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FEBRUARY 2024 ISSN 1030-2662 02 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST Build your own Mains POWER-UP SEQUENCER Data Storage Systems Exploring Singapore: • Sim Lim Tower • Sim Lim Square Stay connected with our 4G Antennas & adaptors Compatible with 2.4GHz & 4/5G networks for cross-compatibility 1 5dBi Antenna • Magnetic mount • Suitable for LTE, AMPS, GSM, PCS, UMTS and Wi-Fi • 2m lead with FME connector • 337mm long AR3340 ONLY $64.95 3 5m SMA Extension Lead 4 SMA to Induction 3G Plug 5 SMA to Modem Leads • Low loss • 50Ω coax • Flexible lead WC7824 ONLY $59.95 7dBi Antenna • Magnetic mount • 3m lead with FME connector • 435mm long AR3344 ONLY $89.95 2 • Adhesive backing AR3330 ONLY $32.95 7dBi Spring Mount Antenna • ½ wavelength design • 5m lead with FME connector • 740mm long AR3342 ONLY $169 Range of leads that plug into the antenna socket on your USB modem. AR3332-AR3336 ONLY $32.95 EA SMA to Huawei E160/618 Plug AR3332 1 2 SMA to Sierra TS9 Plug AR3334 Telstra 4G USB Modem AR3336 We stock a great selection of Networking Antennas, Leads, Plugs, Sockets and Adaptors to improve the range and reliability of your wireless network. Explore our wide range of wireless networking products, in stock on our website, or at over 115 stores or 130 resellers nationwide. jaycar.com.au 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.37, No.02 February 2024 14 Computer Storage Systems, Pt1 From punched cards to flash memory, we cover in depth many of the various permanent storage data systems. The first part of our series will focus on the early storage technologies, while the next part will move towards more modern (and future) inventions. By Dr David Maddison Computer technology 60 ESP32-CAM WiFi Camera Module The Altronics Z6387 is a WiFi and Bluetooth-enabled 2MP (two-megapixel) digital camera utilising the ESP32-S3 microcontroller. It can be interfaced with another microcontroller or used as a standalone device. By Tim Blythman Microcontroller review 68 Electronic Markets in Singapore Sim Lim Tower and Sim Lim Square, in Singapore, are two centres full of shops containing all manner of electronic items. By Tim Blythman Electronic components 104 STC Radiotym model 5160 STC’s model 5160 stands out from other clock radios in the 1950s. While the radio was US-designed, it was assembled in Sydney due to high tariffs on importing completed radios at the time. By Associate Professor Graham Parslow Vintage Radio 28 Microphone Preamplifier This compact microphone preamplifier runs from a 9-15V DC plugpack, offers a flat frequency response, low distortion, low noise and adjustable gain (-15dB to +50dB). It also includes switchable 48V phantom power. By Phil Prosser Audio project 48 Mains Power-Up Sequencer, Pt1 The Mains Power-Up Sequencer offers four independently-controlled 10A mains outputs, making it easy to power up several devices together. This helps with circuit breakers tripping, audio equipment thumps and more. By John Clarke Power control project 72 Raspberry Pi Clock Radio, Pt2 In the final part of this series, we show you how to build and use our Clock Radio and combined media player. Because it’s designed with a Raspberry Pi, you can remotely configure the Clock via the internet. By Stefan Keller-Tuberg Clock radio project 83 Model Railway Points Controller Monitor and switch up to eight sets of points (“railroad switches”) from a single Controller. We also show you how to make LED-based signals to go with each set of points. By Les Kerr Model railway project Microphone Preamp Page 28 Part 1: Page 48 Mains Power-Up Sequencer Page 60 Altronics’ Z6387 ESP32 WiFi Camera Module 2 Editorial Viewpoint 5 Mailbag 43 Circuit Notebook 94 Serviceman’s Log 100 Product Showcase 102 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index 1. Latching relay toggle circuit 2. DHT22 temperature/humidity chart 3. Isolated mains V/I monitor 4. ESP32-based ChatGPT terminal 5. WiFi night light 6. LED-based motion sensor SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $127.50 24 issues (2 years): $240 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Check your backups The data we produce at Silicon Chip (magazine layouts, software, PCB files etc) is very valuable to us, so we are careful to back it up, possibly to the point of paranoia. Our internal data store also has quite a bit of redundancy, so even if a storage device fails, we shouldn’t lose anything or even have our workflow interrupted. Backups are for situations like accidental file deletion, file corruption and so on. The general advice is to have three copies of critical data, including at least one off-site. I am a little more relaxed in backing up personal data that I consider less important. I back up important things like family photos and tax documents, but I don’t worry so much about some things that would be more of an annoyance if I lost them, rather than a disaster. However, a recent ‘near-miss’ incident was a wake-up call. For this data, I relied on software with built-in a ‘cloud backup’ feature that told me that the data was ‘up to date’ and ‘synchronised’. But when my Samsung EVO 870 SSD began faltering – disappointing, as I chose it based on Samsung’s reputation for reliability – I realised the perils of overconfidence in technology. Luckily, it didn’t fail completely; most of the data remains readable, with only a fraction corrupted. The