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SEPTEMBER 2024 ISSN 1030-2662 09 9 771030 266001 $1250* NZ $1390 INC GST INC GST OLED CLOCK/TIMER MULTIPLE TIMEZONES, WIFI TIMEKEEPING AND MORE How Mains Earthing Systems Work Raspberry Pi Pico Mixed-Signal Logic Analyser Make amazing projects with our microcontrollers & mini computers. EXPANDABLE WITH SHIELDS, SENSORS & MODULES We have an incredible line-up of micros for beginners, hobbyists and professionals. 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No rain checks. Savings on Original RRP (ORRP). ONLY 129 $ RASPBERRY PI 4B MICROPROCESSOR XC9100 1800 022 888 Contents Vol.37, No.09 September 2024 16 Energy Harvesting Page 16 Image source: Tex Energy Energy harvesting is the process of obtaining small amounts of energy from the environment. While this type of power generation is not always cost-effective, it is useful for powering small devices away from the grid. By Dr David Maddison, VK3DSM Off-grid energy 29 Exteek C28 transmitter/receiver This device acts as an audio transmitter or receiver over Bluetooth. It uses a 3.5mm jack and works great with headphones, amplifiers or even in a car. Review by Allan Linton-Smith Bluetooth audio 48 Mains Earthing Systems We take a look at the different Earthing systems that are used worldwide and describe how they work. By Brandon Speedie Mains power Unconventional Power Generation upgrade your instrument with these Electric & Bass Guitar Pickguards 71 Electronics Manufacturing in Oz Continuing the tale of the long history of electronics manufacturing in Australia, from the 1930s to its pseudo-demise in the 1970s. Part 2 by Kevin Poulter Historical feature 32 Compact OLED Clock/Timer This portable and rechargeable device combines a clock, timer and stopwatch into a single unit. It can display different time zones, and uses an internal crystal plus WiFi time source to make sure it is always accurate. By Tim Blythman Timekeeping project 52 Pico Mixed-Signal Analyser Our USB PicoMSA monitors and decodes serial buses and other logic signals in an inexpensive package. It uses a single Raspberry Pi Pico and features up to 20 protected digital inputs with three protected analog inputs. By Richard Palmer Test instrument project 66 Jaycar-sponsored Mini Projects This month, we have an IR helper that can help reduce the number of IR remote controls you need to juggle. Next, we have a circuit that demonstrates RGB LED colour shifting using no ICs. By Tim Blythman Mini projects 78 Discrete Ideal Bridge Rectifiers Providing active rectification of a centre-tapped transformer or combining two DC supplies are just two very handy features of these Bridge Rectifiers, which have maximum ratings of 80V and 10A. By Phil Prosser & Ian Ashford Power supply project 86 Electric Guitar Pickguards These PCBs suit many popular models of electric & bass guitars, offering advanced features and a cool aesthetic. By Brandon Speedie Musical instrument project Starting on Page 86 2 Editorial Viewpoint 5 Mailbag 15 Subscriptions 45 Circuit Notebook 96 Serviceman’s Log 102 Vintage Radio 107 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata 1. Power control for a dashcam 2. Ball maze game Stromberg-Carlson “Air Hostess” model 4A19 by Graham Parslow SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $127.50 24 issues (2 years): $240 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Intel is in trouble If you have kept up with computers over the last few years, you will know that Intel’s major competitor, Advanced Micro Devices (AMD), has been giving them a run for their money, especially in the server space. For many years, Intel had such a commanding lead in the computer CPU market that they did very little R&D. They would release a new generation of processors that was marginally better than the last one every couple of years, raking in cash while putting in minimal effort. That came back to bite them over the last few years as AMD got over the problems it had in the early 2010s and brought out its very successful lineup of ‘Zen’ processors. Apple also shook up the laptop market with their M-series of processors from 2020. One big advantage of these processors is that they have much better performance per watt compared to many of Intel’s offerings. As this is going to press, AMD has just started launching their Zen 5 line of CPUs, with modest performance improvements over Zen 4 but significantly lower power consumption. Intel has pushed its technology too hard in an attempt to deal with this threat. The 12th-generation Core CPUs were perfectly fine, but the 13th and 14th-generation processors were pushed to higher frequencies, voltages and power levels in an attempt to compete with AMD on performance. To put this into perspective, the 16-core AMD Ryzen 7950X draws around 140W under heavy load with its default settings, giving similar overall performance to Intel’s 24-core 14900K. However, in its launch configuration, the 14900K drew over 300W under heavy load – more than twice as much as the AMD part! That high power draw is undesirable, but that isn’t why Intel is in trouble. To get the chips to run fast enough to be competitive with AMD’s, they have pushed their clock speeds as high as possible. To achieve high ‘boost’ clock speeds, when just a couple of cores are loaded, they are feeding some CPUs with 1.5-1.6V (it’s closer to 1.0-1.3V under normal conditions). It seems that is too much, and it is killing them. Intel has promised a patch to fix this. However, many 13th and 14th-generation Intel CPUs are affected, and some will have already been damaged. The patch might stop future damage but won’t fix that which has already occurred. So, they will likely be replacing a large number of processors as they just announced a two-year warranty extension on affected products. There’s also the problem that some people with these faulty chips have had their warranty claims denied. They really need to fix this properly but they must know it will cost them a lot of money, so they are putting it off. It doesn’t help that they just announced massive layoffs, with around 15,000 jobs gone. While I think AMD’s technology is currently better overall than Intel’s, mainly due to superior power efficiency, I don’t want a situation where AMD gets lazy because they have no major competitor, the reverse of what happened 10 years ago. We need both companies to be healthy so there is active competition in the space. Intel needs to fix this pronto. While they have admitted that some of their processors have stability problems, they have not fully explained the cause and they have yet to deploy a proper solution. Their reputation is suffering as the situation remains unresolved for so long. New Prices Print (AU) Combined (AU) Print (NZ) Combined (NZ) 12 months $130 $150 $155 $175 24 months $245 $280 $290 $325 Prices from October 1st, 2024; 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip all prices are listed in Australian dollars (AUD). Australia's electronics magazine by Nicholas Vinen siliconchip.com.au The key to unrestricted access Explore millions of components for your next design While you can’t set foot on this protected aviary sanctuary, you can find refuge in the mouser.com tent, where you have access to millions of electronic components, from well over a thousand leading brands engineers know and trust. Let your designs take flight. au.mouser.com 03 9253 9999 | australia<at>mouser.com 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”. Test equipment for sale Following my retirement, I have the following test instruments available for sale. All are used rather than new, but they are all in good condition: 1. A Siglent SDS2104 four-channel DSO with a bandwidth of 100MHz and a maximum sampling rate of 2GSa/ sec. It also has eight digital channels, and I can provide a user manual and a service manual with it ($600). 2. A Gratten GA1484B RF Signal Generator with a frequency range of 250kHz to 4GHz. I can provide a user manual and a programming manual with this one ($500). 3. A Siglent SDM3045X Bench Digital Multimeter with a 4.5-digit display. This one comes with a user manual ($300). 4. A Yokogawa 7562 Bench Digital Multimeter with 4.5 digit display. This one also has an instruction manual ($300). 5. A Digitech QM1240 True RMS bench type DMM ($200). 6. A Hewlett-Packard E3631A Triple Output Bench Power Supply, with outputs of 0–6V at up to 5A and 0 to ±25V at up to 1A. This comes with the original HP user’s guide and service guide and would be good value at $150. If any of these instruments interest you, please email silicon<at>siliconchip.com.au and they will pass it on to me. Jamieson ‘Jim’ Rowe, Sydney, NSW. The EDUC-8 is known worldwide Your farewell to Jim Rowe showed how long he has been pivotal in advancing digital technology in Australia. His EDUC-8 was published over 50 years ago, in 1974; I still have a Digital Electronics – Theory, Instruments and Computers book he wrote, published by EA in 1967. My son recently went to Silicon Valley and visited many of the digital tragic shrines: Xerox PARC, the Sun siliconchip.com.au Microsystems sign, Steve Jobs’ garage and the Computer History Museum. In that museum, he found an original EDUC-8. Thanks to Jim for his work over such a long time. Dave Dobeson, Berowra Heights, NSW. Working with Jim Rowe I just received the July issue of Silicon Chip and discovered that Jim Rowe has retired. I first met Jim when I finished a traineeship with AWA and joined the Electronics Australia staff around January 1967, when I was 21 years old. I have just celebrated my 78th birthday; I will not try to figure out Jim’s present age. Soon after, Leo Simpson joined the EA staff and subsequently went on to be very successful. During my time at EA, I found Jim to be a great mentor, very kind and encouraging. His electronics knowledge and writing talent were pretty awesome. My very best wishes to Jim. Anthony Leo, Cecil Park, NSW. Getting a MicroMag working with the Micromite Thanks for your article on the MicroMag3 magnetic sensor (June 2024; siliconchip.au/Article/16290). I set myself the task of translating the code to work with a Micromite; you might find the problem I encountered interesting. The translated code worked perfectly, with seemingly valid readings on the three axes. The problem arose when I calculated the heading. There is no ATAN2 function on the Micromite, so one has to use the ATN function and then work out which quadrant the heading lies and adjust the result to get the correct heading. To my surprise, assuming the SWD convention was being used, the headings made no sense at all! Upon closer examination of the readings, I found that, at least for my sample, it did not use the SWD convention. The X-axis and Z-axis readings were as expected when using this convention, ie, negative readings were associated with NORTH and DOWN directions, respectively. However, the EAST direction was associated with positive readings and WEST with negative readings. When I took this disparity into account, the calculated headings were completely consistent. Further, the arrow pointed to magnetic north, not the other way around, as in your Arduino sketch. I used the DATA READY signal to determine when to read the data; there were no problems with that on the Micromite. I completed the project by adding code to show the heading on a 1.3-inch OLED screen. Jack Holliday, Nathan, Qld. Australia's electronics magazine September 2024  5 Australian component manufacturing in the past Many thanks for the article on Electronics Manufacturing in Australia in the August issue, which I really enjoyed (siliconchip.au/Series/426). I am looking forward to part two. I was involved in local equipment manufacture in my earlier days in electronics, back in the 1960s when we had large tariff protection for products that ‘could’ be manufactured in Australia. I want to suggest an article on components that used to be made locally by companies such as Ducon, IRC etc. It could be of interest to your readers. Before I met her, my future wife worked at Ducon making special-order precision capacitors, which were used by the company for which I worked to make specialty notch filters. By some strange quirk of fate, that same lady started working for my employers, and the rest is a 60-year history. Of course, all those local component manufacturers have long gone, but a summary of them might be an interesting journey back into the past. David Coggins, Beachmere, Qld. Comments on single-valve radio Congratulations to Fred Lever for squeezing the last drop of juice out of the lemon with his one-valve superhet radio! (July 2024; siliconchip.au/Article/16332) It was an impressive ‘adventure’ for sure. His solution to instability – which he discovered by diligent effort – is, in fact, seen in some commercial radios, like AWA’s B15 (July 2013; siliconchip.au/Article/3945). And thank you for your explanation of neutralisation in the July article. Invented by Harold Wheeler at Louis Hazeltine’s laboratory in 1923 (US Patent 1,450,080), neutralisation revolutionised receiver design. It was also vital to transmitter design. It was used universally in grown-junction and alloyed-junction IF strips for AM transistor radios, only obsoleted by the much lower feedback capacitances of alloy-diffused and mesa/planar devices. On reading the word “feedback”, most of us understand the common use of negative feedback to improve designs. That includes everything from hifi amplifiers to the servomechanisms used in the robotic assemblers that place the chips in your smartphone onto their circuit boards. Conversely, we commonly believe positive feedback to be a problem. It’s the cause of the ‘howling’ oscillation that bedevilled de Forest’s early attempts at amplification. Wheeler’s patent identified the problem of Miller feedback in triodes. The patent describes how this feedback lowers input impedance. Since this feedback is shunted across the grid circuit, its impedance-reducing effect defines it as negative feedback. Given that, according to all our textbooks, negative feedback reduces gain, how can this produce oscillation, the effect of positive feedback? Confusingly, Wheeler’s patent applied a feedback signal that balanced the Miller feedback. Wheeler’s signal was in phase with the input and was thus positive. So, we fix the problem of uncontrolled positive feedback by applying an extra, controlled amount? Let’s put aside the idea of feedback for a moment. Wheeler’s patent sent back some signal in opposing phase to that on the grid. Adjusting the opposing-phase signal must, at some ‘sweet spot’, nullify the anode-grid feedback, allowing 6 Silicon Chip the amplifier to operate at its maximum design potential. The amplifier is neutralised. If that all makes sense, we can now look at howling. Anode-grid feedback inverts the original signal; it is 180° in opposition, but this is only true in a resistive circuit. One tuned LC circuit in the grid and one in the anode will be resistive at exactly their resonant frequencies. But what if those frequencies differ? In the worst case, they will both be reactive, with one leading and one lagging. It is quite possible for the reactive circuits to create a feedback signal in phase with (or close enough to being in phase with) the input signal to provoke oscillation. The entire problem is solved by neutralisation. If the anode-grid feedback is phase-shifted, the neutralising signal should suffer the same but opposite shift and still oppose the anode-grid feedback. Look at any AM transistor radio circuit from the early days, such as our first “trannie”, the AWA 897P (April 2015; siliconchip.au/Article/8458). You will observe that a neutralised IF stage could be mistaken for a Hartley oscillator, where the collector signal is inverted and applied to the base. Ian Batty, Rosebud, Vic. Excessive bending shortens extension cord life Regarding the June 2024 Editorial Viewpoint, cheap electrical cables do fail more readily than older, more ruggedly built ones. The photo in that article shows a cable that has had a hard life and is ‘corkscrewed’. The cable cores have rotated due to the cable being repeatedly rolled in the same direction all the time. That is a common problem with long cables of any type, but it does seem to occur more readily with thin cable sheathing. As you mentioned, the repeated twisting results in broken strands. Once a couple of strands break at a point, that area of the core becomes weakened, so it will twist more readily there, and further strands break. It’s a cascading effect that leads to rapid failure. The solution is to treat cables well. Always roll longer cables with the ‘over & under’ technique, where alternating turns of the cable cancel the twisting tendency. Numerous YouTube videos show variations of the technique. Editor’s note: I found the video at https://youtu.be/ L7av0C0jWQw helpful. Any cable (or hose) over about two metres long will last much longer if it is rolled correctly. But it can be more practical to roll very long and/or heavy cables onto a drum. A garden hose reel is helpful for storing cables for a mains-powered mower. Still, if the cable is not in good condition, a reel should probably be avoided. Noel Bachelor, Seven Hills, NSW. The adoption of DVB-T2 and HEVC I’m a relatively new reader of your publication and have come to appreciate the fantastic articles you provide on all things technical. Please find my reply to Alan Hughes’ letter from the July 2024 issue regarding “European countries switching to HD TV only”: For over a decade, I have worked in television master control rooms, where I oversee several transmitter sites across the continent. I have had the same questions as Alan concerning DVB-T2 in Australia. Australia's electronics magazine siliconchip.com.au FREE Download Now! Introducing DaVinci Resolve 19 Edit and color correct video with the same software used by Hollywood, for free! DaVinci Resolve is Hollywood’s most popular software! Now it’s easy to create feature film quality videos by using professional color correction, editing, audio and visual effects. Because DaVinci Resolve is free, you’re not locked into a cloud license so you won’t lose your work if you stop paying a monthly fee. There’s no monthly fee, no embedded ads and no user tracking. Creative Color Correction Editing, Color, Audio and Effects! Designed to Grow With You DaVinci Resolve is the world’s only solution that combines editing, color DaVinci Resolve is designed for collaboration so as you work on larger jobs correction, visual effects, motion graphics and audio post production all in you can add users and all work on the same projects, at the same time� You can one software tool! 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It has exciting new features to make it easier to get amazing results, even while learning the more advanced color correction tools� There’s PowerWindows™, qualifiers, tracking, advanced HDR grading tools and more! editors� You also get a library full of hundreds of titles, transitions and effects that you can add and animate! Plus, DaVinci Resolve is used on high end work, Learn the basics for free then get more creative control with our accessories! so you are learning advanced skills used in TV and film� Learn more at www.blackmagicdesign.com/au Download free on the DaVinci Resolve website NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING Over the years, I have posed this question to my colleagues and, through a combination of feedback and personal research, have found the following reason why Australian terrestrial television is the way it is. The examples of continental European television markets are correct; it is impressive how they have been able to move onto DVB-T2 and get rid of standard-definition broadcasts. However, there are a few factors to consider with these markets. A key point is that they have very dense population centres that only require a small number of transmitters for terrestrial coverage. Consider the city of Paris, where two million people are in a 105km2 area. Compare that to Perth, where a comparable population is spread out over nearly 6420km2. The costs to cover the same population start multiplying as repeater/translator sites are required to ensure the population can be reached. Converting to DVB-T2 requires upgrading all transmission infrastructure; while major tower sites such as Carmel or Artarmon are only a software update away, other sites will require a complete overhaul to have such capabilities. DVB-T2 allows for more data in the same RF space, meaning that more high-definition (HD) services (channels) could be broadcast. However, there are reasons why the existing parameters used in DVB-T are what they are. Australian terrestrial broadcasters have only 7MHz of bandwidth at their disposal; I suspect this is a hangover from the analog days, as the single-channel carriers were the same size. With the current DVB-T parameters, we can only broadcast up to 23Mb/s (using 64QAM modulation with a Forward Error Correction [FEC] rate of 75%). Reducing the FEC would be a quick way to increase this while preserving DVB-T compliance, but that would come at the cost of signal robustness. DVB-T2 uses other tricks to fit more data, but it would still hit a wall with the signal integrity that needs to be provided. The Broadcast Act does not obligate commercial broadcasters to maintain standard-definition services, so their continued existence is for purely economic reasons. It is my opinion that standard-definition television has no place in 2024. However, my industry perseveres to ensure it reaches those few who still have equipment that can only handle such a format. It is worth noting that certain broadcast areas have minimal SD services, such as rural Queensland, where the Seven Network maintains a majority of its services not only in HD but also with MPEG4 compression. The software-defined infrastructure that is used to produce these signals is getting very close to completely replacing any dedicated FPGA or ASIC hardware that was previously used. Producing multiple compressed video services that are multiplexed and combined with data services (such as electronic program guides) uses a lot of processing power. That requirement drastically increases with HD MPEG4. While compression formats such as HEVC are fantastic for their efficiency and are used in broadcast for professional and consumer reception, producing such signals requires even higher computing power. That, combined with HEVC’s licensing fees for equipment to use that format, is the reason why, besides Foxtel boxes, few receivers support it. I hope this helps clarify a few things about why Australian 8 Silicon Chip Australia's electronics magazine siliconchip.com.au terrestrial television is what it is. Ignoring the doomsayers, who will be quick to write off the medium as dying, there are glimmers of hope on the horizon. Our biggest endeavour at the moment is enhancing accessibility by implementing descriptive audio tracks on all broadcast networks. While the government broadcasters already maintain such facilities, the commercial broadcasters have many specific licence areas that multiply the amount of work required. Nicolas Mason, North Parramatta, NSW. Melting power boards In relation to the comments on dodgy power boards, I wonder how some of this garbage gets into the country and who approves it. I do tagging and testing. On several occasions, I have been presented with some that have suffered melting damage. The 10A rating on some seems to be folly; most of the meltdowns were at 8A. If it exceeded 10A, the circuit breakers would have to be considered useless; a thermal fuse may be more appropriate. There is a serious problem here and clearly, they have not been tested to verify that they comply with any regulations we may still have. I have, on occasion, tested cables that have turned up as charitable donations to an organisation. Most of these come from dad’s shed after he has passed away. Over 10% are seriously and often dangerously non-compliant, and the accompanying mains-powered tools (drills etc) are also mechanically defective and unsafe. Marcus Chick, Wangaratta, Vic. Stick with name-brand extension cords I read your June editorial with interest. You may be interested in my experience with faulty extension cords. I purchased a “heavy duty” extension cord from a wellknown hardware store a few years ago. It lasted about two years before becoming open-circuit somewhere. I only occasionally used it as an extension for a pressure washer. I later purchased a “normal duty” extension cord from the same store. It lasted about six months and also went open-circuit. Neither cable showed any obvious damage. This suggests the faults are with the wire quality and/or the wire gauge, which cannot withstand even moderate flexing. I have recently purchased a “heavy duty” HPM cable. Being an Australian brand, I thought it would be locally made to a better specification or at least made elsewhere to HPM’s specification. I hope my faith in Australian manufacturers is not misplaced. Alan Brodie, Box Hill, Vic. Many Li-ion batteries advertised online are scams I buy lots of stuff from AliExpress, and generally, the quality is good. However, I was searching for some rechargeable batteries and came across these: • AliExpress 1005007071030132 • AliExpress 1005006600481659 You’ve got to be kidding! The claimed capacities of 20,000mAh <at> 12V and 28,000mAh <at> 9V are not possible in batteries of those sizes. These are just two examples of ludicrous battery capacities; many more are being sold from the site. This is very much a case of caveat emptor. But how many are going to be fooled by these? Charles Kosina, Mooroolbark, Vic. 10 Silicon Chip Comment: this has been going on for more than a decade. It isn’t just AliExpress; fraudulent battery capacities are rife on other sites like eBay. We gave a warning about this in the August 2017 issue, p93. It’s not just batteries, either. Other specifications being faked are the brightnesses of LED torches and lamps; even the capacities of jerry cans are often inflated! Oscillation problem with Automatic LQ Meter A few constructors have contacted me with a problem with their Automatic LQ Meters (July 2024; siliconchip. au/Article/16321). It only seems to affect a small number of units. I don’t fully understand why; the precision halfwave rectifier based around IC1b is identical to that used in the original Q Meter design (January 2023; siliconchip. au/Article/15613). It manifests as a high current draw from the supply due to IC1 oscillating at a high frequency, and the device naturally does not work properly. The two LQ Meters I built had no such problems. Likewise, with three of the original Q Meters I built, there were no problems. I tried swapping the OPA2677 IC in the unit that a reader sent me but that did not fix it (the reader had already tried doing that). I thought there could be some strange problem with pin 5 of IC5, so I swapped that as well, with no result. Without D1 in the circuit, the current drain is about 160mA, and it will measure L and Q. However, the rectified output on TP4 (Vin) drops off markedly with frequency, which results in incorrectly high Q readings, as Q = Vout ÷ Vin. This is because the op amp does not recover fast enough from the negative excursions on pin 7. I found a workaround: add a 220W resistor in series with D1. This reduces the op amp’s gain to about ¼ on the negative excursions. The maximum current is now 170mA because, on the negative excursions at pin 7, it has to drive the current through the 220W resistor. I believe this problem is a characteristic of the op amp, as it is a current feedback rather than a voltage feedback type. However, I can’t explain why it has never shown up in testing before. At least the solution is simple; it just needs a 220W 1/4W resistor added in series with D1, which can be done neatly. Charles Kosina, Mooroolbark, Vic. Recovering parts from power supplies & monitors Recently, I was wrecking some old computer power supplies, both AT and ATX. These PSUs had rusty cases and were just taking up room as they would never be used again. They were mostly old AT PSUs and low-wattage ATX PSUs. A few non-working later-model ATX PSUs were included as well. I noticed that most of the old AT PSUs and older ATX PSUs had good electrolytic capacitors that I could salvage (as well as other parts). However, the newer, non-­ working ATX PSUs almost always had bad capacitors; in some cases, most of the larger low-voltage capacitors had blown tops. It seems that these later ATX PSUs were made in the era when the market was flooded with cheap non-Japanese electrolytic capacitors. Back in the day, I replaced many bad capacitors on motherboards. One particular brand of motherboard was particularly notorious for using these Australia's electronics magazine siliconchip.com.au Measuring tools for now and the future DIGITAL READOUT 7” Colour LCD Screen Colour Display Multiple Pre-Set Colours ZERO Programmable Up To 3 Axis One Touch Axis Zero Keys SCAN HERE FOR MORE INFORMATION Multi Language Menu 2-Year Warranty NEW RELEASE 352 (Q8500) $ 120mm Compact Linear Scale - MX-500-120/5U Touch Point Sensor TPS-20 3-Point Internal Micrometers - 25-161 Centre and Edge Finder SME-420 • Compact Scale • Glass scale with 5µm resolution • 3m connection cable • Accuracy within 0.005mm • Ø10mm hardened & ground ball end • LED Light & Beeper Sensor • 12-20mm • Carbide tipped contact points • Supplied in deluxe foam lined aluminium case • Ø10mm Shank x 88mm long • Precision ground • Ø4mm tip 198 (Q8510) $ 93.50 (M690) $ 693 (Q161) $ $ Measuring Box set 70-605 • CNC machined for high accuracy • Ground measuring face • Black anodized coating for a protective anti rust coating • Precision laser engraved markings Measuring Kit - 4 Piece - M012 HAIMER Universal 3D Tester - EL-3D • 0 - 25mm micrometer • 150mm / 6” rule • 150mm / 6” vernier • 100 x 70mm square • X, Y, Z-Axis readings • 0.01mm accuracy • 4mm round probe • Ø20mm shank • 163mm overall length 77 (M012) 979 (M694) $ $ View and purchase these items online: www.machineryhouse.com.au/SIC2408 NOW OPEN SYDNEY BRISBANE MELBOURNE 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains (02) 9890 9111 (07) 3715 2200 Specifications and prices are subject to change without notification. All prices include GST and vild until 29.09.24 (03) 9212 4422 PERTH (08) 9373 9999 ADELAIDE 4 Abbotts Rd, Dandenong 11 Valentine St, Unit 11/20 Cheltenham Pde Woodville SA 5011 Kewdale (08) 9373 9969 07_SC_290824 99 (Q605) $ 44 (M6925) capacitors. [Editor’s note – see our article on the ‘capacitor plague’ in the May 2003 issue, starting on page 8] I suspect that penny-pinching using cheaper non-­ Japanese capacitors put this particular manufacturer out of business when their warranty claims exceeded their new sales. I was also scrapping a lot of old CRT monitors that I had in my shed. I did not find a single monitor with even one bad electrolytic capacitor in it. However, I salvaged very few capacitors from the monitors, as most were 85°C types; I only bothered to salvage 105°C ones. I got lucky with one monitor, which had several Rubicon capacitors in it. Wrecking this old ‘junk’ has the benefit of making a few dollars from the scrap metals. Depending on the construction, monitors can contain up to $5 worth of copper, aluminium and steel. Some yield much less scrap, some more. One particular monitor weighed 24kg and had 4kg of steel in it. The most valuable metal is what they call burnt copper wire, which is the enamelled copper wire from the yoke and degaussing coil. Insulated copper wire is the next most valuable, with aluminium following. Steel is the least valuable. So it has been worth cleaning out my shed and getting rid of the old ‘junk’, making a few dollars in the process. Bruce Pierson, Dundathu, Qld. An easy way to switch Ethernet on and off On page 101 of the July 2024 issue, D. S. of Maryborough, Qld asked for a method to ‘switch’ a network cable on and off to restrict his son’s internet use. My simple solution, instead of switching eight data lines, is to use a cheap network switch/hub powered by a DC supply. The ideal choice is a model like the TP-Link TL-SG108E or similar (with an external DC plugpack). Simply switching the power to the network switch/hub causes all the physically connected network ports to disconnect. It’s a very simple, reliable method of switching Ethernet connections on/off. It can also be used for switching multiple access points on/off with a physical switch, which can be a key switch for security. As the reader mentioned, he could build a timer with an Arduino Uno board, but why go to that trouble? Simply buy a plug-in mains electronic timer switch and set the on/ off times – problem solved! SC Brett Neale, Bertram, WA. PRODUCT SHOWCASE Introducing the PIC64 Microchip’s 64-bit PIC64 family supports applications that require both real-time and application class processing. PIC64GX MPUs, the first of the new product line to be released, enable intelligent edge designs for industrial, automotive, communications, IoT, aerospace and defense. The intelligent edge often requires 64-bit heterogenous compute solutions with asymmetric processing to run Linux, real-time OSes and bare metal in a single processor cluster with secure boot capabilities. Microchip’s PIC64GX family includes a 64-bit RISC-V quad-core processor with asymmetric multiprocessing (AMP) and deterministic latencies. It is the first RISC-V multi-core solution that is AMP capable for mixed-criticality systems. It is designed with a Linux-capable CPU cluster, fifth microcontroller class monitor and 2MB of flexible L2 Cache running at 625MHz. The PIC64GX family is pin-­ compatible with Microchip’s PolarFire SoC FPGA devices, offering a large amount of flexibility in the development of embedded solutions. Additionally, the 64-bit portfolio leverages Microchip’s easy-to-use ecosystem of tools and supporting software, including a host of powerful processes to help configure, Microchip Technology Australia Suite 32, 41 Rawson Street, Epping NSW 2121 Phone: (02) 9868 6733 www.microchip.com 12 Silicon Chip develop, debug and qualify embedded designs. The PIC64 High-Performance Spaceflight Computing (PIC64-HPSC) family is also being launched as part of Microchip’s first wave of 64-bit offerings. The space-grade, 64-bit multi-core RISC-V MPUs are designed to increase compute performance by more than 100 times while delivering unprecedented radiation and fault tolerance for aerospace and defence applications. NASA’s Jet Propulsion Laboratory (JPL) announced in August 2 0 2 2 t h at i t h a d selected Microchip to develop HPSC processors as part of its ongoing commercial partnership efforts. The PIC64-HPSC family represents a new era of autonomous space computing for NASA-JPL and the broader defence and commercial aerospace industry. Microchip is now the only embedded solutions provider actively developing a full spectrum of 8-, 16-, 32- and 64-bit MCUs and MPUs. Future PIC64 families will include devices based Australia's electronics magazine on RISC-V or ARM architectures; embedded designers will be able to take advantage of Microchip’s end-to-end solutions for faster design, debug and verification and a reduced time to market. To learn more, visit the Microchip 64-bit web page: www.microchip.com/en-us/ products/microprocessors/64-bit-mpus The PIC64GX Curiosity Kit is now available for early adopters. Production versions of the Curiosity Kit and PIC64GX1000 parts are due for release by September 2024. siliconchip.com.au Spring CLEAR OUT! Pick up a stock run out deal on handy tech. Ultimate benchtop charging station! SAVE $80 SAVE $39 150 $ M 8882A* Recharge TEN USB devices at once! Great for families, class rooms & business. Massive 19A charge output across 10 x USB type A outputs. QC3.0 on 2 ports. Includes adjustable dividers & power supply. Size: 238 x 118 x 26mm. *Devices & charging leads not included 199 $ X 7063 With outdoor sensors & smartphone app! Get live, local weather at home every day. This fantastic weather station displays your local weather data - great for boaties & gardeners. Bright & clear base station provides readings for indoor/outdoor temps, humidity, air pressure, rainfall, wind speed & direction. You can even connect it to wi-fi for monitoring data with your phone. 100m sensor range. D 2038 SAVE $54 2 For 50 185 $ $ M 8195B SAVE $35 SAVE 30% H 8126C Compact Can Speaker Cantilever Arm TV Bracket This nifty Bluetooth can speaker offers great sound and 3-4 hours listening. Pairs with a second unit for wireless stereo. Water resistant. SAVE $20 79 $ D 2358B USB C Multi Hub Provides HDMI (4K <at> 30Hz), wired ethernet, plus three USB 3.0 ports, SD/Micro SD and 60W power pass. 145 $ Silky smooth cantilever adjustment, stays just where you want it to. Suits screens up to 90” using 800 x 400mm VESA. Max weight, 60kg. Lithium-Ion Vehicle Jump Starter SAVE $59 140 $ D 2363A Perfect for t the family ho desk! 13 In 1 USB C Laptop Docking Station A handy laptop docking station hub for USB C type equipped laptops. Fitted with all the ports you could need! Max 4K <at> 30Hz. Don’t get stuck with a dud battery! Suits 12V battery vehicles. 20000mAh rated battery provides up to 2500A peak output when cranking. Three USB ports are provided for charging devices (like a giant battery bank!). It also has a super bright 1W LED torch in built. 192L x 90W x 36Dmm. Your electronics supplier since 1976. Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/9/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. Spring SAVE $20 K 8300A 59 $ Repair plastics & add to 3D prints 3D Printing Pen A crafty addition to any work space, this handheld pen extrudes 1.75mm PLA or ABS filament for decorating objects, plastic repair jobs or touch ups to 3D printed models. Easy to use with adjustable speed. Includes 12m of PLA filament. Z 6513 5” 800x480 CLEAR OUT! Pick up a stock run out deal on maker bits. Dual 4K <at> 60Hz HDMI outputs. SAVE $34 Pi HAT and camera friendly. 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SAVE $19 80 $ H 8932 25 $ 25 $ H 8959 Dual Fan H 8953 Raspberry Pi® 4 SNES Case Raspberry Pi® 4 Aluminium Cases Perfect for retro-pi game consoles. Provide protection and thermal dissipation for your Pi 4. Also suits the Rock-Pi above. SAVE $50 EL Wire For Creative Projects 99 $ SAVE 40% 29 $ H 8930 Z 6457 Argon ONE Pi 4 Case Mini Game Console Kit A top notch no compromises Pi 4 case with aluminium construction and excellent cooling. This Arduino based kit allows you to play hundreds of open source games - or have a go at coding your own! Uses a atmega32U4 chip with USB programming. 1.3” mono screen. ® HALF PRICE! 3m rolls 5 $ .75 A favourite of e-textile/cosplay builders providing a way to light up costumes, decorations and DIY signs. All sold in 3m rolls. Works with X 4101 controller which is powered by 2xAA batteries. n X 4105 Green n X 4106 Blue n X 4107 Red n X 4108 White X 4101 controller just $6. Normally $11.50 Your electronics supplier since 1976. Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/9/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. Subscribe to AUGUST 2024 ISSN 1030-2662 08 The VERY BEST DIY Projects ! 