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MARCH 2022 ISSN 1030-2662 03 9 771030 266001 $ 50* NZ $1290 11 24 Capacitor Discharge Spot Welder 35 Raspberry Pi Pico LCD BackPack 68 Amplifier Clipping Indicator 79 Advances in Drone Technology 96 Module: Gesture Recognition INC GST INC GST The History & Manufacture of TRANSISTORS siliconchip.com.au Australia's electronics magazine March 2022  1 Gesture Controlled Powerpoint This gesture controlled powerpoint kit allows you to turn on/ off power sockets around your home, office etc. Connect it to lights, fans, or even the TV and amaze your friends by turning them on/off with a simple wave of the hand - fun! SKILL LEVEL: BEGINNER CLUB OFFER BUNDLE DEAL For step-by-step instructions & materials scan the QR code. 5995 $ www.jaycar.com.au/gesture-controlled-ppoint See other projects at SAVE 25% www.jaycar.com.au/arduino KIT VALUED AT $83.75 CONTAINS EVERYTHING NEEDED FOR BASIC ELECTRONICS WORK. JUST 49 $ $ 25W Soldering Iron Starter Kit with DMM The ideal starter package for electronics enthusiasts or the home handyman. It contains everything needed for basic electronics work. TS1652 100 $ gift card Awesome projects by On Sale 24 February 2022 to 23 March 2022 JUST FROM 11 95 495 95 Breadboard Jumper Kit - 70 Piece Includes 5-pieces each of 14 different lengths, single core wires. PB8850 Got a great project or kit idea? $ Prototyping Breadboards Ideal for electronic prototyping and Arduino® projects. 170, 400 & 830 tie points available. PB8815-PB8820 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 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.3 March 2022 12 The History of Transistors, Pt1 24 Since their invention nearly 75 years ago, transistors have reshaped the world. This series of articles will cover the most interesting bits of their history and describe how manufacturing methods have changed over time. By Ian Batty Semiconductors 44 All About Batteries, Part 3 In the final part of our series on batteries, we cover one of the ‘bigger’ uses of batteries in electric vehicles such as cars, bikes and even aircrafts and submarines. By Dr David Maddison Science 35 79 Advances in Drone Technology Quad-rotor drones have been extensively tested and used, so what does the future have in store for VTOL (vertical take-off and landing) drones? We take a look at how quad-rotor drones and quadplanes could be improved. By Bob Young Drones 96 A Gesture Recognition Module 79 The CJMCU-7620 can sense and recognise gestures made with your hands and can be connected to an Arduino or Micromite. It comes as part of a module sized just 16 x 20mm for under $20. By Jim Rowe Low-cost electronic modules 24 Capacitor Discharge Welder, Pt1 Build your own safe, low-voltage mini spot welder, which runs from a 24V DC supply. Despite this, it can deliver over 1000A. This CD Welder is perfect for making your own thermocouples or even battery packs! By Phil Prosser Tool project 35 Raspberry Pi Pico BackPack This BackPack design simplifies interfacing a Raspberry Pi Pico with a 2.8inch or 3.5-inch touchscreen. It also includes some extra capabilities, such as a real-time clock, infrared receiver and more. By Tim Blythman Raspberry Pi Pico project 68 Amplifier Clipping Indicator It’s good practice to determine whether your amplifier is about to run into clipping, as it can potentially damage your speakers. This project will show you even the briefest of clipping events, to help keep your speakers safe. By John Clarke Audio project 84 Dual Hybrid Power Supply, Pt2 The final part in this series focuses on assembling and calibrating the Power Supply. That includes preparing the heatsink and case, mounting all the modules and wiring them together, including the mains wiring. By Phil Prosser Power supply project Cover Image: A Texas Instruments SN7400 quad NAND gate from 1965 – https://w.wiki/4mri 2 Editorial Viewpoint 4 Mailbag 61 Serviceman’s Log 72 Circuit Notebook 100 106 1. Alternative Arduino Power Supply 2. Illuminated doorbell press switch 3. Reading three digital signals with a two-channel oscilloscope Vintage Radio Phenix Ultradyne L-2 by Dennis Jackson Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index Dick Smith Competition: winners have been notified; full details will be in the April 2022 issue of Silicon Chip. 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 Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel www.louisdecrevel.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. Editorial Viewpoint RIP Brendan James Akhurst, cartoonist extraordinaire I was very sad when I heard that Brendan had passed away recently, aged 73. That isn’t just because he was a great cartoonist who worked with us for 34 years (and for Electronics Australia before that), but also because he was a great person and a friend. I think I became his friend the day I bought my Ford Falcon. Brendan was definitely a ‘petrolhead’. While he liked cars in general, his last car was a Tickford Falcon that I know he loved driving. His fondness for cars was also reflected in his work for magazines like “Street Machine”. I was quite surprised when I found out how old he was. Based on the way he spoke and behaved, I thought he was barely in his early 60s, possibly even younger than that. Brendan was a passionate and active man to the end and certainly did not seem ‘old’ to me! I hope I can ‘stay young’ like Brendan did, if not in body, then at least in spirit. I think most Silicon Chip readers would agree that he was a very talented artist who produced magnificent work. Some of the cartoons he drew in his prime were utterly hilarious, and I couldn’t help but burst out laughing when I first saw them. It wasn’t just that he could draw, he was also very creative in coming up with the ideas for cartoons. Brendan wasn’t just a talented artist. He worked for many years as a police diver; an occupation not for the faint-of-heart. He also helped to raise three fine sons. We at Silicon Chip are going to miss him. When you read the Serviceman’s Log column this month, you will see that we have a new cartoonist who is also very talented. I am sure he will bring something unique and individual to those pages over the coming months and years. The last cartoon Brendan ever drew is reproduced below. It reflects his affinity for animals, especially the charity “Wombatised” that rescues sick, injured, or orphaned Wombats. If you’d like to donate to them in his memory, you can contact them via www.facebook.com/wombatised/ Editorial by Nicholas Vinen 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: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine March 2022  3 MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd 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”. RIP Joe Talia Sadly, Joe Talia (pictured below) founder of the Australian company “Talia Sound and Vision”, recently passed away. Talia Sound and Vision (also known as TSV or Talia) was one of the greats of the Australian broadcasting industry, in design and manufacturing, for more than 30 years from the mid-70s. They manufactured products that were highly regarded and recognised around the world. For example, they designed and built a custom Vision Mixer for the Adelaide Grand Prix for Channel 9, also used in the early Melbourne races. They also designed and built the routing switcher for Channel 7 that was used for the 1992 Barcelona Olympics broadcast. It was a ground-­ breaking compact SMD design called “EOS”. That project saved the company during the ‘90s recession. TSV sold an extensive range of video & audio broadcast products in Australia and overseas, including the “Gatton Video Isolator”. Talia Sound & Vision received an ETI award for outstanding electronic products (See ETI, October 1989). Codan acquired the company in 2005, which then merged with Provideo to become Codan Broadcast. Ross Video Canada acquired Codan Broadcast in 2010. Placid Talia, Melbourne, Vic. 4 Silicon Chip House-scale batteries are not financially viable Dr Wilson’s detailed numerical modelling of his PV system published in the January 2022 issue (siliconchip. com.au/Article/15170) concluded that storage batteries are not cost-effective for the costs and charges he quotes. I can come to the same conclusion with calculations on the back of a postage stamp. Consider his costs and charges if a 10kWh battery were to be fully charged each day from PV solar panels and all that energy were used to mitigate power being drawn for the grid at 32¢/ kWh, the cost he quotes. That would result in a saving of $11,680 over the life of 10 years. Dr Wilson mentions the approximate cost for a 10kWh battery as $8,000 to $10,000, which seems about right. A battery will never be deployed to anything like this best-case scenario. There will be many days when the battery will not experience the full round trip of 10kWh. There are so many unknowns in a 10-year investment of a battery that there are no sound financial reasons to do so. I agree with Dr Wilson. Dr Kenneth E Moxham, Urrbrae, SA. Possible home for old PMG test gear I’m writing regarding Patrick Durack’s Mailbag letter regarding a suitable home for the old PMG test instrument he has in his possession (January 2022, page 4). He could contact the Queensland Telecommunication Museum at 3 Oriel Road, Clayfield Queensland 4010, phone (07) 3862 2958 or visit their website www.telemuseum.org That would be a good place to start making inquiries about finding a suitable home for the device. Mark Perry, Indooroopilly, Qld. Australia's electronics magazine Another telecomms museum The Victorian Telecommunications Museum is a small museum in the Hawthorn Telephone Exchange, Burwood Road, Hawthorn, Victoria, Australia. It houses historical telecommunications equipment that had been used by what originally was called the Postmaster-General’s Department (PMG). Its address is 375 Burwood Rd, Hawthorn Vic 3122; phone 1800 687 386. It might be worthwhile for Patrick Durack to contact them and see if they want the PMG test gear he mentions in his letter. Bob Backway, Belgrave Heights, Vic. More misleading solar panel ratings I am writing regarding Dr David Maddison’s correspondence on dubious solar panel ratings in the January 2022 issue (pages 4 & 6). I purchased a panel labelled as 350W (and a suitable battery) to run our internet connection, charge all our USB devices and power anything else that would charge or run from a 12V DC system without using grid power. It all works without any problem. However, upon reading David’s letter, I made a few measurements and calculations. This panel measures 104cm x 80cm. So I’m lucky if I get any more than 155W on a bright sunny day (measurements confirm this). It is caveat emptor, people. There are many sellers of panels with dodgy ratings, especially via the internet where I purchased mine. While of good mechanical quality, given what I paid based on its published & labelled ratings, it is still very disappointing. Denis McCheane, Allawah, NSW. Problems with new R80 Receiver kit I ordered the R80 Aviation Receiver kit reviewed in your November issue. I siliconchip.com.au Established 1930, 100 % Australian Owned “Setting the standar EXTENDED TRADING HOURS! ONLY ON d for quality and valu e” 19TH MARCH! WE ARE OPEN TILL 4PM SAT. E! 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All prices include GST and valid until 19-03-22 Established 1930 01_SC_280222 M012 - Measuring Kit - 4 Piece fired up the soldering iron and started to assemble the board, but after I had soldered about ten resistors, I realised that something didn’t add up. And sure enough, when I checked the PCB, it was revision HM00ABRC_7, whereas the description/parts list/ schematics are for HM00ABRC_6. The new board is quite different with two relays, which are not present on the earlier board. I found a YouTube video where a bloke described this new circuit board, and he had some video footage of the schematics. From that, I managed to reconstruct a parts list. It turns out that this receiver is entirely different from the version you described. They have added the facility to listen to the FM broadcast band by switching the input signal with the two relays. Unfortunately, this new design makes the receiver less sensitive. There is no facility to tune the receiver manually. After I assembled it, I powered it up and the green LED lit, but nothing more happened. Then, after a couple of minutes, the display came to life. I connected the speaker and got some noise and hum, but nothing more. A wire connected to the antenna input made no difference. I then connected the GP antenna I have for the 2m band and then I could receive local FM stations, although with poor audio quality. When I switched to the air band, I could hear a helicopter pilot within eyesight from my location, but nothing else. All in all, this receiver kit is not what I have hoped for. I was not interested in the FM band and, as it doesn’t have an HF stage, like the previous version, the receiver’s sensitivity is poor (the bloke on YouTube came to the same conclusion). I checked the MCU, and it is a PIC16F1938, so different from the one on the V6 board. I took a closer look at the pre-assembled PLL board with my magnifying glass. There is a filter on the PLL output with two tiny SMD inductors, and inductor L1 had been soldered standing up. Consequently, only a tiny fraction of the clock signal could have passed through. I have now corrected this, and it is working more like it is supposed to, but it still isn’t very good. With my scanner, it is no problem to receive the ATIS from Williamtown, but with this receiver, I can hear it is there but not clearly enough to understand the message. I think I found the intermittent fault with the slow-starting of the PIC. Pin 4 of the MCU has not been soldered properly. Since I rectified it, the receiver starts up normally. The squelch kind of works now, but not very well. The receiver picks up unwanted noise here and there on the air band, and I can hear music, which I’m guessing is a local AM station. I’m not impressed with the design and certainly not with the quality control. Olle Scholin, Stockton, NSW. Comments: that is some pretty bad ‘tombstoning’ of the SMD inductor! Overall the soldering does not look great. Andrew Woodfield has some further comments about this new receiver design: I’ve never thought much of the TA2003 IC. At 25¢ (US) each, you don’t quite get the same silicon as you do from the more costly chip lineup in the original V6 receiver. That receiver, albeit with a fixed squelch, has very good performance. The overall sensitivity for the new one is quoted as 12dBμV, which is not wonderful. I was going to do a simulation on the squelch circuit which, to my eye, looks very squiffy. Curiously, in the original Chinese text, the designer Inductor L1 was soldered standing up. The micro wasn’t soldered properly. 6 Silicon Chip Australia's electronics magazine writes, “You should probably just turn off the squelch in FM because it’s very erratic.” Say, what? It’s unlikely to work well in AM if it doesn’t work with loads of noise and signal in the wideband FM mode. I’ve seen a receiver design using the TA2003 chip with a single NPN gain stage (16dB?) ahead of the chip. Adding such a gain stage might improve the sensitivity. Nulling DC offset on Hummingbird Amplifiers I built a couple of Hummingbird Amplifier modules (December 2021; siliconchip.com.au/Article/15126) but modified the boards to allow the DC offset to be adjusted. I am running my modules from two separate 160VA transformers. I did this by removing the two 100W resistors that join the emitters of Q7 and Q8 to the collector of Q3. Instead, I connected a 200W 10-turn potentiometer with either end of the track to the collectors of Q7 & Q8 and the wiper to the collector of Q3. Before powering the module up, it’s important to check that the pot is set to have roughly equal resistances of around 100W each between the wiper and the other two terminals. Then, once powered up, measure the amplifier’s output DC voltage with no signal and tweak the trimpot setting to get it as close to 0V as possible. Brian Chancellor, Albion, Vic. Alox capacitor logo mystery solved In my December 2021 Vintage Radio article on the Sony 5-303E Micro-TV (siliconchip.com.au/Article/15145), I showed some “Alox” capacitors (page 101) that were stamped with an unusual logo I didn’t recognise. I wrote there that “it has some similar features to the Siemens logo, but it is not exactly the same.” Recently, I stumbled across this web page: www.fujitsu.com/fts/about/ brandmanagement/logo/transition/ The logo shown there is pretty close to the logo on those Alox capacitors in the TV, so it was probably an early Fujitsu logo. I think they were likely made by Fujitsu. And it now makes sense why it sort of looked like a Siemens logo. That web page explains that the origin of Fujitsu was as a joint venture between Furukawa Electric Co Ltd and siliconchip.com.au Siemens, with the logo being a combination of a lower case “f” and an “S”. Dr Hugo Holden, Minyama, Qld. Seeking good banana connectors I like to move my loudspeakers from room to room and from amplifier to amplifier, and most connections use banana plugs, but I continually encounter two problems: 1. Most is not all. It isn’t a big deal and hardly the end of the world, and I just take the bananas off and use bare wire, but I’m getting grumpy in my old age and I’d like not to need to do this. 2. Banana plugs and sockets seem not to be very consistent. Some loudspeakers seem to have holes in their sockets at the upper limit allowed by the standard, while others seem to have holes at the lower limit. Banana plugs vary enough to be a nuisance too. The result is that some connections are too loose, but others are too tight, sometimes impossibly so. Many years ago, I found the banana plug and socket combination in the photo supplied●. I think I bought them from Jaycar, but they have not stocked them for years, and I can’t find any other suppliers. I have the one in the photo, but I’d like some more. Does anyone have some they can give or sell to me? Keith Anderson, Kingston, Tas. ● The photo showed a Jaycar Cat PP0440 4-way goldplated banana plug & socket assembly (www.jaycar. com.au/p/PP0440), which is no longer being sold. If any readers have a spare set of these they want to get rid of or sell, e-mail us, and we will pass on the message to Keith. The old AWA type numbering system Patrick Durack (Mailbag, January 2022) queries the date of an AWA CAPACITY UNBALANCE MEASURING SET, type R667. I have been in contact with Patrick and have determined the following: 1. The type number is actually R6667. 2. The measuring set contains a sub-assembly DIFFERENTIAL CONDENSER 550µµF (pF), type U6781. 3. The active components are three OC72 transistors. I have been researching AWA’s Engineering Products type numbering system for some time and can offer the following advice. Before the early 1950s, the type number was formed as a category letter – sometimes preceded by a revision number for design changes during production – followed by a four-digit number taken more or less sequentially from a master type number register. An example is the BEAT FREQUENCY OSCILLATOR, type R7077 (“Vintage Radio”, December 2011). No records of the category letter allocation during this period still exist, and engineers from those days who might have remembered how the system worked will have all passed away by now. After the early 1950s, the system was changed to a more predictable category letter, sometimes preceded by a revision number, followed by a five-digit number starting from 50000. Under the new system, the category letter was “A” for test equipment. An example is the wellknown VOLTOHMYST, type A56010. 8 Silicon Chip Australia's electronics magazine siliconchip.com.au WHAT IF WE COULD CREATE MORE BY WASTING LESS? By 2050, global energy demand is projected to rise by over 60%. ADI’s expertise in power management has enabled breakthroughs like energy harvesting and robotic miniaturization. Which means we can make progress, while making less waste. Analog Devices. Where what if becomes what is. See What If: analog.com/WhatIf Helping to put you in Control ECO PID Temperature Control Unit RS485 ECO PID from Emko Elektronik is a compact sized PID Temperature Controller with auto tuning PID 230 VAC powered. Input accepts thermocouples J, K,R,S, T and Pt100 sensors. Pulse and 2 Relay outputs. Modbus RTU RS485 communications. SKU: EEC-022 Price: $104.45 ea Mini Temperature and Humidity Sensor Panel mount Temperature (-20 to 80degc) and Humidity (0 to 100% non condensing) sensor, linear 0 to 10V output. Cable length 3 meters. SKU: EES-001V Price: $164.95 ea ESM-3723 Temperature and RH Controller 230 VAC Panel mount temperature & relative humidity controller with sensor probe on 3 metres of cable. It can be configured as a PID controller or ON-OFF controller. 230 VAC powered. Includes ProNem Mini PMI-P sensor. SKU: EEC-101 Price: $619.95 ea PTC Digital ON/OFF Temp Controller DIN rail mount thermostat with included PTC sensor on 1.5m m lead. Configurable for a huge range of heating and cooling applications. 230 VAC powered. SKU: EEC-010 Price: $98.95 ea Software update woes and TV sound levels Ursalink 4G SMS Controller The UC1414 has 2 digit inputs and 2 relay outputs. SMS messages can be sent to up to 6 phone numbers on change of state of an input and the operation of the relays can be controlled by sending SMS messages from your mobile phone. SKU: ULC-005 Price: $228.76 ea 20% off! 4 Digit Large 100mm Display Accepts 4~20mA, 0~10Vdc, is visible 50m away with configurable engineering units. 10cm High digits. Alarm relay and 230VAC Powered with full IP65 protection SKU: FMI-100 Price: $1099.95 ea Touchscreen Room Controller SRI-70-BAC Touchscreen Room Controller are attractive flush mounted BACnet MS/TP controllers with a large colour intuitive 3.5” touchscreen for viewing the system status and modifying the settings. SKU: SXS-240 Price: $306.90 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 10 Silicon Chip Again, no records of the category letter allocation system still exist, but several extant fellow AWA veterans have been able to give me a partial listing from their recollections. Note that, as in the case of the R6667, AWA allocated type numbers as soon as a product was conceived, not when it was finally designed, manufactured or released. I believe that the new type number allocation system came into use in late 1952 or early 1953. This is based on the fact that the above mentioned VOLTOHMYST drawings were dated early 1953, and it was among the first of the new-generation test instruments of the period. The fact that the CAPACITY UNBALANCE MEASURING SET contains OC72 transistors, which weren’t introduced until 1954, suggests that it was planned during or before 1952 (four-digit type number) but couldn’t have been produced until 1954 or later. The category letters are post-1952: “R” means transmission line equipment while “U” means a capacitance device. Changing the subject, I am indebted to Peter Caprin (Mailbag, June 2021) for identifying my TRANSISTOR TEST SET (Mailbag, May 2021) as a design by Jim Rowe from Electronics Australia, August 1968. I spent some time searching my collection for this issue, but unfortunately, it is missing – one of the few copies since 1953 (Radio and Hobbies) that have escaped me. Fortunately, I found the preceding issue, July 1968, in which Jim had described the design principles of the final instrument. With that knowledge, I was able to restore and recalibrate the instrument to give accurate readings after correcting a couple of wiring errors the original kit constructor made. Ross Stell, Kogarah, NSW. I totally agree with the thrust of your several editorials where you discuss the now-common practice of software apps and electronic hardware being rendered inoperative by updates or new developments. I find that the pushed Windows 10 updates often break or otherwise meddle with existing functions. It seems to me that thorough testing for backwards compatibility has a low priority, or perhaps in the industry, there is the temptation to compel users to spend money ‘upgrading’ or replacing perfectly operative apps or devices. If I may have a second bite of the cherry, I saw with interest the reader’s letter from Stephen Gorin and your comment about varying sound levels between channels (February 2022, page 7). Most irritating to my mind is the appalling imbalance between segments on a given channel and sometimes in a single program, the ABC News in particular. We always have to ride the remote during the News as there are crosses to various reporters, sound levels varying enormously – apparently not having been previously checked. Some channels also suffer occasionally from ‘woolly’ studio mics. Protestations to the feedback facilities remain unanswered. Uniform levels and good sound reproduction were pioneered by the BBC in the 1920s, so it should be possible to have them right by now! Finally, regarding TV transmissions, in our particular Australia's electronics magazine siliconchip.com.au location sometimes in very hot weather we have a pixelated TV picture with breaking sound. This is understandable, but it is interesting that the adverts are always perfect. Obviously, there is a differing transmission characteristic for them. I wonder why it can’t be universal. Alan Ford, Salamander Bay, NSW. More on TV sound levels I’m responding to the letter by Stephen Gorin in the February issue. From my long-time-ago training in TV transmission, sound energy levels have been a historical problem on commercial television since advertisers found out about sound compression. Compression was initially devised to protect analog transmitters from over-modulating and was also used in the recording industry. Compression effectively increases the low sound levels, making normal sound levels louder. Advertisers are addicted to blasting their message across living rooms. Hence, adverts contain more sound energy but are not actually greater in maximum amplitude. With the advent of digital transmission, with vastly superior dynamic range, there is no longer a need for transmitter protection in the analog sense. However, the advertisers want their message above the normal program transmission levels, and submit their source material with excessive compression. Therefore, inserting a keying system will be resisted by advertisers and may be useless even so. With digital sound, I have noticed some HD channels using Dolby are considerably lower than straight PCM for some reason, possibly to do with the +10dB of the LFE channel (commonly called the subwoofer). Still, it is not universal or consistent in level difference across broadcasters. Also, more LF or more of certain frequencies of HF sound content can be present, giving the impression of increased sound level. Usually, TV stations correct small variations between normal program material. Kelvin Jones, Kingston, Tas. Incipient motor capacitor failure causes starting difficulty Next time someone complains about a motor having “stiction” problems, get them to try replacing the motor start capacitor before anything else. Mine has been failing for the past couple of years. It was masked by the fact that the motor would start if I removed the Induction Motor Speed Controller (April-May 2012; siliconchip.com.au/ Series/25) and connected it directly to mains. Now that I have replaced that capacitor, it starts promptly and reliably with no other modifications required. I wish I had known that before I went chasing problems in the Speed Controller. Also, I note that the SL32 10015 NTC thermistor used as an inrush current limiter can fail prematurely due to operating over long periods at high temperatures. As an alternative, Ametherm also has the MS32 series of NTCs (as opposed to the SL32 series). These appear to be identical but have a higher surge energy rating. The MS32 10015 is available from element14 part (Cat 1653452). Peter Wilson, Canberra, ACT. SC siliconchip.com.au POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au Australia's electronics magazine March 2022  11 The History of Transistors Transistors have reshaped the world since their invention 75 years ago. Computers, mobile phones, tablets, the internet, high definition TVs... none of this would be possible without transistors. While the history of the transistor could fill a book (and properties of transistors several more), this short series of articles covers the most interesting bits. Part 1: by Ian Batty 12 Silicon Chip Lead image: John Bardeen (left) and Walter Brattain (right) explain their invention to William Shockley (centre) Australia's electronics magazine siliconchip.com.au , to most electronic devices, you’ll design repair or understand need to understand how various types of transistors work. Since their first commercialisation, transistors have gone through ten distinct manufacturing methods (and hence transistor technologies). It has been difficult to find, in a single source, straightforward descriptions of transistor construction and operation. These articles are intended for casual reading, as a guide to operation and repairs and as a compact reference work. We’ll start by describing the invention of transistors and the major developments that followed. After that, we’ll have some details of more modern manufacturing techniques, semiconductor physics, doping, and diode and transistor behaviour. Thermionic valve (tube) limitations Valve technology underwent explosive development between Fleming’s patent for the thermionic diode in November 1904 and Bernard Tellegen’s patent application for the pentode in 1926. Receiving valve technology matured in the 1960s with miniature ceramic devices. But three problems inherent in thermionic valves persisted over that time, none of which was ever fully solved. Heater/filament power consumption Leaving aside some special types, amplifying, rectifying and oscillating valves use thermionic emission from a heated filament or cathode. The tiny DL66 hearing-aid output valve delivers only 0.95mW of output, yet needs 12.5mW of filament power – almost thirteen times its useful output. The 6SA7 converter delivers a voltage signal of virtually zero power but demands about 1.9W of heater power! A fair comparison would be between a 12CX6 ‘hybrid’ valve, using both 12V heater and HT supplies, and a relatively early (1965) AF121 diffusion-­ alloy germanium transistor, in both cases having a 12V DC supply. The 12CX6 will draw ~4.4mA of anode/screen current from the 12V HT supply, for a total HT power of about 53mW. The AF121 transistor will draw ~3mA from its 12V supply, giving a comparable figure of 36mW. But we need to add in the valve’s heater current of 150mA. This adds 1.8W, for a total of 1.85W; over 50 times the power for a transistor doing the same job. Limits to miniaturisation Thermionic valves rely on a vacuum to separate their electrodes. Conventional valves use a concentric structure, with the grid or grids and anode surrounding the filament or cathode. This demands great manufacturing precision and limits the minimum size. A planar (layered) structure can be made to much higher precision and much smaller. This approach delivered the 7077 ceramic triode – just 11.3mm tall and 12.2mm in diameter. Impressive as this is, the 7077 is hardly smaller than most transistors of 1958, which points to the limits of thermionic valve miniaturisation. Fig.1 shows a 7077 beside an OC76, one of the second generation of junction transistors, reproduced at an enlarged magnification. Transistors are now manufactured with dimensions measured in nanometres, a degree of miniaturisation impossible for thermionic valves. Frequency limitations Electrons in a thermionic valve pass from the cathode to anode across an evacuated space. At very high signal frequencies, transit time effects (the time taken for electrons to travel that distance) set absolute limits to triode valve operating frequency. The problem is most easily understood by considering the electrons just approaching the grid being out of phase with those just leaving. More are arriving than leaving, or more leaving than arriving. Now that these numbers no longer balance, the grid no longer appears as a small capacitance but instead as a low impedance. This grid loading demands power from the driving stage, even in voltage amplifiers. As a result, the 6BL8 converter has an input impedance of only a few kilohms at around 100MHz, limiting the gain available in an FM radio. Grid loading and other more complex effects set an upper limit of around 2.5GHz for thermionic triode amplifiers such as the 7077, with a few types extending to some 7.5GHz. Three main ‘non-triode’ types of thermionic valve were developed: magnetrons, klystrons and travelling-wave tubes (TWTs). Although these can operate at frequencies approaching 100GHz, only the klystron and TWT can amplify. Klystrons and TWTs are pretty noisy, with the better-performing TWTs having noise figures of about 7dB, making them unsuitable for weak-signal amplification. These three thermionic types are physically large, and the amplifying versions consume many watts of power. One variant of the TWT, the Backward-Wave Oscillator (Carcinotron), can work as an oscillator up to 1THz (1000GHz). Current transistor developments (as of 2022) are yielding low-noise amplifiers with operating frequencies exceeding 500GHz and gains of 20dB. In summary, thermionic valves for general-purpose amplification had reached their limits of development by the early 1960s. The 7077 ceramic triode is a fine example of how far valve development had come and the limits to further practical development. 12.2mm 5mm Fig.1: the 7077 ceramic triode (12.2mm diameter), along with an early germanium alloyed-junction transistor (OC76, 5mm diameter), both shown larger than life. While they are similar in size at this early stage of transistor development, it didn’t take long for transistors to shrink further. siliconchip.com.au Australia's electronics magazine March 2022  13 Early transistor attempts Brought into public consciousness by Michael Faraday’s popularisation in the early 1800s, electrical science seemed to produce a new miracle in every decade of the 19th century. Willoughby Smith’s 1873 work with selenium rods demonstrated an oddity: selenium’s resistance was affected by incident light. Clearly, there was more to electricity than Ohm’s Law of conduction in metals. Smith’s results foreshadowed the semiconductor revolution. Semiconductor diode action was demonstrated by Karl Braun just a year later in 1874, followed by Bose and Pickard’s 1904 practical application of these detectors to radio reception. Many military receivers used in World War I were based on solid-state ‘crystal’ detectors. Once Lee de Forest had demonstrated his triode Audion valves, some must have wondered whether that same principle could be applied to triode amplifiers. In 1925, Julius Lilienfeld formerly of Leipzig University filed a Canadian patent for a solid-state device that foreshadowed the modern field-effect transistor, similar in operation to thermionic triodes. The device passed current through a thin sheet, but subjected that current to a controlling electric field. His US patent was granted in 1930 (see https://patents.google.com/ patent/US1745175). Lilienfeld did not publish research papers, so his device was not taken up by industry. A replica was finally built and tested in the 1990s and proved effective as an amplifier (see https://w. wiki/4YLL). It’s less well known that Lilienfeld also lodged the first known patent for the junction transistor design in 1928 (https://patents.google.com/ patent/US1877140A). This was around 20 years before William Shockley’s 1948 patent (which we now know as the transistor). Shockley’s design was fundamentally identical to Lilienfeld’s (https://patents.google.com/patent/ US2569347A). The two devices are identical in current flow (emitter-through-baseto-collector) and physical design (two back-to-back diodes with one reverse-biased). Fig.2 from Lilienfeld’s 1928 US patent 1877140 shows the circuit for a solid-state amplifier; the current path and structure of the device clearly 14 Silicon Chip Fig.2: Lilienfeld’s junction transistor as part of an amplifier circuit, from US patent 1,877,140. anticipate the junction transistor. The operation of Lilienfeld’s design is described briefly in his patent application. human skill to fabricate with the fineness necessary to produce amplification.” Bardeen and Brattain’s patent (1950) lists the first known transistor specifiFast-forward to 1947 cations for their point-contact design, On receiving his doctorate in 1936, including power gains of just 16-19dB William Shockley was recruited to Bell and a current gain of merely 1.3 times. Laboratories and joined a team of physWalter Brattain, John Bardeen and icists researching solid-state electron- Robert Gibney, working at Bell Labs’ ics.With the outbreak of World War Solid State Physics Group (led by WilII, Shockley began working on radar, liam Shockley), made several attempts joining Columbia University’s Anti-­ at the “solid-state triode”, but many Submarine Warfare Group in 1942. were found to infringe Lilienfeld’s Since thermionic diode mixers had existing patents. proven inadequate at the ultra-high Their first material of choice was silfrequencies used in radar systems, icon, but the high temperatures needed Shockley developed high-­performance (melting point 1414°C) proved diffiultra-high-frequency silicon diode cult, so they switched to germanium mixers. (melting point 938°C). His success led him to consider Shockley started wanting to repwhether his diode design might be licate thermionic triode operation transformed into a triode structure, – electron flow controlled by a non-­ thus allowing amplification. conducting electrode. This looked Papers show that Shockley and his forward to the modern family of field-­ colleague Gerald Pearson had actually effect transistors (including those used built ‘Lilienfeld’ devices but didn’t in CMOS chips such as microprocesrefer to that in their published papers. sors). But Shockley was unable to It is notable that the successful Bar- demonstrate any useful effect. deen and Brattain point-contact tranHe eventually developed a transissistor patent (https://patents.google. tor explicitly using two types of curcom/patent/US2524035A) describes rent carriers: electrons and holes – the Lilienfeld’s 1925 (Canadian patent) junction transistor. We’ll return to that mechanism – which would become a little later. today’s overwhelmingly-used field-­ Bardeen and Brattain, working effect technology – as “…beyond without Shockley due to his abrasive Fig.3: the point-contact transistor, from Bardeen & Brattain’s US patent 2,524,035. These performed reasonably well, but they were tricky and expensive to manufacture. Australia's electronics magazine siliconchip.com.au Fig.4: Shockley’s junction transistor (this drawing from US Patent 2,569,347) was a significant step from the point-contact transistor. It was much easier to manufacture in bulk and less fragile too. Fig.5: Shockley’s patent also included this five-layer compound transistor that was intended to operate similarly to a pentagrid mixer valve like the 6L7. management style, eventually demonstrated the device we know as the point-contact transistor in December 1947 and filed for the patent in 1948 (Fig.3). A press conference in June 1948 showcased the new device. Demonstrations included an amplifier and a radio receiver. Regrettably, no details of that radio are available. John Bardeen, Walter Brattain and William Shockley were jointly awarded the Nobel Prize for Physics in 1956 “for their researches on semiconductors and their discovery of the transistor effect”. Bardeen went on to win a second Nobel Prize in 1972 for his theory of superconductivity. of Shockley (who was unconvinced about the need for ultra-pure stock) and on his own initiative. Teal said, having previously been involved in germanium processing and diverted to other projects, only to return: “If I ever had another idea I considered a world-beater, I’d work on it even if nobody gave me any help.” The program also established processes such as the production of P-N junctions and attachment of leads to devices. Morton made an important strategic decision to share transistor technology with other researchers so that Bell Labs and parent AT&T could benefit from a cooperative approach. Bell Labs held three famous seminars where scientists and engineers visited Bell Labs to learn the new semiconductor technology first-hand. The first meeting, in September 1951, specifically addressed military uses and applications. Proposals to classify the transistor (and thus make it unavailable to the civilian world) were, thankfully, not pursued. In April 1952, over 100 representatives from 40 companies that had paid a US$25,000 patent-licensing fee came for a nine-day Transistor Technology Symposium, including a visit to Western Electric’s ultramodern transistor manufacturing plant in Allentown, PA. There were participants from such Out of the lab and into the fab Bell Telephone Laboratories realised that the transistor was a revolutionary device with the potential to transform electronics. Bell Labs pursued a vigorous program of “fundamental development” in the late 1940s and early 1950s, promoting rapid improvements in transistors and other solid-state devices. Electrical engineer Jack Morton led this program, developing processes such as zone refining – critical to the high purity of materials needed – and growing single crystals of germanium and silicon. Gordon Teal perfected his refining processes against the advice Fig.6: while it’s reasonably certain that Lilienfeld transistors were built, there isn’t much information left outside his patent on just how they worked. Their structure is quite different from modern transistors and, as shown here, they were made from metals and a semiconductor (silver sulfide). siliconchip.com.au Australia's electronics magazine electronics titans as GE and RCA, as well as from then-small firms including Texas Instruments. The Bell Telephone Company was established by Alexander Graham Bell, who had started as a teacher of the deaf and who spent much of his career in service to the hearing-impaired. So, commendably, Bell Labs waived all patent royalties for the very first transistorised consumer product in 1953 – a hearing aid. The one-month wonder The personal story of the people behind the junction transistor is as interesting as the story of the technology itself. In brief, Bardeen and Brattain were pivotal in developing the working point-contact transistor, and Shockley felt that he had been excluded from the project; indeed, the patent was issued only to Bardeen and Brattain. So, working by himself, Shockley designed the junction transistor in one month, claiming an entirely new approach to solid-state electronics (https://patents.google.com/patent/ US2569347A), and one which would become the basis for all subsequent development. Fig.4 (from the patent) is the basic ‘triode’ device. Aside from Shockley’s design using homogeneous material (all germanium), it is remarkably similar to Lilienfeld’s 1928 patent, shown in Fig.2. The patent shows that Shockley also envisaged complex multilayer devices. One five-layer proposal (Fig.8 in the original Shockley patent, or Fig.5 here) would operate similarly to the 6L7, a pentagrid mixer valve. Shockley defined two active layers (92 and 94) for signal injection and local oscillator injection. Early junction transistor designs Shockley’s design differs from Lilienfeld’s earlier junction transistor (Fig.6) in several important ways. As with the vacuum tube triode, both Lilienfeld and Shockley aimed to produce a space charge within the device that could then be controlled by an electrode intermediate between the ‘emitting electrode’ and ‘collecting electrode’ (cathode and anode in valve terminology). In this most fundamental way, junction transistors are similar to vacuum triodes. March 2022  15 Regrettably, no detailed description of Lilienfeld’s device exists. What follows is based on the Lilienfeld Patent. Lilienfeld’s device used a thin, deposited intermediate base layer overlaid on a substrate. The base was then deliberately micro-fractured to present a fine mesh-like surface. The collector deposition covered the base surface, penetrating gaps in the base ‘mesh’ layer to give electrical contact with the emitter layer. In operation, the forward-biased base-emitter junction created a space charge in the interface between base and emitter, presumably of electrons. The space charge existed on the underside of the base, just as with any planar diode such as a copper-­ oxide rectifier. But the space charge also existed in the minute crevices in the base layer, so it was subject to the attracting field from the collector. Thus, the base-emitter forward bias would establish a space charge that could be drawn through the base region to become collector current. By contrast, Shockley’s design created a voluminous space charge entirely within the homogeneous and continuous base layer, allowing the space charge to diffuse in all directions throughout the base, most notably towards the base-collector junction. This is described in detail in his patent, beginning on page 29. To reinforce the distinction, Lilienfeld’s design created a useful space charge at the interface between base and emitter, where Shockley’s created it entirely within the base. Lilienfeld’s collector-base junction is – like Shockley’s – reverse-biased. For both designs, zero bias means zero collector current. They both operate in contrast to a vacuum triode, where zero grid bias means maximum anode current. It’s not known how well Lilienfeld’s device worked. Shockley’s design intentionally created a large surplus of charge carriers in the base region due to its low doping concentration. Lilienfeld does not address this matter, and it is unclear how such a surplus could have been established, and consequently, whether his device could have worked as he claimed. Lilienfeld states a base thickness of 200µm, comparable to first-generation grown-junction transistors. He also mentions the need for overall small size to lessen capacitive effects. 