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DECEMBER 2023 ISSN 1030-2662 12 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST Secure Remote Switch Control devices remotely with up to 16 transmitters 5 in DSOs to w (see p9) Multi-Channel Volume Control Simultaneously adjust up to 20 audio channels Six unique designs to build Ideal Diode Bridge Rectifiers Laboratory Power Supplies A GREAT RANGE of fixed and variable output power supplies at GREAT PRICES for hobbyist or industrial workbenches. 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MP3079 MP3078 MP3089 MP3096 MP3097 MP3800 MP3098 MP3802 MP3842 MP3840 MP3091 MP3087 Type Fixed Fixed Fixed Fixed Fixed Variable Fixed Variable Variable Variable Variable Variable Output Single Single Single Single Single Single Single Single Single Voltage DC 13.8V 13.8V 13.8V 13.8V 13.8V 0 to 24V 13.8V Current 12A 20A 40A 5A 10A 15A 20A Backlit Analogue Recommended Retail Price (RRP) $87.95 $129 $239 $139 $189 $219 $249 Single • • • • Backlit Analogue Backlit LCD LED Backlit LCD Backlit LCD $279 $219 $259 $439 $439 Shop at Jaycar for: • Isolated Stepdown Transformers • AC/DC Power Supplies • Auto Transformer (VARIAC) • Plugpacks & Desktop • Power Leads & Boards Power Supplies Explore our full range of power supplies, in stock at over 115 stores or 134 resellers or on our website. Dual 0 to 16V 0 to 16V 0 to 5A 0 to 30V 0 to 15V 2 x 0 to 32V 0 to 27V 0 to 3A 0 to 36V 0 to 2.2A 0 to 5A 0 to 40A 2 x 0 to 3A 25A Current Limiting Display Single jaycar.com.au/laboratory-psu 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Contents Vol.36, No.12 December 2023 12 The History of Electronics, Pt3 This final part in our series covers the many significant electronic developments that were not the work of individuals, but came from universities, companies and other organisations. By Dr David Maddison Electronic inventors & inventions 24 Arduino Uno R4 Minima The Arduino Uno R4 Minima is the latest version of the well-known Arduino Uno. It marks a major upgrade for the Uno series, because of its 32-bit ARM microcontroller and greatly expanded memory among other additions. By Jim Rowe Microcontroller review 57 Electronic Markets in Shenzhen Shenzhen is home to one of the biggest public electronic marketplaces in the world, full of everything from cameras, drones and individual electronic components such as resistors, capacitors and integrated circuits. By Edison Zhang Electronic components 86 Recreating Sputnik-1, Part 2 Completing a replica of the Sputnik-1 radio transmitter wasn’t easy. Learn how Dr Hugo Holden reverse-engineered and built one of the two D-200 radio transmitters used in the satellite. By Dr Hugo Holden Vintage Radio The History of Electronics Inventors and their Inventions Part 3: page 12 Reviewing the Arduino UNO R4 Minima Page 24 Page 72 Coin Cell Emulator Recreating Sputnik-1 34 Ideal Diode Bridge Rectifiers We have six different Bridge Rectifiers you can build, each acting as a highefficiency drop-in replacement for existing bridge rectifier designs. The ‘Ideal’ Rectifiers can handle currents from 2A up to 40A (continuous). By Phil Prosser Power supply project 42 Secure Remote Switch, Pt1 Our Secure Remote Switch is designed to control low-voltage appliances, such as a garage door controller, fans, pumps or LED lighting. It’s powered from 12V or 24V DC and can be controlled by up to 16 transmitters. By John Clarke Remote control/security project 60 Multi-Channel Volume Control, Pt1 Control the volume of up to 20 audio channels simultaneously using this Volume Control. The Volume Control can be adjusted using its touchscreen, rotary encoder or via an infrared remote control. By Tim Blythman Audio project 72 Coin Cell Emulator This device is used to emulate a coin cell to power a circuit, and at the same time measure the current, voltage and charge plus other statistics. It is a versatile tool when designing or testing low-power circuits. By Tim Blythman Test & measurement project Part 2: Page 86 2 Editorial Viewpoint 5 Mailbag 33 Online Shop 80 Serviceman’s Log 98 Circuit Notebook 101 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 1. Wireless power transfer demo 2. MIDI Spectral Sound software update 3. Battery-powered timer SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen How our magazine is distributed 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: I thought it would be worthwhile to describe how Silicon Chip is distributed to clarify why the magazines don’t necessarily arrive or go on sale on exactly the same day each month. Newsagents require that the magazine goes on sale on either a Monday or a Thursday; thus, we can’t have the same on-sale date each month. We try to keep it between the 26th and the 29th of the month before the cover date, although public holidays sometimes stymie that. That is also our target date for deliveries to Australian subscribers via mail, but with the quantity we send, they are all prepared and handed over to Australia Post on the same day. That means subscribers who are further away from us will get their magazines later. Overseas subscription copies are a whole other kettle of fish that I won’t get into here. We mail subscription copies around the 15th of the previous month, expecting the average transit time within Australia to be around 10-14 days. Thus, most subscriber copies (but likely not all) should arrive by the time the magazines go on sale in newsagents. Then again, some newsagents may decide to put them on shelves early. The other main avenue by which Silicon Chip is sold is dealers like Jaycar, Altronics and Aztronics. They receive the magazines in bulk on the same day as the newsagent distributors, but we find they usually get them to their stores quickly. So those stores may be the first ones you notice a new issue of Silicon Chip on sale. After all, they have smaller networks than the newsagents and Australia Post. That leads me to the most common complaint we receive: that a subscriber’s magazine hasn’t arrived on time. The first question is usually, “Has there been some sort of a delay?” I don’t recall a time in the fifteen years I have been involved with Silicon Chip that we were late enough going to press that it affected the magazine’s distribution. There was one time I recall that the printers took longer than usual (due to equipment failure), and the newsagent on-sale date had to be pushed back a few days to the next opportunity, but that’s it. So if you usually get your magazine delivered around a certain point in the month and it hasn’t come, it has almost certainly been held up in the mail. That seems to happen pretty much randomly. A few people complain that their magazines arrive late each month, and a few more never get them (and we have to send another copy). We have never received a good explanation as to why this happens. Still, you have to expect the occasional mistake when delivering the volume of mail that Australia Post handles. By all means, let us know if your magazine hasn’t come on time, and definitely tell us if it was lost so that we can send a replacement. Still, I hope readers understand that we are at the mercy of the postal system for subscription deliveries. Occasionally, there have been times when many people have had their magazines delivered late or lost, but that’s pretty rare, and the remedy is the same regardless. The last time that happened was when the Trans-Australian railway line was damaged by flooding in February 2022. Finally, note that our newsagency distributors determine precisely which newsagents receive how many copies of the magazine. If your local newsagent has no copies (left), let us know their address so we can follow up with the distributors. 24-26 Lilian Fowler Pl, Marrickville 2204 by 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 2 Editorial Viewpoint Silicon Chip Australia's electronics magazine siliconchip.com.au Easily check price and availability for every part you need au.mouser.com/price-availability-assistant +852 3756-4700 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”. Parts and tools for sale after retirement After 21 years as a product development specialist, it’s time to retire and dispose of surplus equipment and components. I’m offering them at less than half the current new price while stocks last. Bulk sales are negotiable, so feel free to make an offer. All components are new but repackaged for sale. Items include Microchip PIC32MX360 processors, development boards, break-out boards, capacitors, resistors, transistors, oscillator crystals, linear ICs, interface ICs and in-circuit debuggers for MPLAB. For a complete list, further information, or to make a purchase, please email me: Phil Carden, ISPI Limited, Auckland, New Zealand. info<at>ispi.co.nz Earth stakes can be marginal Over the years, there have been various comments on Earth stakes and Earthing in general. I fail to see how, in many places, just a rod in the ground suffices, especially when the soil dries out. Being rural may be an advantage in terms of the amount of surface area available. The now-discontinued SWER system, a ‘grid’ in the ground, was installed by the thenSECV. Fortunately, there are several wet patches here and in a similar fashion to the SEC, a grounding wire was laid in the same trenches as the power. That gives a vastly superior Earthing system, as it is in an old creek bed. On the German guy with the coffee grinder that had an arcing mains switch and tripped the circuit breaker (Ask Silicon Chip, October 2023, p106), some fridges here were apt to do that, as well as some twin-tub washing machines with switched Neutrals. There are motor caps in a lot of that stuff. Marcus Chick, Wangaratta, Vic. Comment: that is why the MEN system connects an Earth rod (or multiple) at each premises into the mains Earth/ Neutral network. The Earth rod of every premises is in parallel, so even if the local Earthing is not that great, the impedance to other nearby (hopefully good) Earth rods is kept low. Memories of 200V DC in suburbia I grew up in Surrey Hills, then outer Melbourne, just north of the Surrey Hills railway station. There were farms between Mont Albert and Box Hill, within pushbike range. In the late 1940s, the power supply there was 200V DC. I remember that we could not use some of the new-fangled siliconchip.com.au electric appliances as they could not switch the current off safely. The brass and ceramic wall switches opened and closed with a heavy click. Many years later, I found a board with a switch and a three-pin socket of the type I remembered, in my father’s shed. The switch was a double-pole, single-throw type and the contacts were moved by an over-centre spring action. As I remember it, the moveable contactor came to rest a good ¼-inch (6.35mm) from the live contacts. Our main appliances, a stove, a sink heater, and a bath heater, were fed by town gas. The plumbing for the gas lights was still installed but disconnected. My grandmother had a Bakelite mantle radio that sat on a shelf in the breakfast room. It was supposed to be turned off and on at the wall, but was usually just left on with the volume turned down. One day, it caught fire. It burned through the shelf; my father pulled the cord out of the wall socket and dropped the radio into a tub of water. The MFB (Metropolitan Fire Brigade) turned up in a red truck with the brass bell on the front, the men wearing their brass helmets. I do not remember a replacement radio, but my parents bought a refrigerator and a cake mixer in August 1952, so by that stage, the power must have been 240V AC. I know that the bills for the electricity came from Victorian Railways, and I wonder if there is any knowledge of the history of this type of supply in Australia. What modifications would have been made to the radio to allow it to run from a DC mains supply? Brian Wilson, Gowrie, NSW. Praise for article on photographing electronics I wish to congratulate Kevin Poulter on a magnificent article on radio photography (October 2023; siliconchip. au/Article/15969). His writing style is both relaxed and inspiring, so I’m sure anyone who reads the article would have had their interest piqued in the subject. I particularly liked the encouragement to the reader regarding lower-cost cameras, software and the home ‘studio’. The article was an excellent descriptive blend of the issues. It dealt with the technical, the functional and the practical processes. The photos of the radios in the article are truly magnificent. Those alone will fire up the minds of readers, let alone his words. The placement and lighting used for the radio photos are exquisite. They clearly show what is possible, and Silicon Chip presented those images beautifully. Australia's electronics magazine December 2023  5 He also does a wonderful job promoting the Historical Radio Society of Australia (HRSA) in his articles. He is a great champion for the HRSA. I expect more new members will be in contact with Jim Greig. My thanks to Silicon Chip for the effort, time, cost and willingness to present the article in the grandest of manners. It is a pinnacle article from many perspectives. Those of us with an interest in historical radios are so very well served on numerous fronts in this country. How fortunate we are. Graeme Dennes, Bunyip, Vic. Since 1964 Videos on rocket launches in Australia ID-50A VHF/UHF DUAL BAND DIGITAL TRANSCEIVER In the spirit of Dr David Maddison’s articles on WRESAT (October 2017; siliconchip.au/Article/10822) and the information on space and rocketry in the Avalon Airshow article (May 2023; siliconchip.au/Article/15773), I would like to present the following video links. I think readers who are interested in the Australian space industry will find them a great watch. • “Rocket Range Australia”: youtu.be/o9ObtDCUNCE • “Guided Weapons Testing In Australia - Woomera Test Range”: youtu.be/ESi4ncoGk2Y Andre Rousseau, Auckland, New Zealand. Earthquake Early Warning module not initialised correctly  I am an electronics amateur writing from Turkey. You may know that strong earthquakes occur frequently in our country. For this reason, I built the “Earthquake Early Warning Alarm” circuit (March 2018; siliconchip.au/ Article/10994) but could not get it to work. I looked at the software that I downloaded from your website because the circuit was very simple. Ultimately, the circuit worked when I added the following lines to the “setup” section. Without these lines, the sensor cannot reset and become active: Wire.write(0x6B); Wire.write(0x00); |905 MULTI-BAND 144 MHz TO MICROWAVE TRANSCEIVER Then I realised that the sensitivity settings weren’t perfect; it was either very sensitive or not. I think the filter settings are also problematic. There is no code line about included filter frequency settings like this: FilterOnePole highpassFilter (HIGHPASS,filterFrequency); Also, the lines below in the setup section do not make any high-pass filter frequency settings to the sensor because, according to the sensor’s register map, there are only selftest bits and full-range settings, with no filter settings: Wire.write(MPU6050_ACCEL_CONFIG); // 0x1C Accel. Wire.write (MPU6050_ACCEL_HPF_0_63HZ | MPU6050_AFS_SEL_2G); |T10 |V3500 VHF/UHF DUAL BAND FM TRANSCEIVER 144 MHz FM TRANSCEIVER www.icom-australia.com 6 Silicon Chip Ferudun Yurdabak, Turkey. Comment: this goes to show the danger of using sample code. We based our Earthquake Early Warning sketch on an example we found on the internet that we tested, and it seemed to worked fine. We could pick up the vibrations of cars and trucks driving down a nearby road. We cannot easily explain how it worked for us then but it does not work for you now; perhaps it is due to changes in the Arduino IDE, or somehow our accelerometer Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine December 2023  7 module was already set up or responded differently to commands. Upon review, we determined that each I2C register write must be in separate transmissions to work correctly. The original sketch performed a series of register writes backto-back within the same I2C ‘packet’, while the updated sketch separates them into three individual packets. That’s necessary as the MPU6050 treats subsequent data bytes as writes to consecutive addresses. We have uploaded a revised sketch to our website that fixes that. We also moved the initialisation code so it works more reliably. The filter frequency settings are near the start of the sketch: FilterOnePole XFHigh(HIGHPASS, 1), YFHigh(HIGHPASS, 1), ZFHigh(HIGHPASS, 1); According to the register map we have, register 0x1C also configures the Digital High Pass Filter (DHPF). DIY Capacitor Discharge Welder works well I built Phil Prosser’s CD Welder last year (March & April 2022; siliconchip.au/Series/379) and had great success making a couple of 10S7P Li-ion packs for my ebike, plus all those little projects that can be powered with Li-ion batteries instead of AA cells. Isn’t there just a fantastic range of DC-DC switch-mode ICs? Last week, I discovered that I can spot-weld tabs to coins. My nephew brought back a load of US coinage from his trip (and I have a big jar of NZ 5c coins). I have some wood-turning ideas for using them (hopefully, they won’t turn out too cheesy). Having tabs will make it a lot easier and more secure to incorporate them, rather than gluing. Joe Colquitt, Auckland, New Zealand. Untracked postal deliveries can be slow I placed an order with your Online Shop on the 28th of September and selected the less expensive untracked postage option as I was not in a great hurry and thought it would arrive in around a week. I am in Seven Hills, NSW, while your office is in Brookvale – both within the Sydney metropolitan area. I was advised that the order was sent to me on the 29th. However, it didn’t arrive until the 17th of October, nearly three weeks later! I was pretty surprised by how long it took. Upon receipt, I noticed that the package had two postmarks, which usually indicates it landed at the wrong address the first time. One was dated the 3rd, while the other was illegible. Name withheld. Comment: while we generally find Australia Post’s letter service fairly reliable, it is not as reliable as the tracked parcel service. Over the last 18+ months, not a single domestic tracked parcel we sent has been lost out of thousands, although a handful were delayed significantly. Unfortunately, we can’t say the same for untracked packages or letters. We want to continue to offer the untracked option, as it’s slightly less expensive, but we have some concerns. While it’s out of our hands once the package leaves our office, it still reflects poorly on us when deliveries are delayed or lost. 8 Silicon Chip Australia's electronics magazine siliconchip.com.au Emona WIN 1 OF 5 RIGOL 250MHZ DSOs You can win one of five new Rigol DHO-924S ultra-portable 12-bit digital storage oscilloscopes, each valued at $1592 $1592.. Simply click on the link below and complete the form to enter the competition. Hurry, enter now! Competition closes on December 13, 2023. To enter visit: www.emona.com.au/win-rigol Rigol DHO-924S features: • 250MHz bandwidth, four channels • High vertical resolution: 12 bits • Real-time sampling rate up to 1.25GS/s • Maximum memory depth: 50Mpts • Built-in 25MHz Arbitrary Waveform Generator • 7-inch (18cm) multi-touch screen • USB, LAN and HDMI interfaces • 16 digital channels standard (requires optional probes) All eligible entries also receive a discount coupon for any Rigol online purchases from the Emona website, valid until 31st of January, 2024. Contest open to residents of Australia and New Zealand only. Terms & conditions apply. See website linked above for details. One of the first questions usually asked when the item has not arrived in a reasonable time is whether we actually sent it; we don’t send dispatch notifications unless the package has been handed over to a delivery service (typically Australia Post). There’s also the cost involved in sending replacement orders, which usually falls on us. Any savings made in the less expensive postage could easily be wiped out by having to send more than the occasional order twice. We are still giving customers the option for now, but that might have to change if too many packages go astray. Leakage current causes LED lamps to glow or flash Have you ever had mains-powered LED ceiling lamps glow after being switched off, or worse, flash slowly while also glowing? Maybe not if they are being switched by a standard light switch on the wall; however, if you are using a solid-state device, like in a dimmer, you likely have had this happen. Years ago, I built a holiday house on the North Coast of NSW. I decided to make all the light switches low-voltage switching. The low-voltage signals controlled solid state relays made from Triacs and opto-couplers like the MOC3021. I envisioned that one day, when the technology arrived, I could remotely switch lights on and off. For example, to make the house look occupied while we were away. It worked well, without problems, for many years, although I never got around to setting up the remotely controlled lights. With the pandemic and flooding on the NSW North Coast, I decided to rent the house out as there was a desperate need for rented accommodation in the area. The lights were all still working fine. Then, the tenant advised that some lights were glowing at night when switched off, and one or two were flashing slowly. It only happened when incandescent light bulbs finally blew their filament and were replaced with LED bulbs. Filament bulbs are, of course, now almost impossible to source. I did some research and it soon became apparent that this is a big problem, particularly in theatre and stage productions, where special lighting effects require rapid light switching. They would be using solid-state switching of the mains voltage, so they would have similar problems to my system. < Electronic & Mechanical Design > PCBWAY’s 6th Project Design Contest Up to $6000 in cash prizes! Participate and get a free Raspberry Pi Pico! Enter by the 15th of January 2024 WWW.PCBWAY.COM/ACTIVITY/6TH-PROJECT-DESIGN-CONTEST.HTML 10 Silicon Chip The problem appears to result from the high efficiency of mains-powered LED lamps, which draw very little current. Therefore, even very small leakage currents through the Triac switching devices, or snubbers & filtering around these Triacs, allow the LED lamp power supplies to power up periodically (flashing) or power the LEDs at a low power (glowing) even when ‘off’. There were suggestions on the internet of simply fitting a simple 15W pilot filament bulb in parallel with the LED lamp to shunt this leakage current and prevent the LED lamp from glowing. I set this up on my bench with an LED lamp, and it certainly worked. There were stories on the internet of stage lighting setups with hundreds of small filament bulbs hooked up in parallel with the LED lamps. The filament bulbs are so inefficient that they don’t produce any visible light output while passing the leakage currents. However, that doesn’t seem practical in a home setting. So I experimented with alternative methods of shunting the power around the mains-powered LED lamps. One simple technique is to place a 47-100W resistor and 100nF X2 capacitor in series with each other, directly across the mains-powered LED lamp to shunt this leakage current. I tried this out with several mains-powered LED lamps, and it worked on most, but there was one where the lamp still glowed when switched off. Hmm! I had two 92mm flush-mount LED ceiling lamps, identical in all respects, except one was labelled 7W and the other 9W. The 9W one said it was dimmable, while the 7W one was not. I powered both lamps in parallel with my Triac switch. With the switch off, one was off completely while the other glowed. I had the 47W resistor and 100nF capacitor across them, and I figured that was creating a voltage divider with the resistor and capacitor snubber across the Triac switch. The snubber across the LED lamps was to shunt the leakage current, whereas the one across the Triac was to prevent noise on the incoming mains from false-­triggering the Triac. The easiest solution was to remove the snubber across the Triac and switch to using an MOC3063 Triac opto-­coupler with zero-crossing detection. Even the 47nF capacitor, designed to remove line noise from the Triac trigger signal, had to be removed. Finally, it worked perfectly, with both LED lamps switching off. I would be interested to know if others have experienced a similar problem and if they have found any other way of overcoming this problem, besides using a relay instead of a Triac. Keith Bennett, Greenbank, Qld. Comment: we have seen fluorescent lamps glow/flash with the switch off in buildings with old wiring, which we figured was due to leakage through the old wire insulation (which might have become damp at some point or just degraded with age), or possibly leakage in the regular mechanical switch. So what you describe can happen even with standard switches. It would be nice if the lamps could be designed to remain switched off unless they have the full mains waveform applied; the problem may be that they are universal (110240V) designs, so they can’t be too sensitive to the supply voltage. SC Australia's electronics magazine siliconchip.com.au PCBWay PCBWay is a fully-featured PCB production service. We have turnarounds as quick as 24 hours, with real-time tracking of your orders. New customers get a $5.00 credit to go towards their first order! 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We offer a Design Service using our team of professionals to produce your own custom PCB, software, 3D enclosures and more: www.pcbway.com/design-services.html Start manufacturing with www.pcbway.com The History of Electronics Inventors and their Inventions Over the last two issues, we have described many individuals who made vital contributions to electronics. Their work made modern technology possible. Many significant developments also emerged from universities, companies and other organisations, described in this third and final part of the series. Part 3: by Dr David Maddison T his final article covers significant inventions that cannot be attributed to an individual, either because we don’t know their name(s) or because they were part of a team. Unlike the last two parts, which were organised by the date of birth of the inventor, we will list them by the year of the invention or discovery. electric catfish ~2750BCE An Ancient Egyptian mural in the tomb of the architect Ti in Saqqara, Egypt refers to electric catfish, later reputed by Pliny and Plutarch to treat arthritis pain and other maladies. This could be one of the earliest discoveries involving electricity. Fig.54: a drawing of the Baghdad Battery. Source: https://w.wiki/7FNe 12 Silicon Chip Baghdad Battery Image Source: www.pexels.com/photo/2047905/ ~150BCE – 650CE The Baghdad Battery (see Fig.54) is thought to be a battery cell by some, but it could have had other uses and there is no evidence it was used as a battery. See our article on Batteries in the January 2022 issue (siliconchip. au/Series/375). optic fibres 27BCE Romans are known to have drawn glass into long flexible fibres, an idea later used for optical fibres for communications and light transmission. lighthouse, transatlantic cable 1858 The South Foreland Lighthouse near Dover, UK was the first lighthouse with an electric lamp. It used a carbon arc lamp developed by Frederick Hale Holmes and was on trial until 1860. In 1872, it received a permanent electrical installation. The light was powered by a pair of coke-fuelled steam engines driving four magnetos, shared with an adjacent lighthouse. Michael Faraday was then investigating electric lighting for lighthouses, and Holmes demonstrated the lamp to him. The first transatlantic telegraph cable was laid. It worked for only three weeks and took two minutes to Australia's electronics magazine transmit one character, about 10 minutes per word. undersea telegraph cable 1859 An undersea telegraph cable was laid between Victoria and Tasmania, the longest undersea cable at the time. It was retired in 1861. US transcontinental telegraph 1861 The US transcontinental telegraph line was completed. 1866 transatlantic cable A more functional transatlantic telegraph cable was laid. Messages could be transmitted at eight words per minute. international telegraph cable 1872 Australia connected to the international telegraph cable between Darwin and Java. 1876 AU-NZ telegraph link The Australia to New Zealand telegraph link was completed. transcontinental telegraph line 1877 The transcontinental telegraph line became operational between Port Augusta, SA and Albany, WA, a distance of 3196km. first international phone call 1881 The first international phone call was made between New Brunswick, Canada and Maine, USA. siliconchip.com.au The Sydney telephone exchange opened with 12 subscribers. public power station 1882 The first large public power station, the Holborn Viaduct power station (also known as the Edison Electric Light Station) was built in London. It produced 93kW at 110V DC, with the generator driven by a steam engine. It was preceeded by a small waterwheel-powered generator in Godalming, Surrey that only generated 7.5kW. The Pearl Street Station opened in New York. It had six 100kW dynamos, was powered by steam and its waste heat was also used for local heating. hydroelectric generation system 1883 The Adelaide telephone exchange opened with 48 subscribers, and the Port Adelaide exchange with 21 subscribers. Australia’s first hydroelectric generation system opened at the Mount Bischoff Tin Mine, to power about 50 Swan incandescent lights. Graphophone (phonograph) 1887 At the Volta Laboratory (established by A.G. Bell), Chichester A. Bell and Sumner Tainter improved Edison’s phonograph by using wax rather than tin foil as the recording medium. Along with Alexander Graham Bell, this confirmed wax as the superior recording medium. They established the American Graphophone Company to sell their Graphophone product, which was a commercial success. public electricity supply Electric generator producing 2.4kV at 1082A (2.6MW). standards for electrical units 1893 Standards and definitions for electrical units of ohms, amps and volts were refined at the International Electrical Congress in Chicago, Illinois, USA. public hydroelectric scheme 1895 Australia’s first public hydroelectric scheme began operating, to power street lights in Launceston, Tas. In 1921, it was converted to three-phase and 2MW, and was used until 1956. international telegraph 1902 Telegraph operations began between Australia and Canada, with connections via Fiji and Norfolk Island. Morse Code transmission 1906 The Marconi Company made the first official Morse Code transmission in Australia from Queenscliff, Vic to Devonport, Tas. Some claim Morse radio transmissions were made in 1897 by Professor William Henry Bragg of Adelaide University alone, or with G. W. Selby of Melbourne. By 1906, Australia had 46 electric power stations with an aggregate capacity of 36MW. production of tungsten-filament bulbs 1907 Tokyo Electric Co (predecessor to Toshiba) started small-scale production of tungsten-filament bulbs, reaching full production in 1910. 1909 radio broadcasting Radio station KQW started broadcasting in California for experimental, promotional and training purposes by engineer Charles David Herrold (18751948). By 1912, he was making scheduled news and music broadcasts (see Fig.55). Many others at the time were only broadcasting Morse Code. He received a commercial license in 1921. The station still exists today as KCBS. amateur radio frequencies 1912 The US Government passed the Radio Act of 1912, limiting radio amateurs to frequencies above 1.5MHz, as those frequencies were considered useless. This led radio amateurs to discover HF radio propagation via the ionosphere. In 1921, a one-way transmission was made across the Atlantic; then, in 1923, two-way transmission (see siliconchip.au/link/abnv). transcontinental phone call 1915 The first transcontinental phone call was made in the USA, over 5794km, facilitated by the newly-­invented vacuum tube amplifier. rotary dial telephones 1919 Bell System, USA made the first rotary dial telephones. commercial radio 1920 The world’s first commercial licensed radio station, KDKA in Pittsburgh, Pennsylvania, USA started broadcasting. 1888 Tamworth, NSW was the first town in Australia with a public electricity supply for arc and incandescent lighting (240V DC). three-phase AC power 1889 Young, NSW got three-phase AC power for street lighting, shops, offices and homes. AC hyroelectric power plant 1891 The first German three-phase AC power plant started operating in Lauffen am Neckar. 15kV was generated and transmitted 175km to the International Electro-Technical Exhibition in Frankfurt. Possibly the first commercial AC hydroelectric power plant became operational in Ames, Colorado, USA. It had a capacity of 3.75MW at 3kV, 133Hz, single-phase. That location is still producing electricity but not with the original equipment, although a powerhouse dating from 1905 is still in operation, with a 1904 General siliconchip.com.au Fig.55: Charles Herrold’s San Jose, California radio laboratory, circa 1912. He transmitted from this location as radio KQW. Herrold is standing in the doorway. Source: https://w.wiki/7EFw Australia's electronics magazine December 2023  13 double-coiled tungsten filament 1921 At Tokyo Electric Co, Junichi Miura made the first double-coiled tungsten filament light globe using the technique developed by Benbow (1917). It entered small-scale production in 1930 and mass production in 1936. “mobile phone” 1922 Early experiments were conducted with a “mobile phone”. The phone was a portable two-way radio that used an umbrella antenna with a fire hydrant for its Earth. Music was transmitted from a base station to the radio. See the YouTube video titled “World’s First Mobile Phone (1922)” – https://youtu. be/ILiLaRXHUr0 transatlantic telephone call 1926 The first transatlantic telephone call was made. car radio, Phonovision 1927 The first mass-produced car radio was made, the Philco Transitone. Before that, radios were adapted for car use. The exact year is subject to some dispute. John Logie Baird made the first “videodisc” player as a proof-of-concept called the Phonovision. The output of mechanical television scanning from a Nipkow disc was recorded to a gramophone record. It only had a 30-line resolution at 5FPS. Some recordings were found, and in 1982-87, software was made to recover the images. See the website at siliconchip.au/ link/abnw and the video titled “30-line TV video recordings news feature”, plus other videos below: https://youtu.be/J2mb4R9W9TI siliconchip.au/link/abnx https://youtu.be/G3CFkK5OORw blind aircraft take-off and landing TDK incorporated the first ferrite cores in radios in 1937, making them smaller and lighter. TDK was the only company that could supply ferrite cores until the end of WW2. LP records 1931 RCA introduced the first commercial LP (long play) records. They were 12 inches or 30cm in diameter, ran at 33⅓RPM and contained up to 11 minutes of audio per side (the same time as a standard 1000ft/305m movie reel). They were a commercial failure due to the expense of playback equipment and the Great Depression. Magnetophon K1 tape recorder 1935 German company AEG introduced the Magnetophon K1, the first practical tape recorder (see Fig.56). It used iron-oxide-coated non-metallic magnetic tape. The tape was originally based on Fritz Pfleumer’s idea (see his entry last month), with further development by Friedrich Matthias. A non-­ damaging head was designed by Eduard Schüller, who also built the prototype machines. The audio quality was poor until Walter Weber (1907-1944) discovered the AC biasing technique (by accident!), dramatically improving audio quality. These recorders had all the basic features that were incorporated into later analog tape recorders. You can see a video on the similar 14 Silicon Chip 1939 German company Fernseh AG demonstrated high-definition 1029line TV for displaying military maps. This system required 15MHz of bandwidth, which is why HDTV wasn’t widely introduced until the advent of digital broadcasting in the 1990s. commercial FM broadcasting, NTSC 1941 Commercial FM broadcasting formally began in the USA, although there were experimental transmissions before that. It was on the 42-50MHz band, split into 40 channels. In 1945, it was reassigned to 88-106MHz band with 80 channels, then extended to 108MHz and 100 channels. The monochrome NTSC television standard was released. “Colossus” digital computer 1943 The first programmable digital computer was built, the British “Colossus”. “ENIAC” digital computer 1945 The US “ENIAC” computer was built, the world’s first general-purpose programmable digital computer. The electronic Merrill Wheel-­ Balancing System for cars was also invented. FM broadcasting in Australia 1947 Experimental FM broadcasting in Australia took place from 1947 to 1961 but with an extremely limited audience (the receivers were costly). It was discontinued to clear the TV band and eventually reintroduced on a band that no one else in the world used. Fortunately, in 1975 it was reintroduced on the widely used 88MHz-108MHz. 1948 Columbia Records used PVC to make vinyl records, which are more durable than previous shellac compounds. They could be made with much finer grooves called “microgrooves”. These allowed for a playback time of about 22 minutes on a 12in/30cm disc (there was also a 10in/25cm disc). Peter Carl Goldmark (1906-1977) developed the format. 45RPM records 1930 Yogoro Kato and Takeshi Takei at the Tokyo Institute of Technology first synthesised ferrite compounds. These materials are used in inductors, transformers and electromagnets, electrical noise control, early computer memories, magnetic tapes, radar absorbing materials, loudspeakers and magnets. high-definition television vinyl records 1929 The first blind aircraft take-off and landing was made by Lt James Doolittle in a Consolidated NY-2 biplane. It was instrumented with a Kollsman altimeter, Sperry directional gyroscope and an artificial horizon, with a radio range and marker beacon by the National Bureau of Standards and a special radio receiver with a vibrating reed display by Radio Frequency Laboratories. synthesis of ferrite compounds Magentophon FT4 at https://youtu.be/ cLjD0B6QoaM Fig.56: the AEG Magnetophon K1 tape recorder being delivered to the Berlin Radio Show in 1935. Source: https:// museumofmagneticsoundrecording. org/ManufacturersAEGMagnetophon. html Australia's electronics magazine 1949 Columbia competitor RCA introduced the 45RPM record with a 7in/18cm diameter, intended as a replacement format for 78RPM records, with a similar duration of about five minutes per side. Eventually, “quality music” was distributed on 33⅓RPM records, with “popular music” on 45RPM records. Both formats are still around today. siliconchip.com.au Fig.57 (above): an image from the 1956 US Army patent 2,756,485 for PCB manufacturing. Fig.59 (above): the Regency TR-1, the first commercial portable transistor radio. Fig.58 (right): an advertisement for the first practical solar cell by Bell from the 25th of April, 1954. It had a 6% efficiency. Source: www.onthisday. com/photos/1st-solar-battery permanent magnets, PCBs 1950 Philips accidentally discovered barium hexaferrite, which became a popular permanent magnet material. The US Army applied for US patent 2,756,485, granted in 1956, titled “Process of Assembling Electrical Circuits” (see Fig.57). This led to the mass production of printed circuit boards. nuclear power, colour TV etc 1951 Sony released the H-1 magnetic audio tape recorder for consumer use. It was the first tape recorder designed for domestic use and weighed 13kg. The first nuclear power reactor (EBR-1) became operational in Arco, Idaho, USA. It could power four 200W light globes. CBS in the USA demonstrated colour TV broadcast using the electromechanical field-sequential system (FSC) standard. There were very few appropriate receivers. That standard was withdrawn and the NTSC standard was subsequently used instead. speech recognition system, video game 1952 The first speech recognition system was demonstrated, which could recognise one speaker saying the digits zero to nine with 90% accuracy. It was called Audrey (Automatic Digit Recognition machine) and was produced by H.K. Davis at Bell Laboratories. The first computer game was created by Alexander Shafto Douglas (19212010) at the University of Cambridge in England. It was called “OXO” and was a version of noughts and crosses (also known as tic-tac-toe). maser, nuclear submarine, NTSC by Charles H. Townes, James P. Gordon, and Herbert J. Zeiger at Columbia University. Masers are used as highly-stable frequency references and extremely low-noise amplifiers for microwave frequencies. They can also generate electromagnetic waves at microwave and other frequencies. The first nuclear-powered submarine, the USS Nautilus, was launched. The NTSC colour TV standard was released. photovoltaic cell, transistor computer 1954 The first practical photovoltaic cell was developed at Bell Laboratories (see Fig.58) by Calvin Souther Fuller (1902-1994), Daryl Chapin (19061995) and Gerald Pearson (1905-1987). The world’s first commercial colour television broadcast (NTSC) began in the USA. However, most programming remained in monochrome for some time due to the high cost of sets and lack of colour source material. TRADIC (for TRAnsistor DIgital Computer or TRansistorized Airborne DIgital Computer) was the world’s first fully-transistorised computer, built by Bell Labs for the US Air Force. It included 684 Bell 1734 Type A point contact cartridge transistors and 10,358 germanium diodes. The first transistorised portable radio went on sale, the Regency TR-1. It used four Texas Instruments NPN transistors, a 22.5V battery and cost US$49.95, equivalent to about $850 today (about what collectors pay!). See Fig.59 and our article in the April 2013 issue (siliconchip.au/Article/3761). programmable music synthesiser etc 1955 The RCA Mark I Synthesiser was the first programmable music synthesiser. There is an interesting article about how it works at siliconchip.au/ link/abny The first wireless TV remote control was introduced, the Zenith Flashmatic. It used visible light and had to be directed at one of four photocells in each corner of the screen to perform various functions (on/off, mute or change channel). IBM 350 drive, VRX-1000 recorder etc 1956 The first commercial disk drive, the IBM 350 (Fig.60), went on sale. Fig.60: two IBM 350 disk drives at the US Army Red River Arsenal. Source: https://w.wiki/7EFy 1953 The first maser (microwave laser; microwave amplification by stimlated emission of radiation) was built siliconchip.com.au Australia's electronics magazine December 2023  15 Fig.61: CBS engineer John Radis operating an Ampex VRX1000 videotape recorder on the 30th of November, 1956. It was the first time this machine was used on a broadcast program. Source: www.quadvideotapegroup.com/2015/12/ It stored 3.75MB and weighed about one tonne. The first commercial video tape recorder, the monochrome VRX-1000, was introduced by Ampex for studio use (see Fig.61). It used two-inch (5.08cm) wide tape in the Quadruplex format. It cost US$50,000, equivalent to about $840,000 today. The machine’s major innovation was transverse recording, where the video image was written across the tape rather than linearly, allowing for a reasonable tape speed of 38cm per second. Before its introduction, the only way to record TV programs was with film. See our detailed article on Quadruplex recording (March 2021; siliconchip.au/Article/14782). The first transatlantic telephone cable was laid, TAT-1 (Transatlantic No. 1). It could carry 35 simultaneous telephone calls with a 36th channel that carried 22 telegraph circuits. R-7 ICBM, Sputnik 1 satellite etc Silicon Chip the reactor transmutes non-fissile fuel into fissile fuel at the same time as producing power. It remained in operation until 1982. The first ICBM (intercontinental ballistic missile), the Soviet R-7 Semyorka, was introduced. ICBMs were later reused by multiple nations as rockets for launching satellites and other space missions. The FORTRAN computer language was commercially released. It is still used by mathematicians, scientists and engineers. The Soviet Union launched the first artificial satellite, Sputnik 1, using an R-7 Semyorka rocket. See our detailed articles on Sputnik’s radio transmitters on page 86 (siliconchip.au/Series/407). colour videotape, modems, pacemaker 1958 The first US satellite, Explorer 1, was launched. 