9 771030 266001 $12 50* NZ $13 90 INC GST INC GST The Styloclone build your own instrument Tracking & Locating Devices Byline text, anything good to now before prices increase from October 1st Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. put here? Dual Mini LED Dice and much more in this month’s issue Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $70 $80 $52.50 1 year $127.50 $147.50 $100 2 years $240 $275 $190 6 months $82.50 $92.50 1 year $150 $170 2 years $285 $320 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 Prices are valid for month of issue. Try our Online Subscription – now with PDF downloads! The Styloclone Musical Instrument; August 2024 Adding solar charging to a van; July 2024 The Raspberry Pi 5; July 2024 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe Generating Power by Unusual Means By Dr David Maddison, VK3DSM The Landesbergen biomass power plant in Germany; it generates power by burning scrap wood. Image source: Statkraft – www. flickr.com/photos/statkraft/49866093642 (CC-BY-NC-ND 2.0) Energy is all around us in one form or another, but often in small amounts. Energy harvesting, otherwise known as power harvesting or energy scavenging, is the process of obtaining small amounts of energy from the environment to supply low-power devices. W ith a few exceptions, the amounts of power available from energy harvesting are small, and the expense required to obtain that power makes these methods not competitive with grid power, where it is available. However, these tiny amounts of energy can be very useful for powering small devices away from the grid; modern efficient electronics can often run on minimal amounts of power. This article will cover methods of power generation other than the ones most people are familiar with, like coal and gas generators, nuclear power plants, hydroelectric plants, solar, wind and wave power or burning biomass or waste. With these alternative power-­ generating methods, the power available is often on the order of nanowatts to milliwatts. In some cases, it may 16 Silicon Chip be possible to generate several watts (or more). The main applications for energy-­ harvesting devices include powering IoT devices such as remote sensors, ‘wearable electronics’, powering biomedical devices (like pacemakers) or charging portable devices like mobile phones. Energy harvesting principles The basic principles and technologies that energy harvesting devices utilise include the following. We will describe their uses when we look at particular implementations. • Using chemistry, such as in an electrochemical cell. • Using biochemistry, including the generation of electricity using bacteria or plants. • Using biomechanical principles, Australia's electronics magazine such as utilising bodily movement. • Using an electret, a dielectric material that maintains electric polarisation after it has been subject to a strong electric field. It is the electrostatic equivalent of a permanent magnet. • Using electric field gradients, such as causing a fluorescent tube to glow near a power line. • Using electromagnetic induction to generate electricity by Faraday’s Law, the “production of an electromotive force (EMF) across an electrical conductor in a changing magnetic field”. • Capturing electromagnetic radiation from radio waves via an antenna or from light, such as in a solar cell via the photoelectric effect. • Using electrostatic power generation to produce high voltages at very siliconchip.com.au low currents. This frequently involves materials rubbing against each other (via the triboelectric effect). • Using metamaterials, artificial materials with repeating structures that can interact with and manipulate electromagnetic waves in various ways. • Converting motion to electricity using electromagnetic, electrostatic or piezoelectric effects. • Using changes in air pressure to expand or contract bellows. • Using a temperature gradient, such as with a thermoelectric device. • Using the movement of air, like in a wind turbine. • Using the movement of water, ie, hydroelectricity. Below we will cover what energy-­ harvesting devices and techniques that we have found: Fig.1: the first self-winding mechanical watch that harvested energy from the motion of the wearer’s arm. Source: Fratello Watches – siliconchip.au/link/abxy Watches Since watches are small, low-­ powered devices, there has been much interest in energy harvesting to power them. Self-winding automatic mechanical watches were common before the advent of electronic quartz watches. They had a pendulum activated by swinging one’s arm that wound the mainspring. The first credible report of a self-winding pocket watch dates to 1777. In 1922, the first self-winding wristwatch was invented by John Harwood, and he was awarded Swiss patent 106583 in 1924. The watch was released to the market in 1928 – see Fig.1. The first solar-powered clock was demonstrated by Patek Philippe at the Basel Fair in 1952! Four hours of light per day was enough to keep the clock running indefinitely. The solar cell drove a motor that wound the mainspring. Patek Philippe went on to make a range of solar clocks; see siliconchip.au/link/abxm The solar-powered watch was first patented by Timex in 1969, but the first solar watch, the Synchronar 2100, was invented by American Roger Riehl. He partnered with Palo Alto, California based electronics company Ness Time for the project. The watch (Fig.2) was shown at the RJA Fall trade fair in July 1973 and remained in production until 1983; you can see a TV ad for it at https:// youtu.be/mIwxNkGKXb4 siliconchip.com.au Fig.2: the Synchronar Sunwatch was the world’s first solar-powered watch, released in 1972. Source: https://solarmuseum.org/cells/ synchronar-2100/ In many modern solar watches, the dial is translucent and the solar cell(s) are hidden beneath it. Seiko pioneered the so-called automatic quartz watch concept that used a rotating pendulum inside the watch. Instead of winding a spring, it drove a highly-geared miniature generator at up to 100,000 RPM to charge a capacitor or rechargeable battery. Seiko unveiled the technology in 1986 and today sells them under the Kinetic brand. Seiko still maintains a web page for these watches (siliconchip.au/link/ abxn) but we have seen statements that they are being phased out (see siliconchip.au/link/abxo). About eight million have been sold to date. The generator mechanism of the Kinetic watch has been experimentally used to power a cardiac pacemaker in an animal (more on that later). The PowerWatch uses a Matrix thermoelectric device to power it, in addition to solar energy (www. powerwatch.com). A review of the Australia's electronics magazine Fig.3: the Atmos clock mechanism: 1. Expansion chamber 2. Brass cover 3. Balance spring (counterweight) 4. Small chain 5. Mainspring 6. Pulley 7. Return spring 8. Balance wheel 9. Elinvar wire 10. Escapement 11. Winding spring Original source: Watch Collecting Lifestyle – siliconchip.au/link/abxs PowerWatch Series 2 is at siliconchip. au/link/abxp Atmospheric & solar clocks The Atmos is a very expensive clock currently available from Jaeger-LeCoultre that obtains its energy from environmental temperature and pressure changes. Expansion and contraction of liquid and gaseous ethyl chloride in a bellows as the temperature or pressure rises and falls cause a spring to be wound to power the mechanism – see Fig.3. The Beverly Clock in New Zealand (https://w.wiki/AUgH) has been running since 1864 without winding. However, it did stop a few times, mainly when there was insufficient change in atmospheric pressure or temperature to keep the mechanism wound. The Long Now Clock (funded by Jeff Bezos; https://longnow.org/clock), being built in the USA, is designed to run for 10,000 years. It uses sunlight falling on a chamber of air to move September 2024  17 Fig.4: harvesting atmospheric electricity to run an electrostatic motor. This type is called a corona motor. Original source: Rimstar – siliconchip. au/link/abx7 Fig.5: conventional (a) and auxetic (b) piezoelectric bimorphs for energy harvesting. Original source: https://pubs. aip.org/aip/adv/ article/7/1/015104/­ 240312/ a cylinder, which provides enough winding force to keep the pendulum going. It is also used to synchronise the clock to solar noon. So, in a sense, it is solar powered, although it does not use a photovoltaic panel. Atmospheric electricity There is a substantial electric field gradient in the atmosphere, so an electrostatic motor can be made to turn by having one electrode high in the air with the other at a lower level (see Fig.4). The power is meagre; at most a current of a few microamps can be drawn. For more on this, see the panel in this article on Hermann Plauson (page 26), the video titled “How Powering with Atmospheric Electricity Works” at https://youtu.be/2rVdEhyMR6A and the web page at siliconchip.au/ link/abx7 Piezoelectric energy Piezoelectricity involves the production of electrical energy from mechanical strain. Examples of sources of strain include motion, sound and vibration. The power generated is typically minimal, milliwatts or less. Piezoelectric materials include ceramics like quartz crystals and, more recently, piezoelectric polymers like polyvinylidene fluoride (PVDF) – see Fig.6. An example of a piezoelectric energy harvester is shown in Fig.7. Some piezoelectric substances are also pyroelectric. These crystals are naturally electrically polarised and produce a voltage when heated or cooled. This could be used for energy harvesting over a day by taking advantage of the natural changes in ambient temperature. Auxetic materials are artificially-­ structured metamaterials that expand in width rather than contract when stretched. Conversely, when subject to compression, they reduce in width. It has been proposed that auxetic materials could increase the energy-­ harvesting efficiency of piezoelectric devices, as shown in Fig.5. In that figure, (a) shows a conventional piezoelectric bimorph, which can generate power mainly in the stretching direction, while (b) represents a bimorph of auxetic construction. This can generate power simultaneously in both the stretching and transverse directions, resulting in an expected power increase of 176%. That is because it has increased power output in the transverse direction, as it can generate more stress in that direction, and the power output is proportional to the applied stress. Clothing has been proposed that incorporates piezoelectric materials to generate power for powering or charging devices. Such fabric utilises nanofibres and is said to be stretchable and breathable. See siliconchip. au/link/abxe Thermoelectricity Thermoelectricity involves the production of an electric current due to a thermal gradient between two dissimilar electrical conductors. A typical example of a device that utilises this effect is a thermocouple, although it produces tiny amounts of power at very low voltages. Peltier devices (Fig.8) also utilise this effect but with many more thermoelectric junctions. When a current is applied, it can move heat towards or away from an object. Alternatively, when a temperature differential is applied, it can generate a voltage and current, and thus be used for energy harvesting. Fig.6 (left): polyvinylidene fluoride (PVDF), a piezoelectric material, with deposited electrodes from a commercial supplier. Source: www.he-shuai.com/pvdf-piezo-film Fig.7 (right): a commercial piezoelectric energy harvester, model S118-J1SS-1808YB (from https://piezo.com). It can produce up to 0.7mW. Source: Piezo S118-J1SS1808YB – siliconchip.au/link/abxv Australia's electronics magazine siliconchip.com.au Fig.8: a Peltier device. It uses a combination of p-type and n-type semiconductor materials to create thermoelectric junctions. They are connected electrically in series and thermally in parallel. Original source: https://w. wiki/AUjV Electricity can be generated from a campfire using thermoelectric principles. Fig.9 shows a Peltier device attached to a heatsink that can generate power from a fire. The CampStove 2 from BioLite can produce up to 3W to power or charge USB devices (see siliconchip.au/link/abxa). The MATRIX Prometheus Thermal Energy Harvesting Module produces power by exploiting small environmental temperature differences, using the thermoelectric effect. The most powerful Prometheus device, the PRMT02-34465, produces up to 14mA (www.matrixindustries. com/0234465). This technology is used to power the MATRIX Perceptive Health Monitor, their Proximity Sensor and the PowerWatch (www.powerwatch.com). Stirling engines A Stirling engine is a type of heat engine that can function with very small heat differences and thus can be used for energy harvesting from lowgrade heat sources – see Fig.10. The Stirling engine can be connected to a generator to produce electricity. Stirling engines have been proposed by NASA to produce power on a future mission to Mars (see page 24 Fig.9: a DIY thermoelectric generator using an off-theshelf Peltier device, heatsink and other components. Source: https://youtu.be/x9a2rB-xWkY of the July 2024 issue; siliconchip.au/ Article/14916). Energy from bacteria Some exotic bacteria exchange electrons with the environment (‘extracellular electron transfer’ [EET]), so theoretically, they could be used to produce electricity. Mechanisms from these exotic bacteria have been genetically engineered into common E. coli bacteria. Such an approach could be used to convert wastewater effluent streams into electricity. However, this is very early work and practical applications are a long way off. The work was published at siliconchip.au/link/abxd Also see the video titled “Scientist engineered bacteria to generate electricity from wastewater” at https:// youtu.be/beI_qlsmNQ8 Power from plants A common experiment for children is (or used to be) to use a lemon, potato or other fruit or vegetable to make a basic electrochemical cell (see Fig.11). Pieces of different metals, such as zinc and copper, are used as electrodes, while the juice of the fruit or vegetable acts as the electrolyte. One such cell might produce 0.9V at 1mA. Several lemons can be connected in series to power one LED. A fun experiment was once performed to see if a 1000-lemon battery could start a car. See the video titled “Can a battery made from 1000 lemons start a car?” at https://youtu.be/­ 4f2wsQkQ71o Light can be turned into electrical energy via the photosynthesis mechanism using bio-­photoelectrochemical cells (BPECs). This early work is described in the scientific publication at siliconchip.au/link/abxl Biomechanical energy from the human body Raziel Riemer and Amir Shapiro calculated the energy available from the Fig.11: a drawing of a three-lemoncell battery lighting one LED. Source: https://w. wiki/AUjy Fig.10: the operating cycle of a Stirling engine, which can run from relatively low temperature differentials and could be used as part of a generator. Original source: https://youtu.be/ hbfkbcdw_OM siliconchip.com.au Australia's electronics magazine September 2024  19 Fig.13: an image from the Author’s 1989 US Patent 4798206 for “Implanted medical system including a self-powered sensing system” showing an assembly of piezoelectric PVDF polymer as the sensing element (#14). Fig.12: a biomechanical energy-harvester that mounts on the knee. Original source: www.researchgate.net/publication/51078340 motion of an 80kg human body under various circumstances (siliconchip.au/ link/abx9) and found the following power available: • heel strike: 2-20W • ankle motion: 67W • knee motion: 36W (see Fig.12) • hip motion: 38W • movement of centre of mass: 20W • elbow motion: 2W • shoulder motion: 2W They point out that the typical human body consumes the equivalent of 800 AA cells (which would weigh 20kg) by burning just 200g of fat. Cardiac pacemakers A rough estimate for the energy consumption of an implantable cardiac pacemaker is around 10-100µW. Over 5-10 years, that amounts to about 0.52Ah. The low power level makes it an ideal target for energy harvesting. That would mean, instead of the pacemaker having to be replaced when the battery goes flat, it could be powered indefinitely. Fig.13 shows one of the Author’s US Patents from 1989 for a pacemaker “self-powered sensing system”. It generates electrical signals from the heart’s motion using a polyvinylidene fluoride (PVDF) piezoelectric film. A Seiko Kinetic watch mechanism was also demonstrated experimentally to generate power for a pacemaker; see siliconchip.au/link/abxt Another option for powering a pacemaker is an ‘inertia-driven triboelectric nanogenerator’ (I-TENG), as described at siliconchip.au/link/abxb Triboelectricity The triboelectric effect is electric charge transfer due to two objects rubbing together. For example, a shoe rubbing on a carpet can result in a static electricity shock to the wearer when they touch a grounded object. A ‘drinking bird’ toy can be turned into a ‘triboelectric hydrovoltaic generator’ using two effects. A temperature differential powers the bird, while triboelectricity is used to generate power. Experiments demonstrated such a generator powering items like liquid crystal displays, temperature sensors and calculators. For further details, see siliconchip.au/link/abxc A triboelectric nanogenerator (TENG) is an energy-harvesting device that generates an electric charge using the triboelectric effect involving a periodic contact or sliding motion – see Fig.16. Low currents are produced at high voltages. Electret power generators Fig.16: four modes of triboelectric generators. Original source: www. researchgate.net/publication/322251641 20 Silicon Chip Australia's electronics magazine An electret is the electrostatic equivalent of a permanent magnet, and a moving electret can be used to produce power similarly to a magnet. You would probably be familiar with electrets in electret microphones; they serve to bias on the FET within the microphone capsule in the absence of an external voltage source. An electret-based power generator has been demonstrated using siliconchip.com.au ► Fig.14: an energy-harvesting prototype that converts vibration into electricity using MEMS technology and the electret principle. Original source: www.mesl.t.u-tokyo.ac.jp/ en/research/electret.html Fig.15: the circuit of the simplest possible crystal radio using a diode, long wire antenna and highimpedance headphones. Lacking a tuned circuit, it will receive all stations at once, but in practice, the strongest station will probably drown out the rest. Original source: https://w.wiki/AUjt microelectromechanical (MEMS) principles as described at siliconchip.au/ link/abxi (see Fig.14). The prototype produced 6µW from an acceleration of 13.73m/s2 at 40Hz Power from radio waves Crystal radios were made by children back in the day and could obtain useful radio reception without a battery. They were powered by harvesting the energy of the radio wave itself – see Fig.15. RF energy can also be harvested for other purposes using a tuned antenna and a rectifier that works at the desired frequency. They must be close to a source of RF, such as a WiFi router. Commercial modules to harvest RF energy include the Powercast P2110B, which converts RF to DC. It is optimised to absorb energy in the 850-950MHz range and can provide a regulated output of up to 5.5V – see Fig.17. Some YouTube videos demonstrate harvesting small amounts of power from commercial radio stations. The author of the following video manages to light ten LEDs, although he is only 1.6km from the radio station: “Free Energy From Radio Waves (https:// youtu.be/_pm2tLN6KOQ). Fig.18 shows another RF-energy-harvesting circuit. Peter Parker VK3YE looks at whether you can harvest enough power to drive a speaker with a crystal set next to a commercial radio station transmitter in the video titled “Crystal siliconchip.com.au set under a 100kW radio station: How does it sound?” at https://youtu.be/ xglEsaNkPSA cell) is made by inserting two dissimilar metal electrodes in the ground. Zinc and copper are two metals that can be used as electrodes. The soil Würth Elektronik’s energy must be moist for the cell to work. harvesting evaluation kit Multiple cells can be connected to Würth Elektronik (www.we-online. make a battery. com/en) offers an energy-harvesting It is not “free” energy because, as evaluation kit with several energy-­ with any cell, one or both of the elecharvesting options – see siliconchip. trodes will eventually be consumed au/link/abxq or deteriorate. Also, the ions in the soil will eventually be depleted, Earth batteries and a new location will have to be An Earth battery (or, more correctly, selected. Fig.17: a P2110B energy harvester module on a Powercast evaluation board. The module needs a suitable antenna and capacitor to operate. Source: All About Circuits – siliconchip.au/ link/abxw Fig.18: an energyharvesting circuit for ambient radio waves, although the amount of energy collected is tiny. Original source: https://youtu.be/ XpLCK88nVgU Australia's electronics magazine September 2024  21 The first Earth battery was invented by Alexander Bain in 1841; he used zinc and copper electrodes. From an electrochemical point of view, there is nothing unusual about an Earth battery, apart from the medium being the ground rather than a more conventional container such as a battery case. Power harnessed from Earth batteries should not be confused with telluric currents. Still, telluric currents might contribute to the overall EMF of the cell if the electrodes are sufficiently far apart. Telluric currents Telluric currents are electrical currents within the Earth or sea induced by magnetic disturbances from various sources, both natural and artificial. That includes space weather, such as the solar wind, sunspots and their interaction with the ionosphere. They can be a problem for underground and undersea cables and buried pipelines. As they can be influenced by the sun, they vary during the daily solar cycle. In the 1800s, problems in telegraph operation were recognised to be related to telluric currents due to sunspots. In 1903, W. Finn reported in Scientific American that an EMF of 768V with a current up to 300mA was recorded over hundreds of miles/ kilometres of telegraph lines in 1891. Telluric currents can be utilised in mineral exploration, to help locate areas of changes in the electrical conductivity of rocks that may indicate mineral deposits. Gravity batteries A gravity battery is a type of electromechanical battery where a mass is raised and then lowered by gravity to generate electricity. It can be used as a type of energy storage, powering a motor to raise the mass when power is cheap (excess is available) and then lowering it to generate power when it is more expensive (when demand is higher). We discussed some of these ideas in our article on Grid-scale Energy Storage (April 2020; siliconchip.au/ Article/13801). A gravity-powered light called the GravityLight was developed for use in less developed countries (see Fig.19). It is ‘charged’ by raising a 10kg mass by 1m and provides light for five minutes by delivering 20mA continuously. Unfortunately, the project was not a success. Hydroelectricity for camping A portable hydroelectric generator was produced for bushwalkers or campers (Fig.20). You have to anticipate being in an area with reasonably fast-running water. That is not always possible in the Australian bush but is more realistic in parts of the USA, Europe or New Zealand. The device is a bit heavy for many bushwalkers, at 1.5kg, and appears to be no longer available. Electromagnetic fields around power lines It used to be a classic demonstration to hold a fluorescent tube under a high-voltage power line. An electrical Fig.23: the electric field around highvoltage power lines. The red region is a reading of >15kV/m. Source: Quora – siliconchip.com/au/link/abxu current is induced due to capacitive coupling, causing the gases in the tube to fluoresce (see Fig.21). The electric field around a high-voltage power line is shown in Fig.23. There must be a sufficient voltage differential between both ends of the tube for it to light. There is a sufficient electrical field gradient to cause the tube to glow if held vertically but not horizontally. There are many anecdotal accounts (but few documented cases) from the USA of farmers and others building large coils or fences beneath power lines running across their properties to harvest power via electromagnetic induction. It is theoretically possible, but power theft is still illegal even when done ‘over the air’. Very large structures would be required to obtain useful amounts of power (to do more than, say, power some LEDs). With the cost of copper these days, the cost of the wire would exceed any worthwhile savings in electricity, despite the high cost of power. It would be cheaper to buy some solar panels and batteries. Fig.19: the GravityLight provides 20mA to a small lamp for five minutes by slowly lowering a 10kg weight. Fig.20: the “WaterLily Turbine”, a portable hydroelectric generator for charging USB or 12V devices in a running stream. 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.24: Alfred Traeger demonstrating the pedal-powered radio he invented in 1928. Source: https://w.wiki/AUk2 There is an interesting video that explains how to use a coil and capacitor to make a resonant LC circuit to harvest enough power to light an LED from various sources. It is titled “Stealing Electricity (the safe way)” and is at https://youtu.be/CLS8pbDNHbk Also see the video titled “Fences sucking power from under HV transmission lines” at https://youtu.be/­ lDm00Ww6qE4 Human-powered generators While pedal-powered generators are less common today due to the low power consumption of LED lights and the advent of lithium-ion batteries, they used to be a common way to power bicycle headlights. They draw power from the rider’s pedalling (see Fig.22). They could be either wheel-mounted (‘bottle dynamos’) or hub-mounted. They can generate about 3W at 6V Fig.25: the Author’s collection of hand-cranked devices. The red hand-cranked torch is from the former Soviet Union and has an incandescent bulb, while the blue one is a modern Chinese torch with LEDs and a reserve battery. The item at upper right is a magneto from an old telephone. (500mA), with some delivering 6W at 12V (also 500mA). Modern hub dynamos such as those from SON can also be used to recharge batteries or mobile devices. In earlier times, electricity was not readily available in the Outback, so Alfred Traeger invented a pedal-­ powered radio that was used for the School of the Air and for calling the Royal Flying Doctor Service (see Fig.24). The pedal generator produced around 200V at 100mA (20W). Transceivers from the Traeger Transceivers company were sold to Nigeria in 1962 and Canada in 1970. For further information about Traeger Transceivers visit siliconchip.au/link/abxf A human on a stationary bicycle can drive a higher-power generator, such as to charge a laptop. Instructions to do this are at siliconchip.au/link/abx8 There is a large variety of hand- Electric shoes Experimental shoes have been designed to harvest energy for a variety of possible purposes; one example Fig.22: a modern bicycle hub dynamo by SON (https:// nabendynamo.de/en/): Source: https://w.wiki/AUjW Fig.21: a fluorescent tube glowing under a high-voltage power line due to capacitive coupling of the electric field. siliconchip.com.au cranked devices that generate electricity for lighting or other purposes, such as those shown in Fig.25. Many early telephones had a hand crank magneto that generated 50-100V AC to ring a bell at the called party’s end, or alert an operator. While current for talking was supplied by batteries, they did not have sufficient power to ring the bell. Dynamite plungers were similar, although they are now obsolete. They comprised a T-handle attached to a linear rack gear that engaged with a circular gear connected to a generator. When the handle was pressed down, they generated a brief electrical current to trigger a detonator. Australia's electronics magazine September 2024  23 is shown in Fig.26. That energy-­ harvesting combat boot produces elecGPS Transmitter trical power via compression of bulbs in the sole of the boot, which drive Power Management Module microturbines to produce electricity to power a GPS tracker. Turbine Enclosure Children’s shoes that light up genAir Bulbs (3x) erally have batteries and are not self-powered, as explained in the video titled “How Light Up Shoes Work – See What’s Inside Sketchers Kids Litebeams” at https://youtu.be/ IIlpRgVBDYo On the other hand, kids’ scooter Fig.26: an energy-harvesting combat wheels that light up do use a small boot that powers a GPS tracker. Source: www.researchgate.net/ generator built into the hub. Power from trains coming down mountains On page 79 of the April 1988 issue, we described how regenerative braking by heavy ore- and coal-laden trains descending the Blue Mountains in Sydney (from mines in places like Lithgow) generated a significant amount of power, which was used to power passenger and empty freight trains ascending into the mountains at the same time. If ore or other heavy material is mined from mountains and carried down to sea level by trains, which then ascend empty, you effectively have a publication/325211019 generator powered by the potential energy of that ore (see Fig.31). Fortescue is developing an iron ore freight train in Australia that will charge batteries as it coasts down hills, to provide power for the return journey uphill to get more ore. Power from roads Energy-harvesting experiments have been performed for roadways. Methodologies that have been tried, shown in Fig.27, include: • Harvesting thermal differentials in between pavement and lower levels underground. • Devices exploiting Faraday’s Law of Induction to harvest mechanical energy (a magnetic field will interact with an electric circuit to produce an electromotive force). • Piezoelectric devices to harvest mechanical energy. • Solar panels embedded in, around and above roadways. Electrodynamic tethers An electrodynamic tether is a long wire deployed from an Earth-orbiting spacecraft – see Fig.28. As it passes through the Earth’s magnetic field, a current flow develops, according to Faraday’s Law of Induction. It can be used as a power source, but it results in some drag on the spacecraft. In 1996, NASA deployed a long tether from the Space Shuttle Columbia, which generated a potential of 3500V. The tether was intended to be 20.7km long but an electric arc caused the tether to break after 19.7km had been spooled out. It works as follows – ionospheric electrons are collected from the positively-­ biased anode at the end of the uninsulated tether. They flow through the electrical load, then to the negatively-­biased cathode, where they are discharged into the space Fig.27: some concepts of energy harvesting from vehicles travelling on roads. Original source: www.mdpi.com/1996-1073/16/7/3016 24 Silicon Chip Australia's electronics magazine siliconchip.com.au plasma and complete the circuit. Electrostatic generation from lunar soil NASA has proposed harvesting the electrostatic charge from lunar soil. The charge builds up over long periods due to the solar wind. They propose to collect the charge using a moving capacitor array that’s ‘raked’ through the lunar soil (see siliconchip. au/link/abxj). NASA estimates that a 1/3m2 collecting array could produce a maximum theoretical power of 147W (700V <at> 0.21A) – see Figs.29 & 30. Tiny solar cells Inexpensive, tiny solar cells can be used to power IoT or sensor devices, with energy stored in a small battery or cell. Even photodiodes can be pressed into service to generate power; see Fig.32. People in the developed world might not appreciate it, but for people living in less developed countries, night-time lighting is not always available and it is highly beneficial if they can get it. Certain charities, such as SolarAid (https://solar-aid. org), produce solar lights for people in these countries, and donors can also Fig.31: the ARES rail car, which climbs a hill using electricity during off-peak hours, then is released downhill during peak hours to produce energy via regenerative braking. Source: ARES North America – aresnorthamerica.com buy them for their own use. Many small solar panels are available for bushwalkers and campers to recharge devices. Some can be affixed to backpacks, while others are set up when camped. However, panels that are small and light enough to be affixed to a backpack provide only small amounts of power. I find that you typically get to a campsite well after peak sun. In my experience, it is better to carry batteries. Micro hydroelectric schemes New Zealand YouTuber Marty T made a ‘microhydro’ installation on his wilderness property using the motor from a scrap Fisher & Paykel Fig.29: the circuit of a theoretical capacitive charge collector with a differential drain to harvest electrostatic charge from the negatively charged lunar soil (regolith). Original source: https://ntrs.nasa.gov/api/ citations/20100032922/downloads/20100032922.pdf Fig.30: a proposed charge collector with an array of electron capture blades that can be raked through lunar soil to harvest electrostatic charge. Original source: https://ntrs. nasa.gov/api/citations/20100032922/ downloads/20100032922.pdf Fig.28: an electrodynamic tether deployed from a spacecraft. Original source: https://w.wiki/AUjv siliconchip.com.au Australia's electronics magazine September 2024  25 Fig.32: a BPW34 PiN photodiode can be used as a solar cell, producing up to 47µA at 350mV. The coin diameter is 24.26mm. Source: Core Electronics PRT-09541 – siliconchip.au/link/abxz Fig.33 (below): a wind turbine that can be used at a campsite. Source: Tex Energy – siliconchip.au/link/abxx Energy harvesting is not new In 1925, Estonian inventor Hermann Plauson obtained US Patent 1540998 for “Conversion of atmospheric electric energy”. He proposed harvesting atmospheric electricity with a network of balloons. H. Gernsback earlier described this idea in “Science and Invention”, February 1922 (siliconchip.au/link/abxg). It is unlikely this would have been practical. However, it was claimed in the description that a single balloon at 274m altitude could provide 400V at 1.8A, which certainly would be useful if attained! We suspect that it was under unusual atmospheric conditions and could not be achieved regularly. SmartDrive washing machine (similar to how we used one as a generator on a wind turbine in the December 2004 to March 2005 issues; siliconchip.au/ Series/84). The motor has to be rewired to reduce the voltage and increase the current, to make it more suitable for charging a battery bank. Details of motor rewiring are at siliconchip.au/ link/abxk (or refer to our articles), but many other resources explain how to do it. Also see this series of videos: 1. https://youtu.be/LVoeaKCEd2o 2. https://youtu.be/lbuvTSWh50U 3. https://youtu.be/8SWq5Pskpug A US YouTuber decided to see if he could make a hydroelectric system powered by rainwater collected on a roof. He calculated that 2W could be generated from rain falling on a house roof and going down the downpipes, but on his first attempt, he only got 0.19W. On his second attempt, he generated over 0.61W and, on the third attempt, over 0.91W. Of course, it has to be raining for this to work. In Australia, such a system might work best in the tropics, such as Far North Queensland. See the videos for more details: 1. https://youtu.be/S6oNxckjEiE 2. https://youtu.be/YLb4enCgnP4 3. https://youtu.be/vify0k2sHlQ Portable wind generators A wind generator can be used for bushwalking, provided it is anticipated there will be reasonable wind at the campsite. A model such as the Infinite Air 5T can produce up to 5V at 2A and weighs 1.65kg (Fig.33 shows the larger 3.2kg Infinite Air 18 model). As with the portable hydroelectric generator, we feel the weight is too high for most potential use cases. MEPAP The energy harvesting idea of Hermann Plauson. Source: www.reddit.com/r/Air_Fountain/comments/1cc3dx6/ 26 Silicon Chip Australia's electronics magazine The MEPAP (“Multipurpose and source Electricity Generator with Air Purifier”) is something Heath Robinson or Rube Goldberg might have dreamt up. It harvests electricity using vibration (piezoelectric materials), electromagnetic radiation (metamaterials), electromagnetic induction (inductive coupling), wind energy (mini turbine with dynamo) and thermoelectric energy, all to operate an air purifier device. It is described at siliconchip.au/ link/abxh, but we don’t know how well it works. SC siliconchip.com.au Be a happy camper. F I T O U T T H E C A R & C A R AVA N . N 1114A 100W SAVE $50 HALF PRICE! N 1117A 200W 449 SAVE $70 $ 299 579 $ M 8133 $ Robust, reliable & an amazing price too! 240V Mains Power - Anywhere, Anytime! Powerhouse® Inverter with in-built MPPT solar charge controller. Heavy Duty Solar Blankets Premium quality solar charging for your remote power system. Provide portable charging power for your campsite set up. Double stitched panels, durable webbing straps and metal hanging loops and zippered cable pocket. 200W version has folding legs which allow the panel to be used freestanding. 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Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Centre® © Altronics 2024. E&OE. Prices stated herein are only valid until 30/9/24 or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. Exteek C28 Bluetooth 5.0 Audio Transmitter/Receiver For only $10.99 (from eBay) or about $8 (AliExpress), this little device can act as either an audio transmitter or receiver. That means you can create a shortrange wireless audio link, convert a regular amplifier into a Bluetooth amplifier, use a CD player with Bluetooth headphones/earphones and more. AC7006F Features (taken from the data sheet) » CPU: 32-bit dual-issue DSP, up to 160MHz, single-precision FPU with CORDIC accelerator engine » SBC & AAC audio decoding supported » mSBC voice codec supports MP2, MP3, WMA, APE, FLAC, AAC, MP4, M4A, WAV, AIF and AIFC audio decoding » Packet Loss Concealment (PLC) for voice processing » Single/dual mic Environmental Noise Cancellation (ENC) » Multi-band DRC limiter » 20-band EQ configuration for voice effects » Stereo 24-bit DAC, SNR ≥ 102dB » Stereo 24-bit ADC, SNR ≥ 95dB » DAC sampling rates of 8kHz, 11.025kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz, 64kHz, 88.2kHz & 96kHz » ADC Sampling rates of 8kHz, 11.025kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz & 48kHz » Stereo microphone amplifier with built-in bias generator » Can drive 16Ω & 32Ω speakers Bluetooth » Compliant with Bluetooth V5.3+BR+EDR+BLE specification » Meets class 2 and class 3 transmitting power requirements » Supports GFSK and DQPSK for all packet types » Provides a maximum +10dbm transmitting power » EDR receiver with -94dBm sensitivity » Fast AGC for enhanced dynamic range » Supports A2DP 1.3.2, AVCTP 1.4, AVDTP 1.3, AVRCP 1.6.2, HFP 1.8, SPP 1.2, SMP, ATT, GAP, GATT, RFCOMM 1.1, SDP core 5.3, L2CAP core 5.3, PNP 1.3 & HID 1.1.1 Review by Allan Linton-Smith siliconchip.com.au Australia's electronics magazine T he device has an internal battery and comes in a neat package with a 3.5mm to 3.5mm jack, a charging cable and a user manual. It can be charged from any 5V USB source and lasts for around four hours of use (140mAh). The receiver will power a small speaker or headphones as long as the impedance is at least 16W. You can make your average analog headphones or earbuds into a Bluetooth model by plugging them into this. It has many other practical applications. For example, if your TV has a regular headphone output jack, you could plug this in, set it to transmit mode and watch TV using wireless Bluetooth earphones. Or if you have a regular analog amplifier or receiver, plug this in, set it to receive mode and stream music from your computer, smartphone or tablet. You could also use it to convert an Aux input on an older car to Bluetooth, so you can stream music from your phone (an application suggested by the seller). Its signal-to-noise ratio and handling of low-level signals are good enough that you could even consider using it to turn musical instruments like electric guitars, or even microphones, from wired devices into wireless. The microphone would need to be battery-powered to become truly wireless. The heart of this device is a BPOY120356F4 chip manufactured by Zhuhai Jieli Technology Co Ltd (JL), who describes it as an “AC7006F Bluetooth Audio Chipset”. Performance We tested the performance using a pair of these as a Bluetooth wireless audio bridge. That means the performance reflects both the inbuilt ADC (analog-to-digital converter) of the transmitter and the receiver’s DAC (digital-to-analog converter). Therefore, our measurements can be considered a ‘worst-case’, and you will likely get better results using the transmitter or receiver alone. These tests also take into account the quality of the Bluetooth link itself, although most of our tests involved a sinewave signal, which would be a best-case scenario for a digital compression scheme. The transmitter unit was connected September 2024  29 Fig.1: this spectral (FFT) plot of the receiver output shows the 1kHz peak from the signal being transmitted plus the noise and distortion harmonics at all other frequencies, which are reasonably low. It is not quite CD quality, but it is close, with a signal-to-noise ratio of 93.6dB. For comparison, a CD has a maximum dynamic range of 96dB. to the audio generator output of an Audio Precision analyser and then paired with the receiver, which was connected to the analyser’s analog input. Pairing between the devices was automatic and took only a few seconds. With this configuration, we analysed the frequency response, distortion (THD+N) vs frequency, THD+N vs input level and inter-channel crosstalk. We also measured the signal-tonoise ratio. To eliminate the 192kHz carrier of the Class-D amplifier in the receiver, we used an AP AUX-0025 ‘brick wall’ filter together with an S-AES17 low-pass filter. These are necessary to enable accurate measurements because the slew rate of the analyser input stage (which uses AD797 op amps) is too low to handle the digital carrier. The manufacturer data sheet recommends a minimum load impedance of 16W, so we added a 32W dummy resistive load across the output for all measurements to make them realistic. Signal-to-noise ratio We determined the signal-to-noise ratio by spectral analysis (FFT) of the receiver output, delivering a 1kHz sinewave – see Fig.1. The noise spectrum is fairly low. The resulting signalto-noise ratio is 93.6dB, which falls short of perfection (we would prefer to get closer to 100dB), but it is suitable for most domestic uses. It is not far off from the best dynamic range you can get from a CD, which is around 96dB. Remember that this measurement includes the noise contributions of both the transmitter and the receiver. Frequency response Fig.2: the frequency response between the C28 transmitter and receiver was surprisingly good, having only a slight 2dB fall-off at the low end. The dip at the upper end (above 15kHz) is just an artefact of the brick wall filtering used to remove the residual high-frequency carrier. With the transmitter and receiver one metre apart, I injected a swept frequency signal into the transmitter at 500mV RMS. Because the signal is delayed slightly between being fed to the transmitter and coming out of the receiver, I had to delay analyser measurements by 500ms to ensure accuracy. Fig.2 shows the resulting frequency response plot. It is pretty good, with a slight roll-off below 100Hz, resulting in a response that is down by 2dB by 20Hz. The 0.5dB dip at the high end is just an artefact of the ‘brick wall’ filter. The result was better than expected, especially compared to older AV Australia's electronics magazine siliconchip.com.au 30 Silicon Chip transmitters/receivers we have tested previously. Total Harmonic Distortion The THD+N measurements gave fairly reasonable results of around 0.04-0.05% across the audio band. This is a combination of the distortion of the transmitter’s ADC, the receiver’s DAC, and the audio power amplifier in the receiver. Therefore, the distortion from either the transmitter or receiver would be lower. THD+N is usually measured with 80kHz bandwidth, but that is not possible with a brick wall filter as it will filter out any harmonics above 20kHz anyway. Given how flat the THD+N vs frequency plot (Fig.3) is, we don’t think it would make much difference. We also measured the THD+N against the input signal level (Fig.4), with the 1kHz signal fed to the transmitter swept from 1mV to 2V. It also turned out to be pretty flat at around 0.02-0.08% THD+N. We think this is due to the Class-D amplifier; it must introduce a non-linearity into the output signal that manifests as a floor on the distortion level. The receiver started to clip at around 900mV. Still, the distortion was reasonably good even at low input levels, again suggesting that this unit is suitable for microphone or musical instrument applications. It would be possible to use this with a record player (phono signal). However, you would be better off passing that signal through an RIAA preamplifier before feeding it to the transmitter. Fig.3: this plot of THD+N for the left and right channels with the signal frequency swept is the total distortion generated by the transmitter and receiver. This distortion level provides generally acceptable sound quality for domestic purposes. Availability We purchased our test units from eBay, via the link below, but the same ones appear to also be available from AliExpress at a slightly lower price: • eBay 133868488058 (siliconchip. au/link/abtn). • AliExpress 1005005459972095 (siliconchip.au/link/abto). Conclusion Compared to tests I have conducted on similar devices, this Bluetooth transmitter/receiver is excellent value for money, with reasonably low distortion and noise. It is not perfect, but you would need to pay significantly more to improve the quality even slightly. The inclusion of an internal battery and output amplifier makes it very versatile. SC siliconchip.com.au Fig.4: THD+N with a 1kHz signal of varying amplitude. The signal starts to clip at around 900mV, but the distortion is good at low input levels, making it suitable for microphone or guitar applications. Australia's electronics magazine September 2024  31 PROJECT BY TIM BLYTHMAN This handy, portable, rechargeable device combines a clock, timer and stopwatch and can display different time zones. It has an internal crystal and incorporates a WiFi time source, so it is always accurate, even if a leap second occurs. COMPACT OLED CLOCK/TIMER Y OU MIGHT THINK THAT WHAT THIS CLOCK/TIMER does could easily be done by an app on a smartphone, and you are probably right. The March 2018 Editorial