16 Silicon Chip Lilienfeld’s 1925/1930 field-effect patents did specify “a film of copper sulphur [sulfide] compound”, but only to provide the extremely thin, high-­ resistance film needed for his design. Modern field-effect devices use a single semiconductor (silicon) for all of the device’s elements. Oskar Heil filed for a UK patent on a field-effect device in 1935 (patents. google.com/patent/GB439457A). His device specifically described the use of semiconductors and a thin insulating layer between the control electrode and the conduction part. It’s essentially the insulated-gate construction of virtually all metal oxide semiconductor (MOS) devices, from memory chips to microprocessors. Shockley Semiconductor Lab Arnold Beckman had built a substantial instrument company by the 1950s, beginning with a successful pH meter. He and Shockley had been friends for some years. Shockley left Bell Labs in 1955 and negotiated with Beckman to form his own Shockley Semiconductor Laboratory in mid-February 1956 (Fig.7). Gathering a stellar team of physicists and engineers and intending to develop and market junction-technology transistors, this ought to have been a very successful industry startup. Amusingly, Beckman had already paid Bell Labs the $25,000 licence fee for patent rights to transistors. Shockley Semiconductors was even forced to send two of its employees to the final Bell Labs Seminars on diffusion so that Shockley’s new company could be updated on the latest transistor theories. After a year’s intensive effort, Shockley’s company had failed to sell a single device, and Shockley had proven a poor leader. Rather than directing efforts towards perfecting his own patent of the junction transistor, he proposed distracting projects, including the development of his Shockley Diode. It was a four-layer PNPN device that would develop into the SCR/thyristor, today widely used in power control and finally developed as the Triac family of devices. This focus seems puzzling at a time when analog signal processing and amplification dominated domestic, communications, telephone and military electronics. But Bell’s gargantuan Australia's electronics magazine telephone network was switched by noisy, power-hungry electromechanical relays and switches needing constant maintenance. Shockley’s device would have revolutionised telephone exchange technology. But internal friction, fuelled by Shockley’s domineering management style, led to the exodus of Julius Blank, Victor Grinich, Jean Hoerni, Eugene Kleiner, Jay Last, Gordon Moore, Robert Noyce and Sheldon Roberts. This group are known as the “Fairchild Eight”. Shockley Semiconductor was sold to Clevite in 1960, having produced no commercial product. The “eight” were snapped up by the Fairchild Camera and Instrument Company, spinning off to become Fairchild Semiconductors. Work there ultimately led to the planar design, the basis of all modern silicon devices, from single transistors to microprocessors and memory chips with billions of individual components per chip. Fairchild Semiconductor remained a commercial success until September Fig.7: public artworks in Mountain View, California commemorate the site of Shockley Labs. Source: Wikimedia user Baltakatei (CCAShare Alike 4.0 International) siliconchip.com.au 2016, when the company was acquired by ON Semiconductor (previously Motorola’s semiconductor division). Ironically, Robert Noyce’s management style led the inventors of the integrated-­ circuit op amp to desert Fairchild and join National Semiconductor (which merged with Texas Instruments in September 2011), taking their extensive analog design expertise with them. Technologies in more detail Having gone over the basic history of transistors, let us take a more detailed look at the different processes used to fabricate those early transistor types. Point contact transistors The path to Bell Labs’ most famous patent was somewhat torturous. Bell Laboratories was formed in 1925 as an amalgamation of the research arms of Western Electric and American Telephone & Telegraph. Aside from their principal work on telephone systems, Bell Labs contracted to the US Government and, focusing on basic research, produced several Nobel Prize winners. The Bell System Technical Journals (https://archive.org/details/bstj-­ archives) detail Bell’s work from 1922 to 1983, which includes some of the foundations of today’s electronic and communications technologies. Shockley had begun from a ‘thermionic triode’ perspective, intending to pass current through a single piece of semiconductor. He would add an insulated metal contact with an applied potential on one side and use that contact’s electric field to control the current in the main channel. Fig.8 shows his intended device, which today we would call a depletion-­mode Mosfet. Over some two years of frustration, Shockley attempted to demonstrate his expected effect and failed each time. At this early stage of research, no one had anticipated two requirements: near-absolute purity of the semiconductor material and crystal regularity approaching perfection, especially at the surface. Fig.8: this is the device that Shockley was trying to build – essentially a semiconductor analog of the vacuum tube triode. Such devices were eventually built and are known as depletion-mode Mosfets (they’re similar to JFETs but have an insulating layer between the gate and channel) like the BSS139. Fig.9: the operation of point-contact transistors is still not fully understood, and it probably never will be as they are obsolete devices and there is no longer any active research. This is our best guess as to how they work. siliconchip.com.au Australia's electronics magazine Later research proved that the chaotic ‘tangled’ surface states which diffused and opposed any external field’s influence were the principal cause of Shockley’s failures. Gordon Teal’s advice regarding feedstock purity (noted earlier) and crystal regularity may well have delivered Shockley the device he had envisaged, had Shockley heeded it. In desperation, Bardeen and Brattain flipped the device: current would enter via a surface emitter contact, flow through the base material, then exit via a second collector contact. The strangest (but most successful!) results were obtained by adding a small drop of liquid – some electrolyte from a butchered electrolytic capacitor – to improve conductivity between the applied electrodes and the germanium surface. Finding an effect only at very low frequencies, they reasoned that a point contact (of the smallest possible diameter) would establish an intense electric field at the surface and perhaps give a higher operating frequency. They calculated they would need a separation between the points of about 0.002in (close to 50μm). Bardeen and Brattain then took a shortcut. Rather than waste time manipulating fine-pointed wires, Brattain had an assistant attach a strip of gold foil to a plastic wedge. Brattain then slit the foil with a fine knife and used the plastic wedge to press the two gold electrodes against the germanium base substrate. It was a revolutionary transposition. The first crude transistor’s operation came from abandoning expected theory and inventing a wholly new device with no ancestor: Lilienfeld and Heil’s prior devices (the bipolar junction and field-effect forms) contributed nothing to this radical invention. This also demonstrated that a transistor need not be made from only semiconductors: metal-semiconductor interfaces would also work, a fact exploited by later developments of micro-alloy and Schottky devices. The exact physics of the point-­ contact transistor (Fig.9) have never been fully described. Coblenz and Owens, writing in the 1955 book “Transistors: Theory and Applications” state “theories which adequately explain all the known phenomena of point contact operation have not been completed.” March 2022  17 Fig.10: the first point-contact transistor, created by Bardeen & Brattain. Source: Wikimedia user Unitronic (CC BY-SA 3.0) Fig.11: commercial point-contact transistors. They were potted in a plastic compound to protect the physically fragile device and prevent moisture/dust/etc from affecting their operation. Despite being produced commercially, they were still essentially hand-made devices and thus expensive. Image copyright 20012017 by Jack Ward, Transistormuseum.com It appears that much of the action took place under the upper surface of the germanium body. Still, it was the neutralisation of surface states in the collector region that contributed to increased collector current and thus current gain. The simplest complete explanation appears in the book “Fundamentals of Transistors” by L. M. Krugman & John F. Rider (1954) – see archive.org/ details/FundamentalsOfTransistors As well as owing nothing to any previous electronic device, the point-­ contact transistor’s method of operation is unlike any that followed it (including junction and field-effect transistors); its operation was unique. This allowed Bell’s patent attorneys to file with confidence. Most equipment using point-contact transistors has not survived. The majority is preserved in museums and the hands of collectors, with rare examples available online. As shown in Fig.9, the electron flow from the base to the emitter liberates ‘holes’ in the crystal. The liberated holes form a space charge and are attracted to the negative potential of the collector. Arriving at the collector, the holes from the space charge recombine with electrons entering from the collector lead. This recombination provokes additional collector current. Were the collector current only due to the space-charge holes from the emitter-base region, the collector current would be about the same as the emitter current. The transistor would show an emitter-collector current gain of about unity. But the extra collector electron flow to the base means that the collector current is greater than the emitter current. The result is a collector current about 2.5 times the emitter current. The microscopic contacts produce very strong local fields in the substrate, essential for power gain. Even in production, this was a hand-made structure, with the refinement of a ‘flash’ of current to form a more effective collector site. Somewhat reminiscent of Lee de Forest’s difficulties in understanding his Audion, Bardeen and Brattain struggled to describe the device they had invented. There was little ‘transistor action’ deep in the bulk of the crystal – the 18 Silicon Chip current amplifying action was mainly at (and just below) the surface. Yet today, bulk conduction is the sole mechanism used in bipolar transistors. Abandoning the idea of surface-only activity, the principle of bulk conduction was proven by John Shive in 1948 (see siliconchip.com.au/link/ abbe). This paved the way for Shockley’s groundbreaking junction transistor patent. The point-contact transistor’s handmade structure was difficult to manufacture with widely-varying characteristics, and susceptibility to surface moisture. This demanded meticulous and complete protection of the surface, leading to the development of Fig.13: the first European prototype transistor, made by Herbert Mataré in June 1948 by F & S Westinghouse in Paris, France. Source: Deutsches Museum, Munich, Archive, R5432 Australia's electronics magazine siliconchip.com.au applications, saw transistors in limited commercial use in the United States by 1953. RCA released several types and registered them with the then-new industry body, the Joint Electron Devices Engineering Council (JEDEC); the 2N21~26 and 2N50~53 series, 2N32/33 and 2N110 among them. TI also offered their Type 100 and Type 101 devices. Simultaneous discovery Fig.12: the physical structure of the prototype transistor shown in Fig.10. hermetic (airtight/watertight) sealing techniques – see Figs.11 & 14. One manufacturer said that the first transistor off his production line had cost a million dollars; 1954 dollars at that! The point-contact transistor had an appalling noise figure of about 45dB and was unreliable. It also exhibited negative resistance, causing it to oscillate and making it unusable as an amplifier in some configurations. It was, however, the only proven solid-state amplifying device in the early 1950s. Its small size and low power consumption made it a candidate for hearing aids. This, along with telephone repeater (amplifier) The improvement of radar technology was critical to aerial warfare in World War II, with both sides making full use of this technology. Heinrich Welker worked on the production of ultra-pure germanium crystals at the University of Munich during World War II. At around the same time, Herbert Mataré worked on microwave mixer diodes at the Telefunken plant in Silesia (at Bielawa, now part of Poland). Radar receivers must detect very faint signals – any noise generated within the receiver reduces sensitivity and, therefore, the maximum detection range. Local oscillator noise is the limiting factor in a set with a diode detector but no RF amplifier. Mataré discovered that a balanced push-pull detector, with two antiphase local oscillator signals, cancelled some of the local oscillator noise Fig.14: production versions of the European transistor, known as “Transistrons”. Inside each tube is a point-contact transistor. Source: Deutsches Museum, Munich, Archive, R5432 siliconchip.com.au Australia's electronics magazine and gave much-improved sensitivity. Mataré used point-contact diode mixers, the only device that would work at radar frequencies. Experiments in 1944 with two contact wires (for a push-pull circuit) showed that if the wires were very closely spaced, current in one wire would influence that in the other (see siliconchip.com.au/link/abbf). Mataré had discovered, prior to and independent of the work at Bell Labs, the principle of the point-contact transistor. Wartime demands prevented Mataré from pursuing his ‘transistor’ observations. Following the German surrender, Mataré taught physics at a US military academy near Kassel and Aachen university. During one briefing session, he was invited to move to Paris and set up a semiconductor plant for F.V. Westinghouse. Mataré and Welker’s research led to the production of diodes in 1946. Taking up his ‘double diode’ design, Mataré was granted US patent 2,552,052, lodged April 21st, 1948. More importantly, Mataré was able to demonstrate amplification in that year, 1948 – see Figs.13 & 14. His development program differed from that of Bardeen, Brattain and Shockley, as shown by Mataré’s different approach to surface preparation (see the PDFs at siliconchip. com.au/link/abbg and siliconchip. com.au/link/abbh). Like the Bell Labs team, Mataré and Welker struggled to unravel and understand the complex mixture of bulk and surface effects. Their first confirmed device was demonstrated in July 1948. Bell Labs’ release of their design prompted Mataré and Welker to rush a patent application to the French office. Their company, F.V. Westinghouse, applied for a French patent on August 13th, 1948, granted on March 26th, 1952. Stuck for a name, the French device became the “Transistron” to differentiate it from Bell Labs’ transistors. Transitrons were successfully used as early as May 1949 in telephone repeaters and were widely used by 1950. Despite the French devices being reported as superior to those from Bell, in the words of Michael Riordan, “Europe missed the transistor”. The French government, distracted by the threat of nuclear warfare with the Soviet Union, failed to support March 2022  19 Fig.15: probably the first public demonstration of a transistor radio at the 1953 Düsseldorf Radio Fair in Germany. Fig.16: a closer view of the radio shown in Fig.15. semiconductor manufacturing. Mataré left France for Germany and founded Intermetall (“Semiconductor”) in Düsseldorf, Germany. At the 1953 Düsseldorf Radio Fair, “a young lady wearing a black sweater and a multicoloured flowery skirt demonstrated to the public a tiny battery-operated transistor radio” – shown in Figs.15 & 16. The revolutionary work of Bardeen, Brattain, Mataré and Welker resulted in the creation of a solid-state amplifier that owed nothing to any ‘prior art’. However, the point-contact transistor was a dead end; poor performance, reliability and economics of manufacture condemned it to the dustbin of history. No complete functional and mathematical description of the device is ever likely to be written. with point-contact technology. His patent (https://patents.google.com/ patent/US2763832) gives an excellent description of the grown-­junction process. Source material of exceptionally high purity (highly regular germanium with no crystalline faults) was critical to reliable transistor production. Among other requirements, exceptional purity meant that electrical conductivity would be due only to carefully-measured doping chemicals, resulting in devices with predictable characteristics. Ordinary chemical methods were unable to produce highly-purified, regular crystalline stock. Zone refining passes ingots through a coil that heats the stock to its melting point. As the ingot passes through, it solidifies in cooler parts of the furnace. Impurities remain in solution and are ‘swept’ backwards relative to the ingot’s motion. In practice, furnaces used several heating coils, producing multiple refining zones in a single pass (see Fig.17). Germanium’s relatively low melting temperature allowed it to be conveyed in graphite ‘boats’. While this method gave much higher purity than simple chemical methods, it could not produce the ultra-high purity needed for transistor manufacturing. What about Doctor Adams? There are online claims that New Zealander Robert George Adams made transistor devices in the 1930s. For example, see http://blog.makezine. com/2009/04/02/the-lost-transistor/ You will find many references to candidates for ‘the inventor’ of the transistor. Some of these appear credible, others simply argumentative. I have focused on designs that were patented, and – more importantly – were either the direct antecedents of commercial devices or commercial devices themselves. Junction technology Taking up Shive’s work on bulk conduction (which had led to Shockley’s Junction Transistor patent), Gordon Teal’s patent for grown-junction devices revolutionised transistor manufacturing, making a complete break 20 Silicon Chip Fig.17: zone refining was one early method of purifying germanium feedstock. By passing an ingot through multiple induction heating coils, impurities could be ‘swept along’ the rod and ultimately removed. Australia's electronics magazine siliconchip.com.au Silicon’s much higher melting point necessitated running the ingot vertically without any form of container or support, relying on molten silicon’s natural cohesion to restrain the molten zone and not let the ingot collapse. This method needs no mechanical support. It also gave very high purity, so it was adopted for germanium. For germanium, Teal’s method was to melt well-purified germanium at about 940°C, then dip a seed crystal into the liquid, slowly rotating and withdrawing the seed vertically (at about 60 rpm and 0.8mm/second), as shown in Fig.18. The ‘pulled’ melt solidified into a highly-purified cylindrical crystal with a regular structure. The pulling furnace used a dry hydrogen atmosphere as air would affect the nature of the pulled crystal. This method worked equally well for germanium or silicon. Critically, it opened the door to the first truly successful transistor construction: grown junction. Semiconductor doping Practical semiconductors use highly-purified feedstock with tiny amounts of purposefully-added elements other than germanium or silicon. These ‘doping’ elements greatly improve conductivity (pure germanium and silicon are both very poor conductors). Doping creates the P- or N-type materials needed to make diodes, transistors and integrated circuits. Just one doping atom for about every ten million germanium atoms will give the conductivity needed for semiconductor action. A pentavalent element such as phosphorus donates electrons, so it is a donor impurity, making an N-type semiconductor. This is different from a common metallic conductor, which has a population of free electrons; the excesses in P- and N-type semiconductors are permanent, not like the mobile ‘electron clouds’ in metals which are, overall, electrically neutral. A trivalent acceptor impurity (such as aluminium) ‘steals’ an electron, leaving a positively-charged hole in the germanium, making it P-type. This means that the semiconductor has a permanent positive charge. Holes can be made to move in P-type material by an electric field, just as electrons can be made to move in N-type material. An excess of electrons (N-type) or holes (P-type) means that a doped semiconductor is a good conductor. It’s the ability to create different conductors with different current carriers that makes semiconductor devices possible. This is why the purity of the raw stock is critical. Precise electrical characteristics can only be guaranteed by starting from raw material of virtually absolute purity and adding precisely-­ controlled amounts of impurities. We’ll have more details on the effect of doping in a later article of this series. Teal’s development on the basic refining process was to add minute concentrations of doping gases to the furnace atmosphere. With an arsenic-­ containing atmosphere, P-type germanium was pulled. For N-type, phosphorus could be used. Fig.19 shows the process, with a doping ‘pill’ (rather than a gaseous doping atmosphere) controlling semiconductor polarity. But if the atmosphere were changed from, say, arsenic-rich to phosphorus-­ rich during a pull, the drawn crystal would begin as P-type, then transition to N-type. On completion of the pull, the crystal cylinder could be sliced, discarding most of the ends and leaving a disc containing the P-N junction, then cut across the disc to separate out numbers of individual square junctions. Voila! Diodes. Grown junctions If the pull was conducted slowly, and the melted pool sequenced from arsenic-rich to phosphorus-rich then back to a final arsenic-rich composition, the pull would contain three regions: P-type, N-type and P-type in a ‘sandwich’ (https://patents.google. com/patent/US2631356). Fig.18: one of the biggest breakthroughs in semiconductor manufacturing (which is in use to this day) was the pulling furnace process for generating ultra-pure giant crystals of germanium or silicon. These days, silicon crystals up to 400mm in diameter are made, although 300mm is a more typical size. Fig.19: it is possible to dope the molten germanium during the crystal pull. This results in graduated doping across the length of the crystal, or possibly even different doping zones within the crystal. siliconchip.com.au Australia's electronics magazine March 2022  21 This construction resulted in a large, single ‘transistor’. Fig.20 shows how careful slicing and dicing yields numerous individual transistors. This was William Shockley’s original Bell Labs patent. The world’s first transistor radio (the 1954 Regency TR-1) used grown-junction transistors (types X1 to X4) from the newly-formed Texas Instruments. Many types were given ‘in-house’ numbers, and grown-junction technology was being phased out as the 2Nxxx JEDEC nomenclature became established. NPN types 2N27~29 are among the registered grown-junction devices. The grown-junction process favours NPN construction. Many early transistors are NPN, including those in the Regency TR-1. NPN types also appear in the Regency’s TR-4/TR-5 and the Zenith Royal 500, implying that grown-junction technology was used at least until the issue of the Royal 500’s IF devices, type 2N216. TI released their germanium type 200 and type 201 in 1953 and returned to the technology with their silicon 2N389, as one JEDEC-registered example. Being a single, solid crystal, the grown junction was much more reliable and stable than the point-­contact construction. Since the regions – and their junctions – had been doped during the pull, no ‘forming’ was needed, as was necessary for the point-contact types. The characteristics were essentially stable from the moment of solidification until the end of life. Each sawn sliver needed to be mounted in a case and connections made to it, with the principal difficulty being the base’s location between the outer emitter and collector regions. There were also practical limits to base thinness – thinner bases give better gain and higher operating frequency, so this manufacturing technique limited the achievable performance. Fig.21 shows the long sliver sitting horizontally, soldered at each end to the emitter and collector lead-out wires. millions or even hundreds of kilometres per hour. Instead, they diffuse, like a swarm of bees buzzing about. This means that the current carrier (hole or electron) lifetime is critical – they must exist long enough in the base to complete their slow journey across it. It’s this diffusion process that held the key to transistor operation. Lee de Forest, believing that current flow in his “Audion” was solely dependent on gas ions, did not fully understand valve operation and could not capitalise on his invention. It was Thinner bases Irving Langmuir who discovered the For VHF and UHF operation, triode vital need for near-perfect evacuation valves become smaller and smaller, of valve envelopes. with anode-cathode spacings meaLikewise, transistor development sured in tenths of a millimetre or less. did not truly take off until the nature of Audio transistors need base thick- base diffusion was understood. Once nesses of micrometres, some one-­ it was, the principal effort was aimed thousandth of their valve equivalents. at reducing the width of the base juncWhy is this? tion. By the necessity of its microthin Electron flow in valves is driven by base, every transistor is going to be the anode-cathode voltage. As soon as a tiny device compared to its valve an electron escapes the space-charge cousins. cloud around the cathode, that electron is powerfully accelerated by the Conclusion anode-cathode field. All of the manufacturing methods A speed of 300 million kilometres described above are now obsolete. per hour (!) is common, and you may The second article in this series, to see perfectly good receiving valves be published next month, describes with a faint blue glow on the inside of improvements upon these techniques the glass envelope. This is caused by which included alloyed-junction electrons that miss the anode hitting transistors, diffused construction, the envelope so powerfully that they graded doping, base-substrate etchcause the glass to fluoresce. ing, micro-alloy diffusion and all-­ Electrons and holes in the transistor diffusion techniques. do not experience such an accelerating Having explained those, we’ll then field in the base. The base is essentially cover in detail the two transistor manat a constant potential across most of ufacturing methods still in use: mesa its width – there is no powerful field and epitaxial planar, both of which rely SC to accelerate electrons or holes to on photolithography. Base Collector Base region Emitter Fig.20: many grown-junction transistors are made in a single ‘pull’. After the billet is complete (with a thin P-doped layer in the middle), it is sliced into hundreds or thousands of slivers to form individual transistors. After having leads attached, they are encapsulated. Fig.21: a photo of a grown-junction transistor. The base connection wire is very thin since it must connect to the narrow base region in the middle of the slice. Source: David Forbes [CC BY-SA 3.0] Australia's electronics magazine siliconchip.com.au 22 Silicon Chip A Timeline of the Transistor 1873 Willoughby Smith 1948 Mataré & Welker 1956 Abramson & Danko Photoelectric Effect Point-Contact Photolithography He discovered that the electrical resistance of selenium varies with the amount of light falling on it. They independently developed a pointcontact transistor called the “transistron” that was used in France’s telephone network. This early technique was the start of mass PCB fabrication, and involved board lamination and etching. 1874 Karl Braun 1948 John Shive 1957 J. R. A. Beale Diode Detection Bulk Conduction Alloy-Diffused Transistor Braun noted that, when probing a galena crystal with a metal wire, current only flowed freely in one direction. Shive proved that conduction could occur through the bulk of a crystal, paving the way for Shockley’s junction transitor. See video: https://youtu.be/s2H3u-OPSIE Beale reported experimental production with operating frequencies up to 200MHz. 1904 Bose & Pickard 1950 Morgan Sparks 1958 Fred B. Maynard Practical Detectors Grown-Junction Micro-Alloy Diffusion The cat whisker detector was one of the most common early type of semiconductor diode, frequently used in crystal radios. Sparks helped develop the microwatt bipolar junction transistor. A grown-junction transistor can be seen at https://w.wiki/4Yv2 A transistor which employs a base layer with a graded impurity concentration, which is then etched to produce a thin active section. 1925 Julius Lilienfeld 1951 Christensen & Teal 1958 Arthur Varela Field-Effect Principle Epitaxial Fabrication Surface Barrier Lilienfeld filed a patent describing a thin-film device that is now recognised as a precursor to the FET (field-effect transistor). Also called epitaxial deposition, this technique increased both the transistor’s breakdown voltage and switching speed. Varela used chemical etching to create very a thin base structure, with the emitter and collector “plated” into the base wells. 1928 Julius Lilienfeld 1952 William Pfann 1959 Jack Kilby Junction Transistor Zone Refining Integrated Circuit (fabricated) Lilienfeld filed a patent describing a 3-layer device whose structure would be developed by William Shockley as the junction transistor. Also called zone melting, this is a technique used to purify materials and was first used for germanium transistors. Kilby created the first prototype IC, which was a hybrid, not monolithic. A photo of him can be found at: https://w.wiki/4Yvw 1935 Oskar Heil 1952 Pankove & Saby 1959 J. F. Aschner Field-Effect Alloyed-Junction Mesa Transistors Heil discovered the possibility of controlling the resistance of a semiconducting material with an electric field (as in a MOSFET). Alloy-junction transistors were well-suited for mass production, but suffered from poor RF performance. One of these transistors can be seen at https://w.wiki/4YvL Produced by Fairchild Semiconductor, but developed at Bell Labs in 1955. Both base and emitter were diffused, but they still suffered from leakage. 1943 Paul Eisler 1953 Herbert Kroemer 1959 Atalla & Khang Printed Circuitry Drift-Field Transistors The MOSFET Eisler designed a radio in 1942, the first to use a PCB. He was granted a patent for it in 1943. High-speed bipolar junction transistor using graded doping. At Bell Labs, Atalla’s work on oxidising silicon surfaces led (with Khang) to the MOSFET, and to planar transistors and the monolithic IC. 1944 Herbert Mataré 1953 Dacey & Ross 1962 Jean Hoerni Point-Contact Effect Field-Effect Transistor Epitaxial Planar Mataré noticed this effect while developing crystal rectifiers from silicon and germanium during WW2. A working JFET was built by George Dacey and Ian Ross. A photo of them can be found at siliconchip.com.au/link/abcb An oxide layer is left in place on the silicon wafer, reducing leakage. 1947 Bardeen & Brattain 1953 Harwick Johnson 1963 Sah & Wanlass Point-Contact Transistor Monolithic Integrated Circuit CMOS At Bell Labs, these two, led by Shockley, created the first point-contact transistor from germanium. A patent for a phase-shift oscillator fabricated in a single “slice” of semiconductor, which needed no interconnecting wires. CMOS (complementary MOSFET) technology was developed at Fairchild Semiconductor, paving the way for the computer revolution. siliconchip.com.au Australia's electronics magazine March 2022  23 Capacitor Discharge Welder Part 1: By Phil Prosser safe and low-voltage Make your own thermocouples or battery packs! If you're skilled enough, you might even be able to weld studs to sheet metal. This project lets you build a safe low-voltage mini spot welder. Safety warning Capacitor Discharge Welding works by generating extremely high current pulses, and consequently, strong magnetic fields. Do not build or use this project if you have a pacemaker or similar sensitive device. This device can generate sparks and heat. Users must wear appropriate personal protective equipment such as AS/NZS 1337.1, DIN 169 Shade 3 welding glasses. These provide mechanical and IR/UV protection. 24 Silicon Chip Australia's electronics magazine siliconchip.com.au Features & Specs Weld energy: adjustable, from a few joules up to 208-365J (depending on number and type of capacitors used) Weld pulse duration: 0.2-20ms with optional 0.1ms pre-pulse, 5ms before main pulse Safety features: trigger lockout during charging, foot switch triggering, kill switch Capacitor charging: 2A or 5A (selectable); switch-mode for high efficiency and fast charging Welding leads: 1m min length suggested but can be customised Power supply: 24V DC, 2.5A minimum (6A+ recommended) It costs more to buy thermocouples than to weld the tips of K-type thermocouple wire, available cheaply by the reel. And getting a custom-­made battery pack for repair or your project is also expensive. With the availability of used battery packs and individual cells, building custom batteries yourself is a real option – as long as you have a way of welding tabs onto them. Safely welding tabs to batteries is more challenging than you might think. You cannot use solder to make the joints as the metal does not ‘wet’ easily, and you need to get it dangerously hot to make the joint. This can damage the plastic insulators inside the battery, leading to catastrophic failure of the cell. Tabs on professionally-­ made cells are welded on. This project allows you to do the same yourself. Professional battery welders are generally ultrasonic welders, capacitor discharge welders or high-current spot welders. Most are way out of the ability for hobbyists to build. Capacitor discharge welders are at the lower end of the professional spectrum. These use energy stored in a bank of capacitors to deliver the weld energy to the workpiece. A common characteristic of all battery tab welders is that they deliver an awful lot of energy (typically 100-200 joules or more) to the connection in as short a period as possible. Options for DIY One approach is to use a car battery or Li-ion cell with a beefy switching siliconchip.com.au The front panel of the Capacitor Discharge (CD) Welder. device. A very large SCR or FET is used to short the battery across the ‘weld spot’ for a short period. While this can work, it has a hidden problem. The current is high enough to create a weld but not high enough to do it quickly. As a result, there can be a large ‘heat-affected zone’ and the weld quality varies depending on the health of your battery. The other practical alternative is to roll your own Capacitor Discharge Welder. This is somewhat more expensive than using a big battery but provides more predictable results. Our design also gives you a lot of control of the weld energy and time. Capacitor Discharge (CD) Welders These do exactly what they say on the box. They comprise a capacitor bank that you charge up, and then electronically short it across the workpiece using one or more large FETs, SCRs or other very tough semiconductor switches. The weld is formed by resistive heating in the workpiece. All of the energy that goes into the weld is from the capacitors. This provides you with certainty and repeatability about how much energy is delivered. The energy is also delivered very quickly, in a few milliseconds, which means the weld is done before heat conducts far from the joint. The downside of this is that you need capacitor(s) that can take the abuse of massive discharge pulses, which can get expensive. The upside is that you can control the energy Australia's electronics magazine delivered to the weld in two dimensions, both by selecting the voltage the capacitor is charged to and by how long you turn the switches on. Our approach We want to do better than simply paralleling as many capacitors as we can find and using a giant SCR to switch them. Our goal is a project that allows you to choose the overall scale of the CD Welder, allowing you to select the most cost-effective capacitors for your application. While researching this, we came across Ian Hooper’s work (www.zeva. com.au/Projects/SpotWelderV2/) which prompted the modular and scalable approach presented here. Our design uses multiple Energy Storage boards which stack, allowing you to build a welder with the capacity you need. A separate Power Supply Module allows you to control the voltage and provides a constant charge current to the capacitor bank. A Controller Module enables you to program the weld pulse width you want. These features are typically found on a professional kit. Our charger is based on a switch-mode regulator, which means that we can control the current charging the capacitors without using a resistor or linear regulator – both of which would otherwise get stinking hot! With the recommended 10 Energy Storage Modules (ESMs), we have 1.2 farads of storage, which we can charge to about 2-25V DC. The pulse width can be varied from under one March 2022  25 The finished Power Supply Module used in the Capacitor Discharge Welder. Its main job is to charge the capacitor bank, but it also provides power to the rest of the circuitry. millisecond through to 20ms. Hold up there, Dr Evil! Are we seriously talking about shorting a 1.2F capacitor across the weld joint? At just 25V, this is 375J! Let’s think this through; there are safety issues to be considered here! We have intentionally used a maximum charge voltage of 25V, which is well below the Extra Low Voltage threshold and reduces voltage-related safety hazards to operators. We use a 24V DC 6A plug pack to charge it up, so no mains wiring is involved. But the CD Welder stores an awful lot of energy. This warrants great caution in use, with the risk of burns and arcing. Safety must be in the front of your thinking when using it. From a design perspective, we seek to minimise the risk of inadvertent firing, ie, “uncontrolled output”, including by using: • A fire button that only enables the output for a few milliseconds, minimising the risk of creating an arc when placing the weld probes on the workpiece. • An interlock stopping firing during charging, avoiding multiple shots. • An enable/kill switch. • A footswitch to fire the Welder while keeping both hands free. need a model of all the parts involved, starting with the capacitors and the boards on which they mount. Most of the recommended capacitors have an ESR (equivalent series resistance) specification close to 20mW, so we’ll start with that figure. For the capacitor closest to the ‘output’ end of the board, we calculate a trace resistance (both positive and negative) of 0.5mW, giving 20.5mW. The other capacitors are a bit further away, so we calculate figures of 21.27mW and 22.05mW. These three capacitors are in parallel, so we can calculate their combined source resistance as 20.5mW ∥ 21.27mW ∥ 22.05mW = 7.08mW. Then we add the Mosfet on-resistance (1.7mW ∥ 1.7mW = 0.85mW), the PCB track resistance from the Mosfets to the bus bar and the resistance of the connections to the bus bars, giving us a total of 8.33mW per module. We’ve paralleled ten of these modules, giving an overall source impedance of 0.83mW (ie,10% of the figure given above). To this, we must add the resistance of the bus bars (around 0.1mW each), the welding tips (a total of about 0.5mW) and then the welding cables. We’re using 1m-long cables with 7.1mm2 cross-sectional area for a figure of 2.6mW each, dominating the final source resistance value, which is 7.53mW. Given this, what is the maximum current we can deliver? Will the FETs survive? Of course, the workpiece will never be 0W. With reasonably pointy probes welding a 0.15mm-thick nickel strip, this will be more like 5mW. But we conservatively use a value of zero for our calculations. The above tells us that it would be a terrible idea to fire the Welder with the bus bars shorted. If we omit the lead resistance, the load will be 1.5mW plus whatever shorts the bars. This gives a worst-case current of 16,000A or 800A per Mosfet, which is right up Operating principle The basic idea behind the CD Welder is shown in Fig.1. This simple Welder model consists of the capacitors, connections and Mosfets. Note that the Mosfets pull the negative lead down to ground potential but are ‘flipped’ in this figure for clarity. This seems simple enough, but the question at the forefront of our minds is: will the capacitors and Mosfets survive the very high currents involved, especially on a repetitive basis? To do this, we need to determine what the peak current is likely to be and how it decays over time. To assess this we 26 Silicon Chip Fig.1: the basic concept of the Capacitor Discharge Welder is a capacitor bank of around 30 capacitors in parallel that are charged up and then connected across the heavy welding leads when the Mosfets are switched on. The trick is making sure everything survives this process as over 1000A can flow! Australia's electronics magazine siliconchip.com.au The Control Module uses four 555 timer ICs. against their 1ms safe operating area (SOA) curve. The Mosfets might survive this, but whatever shorts the bus bars might not! Under ‘normal’ operation, the worstcase current will be 3300A with the 1m leads perfectly shorted. This is 166A peak per Mosfet (two per module) for a few milliseconds. The specified devices are rated to handle 192A continuously, and their SOA is 600A for 10ms, giving us a reasonable safety margin. Under more realistic conditions, and with a 5mW workpiece, the maximum current will be 25V ÷ (7.53mW + 5mW) = approximately 2000A. This can be controlled by reducing the operating voltage and pulse width. This analysis might seem over the top – but a CD welder is quite a device! Even my inner Dr Evil was just a little intimidated the first time I fired it in anger! Major parts The resulting CD Welder block diagram is shown in Fig.2. We will discuss each part and explain some of the challenges they present. 