display either volts or amps. I built a small 9V DC supply to run the digital meter from a small, light winding wound on the toroidal core. The switchmode supply runs quite cool with no fan required. The picture (at lower left) shows the power supply with the top cover removed. Mauri Lampi, Glenroy, Vic. Simulating boat sounds In the April issue of your magazine, on page 118 (Ask Silicon Chip), G. C. asked about simulating steamboat sounds. The website www.component-shop.co.uk has a catalog link at the bottom of the opening page. There, you will find quite a range of simulated boat sound devices (starting on page 68 at the time of writing this). They also sell many other small items that may interest electronic minds. I get a lot of enjoyment reading your magazine most months, even though the electronics are past my skill level. I gave up when valves left the scene. Graeme Baker, Grovedale, Vic. Migrating from Microchip mpasm to pic-as I have some information that might help G. C. of Rangiora, NZ, who wrote the letter “Advice on coding PICs and using MPLAB” in the April 2022 Ask Silicon Chip section, on page 117. Yesterday, I worked on an assembler program for the first time since installing MPLAB X v5.50. It seems that since about v5.40, Microchip has replaced the old mpasm assembler with pic-as(v2.32) and is trying to move users to relocatable code instead of absolute location code. We now have to use PSECT instructions in our code to achieve this. If I just added a PSECT code at the top, all the “phase error” errors went away and it built successfully. But looking at the .hex file, no line began “:02000” indicating programming at location 0x0000 – the reset vector. In my case, what had been created was code that was relocated to 0x0FBE. The ORG statements were being treated as offsets from the relocated origin, not absolute addresses. To get it to produce a .hex file that looks like it Australia's electronics magazine siliconchip.com.au KEEP PACE WITH AN EVER CHANGING MARKET, WORK WITH: • A global distributor of technology products, services and solutions that provides you with local support • A reliable partner that offers you a broad range of products • An industry leader providing access to specialised products Single Board Computing Leading distributor of cutting edge technology Semiconductors Over 120,000 semiconductors in stock at competitive prices Passives Over 140,000 passive products Electromechanical Over 60,000 electromechanical components Interconnect Over 550,000 connector, cable and wire products Test and Tools Full range of products to support electronic design and preventative maintenance Authorised distributor of Contact us now au.element14.com | 1300 361 005 will work, I had to restructure my code as follows. processor 12F683 #include <xc.inc> PSECT resetVec, class=CODE, reloc=2 ORG 0 ; reset vector resetVec: goto MAIN ORG 8 ; bytes, not words goto INTERRUPT PSECT code INTERRUPT: retfie MAIN: ...... END resetVec You also need to go to the Project tab in the box a bit below “File” in the top left (it may show as “Pro…”). Right-click your project name, go to the bottom, select “Properties” and click “pic-as Linker”. Find “Additional options:” roughly in the centre of the screen and insert “-Wl,-presetVec=0h” and click OK (That’s a lower-case L after the W). Now build, and you should get a :020000 line in the .hex file, and it should work. David Heckingbottom, St Ives, NSW. Migrating from PIC16F88 to newer 8-bit PICs I sent an e-mail to Silicon Chip about two months ago with a suggestion for an improved Solar Charger. I took your feedback onboard and contemplated why I was still dealing with an ancient PIC16F88. I only had one left, and when I checked to see how available they were from major suppliers, I was in for a bit of a surprise! I researched some possible substitutes from Microchip and found a suitable pin-for-pin enhanced mid-range replacement. Microchip had them available from Singapore, and they came in under two weeks. But I couldn’t find any decent practical guide online on how to go about such a migration process, as the new enhanced mid-range architecture means old code is incompatible. I made notes as I went and produced a migration document. I’m sending you the PDF in case it’s helpful to your readers. Note: the supplied document is available for download at siliconchip.au/Shop/6/6489 Phil Nicholson, Mentone, Vic. 500W Amplifier cooling efficacy I used to design products for a major equipment supplier, so I’d like to make some comments regarding your new 500W Amplifier (siliconchip.com.au/Series/380). Those vent holes on the side are grossly inadequate for anything other than if the amplifier is used for home, where its high power rating is more of a way to achieve a high dynamic range. For fans to be effective, the inlet area should be about the same size as the fan blade area, and the exhaust area 20% bigger to allow for expansion of the air. 8 Silicon Chip You also want to include baffles to prevent the air from circulating inside the product – in your design, you need to block off the area between the fans and the chassis rear, and probably at the top too. A sheet of plastic is all that is required. The rack case that it goes into also needs similarly sized vents on the side. I’d also like to comment about SMDs. I’ve been working with them since we started designing products with them in the 90s. I agree they’re intimidating at first, but you get used to them, opening the packets, using tweezers and making sure you don’t breathe too hard. The smallest I generally design with these days is imperial 0603 (M1608). Still, I use the occasional 0402 (M1206) – you can save a fair bit of space using 0402-sized 100nF decoupling capacitors, for example, because you use so many of them. You can also fit them in easily, nice and close to the noise source. Parts on both sides of the board is becoming the norm these days, which can make it hard to get decent-sized power tracks. I have a soldering station with a hot air blower but don’t use it much – just a normal iron from Jaycar. D. T., Sylvania, NSW. Comments: while we’ve mounted the 500W amplifier in a rack case, that’s mainly because it’s the most reasonably-­ priced, sturdy case that’s large enough to fit the complete amplifier and not too heavy as it’s made from aluminium. It also looks pretty good. It could be rack-mounted, but you are correct that the cooling system design is not optimised for that. We mainly intended it to be used in spaces like entertainment centres where there will be space above it for air to flow into the top on one side, through the fans, over the heatsink and then out the lid on the other side. That’s why we used quiet fans at low speed; so it can be used in a listening room. If it were placed in a rack with very little (or no) air gap above, you are right that the holes in the side would need to be enlarged. As you say, ducting would also be required to ensure sufficient airflow over the heatsink and minimal recycling of hot air back into the intake. In that case, it would also be a good idea to use fans that spin faster and move more air. Are “repair programs” useful? According to one source, it seems that your campaign for repairability has as least two adherents whose names rather surprise me. In this month’s IEEE Spectrum journal is an article “A Laptop That’s Fit to be Fixed”, which features a repairable Dell laptop, and also contains these words: “Apple, too, is preparing a Self-Service Repair program that will sell parts for iPhones, iPads and Macs directly to consumers. Owners will be able to fix their devices with new, official repair manuals.” Won’t that turn the Apple repairers’ network upside down – or was it a wind-up? Alan Ford, Salamander Bay. Comments: as Louis Rossmann runs an Apple repair business, we think he is in a good position to comment on this repair program. You can see his opinion in the YouTube video at https://youtu.be/agG108sxkyo To summarise, the available parts are pretty limited (for example, spare charge ports are not on offer, even though they wear out). 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On inventions, risk and old batteries In the January Editorial Viewpoint, you imply that large American companies are not risk averse. I disagree. Like most companies everywhere, they risk other people’s money. Why would the management want to risk their own wealth? Let investors and shareholders carry the risk. There is one thing in law that is more valuable than gold that reduces the risk of failure, and that is a patent. An invention must be enshrined in a patent, and not just an Australian patent and/or an American patent, but a patent in every country that supports them. Huge American companies own large numbers of patents and actively pursue smaller companies to obtain more patents. I believe that without patents, America would not be the powerhouse that it has been and still is now. Concerning inventions, my ex-boss recommended that after I had created some invention and developed it fully (a must), I should sell it for as much as I could to whoever will pay the price and let the buyer worry about the headaches that follow. This is advice borne from many years of working very long hours creating and running a medical technology company in Australia. Dr Maddison’s articles on batteries (January-March 2022; siliconchip.au/Series/375) were good. I know I am showing my age, but I owned a few of those very early cells; it is a pity I didn’t keep them. I remember that either large lead-acid cells or large Edison cells were made using a moulded glass case. As well, I can remember timber cases being used for some batteries. While at primary school, I discovered that the PMG was throwing old batteries into their rubbish bin. These were the large zinc-carbon cells as shown in Fig.13 (January 2022, page 17) but with the standard EverReady red labelling. After recovering over a hundred of these, I rediscovered the arc lamp and arc cutting of steel sheets. They made my childhood that much better. George Ramsay, Holland Park, Qld. A plethora of information I love your magazine. I have read every issue since 2018 and wish I knew about it earlier as you have a lot of very useful information. On the subject of information, I have just stumbled across the website www.bitsavers.org and was blown away by the wealth of data sheets and design specifications available. They have a huge cache of documents, including CMOS and TTL data sheets, data books, magazines and application notes. I am having a blast going through all of this, and I know your readers will really appreciate the detail and diversity offered. My favourite is this one on op amps: siliconchip.au/link/abem (Fairchild, 1979). Ben Dempsey, Waimate, NZ. Comment: there does seem to be a lot of interesting information on that website. The Fairchild data book has details on quite a few classic devices. Good suggestions for RF Prescaler I recently built your High Performance 6GHz RF Prescaler (May 2017; siliconchip.com.au/Article/10643), and 10 Silicon Chip Australia's electronics magazine siliconchip.com.au it works very well. I am using it with my old EA frequency meter which only goes up to 500MHz. I sprayed the case satin black as I reckon it looks a lot better than unpainted. I have a few comments/observations. The SMA connector specified (Molex 073391032) is a reverse-polarity SMA connector similar to those used on WiFi modems etc. I believe the correct part is 0733910083. The MMBT3640 PNP transistors (12V 200mA 500MHz) are obsolete, so I used 50A02CH-TL-E (50V 500mA 690MHz) and these seem to work OK. I noticed that the divide-by-5 chip and the counter tend to oscillate with no signal at 450MHz and 150MHz, respectively. An onsemi application note AND8020 mentions this on page 17 and recommends offsetting one input up to 50mV with a high-value resistor. I piggy-backed a 47kW resistor to ground on the 10nF capacitor at pin 2 of IC3. I also added a 2kW resistor from pin 23 of IC4 to Vcc, which fitted neatly between the 100nF capacitor and L4. These stopped the self-oscillations. I chose 47kW as it was the only high-value resistor I had in M2012/0805 size, and for IC4, resistors much above 2kW did not stop the self-oscillation. I would be interested to know if you think this is the best solution. I would also be interested to know the reasoning behind using 1.4V as the bias voltage for the inputs of IC4 rather than something closer to Vbb (measured at 1.84V). Most of my test equipment was/is home built from EA/ ETI/Silicon Chip and I have had many years of good use from them. Congratulations on a great magazine; I hope it continues for many years to come. Kind regards, Mike Hammer. Comments: thanks for your findings which seem thorough and well-researched. We think you are right that those changes are the simplest way to stop self-oscillation. It’s true that a standard-polarity SMA socket would probably make more sense. We used a reverse-polarity socket handy because it mated with most of the SMA cables we had on hand, but perhaps that was not a sound basis for the choice. We generally don’t concern ourselves too much if prescalers and counters self-oscillate because it’s arguably a trade-off between that and sensitivity. In other words, any changes to prevent self-oscillation are likely to reduce sensitivity because they push the device’s operating conditions further from the switching point. Also, you don’t generally use a device like this without a signal applied. Your changes will probably not desensitise it all that much. The reason for using 1.4V for the bias voltage for IC4’s clock inputs is that it is right in the middle of IC4’s logic low-level voltage range (1355-1675mV for Vcc = 3.3V; see the data sheet, p6). We used a single bias voltage for simplicity and thought it was best to have these inputs rest at a low level in the absence of an input signal (although that’s somewhat irrelevant if IC3 is going to self-oscillate). Biasing them to Vbb as you suggest (halfway between the low and high levels) would likely give better sensitivity. We found the output swing from IC3 sufficient to trigger IC4 with reasonable signal levels over the intended operating frequency range, but increased sensitivity would be welcome above 1GHz (and would likely overcome any reduction in sensitivity due to your other changes). SC siliconchip.com.au Helping to put you in Control LabJack T7 Data Acquisition Module A USB/Ethernet based multifunction data acquisition and control device. 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SKU: SMC-410 Price: $319.00 ea + GST LCD Temperature and Humidity Sensor The Pronem Midi from Emko Elektronik are microprocessor based instruments that incorporate high accurate and stable sensors that convert ambient temperature and humidity to linear 4 to 20 mA. Dimensions are only 60x 126 x 35mm. SKU: EES-020A Price: $241.95 ea + GST TxIsoloop-1 Single Loop Isolator Loop isolators provide signal protection by electrically isolating the 4-20mA input signal from the 4-20mA output. SKU: SIG-201 Price: $168.19 ea + GST For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. Australia's electronics magazine June 2022  11 IC Fabrication Image Source: https://pr.tsmc.com/english/gallery-fabs-inside – Taiwan Semiconductor Manufacturing Co., Ltd. from inception to cutting-edge technology We take an in-depth look at the technology this magazine is named after: silicon chips, also known as integrated circuits or ICs. They are critical to most modern technology, and it has taken decades to get these devices to the pinnacle of performance they have achieved. But the technology has not stopped advancing yet! Part 1 – History & Manufacturing – By Dr David Maddison T his three-part series describes IC (integrated circuit) technology. Given their incredible complexity, we can only really scratch the surface of the fascinating and highly advanced manufacturing methods required. Arguably, this technology is the most advanced ever developed. This first article covers the early history of ICs, IC design, silicon wafer production, fabrication and lithography. Next month, the second part will 12 Silicon Chip focus on how IC technology has improved over time, including production nodes, transistor counts, and wafer sizes. It will then describe the extreme UV (EUV) lithography technology that is the current top-tier technology behind advanced ICs like computer CPUs. That article will also look at what components can be fabricated within an IC and how they are made, how ICs are packaged, Australian Australia's electronics magazine manufacturing and some other interesting aspects of the field. The third and final part will cover the latest IC technology such as FinFETs, GAAFETs, stacked dies and multi-chip modules. It will also discuss the challenges of improving this technology into the future. The transistor’s development The development of the planar transistor was a prerequisite for successful siliconchip.com.au integrated circuit construction. We covered the history of transistors in detail, including planar transistor manufacturing, in the March, April and May 2022 issues (siliconchip.au/ Series/378). The field of integrated circuits is vast and developing rapidly. We cannot possibly mention every possible technology, as a comprehensive survey would require thousands of pages of text! But we will attempt to cover all the critical aspects of IC design and fabrication. Making a single IC is a long, multistep process. Advanced chips like computer CPUs (central processing units) and GPUs (graphics processing units) are reported to take up to 15 weeks. Over the last few years, the industry average for advanced 7nm, 10nm and 14nm devices has been 11-13 weeks. Those times are for the actual manufacturing process, from the growth of the silicon crystal that forms the wafer to the finished product being ready for sale. But they do not include the tens of thousands (or much more) hours of research and development for the chip design itself. There is an adage that the first chip costs millions of dollars to produce (due to the cost of research and fabrication equipment), but subsequent copies cost only cents or perhaps dollars per piece (depending upon complexity). The modern production of ICs is almost entirely automated, using ultrapure materials in extremely clean facilities with extensive atmospheric and other controls to eliminate dust contamination. One advantage of automation is that it means fewer workers shedding skin cells, hair or other detritus that would affect production! Early IC history Combining several electronic components into a single physical device was tried with valves in the 1920s to evade a “tube tax” in Germany. Reducing the number of valves meant less tax on the radio. For example, the Loewe 3NF contained three triode valves, two capacitors and four resistors in one glass envelope (July 2020; siliconchip.au/Article/14513). In 1949, just one year after the transistor was patented, German Werner Jacobi filed a patent (published 1952) for an IC style transistor amplifier. On May 7th, 1952, British engineer Geoffrey Dummer proposed a device with several discrete components on a single semiconductor wafer. He wrote: “With the advent of the transistor and the work on semi-conductors generally, it now seems possible to envisage electronic equipment in a solid block with no connecting wires. The block may consist of layers of insulating, conducting, rectifying and amplifying materials, the electronic functions being connected directly by cutting out areas of the various layers.” This is regarded as the first description of the modern IC. However, he did not claim to be the inventor of the IC. Sidney Darlington of Bell Labs was awarded a patent in 1953 for a monolithic device with more than one device on a single semiconductor crystal (siliconchip. au/link/abdn). That patent would be one of the first for an IC had the patent lawyer not insisted on limiting it to two devices. In 1957, Yasuo Tarui of Japan produced a similar device, a “quadrapole” transistor, but unlike modern ICs, the transistors were not electrically isolated. In 1957, Harwick Johnson was awarded a patent for a “Semiconductor phase shift oscillator and device” (siliconchip.au/ link/abdo), on one ‘chip’ of semiconductor material, in accordance with the modern concept of an IC. This invention does not get the acknowledgement it deserves. Three significant factors associated with the commercialisation of ICs toward the end of 1958 were: a) The development of a hybrid IC by Jack Kilby of Texas Instruments; patent awarded in 1964 (siliconchip.au/link/abdp). Unlike Johnson’s device and modern ICs, this one relied on manually placed wires between the devices. Nevertheless, Kilby’s device is usually regarded as the first IC, and he was awarded the Nobel Prize for Physics in 2000 for his efforts. b) Kurt Lehovec of Sprague Electric Company developed a way to electrically isolate individual electronic components on an IC using “P-N junction isolation”. The device is surrounded by a material with the opposite doping to the substrate. A reverse-bias voltage is applied to the junction, creating a region with few charge carriers. A patent for this was awarded to Lehovec in 1962 (see siliconchip.au/link/abdq). c) Fairchild co-founder Robert Noyce developed the concept of the monolithic IC with diodes, transistors, capacitors and resistors in silicon, with aluminium interconnects and a protective silicon dioxide coating (see the diagram at lower left reproduced from siliconchip.au/link/abdr). Noyce died in 1990; otherwise, he might have shared the Nobel Prize with Kilby. In addition to the above patent, Jean Hoerni developed the planar process for fabricating transistors and other semiconductor devices (the patent was awarded in 1962; siliconchip.au/link/abds). This process was critical for Noyce’s work and he improved the process. The “traitorous eight” Jean Hoerni initially worked for William Shockley, but Shockley’s behaviour led Hoerni, along with seven others, to leave Shockley in 1957 to found Fairchild Semiconductor. They became known as the “traitorous eight” (see https://w.wiki/522K). Why use integrated circuits? Compared to devices built with discrete components, ICs allow for much smaller, simpler, more reliable and less expensive devices. This is because most or all of the parts can be made in a single process. Also, modern devices with extremely high numbers of components (in the billions), such as computers and mobile phones, would be practically impossible to make without ICs. They would be incredibly expensive and huge, even if it were possible to build them. siliconchip.com.au Diagrams from Robert Noyce’s (Fairchild Semiconductor) US Patent 2,981,877 (filed 1959, awarded 1961) for “Semiconductor Device-and-Lead Structure”. This is regarded as the first practical IC. Australia's electronics magazine The “traitorous eight”, from left to right: Gordon Moore, C. Sheldon Roberts, Eugene Kleiner, Robert Noyce, Victor Grinich, Julius Blank, Jean Hoerni and Jay Last. Source: Wayne Miller, Magnum Photos (https://w.wiki/53GC) June 2022  13 The first operational IC Fig.1: a die photo of the Micrologic uL903 from 1960, one of Fairchild’s first commercially produced ICs. It is a 3-input NOR gate used in the Apollo guidance computer. It contains four resistors and three transistors. The first operational IC was produced on the 27th of September, 1960, by a group at Fairchild. They were led by Jay Last and used ideas from Noyce (monolithic IC) and Hoerni (Fig.1). This led to a patent dispute with Texas Instruments, which held Kilby’s hybrid IC patent. This was eventually resolved by industry cross-licensing in 1966. Historians do not share a strong consensus on whether a specific individual invented the IC or whether the honour should go to multiple inventors. This author thinks multiple contributions should be acknowledged. The first commercial IC was released to the general public in March 1961, a type F flip-flop under the Micrologic brand, followed by more types in 1962 – see Fig.2. Texas Instruments released their first commercial devices in October 1961, the Series 51 DCTL “fully-­ integrated circuit” family (siliconchip. au/link/abdt). Components in ICs As you would expect, transistors can be fabricated in ICs, including bipolar transistors, Mosfets and JFETs. Most modern processes can produce either polarity of each device (ie, NPN, PNP, N-channel or P-channel). Naturally, diodes can also be made, as they are usually just a single P-N junction. That can include zener diodes, depending on the fabrication process being used. But to make a truly useful IC, it is also necessary to include other components like resistors, capacitors and inductors, and that is certainly Fig.2: IC die patterns from Fairchild Semiconductor, released in October 1962 following the uL903, including (B) a buffer, (C) counter adaptor, (F) flip-flop, (G) gate, (H) half-adder, S) half shift register. Some time after that, they added the 4-input gate (G1) and dual 2-input gate (D). Source: Fairchild Semiconductors siliconchip.au/link/abej 14 Silicon Chip possible, as we will describe next month. But first, we’ll explain how an IC is made, as the limitations of that process determine how these components must be fabricated. Silicon doping Like transistors and diodes, integrated circuits are mainly made of P (positive) and N (negative) doped silicon, conductive metals like aluminium and copper, and insulators like silicon dioxide. We covered doping in the aforementioned series on transistors, so we will only briefly cover it here. Doping alters the electrical conductivity and other properties of the semiconductor material. The semiconductor is typically silicon but may also be: • silicon-germanium • gallium arsenide, in microwave integrated circuits, infrared LEDs, laser diodes and solar cells • gallium nitride, in blue LEDs and other opto-electronic, high-­ frequency and high-power devices • cadmium telluride in photovoltaics and infrared optical windows • gallium phosphide, as used in LEDs Doping involves introducing different metals into the silicon crystal structure, from around one atom in 100 million for “light” doping to one in 10,000 for “heavy” doping. Either way, only trace amounts of the dopants are used. Metals (conductors) conduct electricity because of the free electrons provided by each atom in a metal crystal structure. Semiconductors lack free electrons, but doping the semiconductor with metal atoms introduces extra charge carriers. Therefore, doping One of the pickup tools used to move groups of wafers around the factory. Picture: Bosch Australia's electronics magazine siliconchip.com.au Fig.3: an overview of the VLSI design process. VHDL and Verilog are hardware description languages (HDL). Original source: www.eng.auburn. edu/~strouce/class/elec4200/CADtools.pdf RTL is Register Transfer Level and AUSIM and PSPICE are both circuit simulators. increases the electrical conductivity of the semiconductor. It is possible to make a heavily-­ doped semiconductor conduct almost as well as some metals. This means that it is possible to replace metal tracks with heavily-doped semiconductor material in integrated circuits. Unlike metals, where the charge carrier is almost always an electron, in semiconductors, the charge carrier can be an electron or the absence of an electron, called a “hole”. N-type (negative) doping means the majority charge carrier is a negatively charged electron. P-type doping is where the majority charge carrier is a hole with a positive charge. Typical P-type dopants used for silicon are boron, aluminium, gallium and indium, while N-type dopants are antimony, arsenic, bismuth, lithium and phosphorus. They have advantages in different applications. Other semiconductors use dopants such as carbon, chromium, germanium, lithium, magnesium, nitrogen, phosphorus, selenium, sodium, sulfur, tellurium, tin and zinc. The conductivity of semiconductors in integrated circuits can also be controlled by nearby electric fields (as in Mosfets) or by charge carrier injection (as in bipolar transistors). This means that the current flow through a junction can be electronically controlled, either continuously in an analog circuit, or in an on/off fashion in a digital circuit. The designer specifies what is required using a language like Verilog or VHDL, and the computer then figures out what combination of tiles provides an equivalent function. It lays the tiles out on a grid, calculates the routing between the tiles and generates the physical structure. The result is a set of masks that can be run through simulations to verify that the chip will behave as expected. IC design These masks or photomasks are then Before a chip can be made, it must be used to transfer the design to silicon. designed. As the most complex VLSI An IC mask layout view of a simple designs now contain billions of tran- operational amplifier is shown in sistors, the process is heavily reliant Fig.4, while an actual mask is shown on computers and software tools. The in Fig.5. exact design procedures are many and The highest performance chips varied and beyond the scope of this require significant ‘bottleneck’ areas article, but an overview is provided (such as multiplier-accumulators) to in Fig.3. be designed by hand as they can be Briefly, the design process is usu- made smaller, faster and more effially a combination of computer-aided cient. These hand-made pieces can and manual design. Simpler, less-­ be integrated into the synthesised demanding digital chips can be made designs. It is also possible to manualmost entirely using a ‘tile-based’ ally modify a synthesised design or scheme. Each tile might be a different give the software ‘hints’ to produce a type of logic gate, memory cell, multi- more optimal result. plexer, adder, multiplier etc. The industry-standard digital file Fig.4: a mask layout of a simple IC, an operational amplifier. Red is polysilicon; blue is metal layer 1; green is N-doped Si; brown is P-doped Si and the Xs are cross-layer “vias”. The large square on the right is a capacitor. Source: Wikimedia user Atropos235 (CC BY-SA 2.5) siliconchip.com.au Australia's electronics magazine Fig.5: an IC photomask. Source: Wikimedia user Peellden (CC BY-SA 3.0) June 2022  15 ► Fig.7: the process starts with purified silicon rods (left). Silicon from trichlorosilane gas is deposited onto them (centre), then they are broken up and formed into large silicon crystals by the Czochralski process (right). Source: Silicon Products Group GmbH ► Fig.6: a 3D view of a small “cell” (a standard design element of an IC) generated with the ShapeshifteR software from GDSII mask files. There are three metal layers plus vertical interconnects, with silicon gates in a reddish colour on top of the multi-coloured bulk silicon. The insulating material has been removed from this image. Source: David Carron (public domain) format for masks which can be transferred from designer to foundry is called “Graphic Design System” (GDS, introduced 1971) and “GDSII” (introduced in 1978). Since 2004, OASIS (Open Artwork System Interchange Standard) has been used, which can handle much larger mask sizes than GDSII. The GDSII files for the mask description of a ‘system-on-a-chip’ device like a mobile phone processor (as an example) can exceed 200GB. Fig.6 shows a 3D view of a ‘cell’ within a silicon wafer produced by software called ShapeshifteR that takes a mask design from a GDSII file and renders it into a 3D representation and cross-section of the actual chip. See http://shapeshifter.free.fr/ index.htm A ‘fabless’ design house does not manufacture chips but sends its mask files to a ‘pure play’ (fabrication only) foundry to have its design implemented in silicon. However, companies like Intel also specialise in both design and fabrication. Silicon wafer manufacturing Apart from design, the first stage of IC manufacture for silicon devices is to grow a near-perfect silicon crystal. Quartz ore called quartzite (basically silicon dioxide, SiO2) is the major component of most beach sands. It is extracted from quartz mines and refined to make silicon. Quartzite is crushed and then mixed with coke (coal that had previously been heated without oxygen). The mixture of quartzite and coke is added to an electric arc furnace where high temperatures of around 2000°C are produced. The carbon in the coke reacts with the oxygen in the quartzite, removing it. The result is an impure form of silicon that needs further refining. The silicon is then mixed with gaseous hydrochloric acid to form trichlorosilane, HCl3Si. This is a gas at the temperatures used so that it can be further purified by fractional distillation. The purified trichlorosilane gas is then mixed with hydrogen in a chamber with purified silicon rods electrically heated to 1150°C. It decomposes and is deposited as pure silicon on the rod surfaces to make polysilicon (many crystals as opposed to a single crystal) with a purity of 99.99999% (“seven nines”) or even ten or eleven nines. The polysilicon is then broken up to make a feedstock for the crystal growing process. Dopant metals such as antimony, arsenic, boron or phosphorus are added to the polysilicon to give the silicon the required electrical properties. This is called the Siemens process (Fig.7). It is the most commonly used process, but it uses a lot of energy; other processes have been developed, Fig.8: the Czochralski process for growing single large pure silicon crystals. 