Viewpoint (siliconchip. au/Article/10990) discusses how so many projects could be ‘just an app’. However, there is a good reason to make the Clock/Timer a separate device. My wife runs a business where she needs to keep track of time spent with clients. Using a phone app to do that tends to drain the phone’s battery and makes it difficult to use the phone for other purposes. So, a separate device that can keep track of time has its place. The Compact OLED Clock and Timer also makes it easier to keep track of time in different time zones. This is another handy feature if you arrange appointment times with people in different locations. It has an alarm feature that is tied to a ‘home’ timezone. This means that if you are travelling, you can be alerted each day at the same time in that zone, even if you are using the Clock to see the local time in a different time zone. This feature is notably absent from most clock apps. There are countdown timer and stopwatch functions that can work in the background. For example, you can set the countdown timer running and then switch to the clock or stopwatch. The timer will still alert you when it is finished. Internally, time is kept by a watch crystal. An integrated WiFi time source is also used to keep the time updated OLED Clock & Timer Features & Specifications » » » » » » » » » » » » 32 Clock with multiple time zones Automatic daylight saving adjustments Alarm with day and repeat options Countdown timer up to 99 hours Stopwatch up to 99 hours Rechargeable 600mAh battery Battery charging and status display OLED screen with adaptive brightness Resolution: one second Crystal timekeeping backed by integrated WiFi time source Current draw: 15-20mA during operation, 5mA with screen off Current draw during WiFi operation: up to 80mA (typically for 30s per day) Silicon Chip Australia's electronics magazine and trim out any crystal errors. Time is kept to the nearest second, so you should never be more than a few seconds out. Compact case Readers who remember the Pico Audio Analyser project from November 2023 (siliconchip.au/Article/16011) will see that the Clock bears a striking similarity. It uses the same case, a UB5 Jiffy box, and the same user interface with a small OLED screen and four pushbuttons. We think this size and shape work well for a clock. The box can sit on its edge with the display clearly visible, but it is also unobtrusive. While the form factor is similar, this design uses a different processor from the Pico Audio Analyser, and the circuitry is quite different. Circuit details The complete circuit diagram of the Clock/Timer is shown in Fig.1. Instead of a Pico microcontroller board, it is controlled by a PIC16F18146 microcontroller (IC1). Since this IC is capable of low-current operation, we can dispense with the complexity of providing an on/off switch. Microcontroller IC1, in combination with 32768Hz crystal and its two 4.7pF load capacitors, is responsible for timekeeping. IC1’s oscillator can remain operating even when it is in deep sleep power-saving mode so that siliconchip.com.au Fig.1: microcontroller IC1 keeps time with crystal X1 and displays it on OLED screen MOD1 by updating it over an I2C serial bus. IC1 can also control the power supply to all other components, keeping the idle current low. The battery is kept charged by IC2, which also drives LED1 to display the charge status. it continues to keep track of the passage of time. IC1 also drives OLED screen MOD1 via an I2C serial bus to update the display. The display’s power supply comes from digital output RB4 of IC1 (pin 13), so it is powered down when not in use by pulling that pin low or powered by bringing it high. The I2C bus pullup resistors are on MOD1; IC1 uses ‘bit-banging’ to drive SDA and SCL since high-speed data transmission is not required. MOD2 is a Raspberry Pi Pico W board programmed as a WiFi time source with an NMEA output compatible with GPS modules. We previously described how that works (June 2023; siliconchip.au/Article/15823). Important to the operation of the circuit is that the Pico W has a schottky diode between its VBUS pin, pin 40 (anode) and its VSYS pin, pin 39 (cathode). This diode feeds microcontroller siliconchip.com.au IC1 when USB power is available since it will supply a higher voltage than the battery via schottky diode D1. This arrangement removes the load from the battery while it is charging, allowing it to charge fully. The remainder of IC1’s various I/O pins manage the clock functions and user interface. A 10kW resistor pulls up IC1’s reset pin 4 to allow normal operation, except when a programmer is connected at optional ICSP (in-circuit serial programming) header CON2. Four tactile pushbuttons, S1-S4, connect to pins 8, 16, 12 and 11 of IC1. These pins are set to have internal pullup currents, so the closure of the pushbuttons can be detected when the pin is pulled to ground. Pin 17 is connected to piezo transducer SPK1 to create alarm sounds. Pin 13 of IC1 also powers a divider formed by the 1MW resistor and LDR1. The 100nF capacitor smooths the resultant voltage and provides a Australia's electronics magazine low-impedance input to IC1’s ADC (analog-to-digital converter), sampled at pin 10 to measure the ambient light level. Pin 9 connects to the 3V_EN pin of MOD2. When this is pulled low by IC1, the 3.3V regulator on the Pico W is disabled and MOD2 is shut down. If it is allowed to float, it is weakly pulled up by the Pico W so it can operate. IC1 can thus choose to enable the time source only when needed. The NMEA data stream from pin 1 on MOD2 is fed to pin 5 of IC1 via a 10kW resistor. Software running on IC1 decodes this data, including the time the time source has obtained via NTP. By comparing an internal 2.048V reference to its supply voltage, IC1 can also monitor the battery level or note that USB power is being supplied. IC1 can shut down all of the surrounding circuitry by bringing its pins 9 and 13 low. The normal operating current draw is dominated by September 2024  33 Screen 1: the initial screen; if you see the “NO DATA” message for more than a few seconds, check that the WiFi time source’s LED is on or flashing. Once the time has been acquired, check that IC1 has shut it down. The battery life will be severely affected if the Pico W does not shut down. Screen 2: this will briefly appear to show that the time has been updated. The Clock/Timer can be powered from the Pico W’s USB socket, allowing you also to use the time source’s USB interface for debugging. The 5V lines of the sockets are joined, so don’t plug into both simultaneously. Screen 3: the Clock mode display. The default time zone is Sydney (the same as Melbourne, Canberra and Hobart). To access the settings, press and hold the MODE button until SETTINGS appears on the screen. All settings are kept in EEPROM and generally take effect immediately. the OLED module, except for the brief periods when MOD2 is enabled. Mini Type-B USB socket CON1 provides 5V power to the circuit. It goes directly to IC2, an MCP73831 Li-ion battery charging IC. 10μF bypass/filter capacitors are provided for its input and output, while the 10kW resistor on its PROG pin sets the battery charge current to 100mA. The battery is connected to the BAT+ and BAT− pads. IC2 also provides a status indication at its STAT pin. Bicolour LED1 connects between the STAT pin and a pair of 1kW resistors between the 5V rail and ground. The STAT pin is low during charging and the red LED is driven. When charging is complete, the STAT pin goes high, allowing the green LED to light. When 5V power is unavailable, the STAT pin is high-impedance and LED1 does not light. The power from the battery feeds IC1 via schottky diode D1. IC1 is powered at pins 1 and 20, with the standard 100nF bypass capacitor across them. copper layer and solder mask to create an outline resembling a battery icon. Unlike the Analyser, we have designed the front panel PCB to sit over the edge of the enclosure rather than recess into it. This makes the Clock slightly deeper, giving more room for the battery and other components. While we generally use USB-C sockets for power these days, we have stuck with a mini Type-B USB socket here to save a little more space; the USB-C sockets require two extra resistors to communicate the role of the device. The various headers connect via surface-­ m ounting pads, allowing wires to connect to devices in the space behind the PCB. The battery and speaker are both on flying leads to allow this. Parts List – OLED Clock and Timer We’ve crammed an awful lot into a small enclosure, so we’ve opted for some creative assembly options. Readers familiar with the Pico Audio Analyser will recall the arrangement of the pushbuttons and OLED display, which are reverse-mounted to protrude or show through the PCB that also forms the enclosure’s front panel. The LDR peeks through a hole in the front of the case too, while the LED shines through the PCB substrate from the back of the panel. We’ve used the 1 double-sided PCB coded 19101231, 83 × 53mm 1 UB5 Jiffy box (83 × 53 × 30mm) – translucent blue recommended 1 single AA cell holder with flying leads 1 14500 (AA-sized) Li-ion rechargeable cell with nipple (LiFePO4 type recommended) 1 1.3-inch (33mm) OLED module (MOD1) [Silicon Chip SC5026 or SC6511] 1 Raspberry Pi Pico W programmed as WiFi Time Source for GPS Clocks (MOD2) [Firmware: siliconchip.com.au/Shop/6/188] 4 reverse-mount SMD tactile switches (S1-S4) [Adafruit 5410] 1 SMD mini-USB socket (CON1) 1 5-pin male header, 2.54mm pitch (CON2; optional, for ICSP) 2 4-pin male headers, 2.54mm pitch (for MOD2) 1 single-pin header (for MOD2) 1 100kW (light) to 10MW (dark) 5mm LDR (LDR1) [Jaycar RD3480] 1 32768Hz watch crystal (X1) 1 passive piezo element (SPK1) [Digi-Key 433-PT-1306T-ND] 1 small tube of neutral-cure silicone sealant or similar 4 small self-adhesive rubber feet (optional) Semiconductors 1 PIC16F18146-I/SO microcontroller programmed with 1910123A.HEX, SOIC-20 (IC1) 1 MCP73831-2ACI/OT Lithium battery charge regulator, SOT-23-5 (IC2) 1 SS34 40V 3A schottky diode, DO-214 (D1) 1 bi-colour red/green 3mm LED (LED1) Capacitors (all M3216/1206 size, X7R ceramic unless noted) 2 10μF 2 100nF 2 4.7pF C0G (to suit crystal X1) Resistors (all M3216/1206 size, 1% ⅛W) 1 1MW 3 10kW 2 1kW 34 Short-form kit (SC6979; $45): includes all parts except the case & Li-ion cell PCB arrangement Silicon Chip Screen 4: the OK button will cycle through the available fonts used for all large time displays. The UP and DOWN buttons trim the horizontal position of the display. Adjust the position until the box characters in both lower corners look the same as the one between the arrows. Screen 5: MODE cycles between the SETTINGS pages. GPS refers to the time source; its maximum runtime can be set on this page. You can manually trigger a time update with the OK button. The TRIM value is zero initially but will update as the timekeeping is adjusted daily. Screen 6: test tones are played while this screen is showing. Press OK to toggle between the alarm clock tone and the countdown tone, then use the UP and DOWN buttons to choose which tone to use for each. If you don’t hear a tone, there may be a problem with your piezo speaker. The Pico W only needs connections on a handful of its pins; it is mounted behind the OLED module. The design of the time source puts all of its active pins at one end, which helps everything fit into the case. reprogramming the Pico W or changing the WiFi time source settings. With a small amount of flash memory spare in the chip, we have added alternative fonts to provide some novelty to the main timekeeping display. There are also six different alarm tones, so you can choose your preferred alert sounds for the clock alarm and countdown timer. These sounds are provided by combining a PWM signal with a UART (serial data) signal through the CLC peripheral. The rise and fall of the serial data modulates the signal, giving different tone patterns. Once the pattern is activated, it plays with no further processor input. The details of the software operation and user interfaces will be discussed later. you have the right gear. Our PIC Programming Adaptor from September 2023 (siliconchip.au/Article/15943) has examples of SMD-to-DIP adaptors that can be used to do this. Otherwise, you will have to make a temporary connection to the CON2 ICSP header after the chip is installed. You can see a header in some of our photos; this is what we fitted to CON2 to help with repeated programming during software development. Programming the Pico W module can be easily done before or after soldering it. Simply connect it to a computer using a standard USB cable. See the panel on setting up the WiFi time source for more details. Software The watch crystal is used by a timer on IC1 to generate an interrupt once every second, making accurate timekeeping a priority. Every second, the clock is advanced; if the timer or stopwatch is active, they are also updated. It keeps track of time internally as UTC (universal coordinated time) and calculates offsets based on the time zone and daylight saving status. All the Australian and New Zealand time zones are inbuilt; it also has a custom timezone that can be set to any time zone that is a multiple of 15 minutes from UTC (we aren’t aware of any that are not). The clock can display the current time in any of the time zones by selecting them. A ‘home time zone’ is selected, which is used to check the alarm. Every 24 hours, the WiFi time source is activated and the time is checked and updated (if necessary). The Clock/Timer also checks how much drift has occurred and provides an internal correction for up to 24 seconds of drift per day. Watch crystals are typically well within that tolerance. The WiFi time source can also be manually activated. A switch in the settings menu allows the Pico W that acts as the WiFi time source to be powered up. This can be handy for siliconchip.com.au Programming the chips If your PIC16 microcontroller (IC1) is not programmed, you might find it easier to do it before soldering the chip to the board if Construction The Clock/Timer is built on a double-­ sided PCB coded 19101231 that measures 83 × 53mm. The design necessitates surface-mount construction, so you will need the usual surface-­mount gear such as a fine-tipped soldering iron (a medium tip can be The SMD parts are fitted conventionally, although we recommend splaying the leads of S1-S4 so their stems project more through the panel. Note how we’ve fitted leaded parts like the crystal, LDR and LED. At this stage, the board can be powered from CON1 and (with IC1 programmed) you can confirm that the OLED and pushbuttons work. Australia's electronics magazine September 2024  35 Screen 7: the alarm clock is always based on the HOME timezone, which can be set here. Pressing OK also allows you to set the parameters for a custom time zone, including the default offset and when daylight saving starts and ends. This defaults to Greenwich Mean Time (GMT). Screen 8: the last SETTINGS screen lets you return to regular operation and manually power the time source on and off with the UP and DOWN buttons. This is handy if you ever need to change the settings on the time source or update its firmware. It switches off when you exit SETTINGS. Screen 9: this shows an alternative font. The available time zones can be viewed by pressing the UP and DOWN buttons while the clock is showing. Pressing OK toggles between a 12hour (AM and PM) or 24-hour clock. AM is shown by the letter A, PM by P and 24-hour mode with no letter. Fig.2: the PCB is populated mainly with surface-mounting components, plus a handful of through-hole parts fitted in surface-mounting fashion. This figure is shown at 140% of actual size for clarity. OK if you have some experience), flux paste, solder-wicking braid, tweezers, a magnifier and a good light source. You should have some sort of fume extraction gear; a fan close to your workspace pointing out an open window may be sufficient. You could also work outside or right next to an open window, which might also help with illumination. Note that some through-hole components are fitted in a surface-mounting fashion. You can get an idea of how these are installed by examining Fig.2, the PCB component overlay diagram, and the photos of the partially and fully populated PCB. Start by soldering IC1 and IC2. IC1 must have its pin 1 marker aligned with that on the silkscreen, while IC2 will only fit one way as it has two pins on one edge and three on the other. Apply flux to the PCB pads and rest the chips in place. Tack one lead on each and check that the pins are aligned with the pads before soldering the others. If solder bridges form across any pin pairs, apply more flux and use the braid to draw out the excess. Fit CON1 next. It has plastic locating lugs on its underside, making it easy to position. Solder the smaller pins and confirm that the part is flat against the PCB, then secure the larger pins with a generous amount of solder to ensure that the connector is firmly attached. There are three different capacitor values (two of each), so do not mix them up, as they will not be marked with their values. Like the other parts, Australia's electronics magazine siliconchip.com.au 36 Silicon Chip Screen 10: the alarm symbol in the upper-right corner flashes while the alarm is sounding. Pressing OK stops the alarm. The top of the screen shows the battery status (voltage) display if USB power is not available. During a WiFi time source update, this will show “GPS”. Screen 11: pressing MODE switches to the Countdown Timer; you can then press OK until the SET screens appear. The UP and DOWN buttons on these screens change the clock’s hours, minutes and seconds. The TIMER PAUSED status is shown when the timer is ready to start counting down. Screen 12: pressing OK after setting the countdown time returns to the main Timer screen. Pressing UP will start (or resume) the Timer or pause it if it is running. DOWN will reset the Timer if it is paused or has expired. This screen shows the third font that’s available (refer to Screen 4). use some flux and tack one lead in place. Confirm that the position is correct and that the first joint has solidified before soldering the other lead. Refresh the first lead if necessary (eg, with a touch of flux paste). Follow by fitting the resistors similarly, then move on to D1, the schottky diode. Ensure that its cathode stripe is towards the K marking before soldering it. If this diode is reversed, power from the USB socket could feed directly into the battery, which would be catastrophic! Next, mount the three through-hole components. Keep the lead offcuts from these, as they can be used to mount the OLED module later. Look closely at the photos since they are all arranged in a specific way. Crystal X1 is fitted so that it can be glued against IC1 later. It is not polarised, so it does not matter which lead goes to which pad. Splay the leads slightly to suit the pad spacing and bend them in an arc. They might also have to be trimmed. Once you have the leads adjusted, solder one to its pad, then tweak the leads if necessary before soldering the other lead. For LDR1, trim one lead to around 5mm and bend it in a 180° arc. You can leave the other lead at its full length to ease handling. Press the LDR into the hole and tack the short lead in place. Adjust the position and orientation, if necessary, with the aim of having the front of the LDR flush with the outside of the PCB. Then cut down the other lead and bend it into position over the other pad. Solder the second lead and refresh the first if necessary. LED1 is a bit more tricky. The K cathode marking refers to the green LED of the bicolour device. So it’s best to test the LED as some are marked (with the flat or longer lead) with reference to the red LED instead. Set a DMM on diode test mode and probe the leads. The red probe will indicate the anode of whichever colour LED lights up, and the black lead (cathode). Bend the leads in the shape shown in the photos so that they reach the pads below. We’ve left quite a bit of lead on our prototype to make it easier to position and aim the LED so it shines towards the cutout in the solder mask on the back of the PCB. The finished board, ready to be mounted in the case. The Pico W for the WiFi time source is mounted over the back of the OLED screen while silicone sealant secures the battery leads. We attached our piezo with header pins, but you can use flying leads. We inserted standard headers from the top of the Pico W’s PCB so it would sit at the right height. Note the single-pin header on the right to add some mechanical strength. There is about 2mm between the Pico W and the OLED module underneath it. siliconchip.com.au Australia's electronics magazine September 2024  37 Screen 13: when the Timer finishes, you will see the hourglass symbol flashing in the corner of the display and hear the Timer tone. Press DOWN to stop the alert and reset the Timer. The Alarm and Timer icons and tones will occur in any operating mode except possibly SETTINGS. Screen 14: the Stopwatch is much simpler than the other modes. It is started, resumed or paused by pressing the UP button and can be reset while paused with the DOWN button. The timings are only updated every second by the timer interrupt. Screen 15: pressing MODE takes you to the Alarm clock setup. Press OK to cycle between the options, with UP increasing or enabling the setting and DOWN decreasing or disabling it. You can set the time to the nearest minute, choose days of the week, whether the alarm repeats and whether it is on. Cleanup doing this, ensure the OLED is square and symmetrical within the cutout. At this stage, the assembly should look like the earlier partially completed PCB photo. The circuit is complete enough to do a basic test. If you still need to program IC1, do so before proceeding. It is safe to apply power to the circuit via the programming header, CON2. Alternatively, you can apply power to the board by plugging a USB cable into CON1. The OLED should light up, and the LED will probably show both red and green because no battery is attached. Check the voltage on the BAT+ terminal relative to BAT− (which is also circuit ground). It should be no more than 4.3V. If there are any problems, verify that diode D1 is correctly orientated. The display will show a countdown from 60 seconds. If the countdown is not proceeding, there may be a problem with crystal X1. a sharp hobby knife to trim the hole to fit the USB socket comfortably. Check that no parts prevent the PCB from sitting flush against the case. We’ve squeezed everything in tightly, but nothing should stop the case from closing. If you have soldered a header to the CON2 ICSP pads, that could clash with the pillar inside the case. We found that trimming the plastic on the header was enough to prevent that, but you might consider removing the header if you only fitted it for programming IC1 initially. Now is a good time to clean off any flux residue and closely inspect the board before proceeding to the next step. Use your flux’s recommended solvent or some isopropyl alcohol to dissolve the flux and then allow the board to dry thoroughly. Scrutinise the board with a magnifier to double-check that everything is soldered correctly and that there are no bridges. IC2 and CON1 have closely spaced pins, so look at them carefully. Next, fit tactile switches S1-S4. The reverse mounting types are pretty nifty, but they will benefit from having their leads splayed back slightly to give the switch stems a bit more length projecting through the front of the PCB. Tack one lead on each switch in place and tweak the position so that they are centred in their holes. It’s worth spending some time getting this right, as it looks much better with the stems centred. It also eliminates the possibility of the stems binding. When you are happy, use a generous amount of solder to mechanically secure all four leads on each switch. The next job is fitting OLED module MOD1. Attach a lead offcut to each of the four small PCB pads for MOD1, then thread the OLED over them, ensuring that the protective film is removed and the module is flat against the main PCB. Solder the offcuts to the main PCB. The two large holes along the lower edge can be similarly attached to the large pads on the PCB below. Before 38 Silicon Chip Setting it up If you haven’t already done so, prepare the WiFi time source according to the instructions in the panel opposite. It’s possible to program a Pico W in place or even modify its settings, but this is done more easily before it is attached to the PCB. Male header strips are used to solder Case cutting The only necessary hole in the case is to allow the USB socket, CON1, to protrude out the side. Fig.3 shows the measurements, but this one is relatively easy to do by eye, especially if you use a transparent case like ours. Rest the PCB just inside the case with the USB socket against the wall of the case. You should be able to mark the outline of the socket using a pencil or similar. Perform the downward cuts most of the way and then carefully flex the tab formed by the cuts. You can then use Australia's electronics magazine Fig.3: it is easy to cut out the small rectangular region for the USB socket by eye, allowing you to make it a snug fit. Here are the suggested dimensions of the cut if you wish to measure it out first (viewed from outside the box). All dimensions are in millimetres. siliconchip.com.au the Pico W to the PCB. Locating it behind the OLED module is the only way to get enough clearance to also fit the battery inside the enclosure. The bottom of the Pico W should be about 5mm above the PCB, leaving about a 2mm gap between the OLED module and the Pico W. We achieved the correct height on our prototype by soldering the pin headers with the plastic shrouds above the Pico W’s PCB. You can see the remnants of the shrouds in the photos (we trimmed off the tops of the pins). Solder the two rows of four-pin headers to the USB end of the Pico W, keeping the pins square. Check that your positioning allows enough space to plug a USB cable into the Pico W; the cable’s bezel should just clear the CON1 USB socket on the main PCB. Solder the tips of one of the pin headers to the main PCB and check that everything is aligned. Next, solder the single-pin header from pin 20 of the Pico W to the main PCB. There is a pad for this adjacent to D1. When everything looks correct, you can proceed to add a fillet of solder from each of the Pico W pins back to the main PCB, securing it. Trim any excess height from the pins to give the battery as much clearance as possible. Solder the battery holder to its terminals marked BAT+ and BAT−, taking great care that the polarity is correct. The way we installed the battery holder in the case allowed us to shorten the red (BAT+) wire. Also solder the piezo element to the SPK1 pads. We used header pins, but you could use flying leads (such as offcuts from the battery leads) to allow the piezo to be glued to the case. In that case, we also recommend drilling a hole in the case to enable the sound to escape. Now glue the battery holder into the case as shown in the photos. Also apply neutral-cure silicone sealant to the BAT+ and BAT− terminals to insulate the pads and secure the wires mechanically. If you have the piezo on flying leads, glue it to the case now. You can also add a dab of glue to the crystal to secure it to the top of IC1. After that, wait for all the adhesive to cure fully. Now insert the battery into the holder. The screen should light up, and you should see the LED on the siliconchip.com.au Setting up the WiFi time source The June 2023 project article for the WiFi Time Source for GPS Clocks (siliconchip.au/ Article/15823) details how the time source works, but this overview should have enough information for you to set it up. You will need a Raspberry Pi Pico W microcontroller board programmed with the time source firmware, which can be downloaded from siliconchip.au/Shop/6/188 Hold the white BOOTSEL button of the Pico W while connecting it to a computer. This will put it into bootloader mode, and you should see a drive named “RPI-RP2” appear. Copy the “NEW_CLAYTONS_1.uf2” file to that drive to upload the firmware. If all is well, the LED on the Pico W should light up, the drive should disappear, and you will have a virtual USB serial port available. Use a serial terminal program like Tera­ Term on Windows to connect to the port (you could use minicom on Linux). Set the terminal to use CR or CR+LF as the line ending and press Enter. It should then show the status and command menu. The following is not a comprehensive overview of the time source’s capabilities, but it will be sufficient to program it for use with the Clock/Timer. Use command 9 (press the 9 key followed by Enter) and then enter the two-letter country code (eg AU, NZ, US, UK etc). If you are likely to use the Clock internationally, the global “XX” setting is safest. Next, use command 8 (8, Enter) to save that setting to flash and follow with command J (capital J, Enter) to reboot the time source. This ensures the WiFi radio is initialised with the correct country code at power-up. Use command 1 to run a scan of WiFi networks. The nearby networks should be listed with a number next to each one. Then run command 4 with one of the listed numbers as a parameter. For example, if your home WiFi network is listed first, as number 0, type 40, then Enter. You will then be prompted for the password; type it, then press Enter again. Use command 7 to test the network and, if all is well, use command 8 to save the settings to flash memory. Use J to reboot again and check that the time source connects to the network. The LED should change from solid to flashing when it successfully connects to a network. Flashes occur in groups of three if everything is working and the time has been acquired from the NTP service. You can add multiple networks by running commands 1, 4, 7 and 8 when in the vicinity of each network. If you see groups of three flashes, the time source is working as expected. If you run into problems, you can also examine the output and debugging data to determine the source of the problem. Many other settings are available, but there is little need to change any of them. The Compact Timer has been designed to work with the WiFi time source’s default configuration. With the important pins at one end of the Pico W, near the USB connector, it’s easy to connect to the Clock/Timer PCB without using up much space. Pins 1, 3, 37, 38, 39 and 40 are used in the circuit, while pins 2, 4 and 20 are also connected to add mechanical stability. Australia's electronics magazine September 2024  39 Pico W come on after a second. Carefully fit the PCB into the case, being careful not to pinch any wires. Attach the rubber feet to the bottom edge of the box to complete the assembly. Now is a good time to plug in a USB cable to charge the battery fully. Setup and usage The Compact OLED Clock & Timer mounts in the smallest Jiffy box, UB5 size. We have chosen an all-blue colour scheme. The controls are simple and, once configured, it will always keep time to within a few seconds. The Clock/Timer is shown in its lowest power mode – use the MODE button to switch to the Clock display, then hold the OK button until this screen appears. It will wake when the OK button is pressed again, if an alarm occurs or the countdown timer expires. The Clock/Timer will attempt to set the time via NTP when powered on, so allow that to happen. We’ve included several screenshots of the Clock and Timer in various states. Refer to those screen captions for the basics of setting up and using it, in the order shown. The low power mode (with the screen off) can be activated by holding the OK button in the Clock Mode. When the SLEEPING message appears, release the button. Pressing OK again will reactivate the display. The alarm and timer will also reactivate the display when they sound their respective alert tones. If both alerts are active, their tones and icons will alternate. The software is set to perform several actions at five minutes past the hour (relative to UTC). This is when the clock trimming will occur if you wish to observe it. The automatic time updates occur at five minutes past UTC midnight. That will be, for example, 10:05am in Sydney or 11:05am during daylight saving time. The crystal trimming routine needs two synchronisations before it will make adjustments, so you might have to wait a day or two before the trimming settles. Once that has occurred, the clock should always be within two seconds of the correct time. Operation of the LDR and OLED brightness is fully automatic. Small adjustments are made so that the changing brightness is not noticeable; it can take up to a minute to settle after a change in ambient lighting. If you find the OLED is too bright, try decreasing the value of the 1MW resistor in series with the LDR. Summary The LED and LDR are standard through-hole parts that have been surfacemounted to avoid solder joints on the front of the PCB (see Fig.2). We have also splayed out the leads of the switches to bring them closer to the PCB. 40 Silicon Chip Australia's electronics magazine The Compact OLED Clock and Timer is a portable and easy-to-use device that boasts features that even some clock apps do not. Once set up, it will maintain time within a few seconds as long as it can connect to a WiFi network daily. 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Unfortunately, we are being impacted by supply chain hiccups which may result in some of these Special Offers not being available in-store on the date advertised. We are working hard to get them to you as soon as possible and appreciate your patience. Springtime Making FREE Make with these Tools & Soldering Essentials ONLY 6595 BUTANE GAS $ 150G NA1020 Valued at $8.95 NOW 6995 $ GREAT FOR GENERAL HEATING, DRYING, MELTING, CUTTING, SOLDERING, HEATSHRINKING Mini Gas Soldering Tool Set A handy gas soldering iron with flame or flameless heat blower function. TH1606 SAVE $18 240V 48W Soldering Station Lightweight. Anti-slip grip. 150- 450°C adjustable temp. Mains powered. TS1620 NS3016 FREE FROM $ SOLDER WIRE 15G TUBE NS3008 Valued at $4.55 $ PERFECT KIT FOR BEGINNERS 95 . Soldering Iron Starter Kit Includes 240V 20/130W iron, spare tip, stand, solder & metal solder sucker. TS1651 ONLY 36 $ $ . 95 . BUILT-IN LED LIGHT 49 95 . SAVE 10% . 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TH1848 SALE ENDS SUNDAY 18.09.2024 Scan QR Code for your nearest store & opening hours 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE Rhodes Corporate Park, Building F, Suite 1.01 1 Homebush Bay Drive, Rhodes NSW 2138 Ph: (02) 8832 3100 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au 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. Dashcam power control This power control circuit fulfills the need to switch 12V vehicle power on/off to a dashcam when an ‘accessory’ feed is not readily available. The circuit works by detecting the battery voltage to determine the engine state. The standby (quiescent) current drain is ~250μA when the engine is off. Finding a cable route for switched (accessory) power from the dash to the top of the windscreen was problematic in my car due to airbags behind the windscreen pillar trims. Wires pushed behind the pillar trim could tangle with the airbags during deployment or jam the trim, potentially interfering with the airbags. However, there was a convenient non-switched battery line in the roof cabin light. My solution was to design a low-power circuit that operates from the battery line in the cabin light. It only switches power on to the dashcam when the engine is running. The circuit could be used for powering other devices where an accessory feed is not readily available, eg, in the boot, or even as a low-voltage cutout. It determines if the engine is on or off by measuring the battery voltage. When the voltage is below about 12.9V, it is assumed the engine is not running because the alternator is not charging the battery; hence, the power to the dashcam is switched off. When the battery voltage is above 13.4V, it is assumed the engine is running and the power to the dashcam is switched on. Note that this arrangement is not suitable for cars that do not continuously charge the battery. siliconchip.com.au These voltage thresholds provide hysteresis & trigger points and are software adjustable. Software filters and delays are also programmed to ignore short voltage drops due to switching transients (eg, lights or air conditioning) and longer engine cranking. The microcontroller achieves very low power consumption by going into deep sleep for one second. It will then wake up and measure the battery voltage, taking around 3ms. If the voltage is below the threshold (eg, 12.9V), the microcontroller returns to deep sleep for another second. This lowers the average consumption to 0.3% of the micro’s normal operating current. As a result, the average ‘sleep’ (off) current is dominated by the quiescent current of regulator REG1 and the voltage divider for monitoring the battery. The source code has comments to explain its operation. All voltage and timer values are set in the source code. Due to the use of deep sleep mode, it is advisable to use the “Hard-reset” procedure to reprogram the PICAXE, as per the PICAXE manual, section 1. The battery input is fed via a 1.5A fuse to the regulator for the microcontroller power supply (REG1), the load (dashcam) and the 47kW/22kW voltage divider, which reduces the battery voltage to a level suitable for measuring by microcontroller IC1. Zener diode ZD2 protects the microcontroller’s analog input pin P4. The microcontroller power supply uses a very low quiescent current linear regulator (MCP1703), which has an input limit of 16V. This is borderline for a nominal 12V system. Hence, REG1’s input is limited to 15V by zener diode ZD1 and a 100W series resistor. REG1 is available in SMD (SOT-23) and through-hole (TO-92) packages. The microcontroller used is a PICAXE-08M2, which has a deep sleep (Nap) mode. It would be possible to use an ATtiny85 with the same deep sleep strategy, but the software would need to be rewritten. The microcontroller measures the voltage at pin 3 (analog input P4), which is proportional to the battery voltage, and generates an output on pin 6 (digital output P1). The latter drives NPN transistor Q1 via a 3.3kW current-limiting resistor. A 10kW pulldown resistor ensures that Q1 is off when the IC1 is in deep sleep. Q1 drives the gate of P-channel Mosfet Q2, which in turn applies power to the load (dashcam). When IC1 is in deep sleep, its output is off (0V), so Q1 is also off and the 10kW pull-up resistor holds Q2 off. When IC1 switches its output on (to 5V), Q1 is biased on and pulls the gate of Q2 to ground (0V), switching Q2 on and applying 12V to load. This switching arrangement is designed to avoid pull-up resistors that would draw current when in sleep mode. Q2 is amply rated for driving various loads besides a dashcam, but some modifications may be required (eg, changing the fuse) if the load will draw more than 1A. You can download the PCB design, along with the software for this project from: siliconchip.au/Shop/6/474 George Mackiewicz, Vermont, Vic. ($80) Electronically-controlled ball maze game This puzzle involves controlling a metal ball through a labyrinth so that the ball reaches the finish point. Many of you will have seen the manually-­ controlled version of this game, using knobs and strings. In this version, you move the maze swivel base using a joystick controlling two micro servo motors. The course is split into six stages of similar distance, each with a proximity sensor registering the time taken to reach it. If the time taken to finish a stage is less than any previously achieved saved time, the LCD will confirm this as a ** NEW RECORD ** and save it so that only the best times are always visible when requested. When powered up, the table will automatically tilt so the ball can be placed safely in the START area. You will have the option to view top scores or play. The table is made level and control is passed to the joystick if play is selected. If the ball is lost, the computer will ask whether to start a new game. The most complex part of building the maze is making the plywood tilting maze board. The full instructions for doing that are part of the download from siliconchip.com.au/Shop/6/482 The maze board is mounted within the box on a universal joint; instructions on making that are also included. The servo motors mount in the corners of the box and pull on the corners of the horizontal maze board via sleeved lengths of piano wire so they can tilt it in any direction. The main electronic circuit uses the 44-pin Micromite described in the August 2014 issue (siliconchip. au/Article/7960), as the 28-pin Micromite doesn’t have enough spare I/Os for this job. It has to monitor the optical sensors and mini joystick and also drive the 16×2 LCD and the two servo motors. The main circuit shows how the 44-pin Micromite PIC chip, which can be a PIC32MX150F128D or PIC32MX170F128D, connects to the headers for interfacing with the LCD, optical sensors etc. There is a basic onboard power supply to derive the regulated 3.3V rail required from an external 5V supply. The separate circuit snippet shows how the reflective optical sensors are configured; CON1 in that circuit connects to CON1 on the main circuit, and the two CON2s in each circuit are also joined. Each sensor is powered from the incoming 5V DC rail, with 150W current-limiting resistors for the internal LEDs and 10kW pull-down resistors on the phototransistor emitters. OPTO1-OPTO5 and OPTOFIN track the ball’s progress through the maze while OPTOLOST detects if it has fallen through a hole in the maze and out the hole in the side of the base. As the sensors are powered from 5V, their outputs go to 5V-tolerant inputs on the PIC chip. The optical sensor resistor values have been chosen so those pins will sense a digital high or low value depending on whether the sensor is triggered. Besides monitoring those, the firmware’s main job is to track the joystick’s position and send signals to the servo motors so they follow the joystick’s movements. The joystick is connected to analog inputs at pins 26 & 27 as the voltage output from the joystick is what determines the servo pulse width. The two servo motors and the LED screen are powered directly by the 5V supply. The servo motor operating the Y-axis will need a short extension cable, about 300mm long. When connecting the extension cable to the servo, take note of the correct cable colours to avoid incorrect connections. The wires from the servo are red (+5V), black or brown (GND) and yellow or orange (control signal). The MMBasic program to tilt the maze board works out the mid-range of the joystick X and Y voltages, multiplies the difference by a constant (usually 0.5) and then adds the minimum pulse width of 0.5 (PWMin). The Yoffset and Xoffset values are added to achieve the correct board horizontal balance. The optical sensors activate the 7 INTH interrupts in the software. Although the TCRT1000 sensors have daylight-blocking filters, they are still sensitive to some ambient light, so they may be triggered when exposed to light from different directions. Covering the sensor area with a thin black plastic strip and painting the ball collector and external tray areas black will assist in avoiding unwanted triggering. I have designed a PCB in EAGLE; that file is available as part of the download package, along with Gerber files. When soldering the opto board components, start with the small SMD resistors and attach the sensors last. The TCRT1000 sensors must be soldered so that the sensor’s top edge is about 10mm from the PCB face. The main board is designed to allow the double-sided PCB to be etched, with the via links manually added using thin copper wire, eg, stripped from Bell wire. Gianni Pallotti, North Rocks, NSW. ($150) siliconchip.com.au Australia's electronics magazine September 2024  47 Mains Earthing Systems The Earth is an integral part of our power system. It can be used to improve electrical safety, reduce energy losses or save on the cost of a dedicated conductor. Here, we look at the different Earthing systems used worldwide and how they work. By Brandon Speedie T he Earth’s crust is moderately conductive thanks mainly to the salts of sodium dissolved in water and, to a lesser extent, elements such as calcium, potassium, and magnesium. These charge carriers can move freely through soil and rock as long as they remain dissolved in water. The result is a surprisingly conductive electrolyte – see Fig.1. There are two broad reasons for using the Earth as a conductor. As a functional conductor The most obvious use of the Earth is to save on the cost of a dedicated conductor. One example is the Single Wire Earth Return (SWER) line, a common way to distribute power in rural 0.01 0.1 1 areas. In this case, a significant cost saving can be achieved by only having a single overhead conductor on a power line (see Figs.2 & 3). The return current (for Neutral) flows through the soil back to the substation or generator. This can sometimes be a distance of hundreds of kilometres. The Earth is also commonly used in RF applications. A monopole antenna relies on a ground plane to radiate and receive effectively, a role very commonly allocated to ‘terra firma’ (Latin for “firm land” or perhaps “solid ground”). Another application of Earth is on grid-scale solar farms. Solar panels are effectively three-terminal devices; Resistivity (Ωm) 10 100 1000 10,000 (igneous rocks: igneous and metamorphic rocks mafic felsic) mottled duricrust zone saprolite Safety Perhaps the most prominent function of Earth is to provide electrical 100,000 massive sulfides graphite they have a positive output, a negative output and a frame or chassis. If the frame is left electrically unconnected, it can float to a different voltage from its other two terminals. Charge carriers will then begin to migrate out of the substrate in a process known as Potential Induced Degradation (PID). This leads to reduced yield and eventually, early failure. On commercial solar farms, care is taken to ensure the panel mounting solution is well bonded to Earth and that the array DC voltage does not float too far from the Earth’s potential. shield unweathered rocks weathered layered (metamorphic rocks) clays gravel and sand glacial sediments tills shales sandstone and conglomerate sedimentary rocks dolomite, limestone lignite, coal salt water permafrost fresh water water, aquifers sea ice 100,000 10,000 1000 100 10 1 0.1 0.01 Conductivity (mS/m) Fig.1: resistivity figures for some common components of the Earth’s crust. Note the different units on the top and bottom horizontal axes, which are inversely equivalent; as S (siemens) is the inverse of W (ohms), 1mS is equivalent to 1kW. Source: GeoSci Developers – siliconchip.au/link/abu7 (CCA 4.0). 