1) The Power Supply Module The problem with charging a 1.2F capacitor is that to any regular power supply, it looks like a short circuit. Also, when fired, the CD Welder power supply is shorted out. It must be able to tolerate this on a repetitive, longterm basis. A linear regulator might do the job, but it would face several problems. For a start, it would get hot! Also, if we use a 5W resistor to limit the charging current, the initial current will be 5A, but it will not fully charge the capacitor for close to 20 seconds. We determine this by solving the equation Vcap = Vin × (1 − e-t ÷ (RC)) for t, with a value of Vcap close to Vin. This convinced us to instead use a switch-mode regulator with a 5A (or 2A) constant current output. This only dissipates a few watts even when running flat out. An equation for calculating the charge time is C = Q ÷ V, where C is in farads, Q in coulombs and V in volts. Differentiating and rearranging this equation gives us dV/dt = I ÷ C. With I = 5A and C = 1.17F, dV/dt is 4.3V per second. Note that you can also determine your actual capacitor bank capacity using this equation by measuring its charge rate and then solving for C. 2) The Control Module We need a way to trigger all the capacitors to dump their charge into Fig.2: a modular approach makes building the CD Welder easier. A mains power ‘brick’ is fed into the power supply, which provides a constant current to charge the capacitor bank. Said bank comprises eight or more Energy Storage Modules (ESMs – 10 in our case) connected in parallel using bus bars. The control circuit provides the timing and the ability to trigger all the ESMs to dump their charge into the welding probes simultaneously. siliconchip.com.au Australia's electronics magazine the welding probes simultaneously, for a defined period. We have used the venerable NE555 timer IC to do this. The Controller needs to work in a tough electrical environment, so using a ‘bulletproof’ chip in a simple configuration is the way to go. We hope you are picking up on the attention we are paying to EMI/EMC and the currents involved here! Professional controllers offer a “two pulse weld” mode. The initial pulse cleans the surface between the parts and the second pulse makes the weld. This feature is easy to provide, so we did. Three timer ICs generate the initial pulse, then a delay, then the second pulse. Energy Storage Module (ESM) The Storage Module takes inspiration from Ian Hooper’s work (mentioned above), then extends this to provide us more control over the switching and increases robustness to back-EMF. This ESM accepts 10mm lead pitch (spacing) caps with a diameter up to 35mm. This provides you with many options for sourcing these expensive parts. We recommend you use caps of known provenance from the likes of Mouser, Digi-Key etc. Online prices An example weld of 0.12mm-thick nickel at 15V with a 20ms weld time onto a AA cell used for testing. The tab can’t be pulled off with any reasonable amount of force applied. March 2022  27 Table 1 – suitable 25V-rated capacitors (M=Mouser, DK=Digi-Key) Capacitor value # ESMs Caps per ESM Total capacity Energy stored Suitable parts 56,000μF 8-10 2 0.9-1.1F 280-350J DK: 338-3866-ND 39,000μF 8-10 3 0.9-1.17F 300-365J M: B41231A5399M000 DK: 338-3743-ND 33,000μF 10 3 1F 310J M: SLPX333M025E9P3 | B41231A5339M000 | 380LX333M025K052 DK: 338-1613-ND 22,000μF 14 3 0.92F 288J M: SLP223M025H5P3 | 380LX223M025J052 DK: 495-6159-ND | 338-4172-ND | 338-2431-ND Table 2 – suitable 16V-rated capacitors (M=Mouser, DK=Digi-Key) Capacitor value # ESMs Caps per ESM Total capacity Energy stored Suitable parts 68,000μF 12-14 2 1.6-1.9F 208-243J M: B41231A4689M000 | 380LX683M016A052 DK: 495-6141-ND | 338-2273-ND 56,000μF 10-12 3 1.7-2.0F 220-256J M: B41231A4569M000 | SLPX563M016H4P3 47,000μF 14 3 2F 256J M: B41231B4479M000 DK: 338-2458-ND | 338-2318-ND 39,000μF 14 3 1.6F 210J M: B41231A4339M000 | 380LX393M016A032 | 16USG39000MEFCSN25X50 DK: 338-2261-ND that seem too good to resist are usually a bad choice with capacitors. The ESMs bolt to bus bars, allowing paralleling of an arbitrary number of modules. They provide fast switching using two onboard high-current Mosfets and a dedicated FET driver. They also have an inbuilt flyback diode to protect against the back-EMF and are easy to build, wire up and service. Switching really high currents is not a simple thing to do. By switching each module rather than the whole bank, we can ‘divide and conquer’. All the SMD components are located on the underside of the Energy Storage Module (ESM). 28 Silicon Chip The recommended bank of 30 capacitors on 10 ESMs will each see currents in the region of 50A per capacitor every time a weld is made. The RMS ripple current rating of the recommended capacitors is about 10A, but the limiting factor for aluminium electrolytic capacitors is heating. The average current is very low because of our low pulse rate, so the I2R losses are insignificant. Capacitor choice The capacitors for a CD welder are the main expense. During the development of this project, we spent much time investigating the trade-offs in the total energy stored, capacitor voltage rating and the safety and robustness of the switching system. The choice has also been complicated by parts availability. The 20212022 drought for electronic components (especially semiconductors) is making our life extremely difficult here at Silicon Chip, as even seemingly ordinary parts are hard to get. Perhaps surprisingly, this includes capacitors, especially large electros. Luckily, there is a range of choices you can make in selecting your Australia's electronics magazine capacitors. For 25V-rated capacitors, we recommend that you aim for a total capacitance of no less than 1F. Ideally, hit the 1.2F mark for some spare capacity. Table 1 shows some good choices here. If you choose to use 16V capacitors, you can probably save a few dollars. In this case, aim for a total capacitance of no less than 1.5F and ideally 2F if you want a bit of extra margin. All of the options shown in Table 2 will total around $180 or so. Remember that the welding process is about the energy delivered to the weld – the actual capacitance is a means to an end, and using a higher voltage makes this easier. You will find availability and price can be something of a ‘head-scratcher’, and we are sure you will have hours of ‘fun’ working out your best value for money. Probably the only thing we would advise against is using much larger capacitor values than we recommend – our models show that for the values in the tables above, it should be OK, but much more capacitance on a module could lead to Mosfet failure. So how much energy do we really need? We found that about 130 joules siliconchip.com.au Fig.3: the Power Supply circuit derives a 15V rail to run the remainder of the circuitry from the 24V DC input using a simple linear regulator. The rest of the components form the constant-current switchmode step-down regulator. It’s based around switching regulator IC1 with shunt monitor IC2 and op amp IC3 used to make it deliver a fixed current until the capacitor bank reaches the fully-charged voltage selected using potentiometer VR1. was sufficient for the tabs we welded. We feel confident that a welder with 200J total storage would suit our needs. The recommended design can deliver 370J, which would definitely provide margin throughout its life. Circuit details Fig.3 is the circuit diagram of the Power Supply module. The regulator used is an MC34167 device, a switchmode regulator operating at 71kHz. It is operated in a buck (step-down) configuration, using a 220μH filter/energy storage coil and 15A schottky flyback diode with two 1000μF smoothing capacitors on the output. These will help reduce radiated EMI during charging, but the >1000A pulses will still play havoc with any sensitive electrical device nearby. To turn a voltage regulator into a current source, we need to sense the output current and convert this into a voltage as feedback. This is done by the INA282 shunt monitor IC, IC2, with a 10mW series shunt. The INA282 has a gain of 50 times, so its pin 5 output delivers 500mV/A. This is further amplified by a factor of about 6.5 by op amp IC3a, resulting in 2.8V/A to the feedback pin (pin 1) of IC1. If pin 1 of IC1 is lower than 5.05V, the regulator increases its output. Similarly, if the input is higher than 5.05V, About 10 of these ESMs are joined together to form a capacitor bank for the CD Welder. siliconchip.com.au Australia's electronics magazine March 2022  29 the output duty cycle and thus voltage/current is reduced. So with 2.8V/A, we get an output current close to 1.8A (5.05V ÷ 2.8V/A). The 5A version of the circuit changes two resistors (values shown in green), setting the gain of IC3a to 2.2 times, so its output is 1.1V/A and therefore, the current limit is around 4.6A (5.05V ÷ 1.1V/A). So that the capacitor charging stops when it reaches the desired voltage, the output voltage is applied to potentiometer VR1 via a 27kW resistor and the reduced voltage at its wiper is buffered by op amp IC3b. This is fed into the ‘current sense’ input of IC3a (pin 3) via diode D3, which ‘ORs’ these voltages together. This means that when the output voltage is lower than the set limit, the circuit operates as a constant current source. When the output voltage reaches the programmed limit, the voltage from VR1 exceeds the current sense voltage, and regulation is now voltage-controlled. When in current limit mode, we switch on the CHARGE LED connected across CON3. At the same time pin 7 of CON4 is pulled low, which acts as an interlock in the controller circuit on the ‘fire’ switch. This is used to stop the user from making a weld before the capacitors are fully charged. Controller circuit The controller circuit is shown in Fig.4. Three NE555 devices, IC4-IC6, are set up as monostable (single-shot) pulse generators in series (output to trigger input), with a fourth (IC7) acting as a high-current buffer. This allows us to generate a first pulse, a delay and a second pulse. The main weld pulse is controllable using 100kW potentiometer VR2, variable from under 1ms to about 20ms. If the ‘two-pulse’ switch connected to CON8 is open, only the output trigger pulse from IC6 is fed (via diode D6) to timer IC7, so a single trigger pulse goes to pin 9 of CON7. If that switch is closed, the outputs pulse from both IC4 and IC6 result in a trigger pulse. Timer IC5 provides the delay between these pulses. We chose the NE555 as a driver because it can operate from 15V, can deliver 200mA, has a fast rise time (300ns) and can easily drive our TRIGGER bus. This switches all the energy storage modules simultaneously. The ‘fire’ input to the Controller, connected to CON5, is a switch to ground. We have included PNP transistor Q2 to inhibit the input while the capacitors are charging. When the INHIBIT line from pin 7 of CON7 is low, Q2 is on and it holds the trigger input feeding pin 2 of IC4 high. The 1μF capacitor between its base and the 15V rail avoids noise coupled into the INHIBIT line from causing problems. Similarly, if the pins of the ENABLE header (CON6) are shorted (eg, via a switch), this will prevent triggering by switching on Q2 via diode D8. The control interface PCB design uses tightly-packed surface-mounted components to increase its EMI robustness and avoid false triggering etc. ESM circuit This is shown in Fig.5. There isn’t much to it – mainly just the three (or two) storage capacitors, two Mosfets and the dual Mosfet driver, IC8. We explained earlier why we are using the very high-current IRFB7430 FETs. These must be tightly controlled in terms of switching time and switch After building your CD Welder. It’s useful to make some test welds on scrap metal to get an idea of how much voltage and time is needed to form a decent weld. Too much energy will burn and distort the metal, and even blow holes in it, as shown on the left tab. On the right, you can see that we managed to weld the tab to the can without destroying it. 30 Silicon Chip Australia's electronics magazine on and off cleanly. The TC1427 Mosfet driver can deliver up to 1.2A into the FET gates, switching them in 25ns. It has input hysteresis, which will help our robustness to noise. The alternative, pin-compatible IX4340NE mentioned in the parts list can deliver an even higher current of 5A for very rapid switching indeed. IC8’s inputs are connected to the TRIGGER bus from the NE555 which has a 15V swing, again seeking to avoid false switching due to noise. By driving all Energy Store Modules with the common Trigger signal, we aim to ensure that all Energy Store Modules are switched on and off at as close to the same time as possible. The Welder in action Scope 1 (overleaf) is a digital oscilloscope capture showing the voltage across the capacitor bank just after the Welder is triggered. In this test, only one ESM has been connected. You can see the sudden drop in voltage to around 5V over about 20ms when the weld is made, and the recharge, which takes a few hundred milliseconds. Measurements taken from this screen capture let us calculate the total capacitance and the weld current using the formula C = Q ÷ V introduced earlier, along with C = I ÷ (dV/dt). We know the charge current I is close to 2A. We measure a 10.5V increase in voltage over 616ms, so: C = 2A ÷ (10.5V ÷ 0.616s) = 0.117F, which is pretty much spot on for three 39,000μF capacitors in parallel. Scope 2 shows a similar curve for all ten ESMs in parallel. The voltage increases by 8.03V in two seconds at 4.8A, which tells us the bank in total is just under 1.2F. Turning now to what happens when the Welder is used, Scope 3 shows the Welder set to 15V welding tabs in a typical application. More voltage than this starts to blow holes in the tabs. This scope grab shows the 1.17F capacitor bank voltage dropping by 4.416V in 2.7ms, which we calculate is a discharge of just under 2000A. Next month Next month we’ll have the assembly details of the three modules, then the whole unit, plus testing and usage instructions. In the meantime, you can peruse the parts list and start gathering the components you will need to build it. siliconchip.com.au Fig.4: the control circuit is based on four of the good old NE555. When triggered, IC4 generates the fuse discharge pulse (if the ‘two pulse’ switch is enabled), IC5 produces the inter-pulse delay, and IC6 delivers the second welding pulse. VR2 allows the second pulse duration to be varied between about 0.2ms and 20ms. Fig.5: the capacitors that store all the energy for welding are mounted on these ESMs, two or three per board. Each ESM also has two Mosfets to dump their energy into the welding leads, a dual Mosfet driver to ensure they switch on and off cleanly, and a back-EMF clamping diode to catch any reverse spikes due to lead and other stray inductances. siliconchip.com.au Australia's electronics magazine March 2022  31 Parts List – Capacitor Discharge Welder 1 250 x 200 x 130mm ABS enclosure [Altronics H0364A] 1 Power Supply module (see below) 1 Controller module (see below) 8-14 Energy Storage modules (see below & Tables 1-2) 1 82W 5W 10% resistor (for testing) 1 0.27W 5W 10% resistor (for testing) 1 panel-mount digital voltmeter (optional; to display selected voltage) [eBay, AliExpress etc] Switches/connectors 3 two-way polarised header plugs with pins (foot switch, enable, charge) [3 x Altronics P5472 + 6 x P5470A or 3 x Jaycar HM3402] 12 10-way IDC line sockets [Altronics P5310 or Jaycar PS0984] 1 3-pin circular microphone inline socket (for footswitch cable) [Altronics P0949] 1 3-pin circular microphone chassis-mount connector (for footswitch) [Altronics P0954] 1 footswitch (trigger) [Altronics S2700 or Jaycar SP0760] 1 miniature chassis-mount SPDT toggle switch (two pulse select) [Altronics S1310 or Jaycar ST0555] Wire/cable/etc 1 1m length of 8AWG red power wire (welding lead) 1 1m length of 8AWG black power wire (welding lead) 1 200mm length of 17AWG red tinned extra-heavy-duty hookup wire [Altronics W2283] 1 200mm length of 17AWG green tinned extra-heavyduty hookup wire [Altronics W2285] 1 1m length of twin speaker cable, rated to handle at least 5A 1 2m length of two-core heavy-duty microphone cable (footswitch lead) [Altronics W3028] 1 1m length of 10-way ribbon cable 1 100mm length of 20mm diameter heatshrink tubing (for welding cables) 1 300mm length of 12.7mm diameter heatshrink tubing (for handles) 1 100mm length of 10mm diameter heatshrink tubing (for welding cable lugs) Hardware 2 260mm length of 10 x 10mm square aluminium bar (bus bars) 2 100mm length of 10 x 10mm square aluminium bar (handles) 6 M4 x 10mm panhead machine screws (for handles and welding connections) 2 M4 shakeproof washers (for welding connections) 10 M3 x 10mm tapped spacers (for joining modules together) 4 M3 x 16mm panhead machine screws (for Presspahn shield) 40 M3 x 6mm panhead machine screws (module connections) 44 M3 shakeproof washers 2 6mm heavy duty eyelet crimp lugs for 7/8AWG wire [Altronics H1757B] 32 Silicon Chip 1 60 x 40mm sheet of Presspahn or similar insulating material [Jaycar HG9985] Power Supply (one needed) 1 double-sided PCB coded 29103221, 150 x 42.5mm 1 220μH 5A toroidal inductor (L1) [Altronics L6625 or Mouser 542-2316-V-RC / 542-2200HT-151V-RC] 1 10kW 9mm linear right-angle potentiometer with plastic shaft (VR1) [Altronics R1906] 1 10A M205 slow-blow fuse (F1) 2 PCB-mount M205 fuse clips (F1) 2 2-way mini terminal blocks, 5/5.08mm pitch (CON1, CON2) 1 2-way polarised header, 2.54mm pitch (CON3) 1 2x5 pin header (CON4) 1 micro-U TO-220 heatsink (for REG1) [Altronics H0627] 1 mini-U TO-220 heatsink (for IC1) [Altronics H0625, Jaycar HH8504] 2 TO-220 insulating kits with silicone washers & plastic bushes (for REG1 & IC1) 2 M3 x 10-16mm panhead machine screws, shakeproof washers and nuts (for mounting heatsinks) 4 M3 tapped spacers 8 M3 x 6mm panhead machine screws and shakeproof washers 1 PCB pin (optional) Semiconductors 1 MC34167TV or MC33167TV 0-40V 5A integrated buck regulator, TO-220-5 (IC1) 1 INA282AIDR bidirectional current shunt monitor, SOIC-8 (IC2) 1 LM358 dual single-supply op amp, DIP-8 (IC3) 1 LM7815 15V 1A linear regulator, TO-220 (REG1) 1 BC546 65V 100mA NPN transistor, TO-92 (Q1) 1 6.2V 400mW zener diode (ZD1) [1N753, Altronics Z0318] 1 6TQ045-M3 45V 6A schottky diode, TO-220AC (D1) 1 1N4004 400V 1A diode (D2) 2 1N4148 75V 150mA signal diodes (D3, D4) Capacitors 2 1000μF 50V low-ESR electrolytic 2 220μF 50V low-ESR electrolytic 1 10μF 50V electrolytic 1 2.2μF 50V X7R multi-layer ceramic 6 100nF 50V X7R multi-layer ceramic 1 100nF 50V SMD M2012/0805 size multi-layer ceramic Resistors (all 0.25W 1% metal film unless stated) 1 27kW 1 12kW 6 10kW 1 8.2kW (for 5A version) 1 3.3kW (for 5A version) 1 2.2kW 3 1kW 1 0.01W (10mW) 1% 1W shunt [Mouser OAR1R010JLF] Australia's electronics magazine siliconchip.com.au Partial kits are available for the Power Supply (SC6224) and ESM (SC6225). See page 106 for details. Controller (one needed) 1 double-sided PCB coded 29103222, 150 x 42.5mm 1 100kW 9mm linear right-angle potentiometer with plastic shaft (VR2) [Altronics R1908] 3 2-way polarised headers, 2.54mm pitch (CON5, CON6, CON8) 1 2x5 pin header (CON7) 1 jumper shunt (optional) Semiconductors 4 LM555 timer ICs, DIP-8 (IC4-IC7) 1 BC556, BC557, BC558 or BC559 30V 100mA PNP transistor, TO-92 (Q2) 4 1N4148 75V 150mA signal diodes (D5-D8) Capacitors 2 10μF 50V electrolytic 1 1μF 63V MKT 1 1μF 50V multi-layer ceramic 1 220nF 63V MKT 1 220nF 50V multi-layer ceramic 7 100nF 63V MKT 4 10nF 63V MKT 2 1nF 63V MKT Resistors (all 0.25W 1% metal film) 1 220kW 2 33kW 3 10kW 1 4.7kW 4 1kW Energy Storage module (parts for one module) 1 double-sided PCB coded 29103223, 150 x 42.5mm 1 2x5 pin header (CON9) 1 2-way mini terminal blocks, 5/5.08mm pitch (CON10) 4 M3 tapped spacers 8 M3 x 6mm panhead machine screws and shakeproof washers Semiconductors 1 TC1427COA713 or IX4340NE dual low-side Mosfet driver, SOIC-8 (IC8) 2 IRFB7430PbF 40V 409A Mosfets, TO-220 (Q3, Q4) 1 RFN20NS3SFHTL 20A 350V fast recovery SMD diode or similar, TO-263S-3/D2PAK (D9) 1 red LED (LED1) Capacitors 3 39mF 25V high ripple current snap-in capacitors, 10mm lead spacing, 35mm diameter [Mouser B41231A5399M002 or Digi-Key 338-3743-ND or alternatives as per Table 1 or 2] 1 1μF 16V X7R ceramic, SMD M2012/0805 size 2 100nF 50V X7R ceramic, SMD M2012/0805 size Resistors (all SMD 1% M2012/0805 size unless stated) 1 10kW 1 100W 2 10W 1 1.5kW 1W 5% axial (through-hole) siliconchip.com.au Scope 1: the recharge voltage curve for a single Energy Storage module at 2A. The voltage increases by 10.5V in 616ms. Note also the discharge curve visible here, which we calculate as being 130A. Scope 2: the recharge voltage curve with all ten ESMs in parallel. This time the charge rate is 5A, and using the formula given in the text, we calculate the total capacitance as a hair under 1.2F. Scope 3: 200A pulse into a load. The yellow trace is the voltage on the negative output. The blue trace is for the capacitor voltage, which shows a dip for the initial pulse then exponential decay! The welding cables and copper-tipped probes. Australia's electronics magazine SC March 2022  33 Design, Develop, Manufacture with the latest Solutions! Powering New Technologies in Electronics and Hi-Tech Manufacturing Make new connections at Australia’s largest Electronics Expo. See, test and compare the latest technology, products and solutions to future proof your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Industry experts will present the latest innovations and solutions at this year’s conference. Details at www.smcba.asn.au In Association with 34 Silicon Chip Supporting Publication Australia's electronics magazine Organised by siliconchip.com.au By Tim Blythman The Pico microcontroller board, described in the December 2021 issue, is a versatile and powerful ARM-based microcontroller on a small board for less than $10. There’s quite a lot you can do with it on its own, but it’s even more interesting when connected to an LCD touchscreen. Raspberry Pi Pico BackPack W e reviewed the Raspberry Pi Foundation’s Pico microcontroller board in the December 2021 issue (siliconchip.com.au/Article/15125). It’s based on their own RP2040 microcontroller and is quite different from their popular line of Raspberry Pi single-­board computers (SBCs). However, it shares a resemblance in its low price and ease of use. In that article, we compared it to other well-known microcontroller boards and showed how it can be programmed in several different ways. It can be programmed using a C language compiler and SDK (software development kit) or via the Arduino IDE (integrated development environment), with the option of using the Mbed OS for ARM microcontrollers. It’s also possible to program the Pico using MicroPython, a variant of the Python programming language optimised for use on embedded devices. In the January 2022 issue, we also described the PicoMite software that allows the Pico to be programmed in the BASIC language (siliconchip.com. au/Article/15177). This makes it a close relative to the Micromite, which also runs MMBasic. The Micromite pairs well with an LCD touchscreen, so we decided to create a matching BackPack for the Pi siliconchip.com.au Pico as well. The BackPack allows the Pico to interface to an LCD touchscreen and includes other useful hardware. While several other companies have designed boards around the RP2040 chip (including Arduino’s Nano Connect, with a WiFi module), our BackPack is designed to work with the original Pico board. We decided to concentrate on the Pico because it is low in cost, compact and versatile. Raspberry Pi Pico Here’s a quick recap of the Pico. It’s based around the Raspberry Pi Foundation’s RP2040 microcontroller and has 264kB of internal RAM. Program storage is on a separate 2MB flash chip. The processor is a dual-core ARM operating up to a nominal 133MHz but it can usually be overclocked above 200MHz. The processor has 30 input/ output pins, although not all are broken out. For example, some are used for flash memory access. It supports USB host and device operation. A ROM-based bootloader provides a convenient USB drive interface for uploading firmware images. Programming the Pico is as simple as copying a file. It has the usual peripherals, like UART, SPI, I2C and PWM. There are also two PIO peripheral modules. Australia's electronics magazine These are programmable I/O state machines that you can use to create more peripheral functions, or just more of those we’ve just mentioned. The Pico BackPack We’ve created something similar to the Micromite BackPack V3 (August 2019; siliconchip.com.au/ Article/11764), adding some extra features in the space that’s available. Like the BackPack V3, it is designed to work with both the 2.8in and 3.5in LCD touchscreens. Since we prefer to use the 3.5in display, as it has a much higher resolution and more area at a similar cost, we’ll also show you how the Pico and BackPack can be programmed to use this display. Using the 2.8in screen is possible (and is very easy to do in PicoMite BASIC), but we will leave that as an exercise for the reader. We’ll present comprehensive example code for the PicoMite BASIC language, the C SDK, Arduino IDE and MicroPython languages. However, not all features are available in all languages. Circuit Fig.1 is the circuit diagram for the Pico BackPack. MOD1 is the Pico itself and a 14-pin header is provided to March 2022  35 connect the LCD touchscreen (CON4). Since both the LCD and touch controllers on the panel use the SPI serial interface, we have wired the header to SPI-capable pins on the Pico. The Pico’s I/O pins have two different numbering systems. All have a physical number, which depends on their location on the package. This is the logical numbering that you would use if you think of the Pico module like an extra-wide 40-pin IC. This numbering system includes pins other than just those which can be used as I/Os. For example, pins 3, 8, 13, 18, 23, 28, 33 and 38 are all connected to ground. The RP2040 general-purpose I/O pins also have a consecutive numbering scheme from GP0 to GP29, although some are not connected to pins 1-40. Most programming languages use the GP numbering system (sometimes dropping the GP prefix), although PicoMite BASIC allows you to use either. For the system SPI bus used to Fig.1: the BackPack consists of a motley assortment of components added to the Pi Pico to interface it to the outside world. You can omit any or all of the IR receiver, micro SD card, audio amplifier and RTC sections if you just want a simple LCD touchscreen breakout. Note that the 1kW resistor for the IR receiver can typically be omitted; most IR receivers have a very weak internal pull-up and can be safely connected to the Pico’s 3.3V inputs. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au interface with the LCD panel, GP18 (pin 24) is the SPI clock (SCK), GP19 (pin 25) is MOSI and GP16 (pin 21) is MISO. Note that the MISO signal travels via JP2 to the LCD’s pin 9. This jumper can usually be left off as data does not need to be sent from the LCD controller back to the Pico. Other control pins include the LCD controller’s CS (chip select), RST (reset) and D/C (data/command) lines, which map to GP12 (pin 16), GP13 (pin 17) and GP14 (pin 19) respectively. The touch controller uses the same main SPI lines as the LCD with its own CS and IRQ lines: GP15 (pin 20) and GP17 (pin 22), respectively. GP20 (pin 26) is used to control the LCD panel’s LED backlight if JP1 is in place. If JP1 is absent, the 10kW resistor pulls N-channel Mosfet Q2’s gate high, which in turn pulls P-channel Mosfet Q1’s gate low, continuously supplying 5V into the LED pin and keeping the backlight on full permanently. The same thing happens if GP20 is actively pulled high; the LED pin receives 5V. If GP20 is driven low and JP1 is in place, the LCD backlight is switched off, while a PWM signal from this pin can produce a range of backlight brightness levels. Pushbutton switch S1 is connected between the Pico’s 3V3_EN pin and ground. The 3V3_EN pin connects to the enable pin of the Pico’s onboard 3.3V regulator and is normally pulled high by a 100kW resistor on the Pico. When it is pulled low, the 3.3V supply to the microcontroller is shut down. Thus a brief press of S1 will reset the microcontroller. The RT6150 regulator fitted to the Pico is a buck-boost type and can operate from an input voltage between 1.8V and 5.5V. But be aware that the infrared receiver and LCD controller might not work over that entire range. We recommend supplying at least 3.3V to the BackPack if you plan to use those features. Optional infrared receiver IRRX1 is fed from the board’s USB supply (nominally 5V) via a 100W resistor and bypassed by a 10μF capacitor. The 5V output of IRRX1 is divided by a 470W/1kW divider to 3.3V, and this signal connects to GP22 (pin 29) of the Pico. Some IR receivers have an internal pull-down (open collector/drain) transistor complemented by a weak internal pull-up. In this case, the 1kW siliconchip.com.au The complete Pico BackPack can have the Raspberry Pi Pico soldered directly to the PCB, or mounted on headers. resistor can be left out as the weak pull-up, and the 470W series resistor will limit current from the 5V rail into the 3.3V microcontroller. CON1 is a micro SD card socket powered from the 3.3V rail and with its SPI pins (SCK, MOSI and MISO) connected to the same SPI pins as the LCD touchscreen. Its CS (chip select) pin connects to GP21 (pin 27) on the Pico. The supply to the micro SD card is bypassed by 100nF and 10μF capacitors for reliable operation. IC1 is an optional DS3231 or DS3231M real-time clock & calendar IC with its own 100nF bypass capacitor to the 3.3V supply rail. It communicates with the micro via an I2C serial bus, and the 4.7kW pull-up resistors to the 3.3V rail required for I2C communication are also provided. The I2C SDA and SCL (data and clock) signals connect to the Pico’s GP10 (pin 14) and GP11 (pin 15). A cell holder (BAT1) is also provided to allow the RTCC to keep time when the main power supply is off. 20-pin header CON2 breaks out some of the Pico’s spare pins. These include 17 GPIO pins that are otherwise unused or can be shared with devices on the BackPack. The GND, 3.3V and VSYS (VIN) pins on the Pico also connect to this header. The GND and VSYS pins can be used to power the BackPack or feed power from the BackPack to other parts, while the 3.3V pins should be considered an output only. The circuitry around IC2 is intended to convert a pair of PWM signals from Australia's electronics magazine GP8 (pin 11) and GP9 (pin 12) into stereo line-level signals at CON3. While we could have fitted an I2S DAC IC instead for higher audio quality, the PicoMite can play audio via PWM natively, and it’s pretty easy to implement this in other languages (as we have done in some of our sample code). The PWM implementation also costs much less. Each PWM signal is treated the same. A low-pass and biasing network formed from the 22kW, 47kW and 100kW resistors shifts the 0V to 3.3V signal to around 0.9-2.9V. The 1nF capacitor also removes high-­ frequency PWM artifacts, with a -3dB point around 13kHz. IC2 is a dual op amp fed from the 5V rail with both of its channels configured for unity gain, so it produces a 2V peak-to-peak signal (around 700mV RMS) with a DC offset of 1.9V. The 10μF capacitor and 100kW bias resistor remove the DC offset, with the 100W resistor protecting the op amp from short circuits on the output. The audio output is available at CON3, with the centre pin being ground. The signal here is suitable for driving headphones, a small speaker or an amplifier. PCB features The Pico BackPack PCB is sized to match the 3.5in LCD touchscreen. Header CON4 at one end connects to the LCD touchscreen while CON2, along one edge, provides connections to a breadboard or other hardware (eg, a ‘daughterboard’). March 2022  37 The Pico mounts opposite the LCD header, allowing its micro-USB socket to be accessible from the edge of the PCB (avoiding the need for us to fit a separate USB socket). To match the Pico itself, we’ve provided pads to mount it on headers or to solder it directly to the PCB, as though it were a surface-mounting component. The latter is preferred for permanent installations, as using headers would require extended headers on the LCD panel to provide clearance below. A third option is to fit the Pico with female headers above and male headers below the Pico BackPack, bypassing the clearance issue. Our parts list assumes the direct mounting method. If you wish to use headers, you will need two extra pairs of 20-pin, 2.54mm pitch male and female header strips. You can use the Pico’s onboard bootloader pushbutton (adjacent to its micro-USB socket) along with S1 to enter bootloader mode. The sequence is to hold down the bootloader button, press and release S1, then release the bootloader button. S1 removes the need to plug and unplug the Pico for programming, which would otherwise cause wear to its USB socket (or your PC’s). With the LCD header on the right, the micro SD socket and IR receiver sit at the top for ease of access. The body of the IR receiver can be bent backwards to allow the lens to face the same direction as the screen. Optional sections The photos and overlay diagram show that the PCB is divided by lines into sections corresponding to each hardware feature. This allows you to fit or not fit the various features as needed. The PCB silkscreen also has the pin information printed along its bottom half. The default SPI pins for the LCD, touch and micro SD card are described on the left-hand side, while each pin of CON2 is also marked with its corresponding Pico pin connection. With all the features fitted, you have eleven spare I/O pins: GP0 to GP7 and GP26 to GP28, although the I2C pins GP10 and GP11 can also be shared with other I2C devices. GP26 to GP28 are the only externally-available pins that can be used as analog inputs. Deleting the audio section frees up GP8 and GP9, while not using the LCD 38 Silicon Chip Fig.2: the lines on the PCB mark the regions and components that correspond to the optional features. From the left, the IR receiver, audio amplifier and micro SD card socket sit along the top of the PCB, providing external access. The RTCC is at the lower right. If fitting the RTC components, don’t forget the battery holder on the rear of the PCB. backlight control pin frees up GP20. With only the LCD touchscreen fitted, you can have up to 17 free I/O pins. With this in mind, you can plan what onboard and offboard circuitry will be needed for your Pico BackPack, allowing you to decide what parts you do and don’t need to fit. Our demo code is focused on the BackPack’s features and does not require any external parts beyond the LCD touchscreen and a speaker connected to CON3. Construction We’ll describe the construction as though all parts are fitted. You can skip any that you don’t want to install. As most of the onboard parts are SMDs to save space, you will need flux paste and a magnifier as well as a soldering iron. We also recommend that you have some solder wicking braid and a suitable cleaning solvent for your flux. Since flux can generate harmful smoke, fume extraction is a good idea. Australia's electronics magazine If you don’t have any fume extraction, work outside or near an open window. This may also help with providing good illumination. The Pico BackPack is built on a 99 x 55mm double-sided PCB coded 07101221. Refer to the overlay diagram, Fig.2, during construction. Start by fitting the micro SD card socket, CON1. Apply flux to the pins and rest the socket in place. It has locating posts, so it is easy to align. Add some more flux to the top of the pins too. Clean the tip of the iron, add a small amount of fresh solder and apply it to the socket’s pins, taking care not to contact the metal shell of the socket. If you are happy with the pin soldering, solder the mechanical tabs too. If there are any bridges, use solder braid to remove them by adding some more flux, cleaning the iron’s tip and pressing the braid against the bridge with the iron. Carefully slide both away together once the wick has soaked up the excess solder. siliconchip.com.au Parts List – Pico BackPack 1 double-sided PCB coded 07101221, 99 x 55mm 1 Raspberry Pi Pico Module (MOD1) [Altronics Z6421, Digi-Key, Mouser, Core Electronics] 1 3.5in LCD touchscreen [Silicon Chip Shop Cat SC5062] 1 14-pin, 2.54mm pitch socket header (for LCD panel) 1 20-pin, 2.54mm pitch pin header (CON2) 2 2-pin, 2.54mm pitch pin headers with jumper shunts (JP1, JP2) 1 6mm x 6mm tactile switch (S1) 8 M3 x 6mm panhead machine screws 4 M3 x 12mm tapped spacers Semiconductors 1 IRLML2244TRPBF/SSM3J372R P-channel Mosfet, SOT-23 (Q1) 1 2N7002 N-channel Mosfet, SOT-23 (Q2) Resistors (all M3216/1206, 1%, ⅛W) 1 10kW 1 1kW Optional Components Kit (SC6075) – $80 Includes all parts listed here, plus optional parts, except the DS3231 IC (available separately). SD card 1 SMD micro SD card socket (CON1) [Altronics P5717] 1 10μF 10V X7R SMD ceramic capacitor, M3216/1206 size 1 100nF 10V X7R SMD ceramic capacitor, M3216/1206 size Real time clock/calendar 1 surface-mounting CR2032 cell holder (BAT1) [BAT-HLD-001] 1 DS3231 or DS3231M in SOIC-16 (wide) or SOIC-8 package (IC1) 1 100nF 10V X7R SMD ceramic capacitor, M3216/1206 size 2 4.7kW 1% ⅛W M3216/1206 size IR receiver 1 3-pin infrared receiver (IRRX1) 1 10μF 10V X5R SMD ceramic capacitor, M3216/1206 size 1 1kW 1% ⅛W resistor M3216/1206 size 1 470W 1% ⅛W resistor M3216/1206 size 1 100W 1% ⅛W resistor M3216/1206 size Stereo audio 1 MCP6272(T)-E/SN, MCP6002(T)-I/SN or -E/SN dual op amp, SOIC-8 (IC2) 1 3-pin, 2.54mm pitch pin header (CON3; see text for other options) 2 1nF 25V X7R SMD ceramic capacitors, M3216/1206 size 2 100nF 10V X7R SMD ceramic capacitors, M3216/1206 size 2 10uF 10V X5R SMD ceramic capacitors, M3216/1206 size 4 100kW 1% ⅛W resistor M3216/1206 size 2 47kW 1% ⅛W resistor M3216/1206 size 2 22kW 1% ⅛W resistor M3216/1206 size 2 10kW 1% ⅛W resistor M3216/1206 size 2 100W 1% ⅛W resistor M3216/1206 size Next, fit the two ICs. There are variants of IC1 in both 16-pin and 8-pin packages. The SOIC-16 part uses all the pads, while the narrower SOIC-8 part will use the lower eight extended pads. Regardless, IC1’s pin 1 is at the lower right. If you can’t make out a pin 1 marking on IC1’s case, look for a bevel along one edge. This will be the edge with pin 1. IC2’s pin 1 goes to the upper left. For the ICs, apply flux, rest the part in place, aiming to align it squarely and symmetrically. siliconchip.com.au Add more flux to the tops of the pins and clean the iron tip. Add some solder and tack one pin in place. Confirm that the part is flat against the PCB and still positioned correctly; if not, reapply heat and nudge the part into alignment. Solder the remaining pins and only then remove any bridges if necessary. For transistors Q1 and Q2, use a similar process as the ICs. The SOT23 parts are small but easy enough to solder, as long as you don’t lose them. Move onto the capacitors next. We Australia's electronics magazine recommend working with one value at a time, as they will probably be unmarked. The procedure for passives is much the same as ICs: tack one lead and confirm that the parts are flat, square and centred, then solder the other lead. Refresh the first joint with some flux and a touch of the iron if it doesn’t look glossy. Fit the four 10μF capacitors in the positions shown in Fig.2, then follow with the four 100nF parts and the two 1nF capacitors in the audio section. Now move on to the resistors. Match up the part codes with those given in our parts list and the PCB silkscreen markings. You can use our SMD Test Tweezers (October 2021; siliconchip. com.au/Article/15057) to measure and place these parts. With most of the SMDs fitted, it is a good time to clean the board of flux. While the Pico and cell holder are surface mounting, they will not need much flux, if any. Remember to allow any solvent to evaporate fully before continuing. If you have 2mm machine screws, you can use these to align the Pico (MOD1) with the holes in the PCB. Remember that the USB socket hangs off the edge of the board. If you don’t have screws, tack one or two of the module’s pads in place instead. The pads are large enough that you can apply solder directly after heating the pad with the iron. Work around the edge of the part, applying the iron and solder to the point where the Pico’s outermost half-holes meet the PCB. If you prefer to use detachable headers, use the innermost row of holes on the Pico and PCB. Once the Pico is soldered, you can remove any screws; the 40 solder joints should keep it secure. Flip the PCB over to attach the cell holder BAT1. The opening should face the edge of the PCB. Rest the holder in place, tack one lead down, solder the other lead, then refresh the first. Now snap S1 in place, ensuring it is flat against the PCB, then solder all its pins. Consider how you plan to use the IR receiver and whether it needs to be bent up to receive a signal from the desired direction. If you are unsure, sit it up from the PCB slightly so that there is room to change this later. You could even mount it on the reverse of the PCB, as long as the pins go to the same pads. The only parts left are the headers March 2022  39 and jumpers. Depending on your plans, either of the jumper headers could be left off or replaced with wire loops as a permanent jumper. To run our example code, fit both jumper headers, but place the shunt for JP1 (LCD Backlight) on and leave the shunt for JP2 (LCD MISO) off. You can pre-fit the shunt to the header to help you hold it in position while soldering the first pin. Now add CON3 in the audio section. It’s designed for jumper wires to take these signals where they are needed. You could solder wires directly to these pins if desired. Depending on your application, you might find that fitting right-angled headers will work better, and there is also the option of fitting the headers to the underside of the PCB if required, which is what we did for our prototypes. To ensure that the headers between the LCD panel and main PCB are fitted squarely, you can assemble the stack using the machine screws and tapped spacers, as seen in our photos. Note that the four-pin header on the LCD (for its onboard SD card socket) should not be populated, as this will foul the USB socket on the Pico. Fit the female header to the male header on the LCD panel and assemble the stack. Then solder the female header in place and separate the stack. The last piece is the 20-pin I/O header, CON2. If you wish to use the Pico BackPack with a breadboard, fit this underneath the PCB. Alternatively, use right-angle headers to bring these connections out the side. Or you can even leave it off for now, as none of our examples need any external connections. You can always add it later. Reattach the LCD panel to the BackPack and secure it by screwing the machine screws into the tapped spacers. Testing Before diving in, you might like to quickly test that everything is working as expected with your BackPack. For this, you can simply upload our compiled “BackPackTest.UF2” file. Put the Pico into bootloader mode by holding the bootloader button (on the Pico) while resetting it (by pressing S1) or powering it up. Then copy the UF2 file onto the RPI-RP2 disk that appears. The demo should start as soon as the file finishes copying – see Screen 1. This example uses PicoMite BASIC, so you can also use this file as a starting point for your own BASIC program; simply use Ctrl-C on a serial terminal to stop the running program. The demonstration programs all provide buttons for interaction and let you use the touchscreen to draw on the LCD screen. PicoMite BASIC demo With PicoMite BASIC having native support for the ILI9488 driver on the 3.5in LCD touchscreen, only a few commands are needed to set everything up, if you prefer to do this manually. You’ll need a serial terminal program such as TeraTerm or MMEdit (on Windows) or minicom (on Linux). If you haven’t already done so, load PicoMite BASIC onto the Pico by Screen 1: feature-wise, the PicoMite is about on par with a Micromite Plus, although it has fewer pins, more flash memory and more RAM. The demo program allows drawing on the display and playing tones on button presses. It can also decode IR signals that are received. 