16 Silicon Chip Australia's electronics magazine siliconchip.com.au Picture: Bosch Picture: Taiwan Semiconductor Manufacturing Co., Ltd. such as a fluidised bed reactor. Once purified polysilicon is broken up, it is melted in an inert atmosphere and a ‘seed’ crystal attached to a puller rod is introduced into the melt and slowly withdrawn. The melted silicon solidifies and crystallises onto the seed crystal (set up with a preferred crystal orientation). The growing crystal is withdrawn from the melt as the rod is raised (see Figs.8 & 9). This is called the Czochralski process. It is economically beneficial, up to a certain point, to make crystals with as large a diameter as possible to maximise the number of devices that can be made at once on a single slice of crystal, known as a wafer – see Fig.10. Silicon wafer preparation Once the crystal has been grown, it is sliced into thin wafers, and the surface and edges are ground, polished and cleaned to make uniformly-sized wafers. A typical wafer cut from a 300mm diameter crystal is 0.775mm thick, weighs 125g and 640 10mm x 10mm dies (chips) can be made on it. The planar process The key concept of IC fabrication is the “planar process”. This was initially developed by Fairchild Semiconductor in 1959, and it involves considering the construction of an IC as one (or, nowadays, a series of) 2D plane(s). Individual areas within each plane are either joined together or insulated from each other. Various types of junctions can be created this way, such as P-N, N-P-N or P-N-P. This planar approach means that lithography can be used, where images are projected onto the wafer to form the circuit with the aid of light-­sensitive chemicals and photoresist coatings. This involves selective etching, deposition, implantation and other alterations of desired areas of the wafer. Wafers come in multiple different sizes from 25mm up to 450mmdiameter. The thickness of the wafer is important as it needs to be strong enough not to break during handling; a typical thickness for 300mm wafers is 775μm. Wafers can be stored in “desiccants” or transfer machines as shown above. Conductors on ICs can be made by the deposition of metals or the selective doping of semiconductor areas (eg, silicon). Insulators can be made by oxidising silicon to produce silicon dioxide or using the technique of P-N junction isolation. A silicon dioxide insulator can also be etched to expose underlying material for alteration in various ways. Semiconductor junctions can be made by doping specific regions and depositing additional material on top of those regions. Wafer processing steps Processing a wafer to produce ICs involves four categories of operations as follows. These may be done multiple times, up to around 300 steps for the most complex devices, and in various orders. #1 Deposition This involves depositing coatings ► Fig.9: a silicon crystal grown by the Czochralski process at Raytheon in 1956. The melt is heated by the coils of the induction heater; here, the temperature is being measured. In this case, a 25mm diameter crystal was grown, but today 300mm diameter is typical, and 450mm is under development. Source: Radio and Television News, May 1956 (public domain) Fig.10: a silicon ingot on display at the ► Intel Museum, 300mm in diameter. That is one of the current industry standards, starting around 2002, and it is a compromise between size and productivity. Source: Wikimedia user Oleg Alexandrov (CC BY-SA 3.0) siliconchip.com.au Australia's electronics magazine June 2022  17 Fig.11: one method of exposing individual areas of a silicon wafer with a mask. The lens shrinks the image from the mask to the die size. A more advanced process is ‘step and scan’, where an individual die is exposed through a narrow slit which is scanned to obtain tighter focus and smaller feature size. onto the wafer, such as oxidising the silicon to create an insulating silicon dioxide layer (passivation), deposition of metal conductors, silicon, or other semiconductor materials. The processes to do this are varied and include: • Physical and chemical vapour deposition • Electrochemical deposition • Molecular beam epitaxy • Atomic layer deposition • Thermal oxidation of the entire wafer • LOCOS (local oxidation of silicon), where individual areas of the chip are selectively converted to a silicon dioxide insulating layer that either totally block light or let it all through, unlike a monochrome photograph/slide, where there are grey areas of partial light transmission. Before the 1980s, an “aligner” was used that had large masks containing many duplicate die images so that an entire wafer could be exposed at one time. The pursuit of higher resolution (smaller feature size) meant that around the 1990s, the aligner was replaced with a “stepper”. Only a single die image was produced at a time, with the light focused onto a single area on the die. The mask is moved (stepped) across the wafer to repeat the pattern. In the pursuit of even higher resolution, since the 2000s, the stepper has been replaced with “step and scan” systems where only a small portion of #2 Patterning This involves laying down the desired circuit pattern on the wafer or deposited or etched materials. This is done using a photographic-­like process called lithography (see Figs.1113). The mask, which is like an old photographic slide or negative, is placed between an appropriate light source and the die, and an image is projected onto the die, which has been coated with photoresist. Note that the mask is much larger than the die size; a reducing lens is used to shrink the mask size to the die size. Also, the mask usually has areas 18 Silicon Chip A photo of a clean room at Bosch’s semiconductor factory in Dresden, Germany. Picture: Bosch – www.bosch-presse.de/pressportal/de/en/bosch-semiconductormanufacturing-in-dresden-225609.html Australia's electronics magazine siliconchip.com.au Fig.12: the basic process of photolithography using photoresist. Original Source: Wikimedia user May lam (CC BY-SA 4.0) a mask is exposed at one time, enabling better focusing. Before patterning, the die will have been prepared with a light-sensitive coating called photoresist. In the case of a positive photoresist, the photoresist regions that are exposed to the light become soluble and can be washed away, leaving the unexposed photoresist behind. A negative photoresist will do the opposite. After certain photoresist regions are washed away, the wafer itself can be etched in those areas or processed in some way, such as being doped. After that, the remaining photoresist can be removed. Using shorter wavelengths of light allows for higher pattern resolutions. These days, the density is so high that the light is typically in the UV spectrum, or extreme UV (EUV) in the latest systems. Electron beams can be used as an alternative to light sources. Electron beam lithography provides a high resolution, but it has a low throughput, so it is mainly used for low-volume production of semiconductors and the production of photomasks. There may be multiple masks used and multiple exposures between additional etching, deposition and other procedures. Another possible process is contact lithography, but it is not used for mass production. Figs.14 & 15 will give you an idea of the complexity of the built-up layers of an IC. Figs.16 & 17 are mask and die images of the world’s first microprocessor, the Intel 4004, designed by hand and released in 1971. Consider that modern chips are many orders of magnitude more complicated than that! Other lithographic processes of note, but not currently used for mass production, are: • displacement Talbot lithography (DTL) for periodic patterns • thermal scanning probe lithography (t-SPL), where nanoscale structures are generated with a heated probe moved over the surface of a resist coating which is then etched • UV flood exposure, to expose individual wafers on a small R&D scale Fig.13: a simplified version of the etching process using a positive photoresist. Cr is chromium on the mask, while PR stands for photoresist. Source: Wikimedia user Cmglee (GNU FDL V1.2) Fig.14: a simplified version of the processes to produce a portion of a CMOS IC. Note that the gate, source and drain contacts are not usually in the same plane in real devices. Source: Anonymous Wikimedia user (CC BY-SA 3.0) siliconchip.com.au Australia's electronics magazine June 2022  19 • direct laser lithography, a form of maskless lithography, for small scale R&D use • nanoimprint lithography, in which nanoscale patterns are imprinted into a resist by a mould with the desired pattern and then etched #3 Removal Material is removed from the silicon die by wet or dry etching processes or a combination of chemical and mechanical polishing (called CMP for chemical-­mechanical planarisation). The polishing is also used to ensure that the surface of the wafer is atomically flat before the next layer is added. #4 Modification of electrical properties Fig.15: a cross-section of a multi-layer CMOS chip with five metal layers, denoted Layer 1 to Layer 5. There’s a legend at the top; STI is shallow trench isolation, FEOL is front-end of line and BEOL is back-end of line. Original Source: Wikimedia user Cepheiden (CC BY-SA 3.0) This involves processes such as doping selected areas by methods such as diffusion or ion implantation to create the sources or drains of transistors, with P- or N-type dopants, or the creation or modification of insulating areas, such as through oxidation. Ion implanation is a method of doping in which a beam of dopant ions from a particle accelerator is scanned over the wafer, implanting ions in the areas not covered by the photoresist to a controllable depth. The wafer is then annealed in an oven, reforming the crystal structure and ensuring that the ions are evenly distributed. Alternatively, dopants can be introduced to the surface of the wafer via gas-phase or solid diffusion, followed by ‘drive-in’, where the dopants are diffused deeper into the semiconductor material. The wafer is placed in a furnace with an inert atmosphere and heated, diffusing the dopants throughout the areas on which they have been deposited. Similar furnaces can be used to also convert the top layer of semiconductive silicon to the insulator silicon dioxide by heating the wafer in an oxygen-rich atmosphere. Front-end-of-line and back-end-of-line Fig.18: light is diffracted as an incident wavefront of a beam of light (eg, from a laser) passes by an edge, causing potentially unwanted secondary wavefronts and thus light spreading. In photolithography, the edge would be part of the mask pattern. 20 Silicon Chip Australia's electronics magazine The term “front-end-of-line” (FEOL) refers to the initial part of the fabrication process, where the individual components such as capacitors, diodes, resistors and transistors are formed. But it is before metal interconnect layers are deposited to join them electrically. siliconchip.com.au The FEOL process for CMOS (complementary metal oxide semiconductor) includes the following steps: 1. preparation of the wafer 2. electrical isolation of trenches or other selected areas by oxidation of silicon to silicon dioxide or deposition of other dielectric materials 3. well formation (the well is the first layer fabricated of a CMOS IC and may comprise an N-doped well in a P-type substrate; see Fig.15) 4. gate module formation 5. source and drain module formation The gate, source and drain referred to above are the main parts of a field-­ effect transistor or FET. “Back-end-of-line” (BEOL) refers to the second main stage of IC fabrication, where the interconnection of the devices formed in the FEOL process takes place by adding metal layers. It also includes the addition of insulating layers, vias (vertical conducting elements to connect between layers; see Fig.15) or bonding sites for chipto-package connections. Many metal layers can be added in multiple processing steps. You can think of these a bit like the copper patterns on a PCB. Wavelength of light for lithography Over time, as the number of transistors on a chip has increased, lithography has required shorter and shorter wavelengths of light to produce the smaller IC feature sizes. We’ll have some details on the light sources used when we discuss the shrinking process nodes in part two, next month. Features smaller than the wavelength of light As you can see from the above, IC feature sizes are now much smaller than the wavelength of light passing through the mask and illuminating the wafer. You might expect that diffraction effects (spreading out the light and causing images to be indistinct) would prevent accurate patterns from being made on the wafer, and this is indeed the case. So how is this problem overcome? There is a limit to how short the light wavelength can be (to make smaller feature sizes), so there is obviously the desire to minimise this effect. Note also that EUV equipment is expensive. siliconchip.com.au Figs.16 & 17: images of the Intel 4004 microprocessor from 1971 showing a composite image of the masks (light colour) and the die (dark colour). It was a 12mm2 4-bit microprocessor with 2250 transistors and it started an electronic revolution. Source: Tim McNerney (http://alumni.media.mit. edu/~mcnerney/2009-4004/) Fig.19: an illustration of the Rayleigh Criterion, the theoretical limit of resolution. The two blue peaks merge to form a single large (red) peak when they are close together but become separately resolved as they move apart. Original source: Wikimedia user Mpfiz (public domain) Australia's electronics magazine June 2022  21 Fig.20: (a) a conventional binary mask, (b) an alternating phase-shift mask and (c) an attenuated phase-shift mask. The latter two types can provide finer details for the same wavelength of light. Original source: Wikimedia user Oleg Alexandrov (public domain) Diffraction (see Fig.18) is the production of secondary wavefronts that occurs at the edges of an opening when the primary wavefront of a light beam passes through. This happens with projection lithography, which is the dominant form, but does not happen much with contact lithography, although that is not suitable for mass production. There is a fundamental physical limit to resolution defined by the Rayleigh Criterion. The web page at siliconchip.au/link/abdv states, “The Rayleigh criterion for the diffraction limit to resolution states that two images are just resolvable when the centre of the diffraction pattern of one is directly over the first minimum of the diffraction pattern of the other.” see Fig.19. It is not simply a matter of making a design and specifying it be made smaller; significant new problems have had to be overcome each time the process size has been shrunk. The various techniques that have been used to achieve feature sizes smaller than the wavelength of light are: #1 Phase-shift masks Phase-shift masks make diffraction work for you, not against you. Interference is generated by phase differences brought about by different thicknesses or translucency in parts of the mask, to improve contrast on the photoresist and thus resolution. Fig.21 shows the behaviour of light energy with various mask types. A conventional binary mask either transmits light or doesn’t, depending on the region, as shown in Fig.21(a). In alternating phase-shift masks, some regions are made thicker and others thinner. When the thickness is appropriately chosen, the light going through modified areas of the mask interferes with the light going through unmodified regions, improving contrast and resolution – see Fig.21(b). In attenuated phase-shift masks, light is allowed to pass through particular mask sections but attenuated due to partial transmittance of the mask material. The small amount of light allowed through will not cause a pattern on the wafer, but it will interfere with non-attenuated light from other areas to enhance contrast and resolution – see Fig.21(c) & (d). The half-tone mask has transparent and semi-transparent material regions that cause light interference, enhancing contrast and resolution. These masks are easier to make than alternating phase-shift masks. #2 Photoresists To achieve higher resolution, new photoresists have had to be developed. The following factors have to be considered in developing a photoresist: • contrast between exposed and unexposed portions • sensitivity to the wavelength of the light used (the shorter the wavelength of light, the less absorption of light energy) • viscosity • adherence to the substrate • the ability to resist etching • surface tension #3 High numerical aperture lenses Note the projection (also called objective) lens in Fig.11. The lens Fig.21: different mask types with the resulting patterns that appear on the wafer. Note the middle detail missing on the wafer for the binary mask and the added detail in the phase-shift masks. Source: Wikimedia user Shigeru23 (GNU FDL V1.2) 22 Silicon Chip Australia's electronics magazine siliconchip.com.au should gather the diffracted light from the mask. The higher the numerical aperture (NA) of the lens (similar to the f-number in photographic lenses), the more diffracted light that it will gather and the higher the resolution of the image produced. However, the higher the NA, the smaller the depth of focus, requiring extremely precise mask alignment to avoid parts being out of focus. #4 Immersion lithography Another technique is to use immersion lithography, in which the light passes through water rather than air. The higher index of refraction of water means an effective decrease in wavelength of about 33%, enabling smaller feature sizes. #5 Optical proximity correction OPC (optical proximity correction) is a method to compensate for errors due to diffraction or other reasons – Fig.22 shows one example. Calculating the correct patterns for OPC is extremely computationally intensive and can occupy compute clusters for days. #6 Multiple patterning Double or multiple patterning, also known as self-aligned multiple patterning (SAxP), is a complicated and expensive process. It is used to produce photomasks for the highest possible feature density. In multiple patterning, multiple lithography and etch steps are used to achieve higher Note the overhead system as TSMC’s facility and the row of DD-1223V “12-inch” wafer furnaces. Picture: Taiwan Semiconductor Manufacturing Co., Ltd. resolution than could be achieved with a single step. As an example, a double patterning process results in a 30% smaller feature size, but the number of process steps and therefore cost is increased. Double patterning is used to make NAND flash memory (as used in SSDs and SD cards), random access memory (RAM) and the fins in FinFETs, used in many cutting-edge computer chips. There are many different methods of multiple patterning. Double patterning in its original form was also called pitch splitting. Two adjacent features cannot be made closer together than the minimum pitch allowed by the lithographic system; therefore, one set of features is made first, and the second mask is Next month Next month, we will discuss how feature sizes have changed over time and what advances that progress has allowed, including Moore’s Law. We’ll also go into more detail about the silicon wafer sizes and extreme UV (EUV) lithography, plus describe IC packaging and the various components that can be created using the IC fabrication process described above. There is more to come after that, including the latest 3D stacking and multi-chip module technologies. SC Fig.23: a form of multiple patterning called pitch splitting. Three trenches are first etched, then covered in photoresist (top). Then a second exposure is made, and a second set of trenches is etched (middle). The photoresist is washed away, resulting in pairs of trenches that are closer together than a single exposure would allow (bottom). Original Source: Wikimedia user Wdwd (GNU FDL V1.2) Fig.22: in optical proximity correction, the image is ‘precorrected’, so the projected pattern distorted by projection is the desired one. The thicker areas are the desired pattern; the thinner wavy lines do not print. They are called sub-resolution assist features (SRAFs) and improve depth of focus. Source: Wikimedia user LithoGuy (CC BY-SA 3.0) siliconchip.com.au used to create a second set of features. Therefore, the distance between the features can then be less than the minimum pitch of the lithographic system – see Fig.23. Australia's electronics magazine June 2022  23 QRWH 3RO\SKRQ\ +DUPRQLF 6\QWKHVLV '7LPEUH 0RUSKLQJ 0,', -HUHP\/HDFKÍV 6<17+(6,6(5 0,', 86% ,QSXWV /RZ/DWHQF\ $XGLR 2QERDUG 3DWFKLQJ This advanced MIDI synthesiser is easy to build and can be hooked up to any MIDI compatible device. It lets you explore the broad range of acoustic elements that capture the characteristics of real and imaginary instruments. It is more than an experiment – it is a full-blown instrument capable of forming rich, detailed sounds using a plethora of settings, envelopes and waveforms – a blank canvas. T he Spectral Sound Synthesiser uses seven dsPIC chips running at 70 or 40MIPS each in combination to produce sounds digitally. This gives it 18 note polyphony (ie, the ability to play 18 different notes simultaneously) and complex sound creation, with ‘timbre morphing’ being the module’s key feature. It also has low latency, which is important since you don’t want an apparent delay between pressing a key on a keyboard and the sound being produced. Being a standalone sound module, it has the tantalising possibility of being built into custom DIY musical instruments without the need for a computer. The module is an adventure into real-time sound synthesis, exploring the broad range of acoustic elements that capture the characteristics of real 24 Silicon Chip and imaginary instruments. As such, it is a wonderful way of appreciating types of sound, how musical instruments work and why some instruments are notoriously difficult to emulate. While it is a working device as presented, it’s also a great way to experiment with audio synthesis. This is a fun and stimulating pursuit, with an endearing interplay between digital waveform generation and human perception. The module’s design focuses on true parallel processing by splitting the computational load across six ‘Tone Processor’ chips. All the source code is available for the firmware and the accompanying Windows desktop software. However, the software is also available pre-built, including any version updates. This is an advanced project, and there is even a Technical Reference Australia's electronics magazine Manual for those who want to explore more deeply. The whole topic of sound synthesis, interwoven with music history, is a rich and intensely interesting evolutionary journey, driven by our instinctive desire to understand and create sound. The Spectral Sound Synthesiser taps into that desire. An overview of the system Fig.1 shows how the overall system works. It has a MIDI input for receiving MIDI note and control messages (eg, from a keyboard), a USB input for configuration by the Windows software, and a stereo line-level audio output jack, for hooking it up to an amplifier. You can create patches with the Windows software, and a certain number of these patches are loaded onto the module and stored internally. You can send any tweaks to patch settings siliconchip.com.au immediately to the module and hear the result. The ‘Master Controller’ is a PIC18LF25K50 8-bit micro with useful USB connectivity. This chip is common in embedded systems requiring USB. It functions as a hub, processing incoming USB and MIDI messages. It also allocates processors to tasks in the rest of the system. The six Tone Processors are dsPIC33EP512MC502-I/SP 16-bit chips running identical code to generate digital sound samples. Each calculates up to three live note instances at once, so the system has a maximum of 6 x 3 = 18 note polyphony. Each Tone Processor holds a single patch, but different ICs can have different patches, making this MIDI instrument ‘multi-timbral’. A single ‘Mixer’ chip, a 16-bit dsPIC33FJ128GP802-I/SP, mixes the samples from all the Tone Processors, limits the generated audio level using automatic gain control (AGC), then passes the audio out through its inbuilt stereo DAC to an MCP6022 op amp. The output is ‘pseudo stereo’, using a well-known audio trick called the Haas effect, where delaying a copy of a signal from one ear to the other gives a very convincing impression of a stereo field! The module can hold several patches and ‘performances’ in a 24LC512 EEPROM IC. What is additive synthesis? Ongoing research into hearing and human perception reveals that we are still a long way from completely understanding how our brains process and identify sound. A key element is timbre, which is related to a For samples of what the Synthesiser can do, visit siliconchip.au/link/abeo Fig.1: this block diagram shows how the Spectral Sound Synthesiser works. The Master Controller receives MIDI messages from the MIDI In port and patch data from the computer via USB. It commands the six Tone Processors to generate sounds based on the stored patches and possibly stored performance data. These sounds are fed to the Mixer and then to the analog audio output. sound’s frequency spectrum and how it changes over time. Additive synthesis is a method of creating and modulating timbres based on the fact that any periodic function can be expressed as the sum of a series of sinewaves – the ‘Fourier series’, described by Joseph Fourier in 1822. He was using it to solve heat transfer functions, but this idea soon became widespread, from predicting tides to planetary motion, and much later, audio synthesis. The simplicity of the idea is appealing because it means that complex timbres can be constructed just by adding sinewaves with appropriate weights and phases. The MIDI Synthesiser fits in an instrument case measuring 150 x 100 x 40mm. A different case could be used as long as it’s bigger, the height of it depends on the heatsink you use. Australia's electronics magazine 25 It turns out that phase is not generally important because our hearing disregards it. This makes sense when pondering sound waves bouncing about in a room; despite the phases of different frequencies getting mangled, we generally do not perceive any timbral difference. Another appeal is that sounds in nature are based on vibrations where the timbral sinewaves have frequencies that are integer multiples, or harmonics, of the base ‘fundamental’ frequency. This well-defined relationship lends itself to computation. Musical instruments can be recognised by their characteristic harmonic levels, with some examples shown in Fig.2. The large evolutionary family tree of electronic synthesisers includes prominent examples of additive synthesis. For example, the beloved Hammond organ dating back to 1935 stacks tones generated by pickups placed close to rotating mechanical ‘tonewheels’. Also, the early Fairlight Quasar synth of the 1980s was additive, as were the Synclavier and a few Kawai keyboards. Loom, a modern VST instrument, is also an additive type. With enough computing power, additive synthesis makes the ‘morphing’ of timbres possible by altering the set of sinewaves being summed over time – akin to what happens all around us with natural sounds. Additive synthesis also has the great advantage of operating in the frequency domain rather than the time domain. This makes filtering a simple concept, where the filter contour simply scales the levels of the base sinewaves. Brick-wall filtering is nothing more than including or excluding certain sinewaves. This method of synthesis can create rich, stimulating and captivating sounds. But it has limitations when emulating real instruments compared to sample-based synthesis. The problem is that natural sound is far more complex than just harmonics; there are ‘in-harmonic’ frequencies in the spectrum, especially for percussive sounds. There is noise from blowing, scraping and scratching. The harmonics are not always exact integer multiples etc. So, as a sonic tool, additive synthesis is great. But it cannot always emulate natural sound easily. The Fairlight CMI synthesiser of the 1980s (which took its name from 26 Silicon Chip Fig.2: approximations of the harmonic structure of different instruments. From left to right, the bars represent the sequential harmonics above the fundamental. The harmonic structure is what defines the timbre of an instrument, while the fundamental frequency is determined by the pitch of the note being played. a Sydney Harbour ferry) was a breakthrough in sound production through sampling. It revolutionised pop music with genuinely new sounds. The irony is that the inventors started by using additive synthesis, according to co-founder Kim Ryrie (interestingly, also the founder of ETI magazine): “We regarded using recorded real-life sounds as a compromise – as cheating – and we didn’t feel particularly proud of it.” This Fairlight model was a ‘sampler’, with the ability to record sound, soon followed by cheaper ‘Romplers’ with recorded sound baked into ROM. These days we can have gigabytes of samples on solid-state hard disks. It is undeniable that sample-based synths can give amazing results, especially with many nuanced ‘layers’ for parameters such as note velocity. However, they use masses of memory instead of modelling anything on a physical basis. Still, from the early sampled tape loops of the Mellotron, used on classics such as the pipe organ in the Beatles’ “Strawberry fields”, it is clear that samples are here to stay. Australia's electronics magazine As computing power has steadily increased in recent years, we have seen growth in physically-modelled sound, such as in the popular “Pianotech” VST pianos based on the physics of real instruments, ancient and modern. Additive synthesis can also be categorised as physical modelling to a degree because of its timbre-based approach and dynamic nature. Harmonics and the equaltempered scale Real instrument sounds are generated through vibration, such as the movement of air in a flute, the vibration of a guitar string or the oscillating of the skin of a drum. The vibrations create standing waves, having fixed nodes and moving antinodes. The nodes divide the length into equal divisions, leading to the integral harmonics seen in the frequency spectrum of many instruments. Fig.2 broadly shows how these harmonics have characteristic levels in different instruments, although it is extremely generalised. An instrument plays at a pitch we siliconchip.com.au Fig.3: the equal-tempered scale has the advantage that music can be played in any key without retuning the instrument. But some note harmonics do not precisely match any note in the scale, with the worst being the 7th and 11th harmonics. Usually, though, such high harmonics are not especially loud, so this tends not to matter. ► Fig.4: the main tasks and calculations that are constantly being processed by the six Tone Processor chips that do most of the synthesis work. recognise as the fundamental frequency, but the tone has a ‘colour’ dictated by the relative strength of the harmonics. The fundamental is known as the first harmonic; the second harmonic is at double the fundamental frequency (an octave higher), the third harmonic at three times the fundamental frequency and so on. But it is seldom realised that some harmonic frequencies only roughly match the pitches that we recognise in the chromatic (12-note) musical scale! Our brains have heard the pitches of notes from our earliest memories. Yet, the musical scale we use today is relatively recent, and human beings have tried several alternatives, going right back to Pythagoras. The scale we use today is called the “equal-tempered” scale, where ‘equal’ refers to a fixed frequency ratio siliconchip.com.au between any note and its neighbour. To calculate the frequency of a note a semitone higher, we can multiply by this fixed factor. Since notes one octave apart have a ratio of 2:1, if each semitone has a fixed geometric ratio, that ratio must be the 12th root of two (approximately 1.0595:1). Remember that this is a human invention to get a system of equal ratios so that music can be transposed without altering how it sounds. Although the oddities of previous scales contributed to the richness of music diversity, and some bemoan their demise, the equal-tempered scale makes a certain amount of sense. Fig.3 is a detailed analysis of musical note A3 (440Hz), showing how the harmonics of this note do not always accurately align to the pitches of the equal-tempered scale. Power-of-two Australia's electronics magazine harmonics have an exact match in the scale, but others don’t (although they are often quite close). This reveals a degree of ‘in-­ harmonicity’ in harmonics (ironic, given the name). The analysis applies to all notes; the 7th and 11th harmonics deviate the most from recognisable pitches, and if audible, they sound ‘flat’ and dissonant. These imperfections are wellknown to instrument makers. For example, pianos are designed to have the hammer strike the strings at the seventh vibrational node to suppress this ‘ugly’ seventh harmonic! The 11th harmonic is less noticeable, often being naturally quieter. Tone processors Fig.4 shows the heart of one of our Tone Processor “Note Instances”, June 2022  27 Fig.5: envelopes are time-based profiles that can be applied to various synthesis parameters. The easiest to understand is the volume envelope, which varies the loudness of the note from the time it is triggered until it is no longer audible. Fig.6: ‘3D timbre morphing’ is a solution to the problem that the harmonics of various instruments can vary depending on which note is being played, how hard it is being played etc. This is especially obvious on instruments like pianos, where each key can have a unique sound, and louder notes can trigger various resonances. showing how it generates sound. A note instance represents a note we play on the MIDI-connected keyboard. The Master Controller ensures that the played notes are evenly spread across the available Tone Processors. When a note instance is started on a Tone Processor chip, the first thing that happens is the calculation of the waveform to be used based on the ‘static’ patch settings, plus other ‘dynamic’ 28 Silicon Chip factors such as the note velocity. This involves looping through all active harmonics and adding corresponding sinewaves together. Because harmonics are exactly integer multiples of the fundamental, the wavetable holds exactly one cycle of the summed periodic wave. Once that has been calculated, this physical table in memory becomes ‘active’ for the note instance. To do this, table pointers Australia's electronics magazine are swapped so that we never have to copy data slowly and inefficiently from one table to another. The wavetable for a note instance gets regularly refreshed during its active life cycle. The rate of refresh is not fixed but is approximately 50Hz. As a side note, it is fascinating to read research where they have found that the threshold where humans can detect a change in timbre occurring is often a lower rate than this. Timbre detection is clearly a demanding, abstract recognition task in the brain. During note generation, several ‘gain envelopes’ can be applied to aspects of the sound. This is the sound’s amplitude envelope. Fig.5 indicates how the system calculates envelopes. Both linear and exponential envelopes can be created, and each section of the ADSR (attack, decay, sustain, release) envelope has a ‘target’ value. During each section, the envelope’s current value moves towards the target. Exponential curves exist everywhere in nature, relating to energy decay. So, that is a natural choice, and not just for amplitude. For example, when plucking a string, the high-­ frequency content decays first. The jostling of atoms in high-frequency vibration uses up energy at a higher rate. A note instance also features three ‘Low-Frequency Oscillators’ or LFOs: Vibrato varies the pitch, Tremolo the amplitude and Timbre the harmonic levels. LFO modulation can add so much character to sound. There are also envelopes for the depth of this modulation, allowing, for example, a gradual onset of vibrato. Another interesting point is that whereas many synths would use Tremolo across the total sound output of the synth, this module modulates per note, making the overall sound more complex and interesting. Timbre morphing Determining the harmonic levels to use when constructing a waveform is a complicated process. Fig.6 shows that a patch holds the harmonic data for 75 waveforms, with the waveform to synthesise depending on three parameters. The “Note” parameter is the position of the note on the keyboard. The “Intensity” parameter most often means note velocity. The “Waveform” picks from five waveforms. Each point in this conceptual 3D space grid has a set of harmonic levels siliconchip.com.au defining a waveform. The current parameter values define the required point internal to this space, and the harmonic levels to use are interpolated from the nearest defined grid points in this space. Taking this further by modulating through this space with the Timbre LFO can give impressive realism compared to plain vibrato. Typical vibrato purely modulates the pitch of the whole waveform, whereas timbre modulation is harmonic-based and therefore, a far more complex modulation for our brains to perceive. It is thrilling to hear this difference and realise that our brains feed off the interest in sound. Perhaps, considering the incredibly clever processing that our brains can perform with language, pattern detection and all aspects of sound, this realisation should not be too surprising. Towards greater realism We have already mentioned that natural sound includes in-harmonic elements, which do not fit the neat integer multiples of harmonic frequencies. In an attempt to address this, this synthesiser includes some additional features outside of the purely additive-­ synthesis approach. Firstly, a noise envelope is available to help simulate ‘blown’ instruments. This is a white noise generator with an adjustable low-pass filter. Secondly, you can add short in-­ harmonic samples. These are hardcoded clips of the sound of taps, scratches, clicks and bonks. However, the sample feature also includes an implementation of the well-known ‘Karplus Strong’ delay line technique of plucked string synthesis. The 1983 paper by Kevin Karplus and Alex Strong entitled “Digital Synthesis of Plucked-String and Drum Timbres” first described this technique. It is a computationally simple but effective method of generating realistic, decaying string sounds that start off life in the delay buffer as noise. It adds a powerful tool to this module, even though it does not have anything to do with additive synthesis! There are also settings to randomly or systematically detune the frequency of played notes, in an attempt to introduce the impurities of real instruments. Plus, there is an option of using two wavetable oscillators per note instance, detuned by a specified siliconchip.com.au Fig.7: an overview of all the tasks that the Tone Processor chip has to handle, in order of priority. The highest priority events are those that would cause the sound to break up or otherwise give unexpected results if delayed. amount, giving a chorus-like effect, which tries to account for the fact that instruments like the piano use multiple detuned strings per note. A final feature is the ‘Body Resonance Filter’. This attempts to emulate the body resonance of a real instrument by filtering the overall system sound. After specifying the filter contour in the app, it scales the harmonic levels. Although this method has great theoretical appeal, it has mathematical limitations. Despite all these extra features, there are still real-life complexities that the module just cannot tackle. For example, a piano has peculiarities due to the stiffness of its strings, where the higher harmonics get sharper compared to the expected harmonics of the string. This is because the stiffness effectively shortens the string for higher Australia's electronics magazine frequencies, raising the harmonic oscillation frequency. This effect applies to all stringed instruments, and is something our system cannot address because the model relies entirely on integral harmonics. A real-time system The whole of the module is an example of a ‘hard’ real-time system, where the deadlines of sample production and processing are immovable. This presents considerable challenges, and the development of the module was a slow evolution of coding, measuring, refining and sometimes redesigning. The Tone Processors all run entirely in parallel and are polled by the mixer chip to provide samples at the audio sampling rate of 41.7kHz. Inside each Tone Processor is a hierarchy of interrupts, as shown in Fig.7, made possible June 2022  29 30 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: the entire Synthesiser circuit, which is somewhat unusual in that it mainly consists of eight PIC microcontrollers (of three varieties), all communicating via two separate SPI serial buses. The remainder of the circuit comprises the EEPROM (IC11) used to store patch and performance data, the power supply, MIDI input and audio output. siliconchip.com.au Australia's electronics magazine June 2022  31 The Spectral Sound Synthesiser PCB is relatively easy to build. Although with about a dozen ICs, many of them having 28 pins, there are lots of solder joints to make. Be careful to make each joint properly or it might not function correctly. by the dsPIC’s ability to assign priorities. The main routine of a Tone Processor, the centrepiece of the entire system, is just a simple loop that recalculates wavetables. This ‘background’ task is unpredictable in duration, is not on a deadline, and can vary depending on the interrupt activity and the complexity of the waveform being built. This means that the timbre refresh rate could slow down in certain circumstances – although, in use, performance is very acceptable, and timbre changes are perceived as fluid and smooth. The processing ‘layers’ above this base main loop are concerned with calculating envelope steps, calculating the sample output and processing received data. A trick used to improve throughput on the SPI bus between the Tone Processors and the Mixer is only sending the changes in sample values. The summing of sines in a Tone Processor can result in a total value exceeding 16 bits. The total on the Tone Processor is a 32-bit signed integer, but the Tone Processor only sends the change in this total, capped at 16 bits, to the Mixer. This can cause signal distortion, but statistically, this will happen rarely. 