48 Silicon Chip Australia's electronics magazine Fig.2: SWER line in South Australia. The unusual pole construction is concrete sandwiched between two steel beams, known as a “Stobie pole”. siliconchip.com.au safety. In normal operation of a single-­ phase AC circuit, current flows into or out of the Active conductor, through the load, and returns via the Neutral conductor. In a fault scenario, an Earth connection gives a low impedance path for current to flow, which will usually trip a circuit breaker. In some scenarios, the fault will not draw enough current to trip the circuit breaker, but it should be enough to trigger a Residual Current Device (RCD). In an RCD, the Active and Neutral conductors both pass through a current transformer (CT). In the absence of a fault, the current flow is balanced between Active and Neutral, so the magnetic fields of these two currents cancel, and no net current is detected – see Fig.4. In a fault scenario, current flows through Active, but not all is returned via the Neutral; some flows through the Earth connection. This imbalance is detected in the RCD, which will typically trip once the imbalance exceeds 30mA (although more sensitive RCDs exist, eg, 15mA; the trip current is a balance between sensitivity and nuisance tripping). The Earth can also be used to ensure electrical safety during the normal operation of a grid. The most prominent such application is lightning suppression. If the potential difference between the Earth’s surface and the power lines were left uncontrolled, a direct strike from a lightning bolt would charge up the network to a high voltage, leading to arc-over at the insulators. It is therefore critical that this energy is shunted to Earth to maintain grid tolerances. Earth is also a logical place to shunt this charge as the lightning originates from a static buildup between the ground and the atmosphere. Types of Earthing systems Earthing schemes used in a mains grid are commonly described by a sequence of letters based on where the circuit Earth originates from. “T” (terra; Latin for “Earth”) refers to a direct connection to the soil of the Earth. This is typically achieved by driving a conductive stake into the ground, or perhaps multiple stakes and/or bonding to buried metal pipes. In larger installations, such as substations or generators, a dedicated buried circuit or ‘Earthing ring’ made of bare wire (usually copper) encircles the installation. “I” (insulatum; Latin for “insulated”) means no connection to Earth or a high-impedance connection through an Earthing resistor. “N” (network) means the Earth connection is via the network or grid. Network Earths will still connect to the soil at some point, but this may be some distance away, not at a local Earth stake, as with terra (T). Fig.4: a Residual Current Device (RCD). Usually, current flows to or from the Active conductor through the load and is returned via Neutral. The magnetic fields of the two conductors are cancelled, so the CT detects no net current. A small amount of leakage between Active and Earth, shown as a thin red line here, is enough to trip the RCD. “C” (combined) means the circuit Neutral and Earth are combined into a single conductor in the network. “S” (separate) is where the circuit Neutral and Earth are run as separate conductors in the network. The Earthing system can thus be described by two letters, the first indicating the source Earth, and the other the load Earth. TT (Terra-Terra) Terra-terra networks are physically connected to Earth at both the generator and load (see Fig.5). Typically, this will be at the low-voltage distribution transformer and the customer’s premises. TT networks rely heavily on the Earth connection’s integrity, so care is taken to ensure a sufficiently low Earth loop impedance. This can include tight specifications around Earth stake Terminology Fig.3: the start of the SWER line shown in Fig.2. The three conductors on the right are 33kV phase-to-phase, or 19kV from phase to Neutral/Earth. The SWER line taps off the middle phase and extends to the left. The return Neutral current flows via Earth. Phrases such as Earth, Neutral, common and ground are sometimes used somewhat interchangeably. They can be confusing terms, particularly from our perspective as electronics enthusiasts. Earth: a connection to terra firma, either directly through an Earthing stake, or via a conductor that is bonded at some point with Earth. Neutral: the return current of a single-phase AC supply. Typically, this will be the centre point of a star-connected three-phase circuit. In regular operation, most networks should have very little voltage difference between the Neutral and Earth. Ground: a common node in a circuit, usually at 0V DC potential. Confusingly, ground can be ‘grounded’ by tying to ‘Earth’, but it is uncommon in modern usage. Floating circuits are generally considered to have a ‘ground’, but it could drift relative to Earth; it is usually the negative end of a battery or similar and is used as a local reference and/or current return. In a circuit running directly from the mains, ‘ground’ may even be connected to (or very close to) the Active potential! Some circuits can have multiple grounds (analog, digital etc). Common: a node in a circuit shared by many components. It is sometimes used interchangeably with ‘ground’ but can also be used where multiple signals are tied together. Examples are a common bus in a multiplexed display or a common signal tying multiple opto-isolators together. siliconchip.com.au Australia's electronics magazine September 2024  49 construction and placement, as well as considerations of soil conductivity. This is particularly important in cold areas, where frozen soil dramatically increases resistivity, or in high rainfall regions, where soil electrolytes are diluted, leaving few charge carriers for conduction. Even given these additional requirements, a standard overcurrent breaker is not guaranteed to trip from an Earth fault. As a result, TT customers will almost always need Earth leakage protection in the form of an RCD. Historically, TT networks were not popular due to the difficulty of ensuring safety without Earth leakage protection. The advent of cheap RCD breakers has led to its increasing use worldwide, such that it is now the most common scheme. Many parts of Europe, including France, Denmark, Belgium, Spain, Italy, and Portugal, are now predominantly TT, as well as Japan, Malaysia, Argentina and many others. Germany extensively uses TT outside of metropolitan areas. IT (Insula-Terra) Insula-terra networks are connected to Earth at the customer’s end but not at the generator or distribution transformer (Fig.6). Therefore, the Active and Neutral connections have no reference to Earth, which minimises shock hazards. The reader may recognise this advantage from using an isolation transformer when working on mains-powered electronics. IT networks are often referred to as “first fault free”, as any fault will convert the system into another scheme (usually TN) while the fault is present, and subsequent faults may be dangerous. This is why IT networks are not common worldwide, except in specialised applications. This includes hospitals, where patients are at a higher risk of shock when coupled to medical equipment, and industrial areas where a flammable atmosphere may be present, so the risk of sparking needs to be minimised. Fig.5: the TT Earthing scheme. 50 Silicon Chip Scandinavia is an exception, where frozen ground and rocky geology make Earthing difficult. Norway in particular makes heavy use of IT Earthing. In India, a variation of the IT network called Resistance Earthed Neutral (REN) is used in mining areas. A Neutral grounding resistor limits the Earth current to 750mA. TN-C (Terra-Network-Combined) Terra-network-combined systems get their Earth from the network by combining it with the Neutral conductor (Fig.7). This combined conductor is commonly referred to as the Protective Earth Neutral (PEN). In a TN-C network, the distribution transformer is Earthed at the source end, which is also connected to the circuit Neutral. This PEN conductor then runs along the poles and wires of the grid to customer premises, where it is used as the “Earth”. TN-C networks do not require an Earth stake at the customer premises or RCD breakers as in a TT or IT network, but they are extremely reliant on the integrity of the PEN. If there is a break in this conductor, the customer load will act like a pullup resistor, raising the potential of Neutral/Earth to mains voltage; a hazardous situation (see Fig.11). TN-C networks also suffer from conducted interference. As the circuit Neutral is combined with the Earth, coupled noise from heavy industrial equipment can pass through the network and cause problems with sensitive equipment such as telecommunications broadcast infrastructure. Fig.11: a Neutral fault with the TN-C scheme. The customer load acts like a pullup resistor, raising the Earth to a high voltage and creating a shock hazard. conductor. TN-S is used extensively in India. TN-C-S (Terra-Network-Combined-Separate) Terra-network-combined-separate networks are a hybrid of the TN-C and TN-S systems. The source transformer is Earthed, while a combined PEN conductor emanates onto the network (Fig.9). The PEN is split into dedicated Neutral and Earth conductors at some agreed location (usually the customer’s switchboard). TN-C-S is widely used in the UK, USA, Canada, Israel, Australia and New Zealand – see Fig.14. Germany also predominantly uses TN-C-S in metropolitan areas. MEN (Multiple-Earthed-Neutral) Terra-network-separate networks run a dedicated Earth on the network, separate from the Neutral conductor (Fig.8). The distribution transformer is Earthed at the source end and connected to two conductors. One is the Neutral, while the other is a dedicated Earth – see Fig.13. TN-S networks are the safest configuration but are also more expensive, given the added Australia and New Zealand use the Multiple Earthed Neutral (MEN system) – see Fig.10. It is a TN-C-S system, though TT may be permitted in some situations – usually rural areas. Unusually for TN-C-S, an Earth stake is mandatory at each customer premises. In MEN networks, the source distribution transformer is Earthed, and a combined PEN conductor runs in the grid. The PEN is Earthed at multiple points throughout the network, including at the customer stake. This gives good immunity against a broken Neutral; if the customer is downstream of the fault, their PEN will not rise to a dangerous potential thanks to the Earth stake at their premises and any neighbouring premises or network Earths. Fig.6: the IT Earthing scheme. Fig.7: the TN-C Earthing Scheme. TN-S (Terra-Network-Separate) Australia's electronics magazine siliconchip.com.au Fig.12: this configuration stops the communications cable shield from drifting too far from Earth. It keeps it at a low AC impedance via the capacitor but will not form an ‘Earth loop’. At the customer premises, the combined PEN connects to the Neutral bar in their switchboard. This busbar then distributes the Neutrals to all of the circuits within the installation. Separately, a dedicated Earthing busbar connects to the “Earth” conductor emanating throughout the property, as well as the Earth stake. The Earth busbar and the Neutral busbar are joined by a single strap, known as the “MEN link”. This link is the separation point between the TN-C scheme on the network and the TN-S scheme within the customer premises. Earth integrity The Earth connection is convenient, as it can be assumed to be the same voltage across multiple installations, even if they are geographically separated. But as the soil has a finite resistance, this is not always true. This can create problems where two circuits are bonded to mains Earth and are also linked by conductors, similar to a local ‘ground loop’ or ‘earth loop’ that can cause problems with audio electronics. This is particularly problematic when large conductive structures are located near high-power switching gear. This might be a steel fence around a switchyard or a buried gas pipeline adjacent to power lines. In a fault, a large current might flow into ‘Earth’, raising the local voltage near the Earthing stake/ring. If the metal structure is close enough to this fault, its voltage will rise. Fig.8: the TN-S Earthing scheme. siliconchip.com.au If someone touches this structure, they may receive a lethal voltage despite being far from the actual fault. This is because the metal is a better conductor than the Earth, so the ground they are standing on is at a different voltage than the ground near the fault. This is known as a ‘touch potential’ and is a major hazard in high-power assets. Editor’s Note: in extreme cases, there can be enough potential between workers’ feet to electrocute them. Electrical workers are trained to hop if they suspect such a fault exists! Similarly, industrial Ethernet networks can also suffer from ground loops and unequal Earthing. Ethernet uses differential signalling, so it is commonly run over UTP (Unshielded Twisted Pair) cabling. A high Common Mode Rejection Ratio (CMRR) amplifier cancels any coupled noise or interference at the receiver. Thus, shielded cable is not needed for noise immunity. Despite this, shielded or foiled Cat6 cabling is common in industrial settings. Often, the designer will reason that shielded cable will be better than unshielded, so it is worth the marginal cost increase. However, it can often be more trouble than it is worth. Ethernet uses “magnetics” (signal transformers) at the receiver and transmitter to galvanically isolate the channel, preventing ground loops from forming. Shielded cable effectively breaks this isolation by connecting a conductor directly between the receiver and transmitter. If there is any Earth imbalance between this equipment, large currents can flow, which can cause interference or damage. For this reason, if shielded Ethernet cable is used, it is often only Earthed at one end of the cable, or better still, connected through a parallel RC combination, perhaps 1MW || 100nF (see Fig.12). The resistor weakly holds the shield at a known voltage, while the capacitor offers a low impedance path for AC SC voltages (coupled interference). Fig.9: the TN-C-S Earthing scheme. Australia's electronics magazine Fig.13: the TN-S scheme in Namibia. The five conductors (from bottom to top) are Earth, Neutral & three Active phases. Note how the Earth wire has a smaller diameter than the others. Fig.14: the TN-C-S scheme in Melbourne. The distribution transformer feeds the four horizontal conductors directly above it. The second conductor from the left is the combined Neutral/Earth (PEN), while the other three conductors are the Active phases, 400V line-to-line or 230V line-to-Neutral. An Earth stake (out of shot) connects to the conductor running up the left of the pole, partially covered by a white conduit. The transformer is fed on the primary side by the three conductors at the top with 22kV between phases. Fig.10: the MEN Earthing scheme. September 2024  51 Project by Richard Palmer USB Mixed-Signal Logic Analyser using a Raspberry Pi Pico A mixed signal analyser can be invaluable as it lets you monitor and decode serial buses and other logic signals while observing other analog signals. Based on a Raspberry Pi Pico, this one provides 16 digital and three analog channels. A logic analyser is a fundamental tool for debugging digital circuitry, whether it is hard-wired logic or involves a microcontroller. Along with traditional parallel and sequential logic, circuit elements are now commonly connected to microcontrollers using I2C, I3C, SPI, or serial connections. Often, analog signals trigger or are triggered by digital signals. This is the domain of the mixed-signal oscilloscope (MSO). While this project does not claim to be an all-bells-and-whistles MSO, it provides flexible logic analyser functionality and the ability to view up to three analog signals synchronously. It is relatively compact and inexpensive. Design overview A block diagram is shown in Fig.1. At the heart of the design is a Raspberry Pi Pico microcontroller. The Pico’s very fast PIO (Programmable I/O) processor captures digital signals, while its inbuilt ADC (analog-to-­ digital converter) captures the analog signals. The captured signals are translated into serial format and transmitted to the host computer via a USB serial connection. 52 Silicon Chip The open-source PulseView program decodes and displays the waveforms. Input signal conditioning and overvoltage protection are provided for both analog and digital channels. The digital side employs logic translators and schottky protection diodes, while the analog channels offer an amplifying buffer, diode protection, AC/ DC switching and potentiometers for gain control. Performance As with digital oscilloscopes, the sampling rate is a critical specification for logic analysers, determining the maximum frequency that can be reliably displayed and, possibly more importantly, the smallest difference in signal timing that can be distinguished. The Pico can sample up to twenty digital signals at an impressive 240 million samples per second. To achieve that, it is overclocked from its default 133MHz to 240MHz, which is well within safe limits. The achieved sampling rate depends on the number of enabled channels and the desired number of samples to be captured – see Table 1. The maximum capture rate reduces when the quantity of data to be captured exceeds the Pico’s internal buffer space and data needs to be streamed via the USB link. The manual contained in the download pack for this project has further details (siliconchip. au/Shop/6/452). PicoMSA Features & Specifications » 20 protected digital inputs for 1.8V, 3.3V or 5V logic » Three protected 7-bit analog inputs » Four additional 3.3V protected digital inputs » 240MHz digital sampling rate » Analog inputs have adjustable sensitivity of 0.33-120V peak-to-peak » 2.4MHz maximum shared ADC sampling rate » Flexible, multi-platform PulseView software with multiple protocol decoders » USB powered and connected Australia's electronics magazine siliconchip.com.au The logic-level translator ICs can handle sixteen 5V, 3.3V or 1.8V logic inputs (D2-D17). The last four digital inputs, D18-D21, do not have logic-­ level translators and are optimised for 3.3V logic levels. All analog and digital inputs are protected against excessive positive or negative voltages. The digital inputs are protected for an absolute maximum signal range of -5V to +20V. The input capacitor’s 250V DC rating determines the upper limit to the analog input voltage, although applied signals should be limited to 25V RMS or 60V peak for safety. Analog signals may be AC or DC coupled, with a selection switch for each channel. The maximum sensitivity for analog inputs is 330mV fullscale. They are sampled with 7-bit accuracy, translating to 2.5mV steps at maximum sensitivity. When analog signals are captured, the maximum sampling rate is limited by the ADC’s 2.4MHz conversion rate, which is shared among the enabled analog channels. As PulseView does not smooth analog signals, five samples per cycle is a practical lower limit for displaying a recognisable sinewave (Screen 1). That gives us a theoretical AC bandwidth of around 500kHz when capturing a single analog channel or 160kHz when all three channels are enabled. With a small number of samples per cycle, if the signal being displayed is not an exact sub-division of the sampling frequency, patterns like the one shown in Screen 2 may appear. It looks like an amplitude-modulated signal due to the sample points near the peak occurring at a slightly different part of the waveform each time. siliconchip.com.au Table 1 – maximum sampling rates # digital # analog # samples Maximum sampling rate Limitation 1-4 0 ≤200k 240Msps PIO 1-4 0 >200k 500ksps+ USB w/RLE 5-7 0 ≤100k 240Msps PIO 5-7 0 >100k 500ksps+ USB w/RLE 8-14 0 ≤50k 240Msps PIO 8-14 0 >50k 250ksps+ USB w/RLE 15-20 0 <25k 240Msps PIO 15-20 0 ≥25k 167ksps+ USB w/RLE 0 1 ≤200k 2.4Msps ADC 0 1 >200k 500ksps USB 0 2 ≤100k 1.2Msps ADC 0 2 >100k 250ksps USB 0 3 <67k 800ksps ADC 0 3 ≥67k 160ksps USB 1-7 1 ≤100k 2.4Msps ADC 1-7 1 >100k 250ksps USB 1-7 2 <67k 1.2Msps ADC 1-7 2 ≥67k 160ksps USB 1-7 3 ≤50k 800ksps ADC 1-7 3 >50k 125ksps USB 8-14 1 <67k 2.4Msps ADC 8-14 1 ≥67k 160ksps USB 8-14 2 ≤50k 1.2Msps ADC 8-14 2 >50k 125ksps USB 8-14 3 ≤40k 800ksps ADC 8-14 3 >40k 100ksps USB Table 1: the maximum sampling rate depends on the number and type of channels active and the number of data points to capture. In each case, the limitation is either the maximum PIO, USB or ADC speed. Fig.1: incoming digital and/or analog signals are conditioned before being captured by the Pico’s internal PIO (digital) and ADC (analog) peripherals. The captured data is transferred to the host computer via USB for display on the open-source PulseView application. Australia's electronics magazine September 2024  53 The frequency of the apparent modulation is related to the remainder of the signal frequency divided by the sampling rate. In DC mode, the analyser has an analog frequency response within +0/-0.5dB to 100kHz and +0/-2dB up to 300kHz. The equivalent lower limits are 2Hz (-0.5dB) and 5Hz (-2dB) in AC-coupled mode (see Fig.2). The Pico PIO peripheral Fig.2: the analyser’s AC analog channel bandwidth. The DC bandwidth is within 0.5dB from DC to 100kHz and within 2dB to 300kHz. Fig.3: the Pico’s PIO (programmable I/O) processor has flexible facilities for interacting with I/O signals at very high speeds, communicating with the main CPU via FIFO buffers. The Pico’s internal PIO is a very fast and flexible secondary processor, optimised for I/O processing – see Fig.3. It can operate up to the CPU speed which, in this case, has been moderately overclocked to 240MHz. The PIO’s instruction set consists of only nine instructions and the maximum length of a PIO program is 32 instructions. Those are not major limitations as each PIO instruction word can accomplish multiple actions, so complex I/O programs can be written with few instructions. For instance, an SPI port can be created with just three PIO instructions. In this project, the PIO executes a loop with a single instruction: read from a defined number of pins and move them into the PIO’s eight-entry first-in, first-out (FIFO) buffer to be picked up by the Pico’s main CPU for further processing. The FIFO buffer is 32 bits wide and, when the number of digital inputs being captured is less than 16, the PIO automatically packs multiple sets into one FIFO entry. Firmware The top of the prototype PCB with the front panel wiring in place. Several components have been moved in the final version to clear space under the switches. Wires are soldered directly to the PCB instead of headers to give enough clearance for the pots & switches. 54 Silicon Chip Australia's electronics magazine The firmware, developed by someone using the nickname ‘pico-coder’, has several main elements. It initially communicates with PulseView to inform the software of the unit’s capabilities and then accepts instructions on how many inputs to capture, the desired sampling rate and capture length. When PulseView’s Run button is clicked, the Pico begins the capture process and starts transmitting data. When PulseView has collected sufficient data, it sends a command to disarm the PIO and stop the data flow. Triggering – selecting the beginning of the saved and displayed capture stream – is left to PulseView, as the additional processing is beyond the Pico’s capabilities at higher sampling rates. siliconchip.com.au The PIO captures digital data and packs it into the FIFO buffer for the main CPU to convert into a suitable form to transmit via USB. While waiting for transmission, the digital samples are stored in another buffer that uses most of the Pico’s onboard 264kiB of SRAM. The size of this buffer determines the maximum number of digital samples that can be captured when the capture rate exceeds the USB data transmission rate. The unit can operate at full speed when the overall capture size is less than the RAM allocated to the buffer. When capturing larger data sets, the acquisition rate is constrained by the USB interface’s maximum transfer rate of 400-800kB/sec; the actual rate depends on the host computer’s capability. For digital-only signals, run-length encoding (RLE) compression automatically increases the effective transfer rate. In situations where there are bursts of digital signal activity followed by long gaps, such as the I2C signal captured in Screen 3, RLE encoding improves the effective data rate in the gaps between bursts by several orders of magnitude. However, when analog signals are (also) being captured, compression is not used. Analog signals are directly captured by the Pico processor’s inbuilt ADC, using round-robin sampling and a second software FIFO. While the Pico’s ADC has a specified twelve-bit resolution at a maximum sampling rate of 500kHz, silicon errors in the chip reduce the accuracy to just under nine bits. Some clever software tweaks (Raspberry Pi forums – siliconchip.au/link/ abwb) increase the maximum ADC sampling rate to 2.4MHz. The accuracy is reduced to slightly over seven bits at this higher rate. In our use case, the sampling rate vs accuracy tradeoff is justified. Keep in mind that your average low-cost DSO only uses eightbit sampling. Circuit details The complete circuit is shown in Fig.4. The first sixteen digital inputs have their signals conditioned by a pair of SN74LVCC3245ADW logic level translators, IC1 & IC2. The 74xxx245 is offered in a plethora of different logic families. It is possible to substitute families other than LVC siliconchip.com.au Screen 1: a 3V 50kHz analog signal captured at 500kHz. With ten samples per cycle, the signal is recognisable as a sinewave. Screen 2: a 60kHz sine wave sampled at 250kHz shows what appears to be amplitude modulation. However, this is simply a macro view of the effect depicted in Screen 1. as long as the selection allows 3.3V logic on the A-side and 1.8V to 5V or better on the B-side. The input logic voltage (VCCB) is selected by a jumper on CON3, with the options being the 5V and 3.3V digital voltage supplies available from the Pico and 1.8V from REG2. This voltage also supplies the cathodes of the protection diodes for channels D2-D17 (GP pins on the Pi Pico). While a voltage selector switch would have been preferred, all the major suppliers’ SP3T slide switches are make-before-break types, which would temporarily short two of the three power rails when the voltage setting is changed! The translator ICs include negative-­ voltage diode protection, while over-voltage protection is provided by BAS40 low-capacitance schottky diodes. Each dual diode protects a pair of inputs from voltages greater than VCCB + 0.3V. 100W input resistors limit the input currents through Australia's electronics magazine the protection diodes and reduce ringing on the input signal lines due to stray capacitance and impedance mismatches. The BAS40 diodes have a maximum continuous current of 200mA, and the logic level translators can handle -50mA, so the absolute voltage limits are -5V/+20V. The final four digital inputs, D18D21, accept only 3.3V logic and have reverse- and over-voltage protection provided by 100W resistor arrays and BAS40-04 serially-connected diode pairs protecting the inputs to ±20V. The digital channel input resistors are SMD quad resistor arrays to reduce the parts count. However, individual M2012/0805 SMD resistors may be used, mounted on their edges. The three analog input channels are configured identically. BNC connectors allow standard ×1/×10 oscilloscope probes to be attached. Each input’s AC/DC selection is via a toggle switch, with 100nF capacitors feeding September 2024  55 into 1MW, allowing AC response down to a few hertz. With oscilloscope probes in ×10 mode, the 50pF capacitors in the circuit are balanced out by 20pF capacitors in parallel with the 10MW series probe resistors. 56 Silicon Chip If oscilloscope probes are not going to be used, panel-mount RCA connectors may be substituted for the BNC connectors. In this case, the 50pF capacitors in parallel with the pots should be omitted, as they may cause a roll-off in sensitivity at higher Australia's electronics magazine frequencies. The amount of roll-off will depend on the impedance of the source signal. The Pico’s ADC has a 0-3.3V input voltage range. As the buffer’s gain is set to 10, this translates to 330mV at the input to the buffer. However, the siliconchip.com.au Fig.4: digital signals pass through protective resistors and are clamped to the positive supply rail by schottky diodes before reaching level shifters IC1 & IC2. The analog inputs have similar protection, but there is also a series capacitor that can be shorted to select between AC and DC coupling, a potentiometer in series for variable attenuation and an op amp gain stage before the signals reach the Pico’s analog input pins. variable attenuator formed by the 1MW potentiometer and 1.2kW fixed resistor in each channel allows much higher voltage signals to be probed, up to the 60V peak safety limit. siliconchip.com.au 24mm diameter pots may provide smoother operation than the 16mm variety, and logarithmic tapers give a more even control of the input voltage. 9mm and 12mm pots should be Australia's electronics magazine avoided, as they are generally only rated to handle up to 20V DC. The 10kW op amp input resistors limit any current through the BAS4004 (series) protection diodes and September 2024  57 Fig.5: most of the components mount on the top of the PCB, including the Raspberry Pi Pico, ICs, connectors and many of the passives. Note that the two resistors marked in red (R17 & R19) can be replaced by a single 19.1kW resistor on R17’s pad. Fig.6: many of the dual diodes are soldered to the underside of the board, along with a few of the passive components. decouple the 10pF combined diode capacitances from the input. They do not impact the gain, as the FET-input op amps have input impedances of 1TW (1012W). TL074H FET-input op amps were chosen to meet the need for high input impedance and bandwidth. They have improved specifications compared with the garden-variety TL074. The most important of these for our purposes is a 5.25MHz gain-bandwidth product. This translates to a theoretical 3.3V peak-to-peak output bandwidth of more than 500kHz at ×10 gain. While these op amps do not have rail-to-rail outputs, they are capable of a positive swing of more than 4V with a 5V supply rail. 58 Silicon Chip The ADC zero point is set by the -165mV reference voltage, Vref. An inverting op amp halves the forward voltage of a schottky diode to create this reference voltage. As the schottky diode’s forward voltage varies slightly with current, trimmer resistor VR4 allows it to be trimmed. The buffer’s feedback capacitor helps filter any high-frequency noise. The input resistance to this op amp is 19.1kW, so the required gain of 0.5 is achieved when VR4 is near its halfway point. While such E96 values are generally not difficult to obtain in the required SMD package, two parallel footprints are provided, allowing you to use 22kW in parallel with 150kW instead. Australia's electronics magazine +5V power for the op-amps is taken from the USB socket’s power pin (Vbus), while -5V is provided by an LM2664 switched capacitor voltage inverter. Larger (3.2 × 2.5mm) SMD ceramic capacitors are used on the voltage inverter for their lower ESR and, therefore, self-heating losses. Separate ground planes are provided for the analog and digital sections of the circuit to limit the transfer of digital noise into the analog environment. The copper is joined on both sides (top and bottom) in the middle of the board. All analog power rails are filtered and decoupled from the digital ground plane by 10W resistors and capacitors. As the LM2664 has siliconchip.com.au a 160kHz switching frequency, only 10μF capacitors are required in the output filters to effectively filter the switching noise. Linear regulator REG1 ensures the Pico’s 3.3V ADC reference voltage is stable and low-impedance, which helps with accuracy, particularly at high sampling rates. Construction The Mixed-Signal Logic Analyser is built on a double-sided PCB coded 04109241 that measures 77 × 148mm. There are parts on both sides; use the overlay diagrams (Figs.5 & 6) as guides during assembly. When sorting the parts for construction, be careful to keep the BAS4004 (series connected) and BAS40-05 (common cathode) variants separate. While they have different markings, these may be difficult to distinguish without a bright light and a magnifying glass. The only place where the variant does not matter is diode D17, where either part would work. Solder IC1 & IC2 first, as access to these becomes more difficult once the Pico’s header sockets are in place. If you have a reflow oven, you can use solder paste, but if you’re using a soldering iron, it’s better to use flux-cored solder wire with a syringe of flux paste. Apply a thin layer of flux paste to all the pads for one IC, then place the IC over its pads. Double-check that its pin 1 orientation is correct, then add a small amount of solder to the clean iron tip and touch it to the junction of one corner pin and its pad. That should tack the IC down. Check that it is correctly aligned with all its pads; if not, remelt that solder joint and gently nudge it in position. Once it’s correctly located, solder the other three corner pins similarly. Then add more solder to your iron tip and gently drag it along the edge of the pins on one side, in contact with the PCB. The solder will flow onto the pads one after another. Don’t worry if some pins are bridged; continue adding solder until all the pins on one side are soldered, and repeat on the other. Once all the pins are soldered, add a little more flux paste to any bridged pins and press solder wick down between the two pins with the iron tip until it sucks up the excess solder. When finished, clean off the flux residue using a flux cleaner or alcohol (eg, isopropyl) and inspect all the joints carefully to ensure they have all formed correctly. If any are no good, clean them up with more flux paste. Next, mount the three voltage regulators, the passives surrounding them and the headers for the Pico. Attach the Pico and connect its USB cable to a power source. I use a USB power monitor on the first connection to check the current draw. For this project, more than 50mA indicates a possible problem. The 1.8V, 3.3V (ADC_VREF), +5V and -5V rails should now be active; check that they are the correct voltages by carefully probing the regulator pins with a DMM. The -5V rail may read a few hundred millivolts less than the +5 rail due to the voltage lost in the switched capacitor voltage inverter. If there are any problems, switch the power off and check everything under magnification. Assuming it passed the tests, fit the remaining SMD ICs, diodes and passive components on both sides of the PCB. We recommend fitting all the SMDs to the top before you move onto the bottom. Remember the comments earlier about not getting the two different kinds of diodes mixed up and I didn’t have any resistor networks on hand when building the prototype, so I used 100W M2012/0805 SMD resistors mounted edge-wise. recall that you can either fit a single 19.1kW resistor on the pad marked R17 (as marked on the overlay diagram) or 22kW for R17 and 150kW for R19. Soldering the five resistor arrays will be a little tricky because each they are not much larger than a single resistor (5.1 × 2.2mm), so the contact pads for each element are tiny. You will need to use flux paste to get the solder to flow into the concave leads and onto the pads below. When finished, clean off the residue and check the solder joints carefully under magnification. With all the SMDs in place, the flux residue cleaned off, and your work checked, proceed to fit the throughhole components, starting with the three 10W axial resistors. Follow with the trimpot, leaving the switches, BNC connectors and right-angle pin header until the end. The right-angle header is configured as two blocks of 8 × 2 pins and one Screen 3: the PulseView display of a decoded I2C signal being read from an EEPROM chip with a clock frequency of 400kHz. Fig.7: remove the pins from the locations shown here on the 23-row dual right-angle header to provide a continuous length of support plastic behind the case opening. You can also check the photos. siliconchip.com.au Australia's electronics magazine September 2024  59 A USB power monitor is useful for identifying faults that draw additional current, such as power rail shorts to ground. We published a DIY version in the December 2012 issue (siliconchip.au/Article/460). Shields made from thick cards can help cover cut-outs in the case, preventing dust ingress and making it look nicer. of 3 × 2 pins with the first, last and intermediate columns of pins removed (see Fig.7). This arrangement provides a solid wall of plastic retaining strip inside the case, extending one unit beyond the pins at each end. Mount the header after removing the pins from the columns shown. Put the jumper on the middle (3.3V) pin of the 3×2 pin section of the header. The BNC connectors may be mounted at this stage or left for later. After soldering them, secure the BNC connectors with a small amount of hot glue or epoxy adhesive on the mounting pins. The analog channel gain potentiometers, AC/DC input switches and the LED on the top of the case connect to the PCB using short lengths of hookup wire (wire stripped from ribbon cable is ideal). As the pots and switches are mounted fairly directly above their connection points to the PCB, 10cm flying leads should suffice. Make them by stripping sets of two or three wires off a 10cm length of ribbon cable. Connect the switches and pots now, as they will be needed for testing. Testing The top and bottom of the finished prototype PicoMSA (mixed-signal analyser) PCB. The final version has some minor differences. 