40 Silicon Chip entering bootloader mode and copying the PicoMite UF2 file. Find the serial port of the Pico and open it with the terminal program. As it is a virtual serial port, no baud rate needs to be set. The following options will configure the PicoMite to use the BackPack hardware, including the LCD, touchscreen, micro SD card socket, I2C for the RTCC, audio and the GUI controls that are used in our demo: OPTION SYSTEM SPI GP18,GP19,GP16 OPTION SDCARD GP21 OPTION LCDPANEL ILI9488, LANDSCAPE,GP14,GP13,GP12 OPTION TOUCH GP15,GP17 GUI CALIBRATE OPTION SYSTEM I2C GP10, GP11 OPTION AUDIO GP8, GP9 OPTION GUI CONTROLS 20 Note that the PicoMite resets every time an option is set, dropping the serial connection; we like how Tera­ Term reconnects automatically after a reset as this makes issuing a string of such commands easier. After doing this, you can load our example code. To do this via the terminal, enter the “AUTOSAVE” command and paste the BASIC program into the terminal. The supplied file ends with an ASCII code 26 (0x1A) character, which BASIC interprets as a Ctrl-Z keypress signifying the end of the file. Then type “RUN” followed by Enter to start the demo. After this, the Pico is in much the same state as if loaded with our example UF2 file, although possibly with more accurate touchscreen calibration. Screen 2: even though we wrote the display driver in MicroPython, it is still very responsive. MicroPython also provides a file system for the flash storage and has numerous libraries for hardware interfacing. Australia's electronics magazine siliconchip.com.au We recommend having a read through the PicoMite manual to learn the minor differences from the Micromite. However, most of the differences that we came across are in the OPTIONs described above. MicroPython demo MicroPython has some parallels with BASIC in that it features an interactive prompt, allowing commands and programs to be easily tested. MicroPython has been ported to several other 32-bit microcontrollers such as the ESP32. If you’d like to find out more, see https://micropython.org/ It is open-source, and you can find the source code at https://github.com/ micropython/micropython but we’ve also included a copy of the version 1.17 UF2 file that we used to develop our examples. Typically, you will need an IDE to manage the code files, although it is possible to get by with a serial terminal program. We used “Thonny” as our Python IDE, as it appears in recent Raspberry Pi OS distributions and is also available on Windows. You can load the “BackPack MicroPython Example.UF2” file directly via bootloader mode. This is the easiest method if you don’t have a Python IDE installed. As with the PicoMite BASIC example, you can interrupt code loaded via the bootloader and interact with it through a serial terminal. Otherwise, follow the steps below to view and work with the source files separately. We are using MicroPython for Pico version 1.17. To load our example manually, first load the MicroPython UF2 file onto the Pico, then use your IDE to copy the “ILI9488LIB.py” and “LSNBFONT.py” files to a “lib” folder on the Pico’s internal storage. The way this is done will vary depending on the IDE you’re using. These two modules constitute the driver and font that are used in our software, and keep the main program file legible and to a manageable size. Now load the “main.py” file and run it. If all is well, you should see the screen initialise – see Screen 2. Unlike PicoMite BASIC, we had to implement the display driver in Python. While this makes it noticeably slower than BASIC’s integrated driver, it is certainly fast enough to be usable. We haven’t delved into creating libraries for the micro SD card, RTCC siliconchip.com.au The rear of the Pico BackPack has the coin cell holder and possibly also some of the headers. or IR receiver as there are numerous publicly available libraries for these features. Do not insert a micro SD card unless you have already installed a library to initialise it correctly. Otherwise, it will interfere with the SPI bus operation of the LCD and touch controllers. Arduino demo We used a board variant based on the C SDK for our Arduino software, which simplified developing software for the C SDK by itself. This is the board variant we mentioned in the Pi Pico Review (https://github.com/ earlephilhower/arduino-­pico). To add this variant to the Arduino IDE, add the text “https://github. com/earlephilhower/arduino-pico/ releases/download/global/package_ rp2040_index.json” to the list of Board Manager URLs under Arduino Preferences. Next, install the “Raspberry Pi Pico/RP2040” option from the Boards Manager by selecting it and clicking “Install” (as shown in Screen 3). Our example code just needs one example library; search for “rtclib” in the Library Manager and install the version provided by Adafruit. It can also be downloaded and installed manually from https://github.com/ adafruit/RTClib The SD card library included with the Arduino IDE is used by our code. We’ve also written simple drivers for the LCD touchscreen (including backlight PWM) and audio output. The files for these are included in our sample code. Unfortunately, it appears there are no readily-available IR receiver Screen 3: we’re using a custom board profile for the Pico under the Arduino IDE. It can be installed easily, and because it is based on the C SDK, it supports using C SDK functions in projects. It’s the bottom-most item in the screenshot seen here (highlighted in red). Australia's electronics magazine March 2022  41 libraries for the Pico under Arduino yet. We previously used the Arduino IRremote library (https://github. com/Arduino-IRremote/Arduino-IRremote) and expect that it won’t be long before someone ports this over to the Pico. The Arduino demo allows drawing on the LCD by use of the touchscreen – see Screen 4. It reads the SD card and displays the first file found; pressing the “Files” button on the screen will look for additional files and show their name. The backlight brightness can be adjusted by the slider at the bottom of the screen. The time found on the RTC chip is displayed. There is sample code in the RTClib library to set the time in the DS3231 chip if that has not been done already. Sounds are played every time a button is pressed or released; you will need a speaker or headphones connected to hear them. The sounds are sinewaves defined in the “sounds.c” file. C SDK demo We found it was a bit trickier to get the C SDK working on its own. While our previous article about programming the Pico discussed doing this under Windows, we found that many of the required tasks were easier in the Raspberry Pi OS. So if you have a Raspberry Pi, we recommend using it to compile projects for the Pico, especially if you want to work in C. The documentation is written with this in mind, so it makes sense. While a Raspberry Pi is a bit slower than a modern Windows PC, we saved time overall because things seemed to work more often the first time around. You can load our demo firmware file by putting the Pico into bootloader mode and copying the UF2 file to the RPI-RP2 drive. It should show the LCD and touchscreen working – see Screen 5. You can draw on the LCD by using the touchscreen. The backlight can be cycled between several brightness levels by the LIGHT button and a sound is produced every time a button is pressed or released. We haven’t found any libraries for SD cards, IR receivers or real-time clock modules to suit the C SDK, so we have not implemented these features. Still, we expect that the rapidly growing community around the Pico could see these developed sooner or later. One advantage of using C is that the LCD is updated very quickly using the native SPI interface. That could be handy for projects that need rapid screen updates. Using the C SDK files It is not easy to create a portable project, even with the Project Generator program. Still, the following method should allow you to build your own projects from our example code. Use the Project Generator to create a project, being sure to check at least the SPI peripheral option. The Pico review Screen 4: our Arduino demo is one of the more comprehensive tests of the Pico BackPack’s features, primarily due to the extensive open-source libraries that are available. You can test the LCD and touchscreen by drawing on the screen, and if you have a speaker connected, it will emit tones when a button is pressed. 42 Silicon Chip article from December shows the Windows version of the Project Generator. We also like to enable the USB console and disable the UART console if we aren’t using the USB peripheral for anything else. This makes it easier to send debugging information directly to a virtual USB serial port and frees up the I/O pins that would otherwise be used for the hardware console. After the project is generated, there will be a .c file in the project folder; it will have the same name as the project you just generated. Copy the contents of the main.c file (from our example) over the contents of this .c file, replacing the boilerplate code that the generator has created. Then copy the remaining .c and .h files from our example folder. There will also be a CmakeLists.txt file in the project folder. Open it and find a line like this: target_link_libraries(LCD_TEST pico_stdlib) The first item will be the project name. Add a reference to “hardware_ pwm”: target_link_libraries(LCD_TEST pico_stdlib hardware_pwm) Then save the file. Switch to the “build” subdirectory and run “nmake” on Windows or “make” on Linux (including Raspberry Pi OS). If all goes well, the compilation will proceed, and it will create the UF2 file in the build subdirectory. This is the firmware image you can transfer Screen 5: the C SDK is trickier to work with than the Arduino IDE or PicoMite BASIC, but it allows for highperformance operation of the Pico if needed. We found it was easily the fastest of the lot when updating the display. Our demo shows off the LCD, touchscreen, backlight control as well as sounding tones when the buttons are pressed. Australia's electronics magazine siliconchip.com.au Screen 6: the 2MB of flash memory on the Pico is generous, and flash file systems like LittleFS are a great way to make use of it. The Arduino IDE even provides a tool for uploading files to the file system via the serial port (“Pico LittleFS Data Upload”). The amount of flash memory set aside for the file system is configurable. to the Pico to run your new program. Using the C SDK is quite different to Arduino, BASIC or MicroPython, but it appears that many questions are being asked and answered on the Raspberry Pi forums. There is a Pico C SDK section of the forum at siliconchip.com.au/link/ abc1 and a list of community provided libraries at siliconchip.com.au/ link/abc2 With the Pico being so cheap and already having broad community support for several languages, as well as official (Raspberry Pi Foundation) support for the C SDK and MicroPython, we expect that what is possible will expand quite rapidly. More features There are a couple of extra features on the Pico that we should mention, mainly because they are reasonably novel or interesting. The USB peripheral is not easily usable from PicoMite BASIC or MicroPython. However, the Arduino IDE provides examples to allow the Pico to act as a CDC (serial) device, HID device like keyboard or mouse, mass storage and even a MIDI interface. Being small, the Pico is ideal for turning into a small USB widget with a dedicated function. Having a dualcore processor also opens up other possibilities, such as real-time monitoring and control. Dual cores The RP2040 on the Pico has two ARM processor cores and these can be used in a few different ways. The Arduino IDE & C SDK provide means of running programs on both cores. Sharing memory between two processors is not always trivial, but it is not too tricky with the Pico. Still, you need to ensure that one core isn’t trying to access flash memory that the other core is erasing, or you’ll crash it! The Arduino IDE provides simple setup1() and loop1() functions to allow a second parallel process to start up, while the C SDK provides some lowlevel interfaces to control this. MicroPython can use threads to run tasks concurrently using the dual cores, but the dual cores are not exposed at all in PicoMite BASIC. Storing data in flash memory The large, external flash chip on the Pico also means that there is ample siliconchip.com.au onboard storage for large amounts of data. This could be graphics, sounds or lookup tables. It can be accessed as constants from within your program, but some languages provide ways of treating the flash memory more like a file system. Another thing worth noting is that the 2MB of flash available on the Pico is pretty generous for a microcontroller. Like the ESP8266 and ESP32, there are options to use some of this flash for storage on the Pico in some of these programming environments. While the removable micro SD card makes it easier to update data by simply popping it out and connecting it to a computer, keep the internal storage in mind if you need a small amount of non-volatile storage. MicroPython makes native use of this to store files; it’s how our two library files and the main.py file are stored in our earlier example. The IDE you use should have a way to read and modify the internal storage. There are also methods available to read and write these files from within the MicroPython language. The Arduino board profile we used earlier supports the LittleFS file system. You can add a separate tool to the Tools menu to manage uploading files to the flash, and different program and storage profiles can be set to share the available space. The Pico LittleFS Data Upload is available (after being added) in the Tools menu along with several different memory partitions – see Screen 6. Files to be added are placed into a “data” folder in the sketch folder and uploaded from there. Australia's electronics magazine There are example sketches under the Examples → Examples for Raspberry Pi Pico → LittleFS menu; the “FSUpload” example has a link to the upload tool too. The C SDK provides low-level routines for writing directly to flash memory, which can be handy if you know what you are doing, but disastrous if you do not. You might overwrite your program! Or perhaps worse, perform too many writes and wear out the flash. Still, this can be handy if all you need is a large block of non-volatile storage to store data without needing file type access. PicoMite BASIC has ten flash memory slots for programs to be stored and the VAR SAVE feature sets aside 16kB for user data to be stored and accessed by a BASIC program. Conclusion With four different ways of being programmed, a generous amount of RAM and flash, the Pico microcontroller board is bound to be used in a variety of projects. And it’s inexpensive to boot. Combined with our Pico BackPack, we can see this combination being versatile enough to become the core of many different projects in much the same way that the Micromite Backpack did. It’s easy to work with the Pico and the Pico BackPack using either the Arduino IDE or PicoMite BASIC. We would not be surprised if a Pico BackPack programmed in one of these languages found a way into future Silicon Chip projects. In fact, we’re already planning more than one... SC March 2022  43 A ll A bout Part 3: by Dr David Maddison Batteries Batteries have been an important part of vehicles from some of the earliest cars, which were electric. They continue to be used for engine cranking and to run accessories in vehicles with internal combustion engines. The latest and greater lithium-ion types are being developed Background Source: once again to provide motive energy. https://unsplash.com/photos/ZZ3qxWFZNRg V ehicles like cars are a major user of batteries today, as are aircraft, submarines and so on, so we will examine some of these applications. We will also cover battery measurements and other aspects of batteries in this third and final part of the series. In case you missed them, the first part in the January issue described the history of battery technology and described common or important battery types. The second article in the last issue had more details on lead-acid batteries, less common battery types, and many still under development. Electric vehicles The history of electric vehicles could be a whole series of articles in itself, but here are some significant highlights. The first electric car (or “electric carriage”) was developed by Scottish inventor Robert Anderson. He invented this carriage between 1832 and 1839. It used non-rechargeable primary cells. Note that there are other claims to this title, but Anderson seems to be the first to produce a full-size vehicle. Rechargeable batteries were invented in 1859, and in 1884, Englishman Thomas Parker developed an electric car. In 1890, William Morrison of Des Moines, Iowa (USA) applied for a patent for an electric carriage he had built as early as 1887. The vehicle had front-wheel drive, a 2.9kW (4hp) motor, a top speed of 32km/h (20mph), 24 cells and a range of 80km (50 miles). The first commercially successful electric vehicle enterprise was by Philadelphians Pedro Salom and Henry G. Morris. They patented a vehicle in 1894 called the Electrobat (see Fig.58). By 1896, these vehicles had been developed to have two 1.1kW motors, a top speed of 32km/h and a range of 40km. They then built some electric Hansom cabs and sold the idea to Isaac L. Rice in 1897, who then incorporated the Electric Vehicle Company in New Jersey. Rice attracted investors and built electric taxi cabs that operated in New York City and surrounding areas (see Fig.59). Fig.58: Morris and Salom in the 1894 Electrobat, the first commercially-produced electric vehicle in the USA. Fig.59: an Electric Vehicle Company Hansom cab in 1904. Source: Bundesarchiv, Bild 183-1990-1126-500 (CCBY-SA 3.0) 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Because of the time taken to recharge the batteries, the depleted batteries were swapped with fully-charged batteries at a central location as needed. The enterprise failed in 1907. Thomas Edison’s first car was a Baker electric vehicle, for which he designed the nickel-iron batteries. The Baker Motor Vehicle Company was based in Cleveland, Ohio and made electric vehicles from 1899 to 1914 (see Fig.60). Jay Leno owns a 1909 Baker & there is a video from MyClassicCarTV featuring this vehicle, titled “Jay Leno’s Baker Electric Car” at https://youtu.be/ OhnjMdzGusc Electric vehicles were quite successful in the early 20th century but interest faded after about 1920. Part of the reason was that road networks expanded dramatically, plus there were large discoveries of cheap oil from which gasoline was derived. Electric cars with ranges of about 80km were fine in urban areas, but the range was unsuitable for intercity travel, at which gasoline vehicles excelled. The availability of suitable batteries limited their range. There was also a lack of suitable control electronics, which would come later, using Mosfets, IGBTs and microcontrollers (among other parts). Until about the 1990s, electric vehicles remained in the realm of specialty uses such as for local deliveries or shopping vehicles, or curiosities. They relied mainly on lead-acid batteries and had much the same range as the EVs before the 1920s. A significant development was the General Motors EV1, introduced in 1999 with a range of 260km using a NiMH battery (see Fig.61). It could not be purchased and was only available to lease. GM inexplicably cancelled the program and eventually, they destroyed all but 40, with the remainder deactivated and donated to museums and educational institutions. See the video titled “Who Killed The Electric Car” at https://youtu.be/ l3OnYjP4FTk – a shortened free version of a much longer documentary of the same name. In 2008, Tesla released the Tesla Roadster (Fig.62), which used a lithium-­ion battery and had a range of up to 393km. This was a major breakthrough because it was the first EV available with an acceptable range since GM cancelled the EV1. siliconchip.com.au Fig.60: a 1904 Baker Runabout at a German motor museum. It had a 560W motor, weighed 290kg and had a 12-cell battery. Source: Michael Barera (CCBY-SA 4.0) Fig.61: the NiMH-powered General Motors EV1. Experimental variants had lead-acid batteries, fuel cells or ran on compressed natural gas (CNG). Source: RightBrainPhotography (Rick Rowen), derivative work: Wikimedia user Mariordo (CC BY-SA 2.0) Fig.62: Tesla’s first car, the Roadster. Source: Alexandre Prévot (CC BY-SA 2.0) Australia's electronics magazine March 2022  45 It was based on a Lotus Elise “glider”, a car body without a powertrain. The battery consisted of 6831 lithium-ion cells in the 18650 form factor. The battery packs had better longevity than expected, retaining 80-85% of their original capacity after 160,000km. Fig.63: this surely must be one of the cheapest EVs available at US$1040 (about $1500). It almost certainly cannot be registered for Australian roads, though. Cheapest electric cars Electric vehicles continue to drop in price, but one of the cheapest is probably the Chinese made Lu Bei LB-6 by Beijing Yezhiquan Technology Co Ltd (see Fig.63). You can buy it from Alibaba (siliconchip.com.au/ link/abbu). It seats four people and has a claimed range of 100-200km from a 30-50kWh lead-acid battery pack and costs US$1040 (about $1500) excluding delivery. It almost certainly cannot be registered on Australian roads. There are many similar ultra-lowcost EVs available from China. You can view a video about driving a similar car to this one by a different manufacturer (Changli) titled “Here’s What The World’s Cheapest Electric Car Is Like To Drive” at https://youtu.be/1GG1RC7GV0Y – that car is not street legal in the USA either. Electric boats Many electric boats of all sizes are now available. Some have solar panels to recharge the batteries. They can also be made in a DIY fashion. Electric race cars Fig.64: typical discharge curves at a constant load current for a rechargeable battery & supercapacitor. Original source: Wikimedia user Elcap (CC BY-SA 1.0) There are several racing series for electric cars of various kinds. Interestingly, all early land speed records, from 1898 and 1899, were held by electric vehicles. The Pikes Peak International Hill Climb record in the USA was set by an electric vehicle in 2018. See the video titled “World Record Run of VW IDR Pikes Peak” at https:// youtu.be/5c2m5hhh5Kw Supercapacitors as a “battery” in a bicycle Fig.65: a supercapacitor-powered electric bike. The supercapacitor bank (blue) stores 11,881J, about the same as one AA cell. The designer also compares a 400F (0.4Wh) supercapacitor to a 21700 size Li-ion cell (14Wh, 45 minutes to charge). 46 Silicon Chip Australia's electronics magazine There are many successful applications of lithium-ion batteries in small vehicles such as bicycles, scooters, skateboards, monowheels etc. We won’t review those here; however, ranges of tens of kilometres are easily possible. In recent years, supercapacitors (and ultracapacitors) have been developed which have incredibly high charge siliconchip.com.au storage compared to standard capacitors (see Figs.64 & 65). We described ultracapacitors in the article “Beyond the capacitor there is the Ultracapacitor” (April 2008; siliconchip.com.au/ Article/1793). These have the advantage of almost instantaneous or extremely fast charging and discharging. However, at the moment, they are not able to replace batteries in high power consumption or high capacity applications. Supercapacitors and ultracapacitors have different discharge characteristics to a battery. A typical battery voltage will remain relatively constant until the end of its discharge cycle, but a supercapacitor will gradually drop to zero voltage as it discharges. Thus, the control electronics have to be designed to power the load over the entire capacitor voltage range (or at least most of it). One YouTuber built a bike powered by supercapacitors to test its usability. See the video titled “Super Capacitor Bike” at https://youtu.be/V_ f8Q2_Q_J0 Fig.66: the Eviation Alice electric aircraft. It has an endurance of three hours and can make about 1000 flights before the battery pack must be replaced. Despite that expense, its long-term projected cost per flight hour is still lower than a turboprop-powered equivalent aircraft. Fig.67: an Australian-made NKD streetlegal electric motorcycle from Fonzarelli (www.fonzmoto. com). The NKDx model has a stated range of 200km, a 12kW motor and a top speed of 100km/h. Fig.68: inside the battery room of an old diesel-electric submarine using leadacid batteries. The technician accesses the batteries via an overhead trolley system. Don’t drop that spanner! Electric aircraft Battery-operated electric aircraft are becoming commercially available. One example is the Eviation Alice from Israel (www.eviation.co), which is now being purchased for courier work by DHL (see Fig.66). It uses a 900kWh battery pack weighing 3460kg. This needs to be replaced after 1000 cycles (about 3000 flight hours) at a cost of US$250,000, which is similar to the cost of an engine overhaul for a liquid fuel powered aircraft of similar capability. The savings seem to be in lower fuel costs and less regular maintenance. The operating cost is about US$200 per hour compared to an estimated US$600-$1000 for equivalent liquid-­ fuelled aircraft. Li-S batteries Soryu class submarine SS-511 SS-512 All-solid-state Lithium-sulfur batteries (Li-S) 230,400kWh Submarine electric motor 8000hp (6000kW) maximum fully submerged speed and time 5 knots: 2094h 87 days 10,470nm (19,390km) 7 knots: 802h 33 days 5614nm (10,397km) 10 knots: 284h 12 days 2841nm (5261km) 15 knots: 90h 20 knots: 39h Electric motorcycles There have been many electric motorcycles produced. Not all of them were commercial successes. A newly developed Australian electric motorcycle is shown in Fig.67. (LiB) 2010 ~ 100Wh/kg 76,800kWh Submarine batteries Since the early days of submarines, batteries have been critical for movement underwater where they cannot run their main engines (see Figs.68 & siliconchip.com.au All-solid-state (Li-S) 2020 ~ 300Wh/kg 230,400kWh (Li-S) 2030 ~ 500Wh/kg 384,000kWh Fig.69: a modern Japanese submarine with proposed future lithium-sulphur batteries. Current versions of this submarine use lithium-ion batteries. Australia was offered the Soryu class submarine as a possible replacement for the Collins Class. Australia's electronics magazine March 2022  47 69). That has changed with the advent of nuclear submarines and, more recently, air-independent propulsion systems or AIPs, although submarines with these power plants would still have batteries. Before the Australian Government wisely decided to purchase nuclear-­ powered submarines, diesel-electric submarines were going to be purchased (although the price and delivery time frame were unrealistic). These could have used either leadacid or lithium-ion batteries; a controversial but conservative decision was made to stick with tried-and-tested lead-acid batteries. For a discussion of why lithium-ion batteries should have been used, see siliconchip.com. au/link/abbv The batteries for the existing Australian Collins Class submarines are made locally and replaced every six years, and will continue to be until 2040. (We contacted the Australian manufacturer for permission to use a photo but they did not respond.) Electric car batteries We described the main battery types used in electric cars last month, but some batteries are being specifically developed for electric vehicles as follows. BYD Co Ltd subsidiary A Chinese company (https://en.byd. com/) has developed a proprietary lithium iron phosphate battery called the Blade battery, which is claimed to use less space than other batteries and be very safe. It has a rectangular form factor. Desten A Hong Kong based company (www. Fig.70: a cross-section of Tesla’s 4680 cell (46mm diameter, 80mm long) along with an exterior image. desten.com), has developed a battery which is said to produce 900kW peak power, have a range of 500km, can be 80% recharged in under 5 minutes and has a 3000 cycle life and 1,500,000km total lifetime range. The battery is expected to be used in the Piëch GT motor vehicle. The battery chemistry and structure is not disclosed. Tesla Tesla first used 18650 cells in their battery packs, then moved to Panasonic 2170 cells and are now migrating to 4680 cells (46mm diameter, 80mm tall – see Fig.70). Tesla believes these cells will halve the cost of the battery packs and increase range by 16%, as they have a much higher energy density than previous cells. 130kWh of these new cells could occupy the same space as 72kWh of the 2170 types. The cells do not use cobalt, a strategic metal. The conductive pathway through the 800mm spiral-wrapped “jellyroll” is reduced due to multiple tabs at the edges of the roll. This is in contrast to a normal jellyroll, where the conductive pathway extends through the entire length of the roll. This is similar to the construction of low-ESR capacitors – Editor Penn State University They have potentially developed a lithium iron phosphate battery (LiFePO4) with a range of 402km in a proposed application that can be recharged in 10 minutes and is good for a 3,200,000km lifetime (see siliconchip.com.au/link/abbw). The battery operates at 60°C. Why use many small cells? Electric vehicles use battery packs made up of a large number of individual cells. There are several good Fig.71: a diagram of part of a Tesla Model S battery module, showing the shape of the coolant passages. The coolant path around individual cells is shown at the left, while on the right, it illustrates how the tubes go through part of the ensemble of cells. There are 7104 18650 cells in the pack in total. 48 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.72: a drawing of an A cell compared with an actual AA cell. Source: Wikimedia user Lead holder (CC BY-SA 3.0) Fig.73: a B size cell is on the right, compared to a common AA cell. Source: Wikimedia user Lead holder (CC BY-SA 3.0) Fig.74: a 4.5V lantern battery that contains three B cells in series. Source: Wikimedia user Lead holder (CC BY-SA 3.0) reasons for this, rather than using one giant cell (or a few large ones). • In the case of 18650 cells that Teslas initially used, these were already widely optimised for cost and performance, and were readily available as they were used in laptops. • Cooling is much easier to implement with many small cells. A cooling/ heating jacket can easily be wrapped around a stack of small cells. In the case of one large cell, the pipes would have to go through it (see Fig.71). • When many small cells are manufactured, defective or inferior cells can be recycled or used for other, less demanding applications. The best cells can be selected for use in longrange packs. • There is a certain amount of redundancy possible with small batteries. The failure of an individual cell will not destroy the pack. Plus, in theory, individual cells or modules can be replaced, whether by official repair procedures or not. For example, see the video titled “Tesla wanted him to pay $22500 to replace a battery pack, we did it for 75% less!” at https://youtu. be/T7Q0nNkQTCo • A very high density can be achieved with small cells by design optimisation. A large cell might not be so easy to optimise. The ‘wasted’ space between cells is not that large with small cylindrical cells because that space is used for cooling (or heating in winter). • In a pack of small cells, each cell is effectively isolated and can be individually fused. If something goes wrong, only the individual cell and those in series with it will be affected, unlike with a large cell, where everything is affected. This improves safety and reliability. or NiMH rechargeable cells, rather than primary cells. It was also available in fractional sizes (eg, 2/3 length). They were used in old laptop battery packs and radio-controlled vehicles (see Fig.72). The B cell is most commonly found as a group of three in series within the 4.5V rectangular lantern battery, introduced in Europe in 1901 and used in bicycle lanterns until the 1970s (see Figs.73 & 74). They are almost discontinued today. They are not to be confused with the old radio “B” batteries that typically gave 67.5V. siliconchip.com.au More battery information We now look at aspects of batteries and cells that didn’t fit elsewhere in this series. What about A & B size cells? A little mystery of life is why are there no “A” or “B” size cells. Well, it turns out that there are! “A” was a common size for NiCd Internal resistance A cell is not an ideal voltage source where the voltage remains constant The Joule Thief This interesting and simple circuit can drain just about every last drop of energy out of a zinc manganese battery. It is known as the “Joule Thief”. It is essentially a very simple voltage boost circuit that can drive small loads from as little as 0.35V. There are a great many similar designs available online if you want to build one. Only about four components are needed, and according to some designers, these can be salvaged from an old compact fluorescent light (CFL). Australia's electronics magazine A typical “Joule Thief” circuit; it can power the LED until the cell voltage is extremely low, around 0.35V. Source: Wikimedia user Acmefixer (CC BYSA 3.0) March 2022  49 Fig.75: the equivalent circuit of a real battery, showing the ‘ideal’ part with no internal resistance plus the ‘nonideal’ internal resistance. Fig.76: measuring the open-circuit voltage of a cell as part of the process of calculating its internal resistance. Fig.77: measuring the voltage of a cell under load; the reading is lower than in Fig.76 due to the voltage drop across the internal resistance caused by the significant current flow. regardless of the load. In reality, the voltage a battery produces depends on the load due to a property called internal resistance (see Fig.75). This arises from the electrical resistance of the connecting components such as electrodes (eg, carbon rods or metal) and ionic resistance due to aspects of the electrochemical reactions inside the battery such as ionic flow, electrolyte resistance and electrode surface area. The lower the internal resistance, the better. As a battery ages or is discharged, the internal resistance tends to increase. The internal resistance can be calculated by measuring the voltage drop under a known load, but many test parameters affect the value. Internal resistance can be measured using AC impedance methods, provided by a dedicated meter or some battery chargers. AC methods will give a different result to DC methods. Strictly speaking, AC measurements of a battery’s “internal resistance” are actually measuring internal impedance. For batteries, these measurements are typically made at 1kHz. According to Energizer, the internal resistance of a fresh alkaline cell is 150-300mW, depending on size. Other typical values are around 1mW for a car battery or other large lead-acid battery, and for an 18650 Li-ion cell, 30-60mW (AC 1kHz) or 100-130mW (using the DC method). Lead-acid car starting batteries have a very low internal resistance to deliver very high currents for a short period. Note that quoted values for internal resistance vary a fair bit. This same current flows through the internal resistance, so we can reverse Ohm’s Law by saying that the voltage across this resistance is 54mV (1.5V − 1.446V), then since R = V / I, determine that R = 149mW (54mV ÷ 361.5mA). That’s the same answer as using the resistive divider formula. Some other methods of measuring internal resistance or impedance that you can try at home are discussed at siliconchip.com.au/link/abbx Measuring internal resistance Internal resistance (DC) can be measured as follows: 1. Measure the open-circuit voltage of the battery or cell (Fig.76). As there is no external load, this will be the ‘true’ voltage regardless of internal resistance. In this example, we get Voc = 1.500V. 2. Add a load to the cell or battery. In this example, a 4W resistor is used. 3. Measure the new voltage of the battery. In this example (Fig.77), we get Vloaded = 1.446V. The voltage drop is due to the battery’s internal resistance forming a voltage divider with the load. 4. Calculate the internal resistance: Rint = Rload × (Voc ÷ Vloaded − 1). In this case, we get Rint = 4W × (1.5 ÷ 1.446 − 1), ie, Rint = 4W × (1.037344 − 1) which gives Rint = 0.149W or 149mW. For a longer but easier to understand method, calculate the current flow through the load using Ohm’s Law as 1.446V ÷ 4W = 361.5mA. Reproduction batteries for classic cars Some companies produce periodcorrect-looking batteries to provide a perfect authentic look to a restored classic car (see the adjacent photo). Note the external lead bridges connecting adjacent cells. See siliconchip.com.au/link/abca for more details. A reproduction battery for a classic car, in the original style. The internals are modern, however. 50 Silicon Chip Australia's electronics magazine Depth of discharge and battery life Depth of discharge and storage charge can both affect battery life. Panasonic says that their NiMH cells should be recharged when 70-75% of their capacity has been used for maximum service life. A lead-acid car battery should not be discharged more than 50% of rated capacity unless it is a deep-discharge type. Lithium-ion cells benefit by minimising the depth of discharge, avoiding full discharges and charging the battery as often as possible. Many factors affect lithium-ion battery life and these are examined in detail at siliconchip.com.au/link/abby Battery storage It is not necessarily ideal to store batteries fully charged. For example, a lithium-polymer (LiPo) battery rated at 4.2V when fully charged should be stored at around 40% to 50% of battery capacity, a terminal voltage of about 3.6V to 3.8V. One study showed that when a LiPo battery was stored at 40% charge, it only lost 4% of rated storage capacity after one year due to degradation. Another LiPo battery stored at 100% capacity lost 20% of its storage capacity over the same period. Also note that most batteries should not be stored fully drained either. In siliconchip.com.au general, follow the manufacturer’s recommendation for battery storage voltage and temperature. Storage temperature Panasonic recommends storing its NiMH Eneloop cells at 10-25°C, but they should ideally be kept in a refrigerator for maximum life. However, condensation upon removal can be a problem. In general, most cells, such as alkaline types, will have their storage life extended if they are kept in a refrigerator. But don’t put them in a freezer as the electrolyte might freeze and damage the cell. The general principle is that chemical reactions (including those which cause degradation) are slowed down at lower temperatures. Grouping cells When combining multiple individual cells into a battery, such as in a child’s toy or a torch, use matched cells. Cells will age differently in different equipment due to varying current draws or depth of discharge, usage temperature and ageing. If cells are mixed, this can lead to unbalanced cells, and most likely one will go flat before the others, killing the battery prematurely. Low temperatures and lithium-ion cells I was once camping in the snow and found that my camera and phone both stopped working. This is because most common lithium-ion batteries do not work well or at all below about 0°C. This is also a problem with electric vehicles in cold climates. According to the American Automobile Association, temperatures below 4°C reduce the range of typical EVs by 41% or even more if the heater is used. Links for further reading An interesting free book to view online, from 1922, is “The Automobile Storage Battery Its Care and Repair” by O. A. Witte. It’s a fascinating look at the automotive battery technology of that era. See: siliconchip.com.au/link/abc9 Another interesting, short book available online is “General Information and Instructions For the Operation and Care of the EDISON ALKALINE STORAGE BATTERY” from 1925 at www.evdl.org/docs/edison_Fbrochure.pdf There’s also this web page about No.6 dry cells: https://prc68.com/I/No6. shtml Other interesting videos on batteries are: ● “Taking Batteries Apart - Free Carbon Rods & More” at https://youtu.be/ pqmGFfiuXrM ● “Get Lithium Metal From an Energizer Battery” at https://youtu.be/ BliWUHSOalU ● “Don’t Waste Your Money On Batteries – The Shocking Truth I Discovered When Testing RV Batteries” at https://youtu.be/iy3hga_P5YY ● “Shocking Things With 300 9 Volt Batteries!” at https://youtu.be/ ousUTivJoaM ● “Build a DIY Lithium LiFePo4 Headway 12V Battery replacement” at https://youtu.be/5IPnQieycyA ● “Lemon battery breaks Guinness World Record - Royal Institution Christmas Lectures 2016 – BBC Four” at https://youtu.be/6fDail5bvss – they achieved 1275V! ● “This Startup Says Its New Battery Tech Will Beat Every Rival!” at https:// youtu.be/7bgWNQzByOw (Nanograf batteries) short circuit and may also include battery balancing to ensure the individual cells are kept at similar voltages. If you are purchasing a device powered from Li-ion cells such as a torch and you plan to use a protected battery, make sure it will accommodate the several extra millimetres of length taken by the protection circuit. Alternatively, the torch or other device might have its own inbuilt battery protection circuitry. A good discussion on the subject of protection circuits can be found at siliconchip.com.au/link/abbz and more information on batteries and torches in general at siliconchip.com. au/link/abc0 Be wary of cheap chargers Like all extremely cheap items from sites like eBay, be wary of chargers that don’t come from a reputable manufacturer or don’t have good reviews. Some don’t charge according to the correct sequence or termination voltage and can even cause fires. Even with quality chargers, it’s best to avoid unattended charging and to charge batteries (especially lithium-ion types) in a fire-resistant area such as on a concrete or tile floor “Protected” lithium-ion batteries Some lithium batteries are “protected” while others are not. Protection circuits prevent overcharging, overdischarging and damage from short circuits or overload (see Fig.78). You can buy protection circuit boards for 18650 cells and modify or rewrap batteries with them, such as cells salvaged from laptops. There are numerous inexpensive battery management boards available online (eg, from eBay) that protect against overcharge/overdischarge/ siliconchip.com.au Fig.78: the anatomy of a protected 18650 Li-ion cell showing protection circuit, spacers, separators, wrapper and connecting leads. Source: siliconchip.com.au/ link/abbz Australia's electronics magazine March 2022  51 Previous Silicon Chip articles on battery technology Say Goodbye to the 12V Car Battery – July 2000 (siliconchip.com.au/ Article/4313) Fuel Cells – May, June & July 2002 (siliconchip.com.au/Series/226) Get a LiFe with LiFePO4 Cells – June 2013 (siliconchip.com.au/ Article/3816) Tesla’s 7/10kWh Powerwall Battery: A Game Changer? – June 2015 (siliconchip.com.au/Article/8597) Lithium-ion cells – What You Need to Know! – August 2017 (siliconchip. com.au/Article/10763) Grid-scale Energy Storage – April 2020 (siliconchip.com.au/ Article/13801) ● ● ● ● ● ● with no flammable materials close by. Also, never use a charger or other mains-connected device while taking a bath or a spa. Surprises inside some batteries If you open up a 6V lantern battery as used in a “Dolphin” torch, you will typically find four “F” cells or smaller D cells in series. The non-alkaline 6V versions of lantern batteries are a good source of four carbon rods or D cells. Inside a 9V battery, as used in smoke alarms, there are often six 1.5V cylindrical AAAA-like cells in series, although they are 3.5mm shorter (cheaper types contain non-standard ‘pancake’ cells). 