1957 The RCA Mark II synthesiser (Fig.62) was a successor to the Mark I and much easier to program. It had two punch paper terminals for playing compositions. These stored data for playback; the machine’s output was recorded on lacquer-coated record-like discs. See: https://youtu.be/rgN_VzEIZ1I siliconchip.au/link/abnz The world’s first large-scale civilian nuclear power plant began operation in Shippingport, Pennsylvania, USA. Its primary purpose was to produce electricity, but it was also a proof-ofconcept of the breeder reactor, where 16 Fig.62: the RCA Mark II synthesiser. Note the punch paper terminals. Source: https://electronicmusic.fandom.com/ wiki/RCA_Synthesizer (CC-BY-SA). The Ampex VR-1000B commercial colour videotape recorder was released. It supported multiple international video standards. You can see the product brochure at siliconchip. au/link/abp0 Telephone-line modems (modulators/demodulators) were mass-­ produced for the military in the USA as the Bell 101 modem in 1958 (Fig.63), used for the SAGE air defence system. The technology was made available to the public in 1959, with a 110bit/s speed. They were a development of the teleprinter multiplexers used by news services and the like in the 1920s. The first implantable cardiac pacemaker was released. Australia’s first nuclear reactor for research and radioisotope production, HIFAR (High Flux Australian Reactor), was commissioned. It operated until 2007. The second computer game was created by William Higinbotham (19101994) at Brookhaven National Laboratory, New York, USA. It was called Tennis for Two, similar to Pong. Veroboard, Mosfet, planar process etc Fig.63: the Bell 101 modem, released by AT&T in 1958. Source: https:// history-computer.com/modemcomplete-history-of-the-modem/ Australia's electronics magazine 1959 The first American ICBM, the SM-65 Atlas, went into operation. It was also used to launch Project Mercury astronauts. What was to become Veroboard for electronics prototyping and one-off circuits was invented. The first commercial plain-paper photocopier, the Xerox 914, was introduced. See the video at https://youtu. be/9xZYcWsh8t0 siliconchip.com.au Fig.64: the ECHO 2 satellite undergoing testing and inspection, dwarfing the people around it. The first transmission using ECHO was from California to New Jersey in 1960. Source: NASA. Fig.65: the Anita Mk VII & VIII (pictured) were launched simultaneously in 1961. VII was the first model because they had used the previous numbers for their mechanical calculators Source: https://w.wiki/7EFz (GNU FDL). Mohamed Atalla and Dawon Kahng at Bell Laboratories invented the Mosfet (metal-oxide-semiconductor field effect transistor). See our May 2022 article on transistors (siliconchip.au/ Article/15305). The semiconductor planar process for fabricating integrated circuits was invented by Jean Amédée Hoerni (1924-1997). See our June-August 2022 articles for more on the history of ICs (siliconchip.au/Series/382). and played on a Digital PDP-1 mainframe computer. It was called Spacewar! – see Fig.66 and the video titled “Spacewar! (1961) - First digital computer game”: https://youtu.be/CwZAKJ8Y6YU The Josephson effect was observed but not recognised for what it was. It led to a superconducting circuit called the Josephson junction, with applications in quantum computers, voltage standards and digital signal processNASA’s Project Echo, SMT components 1960 ing, among others. It was named after NASA started Project Echo. Echo Brian David Josephson (1940~). 1 and Echo 2 (launched 1964) were The IBM Shoebox speech recogniexperimental passive reflector com- tion system could recognise 16 spoken munications satellites (Fig.64), 30m words (numerals and arithmetic operdiameter inflated balloons with some ators). It was a voice-operated printing electronics onboard. They provided calculator (see Fig.67). valuable data about atmospheric drag The Telstar 1 communications satand other information. ellite was launched into an elliptical IBM first demonstrated surface-­ orbit (not geostationary). Telstar 2 was mounting component technology launched in 1963. Both satellites were (SMT) in a small computer. It was later experimental; neither are still in use applied to the Launch Vehicle Digital Computer in the Saturn IB and Saturn V in the 1960s. ANITA electronic calculators, LEDs but are in orbit. Telstar 1 carried the first transatlantic TV transmission via satellite that same year; data was also transmitted between two IBM 1401 computers via Telstar 1. Philips compact casette, ASCII etc 1963 COMPAC (the Commonwealth Pacific Cable System) undersea telephone cable was completed, linking Australia, New Zealand and Canada via Hawaii and Fiji. Parts had been operating since 1961. This coaxial cable could handle 80 phone calls or 1760 teleprinter circuits. It replaced HF radio telephone calls, which had to be booked and were delayed if transmission conditions were bad. Philips introduced the first audio cassette tape, the “Compact Cassette”. See our article on this in the July 2018 issue (siliconchip.au/Article/11136). The first transpacific television transmission via satellite was made between Japan and the USA, via the 1961 The first electronic calculators were the ANITA Mark VII and Mark VIII, released in 1961, using vacuum tubes and cold cathode tubes (see Fig.65). The first solid-state electronic calculator was the Friden EC-130 in 1963. J. W. Allen and R. J. Cherry invented the first visible light LEDs at SERL in Baldock, UK. Josephson junction, Telstar 1 etc 1962 The third computer game was invented by Steve Russell (1937~) siliconchip.com.au Fig.66: Spacewar! Running on a PDP-1 computer. Source: https://w. wiki/7EF$ (CC-BY-2.0). Fig.67: an IBM ‘Shoebox’ voice recognition system/calculator. Source: IBM. Australia's electronics magazine December 2023  17 experimental Relay 1 communications satellite in an elliptical orbit. Nottingham Electric Valve Company in the UK released the Telcan (Fig.68), a videotape recorder intended for domestic use. It used ¼-inch audio reel-to-reel tape running at 305cm per second, a very high speed for this type of tape, and could record up to 20 minutes of monochrome video on one of two tracks. The recording bandwidth of 2.6MHz provided 405 lines. It was mainly sold as a kit, for £60, equivalent today to about $2000. It was a commercial failure; for more details, see siliconchip.au/link/abp1 The first edition of the ASCII character encoding standard was published. TPC-1, Xerox fax system, BASIC etc 1964 The Trans-Pacific cable system, TPC-1, linking Japan, Guam, Hawaii and the mainland USA became operational. It carried 128 telephone circuits. Xerox introduced the first modern commercial fax system, which they called Long Distance Xerography or LDX. The BASIC computer programming language was released. The first prototype Moog electronic music synthesiser was built by Robert Moog (1934-2005). Commercial models were produced from 1967. geosynchronous satellite Intelsat I etc 1965 The Dadda hardware binary multiplier was invented by Luigi Dadda (1923-2012) for computer arithmetic operations. It was smaller and faster than the previous implementation. Sony released the CV-2000 (CV = “consumer video”), the first mass-­ produced domestic video tape recorder (see Fig.69). It recorded in monochrome and used 13mm tape in a reel-to-reel format. It had broad uptake among business and educational institutions. Its inability to adjust head tracking meant it was impossible to swap tapes between machines; that was corrected in later versions. The first commercial geosynchronous satellite, Intelsat I, was launched. It carried either 240 telephone circuits or one TV circuit. It was in use for over four years until it was deactivated, with a temporary reactivation for use for the Apollo 11 mission, and another temporary reactivation in 1990 to mark its 25th Anniversary. It is still in orbit. Magnafax telecopier (fax machine) PAL standard, ATM, WRESAT etc Silicon Chip 1967 The SECAM colour television standard was released and adopted in France. PAL standard colour television started broadcasting in the UK. The world’s first automated teller machine (ATM) was installed at Barclay’s Bank, Enfield, UK. It was operated by inserting cheques, previously issued by a teller, marked with radioactive carbon-14 for machine readability and to confirm their authenticity. Australia’s first locally made satellite, WRESAT, was launched. See our article on WRESAT (October 2017; siliconchip.au/Article/10822). LCDs, Group 1 fax standards 1968 A team at RCA Laboratories demonstrated an 18×2 matrix liquid crystal display (LCD) using dynamic scattering mode (DSM), invented by George Heilmeier (see his entry last month). Figs.68: a Telcan home video recorder, sold mainly as a kit using ¼-inch audio tape. Source: www. nottinghampost.com/news/history/20-best-thingsnottingham-given-192680 18 1966 Xerox introduced the first easy-touse fax machine, the Magnafax Telecopier, that used standard telephone lines. The ITU (International Telecommunications Union) released Group 1 fax standards. Conforming machines took about six minutes to transmit a page at 96 lines per inch (38 per cm). MOS DRAM, Unix, ARPANET etc 1969 Commercial production of MOS DRAM (metal oxide semiconductor dynamic random access memory) was started by Advanced Memory Systems, Inc, and was offered to selected companies. The chips contained 1024 bits of memory. In the same year, Intel produced the 1103 memory chip, also with 1024 bits, and sold it on the open market. It was used in popular computers such as the HP 9800 series and the PDP-11. For more on the development of DRAM, see our articles on Computer Memory in the January & February 2023 issues (siliconchip.au/ Series/393). The Unix operating system for computers was released. The first commercial quartz oscillator watch was introduced, the Seiko Quartz-Astron 35SQ. It had an accuracy of ±5 seconds per month and a battery life of around one year. The US Department of Defense (DoD) Advanced Research Projects Agency (ARPA) established a packet-switched computer network, ARPANET (see Fig.70), which eventually evolved into the internet we have today. digital fax machine, pocket calculator 1970 Dacom produced the first digital fax machine, the DFC-10, that used data compression and could transmit a page in under one minute. The Pascal computer programming language was released. Fig.69: the Sony CV-2000, the first mass-manufactured video recorder for the domestic market. It used half-inch (12.7mm) reelto-reel tape. Source: www.smecc.org/sony_cv_series_video.htm Australia's electronics magazine siliconchip.com.au The first commercial handheld pocket calculator, the Canon Pocketronic (Fig.71), became available. It was influenced by the prototype Texas Instruments Cal Tech calculator of 1967 and used three TI MOS integrated circuits. It had no display; results were printed on paper tape. For more information, see siliconchip.au/link/abp4 Intel 4004, Kenbak-1 PC, EPROM etc 1971 The first commercial microprocessor, the Intel 4004, was released. It was mainly intended for calculators and cash machines. The US DoD funded a five-year program to make a speech recognition machine that could recognise 1000 words within sentences. A machine called Harpy was built that recognised 1,011 words; see the PDF: siliconchip. au/link/abp5 Docutel introduced the “Total Teller” machine, an ATM that could accept deposits, transfer from one account to another and dispense cash. It operated offline using plastic cards and had a mechanical display with messages on a printed cylinder. By 1975, 3000 ATMs had been installed worldwide, 80% from Docutel. In 1982, Docutel merged with Olivetti. The first personal computer (without a microprocessor) was released, the Kenbak-1 (Fig.72). Only 40 were sold. Intel released the first EPROM (Erasable Programmable Read Only Memory), invented by Dov Frohman. The Intel 1702 could store 256 bytes of data. Sony released the U-matic video cassette format to market, the first commercial video cassette format. It used ¾-inch (19mm) tape. It was initially intended for the consumer market but was too expensive; it became popular in the institutional and industrial markets, plus the television industry. See our series on videotape recording (March-June 2021; siliconchip.au/ Series/359). Intel 8008, C, Pong, blue LEDs etc Fig.70: a map of ARPANET, the internet’s predecessor, as it appeared in 1973. Source: https://w.wiki/7FPK Fig.71 (below): the Canon Pocketronic, the first commercial handheld electronic calculator. Source: https://w. wiki/7EG3 (CC-BY-SA-4.0). Fig.72 (below): Kenbak-1, the first personal computer from 1971. Source: https://w.wiki/7FPV (CC-BY-SA-4.0) 1972 The Philips VCR (video cassette recorder) format N1500 player/ recorder was introduced for the domestic market. The last Philips VCR recorder was released in 1979. The eight-inch (20.3cm) floppy disk was commercially released. The ITU (International Telecommunications Union) Group 2 fax standards were published. Conforming machines took about three minutes siliconchip.com.au Australia's electronics magazine December 2023  19 to transmit a page at 96 lines per inch (38 per cm). Cartrivision, a consumer videotape cartridge format, was introduced. The machines were built into expensive TV sets, which were a commercial failure. See www.angelfire.com/alt/ cartrivision/ The Unix operating system was rewritten in the C language, so 1972 could be considered a date when C became mainstream. C was mainly developed between 1969 and 1973 and is still widely used today (in its original form and derivatives like C++ and C#). The first microprocessor for personal computers was released, the 8-bit Intel 8008. The world’s first scientific pocket calculator was introduced, the HP-35. Pong, the first commercially successful computer game, was released. We published a project to recreate the original game in the June 2021 issue and a modernised, miniaturised version in August 2021. For more information, see www.pong-story.com The first blue LED was invented at RCA by Herbert Paul Maruska (1944~), but the company was in turmoil and the project was cancelled. Also, the device was too dim for practical use; see siliconchip.au/link/abp6 Eventually, Isamu Akasaki (19292021), Hiroshi Amano (1960~), and Shūji Nakamura (1954~) won the Nobel Prize in 2014 for their 1993 invention of high-brightness blue LEDs at Nagoya University in Japan. White LEDs are blue LEDs with a scintillator coating (similar to a phosphor). SPICE, Ethernet, graphical interfaces EDUC-8 computer, CP/M OS etc 20 Silicon Chip 1974 Electronics Australia published what was thought at the time to be the world’s first kit computer, the EDUC-8 (Fig.75), but it was later found to have been beaten by a competitor by one month, the Mark-8. However, the EA design was considered superior. Bravo was the first ‘WYSIWYG’ document preparation program, running on the Xero Alto computer, an early word processor. The CP/M computer operating system was introduced, later displaced by MS-DOS. Kodak digital camera, Betamax etc Fig.73: the Xerox Alto computer from 1973. Source: https://w.wiki/7EG4 1973 Micral released the first personal computer with a microprocessor (the Intel 8008). The SPICE (Simulation Program with Integrated Circuit Emphasis) analog circuit simulation program was introduced. It and its derivatives (like LTspice) are still widely used today. Ethernet was invented by Robert Melancton Metcalfe (1946~) and his team working at Xerox Palo Alto Research Center (Xerox PARC) in California. It is one of the key technologies of the internet. Motorola demonstrated the cellular mobile phone, although it took some time to commercialise. The first tuneable laser was demonstrated at Bell Labs. The Xerox Alto computer (Fig.73) was released, the first computer with a graphical user interface and a mouse (see Fig.74), ten years before the Apple Lisa. It cost US$32,000, equivalent to $330,000 today. It also had a portrait-­ orientated display. 1975 The first self-contained digital camera was invented by Steven Sasson (1950~) at Kodak. It had a 100×100 pixel resolution and images were recorded digitally on cassette tape, taking 23 seconds. The Altair 8800 personal computer kit was released, considered by many to have started the microcomputer revolution. The Betamax home video recording system was released (our series on videotape recording has all the details). The Steadicam was invented by Garrett Brown and produced by Cinema Products Corporation. It is used for camera stabilisation, as it isolates the operator’s movement from the camera Australia's electronics magazine (see our article on it in the November & December 2011 issues; siliconchip. au/Series/33). VHS tape system, 5.25in floppy etc 1976 The first word processor for home computers was released, called “Electric Pencil”, for use on computers such as Altair 8800, Sol-20 and later, the TRS-80 and the IBM PC. The VHS home video tape system was released. 5.25-inch (13.3cm) floppy disks became available. Apple II, Commodore PET, TRS-80 etc 1977 The first practical optical fibre link was installed in Turin, Italy. The influential Apple II, Commodore PET and TRS-80 home computers were released. speech synthesis, LaserDisc etc 1978 Texas Instruments released the first speech synthesiser chip, the TMS5100. It used “pitch-excited linear predictive coding” to greatly decrease the volume of data required to generate speech. It was used in the “Speak & Spell” educational toy. The LaserDisc was released on the market. Machines could play prerecorded videos but could not record. Technology from LaserDisc was later incorporated into Compact Discs, DVDs and Blu-rays. It was never hugely popular but offered good-­ quality video reproduction for the period, far superior to VHS. Fairlight CMI, 1G phone networks etc 1979 The Australian Fairlight CMI (Computer Musical Instrument) was released. It was based on a design by Tony Furse, licensed by Kim Ryrie and Peter Vogel (ex ETI magazine). It was “one of the earliest music workstations with an embedded sampler”, considered revolutionary at the time. See the video titled “How the Fairlight CMI changed the course of music” at https://youtu.be/jkiYy0i8FtA The very popular WordPerfect word processor was released. Japan’s Nippon Telegraph and Telephone (NTT) deployed the first 1G cellular phone network. Philips and Grundig released the Video 2000 consumer video cassette format, discontinued in 1988. The VisiCalc spreadsheet program was released. It was considered a “killer application” for the Apple II and ran on many other computers. It is the predecessor to programs like Excel. For more details, visit: http:// danbricklin.com/visicalc.htm siliconchip.com.au Commodore VIC-20 computer etc 1980 The ITU (International Telecommunications Union) Group 3 fax standards (digital) were released. The time to transmit a page was reduced to 6-15 seconds, not including handshaking. It supported a variable scanning resolution, up to 400 lines per inch (157 per cm). The Commodore VIC-20 computer was released. MS-DOS V1.0, 16-bit DAC etc 1981 The MS-DOS V1.0 computer operating system was released, along with the IBM PC. The Osborne 1 was released, it is considered to be the first commercial truly portable/luggable computer. It is not obvious what device should get the credit for the first ‘laptop’; many contenders exist. The PCM53/DAC700 16-bit single-­ chip audio digital-to-analog converter (DAC) was released. Designed by Jimmy Naylor and a Texas Instruments/Burr-Brown design team, it became the basis of nearly all audio CD players. RCA released its Capacitance Electronic Disc (CED), an analog video disc playback system. A stylus with mechanical tracking read the disc. The discs were 30cm in diameter and could record 60 minutes of NTSC video per side. The product was unpopular and discontinued due to competition from LaserDisc players and other reasons. CD player, Commodore 64 1982 The first audio Compact Disc (CD) player (co-developed by Philips and Sony) was released in Japan. The Commodore 64 computer was introduced. 3.5in floppy disk, C++ language etc 1983 The first 3.5-inch (8.9cm) floppy disks became available, based on the Microfloppy Industry Committee (MIC) specification. The C++ programming language was released, an ‘object-oriented’ version of C that’s still widely used today. The first personal computer with a built-in hard disk, the IBM PC XT with 10MB standard capacity, went on the market. Motorola released the first ‘mobile’ phone, the DynaTAC 8000X. It weighed nearly a kilogram, took 10 hours to charge and retailed for US$3995 (about $18,750 in today’s money) – see Fig.76. Dr Mitsuaki Oshima at Panasonic invented electronic image siliconchip.com.au Fig.74: the Xerox Alto GUI from 1973. Source: https://interface-experience.org/ objects/xerox-alto/ Fig.75: the Electronics Australia EDUC-8 computer. Source: https://w.wiki/7EG6 Australia's electronics magazine December 2023  21 thought that its capacity would never be reached. Sharks also attacked the cable, possibly due to them being able to sense its electromagnetic radiation. It was instrumental in the development of the internet, providing a dedicated high-speed T1 connection between CERN in Europe and Cornell University in the USA. GPS receiver, World Wide Web etc 1989 The first commercial handheld GPS receiver was released, the Magellan NAV 1000. CDMA (Code Division Multiple Access) was demonstrated for cellular telephone systems. The World Wide Web was invented by Tim Berners-Lee and released to the public in 1991. DragonDictate speech recognition 1990 The first consumer speech recognition software, DragonDictate, was released. Nowadays it’s called “Dragon NaturallySpeaking” and is now owned by Microsoft. 2G networks, Linux, Python Fig.76: a Motorola DynaTAC 8000X mobile phone. Source: https://w. wiki/7FPn (CC-BY-SA-3.0) stabilisation. Panasonic released the first video camera to feature electronic image stabilisation later, in 1988. Apple Macintosh, CD-ROM 1984 The Apple Macintosh was released. The Commodore Amiga computer was also introduced. The CD-ROM for data storage, based on the audio CD, was announced. IBM Tangora speech recognition 1985 The IBM experimental speech recognition system Tangora became available. It ran on an IBM PC AT and recognised 20,000 words, converting them to text. Sony D-1 video recording format 1986 The professional studio Sony D-1 digital video recording format was introduced. Higher temperature superconductors 1987 “Higher temperature” superconductors were discovered. Currently, the highest-temperature superconductor works at around -135°C at normal atmospheric pressure. TAT-8 transatlantic optical fibre cable 1988 The first transatlantic optical fibre cable, TAT-8, became operational. It had a capacity of 280Mbit/s, equivalent to 40,000 telephone circuits. It was retired in 2002; it rapidly reached capacity when it was initially 22 Silicon Chip 1991 2G (GSM) telephone networks were introduced. The Linux operating system for computers, a free/open-source version of Unix, was released. The Python programming language was released. TASMAN2 cable, Windows 3.1 etc 1992 Australia’s first undersea optical fibre, TASMAN2, connected us to New Zealand with a speed of around 1Gbps. Windows 3.1 was released, marking a shift away from the command-line DOS interface on PCs towards graphical interfaces. The Apple Newton MessagePad was released, an early ‘personal digital assistant’ with handwriting recognition that helped form the basis of later smart devices. Windows NT, HAARP 1993 Windows NT was released. Its core still underlies modern Windows versions such as 10 & 11. However, its GUI was still similar to that of Windows 3.1. HAARP (High-frequency Active Auroral Research Program) was established for upper atmosphere and ionospheric research. See our article on HAARP (October 2012; siliconchip. au/Article/492). CompactFlash memory cards etc 1994 The first CompactFlash memory cards were produced by SanDisk, starting at 2MB. It was the first widespread, dedicated flash memory card format. Australia's electronics magazine Apple released home and office computers using IBM’s 32-bit PowerPC processors, marking a shift away from the Motorola processors they previously used. IBM released the Simon Personal Computer (SPC), the first ‘smartphone’, although that term didn’t exist at the time. It had an LCD touchscreen and could be used to make or receive phone calls, send and receive faxes, emails and pages (‘instant messages’). 50,000 were sold for US$1099 (about $3500 today). 1995 Windows 95, DAB radio Windows 95 was released, with a GUI reminiscent of modern Windows versions. DAB digital radio broadcasting began in Europe. DVD player, PalmPilot “smartphone” 1996 The first digital video disc (DVD) player was released in Japan. The ATSC digital television standard was released. The PalmPilot was released, an early predecessor to the modern smartphone. MPMan F10 portable MP3 player 1997 The DVB-T digital television standard was released, with the first broadcast in Sweden. The first portable MP3 player was released, the MPMan F10 by Saehan Information Systems. 1998 ADSL standard ADSL (Asymmetric digital subscriber line) technical standard ANSI T1.413 Issue 2 was released. ADSL enabled high-speed data over standard copper telephone lines. It was introduced in Australia in 2000. 1999 Bluetooth devices The first Bluetooth device was introduced to the market. SD memory cards, Windows 2000 2000 The first SD (Secure Digital) memory cards were released with 32MB and 64MB capacities. Windows 2000 was released, merging the core of Windows NT with the graphical interface of Windows 95. It was the basis of the modern Windows operating system in 2023. 3G networks, Mac OS X, iPod 2001 3G telephone networks were introduced, offering high-speed mobile data, up to 7.2Mbps. Apple released Mac OS X, a cleansheet redesign of their graphical operating system based on FreeBSD, still their primary operating system today. Apple released the iPod MP3 player. siliconchip.com.au ISDB-T digital TV broadcasts 2003 Japan started digital TV broadcasts using the ISDB-T standard. LongPen remote signing device 2004 Margaret Atwood (1939~) invented the LongPen, a remote signing device, mainly for authors to sign copies of books. It was released to the market in 2006. It is reminiscent of Elisha Gray’s telautograph from 1888. DMB standard 2005 South Korea adopted DMB (Digital Multimedia Broadcasting), for mobile video streaming, a development of the DAB radio broadcasting standard. DTMB standard, OPAL reactor 2006 The DTMB (Digital Terrestrial Multimedia Broadcast) TV standard was adopted in China. OPAL (the Open-pool Australian lightwater reactor) was commissioned to replace HIFAR for research and radioisotope production (eg, for medical procedures and industrial applications). Apple iPhone 2007 Apple introduced the iPhone, the first truly modern smartphone (the Blackberry was released in 2000, but phones with inbuilt keyboards eventually fell out of favour). Further reading ● “Phonogram Images on Paper, 1250-1950” at https://youtu.be/TESkh3hX5oM ● “Experiments and Observations on Electricity” made at Philadelphia in America by Benjamin Franklin, 1751 – siliconchip.au/link/abpf ● Simple construction project video: “Voltaic Pile, the First Battery” at https://youtu. be/pW4UUOgJX6k ● “Electric Incandescent Lighting” by Edwin James Houston and Arthur Edwin Kennelly, 1896 – siliconchip.au/link/abpe ● “The Progress of Invention in the Nineteenth Century” by Edward W. Byrn, 1900 – siliconchip.au/link/abpc ● “A History of Wireless Telegraphy” by J.J. Fahie, Third Edition, 1902 – siliconchip. au/link/abpd ● “How does a spark gap transmitter sound?” at https://youtu.be/VMdYte66D2Y ● The First Digital Voltmeters and the Birth of Test Automation – www.hp9825.com/ html/dvms.html ● The oldest surviving video recording: “The Edsel Show - CBS-TV (October 13, 1957)” at https://youtu.be/Ze0Az9tdkHg ● “Oldest surviving color videotape recording: WRC-TV dedication May 22, 1958” – https://youtu.be/4vBEMGTdDYc DAB+ broadcasting began, starting in Australia, using less bandwidth for similar audio quality to DAB. 4G networks 2009 4G (LTE) telephone networks were introduced. Apple iPad 2010 Apple released the iPad, an early touchscreen tablet computer. 2019 5G networks 5G telephone networks were introduced. Apple Silicon (ARM CPU) 2020 Apple brought to market computers using its own Apple Silicon processors, the M1 series, using memory package stacking for high performance SC with low power consumption. 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 December 2023  23 Review by Jim Rowe Arduino UNO R4 Minima A leap forward for Arduino The R4 is the latest version of the ubiquitous Arduino Uno. It is a major upgrade as it has a 32-bit microcontroller, part of the Renesas RA4M1 series, with 256kB of flash, 32kB of SRAM and 8kB of EEPROM; significantly more than previous versions. Other features include a DAC with 12-bit precision, an ADC with 14-bit precision, a USB 2.0 full-speed module and a real-time clock. T he Arduino Uno R4 Minima resembles earlier versions, such as the Uno R3. The PCB is identical in size (68 × 53mm) and shape, and the SIL header sockets along the sides are compatible with those of the R3 and earlier versions. However, if you look a bit closer, significant differences become apparent. For a start, the USB connector at the top is now a USB-C socket rather than the Type-B socket used in earlier versions. There are also fewer components visible; for example, only two ICs instead of four, and no power transistor or large electrolytic capacitors. The Uno R4 Minima is undoubtedly a big step up from its predecessors like the Uno R3 and the Nano. The main reason for the improvements is that the R4 Minima no longer uses an Atmel ATmega328P 8-bit microcontroller, but is now based on a much faster and more powerful microcontroller: the Renesas R7FA4M1AB#CFM#AA0. This is part of Renesas’ RA4M1 series, a 32-bit micro with a 48MHz ARM Cortex core. As shown in the block diagram, Fig.1, the R7FA4M1 also has much more internal memory than the ATmega328: 256kB of flash vs 32kB, 32kB of RAM vs just 2kB, and 8kB of EEPROM for data storage compared with just 1kB. So it has eight times the flash, 16 times the RAM and eight times the EEPROM. But that’s just for starters. The R7FA4M1 also includes a floating-­point 24 Silicon Chip unit (FPU) for faster mathematical calculations, a USB 2.0 full-speed module, a 14-bit ADC (analog-to-­ digital converter) compared to 10-bit in the ATmega328 and a 12-bit DAC (digital-­ to-analog converter), which the ATmega328 lacked entirely. It also has an RTC (real-time clock) module, a CAN communications module, and the familiar UART, I2C and SPI serial interfaces. The CAN port does need an external transceiver, though. With a clock rate three times that of the older ATmega328, we expect it to be more than three times faster since its word size is four times larger (32 bits vs 8 bits). The floating point unit should make the gulf in performance even larger when working with decimal floating point numbers. There are also four on-chip op amps (another feature the ATmega328P lacked) and a temperature sensor, plus a choice of six different on-chip clock oscillators: a main clock oscillator, a sub-clock oscillator and high, middle and low-speed clock oscillators, plus a 15kHz on-chip oscillator dedicated to the independent watchdog timer (IWDT). There’s a clock trim function for the high, medium and low-speed oscillators. The R7FA4M1 has two hardware SPI (serial peripheral interface) serial units, two I2C interfaces and four SCI (serial communications) interfaces. Also, the R4 Minima can easily simulate a mouse, keyboard or other HID Australia's electronics magazine (human interface device) when connected to a computer via a USB cable. The new 12-bit DAC gives the R4 Minima the ability to produce analog signals and waveforms without using PWM (pulse-width modulation). That means that the R4 Minima can generate cleaner audio signals and waveforms. It also means that the R4’s six PWM outputs can be used for other things like driving LEDs and Mosfets. Another feature of the R7FA4M1 MCU is its serial wire debugging support. It has a very small 5×2-pin DIL header near the 3×2-pin in-circuit serial programming (ICSP) header, labelled “SWD”. Serial Wire Debug is a modified version of the JTAG protocol, designed specifically for ARM processors. It means that, with the right hardware and software, you can monitor and even pause the operation of the processor core without using or affecting any of its I/O pins. As you can see, the R7FA4M1 microcontroller is very powerful indeed. All those feature are packed inside an unassuming 64-pin LQFP package measuring only 12 × 12mm, including the leads on all four sides. For more information you can view the Uno R4 Minima data sheet at: siliconchip.au/link/abq0 Other features But wait, there’s more! (No, you don’t get a free set of steak knives…) Like the earlier versions, the R4 siliconchip.com.au Minima can be powered with 5V via the USB socket, or it can be powered via either the concentric barrel connector or the VIN pin. In the latter cases, it can handle a DC voltage between 6V and 24V. That wide range is thanks to the Renesas ISL854102FRZ-T buck converter chip (the second IC on the module PCB, up near the concentric power connector), which retains good efficiency even at higher input voltages. As a result, the R4 Minima can be powered from almost any external DC power source of no more than 24V. Schottky diodes are also provided for reverse polarity and overvoltage protection. Another nice feature of the R4 Minima is that it has a five-in-one ESD protection diode between the pins of the USB socket, to protect the micro and the rest of the module from electrostatic damage. The device used is a Nexperia PRTR5V0U2X, which includes two pairs of ultra-low-capacitance diodes between the USB D- (DM) and USB D+ (DP) signal lines and the USB+5V and ground lines. There is an additional ESD protection diode between the two power lines to ensure signal line protection, even if no supply voltage is present. So the Arduino Uno R4 Minima is a really impressive step up from the R3 and earlier Unos. It has a faster and more powerful MCU with much more memory and many additional features like an inbuilt USB 2.0 interface, a realtime clock and a 12-bit DAC capable of providing smooth audio signals, plus the ability to run from a wide range of power sources. Fig.1: the block diagram for the Renesas R7FA4M1AB#CFM#AA0 32-bit ARM Cortex microcontroller. One of the biggest improvements over the old ATmega328P is the extra storage space (256kB vs 32kB of flash etc). How about compatibility? As you can see from the pinout diagram in Fig.2, the R4 Minima is basically hardware-compatible with the earlier versions of the Arduino Uno. So, it should be capable of interacting with most shields designed to work with the earlier versions, especially if they have the same operating voltage. However, in their product reference manual, Arduino states that they cannot guarantee that all sketches and libraries intended for use with earlier versions will be fully software compatible with the R4 Minima because of the significantly different microcontroller used. They advise that all sketches developed to run on the Uno R3 siliconchip.com.au Fig.2: the pinout diagram for the Arduino Uno R4 Minima. The board layout is designed so that it is hardware-compatible with the earlier versions of the Arduino Uno and its shields. Australia's electronics magazine December 2023  25 should run on the R4 Minima, provided that they were developed using the Arduino API. Still, changes will be needed if your sketch uses instructions only suitable for the AVR architecture. Similarly, they advise that not all libraries written to suit the Uno R3 would be compatible with the R4 Minima. Apparently, some libraries have already been ‘ported over’ as part of their early adopters program. Arduino has already produced eleven tutorials demonstrating the various special features of the R4 Minima, plus a guide to popular shields and their compatibility with it. These are all available on the Arduino website, at siliconchip.au/link/abq1 The titles are: 1 2 3 4 5 6 7 8 9 10 11 Getting Started with Arduino Uno R4 Minima Arduino Uno R4 Minima Real Time Clock Arduino Uno R4 Minima ADC Resolution Arduino Uno R4 Minima Digital-toAnalog Converter (DAC) Arduino Uno R4 Minima EEPROM Arduino Uno R4 Minima USB HID Arduino Uno R4 Minima CAN Bus Arduino Uno R4 Minima Shield Compatibility Arduino Uno R4 Minima Cheat Sheet Arduino Uno R4 Shield Guide Debugging the Arduino Uno R4 Minima One was that the analog output of the DAC appears on pin A0 of the Minima; another was that in the Arduino programming language, the simplest way of programming the DAC is by using the instruction analogWrite(A0, value); where ‘value’ can be any integer value between 0 and 255. Why only values between 0 and 255? That’s because, although the DAC does have a resolution of 12 bits, the Arduino firmware gives it a default resolution of 8 bits. If you want to increase it to the full 12 bits, this can be done in the Setup() section of your sketch by using this instruction: analogWriteResolution(12); This allows you to feed the DAC with values between 0 and 4095, rather than the previous 0 to 255. Armed with this basic information, I worked through the examples in the Arduino tutorial on the Uno R4 Minima’s DAC. There were three example sketches (see github.com/ arduino/ArduinoCore-renesas/ blob/main/libraries/AnalogWave/ examples/), all using a library called analogWave. The first sketch generates a nominal sine waveform, the second plays “Frere Jacques”, while the third generates any of the 88 notes on a piano keyboard. All three allow output frequency adjustment by varying the voltage fed to the A5 analog input pin using a potentiometer connected between +5V and ground. The analog output from A0 can be either fed directly to a small piezo sounder or the input of a small amplifier driving a speaker; I used a tiny low-cost amplifier module based on an LM386. Scope 1: the output of the sketch “DACEqual­ TemperedScale” which generates a 3.788kHz sinewave. Trying it out I ordered an Arduino Uno R4 Minima from a supplier on eBay. It cost me US$20, roughly $31 at the current exchange rate. It arrived about 10 days later. First, I tested its compatibility with some sketches I had written for the Uno R3 and found that they ran just fine. The only thing I had to change was to install the latest version (2.2.1; siliconchip.au/link/abq2) of the Arduino IDE, because the version I had been using (1.8.19) had trouble uploading sketches to the Uno R4 Minima. I think that was because the USB interface of the R4 Minima is built into the R7FA4M1 MCU itself, rather than in a separate chip as in the R3 and earlier versions of the Uno. I then decided to try one of the R4 Minima’s interesting new features: the DAC. I learned a few basic facts by reading the information on this in the Renesas RA4M1 data sheet (pages 1149-1156; siliconchip.au/link/abq4) and the brief information in the Arduino ‘Cheat Sheet’ on the R4 Minima (siliconchip.au/link/abq3). 