32 Silicon Chip The performance advantage of this method massively outweighs rare anomalies that are probably not even noticeable. The software and hardware are designed for speed. All the dsPICs are running at their fastest. All calculations are integer-based, coupled with extensive use of the on-chip hardware multiplier via the compiler’s “__builtin” commands. The code extensively uses shift operations for fast multiplication and division, and numerous lookup tables are used, including a detailed sine lookup. Circuit details The full circuit is shown in Fig.8. The first thing to note is that the six Tone Processors (IC5-IC10) are identical dsPICs configured in the same fashion, each with just a handful of associated components: one Vdd bypass capacitor, one Vcap capacitor (required for the chip’s internal regulator) and one 10kW MCLR pull-up resistor to prevent spurious resets. Besides the power supply, the only connections to these chips are a common SPI bus, as they are pure number crunchers, and all commands and data are sent on this bus. The only differences between the connections Australia's electronics magazine to these chips are that each Tone Processor’s CS2a-CS2f input (pin 4) connects to a different select line on the Mixer, IC3. The Mixer is a different (but related) type of dsPIC processor. Besides being connected to this SPI bus and the six chip select lines for the Tone Processors, it also has two differential analog outputs from an internal stereo DAC. These signals are fed to op amp IC4, which converts the differential signals to single-ended audio signals suitable for feeding to the CON2 output jack. Simultaneously, this circuitry filters out the DAC step artefacts using lowpass filters built from added capacitors and the existing gain-setting resistors. A virtual ‘half-supply’ rail is generated using zener diode ZD1 biased from the +3.3V rail so that the audio signals from IC3 remain within the supply rails of the op amp. Mixer IC3 also connects to the 24LC512 EEPROM (IC11) using a twowire I2C serial interface (SDA & SCL). That chip has its own bypass capacitor plus pull-up resistors for those serial lines, and that’s it. The last task for IC3 is to drive the Mixer Alert LED, LED2, from its RA0 output (pin 2). MIDI input, USB and other control tasks fall on the PIC18LF25K50, IC2. It monitors the presence of USB 5V at its RA0 digital input (pin 2) via a 2.2kW/10kW ‘divider’, which mainly exists to limit the current into that pin and ensure that it’s pulled to 0V when no USB connection is present. IC2 and IC3 communicate via a second separate SPI bus, with a dedicated chip select line, from pin 7 of IC2 to pin 22 of IC3. IC2 also drives LED1, the MIDI Alert LED, from its RB6 digital output (pin 27). External potentiometer VR1 (the volume control) connects to CON4, placing it across the 3.3V supply. Its wiper goes to analog input AN11 of IC2 (pin 25). IC2 reads the voltage at the wiper using its analog-to-digital converter (ADC) and passes the digital value along to IC3, which then scales its output to provide the desired volume level. The pot value or type isn’t critical, but 100kW is reasonable. Scaling the audio sample values entering the DAC, rather than directly adjusting the op-amp gain, simplifies the PCB at the cost of reduced audio bit-­ resolution with the volume turned siliconchip.com.au down. In practice, it’s hard to hear this degradation. That just leaves the MIDI input, clock signal distribution and the power supply to describe. The MIDI signal is applied to CON6, and it powers the IR LED within FOD260L opto-isolator OPTO1. A 220W resistor provides current limiting, while diode D2 prevents the LED from being reverse-biased. It is essential to use the FOD260L opto-coupler as this is suitable for 3.3V operation – other varieties may well not work. The output transistor in OPTO1 is operated in common-emitter mode with a 470W pull-up resistor. The resulting signal goes to the RX input (pin 18) of IC2. A single external oscillator is used because we have eight microcontrollers that all need clock sources. This is built using crystal X1, its two 33pF load capacitors and unbuffered inverter IC1a. The resulting 16MHz signal is inverted by IC1b and buffered by IC1c and IC1d, then fed to all the microcontrollers’ clock input pins. We don’t recommend using a buffered inverter in place of IC1, such as the more common 74HC04, as it might not oscillate correctly. The power supply is simple; the unit is powered with 5V DC from barrel socket CON1, and this flows via reverse-polarity protection diode to the inputs of linear regulators REG1 and REG2. REG1 powers all the digital circuitry while REG2 powers the analog circuitry, which is basically just op amp IC4 and the bias for zener diode ZD1. Increasing the signal-to-noise ratio (SNR) A challenge with any system comprising mixed digital and analog circuitry is to stop the digital noise bleeding through into the audio output. The module PCB takes the basic steps of separating audio and digital components as much as possible, with separate regulators and the use of a ground plane. However, additional measures have been taken to ensure a generally quiet and acceptable audio system. One such measure is an audio limiter in the mixer audio code using advanced look-ahead AGC. A limiter squashes the dynamic range slightly by attenuating peaks, thereby effectively boosting the quieter sounds and lowering the noise floor. siliconchip.com.au Parts List – Spectral Sound MIDI Synthesiser 1 double-sided PCB coded 01106221, 145 x 94mm 1 instrument case [Takachi YM-150; RS Cat 373-2255] 4 stick-on rubber feet 1 front panel label, 145 x 37mm (see Fig.10) 1 lid label, 141 x 85mm (see Fig.11) 1 5-6V DC 1A regulated plugpack • 1 16MHz crystal, HC-49 (regular or low-profile) (X1) 1 PCB-mount DC barrel socket, 2.1mm or 2.5mm ID to suit plugpack (CON1) 1 3.5mm stereo DPST switched jack socket (CON2) [Altronics P0094, RS Cat 913-1021 or CUI SJ1-3555NG] 1 2-pin polarised header and matching plug (CON3, for power switch) 1 3-pin polarised header and matching plug (CON4, for volume control) 1 through-hole full-size type-B USB socket (CON5) [Jaycar PS0920, Altronics P1304A/P1304B] 1 5-pin 180° DIN socket, right-angle PCB mount (CON6) [Jaycar PS0350, Altronics P1188B or RS Cat 491-087] 1 SPST or SPDT panel-mount slide switch (S1, power) 1 100kW panel-mount linear potentiometer & knob (VR1, volume control) 8 28-pin narrow DIL IC sockets (optional; for IC2, IC3 & IC5-IC10) 3 8-pin DIL IC socket (optional; for IC4, IC11 & OPTO1) 1 TO-220 heatsink (REG1) [maximum 40mm wide, 13mm deep from tab, <18°C/W; RS Cat 263-251 used for prototype] 4 M3-tapped 6.3mm spacers 1 M3 x 10mm panhead machine screw, shakeproof washer and hex nut 8 M3 x 5mm panhead machine screws 2 M2 x 10mm countersunk screws and nuts (for slide switch mounting) 1 100mm length of rainbow cable (for wiring to S1 & VR1) 1 small tube of thermal paste • up to 9V can be used, but 5-6V results in more reasonable dissipation Semiconductors 1 74HCU04 unbuffered hex inverter, DIP-14 (IC1) 1 PIC18LF25K50-I/SP 8-bit micro programmed with 0110622A.HEX (IC2) 1 dsPIC33FJ128GP802-I/SP 16-bit microcontroller programmed with 0110622B.HEX (IC3) 1 MCP6022-I/P rail-to-rail op amp, DIP-8 (IC4) 6 dsPIC33EP512MC502-I/SP 16-bit microcontrollers programmed with 0110622C.HEX (IC5-IC10) 1 24LC512-I/P 64Kbyte I2C EEPROM, DIP-8 (IC11) 1 FOD260L opto-coupler, DIP-8 (OPTO1) 2 LF33CV 3.3V low-dropout linear regulators (REG1, REG2) 2 3mm high-brightness green LEDs (LED1, LED2) 1 1.8V 250mW zener diode (ZD1) [eg, 1N4614] 1 1N4004 400V 1A diode (D1) 1 1N4148 75V 150mA signal diode (D2) Capacitors 1 100μF 6.3V electrolytic 1 10μF 16V electrolytic 8 10μF 16V X7R ceramic 2 1μF 63V MKT 4 100nF 63V MKT 13 100nF 50V X7R ceramic 2 33pF 50V ceramic Resistors (all 1/4W 1% metal film axial) 1 1MW 6 4.7kW 1 1kW 1 100kW 4 3.3kW 2 470W 10 10kW 4 2.2kW 1 220W Kit – SC6261 An almost complete kit is available, which includes everything except the case, feet, labels and plugpack. It is priced at $200. Australia's electronics magazine June 2022  33 Fig.9: like the circuit diagram, the eight PICs dominate the overlay, all in 28-pin DIL packages. Make sure to orientate those correctly and don’t get them mixed up. Fig.11: the lid panel ► artwork (shown at approximately 85% actual size) is a nice finishing touch to the project. It’s designed to be printed onto a transparent medium. Note that the two LED positions could vary somewhat, especially if you’re using a different case; you could simply cut that part of the decal off and position it separately. This does not seem natural when trying to emulate polyphonic instruments; however, limiters and compressors are commonplace in audio reproduction, and it has a significant beneficial effect in this system. We are also using a trick called pre-emphasis and de-emphasis. The digital audio generated has high-­ frequency boost applied, and the analog signal processing circuitry has a matching high-frequency attenuation applied through a low-pass filter on the op amps. This way, the higher, more noticeable element of circuit noise is suppressed. The module actually ‘boosts’ the higher harmonic levels by carefully attenuating lower harmonic levels. It is nice that complex digital filters are not needed to do this! Finally, the Patch Editor application automatically boosts harmonic levels to the maximum, ensuring that the summed wavetable waveform is across the full signed 16-bit range, maximising the SNR. Construction The Spectral Sound Synthesiser is relatively straightforward to build, as the use of numerous microcontrollers minimises the number of separate components required. Most components mount on a double-­sided PCB coded 01106221 that measures 145 x 94mm. The overlay diagram for this PCB is shown in Fig.9. There is nothing remarkable about construction except that it requires good soldering skills to solder 200+ pins accurately! We recommend using IC sockets throughout, including for the opto-coupler; while sockets can cause long-term reliability problems due to oxidation of the contact points, there is no real provision for in-circuit programming. Still, since most constructors will be using pre-programmed micros (or programming them before assembly), you could consider soldering them directly to the board as long as you are confident they have been programmed correctly. Note that we haven’t specified a socket for IC1 as there’s little reason to use one there. Start with the resistors, checking each lot of values with an ohmmeter before soldering them in place. Follow with the three diodes. Each is a different type, so don’t get them mixed up, and ensure they are fitted with the cathode stripes facing as shown. Next come the IC and opto sockets (or ICs and opto-coupler). Ensure they all have pin 1 facing towards the top of the board and if soldering the ICs to the board, be very careful not to get the different 28-pin types mixed up. After that, mount all the non-­ polarised ceramic and MKT capacitors; there are 100nF ceramic and MKT capacitors, so make sure the MKTs go in the positions shown in Fig.9. Now install the electrolytic capacitors with the longer positive leads to the pads marked + in Fig.9, followed by the polarised pin headers and jack socket CON2. Next, solder the LEDs in place with the longer leads to the side marked A. Fig.10: the front panel artwork can be downloaded, printed, laminated (or protected in another manner) and then attached to the drilled panel. 34 Silicon Chip Australia's electronics magazine siliconchip.com.au so that its top edge is right up against one side of the case (for an instrument case, it should be the front panel). After that, mark and drill/cut holes in the adjacent panel for the DC power barrel plug, MIDI input socket, USB socket and audio output jack. If you’re using the specified case, you can use the drilling diagram, Fig.12, to assist you. It could also be used on other cases, but you will need to adjust the placement on the panel to match your PCB mounting location. Wiring it up Fit these with sufficient lead length so that they will reach the top panel of the case once the PCB has been installed (see the section “Wiring it up” below for a discussion on case selection). Follow with the two regulators, first attaching the heatsink to REG1 using the machine screw, nut and washer. That just leaves crystal X1, DC socket CON1, USB socket CON5 and MIDI socket CON6 on the PCB. Mount those in order of increasing height. Finally, if you’ve soldered sockets to the board, plug in all the ICs and the opto-coupler now, paying careful attention to their pin 1 orientation and not getting the different 28-pin and 8-pin ICs mixed up. Case selection The PCB is designed to fit into the case specified in the parts list, and the front panel label (Fig.10), lid artwork (Fig.11) and drilling template (Fig.12) all fit that case. These can also be downloaded as PDFs and a PNG from siliconchip.com.au/Shop/11/6416 You could use a different case as long as it’s large enough to house the PCB, since all the connectors and controls (apart from the two which are panel-mounted) are along one edge of the PCB. With a 145 x 94mm PCB, most cases measuring at least 165 x 100mm should be suitable. The height required depends on the heatsink you are using for REG1. The specified heatsink is only 20mm tall, so cases at least 35mm tall should be fine. If you’re using a taller heatsink, add 10-15mm to its height to figure out what cases will be suitable. Possible alternative instrument cases include Altronics Cat H0374 or Cat H0378 (with a short heatsink), Jaycar Cat HB5912 or the Hammond RM2055M, which is available from Digi-Key and Mouser. It should also fit into a UB2 Jiffy box like Jaycar Cat HB6012, Altronics Cat H0152 or H0202, but they don’t look as good as instrument cases, and it will be a bit harder to fit the board in. Mount the board in the case using machine screws and tapped spacers Once you’ve confirmed these are all accessible through the panel, if you haven’t already, drill holes for the volume pot and power switch in convenient locations. Then solder appropriate lengths of ribbon cable strips to those parts and crimp/solder pins to the other ends that you then push into the plastic polarised header blocks (or solder direct to the PCB). You will also need to mark and drill two 5mm holes in the lid for the LEDs to protrude through. Depending on their lead lengths, you might have a little bit of flexibility in where those LEDs are placed as you can bend the leads slightly. Keep in mind that if you are applying the lid panel label, it will have to line up with those holes. Now is a good time to adhere the front and/or lid panel labels (see below for hints on making them) and cut out the holes using a sharp hobby knife. Verify that S1 and VR1 are wired up correctly, mount them on the front panel and then plug them into headers CON3 & CON4. You can then ‘button up’ the board inside the case, power it up and check that it’s operational. To do that, you will need to plug it into a computer running Windows, download and install the software described in the following section, Fig.12: the positions of the holes to drill/cut in the front panel. The volume control and on/off switch are panel-mounted, so they could be moved, but these positions are designed to clear other nearby parts. You can use this for cases other than the recommended one, but you’ll need at least one reference point to position it correctly. siliconchip.com.au Australia's electronics magazine June 2022  35 and verify that it can connect to the Spectral Sound Synthesiser. Making the labels I’ve found that just printing with an inkjet printer then spraying over with art ‘fixing’ spray works well. For the lid label, I used special decal sheets for my inkjet printer from eBay (www.ebay.com. au/itm/181840164873), which works. They have a paper backing. The process is: 1. Print just like you would to any sheet of paper (but with the shiny side up). 2. Spray with varnish/lacquer/fixative. 3. Submerse in water for 30 seconds to a minute. 4. Gently slide the decal off (the very thin decal detaches from the paper backing when wet) and onto the case. 5. You might want to varnish over the dried decal again, for added protection. The ‘Patch Editor’ software Fig.13: the MIDI Synthesiser was combined with a standard MIDI controller keyboard, amplifier and speaker to form this electronic clavichord. Programming the microcontrollers This project uses eight microcontrollers of three different types. They are all Microchip products (one PIC and seven dsPICs), so they can be programmed with a PICkit 3, PICkit 4, Snap programmer or similar. Or you can build it from our kit, which will come with all the micros pre-programmed. Each different type of micro has its own software. In other words, there are three sets of firmware. The codes are given in the parts list, and the download package on our website includes the source code for all three, plus the three HEX files you need to program them. If you want to rebuild the source code to produce new HEX files (eg, you want to make changes to the way it functions), you’ll need the Microchip XC16 Pro compiler (which can be ordered from the Microchip website; there are also free trial versions). Otherwise, optimisation level 3 will not be available, and the resulting firmware will not be fast enough to work correctly. The PIC18 code is less critical, so you can probably get away with using the free XC8 compiler to build that HEX file. 36 Silicon Chip Australia's electronics magazine The module has an associated, powerful Windows program called the “Patch Editor”, written in C# Winforms. A screengrab of this software is shown in Screens 1 & 2. This is a ‘Click-Once’ .NET application that I am hosting online at https://collectany.blob.core.windows. net/ssm/SpectralSoundModuleApp1/ setup.exe This is in Microsoft Azure ‘blob’ storage, which means that the user is notified of version enhancements if installed from this online location. A comprehensive user guide for this software is available. The app includes tools to help shape the timbre ‘landscape’, the envelopes, the filters and more. It includes ‘visualisers’ to view the timbres both in the time or frequency domain, and even includes a harmonic analyser, where you can grab the harmonic content from audio! The app also has its own unique programming language called ‘Spectral Definition Language’ (SDL) [not to be confused with Simple Direct­Media Layer – Editor]. You can write SDL code to finely tune the patch definitions and easily reuse chunks of code. The idea is to ‘abstract’ sound design to a higher level, simplifying all the complexities of detailed configuration. siliconchip.com.au To this end, you can store your own code snippets and execute them as necessary via the app menu – a powerful concept, with ‘out of the box’ default examples for setting things like a ‘Hammered String’ envelope! Final thoughts This project has been a very intense but rewarding journey, often feeling like it is ‘shooting for the moon’. It shows that sound synthesis is still fertile soil for experimentation and invention. Fig.13 shows my DIY ‘Electronic Clavichord’ containing a standard MIDI controller keyboard coupled with this module and a tiny amplifier and speaker. One tantalising idea for the future could be to approach the problem of a timbral-based system from a more holistic angle. Rather than each played note having its own wavetable, think of the required harmonics from all played notes as one giant pool of oscillators. We could then use the phenomenon of ‘psychoacoustic masking’ to significantly ‘prune’ the actual harmonics that require calculation. This would require the ability to prioritise the harmonic importance and ignore the ones of least significance. An interesting aspect of this approach would be that the threshold could be based on system performance, always processing the maximum number of harmonics possible but degrading the sound quality in a controlled way if needed. This approach might also be able to deviate from the integer-based harmonic requirement, offering more realism. Another idea is to return to a more sample-based approach, but instead of storing samples in the conventional PCM way, keep them as timbres or even as timbre changes. This might provide significant savings. Other ideas start questioning Screens 1 & 2: sample screenshots from the powerful Windows-based Patch Editor software designed to interface with the Spectral Sound Synthesiser. Its source code is included in the download package. fundamentals about the precision needed for harmonic levels. Since humans perceive sound logarithmically, adequate level scaling might result from simple bit shifting. Can we really tell the difference in harmonic levels to such a degree that it justifies anything better? Moreover, we need to think more about how our brains perceive sound, and less about the purity of mathematical calculation. Our brains work on impression and recognising overall characteristics, so maybe there’s potential in focusing on techniques that make huge computational savings by disregarding things that just do not matter to perception. It seems like there is still much to think about regarding sound synthesis! SC Useful Links The biological bases of musical timbre perception: siliconchip. com.au/link/abdc Synthesising plucked strings: siliconchip.com.au/link/abdd Synthesising wind instruments: siliconchip.com.au/link/abde Sound quality or timbre: siliconchip.com.au/link/abdf Details on timbre: www.dspguide. com/ch22/2.htm siliconchip.com.au The finished Synthesiser has two LEDs on the top of the panel to indicate when it is receiving MIDI messages and when it is communicating with a computer (eg, loading patches). June 2022  37 Review by Allan Linton-Smith This handy little radar speed detector has enough sensitivity to detect the speed of tennis, cricket, baseball, softballs and footballs. It’s also useful for checking the speed of your golf swing, running or even your car. Radar Coach how fast can you run, bowl, serve, kick or drive? T he Radar Coach is available from Tennis Warehouse Australia for $249, including GST and delivery (www.tenniswarehouse.com. au/radar-coach-speed-gun.html). It comes with a small tripod and carry case and is specifically marketed toward tennis players, to help them improve their serving. But as mentioned above, it will work well for all sorts of applications. We don’t usually review this kind of product, but we were surprised by how well it worked and thought some of our readers would be interested in it. The Radar Coach has a large display made of 5mm LEDs behind a translucent housing. The little holes at the bottom are for the loudspeaker, which can be set to announce the speed (in an American accent) in case the display is obscured, and it is remarkably loud. It can also discriminate between the ball speed and the running speed of the bowler or pitcher. The display is 165 x 120mm and the numerals are 60mm high. These look like big 7-segment LEDs but, as mentioned, are made of standard 5mm LEDs. The result is pretty effective. The display is easily visible in sunlight and flashes the speed for a few seconds. It gives you the option to display (and possibly also announce) the measured speed in km/h or mph. One possibly helpful application for the audible speed readings is for race marshals, who can listen for vehicle speeds as they enter the pits without taking their eyes off the track. The manufacturer recommends that the device be put behind a wire fence to prevent damage from fastballs, because it is only housed in a plastic case that could crack if it’s hit hard, especially by a cricket ball. As fencing may obscure the visual readout, the voice message is again helpful. It can record the last ten readings. I like that it can ignore your running speed (such as running up to the cricket pitch) and only detect the ball speed. It does this by assuming you can’t run more than 45km/h and sets this as the minimum activation speed. Usain Bolt tops out at 44.72km/h, so that’s a pretty safe assumption. The circuitry From the outside, I could not see an opening for the radar transmit/ receive pads or antennae, so I opened it up to have a look. Inside, I found a radar module labelled “MC420S-G 10.525 GHz”, which looks a lot like the MDU2750 from Microwave Solutions that I am familiar with. Unfortunately, I couldn’t find any data on the MC420S-G, but it could just be a re-badged MDU2750. These operate from a 5V DC supply, transmit a chopped 10dBm (10mW) signal at 10.525GHz and are accurate to within 0.03%. They use a dielectric resonator stabilised FET oscillator, which provides stable operation over a broad temperature range in either CW or low duty cycle pulsed mode, and a balanced mixer for good sensitivity and reliability. Features & Specifications ∎ Accurate readings of speeds up to 199km/h or 150mph ∎ Easy-to-read numbers ∎ Voice reading can be turned on or off ∎ Portable with free-standing or hand-held use ∎ Ideal for tracking tennis serve and ground-stroke speed ∎ Can measure ball speed or swing speed ∎ Set up on the ground behind a net (for protection) on in-built legs, or use your own tripod for more height ∎ Includes carry case ∎ Powered by 5 AA cells (not included) ∎ Record button repeats the last 10 readings 38 Silicon Chip Australia's electronics magazine siliconchip.com.au They are a type of Doppler radar that detects the frequency shift between the transmitted and reflected signal from a moving object. The mixer produces a low-level signal which contains a signal at the difference frequency between the transmitted and received signals – see Fig.1. The frequency of this signal indicates the speed of the moving body. This low-frequency signal is filtered out, amplified and processed to provide an audible and/or visual speed. The 10.525GHz radar module draws 60mA from a 5V supply and produces a 700Hz output signal for an object approaching at 36km/h. The MDU2750 has a frontal range of approximately 50 metres and a rear range of only 2-3 metres. This unit functions from -30°C to +70°C, but performance may be degraded above 55°C. In the Radar Coach, the radar transmitter is behind a plastic panel, separated by a 2mm-thick piece of rubber. This presumably attenuates the signal somewhat, and we estimate the usable The internals of the Radar Coach. The 10.525GHz radar module is at the top and has a four-patch antenna arrangement. It runs from 5V DC and transmits at 10mW, sufficient to penetrate the plastic housing. Note the small 8W loudspeaker at the bottom for announcing the speed. range to be around 6m. It also depends on the size and reflectivity of the target. Note that it will be inaccurate if an object approaches the detector at an angle. Imagine a ball going diagonal to the radar beam; the detector will only calculate the approach speed, which is considerably lower than the actual speed; 30% low for a 45° angle. So balls should be aimed directly at the device without actually hitting it (hence the recommendation to put it behind a fence). Conclusion The Radar Coach is considerably less expensive than other similar devices we’ve seen, which often cost several thousand dollars. Despite this, it does not compromise accuracy. It seems to achieve this by using a low-cost mass-produced radar module originally designed for automatic Fig.1: the basic arrangement of the Doppler radar module. The oscillator generates a very highfrequency RF signal that’s sent out via the transmitting antenna. The frequency-shifted received signal is mixed with the original signal to produce a difference signal that becomes the IF (intermediate frequency) output. This is filtered, amplified and processed to generate a speed reading. The Radar Coach is ideally located behind a wire fence to protect it from being hit by the ball. Its large display uses 5mm LEDs behind a translucent housing which gives a readable display in full sunlight. The little holes at the bottom are for the loudspeaker. siliconchip.com.au doors, plus a very cost-effective processor, display and audio amplification design. The tripod mounting system is preferred over a radar gun arrangement because it does not require a coach to point, measure and call out each speed reading. It really does replace a coach in that sense (but won’t give you any tips!). Overall, this device is fun to use and is much cheaper than any direct equivalents I can find. If you’re having trouble getting accurate readings, keep in mind that it’s critical that you set it up properly. As for its build quality, I gave it to my grandson and he has dropped it several times, hit it many times with balls and it still works a treat. He is a fast bowler and It has helped him enormously with his wicket-taking. He is SC the fastest on his team now! Australia's electronics magazine June 2022  39 F ∎ Switch-mode buck-boost current/voltage driver module ∎ Suitable for driving a variety of 12V LED panels ∎ Adjustable current and voltage settings using trimpots ∎ Alternative fixed voltage/current settings with fixed resistors ∎ Lower-cost 5A option by omitting some parts ∎ Input voltage range: 11.3V-35V ∎ Output voltage range: 7-34V ∎ Maximum output current: 8A ∎ Maximum input current: 10A ∎ Other uses include charging a 12V battery from another 12V battery or other DC source ∎ Can also be used as a 12 ➿ 24V DC or 24 ➿ 12V DC converter or under $20, you can buy some impressive LED panels from AliExpress (eg, www.aliexpress. com/item/4001275542304.html). They measure about 22cm by 11cm with an active area of 20cm by 10cm. They’re also available from other online sellers such as on eBay or Banggood. The panels are based on an aluminium PCB and have a silicone gel coating over the LED array. They are specified as drawing 70W at 12V DC, and they simply expose two solder pads for the power source. There are several other modules with different sizes and power ratings, although we haven’t tested any of those alternatives. Having received some samples of these LED panels, we ran some tests using our 45V Linear Bench Supply (October-December 2019; siliconchip. com.au/Series/339) and produced the current/voltage curve seen in Fig.1. This is consistent with four groups of LEDs arranged in series, each with a voltage drop of around 3V, giving a forward voltage of about 12V. Running the panel at 50W (close to 4A) for a while, it got pretty hot and was way too bright to look at directly. So we expect that these panels can be run at lower power levels than that and still be very useful. Running them cooler should also extend their working life. When supplied with a small amount of current, the individual LEDs can be seen, and there are 336 of them, arranged in 28 rows of 12 (see the photo at the end of the article). Each group of LEDs connected in parallel corresponds to seven rows. YouTuber Big Clive ran some tests on similar modules, and even tore back the gel coating to see what lies beneath. You can see his video at https://youtu. be/uIspnsBp3o4 He found that each group of LEDs is simply wired in parallel, meaning that the panel is mostly unaffected if one LED fails open-circuit. A short-circuit failure would tend to shunt the entire panel current through a single LED, quickly turning it into an open circuit! It also appears that the LEDs are actually blue, and the gel is a phosphor coating. It’s an interesting construction that is quite robust, but simple and clearly cheap to manufacture. As LEDs are often touted as being around eight times more efficient (in terms of lumens per watt) than Australia's electronics magazine siliconchip.com.au High-Power Buck-Boost LED Driver Since we saw some ridiculously bright, low-cost LED panels for sale, we’ve been trying to figure out the best way to drive them. This Driver is the result; it is very flexible and useful for many other purposes, such as charging batteries from a DC source or converting between 12V DC and 24V DC. By Tim Blythman Background Source: https:// unsplash.com/photos/k4KZVfAXvSg Features & Specifications 40 Silicon Chip incandescent globes, 70W of LED light is equivalent to several hundred watts of incandescent light; easily enough to illuminate a large room very brightly. Fig.1: like any semiconductor diode, the current through these LED panels changes sharply with changes in voltage. As such, it’s not practical to regulate the panel brightness by controlling the voltage. We must instead control the current, one of the features of the LED Driver PCB. Limitations It’s evident from the current/voltage curve that applying much more than 13V will put the panel over its nominal 70W limit. So directly connecting a 12V battery, which could supply as much as 14V or higher, is not a feasible way to drive these panels. A 12V battery that’s nearly flat might only produce around 11.5V, so a resistive voltage dropper is not suitable for powering these panels over a battery’s useful charge range. We also expect the current/voltage curve to change depending on the panel temperature. That will change during operation as the panel selfheats due to its own dissipation. Like most LEDs or LED arrays, a current-controlled or current-limited supply is the best choice for driving this one. While the voltage may drift slightly under constant current conditions, it’s a much more stable arrangement. Thus our Driver incorporates current-control circuitry. The LED Driver Given that a common use case would be running these LED panels from a 12V battery or DC supply, we need a few specific features. The LED panel operating point might be above or below the battery voltage, so we need to be able to increase or decrease the incoming supply. And to provide a consistent level of lighting, we also need to regulate the output current. For efficiency, we need to use a switchmode circuit. For this to both increase and decrease the voltage, it needs to be able to either buck (reduce) or boost (increase) the incoming voltage. Some circuits do this by having two separate stages; for example, first by decreasing the input voltage as needed and then using a second stage to boost the output from the first stage. The design of such circuits can be complex; more so when current limiting or regulation is needed. But chips exist that can work in boost or buck mode as needed. That includes the LM5118, a device we used in the Hybrid Bench Supply from April-June 2014 (siliconchip.com.au/ Series/241). siliconchip.com.au The LM5118 handles the transition from boost to buck mode by using a hybrid mode that is somewhere in between at intermediate voltages, ensuring that the output remains stable at all times. It does provide current limiting, but only to protect the inductor that is used to store energy during the boost and buck phases. So we needed to add some parts to the design to provide independent, adjustable output current limiting. Circuit details Fig.2 shows the circuit that we have designed incorporating all these features. Parts of it look similar to the Hybrid Bench Supply because of the common external parts needed for the LM5118 to operate. Power comes in through a two-way barrier terminal, CON1, with the positive supply passing through 10A fuse F1. The 10A limit was chosen as a convenient level above the 7A limit of the LED panel. A bank of paralleled ceramic 10μF capacitors provides bulk supply bypassing to the power section of the circuit, while a 100nF capacitor is placed close to IC1, the LM5118, to stabilise its supply. The VIN supply feeds into pin 1 of IC1 with grounds at pins 6 and 14. An 82kW/10kW divider across this supply to IC1’s pin 2 UVLO (under-voltage lock-out) exceeds its threshold of 1.23V When the panel is off, you can just make out the numerous small LED chips that provide the light output under the phosphor gel coating (although they are a bit hard to see in this photo). when VIN is around 11.3V. This way, if a battery is used to feed the circuit, it will be prevented from discharging below 11.3V, a fairly conservative level for most lead-acid batteries. The 15kW resistor between pin 3 of IC1 and ground sets the boost/buck oscillator frequency to around 400kHz, which gives decent efficiency and low voltage ripple at the output. IC1’s pin 4 (EN) is pulled to ground by a 100kW resistor, but can be pulled up to VIN by shorting the pins of JP1. Thus, JP1 can be closed with a jumper to provide ‘always on’ operation, or connected to an external low-current switch to give a simple on/off control. The capacitors on pins 5 and 7 (RAMP and SS) set the ramp and softstart characteristics of IC1 to be suitable for our application. IC1’s pin 8 FB (feedback) input is used to set the output voltage. The divider formed by potentiometer VR1 and its two series ‘padder’ resistors feeds that pin with a fraction of the output voltage that is compared with a 1.23V reference within IC1. This adjustment gives a nominal output range between 6.8V and 34.7V. The 34.7V upper limit is chosen to stay well clear of the 60V Mosfet Vds limit for Q2 while maintaining a useful range for 24V systems. The 1kW resistor between the divider and the FB pin reduces the interaction between the voltage control and current limiting, which we will explain shortly. The 2.2nF capacitor, 4.7nF capacitor and 10kW resistor between pins 8 and 9 are a compensation network that forms part of the feedback loop that controls IC1’s duty cycle. IC1’s pins 12 and 13 connect across a pair of current measuring shunts to monitor the current through D3 and D4, thus limiting the current through L1 and L2. This works whether the circuit is operating in boost or buck mode. Pins 19 (HO) and 15 (LO) drive the external high-side (Q1) and low-side (Q2) Mosfets, respectively. Pin 16 is connected to an internal regulator that provides around 7V with an external 1μF capacitor to stabilise this. The 7V supply is used to drive the Mosfet gates and is a good compromise between turning them on fully while maintaining fast switching. It also powers shunt monitor IC2 which we’ll get to shortly. Pins 18 (HB) and 20 (HS) are connected to either end of a 100nF capacitor, which is charged and then used to drive the HO pin above the supply voltage. This ‘floating’ gate supply is needed to switch on the high-side N-channel Mosfet as its source terminal can be at or near the supply voltage when it is switched on. Mosfets Q1 & Q2, inductors L1 & L2 and diodes D1-D4 are arranged in a bridge-like configuration that can be driven in either boost or buck switching modes. Fig.3 shows how such a bridge can work in both modes. The circuit works as a buck switcher for low output voltages (compared to the input voltage). When Q1 is on, current flows through L1 and L2 and then D1 and D2 towards the load. When Q1 switches off, the current continues to circulate via D3 and D4. Above 75% duty cycle on Q1, IC1 operates in the hybrid boost-buck mode. Q2 starts to switch on with a duty cycle that overlaps with Q1’s on-time. This increases the current through the inductors during the on-time, and this extra energy gets fed to the output during the Mosfet off-time, increasing the output voltage. A simple implementation of the boost mode would have Q1 on all the time boost mode is active, but this is not possible with the LM5118, so it is switched on and off in synchrony with Q2. This is necessary because the Fig.2: the circuit is based around IC1, an LM5118 buck-boost controller. It drives the H-bridge made from Mosfets Q1 & Q2, diodes D1-D4 and inductors L1 & L2. These allow it to step down the incoming voltage (by pulsing Q1 on) or step it up (by pulsing Q1 & Q2 on simultaneously). Varying the duty cycle/on-time allows it to change the output-to-input voltage ratio. We’ve added IC2 and some other components to provide an adjustable current limit. 