60 Silicon Chip Australia's electronics magazine Download the firmware to load onto the Pico from siliconchip.com. au/Shop/6/452 and plug the Pico into your computer. A new ‘drive’ should appear the first time you plug it in. If it doesn’t, unplug it and plug it back in while holding the BOOTSEL button on the Pico. Copy the UF2 file from the download package onto that drive; once the Pico reboots, it will be running the required software. Next, download and install Pulse­ View from https://sigrok.org/wiki/ PulseView Start PulseView, connect the analyser and click the device selection button (“<No Device>”) in the toolbar (see Screen 4). From the drop-down list in the pop-up window, select “RaspberryPI PICO”. Click the Serial Port radio button and select the appropriate serial device. In Windows, it should have “CDC” in its name, and won’t be COM1. There is no need to select any baud rate option. Click on “Step 3: Scan for devices”, and you should be rewarded with a “Raspberry Pi Pico with 24 channels” message in the “Step 4: Select the Device box”. Select it and click OK. siliconchip.com.au If you have any difficulty with the process, try restarting your computer. You should not need to use Zadig or another driver updater program to install different drivers. The PulseView display should now have a window with twenty digital and three analog signals. You may need to scroll the screen down to see the analog channels. The digital signals are numbered D2-D21, a carry-over from the GPIO pin numbers to which they are connected. If you click the Run button in the top toolbar, the display should fill with random values for both the digital and analog inputs. Screen 4: the logic analyser’s USB serial port setting in the PulseView device setup screen. Calibration Deselect all the digital channels, leaving the analog channels selected. Connect a 1kHz 1V signal to any analog input and set the AC/DC switch to AC. The frequency and voltage values do not need to be exact. Capture 200 samples at the 50kHz sampling rate. Repeat the captures while adjusting the gain pot so that the PulseView displays a waveform of around 200mV peak-to-peak. The captured waveform may be above or below the zero line, as in Screen 5. Adjust the trimpot until the captured waveform is equally above and below the zero line, as in Screen 6. Enable all the digital inputs and set the logic level to 3.3V using the jumper. Check the channels by capturing a 0-3.3V square wave. Test the input channels individually, as that will show any channel-to-channel shorts, which can be hard to detect visually on the finely-spaced pins of the logic translators. Once the unit is working correctly, mount the PCB into the case using 9mm-long self-tappers. 2mm spacers are required between the PCB and case to prevent the ends of the screws coming through the bottom of the case, which has four dimples. The top has rows of lozenge-shaped depressions down both sides. If you don’t have 2mm spacers, use pairs of 1mm-thick Nylon washers. Mark the height and horizontal position on the side panel and drill 3mm pilot holes as shown in Fig.8. Set the unit on the table and line up one end panel against the BNC connectors to check the position of the holes. Ream or drill the holes out to 12mm (10mm for RCA sockets). siliconchip.com.au Screen 5: a 1kHz AC signal captured before Vref has been trimmed is offset from the zero line in PulseView. Screen 6: after Vref trimming, the waveform is centred on the zero line. Screen 7: a PulseView capture of synchronised square and sine waves on digital channel D2 and analog channel A0. Australia's electronics magazine September 2024  61 Fig.8: there are three round holes to be made in the back of the case (for the analog inputs; the sizes vary depending on what type of connector you use) and one rectangular cutout for the input header. For the latter, you can drill a series of round holes in a row, then file the shape out carefully to a neat rectangle with flat files. Fig.9: seven round holes are needed in the case lid. Parts mounted to the lid are wired to the board via flying leads, so the exact positions are not critical as long as the result is neat. We recommend that you drill them as shown here so our label artwork will fit. If RCA connectors are used, they should be directly mounted on the side panel, in line with the BNC socket pads on the PCB, and high enough on the side panel to just clear the top of the PCB. Repeat the process with the right-­ angle pin headers. There should be a 1mm gap in the side panel around the pins to provide clearance for test leads and the digital voltage selection jumper. Mark the location of the USB socket on the side of the case and drill a small pilot hole to check the position. While a hole just the size of a micro-USB plug (7×2mm) may suffice, I chose to make the cut-out the same size as the plastic surround on my USB lead (8×12mm) so I could be sure it would fully insert without binding on the case. If you choose this approach, cut a small piece of heavy paper to cover the hole. A similar cover can be made for the digital pins by pressing them into a piece of heavy paper to mark the holes, then punching them with a 62 Silicon Chip fat needle. The paper is then pressed over the pins. The top cover should be drilled as shown in Fig.9. You can download the label artwork (shown in Fig.10) from the Silicon Chip website, print it, laminate it and cut it to size. Punch out the holes or cut them out using a sharp hobby knife. Make the holes slightly oversized so they don’t delaminate the label when the pots and switches are inserted. The label can be stuck down with double-sided tape. Mount the pots, switches and LED. The pots and switches have minimal clearance above the PCB, so mount them without any washers or nuts between the cover and the switches or pots. The LED leads should be cut to less than 1cm to clear the PCB, and Fig.10: this artwork can be downloaded from siliconchip.au/Shop/11/456 so you can print it out (at ‘actual size’) to make a label to attach to the lid. Australia's electronics magazine siliconchip.com.au the joins to the hookup wire should be insulated with heatshrink tubing. Snap the case together. As there is minimal clearance between the switches, pots and the PCB, pulling the switch wires out between the BNC connectors, and the pot wires out the other side, makes it easier to fit the top and bottom halves of the case together. Tuck the wires back in before fitting the side pieces. You can then fit the potentiometer knobs. Usage precautions If plugged directly into a computer’s USB port, the Pico MSA’s ground will be Earthed via the computer. If the device under test’s (DUT’s) ground terminal is at a significant potential from Earth, connecting it may damage the USB port, computer or MSA. Therefore, using a USB isolator is highly recommended. They are cheap insurance, typically costing less than $10 from AliExpress. The lowest USB speed option will suffice, as the Pico’s USB port only supports 12MHz full speed operation. Operation The display height of any signal channel can be changed by clicking on its flag and changing the “Div height” value (see Screen 8). This is particularly useful for expanding the vertical axis for analog signals. Click on the red probe icon in the toolbar to reduce the active channels to only those you need to be enabled. The achievable sampling rate is a factor of the number and type of active channels, plus the number of samples to capture, as shown in Table 1. Triggering is handled by the host software; only digital pins can be used Parts List – Pico Mixed-Signal Analyser 1 Ritec grey ABS instrument case, 86 × 155 × 30mm [Altronics H0377] 1 double-sided plated-through PCB coded 04109241, 77 × 148mm 1 Raspberry Pi Pico (MOD1) 3 SPST (or SPDT) mini solder-tail toggle switches (S1-S3) [Altronics S1310, Jaycar ST0546] 3 1MW logarithmic (A) taper rotary potentiometers, 16 or 24mm (VR1-VR3) 3 knobs to suit VR1-VR3 [Altronics HX6020 or H6030, Jaycar HK7705] 1 2kW mini top-adjust trimpot (VR4) [Altronics R2477B, Jaycar RT4354] 1 23 × 2-pin (double row) right-angle header (CON2-CON4) 3 PCB-mount BNC or panel-mount BNC or RCA connectors (CON6, CON8, CON10) [Altronics P0529] 1 jumper shunt (for CON3) 2 20-pin headers (for mounting the Pico) 2 20-pin header sockets (optional; for mounting the Pico) 1 USB micro Type-B cable 1 USB isolator (optional, but highly recommended) [www.aliexpress.com/item/1005001369085297] 1 set of DuPont female plug to mini clip digital test probes (optional) 1 A5 laminating pouch (for label) Hardware, wire etc 4 4G x 9mm panhead self-tapping screws 4 2mm-long 3mm ID spacers OR 8 1mm-thick M3 Nylon washers 1 10cm length of 20-way ribbon cable 1 3cm length of 1.5mm diameter heatshrink tubing (for the LED) 1 small stick of hot-melt glue or tube of epoxy adhesive (to secure the BNC connectors) Semiconductors 2 SN74LVCC3245ADW 8-channel bidirectional level-shifters, wide SOIC-24 (IC1, IC2) [DigiKey, Mouser, element14] 1 TL074H precision quad low-noise JFET op amp, SOIC-14 (IC3) [DigiKey, Mouser] 1 AMS1117-3.3 regulator, SOT-23-3 (REG1) [DigiKey, Mouser, element14] 1 AMS1117-1.8 regulator, SOT-23-3 (REG2) [DigiKey, Mouser, element14] 1 LM2664M6 switched capacitor voltage inverter, SOT-23-6 (REG3) [DigiKey, Mouser] 1 3mm LED in a bezel or LED and separate bezel (LED1) [Altronics Z0238, Jaycar SL2615] 9 BAS40-05 dual common-cathode schottky diodes, SOT-23 (D1-D8, D17) 10 BAS40-04 dual series schottky diodes, SOT-23 (D9-D16, D18, D19) Capacitors (all SMD ceramic M2012/0805-size 16V X7R unless noted) 3 10μF M3225/1210 or M3216/1206 2 3.3μF M3216/1206 8 1μF 3 100nF 250V M3216/1206 or M3225/1210 9 100nF 3 50pF Resistors (all SMD M2012/0805 ⅛W 1% unless noted) 1 150kW 1 22kW 7 10kW 1 4.7kW 1 2.2kW A pinout diagram of CON2-CON4 as shown 3 1.2kW from the front (viewed from outside the enclosure). Note that this diagram and Fig.7 3 1kW shows the plastic shroud on the header 3 100W extending one row beyond the ends. 1 47W 3 10W ¼W axial 5 100W M3216/1206 1/16W Panasonic EXB-S8V101J quad resistor arrays can be substituted with a single 19.1kW resistor 🔹 🔹 This style of female DuPont-style mini probe clips is convenient for connecting to IC leads and test points. They will plug straight into the rightangle header on the unit. siliconchip.com.au 🔹 Hard-to-get parts for the PicoMSA (SC7323; $50): includes the PCB, Raspberry Pi Pico (unprogrammed) plus all semiconductors, capacitors and resistors Screen 8: display parameters for each channel row can be set by clicking on the channel icon at the left of the screen. The vertical resolution in V/div can also be set for analog channels if the default auto-ranging resolution is not optimal. Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. for triggering (see Screen 9). Levels, rising, falling and changing signals across multiple inputs can be used to construct the required triggers. The sampling rate may be limited when triggering is enabled, as the analyser needs to be able to stream the data continuously. When only digital signals are being captured, RLE compression can significantly boost the effective streamed transfer rate, allowing higher sampling rates to be used. Digital input channels need to be selected sequentially, with no gaps. If all channels between D2 and the highest input channel enabled are not selected, an ‘unspecified’ PulseView capture error may result. Thus, you cannot select, say, only inputs D2 & D4 or D2-D9 & D11. If any analog channels are enabled, the sampling rate will be no more than 2.4MHz divided by the number of active analog channels so that the digital and analog samples remain synchronised on the display. For mixed signals, one analog sample is sent for every digital sample. If the sampling rate is higher than the maximum ADC sampling rate, any analog signal is not shown at the correct frequency, as it is captured at a different rate from the digital channels. To avoid this, do not exceed a sampling rate of 2.4MHz divided by the number of active analog channels (see Table 1). Further information on using Pulse­ View’s extensive feature set is available in the online manual (siliconchip. au/link/abwa). Conclusion This project would have been significantly more complex without the speed & flexibility of the Raspberry Pi Pico’s PIO processor, pico-coder’s clever firmware and the volunteers who have helped refine the Pulse­View software. Together, these have made providing a high-performance, mixed-signal logic SC analyser relatively easy. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. 64 Silicon Chip Screen 9: PulseView has flexible triggering options for digital signals. Triggering is processed on the host computer, potentially limiting capture rates. Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine September 2024  65 SILICON CHIP Mini Projects #010 – by Tim Blythman IR Helper Infrared (IR) remote controls make life easier. However, each controlled device typically needs its own remote control, making it awkward when you have many devices. The IR Helper can simplify things by emulating different remote controls. T he main role of the IR Helper is to send IR signals automatically, so you don’t have to juggle multiple IR remote controls. Our prototype can do this in a couple of ways, but since it is programmed using the Arduino IDE, it is easy to extend and adapt. You will need some Arduino knowledge, though, since you will have to change our prototype sketch to suit your equipment and its IR codes. The IR Helper can be programmed to send a signal when it is powered on. Many devices like TVs have USB ports, so you can simply plug the IR Helper in, and it will power on when the TV does and send out the signals it’s programmed to generate. The IR Helper can also respond to IR commands and perform extra actions by sending further signals to other devices. For example, the IR Helper could detect the TV being switched on remotely and then turn on a receiver, amplifier, DVD player or all three! From the photos, you can see that the IR Helper has simple hardware. It uses two main modules: a small microcontroller module and an IR receiver module. We have used a module rather than a simple IR receiver because of its handy onboard LED indicator; it is also slightly cheaper. An IR emitter LED is included so that the IR Helper can transmit as well as receive IR signals. The main processor is a compact Leonardo Tiny board with a USB interface. The USB interface is used to display received codes for testing, among other things. We published an article in the August 2018 issue titled “Turn any PC into a media centre – with remote control!” (siliconchip.au/Article/11195). These two projects use very similar hardware, so you might be interested in reading the earlier article to see what else can be done with this basic combination of parts. Circuit details Fig.1 is the wiring diagram. We assembled our prototype by soldering the parts to the Leonardo Tiny board, using heatshrink tubing to protect the exposed leads where necessary. You could also use a full-sized Leonardo board if you wanted to. If you have the Arduino Beetle board from the 2018 article, you could add the IR Transmitter LED, updating the hardware to suit this article, since both projects use the same pin for the IR receiver. The IR Receiver Module incorporates one LED that illuminates when the IR receiver chip sees a valid, mod- Parts List – IR Helper (JMP010) 1 Leonardo Tiny board [Jaycar XC4431] 1 IR Receiver Module [Jaycar XC4427] 1 IR Transmitter LED [Jaycar ZD1946] 1 220W 1% ½W axial resistor [Jaycar RR0556] 1 3cm length of red wire [Jaycar WH3010] 1 3cm length of 5mm diameter heatshrink tubing [Jaycar WH5553] 66 Silicon Chip Australia's electronics magazine ulated signal. The S pin of the module goes low at the same time, signalling to the processor in the Leonardo Tiny that a signal has been received. The Leonardo Tiny sends an IR signal by driving its A0 pin high, sending current through the IR transmitter LED. The pin does not have a lot of drive capability, but it’s enough for transmitting commands over short distances. The IR LED in your handheld IR remote control will be driven much harder than the one in the IR Helper, but we expect that most readers will situate their IR Helper near the devices it is transmitting to. You can see that the IR receiver and transmitter are on opposite sides to facilitate this. Assembly Solder the short length of red wire to the middle pin of the IR Receiver module, then cover the exposed parts of the pin and wire with a few centimetres of heatshrink tubing and shrink it into place. Solder the two outer pins of the module to the D11 and GND (−) pins of the Leonardo Tiny, as shown in the photos. Note that the module has to be upside-down for this to happen. Next, solder the other end of the red wire to the 5V pad on the other side of the Leonardo Tiny. Prepare the LED by cutting the longer anode lead to around 5mm. Cut one of the resistor’s leads to a similar length. Solder the two cut leads together, then use the heatshrink tubing to cover most of the LED’s leads separately. This LED assembly can now be powered directly from a DC supply. You could use this idea on a breadboard or siliconchip.com.au similar to add LEDs without needing to wire up separate resistors. Now solder the exposed ends of the LED assembly to the A0 and GND pins of the Leonardo Tiny. You should be able to re-check the polarity by observing that the side of the LED with the flat edge connects to GND. You can do a quick test by applying power and aiming a signal from an IR remote control at the receiver module. Its indicator LED should flicker while it is receiving a valid IR remote control signal. Arduino sketch You can download the Arduino sketch for this project: siliconchip. au/Shop/6/450 If you don’t already have it, download and install the Arduino IDE from www.arduino.cc/en/software The sketch uses the “irremote” library. This library contains just about everything you need to send and receive IR signals for all manner of devices. To install it, search for “irremote” in the Arduino Library Manager and click the install button when you find it. We used version 4.3.1 of the library. Then open and upload the IR_ HELPER sketch. You will need to customise your sketch to work with your devices, but this is made easier since the prototype sketch will also show received codes on the Serial Monitor, allowing you to find the correct protocol and codes for customisation. Screen 1 shows the typical result when two different buttons on the same remote control are pressed. Note how the sketch even displays the recommended Arduino code. We used three for the <numberOfRepeats>, but you could try increasing that if you find that codes are not being received. Fig.1: this wiring diagram shows how our prototype is connected, with components and modules wired directly to the processor board. You could instead use a full-sized Leonardo board with jumper wires to make the connections. Protocol=NEC Address=0xEF00 Command=0x3 Raw-Data=0xFC03EF00 32 bits LSB first Send with: IrSender.sendNEC(0xEF00, 0x3, <numberOfRepeats>); Protocol=NEC Address=0xEF00 Command=0x3 Repeat gap=40800us Protocol=NEC Address=0xEF00 Command=0x2 Raw-Data=0xFD02EF00 32 bits LSB first Send with: IrSender.sendNEC(0xEF00, 0x2, <numberOfRepeats>); Protocol=NEC Address=0xEF00 Command=0x2 Repeat gap=40800us Screen 1: the terminal output from the IR Helper shows the protocol, address and command of received IR codes. The sketch also prints the necessary Arduino code to replicate a received signal. Information about supported remote control protocols is at https://github.com/Arduino-IRremote/Arduino-IRremote Press the button you wish to emulate and check its code using the sketch, then copy it to the triggeredAction() function of the sketch and upload it again. You can then check whether the transmitter works by typing ‘t’ into the serial monitor. The prototype sketch also sends this code whenever it sees a code matching the RX_ADDRESS and RX_COMMAND values. The prototype sketch will also run the powerOnAction() function every time it is powered on; you can add another IrSender command to that function if needed. You would use this feature by plugging the IR Helper into the USB port of a device like a TV, so that when it is switched on, the powerOnAction() is run. Since many remote controls have a toggle action power button (ie, pressing power can both switch the device on and off), this can be a good way to distinguish an ‘on’ action from an ‘off’ action. From here, you should be able to see what changes you need to make to fit the sketch to your situation. You could also add other sensors to automate other functions. For example, you could rig up a light or motion sensor to switch on a lamp that has IR remote control when it gets dark or movement is detected. The IR Helper could also be used to add IR remote controls to devices that do not have it by wiring up a relay module to the Leonardo board to switch things on or off upon receipt SC of certain commands. The assembly is compact at just 10cm long. We’ve left quite a bit of lead on the LED to allow it to be bent for aiming purposes, but it could be made shorter if necessary. The IR Receiver Module is mounted upside-down (relative to the Leonardo Tiny) so the pins align with the correct pads on the Leonardo Tiny board. siliconchip.com.au Australia's electronics magazine September 2024  67 SILICON CHIP Mini Projects #011 – by Tim Blythman This simple circuit causes an RGB LED to constantly shift between various colours using just three transistors and a handful of passives. No-IC Colour Shifter S ometimes, ICs and microcontrollers make things too easy. If you want to understand electronics better, using simpler components can help reveal how things work at a lower level. This circuit is one of the simplest versions of an ‘astable multivibrator’. That is a circuit that changes state continuously. Similar circuits form the basis of a bistable multivibrator, also known as a flip-flop or latch, the basis of many types of computer memory. So these types of circuits are all very important, even to modern digital technology. A ‘monostable multivibrator’ provides a single pulse of a known duration when it is activated. That is another similar circuit used where a timing feature is needed. Variations of this principle using valves or vacuum tubes date back to 1919, well before the invention of the integrated circuit (IC). We published a Circuit Notebook entry that uses the same principle (December 1995 issue; siliconchip.au/Article/6078). Three transistors, six resistors and three capacitors are all it takes to make an RGB LED flash and change colour. Fig.1 shows how we have laid it out on a breadboard, while Fig.2 shows the equivalent circuit diagram. You can see the layout in the photos and this video (siliconchip.au/link/abwi). It would be pretty straightforward to solder these components to a Jaycar HP9570 protoboard since it has much the same layout as the breadboard. We supplied 5V power by running some jumper wires from an Arduino board plugged into our computer, but you might have something else on hand to use. The circuit uses PNP transistors to allow us to use the common-­cathode version of the RGB LED module Figs.1 & 2: this shows how we laid out the components on a breadboard. If you leave off the capacitors and yellow wires, you’ll have three identical sections, each feeding one of the individual LEDs of the RGB LED module. The capacitors between stages are what cause the colour to shift constantly. You can see how it works a little more clearly in the circuit diagram. One capacitor charges until it switches on a stage that is currently off, and in doing so, switches another stage off. That causes it to cycle through three colours: cyan (blue + green), mauve (blue + red) and yellow (green + red). 68 Silicon Chip Australia's electronics magazine siliconchip.com.au (marked BRG−), which is what we got from our local Jaycar store. If you have a different version with a common anode (perhaps marked with something like BRG+ or BRGV), you can use NPN transistors (such as BC547s) instead. They have the same pinout (but opposite polarity), so they are placed the same way. In that case, the capacitors need to be reversed, as do the supply connections (the red and black wires) and positive and negative breadboard connections. The alternative breadboard layout is shown below in Fig.3 (note the slightly different labelling on the RGB LED module), while the resulting circuit is shown in Fig.4. In this version, all currents will flow in the opposite direction. Circuit details Imagine the circuit (Fig.2) without the capacitors connecting between the stages, which would have three identical but otherwise unconnected sections. You could simulate that on the breadboard by removing the yellow wires that link the stages. The 10kW resistors allow current to flow from the emitter of each transistor and out of the base to ground. This biases on the transistors and allows current to flow out of the collector, via the 220W resistors and one of the LEDs in the RGB LED module to ground, lighting it up. The RGB LED would appear white, as all three elements would be lit. Ensure the red wires go to your 5V supply and the black wires go to ground. We’ve used BC557 PNP transistors to make the circuit work with the common-cathode RGB LED module we purchased. You can build and test part of the circuit by fitting all the components and wiring shown here except the yellow wires and capacitors. Powering up the circuit at that stage lets you confirm that the RGB LED is working and shows a solid white colour. You can build the circuit like that, leaving out the yellow links and confirming that is what happens. It’s a good way to check that the wiring is correct so far. Now add the two shorter links and all three capacitors, then power on the circuit. The RGB LED might flicker but will settle back to a solid white. Adding the longer link should cause the RGB LED to cycle through the colours, changing about once per second. Before adding the link, all three collectors are near 5V since all the transistors are on. Adding the last link pulls the base of the right-hand transistor (Q3) up to 5V too, switching it off. The 10kW resistor slowly charges the associated capacitor until Q3’s base voltage drops far enough to allow it to switch on. However, Q3’s collector is connected to Q2’s base via another capacitor. So Q3 switching on causes Q2 to switch off. Now the middle 10kW resistor slowly charges up the next capacitor, and the cycle continues around the loop of three subcircuits. The colour Figs.3 & 4: this layout is similar to Fig.1 but suits a common-anode RGB LED module in case you come across one. The circuit at right is basically the same as in Fig.2 but flipped upside-down, with the PNP transistors switched to NPN and the polarised electrolytic capacitors reversed. siliconchip.com.au Australia's electronics magazine September 2024  69 Silicon Chip PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). A top-down view of the finished Colour Shifter. Note the capacitor orientations; they are reversed on the version using NPN transistors (such as Jaycar ZT2152). showing on the RGB LED changes as it does. The cycle will start even if the circuit is powered on with all three links in place. That’s because there is enough variation in the component values to ensure that one transistor switches on before the others, which will start the cycle. You might have realised that the electrolytic capacitors will sometimes be reverse-biased, with the positive end actually being more negative. This will be at most around -0.7V (limited by the 0.7V across the transistor base-emitter junction). Reverse voltages below 1V are generally not a problem for electrolytic capacitors as the voltage is not high enough to affect the insulating oxide layer. Tweaks EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 You could replace the RGB LED with three individual LEDs if you like, or even a discrete RGB LED like Jaycar’s ZD0270. If you do this, double-check the pinout and make sure the cathode or cathodes (for individual LEDs) all go to the black wire in Fig.1. You could even add some jumper wires to place the LED module fur- ther away from the main board. You can modify the capacitor values if you want to change the cycle speed. Higher capacitor values will slow the rate (as they take longer to charge and discharge), while lower values will speed it up. Experimentation You might be wondering if the circuit will work with more than three stages. We tried it with four & five stages and found that the cycle did not start reliably. If it did start, two or more impulses travelled around the loop! However, it works well with two stages. If you build the circuit without the third stage, you should see the two lights alternate, making it useful for something like a model railway level crossing. Earlier, we mentioned that devices like timers are closely related to this circuit, even though they have different functions. If you swap one of the capacitors with a wire link, the cycle will run until it stalls on one colour. If you remove that link, the colours will change a few times, then stop again, making it a very basic countSC down timer. Parts List – Colour Shifter (JMP011) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS 1 30-row breadboard [Jaycar PB8820] 1 RGB LED module [Jaycar XC4428] 3 BC557 45V 100mA PNP transistors (Q1-Q3) [Jaycar ZT2164] 3 100μF 16V electrolytic capacitors [Jaycar RE6130] 3 10kW ½W 1% axial resistors [Jaycar RR0596] 3 220W ½W 1% axial resistors [Jaycar RR0556] 1 5V DC power supply (eg, USB/serial adaptor plugged into USB supply) assorted solid-core wire [Jaycar PB8850] 70 Australia's electronics magazine JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OR PAY $500 FOR ALL SIX (+ POST) Silicon Chip siliconchip.com.au Electronics Manufacturing in Australia Australia’s electronics manufacturing was world class. In the 1930s, over a thousand Aussie radio manufacturers supplied local and international markets, with production facilities ranging from home garages to massive factories that compared to most in the world in size and product quality. Part 2 by Kevin Poulter Captions, left-to-right, top-to-bottom: • Nicholson’s had a fine HMV display, organised by the HMV ad department. Note the three theatre productions advertised in banners at the top of the window. Many theatre booklets available at shows advertised the local radio & TV store. • An AWA Radiogram from around 1954, photographed by Max Dupain for the leaflet. • The EMI /HMV TV production line. Note the frames used to hold the partially assembled TVs. siliconchip.com.au Australia's electronics magazine September 2024  71 M any of the largest plants were branches of the big international names like Philips, Pye and EMI. Other big companies were inspired by or agents of international companies. For a long time, Amalgamated Wireless of Australia (AWA) was linked to Marconi Ltd of the UK, while Astor drew on the Radio Corporation of America (RCA) for inspiration. These arrangements resulted in many items being designed in Australia and produced with manufacturing techniques and quality compared to anywhere in the world. That was boosted by staff emigrating to Australia from countries like the UK to impart their knowledge here. AWA, in particular, made nearly all products and parts in-house, including valves, transistors, stamped and folded steel chassis and pressed Bakelite cases. Philips’ manufacturing was centred in Hendon, South Australia, where they also produced transistors. However, it was reported that the ordering process for Philips parts to make radios went via Sydney and was cumbersome, with long delays. So Philips radios were known to be assembled with components from other brands. Well-known local brand parts like IRC resistors and Ducon capacitors were installed in many local radios. In the 1930s, radio factories often made timber-case consoles at the factory; however, by the 1960s and 1970s, both TV and radiogram cabinets were often built to order by specialist furniture companies like Gainsborough Furniture. They were then delivered to the manufacturer to have the electronics installed. The furniture company’s name was often stamped inside the cabinet. Gainsborough established a plant next to the Astor Clayton Works on Clarinda Road, Clayton, Vic. The huge 3-in-1 (TV, radio and record player) cabinets were coated with a nearly indestructible polyurethane finish that had superb gloss and resistance to scratches. Each 3-in-1 needed buffing before despatch, but the cabinets were extremely heavy. So big men from Europe emigrated to Australia to lift and buff them. This worked well, but unfortunately, the dust from buffing was a lung irritant, and many workers became ill (or worse) years later. Large-scale manufacturers like AWA, HMV & Philips were like little 72 Silicon Chip Here the electronics are being installed into beautiful timber cabinets. Carpet and soft materials were used everywhere to avoid scratches. Modern collectors would love to have the brand-new turntables. AWA made a massive statement of their superiority in 1939 by building the AWA Tower as a new headquarters in York Street, Sydney. AWA was incorporated in 1913 and was the first to manufacture commercial radios in Australia, in 1920. The AWA Tower is now heritage listed. An AWA Radola promotional photograph with actress Alma Adey, circa 1953. Photograph by Max Dupain. Valve Works Manager Mr R. Lambie inspects the millionth miniature valve made by AWA around 1950, still hot from the Sealex machine. The valve is held by Mr Kevin Ward, while operator Miss Pat Wood starts on the next. Australia's electronics magazine siliconchip.com.au The Marketing departments produced promotional materials like Point of sale headers, leaflets and more. Prizes were offered for competitions, plus anything to showcase the new products. In the 1950s, it was much easier to use an artist’s painting to produce a result with accurate colours. Often the artwork was based on a photograph. The header says HMV Golden Jubilee Year – 1900 to 1950. Below: testing a completed HMV chassis, sans CRT. A fixed CRT for testing is above the test technician. cities, with their own post office (for business mail), cafe, accounts (in and out), purchasing, design, sales, shipping, machine shop, carpentry department, administration, managers, despatch/packing, order processing, switchboard, pay office, tea and coffee lady, and sometimes even a staff store. The staff stores offered staff prices significantly below retail. Staff in the office would see a ‘mail girl’ arrive at each desk once a day, as well as the tea and coffee trolley in the morning and afternoon. A charming lass also delivered pay to every desk or work area, so your work was never interrupted. The wages were delivered in small envelopes as notes and coins. Radio design It’s reasonable to expect that the parent companies of international brands would design products and send kits of parts to Australia or supervise a worldwide design manufactured here. After all, the Philips head office in Eindhoven, Netherlands, employed 2000 people, including more than 500 scientists in their research laboratories during the early 1980s. In practice, Australians designed most locally-distributed products. Philips Australia even set up a manufacturing plant at a university in Bandung, on Indonesia’s main island. AWA and Astor, plus many others, designed local radios and machines that reduced the number of employees needed. It was a hint of what was to come in today’s robotic factories. The larger companies boasted an advertising manager in-house, with photographers like Max Dupain and later myself on contract. A lesser number, like EMI/HMV, had their own photographer. In the 1950s, professional colour film was difficult to colour balance and still unusual, so outstanding paintings were produced for colour advertising in the likes of Women’s Weekly. There were still some engravings made for best reproduction in newspapers. Many of the photographs here were made on quality cameras, with 4 × 5-inch negatives (that’s postcard size, around 100 × 125mm!), so the quality was very good, mainly depending on the lighting. Manufacturers had special promotions; here, the Philips logo is on Frank Fry’s aircraft (photo by Kevin Poulter). Frank was the world acrobatic champion. Another major promotion was sponsoring Dire Straits’ Australian tour. siliconchip.com.au Australia's electronics magazine From design to customer Parts were ordered once a product was designed, with some made September 2024  73 This window celebrates the film “The Great Caruso” from 1951. Caruso was the”Rock Star” of the early 1900s, with millions of followers. The film won an Academy Award for “Best Sound Recording”. internally. When final production began, the sales staff responded to orders they received by raising an internal order on the factory. Next, the production supervisor managed the factory supply schedule, sometimes coerced by enthusiastic salespeople pushing to get their orders fulfilled first. The completed products went through testing processes and remained allocated to internal orders, which may have been 100 or more units for one customer. Testing involved checking many performance factors. Military customers expected testing over a temperature range or testing after aging. Mobile two-way radios would have a bumpy ride in many cases, so a bump machine was designed to test for loose connections. I witnessed a cost-cutting idea, where only a percentage of radios were tested, about 1 in 5 or 1 in 10. This really sped up production, but it was soon a disaster, as customers found the units that didn’t work. Not very good PR! Shipping An HMV radio and television display circa 1969. This was very likely at the Royal Easter Show in Sydney. On arrival at despatch, products were packed for a safe passage. Packing for sea freight overseas required something more sturdy than a cardboard box, so a specialist international freight-packing business often made timber boxes for this purpose. The inside of the box was lined with waxed paper or something similar to resist dampness and water incursion. On at least one occasion, I filled a large part of an aircraft with tonnes of rack-mounted equipment and a later shipment of many more tonnes via sea to Kota Kinabalu, the state capital of Sabah, Malaysia. From the beginning of radio broadcasting, just 100 years ago, AWA supplied many of Australia’s broadcast transmitters, so they made very large shipments too. Communications & Exports Elvy Carnegie (Elvy’s) Radio TV Records, a multi-storey store circa 1958. HMV put up a big display. Like other major stores, they offered in-home TV demonstrations, erecting a TV antenna and even doing the paperwork for the reception license required by the government. Australian employees occasionally travelled overseas to learn about the latest technology. However, when the local Philips K9 colour TV was doing well, one of the Aussie technicians turned the tables and went to Germany to help them with their version of the K9. A noticeable servicing feature of the set was that the two main Australia's electronics magazine siliconchip.com.au 74 Silicon Chip Left: a 1942 leaflet; despite a world at war, people were still purchasing new radios. Most were revisions of existing radios to avoid new tooling. Many domestic radio companies also made military radios. circuit boards would hinge open for easy access. Australia exported electronic products, especially communications devices, to regions like Southeast Asia and Pacific countries. At Pye, we had a telex machine, which was like an in-house telegram service. International phone calls on the lines transmitting telex were expensive. So, the telex operator would type messages on a narrow paper punch tape all day. Then, at the end of the day, she would send the messages via high-speed transmissions by pressing “send”. The pre-punched tape would feed through the telex, sending messages out very quickly. I remember one telex coming in from Kuala Lumpur asking Export how long their order would take. My first thought was, “wish you luck with that enquiry”. After about a week, a siliconchip.com.au different approach from KL: “Are you all dead? I would like a reply to my delivery enquiry of last week.” Marketing Australians can make electronics comparable to some of the best products in the world, but a company is doomed without sales. So photographs and technical information were needed for sales staff, service manuals, newspaper and magazine advertising, slides in theatres, attachments to contract pitches, sending to potential clients and more. During the era of large console radios in the 1930s, some consoles were made as small replicas, about the same size as a cathedral tabletop radio. That allowed the salespeople to transport and demonstrate the console more easily, as it had all the same electronics – just in a smaller package! Australia's electronics magazine By the 1950s, plastic mantel radios with no internal parts were made for easy handling by the salesman so the store owners could more easily see the style of the mantel radio. Competition The market was big enough for a fair number of manufacturers. AWA and Astor were the main players, with AWA being the strongest in its home state of NSW and Astor being the leader in Victoria. At various times, each claimed to sell the most radios in Australia. AWA boasted the first fully Australian-made transistor radio. It was an interesting time for retailing products. Have you ever wondered why some radios were sold under multiple name badges? For example, the Philips metal-cased valve portable is still collected with September 2024  75 All components were made in-house During the 1920s and 1930s, AWA made virtually everything in house, including screws, resistors and foil capacitors, although the latter were sourced from IRC and Ducon after WW2. Bakelite moulding was a speciality for knobs, cabinets, component parts, telephone handsets and parts for Sunbeam and Hotpoint appliances. AWA had some of the largest specialised injection moulding presses in Australia for precision moulding. Before tariffs were removed, AWA manufactured approximately 975,000 loudspeakers. Many AWA valves were made under license. It was intricate work, yet people said valves were expensive! one of three brands: “Philips”, “Fleetwood” or “Mullard”. Well, it was to increase sales. Before Australia’s restrictive sales legislation, a manufacturer could refuse to supply electrical products to some stores, especially if they already had a good dealer in that town. The existing dealer could force this, too, by saying they would not stock the brand if the nearby store could compete with him. For example, a retailer in Gippsland (Vic) applied to sell Philips products. Philips told him he could not sell Philips Radios, as his area already had an outlet. “But no problem, you can sell Mullard.” Philips owned Mullard at the time, and this demonstrates one of the reasons for rebadging! so they were not seen on the production line. In the panorama of the production line image in this article, a male supervisor watches to check that there is little or no talking and that everyone is dedicated to the task in front of them. After the TV finishes going through each sub-assembly, the completed chassis is transferred to a man in the inspection department. If it passes visual inspection, he runs the TV through its electronic testing and visual paces, including stability and linearity, using a test pattern on the screen. The men were selected for this role due to their training at Radio Colleges. The Astor brand shop in Melbourne. The brand name Astor was coined when Sir Arthur Warner was staying at the Astor Hotel in New York, and he thought, “That’s a good name.” Looking at Astor’s 1964 “Your Job” booklet reveals a lot about electronics manufacturing in the 1960s. Each employee worked from 9am to 5pm and had a number to clock in and out with. Lunch was just half an hour, even though the canteen served big meals and there was a queue to get yours. ‘Reverse sexism’ and chivalry meant that female employees got ten-minute morning and afternoon tea breaks. Referring to toilet breaks was frowned upon, so they were likely intended as toilet breaks. Working in the Astor accounts department was a superior position. Still, in 1964, the weekly pay was just six pounds, twelve shillings ($13.20 in decimal currency or about $220 per week in today’s inflation-adjusted dollars). However, money went much further at that time. Employment was on a weekly basis, which sounds extremely brief, but I never saw it exercised. You could be dismissed without notice for “malingering, inefficiency, neglect of duty or misconduct”. Even in non-union companies, the employee was highly valued in the 1950s and 1960s, as there was nearly 100% employment. When I applied as a 16-year-old, I was shown around the factory and then asked if I could start on Monday! There were no queues out the door, like in many places where people apply for jobs today. All employees were required to have a medical examination before starting, supposedly for their benefit. This was so they would only be required to do work within their health limitations. On the positive side, the company usually selected candidates for senior positions from existing employees. Lifting the veil Electronic Industries, later Astor, began in 1923 in a small basement Many of the EMI/HMV photographs here are the only ones in existence, published here for the first time. They show more than many words could describe. The big factories had rows of women, usually housewives, each assembling a small portion of products like TVs. These ladies were the backbone of the assembly and had the wonderful character of not being too bored by repetitive tasks. Males were considered more ambitious, with a shorter attention span, Philips AC/Battery portable radios about 1953. For marketing purposes, these radios were badged either Philips, Fleetwood or Mullard; one of each is shown. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au Negotiation for a pay rise was almost unheard of, although the company stated they would review pay from time to time. What happened to Australian electronics manufacturing? A parliamentary submission after the big electronics nose-dive into collapse says it well: “The demise of Australian manufacturing started when the then Prime Minister Mr Gough Whitlam took advice from the Industries Assistance Commission and (in 1973) reduced tariffs by 25%. The country could not compete with the low wages in Asian countries.” I saw mass closures of electronics factories shortly after, and talented Australians were left without a job. Companies like Philips Mobile Communications had lower sales due to cheaper imports from companies like Motorola. Then, with the advent of mobile phones, sales plummeted. Philips threw in the towel and shipped essential production equipment to China. A good number of Philips two-way comms staff were later employed by Simoco Australia, who develop and sell the latest communications equipment. Radios and TVs were given to excited viewers and listeners as prizes. This publicity was cheaper than paid advertising. Who owns AWA now? The answer will surprise many. After their radio sales fell to unsustainable levels, they ran AWA Computer Services for a while. Eventually, the copyright and trademarks for the radio side of the business apparently lapsed, so cheap imported products had AWA badges. Cabrini Catholic Hospital in Melbourne wanted to continue using the IP in the software that was important to running the hospital, so Cabrini is now the owner of AWA. Entrepreneurs became very successful importers, including Dick Smith and the late Gary Johnston of Jaycar. In an address to the HRSA, Dick Smith said the upheaval was good for Australia, as we then all paid much less for electronics, including TVs. Certainly, Australians can now purchase and import an amazing array of electronic technology. Only speciality local manufacturing remains, like producing technology for satellites and radio imaging to detect food production problems. Many who worked in electronics will say, “It was great while it lasted.” SC siliconchip.com.au Above: Astor valve radio production. The frame holding a chassis in the foreground is a simple timber truss. Astor chassis are punched in one operation on these automatic presses. After stamping the holes for valve sockets etc, the metal is cadmium plated. Cadmium, and the compounds formed when it corrodes, are toxic by ingestion and acutely toxic if inhaled. Australia's electronics magazine September 2024  77 Discrete Ideal This deceptively simple circuit uses just a handful of transistors, diodes and resistors. But it still provides a very useful function: active rectification of the output of a centre-tapped transformer or combining two DC supplies with low losses. It is much more efficient than a bridge rectifier or diodes at higher currents, producing less heat without costing much more. Project by Phil Prosser & Ian Ashford T he Ideal Diode Bridge Rectifiers project, published in December 2023 (siliconchip.au/Article/16043), included six different PCB designs to suit different situations. It was popular, with many built, but two aspects of that design bothered me (and others). Firstly, it used a pretty expensive custom IC, with the SMD version being a bit tricky to solder. Secondly, despite that expense, it could only handle rectifying the output of a single transformer secondary. So you couldn’t use it at all with a centre-tapped secondary, and two complete boards were required to derive split rails from a transformer with separate secondaries, doubling the cost. Wouldn’t it be nice to have a direct drop-in replacement for a bridge rectifier that could handle single, dual or tapped secondaries? And it’d be great to use standard parts, so we don’t need to source that expensive IC. Reader Ian Ashford sent us a circuit design he uses for dual-rail rectification but didn’t have a PCB design. When the Editor asked me if I wanted to turn it into a full-on project, there was only one possible answer to that! Ian and I performed further testing, development and tweaking, finally arriving at this very flexible, robust and useful circuit. So, this project is a collaboration that follows the ideal rectifier theme but with a different focus from the previous design. When to use this design As well as rectifying a transformer’s output(s), this design is also suitable for combining DC supplies with low losses, eg, combining the output of a solar panel and a battery, or a solar panel and wind generator. While it costs a little more than a bridge rectifier to build, it is significantly more efficient at higher currents and has a much lower voltage loss. So it’s ideal for high-power devices like power supplies and audio amplifiers. Its only real drawbacks are a limited voltage handling capability (up to ±40V or +80V) and the fact that it’s larger than a 35A bridge rectifier, so you’ll need room to fit the PCB. This project uses high-current, low RDS(on) Mosfets. To keep the circuit simple, we have used P-channel Mosfets on the positive rail and N-channel Mosfets on the negative rail. If your current demands are only modest, you could use the ubiquitous IRF9540 (P-channel) and IRF540 (N-channel) power Mosfets, which are available from Altronics and Jaycar. They can handle up to about 5A. Much more significant currents can be handled using the devices in the parts list, which are not all that expensive but are unlikely to be available from your local shop (but kits are available). All the other parts in the design are bog-standard, and you will surely have them in your parts drawer or at your local shop. Design process Between Ian’s initial email with the circuit he uses in DC and low-power Figs.1(a) & (b): the two main ways to use the Discrete Ideal Bridge Rectifier. At the top, a centre-tapped transformer secondary winding is used to generate split (positive and negative) rails. Two separate secondaries can also be used if they are connected in series. The connections at right show how to use the same board to combine the outputs of two DC supplies (the solar panel and battery are just examples). OUT+ will be fed by whichever has a higher voltage. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Bridge Rectifier » Generates split rails (positive and negative DC supplies) from a single centre-tapped transformer secondary (or two secondaries wired in series) » It can also be used to combine two DC supplies (whichever has a higher voltage feeds the load) » Maximum output voltage: ±40V or +80V (transformer applications), +40V (combining DC supplies) » Maximum current: 10A RMS without heatsinking, more with heatsinking » Typical voltage drop: <100mV input-to-output » Typical dissipation: 1.7W <at> 5A RMS, 6.8W <at> 10A RMS AC applications and the final design presented here, we exchanged many ideas, questions and refinements. Some requirements we decided on are: ; A low part count was important. ; The design had to ‘just work’ without tweaks. ; Reverse current when Mosfets switch on and off had to be minimal in all applications. Many ideas were shared, and challenges were presented in every direction. In the process, the conceptual circuit grew to something larger and more complicated than was strictly necessary. It was at this stage that we tabled those design goals. Ian was keen to keep the size of the board down, so we designed a throughhole version and an alternative that uses some SMDs to fit in tighter spaces. We realised that this would never be the size of a conventional bridge rectifier, so we just aimed to produce reasonably-sized boards that would likely fit into an existing chassis but that aren’t too fiddly to build either. The final design is vastly ‘tighter’ than the test board. I often build a prototype board that is purely functional and worry about improving the layout later, once I’ve proven it works. In discussing what changes were warranted to Ian’s concept, achieving a design that ‘just worked’ became important. That led to the introduction of constant current sources as loads in the design. It makes the operation largely independent of supply rail voltage and allows constructors to use the Ideal Bridge with 9-25V AC transformers without any changes. We also changed the sense circuit siliconchip.com.au to only switch on the Mosfet when the input is at a programmed voltage above the rectified output. This blocks reverse currents and allows it to be safely used for combining DC supplies, which might be very close in voltage at times. The resulting circuit is simple and works well. We’ll get to a couple of subtleties later in the description, once we’ve gone over its operating principle. Two versions There are two PCBs for this project: an SMD version and a throughhole version. They use the same circuit. The SMD version is smaller than the through-hole version, which may be helpful in some circumstances. It doesn’t use any tiny parts (the resistors are M3216/1206 and there are SOT23 transistors), so it isn’t hard to assemble. Both versions use the same TO-220 (through-hole) Mosfets. That is because it makes it easy to add flag heatsinks if necessary for your application. High-current SMD Mosfets are available, but they are trickier to heatsink if necessary and will take up more room than a TO-220 in this application. Design limitations This circuit is suitable for rectifying the output of dual or split secondary transformers where the junction of the windings from the ground point for output capacitors, as shown in Fig.1(a). This design will work if you have a transformer with a single secondary Australia's electronics magazine winding, but the switching could be noisy. ICs like the LT4320 used in the December 2023 designs switch the bottom Mosfets on for a full half-cycle to ensure clean switching. So, for that sort of application, we recommend you build one of the designs we published then (kits are available at siliconchip. au/Shop/?article=16043). Regarding how much current the board can handle, P-channel Mosfets typically have a higher RDS(on) figure than N-channel Mosfets. This means that the positive-rail Mosfets will be the limiting factor in how much current can be drawn due to their voltage drop and consequent power dissipation. We have avoided the complexity of a gate drive boost circuit there. Using one would have allowed us to use four identical N-channel Mosfets, but we didn’t think that was worth the extra parts and possibly new failure modes. Up to about 10A, the Mosfets will not require heatsinking, although it wouldn’t hurt to add small flag heatsinks above 5A. Above 10A, you must add a substantial flag heatsink on each Mosfet. Decent flag heatsinks should let it handle at least 15A. Beyond that, you might need a more serious cooling solution, like forced airflow over heatsinks. Circuit details The circuit is shown in Fig.2. Unlike the previous Ideal Bridge Rectifier, this circuit can have its inputs connected across a single secondary or a pair of series-connected secondaries to generate split supply rails. In those cases, the secondary winding’s September 2024  79 centre tap does not connect to this circuit. Instead, it connects to the output capacitor bank ground and the load’s ground, as shown in Fig.1(b). So that it can produce split rails, it contains two similar sections stacked on top of each other. They would be identical except that they have opposite polarities to handle current flowing in opposite directions. The upper section uses two P-channel Mosfets, four PNP bipolar junction transistors (BJTs) and two NPN BJTs. The lower section has two N-channel Mosfets, four NPN BJTs and two PNP BJTs. Each of the four sections senses the input AC voltage at one terminal. When it is about 34mV greater in magnitude than the output voltage (higher than the positive rail or lower than the negative rail), the corresponding Mosfet is switched on by driving its gate with an appropriate voltage. We only want the Mosfet on when the input exceeds the output by a small margin to ensure that the Mosfet is off when these voltages are equal and that there is no chance the Mosfet is on as the input voltage magnitude drops below the output. If that were to occur, current would reverse and flow from the capacitor bank through the transformer, creating current spikes and a great deal of electrical noise, plus possibly overheating the Mosfets. Fig.2: the Ideal Bridge Rectifier circuit comprises two identical sections at the top to deliver current to the DC OUT+ terminal, with two more sections below to handle current flow through the DC OUT− terminal. The lower sections are ‘mirror images’ of the upper sections, with components of opposite polarity (NPN transistors instead of PNP etc). The circuit is the same for the TH and SMD versions; the alternative devices are direct equivalents except for their packages. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au As the four separate sections all work the same way, let’s concentrate on the one shown in the upper-left corner of Fig.2. The voltage sensing circuit comprises diodes D1 and D2 plus PNP transistors Q5 and Q6. Q5 acts as a diode, since its base and collector are joined. Ignoring the 68W resistor for now, with a constant current flowing through these transistors, both will conduct if the AC input voltage at CON3 is the same as the DC output voltage at CON1. If Q6 is on, Mosfet Q1’s gate voltage is high, and it is off. As the input voltage increases, Q6 switches off, so the gate of Mosfet Q1 is pulled low by its 22kW collector resistor – see Scope 1. The 68W resistor is important as it alters how the comparator works. The total current through the two 22kW collector resistors is determined by a constant current sink comprising NPN transistors Q7 and Q8. On the positive cycle for the AC1 input, about 0.5mA is drawn through each of these resistors (as well as the matching pair for Q9 & Q10). This 0.5mA flows through the transistor and diode pairs Q5/D1 and Q6/ D2, which drop the voltage by about 1.2V, but on the AC input path, it also flows through the 68W resistor, dropping 34mV or so in the process. This extra voltage drop means we draw more current from the base of Q6 than Q5 until the AC input is 34mV above the output voltage. Mosfet Q1 remains switched off until that condition is met. Once the input exceeds the output by 34mV, Q6 starts switching off and the Mosfet switches on. This charges the output capacitors until they get to 34mV below the input. Essentially, the circuit contains a negative feedback loop, where Q5 and Q6 try to maintain a 34mV difference across the Mosfet by controlling its gate voltage. Without the 68W resistor, they would try to maintain 0V across the Mosfet, and due to various tolerances in the circuit, the Mosfet might be held on all the time, which is not what we want! As a result, at lower load currents, we are not simply switching the Mosfet hard on and off; instead, it is operating in linear mode with a low voltage drop across it due to the negative feedback. Part of that voltage drop is a result of the RDS(on) of the Mosfet, while part is from the gate voltage being moderated, siliconchip.com.au Scope 1: an oscilloscope grab of the Ideal Bridge in operation, showing rectification of the voltage at the AC1 terminal. The pink trace is the output voltage at 5A, cyan is the AC input voltage, and yellow is the gate drive for Mosfet Q1, which peaks at about -8V. Scope 2: the Discrete Ideal Bridge starting into two 35,000μF capacitor banks. This is a pretty brutal thing to do to any bridge. Usually, you would use a soft-start circuit to keep the initial current surge under control. Still, the Bridge survived it! which we can see in the oscilloscope screen grabs. As the load current increases, we see the sense circuit driving the Mosfet harder, ie, its Vgs increasing until it is 12V, at which point the gate protection zener diode (ZD1 in this case) conducts to prevent the Mosfet gate from being driven beyond its ratings. If you look at the scope images (especially Scope 4), you will see that when drawing high currents, the circuit transitions from the linear feedback operation to driving the Mosfet fully on with 12V. This occurs because the voltage drop across the Mosfet exceeds 34mV due to its minimum RDS(on). As a result of the way we are driving the Mosfet, there is little value in utilising ultra-low RDS(on) Mosfets in a dual-rail bridge. 10mW or so is fine. We felt this was the sweet spot at which the voltage drop across the Mosfets is defined by the feedback loop up to about 5-6A. Because of how Mosfets are made, P-channel Mosfets tend to have a higher RDS(on). The constant current sink based around Q7 & Q8 is a standard two-­ transistor current source/sink configuration. We could have tied this to the output ground and reduced the dissipation in transistor Q7, but we chose to tie it to the negative output rail for the positive rail comparators and positive rail for the negative comparators. This is because it gives maximum gate drive to the Mosfets for low-­ voltage operation, especially during startup when massive currents are often drawn for charging capacitor Silicon Chip kcaBBack Issues $10.00 + post January 1997 to October 2021 $11.50 + post November 2021 to September 2023 $12.50 + post October 2023 onwards All back issues after February 2015 are in stock, while most from January 1997 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com. au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer Australia's electronics magazine September 2024  81 Scope 3: a close-up of the rectified output. Again, pink is the output, cyan is the AC input, and yellow is the gate drive. This neatly shows the Mosfet switching as the AC input voltage slightly exceeds the DC output voltage. Scope 4: the negative rail behaviour, which is a ‘mirror image’ of the positive rail. Driving the rectified 12V AC into a 1W load is clearly giving the transformer a workout, as seen by the flattened top and bottom of the cyan waveform. Under these conditions, it would be advisable to mount a flag heatsink to each Mosfet as they individually dissipate about 1.5W. banks. This reduces dissipation in the Mosfets during these high-stress phases of operation. It also has the benefit of the PCB not needing a GND connection. If you look at Scope 2, which shows the startup behaviour, the Mosfet has over 10V of gate drive in the first cycle of operation. One benefit of using a constant current source/sink is that the circuit’s behaviour is mostly independent of the operating voltage, as long as it’s above the minimum threshold required to bias on the Mosfets. The 22kW resistors in the circuit allow one current source/sink to drive the sense amplifiers for both input rails. The actual value of these resistors is not that important, although we don’t want a large voltage drop across them so that we can use the Ideal Bridge at modest AC input voltages. For the PCB layout we need to consider the thermal characteristics of D1, D2, Q5 and Q6 (the sense amplifier). Silicon diodes have a -2.1mV/°C thermal coefficient for their forward voltage drop, so for every 1°C increase in temperature of a diode junction, its forward voltage falls by 2.1mV. This means that if one diode is hotter than the other, we will get an error in the switching voltage. A similar effect is seen with the base-emitter voltages of Q5 and Q6. For this reason, we have placed the diodes right next Application Max current Low-Current Full Bridge 2-3A no heatsink Max voltage N-channel P-channel Source/comments 40V IRF540 IRF9540 Altronics & Jaycar IRFB4410ZPBF SUP70101EL-GE3 IRF135B203 IXTP76P10T ±40V High-Current Full Bridge 10A no heatsink DC Combining 5A no heatsink DC Combining 10A no heatsink to one another, and placed the transistors so they can be glued together. This will ensure our switching margins are stable even as the board heats and cools during use. The ‘sense’ transistors (Q5 & Q6, Q9 & Q10 etc) only ever have 12V across their collector-emitter junctions, so we have specified standard BC546-9 or 556-9 devices (or their SMD equivalents, BC8xx). However, the current source/sink transistors will have the full dual rail voltage across them, which could be up to ±40V or 80V total. Therefore, we have specified MPSA42/92 transistors for these (or the SMD equivalents, MMBTAx2). These standard high-voltage, lowpower devices are available from all the larger online suppliers. If you have ±25V or lower voltage rails, you could use BC546/556/846/856 transistors there instead. It is important to consider that the BC546/BC556 have the opposite pinout to the MPSA42/92 transitors, so you would need to install them backwards if you do this. Luckily, for the SMD transistors, the BC846/856 series SMD pinouts are the same as the MMBTA42/92 pinouts, so they are a direct swap for applications below ±25V. Note that the 47kW resistor values were chosen to allow operation from low voltages to about ±40V at the output. At the upper limit, the 47kW resistors will dissipate 130mW each. While that is well within the ratings of a 1/4W resistor, we have specified 1/2W resistors just to be safe. If you will only use this bridge at the higher end of its voltage range, you could increase those resistor values slightly to, say, 68kW. That will reduce their dissipation to a maximum ±30V As above 12-24V Not required 12-24V Not required Table 1 – examples of suitable MosfetsAustralia's electronics magazine SUP90P06 Mouser, DigiKey & Silicon Chip kit IXTP96P085T IRF9540 Altronics & Jaycar 100mV/A drop SUP90P06-09L-E3 Mouser & DigiKey 7.4mV/A drop SUP70101EL-GE3 Mouser & DigiKey 11.4mV/A drop IRF4905 Mouser & DigiKey siliconchip.com.au of 94mW, so 1/4W resistors should be fine. You could also lower their values for low-voltage applications, although that shouldn’t be necessary. Startup behaviour Scope 2 shows the circuit starting up when AC power is first applied. On that first cycle, the AC input blue trace goes negative. This charges the negative capacitor to about 5V, although we don’t have a plot of the negative rail here – we know that the negative and positive rails will be about the same. The Mosfet body diode conducts on this cycle in the absence of voltage at the Mosfet gate (due to the low initial voltage). Once there are a few volts on the output rails, the constant current source/sink and BJT-based voltage sense circuits kick in. By the time we are into the first positive excursion of the AC1 input in cyan, we can see the gate drive pulling the gate low (in yellow), having already charged the large capacitor bank enough in the first cycle. Indeed, the gate voltage on that P-channel Mosfet goes below 0V, being pulled toward the negative rail, and we see a full 12V on that P-channel Mosfet gate in the first real cycle of operation. This shows the benefit of connecting the current source/sink to the opposite rail rather than ground. I love the simplicity of circuits like this, which squeeze more out of a handful of components than seems reasonable. I also like going back to basics and using BJTs in the current sink and sense amplifier. PCB layout We touched on some PCB layout considerations earlier. There are a few aspects of the PCB design that are very important: Parts List – Discrete Ideal Bridge Rectifier 4 6.3mm pitch PCB-mount vertical spade connectors (CON1-CON4) [Altronics H2094, Jaycar PT4914] 2 SUP70101EL 100V 120A P-channel Mosfets, TO-220 (Q1, Q2) 2 IRFB4410ZPBF 100V 97A N-channel Mosfets, TO-220 (Q3, Q4) Resistors (1% ¼W axial – TH version | 1% ¼W M3216/1206 – SMD version) 4 100kW 2 47kW 0.5/0.6W (5% OK) 8 22kW 2 330W 4 68W Through-hole version 1 double-sided PCB coded 18108241, 87.5 × 45.5mm 4 BC556/7/8/9 100mA PNP transistors, TO-92 (Q5-Q6, Q9-Q10) 2 MPSA42 300V 500mA NPN transistors, TO-92 (Q7, Q8) 2 MPSA92 300V 500mA PNP transistors, TO-92 (Q15, Q16) 4 BC546/7/8/9 100mA NPN transistors, TO-92 (Q17-Q20) 4 12V 0.4W zener diodes, DO-35 (ZD1-ZD4) [Altronics Z0332] 12 1N4148 75V 200mA diodes, DO-35 (D1-D12) SMD version 1 double-sided PCB coded 18108242, 54.5 × 54.5mm 4 BC856/7/8/9 100mA PNP transistors, SOT-23 (Q5-Q6, Q9-Q10) 2 MMBTA42 300V 500mA NPN transistors, SOT-23 (Q7, Q8) 2 MMBTA92 300V 500mA PNP transistors, SOT-23 (Q15, Q16) 4 BC846/7/8/9 100mA NPN transistors, SOT-23 (Q17-Q20) 4 12V ¼W zener diodes, SOT-23 (ZD1-ZD4) [BZX84C12] 12 1N4148WS 75V 150mA diodes, SOD-323 (D1-D12) [Altronics Y0162] For combining DC supplies, halve the numbers of all components except the PCB and spade connectors. – TH version kit (SC6987, $30) – SMD version kit (SC6988, $27.50) ● The layout of the current sense amplifier with its two transistors, two 1N4148 diodes and 68W resistor is kept very tight as it must accurately sense small voltages with relatively low bias currents. ● The sense transistor pairs, like Q5 and Q6, are face-to-face, so you can super glue these together to keep them as tightly thermally coupled as possible (or add a smear of thermal paste between them). On the SMD version, these parts are tight against one another. The SMD version of the Discrete Ideal Bridge Rectifier is 54.5 × 54.5mm, while the through-hole only is a bit larger at 45.5 × 87.5mm (not shown to scale). siliconchip.com.au Australia's electronics magazine Both kits include the PCB and everything that mounts on it ● The pairs of 1N4148 diodes (D1 & D2) are right next to one another, so they stay at similar temperatures. ● The path from the AC inputs through the Mosfets and to the DC outputs is kept as short as possible and uses large copper fills to maximise the current carrying capacity of the PCB. PCBs do not have a fixed ‘current rating’, but we must ensure that the voltage drop and heating in the tracks is reasonable at any current likely to be drawn. At the AC1 input, which has the thinnest connection to the Mosfet, we have parallel copper on the top and bottom layers of the PCB. September 2024  83 83 Fig.3(a) & (b): the full-populated through-hole version of the PCB (left) and the reduced version for combining DC supplies only (right). The full version can also be used to combine DC supplies. Watch the diode and Mosfet orientations, and remember that Q7/Q8 and Q15/Q16 need to be reversed if you are using BC546/BC556 transistors instead for lower voltage applications, compared to what’s shown here. Mosfet selection We have included 100V low-RDS(on) Mosfets in the parts list. They only cost a few dollars each and work well. If selecting alternative Mosfets, look for a voltage rating well above the rail voltage you want; we feel that 80-100V is about right. Select an RDS(on) of 10mW or less. The P-channel Mosfet will usually have a higher RDS(on); there is little point in selecting N-channel Mosfets with a significantly lower on-­ resistance than the P-channel devices you will be using. For lower currents, you can get away with less expensive Mosfets. Even though the savings in dissipation won’t be as great, the reduction in voltage loss can still make this design very beneficial in lower-current designs. For example, we used IRF540/ IRF9540 Mosfets from Altronics in some tests, and it was fine up to about 3A, still giving a much lower voltage drop than a conventional bridge. Table 1 includes some advice on Mosfet selection. Construction The through-hole version is built on a double-sided PCB coded 18108241 that measures 54.5 × 87.5mm, while the SMD version is coded 18108242 and is a bit smaller at 54.5 × 54.5mm. For the former, refer to the Fig.3(a) PCB overlay diagram, while Fig.4(a) is the overlay for the SMD version. The smallest SMD parts are the SOT23 transistors and SOD-323 diodes. These are large enough that they are not too challenging if you have a desk magnifier and a reasonably good soldering iron. If you are using it to combine solar panels or DC power sources, you can leave off all the negative rail parts, shown in a dashed box in Fig.1. These Figs.4(a) & (b): the SMD versions of the PCB, with the full version on the left and the DC combining version only on the right. If substituting BC846/BC856 transistors for the MMBTA types, you don’t need to change how they are fitted to the board. Only diodes D1-D12 and the Mosfets could be easily installed backwards, so ensure they aren’t. 84 Silicon Chip Australia's electronics magazine versions are shown in the alternative overlay diagrams, Figs.3(b) & 4(b). Start by fitting all the resistors. Follow with the diodes, making sure you orientate them correctly, with the cathode stripes facing as in the relevant PCB overlay diagram. We found that for the SOD-323 SMD diodes we got, it was tough to tell which end was the cathode. If unsure, use a magnifier or a DMM set on diode test mode. Next, solder the signal transistors in place. As mentioned earlier, if you are using this at low voltages only, you can use all BC546/556/846/856 transistors throughout. If you do this, remember that the through-hole devices for Q7, Q8, Q15 & Q16 must be rotated by 180°, as the MPSA42/92 types have a different pinout. Mount the 12V zener diodes next. The SMD SOT-23 parts are small and in the same packages as the bipolar transistors, so make sure you don’t mix them up. Place them with tweezers and tack one leg, allowing you to adjust it (if necessary) by reheating the initial joint before soldering the remaining leads. Fit the power Mosfets next. Watch the layout here, as they face in alternate directions on the board to optimise the track layout. Also, don’t get the two different types mixed up. Tack one leg of each and fiddle them so they are neatly aligned and the same height, then solder the remaining leads. Finally, mount the 6mm connectors. You could solder wires directly to the board, but we reckon using crimp spade lugs is much neater. Testing We suggest testing the board in two siliconchip.com.au PIC Programming Adaptor Our kit includes everything required to build the Programming Adaptor, including the Raspberry Pi Pico. The parts for the optional USB power supply are not included. Use the Adaptor with an in-circuit programmer such as the Microchip PICkit or Snap to directly program DIP microcontrollers. Supports most newer 8-bit PICs and most 16-bit & 32-bit PICs with 8-40 pins. Tested PICs include: 16F15213/4, 16F15323, 16F18146, 16F18857, 16F18877, 16(L)F1455, 16F1459, 16F1709, dsPIC33FJ256GP802, PIC24FJ256GA702, PIC32MX170F256B and PIC32MX270F256B Learn how to build it from the article in the September 2023 issue of Silicon Chip (siliconchip.au/Article/15943). And see our article in the October 2023 issue about different TFQP adaptors that can be used with the Programmer (siliconchip.au/Article/15977). Complete kit available from $55 + postage siliconchip.com.au/Shop/20/6774 – Catalog SC6774 halves. The following steps test the two positive sections. 1. Connect the Bridge outputs to an electrolytic capacitor of at least 470μF. Make sure you get the polarity correct. 2. Connect the negative of a 12-24V power supply to the negative of your capacitor and the positive to either of the AC inputs. If you can set a current limit, set it to a few hundred milliamps. 3. Switch on the supply and check that the capacitor charges up to the input voltage. 4. Put a 100W 1W resistor (or similar) across the capacitor and check that the voltage across it does not droop significantly (no more than 100mV). This verifies that the appropriate Mosfets are on; otherwise, the voltage would drop by 600mV or more. It also confirms there are no catastrophic shorts, or you would get smoke. Now test the other AC input using the same method. If you run into trouble in either case, go through the following checklist below: 1. Is your power supply going into siliconchip.com.au current limiting? Use a multimeter to check for the expected voltage at the AC input. 2. Are your Mosfets the right way around? 3. Check that the diodes are all orientated correctly. If any are wrong, the Rectifier will not work. 4. Check your soldering and look for solder bridges. 5. Check that the current sink and source work by measuring the voltage between the base and emitter pins of Q8 and Q16. The reading should be close to 0.6V in both cases. Also check for a ~600mV Vbe on Q7 and Q15. If the readings are low, check that the associated 47kW resistors are OK. 6. Check the voltage across the zener diodes. Are they the right way around? If the capacitor bank is charged up and there is no load resistor, the voltage across them should be low, while you should get a reading of several volts with the 100W resistor across the capacitor. 7. If the behaviour is correct for one AC input of the Bridge but not the other, check the circuitry around the misbehaving input and compare voltages to the other half. Australia's electronics magazine 8. If both inputs don’t work, you have a systematic problem since they are essentially independent. Having tested it with one polarity, switch off the supply and connect its positive output to DC OUT+ on the Bridge and the negative of your power supply to one of the input terminals. You should see the capacitor charge up to the input voltage again. Proceed with testing in this configuration as above. Using it Once installed, it will pretty well look after itself. Refer to Figs.1(a) & (b) to see how the connections should be made. If you expect to draw continuous high currents from the power supply, you will probably want to put some flag heatsinks on the Mosfets. Aside from that, you should find that it just works. Remember that you may need a mains soft-starting system if you have a really substantial capacitor bank and low-impedance transformer like in a big audio amplifier. We published such a design in April 2012 (“SoftStarter”; siliconchip.au/ Article/705). SC September 2024  85 Project by Brandon Speedie upgrade your instrument with these Electric & Bass Guitar Pickguards The control circuitry on electric basses has remained remarkably simple since Leo Fender first introduced the instrument over 70 years ago. These modern PCBs offer more advanced features and a cool aesthetic. They suit many popular models of electric bass as well as the Fender Telecaster electric guitar. Image source: https://unsplash.com/photos/teal-and-brown-electric-guitar-phS37wg8cQg M ost electric guitars and basses have circuitry built into the instrument’s body. Typically, it includes a passive network of potentiometers and capacitors to give the musician control of output volume and ‘tone’. The standard configuration is shown in Fig.1. The volume control is a potentiometer that divides the audio signal voltage from the pickup(s). The tone control is an adjustable low-pass filter to reduce the amount of treble and therefore change the instrument’s sound to suit different music and playing styles. Its simplicity has made it a popular circuit, remaining relatively unchanged since the early 20th century. However, it has some weaknesses. These updated circuits aim to correct some of those shortcomings and add some handy new features. Most electric instruments, including guitars and basses, use passive inductive pickups to sense the vibrations of the metal strings, converting them into electrical signals that can be amplified. Pickups There are predominantly two types of electromagnetic pickups used on guitars and basses. The most common is the ‘single coil’ type, so called because it is constructed of a single inductor wrapped around a set of permanent magnets. The magnets are made of an iron alloy known as alnico (aluminium, nickel & cobalt), which are positioned under the instrument strings to form ‘pole pieces’. Wrapped around these magnets are several thousand turns of enamelled copper wire (see Fig.3). The pole pieces magnetise the strings, Fig.1: a typical control circuit on an electric guitar or bass. The ‘tone’ control is an adjustable low pass filter, while the volume control is an adjustable voltage divider. 