26 Silicon Chip Scope 2: the output of the sketch “Using_ the_R4_DAC_to_ gen_a_sawtooth. ino” which generates a sawtooth wave with 63 rising steps followed by a singlestep fall. Scope 3: the output of the sketch “Using_ the_R4_DAC_to_ gen_a_sinewave.ino” which generates a smoother sinewave than the one shown in Scope 1. Australia's electronics magazine siliconchip.com.au All three sketches use a previously calculated set of samples to produce a sine waveform, called wave.sine(freq). Although the sketches all worked, they did generate rather rough and noisy waveforms, with a significant amount of accompanying noise and harmonic content. Scope 1 shows the output from the first sketch generating a 3.788kHz sinewave. When I looked around on the Uno R4 Minima section of the Arduino Forum, I found others expressing reservations about the performance of sketches using the analogWave library. There were also a few suggestions on how to get the R4 DAC to produce smoother and cleaner waveforms, from contributors like “Grumpy Mike” and “susan-parker”. Ms Parker (who also calls herself ‘TriodeGirl’) seems to be a very experienced programmer who has produced her own sketch, using direct register setup and interrupts. She explained that one of the reasons why the analogWave library produces noisy or ‘hairy’ waveforms is because it performs DAC initialisation each time it is called. I also found a sketch from a contributor calling themselves “daueb” that didn’t make use of the analogWave library at all but instead used the basic instruction analogWrite(A0, value). After looking at daueb’s sketch, I decided to write a small sketch of my own to test the R4 Minima’s DAC. The sketch is called “sketch_for_ testing_the_R4_DAC.ino”, and all it does is prompt you to feed in a value between 0 and 255 via the Arduino IDE’s Serial Monitor, after which it feeds this value to the DAC so you can measure the output voltage from the A0 pin using a DMM. The sketch uses the default DAC resolution of eight bits but also has provision for changing to 12 bits if you want. Fig.3 shows what I found when I used this sketch to plot the output of the R4 Minima’s DAC over the full range of input values from 0 to 255. It is basically a straight line from 0.0034V to 4.7468V. Encouraged by this result, I wrote a small sketch to generate a linear sawtooth waveform, again using the analogWrite(A0, value) instruction suggested by daueb. It is called “Using_the_R4_DAC_to_gen_a_sawtooth.ino”, and like the first sketch, you can download it from siliconchip. com.au/Shop/6/306 siliconchip.com.au Fig.3: the output from the Arduino sketch “sketch_for_testing_the_R4_DAC.ino”, which plots the output for the R4’s DAC over an input range of 0 to 255. This sketch generates a sawtooth wave consisting of 63 rising steps followed by a single-step fall; the result is shown in Scope 2. You can vary the number of upward steps simply by changing the step size in the ‘for’ instruction inside the sketch’s loop(): for (x = 0; x < 255; x += 4) A smaller value in the place of 4 will give a smoother sawtooth (at a lower frequency), while a larger value will give a ‘staircase’ sawtooth at a higher frequency. Next, I came up with a similar small sketch to generate a sine waveform, called “Using_the_R4_DAC_to_gen_a_ sinewave.ino”. Scope 3 shows the waveform that this sketch can produce – it’s much smoother than the waveform in Scope 1, but much lower in frequency. As before, you can change the waveform’s smoothness and frequency simply by changing the step size in the ‘for’ instruction inside the sketch’s loop: for (deg = -180; deg < 180; deg += 5) If you increase the step size from 5 degrees to, say, 10 degrees, you’ll get a more stepped sinewave at a Australia's electronics magazine higher frequency. If you decrease it to, say, 1 degree, you’ll get an even smoother sinewave but much lower in frequency. So there you have a demonstration of the basic trade-off when you are trying to generate waveforms using a DAC: decreasing the step value gives greater waveform smoothness but also lowers the frequency. These simple sketches are only suitable for generating smooth waveforms at low frequencies. Unfortunately, those using the analogWave library are not much better. As far as I can see, the only way to get smoother waveforms at higher frequencies from the Arduino R4 Minima’s DAC would be to use Ms Parker’s approach, using direct register setup and interrupts. You can find her sketch on GitHub: github.com/TriodeGirl/ Arduino-Uno-R4-code-DAC-ADCints-Fast_Pins/ Summary The DAC is only one of the features of the R4 Minima that makes it so attractive. There’s the much larger flash memory, RAM and data EEPROM; the faster CPU with an inbuilt floating-point unit (FPU); the December 2023  27 inbuilt real-time clock (RTC); the inbuilt capacitive touch sensing unit; the inbuilt USB 2.0 full-speed comms module; an ADC with 14-bit resolution; and the inbuilt op amps and CAN port. We’ve only just scratched the surface of the Uno R4 Minima in this article. If you’d like to delve further, we suggest you get one and explore all its capabilities yourself. It really is a big step forward in the Arduinosphere! Where you can get it You can buy the Arduino Uno R4 Minima directly from the main Arduino website, but it’s also available from several suppliers on eBay. In most cases the cost will be around US$20, possibly with shipping costs added. WiFi version One last thing: the Uno R4 Minima isn’t the only new addition to the Arduino Uno family. It also has a sibling, the Uno R4 WiFi. That one has all the new features of the R4 Minima plus more: the addition of an Espressif ESP32-S3 to provide WiFi and Bluetooth comms, plus an onboard 12×8 LED matrix and a While we’ve reviewed the Uno R4 Minima (shown enlarged), there’s also a WiFi version of the board, see: https://store.arduino.cc/products/uno-r4-wifi SparkFun Qwiic I2C+power connector that can be used to plug in their add-on boards. As you’d expect, the Uno R4 WiFi costs more than the R4 Minima, at US$27.50. Still, those extra features are pretty tempting for an increase in cost of less than 50%, especially if you want wireless communications SC and networking. Silicon Chip as 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. ¯ 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). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 28 Silicon Chip Australia's electronics magazine siliconchip.com.au The Big Build It Yourself Electronics Centres® D 2321 Gift Idea! 54 $ .95 Festive Wrap up! Finish up 2023 with sleigh loads of tech gift ideas for the whole family. Prices end December 31st. Stay charged. Stay on time! A stylish bedside or desktop alarm clock with in-built 15W wireless charging for your phone & FM radio. Display also shows calendar and temperature. A USB type A output is provided for recharging a secondary device such as your watch. Great picture quality! 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USB C recharging with 60 mins operation. 42 accessories included. Vehicle & Trailer Tyre Pressure Monitor System SAVE $54 225 $ X 7063 With outdoor sensors & smartphone app! FIRE THE WEATHER MAN! 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 temperature, humidity, air pressure, rainfall, wind speed and direction. Plus handy weather trends. You can even connect it to wi-fi for monitoring readings & data with your phone. 100m sensor range. This solar powered TPMS unit sits on your dash and provides wireless monitoring of your tyre pressures. It helps keeps you safe on the roads with your camper or caravan this summer. Provides high/low pressure alarms, leak detection and temperature monitoring. Optional signal booster Q 1302 $95. NEW! 175 $ Q 1300 Shop online 24/7 <at> altronics.com.au Give the gift of FUN! NEW! Hover balls are back! 259 $ We dare you to find more fun for under $20 this Xmas Hugely popular when we first sold these in 2019, they scoot across hard floors for your very own family world cup! Requires 4xAA batteries. Ages 4+ K 8673 19 $ .95 X 3090 BARGAIN STOCKING STUFFER! or 2 for $30 Robot Master Premium 200 in 1 Set Build up to 200 different projects or create your own! Great for inspiring kids to invent and design with staged learning from the basics up to advanced Scratch programming. Each set contains hundreds of blocks, plus multifunction sensors, programmable motor and host controller. Compatible with big brand name blocks. RC Drifting Motorcycle Ride like a MotoGP pro with this USB rechargeable bike, only requires 2xAA batteries for the controller (not included). Blasts around smooth surfaces for hours of fun. Ages 3+. 49 $ X 3062 NEW! 45 $ NEW! X 3063 K 8671 99 $ Smart Robot STEM Building Set 19.95 $ Learn to fly with the RC mini glider! 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Hours of fun for kids aged 8+ (or younger with adult help). Tribo 3 in 1 Coding Robot An easy to build and program robot which uses keypad entry commands to program movements and actions. No PC required! Uses 4xAAA batteries. Ages 8+. Makerzoid® Superbot STEM Building Set A 400pc set allowing kids to build up to 26 different projects, and create designs of their own. Includes control unit and intelligent sensors (2) that allow building of line tracking, obstacle avoiding and following robot designs. Blocks are compatible with other major brands. Fully programmable using Scratch. Includes storage box. Your one-stop electronics shop since 1976. | Order online at altronics.com.au Top deals in POWER. Save time in the car with this handy motorised windscreen (or air vent) phone mount. It automatically secures your phone in the mount and starts charging! Works with Qi wireless charging equipped phones. P 8164 15W Wireless Charger Phone Holder Fast Charge 59.95 $ 8 Way Surge Board & USB Charger Provides connection for all your appliances with surge protection and 4 way USB charger (max total 3.1A output. 2.1 single port). D 2208A SAVE 23% 44 Power up your work space. $ 49.95 Perfect for the work bench - two top mount GPO’s for your appliances, USB charger (20W PD+2x USB A) and 10W QI wireless charger for your phone. $ P 8159 STOCK RUN OUT DEAL! M 8990A HALF PRICE! D 2327* SAVE $25 22 $ Dual Wireless Charging Pad Charge two phones at once with cable free wireless charging. Requires QC3.0 USB wall charger (such as M8863A $29.95). N 0700A Protect your car battery. 80 $ SAVE 24% 30 $ This compact 5W solar panel is designed for keeping your vehicle batteries topped up when parked. Replacement 90W Laptop Supply This unit includes mains lead and 10 tips to suit popular laptop models. 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IP54 Rated with stainless hardware NEW! 39 $ .95 29.95 $ Genlamp LED Solar Sensor Lights ® Add instant security to your place with these weather resistant solar lights! Shed some light on pathways, driveways, gardens and patios. These super bright PIR activated lamps require no wiring. 3 dusk activated lighting modes. 29.95 $ Camping, Fishing, Anything Light! X 0226 Compact yet powerful! Standard torch PLUS 5W LED flood light in one convenient folding design. Multiple light modes. In-built magnets for attaching to under car bonnets, campers etc while you work. Size: 102 x 65 x 32mm. NEW! Featuring 10W dual 2” full range drivers and bottom mount bass driver, this speaker is a great way to take your music anywhere. Can be easily recharged from a USB type C charging cable (included). Includes a variety of LED lighting colour modes, including beat triggering. Can pair to a second unit using True Wireless Stereo (TWS). Size: 195L x 87Ømm D 2045 59.95 $ Magnetic Car Phone Holder T 2266 2 for 19 $ SAVE 27% 10 .95 $ X 0219 Handy Luggage Scales Mini USB Lamp Don’t get caught over the limit at the airport! Measures up to 50kg. Plug it into any USB port for an instant 1W light. Natural white. Build It Yourself Electronics Centres® Sale Ends December 31st 2023 Find a local reseller at: altronics.com.au/storelocations/dealers/ 65 2 for $ RGB Bluetooth TWS Speaker X 2387 7W 800 Lumen X 2386 4W 500 Lumen 189 $ A 3615 X 0208 10 $ 3W UV LED Torch Ideal for detecting counterfeit notes, finding dust & household spills. Requires 3 x AAA bartteries. Simply clips onto your car air vent and provides super strong magnetic hold of your phone (includes 4 metal stick on discs for your phone). 11.95 $ D 2202 Mail Orders: mailorder<at>altronics.com.au Victoria Western Australia » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 » Auburn: 15 Short St 02 8748 5388 » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 New South Wales Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 » Prospect: 316 Main Nth Rd 08 8164 3466 South Australia © Altronics 2023. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0012 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. ONLINESHOP SILICON CHIP .com.au/shop PCBs, CASE PIECES AND PANELS V6295 VIBRATOR REPLACEMENT PCB SET PI PICO-BASED THERMAL CAMERA MOSFET VIBRATOR REPLACEMENT CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 JUN23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 18105231/2 04105231 18106231 01108231 01108232 04106181 04106182 15110231 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 Subscribers get a 10% discount on all orders for parts $5.00 $5.00 $2.50 $2.50 $2.50 $5.00 $7.50 $12.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) PICO AUDIO ANALYSER (BLACK) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) NOV23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 04108231/2 04107231 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 $10.00 $5.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 PRE-PROGRAMMED MICROS As a service to readers, Silicon Chip Online Shop stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. $10 MICROS $15 MICROS ATmega328P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F617-I/P Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Auto Train Controller (Oct22), GPS Disciplined Oscillator (May23) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) 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) PIC16LF15323-I/SL Secure Remote Switch (TX, Dec23) W27C020 Noughts & Crosses Computer (Jan23) PIC16F18877-I/P PIC16F18877-I/PT PIC16F88-I/P PIC24FJ256GA702-I/SS PIC32MX170F256D-501P/T PIC32MX170F256B-50I/SP PIC32MX170F256B-I/SO PIC32MX270F256B-50I/SP USB Cable Tester (Nov21) Wideband Fuel Mixture Display (WFMD; Apr23) Battery Charge Controller (Jun22), Railway Semaphore (Apr22) Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $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 DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS & SPECIALISED COMPONENTS COIN CELL EMULATOR KIT (CAT SC6823) (DEC 23) MULTI-CHANNEL VOLUME CONTROL (DEC 23) Contains all parts and the optional 5-pin header (see page 77, Dec23) - Control Module kit: see page 68, December 2023 (SC6793) - Volume Module kit: see page 69, December 2023 (SC6794) - OLED Module kit: see page 69, December 2023 (SC6795) SECURE REMOTE SWITCH (DEC 23) - Receiver short-form kit: see page 43, December 2023 (SC6835) - Discrete transmitter complete kit: see page 43, December 2023 (SC6836) - Module transmitter short-form kit: see page 43, December 2023 (SC6837) IDEAL DIODE BRIDGE RECTIFIER - 28mm square spade: see page 35, December 2023 (SC6850) - 21mm square pin: see page 35, December 2023 (SC6851) - 5mm pitch SIL: see page 35, December 2023 (SC6852) - Mini SOT-23: see page 35, December 2023 (SC683) - D2PAK SMD: see page 35, December 2023 (SC6854) - TO-220 through-hole: see page 35, December 2023 (SC6855) MODEM / ROUTER WATCHDOG (CAT SC6827) (DEC 23) (NOV 23) PICO AUDIO ANALYSER SHORT-FORM KIT (CAT SC6772) (NOV 23) $50.00 $55.00 $25.00 K-TYPE THERMOMETER / THERMOSTAT (CAT SC6809) (NOV 23) $35.00 $20.00 $15.00 PIC PROGRAMMING ADAPTOR KIT (CAT SC6774) (SEP 23) ARDUINO ESR METER (AUG 23) $30.00 $30.00 $30.00 $30.00 $25.00 $35.00 $45.00 Short-form kit: includes all non-optional parts, plus a 12V relay and unprogrammed Pi Pico. Does not include a case (see page 71, Nov23) $35.00 Includes most parts, unprogrammed Pi Pico and OLED screen. The case, battery, chassis connectors and wires are not included (see page 41, Nov23) $50.00 Short-form kit: includes most of the parts needed except the case, LCD, thermocouple probe, cable gland and switches S4 & S5. A 10A relay is included to suit the 12V supply (see page 58, Nov23) $75.00 Includes all parts, except the optional USB supply (see page 71, Sept23) - 20x4 blue backlit LCD with I2C interface (Cat SC4203) - red & black PCB-mount banana sockets (two sets are needed; Cat SC4983) - two 1nF ±1% capacitors (Cat SC4273) VARIOUS MODULES & PARTS - 0.96in SSD1306 cyan OLED (Multi-Channel Volume Control, Dec23; SC6176) - 1.3in blue OLED (Coin Cell Emulator, Dec23; SC5026) - 5V 3-pin boost regulator module (2m CW/FM Test Generator, Oct23; SC6780) - 5V 3-pin buck regulator module (2m CW/FM Test Generator, Oct23; SC6781) - 0.96in SSD1306-based yellow/blue OLED (RF Signal Gen, Jun23; SC6421) $55.00 $15.00 $6.00/set $2.50 $10.00 $15.00 $3.00 $4.00 $10.00 $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 and included GST where applicable. To Place Your Order: INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00, Mon-Fri) siliconchip.com.au/Shop Use your PayPal account silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au Your order to PO Box 194 Matraville NSW 2036 Call (02) 9939 3295 with with order & credit card details You can also order and pay by cheque/money order (Orders by mail only). Make cheques payable to Silicon Chip Publications. 12/23 Ideal Diode Bridge Rectifiers By Phil Prosser Rectifiers have evolved a lot over the last century, from selenium piles and mercury arc rectifiers to vacuum tube diodes, then germanium and silicon diodes. Now, active rectifiers offer much greater efficiency than silicon diodes, running much cooler. We show you how to make up to six different Bridge Rectifiers depending on how much power you want. n the simplest terms, an ‘ideal diode’ Icircuit uses a power Mosfet with a control to replace a rectifier diode. Combining four such devices gives you an ‘ideal bridge rectifier’. While they are not truly ideal, they are much closer than a regular diode, with a forward voltage (and thus power loss and heat dissipation) typically around 1/10 that of a normal diode. This idea caught my attention because I realised it would allow us to build devices like power amplifiers or power supplies that operate more efficiently and deliver more power, as less is lost in the bridge. Bridge rectifiers used in large power amplifiers need a lot of heatsinking! They can dissipate tens of watts under heavy load. That all changes with this design, which is a drop-in replacement for many existing bridge rectifiers. When designing my Dual Hybrid Power Supply, (February & March 2022; siliconchip.au/Series/377), I wished I had the time to delve into these active bridges, as the power loss in a high-current DC power supply bridge is also significant. For example: ● The PB1004 10A bridge rectifier (Altronics Cat Z0085) has a forward voltage drop of over 1V at 5A, or 2V across the bridge. This means it is dissipating 10W at 5A. ● The KBPC3510 35A bridge rectifier (Altronics Cat Z0091A) drops 1V at 10A, resulting in a 2V loss and 20W dissipation at 10A. The 2V drop is manageable, if annoying, by increasing the transformer voltage. However, transformers often come in 5V steps, meaning you might be wasting a lot of power to compensate for that relatively small voltage loss. On the other hand, that 10-20W dissipation is troublesome, as it demands a substantial heatsink and forces Lessons learned during the design process The design of these modules served as a reminder on the need for attention to detail and the value of peer review. I did the bulk of the PCB layout while I was on holidays, and since there were only seven parts, what could go wrong? Plenty. When I was making the CAD library for the LT4320 IC, I stuck the ‘pin’ that denotes the thermal pad for the IC in the wrong spot. This led me to assume it connected to the positive pin rather than the negative, where it belonged. I then laid out seven variants of this board from the schematic, all with the pad connected to the wrong output. I now know that the LT4320 will work for several minutes with the thermal pad tied to the wrong pin, but after that, it will blow up, take out your Mosfets and short your transformer! I found the bug after blowing many fuses, $100 worth of bits, wasting a couple of days, and my whole budget of four-letter words. To add insult to injury, I had to respin all the different prototype boards, another $100 lesson. Ouch! All for about 2mm of misplaced PCB trace. 34 Silicon Chip Australia's electronics magazine physical layout decisions to enable this heat to be dissipated. Pros and cons By comparison, if we use an LT4320 ‘ideal bridge’ controller and TK6R9P08QM power Mosfets, we will see 70mV maximum drop per device at 10A, which is a total of 1.4W or about 1/10th of the heat you get from a standard bridge rectifier! So what is the catch, and why aren’t these used everywhere? I suspect there are a few reasons: 1. One of the complications that needs to be dealt with is generating the Vgs drive for the N-channel Mosfet, which requires a boost circuit to drive the gates well above the source voltages. 2. For a bridge, you need four power Mosfets and a controller, which increases parts count and cost. 3. The real benefits are accrued when rectifying lower voltages at high currents or if you cannot afford losses in your system (or when high efficiency is essential). 4. Because of how the control and switching works, for the simplest off the shelf solution, a dual-rail power supply (such as for a power amplifier) needs two bridges, each fed by one of the two secondary windings. 5. Your rectified output voltage rail needs to stay above 9V, or bad things happen (more on that later). The best use cases for an ideal diode bridge rectifier are where space and capacity to dissipate power are limited, where voltage drop from the transformer is undesirable and where siliconchip.com.au One of our Ideal Bridge Rectifiers on a Dual Hybrid Power Supply board. This increases the maximum output voltage by about 2V at full load while increasing efficiency and allowing it to run much cooler under load! lower voltages at higher currents need to be rectified. In terms of using Mosfets to replace diodes, it is interesting to note the growing use of ‘synchronous’ switchmode converters. In this case, the usual schottky diodes are replaced with power Mosfets. Many synchronous switch-mode controllers include an output to drive the diode replacement Mosfets, resulting in increased efficiency. Design approach Given the desire to investigate this technology, our efforts turned to an integrated solution. We wanted an option that could be used in a range of projects and showcase the potential of this technology, without making construction too tricky or the device too expensive. A survey of ideal diode controller ICs shows that many are intended for hot-swap and redundant power supply applications. In this case, multiple power supplies are combined in an ‘OR’ function so that if one supply fails, the other picks up the load. Supply currents can be very high in a server application, so reducing diode losses is critical. We also found several controllers for automotive applications, in alternators and circuit protection. These are generally intended for single-rail applications and are not suited to more general AC rectification. In particular, most utilise the diode to operate the circuit itself. This limits their application as generic diode replacements. siliconchip.com.au The range of available parts in this field is growing, so new ICs that are useful in a range of applications are coming on the market. In this project, we show how to use the most available controller IC and build a range of ‘ideal diode bridge rectifiers’ that can replace conventional diode bridges in various projects. The controller we have selected is the LT4320, as this allows simple and compact boards to be built, ranging from tiny SOT-23 Mosfet based bridges through DPAK (TO-252) to very high current TO-220 based through-hole versions. Where might each of these be used? ● The SOT-23-based bridge is only 9 × 15mm and can be used inline on the DC power supply lead to a device or soldered in place of a small bridge. This can make the power lead for your device polarity agnostic without affecting its operation noticeably. ● Our boards using DPAK SMD Mosfets can replace the common 5mm pitch 19mm SIL bridge or rectangular bridges with corner pins or spade connectors (see the photo above) and handle high currents. ● There are also two ‘standalone’ versions that are basically just small boards you can mount in a chassis to provide the rectification function. One uses TO-220 Mosfets and other through-hole parts and can handle very high currents, limited mainly by the PCB itself! There are a few limitations or requirements we need to work with that initially may sound onerous. However, in a real-world application, Australia's electronics magazine the following are not that hard to meet: ● The LT4320 works in a ‘single-­ rail’ configuration only. ● For an audio amplifier, you need to rectify the outputs of the two secondary windings independently. You then connect the negative output from one bridge to the positive output from the second bridge to get your split supply, usually at the main capacitor bank. ● We have achieved pin compatibility for all the larger bridge types. But DIP-8 and W02/W04 type bridges are a bit small for us to match, so if replacing one of those, you will need to mount the SOT-23 version on leads. ● The minimum output voltage allowed is 9V DC, while the maximum is 72V peak. This means that we should limit the AC input to 40V RMS to provide reasonable safety margins. We must ensure that the rectified output’s minimum voltage does not drop below 9V during operation. How it works Its operation is similar to a diode bridge but with a controller IC that turns the Mosfets on when required to minimise losses. Fig.1 is the circuit diagram while Fig.2 shows how current flows during the two main phases when the bridge is conducting. The Mosfets are arranged so the current flows from their source to drain terminals in regular operation, the opposite to a standard common-source Mosfet switch application. This is so that the current flows through the Mosfet body diodes in the forward direction. Therefore, in the absence of the controller, current would flow through those body diodes. However, there would be a high typical 1V forward drop at high currents, similar to a silicon power diode. During operation, the LT4320 determines which of the input voltages (IN1 Ideal Bridge Rectifier Kits SC6850 ($30) 28mm spade version SC6851 ($30) 21mm square PCB pin version SC6852 ($30) 5mm pitch SIL version SC6853 ($25) mini SOT-23 version SC6854 ($35) standalone D2PAK SMD version SC6855 ($45) standalone TO-220 through-hole version December 2023  35 & IN2) is lower and switches on either Q3 or Q4 full to connect the input terminal with the lower voltage to the negative rail and hence the negative output. The controller switches Mosfet Q1 or Q2 on when current flows through them, reducing the effective forward voltage to about 20mV. The drop is set by the controller; if the LT4320 detects a differential greater than 20mV between the highest AC input voltage and the output terminal, it switches the respective Mosfet on harder. If the Mosfets have a relatively high Rds(on) figure resulting in more than 20mV across the Mosfet, it will be switched on fully, and the input/ output differential will be higher than 20mV. The gate drive to the Mosfets is not very ‘strong’ in that a fairly low current is supplied. This reflects the application for this IC in low-frequency Fig.1: the circuit is slightly more complex than a conventional bridge rectifier. Pin numbers in black are for the MSOP-12 package while those in brackets in cyan are for DIP-8. Dashes in parentheses indicate pins that don’t exist on the DIP-8 package. (50/60Hz mains) or for the MT4320-1 (to 600Hz) operation. With a 9V DC output voltage and the top Mosfet (Q1 or Q2) Vgs at 2V, the pullup current is only 500μA. Our recommended DPAK SMD Mosfet, the TK6R9P08QM, has an input capacitance of 2.7nF. So the gate voltage will change at a rate of 180mV/μs. That is terribly slow compared to most Mosfet applications, but for mains-frequency operations, if each Mosfet is on for 10% of the cycle, that’s 2ms. The switch-on time of 20μs or so is only 1% of that period. The losses are minimal because this switching is just as the mains cycle crosses over. The 1μF ceramic capacitor across the OUTP and OUTN pins is important for the correct circuit operation as it prevents the output voltage from changing too rapidly. It should be kept as close to the LT4320 as possible. The Ideal Bridge Rectifier can operate from 9-72V. If the rectified output goes below 9V, the LT4320 will not drive the Mosfet gates, and rectification falls back to the body diodes in the Mosfets. This is OK at startup, but we must ensure the rectified rail remains above 9V afterwards. We will come back to this later on. During tests where we were hammering the bridge and applied a load so severe that the output voltage dropped below 9V, we found that the Mosfets were getting hotter than we expected. However, that’s a fairly unusual situation for a real bridge rectifier. Parts selection Fig.2: during part of the mains waveform, when the upper AC input voltage is higher than the lower, IC1 switches on Q1 & Q4 and current flows via the red paths. During the opposite part of the waveform, the upper AC input voltage is lower, Q2 & Q3 are on and current flows via the blue paths. There were a few things to keep in mind when choosing the Mosfets for this design. We have tested the devices specified in the parts list and in the panel titled “Ideal Bridge Recitfier PCBs”, although there is no doubt that many others would work. Besides being in the correct package for the board, they need sufficiently high voltage and current ratings, low on-resistances (for highest efficiency) and a gate-source threshold voltage in the correct range. For the latter, the recommendation is that it should be more than 2V. This is required to ensure that the controller can switch the Mosfet off quickly, to keep efficiency high. Many modern Mosfets have a low gate threshold to allow them to be controlled by lower voltage circuits (often Australia's electronics magazine siliconchip.com.au 36 Silicon Chip called ‘logic-level’ Mosfets), making them unsuitable. These can sometimes be spotted as they tend to have a lower maximum Vgs rating, below the ±20V to ±30V that used to be typical. However, there are still logic-level Mosfets with a higher Vgs rating, so you need to check the data sheet. As for the current rating, in a bridge rectifier, the current usually only flows while the reservoir capacitors are charging. With very large capacitor banks and a low internal impedance transformer, this can be pretty short, resulting in peak charging currents much greater than the average (or “DC”) current being drawn from the power supply. The recommendation is that the Mosfets have a DC rating triple the average direct current. Therefore, we have selected Mosfets with higher current ratings than you might expect are necessary. However, we tried not to go overboard with this as ultra-high-current Mosfets tend to have a high gate capacitance. The LT4320 does not have a strong gate drive capability, so that would slow switch-on and switch-off, resulting in increased losses. The Vds(MAX) rating should be well above the voltage at which you want to operate the bridge, with a solid margin to allow for ringing and spikes. We looked for a minimum rating of 80V, although our SOT-23 version is limited to 40V. Mosfet heating is primarily determined by the average current and their Rds(on). For the TK6R9P08QM DPAK Mosfet we use in many module versions, the typical Rds(on) is specified as 5.5mW for Vgs > 10V. The LT4320 delivers about 11V to the gates for voltages greater than 13V. For an average current of 10A, this results in 550mW dissipation in each conducting Mosfet, or 275mW per Mosfet for an AC input, which is easily manageable, and the boards only get warm. For a current of 20A, this dissipation increases to about 1W per Mosfet, making them very warm indeed, at which point you should consider building the TO-220 version. The recommended TO-220 Mosfet has an Rds(on) of 4.2mW at full drive and, at 40A, will drop 160mV; it would be closer to 1.2V in a regular bridge at this sort of current. The power dissipation in each Mosfet would be 3.5W for siliconchip.com.au Ideal Bridge Rectifier PCBs For maximum flexibility, we have produced six different PCBs that implement essentially the same circuit, as follows: #1 Square 28mm metal bridge using 6.3mm spade connectors Compatible with KBPC3504 PCB code: 18101241 (28 × 28mm with a central mounting hole) Current & voltage handling: 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK/TO-252 SMD) Operates at 10A continuously and much higher currents intermittently but will get hot. In a long-term 8A test, it reached 79°C in free air. #2 Square 21mm plastic bridge with 13mm pitch pins Compatible with PB1004 PCB code: 18101242 (22 × 22mm with a central mounting hole) Current & voltage handling: 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK/TO-252 SMD) A PB1004 leaded bridge replacement, typically capable of 5-10A. We used these to upgrade our Dual Hybrid Power Supply module. #3 5mm pitch SIL Compatible with KBL604 PCB code: 18101243 (23 × 20mm) Current & voltage handling: 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK/TO-252 SMD) The 5mm pitch SIL bridge rectifier drop-in replacement module. #4 Tiny inline bridge Width of W02/W04 PCB code: 18101244 (9 × 15mm) Current & voltage handling: 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 (SMD) Mosfets: SI2318DS-GE3 (SOT-23 SMD) The baby of the crew, the SOT-23 based version optimised for putting inline with lower-power circuits. These Mosfets are rated at 40V & 3.9A, but we reckon a safer limit would be 1.5-2.0A. #5 Standalone SMD version PCB code: 18101245 (59 × 36mm with mounting holes in 49 × 26mm rectangle) Current & voltage handling: 20A continuous, 72V Connectors: 5mm screw terminals at either end IC1 package: MSOP-12 (SMD) Mosfets: IPB057N06NATMA1 (D2PAK/TO-263 SMD) The D2PAK version, which I have tested for half an hour at 12V AC and 8A (into a 35mF capacitor with a 2Ω load across it). You can see this being stress tested on page 40. #6 Standalone through-hole version PCB code: 18101246 (38 × 28mm with 70μm-thick copper and mounting holes 29mm apart) Current & voltage handling: 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 (through-hole) Mosfets: TK5R3E08QM,S1X (TO-220 through-hole) The TO-220 version is a bit of a beast and, along with the D2PAK version shown above, it will easily handle 8-10A RMS continuously. It uses a DIP-8 controller IC and allows you to mount a heatsink to the Mosfets if you want to rectify some serious currents. All the images here are not shown to scale. Australia's electronics magazine December 2023  37 Fig.3: the cyan trace is the positive portion of the incoming AC waveform, yellow is the filtered DC output, while mauve is the positive Mosfet gate drive. The cyan AC trace is offset by -2V; otherwise, the mauve trace would obscure it much of the time. Fig.4: a similar setup to Fig.2, but this time, we’re monitoring the gate of one of the low-side Mosfets (mauve). You can see how it’s switched on with a duty cycle close to 50%, synchronised with the zero crossings of the AC waveform. an AC input, which is significant but manageable with small heatsinks. In this case, a regular diode-based bridge would get toasty, as it would dissipate 48W per diode! The LT4320 IC comes in an SMD (MSOP-12) and through-hole (DIP8) version. These are available from all the major component suppliers and will be included in the Silicon Chip kits. For the Mosfets, we have tried to stick to standard parts, with DPAK (TO-252) being our overall preference as they are large enough to handle a decent amount of dissipation (~1W) without being so large that they take up a lot of space. The other Mosfets we’ve used come in TO-220 packages (for really high current applications) and the tiny SOT-23 (for when space is tight). By sticking to these standard footprints, you can use alternative parts if necessary. PCB design Most of the modules we present use surface-mounting parts to fit into the space we have. We have also resorted to placing components on both sides of the PCB, as doing that was essential to match some of the common bridge rectifier form factors. For higher-current modules, we need to be conscious of the current rating of the PCB traces. To fit the parts onto the KBPC3504 form-factor board, along with the very wide tracks that a 30-40A rating warrants, is quite a challenge. Our version manages to keep all high-current tracks short and thick, but that forced the layout to be slightly larger than the original rectifier. There is no specific ‘rating’ for PCB traces; there are guidelines, but too many variables exist to realistically put a simple, accurate number to a track width. Still, voltage drop and heating must be considered. In the limiting case, tracks can fuse or melt. We have specified ‘2oz’ (70μm thick) copper traces on the TO-220 PCB, twice as thick as a standard ‘1oz’ (35μm) PCB. This will halve resistive losses in the PCB at the price of it being a lot harder to solder due to the thick copper acting as a heatsink (although that will have benefits during operation, drawing heat away from components faster). It is evident that at high currents, even an ‘ideal diode’ warrants careful attention to power ratings, losses and dissipation. But these are reduced to a level where a practical solution can be developed. We recommend that you pay careful attention to losses and heat if you use this at really high currents. At least verify that the chosen module doesn’t get overly hot at your expected maximum current draw. Waveforms & verification Figs.3 & 4 show the input, output and gate drive waveforms for the Ideal Bridge Rectifier operating at 4A RMS. Note that the AC input is offset -2V to allow a clearer view – there is so little voltage drop across the Mosfet that the output visually ‘tracks’ the input AC much of the time. The gate drive is over 10V, so the Mosfet is switched fully on. To illustrate the low voltage drop across the power Mosfet even at 4A, Fig.5 shows the input and output waveforms with no offset. Figs.6-11: use these overlay diagrams to guide the component placement on each version. The four smaller PCBs have components on both sides. Generally, it’s best to fit all the SMDs on one side, then all the SMDs on the other, then any remaining through-hole parts. Note that while we’ve specified non-polarised ceramic 10μF capacitors for the first four variants, tantalums are shown in case you want to use them, in which case they must be orientated as shown. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au Having built the modules, we decided to run some extreme tests as we didn’t want our readers to make them only to have them blow up! We loaded the 28mm bridge design (KBPC3504 compatible) to draw 5A RMS from a toroidal transformer and left it running for several hours. The Ideal Rectifier stabilised at 42°C. Ramping the current to 8A led to it reaching 72°C, which is not unreasonable for the current. Swapping in a regular KBPC3504 at 4A without heatsinking, it reached 79°C after a few minutes. As shown earlier, we ‘upgraded’ our Dual Hybrid Power Supply with Ideal Rectifiers, which saves 10W of heat per board at full output or 20W in total. For this, we used the PB1004 format modules and soldered them on leads directly to the PCB, as at 5A, they do not get hot enough to demand a heatsink. During testing, we had a test setup with a 12V AC output transformer, an Ideal Bridge Rectifier and a 22mF capacitor. Things were going great until we reduced the load resistance to somewhere near 1W, and the output voltage dropped below 9V due to the capacitor discharging between cycles. The LT4320 stopped driving the Mosfets, and instead of there being 20mV across them, there was suddenly about 1V across the body diodes at about 15A. The smoke quickly escaped from the DPAK Mosfets. We recommend that you avoid that situation. Construction With so few parts on the board, construction is straightforward. Refer to the PCB overlay diagram(s) for whichever version(s) you are building, shown in Figs.6-11. The principal challenge is that for all but the TO-220 version, we’re using the LT4320 IC in an MSOP-12 package siliconchip.com.au Fig.5: the same waveforms as in Fig.2 but without the -2V offset on the AC input. The IPP083N10N Mosfets on this board stabilised at 38°C in the lab. The dummy load, on the other hand, measured 130°C. with a thermal pad on its base. This thermal pad makes this part a tad harder to solder than your average SOIC/SOP SMD part. There are two (or three) practical soldering options: 1. Using a reflow oven. If you already own one of these, chances are you are all over how to mount the part. Each oven has its own quirks, so we will leave this to you. 2. Use a toaster oven as a ‘bodge’. You can read articles on turning a toaster oven into a reflow oven (April & May 2020; siliconchip.au/Series/343), but there is also a ‘quick and dirty’ method that works. Buy a super-cheap toaster oven (we often see these for sale under $50) and stick a K-type thermocouple alongside your board. Apply solder paste to the pads and carefully place the parts on top. Preheat the PCB to 100°C in the oven, then turn the oven up to maximum. Watch closely until the temperature hits 220°C. At this point, you should have seen the solder flow. Immediately turn the oven off and open the door. 3. Use a hot air gun. That is how we built all the prototypes, to convince ourselves that it would work for you (see the photo overleaf). Even though we have a reflow oven, we often use the hot air gun as it is quick and easy Australia's electronics magazine (they’re also surprisingly inexpensive). We used this technique just for the LT4320, leaving the easier capacitors and Mosfets to be hand-soldered. The key steps are: a Apply a small amount of solder paste to each pad and the central thermal pad. Do not overdo this; a modest smear is sufficient. We use 60/40 tin/ lead solder paste as it melts at a lower temperature, making it generally easier to work with. Nothing is stopping you from using lead-free solder, but remember that it requires higher temperatures. b Place the LT4320 using tweezers. There should be sufficient solder paste to stick in place, but not so much that it squishes everywhere. c Check that the LT4320 is the right way around. Double-check, as this is by far the most expensive part in this project. d Put the board on a heat-resistant surface, such as a PCB off-cut. Do not use your desk as it will get quite hot! e Set your hot air gun to about 300°C. f Apply heat to the board in a gentle waving motion from about 15cm away, so the board around the IC is heated reasonably evenly. We want to preheat the board to something in the region of 100°C over a minute or so. g Once the board is well warmed up, bring the hot air gun to about 5-10cm from the board and work around the IC. Have your tweezers handy; if the IC moves a lot, you might need to nudge it back into position. Having said that, surface tension will typically pull it into place if you’re blowing the air directly from above. h Watch the solder paste. As the board approaches 220°C, you will see the paste changing from dull granular material to a shiny liquid. The change is significant, so you shouldn’t miss it. December 2023  39 My poor wirewound nichrome dummy load reached 320°C while the Mosfets on the D2PAK standalone module only reached 67°C. i As the solder melts, it also creates a lot of surface tension and will pull the IC into position. j Do not overheat the board. Once all the solder has reflowed, take the heat gun away. k Allow the board to cool naturally. Do not put any liquid on the board to accelerate the cooling. l You might see several pins with solder bridges across them. Fold some solder wick across the tip of your iron and ‘dab’ the pins to melt the bridge into the wick. Adding a little flux paste to the bridge first usually helps. With a little practise, this is quick and easy. We get quite a few bridges to fix as we are too generous with the solder paste! For the remaining SMD parts, a regular soldering iron works fine. We generally tack down one of the SMD leads and make sure the part is straight. For the two-pin passives, all that’s left is to solder the second lead. For the Mosfets, apply the iron to the source (main tab) at the junction of the tab and the PCB pad. Put a small amount of solder between the iron and the tab and wait until the solder flows. Once both the pad and the component lead are hot, the solder will flow freely under the component. After that, you can solder the remaining small pins. The 6.3mm spades, screw connectors or wire leads are through-hole parts, so solder them as usual. Testing Soldering the MSOP-12 LT4320 IC using a low-cost hot air ‘rework’ station. These are invaluable for all sorts of jobs; they make it especially easy to desolder SMDs. In this case, the killer feature is the ability to heat the IC enough to solder the pad underneath. 