42 Silicon Chip Australia's electronics magazine siliconchip.com.au bootstrap capacitor needs to be periodically refreshed to maintain the gate voltage, which can only happen while Q1 is off. All this is done transparently by the controller inside the LM5118. Current limiting The voltage at the cathodes of D1 and D2 is smoothed by a bank of five 10μF capacitors accompanied by a 100nF capacitor. From there, it passes through another 15mW current sensing shunt, then through fuse F2 to output connector CON2. We can keep the grounds common between the input and output by placing the current shunt in series with the positive output. This has several advantages, one of which is that you don’t need to have the ground current pass through this module; it can go straight from the load to the power source, possibly simplifying the wiring and reducing wire-related power loss. The voltage across the shunt is measured by IC2’s pins 1 and 8 and amplified with a gain of 50. IC2 is an INA282 current shunt monitor, and it takes its supply on pin 6 from IC1’s internal 7V regulator. It also has its own 100nF supply bypass capacitor. IC2’s pins 3 and 7 are both connected to ground, so the output voltage from pin 5 is relative to ground. The voltage at pin 5 is divided and smoothed by the network consisting of the 100W resistor, 5kW trimpot VR2, 1kW resistor and 10μF capacitor. The smoothing is necessary to eliminate instability which would cause LED flickering due to oscillations in the output voltage. The resulting voltage is fed into IC1’s FB pin via schottky diode D5. Thus, as the output current increases beyond a certain threshold, the voltage at the FB pin increases similarly to the situation where the output voltage is too high. IC1 attempts to control this by reducing its output voltage, thus reducing the current. The diode ensures that an output current below the limit does not drag down the reference. If the target current is not met, the control loop is based only on the output voltage. The result is not a ‘brick wall’ current limit; it allows higher currents at lower output voltages. This is because a higher voltage is needed at D5 to maintain balance at the FB pin as the siliconchip.com.au Fig.3: an illustration of how the LM5118 works, in buck mode (diagrams at left) and boost mode (at right). The mode of operation is determined by whether S2 (actually a Mosfet) is switched with S1 or just left open (ie, off). In buck mode, as the duty cycle approaches 100%, the output voltage approaches the input voltage while in buck/boost mode, a 50% duty cycle gives an output voltage equal to the input with higher duty cycles boosting the output voltage above the input, approximately doubling it at 75% duty, quadrupling it at 87.5% and so on. The LED Driver is designed to mount directly to the 70W LED panels, with just two flying leads between the two. As it has many other potential uses, you can mount it in just about any kind of box using tapped spacers. Australia's electronics magazine June 2022  43 output voltage drops further below its setpoint. The 1kW resistor between VR1 and the FB pin helps maintain this balance and limit the extent to which the two parts of the circuit interact. With VR2 at its minimum setting, an output current of 1.8A will induce 27mV across the shunt or 1.35V at pin 5, which corresponds to 1.23V at the divider output, meaning that this is the point that current limiting begins. With VR2 set higher, a smaller fraction of the pin 5 voltage is sampled, and thus a higher output current is allowed. In practice, since IC2’s supply is around 7V, the maximum current setting is around 8A. So setting VR2 above around 3/4 of its travel will effectively disable the current limiting. Lower output current settings can be achieved by increasing the shunt resistance, although that would arguably be a poor use of a circuit capable of 8A. That the current limit tapers off is actually an advantage as it tends to put the system closer to constant-power operation. For the LED panels, the operating voltage range will be quite narrow in any case. Pairs of parts You might notice from the schematic that a few parts are duplicated and paralleled. These include L1 & L2, D1-D4 and the 15mW current shunts connected to D3 & D4. The circuit has been designed with these extra parts to handle up to 8A, by splitting the current between the pairs of components and thus moderating the heating of any single part. For operation up to 5A, L2, D2, D4 and one of the shunts can be omitted. The input and output fuses should also be changed to suit 5A operation. All other components can work happily up to the 8A limit. While the shunt resistors do not dissipate any significant amount of power, they are used by IC1 to monitor the current through the inductors. Whether one inductor and one shunt or two inductors and two shunts are present, the current limit through each inductor is the same. Extra parts There are a few component locations that are usually left empty. These are shown in red on the circuit and PCB overlay diagram. We’ve incorporated these in the design as they are Table 1: resistor values for fixed output voltages Target voltage Calculated resistance E24 resistor value Resulting voltage 8V 210W 220W 8.05V 10V 568W 560W 9.95V 12V 926W 910W 11.91V 14V 1284W 1300W 14.09V 15V 1462W 1500W 15.21V 20V 2357W 2400W 20.24V 24V 3072W 3000W 23.59V 28V 3788W 3900W 28.63V 30V 4145W 4300W 30.86V Target current Calculated resistance E24 resistor value Resulting current 2A 119W 120W 1.98A 3A 729W 680W 2.92A 4A 1339W 1300W 3.93A 5A 1949W 2000W 5.08A 6A 2558W 2700W 6.23A 7A 3168W 3000W 6.72A 8A 3778W 3600W 7.71A Silicon Chip Options R13, adjacent to VR2, is a different case. This fixed resistor is intended to replace VR2 for a fixed setpoint. Alternatively, you can replace either VR1 or VR2 with a fixed resistor between their two leftmost terminals, as they are simply wired as variable resistors (rheostats). Table 1 shows typical resistor values for fixed output voltages, including the exact and nearest E24 series values. The values are linear across the range, so you can interpolate them to find intermediate values if necessary. Table 2 does the same for current, with the listed values being at the point that current limiting first kicks in. Similarly, exact and nearby E24 series values are given, and the correlation is relatively linear. Battery charging Table 2: resistor values for fixed output currents 44 shown in the application notes for the LM5118, and are useful in certain situations. We were initially unsure whether these parts were needed for stable operation, but it turned out they were not. Some enthusiastic readers might be tempted to experiment with the design and use these component locations, as shown in the LM5118 data sheet. The optional parts include an RC snubber for the switching node and components to disable IC1’s internal regulator if the input supply voltage will always be within a suitable range (about 5-15V). Since the LM5118 can operate up to 76V (with some parts changes needed in our design to achieve that), this board would have many potential applications. Some configurations may not be as stable as the one presented here, so figuring out what components are needed in different use cases is left as an exercise for the reader. Australia's electronics magazine Although we have not done thorough testing with this configuration, the Driver is well-suited for charging a 12V battery from another 12V battery. This might seem like an unusual requirement, but it often crops up in situations involving a caravan or similar that has a ‘house’ battery, usually a deep-cycle type. Such a battery is typically charged from the 12V system of a towing vehicle while the vehicle is charging its siliconchip.com.au starter battery. Due to voltage drops over long cables and the tendency of modern vehicles not to fully charge their starter battery, there may not be enough volts available to fully charge such a house battery via a direct connection. The Driver can overcome this and comfortably deal with batteries in all charge states due to the current limiting feature. The Driver is set to provide a voltage that suits the desired house battery’s fully charged level, with the current limit set to a safe level for the batteries and wiring. A diode or VSR (voltage sensitive relay) on the Driver’s output may be necessary to prevent the house battery from draining through the Driver’s voltage sense divider. The Driver should be located close to the house battery so that cable resistance does not affect sensing the house battery voltage. Construction The LED Driver is built on a double-­ sided PCB coded 16103221 that measures 85mm x 80mm. Fig.4 shows where all the parts go on the board. This design uses almost exclusively surface-mounted parts of varying sizes, so you will need the usual set of surface mount gear. A temperature-adjustable iron will help greatly in dealing with the wide range of part sizes that are used. Several of the components connect to solid copper pours (for current and thermal handling) and will likely require the iron to be turned up to a higher temperature to make the joints. Tweezers, flux, solder wicking braid, magnifying lenses and fume extraction are all important requirements for assembly. Also, since you’ll need to keep the iron’s tip clean, have a tip cleaner on hand. Begin construction with the two ICs. IC1 has the finest-pitch leads, so start with it. Apply flux to its pads, then align the part with the pin 1 marker and tack one lead in place. Use a magnifier to confirm that the part is aligned with the pads and flat against the PCB, then tack the diagonally opposite lead and re-check its position. Solder the remaining leads one at a time, or by gently dragging the iron tip loaded with solder along the edges of the pins. These techniques depend on loading a small amount of solder onto siliconchip.com.au Fig.4: most of the components on the board are SMDs, but only IC1 has closely-spaced leads. Having said that, some of the other components can be somewhat challenging simply due to the combined thermal mass of those parts and the PCB copper. Most components are not polarised or only fit one way; it’s mainly the ICs and trimpots that you have to be careful orientating. Parts List – Buck-Boost LED Driver 1 double-sided PCB coded 16103221, 85mm x 80mm 2 2-way 10A barrier terminals, (CON1, CON2) [Altronics P2101] 1 2-way pin header, 2.54mm pitch, with jumper shunt (JP1) 2 10A 10μH SMD inductors, 14 x 14mm (L1, L2) [SCIHP1367-100M] 4 M205 fuse clips (F1, F2) 2 10A M205 fast-blow fuses (F1, F2) 6 M3 x 10mm tapped spacers (to mount to LED panel) 10 M3 x 6mm panhead machine screws (to mount to LED panel) 2 5kW 25-turn vertical top-adjust trimpots (VR1, VR2) [Jaycar RT4648 or Altronics R2380A] Semiconductors 1 LM5118MH buck-boost regulator, SSOP-20 (IC1) 1 INA282AIDR current shunt monitor, SOIC-8 (IC2) 4 SBRT15U50SP5 schottky diodes, POWERDI5 package (D1-D4) 2 PSMN4R0-60YS or BUK9Y4R8-60E N-channel Mosfets, LFPAK56/SOT669 (Q1, Q2) 1 BAT54, BAT54S or BAT54C schottky diode, SOT-23 (D5) Capacitors (SMD M3216/1206-size SMD X7R ceramics, 35V or higher rating) 16 10μF 1 1μF 6 100nF 1 4.7nF 1 2.2nF 1 330pF Resistors (all SMD M3216/1206-size 1/8W 1% except as noted) 1 100kW 1 82kW 1 15kW 2 10kW 3 1kW 1 220W 1 100W 3 15mW 3W M6332/2512 A complete kit (Cat SC6292; siliconchip.com.au/Shop/20/6292 siliconchip.com.au/Shop/20/6292) is available for $80. It includes everything in the parts list above. We can supply the LED panels, cool white (~6000K, SC6307) or warm white (~3000K, SC6308) for $19.50 each. Australia's electronics magazine June 2022  45 the iron’s tip. Practice is the only way to get this right. Once finished, carefully inspect the leads for solder bridges. If you see any, add some extra flux paste and then use solder wick to gently remove the excess solder. Finally, clean away the flux residue with a flux cleaner (or pure alcohol if you don’t have one) and a lint-free cloth, then check again with a magnifier to ensure all the pins are correctly soldered, and no bridges are left. Use a similar technique to fit IC2 to the board. Then mount the smaller passive SMDs (except for the shunt resistors) using a similar approach; their larger pads are a bit more forgiving. Remember that some of these parts are not needed (they’re labelled in red in Fig.4). The main trick here is to avoid touching the iron to one side of the part until you are sure the solder on the other side has solidified, or it might shift out of place. The SMD capacitors are unmarked, so be careful not to mix them up. It’s best to unpack and fit all the capacitors of one value at a time. As some of the capacitors (particularly the 10μF parts) are across ground planes, you might need to turn your iron up to make good joints. Ensure the solder flows both onto the end of the part and onto the PCB pad below. The solitary SOT-23 part, D5, is a BAT54 schottky diode. With one lead on one side and two on the other, its orientation should be obvious. Just make sure its leads are flat on the board, not sticking up in the air, which would indicate that it’s upside-down. Note that you can substitute a dual BAT54S (series) or BAT54C (common cathode) diode as one of their two internal diodes connects between the same set of pads. The other diode in the package will be unconnected and unused. The remaining surface-mounting parts are larger, so you might like to raise your iron temperature before proceeding. Also, they are mostly arranged around the top half of the PCB. Solder the three larger 15mW shunt resistors, then the four power diodes. The diodes have two small leads on one end and a larger one on the other. In each case, the ends with two small leads go towards CON1 while the 46 Silicon Chip larger single lead is towards CON2. The pad arrangement on the PCB should make this clear. Solder these like the passives, but take extra care that the part is aligned correctly so that the large tab that runs under the part does not short onto the smaller pads. While the packages used for Mosfets Q1 and Q2 may look unusual, they are actually much the same as an 8-pin SOIC package IC, but with the leads along one side joined into one larger tab. This improves heat removal, lowers resistance and also makes correctly orientating them easier. Take care that the leads are aligned within their pads. The only real difference in soldering these compared to SOIC-8 parts is due to the greater thermal mass of the large metal tab and the copper areas on the PCB. Moving on to inductors L1 and L2, the thermal effect will be even more apparent here. They are not polarised, but you will need a good amount of heat to complete the soldering. It’s best to lay down some flux paste on one pad, add some solder to the other pad, slide and/or press down the part into place while heating that solder, then add solder to the opposite pad. Finally, refresh the first pad you soldered. Check that the solder fillets are joined to both the inductor and PCB pads before proceeding further. Now clean the PCB of excess flux and thoroughly inspect all the parts for bridges and dry joints; they will be easier to see and fix after cleaning. There are only a handful of throughhole parts remaining. You can mount fuse holders F1 and F2 by installing a fuse and slotting the whole assembly into the PCB. This ensures that the tabs are aligned correctly and spaced far enough apart to allow a fuse to be fitted. Like many of the parts, they may need more heat to let the solder take to the large copper areas. Next, mount the terminals for CON1 and CON2, ensuring that any connected wires can exit from the board (most barrier terminals allow wires to be inserted from either side, but there are exceptions). JP1 and its jumper can then be installed near CON1. Leave the jumper in place for testing. Finally, fit the two multi-turn trimpots, VR1 and VR2, near F2. Make sure their screws are to the left, as shown in the overlay and photos; if Australia's electronics magazine they are reversed, they will not operate correctly. Ensure that they are both wound to their minimums by turning their adjustment screws anti-clockwise by 25 turns or until you hear a clicking indicating that they have reached the end of their travel. There are seven test points on the board, but you do not need to fit PC pins; you can simply probe them with a standard set of DMM test leads. Testing You will need fuses installed for testing, but since initial testing is done with a multimeter, you can fit lower-­ rated (eg, 1A) fuses if you have them on hand. If you have a current-limited PSU, you can use that too. Connect a voltmeter across CON2 and apply a power source of around 12V DC (above 11.5V) to CON1. You should see about 6.6-7.0V at CON2. If you get a reading near the supply voltage instead, you could have a short circuit somewhere. In that case, switch off and check the PCB for faults before proceeding. Slowly turn VR1’s screw clockwise. After the trimpot’s mechanism re-­ engages, you should see the voltage on CON2 increase, rising to nearly 35V at its maximum setting. If so, wind it back down around 11V. If you can’t adjust the output voltage correctly, switch off and check for faults. If you have used low-value fuses, change these now to your nominal value; for the LED panels we described earlier, 10A each is a good choice. You can also test that the current limiting works if you have a suitable load such as a power resistor or test load (like the one described starting on page 48 of this issue). The minimum current limit when VR2 is set fully anti-clockwise is around 1.8A. You can easily monitor the output current at TP5 (near IC2) relative to TP3 (ground, at top left). This is the raw output from IC2, and it gives 0.75V per amp. So 1.5V at TP5 corresponds to 2A. Also, you can monitor the output voltage at TP6 (near CON2) relative to ground. Adjust your load until the current limiting kicks in. Reducing the load resistance should let the output voltage drop while the current stays mostly constant. siliconchip.com.au LED panel mounting The Driver is designed to mount on the back of the LED panel using the mounting holes near the power terminals, so you can use short flying leads to connect from CON2 to the panel’s inputs. While your iron is on, you can connect some leads to the LED panels. As you will know by now, soldering inductors L1 & L2 to the PCB requires much heat, but nowhere near as much as is needed for soldering to the aluminium-­cored PCB that forms the LED panel. You might even find that you need to preheat the panels with a hot air rework tool or similar before you can successfully solder those leads. We also suggest that you pre-tin the leads and have a generous amount of solder on the iron’s tip (to accumulate some thermal mass). To set up the Driver to work with LED panels, disconnect all loads, set the output voltage to around 13V and adjust the current limit fully anti-clockwise to 2A. The 13V setting is simply a failsafe in case the current limiting stops working. Keep in mind that the LED panels are very bright; even at 2A, it will likely be too bright to look at! We rested them on their edge during testing to aim them away from our faces. If you then connect the LED panel and power up the Driver, you should see the output voltage drop to approximately 12V as the Driver switches to its current-limited mode. If you don’t see the voltage drop, the current limiting may not be working. In that case, measure the voltage at TP7 neat VR1. This feedback voltage should always be around 1.23V when the Driver is operating correctly. Check that there is a slightly higher voltage at D5’s top right (anode) terminal; this means that the diode is feeding current into TP7 and controlling the output. If this is more than around 0.3V higher, D5 may be the wrong type or not injecting current correctly. If all is well, you can then permanently wire up CON2 to the LED panel and mount the Driver using tapped spacers. Use four tapped spacers with a screw at each end to mount the Driver PCB to the LED panel at its mounting holes. Then use two further tapped spacers mounted to the PCB only as standoffs siliconchip.com.au These panels are incredibly bright, and the two photographs above do not do them justice. They are too bright to look at directly when set to anything but the lowest setting (at left). to keep the PCB from moving, flexing and shorting against the aluminium back of the LED panel. See our photos for details of this arrangement. Adjust VR2 to provide a suitable current and thus brightness. If you get much above 5A, you might find that the current limiting no longer dominates, and the VR1 voltage setting may need to be increased above 13V. Keep in mind that both the Driver and LED panel will get quite warm during use, so they should be mounted to allow free air circulation. Suppose you see the LED panel rapidly flickering during operation. In that case, the supply voltage is probably dropping below the UVLO threshold, causing the Driver to cut out and then switch back on when the input voltage recovers. Check your supply and that the connections to CON1 do not have too much resistance. Driving two panels We briefly experimented with running two panels in series, as this is the Australia's electronics magazine easiest way to guarantee they operate at the same current. The main difference is that the voltage needs to be set to around 26V. This certainly seems to work fine, but the Driver is likely to be less efficient in this mode unless the input voltage is raised to about 24V. You can change the UVLO threshold to suit a 24V battery by changing the 82kW resistor to 160kW, and 10kW resistor to 9.1kW. This will set the threshold to approximately 22.8V. As noted in the Features panel, you can also use the Driver as a DC-­ powered battery charger, a 24V to 12V converter, or a 12V to 24V converter for many different purposes. For the 24V to 12V arrangement, the output limit can be set up to 8A, with a 10A fuse at F2, but with F1 reduced to 5A. In this case, you would also change the 82kW resistor to 180kW. For a 12V to 24V arrangement, F1 should be 10A and F2 should be 5A, with an appropriate current limit near 5A set using VR2. SC June 2022  47 Arduino Programmable Load Project by Tim Blythman To test devices like power supplies, driver circuits and current sources, you often need a particular or variable load resistance that can handle a bit of power. This Programmable Load is based on an Arduino shield that is easy to understand, build and use. It can be controlled manually or automated in a way that suits your application. D uring the design & testing of our High Power Buck-Boost LED Driver (starting on page 40), we wanted to check how it handled various loads to test the robustness and versatility of the design. To do that, we came up with this design, and it was so handy that we have turned it into a standalone project. Unlike the 50W DC Electronic Load (September 2002; siliconchip.com.au/ Article/4029), the Programmable Load is not infinitely adjustable and is not intended to sink a constant current. Instead, it uses switched resistance elements that apply discrete load resistance steps. But being connected to an Arduino microcontroller means that it’s possible to add some smarts. The circuit also includes components to allow the applied voltage and sunk current to be measured. This means that it can calculate the power dissipated in the Load (P = V × I) too. Thus, you can program the Load to behave differently depending on the application. Its functions include fixed resistance or current tracking modes. It can even be programmed to provide a dynamic load so that you can test equipment under changing conditions. A typical test for a power supply Features & Specifications ∎ Handles up to 70W continuous, at up to 15V and 4.7A ∎ Presents a load resistance between 3.1W and 47W in 15 steps, or 43kW when ‘off’ ∎ Sinks 255mA to 3.83A in 255mA steps from a perfectly-regulated 12V source ∎ Manual control of unit loads or resistance ∎ Software provides an approximately constant-current mode ∎ Measures voltage up to 20V ∎ Measures current up to 6.5A ∎ Calculates power up to 130W 48 Silicon Chip Australia's electronics magazine or regulator is to see how it responds to sudden changes in load resistance, and it is capable of doing that. Our sample code provides just the basic features, including manual resistance and current tracking modes, but it’s easy to modify the code to add custom features. Our sample code also displays all the data that is collected. Circuit details The 50W DC Electronic Load from 2002 uses a single Mosfet bolted to a large heatsink as the load element. That requires some careful circuit design so that the Load can respond to dynamic conditions. On the other hand, our Programmable Load consists of 15 high-power resistors which have no trouble dealing with rapidly changing conditions. Crucially, there is no chance of them presenting a short circuit as long as the circuit is operated within its working voltage range. The concept is simple. There are four groups of 5W 47W power resistors. The groups consist of one, two, four and eight resistors respectively, which can be switched into any combination from none to 15 resistors in parallel. The Load is optimised for use with siliconchip.com.au Fig.1: four Mosfets, Q1-Q4, are used to switch up to fifteen 47W resistors, applying a varying load resistance across CON1. IC1 and the 15mW shunt allow the load current to be measured, while the 33kW/10kW divider measures the voltage, allowing the dissipation to be calculated. voltage sources up to 12V nominal. But we’ve kept in mind that there can be some variation in voltage; for example, a 12V battery could put out up to 14.4V during charging, and a 12V LED might require 13V or more to produce full power. So we’ve selected components that will handle up to 15V continuously (more on a pulsed or intermittent basis). 47W is the lowest E24 series resistor value that produces less than 5W of dissipation with 15V applied across it, hence our use of 47W resistors. siliconchip.com.au Fig.1 shows the circuit we came up with. Four N-channel Mosfets, Q1-Q4, switch the resistors in and out of circuit. Their sources are connected to circuit ground, and their drains go to the groups of one, two, four or eight resistors, respectively. Their gates are held low by 10kW resistors, so they usually are off. The gates also connect to four digital I/O pins (D3, D4, D5 and D6) of an attached Arduino board via 470W resistors. The resistors provide a degree of protection in the event of Australia's electronics magazine a catastrophic failure. Otherwise, the circuits are entirely separate, apart from their common grounds. The other end of the load resistors connects to a 15mW current-­measuring shunt and then to the Load’s positive terminal. The connection to the external circuitry is via the screw terminals at CON1. Also connected to the top of the load resistors is a 33kW/10kW divider with a 100nF capacitor across the lower resistor. This allows the attached Arduino board to measure up to 21.5V, assuming June 2022  49 it has a 5V analog-to-digital converter (ADC) reference voltage. The divided and smoothed voltage is fed to the attached Arduino board’s A0 analog input pin. This divider means that the Arduino Programmable Load always presents a minimum load of 43kW. The voltage across the shunt is measured by IC1, an INA282 current shunt monitor with a gain of 50. A current of 1A results in a 15mV drop across the 15mW shunt resistor, and thus an output of 750mV at IC1’s pin 5. The maximum measurable current with a 5V reference is therefore 6.67A. This voltage goes to another ADC channel at the Arduino A1 pin via a 10kW resistor, and it is filtered by a 100nF capacitor. The output voltage of IC1 is set to be referred to circuit ground by its pins 3 and 7 being connected to ground. IC1 is fed with a 5V supply to its pin 6 with a 100nF bypass capacitor from the attached Arduino board, and its power ground connection is at pin 2. By changing which of Arduino pins D3-D6 are high or low, the load presented can be varied between the value of 1-15 parallel 47W resistances, or even disconnected completely. The Arduino monitors the voltage and current and reports them along with calculated power dissipation. Depending on its programmed mode, the Load can provide a fixed resistance or attempt to emulate constant current, or even a changing load to check the response of the supply. Arduino board selection We’ve specified an Arduino Uno in the parts list, but any 5V Arduino board, including other AVR-based R3 shield-compatible boards like the Leonardo or Mega, should work fine. The sample code doesn’t use any pin-specific peripherals, so it isn’t tied to a particular board. But 5V digital I/O levels are necessary to ensure that the Mosfets turn on fully. If you really want to use a 3.3V board, you could do so with some changes, but note that many are not compatible with the R3 shield form factor (they typically use the MKR form factor instead). One exception is the Due. We have not tested the design with a 3.3V Arduino board, but we believe it will work with the following changes. Firstly, ensure you use the 50 Silicon Chip IPP80N06S4L-07 or similar Mosfets as the CSD18534KCS are not suitable for 3.3V gate drive. Secondly, change the 33kW resistor to 56kW and change the 15mW shunt to 10mW. This is to avoid overloading the ADC pins with voltages above 3.3V and assumes a default ADC reference of 3.3V (as per the Due). In the sketch, change the V_CONST define to 0.0212695 and the I_CONST define to 0.0064453 to account for the different component values. Construction The Load is presented as a bare shield PCB with external screw terminals. It’s expected to be used similarly to the Arduino PSU (February 2021; siliconchip.com.au/Article/14741), as a bare board on top of an Arduino-­ compatible microcontroller board. The lack of enclosure actually helps us somewhat. With up to 70W of dissipation, a good amount of free air convection is necessary to avoid overheating. Ideally, a fan should be pointed at the module when it is used at or approaching its maximum power rating. The Load is built on a double-sided PCB coded 04105221 that measures 89 x 54mm, and Fig.2 shows where all the components go. Start by fitting the small components. IC1 is an SMD part in a SOIC-8 package and is best soldered with the aid of flux paste and tweezers, although you might get by without them. Apply flux to the pads and tack one lead in place with a clean iron tip, ensuring pin 1 is aligned with the dot on the PCB. If the part is still correctly aligned, solder the remaining pins; otherwise, adjust it using tweezers until you can do so. The 15mW shunt resistor adjacent to CON1 can also be handled similarly, although it is not as fiddly to mount. Clean up any excess flux at this point as the remaining parts are all through-hole. Note that the PCB will also accept a through-hole resistor for the shunt if that suits you better. You will have to tweak the calibration in the software if changing its value, though. Next, fit the remaining small axial resistors, as marked on the PCB silkscreen. Check the resistors with a multimeter if you are unsure of their values. Follow with the three 100nF capacitors, all of which are near IC1. These are not polarised. Trim all leads close on the underside of the PCB. Screw terminal CON1 can be soldered next. Ensure that the lead entries face out of the board. The next tallest components are Mosfets Q1-Q4, all of which are the same type. Make sure to orientate them correctly, with the tabs aligning to the silkscreen markings. You can also refer to the photos and Fig.2 to confirm the mounting arrangement for these Mosfets. The Mosfets are mounted freestanding and vertically. They do not drop much voltage when on and do not handle much current relative to their ratings, so they do not need heatsinking. Prepare the 5W ceramic resistors by bending one lead 180° down one side so that they can be slotted vertically onto the PCB. Bending the lead down the side opposite the markings gives the neatest result. When fitting the 5W resistors, it will We suggest that the Load is used without a case, although you should ideally add some tapped spacers to stand it off your work surface. There isn’t any point in using stackable headers, as there is no room for a shield above, and it would limit convection cooling of the resistors. Australia's electronics magazine siliconchip.com.au also help to stand them slightly above the PCB to allow more room for air to circulate; you can see this in our photos. We’ve made a 3mm gap, although the length of their leads might limit you in this. Start with the resistors near the centre of the PCB and work outwards, trying to keep the tops level for uniformity and square up the parts within their pads. Note that some parts are not on the ‘grid’ to provide clearance from the DC socket and USB socket. Trim the leads neatly and flush against the rear of the PCB. The only remaining parts are the pin headers. First, plug them into the Arduino board so that they are correctly aligned, then slot the shield on top. Before soldering them, check for any conflicts below. The in-circuit serial programming (ICSP) headers on the Uno board are exposed high points and are the most likely to foul any pins on the Load PCB that are not trimmed short enough. Also ensure that the PCB is down firmly against the pin headers, then solder them together from above. Programming it Our fundamental control sketch (program) for the Load is controlled through the Arduino Serial Monitor for simplicity. The voltage, current and power are also reported this way. Screen 1 shows a typical display on the Arduino Serial Monitor during use. If you don’t have the Arduino IDE (integrated development environment), start by downloading it from siliconchip.com.au/link/aatq and then install it. Now open the sketch file (download from siliconchip.com.au/Shop/6/6330) Parts List – Arduino Programmable Load 1 double-sided PCB coded 04105221, 89 x 54mm 1 5V Arduino-compatible board (eg, Uno, Leonardo or Mega) 1 10-way 2.54mm-pitch pin header 2 8-way 2.54mm-pitch pin headers 1 6-way 2.54mm-pitch pin header 1 2-way 5/5.08mm pitch screw terminal block (CON1) Semiconductors 1 INA282 current shunt monitor, SOIC-8 (IC1) 4 CSD18534KCS, IPP80N06S4L-07 or similar N-channel logic-level Mosfets, TO-220 (Q1-Q4) [2 x Cat SC4177 or 4 x Cat SC6184] Capacitors 3 100nF MKT capacitors Resistors (all 1% 1/4W axial unless otherwise stated) 1 33kW 6 10kW 4 470W 1 15mW 1-3W M6332/2512-size SMD [Cat SC3943] 15 47W 5W 10% wirewound Q1-Q4 could be just about any logic-level (ie, suitable for 5V drive) N-channel Mosfets in TO-220 packages with sufficient voltage and current ratings. and select your board (eg Uno, Leonardo or Mega) and serial port from the Tools menu. Upload the sketch and then open the Serial Monitor from the Tools menu. Set the baud rate to 115200. You should start to see an output similar to Screen 1, with updates occurring several times per second. Note that the measured voltage is across the Load itself, so the power shown is what is being dissipated in the Load. Testing and usage A good way to test the Load is to connect a multimeter to CON1 to measure the resistance between its terminals. Fig.2: the board is easy to assemble, but it’s best to take some care to line up the 5W resistors neatly or it will look messy. Watch out for the orientation of the Mosfets and IC1. Also, check the underside of the PCB when it is fitted to the Arduino board to ensure that none of the shield component leads short against anything on the Arduino. The 15mW shunt can be fitted as an SMD or through-hole resistor. siliconchip.com.au Australia's electronics magazine The positive multimeter lead should connect to the ‘+’ terminal and the negative to ‘-’. Note that if a reverse current is applied, it will be conducted by the Mosfet body diodes (and thus all the resistors) and will appear as a 3W load. There are three modes that our software can operate in. The first is manual mode, selected by typing the letter ‘m’ into the Serial Monitor, followed by a number from 0 to 15. This is simply the number of resistors that will be paralleled and presented as the load. So for “1”, Q1 is switched on, while “2” means that Q2 is on, “3” results in both Q1 and Q2 being on etc. This continues up to “15”, when all the Mosfets are switched on. For example, typing “m1” and pressing Enter (ensuring the ‘CR’ line ending is selected) will cause a 47W load to be presented on CON1. Entering “m2” will choose a 23.5W load. You can check these with your multimeter, although you might see slightly higher values than expected due to lead resistance. At any time, the “m0” command will disconnect all resistors, so that’s a good one to remember if something goes wrong. The second mode is where a resistance is entered using the “r” command. The software finds the nearest possible resistance value to the entered value. Of course, there are only 15 June 2022  51 discrete steps, so it will hardly ever be exact. But it is a good way to approximate resistive loads of a known value. The emulated constant-current mode is started with the “i” command, and it attempts to match the measured current to the setpoint by ramping up and down the number of unit loads. With the limited number of steps, it too can only approximate the set current, and will not respond to rapidly changing conditions. In practically all cases, it will jump between two adjacent load levels, and the current will zigzag around the setpoint. Screen 1 shows this, with the Load switching between 3 & 4 resistors to maintain a current near 70mA. This was set using the “i0.07” command. If the voltage rises above 15V or the power goes over 70W for an extended period, shut the Load down with the “m0” command to avoid damage to the resistors. There should not be any damage to the Mosfets as long as the voltage stays below the Mosfets’ rated drain-source voltage, which is 60V for the recommended types. Remember that the displayed voltage cannot go above 21.5V, so it might be much higher than shown if it is above 20V. More usage tips Connect the Arduino Programmable Load’s negative terminal to your circuit ground (remember that it is also commoned with the computer controlling it) and the “+” terminal to a positive output. For example, a power supply should simply be connected “+” to “+” and “-” to “-”. If other loads need to be 52 Silicon Chip Screen 1: the Serial Monitor (or another serial terminal program of your choice) is used to control the unit and show its status. It has current, voltage and power read-outs, and the applied load is displayed as both ohms and the number of 47W units. In the ‘constant current’ mode used here, the load resistance is controlled to keep the current near a setpoint. inserted in series, they should be connected between the PSU “+” and Load “+” to ensure that the Load “-” stays at ground potential. The Load is well suited to testing solar panels, with the proviso that the Mosfet drain-source voltage is respected, especially under open-­ circuit conditions when panels produce their highest voltages. This limits it primarily to solar panels with a nominal 24V output; these can produce up to 44V under open-circuit conditions. A manual scan of the sixteen different load levels will create sixteen data points that can be plotted on an I/V or P/V curve. But note that we are also designing a Solar Panel Tester which will have more features than the Load Australia's electronics magazine can offer, so stay tuned for that in the near future. Making modifications The software is written with most parameters set by #define statements near the start. If you wish to modify the load resistors, all must remain the same resistance (unless you make significant changes to the software). The unit load resistance is specified by the R_ CONST value. A higher test voltage might require a different divider to change the range (although you will need to check that the Mosfets can also handle a higher voltage). A different divider will mean that the V_CONST multiplier will need to change. To calculate the new value for V_ CONST, work out what applied voltage will deliver 5V to the A0 pin of the Arduino, then divide that higher voltage by 1024. The default value of 0.0209961 is simply 21.5V divided by 1024. We have used (as much as possible) PWM-capable pins so that it is possible to emulate intermediate resistance values by applying PWM signals to the Mosfets. We have not tried this technique, but you could experiment with it if you need finer resistance controls than the discrete steps presented here. Note that this will present a pulsed load to the current/voltage source, and depending on what it is, it might react in an unexpected manner. SC siliconchip.com.au TAX TIME Mid-Year SALE <at> 50% OFF! 3D PRINTING LASER ENGRAVING CNC ROUTING On Sale 24 May - 23 June 2022 NOW 119 $ 4.3" OLED DISPLAY NOW FROM 99 SAVE $40 $ SAVE<at>$50 60W ESD Safe Soldering Station SAVE $350 Digital Microscopes Excelllent for educational purposes and suitable for many applications. 