86 Silicon Chip Australia's electronics magazine producing a changing magnetic field for the copper coil when plucked. This movement induces a voltage in the coil, which is ultimately sent to an amplifier for playback or recording. The other type of pickup is called a “humbucker” because it can cancel interference and therefore reduce the hum induced by noisy sources such as nearby transformers and fluorescent lighting. The humbucker has two coils mounted next to each other in the Fig.2: the magnetic field lines around a typical humbucker pickup. Source: Lawing Musical Products – siliconchip.au/link/abw4 siliconchip.com.au bridge-mounted pickups will sound brighter with strong mid-range and treble sounds. The electronic control circuitry allows the musician to select these different pickups and control the final sound. I have designed four different circuits with custom-shaped PCBs to suit some of the more common or interesting electric basses and guitars. J&D Luthiers T-Style electric bass Photos 1 & 2: the outside surface of the T-style bass pickguard has a nice tinned pattern. The labels aren’t upside-down; at least, not from the player’s perspective! same package. One coil has its north magnets facing the strings, while the other has its south poles facing the strings (Figs.2 & 3). The coils are wired 180° out of phase, so any external interference that impinges on the pickup will induce an opposing voltage in each coil that is therefore cancelled out. Any (wanted) voltage induced by the strings will be out-of-phase due to the opposite orientation of the pickup magnets, and those signals will reinforce due to the out-of-phase wiring. Humbuckers are known for their stronger and fuller sound but tend to lack clarity and brightness compared to a single coil. These differing characteristics, as well as pickup placement, can be used by the instrument designer to influence its overall voicing. Pickups placed towards the neck of the instrument tend to have more bass and sound more mellow, while The inspiration for this project came during the restoration of an old bass guitar, known as a T-Style, from the Australian designer J&D Luthiers (see Photo 1). The existing circuitry was mounted directly to timber veneer, which was showing its age and needed replacement. I routed the veneer off, leaving a hole in the body to be covered by a new fascia. The obvious choice for a new material would be custom-machined sheet metal, but making that is time consuming and quite expensive. Most parts of this nature are also chrome-coated, which adds further expense. Instead, I decided to make a new fascia from a printed circuit board (PCB), which could act as both a visually appealing fascia and house the new circuitry (see Photo 2). The new circuit is shown in Fig.4 and Photo 3. The instrument features two pickups: a single coil near the neck and a humbucker near the bridge. These wire directly to CON1, a 7-way screw terminal. Both coils’ negative ends and the humbucker shield are grounded, along with the instrument drain wire. The drain is electrically connected to Fig.3: the internal construction of a single coil pickup, an early “PAF” Humbucker with bottom-mounted magnet and steel pole pieces, and a more modern form of humbucker with alnico magnet pole pieces. Source: https:// lawingmusicalproducts.com/dr-lawings-blog/the-wide-range-humbucker-and-the-genius-of-seth-lover siliconchip.com.au Australia's electronics magazine September 2024  87 Fig.4: my new circuit for the J&D Luthiers T-Style bass allows you to select which pickups are active and the configuration of the humbucker. It also provides tone, overdrive and volume controls and has compensation so that the frequency response doesn’t change too much with volume level. the bridge, to suppress interference induced on the strings and metal hardware. The ‘middle’ of the humbucker (coil one negative, coil two positive) connects to switch S1, a DP3T toggle switch with a slightly unusual on/ on/on switching pattern, as shown in Fig.5. This provides the option of series/split/parallel selection for the humbucker coils. When in the split position (centre), one of the coils is grounded, so the humbucker operates as a single coil, giving a clear and bright tone. When in the series position (down), the coils are in series. This gives the strongest output and a rich tone but less brightness than a single coil. When in the parallel position (up), the coil one negative is grounded and the coil two positive connects to the output, placing the coils in parallel. This gives a tone somewhere between the other two modes. The output of the humbucker switch leads to S2, the bridge/neck pickup selector switch. In the bottom position, the neck single coil will be active; in the top position, the bridge humbucker will be selected (in whatever mode S1 has it operating in); and, in the centre position, both pickups are active. Switches S1 & S2 provide a lot of flexibility for the musician, selecting between a total of seven different configurations for the two pickups. Photo 3: there’s a fair bit of room inside the T-Style bass guitar body for the components on the underside of the PCB. 88 Silicon Chip Australia's electronics magazine The signal is then fed to the traditional tone control, made from potentiometer VR1 (connected as a rheostat) and the four paralleled capacitors. This configuration forms a low-pass filter but in a slightly unusual way. Because the pot is in series with the capacitor(s), it effectively works as a magnitude control. With the pot all the way up, the signal sees a high impedance and very little of the high end is shunted. With the tone all the way down, the capacitor(s) are connected directly in parallel with the output, giving a strong high-frequency roll-off. The RC combination of the pickup source impedance and filter capacitance will loosely set the cutoff frequency. Still, with no buffering, there is a strong interaction with the other controls. Because we prefer to use plastic film dielectric capacitors for linearity, the range of values available in the size used (SMD M3216/1206) is only up to about 1μF. The four footprints therefore allow for a broader range of capacitances and for tuning the sound by connecting smaller capacitors in parallel with larger ones. A typical value is 47nF, but I prefer higher values to scoop out a bit more of the mid-range, so I use 200-220nF. In the prototype I built, I used two 100nF film capacitors in parallel, but I’ve specified a single 220nF in the parts list for simplicity. The next control in the signal path is potentiometer VR2, which is a new feature: a passive overdrive/distortion control. It works similarly to the tone control, except there are back-to-back (inverse parallel) schottky diodes (D1, D2) in series with the rheostat. When the pot is fully down, there siliconchip.com.au Silicon Chip kcaBBack Issues $10.00 + post January 1997 to October 2021 $11.50 + post November 2021 to September 2023 $12.50 + post October 2023 onwards All back issues after February 2015 are in stock, while most from January 1997 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com. au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer Fig.5: the unusual switching patterns of the “on/on/on” and “Les Paul” DP3T switches used in these circuits allows the coils to be used together or individually. is a high resistance in series with the diodes, so they have little effect on the signal. When the pot is all the way up, the diodes are connected directly to the signal line. The voltage from the pickups is too low to fully forward bias these diodes, but even operating in their square law region, they introduce some nonlinearity to produce a subtle ‘overdrive’, a popular effect amongst guitarists. The seasoned musician will note that the overdrive effect is applied before the volume control, so its impact won’t be reduced if the volume is adjusted. This offers a useful contrast to other distortion sources, such as downstream foot pedals or amplifiers, which are mellowed by their input voltage level. By combining the onboard distortion with downstream effects, the musician has the flexibility to dial up or down distortion from a mixture of sources. Constructors might like to exper- iment with different combinations of diodes here; for instance, a single schottky diode would give asymmetric distortion, while back-to-back combinations of small signal diodes like the 1N4148WS would provide a more mellow effect. You could even have a combination, with one 1N4148WS and one schottky diode facing in either direction. The final potentiometer, VR3, is a traditional volume control with a twist. In a conventional circuit, the output signal is simply tapped off the pot’s wiper. But this arrangement has a drawback: as the volume is turned down, the pot resistance appears in series with the output. When connected to an amplifier via a coaxial cable, this resistance forms an unwanted low-pass filter (with the cable parasitic capacitance), reducing upper frequencies. In this updated circuit, a 1nF capacitor is placed in parallel with the volume control to ‘bleed’ additional treble into the output as the volume is turned down, compensating for the undesirable tone loss. Additional series and parallel footprints R5, C6 and C7 are provided for other combinations of capacitance or resistance to do this job. For instance, 100kW || 1nF may sound more linear as the control is turned down. The output signal appears at the output jack, CON, a ¼-inch (6.35mm) TS socket to suit a standard instrument cable. The PCB is secured to the front of the instrument using 3mm stainless steel self-tappers. They mount through 3mm plated through-holes and secure directly into the timber. I prefer plated holes for mechanical mounting, as they are a bit more hardy than bare fibreglass against the metal screw threads. A standard 1.6mm thickness PCB with black solder mask is best; any thinner would be too flimsy, any thicker would present too much of a lip. We will be supplying boards with a lead-free HASL finish (basically tin plating) as the solder will be on the outside of the guitar. If a gold finish would suit your guitar, you could go for an ENIG finish, although it will make the board considerably more expensive. The Fender Jazz Bass Many of the features of this T-style bass circuit can be applied to more Fig.6: my Jazz Bass circuit is similar to the one for the T-Style bass shown in Fig.4, except the pickup switching is simpler because both pickups are single-coil types. siliconchip.com.au Australia's electronics magazine September 2024  89 Photo 4: a Fender Jazz electric bass. Source: www. megamusiconline. com.au/product/ fender-americanperformer-jazzbass-guitarrosewoodfretboard-3colour-sunburst/ Photo 5: the unusual ‘Les Paul style’ DPDT switch closes all contacts in its central position, rather than opening them all, as in a normal DPDT centreoff switch. 90 Silicon Chip common instruments. One of the most popular bass guitars is the Fender Jazz Bass (Photo 4), which has two single-­ coil pickups. Jazz basses have been played extensively by legends like Jaco Pastorius, John Paul Jones of Led Zeppelin, Flea of Red Hot Chili Peppers, Adam Clayton of U2 and Geddy Lee of Rush. There are also clones of the Jazz Bass (and the other guitars listed below) that would likely fit my new pickguard designs, possibly with slight modifications to the inside of the body. Traditionally, the two pickups would be wired to individual volume control potentiometers with a shared common tone control. My new arrangement is shown in Fig.6. The negative of the second coil and the bridge shield are connected directly to circuit ground, similarly to the T-Style circuit from above. The first coil’s negative and the second coil’s positive are routed to S1, a DPDT toggle switch that provides series/individual switching for the two coils. With S1 in the position shown, S2 allows the player to select either coil or both in parallel. Parallel is the standard configuration for a Jazz bass, while series is a new mode that will give a stronger and fuller tone. Series switching with two single-coil pickups is a rare configuration but, in my opinion, heavily underrated. On a genuine Fender, it can give the player a beefier tone that is more akin to a humbucker. It can compensate for low-cost pickups, which tend to sound thin on a cheap imitation. Photo 5 shows how this special ‘Les Paul style’ switch works; with the toggle in the central position, all contacts are closed. Moving it to one side opens the contacts on the opposite side, while leaving the set on the same side closed. In its standard configuration, that lets you choose one pickup, the other or both in parallel. With S1 in the standard parallel mode, S2 can select between the neck pickup only, bridge pickup only, or both pickups in parallel. With S1 in the series position, S2 selects between both in series or mute. Mute can be helpful for live work, to avoid unwanted sounds when moving around on stage between songs, or it can be rapidly switched on and off to give a tremolo-style effect. The signal is then sent to the tone control potentiometer, VR1. A single capacitor is used here (220nF recommended), as there is no space for more footprints. Following this is pot VR2, the passive overdrive with dual schottky diodes. After that is pot VR3, the volume control with a single 1nF treble Photos 6 & 7: the outside of the Jazz Bass pickguard has a pleasing zigzag pattern in tin along with the necessary labels. The other side of the pickguard is where all the components are mounted. Australia's electronics magazine siliconchip.com.au Fig.7: the Music Man Stingray circuit is virtually identical to the one for the J&D Luthiers T-Style bass, except that there is no switch S2 as it doesn’t have a neck pickup. bleed capacitor. Again, there is no space for additional footprints or series/parallel combinations as there was on the T-Style circuit. The entire PCB fits in place of the existing chrome-plated controls (visible in Photo 4) and is screwed down to the body. If your instrument doesn’t quite fit the new controls (shown in Photos 6 & 7), additional space can be made by filing, rasping, or routing out a larger body cavity. Music Man Stingray Another very popular bass guitar, the Stingray (Photo 8), was designed by Leo Fender after he sold his interest in his founding business, the Fender music instrument company. Unusually for a Fender design, it features a humbucker pickup. Legends who have used this bass include Cliff Williams of AC/DC and John Deacon of Queen on tracks like Another One Bites the Dust. The standard Stingray was the first electric instrument to feature active electronics, with a volume control and a two-band EQ powered by a 9V battery. Some models add a knob to provide a three-band EQ. Cheaper copies of the Stingray will come with a similar circuit to the Jazz Bass: two volume control potentiometers for each of the humbucker coils and a common tone control. My replacement circuit is shown in Fig.7 and Photos 9 & 10. The bridge shield and humbucker coil two negative are connected to circuit ground. Like the humbucker wiring in the T-Style circuit, humbucker coil two positive and humbucker coil one negative connect to S1, a DP3T toggle switch with the special on/on/on switching pattern. This provides the same series/split/ parallel switching for the humbucker as the T-Style circuit, with the same tonal flexibility. When in split mode, only a single coil is active. Depending on which coil the user prefers, this can be the one closest to the bridge or nearest to the neck. It can be changed by simply swapping the wiring of coil 1 with coil 2 in the screw terminal. As the two pickups are mounted so close to each other, there is only a very minor difference in sound between the two, but the bridge coil will be marginally ‘brighter’, so I prefer to use it. The signal from S1 connects with the humbucker coil one positive and is sent to the tone control formed by potentiometer VR1 and up to four paralleled capacitors. In this example, a single 220nF film Photo 8: a Music Man Stingray bass with my new pickguard in place. This guitar has seen plenty of use! ► Photos 9 & 10: a close-up of the controls on the Stingray, showing how the orientation of the labels makes sense for the guitar player. Generally, only capacitors C1 and C2 are required, as shown here, but the extra pads give you more options. siliconchip.com.au Australia's electronics magazine September 2024  91 Fig.8: while the other three circuits were for bass guitars, this one is for a Fender Telecaster standard electric guitar. It’s the simplest of the four due to the minimal space available on the guitar, with pickup switching, tone and volume controls and a simple on/off overdrive option. cap is loaded. After this is the overdrive control, formed by potentiometer VR2 and inverse-­parallel schottky diodes D1& D2. The final control is the volume control, VR3, with the treble bleed circuitry already described. A single 1nF capacitor (C2) is used in my prototype, but footprints R5, C6, and C7 are also provided to give flexibility to the builder. Fender Telecaster The previous circuits have all been designed for electric bass guitars but can also be applied to electric guitars. The Fender Telecaster (Photo 11) is one of the oldest and most popular electric guitars, and its two-pickup combination can work with a circuit similar to that of the Jazz Bass. There are too many famous Telecaster players to list, including Jimmy Page, Keith Richards, Bruce Springsteen, George Harrison and Muddy Waters. The standard controls on a telecaster are a three-way pickup selector switch (neck/bridge/both) and the typical volume and tone controls. These can be replaced with the circuit shown in Fig.8, Photo 12 & Photo 13. The output jack negative, the second single coil negative and the bridge shield connect directly to circuit ground. The negative of the first single coil and the positive of the second single coil are routed to S1, a DPDT toggle switch providing series/parallel switching for the two coils. The output from S1 is sent to S2, a three-way bridge/neck selector switch. With S1 in the standard parallel mode, S2 can select between the neck pickup only, bridge pickup only, or both pickups. With S1 in the series position, S2 selects between on and mute. The signal is then sent to the tone control potentiometer, VR1. Two footprints are provided for capacitors. After this is the passive overdrive, which differs from other circuits in its use of a switch rather than a potentiometer. Due to space constraints, the dual schottky diodes are simply switched in or out of circuit. An SPST or SPDT toggle switch can be used here. After that is pot VR3, the volume control, with a single 1nF treble bleed capacitor. This circuit does not include a ¼-inch output jack, as the Telecaster mounts this off-board on the bottom edge of the body. The output signal instead connects back to the 7-way Photos 12 & 13: once your Telecaster pickguard has been assembled and the wires added, it should look like this, ready to install in the guitar. The pickguard is packed with controls and has a zigzag pattern to add a bit of interest. Australia's electronics magazine siliconchip.com.au Photo 11: a Fender Telecaster electric guitar. Source: www. keyboardcorner.com.au/fender-player-telecaster-pau-ferrofingerboard-3-color-sunburst/ Parts List – Electric & Bass Guitar Pickguards screw terminal, where it can connect to flying leads that wire down to the output jack. Construction All versions can be approached similarly, referring to the photos presented so far and the relevant PCB overlay diagram (one of Figs.912). Begin by mounting the toggle switch(es) and securing them to the PCB with the supplied washer and nut. I prefer a flush mount; if the toggle stands too proud for your liking, an additional nut can be placed on the back of the switch to adjust the length of shaft that protrudes through the PCB. Tin the SMD pads and toggle switch terminals with solder, then run short lengths of fine-gauge wire from the pads to the terminals. The DPDT and DP3T switches require all six connections, while the SPST/SPDT on the Telecaster circuit only needs the two connections as marked. Continue by mounting the ¼-inch jack (excluding the Telecaster). Secure it to the circuit board using the supplied washer and nut, like the toggle switches. Tin the two terminals and the pads and make connections with the fine gauge wire. The hot pad connects to the tip of the instrument cable, the longest conductor on the jack. The ground connection is to the jack’s sleeve. Now mount the potentiometers. The Volume and Tone controls are nominally 500kW audio taper, but other values can be substituted if the builder prefers. siliconchip.com.au Parts common to all versions 2 500kW logarithmic taper single-gang 16mm spline shaft potentiometers (VR1, VR3) [Altronics R2237] 1 6.35mm switched SPST mono jack socket (CON2) [Altronics P0062] * 3 16mm aluminium ¼-inch shaft grub screw knobs [Altronics H6331] 2 BAT43W 30V 200mA SMD schottky diodes, SOD-123 (D1, D2) [DigiKey, Mouser etc] 1 220nF 16V metallised plastic film or NP0/C0G ceramic capacitor, M3216/1206 size [DigiKey ECP-U1C224MA5] 1 1nF 100V metallised plastic film or NP0/C0G ceramic capacitor, M3216/1206 size [DigiKey ECW-U1102JX5] 1 1m length of black light-duty hookup wire * omit jack socket and one knob for Telecaster Fender Jazz Bass specific parts 1 double-sided PCB with black solder mask coded 23109241, 127 × 105.5mm 1 5-way SMD screw terminal, 3.5mm pitch (CON1) [DigiKey 2383942-5] 1 DPDT solder tail mini toggle switch (S1) [Altronics S1345] 1 "Les Paul 3 Way Selector" DP3T switch (S2) [AliExpress 1005001900886767] 1 100kW linear taper single-gang 16mm spline shaft potentiometer (VR2) [Altronics R2228] J&D Luthiers T-Style specific parts 1 double-sided PCB with black solder mask coded 23109242, 200.5 × 87.5mm 1 7-way SMD screw terminal, 3.5mm pitch (CON1) [DigiKey 2383942-7] 1 ‘on-on-on’ DPDT miniature toggle switch with solder tags (S1) [Pedal Parts Australia SWTS0008] 1 "Les Paul 3 Way Selector" DP3T switch (S2) [AliExpress 1005001900886767] 1 100kW linear taper single-gang 16mm spline shaft potentiometer (VR2) [Altronics R2228] Music Man Stingray specific parts 1 double-sided PCB with black solder mask coded 23109243, 190 × 71mm 1 5-way SMD screw terminal, 3.5mm pitch (CON1) [DigiKey 2383942-5] 1 ‘on-on-on’ DPDT miniature toggle switch with solder tags (S1) [Pedal Parts Australia SWTS0008] 1 100kW linear taper single-gang 16mm spline shaft potentiometer (VR2) [Altronics R2228] Fender Telecaster specific parts 1 double-sided PCB with black solder mask coded 23109244, 28.5 × 148mm 1 7-way SMD screw terminal, 3.5mm pitch (CON1) [DigiKey 2383942-7] 1 DPDT solder tail mini toggle switch (S1) [Altronics S1345] 1 "Les Paul 3 Way Selector" DP3T switch (S2) [AliExpress 1005001900886767] 1 SPDT solder tail mini toggle switch (S3) [Altronics S1310] Australia's electronics magazine September 2024  93 Fig.9: the replacement pickguard for the T-Style bass is relatively large and easy to assemble. Connections to the guitar are made via a 7-way SMD screw terminal, as through-holes would mar the appearance of the outer (visible) side of the PCB. Fig.10: the Jazz Bass pickguard is quite a bit smaller than the T-Style bass but all the controls still fit neatly. A 5-way terminal is used this time because the bass doesn’t have a humbucker pickup with its two extra terminals. For instance, 250kW and 1MW pots are also commonly used on many instruments. Generally speaking, higher values will give a brighter voicing to the instrument but will also increase the circuit’s output impedance. The potentiometers are mounted flush against the PCB, with the provided keyway holding the control in place to prevent unwanted body rotation. The terminals can be bent down towards the pads on the PCB and soldered with a blob. Begin by applying 94 Silicon Chip solder to the legs of the pot and wait for the solder to reflow down onto the pads for a good connection. Finish the potentiometers by mounting the brushed aluminium knobs to the shaft. If the pot shaft is too long, it can be cut with a hacksaw and filing to give a flush mount. The knobs secure to the shaft by tightening the grub screw. Next, mount the SMD screw terminal. Solder each leg individually in a similar way to the pot legs; flow solder onto the legs and wait for it to reflow onto the pads of the PCB. Australia's electronics magazine Finally, the passives can be soldered to the pads on the circuit board. I used plastic film caps throughout, as plastic dielectrics are highly linear. Finish by soldering the schottky diodes with opposite orientations. Editor’s note: C0G ceramics are more linear than many common film caps, such as polyester types, so they might give a more neutral sound. The pickups can now be wired to the screw terminal, and the entire assembly mounted to the body of the instrument with 3mm wood screws. Happy playing! SC siliconchip.com.au ALL DIAGRAMS ARE SHOWN AT 100% FULL SIZE N/I = NOT INSTALLED FOR STANDARD BUILD Fig.11: the Music Man Stingray pickguard can double as a boomerang! It’s pretty large, so all the controls are nicely spaced out. The single humbucker pickup means that only a five-way terminal is required for this one. Fig.12: the Telecaster pickguard is the most compact of all, so there’s only room for the necessary components. To save space, the overdrive pot is replaced with a switch. Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 siliconchip.com.au Australia's electronics magazine September 2024  95 SERVICEMAN’S LOG Turning to the dark side Dave Thompson Fear leads to anger; anger leads to hate; hate leads to... suffering broken garden lights? It is that time of year again. No, not the tech column awards (I’ve never been invited!). I’m talking about it being cold, damp, and dark. Down here in the lower southern hemisphere, we are somewhat used to the weather bombs that occasionally circle up from the Antarctic and blanket this part of the country with bitterly cold winds, snow to low levels and lashings of ice thrown in to make things especially difficult. Last year, we were clever and avoided much of this cold and frosty weather by going to Europe, where there was a smoking-hot summer. However, that gets quite expensive, and it takes months of planning, so it is impractical to go every year just to chase the summer sun. On the darkest days here, during June, July and August, even if we have sun, it is barely warm and hangs very low in the sky. A 40W incandescent bulb would be warmer! It is pitch dark from 5pm until 8am. If we get a cloudless night during these months, the mercury drops like Wile E. Coyote in a Roadrunner cartoon, and we get hard frosts well into the negative digits. Usually, when we have an ultra-crispy morning, we have a reasonably nice day. It’s a paltry silver 96 Silicon Chip lining, but it’s better than rain. If it does cloud over during the night, the temperature can drop to zero, and everything will be cold, damp and miserable all day long. This winter, and what remnants of winter we encountered on our return last year, have mostly been about cloud cover and rain. It seems those halcyon days of clear and frosty but dry winter days have gone, perhaps due to climate change or perhaps just because weather is notoriously unpredictable and a pain in the bunions! It also turns out my workshop is leaking, which makes working in it a chore and a potential health hazard, as the carpets are all damp and don’t get the chance to dry out. To be honest, the whole garage/workshop needs bowling and rebuilding. Oh, for a spare 60 grand! Lighting my way My point, as usual a long time coming, is that with all this darkness about, outside lighting is really important. Falling down the front steps would not only be embarrassing but, at my age, potentially damaging. It is more than essential that I have decent motion-activated security lighting and, even better, outside pathway lighting. Most of the old-style Par-38-style security lights were mains powered, so one had to wire them in somehow. They were great, don’t get me wrong. Still, where they are mounted, under the barge boards, there was not always handy mains wiring present, so we usually had to get a friendly sparky to come in and wire the lights in for us (I am legally obliged to say this). My current house was once a single-storey bungalow until a previous owner added a second storey and made it quite large. The problem is that to gain access to areas where security or flood lighting needs to be mounted, I’d have to be rake-thin and as agile as a circus monkey. These days, sadly, I am neither of those things! I once used to crawl around wing tanks in airliners, wiring looms and basically fighting my claustrophobia, but those days are long gone. I was chosen for that task because I was small and thin. All I could do these days would be to use my body to plug a leak! A few years ago, I decided to install some decent security lighting on our driveway and along our pathway. The house is on a back section, down a long shingle drive. The neighbour’s dog does a good job of letting us know if anyone is walking up our driveway with a typical territorial protection Australia's electronics magazine siliconchip.com.au Items Covered This Month • The importance of home maintenance • A modified Crosley radio • Distorted and damaged PA speakers • Repairing the solenoid in a washing machine • Seismograph coil repair Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com bark. This, coupled with the scrunch of feet on shingles, is usually enough to let us know if someone is visiting. However, in the dark of night, and with my workshop being just inside the gate at the end of the driveway, this often isn’t enough to know if someone might be creeping up there. Strategically placed security lights were the answer. They worked perfectly for the first few years and, once set up, operated with no problems at all. I have two solarcharged, battery-powered units now: one on a handy telegraph pole at the end of the driveway where it meets our yard (a story in and of itself) and one mounted on the corner of the house. I also have a relatively expensive mains-powered unit halfway between the two. I chose mains powered one for this location because I could wire it into my garage without any major hassles. (Or at least, my sparky could!). It is also dazzlingly bright compared to the other two, no doubt due to it having access to mains power. the ladder and climb up to the lights’ locations and have to work on them! I know what you are thinking: I should have carried out preventative maintenance in good weather to ensure they would work over the whole winter. You’d be correct, though it might surprise you that I did just that. When the days were getting shorter and the mercury was dropping, I went around and cleaned the solar panels (on those that used them) and cleared away the cobwebs of the spiders that made their homes in the nooks and crannies of my lights. I also ensured that the Fresnel lenses on the sensors were not obscured by the usual guano, spider webs or anything else that might prevent them from working. While they looked a tiny bit crazed from a few years in the sun, they seemed clear enough to allow things to work as expected. The thermal sensor units are sealed, so there was no way anything could get into them and obfuscate them. The only way they could malfunction is electronically within the electronic gubbins or if the lens was somehow obstructed. Since the lenses seemed clear, I assumed the problem lay inside the units. Time to crack them open The first thing I did was go up and really clean the solar panels of the battery-powered lights. Admittedly, they were a little dirty, but not so much that I thought the lights would not charge. Nothing is built to last any more All these lights feature impressive LED arrays and, when new, were very satisfactory for their roles. Now, not so much. Over just a few years, the polycarbonate frontages have crazed (likely due to the ultra-high UV rays we have beaming down on us here because of the ozone hole – remember that crisis?). The plastic cases inevitably break down and fall apart for the same reason. I guess this is the problem with imported stuff that has not been made to suit our environment. One could argue that, as they are inexpensive, we can just replace them every few years and we can all carry on with our lives, but in my mind, that isn’t the point. If I spend hours installing and setting up something, I expect it to last more than mere months. Perhaps that’s just my naive expectations of how things should be these days, but if I shell out good money (and bigger money for a ‘proper’ security light rather than some cheap rubbish from a big box store), I expect a reasonably long time. My parent’s security lights, installed by my dad at their home, lasted for as long as I can remember. I helped him change bulbs in the latter years, when he couldn’t, but the unit itself worked for decades. So, I have three such lights set up in different positions. As I am writing this, not one of them works. If I go out at 6pm, I’d really like my lighting to come on so that I don’t trip over something in the dark. Of course, when it is freezing and raining and generally nasty weather is outside the window, that is not the ideal time to go and get siliconchip.com.au Australia's electronics magazine September 2024  97 old friends, a bank of 18650 cells. A couple had vented and made a mess of things, so that was likely why it wasn’t working. No problem; a battery swap should see it going for another two years – hopefully – before it completely falls apart. The second one, though, had six D-sized cells. Well, they seemed not quite D-sized. They were odd, and like much of the innards we find in this stuff, had no information on them at all. They would likely measure 1.3-1.5V factory fresh; I’m reasonably sure of that. But now not one measured more than 0.7V. No wonder it wasn’t working. I know they build these things down to a price, but these were more top-line than others, so I would have expected a bit more life from the batteries, at least. Not very repair-friendly The solar panel assembly simply plugs into the unit’s main body with a standard barrel connector, so it is easy enough to unplug it and measure the juice coming from it. Even in dim, grey weather, I was still getting a healthy 11V (plus change) from the panel, so obviously that wasn’t the problem. I was surprised to see so much output from the smallish panels, even in low-light conditions. There was not much else that could be at fault, so it was time to demount the units, open them up and check the batteries. Getting them down is the first problem. Weather, especially with the extremes we have here, does weird things to screws and plastic, so taking all that off was a bit of a mission. I think I need to invest in better-quality screws! There’s not much I can do about the plastic breaking down, but even the cadmium-plated big-box-store superscrews I’d used had corroded and most of them just sheared off as I was trying to undo them. The ones screwed into the telegraph pole all broke off at the holes, so perhaps whatever they treated the pole with to stop it from rotting had a detrimental effect on the screws; they seemed especially weak. Once off, I got the units into my workshop. As you can imagine, they are a little grubby. Birds tend to sit on them and, well, you know. But at least the units came apart easily once I’d given them a wipe-down on the outside. Mostly, they are pretty well made. I doubt they are designed to withstand our summer sun, but the plastics seem to have stood up well. All the screws holding things together have little O-rings on them; another nice touch. The covers have a recessed O-ring as well, I guess just to keep the worst of the weather out of them. That’s a question for the techies: is a square seal still an O-ring? The things we think about! Once open, I could see that light number one hosts our 98 Silicon Chip The problem I had now was how to replace them. As usual, they are all spot welded together using nickel links with perma-soldered connections to the PCB. Finding replacement batteries shouldn’t be too hard, but finding them with solderable tags on them is a whole other story. I have one of those cheap spot-welders purchased from the usual Chinese sites, but it seems to kill batteries; not the batteries I’m trying to weld, but the model car/aeroplane-­ type battery packs that power it. I’ve had two high-­capacity batteries for it now, and they’re not as cheap as they used to be (nothing is!). Both failed internally after only a few uses of this welder. It must suck a tremendous amount of power out of the battery, but either the batteries are just poorly made, or the welder itself has some huge back-EMF that kills the cells or fries some fuse. I’m not about to pour more money down the drain buying expensive high-capacity batteries in an effort to get that working. There are far better options, but as I don’t do much of this work, it would end up like the treadmill still taking up space in my garage – used for a while, then forgotten about or pulled out once in a blue moon to be utilised. I did manage to find some 18650 cells with solder lugs; they’d have to do, and that got light number one back up and running. Light number two with the bigger batteries was a little more work. While I could find cells, I couldn’t find any readily available with solder lugs, so I had to use my soldering station. That is not ideal because adding that kind of heat is detrimental to this type of battery. However, I rubbed the contacts clean with a diamond file just before I soldered them and used flux, so the solder flowed well onto the joints. By spreading out the soldering process, I didn’t get too much heat into them. That light is now working again as well. Light number three, the mains-powered one, the most expensive and brightest by a wide margin, is 18 months old now. Obviously, it is out of warranty (darn it), and while it triggers, it is almost like a camera flash. It will not lux adjust or stay on. I took it down and opened it up, but the electronics are potted, and there is nothing to see there, so for this one, the only option is replacement, and that bites. The LED arrays and the rest of it, while very well-built and durable, are all just junk now because the brain is dead. While it cost more than the others, it is still not really worth digging into that much before it becomes one Australia's electronics magazine siliconchip.com.au of those jobs that are just too complex to solve rather than just buying another one. Yet another instance of built-in obsolescence... At least I got the other two back up to par (heh) and can now see where I’m going at five o’clock of an evening. And, as an added bonus, anyone coming up the driveway will be flooded with light, which is good for good guys and bad for bad guys (of which we know there are a few around). Vintage radios and the modified Crosley set I have held a ham license for around 65 years. When I got my license, the exams were only held twice a year, in February and August. They consisted of a 2½-hour paper on theory, half an hour on regulations, and the demonstration of 10 words per minute Morse code transmission. In many cases, the exams were held in the local post office as the Post Master who oversaw the exams was usually quite proficient in Morse code since telegrams were sent and received by Morse, and sometimes he had to fill in for other staff off sick or on holidays. Naturally, I grew up with all-valve equipment. The first transistor I purchased was an OC70, a germanium transistor that cost me nearly half my weekly wage as an apprentice: 4 pounds, 8 shillings and 6 pence, around $9.00. I have been involved in repairing and modifying a large number of old valve radios for many years. I lived for each month when Radio & Hobbies, then Radio, Television & Hobbies and finally Electronics Australia came out. Many hours were spent poring over circuits for transmitters, receivers, amplifiers etc. I have built up an extensive collection of valves of all types, as well as capacitors and resistors from the valve era. I always try to make the repairs look as original as possible. To that end, I found that I could carefully split old mica capacitors in half using a small hand-held grinder. I can then make a pocket inside the shells, insert a modern greencap or polyester capacitor of the required value inside, then cement the shell back together. For the paper capacitors, I cut off the lead on one end and carefully drill out the insides, replacing it with a modern one and then closing the end with beeswax. This results in a very original-looking unit. Unfortunately, replacement power transformers for valve radios are becoming very hard to obtain. I have endeavoured to use my metal lathe to wind new windings and resurrect some, but it becomes impossible unless I know the turn ratios. One of my pet hates is the American transformerless radio chassis. For some reason (probably cost-cutting), many US-made radios do not have power transformers. They use valves with the heaters in series, quite often with 17V, 25V, or 50V heaters to make the heater chain add up to the 110V AC mains. These valves also frequently have low plate voltages, although some radios use voltage-­doubling circuits to get a higher plate voltage. These radios are deadly. They rely on the operator inserting the power plug into the GPO the correct way around. However, because many power leads only have two pins on the plug, it is very easy to make the chassis live. Most of these radios don’t have an Earth wire because it would blow a fuse if plugged in the wrong way around! siliconchip.com.au Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. 