40 Silicon Chip Australia's electronics magazine Testing the Ideal Bridge Rectifier is not complex and can be undertaken at low power. First, connect a 220W 1W resistor across the output, or an alternative resistor with a power rating that can withstand the DC voltage we will apply in the following steps. Connect a multimeter across the test resistor with the meter’s positive line to the positive output of the ideal bridge rectifier. Connect a 12V DC power supply to the input of the Ideal Bridge Rectifier and verify that the output gives a +12V reading on the meter. Verify that the voltage drop is less than 100mV. Then swap the polarity of the input voltage and verify that the output is still giving a +12V reading on the meter, and the voltage drop is still less than 100mV. If this does not work: ● Check all solder connections. siliconchip.com.au ● Check the orientation of the LT4320 IC. ● If using TO-220 Mosfets, check their orientations. ● If building the through-hole board, check the orientation of the electrolytic capacitor. ● Check your test setup; is the power supply in current limiting? Check the input voltage. Using it Among the six different modules, you will likely find a ‘drop in’ solution. The SIL and 19mm pin bridges should solder straight to a PCB that’s designed for a regular bridge rectifier. For an audio amplifier, you would ideally mount two of the standalone versions in the chassis and run individual windings to each. Remember that the LT4320 operates from 9V to 72V. If your output voltage falls below this, the LT4320 will not drive the Mosfets, and the bridge will only operate using the body diodes. That is OK to get the circuit started, but at high currents, the dissipation can be very high. This is only a concern if your design uses low rail voltages, or you are likely to do something as silly as we did and drive the rectifier so hard that your capacitor discharges massively between 50Hz cycles. That won’t happen in a typical power supply or power amplifier. Conclusion The Ideal Diode Bridge Rectifier can significantly improve the efficiency of just about any circuit that requires a rectifier for only a modest increase in the device’s overall cost. Best of all, for devices like power supplies and audio amplifiers, you can get even more output voltage or power than you would with a standard diode-based rectifier. Don’t forget, though, that for applications like an audio amplifier with split rails (positive and negative), unlike a diode-based rectifier, you will need two of these devices, one for each supply rail. The transformer also needs to have two separate secondary windings. That’s because the control chip only monitors the voltage across the upper two Mosfets. With six different designs in a range of sizes, current and voltage ratings, you’re bound to find one that suits your application. SC siliconchip.com.au Parts List – Ideal Diode Bridge Rectifier Common parts for versions #1 to #4 (from Mouser, DigiKey or element14) 1 LT4320IMSE#TRPBF ideal bridge controller IC, MSOP-12 (IC1) 1 1μF 100V X7R M3216 SMD ceramic capacitor [CL31B105KCHNNNE] 1 10μF 100V X7S M3225 SMD ceramic capacitor [GRM32EC72A106KE5K] #1 28mm spade version 1 double-sided PCB coded 18101241, 28 × 28mm 4 6.3mm PCB-mounting vertical spade connectors [Altronics H2094, pack of 10] 4 TK6R9P08QM,RQ, IPD50N06S4-09 or TK5R1P08QM,RQ N-channel Mosfets, DPAK/TO-252 (Q1-Q4) #2 21mm square PCB pin version 1 double-sided PCB coded 18101242, 22 × 22mm 1 10cm length of 1.5mm diameter tinned copper wire 4 TK6R9P08QM,RQ, IPD50N06S4-09 or TK5R1P08QM,RQ N-channel Mosfets, DPAK/TO-252 (Q1-Q4) #3 5mm pitch SIL version 1 double-sided PCB coded 18101243, 23 × 20mm 1 10cm length of 1.5mm diameter tinned copper wire 4 TK6R9P08QM,RQ, IPD50N06S4-09 or TK5R1P08QM,RQ N-channel Mosfets, DPAK/TO-252 (Q1-Q4) #4 Mini SOT-23 version 1 double-sided PCB coded 18101244, 9 × 15mm 1 10cm length of 0.7-1mm diameter tinned copper wire 4 SI2318DS-GE3, SI2316BDS-T1-BE3 or SI2316BDS-T1-E3 N-channel Mosfets, SOT-23 (Q1-Q4) #5 Standalone D2PAK SMD version 1 double-sided PCB coded 18101245, 59 × 36mm 2 mini horizontal terminal blocks, 5mm or 5.08mm pitch 1 LT4320IMSE#TRPBF ideal bridge controller IC, MSOP-12 (IC1) 1 1μF 100V X7R M3216 SMD ceramic capacitor [CL31B105KCHNNNE] 1 10μF 100V radial electrolytic capacitor, 2.5mm pitch, ≤6.3mm diameter [Kemet ESL106M100AE3AA] 4 IPB083N10N3GATMA1 N-channel Mosfets, D2PAK/TO-263 (Q1-Q4) [ESL106M100AE3AA] #6 Standalone TO-220 through-hole version 1 double-sided PCB coded 18101246, 38 × 28mm, with 70μm-thick copper 4 6.3mm PCB-mounting vertical spade connectors [Altronics H2094, pack of 10] 1 LT4320IN8#PBF ideal bridge controller IC, DIP-8 (IC1) 4 TK5R3E08QM,S1X (80V) or RFB7545PbF (60V) N-channel Mosfets, TO-220 (Q1-Q4) 1 1μF 100V X7R radial ceramic capacitor, 5mm pitch [RDER72A105K2M1H03A] 1 10μF 100V radial electrolytic capacitor, 2.5mm pitch, ≤6.3mm diameter [Kemet ESL106M100AE3AA] Silicon Chip kcb a Back Issues $10.00 + post January 1995 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 1995 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com. au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer Australia's electronics magazine December 2023  41 Part 1 of John Clarke’s Secure Remote Switch This UHF remote switch uses a secure rolling code system. The receiver uses all through-hole parts, fits in a compact plastic case and can be powered from 12V or 24V DC. Up to 16 transmitters can be used per receiver; they fit into handy keyfob cases, and you can use a prebuilt transmitter module or discrete components. T his project is an update to the Secure Remote Mains Switch described in the July & August 2022 issues. It uses the same rolling code system but the receiver is smaller and simpler; it is designed with a DC power supply and low-voltage switching in mind. That makes it ideal for applications like a garage door controller. Finding new remotes compatible with many garage door controllers can be challenging. However, most controllers have terminals for the external triggering of the garage door, and many also have 12V or 24V power outputs. That means you can build the Secure Remote Switch, wire it to your garage door controller and add up to 16 more remotes! Other potential applications include gate control, remote operation of door strikes or switching DC-powered Transmitter » » » » » » » » » » » Professional keyfob enclosure Secure rolling code communication Up to 16 transmitters per receiver Powered by a 12V 55mAh A23 battery, giving more than two years of life with typical use Range: 22m line-of-sight Standby current: typically 3μA (26mAh/year) Transmitting current: 10mA average over 1s (2.77μAh per transmission) Registration current: 10mA average over 2.75s (7.6μAh per registration) Transmission rate: 976.5 bits/s (1.024ms per bit) Data encoding: Manchester code with a transmission time of 82ms Unique code generation: secure UHF rolling code control with 48-bit seed, 24-bit multiplier and 8-bit increment value Receiver » » » » 42 12V or 24V DC operation Supply current: 15mA with relay off, 45mA with relay on Relay contact rating: 10A (can handle up to 60V DC/42V AC) Relay-on timer range: 250ms to 4.5h (see Tables 1 & 4) Silicon Chip Australia's electronics magazine appliances on and off, such as water pumps, fans, LED lights etc. It is compatible with most 12V or 24V solar power systems or can run from mains power via a suitable supply. The transmitters have also been redesigned compared to the 2022 project. There are now two versions: one that uses a prebuilt 433.9MHz transmitter module and another which is slightly cheaper to build and uses all discrete parts for those who like to ‘roll their own’. Also, the transmitter fits into a nice little keyfob case that we will supply in kits for the transmitters. We’ll have kits for the discrete and module-based versions; the discrete kits are complete, while the module-based kits come with everything but the transmitter module, for compliance reasons (you can get it from Jaycar or Altronics). The new transmitters also use small A23 alkaline batteries rather than lithium coin cells; this is mainly due to the design of the cases, but it has the advantage that the quality of A23 alkaline batteries is more consistent than lithium coin cells. This also avoids the serious ingestion hazard that coin cells pose for small children. The discrete transmitter circuit is based on the Remote Control Range siliconchip.com.au The receiver switches an onboard SPDT relay when triggered, either for a fixed time or toggled with each button press. Extender (January 2022; siliconchip. au/Article/15182). However, in that design, tiny components were used (some as small as 0.6 × 0.3mm!), which made it a real challenge to assemble, even for us. This time, we have used much larger components that are easier to solder, so only modest soldering skills are required. Low-voltage switching This design can only directly switch low voltages. You have two options if you require a remote switch that controls mains voltage. The simplest is to build the Secure Mains Switch described in the July and August 2022 issues (siliconchip.com.au/ Series/383). That project is still perfectly valid, and you can use the transmitters described here with the Mains Switch receiver if you want to. Alternatively, you can use the onboard relay in this design to switch 12V or 24V DC to an external mainsrated relay. It will need to be in its own box with suitable mains connectors, wiring and insulation. We have decided also to offer a short-form kit for the receiver. You’ll need to get a handful of parts yourself, like the case and a few switches, but the kit will save you time and effort siliconchip.com.au gathering the parts to build the Secure Remote Switch. Security The Secure Remote Switch uses rolling code wireless transmission to ensure security. That makes it very difficult for someone to trigger the relay on the receiver without having one of your registered remotes. So if it is used to trigger remote-controlled doors, gates and door strikes, the security of your home or premises is maintained. While secure codes are required for security applications, they also ensure that a similar remote control does not inadvertently switch your appliance on or off. This could happen due to someone close by controlling their own equipment. We’ve experienced spurious operation of security shutters that we think must have been due to someone using a different remote nearby. That’s almost impossible with a rolling code system! Other controls will not operate the Switch because the transmitter and receiver must be paired before they will work together. Additionally, the code sent between the transmitter and receiver changes each time it is used. That thwarts anyone who might try to capture the code and subsequently Australia's electronics magazine resend it in an attempt to control the Switch. Since the captured code immediately becomes obsolete after use, the Switch will not respond if it is repeated. You can also build more than one Switch without being concerned about interference between them. The unique transmission code ensures that the Switch receiver will not be activated by anything other than one of the paired handheld remote controls. The remote control code sent by the handheld remote units can be considered an electronic lock similar to a physical key, except that the key and lock combination changes each time it is used. For the Switch, this key is a specific code the transmitter sends to the receiver. It comprises a long digital data sequence sent in a particular order over a set period. The code must be correct for the receiver to respond. With a fixed remote control code, an intending thief can receive and store the code sent by the remote control and re-transmit it in an attempt to operate the receiver. However, with a rolling code, the reused code will not trigger the receiver because it requires a different code each time. Each code that’s transmitted differs markedly from one transmission to the next. The codes sent are based on an algorithm (calculation) the transmitter and receiver have in common. An initial seed value is based on a Microchip Unique Identifier (MUI) value in the transmitter IC. This IC produces a unique set of values that is synchronised with the receiver during registration. These values change each time the Switch is used. Since the handheld remote will have a unique identifier different from any other handheld remote, the uniqueness of the code is ensured. The odds of picking a correct code at random for our rolling code Receiver short-form kit (SC6835, $35): comes with the PCB and most onboard components, including a 12V or 24V relay (specify), except receiver module RX1, switches S1 & S5 and the case. Discrete transmitter complete kit (SC6836, $20.00): comes with all parts including the case. Module-based transmitter short-form kit (SC6837, $15.00): comes with all parts except the transmitter module but including the case. December 2023  43 Parts List – Secure Remote Switch (Transmitter) 1 Supertronic PP43 keyfob enclosure 1 A23 12V battery 1 PIC16LF15323-I/SL programmed with 1010923A.HEX, SOIC-14 (IC1) 1 MCP1703-3302E/DB 3.3V low-dropout regulator, SOT-223 (REG1) [element14 2113888] 1 1N5819 40V 1A schottky diode (D1) 3 SPST two-pin momentary PCB-mount tactile switches (S1-S3) [Jaycar SP0611, Altronics S1127] 1 3mm high-brightness red or green LED (LED1) 2 1μF 25V SMD X7R ceramic capacitors, M3216/1206 size 2 100nF 50V SMD X7R ceramic capacitors, M3216/1206 size 1 220W 1% SMD resistor, M3216/1206 size – up to 16 transmitters can be used per receiver Extra parts for the module-based version 1 double-sided PCB coded 10109232, 29.8 × 39.4mm 1 433.9MHz UHF ASK transmitter module (TX1) [Jaycar ZW3100, Altronics Z6900] 1 147mm length of 0.8mm enamelled copper wire Extra parts for the discrete version 1 double-sided PCB coded 10109233, 29.8 × 39.4mm 1 MICRF113YM6 UHF ASK transmitter, SOT-23-6 (IC2) [element14 2810141] 1 13.56MHz 5 x 3.2mm SMD crystal (X1) [element14 1611805] 1 470nH SMD inductor, 610MHz SRF, M2012/0805 size (L1) [Coilcraft 0805HT-R47TJLB; element14 2286517] 1 68nH SMD inductor, 1.7GHz SRF, M1608/0603 size (L2) [Coilcraft 0603CS-68NXJLU; element14 2286005] 1 1μF 25V SMD X7R ceramic capacitor, M3216/1206 size 2 18pF 50V SMD C0G/NP0 ceramic capacitors, M3216/1206 size 1 12pF 50V SMD C0G/NP0 ceramic capacitor, M3216/1206 size 1 5pF 50V SMD C0G/NP0 ceramic capacitor, M3216/1206 size 1 167mm length of 0.8mm diameter enamelled copper wire transmitter is one in 2.8 trillion, making any attempt to break the code by sending out guessed codes unrealistic. The code must also be sent at the correct data rate, with the correct start and stop bit codes and other transmission requirements, including data scrambling that changes for each transmission. Other features Our Switch system has two parts: a professional keyfob-style transmitter and a separate receiver. The keyfob has three pushbutton switches and an acknowledge LED that briefly lights each time one of the switches is pressed. Up to 16 different keyfob transmitters can be used with one receiver. The receiver has a 10A-rated relay, making it suitable for switching many items. Relays with even higher ratings (eg, 16A) are available if needed. The relay can be controlled by a remote control or a switch on the receiver, and either way, it can be toggled on and off, or switched on for a fixed time. The on-period can be adjusted from 250ms to 4.5 hours in two ranges. Security and registration Each keyfob transmitter is allocated an Identity number from 0 to 15, set by coding links on the PCB. Each transmitter is registered to the receiver by sending a synchronising code to the receiver when the receiver is in registration or learning mode. A facility is included to lock out a particular transmitter after registration. This is useful if a transmitter has been lost. If the lost transmitter is found, it can be easily re-registered. If the identity of the lost transmitter is not known, all transmitters can be locked out, and the ones still in use can be re-registered. Circuit details Fig.1: in the module-based transmitter circuit, microcontroller IC1 monitors buttons S1-S3. When one is pressed, it lights LED1, powers up the transmitter module by bringing its pins 8 and 9 high, then produces the ASK data to transmit at its pin 3. When finished, it brings pins 5, 8 and 9 low again and returns to sleep mode. 44 Silicon Chip Australia's electronics magazine The transmitter circuits are shown in Figs.1 & 2. They have many common parts; each mainly comprises a microcontroller, IC1, and a 433.9MHz UHF transmitter. The UHF transmitter can be either a prebuilt module (Fig.1) or a discrete circuit using a Micrel UHF transmitter IC and associated inductors and capacitors (Fig.2). Both versions have the same transmission range and fit into the same keyfob enclosure. So which version you wish to build depends on whether siliconchip.com.au you prefer to source the module or solder the discrete parts onto the PCB. The discrete version does have the advantage of potentially being less costly. Both versions utilise a similar wire coil antenna. The PIC16LF15323 was chosen for IC1 due to its very low standby current and the inclusion of a unique identifier called the Microchip Unique Identifier (MUI). We use the MUI to generate a unique rolling code sequence for each IC; no two transmitters will have the same sequence. IC1 is usually kept in sleep mode with its internal oscillator stopped and most of its internal circuitry switched off. Switches S1, S2 and S3 connect to the RA5, RC4 and RC3 digital inputs of IC1, which have internal pullup currents enabled, so those pins are usually high but are pulled low when a button is pressed. The Identity links (1, 2, 4 & 8) connect to the RA0, RA1, RA2 and RC0 digital inputs, respectively. These are used to differentiate between multiple transmitters used with a given receiver. If only one transmitter is used, it can be set to Identity 0, so none of the Identity pins need to be connected to ground. At power-up, each Identity input is held high by pullup currents/resistors (within IC1) to the 3.3V rail, similar to the pushbutton inputs. The software then switches off the pullup current for any identity input that is found to The module-based (left) and discrete (right) versions of the transmitter PCB shown enlarged. We have used an A23 12V battery, which fits snugly with the recommended battery clips. be at a low level. That prevents the IC from continuously sourcing current from those pins, which would otherwise add some 25-200μA battery draw per Identity input that’s tied low. The pullups for pushbutton switches S1-S3 are left on permanently since they are only pressed momentarily. IC1 is programmed to wake up from its sleep condition when any one of switches S1-S3 is pressed and the corresponding input goes low. It then runs the program to send the rolling code for the function associated with the pressed switch. When a button is pressed, the micro drives its RC2 and RC1 digital outputs high, to 3.3V. These are connected in parallel to power the UHF transmitter (module or discrete components). This way, UHF transmit circuitry only draws current from the battery when it is in use. With the transmitter powered up, IC1 sends the rolling code and registration codes on the data line from its digital output RA4 (pin 3). This feeds the data input of the UHF circuitry. UHF code transmission switches between two different carrier wave amplitudes, a technique known as amplitude shift keying (ASK). In this case, there is no UHF transmission when the digital signal is low, but the 433.92MHz carrier is transmitted when the digital signal is high. After sending the code, IC1 powers down the UHF transmitter and returns to sleep mode. Discrete UHF circuitry Referring to the additional UHF transmission circuitry in Fig.2, the MICRF113 is a single-chip ASK UHF transmitter IC. Its transmission frequency is set using a crystal oscillator multiplied by 32 within IC2 to produce the UHF carrier. So the 13.56MHz crystal results in a 433.92MHz carrier. This matches the carrier frequency used by most UHF ASK transmitter/receiver modules available for Fig.2: the left side of the discrete version of the transmitter circuit is identical to Fig.1. This time, the MICRF113 ASK IC generates a 433.9MHz carrier from the 13.56MHz crystal and switches it on and off based on the digital signal at its ASK input (pin 6). Inductor L1 is its output load, while L2 and the 12pF & 5pF capacitors filter out unwanted harmonics. siliconchip.com.au Australia's electronics magazine December 2023  45 Parts List – Secure Remote Switch (Receiver) 1 double-sided plated-through PCB coded 10109231, 70 × 96.5mm 1 set of front and rear panel labels 1 Ritec 105 × 80 × 33mm plastic enclosure [Altronics H0191] 1 433.9MHz UHF ASK receiver (RX1) [Jaycar ZW3102, Altronics Z6905A] 1 10A SPDT relay (12V or 24V coil) (RLY1) [Jaycar SY4066 (12V) / SY4067 (24V), Altronics S4160C (12V) / S4162C (24V)] 1 subminiature SPDT PCB-mount momentary horizontal pushbutton switch (S1) [Altronics S1498] 1 button cap for S1 [Altronics S1481] 2 SPST PCB-mount tactile micro switches (S2, S3) [Jaycar SP0600, Altronics S1120] 1 4-bit (0-9 & A-F) 6-pin BCD PCB-mount rotary switch (S4) [Jaycar SR1220, Altronics S3000A] 1 subminiature SPDT PCB-mount horizontal toggle switch (S5) [Altronics S1421] 1 PCB-mount barrel socket, 2.1mm or 2.5mm inner diameter (CON1) 1 2-way screw terminal, 5/5.08mm pitch (CON2) 1 3-way screw terminal, 5/5.08mm pitch (CON3) 1 10kW miniature single-turn top-adjust trimpot (code 103) (VR1) 3 2-way pin headers, 2.54mm pitch (JP1-JP3) 3 jumper shunts (JP1-JP3) 1 20-pin DIL IC socket (for IC1) 1 PG7 (3-6.5mm cable) or PG9 (4-8mm cable) cable gland for rear panel 1 169mm length of 0.8mm diameter enamelled copper wire 1 169mm length of 1mm diameter heatshrink tubing (optional) Semiconductors 1 PIC16F1459-I/P programmed with 1010923R.HEX, DIP-20 (IC1) 1 7805 5V 1A linear regulator, TO-220 (REG1) 1 BC337 500mA NPN transistor, TO-92 (Q1) 2 1N4004 400V 1A diodes, DO-41 (D1, D2) 1 3mm high-brightness red LED (LED1) 2 5mm high-brightness LEDs (eg, red & green) (LED2, LED3) Capacitors 1 100μF 25V PC electrolytic ● 1 100μF 16V PC electrolytic 1 10μF 35V PC electrolytic ● 2 100nF MKT polyester or ceramic (code 104 or 100n) ● can be 16V rated for 12V supply Resistors (all 1/4W, 1% metal film unless noted) 5 10kW 3 560W 1 330W 470W 1W for 24V supply, 100W 1/2W for 12V supply (R1) low-power UHF data transmission. IC2’s power rail at pin 3 is bypassed with 100nF & 1μF ceramic capacitors while the supply current for IC2’s RF output stage is via a 470nH inductor acting as a driver load. The following 12pF series capacitor and 68nH inductor plus the 5pF capacitor to ground act as a filter to remove second and third harmonics from the UHF signal before it passes to the antenna. Any inductor used for the output stage and filter circuit must have a self-resonance (SR) frequency above 433.92MHz; otherwise, it will not function as an inductor at that frequency. This is a critical requirement for any substitute components to those specified in the parts list. Power supply In both cases, IC1 is powered using an A23 12V battery and a 3.3V low-­ quiescent-current low-dropout voltage regulator (REG1). This supplies the UHF transmitter section as well as the microcontroller. REG1 typically draws a 2μA quiescent current at 25°C, although that could be as high as 5μA over the range of -40°C to +125°C. With IC1 in sleep mode, it draws a typical standby current of 60nA from its 3.3V supply and so can essentially be ignored compared to the regulator’s quiescent current. We measured the quiescent current draw from the 12V battery on our two prototypes at 2.7μA and 3μA, respectively. When a switch is pressed on the transmitter, that increases but only briefly, so that does not affect the longterm battery life much. During transmission, the current draw from the battery briefly rises to about 10mA. If you keep holding one of the buttons down after the transmission is complete, the current will drop to about 220μA until the button is released. This is due to the pushbutton switch pullup current. Considering the low quiescent current and intermittent bursts of higher current when transmitting, battery life should be more than two years with typical use. Receiver circuit The rear of the receiver case includes the power socket and cable glands for wiring to the relay terminals. 46 Silicon Chip Australia's electronics magazine The receiver circuit (Fig.3) uses a PIC16F1459-I/P microcontroller (IC1) and UHF receiver module with an onboard wire antenna to provide a good reception range. When no signal is present, the siliconchip.com.au receiver’s output produces random noise since the module’s automatic gain control (AGC) is at its maximum. Upon reception of a 433.92MHz signal, the receiver gain is reduced for best reception without overload, and the coded signal from the data output of the module is delivered to the RC7 digital input of IC1 (pin 9). IC1 flashes the Acknowledge LED (LED2) whenever a valid signal is received. This also doubles as a relay-on indicator. It is lit when the relay is on and off when the relay is off. The RC5 digital output of IC1 (pin 5) drives NPN transistor Q1, which switches the relay coil. When RC5 goes high, it delivers current to transistor Q1’s base, and Q1 powers RLY1. Diode D2 clamps the back-EMF that causes a voltage spike at the collector of Q1 as the relay switches off. The relay contacts are rated at 10A for AC or DC. The unit can be set up to power the relay for a fixed period when a transmitter button is pressed (or S1 on the receiver) or toggle it on or off for each button press. This on/off functionality can be set differently for the transmitter buttons and the onboard pushbutton, S1. Since the transmitters have three buttons, they can provide different functions (more on that shortly). When jumper JP3 is closed, the relay switches on with one press of onboard button S1 and off with the next. When JP3 is open, the relay is switched on for a fixed time with a press of S1 and switches off automatically at the end of this period – see Table 3. The remote control has three buttons; usually, S1 on the remote switches the relay on, and it is then switched off with the timer. S2 switches it on continuously (or for a much longer time if JP2 is inserted), and S3 switches it off – see Table 2. The timer period is set using trimpot VR1. The trimpot wiper can be Table 1 – JP1 timer settings JP1 Timer range Out 0.25-60s (1x) In 1m-4.5h (255x) Table 2 – JP2 settings TX Function with Function button JP2 out with JP2 in S1 Relay on with Relay on a timer, range with a timer, per JP1 0.25-60s S2 Relay on continuously Relay on with a timer, 1m-4.5h S3 Relay off Relay off adjusted from 0V through to 5V; this voltage is monitored at the AN6 analog input of IC1, which converts the voltage into setting a period from 0.25 seconds to 60 seconds or one minute to four hours and 30 minutes, depending on the settings of JP1 & JP2 (see Tables 1 & 2). Fig.3: the receiver circuit is based on a prebuilt 433.9MHz receiver module, shown at left, and a 20-pin 8-bit PIC microcontroller, IC1. When IC1 receives a valid rolling code, it brings its pin 5 high to power NPN transistor Q1 which switches the relay coil. The relay is a 12V or 24V DC coil type to match the supply voltage. siliconchip.com.au Australia's electronics magazine December 2023  47 Table 3 – JP3 settings JP3 Onboard S1 function Rolling code transmission format The rolling code is transmitted using UHF ASK in Manchester code. A zerobit is sent as a 512μs period of no transmission followed by a 512μs burst of 433.9MHz carrier. In contrast, a one-bit is transmitted as a 512μs burst of 433.9MHz carrier followed by a 512μs period of no signal. Each transmission consists of four start bits, an eight-bit identifier, a 48-bit code and four stop bits, for a total of 64 bits. The start bits include a 16.4ms gap between the second and third start bit, while the code scramble value is altered on each transmission with 32 variations. Unique codes are generated with a 48-bit seed, 24-bit multiplier & 8-bit increment value. That is initially set by a unique identifier within IC1 on the transmitter. The registration code is sent as two blocks. Block 1 sends four start bits, the eight-bit identifier, a 32-bit seed code and four stop bits. Block 2 sends four start bits, the 24-bit multiplier, the eight-bit increment and eight-bit scramble values and four stop bits. Again, the start bits include a 16.4ms gap between the second and third start bit. IC1’s digital input RC0 for JP1 has an external 10kW pullup resistor. If JP1 is inserted, this pin is held low. IC1 senses that and, in that case, changes the maximum timer setting from one minute to 4 hours and 30 minutes. You can monitor the timer setting voltage between test points TP1 and GND. Table 4 shows the typical periods for five different voltages in each range. Transmitter Identity The receiver Identity selection is made using a BCD rotary switch (S4) with 16 positions, labelled 0-9 and then A-F. Those hexadecimal values correspond to 0-15 in decimal, with A-F representing 10-15. This switch is only monitored by IC1 for lockout Out Off if already on, otherwise on for a time set by JP1 and VR1 (see Table 1) In Toggle on/off Table 4 – period vs TP1 voltage TP1 Time with JP1 out 0V 0.25s Time with JP1 in 1m 1.25V 15s 1h 7.5m 2.5V 30s 2h 15m 3.75V 45s 5V 60s 3h 22.5m 4h 30m selections; it plays no part in the keyfob transmitter registration. S4’s four contacts connect to the RB7, RB6, RB5 and RB4 digital inputs of IC1. These all have internal pullups, so the inputs are at 5V when the corresponding switch is not closed. All four inputs are high when the BCD switch is set at 0. Position 1 on the switch has the ‘1’ output at RB7 pulled low, while position 15 (or F) sets all four pins to 0V. be acknowledged by the Learn/Clear LED (LED1) lighting. Table 5 shows the identity selection coding for both the transmitter and receiver. The Learn switch (S2) tells the program within IC1 to be ready to accept the synchronising signal from a handheld remote. The Learn/Clear LED (LED1) stays lit while waiting for a signal from the remote unit. It extinguishes once the synchronising signal has been correctly received. Deregistration & registration Power supply S3 is used for deregistering a transmitter. Pressing S3 for more than one second will deregister the transmitter specified by the BCD switch, preventing it from operating the receiver again. Successful deregistration will Receiver Transmitter Transmitter Transmitter Transmitter S4 ‘1’ ‘2’ ‘4’ ‘8’ 0 open open open open 1 shorted open open open 2 open shorted open open 3 shorted shorted open open 4 open open shorted open 5 shorted open shorted open 6 open shorted shorted open 7 shorted shorted shorted open 8 open open open closed 9 shorted open open closed A (10) open shorted open shorted B (11) shorted shorted open shorted C (12) open open shorted shorted D (13) shorted open shorted shorted E (14) open shorted shorted shorted The receiver can be powered from 12V or 24V DC, from a DC plugpack or similar DC supply; some garage door controllers have DC supply terminals that could also be used. Regardless of the source, power can be connected via CON1 (a barrel socket) or two-way screw terminal CON2. Reverse polarity protection is via diode D1, which only allows current to flow into the circuit if the supply polarity is correct. The relay has a 12V or 24V DC coil, matching supply voltage. For 24V, a 470W 1W resistor (R1) reduces the voltage applied to 5V regulator REG1. For a 12V DC input, a 100W ½W resistor is used instead. The 470W resistor reduces the dissipation in REG1 when the supply is at 24V. This resistor also filters the DC supply to REG1 in conjunction with the 100μF input capacitor, removing most of the noise from a switchmode supply that could otherwise affect the UHF receiver sensitivity. Note that for a 24V DC supply, the 100μF capacitor is rated at 25V, and the 10μF capacitor bypassing the relay supply is 35V. For a 12V supply, the capacitors can all be rated at 16V. SC F (15) shorted shorted shorted shorted siliconchip.com.au Table 5 – Transmitter Identity selection Christmas Gift Guide ON SALE WED 29.11.2023 - SUN 24.12.2023 1080P HD CAMERA WITH FIRST PERSON VIEW NOW 99 $ NOW 199 $ SAVE $20 OFF REG. 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HANG HOOK FOR EASY SET UP 95 . Personal Breathalyser EA HEATS UP IN MINUTES SAVE $15 OFF REG. PRICE 710MM DIAMETER Keep cool and comfortable in your caravan, camper or outdoor patio. 3m lead. Cigarette lighter plug GH1405 / Battery clamps GH1407 Gi fts Un de r $2 0 19 $ 95 19 $ Portable Table Tennis Set Includes a retractable net, two paddles and two ping pong balls. GH1162 $ . . 95 SAVE $5 5m Flexible Multi-Coloured Waterproof LED Strip Lights 12V Portable Stove Variable RGB colour and effects. Adhesive backing. 12VDC. Remote control and power adaptor included. SL3942 ONLY 19 $ 95 Cook and warm up food while on the road or at the campsite. 3L capacity. YS2811 BUILT-IN WHISTLE . . . SAVE 20% NOW SAVE 20% USB Plasma Ball Create cool dazzling effects. 100mm dia. GE4089 NOW 6995 95 SAVE $8 12V Portable Ceiling Fans NOW NOW 64 $ NOW 1995 $ . EA SAVE 10% OFF REG. PRICE Multi-function Survival Knife Fire starter, belt cutter, window breaker. TH1960 Age restriction laws apply in some Australian states. Portable Rechargeable Fan 3 speeds. Available in blue, maroon, or pink. GH1072 Gift a gift card & let them choose. Gift cards can be purchased in increments of $20 to $500* *Conditions apply - see page 7 for full T&Cs. GEAR FOR THE OUTDOORS ONLY 299 $ 599 $ Power Core E90 Kids Electric Scooter 90W KICK-TO-START MOTOR UP TO 80MIN RIDE TIME LARGE 2.8" DASHBOARD UP TO 20KM/H Electric KickScooter E2 Features a lightweight steel frame, hand-operated front brake & retractable kickstand. Ages 8+. GG2410 UP TO 16KM/H ONLY 2.1W LIGHT FOR NIGHT RIDES POWERFUL 250W MOTOR Up to 25km range with 3 riding modes. Dual brake system for safety. Features a durable automotive-grade steel frame. IPX4 weatherproof body. Foldable for portability. Manage your trip, lock your scooter and more through the Segway-Ninebot app. Ages 14+. GG2600 BRAKE ACTIVATED REAR LIGHT UPGRADE YOUR DAILY COMMUTE ULTRA BRIGHT 1W LED LIGHT SAVE<at>$100 NOW AIRCRAFT GRADE ALUMINIUM PURE SINE Advanced, compact, feature rich and lightweight. WAVE INVERTER Keep your 12V, USB and mains powered devices running when you don’t have access to mains power. FOR ALL YOUR 300Wh MB3774 NOW $439 SAVE $60 (Shown) CAMPSITE 500Wh MB3776 NOW $549 SAVE $100 POWER NEEDS Rechargeable LED Torch Built for the toughest conditions. ST3524 THE ULTIMATE BATTERY BOX FOR ALL YOUR PORTABLE POWER NEEDS DC1103 NOW FROM SAVE<at>$20 . SAVE $15 Mosquito Zapper with LED Lantern Multiple light modes. Weatherproof. Charged by USB. YS5544 2 Portable Battery Box Power Station with 25A DC-DC Charger Features hands-free function, CTCSS and more. Battery powered. 2 PK DC1103 NOW $49.95 SAVE $10 4 PK DC1104 NOW $89 SAVE $20 19 NOW FROM NOW SAVE $120 0.5W 80Ch UHF Radios 95 METER INDICATOR SHOWS DIFFERENT METAL TYPES EQUIPPED WITH SOLAR CHARGING CAPABILITY 629 $ . NOW EXTRA LARGE WATERPROOF COIL FOR FINE & PRECISE DETECTION 30 4995 $ $ DEEP TARGET SEARCHING Huge Capacity Portable Power Stations P2 . SAVE $22 12V & 4 USB OUTPUTS Q 49 95 5 OPERATION MODES 08 439 $ WIRELESS QI CHARGER 23 NOW FROM PERFECT FOR BEACHCOMBING, PROSPECTING AND MORE QP SUPER BRIGHT 1000 LUMEN $ GIFT A GIFT CARD & LET THEM CHOOSE Compatible with most battery types. Features 6 x 50A & 1 x 175A high current connectors, 2 x dual USB ports, 3 x cigarette sockets, and LCD voltmeter. HB8506 NOW 24 $ 95 . SAVE $5 SAVE<at>$50 Metal Detectors Beginners w/ Auto Tune QP2302 NOW $99 SAVE $30 Pro w/ LCD Screen QP2308 NOW $169 SAVE $50 Gif ts Un de r $4 0 NOW 29 $ 95 . SAVE $5 99 $ NOW 3995 $ WITH QUICK CHARGE™ AND POWER DELIVERY . SAVE $5 12V RGB LED Light Strips for Car Interior Add colour and lighting effects to your car interior. SL3948 12V Kettle Features a water level window, auto-shut off and a boil dry protector. GH1386 10,000mAh Power Bank Charge via USB Type-A or Type-C. Up to 3A combined output. MB3810 TERMS & CONDITIONS: Prices valid from 29/11/23 to 24/12/23. Stock may be limited on sale items. No rain checks. Savings on Original RRP (ORRP). Prices are correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. For full gift card T&Cs see www.jaycar.com.au/giftcards. Page 1: MULTIBUYS: 2 x AA2165 for $30. Page 4: Buy 1 x YS5545 & get second free. Page 8: MULTIBUYS: 2 x AB1240 for $30. 2 x GT4106 for $30. 2 x GT4259 for $30. 10% OFF BRASS MONKEY ACCESSORIES with purchase of a full priced Brass Monkey fridge/freezer. Excludes Lithium Batteries. Discount on accessories applies at time of purchase. All items must be purchased in the same transaction. SUPPLY CHAIN DISRUPTION. We apologise for factors out of our control which may result in some items not being available on the advertised on-sale date of the catalogue . + For details and terms on payment options see. www.jaycar.com.au/paymentmethod. HALF PRICE SELECTED 12/24V PORTABLE FRIDGE/FREEZERS NOW 199 $ HALF PRICE 25L with Metal Case INTERNAL LED LIGHT STURDY METAL CASE 36 Compact and fits easily in the boot. GH2006 82 DUAL ZONE NOW 299 $ HANDY CHOPPING BOARD & WIRE BASKETS NOW 224 $ HALF PRICE DIGITAL TEMPERATURE CONTROLS 55L with Battery Compartment Battery sold separately 35L with Battery Compartment Ultra-portable and versatile with fridge and freezer, extending handle, wheels and battery compartment. GH2020 Compact and portable fridge or freezer. Compatible with optional batteries and solar charging. GH2077 Lithium Fridge Batteries EA 52 5.2Ah - 15.6Ah. GH2049-GH2053 RRP $109 - $269 WORKING LED LIGHTS $3 0 2 G re a t G if ts fo r * of the sam e item INTRO OFFER 2 FOR 2 FOR 30 30 $ SAVE 20% SAVE 20% Mini Boomerang Spinner Drone Boomerang, frisbee & spinner in one! Ages 14+. GT4106 RRP $19.95EA Battery sold separately HALF PRICE FITS OPTIONAL LITHIUM BATTERY $ FITS OPTIONAL LITHIUM BATTERY AVAILABLE IN RED OR BLUE Bubble Blower Bazooka AVAILABLE IN GREEN, YELLOW OR PINK 2 FOR 30 $ SAVE 35% RC Car in a Can 8 colours available. 