problem manifested when I tried to write a significant amount of data to the drive. It would stop responding, often making the computer unusable until it was rebooted. So I bought a new SSD and swapped them. That only took a few minutes, as it was mounted on the back of the motherboard and thus was readily accessible through a hole in the chassis after removing the panel on that side of the case. With the new SSD in place, the computer worked properly again. Still, I would have to wait until I could grab my external M.2 SSD adaptor from the office to get the data off the old drive. In the meantime, I decided to restore some data from the cloud backup. That didn’t go very well. There was data in the cloud backup, but only a fraction of what I expected. It looks like it was only backing up the first file in some directories instead of all of them. It was lucky that I still had most of the data on the drive; I would just have to wait a few days to access it. I filed a bug report with that software vendor, so hopefully, they will fix it for other users. Lessons learned The experience was a good reminder that you can’t just assume that, because you are making backups, you can restore them later if you need them. Not only must you check periodically that the backups are up to date, you need to try to restore some data regularly. The worst possible time to discover that you can’t restore your backups is just after losing the original data! For most people, cloud backup services are the only realistic way to have those all-important off-site backups, but make sure you consider security and reliability when choosing such a service. If your data is very valuable (eg, you make a living from it), consider backing it up to two different providers after ensuring they do not share any infrastructure. In general, it’s a good idea to have diverse backups. I do not recommend backing up to an SSD or flash drive, except in the short term. External mechanical hard disks are inexpensive; while they can be slow, they usually will retain data for years without a problem. Cover image: unsplash.com/photos/grayscale-photo-of-a-land-zcx5ztIjQAM by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au Full speed ahead Trust the new product introduction leader™ to move from concept to prototype at lightspeed au.mouser.com/new 0392539999 | 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”. Australia’s first hydroelectric scheme I enjoyed reading the articles on The History of Electronics by Dr David Maddison (October-December 2023 issues; siliconchip.au/Series/404). In an extensive work, he reported that “Australia’s first hydroelectric scheme began operating, to power street lights in Launceston, Tas”. However, my colleague and I are currently researching the history of the Hillgrove hydroelectric scheme. There is significant evidence to challenge the statement that the Launceston scheme was the first in Australia. In March 1893, the Hillgrove and Armidale Water Power Electric Bill was passed through the NSW Legislative Assembly. One stipulation was that the company should have the works in practical operation 18 months from the passing of the bill. It was reported in the Daily Telegraph of the 11th of September, 1894, that the “The long-looked for lighting of Hillgrove by electricity took place this evening, at 8.30 [PM], and the installation went off without a hitch”. The scheme involved generators in a powerhouse by the Gara River and high-voltage cables up the escarpment to the town of Hillgrove. Professor Threlfall of Sydney University provided engineering supervision. Later, the mines became sporadically uneconomic (although they were still in operation when gold prices were high enough), and the power company unsuccessfully tried to convince the town of Armidale to accept power from the scheme. Without adequate customers, the scheme was closed and some of the equipment was moved to the later scheme in Tasmania. Although there are Engineering Heritage Plaques at the site in Tasmania, over thirty years ago, papers citing Hillgrove as a precedent were published. Gojak, Giopoulos and Dunnett published in 1988, and Wilson published a Master’s thesis in 1990. Gojak et al. reported that “The Gara River scheme was the first substantial hydro-electric scheme to reach fruition in Australia. It began to generate power in late March 1895. The Launceston scheme, generally but wrongly credited as the first hydroelectric scheme to light an Australian town, did not operate until December of that year”. We are still hoping to find further pictures and information about the Hillgrove scheme if anybody has such data, and we will publish more details in the coming year. Dr John C Moore & Adjunct Associate Professor Rex Glencross-Grant, Armidale, NSW. How two-speed motors work motor (Ask Silicon Chip, December 2023, p101), I initially couldn’t understand how they could put a six-pole and a four-pole motor in the same housing. After pondering it for a while, I realised that a twelvepole motor could be arranged as a six-pole or a four-pole motor, as shown in the diagrams I drew (shown below). The diagram shows how a two-pole, two-position switch could select between 1420 RPM and 930 RPM. I have drawn parallel-­ connected poles, but the manufacturer would build it with series-connected poles to reduce the number of turns required. Assuming the motor is a capacitor-start type, I would expect the start winding to