1080p 600x Magnification (Shown) QC3193 NOW $99 SAVE $30 5MP 10x, 300x Magnification QC3199 NOW $149 SAVE $50 Powerful 60W heating element. 160-480℃ temperature range. Celsius or Fahrenheit temperature display. 240VAC powered. 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Prices and special offers are valid from 24.05.2022 - 23.06.2022. 500 POWER WATTS AMPLIFIER PART 3 BY JOHN CLARKE To finish our new 500W Amplifier, we shall now describe the power supply configuration and the complete assembly details. That includes mounting all the modules and parts in the enclosure, wiring it up, checking that it works and making the calibration adjustments. T he 500W Amplifier module we’ve described over the last two issues cannot operate alone. It needs a power supply and added circuitry to protect the loudspeaker and keep it cool. We are using two projects for these tasks: the Amplifier Clipping Indicator (March 2022; siliconchip.com.au/ Article/15240) and the Fan Controller & Loudspeaker Protector (February 2022; siliconchip.com.au/Article/ 15195). The final circuitry to be described is the Amplifier’s power supply, and its circuit is shown in Fig.9. As you would expect for this Amplifier, the power supply uses a large transformer, rated at 800VA. siliconchip.com.au The transformer has two independent 115V primary windings and two independent 55V secondary windings. The two 115V windings are connected in series so it can be powered from the nominally 230V AC mains. Similarly, the two 55V windings are connected in series with a centre tap so that after rectification and filtering, we get approximately ±80V DC. Considerable capacitance is used to filter the DC supply, with four 10,000uF 100V capacitors filtering the positive supply and another four for the negative supply. This is to remove much of the ripple from the DC supply rails, especially when under load, as the Amplifier can draw many amps when delivering the peak power it is capable of. Danger: High Voltage The 160V DC supply across the filter capacitor bank and the amplifier supply rails is potentially lethal! After the power supply wiring is complete and before you apply power, mount a clear Pers­pex sheet over the cap­acitor bank to protect against inadvertent contact – now or in the future! Note that the capacitors take some time to discharge after the power is switched off. Australia's electronics magazine June 2022  61 Fig.9: the only remarkable aspect of the power supply circuit is the large 800VA transformer and relatively high ±80V supply rails. Several 15kW discharge resistors are needed due to the high total capacitance. Three 15kW 1W resistors are connected in parallel from both supply rails to ground, to discharge the capacitors when the amp is switched off. LEDs are included in series with one resistor on each side of the supply, as voltage presence indicators. They ensure that the capacitors do not remain charged to high voltages for too long after the power is switched off. This is for safety reasons since the total of around 160V DC is an electrocution risk. Additionally, a plastic cover over the capacitors (removed in some photos for clarity) prevents accidental contact with the high-voltage wiring and capacitor terminals. The bridge rectifier is rated at 35A 400V. This rating is sufficient to handle the initial surge current that charges the capacitors at power-up, and the repetitive capacitor charging current peaks that occur near the peak of the rectified waveform each mains half-cycle. The transformer is a toroidal type, and a slow-blow fuse is required to prevent it from blowing when power is initially applied, as the inrush current can be very high. For this transformer, a 3.15A M205 slow-blow fuse is specified. It is installed within the IEC power connector housing. This has a safety fuse enclosure, where the fuse cannot be accessed until the IEC power lead is unplugged. The power supply is installed and wired up within a 3U rack case that houses the Amplifier Module, heatsink fans, the Amplifier Clipping Detector, Loudspeaker Protector & Fan Speed Controller and other necessary components. Enclosure layout The internal layout for the Amplifier and associated parts is shown in Fig.10. The Amplifier is built into a 3U rack case with a solid baseplate and vented top lid. This layout allows the amplifier heatsink to be mounted inside the enclosure with three cooling fans that draw air in from one side of the lid and pass this air across the heatsink fins. That forces airflow upwards, to remove heat from the heatsink. The fans are taller than the heatsink, so any air coming up past the fins is blown sideways and then out through the vented lid on the other side. There are quite a few holes that need to be drilled for all the mounting hardware, various cutouts made for the power switch, XLR and IEC sockets, the loudspeaker terminals and clipping indicator LED. The locations for these are shown in Fig.10, and the close-up detail drawings in Figs.11-13. Begin with the front and rear panels. Some of the required cutouts are not circular; you can cut these by drilling a series of small holes around the inside of the required perimeter, knocking out the piece of metal and filing to shape. Note that you could dispense with At left is a close-up of the power supply section of the Amplifier, with the rest of it, transformer and all, shown adjacent. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au REAR PANEL (inside view) IEC CONNECTOR WITH FUSE E N A LOUDSPEAKER TERMINALS XLR INPUT SOCKET + INSULATION BOOT Piezo Transducer Cooling Fan and Loudspeaker Protector Controller SILICON CHIP C 2021 4004 2 NC 1 4 .7 V COM 3 4148 2 15V 1 coil 5819 15V 4 To FAN1 * REV.B C 2021 01112211 To FAN2 NO 4004 5819 4 3.9V To FAN3 4148 * A Clipping Indicator Cooling Fan and Loudspeaker Protector Controller 01111211 3 4148 REV.C 4 4.7V Earth 4.7V Clip SILICON CHIP Indicator 3 + 4004 2 + 1 5819 RLY1 + TP1 TP3 THIS SECTION SHOWN ENLARGED IN FIG.11 A To TH2 + To TH1 TP2 0.47W 5W CON2 0.47W 5W FAN 1 THIS SECTION SHOWN ENLARGED IN FIG.13 Earth Please note that inductor L1 is wound using 13.5 turns of 1.25mm diameter wire, not 30.5 turns or 1mm diameter as stated in two places on p64 & p65 last month. Around 900mm of wire will be consumed. 0.47W 5W 12V SUPPLY 0.47W 5W 0.47W 5W * 3.3kW 0.47W 5W A N E 0V12V ~ + 4148 + ALUMINIUM ANGLE 4148 WARNING! HIGH VOLTAGES PRESENT FAN 2 Earth ~ + + Insulation Board 0.47W 5W + 0.47W 5W FAN 3 M8 nut RCA PLUG: RED TO CENTRE, BLUE TO BODY. 0.47W 5W FRONT PANEL (inside view) CLIPPING LED C 2021 01107021 0.47W 5W REV.B 0.47W 5W 500W AMPLIFIER Mounting Plate CON1 0.47W 5W Transformer T1 BASE PLATE THIS SECTION SHOWN ENLARGED IN FIG.12 A + + * Fig.10: here’s an overview of the chassis layout and wiring; more details are shown in the close-up drawings of Figs.11-13. Use this diagram to arrange the components in the chassis and to get an idea of where the wires and cables run, then use the following figures to determine where exactly each wire connects. Note: the wiring between the fans and thermistors TH1 & TH2 (mounted to the heatsink), the Cooling Fan Controller module and fan wiring has been omitted for clarity. The corner instrument feet mounting holes are also not shown. June 2022  63 All of the various modules are attached to the case by mounting screws. The wiring between these modules are also cable tied to the case. It’s a good idea to be generous with cable ties as it keeps everything secure and neat. Note that the XLR input socket has a 560nF capacitor soldered to it as shown above. Table 1: Screw & nut usage the XLR input socket and just use an insulated panel-mount single RCA socket. This depends on your intended application; XLR would be better suited for PA use, while RCA might be fine for home use. If using an RCA socket, a single-core shielded cable is all that’s needed to connect internally to the Amplifier Module input. We specify an insulated RCA socket because the connections need to be isolated from the chassis. Otherwise, a hum loop will be caused by Earthing the signal ground to the chassis in two places, since it is already Earthed by the Amplifier Module. If using the XLR socket, the main XLR cutout can be made using a 22mm Speedbor drill and then filing the hole shape. Now make holes in the front panel for the power switch and clipping indicator LED bezel similarly. You can make a copy of the front panel label (Fig.14) and use that as a template for positioning those two holes. Next, prepare the insulating material sections to go under the transformer, the 3-way mains terminal strip and the 12V switchmode supply. The insulation for the transformer prevents voltage flash-over to the Earthed chassis should there be an insulation breakdown. The other insulators prevent a live wire from contacting the chassis if it disconnects from its terminal. Cut the required insulation pieces from the 208 x 225mm sheet with scissors or a sharp knife and ruler. The sizes required are 63 x 97mm for the 12V supply, 57 x 45mm for the 3-way Equipment feet four M3 x 10mm machine screws, four hex nuts Amplifier PCB mounting six M3 x 5mm machine screws, three 9mm M3-tapped Nylon standoffs Heatsink mounting four M3 x 10mm machine screws Speaker Protector PCB eight M3 x 5mm machine screws, four 9mm M3-tapped standoffs Clipping Indicator PCB eight M3 x 5mm machine screws, four 9mm M3-tapped standoffs 12V switchmode two M3 x 6mm machine screws supply Capacitor mounting 20 M4 x 10mm machine screws, 32 M4 hex nuts, eight M4 x 50mm machine screws, four M4-tapped joiners (for mounting protective cover) 3-way mains terminal block two M3 x 15mm machine screws, two M3 hex nuts 64 Silicon Chip terminals and 162 x 162mm for the transformer. An 8mm hole is needed in the centre of the transformer insulator. That can be made using a wad punch (giving a cleanly cut hole) or an 8mm drill, after which you can clean up the resulting furry edges with a hobby knife. 3mm holes are also needed in the other insulation pieces for the mounting holes of the 3-way terminals and those on the underside of the 12V supply. Again, a small wad punch is ideal for making these holes. A 3mm drill can be used instead, although the resulting holes will not be clean. Arranging the parts At this point, it’s a good idea to place all the major components in the Bridge rectifier one M4 x 20mm machine screw, one M4 hex nut Earth connections three M4 x 15mm machine screws, three 4mm star washers, four M4 hex nuts, 3 5.3mm diameter crimp eyelets Transformer mounting one M8 x 75mm bolt, M8 washer, M8 hex nut Aluminium angle two M4 x 10mm machine screws, two mounting M4 hex nuts Relay two M3 x 10mm machine screws, two M3 hex nuts IEC connector two M3 x 12mm countersunk head machine screws, two M3 hex nuts XLR connector two M3 x 12mm countersunk head machine screws, two M3 hex nuts two No.4 x 6mm self-tapping screws Piezo transducer or two M2 x 6mm machine screws and two M2 hex nuts Australia's electronics magazine siliconchip.com.au Fig.11: a close-up of the chassis’ right rear corner showing the wiring between the three main PCB modules, the speaker protection relay, the warning piezo, the loudspeaker terminals and the XLR input socket. chassis and make sure you’re comfortable with all their positions. Mark them out with a fine felt-tip pen. That way, you can be sure everything is positioned correctly before you start making holes. When initially laying out the parts in the baseplate, be sure to allow room for the equipment feet to be secured in the corners with M3 screws and nuts. In particular, check that the transformer can be positioned without the screw and nut for the equipment foot in that corner interfering. siliconchip.com.au The holes required in the aluminium baseplate include the mounts for the four corner equipment feet (3mm), the three PCBs (3mm), the heatsink (3mm), the relay (3mm) and piezo transducer (2.5mm), the Earth lug holes (4mm), capacitor mounting holes (4mm), the 12V supply (3mm), the three-way mains terminals (3mm), the bridge rectifier (4mm) and transformer (8mm). Refer to Figs.10-13 to see the locations. You’ll also need to make holes to hold the aluminium right-angle Australia's electronics magazine bracket for mounting the fans near the heatsink (4mm). It’s best to locate it after the heatsink has been mounted. The aluminium bracket itself will also need holes to attach the fans that are spaced evenly along the 400mm length, with one fan in the centre and the others at each end. The angle piece is secured to the base by two 4mm screws in the gaps between the fans. We made a small semicircular cutout for each fan to prevent the lower portion of the bracket from covering the fan blade area. But June 2022  65 Fig.12: a close-up of the chassis’ left front corner showing the wiring of the toroidal transformer, bridge rectifier, mains terminal block and front panel. 66 Silicon Chip Australia's electronics magazine that is not strictly necessary; it’s just nice to have. While there needn’t be any particular order to install the parts within the case, it is easier to mount the lighter ones first. The transformer is the heaviest part, so attach it last. There is a list of the screws and nuts in Table 1 to help you select the correct hardware for each job. Install the IEC socket, the speaker terminals and the XLR socket on the rear panel. Then mount the switch and clipping indicator LED bezel on the front panel. However, leave these panels detached from the enclosure until the rest of the wiring is complete. Now is a good time to mount the thermistors for the Cooling Fan Controller. These are mounted against the amplifier heatsinks behind the Q25 and Q26 transistor clamp screws. The wires from the thermistors will need extending with an approximately 350mm length of light-gauge figure-eight wire; insulate the joints with heatshrink tubing. Next, mount the three PCBs in the chassis on 9mm Nylon standoffs using M3 x 5mm screws. The Amplifier Module’s primary mounting is via the screws into the heatsink. The Amp Module has three PCB mounting locations at the edge away from the heatsink that attach using spacers and short machine screws, but these should be installed last to avoid stressing the PCBs. Before mounting the capacitors, cut out the capacitor plastic covering piece measuring 295 x 125mm, place this on the base plate and mark out the four 4mm mounting holes. These coincide with the capacitor mounting clamp screws marked with asterisks in Fig.10 & Fig.13. Now mount the capacitors. These must be orientated with the correct polarity. The negative side is marked with a minus symbol down one side of the capacitor body. When orientated correctly, tighten down the clamps to prevent them from rotating. Note that the four capacitor bracket mounting locations marked with asterisks are secured using 50mm-long screws and nuts. Once all the capacitors are mounted, place M4 joiners on the end of these four 50mm screws, ready to attach the capacitor covering piece using four more M4 x 50mm screws. Now mount the 12V switchmode siliconchip.com.au supply with the insulation board beneath it, and the three-way mains terminal block, also with the insulation underneath. Next, attach the fans to the aluminium bracket using the securing screws supplied with each fan, then mount the bracket and fan assembly to the baseplate. To improve heat transfer, when attaching the bridge rectifier to the base, smear a little heatsink compound on the mating surface and the chassis. Fig.13: a close-up of the chassis’ left rear corner showing the wiring of the capacitor bank, 12V switchmode supply, mains IEC input socket and the Earthing. Transformer mounting Place a washer onto the M8 bolt for the transformer and insert it from the underside of the baseplate. Place the insulation square onto the baseplate over the screw, then add a Neoprene washer on top of this, followed by the transformer, the second Neoprene washer, the mounting disc and then the M8 nut. Orientate the transformer as shown in Figs.10 & 12 and tighten the nut. Wiring it up Most of the work left involves the heavy-duty power supply wiring. Wire the two banks of four capacitors in parallel using strands of 0.5mm diameter copper wire. We twisted two strands together using a drill and then bent this in half, interweaving the wire around the capacitor terminals as shown in the photos. Solder the wires securely to the terminals. Both sides of the filter capacitor bank have two 15kW 1W bleed resistors connected across them. Also, a red LED is connected across each side of the capacitor bank in series with another two 15kW resistors. The LEDs are positioned to protrude through 5mm holes in the capacitor cover plate. If your cover plate is made from clear or translucent plastic, you could skip making those holes. These LEDs indicate when voltage is present across the capacitors. As you will find, even with these bleed resistors, it takes quite a while for the capacitors to discharge after the Amplifier is switched off. The whole Amplifier uses single-­ point Earthing, so it is important to follow the wiring details in Figs.1013 closely. Mains wiring The mains supply is via the IEC power socket, then a length of siliconchip.com.au Australia's electronics magazine June 2022  67 Earth connection to the chassis using an eyelet secured to the baseplate with an M4 screw, star washer and nut. Transformer wiring For safety, the capacitor bank needs a sheet of Perspex mounted on top of it to prevent accidental contact. This photo shows the capacitors without the cover, to clearly present how they are arranged. twin-core mains flex rated at 7.5A or more. This wire needs to pass through the IEC insulation boot before being terminated (soldered) to the IEC socket terminals. The Earth wire also passes through the insulation boot and is secured to the Earth terminal on the IEC socket, and to the chassis using a crimp eyelet secured with an M4 screw, star washer and nut. Note that this Earth continues to also connect to the baseplate via another eyelet. Tie the mains wires with a cable tie before placing the insulating boot cover over the rear of the IEC socket. A third eyelet and Earth wire connects from the baseplate Earth point to the star Earth between the capacitor banks. The mains wires from the IEC socket connect to the power switch using crimp spade connectors on the top two terminals. It is important to wire this switch the right way around; otherwise, the neon LED will be lit, regardless of whether the Amplifier is on or off. We placed unused insulated crimp spade connectors on the lower two switch terminals just for safety. The mains wires from the power switch at the centre terminals run to an insulated three-way terminal block. Further mains wiring connects to the 12V switchmode supply. The mains wires must all be cable tied together so that if one comes loose, it will not cause a safety issue by shorting to chassis. Note that the 12V supply also has an We’ve shown the transformer wiring using the colour coding of the recommended transformer. But check on the transformer label that your winding colours are the same as we used; if not, wire it up according to the colours for your transformer. Connect the two 115V primary windings in series by joining the purple and grey wires using the centre terminal of the 3-way terminal block. Run the wiring to the filter capacitors from the bridge rectifier using the 2.9mm2 (cross-sectional area) wire with red for positive and black for negative. You will find that the yellow and black transformer wires are not long enough to reach the star Earth point, so extend them using one of the 2.93mm2 figure-8 cables. The power supply wiring is basically complete at this stage, but it is not connected to the Amplifier Module. Check for continuity between the chassis and the Earth connection on the IEC connector. You should get a reading very close to 0W. Next, install the 3.15A slow-blow fuse into the IEC socket. Check your work to ensure everything is connected correctly. Be sure that the capacitors are all orientated correctly. Check that the positive terminal on the bridge rectifier connects to the positive side of the capacitor bank, and that the negative terminal of the bridge rectifier connects to the negative side of the capacitor bank. The 120mm PWM fans for the 500W Amplifier are attached via a metal bracket on the base of the case. These types of fans are quite common in computers, and be purchased at a low cost. Smaller fans (eg, 80mm) could be used, but they will probably be louder and, due to how common 120mm fans are, likely more expensive too. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au It’s important to check the winding colours for the transformer, as your transformer might not match the colours we’ve used here. Safety precautions After the power supply wiring is complete and before you apply power, we suggest that you mount the cover sheet over the bank of capacitors. This will prevent accidental contact with the 160V DC supply. The total DC supply is potentially lethal. The cover will also provide a degree of safety if one of the capacitors siliconchip.com.au overheats and vents to the atmosphere. Before powering it up for the first time, wear safety glasses or a face shield. Briefly apply power and check that both LEDs light. Then switch off the power and allow the capacitors to discharge completely. It should take a while for the LEDs to stop glowing, and they should go out at around the same time. Australia's electronics magazine If all is OK, remove the capacitor safety shield and, taking great care (as the capacitor voltages are dangerous), switch on power again and measure the capacitor voltages. The readings you get should be close to ±80V DC. Check also that the 12V supply provides 12V DC at its output terminals. Switch off the power, and again, wait for the voltage to drop to near zero. Now you can complete the remaining wiring. Run the wiring from the filter capacitors to the Amplifier using the 2.9mm2 wire, with red for positive, black for negative and one of the 2.93mm2 figure-8 wires for the 0V connection. Similarly, use 2.9mm2 or 2.5mm2 wire for the loudspeaker output wiring to the speaker terminals via the relay. The remaining wiring can be completed using lighter-duty wire. Follow the wiring diagram carefully to complete it. Use cable ties and the chassis mount ties to bundle the wires together where needed. We don’t show all the cable ties on the diagram; be generous and use them wherever required. Connect the XLR input socket to the amplifier module via dual-core June 2022  69 The completed Amplifier with its vented lid attached. The functions of the three connections on the rear of the case can be made more obvious by printing out small labels. microphone shielded cable as per Fig.15. If using an RCA input socket instead, use single-core shielded cable. The enclosure can now be assembled by attaching the side panels, rear and front panels to the baseplate. Final checks and adjustments You are now ready to power up the amplifier module and make voltage checks. First, double-check all your wiring against the circuits and diagrams in this series of articles. Then reattach the capacitor safety shield. Remove fuses F1 and F2 on the amplifier module and replace these with blown fuses with 390W 5W resistors soldered across the fuse ends. Ensure that trimpot VR2 is rotated fully anti-clockwise. Apply power and measure the voltage on the amplifier speaker output, at one of the 56W 1W resistor ends closest to the edge of the amplifier PCB. There should be less than ±20mV DC at the output. You can adjust this using VR1, to get a reading close to 0V. Now connect your multimeter across the 390W 5W resistor across fuse F1, and adjust trimpot VR2 clockwise to obtain 30V. This provides a total quiescent current of 77mA or about 13mA per output transistor. Fig.14: the front panel label (shown at 85% actual size) can be used as a template to drill the holes for the power switch and the clipping indicator LED. You can also print a copy on overhead transparency film or photo paper (laminated after printing) and affix it to the front of the Amplifier. This label only covers the left-hand half of the panel, as it would be too wide to easily print otherwise. 70 Silicon Chip Australia's electronics magazine siliconchip.com.au The 500W Amplifier chassis as presented is designed to operate with a reasonable amount of free air above the case, as the fans draw in cool air and exhaust hot air through the substantial vent area in the lid. If it is installed in a constricted space, such as an equipment rack or cabinet without much space above the lid, modifications need to be made, especially if it’s run flat-out. Now measure the voltage across the other 390W 5W resistor in place of fuse F2. It should be within 10% of the reading across F1. You now need to leave the Amplifier running for at least an hour. This will allow it to warm up gradually. Measure the voltage across the 390W resistors again and readjust VR2 to give 30V. Troubleshooting If these voltages cannot be realised, switch off the power and recheck your construction and wiring. You will need to measure voltages around the Amplifier Module to see where there could be a problem. To do this, first reduce the quiescent current by turning VR2 anti-clockwise so that there is minimal voltage across the 390W resistors that are across each fuse holder. First, check for +80V, 0V and -80V at the Amplifier Module supply terminals. Check the voltages across the 470W resistor at Q5’s emitter and the 39W resistor at Q7’s emitter. If these aren’t between 0.6 and 0.8V, check transistors Q5 and Q6 for about 0.60.7V between the base and emitter of siliconchip.com.au each. If not correct, verify that they are the right transistor types. Additionally, the voltages across the 68W emitter resistors for Q3 and Q4 should be about 50-60mV each, and both voltages should be the same provided VR1 is adjusted for minimum output offset. If these are not correct, check the transistors for the correct type. If the correct transistors are in place, but the voltages are incorrect, consider replacing these transistors with reputable brand-name devices. Once the problems are found and fixed, you can adjust the quiescent current again for 30V across the 390W resistors. Once it all checks out, power it down, wait for the capacitor banks to fully discharge, then remove the fuses with the 390W resistors attached and install the correct ceramic fuses; 5A for use with 8W speakers or 10A for 6W or 4W speakers. Finally, follow the instructions for setting up the Fan Controller & Loudspeaker Protector in the February 2022 issue. SC Australia's electronics magazine ► Airflow in a rack can be increased by expanding the small holes on either side of the case in front of and behind the fans. Internal ducting may also be required to prevent hot air recirculation. It’s a good idea to attach the front panel label (Fig.14) so everyone knows what the behemoth is. If you don’t want to do that you can at least affix a small label near the Clipping Indicator LED in the centre. Fig.15: the wiring details for the XLR socket. For home use, an RCA socket could be fitted instead, in which case you could even use a panelmount female-female RCA socket. A standard RCA cable can then connect from the inside of this socket to the Amplifier Module input, avoiding soldering. June 2022  71 Using Cheap Asian Electronic Modules By Jim Rowe MOS metal oxide semiconductor Air Quality Sensors Our recent article took a look at low-cost air quality sensors and sensing modules, explaining what they do and how they work. Here’s a more detailed investigation of some of the currently available MOS (metal oxide semiconductor) type sensor modules. M OS type air quality sensors (sometimes called MOx sensors) rely on the behaviour of particles of a metal oxide (usually tin oxide) when heated in the presence of air and/ or other gases. The basic principle is shown in Fig.1, which depicts a cross-section of a typical MOS sensor. The silicon substrate of the sensing chip has a thin layer of tin oxide on the top, placed there by chemical vapour deposition. Electrodes at each end allow its resistance to be measured. On the underside of the chip is a heater element, used to heat the oxide layer to around 200-250°C, to speed up the sensor’s response. When the oxide layer is heated in the presence of clean air, donor electrons in the oxide attract oxygen molecules from the air, and they are ‘captured’ by the oxide particles. As a result, a depletion layer forms on the surface of the oxide layer, and its electrical resistance rises. But if reducing gases such as carbon monoxide (CO) and some volatile organic chemicals (VOCs) are present in the air, oxygen molecules in the surface of the oxide are released, and the depletion layer becomes thinner. As a result, the effective resistance of 72 Silicon Chip the oxide layer is reduced. So the current passed by the oxide layer varies proportionally with the amount of reducing gas in the air surrounding the oxide layer. The higher the reducing gas level, the higher the current. Therefore, the basic MOS sensor essentially behaves as a reducing gas to DC analog current transducer. We already mentioned several of these modules in the article last month (siliconchip.au/Article/15309) along with some basic specifications. But we did not go into detail regarding how they work and how to use them. The Hanwei MQ-135 Probably the most common of the low-cost MOS sensors currently available is the Hanwei MQ-135, which is designed to be sensitive to ammonia (NH3), nitrous oxides (NOx), carbon dioxide (CO2), alcohol, benzene and smoke. Like the other sensors in the Hanwei series, the MQ-135 sensor comes in a cylindrical 6-pin package 19mm in diameter and 15mm high. Most modules using the MQ-135 simply take the current output from the sensor and convert it to a proportional voltage using a fixed load resistor. The output voltage can then be measured using a DMM, or fed into one of the ADC inputs of a microcontroller unit (MCU). Fig.2 shows the circuit of Hanwei’s Fig.1: shows the cross-section of a MOS (metal oxide semiconductor) sensor and how it works. Australia's electronics magazine siliconchip.com.au Fig.2: the circuit of Hanwei’s MQ-135 air sensor module. The lead photo shows a group of MQ-model sensors. own air sensor module using the MQ-135. The MQ-135’s heater pins (H) are connected between the +5V (Vcc) line and the GND line via a 5.1W series current-limiting resistor. One end of the tin oxide sensing resistor (Rs) is connected to the +5V line via the two A pins, and the other end goes to the GND line via the two B pins and a 1kW load resistor. The two B pins are also connected to the A0 analog output pin, to allow the voltage across the load resistor to be sent to a DMM or an MCU’s ADC input. The rest of the components are so that the module can also be used as a simple gas level alarm. One half of the LM393 dual comparator (IC1b) compares the voltage across the 1kW load resistor with a reference voltage set using trimpot VR1, so whenever the A0 voltage rises slightly above the reference voltage, the output of IC1b (pin 7) drops to near ground level, causing the D0 LED to begin glowing. The voltage level at the D0 output pin is pulled down simultaneously. One change should ideally be made to the module if you want to use it with an MCU for monitoring the gas level, rather than simply using it as a gas level alarm. This involves replacing the sensor’s 1kW load resistor with a 22kW resistor, to give a higher output voltage swing and improve reading accuracy. This resistor is an M2012/0805size (2.0 x 1.2mm) SMD component, so you’ll need a fine-tipped soldering iron and either a magnifying glass or a microscope. Fig.3 shows how to hook it up to an Arduino Uno or a compatible MCU after making that change. You siliconchip.com.au just need to connect the module’s Vcc and GND pins to the corresponding pins on the Arduino, plus the module’s A0 pin to one of the Arduino’s ADC input pins; in this case, we’re using A2. There are quite a few Arduino libraries and sketches available to work with the MQ-135 module. You’ll find links to some of them in the list of links at the end of this article. However, I found many of them a bit tricky to negotiate. But I did find some very helpful information on Rob’s blog (at https:// blog.robberg.net/mq-135-arduino/). Then I came across an elementary sketch using no libraries, but just showing the current analog voltage provided at the module’s A0 pin (at https://arduinolearning.com/amp/ code). I adapted this sketch slightly, and its listing is replicated below along with some of the sample output from when this sketch is running. When I breathed on the MQ-135, that caused the voltage reading to rise from under 700 to about 728 before falling back down again. As you can see, there’s no attempt to convert the A0 voltage readings to equivalent gas levels – for that, you would need one of the fancier sketches relying on their dedicated libraries. The SGX Sensortech MiCS-5524 Another MOS sensor found in lowcost air/gas sensing modules is the MiCS-5524, made by SGX Sensortech (an Amphenol company) in Switzerland. This is much smaller than the MQ-135, coming in an SMD package measuring only 7 x 5 x 1.6mm. The MiCS-5524 detects CO, ethanol, hydrogen, ammonia and methane. It is used in an 18 x 13mm gas sensing module with the same name available from various internet suppliers, including Banggood, which currently has it priced at US$11.00 with free shipping (about $16). Fig.3: the connection diagram for the MQ-135 sensor module with an Arduino Uno or similar. MQ-135 Sketch Program void setup() { Serial.begin(9600); Serial.println(“Silicon Chip’s MQ-135 demo!”); } void loop() { int reading = analogRead(A2); Serial.println(reading); delay(1000); } Sample Output Silicon Chip’s MQ-135 demo! 696 694 694 691 692 710 June 2022  73 Fig.4: the circuit diagram for the MiCS-5524 module, which is simpler than the previous MQ-135 sensor and detects fewer gases. Next to the circuit are two different modules that use this chip. The circuit of the MiCS-5524 module is shown in Fig.4. It’s basically just the sensor itself with an 82W current limiting resistor for the sensor’s heater and a 91kW load resistor for its sensing resistor Rs, with a 100nF capacitor across the latter for noise reduction. P-channel Mosfet Q1 is so that the power to the sensor can be controlled using the module’s EN pin. This pin can be left floating if the module is to operate continuously. Fig.5 shows how easy it is to connect the MiCS-5524 module to an Arduino Uno, while the sketch is shown below with the sample output. The sketch is almost identical to the MQ-135 program and is similarly based on https:// arduinolearning.com/amp/code The SGX Sensortech MiCS-VZ-89TE SGX Sensortech also makes a fancier and slightly larger module (23 x 14mm) called the MiCS-VZ-89TE, available from suppliers like element14 for $24.65, including GST but not delivery. This module incorporates its own dedicated MCU with ADCs (analog to digital converters) and embedded conversion algorithms. As a result, this module can provide both PWM and I2C digital outputs for CO2 equivalent and TVOC (isobutylene equivalent). I couldn’t find any circuit diagram for the MiCS-VZ-89TE module, but its layout is shown in Fig.6. I found it fairly easy to connect to this module by using two 5-pin sections of SIL header strip, with the top of the second and fourth pins