75mm long. Ages 3+. GT4259 RRP $24.95EA GIFT A GIFT CARD Create a steady stream of bubbles. Ages 3+. AB1240 RRP $19.95EA SALE ENDS SUNDAY 24.12.2023 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 Shenzhen’s Electronics Markets By Edison Zhang Have you ever seen an entire shopping mall dedicated to electronics? Shenzhen has two right next to each other! The larger one features not just consumer electronics like cameras, drones and so on but also bustling floors full of almost every electronic component you can think of. T he Huaqiangbei Commercial Street market is described as the world’s largest electronics market. It is about six stories tall, with component sales mainly occurring on the ground floor and a couple of floors above it. Beyond that, the shops mostly sell consumer electronics. While that isn’t what I went there to see, they are well worth a visit, especially the drone vendors. One of the things you’ll immediately notice upon entering the ground floor is shop after shop packed to the rafters with reels and boxes of components. Another is the people constantly wheeling trolleys full of boxes of components in and out. There must be millions of individual parts on some of those trolleys! While there is a lot of wholesale-­type activity, the market is open to the public, and any vendor will happily deal with you. The local dialect is Cantonese, although many people also speak Mandarin. It is possible to shop at the market even if you can’t speak either language, especially if you have a smartphone equipped with a translation app. A human translator would be even better. I found one large vendor selling semiconductors with an employee who could speak English fairly well, but it is uncommon. In some cases, the vendors are happy to sell you just a handful of parts, but many of them deal in volume. While you don’t need to buy full reels or boxes of parts, you might need to start at around a hundred pieces. Don’t feel that would be too expensive, though; depending on what they are, those hundred parts might only cost you one or two Australian dollars; sometimes less than a dollar! Reels with thousands of components that, in my estimation, were of decent quality started at around $10. Shops in the market tend to be specialised; for example, many of siliconchip.com.au the shops sell just one or two of the following component types: ◼ SMD ceramic capacitors ◼ SMD resistors ◼ Inductors ◼ Transformers ◼ SMD transistors ◼ SMD ICs ◼ LEDs ◼ Switches ◼ Solid electrolytic capacitors ◼ Through-hole plastic film and ceramic capacitors ◼ Crystals ◼ USB and SD connectors ◼ Cables Where is Shenzhen? The Chinese city of Shenzhen in Guangdong province was created to complement neighbouring Hong Kong. When Hong Kong was still under British rule, they created a ‘special economic zone’ outside its borders, right next to the ‘New Territories’ of Hong Kong, to bring similar economic benefits. The Sham Chun River separates Shenzhen and Hong Kong. Today, both cities are part of the Pearl River Delta region, a densely populated area with around 85 million people. It has significant industry, including electronics manufacturing. There are 11 major cities in this area, but a lot of the PCB manufacturing and electronics assembly is concentrated in and around Shenzhen. Hong Kong has a great deal of economic activity. Still, with its relatively limited land area, it is more of an international trade Australia's electronics magazine December 2023  57 The markets are housed in a building that spans a small road. Electric scooters are popular here! The other side of the building. Some entrances are at ground level while others take you straight up a floor or two. and finance hub (like London or New York) than a manufacturing powerhouse. Most of the manufacturing occurs in the adjacent mainland China area. will see those types in large numbers, even though you might not have heard of them. For example, the S8050 NPN transistor is quite popular there, with several vendors selling it in quantity. They are rated at 20V and 700mA, so they are useful as general-purpose NPN transistors in low-voltage circuits, where we might use a BC328 (25V, 800mA) instead. Similarly, in terms of Mosfets, certain types will crop up often, usually from the AO (Alpha & Omega brand) or Si (Vishay Siliconix) series; for example, the AO3400-3407 series are popular high-current Mosfets in SOT-23 SMD packages. I am unsure if these are genuine brand-name parts or clones, but from the testing I’ve done, they meet all the relevant specifications. ICs and regulators are similar; you will find a certain subset of parts that Chinese manufacturers appear to have standardised on are widely available, while other parts that you might be used to seeing will be special-order types. Available brands You might be wondering whether the parts sold at the markets are genuine brand-name devices, or some sort of clone/knockoff. Virtually all the parts I saw seemed genuine, although they didn’t always have the expected branding. In some cases, it had been purposefully removed or crossed out, possibly to avoid betraying the ‘grey market’ source of these parts. By that, I mean that they likely come from a factory making brand-name parts, but perhaps not through official sales channels that the manufacturer endorses. Some of the brands that I saw represented at the markets included AVX, EPCOS, Kemet, muRata, Panasonic, Samsung, TDK, Vishay, Wima & Yageo (capacitors), Abracon (crystals), Atmel, Analog Devices, Fairchild, Infineon, Maxim, Nexperia, onsemi, Rohm, ST Micro, Texas Instruments & Toshiba (semiconductors) and MEAN WELL (power supplies). Subjectively, the quality of everything I saw was good. For example, the USB connectors didn’t have a brand name I recognised. However, the materials used seemed appropriate, and the forming of all the leads, shells, plastic mouldings and so on appeared to be done with as much accuracy as you’d want for such complex and detailed assemblies. Similarly, the semiconductors I saw were in modern packages loaded into reels on tape, and they all appeared to have good lead finish, plastic package deflashing and so on. It’s clear that they are being made in modern factories with up-to-date equipment. I would have no hesitation buying and using the parts sold by most vendors there, as long as you use common sense. It’s clear that many manufacturers are buying these parts by the thousands, if not millions. They would be rightly upset if they made a heap of TVs, computers or similar, only to discover that even a small percentage didn’t work! China is full of factories, including numerous silicon fabs, many of which are in the Pearl River Delta and crank out components by the millions. There’s a lot of competition, and I don’t think anyone selling sub-par parts would survive for long. Still, the markets are probably not for you if you need your parts to come with an audit trail. You’re better off ordering from a vendor like DigiKey, Mouser or element14. One thing that takes a little getting used to is that what is considered a ‘standard’ part in China is a little different from in Australia or New Zealand. Manufacturers there have clearly settled on specific parts or series and stuck with them. As a result, you 58 Silicon Chip The AliExpress connection I have no proof of this, but I suspect that many electronics vendors on websites like AliExpress and eBay, a significant proportion of which are based in Shenzhen, are official or unofficial agents for the markets. Locals could easily make money by advertising products they see at the markets on one of those websites at a markup. If someone places an order, they can pop down to the markets, make a purchase and stick it in an envelope addressed to you. They probably do the same for many people all at once for greater time efficiency. I even noticed shops in the markets selling packing materials like I took this photo early, with some shops yet to open. Check out how many reels are in the small shop on the right! Australia's electronics magazine siliconchip.com.au The upper floor shops mostly sell consumer electronics and gadgets. Watch out for knockoffs, unless that’s what you’re after! Some of the large component vendors also have shops upstairs, which they seem to use as local warehouses. boxes and bubble wrap. It’s possible that people can fulfil orders on eCommerce platforms without having to go very far outside of the market building. but it is still worth visiting. I noticed more hifi stores there compared to Huaqiangbei, for example, plus plenty of shops selling devices like cameras and smartphones. Buying from the market Local area While many vendors will accept cash payments, it is more common to pay with a smartphone app like AliPay or WeChat (which isn’t just a messaging app). Both are very convenient for buyers and sellers and generally involve one or the other scanning a QR code with their phone or POS system. You need a Chinese mobile phone number to set up either app, but AliPay now has an English translation. Once in China, it is possible to set up the app and transfer some money from your bank account. That makes purchases much easier throughout China, as virtually all shops offer those two apps as payment options. One of the vendors told me renovations are planned for the lower floor of the markets in late 2023, so they could have changed somewhat by the time this article is published. Still, given how much activity I saw going on there and the evident links to manufacturing, I expect most of the same vendors will be back once renovations are complete. If you want to visit the Huaqiangbei markets, there is an excellent four-star hotel right next door called the Huaqiang Plaza Hotel. It is affordable by Australian standards. The Hotel and the markets are just off Huangqiang Lu, a pedestrian mall with many shops, restaurants and attractions. So there are plenty of other things to see in the area and it is quite tourist-friendly. Like Hong Kong, Shenzhen is an international city where Westerners will feel somewhat at home, although it is not exactly a tourist destination. Still, as I wrote earlier, don’t expect many people to speak English. I found it easy to get around Japan without understanding Japanese (there are many English signs there), but I cannot say the same about China (yet). Conclusion Another building called the Seg Communication Market is across the street from the Huaqiangbei Commercial Street market (www. hqew.com). It is located at 1015 Hua Qiang Bei Lu, Futian District, Shenzhen, Guangdong, China 518028 (https://maps.app. goo.gl/fAAKEci7fFjkqG7V7). It is smaller and is mainly concentrated on consumer electronics, I really enjoyed looking around the Shenzhen electronics markets to see what was available. The massive amount of parts surrounding you makes you feel like a kid in a lolly shop. If you are travelling to Asia, it is very much worth a visit. If you plan to visit Shenzhen from Hong Kong, although they are right next to each other and part of the same country, they operate under the ‘one country, two systems’ scheme. Other places you could consider visiting if in the area include Foshan (famous for food, ceramics & martial arts), Guangzhou SC (zoo, architecture & shopping) and Macao (casinos). This photograph gives you a good idea of how many components are going in and out at one time. While I visited the markets, the ground floor was filled with smaller stalls packed with electronic components. The Seg electronics market siliconchip.com.au Australia's electronics magazine December 2023  59 Part 1 by Tim Blythman Many people now have home theatre/ surround sound systems and need to control the volume of six or more audio channels. This Multi-Channel Volume Control has a touchscreen and receives infrared remote signals. It can be expanded up to 20 channels, although six or eight will suit most applications. Multi-Channel Volume Control T he Multi-Channel Volume Control can be built as a stand-alone unit in its own enclosure, or as a modular system that can be incorporated into a multi-channel preamplifier or amplifier. It can control up to 20 channels in synchrony. A microcontroller senses inputs from the touchscreen, rotary encoder or infrared remote control and drives digital potentiometers to control the volume of each channel. One of the reasons behind this project was our publication of the Hummingbird Amplifier module in the December 2021 issue (siliconchip. au/Article/15126). That small, lowcost 100W amplifier module makes it easy to build an amplifier with four, six or even more channels. You need something like this design to adjust the volume of all those modules together. The alternative would be a fourganged or six-ganged potentiometer, but then you would have poor tracking and messy wiring. Pots can also go scratchy after a while, unlike a digital pot, which generally continues working flawlessly for decades. This design is based on the Touchscreen Digital Preamp (September & October 2021; siliconchip.com.au/ Fig.1: the performance is similar to the Touchscreen Digital Preamp, with THD+N typically less than 0.002% across much of the range. The dashed lines show the degradation with 1μF ceramic coupling caps instead of 2.2μF tantalums. 60 Silicon Chip Series/370), which only sports two channels and is not expandable. Besides this design, another option is Phil Prosser’s “The Digital Potentiometer” (March 2023; siliconchip. au/Article/15693). While it is a two-­ channel design, it does allow you to gang up multiple boards. However, it is a more ‘bare bones’ design than this one, lacking the touchscreen option or any onboard audio sockets. Performance The Multi-Channel Volume Control is based on a Baxandall-style volume control circuit but uses a digital Fig.2: a plot of THD+N against input level. The sweet spot for input levels is ~1.5V, but anywhere in the range of 1-2.3V RMS is fine. Above 2.3V RMS starts to cause clipping while lower levels suffer due to the closer noise floor. Australia's electronics magazine siliconchip.com.au potentiometer rather than the regular kind. Handily, this circuit provides a logarithmic response from a linearly changing resistance, making it easy to map the volume settings to levels in decibels. Figs.1-4 show the resulting performance. Fig.1 plots total harmonic distortion plus noise (THD+N) against frequency for an input signal level of 1.6V RMS. As you’d expect, the plots are similar to those for the Touchscreen Digital Preamp. The red plot was taken with a 20Hz-22kHz bandwidth, which best represents the normal audible range and thus what you would hear. The cyan/blue plot was taken with a wider bandwidth, up to 80kHz, which includes the harmonics of higher-­frequency signals. They are not directly audible but could intermodulate to affect audible frequencies. As you can see, THD+N is below 0.001% for up to 2kHz and below 0.002% up to about 7kHz. Fig.2 shows the total harmonic distortion plus noise (THD+N) against signal level for three volume (gain) settings. The distortion is higher at lower signal levels as the fixed noise dominates the smaller signals. The sharp rise around 2.5V RMS is where the Volume Control enters clipping. The sweet spot is with an input signal around 1.5V RMS. Fig.3 shows the crosstalk between channels. The two plots show the extremes that can be expected within a single Volume Module (explained Features & Specifications » » » » » » » » » » » » » Can control the volume of four, eight, 12, 16 or 20 channels RCA sockets for inputs and outputs Volume levels/gain settings: mute (-100dB) and -48dB to +16dB 1dB or smaller steps from -30dB to +16dB Digital controls, including touchscreen, rotary encoder and IR remote 2.8in LCD screen shows the volume and mute status Can be programmed to support many NEC-compatible IR codes Each channel can have a preset offset applied Volume and mute settings kept in EEPROM for next power on Optional small OLED status display with rotary encoder THD+N: typically less than 0.002% (see Fig.1) Channel separation: >80dB (see Fig.3) Signal handling: 0.1-2.5V RMS Image source: unsplash.com/photos/HLhmbBw6xpY later). The cyan/blue plot shows the crosstalk from adjacent channels and is around -80dB or better; these channels share some components. The red plot shows the separation between channels at opposite ends of a module, which is a little better. Fig.4 shows the frequency responses at three gain settings: +5dB (red), 0dB (green) and -5dB (cyan/blue). There is a slight but uniform roll-off at lower frequencies, but the level difference is uniform across the audible band. In other words, the volume adjustment is consistent, as is expected. Modular design While we are boasting up to 20 channels, most constructors will not need that many. So rather than offering a design based around a single PCB, Fig.3: channel separation is about 80dB at worst and only for adjacent channels that share an op amp in their audio paths. siliconchip.com.au the Volume Control is modular. The three modules are the Control/Power Supply Module, the four-channel Volume Module and an optional OLED Module. The main Control and Power Supply Module incorporates a microcontroller that converts the user input into the necessary actions to implement the volume control. It also contains all the power supply circuitry needed to drive any other connected modules. The power supply section only needs a 12V AC supply, which can be provided from a small mains transformer or AC plugpack if your system doesn’t already have a suitable source. You probably won’t need a separate transformer if your system has a larger transformer incorporating 12V AC taps. Fig.4: a frequency response plot at three different volume settings (-5dB, 0dB and +5dB). There is only a slight roll-off at the bottom end, and the effect of the volume settings is very uniform across the spectrum. Australia's electronics magazine December 2023  61 The Control and Power Supply Module has parts on both sides. This side mostly has the power-supply components. Although we haven’t tested it, a pair of ±15V DC rails could be fed to the Control and Power Supply Module instead. The Control/Power Supply module also incorporates an infrared receiver and a 2.8-inch LCD touchscreen. The Module’s PCB is the same size as the LCD panel at 50mm tall, making it a comfortable fit for a 3U rack case, or anything taller. The Volume Module can control the volume of up to four channels and incorporates an AD8403 precision quad digital potentiometer. This Module also has four input and four output RCA sockets, plus other components to buffer and drive the audio signal as it passes through. A third type of module, the OLED Module, is a simple and compact alternative (or supplement) to the touchscreen display. It includes a small OLED screen for those who want something smaller and simpler; its input control is a rotary encoder. The various modules are connected by a ribbon cable punctuated by IDC connectors. This carries all power and control signals between the modules. The simplest configuration is a single Control and Power Supply Module with between one and five Volume Modules, allowing 4-20 channels to have their levels adjusted as they pass through. If the OLED Module is added, only four volume modules can be connected, which limits the number of controlled channels to sixteen. Still, 62 Silicon Chip we don’t see that as a major limitation! Due to the various ways this project can be arranged, and the fact that many will be building it as part of a larger system, we will not specify a particular enclosure. You can choose an enclosure based on your requirements that will also fit any amplifier modules, transformers and other necessary bits. We’ll start by describing how each module works. Then, next month, we’ll follow up by outlining the assembly of each type of module, along with instructions on how they are wired together, tested and used. Control and Power Supply Module Fig.5 is the circuit diagram for the Control and Power Supply Module. It receives 12V AC via CON7 or CON8. CON7 is a barrel socket and thus can only accept a single 12V AC input. On the other hand, CON8 has three terminals and is intended to connect to a 24V AC centre-tapped transformer, or two 12V AC phases; however, you could connect a single winding via CON8 if that’s all you had. Either way, the AC supply passes through bridge rectifier BR1 and a pair of 1000µF electrolytic capacitors to provide a nominally ±17V DC supply to be regulated. Feeding in two AC phases via CON8 is preferred as the capacitors only need to hold up through the 10ms of each half-cycle rather than 20ms for a full mains cycle. The board generates five regulated Australia's electronics magazine DC rails. REG2 (78L12) and REG4 (79L12) provide +12V and -12V, respectively, to power the analog circuitry. Their outputs are filtered by 100µF capacitors and taken to CON11, which feeds the ribbon cable bus noted earlier, for distribution to the other modules. The +12V rail is further regulated to 5.5V by REG5, an LM317L and its accompanying components. The accompanying resistors and VR2 allow its output voltage to be trimmed to account for resistor tolerances. A 220µF capacitor sits on the output of REG5, and this voltage is also taken to CON11. If the 5.5V rail is adjusted too high, zener diode ZD1 conducts and protects other circuitry downstream. The unregulated positive rail is also dropped via a 22W 5W resistor (to spread dissipation) and reduced to 5V by REG1 (7805). It has a 100µF bypass capacitor on its input and a 220µF filter capacitor on its output. This 5V rail is used on the Control and Power Supply Module to power the LCD touchscreen; the power needed by the LCD backlight, and the resulting higher dissipation, is the main reason why this regulator is a larger TO-220 type, while the others are in smaller TO-92 packages. The 5V rail is reduced to 3.3V by REG3 (MCP1700) to power microcontroller IC9. The 3.3V rail is also available on CON11 to power the microcontroller on the OLED Module. Broadly, the +12V and -12V rails power analog components, while the 5.5V rail primarily powers the digital potentiometers. The 5V and 3.3V rails power the digital components. The separate power domains help to minimise any intrusion of digital signals into the analog, which would affect audio quality. On the Control and Power Supply Module, the remaining circuitry consists mainly of the microcontroller, the LCD touchscreen and their essential ancillaries. IC9 is a 20-pin, 8-bit PIC16F18146 microcontroller. It is powered from the 3.3V rail, so it can easily interface with the LCD controller, which also runs at 3.3V from its own regulator on the LCD’s PCB. A 10kW resistor pulls IC9’s pin 4 MCLR pin to the 3.3V rail, preventing spurious resets, while a 100nF capacitor bypasses its supply to pins 1 and 20. These three pins, plus the siliconchip.com.au Fig.5: the Control and Power Supply Module circuit derives +12V, -12V, +5.5V, +5V and +3.3V rails to power the control circuitry and external modules. The microcontroller handles the LCD touch panel and receives inputs from an infrared receiver. It also sends signals to the two other module types over a 20-way bus via CON11. siliconchip.com.au Australia's electronics magazine December 2023  63 PGC and PGD programming pins, go to ICSP header CON10 for in-circuit programming if needed. Another nine of the micro’s digital pins are wired to CON11 to control the other modules. The SCK, MOSI and MISO pins form the SPI serial bus that controls the other modules. The PIC16F18146 can remap its digital peripherals to any digital pin, so the pin allocation was chosen to simplify the PCB routing. Five CS (chip select) lines are also broken out, allowing up to five different slave modules to be independently addressed for the SPI bus. The SHDN (shutdown) line allows the micro to signal to all Volume Modules that their outputs should be muted. The SPI bus pins are also wired to the LCD touchscreen via CON9, along with the other four digital control lines it needs. A pair of Mosfets plus pullup and pulldown resistors power the LED backlight in the LCD touchscreen, controlled by a digital signal (LED_CON) from IC9. Infrared receiver IRRx1 takes its power from the 5V rail, smoothed by the 100W resistor and 1µF capacitor. Its output goes to the last of IC9’s unused pins via a 1kW resistor. These receivers typically have a 30kW internal pullup, so even though it is powered from 5V, it can safely interface to the microcontroller expecting 3.3V levels. That’s because the 5V drive is quite weak and easily clamped by the microcontroller’s internal input protection diodes. Volume Module The circuit diagram for a single Volume Module is in Fig.6. CON5 connects to the Control and Power Supply Module’s CON11 via a 20-way ribbon cable. An adjustable padded divider that includes trimpot VR1 is used to derive a 2.75V rail from the 5.5V supply. VR1 trims this voltage, which is bypassed by a 220µF capacitor. Test points are provided to allow easy measurement during setup. The 2.75V rail must be Fig.6: the Volume Module circuit contains four substantially identical volume control stages, each using one channel of the AD8403 precision digital potentiometer. It receives SPI control signals over the 20-way bus via CON5. Up to five of these Volume Modules can be connected together, allowing the volume of up to 20 channels to be controlled. The modules can be incorporated into a larger system with other parts, like amplifiers. set accurately to maximise the signal swing and ensure symmetrical clipping if the signal level is excessive. The Volume Module has a single AD8403 quad precision digital potentiometer (IC10) powered from the 5.5V rail bypassed by a 100nF capacitor. The potentiometer’s RS (reset) pin is pulled up to the 5.5V rail by 10kW since we do not use this feature (which forces the potentiometers to their midpoints). The remaining digital pins of IC10 (SCK, MOSI, MISO and SHDN) connect to the corresponding lines on the control bus via CON5. The CS pin goes to five-way jumper JP2, so you can choose which of the five CS lines from the microcontroller on the Control Module will control this Volume Module. Each ‘slave’ module in the system is assigned a different CS line. The SHDN pin is also connected to a 47kW pulldown resistor to ground. 66 Silicon Chip This ensures that the Volume Control is muted until the microcontroller initialises and decides otherwise. The microcontroller can also drive the pin low to enforce muting, helping to eliminate noises during startup. The remainder of the Volume Module consists of four practically identical analog sections, each using one of the 10kW potentiometers internal to IC10. This combination of four potentiometers (on each Volume Module) and five CS lines gives us the 20-­channel limit of the Multi-Channel Volume Control. Analog circuitry We will describe the operation of the first channel only, as they all work the same. All 16 op amps (in eight IC packages) are high-performance (low noise and distortion) LM833 types powered from the ±12V rails. Each op amp has a 100nF bypass capacitor. Australia's electronics magazine A 100kW resistor biases the input from the RCA socket to ground so it doesn’t float if disconnected. The 100W resistors, 470pF capacitor and ferrite bead before the first op amp stage protect the inputs from excessive voltage swing and filter out RF noise and ultrasonic frequencies. The first op amp stage is a unity-gain buffer to provide a high input impedance and low source impedance for the subsequent stages. The output signal is AC-coupled and biased to the 2.75V rail. Dual diode D1 clamps the signal if it happens to deviate below the 0V rail or above the 5.5V rail, with the 2.2kW resistor limiting the current that flows in this case. The 0V to 5.5V span has been chosen as the widest that the AD8403 can handle in normal operation. The 2.2kW resistor also forms a divider with the 10kW of the digital potentiometer, meaning that signals up to 2.3V RMS (or 6.5V peak-to-peak) are accepted at the input without clipping via D1. The following two op amp stages implement the Baxandall volume control. The first stage is a unity buffer while also being a type of mixer, while the second stage is an inverting amplifier with a gain of 14.7. One effect of this is that this stage has its output polarity inverted with respect to its input. The potentiometer is connected between the input (‘A’ end) and output (‘B’ end) of these two stages, providing logarithmic gain changes despite the circuit using a linear potentiometer. Another dual diode at the other end of the digital potentiometer’s track to protects it from excessive voltages from the output of the gain stage. When the SHDN signal is asserted (low), the digital potentiometer disconnects the A end of each potentiometer and connects the wiper to the B end of the track; this means that output is fully muted. The potentiometer exhibits a small amount of resistance at the end of each wiper, so even at the extreme ‘low’ setting, a small amount of signal will pass through to the output unless the SHDN signal is used. Another capacitor and resistor bias the signal back to its original ground reference, and the final op amp stage for each channel applies more gain to allow us to get an output swing of up siliconchip.com.au to 2.5V RMS, despite the 5.5V peak-topeak limitation imposed by the digital pot ICs. A 100W resistor between the output and RCA socket isolates the op amp from capacitive loads. There is an option to use a jumper to bypass the last op amp stage to reduce the gain, saving a handful of components in the process. An important feature is that the four digital potentiometers can all be set independently, allowing the channels to have different levels if needed to maintain audio balance. OLED Module The OLED Module provides an optional set of compact, tactile controls. Its circuit is very simple (see Fig.7) as it has been designed so that the PCB also forms a front panel with its components on the back. This Module is intended to be mounted like a bezel over a cutout in an existing panel. It connects to the ribbon cable bus via its CON12, using the same 20-way IDC box header as the other modules. On this Module, only the SPI control lines, the five CS lines, and 3.3V power and ground are connected; its operation is entirely digital and does not require the other supply rails. This optional OLED Module provides a more compact status display and a rotary volume control. If you don’t want to use the touchscreen, you could leave it off and make this as the full interface (and with an IR receiver wired back to the Control Module). A 14-pin 8-bit PIC16F15224 microcontroller (IC11) is connected to the SPI bus as a slave, with its CS line picked from the five on the bus by JP7. JP7 uses solder shorting pads rather than pin headers and a jumper to keep this module compact. A further three pins of IC11 are connected to a rotary encoder, which provides the user input. Two of these pins are for the quadrature encoder and are either pulled to ground by the contacts in the rotary encoder or pulled up by the 10kW resistors. The pushbutton in the rotary encoder is connected to a similar arrangement, with each of these three pins also having a 100nF capacitor to ground to help filter out contact bounce. Two further pins from IC11 are also used to drive the OLED via an I2C serial interface. This OLED shows the Volume Control’s state as it is updated. The typical arrangement for 8-bit PICs is also present, consisting of a supply bypass capacitor between 3.3V and ground with a pullup to the MCLR pin. These three pins and the PGC and PGD pins used for in-circuit programming are also taken to the in-circuit programming header, CON13. Volume control range limitations Using a quad 8-bit digital potentiometer (IC10), rather than a purpose-­ designed volume control IC, helps keep costs down. However, it imposes a limitation on the effective volume control range. A dedicated volume control IC might give a range of 100dB or more, Fig.7: the OLED Module circuit; it is a simple microcontroller-based board with an OLED and rotary encoder. Since it only requires the 3.3V rail and the SPI bus, only 13 of the 20 pins on CON12 are connected siliconchip.com.au Australia's electronics magazine December 2023  67 but an 8-bit digital potentiometer only has 256 steps, meaning it has an effective volume control range of about 60dB. That’s enough for most applications. Still, you should check that the highest output level makes sense, or you might end up without good control at lower volume settings. The default configuration has a maximum gain of 16dB, giving a fullscale output of around 2V RMS from an input signal close to 300mV RMS. That’s well below line level, which is typically more like 775mV RMS. In this configuration, the lowest signal output level with a 1V RMS input before muting is 4mV RMS or -48dB. The steps above that are 9mV (-41dB), 15mV (-36.5dB), 21mV (-33.5dB), 27mV (-31.4dB), 33mV (-29.6dB) and steps of about 1dB or less from there up. While -48dB is 64dB below the maximum output level, the steps are pretty large until around -30dB, giving a useful control range of about 46dB. A variation of, say, 10dB between different input signal sources will reduce the effective volume control range to 36dB. That gives a 4000:1 ratio between the highest and lowest power output with decent control; if maximum volume results in 100W from your amplifier, you will have fine control down to just 25mW. That’s certainly good enough, but the more the maximum possible gain is above what you need, the more apparent the steps at lower volume levels will become. The system’s overall gain is set with resistors, so you can easily adjust it at the construction stage. Practically speaking, if your power amplifier will reach full power with less than 2V RMS (as many will, and all your input-signals are at least line-level), we suggest you omit the final 6dB op amp gain stages. That will give you 6dB more room at the lower end of the volume range. Control firmware We’ve chosen an 8-bit microcontroller for the Control Module as the requirements are not too burdensome. Although it is driving an LCD panel, the user interface is not complex, with only a single screen configuration needed (no menus etc). The LCD screen is overlaid by a touch panel, which the micro scans for user input. 68 Silicon Chip Parts List – Multi-Channel Volume Control 1 Control and Power Supply Module (see below) 1-5 Volume Modules (each handles four channels; see below) 1 OLED Module (optional; see below) 1m length of 20-way ribbon cable (cut to suit application) 1 universal IR remote control (optional; see text) [Jaycar XC3718] 1 12V AC single winding or 24V AC centre-tapped transformer and appropriate wiring/fusing RCA cables to interface to existing hardware Other mounting hardware to suit your application Control and Power Supply Module 1 double-sided PCB coded 01111222, 87 × 50mm 1 2.8in LCD touchscreen [Silicon Chip SC3410] 1 2.1mm or 2.5mm DC jack socket (CON7; optional) 1 3-way 5mm/5.08mm pitch screw terminal block (CON8; optional) 1 14-way 0.1in female header (CON9; for LCD touchscreen) 1 5-way right-angle pin header (CON10; optional, for ICSP) 1 20-way box header and IDC inline plug (CON11) OR 1 20-way IDC transition header (CON11) 1 500W mini top-adjust trimpot (VR2) 1 3-pin infrared receiver, 38kHz (IRRx1) [TSOP4138, TSOP33438, Jaycar ZD1952, Altronics Z1611A] 9 M3 × 5mm panhead machine screws 4 M3 × 12mm tapped spacers 1 M3 hex nut and washer (for mounting REG1) Semiconductors 1 W04M bridge rectifier (BR1) [Jaycar ZR1304] 1 PIC16F18146-I/SO microcontroller programmed with 0111122B.HEX, wide SOIC-20 (IC9) 1 IRLML2244TRPBF or SSM3J372R 20V 1A+ logic-level P-channel Mosfet, SOT-23 (Q1) 1 2N7002 60V 115mA N-channel Mosfet, SOT-23 (Q2) 1 7805 +5V 1A linear regulator, TO-220 (REG1) 1 78L12 +12V 100mA linear regulator, TO-92 (REG2) 1 MCP1700-3.3 3.3V 250mA linear regulator, SOT-23 (REG3) 1 79L12 -12V 100mA linear regulator, TO-92 (REG4) 1 LM317L 100mA adjustable linear regulator, TO-92 (REG5) 1 5.6V 1W zener diode (ZD1) Capacitors 2 1000μF 25V electrolytic 2 220μF 10V electrolytic 4 100μF 16V electrolytic 1 1μF 10V X7R ceramic, SMD M3216/1206 size 2 100nF 50V X7R ceramic, SMD M3216/1206 size Resistors (all SMD M3216/1206 size 1% except as noted) 2 10kW 2 1kW 1 910W 1 560W 1 110W 1 100W 1 22W 5% 5W axial We know of two otherwise interchangeable versions of this panel with touch panels rotated by 180° compared to each other. Our workaround is to display the user control buttons in the bottom half of the screen. Touches in the top half of the panel are assumed to correspond to touches on the bottom half of the rotated display, so either should work with no changes. In retrospect, we might have chosen a more powerful (and faster) Australia's electronics magazine microcontroller, such as the 16-bit PIC24FJ256GA702. At the time of writing, they are not dissimilar in price, although the SSOP version of the PIC24FJ256GA702 is somewhat more tricky to solder than the SOIC part we are using. The lesser flash memory available on the PIC16F18146 meant that we needed to compress the large font that’s necessary to provide a clear and legible display. siliconchip.com.au Volume Module 1 double-sided PCB coded 01111221, 82 × 94mm 2 quad right-angle RCA socket assemblies (CON1, CON2) [Altronics P0214] 1 20-way box header and IDC inline plug (CON5) OR 1 20-way IDC transition header (CON5) 4 SMD ferrite beads, M3216/1206 size (FB1-FB4) [Fair-Rite 2512066017Y1] 1 5×2 pin header and a jumper shunt (JP2) 1 500W mini top-adjust trimpot (VR1) 8 M3 × 6mm panhead machine screws 4 M3 × 12mmm tapped spacers (or other mounting hardware to suit the application) Semiconductors 8 BAT54S dual series schottky diodes, SOT-23 (D1-D8) 8(6) LM833 low-noise dual op amps, SOIC-8 (IC1-IC8) 1 AD8403ARZ10 quad precision digital potentiometer, SOIC-28 (IC10) Capacitors (all SMD M3216/1206 size unless noted) 1 220μF 10V electrolytic 4 22μF 16V electrolytic 4 10μF 16V electrolytic 4 2.2μF 25V SMA size SMD tantalum 🔷 11(9) 100nF 50V X7R 4 470pF 50V C0G/NP0 4 100pF 50V C0G/NP0 Resistors (all SMD M3216/1206 size 1%) 8 100kW 5 47kW 4 22kW 5 10kW 4 2.2kW 10(2) 1kW 4 680W 12 100W n numbers in brackets refer to requirements if the last op amp gain stage is omitted 🔷 not recommended but 22μF 4V+ X5R/X7R ceramics in M3216/1206 can be substituted (see panel on “Lessons learned during development”) OLED Module 1 double-sided PCB coded 01111223, 51 × 76mm 1 0.96in I2C OLED module (MOD1) 1 PIC16F15224-I/SL microcontroller programmed with 0111122C.HEX, SOIC-14 (IC11) 1 pulse-type rotary encoder with 18 tooth spline shaft (RE1) [Silicon Chip SC5601] 1 knob to suit RE1 1 20-way SMD box header or 20-way dual-row SMD header (CON12) 🔵 1 20-way IDC inline plug 1 5-way pin header (CON13; optional, for ICSP) 4 M3 screws, washers and nuts to suit mounting requirements 4 100nF 50V X7R M3216/1206 size SMD ceramic capacitors 4 10kW M3216/1206 size SMD 1% resistors several short pieces of solid wire (eg, component lead offcuts) 🔵 can be made by cutting 10 rows from Altronics P5415 The PIC16F18146 microcontroller we used for this project can store around 16kB of font data in its flash memory, so you can see how important careful managing font data is. We were very close to running out of flash memory before we started looking into compression. Font compression To display text on a graphical screen requires some form of font data to siliconchip.com.au encode the ‘glyphs’ (character representations) to show. The glyphs usually correspond to a subset of the ASCII character set, perhaps with minor alterations to suit the project, such as including the degrees (°) symbol instead of some other less-used character. The font data format we typically use is widely known. It consists of two header bytes describing the width and height of the font in pixels, followed Australia's electronics magazine Control Module Kit SC6793 ($50): also comes with 1m of ribbon cable Volume Module Kit SC6794 ($55): includes all the listed parts OLED Module Kit SC6795 ($25): includes all the listed parts Each kit includes all the parts listed under each module in the parts list. The only other items needed are a case, power supply and remote control. by another two bytes denoting the first ASCII character code point (eg, 32 for a space is typical) and the number of characters within the font. This is followed by bits of pixel data in bitmap form for each character within the font. Since each byte can hold eight pixels, a small 8×8 pixel font of 95 characters (the full ASCII set) takes up 764 bytes. Fig.a (in the panel overleaf) shows how such a font is translated from bitmap data into the corresponding C code. Other languages, such as MMBasic, use a similar format adapted to the syntax of the specific language. A 16×24 pixel font, our typical choice for legible text on a typical 3.5in LCD panel, uses around six times as many bytes or just over 4kB. Larger fonts are possible by upscaling smaller fonts, but the result does not look as good. The flash memory of these 8-bit PICs uses 14-bit words. They are often described as having 28kB of flash memory, but it is arranged as 16k x 14-bit words rather than 28k x 8-bit bytes. The ideal font size for the large dB display in this project is 44×60 pixels; that would take 31,354 bytes to store as a full ASCII font, which obviously wouldn’t fit in the PIC16F18146. We can reduce the space required by only encoding the characters we need. For example, truncating the 12×16 font we use for buttons and smaller text to only include from the space character up to the capital letters brings its size down from 2284 bytes to 1420 bytes. Similarly, we reduced the font used for the dB display to the digits 0-9, a blank space, a negative sign, a decimal point (or full stop) and the ‘d’ and ‘B’ characters. That takes it down to December 2023  69 RLE compression RLE stands for run length encoding and takes advantage of repetitive values in data; in this case, runs of the same pixel colour. RLE has existed in displays and computing for at least 50 years. RLE is used in the JPEG image standard (although it is only part of the compression used there). It was also used by fax machines (remember them?). For our implementation, rather than storing bitmap data, the data encodes a run of pixels of the same state (on/off). The top bit indicates whether the pixels are on or off (ie, add 128 for on pixels), while the remaining seven lower bits encode the number of consecutive pixels with that property. Fig.b shows a glyph encoded using our RLE strategy. This small font is not a great example for this sort of compression, as the resulting data has ballooned from eight bytes up to 25 bytes. RLE could be seen to encode how often the pixel state changes on each line. So characters such as “1” should encode better than “0” and, indeed, the RLE data only comes to 15 bytes for “1” in this particular font. The space character for this font is encoded as a single byte of value 64, meaning all 64 pixels are off. This variability in glyph size is accounted for by adding a header specifying the number of bytes before each group of RLE data. It’s easy to write code to step through the data jumping forward by the header’s byte count until we reach the glyph we need to display; we then have the count of the number of bytes we need to decode. The RLE-compressed font we ended up with only uses 2013 bytes (including all header data) compared to the 4954 bytes for the uncompressed version. As an extreme example, the space character for this large font (which consists of 2640 black pixels) takes up 330 bytes uncompressed, but only 22 bytes after compression. Another extreme, the ‘0’ character, takes up the same 330 bytes uncompressed but only 196 bytes when compressed, a 40% saving. For the numerals 0-9 and space, the RLE encoding provides a notable saving for fonts as small as 16×24 pixels. Different font subsets, including letters like M and W, will not compress as well as they include shorter runs. Other advantages The microcontroller can copy the RLE-compressed data to the screen faster than bitmap data. There is less data to be read from flash in the RLE case and the decoding is simpler too. The uncompressed bitmap data needs to be decoded one bit at a time. Each individual bit has its value checked, then the appropriate colour pixel is written to the LCD. For the RLE data, a group of consecutive pixels is decoded and can be efficiently sent to the LCD in a tight loop. Similarly, the code to show the RLE-encoded font is smaller 0b01111100 → 0b11000110 0b11000110 0b11000110 0b11000110 0b11000110 0b01111100 0b00000000 0 1  1  1  1  1 0  0   → 1  1 0  0  0 1  1 0   1  1 0  0  0 1  1 0   1  1 0  0  0 1  1 0   1  1 0  0  0 1  1 0   1  1 0  0  0 1  1 0   0 1  1  1  1  1 0  0   0  0  0  0  0  0  0  0 const 0x08, 0x00, 0x18, 0x66, 0x6C, 0x18, 0x00, 0x38, ... 