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. Besides using a variac when servicing these radios, I always use an isolating transformer to ensure my safety. There were some really well-made US radios, usually of the TRF type, before superhet radios became common. I had a lady bring in a Crosley radio one morning complaining that it had “blown up”. It was a five-valve transformerless superhet with several strange valve numbers because of the series heater chain. Further questioning resulted in her telling me that they had owned the radio for many years and it was a wedding gift from her husband’s father when they lived in the USA. It apparently had been “modified” by a radio tech in the USA before they came to Australia to suit the higher Australian mains power voltage. I put the radio on the workbench and tried to find the so-called modification she had claimed was done. Everything looked OK, but further checks showed that most of the valve heaters were open-circuit. She said that the radio had worked for years in their old house, but when they moved into the retirement village, the power lead was far too long, so her husband cut about two metres off it and reinstalled the plug. Australia's electronics magazine September 2024  99 I must be getting old because it took me fully five minutes to realise that the power lead he had cut was a ‘resistance’ lead that dropped the 230-240V AC in Australia to the 110-120V AC that’s common in the USA! Unfortunately, the radio was beyond economical repair due to the high applied voltage. I am currently working on a timber-cased STC 528 that has seen better days. It is working again, but it is still very deaf. Still, it keeps me out of the pub and busy at 80 years of age. J. A., Narangba, Qld. hearing was like that caused by a rubbing voice coil in the woofer. It was slightly gritty, but the speaker was still capable of going loud. I took the grille off the woofer so I could push the cone to see if it was rubbing. It felt fine, so I proceeded to remove the amplifier module. Probing the woofer output with an oscilloscope while playing music didn’t immediately reveal anything. The waveforms looked musical and were swinging nicely in both directions. However, when I fed in a sinewave, I could see the waveform wasn’t quite as smooth as the input. I disconnected the speakers so I didn’t have to listen to the tone and proceeded to trace the signal through the circuit. The output of the preamp looked fine. From there, it went into a voltage-controlled op amp used as a limiter (to protect the speaker drivers). The output of this stage is where the distortion appeared. This part of the circuit has only the op amp and four resistors; the control voltage comes from another op amp that rectifies the audio signals from both the woofer and the tweeter. The rectifier stage is fed with different amounts of signal from each driver so it can limit the signal at different levels, depending on whether the overload is HF or LF. I could see with the ‘scope that the rectifier stage was doing what it should. All this suggested the limiter op amp (BA6110) IC was faulty, but I didn’t have any on hand, and they are now obsolete. To prove my theory, I removed the op amp and linked between its input and output to see what happened. The result was nice clean audio, just a bit low in level. Then I remembered I had one of these amp modules in the ‘graveyard’. Ten minutes later, I had the BA6110 out of the donor and into the customer’s amplifier, but the fault was still there! A closer look at the circuit diagram revealed a 47kW resistor from the +15V rail to a pin on the BA6110 labelled “bias”. It measured as an open circuit. A replacement resistor restored proper operation. Several weeks later, the customer delivered another identical speaker, this time with no HF output. Some HF output was apparent when I tested it, but not much. Testing the amplifier module indicated that all was well, so I removed the horn driver for inspection. This revealed that the diaphragm had shattered! The voice coil was intact, but not much was left of the diaphragm. A new horn driver had it sounding good again. P. M., Christchurch, New Zealand. Another tale of two speakers Simpson washing machine solenoid repair A customer dropped off a powered PA speaker for repair, saying it sounded distorted. I played some music through it, and indeed, it did sound distorted. Problems like this present a quandary to me, as I am unsure whether to inspect the amplifier module or to start with the speaker drivers. Many modern, powered speakers have Class-D amplifiers that can deliver hundreds of watts. It is not uncommon to see labels on the speaker grille claiming 2000W, which is usually (!) a peak value. However, if the RMS value is only a quarter of that, it will still need very substantial drivers to handle the power. [I think you can drop a zero to get closer to the RMS power rating from these inflated figures – Editor] This particular speaker is an older model with conventional amplifiers and solid drivers. The distortion I was I refurbished a Simpson Contessa washing machine about two years ago and wrote it up for the October 2022 Serviceman’s Log (page 80). It had been working well until recently, when my wife found that it was not spin-drying the clothes but just bunching them up in one place and then going out of balance... I suspected the spin solenoid was at fault. If that was the case, it could be a problem, as I don’t have any spares left now, having used several over time for repairs to various washing machines. This particular component has a higher failure rate than others for some reason. I started by removing the machine’s lid to access the lid switch so I could hold it in while I turned the machine on in the spin cycle. Sure enough, the agitator started turning, and the familiar clunk of the solenoid was not present. The horn driver from a PA speaker with a shattered diaphragm. The Simpson washing machine solenoid had one of its terminals break off. 100 Silicon Chip Australia's electronics magazine siliconchip.com.au I disconnected the machine and pulled it out so that I could access the back panel and remove the seven screws that hold it on. I then turned the machine on its side to access the spin solenoid underneath it. One of the terminals had broken off, but the solenoid’s core was still moving freely, and there was no sign of overheating. That was a good sign, as it meant I could probably repair it. I removed the two #3 Philips screws holding the solenoid on and turned the solenoid on the elliptical pin to remove it from the machine. Next, I got my multimeter and checked that the wiring was still intact; it was. Another good sign. I plugged in my 20W soldering iron and, while it was heating up, got a pair of long-nosed pliers and a scraper to clean the broken terminal where I would be soldering it back together. I tinned both parts of the broken terminal and, holding the loose piece with the long-nosed pliers, I applied heat and soldered the piece back onto the solenoid. After cleaning the terminals, I checked the solenoid again with my multimeter, and it was all good. The repair might not look as good as new, but it would get the machine working again. I refitted the solenoid in the machine, reattached the back panel and stood the machine back up again. I refitted the lid, grabbed some wet washing, loaded the machine, set it on the spin cycle and pulled up the timer knob. The familiar clunk was present and, after the pump ran for a short time, the machine started spinning and ran for a few minutes before stopping. I checked the clothes, and they were as dry as usual, so the machine was back in action. My wife was happy to have the machine working again, and the repair cost nothing but a bit of time. These solenoids are not readily available and cost around $50 or more, so repairing the old solenoid at no cost was a win. It’s very handy being able to do our own repairs; it saves a fortune in call-out fees, and the old Simpson lives on. B. P., Dundathu, Qld Seismograph coil repair My seismograph stopped responding some time ago and I finally got around to fixing it. The detector coil is 50,000 turns of 0.1mm diameter enamelled wire, about 50mm in diameter. It had gone open circuit, not at the connections but internally. Still, it lasted about 40 years! I remembered the story of a bloke who had an open-­ circuit coil in a radio IF stage. He connected a 500V bridge megger to the ends, wound the crank fairly briskly, and it reconnected the coil. How? Electrostatic attraction? Punching through a corroded spot? Who knows, but it worked. The sensing coil carries almost no current, less than microamps, and is in a strong magnetic field, so how long would such a repair last? I don’t know, but for some time now, I’ve been thinking of upgrading the detector to a lightbased one that will also provide a DC resting graph. The magnetic one only responds to definite movement, whereas the commercial ones respond to very low-­ frequency, almost DC movement. Anyway, after doing that, it is working again, ready to detect quakes anywhere in the world. It is really that sensitive. I feed its output and that of the electrometer into two channels of a four-channel data logger connected to a small notebook PC. P. L., Tabulam, NSW. SC siliconchip.com.au Australia's electronics magazine September 2024  101 Vintage Radio Stromberg-Carlson “Air Hostess” Model 4A19 Stromberg-Carlson was known as a high-end radio producer, but this was one of their more inexpensive models. It had a pretty bare circuit, with just four valves, one IF transformer and a very basic volume control. The volume control, in particular, was its Achilles’ heel. A fter the Second World War, Stromberg-Carlson sold large numbers of their full-specification model 5A27, a medium-size mantel radio. The 5A27 cost £21/10, while the 4A19 radio featured here was priced at 18/7/6 (£sd). Even though Stromberg-Carlson heralded the Air Hostess as Australia’s newest and finest radio, they would have known that the publicity department had overstepped the mark considerably. The radio is cheaply made. It is adequate for the kitchen, and then only if it is left tuned to one station. To be fair, the five-inch (127mm) Rolla speaker baffled by the case provides good quality listening. You will not encounter the likes of the promotional text for this radio today, which you can read in the accompanying advertisement from The Australian Woman’s Weekly, June 26, 1948 (see Fig.2). The 4A19 is shown in the large photo on the right, while the more expensive 5A27 is below it and to the left. 102 Silicon Chip By Associate Professor Graham Parslow It may have proved too edgy even for that time because they changed the name to Air Queen in 1952. Perhaps the coronation of Queen Elizabeth II was an additional factor. Although the case was offered over several years, the circuitry inside varied considerably, with the single common factor of having four valves. If you encounter one of these radios, it may be quite different internally from the one featured here. Whatever components were in stock seem to have been adapted to make this series. In this radio, the only new-at-the-time miniature valve is the 6AV6 IF amplifier and detector. Circuit details The circuit diagram shown here (Fig.1) has been modified from the original to reflect what was inside this radio. The original circuit had a valve lineup of 6A8, 6AR7, KT61 and 6X5, reflecting the use of old valve stock. Unlike the circuit shown in this article, the grid bias to the KT61 output Australia's electronics magazine valve was set by a resistor between Earth and the cathode. In this radio, the 6V6 cathode is tied to Earth, and bias is created by a 240W resistor from the mains transformer centre tap to Earth. I measured the 6V6 output beam tetrode grid bias at -5.9V. That is relatively low, but the HT voltages across the π filter built around inductor L4 were also rather low at 140V at the rectifier end and 122V at the output end. Even so, the volume was more than adequate, and the set consumed a modest 24W, including a dial lamp not shown in the circuit diagram. Using a choke in the π filter is the only extravagance in the component complement. I expected the filtering to be marginal due to using electrolytic capacitors of just 8μF each. However, hum was acceptably low, so there was no need to add extra capacitance to the π filter. This radio was released before the common use of ferrite rods for antennas, so it has a conventional aerial coil, siliconchip.com.au Fig.1: the circuit diagram for the Model 4A19. As it was during the post WW2 period, the radio was manufactured with whatever components they could find, which was likely one of the reasons why the design is so simple. In the original circuit, the capacitor below the primary of L2 is listed as “300” (μF), the correct value should be 300pF. L1, with a tuned secondary for spanning the medium-wave (MW) broadcast band. A 5pF capacitor between the aerial coil primary and secondary boosts signal strength when tuning higher frequencies. The EK2 octode mixer valve was introduced by Philips in 1938 with a proprietary flat-pin C18 base (also known as a P-base). The EK2 and EK32 are electrically identical; most manufacturers preferred the conventional octal base on the EK32. The EK32 mixer was produced with and without a metallised coating that could be grounded to act as a shield; when present, the shield was usually painted red. In this radio, the EK32 made by Philips has no shield. The rubber insulated wire to the EK32 top cap (grid connection from the tuning capacitor) was perished, as were other wires that required replacing. The Armstrong-configuration local oscillator using transformer L2 is a conventional way of introducing the heterodyne frequency to generate siliconchip.com.au the 455kHz intermediate frequency (IF). The big surprise is finding only one IF transformer in the set. Before I acquired the circuit diagram, I was perplexed as to where to find the second IF coil. Other models in the same case could have had two IF transformers. Even with only one IF stage, the station selectivity is surprisingly good. What is not so good is the volume control, as it is actually an RF gain control. A 5kW potentiometer sets the grid bias voltage on the EK32 mixer. Gain is at maximum when the wiper of the potentiometer is connected to Earth. When the potentiometer creates resistance from the EK32 cathode to Earth, that raises the cathode voltage, reducing the effective grid bias. That’s because the EK32 grid is effectively at Earth potential by connection through the aerial coil. The result is that the volume potentiometer sets the negative bias to the control grid. Australia's electronics magazine Photo 1: the Philips EK32 mixer valve can be seen in the foreground of this photo. Often this valve has a metallised coating which acts as a shield, but there was none present. September 2024  103 This is not a particularly good way to achieve volume control. At any particular setting, while tuning through the broadcast band, strong stations blast in at a high distortion level, while weak stations are not audible. If the radio remains tuned to one station, that problem goes away. There is no reflexing of the audio through the 6AV6 because that would require a second IF transformer. The detected output from pin 5 of the 6AV6 is coupled to its grid for audio pre-­ amplification. There is no tone control. However, the 20nF capacitor from the 6V6 anode Fig.2: an advertisement for the Stromberg-Carlson Model 4A19 from Women’s Weekly Saturday June 26th, 1948. Source: https://trove.nla.gov.au/newspaper/ article/47221078 speaker). Initially, I did not notice that the output valve socket was empty. However, as you can deduce, my curiosity was piqued as to how many things can be wrong with such a radio. Once I started, there was no going back. Photo 2, showing the underside of the chassis, was taken during my preliminary assessment. I had not yet replaced the two-core mains lead in case the radio was unsalvageable. Several capacitors had been replaced, indicating that someone had restored it previously. As there was no output valve, I connected a signal tracer to the grid pin of the 6V6 socket. Nothing tuned in. The 20nF coupling capacitor between the 6AV6 and 6V6 had been previously replaced with a polypropylene type that is usually highly reliable. With little reason to expect a different result, I connected the signal tracer to the 6AV6 anode. I was rewarded with a good signal from stations that tuned across the spectrum by manually turning the tuning capacitor. That dud 10nF coupling capacitor hit the bin rather quickly, and my enthusiasm to continue was unabated. The enthusiasm even survived testing the speaker transformer primary by measuring its resistance between pins 3 and 4 of the 6V6 socket – it was open circuit. The speaker transformer was riveted to a bracket on the Rola 5C speaker. Drilling through the rivets and removing the transformer allowed me to confirm the open-circuit primary. The next step was to clean the chassis by brushing residue off using mineral turpentine and then blowing it with compressed air. A spray of green paint on the mains transformer made a significant visual improvement. Next, it was time to restore the stringing to the tuning knob. That initially appeared to be impossibly difficult, but removing the dial backing sheet revealed that it was really rather simple, as shown in Photo 4. The small dial drum has a broad rim with a single hole that exposes the grub screw binding the drum to the shaft of the tuning capacitor. The dial cord is a single piece with a hook at one end and a spring at the other. These can be anchored to the hole in the drum, and three loops of cord can pass over the tuning knob shaft. Australia's electronics magazine siliconchip.com.au 104 Silicon Chip to Earth acts as a top-cut audio filter, as well as filtering out any remaining IF signal. There are circuits from other manufacturers with as few or fewer components, such as the Astor DLP described by Ian Batty in the October 2016 issue (siliconchip.au/Article/10333). Restoration I nearly put the radio aside after a first inspection. It had perished rubber wiring, a two-core mains flex to replace, was very dirty, the tuning system was broken, and the radio did not work (complete silence from the Photo 2 (above): this photo of the underside of the chassis was taken before restoration. Some capacitors had been replaced by the previous owner(s). Photo 3 (below): similarly, this photo of the top of the chassis was taken during the early stages of restoration, A few of the components had been removed to make room for replacements. siliconchip.com.au Australia's electronics magazine September 2024  105 Photos 4 & 5: the front of the chassis with the dial cursor backing sheet removed (above) and the new one in place (below). When the dial backing was reinstalled, the cursor was easily rotated to span the tuning range. An odd thing you may have noticed in the lead photo is the presence of wobbly dial calibration lines on this radio. That is not how it left the factory, as shown by many other photos of the model. It is also not unique because I have seen this on other glass dials. I cannot be certain how station identifiers wander and lines distort, but a combination of heat and moisture are likely contributors. The case was in good condition and brought to a sparkling sheen with Meguiar’s Ultimate Liquid Wax featuring pure synthetic polymers. It has a hefty price tag repaid by the outstanding virtue of leaving no white residue. Used on cars, it produces a finish that is good for a year between polishes. With a new cloth-covered mains cord and a replacement speaker transformer, the project was complete. Some background Photo 6: the completed chassis, with the mains transformer painted green. You can also see the replacement speaker transformer. 106 Silicon Chip Australia's electronics magazine Stromberg-Carlson Australia was an autonomous operation and ran its business largely independently of its American parent. The Australian company began by importing receivers from the USA in 1927, and a year later, started the local manufacture of receivers and most of their components. In 1936, their production volume justified the construction of a large factory at Bourke Road, Alexandria, NSW. Stromberg-Carlson made receivers and components for themselves, as well as for brands including Audiola and Crosley. The 1930s were boom years for Stromberg-Carlson radios. In the war years, between 1939 and 1945, Stromberg-­ C arlson produced telephones and telephone switchboards for the Australian Army. Adverts from the 1940s proclaimed, “... there is nothing finer than a Stromberg Carlson”. Throughout their history, they primarily aimed for the high end of the market, with exquisite woodwork on many products. The radios continued to sell well in moulded plastic cases through the 1950s. The end of the radios was a line of distinctive portable transistor radios clad in patterned leather. Stromberg-Carlson tried to participate in the Australian television market, but they were not competitive and ceased all manufacturing in 1961. SC siliconchip.com.au ONLINESHOP SILICON CHIP .com.au/shop PCBs, CASE PIECES AND PANELS LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) WII NUNCHUK RGB LIGHT DRIVER (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB SKILL TESTER 9000 PICO GAMER ESP32-CAM BACKPACK WIFI DDS FUNCTION GENERATOR 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (BLUE) FAN SPEED CONTROLLER MK2 ESR TEST TWEEZERS (SET OF FOUR, WHITE) DC SUPPLY PROTECTOR (ADJUSTABLE SMD) ↳ ADJUSTABLE THROUGH-HOLE MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 16102241 16102242 07112231 07112232 07112233 16103241 SC6903 SC6904 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 08106241 08106242 Subscribers get a 10% discount on all orders for parts $5.00 $2.50 $5.00 $2.50 $2.50 $20.00 $20.00 $7.50 $15.00 $10.00 $5.00 $10.00 $2.50 $5.00 $10.00 $2.50 $2.50 ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 AUG24 AUG24 AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 08106243 24106241 CSE240203A CSE240204A 11104241 23106241 23106242 08103241 08103242 23109241 23109242 23109243 23109244 19101231 04109241 18108241 18108242 $2.50 $2.50 $5.00 $5.00 $15.00 $10.00 $12.50 $2.50 $2.50 $10.00 $10.00 $10.00 $5.00 $5.00 $7.50 $5.00 $2.50 PRE-PROGRAMMED MICROS As a service to readers, Silicon Chip Online Shop stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. $10 MICROS $15 MICROS ATmega328P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) PIC12F617-I/P Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Railway Points Controller Transmitter / Receiver (2 versions; Feb24) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Digital Volume Control Pot (SMD; Mar23), Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) Compact OLED Clock & Timer (Sep24) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) W27C020 Noughts & Crosses Computer (Jan23) PIC16F18877-I/P PIC16F18877-I/PT PIC16F88-I/P PIC24FJ256GA702-I/SS PIC32MX170F256B-I/SO USB Cable Tester (Nov21) Wideband Fuel Mixture Display (WFMD; Apr23) Battery Charge Controller (Jun22), Railway Semaphore (Apr22) ESR Test Tweezers (Jun24) Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) ATmega32U4 ATmega644PA-AU Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) $20 MICROS $25 MICROS PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS & SPECIALISED COMPONENTS PicoMSA PARTS (SC7323) (SEP 24) COMPACT OLED CLOCK & TIMER KIT (SC6979) (SEP 24) DISCRETE IDEAL BRIDGE RECTIFIER (SEP 24) Hard-to-get parts: includes the PCB, Raspberry Pi Pico (unprogrammed), plus all semiconductors, capacitors and resistors (see p63, Sep24) Includes everything except the case & Li-ion cell (see p34, Sep24) DC SUPPLY PROTECTOR $50.00 $45.00 Both kits include the PCB and everything that mounts to it (see page 83, Sep24) - All through-hole (TH) kit (SC6987) $30.00 - SMD kit (SC6988) $27.50 DUAL MINI LED DICE (AUG 24) Complete kit: choice of white or black PCB solder mask (see page 50, August 2024) - Through-hole LEDs kit (SC6849) $17.50 - SMD LEDs kit (SC6961) $17.50 AUTOMATIC LQ METER KIT (SC6939) (JUL 24) ESR TEST TWEEZERS COMPLETE KIT (SC6952) (JUN 24) USB-C SERIAL ADAPTOR COMPLETE KIT (SC6652) (JUN 24) Includes everything except the case & debugging interface (see p33, July24) Includes all parts and OLED, except the coin cell and optional header Includes the PCB, programmed micro and all other required parts $100.00 $50.00 $20.00 (JUN 24) All kits come with the PCB and all onboard components (see page 81, June24) - Adjustable SMD kit (SC6948) - Adjustable TH kit (SC6949) - Fixed TH kit – ZD3 & R1-R7 vary so are not included (SC6950) WIFI DDS FUNCTION GENERATOR $17.50 $22.50 $20.00 (MAY 24) Short-form kit: includes everything except the case, USB cable, power supply, labels and optional stand. The included Pico W is not programmed (SC6942) - Optional laser-cut acrylic stand pieces (SC6932) COMPACT FREQUENCY DIVIDER KIT (SC6881) (MAY 24) ESP-32CAM BACKPACK KIT (SC6886) (APR 24) PICO GAMER KITS (APR 24) PICO DIGITAL VIDEO TERMINAL (SC6917) (MAR 24) Includes the PCB and all other required parts (see page 38, May24) Includes everything to build the BackPack, except the ESP32-CAM module - SC6911: everything except the case & battery; RP2040+ is pre-programmed - SC6912: the SC6911 kit, plus the LEDO 6060 resin case - SC6913: the SC6911 kit, plus a dark grey/black resin case $95.00 $7.50 $40.00 $42.50 $85.00 $125.00 $140.00 Short-form kit: includes everything except the case; choice of front panel PCB for Altronics H0190 or H0191. Picos are not programmed (see page 46, Mar24) $65.00 $12 flat rate for postage within Australia. Overseas? Place an order via our website for a quote. All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars & include GST where applicable. HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 09/24 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 Treadmill motor doesn’t appear to be a DC type I have two motors that appear to be suitable for the 180-230V DC Motor Speed Controller project in the July & August 2024 issues (siliconchip.au/ Series/418). However, upon examining the circuit diagram, I suspect that at the age of 82, it is now beyond my ability to construct it, especially if surface-mount components are used. But before going any further, I think I have found a minor error in the diagram. REG1 and REG2 have been transposed, which will result in the low-voltage supplies being wrong. The motors I have came from a treadmill that would not work. The manufacturer’s only solution under warranty was to replace the motor, twice. The third time, the treadmill was replaced and then did work. This leads me to suspect that the controller was at fault, not the motors. The motors are branded 260V DC 8A 2HP RPM 4000. They look very much like the one pictured in the article. Some time ago, I disassembled one only to find that it does not have a wound rotor and fixed magnet stator, like your motor, but wound stator coils and a solid magnetic rotor. Therefore, there are no slip rings to contend with. Incidentally, there was no indication that the stator coils were damaged. Two questions arise. Would this motor be suitable to use with your circuit, and will the PCB be available with the surface-mounted components assembled to help somebody like me? I decided to try a bridge rectifier on the mains, giving about the right DC voltage across the motor. The circuit breaker on the switchboard immediately tripped. Connecting a stationary DC motor to a voltage source seems much the same as connecting a dead short. Only the revolution of the motor generates a back EMF which balances out that applied from the source. A comment on how this problem is overcome with 108 Silicon Chip your circuit would be appreciated. (R. G. B., Ararat, Vic) ● Thanks for spotting the regulator labelling error. The PCB is correct, and the rail voltages in the circuit were shown correctly; just the regulator labels were swapped. We have published an erratum and will fix the circuit diagram in the online version of the magazine. Since your motor has a wound stator coil, we suspect that your motor requires some type of polarity switching to the stator winding(s) to cause the motor to rotate. In other words, the stator coil magnetic field would need to rotate. That couldn’t be achieved with the Speed Controller we published, as it is designed for motors with rotor coils that switch magnetic polarity as it rotates. We suspect your breaker tripped because, powering your motor from rectified mains, there is nothing to cause a rotating magnetic field so you are effectively just connecting an inductor across the mains supply. It would saturate, drawing a very high current and thus tripping the breaker. The original controller probably did more than just apply DC to the motor. Our Speed Controller is not overly difficult to assemble. It uses all large through-hole parts where possible. The only parts not available in through-hole packages or where they would be too large to fit are the 6-pin TLP5701 opto-coupler and four 3W shunt resistors. They can be soldered quite easily using hand tools, flux paste and a magnifier to check that no solder bridges have formed. Replacing incandescent lamps with LEDs Hi. Have you ever published an article on replacing old bulbs in equally old equipment with LEDs? The problem, as I see it, is that the former are voltage-driven, whereas the latter are current-driven. Thanks, and keep up the great work! (D. H., North Gosford, NSW) Australia's electronics magazine ● We haven’t published an article on replacing light bulbs with LEDs. This is a large topic as it depends on many variables such as the available voltage, matching the light output and operating temperatures. There is also the question of the colour spectrum required and the colour rendering index (CRI). Typically, LEDs draw much less power than the bulbs they replace, and they are operated well below the maximum specification to ensure long life. Power LEDs require heatsinking. They can be driven via a current-­ limiting resistance, constant current source or a combination of regulated voltage and source resistance. Pulsewidth modulated (PWM) drive can be used for dimming, as long as the frequency is high enough to avoid noticeable flicker. A few hiccups with the Skill Tester 9000 I have worked in electronics and telecommunications for much of my 77 years and still enjoy your magazine, but I must admit the more complex microprocessor-controlled projects are getting a bit beyond my old brain. I have really enjoyed making the more basic component-level projects you have recently published, especially the Skill Tester 9000 (April & May 2024; siliconchip.au/Series/414). However, I have found three problems. 1. In the May 2024 issue (pp82-83), the Siren and Tick Section installation and test, there appears to be no mention of installing the sound IC (IC11) and components. It was fairly obvious (even to me) that it was a requirement. 2. I could not make both songs play together in the Win Song and Lose Song Sections on the same pages. If I lifted one end of diodes D18 and D21, each song would play OK when one diode at a time was connected. This did not affect the overall operation of the complete system. 3. The output level of the Win/Lose siliconchip.com.au songs was very low, maybe due to my poor hearing! I reduced the 100kW resistor in the voltage divider at the input to IC11 to 33kW and the volume seemed more suitable. Please continue to develop and publish similar projects in the future; you have reignited my interest in hobby electronics. Thank you for your excellent work. (D. C., Beachmere, Qld) ● Phil Prosser responds: First, thanks for reading the Skill Tester article and building it. It definitely provides some soldering therapy, which I really enjoy from time to time. You are right; you need to fit the amplifier, IC11, to make sound come out. It was one of those cases where you get so close to something, such as building the board, that you can miss something right before you. I even went to the trouble of building an extra board just to write that section of the article! On playing the win and lose songs at the same time, the way the sound works is not ‘analog’, so the sounds do not mix. The logic interferes, and you get messy noise instead of the two songs. The wording in the article might have been clearer on that point. It might have been better to write that you won’t hear much in this situation. As the designer, I was kind of expecting that, so I was not phased by it. A more casual builder might wonder where all the sounds went. It is strange that you needed to change that resistor. The prototype unit in the photographs ended up at work in the coffee area, where people generally turned it on once before the noise had the whole floor staring at them. Other than that 100kW resistor, the only other component we can see that’s likely to affect the volume so much is the 1kW resistor also connected to pin 3 of IC11. I hope you found the project fun. As you are no doubt aware, the design could have been little more than a PIC microcontroller, and all the young engineers at work probably think I am bonkers taking the approach I did. But there is a lot to be said for good old discrete circuitry. 30V 2A Bench Supply troubleshooting I am at the testing stage of my Bench Supply (September & October 2023; siliconchip.au/Series/403) and I am having a bit of a problem. I set the dials and VR6 as specified and switched it on but got no display unless I turn VR1 clockwise. It shows 0A and around 0.5V, then smoke comes out of the 100W resistor to the right of the 2200μF capacitor. I replaced it, checked over everything the best I could and, well, got more smoke. I am new to this, but I took it slow and triple-checked everything (I know that doesn’t mean I got it right). I just hope I haven’t burnt something else out. I know it’s hard to tell over an email, but I’d appreciate it if you could help in some way. The red stripe on the ribbon cable is backwards but pin 1 is correct; I learned about the little mark on the connector. Anyway, I hope this makes some sort of sense. (B. P., Scottsdale, Tas) ● Please check the voltages around the circuit. With VR1 fully off (anti-clockwise), check for 21V at TP21V and verify that the meter is supplied with +21V. If those are correct, check the other test point voltages. We suspect there is a wiring error to the meter if it only shows digits after VR1 GPS-Synchronised Analog Clock with long battery life ➡ Convert an ordinary wall clock into a highlyaccurate time keeping device (within seconds). ➡ Nearly eight years of battery life with a pair of C cells! ➡ Automatically adjusts for daylight saving time. ➡ Track time with a VK2828U7G5LF GPS or D1 Mini WiFi module (select one as an option with the kit; D1 Mini requires programming). ➡ Learn how to build it from the article in the September 2022 issue of Silicon Chip (siliconchip. au/Article/15466). Check out the article in the November 2022 issue for how to use the D1 Mini WiFi module with the Driver (siliconchip.au/Article/15550). Complete kit available from $55 + postage (batteries & clock not included) siliconchip.com.au/Shop/20/6472 – Catalog SC6472 siliconchip.com.au Australia's electronics magazine September 2024  109 is rotated. It should show 0V when VR1 is fully anti-clockwise. Check the wiring required from the information supplied with the meter. The wire colours for your meter differ from those on the unit we used. The thinner red and black wires are the meter power supply, while the thicker red, black and yellow (or white on your meter) wires are the voltage and current sense wires. We note that the wiring to CON5 appears to have the supply (VS+) and MV+ wires transposed, plus the MIon the meter wiring is transposed with the ‘NC’ wire on CON5. That could explain why the meter is not showing correctly. There must be a serious short for the 100W resistor to burn. That is because that resistor is only used to limit the charging/discharging current for the 47μF capacitor at the collector of Q4, which is charged via a 100kW resistor. So, negligible power is usually dissipated in that resistor. Perhaps there is a bent-over resistor pigtail shorting somewhere under the PCB. Apart from the meter wiring, your construction appears to be very good overall, and the photo supplied shows no other problems. Finally, note that the little arrows that indicate pin 1 on the IDC connectors will only be correct if the cable is routed consistently through them. It doesn’t matter if the red wire corresponds with pin 1 or is on the opposite side, as long as it is the same for all connectors. If the red wire goes to pin 1 on some and not others, your supply will have crossed wires. Capacitor discharger & kitchen timer wanted Has Silicon Chip ever published a project or circuit on a capacitor discharger? Also, have you ever designed a kitchen timer that will go up to 60 minutes? I have looked online but cannot find one. Finally, I would like to build a high-voltage DC supply for charging capacitors. It would need to deliver about 10-150V DC at 2-3mA. What would be the safest way to do that? Could the Electrolytic Capacitor Reformer (August 2010; siliconchip. au/Series/10) be modified to do it? (R. M., Melville, WA) ● We haven’t published a capacitor discharger yet but will have one later 110 Silicon Chip this year. You can use a power resistor to do this job as long as you are careful not to exceed its ratings; the ideal value will depend on what voltage the capacitor is charged up to (or expected to be charged to). The project we will present is a universal solution that will discharge most capacitors rated up to 400V reasonably quickly. As for the timer, we’ve published a few that could be used in that role. For a start, the Remote-Controlled Digital Up/Down Timer (August 2010; siliconchip.au/Article/240) was designed with that sort of job in mind and can count from one second to 100 hours. Then there are two ‘egg timers’, the Really Snazzy Egg Timer (November 1990; siliconchip.au/Article/6606) by Darren Yates and the Egg Timer by Geoff Nicholls (June 2007; siliconchip. au/Article/2253). For the November 1990 version, the 100nF capacitor at pins 1 and 2 of IC1 sets the period. For the June 2007 circuit, the 100nF capacitor at the pin 9 output (OSC OUT) sets the timeout, although it is adjustable within a restricted range using trimpot VR1. A 2.2μF capacitor should typically provide the 60 minutes you want for either timer. If using an electrolytic capacitor, use a non-polarised (NP) type for the June 2007 version. Yes, the Capacitor Reformer would be suitable for your needs without modification. It provides an output between 10V and 630V in 11 steps. The supply current is adjustable between 0-20mA. Programming PIC32s with a PICkit 3 I am trying to program a PIC32MX170F256B microcontroller. MPLAB v5.2 recognises my PICkit 3 programmer but will not connect to the chip. Any MPLAB version higher than 5.2 does not find the PICkit 3. PICkit3.1 finds and will communicate with the programmer, but the device list does not include the PIC32MX170F250B. It would seem that the PICkit 3 is no longer valid, but I do not want to have to buy a PICkit 4. Can the Microbridge do the job? If not, what programming kit options can you offer that will program most, if not all, PIC devices? (I. T., Blacktown, NSW) ● We tried this ourselves using a Australia's electronics magazine PICkit 3 and MPLAB IPE v6.15 (that comes with MPLAB X IDE v6.15). We got it to connect to and read the flash memory of a PIC32MX170F256B. We recall that version 5.20 or thereabouts was when Microchip switched to modular support for devices (the Device Family Packs and Tool Packs), so support might not be automatically included for all devices and tools. If you go to the Tools → Packs menu in MPLAB X IDE, you will see a window to download the add-ons. Check that you have the packs for the PIC32MX family (under Device Family Packs) and the Tool Packs, too. Under the Debug menu in MPLAB X IDE, there is an option to run a programmer self-test; that might also be helpful. Assuming your programmer and chip are both fully functional, perhaps updating to the latest version of the IPE (or at least a fairly recent one) will fix your problem. The Microbridge (May 2017 issue; siliconchip.au/Article/10648) can program some PIC32s, including the one you are trying to program. The kit costs $20+P&P (minus $2 for active subscribers). So you could try that if you strike out with the PICkit 3. Can the 20W Class-A amplifier still be built? I am interested in building the 20W Stereo Class-A Amplifier (May-September 2007; siliconchip. au/Series/58), but it was published nearly 20 years ago, so no kits are available any more. Without the case coming pre-punched, it might be hard for me to build; I am not good at metalwork. I assume that all the parts are still available, though. If I were to build it from scratch, I would probably make two monoblocks without preamps. Is a new version likely to be published in the near future? (D. M., Hughesdale, Vic) ● You should be able to obtain the parts; we can supply the PCBs (see siliconchip.au/Shop/?article=2249). Note that Altronics still have the kit for the December 2004 version of the 20W Class-A amplifier module (Cat K5116). We have improved our Ultra-LD amplifiers to the point that they outperform the Class-A amplifiers while providing a lot more power and much higher efficiency, so it is unlikely we 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 USED TEST GEAR Following my retirement, I have the following test instruments available for sale. All are ‘used’ rather than new, but they are all in good condition: 1. A Siglent SDS2104 Four channel DSO with a bandwidth of 100MHz and a maximum sampling rate of 2GS/sec. It also provides eight digital channels, and I can provide a user manual and a servicing manual with it – $600 2. A Gratten GA1484B RF Signal Generator, with a frequency range of 250kHz to 4GHz. I can provide a user manual and a programming manual with this one – $500 3. A Siglent SDM3045X Bench Digital Multimeter with a 4.5 digit display. This one comes with a user manual – $300 4. A Yokogawa 7562 Bench Digital Multimeter with 4.5 digit display. This one also has an instruction manual – $300 5. A Digitech QM1240 True RMS Bench type DMM – $200. 6. A HP E3631A Triple Output Bench Power Supply, with outputs of 0-6V at up to 5A and 0 to ±25V at up to 1A. This comes with the original HP user’s guide and service guide – $150 Prices are negotiable, if any of these instruments is of interest to you, please contact me via email to: jimrowe<at>optusnet.com.au LEDsales DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDS, BRAND NAME AND GENERIC LEDs, filament LEDs, LED drivers, heatsinks, power supplies, kits and modules, components, breadboards, hardware, magnets. Please visit www.ledsales.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com WANTED PCB PRODUCTION Transistor Driver Transformer: Ferguson TRD223, Special Transformers ST4953 or A&R TD19. To repair an old 1960s amplifier. Call Andrew 0418-170-500 PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au Advertising in Market Centre Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre start at $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip. com.au and include your name, address & credit card details, or phone (02) 9939 3295. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine September 2024  111 Advertising Index Altronics..................... 13-14, 27-28 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................. 11 Jaycar............................. IFC, 41-44 Jim Rowe Test Gear Sale......... 111 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Melbourne Society of Model & Experimental Engineers..........OBC Microchip Technology.................. 9 Mouser Electronics....................... 4 PCBWay....................................... 65 PMD Way................................... 111 Product Showcase..................... 12 SC Pico W BackPack.................. 95 SC Programming Adaptor.......... 85 Silicon Chip Back Issues..... 81, 89 Silicon Chip Binders.................. 64 Silicon Chip GPS Clock........... 109 Silicon Chip PDFs on USB......... 70 Silicon Chip Shop.................... 107 Silicon Chip Subscriptions........ 15 The Loudspeaker Kit.com............ 8 Wagner Electronics................... 101 Notes and Errata 180-230V DC Motor Speed Controller, July-August 2024: in the parts list (July issue, pages 76 & 77), the Altronics part codes for T1 are correct but the transformer is a 12V + 12V type, not 15V + 15V. Also, element14 no longer sells the RURG3060 (D1). You can get the new version, RURG3060-F085, from DigiKey or Mouser. Next Issue: the October 2024 issue is due on sale in newsagents by Thursday, September 26th. Expect postal delivery of subscription copies in Australia between September 24th and October 14th. 112 Silicon Chip will present another Class-A amplifier again. For example, compare the performance of the Ultra-LD Mk.4 (August 2015, p37) to the 20W Class-A amplifier (May 2007, p36). You will see that the Ultra-LD’s distortion level is lower at 100W than the Class-A amplifier at 20W! Calculating guitar pickup inductance I am wondering if you can help me find out how to calculate the inductance of electric guitar pickups. I have been looking online, but most of the information is written by guitar people and is more like alchemy than electronics. What I do know is that the inductance of a guitar pickup is related to the shape of the windings. A pickup can have thousands of turns of wire, usually 42-43 AWG. The resistance usually ranges from about 3kW up to as high as 12kW. In a nutshell, this usually translates into ‘hotness’ or the amount of output. The reactance is affected by the shape of the coil; short and fat coils sound different to tall and thin ones. This translates to the ‘tone’ of the pickup, or the frequency response. If I know how many turns are in the coil and the resistance, and I can measure the height, width and length of the coil, can I calculate the inductance and determine what does it do to the frequency response or ‘tone’? Also, does the actual distance from the pickup to the strings makes a difference? What effect do things like the bobbin material, presence of a metal cover over the pickup or pickups with two coils with opposite windings (called a humbucker) have? How do I measure the shape of the magnetic field of the pickup? What will paraffin or beeswax potting of the pickup do to any of these measurements? The only information I can find on this is usually very light on detail and explanation. The only other stuff I can find is so technical that I need a Nobel Prize to decipher it. What I need is a good source that aims at us mere mortals with a little electronics education at about intermediate level. I also want some equations or a method to calculate this stuff. (A. P., Wodonga, Vic) ● We put this to Brandon Speedie, as he has an article on modifying Australia's electronics magazine electric guitars in this issue, and he responded as follows: Calculating the inductance of a guitar pickup using geometric methods is difficult to do accurately. The common inductance equation L = N2 ÷ R (and its derivatives) will get you in the ballpark, but it is difficult to know permeability with any certainty, and (as you say) shapes and sizes differ widely between types. A better way is to simply measure with an LCR meter. Silicon Chip has published many L meters in the past, but I’m unsure if any would read up to 10H. Commercial LCR meters that can do many 100s of henries are available for less than $200. Given that most guitarists don’t have an LCR meter, despite its pitfalls, DC resistance has become a popular way to compare pickups. It is broadly true that a pickup with more turns of (the same gauge) wire will have higher resistance (and inductance), and thus will be ‘hotter’, ie, have a higher output level. This is most relevant when fitting a guitar with multiple pickups. A common mistake I see is to load a guitar with a ‘hot’ bridge pickup, reasoning that it will be more suitable for solos, while the neck pickup will be used for rhythm work. But when both pickups are active, the bridge pickup will swamp the neck, providing less versatility from the instrument. Therefore, the DC resistance of the pickups is usually kept broadly similar across the instrument. Having said that, inductance is much more important to overall ‘tone’ than DC resistance. The pickup itself acts as an LC circuit, where the pickup inductance and parasitic capacitance form a resonant circuit. The peak frequency, and its Q, are the largest drivers of ‘tone’. To give some examples, a Stratocaster single-coil might measure 2.2H and have around 600pF of capacitance, which gives a peak a bit above 4kHz. By comparison, a Les Paul humbucker might measure 6.6H, which gives a peak closer to 3kHz with the same parasitic capacitance. You might be interested to read my article in this issue (starting on page 86) on replacing the onboard electronics on many common electric guitars and basses. There is some more information in that article on pickup types and their operation, which you may find interesting. 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