of each strip cut short, allowing the tops of the remaining three pins to be soldered to the notches on one side of the module. You can then plug the complete assembly into a small breadboard for testing and use. Fig.7 shows how the MiCS-VZ-89TE module can be connected to an Arduino Uno or equivalent MCU. The GND connection goes to one of the Arduino’s GND pins, while the module’s Fig.6: the layout diagram for the MiCS-VZ-89TE module, which is shown above. MiCS-5524 Sketch void setup() { Serial.begin(9600); Serial.println(“Silicon Chip’s MiCs-5524 demo!”); } void loop() { int reading = analogRead(A0); Serial.println(reading); delay(1000); } Sample Output Fig.5: MiCS-5524 connection diagram. Fig.7: MiCS-VZ-89TE connection diagram to an Arduino Uno. 74 Silicon Chip Silicon Chip’s MiCs-5524 demo! 40 39 40 39 siliconchip.com.au 3.3V power connection goes to the Arduino’s +3.3V pin. The module’s I2C connections SDA and SCL are wired to the Arduino’s pins A4/SDA and A5/SCL, respectively. Each of these pins needs an external 4.7kW pullup resistor connecting to the +3.3V pin, because the MiCS-VZ-89TE module doesn’t provide the pullups itself. I found an Arduino sketch and library to read the CO2 and VOC levels from a MiCS-VZ-89TE, written by H.Grabas and available on his website at https://github.com/HGrabas/MICSVZ-89TE This sketch and its library worked so well that I adapted it to produce the sketch listed below along with a sample of the output from the Arduino IDE Serial Monitor. For this to work, you need to download Mr Grabas’ library from his website and install it as a library in the Arduino IDE. When running, it gives you a VOC reading and a CO2 reading approximately once per second. I eventually breathed on the module’s sensor, causing the VOC readings to rise to around 270.4ppb (parts per billion), while the CO2 reading barely moved MiCS-VZ-89TE Sketch: #include <MICS-VZ-89TE.h> #include <Wire.h> MICS_VZ_89TE voc; void setup() { voc.begin(); Serial.begin(9600); Serial.println(“Reading the MiCS-VZ-89TE sensor”); } void loop() { voc.readSensor(); Serial.print(“VOC =”); Serial.print(voc.getVOC()); Serial.print(“ | ”); Serial.print(“CO2 = ”); Serial.println(voc. getCO2()); delay(1000); } from about 414 ppm (parts per million). Then I sprayed a tiny amount of isopropanol (spectacle cleaning fluid) a few centimetres above the sensor, causing the VOC reading to jump up to its maximum figure of 1000ppb. So the MiCS-VZ-89TE and the sketch and library certainly seem to be working! The ScioSense CCS811 Another MOS sensor found in several low-cost air/gas sensing modules is the CCS811, made by ScioSense BV in Eindhoven, The Netherlands. The CCS811 is in a tiny SMD package, measuring only 4 x 3 x 1.2mm. Despite this tiny size, it incorporates both an ADC and a dedicated MCU with built-in conversion algorithms, plus an I2C digital interface to link directly to a PC or an MCU like an Arduino or a Micromite. It’s described by ScioSense as an “ultralow power digital gas sensor” and detects a range of VOCs and provide both eTVOC (equivalent total VOC) and eCO2 (equivalent CO2) levels. Fig.8 is a block diagram of the CCS811. Pins 4 (PWM) and 5 (SENSE) must be connected together for correct operation of the MOX sensor’s heater control circuit. Pin 1 (ADDR) is to allow the CCS811’s I2C address to be set to either 90d/5Ah (ADDR pin low) or 91d/5Bh (ADDR pin high), while the AUX pin (8) has no internal connection. The CCS811 sensor is used in many air quality sensing modules, including the Keyestudio KS0457 CO2 Air Quality module, the Duinotech SENCCS811 Air Quality Sensor module (Jaycar Cat XC3782), the Adafruit CCS811 Air Quality Sensor and the CJMCU-811 CO2, Temperature and Humidity Sensor from Banggood. Fig.9 shows the circuit for many of these CCS811 sensor modules. Along with the CCS811 sensor itself, there’s voltage regulator REG1, which steps down the incoming +5V power to provide the 3.3V needed by the CCS811, plus Mosfets Q1 and Q2 which, together with four 10kW pullup resistors, perform logic level conversion for the I2C digital communication lines (SDA and SCL). Diodes D1 and D2, together with the two 100kW pullup resistors, allow the WAKE and RST pins of the CCS811 to be pulled low. The WAKE pin must be pulled to ground to allow the chip to operate. Note that pin 1 of the CCS811 is pulled low by a 100kW resistor to set the I2C address to 90d/5Ah. Also, as mentioned earlier, pins 4 and 5 are tied together and pulled high via two more 100kW resistors. Incidentally, some CCS811-based modules (such as the CJMCU-811) have an additional pin on the I/O connector, with the extra pin connected to pin 1 of the CCS811 and labelled “ADD”. This allows the I2C address of the module to be changed to 91d/5Bh by pulling the pin high. It’s quite easy to connect the SENCCS811 and most of the other CCS811based air quality modules to an MCU like an Arduino Uno, as shown in Fig.10. The Vcc and GND pins connect to the +5V and GND pins of the Arduino, while the SDA pin goes to the Arduino’s A4/SDA pin and the SCL pin to the Arduino’s A5/SCL pin. Finally, the module’s WAKE pin connects to another GND pin on the Arduino. Some modules have the pins in a different order, so make sure you check the connections for the module you are using. Fig.8: the block diagram for the CCS811 module. One type of this module is shown below, with a larger variant shown overleaf. Sample Output Reading the MiCS-VZ-89TE sensor VOC = 0.00 | CO2 = 413.97 VOC = 135.37 | CO2 = 413.97 VOC = 270.74 | CO2 = 413.97 VOC = 1000.00 | CO2 = 420.96 siliconchip.com.au Australia's electronics magazine June 2022  75 Fig.9: the circuit diagram for the CCS811 module. Several Arduino libraries are available to support a sketch communicating with these modules. I found the easiest one to use was the Keyestudio KS0457 library (CCS811.h and CCS811.cpp), available from https:// fs.keyestudio.com/KS0457 I also downloaded Keyestudio’s “readData.ino” sketch and adapted it to produce the sketch “read_CCS811_ data.ino”, which you can download from the Silicon Chip website. It’s a bit too long to reproduce the listing here. Shown at right is the output of that sketch. The Arduino provides a stream of measurements for both the eCO2 level in ppm and eVOC in ppb. At one point, I blew in the direction of the CCS811 sensor to give it some extra CO2. That’s the reason for the sudden rise in eCO2 and eTVOC readings, from around 400ppm and 1-2ppb up to peaks of 1743ppm and 384ppb a second later. Then the readings fell slowly after that. Summary After trying several of these modules, I’m less keen on those based on the MQ-135 sensor than on the Sensortech MiCS sensors or the ScioSense CCS811 sensor. That’s mainly because of the scarcity of easy-to-­understand software if you want to do more than simply ‘raise the alarm’ if the CO2/ VOC level rises above a preset ‘safe’ level. I’m also not that keen on modules based on the SGX Sensortech MiCS5524 sensor for much the same reason. 76 Silicon Chip Overall, I prefer the ‘smarter’ modules like the SGX Sensortech MiCSVZ-89TE or most of those using the CCS811 sensor. These modules are all much easier to get going with an MCU like an Arduino as a reliable CO2/VOC sensor. I would give first prize to the MiCS-VZ-89TE module (element14 2925865). But second prize would go to any of the modules based on the ScioSense CCS811 sensor, like the Duinotech SEN-CCS811 from Jaycar (Cat XC3782), the CJMCU-811 from Banggood (ID 1157216), the Keyestudio KS0457 or the Adafruit CCS811 (www.adafruit.com/product/3566). I will describe some of the NDIR and PAS type air quality sensor modules SC in a future article. Sample Output Getting data from the CCS811... eCO2: 400ppm, eTVOC: 0ppb eCO2: 410ppm, eTVOC: 1ppb eCO2: 414ppm, eTVOC: 2ppb eCO2: 1743ppm, eTVOC: 384ppb eCO2: 1345ppm, eTVOC: 143ppb eCO2: 977ppm, eTVOC: 87ppb Useful Links MQ-135: • www.arduinolibraries.info/ libraries/mq135 • https://github.com/ Phoenix1747/MQ-135 • siliconchip.com.au/link/abct • https://blog.robberg.net/ mq-135-arduino MiCS-5524: • www.sgxsensortech.com • siliconchip.com.au/link/abcu • https://github.com/HGrabas/ MiCS-VZ-89TE CCS811: • https://fs.keyestudio.com/ KS0457 • siliconchip.com.au/link/abcv Australia's electronics magazine Fig.10: CCS811 connection diagram. siliconchip.com.au Winter DEALS Build It Yourself Electronics Centres® Huge 2500W Pure Sine Wave Model. Runs coffee machines, toasters & hair dryers 2 year warranty SAVE $200 ESS. GET MORE. PAY L 999 $ across the range. Great deals in electronics M 8067 Power mains appliances on the road! Pure Sine Wave BlackMax Inverter - Ultimate in portable power. h. 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SAVE 20% Western Australia Build It Yourself Electronics Centres Sale Ends June 30th 2022 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd A quality servicing kit for high tech devices - including special bits for iPhone disassembly. Includes a variety of 4mm driver bits & a flexible extension. All in a neat self standing case. Adjustable 5x - 7x Magnifier Croc Clip Test Leads Super bright 3W LED with pop up lantern. 38pc Precision Driver Kit 30 $ X 0432A SAVE 24% Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2022. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ UPDAT Universal Battery Charge Controller ED We have made some changes to our Universal Battery Charge Controller published in December 2019 (siliconchip.au/Article/12159) so that it can be built using parts that are actually available. The changes are modest, and the total cost for parts has been reduced. By John Clarke nce upon a time, we at S C O lived in the land of plenty where electronic components were plentiilicon hip ful and readily available, blissfully unaware of future events that would alter our lives. But all that changed when the COVID-19 pandemic suddenly disrupted many markets and manufacturers. This affected the production of semiconductor devices and ICs and dramatically increased the demand for electronics. This has impacted the supply of motor vehicles, mobile phones and many white goods such as washing machines and refrigerators, amongst other items, all of which now depend on semiconductors. The resulting lack of semiconductor supply is also impacting our readers Fig.1: construction is much the same as before, except you can skip soldering the SMD IC (IC2) and a few associated capacitors. Instead, install the TO-92 transistor (Q4), two resistors and zener diode ZD3. These components are all in the upper right-hand corner. The rest of the PCB is identical to the original. siliconchip.com.au Australia's electronics magazine and us. We put considerable effort into maintaining parts supply for our projects via our Online Shop. But once they are sold, we may not be able to replenish the supply straight away, especially if someone buys up all our stock at once. Turning to the Universal Battery Charge Controller, we used one Si8751 isolated Mosfet driver IC in the circuit. While it was available when the article was first published, this is no longer the case, and we don’t expect these to be available for at least another year, if not longer. So we have come up with a new circuit that performs the function of the Si8751 in another way. Fortunately, the changes are straightforward. Our discrete Mosfet driver comprises small-signal NPN transistor Q4, a few resistors and zener diode ZD3. The N-channel Mosfet is replaced with a P-channel type. These changes are highlighted in a cyan box in the updated circuit diagram, Fig.2. The revised PCB, shown in Fig.1, is essentially identical to the original, except for the Mosfet and gate driver component changes. Also see the panel below outlining the changes in the parts required to build this project. These changes do not affect the operation of the Charge Controller as far as the user is concerned. Original design The original circuit using the Si8751 June 2022  81 Fig.2: the only changes in this circuit from the original on page 27 of the December 2019 issue are in the box at upper right. All the components there have been replaced; the N-channel Mosfet is now a P-channel type. This simplifies the driving scheme greatly; it is now an NPN transistor with a few resistors and a zener diode to limit the drive voltage and current to safe levels. (IC2) would drive the N-channel Mosfet gate (Q1) positive whenever the RB3 output of microcontroller IC1 was high, switching Q1 on. This allowed current to flow from the charger to the battery. When the RB3 output went low, Q1’s gate voltage dropped to its source voltage, so the Mosfet was off, and no current flowed to the battery. The Mosfet switch on-time with this arrangement was 5ms and the switch-off time was typically 15μs. 82 Silicon Chip Fast switching was not required in this application, as we’re only switching the Mosfet on and off once every two seconds. The main reason for using this specialised driver (IC2) was that, with Q1 being an N-channel type and its source connected to the battery, it needed a gate voltage of around 20V to switch on. This is not present anywhere in the circuit; it was generated by stacking the isolated power output of IC2 Australia's electronics magazine on top of the battery voltage. Revised Mosfet driver With the revised Mosfet driver circuit, the RB3 output signal from IC1 still controls the Mosfet on and off periods. The Mosfet is now a P-channel type, so the higher voltage is unnecessary. It is switched on by pulling its gate voltage below the charger output voltage, which connects to its source terminal. siliconchip.com.au Switching from an N-channel type to a P-channel type means we have to swap the drain (D) and source (S) terminal connections. That is so that the parasitic internal diode is still facing in the right direction to block current flow to the battery when the channel is not conducting. Now, when the RB3 output is low, transistor Q4 is off and the gate of Mosfet Q1 is held at its source voltage via the 47kW resistor. The Mosfet is therefore off. When the RB3 output goes high, transistor Q4 is switched on via base current through the 10kW resistor. The transistor conducts, and the gate of Q1 is pulled toward the ground via a 4.7kW resistor. The 47kW resistor between the source and gate forms a voltage divider with the 4.7kW pull-down resistor, but since its value is ten times higher than the 4.7kW resistor, the gate is pulled near to ground. Zener diode ZD3 is included to limit the gate to source voltage to 13V to prevent damage to the Mosfet, as it has a gate-source voltage limit of -16V. The switch-on time for the Mosfet is much faster than before, less than 27μs, and the switch-off time is under 270μs (it’s higher because the pull-up resistor value is ten times high than the pull-down resistor). So the switch-on is much faster than with the Si8751, but the switch-off period is a bit longer. Still, as mentioned earlier, the switching time does not need to be particularly fast for our circuit. Part of the reason we have been able to simplify the driving arrangement is that we can now supply high-­current P-channel Mosfets at a reasonable price (see the revised parts list). Traditionally, they have been harder to get and more expensive than equivalent N-channel types. Construction There is very little difference in construction between the original and revised PCBs. Refer to Fig.1 and simply fit the new components in the upper right-hand corner as shown. The Mosfet mounting is identical. As a bonus, this change eliminates the only SMD component in the design, the Si8751 (IC2). Testing, setting up and using the charger are identical to the original and are described in the original article (siliconchip.au/Article/12159). SC siliconchip.com.au Parts List – Updated Battery Charge Controller 1 double-sided PCB, code 14107192, 111 x 81mm 1 diecast aluminium box, 119 x 94 x 34mm [Jaycar HB5067] 1 2A DPDT 5V coil telecom relay (RLY1) [Altronics S4128B] 1 PCB-mount SPDT momentary pubutton switch (S1) [Jaycar SP0380, Altronics S1498] 1 pushbutton switch cap for S1 [Jaycar SP0596, Altronics S1482] 1 SPST micro tactile switch with 0.7mm actuator (S2) [Jaycar SP0600, Altronics S1122] 1 PCB-mount 3.5mm stereo switched socket (CON1) [Jaycar PS0133, Altronics P0092] 2 PCB-mount M205 fuse clips (F1) 1 10A M205 fuse (F1) 2 NTC thermistors (10kW at 25°C) (TH1 and external thermistor) 1 2-way header with 2.54mm spacing (JP1) 2 3-way headers with 2.54mm spacing (JP2, JP3) 3 jumper plugs/shorting blocks (JP1-JP3) 1 18-pin DIL IC socket (for IC1) 1 3.5mm stereo jack plug 1 TO-220 silicone insulating washer and mounting bush (for Q1) 4 6.3mm-long M3 tapped spacers 3 M4 x 10mm machine screws 3 M4 star washers 3 M4 hex nuts 2 M3 x 10mm machine screws 8 M3 x 5mm machine screws 2 M3 hex nuts 4 insulated crimp eyelets (wire size 4mm, eyelet for M4 screw) 2 cable glands for 4-8mm diameter cable 1 2m length of 15A figure-8 automotive cable 1 1m length of twin-core shielded cable (for thermistor) 1 20mm length of 6mm diameter heatshrink tubing 2 large insulated battery terminal alligator clips (red and black) 6 PC stakes (optional) 4 small adhesive rubber feet Semiconductors 1 PIC16F88-I/P micro programmed with 1410719A.HEX (IC1) 1 LM317T 1.5A adjustable positive regulator (REG1) 1 IPP80P03P4L-07 P-channel Mosfet (Q1) [Silicon Chip SC6043] 2 BC337 NPN transistors (Q2, Q3) 1 BC547 or BC337 NPN transistor (Q4) 3 green 3mm LEDs (LED1, LED5, LED6) 2 orange 3mm LEDs (LED2, LED4) 1 red 3mm LED (LED3) 2 18V 1W zener diodes (ZD1, ZD2) 1 13V 1W zener diode (ZD3) 3 1N4004 1A diodes (D1-D3) Capacitors 1 220µF 50V PC electrolytic 1 100µF 16V PC electrolytic 3 100nF MKT polyester 5 10nF MKT polyester Resistors (all 1/4W, 1% metal film unless otherwise stated) 1 51kW 1 47kW W 4 10kW W 1 4.7kW W 1 3.3kW 1 2kW 7 1kW 1 330W 1 120W 1 100W 1W, 5% 1 56W 4 10kW multi-turn top adjust trimpots, 3296W style (VR1-VR4) (code 103) 1 100W multi-turn top adjust trimpot, 3296W style (VR5) (code 101) Items in bold have been changed or added Australia's electronics magazine June 2022  83 Altium Designer 22 Review by Tim Blythman We use Altium Designer to design all our project PCBs and have done so for many years. New versions and updates are released regularly, with new releases coming yearly for some time now. Therefore, 2022 sees the release of Altium Designer 22, and we installed it immediately to see what new features are available. Y ou might not think that there is much need for PCB software to change. While it is true that some people continue to use older versions of Altium Designer, there are good reasons to stay up to date, as improvements and new features appear with each version. Altium Designer 20 (reviewed December 2019; siliconchip.com.au/ Article/12176) was a significant milestone. There were substantial improvements from Altium Designer 19 for users, such as the Schematic Editor being completely rewritten to make it quite a bit faster. In fact, the entire suite was rewritten, with numerous features and enhancements. Notably, the new software base allowed integration with the then-upcoming Altium 365 ‘cloud’ software. We reviewed Altium 365 and Altium Designer 21 in January 2021 (siliconchip.com.au/Article/14705). Altium 365 is an online platform to allow shared access to projects and libraries and includes a version control system. We weren’t sure that our small team at Silicon Chip would use this sort of feature, but it has been a handy tool, especially with work-from-home now being common. In particular, we have found it a great way to keep our component libraries consistent and up to date. We expect that it is even more helpful for larger workplaces. Even through 2021 and after the release of Altium Designer 21, they brought out multiple updates and minor releases, so some of the features we mention here might have been seen in previous updates. It’s also worth noting that Altium provides numerous training and development webinars to ensure that its users are making the most of the software. For those readers who do not have an Altium subscription, it’s possible to use some of the online features of Altium365 by simply visiting the web page at www.altium.com/viewer/ The YouTube channel “Altium Academy” (www.youtube.com/c/ AltiumAcademy) is another good way to get a glimpse at Altium Designer and pick up some PCB design tips too. Altium Designer 22 Screen 1: here’s where you’ll find the setting to enable Automatic Cross References at the bottom of the Options tab (highlighted in yellow). The dialog window can be easily be reached by right-clicking on a sheet and selecting “Sheet Actions → Automatic Cross Reference Settings”. 84 Silicon Chip Australia's electronics magazine Altium Designer 22 was released in February and was followed closely by the Altium Roadshow, an online event that consisted of a series of technical sessions over two days. Importantly, siliconchip.com.au this included a guided overview of Altium Designer 22’s new features. We always find the Roadshow to be a great way to learn the best way to use Altium Designer and stay up to date with the newest features. We’re currently using Altium Designer version 22.2.1, the most recent release available at the time of the Roadshow. You might find some changes or improvements if you install a later version. Schematic Editor One feature that was added to the Schematic Editor in Altium Designer 22 appears minor. Still, we think it is quite handy and indicates the broad range of incremental improvements Altium provides. This is the Automatic Sheet Cross Referencing setting. You can enable it with a right-click on a schematic, then “Sheet Actions → Automatic Cross Reference” settings, as shown in Screen 1. When Automatic Cross References are enabled, references are shown on the schematic as seen in Screen 2. Note the grid coordinates on the sheet (3B and 3C) identifying the location within the target sheet. A right-click on the reference allows the reference to be followed like a hyperlink. Exporting such a schematic sheet as a PDF will include the cross-references as hyperlinks, allowing signals to be followed throughout the design, even if they aren’t on the same sheet. As it can be pretty frustrating trying to track signals otherwise when using ports, this is a powerful feature. They do tend to clutter the schematic a bit during the design stage, but it was handy to turn this setting on during the later verification stages to simplify broad checking of the design and also when PDFs are generated. PCB counterholes The PCB editor now allows counterholes to be added to a pad or hole. A counterhole is a machining process that does not extend through the full depth of the PCB laminate. A typical example would be a countersunk hole to allow a countersunk screw to be recessed into the laminate. The remaining laminate allows the board to be secured by the screw, but the recess means that the head of the screw does not protrude as much. As well as countersunk holes, which have an angled wall, counterbores siliconchip.com.au Screen 2: the automatically-generated Cross References include the sheet name and a grid reference that indicates the X/Y location of the object on that sheet. The Port Actions menu option also provides selections to jump to the location of any of the Cross References. Screen 3: counterhole settings are found under Pad properties in the Pad Features section. Here, a 90° countersunk hole is specified (45° per side), with the adjacent 3D view showing what it would look like. Screen 4: the same countersunk hole in the Draftsman view shows several dimensional callouts. You can place just about any linear, angular or diameter dimension on any part with such properties, so it is not limited to counterholes. with straight sides can be added to pads or holes on the PCB. Of course, the ability to implement such features will depend on your board manufacturer’s capabilities. Countersinks have the advantage that the bevel of the screw against the hole will positively locate the PCB at its mounting point. However, that may not always be required, especially if movement is expected or needs to be accounted for. Counterbores allow simple panhead screws to be recessed, among other jobs. When the design is exported, it will Australia's electronics magazine create separate files for counterholes on the top and bottom of the board. Screen 3 shows the appearance of a 90° (45° slope on each side) countersunk hole in the 3D view and its corresponding size and angle properties adjacent in the Pad Features section. A counterbore has a diameter (size) and depth properties. Screen 4 shows the same countersunk hole in a Draftsman view. This view was quickly and easily created by adding a new counterhole view to a Draftsman document and then adding some diametrical, linear and angular measurements. June 2022  85 IPC 4761 Screen 5: IPC 4761 Via Types can be found under Via Properties; a drop-down menu lists the types available according to the standard. These types can also be set as templates. Screen 6: an IPC 4761 Type 1A via on a four-layer PCB is shown here in the Draftsman view. This makes it clear that it consists of a simple solder mask on the top side of the PCB. Other types have different degrees of filling, plugging and covering. IPC 4761 is a standard created by the IPC (founded as the Institute for Printed Circuits) regarding the protection of vias (connections through the PCB) on printed circuit boards. Without delving too deeply into the specifics of the standard, it specifies seven different levels of treatment that can be applied to a via to protect it and the PCB. We alluded to the tenting of vias in our review of Altium Designer 20. This involves covering the bare metal of the via with a plastic solder mask layer. That is equivalent to the lowest (Type I and Type II) of the seven levels covered by the IPC 4761 standard. Other levels include various coverings and degrees of plugging (to cover or fully seal the hole left by the via). These may be needed to protect the vias from contact, moisture, corrosion or even to ensure that there are no holes to allow anything to pass through the PCB. Many specialised designs demand higher levels of protection than what our readers and we generally require. For example, boards that operate in very humid environments and with rapid temperature changes could be subject to condensation, and vias are often the first parts of a board to corrode away. So Altium Designer 22 now allows the IPC standard types to be directly chosen from a Via Types & Features section of the via properties. This is shown in Screen 5, a menu that lists the IPC 4761 types with a brief description of each. Those types with an “a” suffix have the treatment applied to one side only (it appears to be the top side), while the “b” suffixes have the covering applied to both sides of the via. The various types can also be chosen as via templates to streamline via placement. You can also add via layout views to a Draftsman document, as seen in Screen 6. The upshot of all this is that the design intent can be better communicated to the PCB manufacturer, and more consistent results can be achieved. PCB design Screen 7: Gloss and Retrace settings now have their own panel, which can be opened from the Panels button. This makes it simple to quickly adjust these settings while tweaking the final location of the PCB tracks. Other improvements to the PCB editor include more flexibility in the Pad properties editor when using top-­ middle-bottom or full-stack views. Each layer now has its own options Australia's electronics magazine siliconchip.com.au 86 Silicon Chip relating to things like corner radius and thermal relief, and they can now be set for each individual layer. A Gloss and Retrace panel has been added (accessible from the Panels button) to allow finer control of the options that are used for the “Route → Gloss Selected” and “Route → Retrace Selected” actions. The panel can be seen in Screen 7. (Glossing is where the routing of the track is automatically ‘fixed up’ to be as clean and direct as possible.) Bringing up this panel allows the glossing and retracing settings to be tweaked interactively as the track layout is finalised. There is also a new routing algorithm that now prevents loops from forming if a trace is brought back on itself. They also added design rules for SMD pad entry location and angle, which make it easier to produce neat designs by keeping SMD pads consistent. Since these are usually not critical criteria, there is also the option to disable the rules if they cannot be met. Screen 8: the Mixed Simulation extension is not installed by default, but can be added from the Extensions and Updates tab of the License Management page. As you would guess, it lets you simulate the circuit represented by your schematic, so you can get an idea of whether it will work before you build it. Screen 9: the Simulation Dashboard is a panel accessible from the Panels button and is actually a ‘wizard’ as it works through the steps necessary to complete a simulation. As well as defining a circuit, you might need to add voltage source(s) to provide simulated power or signals to that circuit. Mixed simulations The simulation extension, accessed directly from the Schematic Editor, is not new. But it was a point of interest during the Altium Roadshow event as this feature has had some upgrades. If you have not seen the simulation feature before, that might be because it is not installed by default. It can be installed from the Extensions and Updates tab of the License Management page, as seen in Screen 8. Altium Designer might need to be restarted after installation. The Mixed Simulations extension is based on the well-known SPICE program (“Simulation Program with Integrated Circuit Emphasis”). We mentioned in our previous review that Altium Designer 21 added a Simulation Dashboard, while Altium Designer 22 adds measurements and plots of many intrinsic and inferred circuit properties. You can open the Simulation dashboard from the Panels button. Apart from your schematic, you may need to add some voltage or current sources; these can be found under the “Simulate → Place sources” menu item. As you can see from the dashboard shown in Screen 9, Altium Designer leads you through the steps needed to complete the simulation. You might siliconchip.com.au expect that the simulation models will be missing unless you have them in your libraries, but Altium Designer includes many inbuilt models that can be used. Of course, the usefulness of these models will depend on how closely they match the parts you’re using in your design. But, at the very least, the included models for resistors, capacitors and inductors will be usable. Summary We have some complicated multiboard projects coming up, so the schematic cross-referencing feature has Australia's electronics magazine come in very handy while checking these designs. It appears that counterholes are not yet widely available amongst PCB manufacturers. But we can see that being a handy feature as it becomes more accessible. For example, designs that use a PCB as a lid on a Jiffy box can be streamlined and improved by using a counterhole to recess the screws that secure the lid. A good number of new and handy features have appeared in Altium Designer 22, making it well worth the time to install the latest version and remain up to date. SC June 2022  87 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. RF burst power meter The circuit presented here enables reasonably accurate and repeatable RF burst transmission and continuous wave power measurements with a simple and low-cost circuit. Although far simpler than the Silicon Chip Low Cost Wide Band Digital RF Power Meter (August 2020; siliconchip.com. au/Article/14542), it has a large analog display and can make burst measurements. The circuit has two novel features: it uses a servo to provide the readout with a dial of any size, and the burst measurement function, implemented as a peak-hold. The peak-hold function is enabled by a mode switch. It was designed to measure the transmit power of 2.4GHz WiFi AP beacons (peak envelope power) and was also tested with other burst transmissions formats and in different bands, eg, proprietary frequency-hopping protocols in the 2.4GHz and 910MHz ISM bands. The implementation is straightforward, consisting of a PICAXE-08M2 microcontroller (eg, Altronics Cat Z6111A) and a miniature servo motor (eg, Altronics Cat Z6392 or Jaycar Cat YM2758). The AD8318 module cost about $18 from AliExpress and came with a metal shield around the AD8318 and input components. 88 Silicon Chip You could likely use any AD8318based module, but it’s worth checking that they do not have a low-pass filter capacitor fitted (CLPF) on pin 5 (if they do, remove it). The benefit of using a servo as a display is the ability to calibrate the meter scale regardless of linearity changes over the dynamic range of the AD8318. For enhanced accuracy, multiple scales for different frequency bands could also be made. The drawback of an analog display is the resolution. I built the meter by attaching a pointer to the servo motor over a calibrated dial scale. Calibration was performed by temporarily attaching a sheet of paper to the meter face and using a pen to mark measured points around the dial at the frequency of interest. Multiple frequency arcs can be calibrated on one scale, mitigating frequency response issues; eg, you could have 2.4GHz and 910MHz scales. After that, I removed the paper and scanned it, then loaded it into a drawing software package. I then redrew the dial scale using the measured markers in appropriate arcs. I extrapolated intermediate points between the measured marks. I then printed the new dial and fitted it to the servo. Australia's electronics magazine The resolution is approximately 0.3dB per servo step. This calculation is described in the source code. As an example, with a large 80mm pointer attached to the servo, the dial scale will have approximately 4mm between 1dB increments over a range of about 60dB. I made another version using a Holden speedometer stepper motor and pointer, with code changes to suit. The BASIC source code for the PICAXE is in a file named “rf-servo_ v1.bas” that can be downloaded from siliconchip.com.au/Shop/6/6479 George Mackiewicz, Vermont, Vic. ($100) siliconchip.com.au Artificial candle is ‘ignited’ by a real flame This 3D-printed artificial candle is not turned on using a switch; instead, it is ignited using the flame of a real matchstick or lighter, just like an ordinary candle. When a flame is brought near the tip of the artificial candle, the LED bulbs magically light up. They also flicker like a real candle. The trick here is simple: a hidden flame sensor is installed at the top of the candle. This signals an Arduino Nano board inside the candle to turn on the LEDs. It uses two yellow LEDs and one red LED to produce the flickering effect. They are switched off in a pattern, one after another, to create the flickering effect. These features make our artificial candle look almost real. It is powered by a small 3V coin cell for portability. I've also added a small slide switch at the bottom of the candle to switch it off. The plan is to eliminate this in a future version of this project where you can blow on it to turn it off! But until then, it has to be manually switched off. Note that a few slightly different IR flame sensor modules are available, but they all work similarly. If using another type, check the pinout and adjust the wiring as necessary. The body of the candle is 3D printed. I designed the model in Tinkercad. It siliconchip.com.au comprises four main pieces: the cylinder, base, top and flame cover. The main cylinder is hollow, and it houses all the electronics. The top and bottom pieces are designed to be a snapfit onto the main cylinder. The bottom piece has a small rectangular opening for the USB port of the Arduino Nano board. There are four small holes in the top part: three for the LEDs and one for the flame sensor's IR diode. The flame cover acts as a cap and diffuses the light from the three LEDs. It needs to be printed in white plastic, and it has very thin walls so that it is translucent. You can download all the 3D printing files from www.tinkercad. com/things/4iuOdy6Wpmp After printing these pieces, insert the LEDs in the central holes in the top piece in no particular order. Also insert the flame sensor's IR diode halfway through the remaining outer hole, then fix the module to the underside using hot melt glue, silicone or another adhesive. You can now connect the wires from the LEDs and the flame sensor to the Arduino Nano board, then wire up the button cell via the slide switch. Insert the circuitry into the candle body, then push the top piece onto the main cylinder. Australia's electronics magazine The bottom piece has a small rectangular opening to accommodate the small slider of our mini DPDT power switch. Insert the slide switch from the inside of the bottom part, aligning it such that the slider can properly be moved from the outside, then fix it in place using hot glue/silicone etc. Once that’s solid, push the bottom piece into the main cylinder. Add the flame cover to the top, and the candle is ready for programming. The Arduino sketch required is relatively short, but we don’t have space for it here, so download the file “Artificial candle.ino” from siliconchip.com. au/Shop/6/6478 Fire up the Arduino IDE, open this file, select the Nano board from the menu and set up your COM port, then choose Upload. Check that you get a success message in the window at the bottom of the IDE. Ensure the slide switch is on, then bring a flame near the top of the candle and check that it switches on and then flickers. When finished, switch off the slide switch in the base. You can use the same principle to light up any other shaped lamp. You could also use different coloured LEDs in the candle to get different effects. Aarav Garg, Hyderabad, India. ($120) June 2022  89 Digital volume control using discrete logic This circuit is based upon a submission from Raj. K. Gorkhali from Nepal. It expands on his concept, providing 16 steps of logarithmic attenuation, a power-up preloaded attenuation setting and end stops for the volume control. The analog switches are low distortion types and op amp buffering is included for the attenuator. The volume is controlled via up and down switches S1 & S2. These connect to the reset inputs of 555 timers IC1 & IC2. Their reset inputs are typically 90 Silicon Chip held low by a 1kW resistor, keeping the timers in reset with their pin 3 