0x7c, char TinyFont[764] = { 0x08, 0x20, 0x5F, 0x00, 0x00, 0x00, 0x00, 0x3C, 0x3C, 0x18, 0x18, 0x66, 0x24, 0x00, 0x00, 0x6C, 0xFE, 0x6C, 0xFE, 0x3E, 0x60, 0x3C, 0x06, 0xC6, 0xCC, 0x18, 0x30, 0x6C, 0x38, 0x76, 0xDC, 0x00, 0x00, 0x00, 0x6C, 0x7C, 0x66, 0xCC, 0x00, 0x18, 0x00, 0x6C, 0x18, 0xC6, 0x76, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // // // // // // // Space ! " # $ % & 0xC6, 0xC6, 0xC6, 0xC6, 0xC6, 0x7C, 0x00, // 0 Fig.a: bitmap font data is encoded with a ‘1’ bit indicating a pixel is set to the foreground colour or a ‘0’ bit if the pixel is the background colour. The last line shows the bitmap data for the number 0. than its bitmap equivalent, about half the size in program flash memory. The bitmap routine also calls another function to perform a multiplication; there would be further savings if the same routine were not needed by other code. Being able to update the display more quickly is a clear upside. We suspect the effect would not be so pronounced with a faster microcontroller, but it would still be present. OLED fonts We have not used RLE fonts in the firmware for the OLED Module. Firstly, these displays are monochrome, so they do not require individual pixel colours to be written. Instead, they expect data to arrive in blocks of eight bits at a time, which maps to eight pixels on the screen. In other words, they natively work with bitmap data. Also, the OLED has a much lower resolution, so it does not need to display very large fonts as often. Given that larger fonts benefit more from RLE, there is less incentive to apply it to the smaller fonts. Bitmaps image compression The Silicon Chip logo shown on the LCD screen is a bitmap and is stored similarly to the bitmap fonts. So, we experimented with a different encoding that stores a run of pixels (from 0 to 15) in each nibble of a byte. The top nibble is assumed to be the background colour, while the lower nibble is the foreground colour. The code to decode this data is similar in speed and program flash memory usage, and we found this algorithm offered about 40% compression on the Silicon Chip logo. So we used this encoding for the logos and icons that are displayed. Conclusion RLE encoding a larger font gives superior image quality than upscaling a smaller font, is faster and can use a similar amount of flash or even less. So it seems like the way to go. The only downside is the extra complexity in the initial encoding. Some font examples can be found at: www.rinkydinkelectronics.com/r_fonts.php Download the FontTweak Font editing program from: www.c-com.com.au/MMedit.htm convert to RLE encoding 0111110011000110110001101100011011000110110001100111110000000000 ↓ 1x0,5x1,2x0,2x1,3x0,2x1,1x0,2x1,3x0,2x1,1x0,2x1,3x0,2x1, 1x0,2x1,3x0,2x1,1x0,2x1,3x0,2x1,2x0,5x1,10x0 ↓ 1,133,2,130,3,130,1,130,3,130,1,130,3,130,1,130,3,130,1,130,3,130,2,133,10 Fig.b: mapping of the pixels to bitmap data is from top left to bottom right in horizontal rows. For an eight-pixel wide font, each row maps to one byte of data. With RLE encoding, each run of same-coloured pixels maps to a byte of data, so one byte can encode up to 127 pixels. It is much more effective for fonts that have more glyphs. 70 Silicon Chip Australia's electronics magazine siliconchip.com.au 4954 bytes before we apply RLE compression. The compression technique used is called run-length encoding (RLE). Rather than storing simple bitmaps for the characters to show on the display, RLE stores a run of pixels as its count and on or off state (hence runlength encoding). The resulting font data is less than half its original size. That is helpful when the font uses up nearly a third of the available flash memory. Another advantage is that the encoding is easy to decompress for display, making screen updates faster! We’ve gone into this in greater detail in a panel, for those interested in that sort of thing. Infrared remote control The IR decoding routine is designed to receive signals encoded with the NEC protocol. It uses pulse position encoding with 38kHz modulation; the IR receiver demodulates this carrier, so the microcontroller only needs to decode the pulse encoding. The microcontroller uses a timer/ counter to measure the pulse lengths and thus extract the necessary data. The NEC protocol transmits 32 data bits, including a device byte, its inverse, a command code and the command code’s inverse. The inverses allow the microcontroller to reject corrupted codes. The Control Module can be programmed to accept different device and command codes, so it can be used with fixed or programmable IR remote controls. We’ll get more into those details later. The Control Module communicates over the SPI bus on the ribbon cable. If an OLED module is present, data is sent out from the Control Module to update its display; the Control Module also receives data back if there has been activity on the rotary encoder or its button. The micro on the control module signals the digital potentiometers to set a new volume level whenever the volume is changed. If the mute function is activated, the volume is ramped down as low as possible, after which the SHDN pin is pulled low to mute the audio fully. Unmuting is simply the reverse. The SHDN pin goes high, then the volume level ramps up. The same process occurs when the unit is powered on, avoiding clicks and pops. siliconchip.com.au Lessons learned during development We solved two significant but subtle problems in developing this design. The first was that, to save components and simplify setup, we generated the +2.75V rail on the Power Supply & Control board and fed it via the ribbon cable to the Volume Modules. The problem with this was that any tiny amount of noise or ripple picked up in the ribbon cable ends up getting injected into the signals because this is a virtual ground rail. Adding extra capacitance to ground for this rail on each Volume Module didn’t fix it. The only way to get acceptable performance was to move the +2.75V rail generation circuitry onto the Volume Modules. The other problem we ran into was that we accidentally used 1μF X7R multilayer ceramic capacitors to couple the signal to the last op amp stage (eg, from pin 1 of IC2a to pin 3 of IC3a). This type of capacitor simply isn’t very linear and the result was a significant rise in distortion below 200Hz, shown by the dashed portions of the curves in Fig.1. There are two solutions to this. Our preferred solution is to switch to using 2.2μF tantalum capacitors, which luckily are available in the same size (the SMA tantalum case is basically the same dimensions as M3216/1206 ceramic chip capacitors). Being electrolytic capacitors, these are not as linear as say plastic film types, but significantly more linear than X7R ceramics. Unlike ceramic capacitors, tantalum capacitors are polarised. There is 2.75V between these points, so the capacitors are orientated with the positive leads to the op amp pin 1 outputs. As a less-desirable alternative, X7R multi-layer ceramic capacitors can still be used but with a significantly higher value; at least 10μF, and ideally 22μF or more. That pushes the distortion down so instead of starting below 200Hz, it starts below 20Hz, which is in the inaudible part of the frequency range. There usually won’t be much signal below 20Hz; our concern is that, if there is, the resulting distortion harmonics could be in the audible range. Hence our preference for the tantalum capacitors. Otherwise, the main loop updates the display when necessary and reads input from the touch panel. We had provision for an IR receiver on the OLED Module, but since the Control Module is mandatory and already has an IR receiver, we have not fitted it to our prototypes and there is no support for it in the firmware. OLED module firmware The microcontroller on the OLED Module monitors the rotary encoder and button for action, sends and receives data to and from the Control Module and updates the OLED screen as required. It acts as an SPI slave device, meaning it must be ready to respond whenever the Control Module wants to communicate. For simplicity, we designed the communication between these two modules to only use a single byte in each direction. The Master sends out the volume level (in steps of 0.5dB) relative to a value of 128. A value of zero means that the mute is active. Thus, the OLED Module doesn’t need to retain any state data; it simply updates its display whenever data is received. Australia's electronics magazine The data that the OLED Module sends back to the Control Module is in a similar format. The OLED module counts the number of rotary encoder steps (forward or backward) that have accumulated and sends that to the Control Module, offset from a value of 128. The offset helps avoid receiving spurious commands if no OLED Module is connected. The data is designed not to use the values of 0 or 255 (00000000 and 11111111 in binary) as might occur if the data line was pulled up or pulled down permanently. A special value of 51 (00110011 in binary) indicates a press of the rotary encoder’s button. This works as a toggle, so the OLED Module does not need to know the current state and simply reports to the Control Module that the mute state needs to change. Next month That’s all we can fit in this month’s article; we will describe construction and assembly in the next issue. Short-form kits for all three modules are available, so you might like to gather the parts together in preparation. SC December 2023  71 Project by Tim Blythman When designing or testing a device that runs from a coin cell, you need to know how much current it draws to determine the cell’s life. That can be difficult given the low currents often involved. This device will power such a circuit while showing the voltage, current and other helpful statistics. Coin Cell Emulator W e have published many designs powered by coin cells (usually the CR2032). They must not draw an excessive current; a high current draw reduces the cell life and causes its voltage to sag due to internal resistance. Coin cells also exhibit a reduced capacity at high discharge rates, compounding the effect. While many circuits can be characterised with a standard multimeter, that doesn’t work well for this type of circuit. A typical multimeter’s shunt on the microamp range has quite a high resistance; values around 100W are typical. That is OK for readings in the microamp range, but when the current draw might briefly jump to 5mA or so, the meter is suddenly dropping half a volt, which can change the circuit behaviour substantially. In other words, the burden voltage starts to dominate the reading. One possible solution is the MicroCurrent DMM Adaptor (April 2009 issue, siliconchip.au/Article/1400). That article discusses burden voltage in detail. However, this Coin Cell Emulator does more than just measure current. It can accumulate the current readings to calculate a capacity value in mAh. It can also produce a varying voltage, so you can test how your circuit behaves as the cell discharges. The Emulator can also mimic some of the non-ideal characteristics of coin cells, such as internal resistance & voltage fall-off as the battery discharges. Design Like the MicroCurrent DMM Adaptor mentioned earlier, the Coin Cell Emulator uses the MAX4238/ MAX4239 ultra-low offset, low noise precision op amp to sense very small currents without influencing them. This op amp has a typical input offset of 0.1µV and an input offset current of 1pA. These are a few orders of magnitude lower than we are trying to Features & Specifications » Emulates the properties of a coin cell, including internal resistance and discharge over time » Emulates reduced capacity at high currents » Adjustable voltage » Current and charge measurement » Stopwatch/Timer » Automatically stops when a threshold voltage is reached » Dummy PCB can be slotted into a coin cell holder » Voltage setting: in 0.1V steps » Typical accuracy: 1% » Current measurement: 0.1μA resolution up to 200mA » Charge measurement: 1μAh resolution up to 9Ah » Voltage measurement: 0.01V resolution up to 3.4V » Time measurement: 1s resolution up to 999 days 72 Silicon Chip Australia's electronics magazine measure, so they are unlikely to interfere with our readings. This is a necessary feature but insufficient to ensure we can measure a wide range of currents. Our design has an upper limit of around 200mA but can measure down to 0.1µA. To do this across a single range would require an ADC (analog-to-digital converter) with 21 bits of resolution. Instead, our design uses two ranges and a 12-bit ADC that’s built into the microcontroller. Oversampling (making multiple measurements and averaging them) gives us a few more bits of resolution, providing the necessary dynamic range. Circuit details Fig.1 is the circuit diagram for the Emulator. 5V power comes in via mini-USB connector CON1, with a 10µF capacitor providing board-level supply bypassing. IC1 is an eight-bit PIC16F18146 microcontroller that controls and monitors the Emulator’s operation. IC1’s internal DAC (digital-to-analog converter) can deliver 0-4V from pin 17. Unlike some older PICs, the DAC on the PIC16F18146 has an internal buffer and thus has a reasonable drive strength. The DAC voltage goes to NPN transistor Q1’s base via a 1kW resistor. Q1 is configured as an emitter follower, so its emitter ranges from 0V to 3.4V, about one diode drop below the 4V maximum from the DAC. Its collector is connected to the 5V rail. The emitter-follower relies on the reasonably constant base-emitter forward voltage of around 0.6V. Assuming the base voltage is constant, the siliconchip.com.au Fig.1: the cunning part of this circuit is the op amp feeding current back into the output through the 10kW resistor to cancel out the voltage drop across the 22W resistor. This allows the circuit to work with two current measuring resistances of vastly differing values, giving it a very wide current measurement range. transistor switches on harder if the voltage at the emitter drops, increasing the collector-emitter current and raising the voltage at the emitter. If the emitter voltage rises, the transistor base current decreases, and less current comes in through the collector. So the circuit maintains the emitter voltage at a steady ~0.6V below the base voltage. A 1µF capacitor provides some filtering and can provide brief bursts of current to the load. The 1kW emitter resistor provides a stable load and ensures that the output voltage decreases if the base voltage decreases. The 22W resistor acts as a current measuring shunt, with two of the microcontroller’s ADC pins monitoring the voltage across the shunt via 10kW resistors. Each ADC pin also has a 100nF capacitor to ground to present a low impedance to the ADC sampling stage. The ADC pins are labelled VSHUNT, upstream of the shunt resistor, and VOUT, downstream. siliconchip.com.au The downstream side of the 22W resistor is the positive side of the emulated coin cell, with circuit ground being the negative side. This is available at a pair of 2-pin connectors (CON3 and CON4) and a couple of large pads on a circular part of the PCB. This part of the PCB has a pad on each side and can be slotted into some 2032-sized coin cell holders. Op amp IC2 has its input pins (pins 2 and 3) connected across the 22W shunt, with its output (pin 6) feeding back into the low side of the shunt via diode D1 and a 10kW resistor. A third ADC pin of IC1 (pin 10; labelled ILSENSE) monitors the voltage at the diode’s cathode via another 10kW resistor and 100nF capacitor arrangement. A 100nF capacitor bypasses IC2’s 5V supply (pin 7) and ground (pin 4). Pin 1 (SHDN) is also pulled up to the 5V rail, allowing the op amp to operate normally when powered. Op amp operation If a small current flows through the Australia's electronics magazine 22W resistor, a voltage appears across the op amp’s input terminals and its output rises. Current flows through the diode and 10kW resistor back to its inverting input and the downstream end of the shunt resistor. The diode ensures the op amp can only source and not sink current. Effectively, the op amp overrules the shunt and supplies current to the output of the Emulator. Smaller currents can be sensed by measuring the voltage across the 10kW resistor and applying Ohm’s Law. Eventually, the op amp output saturates and cannot supply enough current. It has nearly rail-to-rail operation, so its maximum output is around 4.9V. Assuming the Emulator output is at about 3V, there is around 1.3V across the 10kW resistor, with the op amp supplying around 130µA. Coin Cell Emulator Kit SC6823 ($30 + postage): contains all parts and the optional 5-pin header. December 2023  73 The Coin Cell Emulator is a compact but handy development and testing tool. Even if you don’t design circuits for coin cell operation, it’s a useful low-voltage PSU with current monitoring. The voltage across the 22W resistor can now develop and is measured by the ADC channels connected across it. We can thus measure across a wide dynamic range since we are effectively using two shunts with vastly different resistances. Combining the currents is as simple as adding them. Using a high-side measuring shunt also means that the ground circuit is uninterrupted and can be shared with any other gear that needs to be attached (programmers, debugging gear or other meters) without affecting current readings. This is handy, especially if you are running everything from a computer. The test point labelled RST was originally included to allow the Emulator to control a connected circuit by pulsing its reset line low. But since the Emulator can power cycle the circuit, we did not implement this feature. Instead, a nominal 1Hz clock signal is available at this pin. This can be used to trim IC1’s internal timer for accurate timekeeping. Short circuit handling Let’s examine what happens when a short circuit is applied to the output of the Emulator. With the DAC set to its maximum of 4V, around 140mA flows through the 22W resistor. With a typical transistor β (gain) of around 400, the base current is around 350μA and the 1kW resistor on Q1’s base drops 0.35V, so the voltage at the emitter falls from 3.4V to around 3V. The transistor thus dissipates around 280mW (2V × 140mA), comfortably within its 500mW rating. The remaining voltage is across the 74 Silicon Chip 22W resistor and it dissipates around 400mW. That’s a bit on the high side for the typical 1/4W rating of an M3216/1206-size SMD part. Our prototype got quite hot around that resistor with the output short-circuited, but it was not damaged. 1/2W resistors are available in this size, so that’s what we’re specifying. That allows the Emulator to handle a short circuit on its output indefinitely. ADC input impedance One design consideration was ensuring that the ADC sampling did not unduly load the Emulator’s output. A load of even 1MW to ground would be measurable, as it would draw 3µA at 3V. Two ADC channels are fed directly from low-impedance sources and unaffected by loads; transistor Q1 and op amp IC2 drive the VSHUNT and ILSENSE lines, respectively. Effectively, they are upstream of their respective shunts. On the other hand, any load applied to the VOUT line would be indistinguishable from a load at the Emulator output. The ADC input used to sense the VOUT voltage is such a load. The ADC input consists of a small capacitor, nominally 28pF, which is connected to the ADC pin to sample the voltage. The capacitor is then connected to the internal ADC circuitry (and disconnected from the pin) to perform the conversion. The ‘switched capacitor’ model can be used to calculate an equivalent DC resistance. A switched capacitor is simply a capacitor that is switched between two different connections at a known frequency. The resistance of such an arrangement is simply 1/CF, where C is the capacitance in farads and F is the frequency in hertz. With our 100Hz sampling, this comes out to around 350MW, which is more than high enough. Higher sampling rates would reduce this apparent resistance. Another point to consider is that the ADC capacitor is not discharged between samples, so the load presented by the switched capacitor is not equivalent to a load to ground, but rather as a resistance between the different sampling points. That raises its effective resistance. Australia's electronics magazine The PIC16F18146 has an ADCC (analog to digital converter with computation) module. We previously used some of its advanced features in the Digital Boost Regulator (December 2022; siliconchip.au/Article/15588). The differential ADC inputs make it much easier and more accurate to measure the difference between two voltages, as we are doing here. The sampling time is also programmable, so we have extended it slightly to ensure the sampling capacitor can fully settle at the input voltage. There is also a DIA (device information area) that holds information such as the measured value of the chip’s internal voltage references. This means we can measure voltages against this reference without a separate calibration step. The DAC mentioned earlier is an 8-bit type with a 4.096V (nominal) voltage reference. It can deliver up to around 4V in 16mV steps and can produce a voltage with 0.1V precision. The output voltage at VSHUNT and VOUT is thus limited by design to around 3.4V. This works well with circuits using 3.3V microcontrollers that typically have a 3.6V upper limit. The MAX4238 op amp specifies a common mode voltage up to around 3.6V (with a 5V supply) and the op amp inputs stay within that range. Microcontroller and interface IC1’s pins 2, 3 and 5 connect to switches S1, S2 and S3, respectively, with their other sides grounded. The micro applies an internal weak pullup current to each, so it can detect button presses as level changes on those pins. An I2C OLED module is connected to IC1’s pins 12 and 13 for the SDA and SCL signals. The OLED is powered from 5V; it has an onboard 3.3V regulator with I2C pullups, allowing it to interface with a microcontroller running from 3.3V or 5V. IC1 has a local 100nF bypass capacitor between its pin 1 supply and pin 20 ground. Pin 4 (MCLR) is pulled up to 5V by a 10kW resistor, allowing the microcontroller to run. These pins and pins 18 and 19 (PGC and PGD) are taken to CON2 for in-­ circuit serial programming (ICSP) of the microcontroller. Coin cell behaviour model As the saying goes, all models are incorrect, but some are still useful! siliconchip.com.au There are several characteristics of coin cells that we are explicitly modelling. We’re not claiming that the model is comprehensive, but it mimics the behaviour of a real coin cell well enough to be useful. Our model is based mainly on a CR2032 cell, as that is what we have used the most. We fitted graphs provided by several CR2032 manufacturers to curves described by simple equations, adjustable by a single parameter. There is a lot of variation between manufacturers and even between cells from the same manufacturer under different conditions. The default behaviour of the Emulator is similar to a typical coin cell. Firstly, coin cells have internal resistance. For CR2032 cells, the value is around 20W, but it can change with load and state of charge. Other 20mm diameter cells, such as the CR2016 (half as thick as a CR2032 at 1.6mm), appear to have a similar internal resistance. So the Emulator will also be suitable for thinner cells of the same diameter but might not be as accurate for those with a smaller diameter. A simple way to model the internal resistance is with a fixed resistor, and we chose the 22W part that we have already explained. One advantage of using a fixed resistor is that this resistor can also be used as a current measuring shunt. The actual circuit appears to have an internal resistance of around 24.5W, as the 1kW base resistor carries a current in proportion to the load current divided by the β (gain). So it adds We have used a socket header to attach the OLED module in our prototype, but the Emulator will be much more robust if you solder the display directly to the main PCB. around 2.5W (1000W ÷ 400) of resistance for a β of around 400. The next factor is that, like most batteries, the terminal voltage drops as the cell discharges until it is flat. For coin cells, the voltage drops a little at the start, then is quite steady for most of the cell life. Once it starts to fall after that, it does so quite dramatically. While we looked at using a curve to model this, curves that fit all three stages were complex, and we found that they weren’t helpful for observing circuit behaviour as the cell goes flat. Instead, we have implemented a simple model that maintains a flat voltage and then linearly changes the output voltage as the cell’s state of charge (SoC) nears its endpoint. For example, with this set to 10%, the voltage is flat from 100% to 10% SoC, then drops to half by 5% SoC. Finally, the voltage is ramped to zero when the Emulator determines the cell is flat. This feature can be turned off (set to 0%) to disable this behaviour. Fig.2 shows the graph of the data sheet behaviour compared with the emulated behaviour. Fig.2: our emulated cell voltage curve is much simpler than that seen in many coin cell data sheets, but it still mimics the cell going flat. Otherwise, we prefer to manually adjust the voltage and observe what happens. siliconchip.com.au While we could have more closely emulated this with, say, four linear sections, we decided not to do that. We found that a constantly changing voltage during use interfered with monitoring the device’s operation. In other words, we have sacrificed reality for usability. Our simple voltage curve provides a voltage that behaves very predictably. It does omit the higher voltage at the start, but that can easily be emulated manually by initially setting the voltage to 3.2V, observing the operating, then manually dropping the voltage to 3V. Another well-known aspect is that a cell’s apparent capacity (in mAh) is reduced if it needs to supply a heavier load. The manufacturers also provide graphs to characterise this behaviour. One typical graph we saw showed that a nominally 240mAh cell provides only 150mAh with a continuous discharge of 3mA, nearly halving its effective capacity. We found quite a few curves that demonstrate this behaviour. The data varied quite a bit, but it was clearly some form of polynomial relationship. Fig.3: the reduction in useful capacity is modelled as a straightforward quadratic curve. It’s a compromise between simplicity and accuracy. Australia's electronics magazine December 2023  75 Firmware The Coin Cell Emulator shown at actual size, along with the wire added to the back of the PCB (right). This increases the thickness of the PCB to bring it nearer to that of a CR2032 cell (3.2mm thick vs 1.5-1.6mm thick for the PCB). You’ll need to apply a bit of heat to get the solder to take to the large copper area. A good technique for finding the order of polynomial relationships is to take a plot of the logarithms of the variables in question. The order of the polynomial is related to the slope of this graph. Consider the quadratic equation y = x2. The value of log(x2) is equal to 2log(x), for positive values of x, so the graph of log(y) or 2log(x) against log(x) would have a gradient of two, suggesting a quadratic equation of some sort (a quadratic is a second-order polynomial). We found that the slopes of these log/log plots were just over two. So we modelled this with a quadratic equation and found that it fit quite well to the manufacturer data and was simple enough for the 8-bit micro to calculate. We didn’t see any charts that show behaviour much above 5mA but this model also allows us to extrapolate. This extrapolation suggests severely degraded capacity as the current enters this region. Our experience is that coin cells discharge very quickly if you draw much more than 5mA from them, so this makes sense. Our model takes a parameter equal to the current at which the cell capacity is halved. We have used a default value of 3.5mA, which matches the CR2032 data sheets we examined. It also makes it easier to match your Emulator to a specific cell if required. If this value is set to zero, then there is no modelling and the Emulator will show the same capacity no matter what current is drawn. Fig.3 shows the graph of the model against typical data from a cell data sheet. Regarding the short circuit behaviour noted earlier, it should be apparent that, like a real coin cell, the Emulator will quickly ‘go flat’, effectively ending the short-circuit condition. Fig.4: the rise time of the output is limited by the capacity of the circuit to supply the current to charge the 1µF capacitor at its output (the timebase is in µs here). The DAC that controls the voltage has a settling time of around 10µs. 76 Silicon Chip For the most part, the microcontroller allows the user to set the output voltage, although it can modify that based on the discharge modelling. It monitors the voltages around the circuit and calculates and sums the currents in the two measuring shunts. A timer keeps track of time intervals and allows the current to be accumulated over time for the charge and capacity calculations. The measured charge (in mAh) is taken from the actual value, while the SoC calculation is based on the modified behaviour at higher currents. All this information is displayed on the OLED screen. There are modes to allow a test to be started and paused. These tests turn on the output voltage, start the timer and start the charge accumulator. The test can be ended manually or automatically at a previously set endpoint voltage. Alternatively, the Emulator can simply be used as a power supply that can monitor the current consumed by the circuit under test. A settings screen can be used to trim the parameters used to set the output voltage. Since the Emulator can measure its output, a calibration routine can set these automatically. You can also trim the resistance values of the shunt resistors and adjust numerous parameters that control the coin cell emulation. Since the PIC16F18146 has an internal EEPROM memory (which can withstand more write cycles than flash Fig.5: the longer fall time of the Emulator output is almost entirely due to the 1ms time constant of the 1kW/1µF RC combination. After about 4ms (four time constants), the voltage settles near its 0V endpoint. Australia's electronics magazine siliconchip.com.au Assembly The Emulator is built on a small PCB with surface-mounting components. They are the typical range of SOIC, SOT-23 and M3216/1206 parts that are fairly easy to solder. Fig.6 is the PCB overlay diagram; you can also refer to the photo of the PCB before the OLED module is attached. We recommend using a fine-tipped soldering iron, solder flux paste, thin solder wire, tweezers, a magnifier and good lighting. Solder wicking braid is helpful for removing bridges and excess solder. Work outside if you don’t have good ventilation or fume extraction. 1 double-sided PCB coded 18101231, 78 × 44mm 1 Mini-USB SMD connector (CON1) 1 5-way right-angle male header, 2.54mm pitch (CON2; optional, for ICSP) 1 1.3in I2C blue OLED module (MOD1) [Silicon Chip SC5026] 3 2-pin SMD tactile switches (S1-S3) 4 small self-adhesive rubber feet Semiconductors 1 PIC16F18146-I/SO microcontroller programmed with 1810123A.HEX, wide SOIC-20 (IC1) 1 MAX4238 or MAX4239 low-offset op amp, SOIC-8 (IC2) 1 BC817-40 NPN transistor, SOT-23 (Q1) 1 LL4148 SMD diode, SOD-80/MiniMELF (D1) Capacitors (all SMD M3216/1206 X7R) 1 10μF 10V 1 1μF 16V 6 100nF 50V Resistors (all SMD M3216/1206 1% ¼W unless noted) 5 10kW (code 1002 or 103) 2 1kW (code 1001 or 102) 1 22W ½W (code 22R0 or 22R) MAX4239 K CON3 1 10 m F 100nF 100nF + 10kW BC817 – + CON4 – 1kW Q1100nF10k 1kW 1mF 22W 10k 100nF Start with the mini-USB socket, CON1. Apply flux to all its pads and rest the part on top. Its locating pegs should lock into holes in the PCB, aligning it. Clean your iron’s tip and add a small amount of fresh solder, then touch it to where the pins meet the PCB pads. After that, apply a generous amount of solder to the four larger pads that affix the connector’s shell. If you have bridges between the pins, add some extra flux and press some fresh braid against the bridge with the iron. When the braid has taken up solder, slowly draw both away together. If the part is flat against the PCB, surface tension should leave enough solder to form a solid joint. Fit Q1 next by spreading flux on its PCB pads and resting it in place, being sure to align the body with the silkscreen printing. Tack one lead, ensure the part is flat and aligned within all pads, then solder the remaining leads. Solder the two ICs next, using a similar process, starting with one lead to locate the part. Both ICs should have Parts List – Coin Cell Emulator IC1 PIC16F18146 D1 4148 100nF 10kW LL4148 CON1 RS T GND VCC SCL SDA 10kW MOD1 IC2 Figs.4 and 5 show the rise and fall times of the output voltage in response to a change in the setpoint. These charts were taken in an unloaded state (although the Emulator accurately indicated the expected 0.3µA draw from the 10MW scope probe at 3V!). As expected, the rise time is short, about 20µs from 0V to 3V. About half of this is due to the 10µs settling time of the DAC, with the other half being the time to charge the 1µF capacitor with the 200mA available. The fall time is dominated by the 1ms time constant of the 1kW/1µF pair and takes about 4ms to settle near its final value. An external load will speed this up. CON2 100nF Response time Fig.6: assembling the PCB mainly involves fitting SOIC and M3216/1206 SMD parts. Take care with the orientation of the two ICs and D1. ‘Mousebites’ are provided so you can separate the PCB between CON3 and CON4; the two halves can be rejoined with some light-duty figure-8 wire. ICSP memory), the calibration and setup parameters are immediately stored in EEPROM when modified. S1 S2 S3 a small pin 1 divot in one corner, so align that with the PCB markings. For IC2, this might be a notch at the pin 1 end. For diode D1, ensure its cathode stripe aligns with the ‘K’ marking on the PCB. After this, none of the components are polarised. The capacitors will not be marked, so be careful not to get them mixed up. The resistors will be marked with codes, as shown in the parts list. The PCB will now need a thorough cleaning to remove flux residue. At the minuscule currents the Emulator measures, any contaminants can cause leakage and interfere with measurements. Your flux might recommend a solvent, but we find that isopropyl alcohol works well (another great option is Chemtools Kleanium G2). Wipe away any excess solvent and allow the remainder to evaporate thoroughly. Give the PCB a thorough check now that it has been cleaned, as any problems will be easier to spot and repair before the OLED is fitted, as it covers many of the components. Now solder on the three tactile switches, being sure to align them within their silkscreen outlines and keep them flat against the PCB. If you need to program your microcontroller, add the CON2 ICSP header. Next, solder the OLED module in place using its four-pin header, aligning the pin markings and spacing it above the other components on the PCB. When you are happy with its location, solder stiff wires to the lower corners of the OLED module and secure them to the through-hole pads in the PCB below. Finally, attach the rubber feet to the underside of the PCB so it won’t scratch your work surface. Programming PICs supplied in kits or purchased separately from our Online Shop come December 2023  77 Table 1 – Settings Page – Parameter Notes Set Cap The default allows for brief tests. It can be set from 1-10mAh steps of 1mAh or up to 250mAh in steps of 5mAh. Endpoint It can be set from 0 to 3.4V in 0.1V steps, the same as the output voltage. Current Comp. The current at which the effective cell capacity is halved. It can be set in steps of 0.1mA; if set to 0mA, there is no compensation. 