9V lithium batteries usually have three 3V lithium metal cells in series. Inside an A23 12V battery as used in some remotes, you will find eight LR932 alkaline button cells in series (see Fig.79) Fake batteries Battery capacities are often massively overrated on websites like eBay and AliExpress, beyond what is physically possible. It’s also quite common for the packaging and branding of a reputable manufacturer to be faked. A real high-quality NiMH AAA cell like the Panasonic Eneloop will have a capacity of 950mAh, while an Eneloop Pro AA cell is rated at 2500mAh. Any ratings significantly above this for NiMH cells indicates that they are almost certainly fake and probably have an actual capacity that’s a fraction of a good quality cell. No genuine 18650 Li-ion cell will exceed 3600mAh. The record is held by the Panasonic NCR18650G, which is no longer available. Typical capacities for good 18650 Li-ion cells are between 2600mAh and 3400mAh. And certainly not 9900mAh as claimed for some cells (Fig.80). These fake cells usually have a capacity well under 1000mAh. Not only do you lose your money, but fake batteries can also leak and destroy your equipment, or in the worst case, can catch fire or explode. Mercury in zinc batteries Standard zinc-carbon batteries such as AA, C and D cells often say Fig.79: inside a 12V A23 battery we find eight 1.5V LR932 cells. Unsurprisingly, 8 x 1.5V = 12V. Source: Wikimedia user Lead holder (CC BY-SA 3.0) Fig.80: a fake 18650 battery. You can tell this from the impossibly high claimed 9900mAh rating. Its capacity was measured (see https://budgetlightforum.com/ node/45556) and found to be 525mAh. 52 Silicon Chip Australia's electronics magazine “mercury-­free” on the label. Why is that? Once, mercury was alloyed with the inside surface of the zinc case to prevent undesired side electrochemical reactions such as hydrogen generation due to the zinc anode’s corrosion, which would lead to battery leakage. Manufacturers changed to a more pure form of zinc to eliminate the problem, and therefore, the addition of neurotoxic mercury is no longer required. Avo multimeter battery Some old AVO multimeters used a 15V BLR121 or B121 battery. These are hard to find and expensive, although they are still made. Many people make up substitute batteries from common and cheaper cells instead. Battery vs chemical fuel Batteries have a much lower energy density than chemical fuels like gasoline (petrol). That is, they contain less energy for a given volume or weight. While gasoline has a much greater energy density than a lithium-ion battery, in a vehicular application, that is somewhat offset by the fact that electric motors are close to 100% efficient compared with modern internal combustion engines, which are about 40% efficient at best. Also, while an electric motor of a given power is generally lighter than a gasoline motor of the same peak power, battery packs don’t get lighter as they are drained, unlike liquid fuel tanks. Vehicle battery packs can be hefty; for example, the 100kWh battery pack in a Tesla Model S weighs 625kg and gives a range of 560-647km. A typical full petrol tank weighs closer to 50-60kg and can provide a similar or better range in similarly-sized vehicles. Exact comparisons between gasoline and batteries are difficult, but gasoline has about 53-129 times more energy per weight than a lithium-ion battery and about 13-37 times more energy per volume. Batteries will not likely ever achieve similar energy densities to chemical fuels because a battery has many components that do not actively store the chemical energy. Electric vehicles can have decent ranges despite this because they are designed to maximise their efficiency (eg, using low-drag shapes, including the wheels). That allows them to make the best use of the available energy and keeps the battery weight reasonable. SC siliconchip.com.au DIY Projects. Think Jaycar. On Sale 24 February - 23 March 2022 NOW 849 $ SAVE $50 Flashforge Adventurer 3 3D Printer Control print jobs via the cloud. Removable print bed, detachable nozzle, & automatic filament feeding. Prints up to 150Lx150W x150Hmm. TL4256 0-30VDC 5A Regulated Lab Power supply Power your devices with precise voltage level and current limits. Digital control, large LED display. Built-in over-current & short circuit protection. 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SUPPLY CHAIN DISRUPTION. We apologise for factors out of control which may result in some items may not being available on the advertised on-sale date of the catalogue. NOW Sound & Vision 69 $ 95 SAVE $10 GREAT FOR TV OR MUSIC 2 Channel Soundbar Speaker with Bluetooth® 5.0 Enhance the sound of your TV and can also be used as a standalone speaker. Includes 3.5mm stereo and digital optical inputs. 2 x 14W Output. Wall mountable. XC5233 NOW FROM 64 95 $ 399 199 $ PR SAVE $50 SAVE <at> $30 2-Way Indoor/Outdoor Speakers Versatile speakers. Wall or ceiling mount. Can be rotated 180° for perfect sound projection. 4”, 6.5” & 8” available. CS2475-CS2478 2 X 120WRMS Stereo Amplifier Provides crisp rich sound ideal for powering speakers in your home, office or shop. RCA input. 6.5mm output. Remote control included. AA0520 15" PA System $ with UHF SAVE $100 Microphones Massive 300WRMS power. Stream music via Bluetooth®, or via a SD / USB. Playback controls are on the speaker. 2 mics included. 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XC9026 XC9100 Raspberry Pi Single Board Computers FROM $ RPI 4B 109 $ XC9001 SAVE $10 $ RPI 3B 9495 $ Protect your Pi with these stylish red and white designs. 3B+ XC9006 $14.95 4B XC9110 $16.95 THESE ARE SELLING FAST. CHECK WEBSITE FOR STOCK AVAILABILITY. ORDER NOW TO AVOID DISAPPOINTMENT. BUILD YOUR OWN GAMING STATION GAME IN 5 EASY STEPS: INSTALL PI 3B OR 4B INSTALL RETRO PI ON RASPBERRY PI INSTALL GPIO NEXT AND REBOOT COPY OVER ROMS CONNECT TO TV AND READY PLAYER 1 Raspberry Pi Retro Arcade Game Console Let the games begin with this exciting retro arcade console. Simply install a Raspberry Pi 3 or 4 into the console, insert a Retropie installed microSD card (XC9031 $24.95 sold separately), copy over some ROMS, connect it to your TV, computer or projector with a HDMI or VGA cable and you are ready to battle. XC9062 CLUB OFFER Case + 2 Controllers FROM 9 $ 95 Retro NES Style Controller SNES layout. Features A/B/X/Y buttons, start, select, and direction controls. 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JOIN NOW! 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24/02/2022 - 23/03/2022. SERVICEMAN’S LOG The oven with a mind of its own Dave Thompson I’m probably not the only one among us who finds modern appliances failing relatively quickly so annoying, especially as it always seems to happen just outside the factory warranty. Some often joke that they must put a timer in there! Appliances can be a significant investment, and when compared to the whitegoods of old, they seem to reach their end-of-life very quickly. The term “planned obsolescence” comes to mind. My mother used a well-known branded mixer every weekend for nearly 40 years before it needed replacing. Admittedly, it had a new armature fitted after 30 years (by dad) to keep it going, but the mixer she shelled out good money for, as a replacement, lasted just six years, and was deemed ‘unrepairable’ by the service people. There is a tendency to think that because modern equipment is far more ‘feature rich’ (read: complicated) that it is more likely to fail, but that only explains a fraction of the problem. A lack of replacement parts and the high repair cost, even if you can source the parts, is another bugbear. This time, it’s personal When we bought our current house six years ago, we renovated the kitchen (among other spaces) and installed a Samsung wall oven. We’d had a previous model in our old place for several years and liked it a lot, so it was a natural step to upgrade to the newer version here. It’s a very good oven; it even has a feature so you can put a heat-shield divider in it and cook a roast on the bottom and a cake on top, but why you’d want a chocolate-flavoured lamb roast and a lamb-flavoured chocolate cake is beyond me! The controls were also ‘upgraded’, and not for the better (in my opinion). Of course, we only realised that once we had unpacked and installed it. For example: on the old model, the various touch functions were backlit, so in dimmer light, you could see what you were doing. On the new one, they rely on a dull graphic printed on the glass touch panel, and unless you are in good light, they are practically invisible. Why the designers thought that was an improvement is beyond my pay grade [it sounds like it was designed by accountants – Editor]. One of the most commonly-used controls on our oven is the timer function, which is initiated by pressing a bell icon on the aforementioned touch area, then by tweaking one of the two very modern push-in, pop-out infinity knobs to dial in the desired time. Then you either wait for a few seconds for it to automatically set that time, or press the almost-invisible timer button again. To set it, I usually just fish around on the panel in the general area of the timer touch button until I hear the beep and see the timer display show; I then set the knob to my time and walk away. Of course, turning off the timer alarm when it starts harping on at me is another fishing expedition if the light in the kitchen is not that great. I’m used to it enough now that I usually hit it every time, but I still think it is a bad ‘feature’ and a step backwards. One thing we do like is the oven’s ability to self-clean using what they call a ‘pyrolytic’ system. While this might invoke thoughts of robotic hands moving all about the inside and leaving things sparkling clean, the reality is that it is a far cruder system. What it basically does is lock the door and pump the temperature to a ridiculous degree (har!). This turns anything inside the oven to a fine ash, including any burnt-on grime and Items Covered This Month • • • • An oven with a mind of its own Testing lifeboat sets Repairing a bricked NAS A not so fusey MPPT controller Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz siliconchip.com.au Australia's electronics magazine March 2022  61 grease. Obviously, this can be a problem if you forget to take out the roast, or any cookware that might disintegrate above 400°C. But it does seem to work well enough, and it is easy enough to wipe the ash out afterwards with a damp rag (once the oven has cooled down, of course). The rub is this can only be done around 30 times in the entire life of the oven, as it places a lot of stress on the oven’s components and seals, so we have to mete out cleaning as-needed with an eye on the longevity of the appliance. The soup thickens So, besides these gripes, for the last six years it has been going well. That is, until a few weeks ago when I walked past and the LED display was flashing randomly between the different program settings. I touched the left-hand knob (which controls these things) and it suddenly went quiet again. I was a bit perturbed, but after giving the knob a good back-and-forth tweaking and nothing untoward happening, I thought it must be just the pot or encoder inside getting a bit dirty (I’ll call them pots for simplicity; they’re sealed so I don’t know what mechanism is inside). However, one night we were sitting enthralled in the latest streaming drama on the box when I heard pinging from the kitchen. Once again, the display was going crazy but this time we had sound to go with it. And again, merely touching the settings control stopped the graphics and noise. 62 Silicon Chip There was obviously something going on with the pot or something else in the control board. And what’s worse is a few days later, I walked past again and noticed the oven was on. I was pretty sure the wife hadn’t switched it on for anything and I certainly hadn’t, so it was time to do something about this. The biggest problem with wall ovens is that they live in a hole in the wall, and access to the internals is not great until they are removed. I probably could have hefted the thing out myself, but I’m getting too long in the tooth for those sorts of shenanigans, so I asked a friend over for lunch. This was the guy who initially helped us renovate this place, and I Australia's electronics magazine bribed him with a nice meal so I could make use of his muscles. With the retaining screws removed, it was easy enough for us both to manhandle the thing out and onto a piece of carpet I’d put on the kitchen floor. It has a nice long cable, which plugs via the usual wall switch arrangement into the grid and that had been coiled up behind and just came out with it. Once on the floor, it was just a matter of removing a few chassis screws to remove the outer shell and reveal the internals (after making sure the wall switch was off, obviously). This gave me access to remove the panel that held the control PCBs. Everything on this oven is handled by four printed circuit boards mounted internally at the top of the oven cavity; the main PCB that appears to manage all the heavy-duty power switching functions is away from the rest, with the three smaller ones immediately behind the front control panel. It was those three that I was going for first. The manual controls – the two joggling infinity pots mounted on either side of the oven’s control panel – boasted a small circuit board of their own at the rear, and then one larger board housed all the touchscreen buttons and displays that we could see through the front glass bezel. These were mounted directly to the panel. I removed the entire front panel easily after finding the three screws that held it on, unplugging a ribbon connector that runs off to the main board, and sliding it forward out of the chassis. There were many more screws siliconchip.com.au holding the various PCBs to the front panel but once taken out, the boards just lifted clear. My goal here was just to have a good look and possibly squirt some contact cleaner about, or look for and repair obviously dodgy solder joints before calling in someone more specialised in oven repair. It’s the Serviceman’s Curse! Even though well-isolated heat-wise from the rest of the oven, these boards live in an inhospitable environment. Wall ovens (especially) heat right through every time they are used for an extended period, so the effects of constant heating and cooling must have an impact on the boards and various solder and plug/socket joints. There are several fans and ducts to keep the heat away from the electronics, but it still must have an effect, and that’s what I started looking for. Everything was surprisingly clean inside; I was expecting greasy residue and other rubbish, but it looked pretty good. All the boards seemed in good nick. It looked increasingly like this was all a waste of time, and a bit overly ambitious of me to think I could do something with it. I reassembled the boards to the front panel, and we sat back and had a coffee before we put the oven back into the wall. Once the caffeine hit, I considered that one thing I could look at was the mechanical parts of the control pot. On these model ovens, the whole ‘knob’ at the front can be pushed into the panel – clicking into place – to get them out of the way and give that modern, sleek stainless look (and apparently make it easier to keep clean). When needed, a simple push inwards pops the knob out, and it can then be joggled to whatever program is required. In practice, we almost never pop them in and just leave them looking like regular control knobs. Perhaps there was something physically there that was affecting things. This one certainly gets way more use than the one on the right side, but as I was already clutching at straws, I decided to disassemble this left-hand one and have a look at it. Mechanically, it is pretty simple: the mechanism for hiding the knob is similar to many push-on/push-off switches we are already familiar with and it works much the same way. Except this is the whole knob assembly that can move in and out, and a sliding shaft allows it to operate in siliconchip.com.au either the closed or open position. While it can be turned awkwardly closed, it is designed to be operated in the open position. The motion felt smooth, but a little different to the right-hand knob – and in any service situation, it is always good to have a second working component to compare to the suspect one. These knobs also sit in the line of fire; that is, when the oven is up to temperature or something is cooking in there, opening the door exposes the exterior bottom section of the control panel to waves of intense heat and potentially other fumes, steams and smoke – especially the way I tend to cook things. I thought that the control panel could do with a good clean, so I pulled the knobs off, used a spanner to undo the shaft nuts, pulled the pots, removed the display circuit boards and disassembled the whole shebang down to metal parts. It’s all stainless and glass, so I threw it all through a quick wash in the dishwasher. While that was processing, I used isopropyl alcohol and soft rags to wipe everything else down and clear the grime out of the nooks and crannies (which are naturally created by these pop-in knobs). I also cleaned the pots and whatever other contacts I could see with contact cleaner while it was all out, and then Australia's electronics magazine once the metalwork was finished, I put it all back together. I had to bribe my friend with another lunch so he could help me wrangle the thing back into the wall; it all went without a hitch. It hasn’t faulted again … yet, but I fully expect that what I did didn’t do much, and this run won’t last long. If I do need to buy a new control or board for it, apparently there are parts available to order – cost unknown – but it irks me that something this ‘young’ would fault at all, considering the purchase price. Time will tell. Leftovers Another trying job through the workshop recently was an amplifier module – one built by a friend from a design from the ‘80s or ‘90s. It looked like one that I’d seen featured in the likes of Electronics Australia, or perhaps even Silicon Chip, but I couldn’t find a matching project for it in those archives. It had never worked. It came with its own power supply in a case, so I isolated the amplifier board and tested the PSU first; as per the owner’s comments, it did indeed work. The line and output fuses were all good, but after rigging it up on the bench and connecting it to my workshop speakers, there was just no signal getting from the input to the output. March 2022  63 All the soldering looked pretty good, and the owner said he had the original documentation that came with the project somewhere if required. Still, I couldn’t see any obvious component misplacements due to the board overlay or anything else really obvious. I’d have to dig deeper. The output transistors are a good place to start because sometimes one or more can just give up if things don’t go well, so I pulled them one by one and tested them out. All were fine. There were also a couple of homewound inductors on the circuit board, and I wondered if the problem could lie with them. I also pulled them from the board and went to measure them, but I couldn’t get a reading on my LCR meter. And I noticed that the solder that had been holding the inductors to the boards was also just falling off the legs as I tried to get test leads on. I soon clicked to the problem; the enamel coating had not been stripped off the wire sufficiently before the inductors were soldered into the board. How he’d even managed to get any solder to stick was beyond me. I’m sure the documentation that came with the kit clearly stated he had to strip the coating off the copper wire, but I guess he either skipped that part or thought he’d done it using just the soldering iron. This is not the way to do it; that enamel coating is quite tough and while I’ve seen people burn it off – with varying success – on smaller wires with lighters or those wee gas torches, it is far better to do it the old-fashioned way with a craft knife and manual labour. I cleaned off the wire ends, used some liquid solder flux and tinned them properly before reapplying them back into the board. I had a second check for any other dry joints but found none, so I reassembled everything back together and applied power. Now I got a good signal through the amp and, after a few minor tweaks, it was ready to go back to a grateful owner. It just shows that the smallest bad joint can cause an entire project to be a paperweight. Testing lifeboat sets R. C., of Mooroopna, Vic had a frustrating day trying to find a working emergency radio for a lifeboat. It seems that they were not well designed... Back in the 1970s, I was a Commonwealth of Australia Marine Radio Surveyor. The purpose of radio surveyors is to make sure that all the radio equipment onboard ships, from small to as big as they get, was in good order to maintain communications in an emergency. For example, if a ship starts sinking, its emergency communications equipment must function properly. This is a story about a string of faulty lifeboat sets. I was called to the Port of Melbourne to test the equipment on board a tug that was to sail from Melbourne to Sydney. It required a onetrip authorisation certificate, indicating that all the radio equipment was fully functional. Other surveyors dealt with other aspects of the ship like the hull, machinery etc. I tested all the radio equipment, and the only item left to test was the lifeboat set. These operated on 500kHz MCW, 2182kHz AM voice and 8364kHz. They were powered using pedals or hand-cranks, and when stowed, they would float. I tested the set, a Clifford and Snell RN610, and found it was not working as the wave change switch was damaged. As there was a small fleet of tugs in Melbourne, I asked if there was another lifeboat set, and they replied yes, and obtained it. I tested this one, and it also failed with a faulty transistor. I asked if there were any other sets, so another was obtained, and it also failed. They got another one, and it also failed, each with a different fault. Having had four sets in a row fail with different faults, you begin to wonder if you are doing something wrong. Things were getting desperate, as the tug could not sail unless I gave the Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 64 Silicon Chip Australia's electronics magazine all-clear that all radio gear was working correctly. The cost of preventing a ship from sailing is high; it was into the thousands even then. You did everything you could to make sure a vessel was not held up. I asked if they had a Solas III lifeboat set, and they replied that they did. That one worked! I had always found this type of set worked well. The faulty sets were repaired later by shore service as the tugs were telephony-­only ships, with no dedicated radio officer. The Clifford and Snell RN610 was a compact set – too compact, as the top cover was shallow, and it was difficult to get headphones etc in the top cover above the operating controls of the set. This meant that the large wave change switch often had pressure on it, damaging the switch and causing other problems. After I moved on from the surveying work, the following surveyor tested the ability of one of the sets to float (they are meant to). It didn’t and continued to the bottom of the Yarra River. That caused a stir. A significant percentage of the troubles with these sets was because the top waterproof cover of the set was so small/shallow that you had difficulty getting the two sections together to make a watertight seal. If you did get it to seal, was the wave change switch damaged in the process? I often wondered how this particular model set obtained authorisation/ approval under the Safety of Life At Sea (SOLAS) Convention for use on ships, considering how often they were found to be faulty. The case of the bricked NAS K. R., of Auckland, New Zealand knows the saying, “if you don’t have backups, you will be sorry”. He didn’t want to be sorry, so he set up a backup system, but it broke and then he had to fix it back up... About ten years ago, I realised that our home PC had become the de facto family photo album as digital camera images replaced film. Worrying stories of people losing these family memories because of hard disk failure were becoming commonplace. The ever-­ increasing pixel count and decreasing price of digital cameras added to the problem as our media storage needs increased exponentially. Additionally, more and more businesses are emailing invoices and siliconchip.com.au statements, so the PC is also becoming our bill filing system. Then there is that gigantic email archive. With 100GB, including 70GB of photos and growing fast, it was time to put a backup system in place. I was satisfied to add another HDD inside the PC and copy the files across for a while. But what if the PC suffered a serious power incident that fried everything inside it, or it was stolen? My next step was to connect an external USB HDD to run a backup each month so that the backup data was in two places, but these backups ended up being done at somewhat irregular intervals, often three months or more. I decided that we needed a separate appliance that could be kept out of sight in a more secure location, like a Network Attached Storage device (NAS). I selected a Taurus brand enclosure with a gigabit Ethernet interface and fitted two 1TB HDDs running in RAID 1 (RAID = Redundant Array of Inexpensive Disks). RAID 1 mode allows one of the two drives to fail without losing any data by ‘mirroring’ the data across both drives. I was now able to schedule backups of the important data each day, and once a week, I backed up the operating system for good measure. Even when compressed to about 100GB, my 150GB of data took about two hours to transfer over gigabit. All was well for several years, and I had to use the backups when upgrading hard drives in the PC and even fully recovered the operating system after the motherboard failed and was replaced under warranty. Annoying as this failure was, it was a pleasant change to have the failure occur just within the warranty period instead of shortly after it expired. Just as the proof of a pudding is in the eating, the proof of the backup is when it is restored. So I was well pleased when it worked as designed. Then, the scheduled backups started intermittently failing for no apparent reason. Power cycling the Taurus NAS would usually fix it, a clue I ignored completely. When the failures became annoyingly frequent, I searched the Taurus NAS website for updated firmware as my first step in troubleshooting. I downloaded the latest version of firmware and then double-checked the process to load it. It was a good thing that I checked because I had downloaded the wrong version. After finding the correct firmware, I started the upgrade, which went just as expected. Once completed, I navigated to the NAS web interface to find a slightly different menu, and there was no longer an option to set the RAID mode. A frantic check revealed I had managed to delete the correct firmware and uploaded the incorrect firmware instead, designed for a cheaper version with a single HDD! Oh well, no matter, simply download the correct firmware again and reload, right? Wrong! The latest firmware has version check software built-in, and it helpfully refused to allow me to load what it now thought was the wrong firmware. Where was this version checking feature when I needed it? Google helped me find the original earlier version of firmware, but it would not allow that to load either; the computer still said “No”. The NAS worked fine; it just would not recognise the second HDD for RAID operation. Every cloud has a silver lining, and with the NAS opened up on the Silvertone Electronics sells a range of Signal Hound spectrum analysers from 4.4GHz up to 24GHz. There's even a 43GHz analyser coming soon! « This 4.4GHz spectrum analyser is yours from just $1677.50 This product and even more can be purchased from Silvertone's Online Store https://silvertoneelectronics.com/shop/ ► UAV & Communications Specialists 1/21 Nagle Street Wagga Wagga NSW 2650 Phone: (02) 6931 8252 https://silvertoneelectronics.com/ contact<at>silvertone.com.au Spike RF analysis software included for FREE with every Signal Hound analyser Silvertone is a reseller of these brands BitScope siliconchip.com.au Australia's electronics magazine March 2022  65 “workbench” (dining table), I realised that the intermittent failure I was trying to fix was actually caused by the HDDs not spinning up every time. A multimeter revealed the 5V rail was spot on, but the 12V rail was about 9V – the power supply was failing. This was four years after I bought it, but I called in at the supplier Digizone and, bless their after-sales service, they replaced the power supply without question or evidence of purchase. When I explained the firmware mess I was in, they said it would need to be returned to China to be re-flashed. I got the feeling their tech had made a similar firmware error at some stage; he was extremely helpful and even offered me a loan NAS if I needed it to recover any data from my HDDs. Now that I had resolved the intermittent problem, I was more determined than ever to fix the firmware myself. I found a reference to the firmware version inside the “imageinfo.ini” file. Using Notepad, I cunningly changed this reference to the correct firmware description and tried again to upload the RAID capable firmware. Not so simple apparently; again, the computer said “No”. Back to Google, and I found a set of instructions on how to ‘unbrick’ the Taurus NAS by connecting a serial data cable to some solder pads on the circuit board. I soon soldered a donor serial data cable in place (Rx, Tx, Power, GND) and installed PuTTy on my PC. You have to admire the determined person who reverse engineered these factory connections. I set the serial port to 19200 baud but cold-booting the NAS with the serial cable connected generated a meaningless stream of green ASCII characters in the PuTTy window, like a sequence from the movie “The Matrix”. It looked like a voltage compatibility problem, so back to Google, where I found an amazingly simple 5V TTL to RS232 converter that used just two FETs and two resistors. A trip to Jaycar, and $3 later, I had it built on a breadboard and tried again. Success! The now perfectly-readable boot sequence could be interrupted with an old-­ fashioned Ctrl-C to present a Linux boot loader menu. Using the TFTP option (Trivial File Transfer Protocol) and tftp32 freeware software on the PC, I was finally able to upload the correct version firmware files, and the NAS rebooted, as good as new. Learning how to use PuTTy and tftp32 was an exercise in itself, but the reward of fixing the NAS was huge, especially when I caused the problem in the first place. I put in place a truly paranoid backup methodology of daily backups to a separate HDD inside the PC, weekly backups to the Taurus NAS and, just for good measure each month or so, I back up to a portable 1TB HDD that I leave at the office. I can backup gigabytes of data to the cloud, but I still use the NAS just in case. A not so fusey MPPT controller S. L., of Whitfield, Cairns had been ‘gifted’ a dead MPPT controller. Despite it giving him the cold shoulder, he went on his way to having it work again... Several companies make almost identical blue coloured MPPT controllers: Victron, Fangpusun and HanFong, to name some popular ones. Recently, I was given a dead Fangpusun MPPT 100/50 unit to experiment with. Editor’s note: the others are ‘clones’ of the Victron units; our experience is that Victron make quality devices, and we bet that the clones will last nowhere near as long. These units are not designed to be repaired. They have an epoxy solution in the lid when it is attached during manufacture. This epoxy binds to the top of several electronic components, making it impossible to remove the lid without destroying components. (“No serviceable parts inside” – yeah, right. It’s full of serviceable parts; you just can’t get to them!). This faulty unit had no output, and the documentation talks about a non-user-replaceable fuse that protects against reverse-polarity battery connection. On a good working unit, a multimeter will show a reverse polarity diode across the battery connection. On this faulty unit, the battery connection tested open-­circuit, indicating the battery had been connected incorrectly, and the reverse polarity diode had done its job by blowing the fuse. Because there is no way to access this fuse, the unit is deemed a throw-away item. After some checking, I carefully cut away a small part A small part of the MPPT controller’s lid was cut away to access a normally “non-user-replaceable” fuse. This fuse was open-circuit; it was bridged and the unit now uses an external battery fuse. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au of the lid with a Dremel to expose the fuse. It was open-­ circuit as expected, and rated at 250V AC 80A for this 50A controller. I bridged the fuse with solder and wire, and the unit is now fully functional. It now requires an external battery fuse for protection. These units automatically detect a 12V or 24V battery and are further configured with a plug-in switch that allows eight different operational modes to be set, to cater for different battery types. These settings are in the user manual, available on the internet. The absorption, equalise and float settings are different for each mode. This programming switch plugs into a 4-pin RS232 connector on the unit. The RS232 pinouts are 1: GND, 2: RX, 3: TX and 4: Vcc (5V). A cable can be easily made up for communications with a laptop. An RS232-to-USB TTL serial converter module is required. The TX, RX and GND pins from the serial module can then be wired straight to the MPPT controller port. To test the cable, use PuTTy (a serial communications program) by selecting the “Serial” button, changing the “Serial Line” to the COM port number assigned to the device, changing the “Speed” to 19200 and clicking “Open”. You should get about 20 lines of data, repeating every second, showing the status of the MPPT controller. To experiment further with this Fangpusun unit, I downloaded the free “VictronConnect” software from www. victronenergy.com/support-and-downloads/software After installing the software and connecting the homemade interface cable, the “VictronConnect” software talked perfectly to the Fangpusun unit. The first thing it did was advise that the firmware needed to be updated, which I allowed, and the latest Victron firmware was loaded into the Fangpusun unit. The unit then rebooted, and I had access to a lot of historical data, and could modify many settings. Now the absorption, float and equalise settings are all individually adjustable, as well as things like the solar and battery maximum current. The unit retains the last 30 working days of data in history. This is not the last 30 calendar days, but the last 30 days when it was producing power. The only thing left for me to do was glue the piece of the lid that I cut out back on, and I had a fully functional SC MPPT controller. After dealing with the fuse, the unit was tested with the VictronConnect software. siliconchip.com.au Australia's electronics magazine March 2022  67 By John Clarke Amplifier Clipping Indicator Driving an amplifier into clipping can cause some unpleasant sounds and even damage expensive speakers. So it is best to find out right away if you’re about to run into clipping. This easy-to-build Amplifier Clipping Indicator is ideal for that; its LED shows even the briefest of clipping events. A clipping indicator is a valuable accessory for any audio amplifier. It indicates when the amplifier has reached its limit and is clipping the peaks of the audio signal. In practice, quite a lot of clipping can occur before you notice it and even brief clipping events can cause tweeter damage. That’s because when an amplifier is clipping, it ‘squares up’ the waveform; the result contains lots of higher-­ frequency harmonics, which can easily damage the tweeters in loudspeaker systems. Our Amplifier Clipping Indicator flashes its LED whenever clipping is detected. That’s considered to be any time the amplifier output is within about 4V of the positive or negative supply rails. Most amplifiers will clip within about 3V of the supply rail, although some can require slightly more headroom; choosing 4V gives a small safety margin. There can be a significant ripple on the amplifier supply rails when it’s delivering a lot of power (when clipping is most likely to happen). So a proper Clipping Indicator like this one will compare the output waveform to the instantaneous supply voltages to compensate for that. Its thresholds adapt as power supply voltages fluctuate. A timer is included to extend the duration of the LED lighting up, to ensure even momentary clipping is visible. The indicator LED is mounted on the Clipping Indicator PCB, but 68 Silicon Chip it also provides a connection for an external LED mounted on the amplifier’s front panel. This clipping indicator is presented as a bare PCB designed to be housed within an existing amplifier. You can build a single unit for a mono amplifier or two for monitoring two channels in a stereo amplifier. Power for the circuit is derived from the amplifier’s supply; it only draws a few tens of milliamps, so it won’t affect the amplifier’s maximum output power to any significant degree. When building a stereo version, you could use a single, common LED to indicate clipping from either channel or a separate LED indicator for each channel. The second PCB does not require the full complement of components for the common LED version. Circuit The clipping detector circuit is shown in Fig.1. A few components don’t have values: resistors R1a, R1b, R2 and R3 and zener diodes ZD4 and ZD5. Their values depend on your amplifier’s power supply voltage. Table 1 shows the component values required to suit amplifiers with supplies ranging from ±10V to ±80V. The clipping detector generates positive and negative reference voltages. For the positive reference, zener diode ZD1 generates a voltage about 4.7V below the V+ positive rail. Resistors R1a and R1b limit the current through ZD1 to approximately 10mA; together, Australia's electronics magazine they connect across the V+ and 0V amplifier supply rails. The generated voltage is shown on the circuit as V+ − 4.7V at Q1’s emitter. The 4.7V between this rail and V+ is also used to power timer IC1. We allow 5mA for IC1’s supply and 5mA to bias ZD1. More on IC1’s operation later. Zener diode ZD2 and resistor R2 between the V− supply and 0V generate the negative reference; R2 limits the current through ZD2 to about 5mA. Detecting positive clipping The positive reference voltage (V+ − 4.7V) is connected to the emitter of NPN transistor Q1. Its base goes to the amplifier’s output via a 100kW current-­ limiting resistor, while diode D2 stops Q1’s base-emitter junction from being reverse-biased. Just before clipping, the amplifier output voltage will rise above the V+ − 4.7V reference plus Q1’s base-emitter on-voltage of about 0.7V. Q1 switches on when the amplifier output voltage is within 4V of the positive supply. It then sinks current via diode D1, the 100W resistor and zener diode ZD3. The anode of ZD3 connects to the pin 2 trigger input of IC1, and as this voltage drops, timer IC1 starts running. This means that IC1’s pin 3 output goes high, switching on Q4 and the indicator LED (LED1) via a 1kW current-­ limiting resistor. A second external LED will also be lit if connected to the external LED connections. IC1 is a CMOS version of the 555 siliconchip.com.au Fig.1: the Clipping Indicator monitors the amplifier’s output and lights LED1 whenever it comes within about 4V of either supply rail. NPN transistor Q1 detects positive signal excursions, while PNP transistor Q2 detects when the signal approaches the negative rail. IC1 lights the LED for at least 110ms each time clipping is detected. timer and is set up to operate as a monostable timer. Timing is initiated when the pin 2 trigger input goes below a third of its supply voltage. With a 4.7V supply, the trigger point is 1.56V above the V+ − 4.7V rail or 3.13V below the V+ supply rail. Pin 2 is usually held at V+ by a 100kW pull-up resistor. However, when current flows through ZD3, D1 and Q1, the voltage at pin 2 goes low enough to trigger the timer. Once the pin 3 output goes high, the 1μF capacitor at pins 6 and 7 of IC1 begins to charge from the V+ supply through a 100kW resistor. When the capacitor reaches two thirds of the supply (3.13V above the V+ − 4.7V reference), the pin 3 output goes low, and this capacitor discharges into pin 7. This sequence of events occurs when the trigger voltage at pin 2 is only low for a very short period. If the trigger voltage is low for longer than the timing period, the pin 3 output will stay high until pin 2 goes high again. The timing period is about 110ms, as set by the 100kW resistor and 1μF capacitor values. IC1 acts as a pulse extender for brief detection of amplifier clipping. It ensures that clipping is shown on the LED for at least 110ms (ie, a bit more than 1/10th of a second). siliconchip.com.au Detecting negative excursions ZD2, PNP transistor Q2 and diode D3 work to detect negative excursions from the amplifier. When the amplifier output swings low, within 4V of the negative supply, transistor Q2 switches on and, in turn, switches on transistor Q3. This then pulls the pin 2 trigger input of IC1 low via two series zener diodes (ZD4 and ZD5) and resistor R3. Transistor Q3 is rated for a maximum collector-emitter voltage of 80V. Without the two zener diodes, the transistor could be subject to the total of the V+ and V− supply rails and so would only be suitable for use with a maximum of ±40V supply rails. By including the zener diodes, the voltage at the collector is reduced to a maximum of around 66V. While we could have used a transistor with a higher voltage rating, they are not as readily available as the BC546. Table 1 shows the required values for resistors R2, R3 and zener diodes ZD4 and ZD5 for various amplifier supply voltages. Resistor R3 is included to limit current in zener diode ZD3 when transistor Q3 conducts. Australia's electronics magazine While this is not the simplest clipping detector circuit, it has the advantage of presenting an almost entirely linear load to the amplifier output, to minimise the possibility of any distortion due to loading. Note that if you want to monitor clipping in a stereo amplifier and use a single indicator LED, you can dispense with the components in the blue shaded areas for the second channel. Interconnection is made between the two PCBs at the top end of R3. This way, a clip event at either input will trigger IC1 on the board where it is fitted. Alternatively, you can build two complete copies of the circuit for independent channel clipping indication. The boards are small and can 69 Figs.2 & 3: the board is not difficult to assemble; the components are fitted as shown at left. The diodes, LED, IC & electrolytic capacitors are polarised. If you’re building a mono version or a stereo version to drive two independent LEDs, build the fully populated version. For a stereo version with a single clip indicator LED, build one of each version and join the indicated pad between the two boards (not present on the prototype PCB pictured). be stacked to take up relatively little room. Construction The Amplifier Clipping Indicator is constructed on a double-sided, plated-­ through PCB coded 01112211 that measures 54 x 60mm. There are two overlay diagrams shown. Fig.2 is the version used for a mono amplifier, or for the left channel in a stereo amplifier (or both channels if you want independent clip indication). If the second channel is built as shown in Fig.3, clipping in either channel will be indicated with a single LED. Begin by fitting the resistors. First, refer to Table 1 to select the resistor value and power ratings for R1a, R1b, R2 and R3. The parts list contains a resistor colour code table, but you should ideally also check each resistor using a digital multimeter (DMM) before installing it. Once these parts are in place, follow with diodes D1, D2 and D3, orientating them correctly. The zener diodes can be mounted next. ZD1 and ZD2 are 4.7V types, while ZD3 is rated at 3.9V. The ZD4 and ZD5 voltages are as per Table 1, or replaced with a wire link if indicated. Transistors Q1, Q2, Q3 and Q4 can be mounted next. There are three different types (although Q1, Q3 & Q4 can all be BC546s if desired), so take care to install each in its correct place. The screw terminal blocks making up CON1 need to be joined together first by fitting each side-by-side by sliding the dovetail mouldings together. Solder them in place with the wire entry side of the terminals facing the nearest