outputs low. When the associated switch is pressed, the reset input goes high, and the pin 3 output immediately goes high (near 5V). Oscillation starts with the pin 3 output staying high for around 700ms, until the 10µF capacitor at pins 2 and 6 charges via the 100kW resistor to the upper threshold. The upper threshold is detected at pin 6; then the pin 3 output goes low for around 700ms as the capacitor is discharged to the Australia's electronics magazine lower threshold detected at pin 2. The process repeats with pin 3 going high again. When the switch is released, the pin 3 output immediately goes low. The 555 timers allow the volume level to change immediately when the switch is pressed and continue to change if the button is held down. The signal from output pin 3 of IC1 goes through two 2-input NAND gates (IC3c and IC3d). The first gate has its pin 8 input connected to the borrow output of a 4-bit binary up/ siliconchip.com.au down counter, IC4. The borrow output at pin 13 is usually high, so the pin 3 voltage level from IC1 is inverted by IC3c and then inverted again by IC3d. This causes the counter to decrement on the initial press of S1. If the counter’s output at Q0-Q3 reaches 0000, the borrow output goes low, forcing the IC3c output high and hence IC3d’s output goes low, preventing further decrementing. This is the negative ‘end stop’ which prevents the volume from jumping from maximum volume to minimum. A similar operation occurs with IC2 and NAND gates IC3a and IC3b. The difference is that the counter is incremented instead of decremented, and stops when outputs Q0-Q3 reach (1111) or minimum volume. Note that the counter counts down to increase volume and counts up to decrease volume. That’s because maximum volume (minimum attenuation) occurs when Q0-Q3 are all low. IC4 includes a preload feature, where the Q0 to Q3 outputs can be set to a particular value during power-up. Jumper links JP1-JP4 set the power-up volume level. If no jumpers are inserted, the preload inputs at P0 to P3 are all held high via 10kW resistors and the unit is at minimum volume (maximum attenuation). To determine the initial attenuation setting, take the binary number formed by jumpers JP1-JP4 (with a shorting block being 0 and open-circuit being 1), convert it to decimal and multiply it by three. This is the initial attenuation in dB. For example, with JP1 & JP3 in and JP2 & JP4 out, the binary number is 0101, five in decimal, and times three gives 15dB attenuation. Volume control The audio signal is applied to a buffer circuit (IC5a for the left channel) operating as a unity-gain amplifier. The op amp needs ±5V supplies which can be obtained from existing supplies in a preamplifier. Regulators may be required to reduce the voltages (eg, 7805 and 7905 types). The TL072 type op amps shown can handle signals up to about 2.5V RMS before clipping with such a supply. If you use rail-to-rail op amps instead, that would allow for signals up to about 3.5V RMS. You could also consider using lower distortion op amps. Do not use a higher supply voltage siliconchip.com.au since the following analog switches may be overdriven. The output from IC3 is applied to a 16-level attenuator controlled by the Q0-Q3 binary outputs from IC4. The attenuation is logarithmic, and we have set the range to be from zero attenuation down to 45dB attenuation in 3db steps. There are four attenuation stages. The first stage provides 24dB attenuation, the second stage, 12db, the third stage 6dB and the final stage, 3dB attenuation. With various combinations of these attenuators, we can obtain 16 steps. Each attenuator comprises two or three resistors and a changeover switch. With the switch in the ‘NO’ position, it completes a resistive divider from the preceding stage to ground, with the attenuated signal appearing at the resistor junction feeding into the next stage. With the switch in the ‘NC’ position, the divider is disconnected, and the upper resistor(s) are ‘shorted out’, so the stage has no attenuation. Calculating the required resistor values is done assuming that the source impedance is zero for the first stage, which is reasonable as it is from an op amp output. The second stage calculation is for 12dB attenuation, and the source impedance is now 25kW (due to the 25kW output impedance of the first stage). The stage output impedance also 25kW. The following stages are calculated using the 25kW input and output impedance values. The output from the attenuators is applied to another op amp buffer, IC5b. The attenuator switches are TS5A22362 dual-channel SPDT analog switches. These are interesting because not only are they very low resistance switches (0.65W typical), with low distortion (below 0.0041% at 1kHz) but also the signal can be below the supply rails for the switch. So while we run each switch IC from a 0-5V supply, the applied signal can be up to -5V without causing extra distortion. If you plan to use a different analog switch, make sure the supplies (and control voltage) for the switch are suitable. John Clarke, Silicon Chip. Original concept: Raj. K. Gorkhali, Nepal. ($75) Australia's electronics magazine An easy way to measure SMDs Here is an idea inspired by the SMD Test Tweezers project (October 2021; siliconchip.com.au/Article/15057). When using fat leads from a multimeter or similar to test small individual SMD components, they have a habit of acting like a circus flea and jumping out of sight, never to be found again. To solve this, I added a thin copper film recovered from an SMPS transformer to the teeth of a cheap set of callipers (which should be made from an insulating material) and secured the test leads to the copper. I used super glue to hold the film to the callipers. The smallest SMD component can be firmly captured and restrained from escaping. I modified a second calliper with longer leads to connect to a multimeter for holding and measuring resistors. Michael Harvey, Albury, NSW. ($60) June 2022  91 SERVICEMAN’S LOG Ion with the wind Dave Thompson Servicing can be a strange industry. These days, much of what comes through the door is not designed to be repaired. You can imagine how that makes the job a bit of a challenge! I understand that companies want to protect their designs. Still, if someone wants to clone a product, unless it uses cutting-edge technology, they can do it without too much difficulty. Making devices unrepairable usually has the most significant impact on the customer – someone that the company making the goods probably should want to keep happy! Someone, somewhere, always has the wherewithal, resources and ability to ‘deconstruct’ or ‘reverse engineer’ something to find out how it works. If the mood or the promise of commercial gain takes them, they will replicate it and sell it, likely at a lower price. Many countries’ economies are seemingly reliant on copying the ‘intellectual property’ of others. Some of these ‘clone jobs’ are so shameless that they replicate the external appearance of the original product, down to the shape, the colours and even the font. They just replace the original company’s name with their own and sell it for a fraction of the price! I think this is a basic human instinct, illustrated by the fact that I (like many others who would be reading this column) pulled many things apart when I was a wee fella to see what made them tick. Dad had to put most of them back together – that is, until I could do it myself. My first guitar builds were attempts at making copies of existing models as I tried to make an instrument I could afford, hopefully as good (if not better) than those available for what were, to me at the time, vast amounts of money. Whatever the motivation behind copying others’ work, it still happens a lot today. That said, finding an epoxy resin-potted ‘module’ in a commercial unit may have another more practical explanation than obfuscation. Ionisers are positively great Recently, a client brought in a device I’ve not seen for many years; a commercially-produced air purifier/ioniser. These devices were all the rage as far back as the 60s and 70s, in a jet-age, sci-fi sort of way, and were the ‘go-to’ gadget for a while. They were also popular as a project in magazines back then. It got me, too; the subject of purifying air using electronics fascinated me. The result was that I built many negative ion generators over the years, with varying success. However, that didn’t mean all was well in the state of negative ion generators. There have been hundreds of studies showing that negative ions have no real benefit to people or pets, while a similar number of studies have proven that they are beneficial. 92 Silicon Chip Some took them so seriously that hospitals utilised them as part of their air-conditioning systems to minimise or neutralise airborne infections. The recent pandemics (SARS, COVID etc) have resulted in a considerable boost in air ioniser sales. As is typical these days, ‘mileage’ varies with any ‘health’ product. If using one makes one feel better, why not use it? Regardless of the health and well-being implications, making and setting them up is fun and educational. That (for me) makes up for any of the controversies. Many commercial variants are still sold today for use in the health and horticulture industries. The premise of these devices is simple: apply a high voltage to an array of sharp metal “emitters”, and a corona or ion wind will stream from those points. Many airborne pollutants are electrostatically charged by this wind and are attracted to a nearby ground. So the theory of air purification by negative ions is sound. I have seen this for myself; I built several ionisers in the early 1980s for a friend who had a small greenhouse/ hydroponic setup for producing cabbages and cauliflowers. This guy wanted to improve the air quality in his setup, and when he heard me going on (as was my wont) about this new-fangled method I’d been reading about, he was keen to bankroll a couple to see how it worked for him. I scaled up a project from an American magazine and set them up in his greenhouse. They sat on a large baking-tray type metal plate that was Earthed through the mains, and sandwiched between that and the ioniser was a sheet of white paper. After just two days, that paper was turning grey, and when the ioniser was moved, there was a stark white outline where it had been sitting. That proof was good enough for me. Those ionisers ran for the next 15 years until the guy moved, and I was sold on the idea. The last one I built was for a person here who suffers from a seasonal complaint we call “Nor’ West Syndrome”. We get a very hot, dry, gusty wind during the spring and summer months, prevailing from the northwest. It is loaded with pollens and dust picked up by roaring over the nearby Canterbury Plains. As it blasts through Christchurch, it dumps that pollen in buildings, on the ground and anywhere the air reaches. It looks like yellow, granular dust and is sometimes everywhere. Those with hay fever or any sensitivity to pollen or dust can have serious health impacts due to this phenomenon. When this person complained to me about it, I suggested an ioniser might be the answer, especially if set up near Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • Ion with the wind A nomadic TV antenna Repairing a microswitch in a washing machine 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 their bed. I initially built one ion generator for them, then another for their home office; they swear by their use now. Unrepairable but not unbreakable The one that came into the workshop recently is a commercial unit, made in China, and is quite small compared to others I’ve encountered. It runs from a 9V battery and is designed to sit on a bedside table or similar. After determining the battery was good, the only real option was to pull it apart and have a look. There were no screws; it was clipped together, so I got the client’s permission to (literally) crack it open. Inside was a solid mass of black potting compound. There was absolutely nothing I could do with it repairwise. Many such devices are potted like this inside, not to mask the circuitry (although that might be a useful byproduct) but more likely to prevent corona bleeding or arcing between all the components that are in very close proximity. Most of these devices work the same way, though there are different lines of thought regarding the power input. Some apply a relatively low DC voltage (usually from a plugpack supply), via a simple switching circuit, to the primary of a transformer. The stepped-up transformer output then goes through a voltage multiplier circuit. The resulting HV output terminates at the pin array, though sometimes it can just be a single-pointed electrode/antenna. The other method is to use mains power directly into the multiplier circuit, sans transformer (although some use a 1:1 transformer for isolation). But I doubt that is legal here; the whole circuit would run at mains potential; perhaps another good reason to pot everything solid! The output voltage (around -3kV to -10kV depending on the circuit) is safe for anyone touching it (the output pins may be accessible through holes in the case), yet it’s high enough to cause an ion wind to stream from the points. This wind can usually be felt by placing a (wet) finger close to the emitter array, but note that some ionisers employ a fan to fudge/boost the ion output. You might think getting too close to the pins could be dangerous; sometimes, a tiny, weak arc to a fingertip may be visible in very low light. But a line of high-value resistors in series with the HV feed to the pin array limits the available current to a safe level. The idea is that the negative ions from the emitter pins charge any muck in the air, and this finds its way to the nearest ground. Most commercial units don’t come with a ground plane to sit on, or a handy connection to add one, siliconchip.com.au so we can only assume the particles find something else grounded enough to be attracted to. Also, some of these commercial devices are tiny, about the size of a small mobile phone, so it is hard to see how they can be as effective as those boasting a decent-sized pin array. Either way, this device wasn’t running, and there was nothing I could do. They are pretty cheap to purchase off the internet, so I wasn’t sure this would be a feasible job anyway. I talked to the client about it (good communication is essential to a serviceman). In the end, they commissioned me to make one of the models I’d produced before (and likely harped on a bit too much about!). Do it yourself! While not overly complex in the models I build, the actual electronics involved are pretty interesting from a theoretical point of view and are good fodder for the home experimenter. Anyone who likes watching big arcs and making circuits with the potential (!) for lots of high-voltage experimentation can use a very similar layout to power up the likes of Tesla coils and Jacob’s Ladders. The main difference with this circuit is that we want to keep arcs out of the equation as much as we can and feed all that juicy HV energy to the pin array. If we get a flashover at any of the connections on the multiplier, not only do we create a fire and shock hazard, we lose any semblance of decent ion emission at the output. The circuit I use consists of three sections: a driver/ oscillator section, a multiplier/output section and the pin array. Each section has its own circuit board. Anyone familiar with such things would recognise a Cockroft-Walton arrangement of high-voltage capacitors and diodes in a characteristic criss-cross ladder outlay. This is actually a line of half-wave rectifiers connected in series, with each stage boosting the previous stage’s output ever higher. Theoretically, you can just keep adding stages. As long as your components can handle the resulting voltage (and the spacing between components and stages is enough to prevent arcing between them), Australia's electronics magazine June 2022  93 you can get some seriously high voltages out of such a setup. Practically though, it’s a different story. One significant consideration is what to assemble these components on. I could use veroboard or perf-board, but I’d spend most of my time stripping tracks and arc-­proofing it. A better option is to use a printed circuit board with the correct spacing already worked out. Fortunately, because I throw nothing away, I have a spare set of boards from the run of ionisers I made back in the day. These are very much home-made, meat and potatoes PCBs, not like the multi-layer works of art we see today, but they still look good and do the job, which is all I want from them. The driver board boasts a board-mounted barrel jack for DC input (typically from a 9-15V plugpack) powering a 555 timer configured to run as an astable multivibrator that, in turn, drives two NPN power transistors in a pushpull configuration. The relatively square-wave output from the transistors switches current through the primary of a custom-wound transformer. A few other ancillary components ensure everything runs as it should. The secondary of the transformer runs off to the multiplier board. If this sounds familiar to some readers, that is because the April 1981 issue of Electronics Today International (ETI) (which we offer scans for siliconchip.com.au/ Shop/17) featured a very similar circuit. This circuit is also quite close to most oscillator-based ioniser circuits from around that time and even some I see on the web today. I changed it slightly to upgrade the transistors, included heatsinking and added two extra stages to the multiplier, altering the PCB artwork to suit. The rest of the build involved making the transformer and the pin array, both tasks which can put constructors off. But while they both seem to be quite tricky to make, neither is overly difficult. The transformer uses a standard ferrite pot core and bobbin, and it is just a matter of winding the coils carefully and 94 Silicon Chip neatly, insulating well between each layer. I made a jig years ago for such things and keep it handy, just in case. While the wire is still wound by hand, holding the assembly is much easier, and the resulting windings are much neater. This component is the most critical, especially when adding extra stages to the multiplier because the transformer will break down internally – usually before anything else – should the HV output go too high. The pin array is a little trickier, but I used a 0.5mm PCB drill bit and a small manual hand drill to carefully bore the holes for modified (head cut off) dress pins through a 120mm length of 4mm brass tube. Getting them all in line is probably the worst part of it. Still, given that they can be easily bent into shape if they are off-angle a little, it isn’t too onerous. Soldering the pins in is also a bit of a challenge, but I use liquid flux and lots of solder, and it seems to stick them in OK. I also fill the ends of the tube with solder and sand that and each pin end smooth to ensure there are no sharp edges – ions will ‘leak’ from anything sharp. This is also why the capacitors and diodes in the multiplier must be soldered to the PCB with their leads cut very close and what I would usually consider too much solder; a nice round blob will be less likely to arc to another nearby joint or bleed ions. We want all the ions coming from the sharpest parts – the pins. Once it is up and running and mounted in a nice case, the question is how to know it is working. Other than sticking your hand in front of it and hoping to feel the corona wind (no, not that kind of corona!), the ion output can be measured using a simple detector. That ETI version I mentioned included a tester that supposedly lit up when ions were present, but I could never get it to work. That could be because the PCB I made for it wasn’t good enough, the components were not quite right, or perhaps the ioniser I built at the time didn’t work well enough to trigger it. Regardless, I ended up making a little hand-held meter with a couple of transistors and a whip antenna that picked up negative ion emissions quite well. I use that now – not that I build many of these things – but when I do, it’s nice to have the test gear to show they are working. Australia's electronics magazine siliconchip.com.au The client was happy and claimed my version worked way better than their original ever did. That’s always gratifying to hear, especially with something as ‘controversial’ regarding health benefits as air ionisers. The nomadic TV antenna reception G. C., of The Gap, Qld had a lot of trouble with TV reception in his caravan on a trip to Far North Queensland. He traced it to a rather apparent electronic fault... On the first night at Tewantin, we could not receive a single television channel. This was somewhat unexpected as our caravan had been in storage for several months. Before that, we had received television stations without difficulty from the Mt Tinbeerwah transmitters near Tewantin. These UHF transmitters broadcast with vertical polarisation. Most modern caravans use fractal antennas that can receive both horizontally and vertically polarised signals, but our 16-year-old caravan does not have such luxuries. It has a simple Winegard antenna (sometimes called a batwing) with folded dipoles for VHF and UHF signals. It can be raised off the caravan’s roof and rotated in the direction of transmission by a mechanism on the ceiling. Inside the antenna radome is a masthead amplifier that is power-fed through the coaxial cable. The two struts that hold and control the position of the antenna head are in a parallelogram configuration. This enables a simple modification to be carried out that involves raising one of the struts, causing the antenna head to rotate to the vertical position, which is needed at Tewantin. Bypassing the PVR (personal video recorder) and connecting the antenna fly-lead directly to the TV did not fix the problem. Neither did changing the fly-lead or connecting it to the second antenna socket in the van. I checked that there was 12V at the “F” connector at the antenna, and it was fine. As a last resort, I removed the 694MHz filter (to block mobile phone signals) on the drop-side of the power-feed module and, surprisingly, I could then tune in all the channels. It seemed unlikely that a passive device had failed, and I wondered at the time whether its insertion loss was the straw that broke the camel’s back. All went well until we arrived at Rolleston, where the caravan park had a community antenna with coax distribution. Usually, we connect the audio output of the television set to the auxiliary input of the caravan’s CD/radio stereo system. However, with the external coax feed connected to the van, mains hum from an apparent ground loop made listening to the TV virtually impossible. When we reverted to using the television speakers, there was absolutely no sound. We had that problem on a previous trip, and we fixed it by doing a master reset on the TV. But that did not do anything this time, and it wasn’t until a couple of days later in Charters Towers that I had time to dismantle the TV. I was surprised to find that the voice-coils of both speakers were open-circuit. I couldn’t replace them at the time, and when I later got home, I discovered that Sharp no longer sells replacement parts for this set. Eventually, we arrived at Georgetown for a few days exploring. Once again, we could not pick up the single-­ channel broadcast from the transmitter just over 1km away. This ABC transmitter was in the VHF band and transmitted at 4W. Even manually tuning the PVR and TV, I could not find the ABC signal. siliconchip.com.au I decided it was time to check the amplifier in the antenna. It was not easy to get to, as we did not bring a ladder. But by lowering the antenna quite a bit, it was possible to access the F-connector and pins securing the antenna to the struts by sticking my head out of a hatch. These antennas do not appear to be designed to be repaired; umpteen diabolical plastic clips held the two sides of the radome together, plus several plastic dowels from one side to the other, which were ultrasonically welded. When I finally got to the printed circuit board, it was obvious why it was so temperamental – it was severely corroded, presumably due to moisture ingress. I would generally clean a board in this state with isopropyl alcohol, but the best I had on board was plain old methylated spirits. After cleaning it up, there were open-­ circuit tracks that needed replacement. After re-assembling the antenna and re-installing it, it was happy days again when we could receive the ABC. But our joy was short-lived, as after about 90 minutes, there was a complete signal blackout again. The next day, I risked life and limb to again remove the antenna to access the PCB. I checked every plated-through hole with a multimeter and replaced another corroded link. Again, there was apparent success, and the missus could watch her BBC programs. All was well. At Atherton, we could pick up the VHF broadcasts from the powerful Mt Bellenden Ker transmitters but not the UHF The masthead amplifier PCB and components were badly corroded. Australia's electronics magazine June 2022  95 signals from the nearby transmitters at Hallorans Hill. On passing through Mareeba, I was pleased to be able to buy PCB lacquer at an electronics parts reseller and, when I applied it, the board looked much better. But in hindsight, it may have been better to have waited a bit. At Redlynch, Cairns, there is a local broadcast site with all channels in the UHF band, but we couldn’t pick them up. When we arrived at Wongaling Beach just south of Mission Beach, my suspicions that the antenna amp had failed again were confirmed when we could not pick up any UHF channels from the broadcast site on Dunk Island. It was just 8km away, and we could see it clearly. When I again removed the antenna and accessed the PCB, I had a close look at the circuit. The signal split into two paths from the balun: a VHF amplifier with one transistor and a UHF amplifier with two transistors. I quickly sketched out the circuit of the UHF section. At this stage, I got on to the internet to see if there was any information about fixing these boards. There was information about replacing corroded PCB tracks and plated-­ through holes, but someone had figured out that the UHF transistors were BFR93A types. I connected a 9V battery to the output coax connections on the board so that I could make DC voltage measurements. It soon became evident that the second UHF transistor was not conducting at all, even though the base bias voltage was correct. I removed this transistor, which wasn’t easy in a caravan without a fine-tipped soldering iron etc. The missus was the theatre nurse and held a magnifying glass and LED torch so I could see what I was doing, which definitely helped. No wonder we were having so many issues with the antenna – the collector of this transistor was missing! It had totally corroded away. Where do you buy a low-noise RF transistor at Mission Beach? All I could do was bridge the base track to the collector track and see how well the UHF amplifier would work with just one transistor. In practice, it worked surprisingly well, and for most localities, either the PVR or TV signal meter displayed a strength of around 70% and signal quality of 100%. There was only one place when the antenna was pointing at dense vegetation that the level of pixellation was so severe that watching the television was untenable. By the time we got home, an online retailer had delivered a few of the transistors as well as some SMD ceramic capacitors. After soldering in a new transistor, I replaced a filter capacitor that had a corroded end. I also strung an MKT capacitor across the power supply electrolytic. When re-assembling the radome, I siliconed both halves together except for segments to allow egress of any water entering when the antenna is in either the horizontal or vertical plane. The antenna is now working as well as it can, but the real question is: for how long? service manual and parts manual from the Fisher & Paykel website and printed them. Fisher & Paykel must be only one of the few companies left that gives out service manuals. The service manual shows how to enter diagnostic mode, which gives codes for the last eight cycle errors. It also has procedures on how to test the out-of-balance microswitch, the pump and the water valves. The error codes are displayed on the eight wash progress LEDs, with the right-most “spin” LED being the least significant bit and the left-most “long wash” LED being the most significant bit. The code that it came up with was 00101011 binary or 53 octal. The binary decoding table indicates that 3 octal selects the 4th column while 5 octal selects the 6th row down. This points to error code 43, which means that the fault is that the out-of-balance microswitch is permanently on or the harness to it is disconnected. Since I made my repair, the Fisher & Paykel website now has a service diagnostics manual that makes it easier to read the error codes. I activated the diagnostic mode to test the out-of-balance switch. On manually activating the out-of-balance lever under the top deck, the short wash LED did not turn on, which indicated that the microswitch was not working. To get to the microswitch, I removed two screws at the top of the back panel. I could then lift up the top section with the eight wash progress LEDs and remove a screw that holds the grey control module. I then lifted the control module to reveal the microswitch, an SPST-NC type. The normally open (NO) contact that would have made it an SPDT switch had been cut off. I guess that they used an SPST-NC switch to ensure that, during assembly, the quick connector could not be placed onto the wrong terminal. After disconnecting the quick connectors, I used a multimeter to measure the resistance of the normally-closed contacts. This showed that the contacts were open and that the microswitch was faulty. Opening the microswitch revealed that the contacts had become severely oxidised after many years of service in an environment with water and steam. I made a trip to our local electronics store to purchase an SPDT microswitch, and having installed that, the machine worked again. Some time later, after we moved to a new house, it failed with error code 43 again. I knew what to do, so I purchased Washing machine microswitch repair R. W., of Mount Eliza, Vic has discovered that sealed components are needed for harsh environments, including the inside of a washing machine. At least he’s had plenty of practice replacing the failing part. He can probably do it in his sleep by now... I repaired a Fisher & Paykel GW709AU washing machine that was around 17 years old. The symptom was that it would not start. I began by downloading copies of the 96 Silicon Chip An internal view of the GW709AU out-of-balance microswitch assembly. Replacement microswitches are not available from Fisher & Paykel. Australia's electronics magazine siliconchip.com.au another microswitch and installed it. Due to a busy lifestyle, I did not realise that it was only around two years since I had first replaced it. Well, two years on and the washing machine stopped during the spin cycle. This time, the “final spin” LED and “current spin speed” LED were both flashing. On restarting the washing cycle, it would start and run then stop with the same error code. Section 10.5 of the service manual indicated that the fault could be any one of eight causes, mostly related to the machine being out of balance. One of these mentioned, “Check that the switch operates correctly and the contacts measure less than 2 ohms”. I made the mistake of thinking that, as it was not that long ago that the microswitch was replaced, it was unlikely to be the problem. I also thought this because the washing machine would start and then run before stopping. I started a cycle and lifted up the lid a bit to see what was happening without activating the lid switch. I could see that the out-of-balance lever was not being activated, but the washing machine was still stopping. This indicated that out of the eight possible causes, it could only be the microswitch at fault. I measured the normally-closed contacts and got a reading of 8MW, not less than 2W as specified. It appears that the fault was intermittent. Sometimes the switch would be closed but then incorrectly open during a spin cycle. So the microswitch was faulty once again. Opening up the microswitch, it looked OK with no apparent oxidation. So what was wrong? An internet search did not reveal a data sheet for this device. I thought this type of switch might be OK when switching high-voltage, high-current loads but perhaps was no good at switching small currents in a wet and steamy environment. I started looking for a better microswitch. The Fisher & Paykel Parts Manual lists the microswitch part number as 436597 but they no longer sell that part. The replacement is the sealed OOB (out of balance) assembly, part number 420313. That includes a different switch, bracket, lever and two-wire connectors. At ~$70, this is considerably more expensive than just a microswitch. It looks as if the switch is now sealed and requires a different bracket and lever because it is a different size. Searching for the original part number on eBay showed two sellers with photos of their microswitch that had Omron part numbers D3V-6-2C24 and V-16-2C25 on them. The Omron data sheets indicate 30mW and 15mW contact resistance, respectively. The D3V-6-2C24 data sheet also shows a graph for the micro load D3V-01 series at currents as low as 0.16mA. I think that a D3V-01 series microswitch might be suitable in this environment. But at the moment, the washing machine is working with another generic microswitch from my local store, so we will wait to see how it goes first. Next time, the solution will be to use either that Omron device or the Fisher & Paykel replacement part if the OOB micro switch fails again. I now realise why a normally closed switch was used rather than normally open. If the contacts oxidise and the out-of-balance lever operates the switch, the circuit would not be closed, and the washing machine would not stop – it would be hopping and jumping around in the laundry. With an NC microswitch, the washing machine would just stop working with a faulty switch. SC siliconchip.com.au Australia's electronics magazine June 2022  97 Vintage Television The Admiral 19A11S TV and its unique deflection circuit By Dr Hugo Holden This set features a unique horizontal deflection circuit that has been sitting under everyone’s noses for about 67 years, invented by Britons Faudell & White. Over the last 35 years, I have asked many veteran TV technicians if they know about it but so far, none have been familiar with the technique. Early CRT TV sets like the Admiral 19A11S used electrostatic deflection rather than magnetic deflection, which became the standard until cathode ray tubes (CRTs) were made essentially obsolete by LCD screens. The difference is how the electrons in the cathode ray are deflected to land at the desired spot on the front of the screen. As you might guess from the names, electrostatic deflection works by creating an electric field to deflect the electrons, basically by charging capacitors placed on either side of the electron beam (left and right for horizontal deflection or top and bottom for 98 Silicon Chip vertical). In contrast, magnetic deflection uses coils to create magnetic fields that bend the electron stream. The amount of deflection created by the electrostatic method depends on the applied voltage, while the magnetic deflection works on the current through the coil. Either way, this voltage/current must be carefully controlled so that the electrons trace out a zigzag to illuminate the phosphor(s) on the face of the cathode ray tube. The circuit concept used for the horizontal deflection system in the Admiral 19A11S has not been featured or described in standard television technology textbooks such as those Australia's electronics magazine by Fink, Grob or Von Ardenne. As far as I am aware, the only two TV sets which contained this “circuitry masterpiece” were the Admiral 19A11S and the Motorola VT71; both use the 7JP4 electrostatic CRT. Perhaps it was overlooked by people servicing the sets because ‘it just worked’ and they put no further thought into it; they needed to fix the TV and get it back to the customer. I recently posted this circuit on a vintage TV internet forum, again seen by many people with a long history in TV repair, design & construction. Nobody was familiar with it, and it surprised most. Before reading this article, imagine you have studied all there is to know about designing TV sets with valves. You walk into an exam room and are confronted with this question: Design a circuit with a single triode and any other R, C & L components you wish which runs from a 250V DC supply (ignoring the triode’s heater). It must produce two anti-phase 450V peak-to-peak linear sawtooth waveforms (one for each horizontal deflection plate) and be suited to television horizontal scan and flyback timing. It needs an adjustable frequency of around 15,750Hz, and it will be synchronised to the horizontal sync pulses in the usual way. I think most engineers familiar with television scan stage design would find this question too challenging. On its face, it seems impossible. Conventional wisdom is that this task requires a separate oscillator and a two-triode para-phase amplifier running from plate supply voltages of 700V or more to allow enough linear amplification for generating the 450V peak-to-peak anti-phase sawtooth signals. As argued in some texts, electrostatic deflection was abandoned in favour of electromagnetic deflection because sets with larger CRTs required very high voltages for the siliconchip.com.au deflection amplifiers. This is because of the higher drive voltages required for larger tubes. Note that in electrostatic CRTs, the amount of deflection is inversely proportional to the EHT voltage, so if you double the EHT, you have to double the sawtooth deflection voltages to get back to the same picture size. On the other hand, the amount of magnetic deflection is inversely proportional to the square root of the EHT voltage, so if you double the EHT, you only need to increase the deflection current by 41% to get back to the same picture size. How I noticed this circuit I came into the possession of the ‘shell’ of a vintage television set, an Admiral 19A11S, while I was in New Zealand in the very early 1980s. I had to bargain hard to get it. In the end, I think I traded it for a fully working 26-inch colour television monitor. Unfortunately, back then, I did not see the wisdom in making pre-­ restoration photographs. It consisted of a rusted chassis with a tuner unit on it. Most of the RF coils were there, including the RF power supply. All of the deflection oscillator parts, including two blocking oscillator transformers and one horizontal output transformer, were missing. No power transformer was present either. There was no manual available at the time (no internet either). As TV broadcasting didn’t start in NZ until 1958-1959, there was no service The 1949 Admiral 19A11 set in a contemporary advertisement is shown opposite, with my set shown above. information on this 1949 model available from TV service shops. Luckily, the fellow I got it from had an old copy of the schematic. It looked to me like an old treasure map; at least, I thought of it that way. It was faded and drawn over in Biro in places and had tears repaired with clear tape, but enough of it was there. Nowadays, it is simply a matter of searching the ‘net; the entire Rider’s manual for the 19A11S is online, including everything one could ever want for servicing (you can find it at siliconchip.com.au/link/abd4). But perhaps the lack of information back then did me good. I had to carefully study the design of the frame and line deflection systems to work out how to re-create the missing transformers and make the set work again. It was there that I discovered this ingenious circuit. The line deflection stage or horizontal deflection stage generated two anti-phase linear 450V peak-to-peak sawtooth waves, running from a mere 250V DC supply. How does it do that? How it works The circuit documented on the faded schematic (or in the Rider manual) was drawn in a way that almost concealed how it worked. After The functional block diagram (above) and location of the valves on the chassis (right), reproduced from the service manual. The Admiral 19A11S shared a circuit with many other models which are part of the “19A1” series, such as the 19A11SN, 19A12S, 19A12SN, 19A15S and 19A15SN. siliconchip.com.au Australia's electronics magazine June 2022  99 Scope 1: the voltage across C2 is essentially symmetrical about GND as it is connected to the cathode of the 6SN7 valve. Scope 2: the waveform across C1 is a mirror-image of that shown in Scope 1; however, the average voltage is quite a bit higher (around +138V in this case) due to C1 being connected to the anode of the valve rather than the cathode. re-drawing it, I realised what they had done. The designer had nested a blocking oscillator inside a low-frequency (2-3kHz) resonant circuit. Due to the high-Q nature of the resonant circuit, when it ‘rings’, there is voltage magnification above the applied voltage. The really clever part is that since the first 20-30° of a sinewave is pretty much linear, the blocking oscillator simply chops out about ±30° of the oscillation cycle to produce a near-perfect linear wave. The circuit, re-drawn, is shown in Fig.1. And depending on the width adjustment, it can produce 350-450V peak-topeak sawtooth waves. In the set, they are generally about 400V peak-to-peak but adjusting the control can easily give 480V peak-to-peak. The circuit is very efficient, and calculations show that the 6SN7 is run well inside its maximum plate dissipation. The peak-to-peak cathode voltage is just on the edge of its maximum rating. In the blocking oscillator circuit, the valve is not conducting most of the time; it only conducts during flyback. When the valve conducts, it charges C2 to about +200V at the end of the flyback period. By then, C1 is discharged to about -62V. Scope 1 & Scope 2 show the voltages across C2 and C1: As expected, since there is no average DC of any significance on the transformer, the cathode waveform (voltage across C2) straddles zero volts. However, that is not the case for C1, which swings from -62V to +338V here. The 400V peak-to-peak amplitude is the same, but it has a +138V offset (approximately half the +250V HT). Energy is imparted to transformer T2’s magnetic field during the flyback period. When the 6SN7 comes out of flyback (conduction), T2’s field begins to collapse at a rate determined by the values of C1 and C2. Due to the circuit Q, the voltages across C1 and C2 can rise well above the power supply voltage; or at least, they would do if the oscillations were not reset by the blocking oscillator conducting again about 25-30° into the sinewave cycle. Even though the voltage on C1 falls to -62V and the cathode voltage on the valve climbs toward +200V at the end Fig.1: the electrostatic horizontal deflection driver circuit is brilliant in its simplicity. Using just one active device, two transformers, six capacitors, three resistors and a trimpot, it produces both 450V peakto-peak sawtooth waveforms using an HT of just +250V. Transformer T2 acts as a phase splitter and importantly, also forms a resonant circuit with the two 1nF capacitors, boosting the output swing to the required level. 