3.5mA is typical for CR2032 cells. Voltage Fall Below this level, the cell voltage setpoint is linearly decreased to reach 0V at 0% SoC. If set to 0%, then there is no decline in voltage. Nominal emulated cell capacity Default = 10mAh The voltage at which tests stop Default = 2V Determines how cell capacity is affected by high currents Default = 3.5mAh SoC at which the cell voltage starts to decline Default = 5% Screen Calibrate Ensure the output is not connected to any loads and press S1 to start. This sets the Q1 Vbe and DAC span automatically. Pressing S2 sets all parameters back to their defaults. Set Q1 Vbe Set by the Calibrate step. If voltages across the range are still too high, increase this value. There is a slight offset below 0.3V output; voltages are not as accurate in that range. Set DAC span If the voltage offset increases across the range, decrease this; if it becomes lower, increase it. Set R(hi) (22W) It can be set in steps of 0.01W within 10% of 22W. 1% parts should not need calibration. Set R(lo) (10kW) It can be set in steps of 1W within 10% of 10kW. 1% parts should not need calibration. Trim Timer The Emulator’s 1Hz clock is available at the RST pin (with respect to ground). This can be measured to help trim the timer. Each step will change the frequency by about 0.4%. Exit Setup All values are saved to EEPROM as soon as any changes are made and new settings are used immediately. Start automatic calibration voltage Transistor Q1 baseemitter junction voltage Default = 588mV The nominal span of the DAC output Default = 4002mV Actual value of 22W resistor Default = 22.00W Actual value of 10kW resistor Default = 10000W The displayed value is the period of the timer counter Default = 243 Press S1 to return to normal operation 78 Silicon Chip Australia's electronics magazine programmed, so skip this section if you have one of those. The PIC16F18146 requires a PICkit 4, PICkit 5 or Snap programmer. If you are using a Snap (which does not provide power), you can supply power using a USB cable connected to CON1. You might need to use some short extension wires to prevent the Snap from fouling the USB cable. You can use the Microchip IPE to program the 1810123A.HEX file. If you don’t have the IPE installed, it can be downloaded and installed for free as part of the most recent MPLAB X IDE. Once programmed, the startup OLED screen should look like Screen 1. Setup The Coin Cell Emulator is usable without calibration, but we recommend doing it since it is easy and only needs to be done once. Hold in S3 until the screen goes blank, then release it to enter SETUP mode. Table 1 summarises the individual setup pages you can cycle through by pressing S3. In general, S1 decreases a parameter while S2 increases it. On some pages, they trigger specific actions, such as starting the automatic calibration process or returning to normal operation from SETUP. The first four SETUP screens relate to the emulation settings and can be skipped to reach the calibration settings. We recommend just running the automatic “Calibrate” step. If the Emulator’s other measurements are off, you could consider changing other values, such as the resistances or timer trim. Cycle to the Exit Setup page and press S1 to return to regular operation. Connections CON3, CON4 and the circular pads can all be used to connect to a circuit under test. For most of our prototyping, we simply used a header socket for CON3 and ran jumper wires to our circuit. The circular section of the PCB is designed to be slotted into the side of a cell holder. The photo opposite shows the Emulator connected to our Advanced Test Tweezers. It probably won’t work with other cell holder types where the cell is inserted from above. Since the PCB is only 1.6mm thick, it will not be a tight fit for holders that siliconchip.com.au Screen 1: the initial screen seen when the Emulator powers on allows the output voltage setpoint to be changed with pushbuttons S1 and S2. S3 switches to the other screens. Holding S3 for three seconds enters the Setup mode, shown in Table 1. Screen 2: the output can be toggled on and off when this screen is shown. Note also the supply voltage display at upper right. If this is flashing, the supply is lower than 4.5V or higher than 5.5V, and the Emulator may not function correctly. Screen 3: S1 and S2 start and reset the stopwatch timer and charge accumulator measurement, respectively. If the timer is running, this screen will show PAUSE instead, with S1 pausing the timer if pressed. expect a 3.2mm-high CR2032 cell, although many holders are designed to accept 1.6mm thick CR2016 cells. You could carefully bend the cell holder’s tabs to add more tension. We also added some thickness to the Emulator by soldering on some pieces of wire, as shown on page 76. Another option is to carefully break the PCB between CON3 and CON4 (there are ‘mouse bites’ in the PCB to facilitate this). You could then run a pair of wires between CON3 and CON4 to join them. the emulated cell is nearly flat. The fourth line (in larger text) shows the measured current. It is in a larger font as it is the most important parameter to observe. If “I(lo)” is shown, the reading is expected to be accurate to 0.1µA as only the 10kW resistor is being used as a shunt. When “I(hi)” is shown, the Emulator has switched to the higher range and the 22W resistor comes into play. When this happens depends on the output voltage and supply voltage (which relates to IC2’s headroom). At 3V output, it will occur at around 130μA. The second-last line shows the stopwatch timer, which measures up to 999 days, or almost three years. The text on this line indicates if the timer is running and, if so, the charge measurements on the next line are also accumulating. The µAh reading on the last line measures actual charge consumption (not adjusted). It can be used to validate the total current consumption and estimate potential capacity losses due to high current usage. The SoC figure does take into account the adjusted current. Pressing S3 shows Screen 2, which allows the output voltage to be switched on and off; S1 switches it off, while S2 switches it on. Screen 3 is reached by pressing S3 again; it allows the timer and charge accumulator to be paused, started and reset. S1 will start and pause the timer, while pressing S2 resets the timer and accumulator when the timer is paused. Press S3 again to reach Screen 4. Pressing S1 (“GO”) on this screen will switch on the output voltage and start the timer and accumulator; S2 (“PAUSE”) will pause the timer and switch the output off. Thus it can be used to start and stop testing cycles. Once you’ve started a test, the current draw will be shown, and the timer and accumulator will go up while the SoC goes down. As the SoC passes 5%, the output voltage will drop to simulate the cell running flat. When the output voltage reaches the endpoint, the test will pause, as if S2 were pressed on this screen, allowing the statistics to be recorded. Operation Screen 1 shows the default Emulator cell voltage of 3V, which can be changed on that page. Other features on Screen 1 are common to the operating Screens. The third line of text shows the status of the output voltage; the first figure is the setpoint (target) output voltage and whether it is on or off. The other voltages are the values upstream and downstream of the shunt, respectively. They can be considered the internal cell voltage and external ‘terminal’ voltage, respectively. The first should be very close to the set voltage (when on), except if Conclusion We’re already making good use of the Coin Cell Emulator in designing an upcoming project. It’s also coming in handy as a general power supply SC for low voltages and currents. The circular section of the PCB is designed to slot straight into the cell holder we’ve used for various projects, including the Advanced Test Tweezers shown here. In this case, testing would be easier if we separated the PCB between CON3 and CON4 for a more flexible connection. Screen 4: pressing S1 here starts the timer and charge accumulator and switches on the output voltage. S2 pauses the test, allowing the results to be recorded. The test will be automatically paused if the Emulator reaches its endpoint voltage. siliconchip.com.au Australia's electronics magazine December 2023  79 SERVICEMAN’S LOG Mixing it up a bit Dave Thompson It’s frustrating when there is a flawed product on the market, and instead of recalling or fixing it, the manufacturer blames the user instead. Your mobile phone has no reception? You must be holding it wrong! This time, it was our blender, and I had to turn to other users for a solution… It’s hard to be a serviceman these days without hearing ominous stories about the ‘right to repair’, especially regarding large US corporations. This has become a really hot-potato topic and indeed has been commented on with some insight by the Editor and other contributors to this magazine. One of the most serious concerns is the increasing use of subscription models for hardware, which is becoming more and more ‘de rigueur’. I think that is terrible news for consumers and repair people. Court cases and laws preventing monopolies and protecting the right of repair for consumers have driven some companies to introduce subscription models, so they are assured of continued income as well as protecting their ‘intellectual property’. One way they do that is by trying to maintain control of their products after they are sold. I suspect this will put many local repair people and servicemen out of work, often in very small communities, unless, by some miracle, they can score a maintenance contract with the vendors. No doubt they would demand exclusivity anyway. If the manufacturer designs products so that only they can reactivate them after a part is changed, how is anyone else supposed to fix them? The repair business isn’t what it used to be So, a bleak outlook, then. My own computer repair business, almost 30 years old now, has seen the wave and wane of the industry. Throw in a deep recession in the late 2000s and the city and my workshop being ruined by earthquakes in 2011, and it’s a wonder we still have a business at all. At one point in the mid-2000s, we were averaging 65 calls a day. I employed four guys and two vans on the road. These days, it is just me, and I’d be lucky to get 65 calls in six months. It turned out this way because computer service and repair have long been sunset industries. These days, it’s all mobile devices, and they are consumable, so if one is dropped and broken, insurance or savings pays for a new one. In some cases, data recovery may be required, but even that is moot as much of our stuff is backed up in ‘the cloud’ anyway. Every bread-and-butter job we had in the 2000s has long since disappeared, only to be done now by techsavvy householders or the advent of self-install plug-andplay internet. That’s OK with me, as I am nearing that age where I’ll hang up my floppy drive anyway. But for dozens of other companies and service guys, this really is the end of an era. Manufacturing for unrepairability It’s the same with just about everything these days. Most appliances, for example, are manufactured without repair in mind (or, if you are a bit cynical, with anti-repair in mind). If you can even source replacement logic or controller boards, they are usually hellishly expensive because they just aren’t made as available as they were in the past. The manufacturer wants you to buy a whole new unit, not fix the broken one. That’s one reason why repair being monopolised by manufacturers is so troubling. There is a conflict of interest, so they are more likely to quote you unreasonably high repair prices in an attempt to convince you to give up and buy a new one instead. My wife bought a high-end food blender/mixer type thing a while back, and overall, it works pretty well. It has this thing called “wireless detect”, which took us a while to figure out, but all we really use the thing for is blending and mixing, using the various controls on the front of the machine. One thing that always annoyed me is that it will only run with a jug or attachment sitting in it. Actually, many blenders have such a safety feature that prevent them from being used with nothing attached to them. In this particular 80 Silicon Chip Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • Overly complex food mixer ‘repair’ Tracking down interference using an SDR Three different antenna repairs Dual tracking power supply excessive ripple 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 model, this wireless detection feature allows the mixer to detect different-sized attachments and adjust pre-set programs automatically. In other words, it detects the particular attachment and adjusts things accordingly. As there are quite a few different-­sized glass grinder bowls and cups available as optional extras, it seemed like a handy feature to have. These attachments are basically glass bowls that screw into the base that has the blades built into it. The whole thing then mounts on the blender. The glass bowl part is removed from the hard-plastic blade-driver section for loading whatever you want to grind into it. Let’s say you want to make some powdered salt. You fill the glass bowl with the desired amount of granular salt, invert the blade-holder part and screw it blades-first to the glass bowl. You then flip the whole thing up the other way and plop it, blade side first, onto the top of the blender, engaging the splined drive socket. You can then use one of the pre-programmed routines or manually drive the mixer using the controls. An exercise in frustration It all seems simple enough. Except, on this model, with the wireless detect feature, you have to have the main mixing jug, one of these herb grinders or any of the other attachments installed on it to even power up. And it turned out to be so finicky that it made it almost unusable. The main jug – the one that comes with it – seems solid enough in operation. However, those optional glass bowl attachments have what I discovered are NFC (near-field communication) chips buried inside them that are read by electronics inside the device. In practice, though, the majority of the time we tried to use these attachments, the mixer would not detect that the bowl was in place, so it would not start. It was the same with all the attachments we bought for it. Obviously, this was not going to fly. The attachments have arrows moulded into them that show how much the two halves should be torqued for the thing to work, but even when the arrows are perfectly aligned, it just will not switch on most of the time. That certainly created a lot of blue language from the kitchen! Another problem is that, given the size of the smaller attachments, cranking them up to have the arrows aligned means crushing a large O-ring type seal between the two halves. Trying to undo them once torqued is nigh on impossible for my wife and almost impossible for me. The whole thing was starting to reek of poor design and implementation. siliconchip.com.au Of course, this whole idea is product protectionism cleverly disguised as a safety mechanism because thirdparty fittings and attachments that don’t have the correct NFC tag will not work. Only original attachments can be used on this mixer, and they’re not cheap. When it works, it works well, but getting it to work was often highly frustrating for us. Our first stop was the big-box store where we had bought the main unit, along with these extra fittings we thought we’d need. Of course, the guy there, while extremely knowledgeable when we were shopping for it in the first place, now seemed to be struck dumb and claimed he’d not heard anything from customers about it. Perhaps our one was faulty, and if we liked, he could feed it back through the warranty system and in just six short weeks, we could have it back. It was only a month old at this time, so I suggested that if he thought it was faulty, perhaps they could see their way clear to replace it under the Consumer Guarantees Act. Well, you’d think I’d suggested sending his grandmother on a one-way trip to Switzerland! That solution apparently wasn’t going to happen, for various reasons, first and foremost because we had used the mixer! I contemplated going through the finer points of finding faults without actually using an appliance. Still, this guy had obviously been down the annoyed-client road before and, like a debating team captain, had a pat answer prepared for everything and anything I could say. At this point, my serviceman’s lizard brain kicked in, and I thought I’d open it up, have a look and see if there was anything I could do. Perhaps the sensor had fallen off or had been glued in at an angle, or something silly that I’d be able to fix with my rudimentary knowledge of blender repairs. I mean, how hard could it be? We all know the answer to that, and you’d think that after all these years, I’d know too! Australia's electronics magazine December 2023  81 At least it was well made Pulling this thing apart was not that difficult. These are ‘proudly’ made in the USA and using American-made parts, or so the blurb states. That means no dumb security screws, just straight-forward, meat-and-three-veg screws that can be undone with a longish-reach Posidrive screwdriver. Everything came apart so easily. No breakaway clips, no hidden screws under mouldings. Very refreshing! I did have to pop out the rubber feet from the bottom to reveal some case screws, but I’ll give them that as a neat design. Once the screws were out, the two halves of the case came apart easily. There are no warranty-voiding stickers across the join or any of those breakable foil screw covers over anything. At least these appliances are designed to be repaired, and I like that a lot. Spares are apparently widely available from what the sales guy told me the first time we were at the shop looking into buying one. Inside is what you’d typically find in a blender. After removing a well-made protective metal cover, I could see the main space was taken up with a large brushed motor. It directly powers a splined drive socket at the top of the mixer via a square drive shaft at the end of the motor’s armature. The splined drive socket is easily removable by loosening a grub screw with an Allen wrench, if need be, and while the splined and square drive parts are cast from relatively heavy metal, the body of the drive socket is hard plastic. This is actually by design; if something in the jug or bowl fouls the blades and stalls the mixer, this plastic moulding will shear or crack, and the metal square-drive part of it will just spin harmlessly inside the moulding to protect the motor from stalling and potentially burning out motor windings and electronics. It is a relatively crude but very effective protection system. Replacement drive sockets are inexpensive and readily available. Another big plus for the repairability of this device. The mouldings and mounting for the motor and electronics are all super heavy-duty plastics, almost like Bakelite, especially given what I usually see in most cheaper modern appliances. This is definitely higher quality, and it is typical of the brand. The unit is certainly built to last, which you’d hope for, given the relatively high purchase price. The front panel controls – two toggle switches, a speed control pot and the LED display – are all directly mounted to a circuit on the inside front of the case. This PCB is populated with the usual mix of SMDs and discrete components, with heavy wiring to the motor and power switch on the right rear side of the mixer. It all looked pretty standard and what I would expect to see in any reasonably advanced blender. However, I could see nothing in or around the top of the unit that resembled an NFC reader, so I assumed it was mounted on the main circuit board instead. This ‘initiator’ side of the NFC system should throw out a magnetic field that would (hopefully) detect the passive NFC chip embedded in the attachments and then allow the mixer to be powered up, or not. The thing is that I could see the NFC chips embedded in the glass bowls on opposite sides, so why was this not detecting attachments 90% of the time? As the attachments have a spline-shaped base, they can sit at any angle in the drive system, but no matter where they sat, the blender 82 Silicon Chip would not detect them most of the time. There seemed to be no rhyme or reason. So, to my mind, there was either a fault with our unit or the NFC system is somewhat flawed. I reassembled the blender, as there was really nothing I could do, except feel a little better that I had at least tried to do something! An unexpected solution Next, I did what I always do and hit the web to see what was going on. Perhaps unsurprisingly, it turns out that this is a well-known problem with these blenders; a lot of people were moaning about it in online forums and videos. Nice one, big-box store guy; we won’t be shopping with you again! As is typical with the information available, there is a lot of it, and not much is helpful. Plenty of these slick kitchen-type presenters were talking as if we were imbeciles and saying all we have to do is align the arrows on the attachments, and it will work. Oh really? They are either completely ignorant or wilfully obtuse, and the comments sections usually refer to the former. While there are no instructions with the attachments, and the arrows are pretty hard to find unless you are looking for them, this resolution didn’t seem to help the majority of affected consumers. The party line from the manufacturer themselves was that a video would be ‘out soon’ to explain how to make this more reliable. To date, nothing has been posted, so, as is typical for a lot of technology, they leave it to end users to resolve their issues and find a workaround. As it turns out, there was only one video among hundreds where a home-chef type presenter found an almost foolproof way of making it so the attachments were detected and worked every time. She claimed she had just stumbled across it after spending many hours trying to get her (much more expensive model) mixer to work properly. Her method was to screw the two halves of the attachment together and line up the arrows. She would then place the attachment on the blender, and typically, it would not be detected. While it was in place, she cranked the glass part about 30° more and magically, the blender would see it. She could replicate this every single time, and of course, the arrows on the case of the attachment no longer lined up, but the appliance would detect it just fine. This, of course, would make it impossible to undo again due to being so tight. However, she then backed off the bowl in-place, using the grip of the blender to help her. She ensured she was still maintaining the seal – any contents would soon fall out if she undid it too far – and then removed it and flipped it upside down before completing the unscrewing and removing the blades part of the attachment. Of course, the first thing I did was try that method with ours, and it worked every time. The fact that the manufacturer hasn’t modified the attachments to show new arrow positions, or at least put out a workaround video of their own, is extremely disappointing. Sometimes, there is no electronic fix, just a clever end-user who figures out how to make it work. The source of the interference G. G., of Macleod, Vic thought he was solving one problem when he was actually creating a new one. He explains Australia's electronics magazine siliconchip.com.au how a software-defined radio (SDR) helped track down the source of the problems... I have a weather station to monitor the roof cavity temperature so I know when to turn on an extractor fan on a hot day. I realise that it could be thermostatically controlled, but I don’t want it running when we’re away. The roof cavity sensor/sender seemed to be chewing through batteries. Because of the nuisance value of getting into the ceiling, I decided to power it from a plugpack plugged into a ceiling power point. That worked OK for a few weeks, then the display stopped updating. Then I started noticing that the remote controls for our alarm system and garage doors had become less sensitive and we had to be much closer to their receivers to get operation. Next, a remotely-controlled ceiling fan refused to operate. At about this time, I had brought home a system for repair that included radio microphones and a mobile internet dongle. My wife was convinced it was causing the problems. I replaced the batteries in the alarm remotes, which gave a slight improvement. They had tuning capacitors, so I tried tweaking them and got a bit more range, but barely enough. Retraining and new batteries in the garage remotes seemed to gain a little more range. A web search told me that the alarm remotes were on 304MHz, so to check their outputs, I thought I’d install an SDR that had been given to me years ago but that I had never used. The software installation was tedious and even required manual installation of the drivers, but it eventually sprang to life. Stepping across that part of the spectrum, I couldn’t see any response to my button presses. Testing with the radio mic in the system in for repair confirmed that the SDR was working correctly. I then did a web search on the garage remotes. I found a very useful site (www.remotepro.com.au) that gives all manner of Australian wireless remotes and the programming of garage door openers, and even has full installation details for many garage openers. That site told me that my Merlin controllers were on 433.92MHz, so I tuned the SDR to that frequency to check the garage remotes. siliconchip.com.au Australia's electronics magazine December 2023  83 I found that there was already a very strong continuous signal, 30dB greater than the local FM radio stations. Rough direction finding with the whip antenna gave a null when pointed toward the weather station sender. Powering down the circuit going into the ceiling immediately stopped the rogue signal, and all remotes started operating perfectly. Reapplying the power even restored the temperature display, and on the SDR, I could now see a short update burst coming from the sender about once per minute. It seems that an occasional software glitch sent the weather station into a continual transmission mode and, as it was within a couple of meters of all the other devices’ receivers, it swamped their reception. Likely previous similar glitches had flattened the batteries before we’d noticed any effect, but my new power source was able to keep the rogue transmission going. After the reset, it has been performing normally for a few weeks; until I get around to replacing it, I at least know how to restart it. I later discovered that the alarm remotes also operate in the 433MHz band. A trio of antenna repairs Around fifty years ago, I. G., of Banyo, Qld was a Radio Trainee with the Department of Civil Aviation, field training at his home station, the Gold Coast Airport (Coolangatta)... I was lucky to have great mentors at the station, the supervisor and technician, who involved me in fault clearance and regular maintenance. Still, one time I was left to my own devices as they worked on a particularly troublesome fault with the non-directional beacon (NDB). The NDB was the most common and simplest navigation aid at the time. It is a low-frequency 200-400kHz AM transmitter, transmitting a short two- or three-letter identifier in Morse code a couple of times per minute. Before WW2, broadcast stations were used as navigation 84 Silicon Chip aids. With bearings from two stations, you could determine your position on a map or track towards a known location. That was not ideal as few broadcast stations transmitted 24 hours per day, and when broadcast networks became the norm, you could not be dead sure which station you were tuned to. NDBs were a more reliable alternative. The lower frequency gave a better ground wave, with no chance of skip. The Coolangatta beacon’s antenna was electrically short, a single vertical wire supported by several horizontal wires strung between two 22-metre tall towers. These horizontal wires formed a capacitive top-load to increase the antenna current and thus the antenna’s efficiency. The NDB transmitters were a pair of 100W vacuum tube units, providing operational redundancy. They were monitored by a receiver fed from a short whip antenna inside the NDB hut. If any of the monitored parameters fell below the Low-Performance Level, the monitor would change from the running transmitter to the standby. Frequent intermittent faults were causing changeovers. It was determined that the fault was causing a varying carrier level. After a lot of investigation, the fault appeared to be in the antenna itself. The DCA lines section was called in to lower the antenna and investigate its condition. This was reasonable because, being a coastal station, salt corrosion was a likely culprit. However, the antenna checked out OK and was hoisted back into position. The fault persisted. During this process, the trainee (me) was superfluous and left to his own devices. As I wandered about like a lost soul, in one of my walks around the hut, I noticed that the iron roof had a metal drainpipe down one corner that finished just above the ground and level with the ant cap on the building foundation. The drainpipe was not fully anchored and moved in the breeze, bumping into the ant cap. I wedged it back with a piece of timber and sought out the boss. We found that the fault could be induced by pushing the drainpipe against the ant cap. Grounding the roof and downpipe altered the signal strength at the monitor receiver. Problem solved! After completing my training, I was stationed at Charle­ ville in southwest Queensland and became the acting supervisor after a few years. This time, there was another very intermittent fault with the Charleville NDB. It only happened occasionally during wet weather. In this case, the fault kept recurring for a long time with an unknown cause; the short duration made it difficult to pin down. When the beacon was eventually updated, the new installation required re-siting the transmitter in the “transmitter hall” and the complete replacement of the antenna coaxial feeder (changed from 70W to 50W). When the old feeder was removed, they discovered a female-to-female connector under a little ‘sand dune’ in the building’s sub-floor cable duct that dated from the previous NDB upgrade. Heaven knows how long ago that was. It was not weatherproof in any way and showed signs of distress. In the words of Homer Simpson, “D’oh!” The last item is also from Charleville. In the 1970s, before the adoption of SSB high-frequency communications for air/ground communications, comms were amplitude modulated. To cover all of the Flight Information Zone with varying ionospheric conditions, three frequency ranges were used near 3MHz, 6MHz and 8MHz. Australia's electronics magazine siliconchip.com.au The fault this time was interference on one of the 3MHz channels. The interfering signal was the local radio station program (918kHz) mixed with the ident code from the local NDB (267kHz). This was determined by sitting down with a calculator and figuring out what combination of harmonics of these two transmitters fell on the problem receiver frequency. The receiver antenna system was three half-wave dipoles strung between two towers, with the lowest frequency at the top and the highest at the bottom, to maintain the same height relative to the wavelength. The feeders (shielded twin) were laced to a vertical guide wire at the centres of the dipoles. Since the problem manifested itself only in the local receiver, it was likely local. The immediate low-tech solution was to belt the receiver antenna feeders with a broom handle, which alleviated the fault! The fault was located in the supporting guide wire in the receiving antenna system. Initially, the eyes used in the mechanical structure of the supporting cables and other fittings were provided with small plastic sleeves to stop spurious rectifying joints from being formed by contact between the dissimilar metals and/or their oxides, making an unintended but efficient mixer. The plastic sleeves were long gone in the western sun. To clear the problem permanently, all these joints were eventually bonded. Fixing AC ripple in a dual-tracking power supply T. I., of Penguin, Tas had a trusty old power supply until it could no longer be trusted. Some gremlins were lurking within that would need to be dealt with... Following the completion of my electrical apprenticeship last century, I completed a course in Industrial Electronics, culminating in the construction of a Dual Tracking Power Supply kit, the details of which appeared as a project in Electronics Australia in March 1982. The power supply utilises LM317 and LM337 three-terminal regulators and provides ±1.5-22V DC at up to 2A. It has been my main DC source for experimentation in electronics over the years. “Tracking” refers to the magnitude of the negative rail voltage following the positive rail across the entire voltage range. It does this by measuring the positive regulator’s adjust/reference signal, inverting it and feeding it to the negative regulator’s adjust terminal. There is also a fixed 5V reference supplied by a separate regulator. The power supply has performed faultlessly over the years – until recently. Having built Nixie tube projects in the past, I am now in the process of building a VFD (vacuum fluorescent display) clock with a 32,768Hz crystal timing reference. I design, build and test the PCBs using the power supply mentioned above. I completed the crystal oscillator timing board and the divide-by-32,768 circuit to provide the 1Hz count for the clock timing. I connected my CRO lead to observe the 32,768Hz waveform, only to find significant noise on the trace. Although it was a definite sinusoidal waveform, I could not achieve a clean single trace and initially thought that the crystal was possibly being overdriven. However, after spending some unnecessary time changing components siliconchip.com.au around the crystal, I just could not get a clean signal. Instead of a clear trace, it appeared as a sinewave drawn by a 10mm-thick noisy trace. Somewhat frustrated and overdue for lunch, I switched off the AC supply to the power supply with the CRO still connected, and the signal instantly became a clean sinusoidal trace until the power supply’s onboard filter capacitors drained their charge away. That got me wondering whether the unit I’d built all those years ago was in trouble. I was able to prove things weren’t right by powering the crystal oscillator with an alternative DC supply; it produced a perfect trace on the CRO. I then put the CRO leads across my power supply’s output and could see significant AC ripple that obviously shouldn’t be there. My timing circuit was being modulated with AC ripple from the DC supply. I removed the four screws holding on the lid and slid the cover off. I could see four tantalum capacitors and several aluminium electrolytics. Given the age of the unit, I suspected that at least one was faulty. Looking at the circuit, I could see a 1μF tantalum at the input to each regulator, a 100μF electro across the output of each regulator, and a 10μF tantalum across the voltage adjustment potentiometer. I could also see some discolouration on one 120W resistor between the adjust and output terminals of the positive regulator. I clearly needed to remove the PCB and therefore took heaps of photos and marked the wires before going any further. I desoldered the main transformer AC connections plus the wiring to both the regulators, which are mounted on the side of the case for heatsinking. I then removed four other connections to various switches and indicator LEDs. I could then swing the PCB out far enough on the remaining wiring to enable component replacement. While the board was out, I checked the integrity of all the onboard diodes and any suspect dry joints. However, all was good and certainly acceptable, given my inexperience at the time I built it. I replaced the four tantalum capacitors, the two 100μF electros and the discoloured 120W resistor, then set about restoring all wiring connections. After checking and rechecking, I plugged the unit back in with the lid still removed and with fingers crossed, switched it on. Great – no smoke, so a good start. A test of the voltages proved that the unit was functional across the full range. Connecting the CRO leads showed a perfect, ripple-free DC supply. However, I then noticed a red LED fully illuminated. This was the dropout LED, which should only be illuminated if a fault draws too much current on the output so that the regulator drops out of regulation. What was going on here? I had no load connected, and the voltage tested perfectly across the entire range. Spending too much time measuring voltages around the components driving the LED, I finally realised that the sunshine coming through the window (yes, we do get sunshine in Tassie’s winter occasionally) was shining through the back of the LED, which was mounted on the front panel, giving the impression that it was illuminated. Shading the sunlight stopped the glow. No wonder the wrinkles on my forehead keep multiplying! With the lid back on, I connected the crystal oscillator to the power supply and tested the signal with the CRO, to see a perfectly clean trace. Hopefully the unit will serve me for many more years to come. SC Australia's electronics magazine December 2023  85 D-200 RADIO TRANSMITTER /DVWPRQWK,JDYHVRPHEDFNJURXQGRQ6SXWQLN WKHƬUVWDUWLƬFLDOVDWHOOLWH DQGH[SODLQHGKRZ, UHFUHDWHGWKHUHOD\EDVHGq0DQLSXODWRUrWKDW VZLWFKHGWKHWZRUDGLRWUDQVPLWWHUVRQDQGRƪDW +]:HSLFNXSZKHUH,OHƱRƪP\QH[WMREZDV WRUHYHUVHHQJLQHHUDQGEXLOGRQHRIWKHUDGLR WUDQVPLWWHUVWKHQFUHDWHDVXLWDEOHSRZHUVXSSO\ A Vintage Radio Story, Part 2 By Dr Hugo Holden T he Manipulator is an oscillator based on two sensitive relays. It alternately switches off the output valves in the two transmitters by disconnecting the screen grids, stopping the transmitted carrier wave. Each transmitter is on for ~0.2s at a time, then silent for a similar period. Having gotten my Manipulator working like the original, mainly using period-authentic parts, I turned to the three-valve-based transmitters and the chassis they were built into. While I was not planning to go as far as to produce a complete D-200 unit with two transmitters and the Manipulator, I wanted to make a period-­correct recreation of one transmitter along with the Manipulator that I could put on display. I knew some parts would not be identical to the originals, but I was confident I could get very close. Transmitter details The two transmitters are based on 86 Silicon Chip small 2P19B pentode valves, which are still readily available. The data sheet extract shown in Fig.10 includes the customary bottom view of the valve’s base. Another 2P19B data sheet shows screen and suppressor grid connections reversed, as if viewed from the top. Still, it is easy to tell from the valve itself that this data sheet is correct. Before building the transmitters, I made a test jig to verify that the 2P19Bs I had bought (some shown in Photo 2) were functioning normally. They had been stored in corrugated cardboard rolls with a thin paper wrapping, which is not ideal, resulting in some corrosion on the tinned copper leads. I had to clean that off, initially by scraping and then smoothing the lead with 1000-grit sandpaper, being very careful not to bend the wires near where they enter the glass envelope. To determine their ‘normal behaviour’, I tested over 30 valves, Australia's electronics magazine a fair statistical sample. Three were defective: two had low gain, and the other had let in air. Fig.11 is the test jig circuit, while the actual device is shown in Photo 1. I took the sockets on the test jig that receive the wires from the 2P91B valve from some machined-pin IC sockets. I tied grid 3 to +12V rather than ground because it was tied to +10V in the Sputnik transmitter output stage. I added a 1kW series resistor to avoid an accidental short between the grid pin and adjacent heater pin from applying 12V to the heater. I used a 12V gel cell to power the filament circuit and my dual 0-60V CPX-200D bench power supply, connected in series, for the 120V test voltage. Sputnik-1 20.005MHz transmitter design The transmitter circuit is shown in Fig.12. Valve V1 is deployed as a crystal-­controlled oscillator while V2 & V3 (all 2P91Bs) form the push-pull power amplifier. The valves have a 1W plate dissipation, so a pair running in an output stage, sharing the load, will have no difficulty delivering a 1W RF output, provided there is adequate drive voltage (close to 40V peak) at the G1 grids. The circuits for the 20.005MHz and 40.002MHz transmitters are practically identical, aside from the coil and capacitor values. In the 40.002MHz unit, the main change was that they did not tap off the main tank circuit for an impedance match with the antenna, as they did for the 20MHz unit. They used a capacitive divider instead. siliconchip.com.au Photo 1: the test jig in action. The anode wire comes out the top of the valve envelope, hence the need for the clip lead. A detail not shown in the original circuit diagram is that the L5 and L6 coils are built into a rectangular can. Capacitor C28 is not visible in any historical photos, so it most likely was in the same shield can. C29 is visible in the photos, though (see Photo 3). In Photo 4, the shield around the glass-bodied crystal appears to project a little above the housing, but the shield can for L5 and L6 does not look that tall. I determined the transmitter chassis’ dimensions by studying the photos and scaling from the image details and the limited geometry data in the design document. I determined that the housing around the transmitter modules was 93mm wide, suggesting the chassis was 90mm wide, 180mm long and 60mm deep. It was OK that the crystal shield projected a little above the chassis height in the original unit because this side of the transmitter module faced the Photo 2: some of the 30 2P19B valves I bought, of which three had failed. They had not been stored properly, so I had to clean the corrosion off the wire leads before testing them. siliconchip.com.au Fig.10: a page from a data sheet for the 2P19B pentode showing its pinout and critical parameters. Fig.11: a simple test circuit for the 2P19B pentodes that allowed me to weed out three faulty valves from the 30 I purchased. A test signal can be fed in, and the amplified output signal examined with various external load resistances. Australia's electronics magazine December 2023  87 Fig.12: the Sputnik-1 20.005MHz transmitter circuit. The two transmitters were very similar but had some slight differences besides the crystal frequency. Note that most versions of this circuit (including one we published previously) contained errors; this one should be accurate. interior of the D-200 housing, where there was clearance. The original document shows the width of the main unit that carries the two transmitter chassis as 132mm, more than enough to accommodate two 60mm-deep units with 12mm to spare, so a mid-line panel and wiring could run through the main body. Lead dress for the 2P19Bs Photo 5 shows how I insulated the bare valve leads with PVC tubing, although I later decided to use Teflon sleeves instead. Replicating the chassis When it comes to making replicas of a vintage electronic apparatus, the most difficult part is the mechanical engineering aspect of the project. If not done well, the final result does not represent how the unit actually worked and looked. It takes quite a while to examine the historical photos and figure out where the components were placed and the original geometry of the internal and external panel work. A good replica also requires tracking down most of the original parts; not just the valves but also resistors and capacitors, because they have a characteristic look, especially the Soviet chassis-mount and RF feed-through capacitors. Also, for RF apparatus operating above 5-10MHz, physical layout and shielding considerations become very important. This includes the mounting clips that attach the 2P19B valves to the module body. These serve as partial shields and conduct some heat away from the valves as well. Therefore, it is best to stick to the original physical layout closely. To make the transmitter module’s metal chassis precisely the same as the original would require the same tooling. The metalwork had been riveted and soldered together in places. Without the tooling, other methods exist to create a nearly identical-­ looking metal module of almost identical geometry. I decided to make the metalwork out of brass, which is easily soldered. I used 3mm-thick plates to replicate Common mode choke with glued slug C26 Capacitor missing from schematic – C47, 1.2nF 250V R10 C27 C29 C34 20.005MHz crystal in glass envelope Photo 3: a photo of the original transmitter with C27 and C29 visible, but C28 is nowhere to be seen. It makes sense that it was in the shielding can with L5 and L6 since it connects to both. 88 Silicon Chip Photo 4: this photo of the 20.005MHz transmission unit shows that the crystal shield was taller than the shield for L5/L6/C28 and even projected outside the chassis slightly. Australia's electronics magazine siliconchip.com.au Figs.13-20: these are the mechanical drawings that I provided to the machinist who made my reproduction transmitter metalwork. Fig.13 the top and bottom faces of the module, routed and engraved with a groove to fit the side panels, made of 0.8mm-thick brass. The three internal panels were also CNC machined. They are all soldered together too. This method avoided having to fold any metal panels, which can distort the material. I prepared Figs.13-20 to help with this task. Troy at Sunquest Industries in Warana, Maroochydore (Qld) did the CNC machining. The projections on the sides of the plate are 1.5mm tall and 5mm wide. The slots in the other panels that they pass into are 1.5mm wide and 6mm long. These are soldered together. I soldered them with the aid of a gas stove and the result is shown in Photo 6. I finished the chassis with 1000-grit sandpaper and spray painted it, using temporary screws to prevent paint from entering the threads and covering the Earth points. Very few paints stick to polished or shiny brass well. I have been experimenting with paints for this Photo 5: I added insulation tubing to the pentode leads; initially, I used PVC but changed to Teflon later. Photo 6: having received the CNC-machined chassis pieces, I soldered them together with a gas stove. The areas that were masked with screw heads are either chassis grounding points or where I didn’t want paint to get into threaded holes. siliconchip.com.au Australia's electronics magazine application for many years. One excellent product is the clear Dupli-Color spray number DS-117. It helps not to have any pigments or fillers, such as aluminium powder. After coating the brass with this clear coat, I waited 24 hours and applied silver DS-110 spray paint. Once that had dried, I applied a final clear coat. This makes for scratch-­ resistant paint with a good finish and maximum surface adhesion (similar to automotive paint). You can see the result in Photo 6. December 2023  89 Fig.14 Other options that give superior adhesion and scratch resistance are powder coating or electroplating. However, those would have meant sending it away to a factory, which I was reluctant to do. Note that while I used Phillips-head screws to keep the holes clear of paint, the final transmitter has slot-head screws to match the original. Photos 7 & 8 show the completed transmitter with the final 16:3 output coil. Terminal strips The original unit appeared to contain two side-by-side terminal strips with five tags each, each mounted with two screws & nuts and a thinner underlying insulating plate. I decided to make this myself as one 3mm-thick black fibreglass plate with four mounting holes and a rear 1.6mm insulating plate, as shown in Photo 9. It might have been done that way originally. I made a custom connector strip for the unit’s rear wiring connections (also shown in Photo 9). I used a six-row strip rather than eight (as in the original) as the extras were not required, and this way, it would be less crowded. Oscillator & output tank coils I searched for ceramic coil formers for several weeks. I determined the diameter of the original ceramic coils and the approximate number of turns from the photos in the design document. The formers have slots for the winding wire. Most likely, the originals would have been a pre-made part intended for amateur radio projects in the USSR. Generally, the wire used on these sorts of formers is silver-plated copper. I acquired the closest oscillator coil form I could find from the UK. It required a machined base, which I made out of Bramite, to help match the original appearance – see Photo 10. I wound this coil using 0.9mm-­ Fig.15 90 Silicon Chip Australia's electronics magazine siliconchip.com.au diameter silver-plated copper wire. My first attempt was a 12-turn coil with a five-turn centre-tapped secondary. An additional 10pF parallel capacitance was required to bring it to the correct frequency. It is possible that the original trimmer capacitance had a higher centre value than the one I selected. However, the photos of the original suggested a 13-turn coil, which would have given the option of a six-turn or four-turn CT secondary. Experiments showed that a four-turn secondary provided inadequate voltage to get the output stage to full power, so six turns were required. 