edge of the PCB. Now fit LED1 with its longer lead inserted into the anode hole. Mount it so that the top is about the same level as the adjacent screw terminal. IC1 can be soldered directly onto the PCB, making sure its pin 1 is facing as shown. Finally, install the capacitors. The 1μF capacitor must be oriented correctly, with its longer + lead into the pad shown. You could use a non-polarised 1μF plastic film capacitor, but it will be substantially larger Table 1 – component values that vary with amplifier supply rail voltages Supply R1a R1b R2 R3 (½W) ZD4 ZD5 ±80V 15kW 1W 15kW 1W 15kW 1W 33kW 75V (1N4761) 18V (1N4746) ±75V 15kW 1W 15kW 1W 15kW 1W 33kW 75V (1N4761) 9.1V (1N4739) ±70V 12kW 1W 12kW 1W 12kW 1W 33kW 75V (1N4761) wire link ±65V 12kW 1W 12kW 1W 12kW 1W 33kW 33V (1N4752) 33V (1N4752) ±60V 12kW 1W 12kW 1W 12kW 1W 33kW 27V (1N4750) 27V (1N4750) ±55V 10kW ½W 10kW ½W 10kW ½W 33kW 22V (1N4748) 22V (1N4748) ±50V 9.1kW ½W 9.1kW ½W 9.1kW ½W 33kW 16V (1N4745) 18V (1N4746) ±45V 8.2kW ½W 8.2kW ½W 8.2kW ½W 33kW 12V (1N4742) 12V (1N4742) ±40V 7.5kW ½W 7.5kW ½W 7.5kW ½W 30kW 15V (1N4474) wire link ±35V 6.2kW ½W 6.2kW ½W 6.2kW ½W 30kW 3.9V (1N4730) wire link ±30V 5.1kW ½W 5.1kW ½W 5.1kW ½W 27kW wire link wire link ±25V 3.9kW ½W 3.9kW ½W 3.9kW ½W 22kW wire link wire link ±20V 3kW ½W 3kW ½W 3kW ½W 18kW wire link wire link ±15V 2kW ½W 2kW ½W 2kW ½W 13kW wire link wire link ±10V 1kW ½W 1kW ½W 1kW ½W 8.2kW wire link wire link 70 Silicon Chip Australia's electronics magazine siliconchip.com.au and probably more expensive than the electrolytic. If you’re building the two-channel version to light a single clip indicator LED, build a second board as per Fig.3 and solder a ~20mm length of solid-core ‘Bell wire’ to the top of that board, into the pad between ZD3 and Q4. It makes sense for the more sparsely populated board to be at the bottom of the stack as it lacks the LED, and you’ll want to be able to see the LED on the other board. Alternatively, if you’re building a two-channel version with separate LED indicators, make a second identical board and don’t fit the vertical wire. Mounting it & wiring it up Parts List – Clipping Indicator (per channel) 1 double-sided, plated-through PCB coded 01112211, 54 x 60mm 2 3-way screw terminals with 5.08mm spacing (CON1) OR 2 2-way screw terminals with 5.08mm spacing (CON1; for minimised second channel) Semiconductors 1 7555 CMOS timer, DIP-8 (IC1●) 2 BC547 or BC546 NPN transistors (Q1, Q4●) 1 BC557 PNP transistor (Q2) 1 BC546 NPN transistor (Q3) 1 yellow, amber or red 3mm or 5mm LED (LED1●) 1 yellow, amber or red LED (optional; external LED●) 2 4.7V 1W (1N4732) zener diodes (ZD1, ZD2) 1 3.9V 1W (1N4730) zener diode (ZD3●) 3 1N4148 small-signal diodes (D1-D3) 2 zener diodes or wire link (ZD4▲, ZD5▲) 1 LED bezels (optional; for chassis-mounting external LED) 4 M3 x 6mm tapped Nylon spacers (or 15mm spacers for the upper board in the stack) 8 M3 x 6mm machine screws (or 4 M3 x 15mm machine screws for the upper board in the stack) 1 20mm+ length of solid-core hookup wire (optional; to join stacked stereo version) various differently-coloured hookup wires, rated for amplifier supply voltage Capacitors 1 1μF 16V PC electrolytic● 1 100nF 63V or 100V MKT polyester● 1 10nF 63V or 100V MKT polyester● Resistors (¼W, 1% axial metal film) 6 100kW (● 4 required for minimised version) 1 10kW● 2 1kW● 1 100W 4 other resistors, values as per Table 1▲ ● not required for the minimised second channel ▲ see Table 1 for values and power ratings Use the board to mark out four holes in a convenient location within the amplifier chassis, ideally, between the amplifier modules and speaker terminals, or at least near the terminals. If it’s a stereo amplifier, you can stack the two boards by feeding longer machine screws up through the spacers on which the lower board is mounted, then screwing some ~16mm tapped spacers on top of the threads once the first module is in place. If you have space, you could mount the two modules separately, eg, side-by-side. Connect the Clipping Indicator(s) to the amplifier’s V+, V− and 0V supply rails and the amplifier speaker + output(s) to AMP OUT input(s) on the Clipping Indicator module(s). Make sure the wiring is suitably voltage-­ rated, especially when the supply rails are at high voltages from Earth. The external LED connects to the A and K terminals on the board. If you are building the minimised stereo version with IC1 and associated components missing, feed the wire you soldered earlier to the bottom board up through the matching pad on the top board. Solder it on top and mount the upper board using longer tapped spacers and short M3 machine screws. In all cases, when using a second Clipping Indicator module, all three supply connections must be made to both boards, along with the AMP OUT terminal. The only terminals that aren’t needed on the board with components missing are the LED A & K. The external LED or LEDs can be attached to the amplifier chassis using suitable LED bezels, or (less ideally) glued into tight-fitting holes using This shows the Clipping Indicator installed inside our upcoming 500W neutral-­cure silicone sealant. SC Amplifier chassis. siliconchip.com.au Australia's electronics magazine March 2022  71 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. An alternative version of the Arduino Power Supply I designed a slightly different version of the Arduino-based Power Supply from the February 2021 issue (siliconchip.com.au/Series/357). I wanted to remove the need to physically connect the power supply to my laptop, as that means that I need to find a spot for the laptop on my workbench, and there isn’t room. To do this, I based it around an Arduino-­ compatible ESP8266 module, specifically the WeMos D1 R2 mini. The main challenge in adapting the design to this module is that the micro has 3.3V I/Os compared to the 5V I/Os of an Arduino Uno. The circuit is overall similar to the February 2021 design, with the following changes. I added two transistors (Q3 & Q4) acting as a level shifter to switch the relay from the D1 mini’s 3.3V digital output. I also had to add a TMUX1204 4:1 analog multiplexer since the D1 mini only has one analog input. Sensing of supply voltage, output voltage and current are all done via this mux, which adds three extra analog inputs but takes up two digital outputs to select the mux channel. I added an AMS1117 low-dropout regulator to provide the 5V rail from the input power supply; this can handle an input voltage up to about 12V. Above that, a regulator with a heatsink like a 7805 would be needed. I enclosed all the circuitry in a Jiffy box with a voltmeter (since the laptop is not in the same room) and some nice binding posts. The voltmeter is mainly so that I can confirm it’s on the correct voltage before connecting things. The D1 mini module is connected to the PCB with most of the circuitry via 10x2-pin header CON1. This makes creating other daughterboards possible; I also created a board for an Arduino Nano, to provide a wired alternative that’s a little cheaper than the Uno. I have not tested that yet. The PC software acts as a server, waiting for the PSU to connect via WiFi. The PSU connects to the GUI on startup, and everything works the same as Tim Blythman’s original design once the connection is established. The PSU also listens for connections on port 23. Connecting to this allows the user to specify the IP of the GUI program that the PSU should attempt to connect to. The only other firmware modification required was to set the mux channel before reading voltages using the analog-to-digital converter. I discovered one flaw: for up to a minute after initial connection, the communication between GUI and PSU is very slow, and the PSU responds sluggishly. After that time, it responds more or less instantaneously. I am not sure why this happens – perhaps it’s a buffering issue in the D1 mini’s WiFi stack or a bug in the Processing language. Thanks for a terrific design! I learned a lot building this, and now I have a very convenient low-voltage PSU which is enough for many projects. The modified firmware and GUI code can be downloaded from https://github. com/gordoste/d1_mini_wifi_psu Stephen Gordon, Thurgoona, NSW ($150). Editor’s note: Q4 and two 10kW resistors could be eliminated by connecting the coil of RYL1b and D1 (D1 anode to +5V) between +5V and the collector of Q3. The finished PSU is composed of two PCBs and the D1 module. This photo shows how the main PCB is wired into the case. The finished Arduino PSU uses a 3-digit 7-segment digital voltmeter. 72 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine March 2022  73 Illuminated doorbell press switch circuit This circuit allows you to add an illuminated doorbell press switch to a new or existing wireless chime setup. You can also use it to upgrade an existing illuminated press switch to longlife LED lighting. No more costly and hard-to-get specialised light bulbs for your favourite bell switch! Four 3mm super-bright LEDs of any colour are connected in series and housed within the body of the pushbutton switch. They should be arranged to shine through the switch sides; in my case, a Friedland D534 Lightspot. The LED current is limited to a safe level by the 150W 2W resistor, although the resistance of the wires leading to the switch has an effect too, depending on their length. When the button is pressed, the LEDs are effectively shorted and the voltage at the inverting input of the LM393N comparator (pin 2) drops below the reference voltage at the non-inverting input, set by trimpot VR1. This causes the LM393N’s output transistor to turn off, switching on NPN transistor Q1 due to the 10kW pull-up resistor and energising the small relay. The normally-open contacts of the relay can be used to adapt a wireless doorbell transmitter by bridging its pushbutton switch, or simply used to control a bell or chime in a conventional wired doorbell. The circuit can be easily constructed on a small piece of veroboard, powered from a small 12V plugpack and housed in a small plastic case. The only setup required is the adjustment of VR1. With the circuit wired and powered up, the LEDs in the pushbutton switch should be illuminated. First measure the voltage at pin 2 of IC1 with a DVM, then monitor the voltage at pin 3 while adjusting VR1 until it is about 1V lower. The exact setting is not especially critical, but setting it too low can give trouble if the pushbutton switch contacts become more resistive due to corrosion. Setting the voltages too close can produce unwanted spurious chime operation. David Worboys, Georges Hall, NSW. ($70) Reading three digital signals with a two-channel oscilloscope I needed to watch three different digital signals (SPI chip select, clock and data) but only have a two-channel analog scope. So I came up with the idea of using resistors to mix the clock and data signals, as shown, then feeding the combined signal into one of the scope channels. As you can see from the scope grab, it works surprisingly well – the clock pulses ‘ride on’ the data pulses. You can identify the clock pulses and see whether the data bit is high or low during that pulse. The other channel is free to be connected to the chip select line, so it can be used as a trigger to capture the SPI packet. You could change the value of the resistors to suit the job; 22kW is a reasonable middle ground as it will not overly load digital signals while still providing reasonable signal integrity to the scope for moderately fast signals (up to a few MHz perhaps). John Rich, Petersham, NSW. ($60) 74 Silicon Chip Australia's electronics magazine siliconchip.com.au MAKER ! Build It Yourself Electronics Centres® MARCH 30 x 30 x 40cm build volume for larger prints inventors Top deals for makers, March 31st. & tinkerers. Only until K 8606 SAVE $351 799 Dual 4K monitor ready! 125 $ $ Z 6415 4GB RAM The Raspberry Pi® 400 Print bigger with the Creality® CR-10 V2 3D Printer A complete computer the size of a keyboard! A neat new portable design ideal for education environments. With all the same features as the Raspberry Pi 4, it’s a powerful computing platform for work, education and play! Rear panel provides access to all ports including the GPIO header. Add on accessories: P 6631A 1.5m micro HDMI cable $22.95. M 8821 Power supply $19.95. D 0313A Noobs 16GB micro SD card $22.95. screw Torque adjustment prevents chewed out heads! The CR-10 offers reliable large volume printing up to 30Wx30Dx40Hcm! The dual port fan cooled hot end offers reliable and precise print quality whilst the triangular design provides excellent stability. Heated print bed reduces warping, ensuring reliable prints every time. Great for anyone who needs to print larger designs such as cosplay parts, architectural models & replacement parts. Normal RRP value of tools $67.90 SAVE $40 99 $ 30 $ Repair faster with a precision lithium screwdriver. This USB rechargeable screwdriver features a fully adjustable torque drive for fast and accurate driving of precision screws found in modern high tech devices. Two way direction. 40 x 4mm driver bits. 3 hours use per charge. See web for full contents list. Wireless Magnetic Power Bank Charge your phone on the go with this MagSafe compatible wireless charging battery bank. 10,000mAh. 20W USB C PD in/out. *Shown with compatible Iphone 12 for illustration purposes. D 0515A* 29.95 SAVE 25% T 2128A NEW! 69 $ .95 T 2162 ‘Getting Started’ Electronics Kit Great for enthusiasts and students. Includes pliers, cutters, 30W iron, solder sucker & carry case. All you need to get soldering! See notifications while you ! 15W fast charging recharge. Handy upright 15W wireless charging stand allows you to read incoming notifications at a glance without having to stop charging. Requires QC3.0 USB wall charger (such as our M8863) D 2324* USB-C laptop 90W output charges any 34.95 $ 5pc Plier & Cutter Set T 2758A A must have for any electronics enthusiast. Includes: • Side cutters. • Flat long needle nose pliers. • Flat bent needle nose pliers. • Long nose pliers/cutters. • Bull nose pliers/cutters 54.95 $ D 0986 USB C 64.95 $ SAVE 25% VALUE! $ 70 $ D 0987 iPhone NEW! M 8994* Need an extra laptop charger? This 90W USB-C power delivery (PD) charger offers fast recharging for MacBooks, Nintendo Switch etc. Plus a standard 2.4A USB charger output. Get better audio for your vlogging & live streams. Wireless lapel microphone for top quality audio on your next live stream or vlog recording. Plug and play - no app required. Your one-stop electronics shop since 1976. | Order online at altronics.com.au 18.50 $ Great for cleaning jewellery! NEW! High Output Blow Torch Super hot 1350°C flame with high output nozzle. Handheld or self standing design the gas! for tasks such as Don’t forget r can. heatshrinking, model T 2451 $9.35 pe making, silver soldering! Easy to refill. SAVE 22% T 2237 Quick notes while you work Write a reminder, take a phone message or leave a note for your family with our handy eWriter LCD board. Ultra thin, portable design is also great for kids to draw on. Size: 226x146mm. 62 $ prints! Ideal for small, precise SAVE $24 135 80 $ $ X 0109 Clean & revive tiny parts T 2496 Creality® LD-002H Resin 3D Printer SAVE 20% Uses water, detergent and ultrasonic waves to remove gunk from small parts, spectacles, jewellery, even 3D prints! No solvents required. Stainless steel 18x8x6cm tank. Q 1090 9999 Count True RMS DMM With in-built AC mains detection. Featuring a striking easy to read reverse backlit screen & massive 9999 count readout. Auto range with push button operation. Creality® UW-02 Curing & Washing Machine SAVE $80 Affordable entry level resin printer for fast, strong & smooth prints. 499 $ Make cleaning and UV curing your prints simple and fast - no need to get your hands dirty, simply fill with water or isopropyl, place your print into the basket, select your chosen curing/ wash cycle and wait. Provides even 360° curing process for strong prints. K 8640 Resin based 3D printers are rapidly becoming the go to tool for high resolution 3D prints. They offer a faster print process with excellent accuracy and a stronger finished product thanks to UV curing on each layer. The LD-002R can print objects up to 130 x 82 x 160mm. This model is capable of printing a layer in 1 to 4 seconds, making it much faster than traditional FDM 3D filament printers. SAVE $21 K 8650 299 $ Save on workbench upgrades. Great quality for a bargain price! T 2748A 22.95 $ 5” Premium Cutters No more eye strain! 109 $ Tough chrome vanadium blades stay sharp for longer. Ideal for PCB assembly, cutting solid core wiring etc. X 4200 3 Dioptre SAVE $20 37.95 $ 60 $ Whisk away solder/print fumes from your workspace! Also works as a fan. Adjustable speed. K 8494 Translucent K 8495 Red K 8496 Blue K 8497 Black K 8498 Grey K 8499 White SAVE 12% SAVE 24% T 1296 Fume Extractor & Fan X 4201 5 Dioptre Ultra-bright long life LED for fantastic clarity (plus no need to change a globe EVER!). Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. Great for collectors, model makers, jewellers etc. n n n n n n Creality® UV Resin Quality UV resin for your printer. Get top notch results every time. Low viscosity and good fluidity with low shrinkage. 500g. K 8630 79.95 $ T 2164A SAVE 20% Includes bit types for latest phones & laptops 40 $ Pro 72pc Servicing Tool Set A premium finish aluminium driver handle with silent ball bearing ferrule top. 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Z 6421 8 $ .95 The STEM maker platform designed & developed in Australia. Model Z 6419 Z 6590 Z 6591 Z 6580 Z 6581 Z 6582 Z 6583 Z 6584 Z 6585 Z 6596 Z 6597 PiicoDev hardware has been designed from the ground-up with rapid prototyping and maker education in mind. Featuring a unified MicroPython library suitable for Raspberry Pi, Pico and Microbit. Simple to connect modules with consistent sizing for easy stacking and experimenting. The PiicoDev system provides lots of creative freedom for hands on electronics building. Designed and developed by Core Electronics in Newcastle, NSW. Type Adapter Board for Raspberry Pi Pico Adapter Board for BBC micro:bit Adapter Board for Raspberry Pi GPIO TMP117 Precision Temperature Sensor BME280 Atmospheric Sensor VEM6030 Ambient Light Sensor VL53L1X Distance Sensor MPU6050 Motion Sensor MS5637 Pressure Sensor PiicoDev Cable 100mm PiicoDev Cable 200mm S 4725 2000mAh RRP $7.95 $5.80 $4.60 $9.95 $13.50 $4.60 $19.00 $9.25 $8.60 $1.10 $1.50 Available now! 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Perfect for 4WDs, campers, caravans & trade vans. The affordable portable power solution for any vehicle. 299 $ M 8057 1500W The same top notch quality and safety features as our popular Black Max inverter series (left), with a modified sine wave design to bring 240V power to any vehicle at a fantastic price. Models up to 600W have USB and auxiliary 3A 12V DC output for powering devices. 240V outlet runs most simple appliances such as power tools, pumps, lights, fans and heater elements. All models fully isolated for safety and certified to AS/NZS 4763.2011. 89.95 $ Up to 135aH st capacity. Ju 65mm thick! Q 0594 Longer run time than lead acid! SAVE UP TO 20% 1299 $ SL4576W 100Ah Powerhouse® LiFePO4 1499 $ LiFePO4 Lithium Batteries LiFePO4 batteries offer longer service life than traditional lead acid batteries, plus weigh less than HALF as much as SLA batteries. All are 12.8V output with battery management system on board for safe and reliable use. 3 year warranty. 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SL4557A 30Ah (M5 bolt) $299 SL4576A 100Ah (M8 bolt) $749 SL4578A 120Ah (M8 bolt) $999 SL4581A 150Ah (M8 bolt) $1199 $68 $115 $149 $229 $599 $799 $999 Slimline Lithium Batteries SL4580W 135AH Model Western Australia Build It Yourself Electronics Centres Sale Ends March 31st 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 NEW! The Ultimate Battery Fuel Gauge. Accurately measures battery voltage, current, power, real capacity and remaining run time of your connected battery (suitable for any type of chemistry and voltages between 8V to 120V). Includes 50A shunt with 2m cable. 1% accuracy. Cut out dimensions: 53.5 x 37.5mm. Q 0592 SAVE $10 39 $ Handy Digital Power & Solar Meter A comprehensive power monitor panel for solar and remote power systems. Huge selection of on screen power stats. Supplied with a 200A shunt for easy connection. Cut out size: 87 x 47mm. 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 0091 Find a local reseller at: altronics.com.au/storelocations/dealers/ Advances in VTOL Drone Technology By Bob Young With small quad-rotor drones now well established, it is time to examine the advantages and disadvantages of this configuration. What does the future offer in regards to vertical take-off and landing (VTOL) aircraft? Image Source: https://unsplash.com/photos/e3hH6_pSk1g W ith years of extensive and valuable practical experience now behind quad-rotor drones, the little and not-so-little quad- and multi-rotor drones are here to stay. Drones with four, six, eight or even more rotors are in everyday use (see Figs.1 & 2). We reviewed the Parrot AR Drone 2 quadcopter in the August 2012 issue (siliconchip.com.au/Article/566). We also had a look at six- and eight-rotor drones in the same issue (siliconchip. com.au/Article/567) and more unusual designs in August 2016 (siliconchip. com.au/Article/10035). Despite their many advantages and versatility, these drones still fall short in some areas. By far, the biggest shortcoming is the lack of endurance that any vehicle powered by batteries is faced with. The energy density of batteries is sadly lacking compared to chemical fuel (liquid or gas), as shown in Figs.3 & 4. Combine this with the length of time required for recharging, and the shortcomings of electric-powered aircraft are serious indeed! On a brighter note, electric power wins hands down in terms of simplicity, reliability in starting and running siliconchip.com.au and, most importantly for drones, starting and stopping in flight. Combine this with the huge reduction in the number of parts that make up electric motors (and thus cost of manufacture), and we can see why there are incentives to push on with the search for a suitable electric power source. To demonstrate how difficult this problem is to solve, even liquid hydrogen (H2) ranks very poorly against fuels like gasoline (petrol) and diesel. Note that the LiPo batteries used by most drones are marginally better than the standard Li-ion cells shown in Fig.3, but not by much. While LiPo batteries have one of the best energy densities of lithium based Fig.1: a conventional small quad-rotor drone. Source: https://pixabay.com/ photos/quadrocopter-drone-modelling-1033642/ Australia's electronics magazine March 2022  79 Fig.2: this small human-carrying quadcopter basically follows the conventional quad-rotor layout. Source: www.flickr.com/photos/apbutterfield/23632731924/ batteries, they have also been responsible for starting many fires. Some resulted from poor charging procedures, while others are just due to the volatile nature of the chemical composition of the LiPo battery. Essentially, once the LiPo battery decides to fail, it often does so spectacularly. I once was asked to service a radio control transmitter fitted with a LiPo battery which had been left switched on in its aluminium carrying case. For reasons unknown, the battery caught fire; luckily for my customer, the fire consumed all of the oxygen in the case and it fizzled out, but not before it had done irreparable damage to the transmitter. However, the story of the battle for the best fuel for drones does not end with energy density. We have the fuel weight to take into account as well. Fig.4 tells that story. So as you can see, there is a definite requirement for a better way to power multi-rotor drones than batteries. Quad-rotor drones Fig 3: a chart comparing the energy density of a variety of fuels, including batteries. Note that the density (shown in megajoules per litre) relates only to the volumetric efficiency and ignores the weight; weight is considered in the following figure. Original source: US Department of Energy Efficiency and Renewable Energy Fig.4: a comparison of the energy content per unit weight and volume for common fuels against gasoline. Original source: US Energy Information Administration 80 Silicon Chip Australia's electronics magazine To understand how drones can be improved, let’s briefly look at how a typical small quad-rotor drone works. They are built using components like those shown in Fig.5. From left to right, they are a battery, a power distribution module, a flight control module, a receiver, four identical electronic speed controllers (ESC) and four identical motors with two clockwise-pitch propellers and two anti-clockwise pitch propellers. A video camera and associated components may be added to provide what is commonly known as first-person view (FPV). Fig.6 shows the main thrust vectors involved in controlling a quadcopter. Being basically stable, horizontal flight is the main task of the flight controller. Stationary flight (hover) is achieved when Fz = Zworld (Gravity) and Fy = 0. To achieve this, all motors should be delivering equal thrust with two motors rotating clockwise and two motors rotating anti-clockwise. Strictly speaking, there is no front, back, left or right side as the quadcopter can be flown in any direction. However, the flight controller needs to be mounted so that the transmitter sticks are coordinated with the flight controller to give the pilot a sense of control. The quad can move in any direction simply by reducing the RPM on siliconchip.com.au Beoavia Beoavia (https://beoavia.org/) is a non-profit student team within the Association of Aviation Students. The team was founded in April 2018 by students from the Faculty of Mechanical Engineering at the University of Belgrade, Serbia, and deals with the calculation, design, and production of aircraft to participate in various European and international competitions. By their respective area of interest and education, team members are divided into sub-teams: aerodynamics; structure; manufacturing; propulsion; electronics and programming; and marketing. By participating in aerospace engineering competitions, the Beoavia team represents the University of Belgrade, and enables its members to exchange knowledge and experiences with students from other European countries. Fig.5: an example of how a quadcopter is typically built from separate modules. Commercial modules might integrate some of these, but they use essentially the same configuration. the two motors in the direction of travel and increasing the RPM on the two motors on the opposite side. This introduces the thrust vector (Fy) into the equation, and thus the quad moves in that direction. To increase altitude, all four motors increase in RPM, and likewise, a common decrease in RPM will result in a loss of altitude. To achieve rotation in the yaw axis is a little more complicated; it requires the use of yaw torque. There are two sources of yaw torque in a quad-rotor or multi-rotor, but both are pretty weak relative to the other control factors. This will become significant later when we discuss quadplanes. The first is the imbalance between the torque generated by the clockwise spinning rotors and the anti-clockwise spinning rotors. This is entirely a function of friction in the motor bearings and aerodynamic drag. The second is torque arising from the conservation of angular momentum when the rotor speeds are changed, similar to how a reaction wheel works. This effect is present in a vacuum, so it does not rely on aerodynamic forces. The first effect causes angular acceleration of the vehicle proportional to the difference in rotor speeds between the sets of rotors. The second effect causes angular acceleration of the vehicle proportional to the difference in the derivative of the rotor speeds (ie, their rotational accelerations) between the sets of rotors. It is when dealing with rotation that we encounter the concept of props-in and props-out (see Figs.7 & 8). This refers to the relative direction of rotation on all four rotors. Fig.7 shows the direction of rotation for the ‘props-in’ configuration. This is the default for all flight controllers and most multi-copters with a boom span over 7.5cm. The props-out configuration is used by most pros for 7.5cm quadcopters Fig.7: the ‘props-in’ configuration. Fig.8: the ‘props-out’ configuration. Essentially, the clockwise/anticlockwise layout is reversed compared to Fig.7. Fig.6: the vectors involved in quadcopter control and motion. siliconchip.com.au Australia's electronics magazine March 2022  81 Fig.9: a typical quadplane combines a standard aircraft layout and a quad-rotor layout. Note the motor on the front of the centre fuselage to provide forward thrust. For horizontal flight folding props are fitted to the four electric motors. Quadrocopter designed and built by the author. Fig.10: a very neat quadplane featuring a rear-mounted motor to provide forward thrust. Fig.11: the problems confronting a quadplane in the hover position without a motor to provide forward thrust. Original source: MicroPilot (www.micropilot.com) – used with permission. and smaller, at least when they are focusing on notable flight characteristics; a fact that becomes quite obvious when making a sharp turn. A sharp turn will cause a sudden dip and lift when using props-in rotation, just like in a dull 90° turn due to the turbulence during the yaw rotation. Some earlier whoop crafts had this problem until a solution was found, which turned out to be using the reverse (props-out) rotation. There are other factors involved with the props-in/out argument, but 82 Silicon Chip they fall outside the scope of this article. However, one aspect worth mentioning is that props-in helps keep dust and dirt off the camera in the event of a flip-over during landing. So, to summarise the pros & cons of quad-rotor and multi-rotor drones. Advantages: • Multi-rotor drones are easy to control and manoeuvre • They can take off and land vertically • They can hover • They are very stable Australia's electronics magazine Disadvantages: • Multi-rotors have a limited flying time (usually 15-30 minutes) • They only have small payload capabilities • Most of the drone’s energy is spent on fighting gravity and stabilising themselves. Quad-planes It is the last point that has driven the next stage in the quest for better outcomes. That is the addition of wings to the ‘copter to improve the payload and range capability. Such an aircraft is called a quadplane, and typical examples are shown in Figs.9 & 10. Adding two booms to a conventional aircraft makes it possible to mount the quad motors in the correct arrangement. However, just adding the quad motors without a motor to provide thrust for forward flight is not good enough. In this case, we need to tilt the aircraft forward to achieve a thrust vector to provide forward thrust for level flight. This arrangement is far from ideal, as shown in Fig.11. Figs.11 & 12 are originally from the Micropilot web page. Micropilot is a long-established and well-respected autopilot manufacturer in Canada. In Fig.11, we show the quadplane (without motor) in the hover position with a headwind. To hold a position relative to the ground, we must tilt the aircraft forward to provide a thrust vector from the four rotors for forward motion, to cancel the drift. This places the wing at a negative angle-of-attack (AoA) relative to the wind, which is now flowing over the wing and thus producing negative lift, which in turn calls for more power from the motors to hold the required altitude. That means more current from the battery; as is the way of the world, you don’t get anything for nothing! So we must look beyond our simple quadplane concept and go to the next step. This is to provide forward thrust with a propeller mounted either in the nose (tractor) or at the rear (pusher). This propeller can be powered either by an electric motor or an internal combustion motor. Take your pick. For a whisper-quiet surveillance drone, the obvious choice is an electric motor up front. For long-endurance drones, though, the obvious choice is an internal combustion engine (ICE). Fine examples of such aircraft are siliconchip.com.au shown in Figs.9 and 10. So we now have a long-endurance quadplane that can take off and land vertically, capable of holding position in a hover in a strong wind. As we are no longer required to tilt the aircraft to hold the hover due to the thrust provided by the IC engine running at a low throttle setting, this reduces the lift required from the four rotors when in hover, thus saving electrical power. An additional benefit from this style of quadplane is that we can now completely shut down the four electric motors in forward flight, providing an even greater saving in battery power. Thus, rather than being of prime concern, the batteries are needed only to provide power during take-off, hover and landing. However, have we reached the peak of aerodynamic efficiency? We still have two large booms to carry and various protrusions, such as motors and props out in the breeze, which all provide drag. There are many gifted people in this world, and some of them have come up with what I consider to be one of the most ingenious and elegant quadplane layouts I have yet to come across. That is the Beoavia Wasp, a Quadplane designed by a group of European students (see panel). The ability to take off and land vertically is of paramount importance in many applications. It eliminates the need for runways or large clearings for landings or take-offs. But the price to be paid is the expenditure of a considerable amount of energy lifting and lowering the quadplane to and from what is known as transition altitude. This is the altitude at which it is deemed safe to put the quadplane into forward flight. There is another rather complex requirement for quadplanes: a control system that can handle the transition from vector stabilisation and control to aerodynamic control surfaces as in traditional aircraft when in forward flight (controlling the throttle, ailerons, elevator and rudder). Consider the Wasp quadplane shown in Figs.13 & 14. Once it has transitioned to forward flight, the rotors are tucked away inside the fuselage and can no longer play any part in the control of the aircraft. During take-off, landing and hover, the receiver feeds directly through a flight controller into electronic speed siliconchip.com.au Fig.12: problems for a quadplane in a crosswind hover. Original source: MicroPilot (www.micropilot.com) – used with permission. Fig.13: a most elegant and ingenious VTOL quadplane, the Beoavia Wasp. Source: screen grab from Beoavia YouTube video (https://youtu.be/ T8xTAOuBwKc) Fig.14: the Wasp with the undercarriage, motors and props retracted into the fuselage. Now we are talking real aerodynamic efficiency. Source: screen grab from same video as Fig.13. controllers (ESC) and finally, to the motors. However, in forward flight, we must revert to a standard radio control system where the receiver bypasses the flight controller and feeds servos instead. We might need both systems to be Australia's electronics magazine fully functional during the transition, depending upon a host of variables. All of this has been taken care of in the Wasp. It should be evident by now that the future for quadplanes is very bright, and this is only the beginning! SC March 2022  83 Intelligent Dual Hybrid Power Supply PART 2: BY PHIL PROSSER Our new Dual Hybrid Supply has very quiet outputs given its use of switchmode regulators to provide good efficiency and high power output in a small package. The outputs can be used independently or together in series or parallel, all controlled through a single easy-to-use digital interface. We described the circuitry last month, so this article will concentrate on assembling and calibrating the Supply. T here are a few steps in assembling, testing and calibrating this Supply. First, you need to build the four PCB assemblies: two regulator modules, the control board and the front panel board. Then you need to wire them up and put them through some basic checks to make sure they are all functional. Following that, you attach the regulator modules to the main heatsink, prepare the case, mount everything in the case and wire it all up. Once you’ve done that, we’ll take you through the calibration procedure, which is mainly done via menus on the LCD screen, with the aid of a decent multimeter. There’s quite a bit to get on with, so let’s start with populating the regulator PCBs. Building the regulator module(s) Each regulator module is built on a double-sided PCB coded 18107211, measuring 116 x 133mm. Fig.10 is the 84 Silicon Chip PCB overlay diagram; it shows which components go where and indicates the correct orientations for polarised components. Refer to it as you build the board assembly. If you are making a dual power supply, only one board needs the LM2575-5 (REG3) and associated components (L3, D12 etc) to be loaded. It is essential to only fit links LK1 & LK2 on the one board with the LM2575-5 regulator. So install those on one board now – you can use 0W resistors or lengths of tinned copper wire (Bell wire would work too). Construction of the Regulator Module commences with all resistors, except for the 0.01W current sense resistor and 0.05W current sharing resistors. Leaving these off for now will mean that the board lays flatter on the bench, making it easier for you to solder the fiddly components that come later. With those smaller resistors in place, mount all the diodes bar the Australia's electronics magazine TO-220 case diode and bridge rectifier, checking carefully that each is in the correct orientation before soldering. Follow these with the 100nF film capacitors, 10μF electrolytic capacitor and remaining MKT capacitors. Before you fit the ceramic capacitors, solder the SMD ICs in place. Then install the small transistors (TO-92 package). Make sure you don’t get the two different types mixed up. We have described how to do this on many occasions. The basic idea is to tack one pin down, check that the placement and orientation are correct, add flux paste to all the pins, solder all the pins, then clean up any bridges which have formed using more flux paste and some solder wick. Pay attention to the orientation of the MAX14930 isolators, IC6 & IC7; they are mounted in opposing directions. We have added markings near pin 1 of each SMD IC to assist. With the SMD chips in place, fit the ceramic bypass capacitors. siliconchip.com.au There are two 15μF surface-mount tantalum capacitors on the top of the board. These go with the positive end toward the regulator. Double-check their orientation; the positive end should have a stripe. There are also five surface-mount capacitors on the back side of the board; fit them next. Now is a good time to load the components we held back: the 1W, 0.01W and 0.05W resistors. Then mount the headers, connectors and fuse clips and install the fuse. Making the diode heatsink TO-220 diode D3 needs a small heatsink to make it bulletproof. Its dissipation is only high if the Supply’s output is short-circuited, but ideally we want it to handle that continuously. We used a 55mm by 40mm piece of 1.6mm-thick aluminium with a fold in it. We recommend you do the same, as there is no need for a ‘bought one’, and this is the optimum size for the available space. Fig.11 shows how to fold and mount this heatsink. Now fit the larger transistors (Q3 & Q10), three DIP ICs, plus the LM317, LM337 and LM2575-5 regulators. The regulators can be mounted with a couple of millimetres lead length. The +12V regulator (REG1) and negative regulator (REG4) need small flag heatsinks which are attached with an M3 machine screw, crinkle and flat washer, insulating bush and washer, as shown in Fig.12. Before you mount the electrolytic capacitors, attach the heatsink to the TO-220 diode. This will make it easier Here is an example of how to mount the diode to the heatsink. Take note that the heatsink should have a bend in it as shown in Fig.11. siliconchip.com.au Fig.10: the Regulator board is somewhat packed but not difficult to assemble. There are just a few SMDs; none with particularly fine-pitch leads. The only components that mount on the underside of the board are five SMD capacitors, all in the upper right-hand section. They are shown in an ‘x-ray’ fashion here. Fig.11: we couldn’t easily find a commercial heatsink to fit in the space around diode D3, so we made one. It’s simple as you just need to cut out a rectangle of aluminium, drill one hole and fold it 90° where shown. Then attach it to the tab, including connecting the heatsink to the device’s cathode for EMI reduction. Australia's electronics magazine March 2022  85 Heatshrink tubing should be placed over the flying leads to the bridge rectifier as shown. on the PCB. We used 15cm lengths of 7.5A rated hookup wire; red for positive, black for negative and yellow for AC. Also use heatshrink tubing to insulate the connections to the bridge rectifier leads. Building the control boards This shows how the boards should look when mounted to the heatsink. Note that in this picture, there is only one LM1084 per board. The final design has two LM1084s and two current-sharing resistors. Fit those as per the overlay diagrams. to get all the bits aligned and tightened. If you forget, you can poke a screwdriver through the hole in the toroidal inductor, but that is much more fiddly. You can now fit the remaining electrolytics; put the larger ones in last as they tend to dominate the board. All bar two of these have the positive (+) lead toward the main heatsink, or to the left with the heatsink at the top. The two 220μF electrolytics do not follow this rule. These are at the input to the MC34167 and have their (longer) positive leads to the left, as demanded by the pinout of this device. Finally, load the inductors. We put a dab of neutral cure silicone under ours to stop them moving, and recommend that you do the same. At this point, everything except the parts that mount to the main heatsink should be on the board. The bridge rectifier is attached via 150mm flying heads, allowing it to be mounted to the heatsink. Put short lengths of heatshrink tubing over the connection of the flying leads to the bridge rectifier, as shown in our photo above. Route the leads to the rectifier pads Fig.13: the powerful PIC32MZbased control board for this project has been used in several previous projects. Some of the components are not needed for this one, so we have left them off this overlay diagram. Solder IC11 first (watch its orientation!), then IC12, followed by the passive SMDs (resistors & capacitors), then the remaining SMDs and finally the through-hole components. Fig.12: we are using pre-made heatsinks for REG1 & REG4; attach them like this. 86 Silicon Chip The controller for this project is the same one that was originally published in 2019 for the DSP Active Crossover & 8-channel Parametric Equaliser (siliconchip.com.au/Series/335). The main difference is that here, the PIC32MZ is programmed with the Intelligent Power Supply firmware. The PCB overlay for this controller board is shown in Fig.13. We’ve removed most of the components you don’t need for this project, although it won’t hurt if you fit them anyway. As usual, fit the SMD ICs first (watch their orientation and check for bridged pins!), followed by the other SMDs, then the lower-profile through-hole components, finishing off with the taller parts. Besides the ICs, be careful that the cathode stripes of the diodes go in the right locations, plus the SMD LED cathode (which is often marked with a green dot or T-shape). Also make sure that the positive (longer) leads of the electros go to the pads marked with + symbols. If you will be programming your own microcontroller, the HEX file is available for download from our website. It can be programmed in-circuit via CON23, but note that if you plan to plug a PICkit in, it goes to the row of pins closest to the micro, with pin 1 at the end marked with a “1”. Or you can purchase a pre-programmed micro from our online shop, in which case you can skip that step. Australia's electronics magazine siliconchip.com.au This control module connects to both regulator modules with a multidrop 10-way ribbon cable, which we’ll make up shortly. It also connects to the front panel PCB, shown in Fig.14. There isn’t much to assembling this board. Just fit the two resistors, then the seven caps, followed by the header on the top. That just leaves rotary encoders and buttons, which mount on opposite sides. The encoders are on the top side and the pushbuttons on the underside. Make sure all of those are square and pushed down firmly before soldering their pins. We recommend that you use the S3352 rotary encoder from Altronics. Any of the horizontally-mounting “TT” 20-pulse-per-revolution parts with a switch should work (Mouser part code 858-EN11-VSM1AF20 has been verified as working). These are available with either a D-shaft or spline shaft. Once you have assembled this board, it’s a good time to make up the three ribbon cables, as shown in Fig.15. Cut the 10-way cable to 320mm and 250mm lengths and the 20-way cable to one 160mm length. Crimp on the IDC plugs as shown in the diagram. Note how the cable folds through the strain relief clamps at either end, but not on the sole middle plug. Some IDC plugs might not come with relief clamps. These lengths assume you are using the recommended case and will be sticking to our layout. If you are varying either, you might need longer cables, so check that first. Fig.14: this simple frontpanel board carries the two rotary encoders and two pushbuttons used to control the Supply, plus some debouncing components and pull-up resistors. It connects to the control board (shown in Fig.13) via a 10-way ribbon cable with DIL IDC connectors at each end. Metalwork The heatsink used is an Altronics H0545 300mm diecast aluminium type, with the final four fins cut off, as shown in Fig.16. This is to leave room for the power connector and fuse on the rear panel of the recommended case. It might seem an odd thing to do to a perfectly good heatsink, but it is otherwise ideal for the job, just a tad too long! Cutting the heatsink is a 10-minute job using a hand-held hacksaw and a liberal dose of elbow grease. While it might look intimidating, no special tools are required. Clamp the heatsink to a workbench with cardboard protecting its surface and patiently work at it. Finishing off with a file will deliver you a neat result. We taped it up and applied a quick spray of black paint to the cut section, but you don’t have to do that. There are six mounting holes to drill to 4mm, and ten mounting holes for regulators and brackets. We drilled and tapped these to M3 x 0.5mm. We have laid the PCB out so that the mounting holes are between the fins; if you do not have an M3 tap, you can simply drill these to 3mm and use long screws and nuts to mount the power devices straight through the heatsink between the fins. Note how the mounting holes run along the top and bottom edges of the heatsink. All power device mounting holes are along the middle of the heatsink. In addition to the regulator ICs, the diode bridges are mounted to the heatsink, and there is a bracket in the middle of each regulator PCB. Power supply assembly Now it’s time to fit this all into a neat benchtop case. One of the design goals for this project was to keep interfaces and wiring simple and tidy. This is achieved by the PIC32 communicating with the regulator modules using an SPI interface. If you are into Arduino or Micromite, you could design your own controller. The majority of work now is in preparing the case and heatsink. The case we have specified is an ideal size for the workbench, and provides a professional looking finish to the product. You could use any other case of suitable size, with the only provisos being to ensure the case has adequate mechanical rigidity to secure the transformer and heatsink, and that it can be safely Earthed. siliconchip.com.au Fig.15: these are the three IDC cables you will need to make up to connect the boards. The 10-way cable with two plugs connects the control board (Fig.13) to the front panel (Fig.14), the other 10-way cable with three plugs connects the control board to the regulator board(s) (Fig.10) and the 20-way cable connects the control board to the LCD screen module. Australia's electronics magazine March 2022  87 Mounting the regulator modules to the heatsink requires a little care. Our approach was to fix the mounting bracket, insert all the power devices into their PCB pads and jiggle it around to get them aligned. We then screwed them loosely into their mounting holes and soldered their leads, as follows: 1. Install and screw down the mounting bracket in the middle of the PCB. 2. Bend the leads on the MC34167 to ensure that the device will mount flush to the heatsink. This device is a relatively tight fit. 3. Do the same with the two LM1084IT-3.3 devices, ensuring that you get them to about the right height. 