100 Silicon Chip Australia's electronics magazine siliconchip.com.au Faudell and White’s Time Base Faudell and White have developed a time base which gives a push-pull output. It consists of a transformer-coupled blocking oscillator time base in which a large inductance is connected in series with the H.T. supply to the time base. A condensor is connected between the valve side of the inductance and the negative supply rail as shown in Fig.66. Fig.66 Scope 3: this scope grab demonstrates how the valve’s plate (anode) voltage stays above the cathode voltage during the flyback conduction period. The valve is not conducting the rest of the time, so it doesn’t matter that the anode and cathode voltages cross over. Fig.2: a recreation of an excerpt from Time Bases by O.S Puckle, Chapman Hall 1951, attributing the clever horizontal driver circuit to C. L. Faudell and E. L. C. White. It names several British Patents; unfortunately, unlike US patents, they are not viewable or searchable online. of flyback, the valve’s anode voltage stays higher than the cathode during conduction (flyback). This is due to the voltage on the primary of the blocking oscillator transformer. You can see this effect in Scope 3. So the plate voltage is always higher than the cathode voltage at any moment during flyback. After flyback, the valve is cut off, but as shown in Scope 3, the plate voltage falls below the cathode voltage. Thus, the oscillations on the plate from the blocking oscillator transformer do not affect the scan as the valve cannot conduct with its plate voltage below the cathode voltage. Also, because it is a blocking oscillator, the grid-to-­cathode voltage is negative during the active scan time, and the valve is not conducting. This is unlike magnetic deflection, where the output stage valve conducts during the scan time and is cut off during flyback. This is possible because the required scan power for electrostatic deflection is minimal, only a few milliwatts. The ‘load’ for electrostatic deflection is merely the deflection plate tie resistors, which are in the order of 2-5MW. The top of the chassis post-restoration. The only components mounted on this side are the valves, CRT and transformers, lending it a tidy appearance. siliconchip.com.au Rebuilding the set Since I had no data on the missing transformers, I had to guess at their parameters. I wound T2 as two independent The underside is another story; while not exactly the worst mess we’ve seen, the components are mounted in locations based mainly on convenience for the point-to-point wiring employed. The turret tuning mechanism is enclosed on five sides by metal shielding. Australia's electronics magazine June 2022  101 102 Silicon Chip Australia's electronics magazine siliconchip.com.au The entire circuit of the Admiral 19A11S has been reproduced here, as the quality of this scan is much better than the circuit that was used to restore the set. siliconchip.com.au Australia's electronics magazine June 2022  103 windings on a small ferrite core (scavenged from a small transistor TV line output transformer). The inductance turned out to be 4H per winding, but at the time, I was aiming for it to resonate at about 2kHz. Later, I measured a transformer from a VT71 set, and it was 1.62H per winding. So the resonant frequency of T2 in the original system (tuned by two 1nF capacitors) was intended to be about 2797Hz (probably 3kHz). Mine resonated at 1780Hz, and it worked fine. Who was responsible for it? Recently, browsing the textbook Time Bases by O. S. Puckle, Chapman Hall 1951 (the first edition was 1943), I came across the circuit shown in Fig.2 by Faudell & White. Clearly this is the same circuit, although, unlike the Admiral circuit, the low-frequency resonant circuit is split in two. However, the function is the same. Restoring the rusty chassis In the early 1980s, there was no electroplater in my locality that I could trust it with. So the next best move was to have it painted after I had removed A rear shot of the Admiral 19A11S chassis after restoration. the rust. Later, my preferred method for chassis restoration was to use a bead blaster with fine glass beads to blow off the rust and have it plated with electroless nickel. I have completed several TV sets with that method: an Andrea KTE-5, RCA 621TS and HMV 904. You can see the result on the HMV set in my article (November 2018; siliconchip.com. au/Article/11314); there are before and after photos on page 91. Looking retrospectively, I chose an interesting colour scheme of blue and white, as you can see in the restored chassis photos. The paint is two-pack epoxy which is oven baked, so it is extremely tough. The two rectangular aluminium cans on the chassis top contain transformers Fig.3: I came up with these modifications to the set to change the CRT drive from AC-coupling to direct coupling and add vertical retrace blanking. While it worked, I did not keep these changes as I preferred the alternative shown in Fig.4. 104 Silicon Chip Australia's electronics magazine siliconchip.com.au T1 and T2. Notice how on the centre top of the chassis underside, to the left of a smoothing choke, I added a 6AL5 valve (acting as a DC restorer). It is mounted in a socket on two metal posts and held in place by a coil spring. The turret tuner assembly in these sets is quite advanced for 1949, although the 1946 RCA 621TS set had a very good turret tuner using three 6J6 valves. I needed a new CRT socket for this set, as the one that came with it was crumbling away. These are currently available on eBay, but back in New Zealand in the early 1980s, no such part was available. So as shown in the adjacent photo, I machined one out of Nylon. The pin retainer inside is a round section of fibreglass PCB material with the copper removed and countersunk holes with sharp edges. As a result, when the socket is assembled, it rotates into place and locks all of the pins into position. Upgrading the set One failing of the design of this set is that the video output stage is AC-­ coupled to the CRT. This means that As my CRT socket was crumbling and I could not source a replacement, I had to machine this one out of Nylon and fabricate a retention mechanism using a sheet of fibreglass taken from a blank PCB. the video signal’s DC component is lost. The effect that this causes on changing picture scenes is well known to every television engineer. I came up with two possible methods to remedy this: 1) Modify the circuit for direct coupling from the detector-video output stage to the CRT (as shown in Fig.3). 2) Add a DC restorer (see Fig.4). After trying both methods, I elected to keep the added 6AL5 DC restorer. With this circuit, the raster is black or near blacked out when no signal is being received. I also added vertical retrace blanking and a 5.5MHz sound trap (suited to NZ TV reception) to improve the sound take-off gain from the video output stage. This method of wiring in the DC restorer uses typical techniques developed by RCA to minimise the loss of high-frequency signals in the video output. It was interesting to look at the notes I made at the time in the neat handwriting I had back in the early 1980s. Shortly after this, I finished my career in TV and VCR servicing and then went to medical school. I became an Ophthalmologist specialising in cataract surgery which is my current SC line of work. Fig.4: these changes keep the AC-coupling to the CRT but add a DC restorer that alters the DC CRT level to match the average DC signal level. It’s a slightly more complicated scheme, but it provided a better result, so I kept it. siliconchip.com.au Australia's electronics magazine June 2022  105 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 06/22 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. 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Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR DATE MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 PCB CODE Price SC5023 $40.00 01106191 $7.50 01106192 $7.50 01106193 $5.00 01106194 $7.50 01106195 $5.00 01106196 $2.50 04106191 $15.00 01106191 $5.00 05106191 $7.50 05106192 $10.00 07106191 $7.50 05107191 $5.00 16106191 $5.00 11109191 $7.50 11109192 $2.50 07108191 $5.00 01110191 $7.50 01110192 $5.00 16109191 $2.50 04108191 $10.00 04107191 $5.00 06109181-5 $25.00 SC5166 $25.00 16111191 $2.50 18111181 $10.00 SC5168 $5.00 18111182 $2.50 SC5167 $2.50 14107191 $10.00 01101201 $10.00 01101202 $7.50 09207181 $5.00 01112191 $10.00 06110191 $2.50 27111191 $5.00 01106192-6 $20.00 01102201 $7.50 21109181 $5.00 21109182 $5.00 01106193/5/6 $12.50 01104201 $7.50 01104202 $7.50 CSE200103 $7.50 06102201 $10.00 05105201 $5.00 04104201 $7.50 04104202 $7.50 01005201 $2.50 01005202 $5.00 07107201 $10.00 SC5500 $10.00 19104201 $5.00 SC5448 $7.50 15005201 $5.00 15005202 $5.00 01106201 $12.50 01106202 $7.50 18105201 $2.50 04106201 $5.00 04105201 $7.50 04105202 $5.00 08110201 $5.00 01110201 $2.50 01110202 $1.50 24106121 $5.00 16110202 $20.00 16110203 $20.00 16111191-9 $3.00 16109201 $12.50 16109202 $12.50 16110201 $5.00 16110204 $2.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE DATE DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 PCB CODE 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 Price $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER JUN22 JUN22 JUN22 JUN22 16103221 04105221 01106221 04107192 $5.00 $5.00 $7.50 $7.50 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Amplifier power measurements Your description of the 500W Amplifier in the April 2022 issue (siliconchip.au/Series/380) reawakens a query I have had concerning power designation for some time. You describe the Amplifier as rated to deliver 500W RMS into a 4W load. My understanding is that it is actually 500W average power, which can be calculated by inserting RMS values of voltage or current into the formulae V2 ÷ R or I2 × R. Am I correct and, if so, why is power always stated as Watts RMS? (R. H., Bronte, NSW) ● You are right that it’s a measurement of average power, but it’s calculated from RMS voltage measurements, hence the shorthand expression “RMS power”. The ratings we give our amplifiers are continuous ratings, calculated by delivering a full-power sinewave into a resistive load without gross distortion (ie, no significant clipping). While the resistive load is somewhat easier for an amplifier to drive than a reactive load, that is basically counteracted by the unrealistic continuous full-power signal. So it should give a reasonable idea of the power that can be delivered continuously without significant distortion. The main reason that power is stated as “Watts RMS” is to distinguish it from values calculated by other methods like PMPO (peak music power output), which give unrealistically high numbers. We sometimes also give higher “music power” ratings that are similar but based on a sinewave switching between two different levels at a particular duty cycle. The IHF standard is for a continuous -20dB signal with bursts to 0dB for 20ms every 500ms. This is intended to simulate program material and give you an idea of the power delivery you can realistically expect. Usually, the music power rating for a well-designed linear amplifier is about 25% higher than the “RMS 108 Silicon Chip power” rating due to the lower average current drawn from the power supply. Fixing worn out car key-fob buttons I’m a regular reader and I love the spirit of repairing. I repair what I can, but I am stuck with my car keys. As you know, they typically contain a remote control that is in a plastic casing with rubber-sealed buttons that do a simple job. My problem is that one of the rubber seals wore off. This is only a one-year-old car, and to fix this problem, a mechanic quoted a whopping $1300. Perhaps your readers have a solution to this problem. Thanks for the good reading. (V. K., via email) ● $1300 is a joke for a replacement remote as they only cost a few dollars (or at most, a few tens of dollars) to manufacture. And it isn’t like you need your remote reprogrammed; simply swapping the clamshell case should fix it. If the car is only one year old, it will still be under warranty. You could argue that keycaps that cannot handle one year of wear and tear use are not fit for purpose, so they should be fixed under warranty. If you still need to fix yours, there are various approaches you could use. You can sometimes get replacement silicone buttons, or you can buy a silicone key-fob cover like this one: www. ebay.com.au/itm/122695332282 Ideally, you should get one to suit your key, but even if you can’t, you can cut the button caps out and glue them to the inside of your case using neutral-­ cure silicone sealant. The advantage of getting a case to suit your fob is that you could cut the whole section around the buttons out and then glue that in (assuming there’s sufficient space inside the case). Try to use a thin layer of silicone so it won’t interfere with the PCB, but make sure it forms a complete seal around the keycaps. If the PCB doesn’t fit back in, trim the silicone until it does. While Australia's electronics magazine silicone sealant won’t create a fantastic bond with pre-formed silicone, as it will to many other materials, it should still work. Failing that, it is possible to mould new buttons from silicone sealant, although it requires a bit more ingenuity. Stereo version of Speaker Protector I enjoyed Phil Prosser’s article on the Multi-Channel Speaker Protector (January 2022; siliconchip.com.au/ Article/15171). How about a stereo version for some of the old high power (Phase Linear 400/700, Perreaux etc) audio amps running sub-100V DC rails? (D. B., Hazelbrook, NSW) ● This project is not designed for high power audio amplifiers. It’s for lower power multi-channel amplifiers. While you could build it with just one relay, it might not reliably interrupt the fault current of a higher-power stereo amplifier. We’ve published numerous stereo speaker protectors for high power amplifiers in the past that can do just that, such as the Speaker Protector (October 2011; siliconchip.com.au/ Article/1178) and the Fan Controller & Loudspeaker Protector (February 2022; siliconchip.au/Article/15195). PCBs for both designs are available on our website, along with some parts in the latter case. USB Cable Tester stuck on error I recently finished building the USB Cable Tester (November & December 2021; siliconchip.au/Series/374). The unit fires up and counts down, but the next screen shows “UFP: VBUS,RXM2,” and then it won’t proceed past that point. As the article doesn’t have much information on post-construction problems, I would be grateful if I could be given a pointer for where to look. (R. T., New York, USA) siliconchip.com.au ● The fact that you’re getting a UFPonly error without any USB cables plugged in suggests a short-­circuit on the PCB. As long as there is a short circuit, the micro will think there is a cable plugged in and will appear not to respond, but that’s simply because it continues to report the same problem. We expect you would get a different display if you plugged in a cable. Since RXM2 is only present on the USB-C connectors, the problem is almost certainly with the soldering on CON6. Referring to the Fig.1 circuit diagram on page 30 of the November 2021 issue, CON6’s A9 pin (5V/VBUS) is next to A10 (RXN2). So we’re confident you have a short between those two pins. Closely inspect the pins on CON6 and fix any problems you find. Powering a laptop from a car I need to use a laptop when travelling off-grid. I thought it would be far more efficient to run it directly from 12V using a 12V to 19.5V DC-to-DC converter capable of delivering 4-5A rather than running a 1200W mains inverter. Has there ever been a suitable circuit published or one that I could modify? (B. R., Eaglemont, Vic) ● Your question is well-timed as we are just publishing a project this month that can do this (Buck-Boost LED Driver; page 40). However, note that suitable DC/DC converters are also commercially available (Jaycar Cat MP3338, MP3332 and MP3472 or Altronics M8627B). For newer devices that can charge via USB, you can use a USB Type-C PD vehicle adaptor. Note that car ‘12V’ supplies are very noisy and can include quite severe voltage spikes, so we don’t recommend running the High-Power BuckBoost LED Driver directly from such a supply. But it could be used as long as sufficient filtering/spike suppression was provided between the vehicle supply and that board. SMD Tweezers battery drain problem I recently built your SMD Test Tweezers (October 2021; siliconchip. au/Article/15057), and I am very impressed with how convenient they are to use. But I have found that they consistently drain the battery overnight. I thought maybe I had a dud siliconchip.com.au cell, but after going through four, it was clear that something strange was going on with the Tweezers. I measured the standby current at about 19µA, which is a bit high but not enough to drain the cell that fast. Fortunately, I have a logging multimeter which I bought to diagnose a problem with our fridge, so I hooked it up to record the standby current overnight. This revealed that the OLED standby current starts increasing after about 15 minutes, reaching 600-700µA. I cleaned all the flux off the boards, but it made no difference. Could this be a faulty OLED screen? (M. H., Mordialloc, Vic) ● It appears that a small number of the OLED panels do not properly implement the standby mode. Even the 19μA is well above the 5μA we measured on our prototype. We are working on an updated design that will completely power down the OLED and should eliminate that problem. We’ll send you a replacement screen that hopefully will not suffer from the same problem. Queries on Touchscreen Digital Preamp interface I have built the Touchscreen Digital Preamp (September & October 2021; siliconchip.au/Series/370) which seems to be working as expected, but I have run into a problem with the EQ Set screen. For Input 1, I have set the LOUD value to 4, and I am now unable to set it to any other value. I have assigned this set of values to Preset 1 TV with the annotation BYPASS ON. How do I get back to being able to set and save the Low, Mid and High tone settings in the EQ SET screen for Preset 1? Also, I am not sure what the PRE± and LOUD± controls actually do. Can you provide a bit more explanation? (D. H., Mapleton, Qld) ● The way that the Preamplifier works is that you are only ever editing the current ‘live’ settings. So to edit any of the presets, you select that preset to make it active, then adjust the pre/ bass/mid/treble etc and store the current settings back to that preset. Then press the Save button to permanently save these to flash memory. We aren’t sure how you managed to set the BYPASS on, as we removed that feature from the final software version. It is possible that some of the internal Australia's electronics magazine variables have been corrupted. Still, it should not have any effect. Load the preset by pressing the TV button from the main page, then adjust the settings as you wish on the EQ SET page; the values will be seen there. It might be possible to fix the corrupted variables by using the RESET button on the EQ SET page (followed by a SAVE), but it might need to be done directly from the BASIC prompt. The PRE± settings provide a global ‘preamp’ setting that you can use to adjust sources to the same (or different) level without having to adjust the three EQ bands. For example, having preamp at +10 and bass/mid/treble at 0 is much the same as having preamp at 0 and the bass/mid/treble at +10. Loudness is a compensation that boosts bass and treble at low volume levels, with 0 loudness giving no boost and 4 giving the most boost. Can multiple MPPTs charge one battery? I enjoy a range of solar garden lights around my property but was always disappointed with the short life of the batteries. Given the low cost of large solar panels and MPPT chargers these days, I decided to centralise the powering of my many garden lights using an 80W panel and a matching MPPT controller feeding into a pre-loved car battery. To power the garden lights, an adjustable switch-mode regulator drops the 12V to 3.7V. This solution has been highly successful for several years now. The one minor deficiency is that the battery charge in winter is only sufficient for around three hours of lighting before the battery voltage drops to ~10.8V and the MPPT charger switches off the output. The battery receives sufficient charge in summer to keep the lights on all night. An obvious solution is to go to a larger solar panel. Still, I am curious if I could add a second smaller solar panel/MPPT combination and run it in parallel with the existing setup, feeding into the same storage battery. That would allow me to have one panel optimised for morning sun and another optimised for afternoon sun. Do you foresee any problems with two separate MPPT chargers feeding a single battery? (A. G., Smiths Lake, NSW) June 2022  109 ● You have come up with a good system – the small solar garden lights with their own panels and batteries never last very long, and constantly throwing them away and buying new ones is very wasteful. We don’t think using two MPPT chargers with one battery should be a problem as the battery will have such a low impedance that each charger would not be ‘aware’ of the other. A cheaper solution may be to connect the two solar panels in parallel, with one orientated for morning sun and the other for afternoon sun. It would allow one charger to be used, provided it can handle the extra current during midday, when both solar panels are producing power. Note that any paralleled solar panels should be of the same voltage and wattage, preferably the same age, manufacturer and model. Also, ideally, the two panels should be isolated with a high-current schottky diode in series with each output, so the highest voltage panel (the one in the most sun) will not be loaded by the other lower voltage panel. Changing GPS Clock baud rate Is it possible to change the software for the GPS Clock from 2009 to use a GPS receiver with a 96,000 baud rate? (B. F., Dunedin, NZ) ● We published three different GPS Clocks in 2009 – one with a 6-digit LED (May & June 2009; siliconchip. com.au/Series/37) and two others that drove analog clocks; one for stepping hands (March 2009; siliconchip.com. au/Article/1367) and one for sweep hands (November 2009; siliconchip. com.au/Article/1632). Without knowing which one you are enquiring about, it isn’t easy to give a definitive answer. If it’s one of the GPS analog clock drivers you’re referring to, you can consider building the GPS-synchronised Analog Clock Driver (February 2017; siliconchip. com.au/Article/10527). That does the same job as the two 2009 designs but supports a 9600 baud rate. We assume you mean 9600 baud, as 96,000 is not a standard baud rate. The source is available for download from the Silicon Chip website, so you could modify it to support other baud rates and recompile it to produce a new HEX file if needed. 110 Silicon Chip If you’re interested in the 6-digit LED Clock from May & June 2009, the software does not support changing the baud rate. However, note that many GPS modules allow you to change the baud rate via an AT command. Generally, all you need to do this is a USB/ serial converter and the instructions relevant to your GPS module. So you might be able to change your module to operate at 4800 baud to suit that clock design. Where to get the SC200 power transformer I am building a stereo version of the SC200 amplifier (January-March 2017; siliconchip.au/Series/308) but am having difficulty sourcing the relevant 300VA 40-0-40V + 15-0-15V toroidal transformer. A couple of places can sell me the single-winding transformer, but no one seems to have the dual-winding model that can power my preamplifier as well as the main amps. Do you have any suggestions? Jaycar seems to have discontinued the transformer and Altronics is only selling a 45-0-45V model. (N. A., Canberra, ACT) ● We answered similar questions in Ask Silicon Chip August 2021 (page 109), May 2020 (pages 107 & 110), February 2019 (page 105) and April 2018 (pages 89 & 90). Unfortunately, it seems that the multi-winding transformers are sufficiently specialised that they can no longer be regular stocked items for a general electronics retailer. Your main options are to get a custom transformer made (eg, by Harbuch or Tortech) or just use a 300VA 40-040 toroidal transformer plus a small (say, 30VA) 15-0-15 toroidal transformer with the primaries of the two units wired in parallel. If we publish another similar amplifier, we’ll take the dual transformers approach. Building PSU around an existing transformer I need a little help building a power supply for one of your amplifiers. I’m thinking about building either a new stereo amplifier or mono instrument amplifier, and I already have a toroidal transformer left over from an abandoned project. It is 66V CT (33-0-33) <at> 4.5A (300VA). That should give DC rails of around ±45V. Australia's electronics magazine This is less than the specified voltage for some designs, although I’m not particularly concerned about reduced output power from the amplifier(s). If it/they can run at a lower voltage and still get close to the specified performance, that would be nice. I think ±45V is a tad too high for the Hummingbird, which is specified for ±40V supply rails. Will the amplifiers designed to run from ±57V DC, such as the SC200 (January-March 2017; siliconchip.com.au/Series/308) and Ultra-LD Mk4 135W (July-September 2015; siliconchip.com.au/Series/289), work at ±45V? How about the Ultra-LD 110W design (October 2015; siliconchip. com.au/Article/9132), designed to run from ±40V? The Ultra-LDs seem to have flexible power supply requirements. (J. C., Auckland, NZ) ● You certainly can run the SC200 or Ultra-LD Mk.2/3/4 from ±45V DC rails. You might need to change a few resistor values but it probably isn’t critical as the designs need to tolerate some supply voltage variation due to mains variations etc. The 110W version of the Ultra-LD module will be the closest to what you need, and the component values given in that article should work. However, ideally, you would use intermediate values (between that version and the full-power version), given that your supply rails will be between the two voltages. We don’t suggest powering the Hummingbird from ±45V DC if you will be using 4W or 6W speakers, but it might be OK with 8W speakers. Some components might need higher voltage ratings, eg, the 50V capacitors will be a bit marginal. Similar comments apply to the 110W version of the Ultra-LD Mk.4. Using Wideband O2 Sensor with LPG My 1994 LandCruiser has been converted to dual fuel but runs almost exclusively on LPG, with petrol as a backup if LPG runs out or is temporarily unavailable. I read your 2012 Wideband Oxygen Sensor Control and Display articles (siliconchip.com.au/Series/23). Beyond noting that the LPG stoichiometric ratio is 15.5:1 compared to petrol at 14.7:1, I didn’t see an obvious continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE DAV E T H O M P S O N (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, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales SILICON CHIP LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au 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 LEDs and accessories for the DIY enthusiast VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com Lazer Security Silicon Chip Online Shop QUALITY LED PRODUCTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au The Silicon Chip Online Shop stocks project kits, hard-to get parts, along with PCBs, programmed micros and other general electronic components. Visit: siliconchip.com.au/Shop/ For Quality That Counts... ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine June 2022  111 Altronics.................................77-80 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 element14..................................... 7 Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics..................OBC Ocean Controls........................... 11 Silicon Chip Shop............ 106-107 The Loudspeaker Kit.com.......... 10 Tronixlabs.................................. 111 Wagner Electronics..................... 97 way to modify it to run by default using 15.5 as the target ratio. Would this require changing the wideband sensor? (P. F., Willoughby, NSW) ● The sensor actually measures the lambda value, and the air/fuel ratio is calculated from that. That means the same sensor and controller will work fine regardless of whether you are using petrol or LPG. It will show a lambda of 1.0 if the mixture is stoichiometric, irrespective of the actual air:fuel ratio of the fuel being burned. Oxygen sensors measure whether the exhaust has excess oxygen (lean) or no oxygen and unburnt fuel (rich) or completely burnt fuel with no oxygen leftover (stoichiometric). The sensor does not actually measure the air/ fuel ratio directly. If you want to display the air/fuel ratio rather than the lambda value, the unit needs to know the stoichiometric ratio for the fuel you are currently using. The problem is that the fuel type could change. Since you usually use LPG, you could just set that to 15.5:1 and realise that the readings displayed when running on petrol will be 5.5% too high. But the engine won’t care since 112 Silicon Chip Running appliances from higher voltages I would like to request assistance regarding a Panasonic hair dryer made in Japan. It is labelled as 100V 1200W. Can I run this from 110V AC? I can plug it into a 110V outlet, but in the long run, the motor will fail. Could I use a Triac-based circuit? Thank you very much. (D. H., Taipei, Taiwan) ● One method is to use a transformer to reduce the mains voltage, as in our Mains Moderator project (March 2011; siliconchip.com.au/Article/937). The secondary windings are wired in series with the primary but out-of-phase. The result is that the secondary voltage is subtracted from the original mains voltage before being applied to the load. That circuit was designed for the Australian mains voltage, nominally 230V AC. But the same applies to your 110V supply if you use a suitably-rated transformer with a 10V or 12V tapping to reduce the mains voltage by that amount. Note that the 1200W hair dryer draws up to 12A (assuming most of the load is the resistive heater element), so the transformer would need to have a secondary current rating of at least 12A. That’s a large transformer. An alternative is to use two strings of around 10 diodes, one set for either mains polarity, to drop the 10V. But the diodes would need to be rated for 12A and preferably 20A, meaning they would need to be substantial devices. Either circuit would need to be installed in a suitable Earthed enclosure with the correct input and output plugs and sockets. The diodes would need heatsinking to the case and isolated electrically. You could use a phase controller Errata and Next Issue Advertising Index it’s using the lambda value. Note that the air/fuel ratio also varies depending on the fuel grade. So it’s better just to show the lambda value as it will always be correct. with a Triac. We don’t have a circuit that would work at 110V AC, as our designs are for 230V AC and wouldn’t be powered sufficiently. Also, most of our designs are rated for 10A rather than the 12A required for the hair dryer. Also note that the Triac would reduce the RMS voltage, but the peak of the 110V waveform would still be applied to the motor. If you can get a 110V AC rated Triac-based dimmer that can handle 12A or more, you could use that. But we think you might find it easier (and possibly cheaper) to purchase a 110V-rated hair dryer. Is Playmaster 136 up to modern standards? I would like to know if the Playmaster 136 preamp could be used in an Ultra Low Distortion Amplifier, primarily because I’m running out of funds and would like to still be able to use my record player. (M. G. M., Trott Park, SA) ● The Playmaster 136 is from the 1970s era and has a poor signal-tonoise ratio and high distortion compared to anything we have published recently. You could use it, but it wouldn’t be doing the amplifier justice. Given your limited budget, consider building the Ultra Low Noise Remote Controlled Stereo Preamp (March & April 2019; siliconchip.au/Series/333) without the input switcher and using a standard 16mm potentiometer in place of the motorised pot. You can then omit the microcontroller, 5V regulator and all components in that section. You could still use our PCB. That would give you a preamp with excellent performance that you could probably build for around $40 (depending on where you get the parts, which exact parts you use etc). It doesn’t have a built-in RIAA preamp but you can get an external RIAA premap for your turntable from Jaycar for $21.95 (Cat AC1649). SC 500W Power Amplifier pt2, May 2022: inductor L1 is wound using 13.5 turns of 1.25mm diameter wire, not 30.5 turns of 1mm diameter as stated in two places on p64 & p65. Around 900mm of wire will be consumed. Model Railway Semaphore Signal, April 2022: trimpots VR1 & VR2 are 1kW, not 10kW as shown in Fig.8 on p56. Next Issue: the July 2022 issue is due on sale in newsagents by Monday, June 27th. Expect postal delivery of subscription copies in Australia between June 27th and July 11th. 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