40-42V peak was needed at each of the two output valve grids to attain the full power output of 1W. The closest ceramic former I could find for the output tank coil, which closely matched the geometry of the original coil, was from Surplus Sales Nebraska. It was close to the right diameter with the correct number of grooves, so the turns/inch (or turns/ cm) was correct, but it was too long. To solve this problem, I bought a diamond cutting disc from eBay and fitted it to my bench circular saw and removed 7mm of ceramic material from each end (see Photo 11). I machined the end mounting pieces from Phenolic rod, similar to Tufnol, and fitted threaded, machined brass inserts into those for the retaining screws. Because Sputnik-1’s antennas were bent dipoles straddling a 0.58m diameter ball, the antenna feed impedance would have been higher than the 72W typical of a straight dipole, possibly as high as 150W. It would be possible Fig.18 siliconchip.com.au Fig.16 Fig.17 to find the exact value by making a mock-up from a metal sphere and some antenna rods. Also, the antenna rods were a little shorter than ¼ of a wavelength each. When this is the case, for the basic dipole at least, the antenna behaves as a resistor with a capacitor in series and represents a reactive load where the current leads the voltage. This may have helped to tune out the inductive reactance of the three-turn coupling coil on the 20.005MHz unit. From the original document images, I saw that the output coil had close to 15 turns. The centre tap supplying 130V to the coil being on the same side as the end connections suggested an even number of turns. I initially wound an experimental 15:3 coil and later moved to a 16:3 for the final output coil (Photo 12). Fig.19 Australia's electronics magazine December 2023  91 Fig.20 Fig.20: this is the last of the seven mechanical drawings for the chassis. To conveniently measure the output power into a 50W load, I made several coupling baluns that presented the transmitter output with a range of loads, with the results shown in Fig.21. The transmitter was tolerant of load resistances from 70W to around 240W, delivering at least 1W into that range of loads. Output power peaked at 1.32W with a load close to 138.8W, with the plate-to-plate load resistance for the 2P19B valve pair close to 4kW. The applied load resistance affects the exact tuning of the tank coil with the butterfly capacitor. If the output were peaked with a low-range load resistance (around 70W), it would tend to down-shift the graph of load resistance versus power output. If the tuning were peaked with a higher load resistance (around 300W), it would tend to up-shift the graph. Presumably, the D-200 transmitter modules were tuned for maximum power output when connected to the actual antennas in the Sputnik-1 spacecraft. Also, at full power, the plate voltage of the 2P19b with the 138.8W load fell lower than its screen voltage. The RMS voltage swing across the 16:3 output coil primary is 72V, while the peak voltage from plate to plate, across the coil primary, is close to 102V. Each plate sees half of this, so the plate dips to around 79V (51V below the 130V HT voltage), ie, 11V below the 90V screen. This is not a concern for most pentodes unless the plate voltage is much lower than the screen voltage; then, there can be excessive screen-grid current. I measured the screen-grid current under all output loading conditions, even when the plate voltage dipped to 23V below the screen voltage with the 312.5W load, and the screen current altered very little. Also, the output waveform remained normal. With lower load resistances than 138.8W, the plate voltage swing is less. With the 78.1W load, the plate voltage dips only 35V below the 130V HT and stays 5V above the screen voltage. Replica air-variable capacitors The transmitter contains two air-variable capacitors. To help match these as best possible, I machined a matching-looking nut for a Johnson-­ Viking butterfly capacitor (Photo 13) and attached it to a white Bramite plate, which resembles ceramic. I also machined a shroud around the original adjusting nut for the oscillator trimmer capacitor and painted that black to resemble the original parts. It was made from a vintage germanium transistor mounting clamp and ◀ Photos 7 & 8: the completed and operational replica 20.005MHz transmitter. Photo 9 (above): this is the tag strip I made (shown at the top). I wasn’t sure if the original had two parallel 5-terminal strips or a single arrangement like this. Regardless, it was easier to make it as a single unit. I then made the connector strip with six terminals (shown at the bottom) rather than the eight of the original, as only six were used. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au a machined brass insert – see Photos 14 & 15. Replica common-mode choke Photo 17 shows the relative heights of the crystal socket and shield and the common-mode choke in the replica. Coils L5 & L6 were likely wound as a common-mode choke on the one ferrite core; the photos show a single ferrite slug. I think they made this choke tuneable to allow a small amount of fine adjustment of the exact frequency provided by the crystal. The idea behind the choke was to ensure the cathode (filament) of V1 (2P91B) had a very high impedance with respect to ground so the oscillator could work correctly. In a typical Colpitts-style crystal oscillator for medium wave frequencies up to 2MHz, the cathode (or filament, in this case) choke is typically chosen to be around 1mH, with an inductive reactance at that frequency of about 12.5kW. In the case of the 20MHz oscillator, a choke of 100μH or thereabouts is satisfactory, giving about the same reactance. One thing about making an RFC (radio frequency choke) is that it is vital to keep the self-capacitance low. The self-capacitance is in parallel with capacitor C27 (20pF). This means that the construction of the choke must either be a single-­ layer coil, or a wave-wound Photo 10: I was lucky to find this coil former in the UK as it’s very close to the original. I just had to add the base. Fig.21: the reproduction transmitter’s output power vs load resistance. It peaks around 138.8W; we don’t know the exact impedance of Sputnik-1’s antennas but expect they were in the 70-150W range. low-­capacitance coil, to keep the self-­ capacitance below a few picofarads. I could have used two 100µH axial chokes, but that would not make for a good-­looking replica. I therefore made a single-layer coil Photo 12: after some experimentation, this is the configuration I came up with for the output coil. It’s a 16:3 coil, with a 3/4-inch diameter, 3in length, 8 turns per inch using 1mm diameter silver-plated wire. (bifilar wound) with an inductance of 85μH and a self-capacitance of 3pF, determined by a self-resonance test – see Photo 16. I fitted C28 (a Soviet-­made 1200pF capacitor) inside the can, as shown in Photo 16. This arrangement is probably similar to the original part. The choke also provides some of the DC resistance required in the heater chain. Each valve has a 2.2V heater, accounting for 6.6V in total, while the battery supply is 7.5V. The DC resistance of each coil is 4W, and the filament current is close to 100mA. The value of R2, a resistor in series with the filament string, was not specified in the design document. The total voltage drop due to the choke is 0.8V, which would make the value of R2 close to 1W. However, it’s possible they ran the filament chain 15% ‘over voltage’ with fresh batteries. The 2P19B data sheet says the filament should be in the range of 1.8-2.5V, so that should be OK. Replica crystal Photo 11: this former was also almost perfect, but I had to cut the ends off to make it the right length, then machine some end pieces. siliconchip.com.au Photo 13: the shroud (made from the transistor mounting clip) was painted black & can be seen fitted in Photo 14. Australia's electronics magazine The crystal was an interesting challenge. The original crystal was in a 7-pin glass envelope, typical of many of the late 1950s era. While these December 2023  93 Photo 14 & 15: the shroud around the original adjusting nut for the oscillator trimmer capacitor made from a vintage germanium transistor mounting clamp. crystals are still sometimes available from Ukraine, I could not find one at 20.005MHz. A typical 1MHz crystal is shown in Photo 18. To make a replica, I cut the top off a 7-pin valve using a diamond file in the lathe and made a 7-pin base for it, initially only fitting three pins as a trial. The closest crystal I could find was 20.004864MHz. After I cut the glass valve, I heated the cut glass edge to red heat with a blowtorch. This helps to ensure that microscopic cracks in the cut edge don’t start to spread through the glass wall later. Also, to get the modern smaller crystal to operate properly in the circuit, I had to add 12pF of parallel capacitance. I hid that inside the base of the replica crystal – see Photo 19. RF output connectors The photo of the original unit shows what appear to be two round RF connectors. To help replicate them, I used F connectors. When the module was finished, it was time to combine it with the Manipulator. I had considered replicating the entire D-200 housing that contained the two transmitters and the Manipulator but decided against it. The main reason is that it is impossible to inspect one side when the transmitter module is mounted inside the D-200 casing. A better move would be to mount the transmitter module on a rectangular plate, visible on both sides, along with the Manipulator relays and the timing capacitors. This way, all the parts are readily seen. The achieve this, I had a natural anodised 3mm-thick aluminium plate CNC machined and engraved, then 94 Silicon Chip Photo 16: the common-mode L5/L6 choke and their shield can. The photo on the right is with the capacitor C28 added. filled with black paint. This plate mounts on top of an insulated base. The transmitter is fixed on one side of the engraved plate, and the plate is fitted to a Phenolic baseboard – see Photo 20. You can see videos of the replica operating, including reception on a shortwave radio, at https://youtu. be/9N26pkGGPew and https://youtu. be/_rq2yrdeGK8 Transmission test I also built a power supply for the replica of the Sputnik-1 Manipulator and its 20.005MHz radio transmitter module. In the absence of batteries, the standard method to power a valve radio or amplifier in a home or laboratory setting was from a line voltage power supply. These were called “battery eliminators”. Sputnik-1’s silver-zinc batteries (not available to the public at the time) were specially manufactured for the task. The high-tension battery was tapped at +10V, +21V, +90V and +130V. The 10V One does not simply transmit a 1W carrier at 20.005MHz because it might cause some interference. Instead, I fed the transmitter output into a dummy load to absorb the power but, by adding some small whip antennas, the leakage was enough that I could receive the signal on a shortwave radio in the next room. I assembled a 5:3 balun to attach to the transmitter and used a 50W dummy load to present the transmitter with the ideal 138.8W output load (see Photo 21). A battery eliminator Photo 17: the heights of the crystal socket in its shield and the common-mode choke shield can. 47mm 39mm 9mm Australia's electronics magazine 11mm siliconchip.com.au Photo 18: an original glass envelope crystal (right) and my reproduction 20.005MHz unit (left). Replica crystal ◀ Photo 19: the replica crystal and its matching shield can. Original format crystal supply was used for the suppressor grids in the two 2P19B output valves in the transmitter, for which the current draw is negligible. The 21V tap powered the Manipulator relays. The Sputnik design document referred to the common (negative) connection of the B battery and 7.5V filament battery as “-A”. I decided to stick to that on the front panel labelling of this battery eliminator. The version shown here is based on four 15W MEAN WELL RS-15 switchmode power supplies. These supplies are compact, their outputs are isolated and they have become quite inexpensive. They are also overload protected and are available with an output voltage of 3.3V, 5V, 12V, 24V or 48V. These voltages are adjustable to an extent using an onboard potentiometer; a very helpful feature. Since the output of each one is isolated, they can perform the same job as an adjustable battery. The battery eliminator circuit is shown in Fig.23. A large range of output voltages can be provided by selecting these supplies appropriately. The 12V unit has a higher output current, so that is what I used to power the valve filaments. Three 48V units in series provide the B+ voltages. Since the +10V and +21V supplies don’t need to deliver much current, I used zener diodes with a 1.2kW 2W current-limiting resistor to derive them from the output of the first 48V supply. When the replica transmitter unit was running with the Manipulator, loading the supply, I adjusted the 90V and 130V levels to be exactly correct at the supply’s output, aided by some built-in series resistors. The +7.5V, +10V and +21V supply outputs required no adjustments. The power supply module outputs are floating (aside from 2nF of capacitance to the unit’s housing), which to some extent makes them safer because a one-handed contact to the +90V or +130V rail won’t result in a significant current through the body to ground. It is still better to tie the outputs to ground electrostatically so they don’t float up to some unknown value. I did that using a 100kW anti-float resistor. That value limits the one-handed contact current from the +130V terminal to around 1mA, which is reasonably safe. I decided to use robust 5W-rated zener diodes, which require a modest current to get their terminal voltage to the labelled value. Photo 20: the completed, fully functional replica. The Manipulator and transmitter module can both be examined in detail. Photo 21 (upper left): this dummy load plugs into the transmitter’s output socket. A tiny amount of the signal makes it to the antennas and can be picked up by a nearby radio. siliconchip.com.au Australia's electronics magazine 95 Fig.22: the front panel drilling details and artwork for my battery eliminator. There is a 0.24W loss in the 1.2kW resistor and a 1.25W loss in the 18W 2W resistor. 1.875W are lost in the 5W-rated 7.5V zener, dropping to 1.125W under load. There is a combined loss of only 0.3W in the 10V & 11V zeners. This makes the total zener regulator losses in use close to a modest 3W. The shunt zener method is highly beneficial for another reason. The switching supplies have significant noise on their outputs, around 80mV peak-to-peak on measurement. This noise is sourced from a very low output resistance. For example, adding 100µF directly to the supply output terminals does little to reduce this noise. However, the series resistance and the low dynamic resistance of a shunt zener regulator create a voltage divider that flattens most of the noise out, even without significant filter capacitors added, especially for the +7.5V, +10V and +21V outputs. The 90V and 130V output required RC low-pass filters to get the switching ripple low and under 3mV peakto-peak. The finished unit is shown in Photo 22. Line power safety I built the battery eliminator into a very high-quality Takachi MS66-2123G extruded and cast aluminium enclosure that I got by mail from Japan. It has the internal chassis option and the tilt feet option. A switched and fused IEC connector on the rear panel avoids a cord dangling from the instrument when not in use – see Photo 22. It also means running mains power to a front-panel switch is unnecessary. The IEC connector contains a very short physical link between the live pin and the fuse; the link is easily protected with an added insulation sheet with slots punched for three pins. Fig.23: the circuit for my battery eliminator that powers the Manipulator and transmitter. It’s based on four MEAN WELL mains to DC switch-mode power supplies plus some zener diodes, power resistors and capacitors to help filter out the switch-mode noise. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 22: the ‘battery eliminator’ mains supply is built into a very nice instrument case. All the voltages needed to run the Manipulator and transmitter are available at the front panel banana sockets. The IEC mains input socket, power switch and fuse are all in an integrated unit on the rear panel. Some constructors put silicone rubber over this metal link, but I don’t subscribe to that as it can fall off. Another option is an insulating boot, but they are somewhat bulky. Two Earth wires attach to the Earth pin of the IEC connector. One goes directly to the metal housing with a shakeproof internal star lug. The other Earth wire connects to all the Earths on the RS-15 switch-mode supply terminal strip, which are all also grounded to the case by their mounting screws. This double-Earthing makes the Earth wiring a lower resistance with a higher current carrying capability and more electrically robust than the single wire connections comprising the Active/Live and neutral wiring. I soldered the wires to flat circular lugs to suit the screws on the RS-15 units and applied heatshrink insulation. Putting stranded wire directly under the screw connections is a bad idea, as single strands can break. I retained the plastic covers over the RS-15 screw connections. This helps prevent finger contact with the mains terminals while probing inside the powered unit. The RS-15 supplies can be screwed directly to the metal surface of the internal chassis. However, I added an insulating black FR4 fibreglass sheet in the region of the connectors, as seen in Photo 23. The bodies of the units are still double-Earthed to the chassis by their pairs of fixing screws and their individual Earth wires. The front panel dimensions and panel artwork are shown in Fig.22. It was made as a transparent Sticker by Stickerman. The holes for the 4mm banana plug connectors (made by Hirschmann) are not round but have flats to prevent the connector from rotating when it is tightened. So I had to drill the holes to about 7mm, file the flats out to 7.4mm and then finish the holes on the opposite axis with a round file to create the shape. The 11 solder terminals are single 3mm screw-mount Teflon insulated types. One is a solid 10mm tall threaded hex Earth post for the 100kW anti-float resistor. A good aspect of the enclosure and sub-chassis system by Takachi is that you can assemble everything, including the sub-chassis, front and rear panel assembly, before you drop them SC into the main housing. Photo 23 (left): the four switch-mode power supplies just fit into the case with a small amount of space left for the resistors, capacitors and zener diodes. The circuit is simple enough that a PCB is not required. Photo 24 (right): the wiring on the underside of the baseplate (which is separate from Photo 23). Note the power zener across the 7.5V supply of the baseplate, this was added to protect the tube filaments from accidents. siliconchip.com.au Australia's electronics magazine December 2023  97 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. Wireless power transfer demonstration My circuit demonstrating how magnetic levitation works was published in the Circuit Notebook section of the November 2023 issue (“Magnetic levitation demonstration”; siliconchip.au/ Article/16024). This follow-up uses a similar circuit to demonstrate wireless power transfer. I had an H-bridge IC left over from the Magnetic Levitation project, so I decided to drive an air-cored coil with it. This time, I set the drive frequency to approximately 200kHz. I am generating the required 200kHz signal using a 4047 CMOS oscillator (IC1). The top section of the circuit all mounts on a 57 × 52mm PCB (see photo). The second smaller (21 × 21mm) PCB has a 270μH RF choke on its back that is tuned with a capacitor to resonate at about 200kHz. The sinewave induced in the pickup coil is rectified by a voltage doubler circuit 98 Silicon Chip using diodes D1 & D2. The resultant DC voltage is applied to the white LED connected in series with a 1.5kW current-limiting resistor. The frequency of the 4047 drive oscillator can then be adjusted using trimpot VR1 for maximum choke resonance by placing the smaller ‘receiver’ PCB near the ‘transmission coil’ and adjusting VR1 for maximum LED brightness. The circuit’s operation is shown in two videos which you can view at • siliconchip.au/link/abmr • siliconchip.au/link/abms You will see that the LED lights at about 80mm from the coil and increases in brightness until it reaches the centre. Gerber files for the two PCBs can be downloaded from: siliconchip.com.au/Shop/6/308 Les Kerr, Ashby, NSW ($100). Australia's electronics magazine siliconchip.com.au Significant Spectral Sound MIDI Synthesiser software update I have released updated firmware for my Spectral Sound MIDI Synthesiser (June 2022; siliconchip.au/ Article/15338). It is now available for download from the Silicon Chip website at siliconchip.au/Shop/6/6490 (along with some release notes). The most important update is for the six dsPIC33EP512MC502 ‘Tone processor’ chips. Version 8 features significant noise reduction due to correcting the mapping of MIDI note velocity to tone amplitude. It also introduces an option to model string sound more naturally using non-integer-based harmonics, a novel algorithm and a carefully calculated lookup table. The source code to Version 8 is available and has been significantly clarified and streamlined. To build a HEX file from the source code, you’ll need the MPLAB X Pro licence to get the compiler optimisation required. However, a precompiled HEX file is also supplied. The Windows app has also been altered to use the additional in-­ harmonic option; the new feature is turned on in an app setting. I have also produced a logical diagram of the Tone Processor, which was missing from my original article and could help to clarify how it works. The new feature relating to ‘in-­ harmonicity’ is a deep but interesting subject. I spent a lot of time last year improving the Windows app with Dan Amos and adding some features that could extract the timbre from samples This diagram shows how the software works in each of the six Tone Processor chips in the Spectral Sound MIDI Synthesiser. siliconchip.com.au Australia's electronics magazine December 2023  99 of sound automatically (he kindly sampled all the notes on his real piano), adding a lot of improvements since the published version. Since then, I’ve been focused on trying out this inharmonic idea. For those interested in hearing what the Spectral Sound Synth is now capable of, I created a Bach track purely from its sounds (mixed in Audacity). It was inspired by Carlos’ 1968 album “Switched-On Bach” (a very early use of synthesisers). You can listen to it at https://youtu.be/qUR4B8xxSeU I have also created a version of Debussy’s Clair de Lune and posted it at https://youtu.be/WcUckqA5x3k The interesting thing about the Clair de Lune track is that the sound was automatically calculated by the Windows app’s ‘Instrument Analyser’ feature from samples Dan Amos gave me of his real upright piano. He very kindly sampled every note at three velocities, which the App analysed into 264 separate samples and translated into a best approximation of the sounds using additive synthesis. I’ve been improving this analysis recently in relation to the sound envelope. The next step is to try to improve the timbre, which seems to be missing some bottom end for some reason. I’ve been using my ‘scope and spectrum analyser software to study my output compared to the original raw samples, but it is time-consuming. I had a few direct questions about setting the module up, and although they all seemed to be basic problems, it made me better appreciate a new user’s perspective. For example, if you don’t have your keyboard set to transmit on MIDI channel 1, you’ll get no sound from the module because it initially expects channel 1. Also, when you first build the module, it doesn’t have any sound until you connect it to a computer and send a patch into the module. I’ve expanded the Troubleshooting section in the App’s help file to deal with these situations. Although the module seems to work well, my recent effort is trying to make sure it’s as good as it can be. The Windows app automatically updates for any users, but I appreciate that firmware chip upgrades are more difficult (you need a PICkit and a programming adaptor). I’ve been making sure that any Windows app update doesn’t break the system for people with older firmware. Jeremy Leach, Shrewsbury, UK. ($120) Battery-powered timer This small battery-operated timer triggers a 3V relay after a set time delay. It can either latch the relay on or pulse it. I developed it to test electronic gardening equipment. The BASIC program that controls it is pretty simple, which allowed me to use the more limited MX150F128 chip left over from previous testing, thus requiring some variation from the latest BASIC coding versions. The power restriction when using two AAA cells was resolved by using a 10 LED bargraph to show the set time and reducing the PIC chip’s clock speed to 20MHz from the usual 40MHz or 50MHz. 100 Silicon Chip Different timing values and latched/triggered operations are set by the four-way DIP switches. If the Latch switch is off, the relay is pulsed for 200ms when the timer expires; otherwise, it stays on until the unit is switched off. The 5/15/30 minute timer settings can be modified, if required, by changing the values set by PIN(7), PIN(9) and PIN(10) in the BASIC program. If the 200ms trigger time needs to be changed, that can be done by increasing or decreasing the PAUSE 200 under the StarStopTimer subroutine. The battery life is around 7-8 Australia's electronics magazine hours if used in latched mode or 25-36 hours if the relay is triggered only. The PCB gerbers and firmware can be downloaded from our website at: siliconchip.com.au/Shop/6/304 Gianni Pallotti, North Rocks, NSW ($80). siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Viewing circuits in PDF spread across pages I have been subscribing to SiliChip online for some time now and eagerly await each issue, which I download and view on my laptop (usually saving it for beer o’clock on Friday arvo as a personal treat!). But one thing that always annoys me is viewing the PDF schematics over several pages. In the print edition, it is no problem as it is usually on two facing pages. But online, you need to constantly scroll up and down between pages. That makes it cumbersome to follow traces from one page to another. I note that these PDFs are text-based, not imagebased, ie, if I zoom in a lot, the fonts and detail remain crisp. I don’t know if this is possible, but could you embed schematics as a single-­sheet PDF? I don’t know what the limits are to PDF, but is it possible to include a very small version of the entire schematic at the end of an article so that a computer user can zoom into it deeply? Cheers and thanks again for the great magazine. (K. W., Newport, Vic) ● The issue PDFs are intended to be viewed in “two-up” mode, where facing pages appear side-by-side. That way, circuits that run across pages will appear connected. It helps if your screen is large con enough to show both pages, although you can zoom in and scroll around if necessary for smaller screens. You can switch between single-page and two-page views if screen real estate is limited. For the two-up mode to work correctly, you must tell the reader that the first page is the cover. In Acrobat Reader, that’s the “Show Cover Page in Two Page View” option under View → Page Display (the recently updated UI still has this option, but you have to click the menu icon at upper left before View). It usually remembers this option between viewings, so you don’t need to enable it every time. By the way, when referring to the PDFs as “text-based” rather than “image-based”, we would say that they comprise vector images rather than raster images. Vector images scale much better than raster images. The photos in our PDFs are raster images, but everything else (text, diagrams etc) should be vectors. Information needed on electric motor I have a two-speed electric motor that I would like to use (GMF Cadet, frame B56, type ESBD5C2/4-6S; see photos below), but I can’t find any information on how to change the speed between the 1425 RPM and 930 RPM options that are indicated. Would any readers have information on this? Any information/wiring diagram that anyone may have would be greatly appreciated. (B. P., Dundathu, Qld) ● We don’t have this information. If any reader knows the answer, please email us and we’ll pass the information on. Commercial 3D printing services I read with interest the August 2023 issue of Silicon Chip on page 92 about people who have made a case and buttons for their Advanced Test Tweezers like the one I built (siliconchip.au/ Article/15910). I am retired and 75 and do not want to purchase a 3D printer at this stage. Can you point me in the right direction to purchase a ready-made case and buttons? Also, is there one to suit the previous version of the Tweezers (SC5934)? In both cases, any colour or clear will do. (W. J., Trentham, NZ) ● Unless you know someone who has a 3D printer, you would need to use a 3D printing service. There are many about. We have previously used JLCPCB to 3D print parts; their online store is at https://3d.jlcpcb.com/3dprinting-quote Mainly, you just need to upload the STL file(s) (that you can download from our website) and choose The two-speed electric motor, type ESBD5C2/4-6S that B. P. cannot find any information on. If anyone has information on this motor please email it to silicon<at>siliconchip.com.au and we’ll pass it along to him. siliconchip.com.au Australia's electronics magazine December 2023  101 the material and process. You’ll also need to give them your address for delivery and pay for the printing and postage. You could also go to a Jaycar maker hub where they have 3D printers that you can ‘rent’. Other Jaycar stores may also have 3D printers running demonstration prints; it might be worth asking if they can do the printing for you. Some libraries now offer access to 3D printers, too. Of course, you must bring the relevant files with you (eg, on a USB flash drive) if you go to a Jaycar store or a library to do 3D printing. We are not aware of any 3D-printed case designs for the earlier version, the Improved SMD Test Tweezers from April 2022. How to drive relays from a microcontroller Reading the article on the Programmable Mains Timer With Remote Switching in the November 2014 issue (siliconchip.au/Article/8063), I noticed the circuit has relays driven directly by pins on the microprocessor. Is it possible to drive a larger relay via a transistor arrangement like in other projects? (R. M., Melville, WA) ● We got away with directly driving the relay coils in that case because they are small reed relays that only require a low coil current. A larger relay can be driven if a transistor is used to drive the relay coil instead of the microcontroller output. The micro output can then drive the transistor base via a resistor as per other projects and with the reverse diode across the coil. The circuits below show different ways to drive relay coils from a microcontroller digital output (DOUT). (A) & (D) shows direct drive suitable for small reed relays, while the others use external transistors and larger diodes. They should work with just about any low-voltage DC coil relay if V+ matches the coil’s DC voltage rating. Note how (A)-(C) use a high level from DOUT to switch the relay on while (D)(F) use a low level. Circuits (B) & (C) are preferred due to the limitations stated in the note within the circuit diagram. It’s always a good idea to include the diodes for long-term reliability. Touchscreen Digital Preamp volume control It took me a while, but I finally finished building Phil Prosser’s Active Monitor Speakers and Active Subwoofer (November 2022-February 2023; siliconchip.com.au/Series/390). I am very pleased with them. It took me a while to do all the woodwork and metalwork for the subwoofer amplifier chassis, but I learned a few new skills along the way. The Active Crossover and the multiple Hummingbird Amplifiers sound excellent for the bookshelf speakers. Note: for (D), (E) & (F), the V+ supply must also be the microcontroller supply (eg, 5V). Only (B) & (C) allow the relay coil voltages to be significantly different from the micro’s. It’s always a good idea to include the diodes for long-term reliability. 102 Silicon Chip Australia's electronics magazine They are crisp and clear, with excellent bass from the subwoofer as well. It’s a fantastic project and I love the sound. Well done. I also decided to build the Touchscreen Digital Preamp (September & October 2021; siliconchip.au/ Series/370) but have struck a problem that I have not been able to solve. I was hoping for some clues/suggestions in fault finding. The touchscreen/remote and input selection all work fine. The mute function works fine. The sound is clear and clean, and everything seems to work OK (including the tone controls), except the volume control does not work correctly. The touchscreen can select a volume level from -99 through zero up to 99, but the sound levels are far higher than they should be. The minimum volume setting of -99 still provides too high of a sound level. The sound level is far too high for a higher-level input device, such as a CD player (up to 2V output), even with the volume set to the lowest point of -99. The volume control does adjust the volume level; it is just over much too small a range. From -99 to 0, the output level only changes from 0.19V RMS to 1.2V RMS. That’s a range of just 16dB. At a setting of 99, the output is 3.95V RMS, an increase of another 10dB or so. I started checking for obvious construction or component placement errors as simple things like the wrong resistor could explain higher than designed gains/sound levels, but I have not found one. I am puzzled about what I have done wrong or missed in my construction. Any suggestions, please? (P. M., Loftus, NSW) ● There are limitations to the digital attenuators, but the Baxandall configuration used should give a wider range of volume settings than that. We recently designed a new project (that will be published soon) using the same basic volume control project and measured a volume control range of close to 64dB, more than twice what you found. We suspect the problem is that with the earlier software, a setting of -99 maps to a potentiometer setting of 29/256, which is far from the lowest volume setting possible. To fix this, go into the settings and set the input level to -29 or lower, which will bias continued on page 104 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales Lazer Security KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware For a full list of the parts we sell, please visit www.ledsales.com.au After 38 Years, I am looking to move and semi-retire. Lazer Security needs a young and dedicated person to evolve and grow. We are currently based in Wolli Creek, NSW and we sell new components, unused (recycled) components and kits with an emphasis on LED lighting. If you are interested in purchasing the business from me, please contact tony<at>phoslighting.net SILICON CHIP PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au For Quality That Counts... PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have been sold. See photos (recently updated): siliconchip.au/link/abl3 Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine December 2023  103 I would like to get a complete kit for the Lathe-E-Boy lathe controller, as published in your January 2018 issue (siliconchip.au/Article/10933). If that is not possible, then maybe links to suppliers of kits for the Induction Motor Speed Controller (April & May 2012, August 2013; siliconchip. au/Series/25) and the Micromite Plus Explore 100 (September & October 2016; siliconchip.au/Series/304). I appreciate any help on the above. (H. G., Bunbury, WA) ● There is no complete kit for the Lathe-E-Boy as it is too specialised. However, we have an almost complete kit for the Explore 100, just lacking the touchscreen (siliconchip.au/ Shop/20/3834). There were complete kits for the Induction Motor Speed Controller released by Jaycar and Altronics, but that was over ten years ago, and they have both since discontinued their kits. The controller/IGBT IC used in the IMSC has not been manufactured for several years. We bought a small stock that we sold through our website, and at the time of writing, we only have one left (siliconchip.au/Shop/7/2814). The only other source we can find for the controller/IGBT IC is Ali­Express. Their provenance is unknown, but presumably they will work. Therefore, except for the Explore 100 part of the design, you would have to gather your own parts. Before ordering the STGIPS30C60 IC from us or anyone else, check that all the other parts are still available. You would need to get a copy of the IMSC parts list, which is on page 72 of the May 2012 issue. Advertising Index 2.5GHz Frequency Counter troubleshooting all the settings down. That should also result in a wider volume control range. If that isn’t enough, the maximum gain can be changed by varying a couple of resistor values. The value of the 10kW resistors between pins 6 & 7 of IC2b/IC4b will reduce the maximum gain and probably also reduce the minimum output. Increasing the values of the 2.2kW resistors connected to diodes D1-D4 should also reduce the maximum output level. Parts for the Induction Motor Speed Controller Altronics.................................29-32 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Emona Instruments...............9, IBC Icom Australia............................... 6 Jaycar............................. IFC, 49-56 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 I built your 2.5GHz 12-Digit Frequency Counter (December 2012 & January 2013; siliconchip.au/Series/21), and it is partially working but not in all modes. Frequency measurements work and are accurate, but it seems to lock up on the 100MHz or lower range in Period mode. The display simply doesn’t update. The FREQ/PERIOD line toggles LD Electronics........................... 103 Microchip Technology......... 7, OBC Mouser Electronics....................... 4 PCBWay................................. 10, 11 PMD Way................................... 103 Rigol............................................... 9 SC GPS Analog Clock................. 23 Silicon Chip PDFs on USB......... 28 Silicon Chip Shop...................... 33 Silicon Chip Back Issues........... 41 The Loudspeaker Kit.com.......... 83 Wagner Electronics....................... 8 104 Silicon Chip Errata and Sale Date for the Next Issue LEDsales................................... 103 when the button is pressed. Both Green LEDs light up properly in period mode, and there is a 1MHz signal at TP2. Could it be a PIC programming problem? (S. C., Revesby, NSW) ● If it displays the frequency, we know the PIC is working; it’s very unlikely the frequency mode would work if it weren’t programmed correctly. The FREQ/PERIOD signal from O4 (pin 12) of IC23 goes to three places: pins 1 & 2 of IC12a, pin 13 of IC13d and pins 12 & 13 of IC18d. Check that there is continuity from pin 12 of IC23 to all those other pins, and verify that they change levels correctly when switching between frequency and period modes. If those seem correct, check that the outputs of those gates are feeding to the right places. That means checking for continuity from pin 12 of IC12 to pin 3 of that same IC, from pin 11 of IC18 to pin 2 of IC11 and from pin 11 of IC13 to pin 10 of IC12. Use the Fig.4 circuit diagram to follow the flow of all those control signals to their ultimate destinations and verify that everything is connected correctly. You will likely find that one of the signals does not flow through due to either a bad solder joint, a pin of an IC not being inserted properly in the circuit or (less likely) a faulty or incorrect IC. Fixing that should get the period function working. At the same time, it would be a good idea to check that all components are correct types in the right positions and examine all the solder joints to ensure they have been properly formed. The fault can almost certainly be traced back to those sorts of problems. SC Breadboard PSU Display Adaptor, December 2022: there was an error in the software (line 65 of main.c) that meant that the wrong analog channel was read during calibration of the second current setpoint. That did not affect regular operation but made calibration difficult. We have fixed this and updated the software to V7; the correct HEX file for programming the PIC16F18877 is now 0411222B.HEX. 30V 2A Bench Supply Mk2, September-October 2023: in Fig.6 on page 76 of the October 2023 issue, the ribbon cable should loop through the top of the connector and terminate at the bottom, not the other way around, as was shown in the diagram. 16-bit Precision 4-input ADC, November 2023: the name for the second library on p48 under “Arduino software libraries” should be “Rob Tillaart”, not “Rob Tillard” and the link should be https://github.com/RobTillaart/ ADS1X15 Next Issue: the January 2024 issue is due on sale in newsagents by Thursday, December 28th. Expect postal delivery of subscription copies in Australia between December 27th and January 15th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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