4. Using silicone insulators, insulating bushes, flat washers, shakeproof washers and 16mm M3 screws, loosely mount the power devices to their locations on the heatsink. It is best to do this with the heatsink flat on a desk and the regulator module facing upwards. 5. Tack solder on one pin of each device. 6. Where there is a misalignment, reflow the solder on the offending pin to adjust it. 7. Secure the MC34167, then the LM1084IT-3.3 devices. You can access the mounting screw for the MC43167 through the gap between the 4700uF capacitors. 8. Once everything is aligned and there is no stress on the PCB, gently tighten all the mounting screws. Watch out that tightening the screw does not twist the device around, and make sure you don’t overtighten them. 9. Now solder all the pins. 10. Mount the bridge rectifier on the heatsink now. It should already be wired to the PCB. 11. While you have the boards in this location, attach two 15mm long M3 threaded standoffs to the regulator module using 6mm M3 screws, flat and shake-proof washers. This will ensure it sits neatly on the desk. When mounting the MC43167, it is easiest to stand the heatsink on end, slip the regulators into their holes and get the insulator in the right spot. Then using long nose pliers, line up the screws with the insulating bush and washers in the hole so you can do it up. Repeat this process for the LM1084 regulators, then the other regulator module (assuming you’re building two). Now put your multimeter on a high ohms range (eg, 20MW) and check the resistance between the heatsink and the tab of the TO-220 devices. There should be an open circuit in each case. If not, remove the device and check what has gone wrong; check in particular for burrs on the screw hole in the heatsink. This process is repeated for the second module. Initial testing Connect the 20-way cable between the control board and LCD (being careful to line up pin 1 at both ends). Also attach the 10-way cable with two plugs between the control board and front panel board (the same comment applies) and the other 10-way cable between the control board and the one or two regulator boards. You can make some initial checks at low power and without mounting anything to the heatsink. Just don’t draw high currents! Install jumpers on JP1 & JP2. If you are using only one module, select channel one only. For dual rails, select channel one on one board and two on the other. If you are not using our microcontroller-based control board, you do not need to install these and should not have loaded the DAC, ADC or opto-isolators. During this testing, if it has not been mounted to the heatsink yet, make sure that the bridge rectifier Fig.16: this heatsink drilling pattern suits two regulator modules. The holes marked “A” are for mounting the heatsink to the case, while the two sets of holes marked “B” are for attaching the PCB-mounted semiconductors and bridge rectifiers on each module to the heatsink, plus a bracket to prevent the heatsink/PCB assembly from flexing too much. If you can’t tap the holes for M3, they are positioned between the fins, so you can drill through and use long machine screws, washers and nuts. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au can’t short anything out. Either place it somewhere safe or wrap it in insulating tape. Initial testing can be done by injecting ±15V DC into the board. Still, if you don’t have a suitable dual supply (maybe that’s why you’re building this one?), you can instead solder a 10W 5W resistor across a blown M205 fuse and use this in place of the onboard fuse while applying about 24V AC to the input terminals. If you have the dual DC supply, connect +15V to the rectifier side of the fuse, the external power supply ground to a ground point, such as the “-” on the bridge rectifier, and -15V to the large via just next to the 3300μF capacitor. You can solder a piece of wire into this via and clip a lead to it. Switch on and allow it to settle. The current draw should be less than 200mA. Check for the following voltages: • +12V (typically closer to 11.5V) on pin 2 of REG1 (LM317). This is also on the cathode of D2, just below the regulator. This should be within a volt of the expected value. • +5V (5.1V actual) on pin 2 of REG2 (LM317). This is also the cathode of D10, just below the regulator. This should be within 0.5V of the expected value. • -4.5V (-4.5V actual) on pin 3 of We left a 4mm gap between the big capacitors to allow a screwdriver to get to the tab of the TO-220 devices. It is tight, but enough for a standard Philips screwdriver. It’s easiest to start by holding the screw with longnose pliers. REG4 (LM337). This is also on the anode of D17 next to the regulator. This should be within 0.5V of the expected value. • +5V on LK1, generated by REG3 (LM2575). This should be within 0.5V of the expected value. If any of these are outside of the expected ranges, check the following: • Is the supply current high? Feel for components getting warm. • Look for solder bridges. • Check that the electrolytic capacitors are in the right way around. • Check that the regulators, diodes and ICs have been installed with the correct orientations. Assuming that’s all OK, verify that the pre-regulator is working. With no controller connected, the output should be set to 0V automatically. That means the pre-regulator should be producing around 5V. You can probe this on the output side of the 220μH inductor (the pin away from the MC34167). The exact voltage is not critical, but it should be between about 5V and 6.6V. If this is not as expected, check the following: • If you have an oscilloscope, set it to measure 5V/division and probe pin 2 of the MC34167. You should see some serious switching waveforms. It might not be switching at 72kHz, as the regulator will be unloaded and possibly running in discontinuous mode. • Check for solder bridges in the switchmode area. If the output is in the range of 0-0.5V, check for shorts around the schottky catch diode (D3). • Check the voltage on pin 1 of the MC34167. It should be close to 5V. Remainder of case Once you have finished preparing the heatsink, move on to the rear panel. Fig.17: the case’s front and rear metal panels need to be drilled and cut as shown here. The large rectangular opening at the rear allows the regulator PCBs to be admitted into the case after being attached to the main heatsink. The main heatsink then bolts to the rear of the case via the six holes marked “A” around the cutout. See the text for advice on how to cut the large holes. siliconchip.com.au Australia's electronics magazine March 2022  89 Remove it and drill and cut the holes, as shown at the bottom of Fig.17. To make the rectangular hole and the D-shaped hole for the mains socket, we drilled large holes in each corner of the cutouts and used a handsaw with a metal blade to cut along the outlines. Other approaches would be to use a jigsaw with a metal blade or a rotary tool (eg, a Dremel) with a metal cutting disc. In all cases, be somewhat careful as the material in the recommended case is aluminium, and you will easily bend it once cut. Once this is mounted to the heatsink, it will regain its strength. We have used a large hole to allow the complete heatsink assembly, with regulator modules, to slip in from the back. Now present the heatsink and regulator modules to the rear panel. The assembly should slip through the large cutout, and the mounting holes in the heatsink should line up with those in the rear panel. If there is a minor misalignment, simply drill the offending holes to 4mm or so. Fix these using 16mm M3 machine screws, flat and star washers and nuts. Finally mount the IEC panel male socket and fuse holder. The IEC socket is fixed using 16mm M3 screws, flat and star washers and M3 nuts. The base needs a few holes drilled, shown in Fig.18. We have provided locations for the regulator module mounting holes. Still, given the variability in how you have mounted the PCB to the heatsink, you will be better off putting some masking tape at the identified locations, installing the rear panel with regulator modules mounted and marking the exact locations before drilling those holes. While you are there, mark and drill the remainder of holes in the baseplate: the Earth post near the IEC connector, the toroidal transformer mount, the two holes for the terminal block and four holes for the control PCB. Cut Presspahn or similar insulating material and place this under the terminal block. Mount and secure the terminal block with 16mm M3 machine screws and nuts. Remove the paint around the Earth post and mount a 16mm M3 screw with a shake-proof washer and M3 nut. Reserve another shakeproof washer, M3 nut and solder lug to attach the mains Earth wire. Mount the control PCB using four Fig.18: this shows where you need to drill holes in the bottom of the case to mount the regulator modules, transformer, control board and terminal blocks for terminating both the low-voltage and high-voltage windings on the main transformer. It’s best to check where exactly your regulator modules sit when mounted in the case to ensure their holes are drilled accurately. 90 Silicon Chip Australia's electronics magazine siliconchip.com.au 15mm Nylon standoffs and 6mm M3 screws with fibre washers under the heads. This assures good separation of the mains Earth from the control PCB. Front panel The front panel needs a few holes and a large cutout for the LCD. Read through this section and check the measurements of your parts before cutting. This front panel will be right there on your workbench for a long time, so make it neat! The details are in Fig.17. Drill and deburr the holes as shown. For the LCD cutout, provided you are using the acrylic panel with paint to hide the cutout, you can err on the large side for the hole, as the paint will hide the hole you cut. Mount the switches and connectors, then attach the control PCB using the rotary encoders to secure it to the front panel. That just leaves the LCD screen. Mounting the display in a manner that insulates the LCD bezel from the case is fiddly. We found that some panels supplied have the LCD panel ground pin connected to its metal bezel. The display has 2.5mm mounting holes, so unless you have plenty of 16mm M2.5 machine screws and nuts on hand, drill these to 3mm. Clean up any burrs that result. Now take the 3mm acrylic sheet and cut it as shown in Fig.19 (or purchase a laser-cut version from our Online Shop). The mounting holes on our display were 88mm by 65mm apart. We carefully drilled mounting holes through the acrylic as shown, and came up with an arrangement that mounts the acrylic to the front panel and holds the LCD to the acrylic rather than the LCD bezel touching the case. You could be lucky, and your LCD bezel may be isolated from the case – but please do not assume this to be the case, as we want isolation between the power supply and mains Earth. This arrangement gives you good clearance. To make things neat, after cutting and adjusting the cover to fit the LCD and case, we masked off the inside of the cover as shown, then spray painted it black. Once the masking was taken off, we had a neat black shadow line that hides the cut in the case and gives a professional appearance. The assembly of the acrylic cover, the case and LCD is as shown. The acrylic cover mounts to the metal case Secure the acrylic bezel to the case with the M3 screws, then slip the LCD screen onto their shafts and tighten it up against the acrylic with insulators under the nuts. Fig.19: as it’s tough to make a clean and rectangular cutout in the metal panel for the LCD, we designed this plastic bezel to cover up the screen surround. You can order a laser-cut clear bezel with these dimensions from our website (at the same time you order the PCBs etc), but you will have to paint the outer area yourself. siliconchip.com.au Australia's electronics magazine March 2022  91 not desired. These mains Earth points need to be wired back to the front panel Earth lug using green/yellow striped mains-rated wire. The final connections to the front panel are the outputs from each of the two regulators, made with red and black (or blue) 7.5A-rated cable. Make sure these are secure. Ours were 24cm and 34cm in length after twisting together and terminating. While you are here, it is worth terminating the mains side of the toroidal transformer to the terminal block. Mains wiring using M3 (or M2.5) machine screws. The hole in the case is slightly larger than the bezel on the LCD, so the LCD can then be secured using four more machine screws and fibre washers. At this point, all parts of the case should be cut and drilled, and the PCBs mounted and ready to wire up. Refer now to the wiring diagram, Fig.20. There are three control cables, which are routed as shown. Move on to the front panel and low-voltage wiring. We have included the wiring of the bridge rectifiers for completeness, although this should have been addressed while building the regulator module(s). When connecting the wiring to the front panel, solder two 100nF 50V capacitors across the pairs of output terminals. These reduce the noise from the switch-mode section of the PSU on the output. Also install 10nF capacitors from each of the negative outputs of the two channels to mains Earth. Without this, the capacitive coupling through the mains transformer will induce substantial floating voltages on the channel outputs. Now it’s time to mount everything else in the case. Start by locating the mains transformer and wiring the outputs to the terminal strip as shown. We have used colour coding to match the Altronics M5525C 25 + 25V transformer. Check yours before proceeding as an error in this part of the circuit would not be good. 92 Silicon Chip We used 13cm and 25cm pairs of 7.5A-rated cables (red) from the terminal strip to the AC inputs of the regulator modules. Twist these to keep things neat, and tuck them away between the boards. We have made provision on the front panel for mains Earth access at each of the outputs. In some circumstances it can be handy to connect one of the outputs to Earth, but other times it is Use mains-rated cables for all wiring. Be careful to check this and if you have someone you trust, get them to look over it too. With the fuseholder and IEC socket installed, fit the Earth screw at the rear of the case. Make sure you scrape the paint off the case in the bolt area and use star washers on top and bottom. Do it up securely. First, connect the Earth wire from the IEC socket to the Earth lug using a solder lug and heatshrink tubing, to keep things tidy. Make sure this is long enough that it will not be strained. Next, run all the Earth wires from the main Earth screw in the base to the panels shown in Fig.20, including the The Regulator modules mounted to the heatsink slide straight into the case. We used nutserts on the rear panel, allowing us to screw the heatsink straight into them, making assembly a breeze. If you build a reasonable amount of sheet metalwork, do yourself a favour and buy a nutsert tool! Australia's electronics magazine siliconchip.com.au FRONT PANEL PCB RS2 1 FRONT PANEL (INSIDE VIEW) LCD MODULE RS1 POWER SWITCH EARTH LUGS 100nF 100nF LCD ADAPTOR PCB 1 10n F 10n F INTELLIGENT POWER SUPPLY WIRING DIAGRAM (50% OF FULL SIZE) 25V + 25V 300VA POWER TRANSFORMER ALPHA LCD CON12 CON6 DSP SPI1 1 1 2 1 2 0 19 GRAPHICAL LCD CON7 1 CON8 1 CONTROLLER BOARD CON5 CON10 PORTB 1 SPI2/I2S 1 JP5 CON23 ICSP 1 PRESSPAHN 1 1 + + + + + + + + + + + + + + + + + + + – + + + + + EARTH LUG + + + – + + + + + ~ ~ + + + CHANNEL 2 REGULATOR BOARD ~ ~ + + + + + + + ~ + BRIDGE RECTIFIER + + + ~ + + + + CHANNEL 1 REGULATOR BOARD BASE OF CASE GND CON9 PORTE 1 25V + 25V 300VA TOROIDAL TRANSFORMER +7VDC CON11 1 + BRIDGE RECTIFIER EARTH LUG IEC PLUG PANEL MTG 17 12 Fig.20: this wiring diagram should make clear all the connections needed to complete the Supply. Ensure the Earth lugs are making good contact with the bottom of the case and the rear panel; if necessary, clean off any paint or coating around their mounting holes and use shakeproof washers to ensure they ‘bite’ properly. All mains wiring must be properly insulated, including at the rear of the front panel power switch and the rear panel mains input socket. REAR PANEL (INSIDE VIEW) FUSEHOLDER siliconchip.com.au Australia's electronics magazine March 2022  93 Presspahn is required under the mains terminal block for safety (shown along the right edge of the case). This photo shows the wiring in place. Make sure that all of the metal chassis panels are connected to mains Earth when assembled either via the securing screws or Earth wiring. heatsink (eg, using one of the existing bracket mounting screws to attach it). Then using brown wire, connect the Active line from the IEC socket to the fuseholder, and from there to the power switch. We used a 6.3mm crimp connector here; you could solder it directly, provided you insulate the connection properly. Again, keep things secure, and use cable ties to ensure that, should any wire break or joint fail, the ends will be controlled and not create a hazard. Using light blue wire, run the Neutral connection from the IEC connector to the power switch. Ensure that you connect the IEC input to the bottom (switched) pins on the power switch. This way, when the power is off, the unused switch terminals will be connected to the transformer, not the mains. For safety, put heatshrink tubing on the unused power switch pins anyway. At this point, everything should be wired up and ready to go. contains garbage data, it will choose its own defaults to get things running. Do not rely on this as they might not be suitable for you! You can now power the unit back up, and should be able to fully control and monitor voltages and currents from up to two regulator modules. The initial setup procedure is: 1. Click the exit button to the lower left of the voltage set dial. This brings up the setup menu. 2. The voltage dial will allow you to select between three sub-menus: Track, Power and Cal. Enter the Track menu. 3. If you have a single output, N/A will be shown. Otherwise, select dual tracking or independent rails. 4. Enter the Power menu. For the number of rails, select single or dual-channel mode. 5. Set the absolute maximum current limit; this should be 5A in most cases. This can be set lower to limit current below that which the transformer VA rating allows; for example, if you are letting students loose with the Supply. 6. Dial up the maximum output voltage until the stated “required transformer voltage” matches your transformer. 7. Dial in the correct transformer VA rating. The recommended transformer is 300VA. 8. Enter the Cal menu and check the following as an initial starting point for both channels: 8.1 Output offset measured at zero volts set = 0mV 8.2 Set Correction Coefficient = 1.000 8.3 Read Correction Coefficient Scale = 1.000 8.4 Set Current offset = 0mA 8.5 Current Correction Coefficient Scale = 1.000 Calibration and use First, make sure you have the CH1 and CH2 jumpers on! When you power the unit up initially, if the EEPROM 94 Silicon Chip Australia's electronics magazine siliconchip.com.au Now check that the Supply generally works. You can set the voltages for channels 1 & 2 using the left-hand rotary encoder. To swap between them, push the dial and it will click. Channel 1 or 2 will be highlighted on the screen. You can set current limits for channels 1 and 2 using the right-hand dial. Similarly to above, pushing the dial will swap between the channel 1 and 2 limits. By clicking either dial, you will save all settings. Now perform calibration. Check that the calibration offsets are zeroed as described above, or else this procedure will be confusing: 1) Output offset This sets the zero for measured voltage, taking out any offset. Set the Channel 1 voltage to 0.00V on the main menu, and measure the output voltage from the regulator module. Ours was -4mV; it should not be a large value. Go into the CAL menu. The first screen says “Ch#1 Output Offset Measured” (see Screen 1). Adjust the voltage dial in the opposite direction to your reading until the output reading is close to 0V. An output voltage within a few tens of mV of zero is acceptable. If you have to dial in a significant value, check your build as this should not be required. 2) Voltage correction coefficient This step sets the scale correction for output voltage, correcting for gain errors in the DAC and feedback network. Go back to the main menu and set the output to a high output voltage that you can measure accurately. For many meters, 19.99V is a good value. This will depend on the transformer you have selected. Now go to the second calibration screen (Screen 2) and adjust the Voltage dial until you read 19.99V (or your chosen value) on your voltmeter. Our coefficient was 0.966, as shown. A value between about 0.85 and 1.15 would be reasonable, although it’s likely to be in the range of 0.95 to 1.05. Do not worry about what the “Meas” voltage says on the main menu just yet! 3) Voltage reading correction coefficient scale This step sets an ADC measurement correction to ensure voltage measurements displayed in the main menu are accurate. With the voltage still set to 19.99V, click on the Voltage READ siliconchip.com.au correction coefficient scale menu. You will see the output voltage at the bottom of the screen as measured by the Regulator module for that channel – see Screen 3. Adjust the Voltage dial until you get a reading of 19.99V (or your chosen value) on the bottom of the calibration screen. Our calibration factor was 1.037; values between 0.85 and 1.15 are reasonable. Screen 1 Screen 2 4) Current reading offset This step makes sure that you get current readings of 0mA when no current is flowing. With the voltage still set to any value, but no load connected to the power supply, click onto the Current Read Offset menu. At the bottom of the screen, you will see the current as measured by the Regulator module for that channel (Screen 4). Now adjust the Voltage dial upwards until you read a current on the bottom of the calibration screen, then dial it back to get zero. 5) Current scaling coefficient This step sets the calibration scaling for current measurements, so displayed currents are accurate. You need a dummy load for this test. Any highpower resistor will do; you can use quite a low voltage from the power supply, so two 1W 5W resistors in parallel will do for a short test. This keeps the dissipation to 4W per resistor. Depending on your transformer setup, choose a current that is close to your maximum; say, 4A for a 5A unit. Check that the current limit is set above this value. If you cannot set it high enough, go back and check your transformer configuration. Now put an ammeter in series with the resistor and dial the voltage to achieve your target current. Next, adjust the Voltage dial until you see the correct current reported on the bottom of the calibration screen – see Screen 5. Then click on the EXIT button. After that, press the voltage dial to swap channels and SAVE the calibration data. Calibration is complete for channel 1, so repeat the whole procedure for channel 2. You should find that measured values are within 1% or so of the actual values. We have not attempted to make a laboratory-grade voltage source here, but the ADC we have chosen does have better than 0.1% resolution. Long-term Australia's electronics magazine Screen 3 Screen 4 Screen 5 precision will depend on the stability of the +5V internal voltage rail. Current measurement will be similar in terms of precision and stability. You will notice that if the current output is within 5% of the limit current, we highlight the “I” symbol on the user interface. Similarly, if the output voltage is too low or high, we highlight the “V” symbol. There are headers for LEDs that you can wire to the front panel for over-current indication too, if that takes your fancy. This completes the assembly and setup of the Intelligent Power Supply. We think this will be a valuable addition to most workbenches. SC March 2022  95 Using Cheap Asian Electronic Modules By Jim Rowe CJMCU-7620 Gesture Recognition Module With this module, you can experiment with sensing and recognising gestures made with your hands (or others’). It is very small, relatively low in cost and can easily be hooked up to an Arduino or a Micromite. There are some tricks to make it work, detailed in this article. W hen I first saw this little module advertised, I confess I was a bit dubious. How could a 16 x 20mm module selling for as little as $13.50 be capable of sensing and recognising a range of hand gestures? I was intrigued enough to order a couple, to see if the claims were justified. Gestures it is said to recognise include moving a hand left, right, up, down, forward or back, clockwise or anti-clockwise, and waving. While I ordered mine from Banggood, I later discovered that Jaycar sells a very similar module (Cat XC3742) for $19.95, with the significant benefit that you don’t have to wait for it to arrive from overseas. When my modules arrived, I found they were based on an SMD ‘micromodule’ called the PAJ7620U2, made by PixArt Imaging Inc based in Hsinchu, Taiwan (www.pixart.com). The PAJ7620U2 itself measures only 5.2 x 3 x 1.88mm but is surprisingly complex, as seen from the internal block diagram, Fig.1. The sensing is done using pulses of infrared (940nm) light from the IR LED shown at upper left, with reflected light detected by a 30 x 30 pixel IR sensor array shown at centre left. The gesture sensing range of the PAJ7620U2 is specified as being 100-200mm within a 60° cone. The rest of the circuitry is involved in timing the LED pulses and the sensor array scanning, extracting information from the sensor array, recognising any detected gesture and saving the data in a memory register bank. There are also two serial interfaces: an I2C interface used mainly for interfacing the PAJ7620U2 with a microcontroller unit (MCU) for gesture recognition, and an SPI interface primarily intended for the PAJ7620U2’s other mode of operation, ‘cursor’ mode. Cursor mode provides real-time data output describing the position, size and brightness of an object within the range of its IR sensor array. Fig.2 shows the small number of extra components around the PAJ7620U2 in the CJMCU-7620 module. Apart from the PAJ7620U2 (IC1), it has just two tiny 3.3V low-dropout (LDO) voltage regulators, REG1 and REG2, with their associated capacitors, used to supply the logic part of Fig.1: the block diagram for the PAJ7620 gesture recognition sensor IC. The detection range for gestures using this IC is 5 to 15cm, with it typically processing an image size of 30x30 pixels. The datasheet can be found at siliconchip.com.au/ link/abc5 96 Silicon Chip Australia's electronics magazine siliconchip.com.au An enlarged shot of the PAJ7620 IC, which the CJMCU-7620 module in the lead photo is based on. The nine basic gestures that can be detected are: right, left, up, down, forward, backward, clockwise, anti-clockwise and waving. IC1 (REG1) and the IR LED (REG2). Then there are three 2.2kW resistors to pull up the SDA, SCL and INT outputs of IC1 to the positive supply rail. That’s it! The CJMCU7620 module does not provide connections to the SPI interface of IC1, only to the I2C interface, meaning it probably isn’t suitable for use in cursor mode. All the I2C interface connections are brought out to the 5-pin header at lower left in Fig.2. Figuring out how to use it Before trying it out, I looked around on the internet to see if I could find a data sheet or application information on the PAJ7620U2. Although I did manage to find a data sheet (actually, two different data sheets, one of which was more complete than the other), I couldn’t find much in the way of application information. And neither version of the data sheet was all that helpful either. One of them, titled “PAJ7620U2 General data sheet”, gives you a fair bit of information including the pin configuration, main electrical specifications and a set of tables showing the two banks of 256 memory registers. But these tables contain only brief and somewhat cryptic descriptions of the function of most of the registers. There was no information in that data sheet about the PAJ7620’s serial interfaces. For that, you must refer to the second data sheet titled “PAJ7620U2 Product data sheet”, containing details of the device’s I2C and SPI interface protocols and timing parameters. Neither data sheet gives much information on things like what data needs to be written to which registers to initialise the PAJ7620U2 for gesture recognition, the exact order in which the data should be written, or the correct timing for this writing. There is also no real information on decoding the recognised gesture data, apart from a table showing which of the eight bits in register 0x43 of Bank0 indicates the gesture recognised. So instead, I started looking for code to interface the PAJ7620U2 with an Arduino MCU, which proved much more successful. Several people had already solved most of the problems regarding communicating with the PAJ7620U2, so I was able to download a couple of Arduino sketches for communicating with the device, including two different Arduino libraries. Analysing the libraries and sketches provided much more insight into how to initialise the PAJ7620U2 and then use it for gesture recognition. But I still ran into significant problems when I tried writing a Micromite program to initialise the PAJ7620U2 and decode its gestures. But more about that later; let’s start by looking at the situation with an Arduino. Using it with an Arduino Hooking the module up to an Arduino is very straightforward, as you can see from Fig.3. The module’s Vcc pin connects to the Arduino’s +5V pin, its GND to one of the Arduino’s GND pins, its SDA pin to the Arduino’s A4 pin and its SCL pin to the Arduino’s A5 pin. The module’s INT pin is left unconnected as it is not required. As for the software, first, you need to download one of the Arduino PAJ7620U2 libraries. You’ll find two of these on the main Arduino website at www.arduino.cc/en/libraries/ One is written by SeeedStudios, called “Gesture-paj7620”, and the other is written by multiple authors and is called “RevEng-PAJ7620”. Both of them can also be found on GitHub: Fig.2: the circuit diagram for the CJMCU-7620 module, which incorporates the PAJ7620 gesture recognition IC. Data is read via an I2C bus; while the chip has an SPI interface, these pins are not connected on this module. siliconchip.com.au Australia's electronics magazine March 2022  97 Fig.3: when running our sample Arduino sketch, follow this wiring diagram to connect the sensor module to an Arduino or equivalent device. https://github.com/Seeed-Studio/ Gesture_PAJ7620 https://github.com/acrandal/ RevEng_PAJ7620 These GitHub links are probably the most helpful as they provide quite a bit of documentation. Both libraries also come with example sketches to get you going. When you have downloaded one or the other of these libraries (they both come as a ZIP file), save it in a convenient folder and then start up your Arduino IDE (integrated development environment). If you haven’t installed the IDE yet, you can always download the latest version from www.arduino. cc/en/software Now you can install the downloaded library in the IDE by clicking on the top drop-down “Sketch” menu button, clicking on “Include Library” and then “Add .ZIP Library”. You can then direct the IDE to the library ZIP file you saved earlier, and it will install the library (and its example sketches) without further ado. Next, click on the top drop-down “File” menu, go down to “Examples”, select “Examples from Custom Libraries” and then choose the library you’ve just installed (Gesture PAJ7620 or RevEng PAJ7620). You can then select one of the example sketches that came with it. It will then open up that sketch in the IDE window for you to look over and upload. Before you can run the sketch, you will need to connect the CJMCU-7620 module to an Arduino, as shown in Fig.3, then plug the Arduino into one of your computer’s USB ports. Then you should check in the Windows Control Panel or Settings dialog box to make sure that the Arduino has connected properly, and find the virtual serial port it has been allocated. In most cases, this will be something like “Arduino Uno (COM4)”. Next, click on the Arduino IDE Tools menu and you find your Arduino and its port, shown something like this: Board: “Arduino Uno” Port: “COM4 (Arduino Uno)” Fig.4: similar to Fig.3, this is the wiring diagram when connecting the sensor module to a Micromite LCD BackPack. If all seems well, go to Tools → Serial Monitor. This will display a second window so that you can monitor messages sent back from the Arduino. Set the Serial Monitor for 9600 baud since most Arduino sketches use that speed. Then, assuming you have already loaded the example sketch, it’s simply Australia's electronics magazine siliconchip.com.au 98 Silicon Chip a matter of clicking on Sketch → Verify/Compile. If no problems arise, use Sketch → Upload to direct the IDE to send the compiled sketch to your Arduino. Once that finishes, moving your hand in front of the CJMCU-7620 module should result in messages appearing in the Serial Monitor. Note that the CJMCU-7620 module should be orientated so that its five header pins are at the bottom, as shown in Fig.3. This will have the PAJ7620U2 device with its IR LED to the left and the lens in front of its IR sensor array to the right. That is the device orientation assumed by the sketches; other orientations will tend to give recognition errors, like “Up” or “Down” instead of “Right” or “Left”. If you want to orientate the module differently later, the sketch or its libraries can be revised to suit the new orientation. So hooking up the CJMCU-7620 module up to an Arduino and using that combination is pretty straightforward. Now let us look at what’s involved in using it with a Micromite. Using it with a Micromite First, the easy part: connecting the module to a Micromite. As shown in Fig.4, this is much the same as with an Arduino, with one small difference. The SDA and SCL lines connect to pin 18 (SDA) and pin 17 (SCL) of the Micromite and the GND line to the Micromite’s GND pin as you’d expect, but the module’s Vcc pin connects to the Micromite’s +3.3V pin, not the +5V pin. This looks wrong, considering that the module’s circuit in Fig.2 shows that it has its own pair of LDO voltage regulators onboard to provide the PAJ7620U2 with two regulated +3.3V supplies. So connecting the module to a +3.3V supply would seem both unnecessary and likely to prevent the onboard regulators from doing their job. But the fact is that we found the module to give much more reliable and consistent results when it was powered from the Micromite’s +3.3V line, not the +5V line. It’s not easy to explain or understand, but it did seem to work better that way. The next difficulty is the software. I couldn’t find any pre-existing MMBasic code for the PAJ7620U2, so I had to write it myself. Since the PixArt data sheets were so unhelpful, I had to spend quite a bit of time studying the Arduino libraries and sketches to see how they worked. It doesn’t seem too difficult. First, you check for the presence of a PAJ7620 and confirm that it is functional, then send over 200 bytes of initialising data to specific memory registers to set it up correctly in gesture recognition mode. Finally, you keep polling one of its memory registers (Bank0, address 0x43) to read its gesture recognition codes. Taking this approach ended up with a program that seemed to work pretty well, at least from time to time. When I made various gestures in front of the PAJ7620U2 device, the Micromite would correctly identify the gesture on its LCD screen and send the same information back to the MMEdit Chat window. But this would only happen some of the time. At other times, the setup would seem only to recognise one gesture (like “Right” or “Down”) or else become totally ‘blind’ and be unable to recognise any gestures at all. Tim Blythman helped me track this down to the power supply connections; after changing to using the +3.3V Seeed Studios sells an alternative, slightly larger sensor module that can be purchased from www.seeedstudio.com/Grove-Gesture-PAJ7620U2.html Both the original (lower right) and alternative (top) are shown above at actual size. siliconchip.com.au Australia's electronics magazine Micromite supply rail as described above, it started working much more reliably. He also pointed out that I should add an extra write to a register (Bank1, register 0x65, data byte 0x12) at the end of the initialisation sequence which made another improvement. So we ended up with a Micromite program that is at least as accurate and reliable as either of the Arduino sketches. The program is called “PAJ7620 Gesture Rec.bas” and you can download it from the Silicon Chip website. While functional, this program could probably use some tweaking, so if you feel you have improved it, please send us your version so we can share it with other readers. Final comments While writing this article, I learned that Seeed Studio offers a PAJ7620based Hand Gesture module in their “Grove” series of modules. This module is slightly larger (at 20 x 20mm) than the CJMCU and similar modules. It appears to have additional circuitry, including a pair of small P-channel Mosfets to perform level translation on the SDA and SCL output lines. It’s possible that this module would give more reliable gesture recognition when used with our program running on a Micromite, even when running from the Micromite’s +5V supply line, but we haven’t had a chance to get one and try it out yet. You can find documentation for this module on Seed Studio’s website at https://wiki.seeedstudio.com/ Grove-Gesture_v1.0/#resources They also have a library and example Arduino code for their module at: https://github.com/Seeed-Studio/ SC Gesture_PAJ7620 Some sample output from the Arduino running our test program. March 2022  99 Vintage Radio Phenix Ultradyne L-2 superhet radio (1925) By Dennis Jackson Various aspects of a vintage radio can impact its value and desirability including its rarity, condition, brand, nostalgia and appearance. I have witnessed the bidding on an AWA Empire State (model 48R from 1938) rising as high as $15,000 at our local auction house, mainly because it was the very rare green colour. I prefer to collect sets that demonstrate the technical stages of development over time, especially those with a fascinating history. It is not so much what they look like to me, but how they work. An interesting early radio caught my attention as I scrolled through vintage radio ads on eBay around ten years ago. It was described as a Lacault L-1 Ultradyne from November 1924. What interested me is that superheterodyne radios from the early 1920s are rare. But there was a problem: this pioneering radio was located in the Eastern USA, and at that time, I knew little about it. Purchasing it would be expensive, especially considering that the delivery cost could be high, but it was probably my only chance to own such an early superhet. The auction ended the next day without me putting in a bid, and I had regrets, especially after realising that the going price was reasonable. The Ultradyne L-2 designed by Robert Emile Lacault is extremely impressive for its time. It’s a superhet that features regeneration, and uses eight UX201A triodes. It weighs approximately 15kg and comes in a timber cabinet stained to resemble mahogany. 100 Silicon Chip Australia's electronics magazine Surprisingly, an improved model featuring regeneration, the Lacault L-2 Ultradyne from June 1925, was offered by the same seller soon after. To cut a long story short, I threw caution to the wind, and it arrived at my door two and a half weeks later. I was not disappointed. Appearancewise, it was in near mint condition. It cost me around $500, including freight; very reasonable, I thought. I still cannot understand why it cost me so little; I presume that the vast majority of people take technology for granted these days. The superhet radio receiver came out of the turmoil of WW1, when there was an urgent need to improve communications. Also, simple TRF receivers of the time lacked sensitivity and selectivity, making them inferior for A Graham Amplion horn speaker, made in 1925, was chosen to match the L-2’s case. The two main knobs are Accratune vernier dials. Other versions of these knobs may have the letters REL (for Robert E. Lacault) engraved in their centre. siliconchip.com.au direction-finding and triangulation; that became increasingly important during wartime as technology progressed rapidly. The contribution of Major Edwin Armstrong of the US signals Corps while based in Paris is well-documented, and he filed a patent on the superheterodyne principle in 1917. He went on to develop the first commercial superhet, the RCA AR-812 released in March 1924 (August 2019; siliconchip.com.au/Article/11782). Less is known of the contribution of Lucien Levy of the French signal corps. Levy is now recognized as filing the first superhet patent, also in 1917, around seven months before Armstrong. He went on to make many improvements as both a radio engineer and manufacturer in France. The Ultradyne L-1 & L-2 In November 1924, the Phenix Radio Corporation in New York released another superhet, the Ultradyne L-1, designed by R. E. Lacault. Robert Emile Lacault was born in Paris around 1894. Formerly of the Radio Research Laboratories of the French Army Signal Corps, he migrated to the USA after WW1, settling in New York City. He became associate editor of the then popular magazine Radio News, where he published an article titled “A Superheterodyne Receiver with a new type of ‘Modulator’”. The improved Ultradyne L-2 came onto the market during the middle of 1925. The physical layout of my Ultradyne L-2 is well thought out, with a view to show off the internal works as well as displaying the ebony-stained timber cabinet. All conductors are of square-sectioned tinned brass busbar, and all runs are symmetrical with 90° bends. The internal layout is both practical and symmetrical. The components are all screwed down onto a substantial timber breadboard-style chassis or to the Bakelite front panel; typical of radio construction of the period. The Ultradyne was sold in complete kit form, probably to work around the legal minefield of patent litigation. This is indicated by Lacault submitting his patent for the Ultradyne to the US Patent Office in February 1924, but it was not approved until December 24 1929, almost six years later. The high level of construction expertise in my example suggests some factory involvement. Operation The two large tuning controls are spaced about equal thirds across the front Bakelite panel. The inner section of each knob serves as a reduction gear for fine-tuning, with a ratio of about 15:1. The knob on the left is marked “Tuner” and on the right, “Oscillator”. Not being ganged, these controls must be tuned together by hand. This is not too difficult, as the set’s bandwidth is quite broad. I find it easiest to watch the plates of the tuning condensers, keeping both about the same distance apart while slowly rotating the controls. There is also an outer marked dial, but it is simpler to mark station positions with a removable mark once found. Either side of the tuning controls are two smaller knobs. On the left is the “sensitizer”, which controls feedback or regeneration between the plate of the first RF valve and its grid. This is via inductive coupling using a variometer style set of coils, one moving inside the other. The small knob to the right of the oscillator tuning control is marked “stabilizer”, and it controls the negative bias to the grids of the second, third and fourth RF valves. Together, these two controls have a limited effect on the operation of the set. On the far left is a jack for plugging in a loop aerial. At far right are three vertical jacks in a row, marked “Detector”, “1st stage” and “2nd stage”. The circuit diagram for the Phenix Ultradyne L-2 (sometimes labelled L2) shows that nearly all the circuitry is managed by the eight UX201A valves and matching IF transformers. The L-2 was originally manufactured around 1922 using UV201A valves, which had a thorium filament, and there were also later variants that used UX112, 171 & 171A valves. IFT1 (“UA”) is the only type-A Ultraformer RF transformer in the circuit, the rest being type-B, and they all have an aircore with a peak frequency of 115kHz. The difference between the two types is that the Type-A has less coupling (0.25in [6.35mm] between the primary and secondary for Type-A; Type-B has no spacing). You can find an interesting write-up on the set published in the October 26, 1924 issue of the Daily Mail: https://trove.nla.gov.au/newspaper/article/219013077 siliconchip.com.au Australia's electronics magazine March 2022  101 with 5V thoriated directly heated filaments, each drawing 0.25A with a theoretical gain of eight times. My Ultradyne L-2 operates best with around 70V on the RF and AF valve anodes or plates and 40V on the detector anode. The aerial coils, oscillator coils and the sensitizer variometer coils are all of a compact self-supporting basketweave construction. This is designed to reduce inter-coil capacitance, to achieve a high Q factor, maintaining good efficiency. Circuit details The interior of the L-2 is nicely designed, with most components mounted on the timber “breadboard” and connected via point-to-point wiring. Considering this radio was originally designed in 1922, the layout is impressive. Plugging a speaker into any of the three jacks operates a switch which cuts out the last audio stage or stages, reducing battery drain. High impedance headphones would generally be plugged into the Detector jack. The on/off switch is below these, and it switches the A supply (filament cathode rail). design. Both sets of plates are set into two separate parallel shafts, and they move into each other, controlled by a set of gears. Lacault filed a patent on a then new type of tuning condenser while working with the Phenix Co. So this might be one of his designs. Tuning capacitors There wasn’t much choice when deciding on a valve line up in 1924, so all eight valves are UX201A types The two brass tuning “condensers” or capacitors are of an unusual 102 Silicon Chip Component selection Australia's electronics magazine The Ultradyne differs from other superhets mainly within the circuit around the mixer, or “modulator” stage as it was then known, and in the electrical arrangement of the oscillator. In describing this circuit, Mr Lacault explained (and I quote in condensed form): The B+ supply is connected to the plate of the modulator valve. The plate-cathode (filament) space acts as a resistance in this circuit. The plate of the modulator valve is supplied with high-frequency current from the oscillator, which conducts only on the positive half of each cycle. This produces a change in plate cathode resistance which varies from infinity to 20kW during each half-cycle of the oscillator current when no signal is being received. When the grid potential of the modulator valve is varied by incoming signals from the aerial, the lower resistance value is varied above and below the amount mentioned with various degrees of amplitude, according to the phase relationship between the incoming signal and the local oscillations. This produces a beat note which is amplified by the four intermediate frequency (IF) stages and then detected by a grid leak detector. The next three RF stages are coupled via B-type Ultraformers in the usual way, but with only the secondaries being tuned to the intermediate frequency by fixed mica capacitors. With the radio working and measured with a high-impedance digital voltmeter, there is only 0.34V DC on the plate of the modulator, and the impedance is such that the meter shunts away all noticeable signal. However, this circuit is very sensitive picking up local stations with just a 1m wire aerial. siliconchip.com.au “Stabilizer” Thordarson coupling transformers Oscillator condenser Amperite current regulators Grid leakage detector Oscillator coils 4th IFT 3rd IFT Tuning condenser Mica tuning capacitor 2nd IFT “Sensitizer” 1st IFT Aerial coil The radio chassis is tinted with ebony. Note the unusual design of the two tuning condensors and their placements. Below these condensors are Amperites, which are cartridge-type automatic adjusting resistors (rheostats). At the bottom left is the connection board for the A (6V), B (90V) and negative bias C (-6V) supplies. The grid leak detector and following two audio stages are as could be expected of a TRF receiver of the period. The detector recovers the audio information from the 115kHz IF signal. The grid leak detector is simple and very sensitive. It only requires two extra components: a grid leak resistor of about 2MW in parallel with a capacitor of around 255pF. Manufacturers switched to plate or anode-bend detectors when indirectly-heated cathode and screen grid valves became available during the late 1920s, and later to diode detectors. Both audio-frequency stages are coupled by two nicely presented Thordarson “amplifying transformers”. They are called “amplifying” because they have a step-up voltage gain of 1:3 or even 1:5, which boosts the signal voltage between the plate of the preceding valve and the grid of the next. Amperite automatic current regulators are inserted in series with the filaments of the UX201A triode valves, in place of the more common wirewound rheostat of about 8W used to limit the current flow which could otherwise damage the delicate thoriated valve filaments. Amperites consist of a hermeticallysealed glass tube containing either hydrogen or helium gas, through which a resistance wire with a positive temperature coefficient passes. The resistance of this element will automatically change according to the current flow, thus regulating it. Each siliconchip.com.au valve is usually provided with a separate Amperite unit. Metal RF or AF shielding is absent from the RL-2, as was the norm in these pioneering radio sets. However, the four Ultraformers and two Thordarson audio coupling transformers are alternately mounted at right-angles to limit radio-frequency coupling between adjacent units. Initial checks In common with other sets of the period, the breadboard and front panel slide out of the case after removing a few screws. My first job was to check all eight UX201A valve filaments for continuity, as these were prone to burning out if more than the rated 5V was applied. Having 5V filaments allowed a 6V ‘accumulator’ to be used for the valve heater A supply, the extra 1V usually being dropped across an adjustable wirewound rheostat. However, as I mentioned above, my radio uses Amperites instead. Despite the current-limiting Amperites, the first three valves (including the modulator) did have open filaments and had to be replaced, but the remaining five were OK. Next, I connected a period horn speaker, a long aerial and connected its Earth terminal to a copper water pipe. Then I wired up a battery eliminator and checked all the voltages before switching it on. The set should have been operational, but vintage radio is seldom that simple. Australia's electronics magazine Power supply The radio would typically have been powered using one 6V lead-acid battery or four large 1.5V telephone-type carbon-zinc dry cells in series for the A supply. The B supply would have come from a 90V carbon-zinc battery, possibly two 45V batteries in series or four of the less common 22.5V batteries. Four small carbon-zinc cells in tapped series would have been used to provide the negative C bias voltage to the valve grids. But I prefer to use a homemade mains-powered battery eliminator. It does give improved performance with a good Earth attached. Troubleshooting This problem proved to be a real stinker. All voltages appeared close to what was expected, so I brought out my signal tracer. The station signal seemed to disappear at the grid of the first RF valve. Was this a problem with the dreaded modulator? Was the oscillator operating? I checked all of the UX201A valves for emission by swapping them into a known-good TRF set, with positive results. Was there a loose terminal connection or a socket making poor contact with a valve pin somewhere around the RF end? After some more checking, I noticed four thin brass bolts protruding from the face of the first A Ultraformer (or IF transformer in later terminology). These bolts serve as busbar terminals going to the two coils within. Although both small nuts were firm, the grid March 2022  103 busbar had slight movement; this should have been under some tension. It was possibly a broken bolt; apparently, I hadn’t been the first to check that all was firm. The Ultraformer unit would have to come out and be disassembled. It was an interesting job, because I like looking inside things. After drawing a sketch and making some notes, I removed the unit and then opened it by melting away the sealing wax covering a larger central brass bolt. Both fixed inductors inside are aircored and neatly machine-wound on a removable Bakelite sleeve. The first (A-type) Ultraformer has a small gap to give lighter coupling between coils while the other three (B-type) Ultraformers are close-wound side-by-side. The lead wires are soldered to the heads of the four aforementioned thin bolts protruding through the face of the unit. Some heavy-handed force would have been applied long ago, resulting in not only a broken bolt, but also a detached lead. That is likely why the radio was retired from active service. A dab of solder, a bit of Araldite to stop the bolt turning again and a check with the ohmmeter, and the Ultraformer was ready for reassembly. This A close-up of the left side of the radio chassis, from left-to-right are the Thordarson coupling transformers, grid leakage detector, 4th & 3rd IF transformers, plus the oscillator coils at the back (green/white wire). A close-up of the right side of the radio chassis, again the 3rd IF transformer is in view, along with the 2nd and then 1st (A-type) followed by the aerial coil. Behind that is the “sensitizer” regeneration control. 104 Silicon Chip Australia's electronics magazine resulted in sound and satisfaction once more around my workbench. Final comments When listening through headphones at the detector jack, the sound is clear. But there is some deterioration after each of the final audio stages, probably due to the limitations of the Thordarson step-up transformers. Thordarson is still around making transformers under the name Thordarson Meissner (www.thordarsonmagnetics.com). It would not have been difficult for a technically-minded person to assemble an Ultradyne set. The baseboard might have come with pre-drilled holes, or perhaps a paper template to position the parts precisely. The busbar conductors were most likely preshaped and soldered where needed, and just required fitting to screw terminals. The Ultraformers were factory-tuned using selected mica capacitors. The oscillator and the tuning capacitors were hand-adjusted to achieve station alignment. Overall, this set’s assembly would have been straightforward compared to a multi-band superhet of a later decade. Dealers and learned friends probably assembled some for clients also. The price of the radio kit at the time of release appears to have been $90 including the cabinet plus $30 for the tuning coils, Ultraformers and four matched fixed condensers. That’s a lot less than the $269 asked for the RCA AR-812 fully assembled superhet which came on the market in March 1924, just fifteen months before. This kit was sold by Keystone Radio Service, but there is some doubt on how similar it is to the Phenix-branded Ultradyne L-2. An advert describes it as “carrying the last improvements of R. E. Lacault”. Upon reflection, I believe Robert Emile Lacault’s modulator to be a stroke of true genius. Using a primitive triode valve as a mixer in conjunction with the local oscillator and without a high positive voltage supply to its plate was really thinking outside the box. Lacault went on to produce other superhet sets, each an improvement on the previous. His last effort was the RE-29, released for sale in 1929, using three tetrode screen-grid valves. Lacault died on March 12, 1929, at around 34 years of age, cutting short a brilliant career. SC siliconchip.com.au Page 117 of Popular Radio, March 1925: https://worldradiohistory.com/Archive-Popular-Radio/Popular-Radio-1925-03.pdf siliconchip.com.au Australia's electronics magazine March 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. 03/22 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. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F617-I/SN PIC12F675-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P $15 MICROS Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; specify variant) Nano TV Pong (Aug21), SMD Test Tweezers (Oct21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22) Model Railway Carriage Lights (Nov21) Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) Tiny LED Xmas Tree (Nov19) Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) 20A DC Motor Speed Controller (Jul21) Fan Controller & Loudspeaker Protector (Feb22) Flexible Digital Lighting Controller Slave (Oct20) Digital Lighting Controller Translator (Dec21) ATSAML10E16A-AUT PIC16F1459-I/SO PIC16F18877-I/P PIC16F88-I/P High-Current Battery Balancer (Mar21) Four-Channel DC Fan & Pump Controller (Dec18) USB Cable Tester (Nov21) UHF Repeater (May19), Six Input Audio Selector (Sep19) Universal Battery Charge Controller (Dec19) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21) Touchscreen Digital Preamp [2.8in/3.5in version] (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC32MX795F512H-80I/PT Touchscreen Audio Recorder (Jun14) $20 MICROS dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT dsPIC33FJ128GP802-I/SP PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512L-80I/PF Colour MaxiMite (Sep12) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC RASPBERRY PI PICO BACKPACK KIT (CAT SC6075) (MAR 22) CAPACITOR DISCHARGE WELDER (MAR 22) siliconchip.com.au/Shop/ MODEL RAILWAY LEVEL CROSSING (JUL 21) Parts for the Power Supply – includes the power supply PCB, IC1-3, D1, the 1W shunt and sole SMD capacitor (Cat SC6224) $25.00 Parts for the ESM – includes one ESM PCB, IC8, Q3 & Q4 (IRFB7434G), D9 plus the SMD capacitors and resistors (Cat SC6225) → 8-14 sets typically needed $20.00ec AM/FM/SW RADIO (JAN 21) INTELLIGENT DUAL HYBRID POWER SUPPLY (FEB 22) MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) IR-TO-UHF MODULE FOR RANGE EXTENDER (CAT SC5993) (JAN 22) SMD TRAINER KIT (CAT SC5260) (DEC 21) HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) USB CABLE TESTER KIT (CAT SC5966) (NOV 21) MODEL RAILWAY CARRIAGE LIGHTS KIT (CAT SC6027) (NOV 21) SMD TEST TWEEZERS KIT (CAT SC5934) (OCT 21) NANO TV PONG SHORT FORM KIT (CAT SC5885) (AUG 21) Complete kit, includes all parts except the optional DS3231 IC $80.00 Hard-to-get parts for the regulator module – all the ICs & regulators ◉ needed to build one module, plus the schottky diode, 10μH inductor, 4700μF 50V capacitors, 1W shunts and SMD capacitors – does not include PCB (Cat SC6096) $125.00 ◉ does not include the LM2575T as it comes with the CPU module parts Hard-to-get parts for the CPU module – most of the required parts, including programmed PIC32MZ, EEPROM, LM2575T, LM317 & LD1117V regulators etc. You just need the PCB, headers, a ferrite bead, trimpot and electrolytic capacitors (Cat SC6121) $60.00 PCB and all SMDs (including the programmed micro) for the IR-to-UHF module Complete kit includes the PCB and all on-board components, except for a TQFP-64 footprint device $20.00 Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor Short form kit with everything except case and AA cells Includes PCB, IC1 (programmed), IC2, D1, L1, SMD capacitors and resistors. Does not include reed switch, magnet, LEDs or through-hole parts PCBs, micro, other onboard parts and heatshrink (no cell or brass tips) PCB and all onboard parts only (does not include controllers) $25.00 $15.00 $110.00 $25.00 $35.00 $17.50 - Pair of programmed PIC12F617-I/Ps - ISD1820P-based audio recording and playback module - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) $15.00 $5.00 $2.50 $3.00 $7.50 Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $35.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $10.00 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $4.00 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $5.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 VARIOUS MODULES & PARTS - DS3231 real-time clock SOIC-8 IC (Pico BackPack, Mar22) - DS3231MZ real-time clock SOIC-16 IC (Pico BackPack, Mar22) - 4-pin PWM fan header (Fan Controller, Feb22) - 64x32 pixel white 0.49in OLED (SMD Test Tweezers, Oct21) - pair of AD8403ARZ10 (Touchscreen Digital Preamp, Sep21) - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) - EA2-5NU relay (PIC Programming Helper, Jun21) - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) - MCP4251-502E/P (Advanced GPS Computer, Jun21) - pair of Signetics NE555Ns (Arcade Pong, Jun21) - 2.8-inch touchscreen LCD module (Lab Supply, May21) - Spin FV-1 digital effects IC (Digital FX Unit, Apr21) - 15mW 3W SMD resistor (Battery Multi Logger / Arduino PSU, Feb21) - Pair of CSD18534 transistors (Electronic Wind Chimes, Feb21) - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $4.00 $7.50 $1.00 $10.00 $35.00 $15.00 $3.00 $25.00 $3.00 $12.50 $25.00 $40.00 $2.50 $6.00 $5.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT DIODE CURVE PLOTTER ↳ UB3 LID (MATTE BLACK) iCESTICK VGA ADAPTOR UHF DATA REPEATER AMPLIFIER BRIDGE ADAPTOR 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH 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CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR DATE MAR19 MAR19 APR19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 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 PCB CODE Price 04112181 $7.50 SC4927 $5.00 02103191 $2.50 15004191 $10.00 01105191 $5.00 24111181 $5.00 SC5023 $40.00 01106191 $7.50 01106192 $7.50 01106193 $5.00 01106194 $7.50 01106195 $5.00 01106196 $2.50 05105191 $5.00 01104191 $7.50 SC4987 $10.00 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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 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 DATE SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 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 PCB CODE 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 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 Price $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $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 RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB MAR22 MAR22 MAR22 MAR22 MAR22 07101221 01112211 29103221 29103222 29103223 $5.00 $2.50 $5.00 $5.00 $5.00 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 How to unpack SMDs without losing them Thanks for a terrific challenge with the SMD Trainer Board project (December 2021; siliconchip.com.au/ Article/15127). I am looking forward to getting to the smallest part that I can manage. One thing missing from all the descriptions is how do you get the little blighters out of their capsules (cocoons, packaging, enclosures) without them escaping? I have struggled with this problem more than anything else so far, and am only on the large components above the line. This could be a good competition for us old coots – the oldest person to get the smallest component working. I am 82. (D. L., Clare, SA) ● We usually hold the strips component-­ s ide-up and peel the plastic cover off from the side using tweezers. Peel it back to expose just the number of components you want, then turn it upside-down just above your workbench surface, and they should drop straight down onto it. It helps to have a uniformly coloured, flat mat (or even a sheet of paper) to empty them onto so you can easily see where they land. You usually have to flip them over after tipping them out, but there isn’t much you can do about that. We would be interested to hear about the smallest parts that you can manage. There are three of us here in our early-to-mid 40s, and we struggle with anything smaller than M1206/0402. Even they are a bit challenging. We find M1608/0603 easy enough, and anything larger than that is a relative doddle. USB Cable Tester problem solved I recently put together the USB Cable Tester (November & December 2021; siliconchip.com.au/Series/374). It all went together quite easily and the calibration worked well. 108 Silicon Chip But when I put it together finally with the batteries inserted, it would not go to sleep. For the LCD screen to be initialised correctly, I had to wire an external power switch to switch it on with the box closed, after the LCD had plugged into its socket. With this switch connected, the LCD was initialised correctly and showed the countdown screen, but after the countdown finished, I did not get the main idle screen as shown in Screen 7 on page 92 of the December 2021 issue. Instead, I get the following display: USB Cable Tester DFP: VBUS,SHLD, When I insert a cable, the device appears to work correctly. For example, with a Type A to Type B cable inserted, I get: CABLE INSERTED:OK USB 2.0 0+ 0Check DFP and UFP. 327mV at 1A: 326mW This tallies with Screen 8. If I then press S1, nothing happens, so S1 doesn’t seem to act the way it should. The device remains on and doesn’t go to sleep. I hope someone can point out where my mistake could be. (J. H., Nathan, Qld) ● We think you have a short circuit between the Vbus pin and the shield of one of the USB sockets (hence the “DFP: VBUS,SHLD” message with no cable inserted). Check the resistance between those pins with an ohmmeter and inspect the sockets for solder bridges. Note: J. H. sent us a reply which stated: your diagnosis was spot on. There was a short between Vbus and shield, but you would never guess what caused it! After completing the calibration tests, I inserted the jumpers JP1 and JP2 back on one of their respective pins only. Unfortunately, with the jumper for JP1 sideways, the underside of the jumper came in contact with the shield of the neighbouring USB-C socket. Even more unfortunately, there was a little bit of the jumper’s internal metal connector protruding from the base, Australia's electronics magazine which was enough to cause the short between Vbus and shield. After fixing that, the device works perfectly. I’m so happy it wasn’t my soldering that was at fault, as I would have to go back to soldering 101 and repeat the course. Replacing USB Cable Tester sockets I have bitten off more than I could chew by tackling the USB Cable Tester kit (siliconchip.com.au/Series/374)! I successfully soldered CON5 (Mini USB). I then attached CON8, but in testing it, it detached, pulling one of the tracks off the board. So I really need to start again. I see that I can buy a replacement board, but where do I get CON5 and CON8 in the USA? Can you supply these three parts so I can start again? I’m not sure if I can use CON8 in practice because I don’t think it will ever be strong enough to stand having a connector inserted. The alternative is to proceed without CON8. Will the Tester function without it? (R. T., New York, USA) ● You can certainly leave off any sockets, and the circuit will still function otherwise (naturally not being able to test that cable type). We have all our micro-USB sockets (CON8) tied up in kits, but the specified part, Würth Elektronik 692622030100, is currently in stock at both Digi-Key and Mouser. As they are both based in the USA, you should have no trouble ordering from them. CON5 is a very common type of connector made by many manufacturers. You can use EDAC Inc. 690-005-299043 which is inexpensive and also in stock at both Mouser & Digi-Key (search for the part numbers). We think the problem you had with CON8 coming off the board and tearing tracks might be that you didn’t manage to wet the mounting tabs on either side properly with solder. Next time, you could try adding flux paste to both those tabs and the matching siliconchip.com.au pads on the PCB and make sure you get the solder nice and hot so that it fully adheres to both. Not all software includes ASM files I built the SMD Test Tweezers kit (October 2021; siliconchip.com.au/ Article/15057), but it does not work. I need to find a data sheet for the OLED, as I don’t yet know if the fault is in the OLED or the PIC. Also, I tried to download the .asm file from your shop. I found the .hex file but could not find the .asm file. (L. C., Forest Hill, Vic) ● The OLED modules are based on the SH1106 controller IC, although we have seen some very similar modules with an SSD1306 controller. Both data sheets can be found using web searches. The microcontroller code for this project is written in the C language, so there is no .asm file. Assembly language files usually are only used when the micro is programmed in assembly language (which we are doing less these days as it is more work and harder to debug). The MPLAB X project, including the C source code for this project, can be downloaded from siliconchip.com.au/Shop/6/5948 Troubleshooting AM/ FM/SW Digital Radio I have built the AM/FM/SW Digital Radio (July 2021; siliconchip. com.au/Article/14926). When I power the radio, all I get is a blank LCD (it does light up). I built it using a pre-­ programmed micro. What is likely to be the problem? I tried pressing the Reset button but that did not help. (R. B., Burlington, NC, USA) ● It could be any number of problems. Have you checked the voltages at critical points, such as the supply rails? Do you get anything at all when you adjust the contrast potentiometer on the LCD screen? If LCD is not set up due to program fault or wrong connection, usually just a line of squares will appear. SMD soldering can be tricky, and it’s very easy to have short between adjacent pins of fine-pitch devices. I find a jeweller’s loupe is essential for getting a close-up view. Note: we received a follow-up email that states: I just got the radio working! I decided to check the continuity of connections to each pin of the display and ATmega chip. To be safe, I removed the ATmega chip when doing this test. All connections to the display were fine. When testing the connections to the chip socket, I discovered that I had not soldered two of the pins for the encoder. Fixing that, lo and behold, the radio worked. The writing on the display is visible only when I view it at an angle of 45° or so. I see only white rectangles when viewing it head-on. Adjusting the contrast improved things somewhat, but viewing head-on, the writing is not visible. I will fool around with the contrast control some more. If it is still not good, I will get a new display from AliExpress. Ways of mounting ultrasonic transducers The ultrasonic transducer I ordered from your online shop (Cat SC5629) to build the High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com.au/Series/350) came with a threaded steel ‘slug’. I searched those articles and the internet for an explanation of its purpose to no avail. There is a tiny spike at one end of the slug. Also, given that the transducer has a threaded hole in its face, do you think that bolting the transducer to the bath would provide better results than using epoxy? (G. M., Hughesdale, Vic) ● Our suppliers didn’t give us any instructions regarding those slugs either; however, we think that they are to plug the threaded hole in the face of the transducer if it is not being used to bolt the transducer to its mating surface. Doing so would slightly increase the contact area between the two surfaces, but we don’t think the difference is enough to matter. Still, it probably wouldn’t hurt to insert the slug if you will be gluing it to the surface. Just make sure to thread it with the spike first, and turn it until it is flush with the transducer’s face. The spike is just the result of the way the slugs are cut from a longer threaded rod. SMD Test Build it yourself Tweezers ● Resistance measurement: 10W to 1MW ● Capacitance measurements: 1nF to 10μF ● Diode measurements: polarity & forward voltage, up to about 3V ● Compact OLED display readout ● Runs from a single lithium coin cell, ~five years of standby life ● Can measure components in-circuit under some circumstances siliconchip.com.au Complete Kit for $35 Includes everything pictured, except the lithium button cell and brass tips. October 2021 issue siliconchip.com.au/Article/15057 SC5934: $35 + postage siliconchip.com.au/Shop/20/5934 Australia's electronics magazine March 2022  109 As for bolting the transducer on, you certainly could do that, but you’ll have to be careful drilling the hole to avoid distorting the bath face and clean up any burrs after drilling. The surface needs to be very flat at the mounting point. You’ll also have to make sure it’s sealed properly so that it can’t leak. Keep in mind that when gluing the transducer, the epoxy will fill in the gaps between the two faces to ensure good contact. Waterproof grease smeared on the transducer’s face and/ or bath face is needed to provide a similar effect if you’re bolting it on. Unexpected cause for SC200 Amplifier fault I hate having to ask for help, but I’ve spent days on this and I need to move on. My SC200 Amp (January-March 2017; siliconchip.com.au/Series/308) has all the transistors in their correct places. The soldering looks good, so I don’t think there are any dry joints. Transistor isolation from the heatsink measures fine. I’ve put 68W resistors in series with the power supply connections, as shown in Fig.14 on page 80 of the March 2017 issue. I’ve used this arrangement to successfully set up Ultra-LD Mk.3 and Mk.4 amplifiers in the past. When I turn on the power, LED1 doesn’t light up, but LEDs 3, 4 and 5 do light up. I spent a lot of time measuring voltages and couldn’t find the problem. However, I noticed that if I put a DMM probe in the area of the PCB around the bases of Q3 and Q4, LED4 turns off. About 10s to 20s later, LED4 turns on again so that all LEDs are on. That suggests a long time constant, possibly associated with the 1000μF capacitor in the feedback circuit. If I put a DMM probe on the base of Q8, LED1 and LED2 turn on, and LED4 turns off but begins returning to full brightness almost immediately. That said, sometimes when I switch it on, all five LEDs turn on straight away. With LED1 off at first turn-on, the voltages across the safety resistors are very low. With all the LEDs on, the voltages are just less than 1V. There’s no voltage across the output transistor emitter resistors. I tried disconnecting the feedback by lifting one end of the 12kW feedback 110 Silicon Chip resistor and earthing the base of Q2. In this situation, LED1 turns on as soon as power is applied, but all the other LEDs are still illuminated. I’d really appreciate any advice you can give me! (D. H., Sorrento, WA) ● That behaviour is quite baffling and suggests a major fault somewhere, such as an open-circuit or short-­circuit transistor. The fact that probing the base of Q8 causes things to change makes it likely that the problem is around Q7 or Q8. It’s almost as if the base of Q8 is floating. Check carefully around there. You might want to consider replacing Q7 as it is easy enough to do. Also, look at the 22kW and 2.2kW resistors and 1nF and 150pF capacitors in that section to verify they have the correct values, etc. Note: we got a response a couple of days later that read: this is embarrassing. Based on your advice, I decided to re-check every joint and component from the input to the Vbe multiplier. With the benefit of more light and a head-band magnifier, I got to the 10W resistor from input ground to 0V and spotted a green ring. Somehow, a 10MW resistor had gotten into my bag of 10W resistors! I replaced it and all now works well. I will measure all component values in future. More SC200 troubleshooting I have been building your SC200 Amplifier project. I made two modules for a stereo amplifier. One module is working, but the other has some problems. The Clip Detector LED is active, and considering the following measurements, I see it is working correctly. I am using the 5W 68W resistors in series with the power connection as I am still testing. I get the following measurements using the CON2 power connection as a reference: • Positive rail: +55.9V • Negative rail: -57.0V • TP1: -54.2V • TP2: -55.3V • TP3 to TP7: all -54.3V Removing fuse F2 makes no difference to the LED status. Green LED5 stays on while Red LED4 does not turn on under any scenario. On the other side, LED2 and LED3 work as expected. Australia's electronics magazine Measuring around the circuit, I get the following measurements. • D2 A: -54.7V, K: -55.3V • Q7 C: -6.87V, B: -54.8V, E: -55.3V • Q8 C: -55.3V, B: -55.3V, E: -55.9V • Q9 C: -54.3V, B: +54.7V, E: +55.2V • Q10 C: -54.3V, B: -54.7V, E: -55.2V • Q11 C: +56.0V, B: -54.2V, E: -54.8V • Q12 C: -57V, B: -55.3V, E: -54.9V I thought that Q8 might be internally shorted between collector and emitter, but it does not measure as a short. I have not replaced it, though. I have checked the isolation between all the devices and the heatsink. Given the measurements above, I thought there might be a short to the negative rail; however, I cannot find one. Do you have any thoughts as to what would be the cause of the unusual measurements? (B. D., Menangle, NSW) ● The reason that removing fuse F2 doesn’t cause the state of LED4 or LED5 to change is that the entire output stage is being pulled to the negative rail, so there’s never any significant voltage across F2. What we need to figure out is why that is happening. It’s likely to be either due to Q9 not supplying any current (because of a fault in Q9 or incorrect bias) or Q8 being continuously switched on (again, because of a fault or its biasing). You were on the right trail looking for shorts to the negative rail and checking Q8. Q9’s emitter is 0.7V below the positive rail, which is about right, indicating a collector-emitter current of 7mA. So it is probably not at fault. Q8’s base-emitter voltage of 0.6V indicates that it is likely switched on, perhaps too hard. Q7’s emitter voltage indicates that it is supplying enough current to Q8 to be responsible for this. With the output pegged to the negative rail, Q2 should be switched on, supplying current to Q4. As a result, Q3 should also be sinking plenty of current, preventing Q7’s base voltage from rising so high. We suggest you check the voltages across the 68W emitter resistors of Q3 and Q4 to verify that they are similar, indicating that both of these transistors are likely working. If that looks OK, it might be that Q1 is shorted or otherwise faulty and supplying too much current for Q3 to sink. Some measurements of the voltages continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au Lazer Security For Quality That Counts... QUALITY LED PRODUCTS + MORE Massive parts clearance sale, limited stock. Go to lazer.com.au ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some books may have already been sold. Bulk discount available. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote photo numbers when referring to a book: silicon<at>siliconchip.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au DAVE THOMPSON (the Serviceman from 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 KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine March 2022  111 Advertising Index AEE ElectroneX........................... 34 Altronics.................................75-78 Analog Devices............................. 9 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes............................... 5 Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 7 Ocean Controls........................... 10 PMD Way................................... 111 SC SMD Test Tweezers............ 109 Silicon Chip Shop............ 106-107 Silvertone Electronics................. 65 Switchmode Power Supplies..... 11 The Loudspeaker Kit.com.......... 67 Tronixlabs.................................. 111 Vintage Radio Repairs.............. 111 Wagner Electronics....................... 8 around Q1-Q4 would help to diagnose this fault further, but given that they are inexpensive devices that are relatively easy to replace, if you can’t find a soldering problem or component value error in that area, you could just replace all four. wide. This can also damage the ignition coil that could arc over internally and short out the windings. That fault is more difficult to check; the easiest method is to swap the coil and see if that fixes it (after checking the IGBT using a resistance meter). Jacob won’t climb his ladder anymore Modifying EA Active Crossover frequencies We bought our son a Jacob’s Ladder kit for Christmas. We separately bought the coil recommended in this kit. Upon original completion, the kit worked fine. While using it, it stopped working and has not worked since. We asked the retailer about this, and they agreed that we had built the kit correctly. Still, they were concerned by the age of the kit on their shelves (which they stated may have been there for many years) and the possibility that components may have dried out over this period, leading to the failure. Do you have any experience with regards to which components regularly fail? (G. D., Redcliffe, Qld) ● Electronic components sitting on a shelf should not fail after less than ten years. The only parts that are likely to age significantly are electrolytic capacitors, and we have plenty of 30-plusyear-old electros that are still fine. Modern electrolyte formulas handle ageing much better than much older devices. The semiconductors, resistors etc will definitely still work. Check fuse F1, which may have blown. The most likely failure is the IGBT (Q1). Usually, when these fail, they end up with a short circuit between the gate and collector (left and centre pins) or the collector and emitter (centre and right pins). The IGBT is most likely to be damaged due to the spark gap being too I recently came across several Twoway Electronic Crossover kits I started assembling about 10 years ago that I would like to complete. They were sold by Altronics, Cat K5570. The problem is that I have lost the instructions that came with them. Also, they were initially designed for crossing between mid-high and high elements. I would like to use them for crossing over at 100Hz. Can you suggest the component values required for sub-bass applications? (M. O., Croydon, NSW) ● Those kits are based on the Active Crossover for 2-Way Speaker Systems project from Electronics Australia, May 1992. A scan of that article is available for purchase from our website (siliconchip.com.au/ Shop/15/6072). To change the crossover to 100Hz, the component values can be scaled using the original crossover frequency versus resistor value tables. You can change the 2043Hz value to 100Hz by multiplying the resistor values by 10 and the C2-C7 capacitor values by 2.043. So R2-R4, originally 39kW, become 390kW and R5-R7 become 470kW (from 47kW). The original 2.2nF capacitors can be 3.9nF in parallel with 560pF (4.46nF total, within 1% of the required value of 4.49nF). Capacitor tolerance (typically at least ±5%) will be the main cause of frequency shifts from the required crossover frequency. SC Notes & Errata Vintage Radio, February 2022: the 100nF capacitor directly below the 6K8M valve in Fig.8 should connect to the GND rail instead of the AGC line. In that same figure, there’s a 33μF 600V HT filter capacitor missing from the 250V rail to GND. USB Cable Tester, November & December 2021: in the circuit diagram, Fig.1 on page 30 of the November issue, the numbers for pins 8 and 10 on IC1 are swapped. Pin ANE2/RE2 connecting to USBU-GND via a resistor should be pin 10, while pin ANE0/ RE0, connecting to USBU-ID via a resistor, is actually pin 8. The April 2022 issue is due on sale in newsagents by Monday, March 28th. 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