be wound only on the poles that are polarised in common to both motor speeds, ie, the poles at 30°, 60°, 90°, 120°, 180° and 330° (using the mathematical convention of starting at three o’clock and rotating anticlockwise, not the geographical convention). The start winding could be identified by being isolated from other windings and testing as a capacitor. Swap the two wires to that winding to reverse the direction of rotation on the motor. Neville Sleep, via email. An early remote control system I have thoroughly enjoyed the History of Electronics series (October-December 2023; siliconchip.au/Series/404) A 4 Pole 6 Pole A N N N A A N N A A N N N A A A N N A A N A N On reading the request for information on a GMF electric siliconchip.com.au Australia's electronics magazine February 2024  5 and would like to point out an interesting, related development. In 1939-42, Zenith produced a console/radiogram equipped with the “Mystery Control” remote control system. It used a telephone dial to send decadic pulses on a longwave frequency, triggering a thyratron that indexed a uniselector. It allowed the user to control the band, select the phono input and even adjust the volume continuously by holding a button below the dial. It could also turn the radio off but could not turn it on. Wenlock Burton VK3YWB, Darley, Vic. Thoughts on expanding symbols on keyboards Regarding your November editorial, I agree that keyboard symbols are a pain, but I don’t think it will work on our keyboards. While there are indeed a few “redundant” keys that are “never used”, they are used by the system and they do actually do something from the system standpoint. Almost all of these keys are a holdover from even further back in time when dumb terminals were still in use, which were backwards-compatible with Teletypes. While Scroll Lock is rarely, if ever, used by 99% of users, there are some legacy systems out there that still use it. Pause/ Break is similar; it throws a system call from the keyboard buffer. Those keys were never used by 99% of users. About the only regularly-used one of those keys is Print Screen/SysRq, which will take a screenshot and put it on the clipboard. In reality, two solutions are available, but someone needs to actually implement them, probably at Apple or Microsoft. We already have some cool system shortcuts that few people know about unless they go looking. For example, holding down the Windows key with Shift and then pressing “s” fires up a utility called “Snip”, Back in the 1980s, we had problems with computer keyboards not being standard. We had an Ohio Scientific Superboard II machine, also known as a Challenger 1P. When it came to programming, we only had machine code or good old Microsoft Basic (thanks, Bill). Someone wrote a small program allowing us to use keyboard shortcuts instead of typing in all the standard commands. Productivity went through the roof. In the 1990s, we had ALT codes that did something similar, but you had to remember them all. So you could have a solution where you, say, hold down Alt+O instead of going through all that effort to get a degree sign or CTRL+8 to get “π”. It would not be hard to program, but getting people to agree to an international standard would be fun. Andrew Pullin, Wodonga, Vic. Comment: some keyboards already lack keys like Scroll Lock because they are so seldom used. Their function could easily be relegated to a secondary key combination (eg, ALT+pause/break). The problem with using something like Alt+O is that many programs already use that as a shortcut for certain actions. The modifier key would need to be a new one (“Sym”?) to avoid conflicts. We are considering creating a programmable keyboard that lets you quickly and easily type a custom set of Unicode characters. Solar hot water heating Marcus Chick’s explanation of mains-powered lights 6 Silicon Chip flashing when off (January 2024, page 8) is correct. However, I have only experienced it with two-way switching, where there is a long cable run between the switches. Regarding solar hot water heating, I have reduced my offpeak hot water bill to zero. This only applies to premises fitted with solar power. I fitted a timer at the switchboard to turn on the water heater at 10am and off at 4pm on the normal tariff. This means it draws power when the solar system can provide the most energy. We export twice what we use with our 10kW system, so it makes sense to use as much as possible during the day. The timer is available from most electrical wholesalers, but ensure you get a model with a backup battery in case of a blackout. I fitted a timer to my son-in-law’s place, which has reduced his electricity bill by $100 without affecting his use of hot water. As an electrical contractor, I could do the work myself, but even if you pay an electrician to do it, you would be better off in no time. John Chappell, Pelican Waters, Qld. Comment: we have experienced flashing fluorescent lights (when ‘off’), controlled by a single switch and a relatively short cable run. However, the cotton-covered wiring in the building was close to 100 years old. Advice on typing extended characters In response to your November editorial, I have been using extended ASCII characters in most applications for decades. For example, ° is ALT+167. Back in the 1980s, my employer used an é in their name; that is ALT+130. There are more than 250 of them (but not everything you may want). So that I don’t need to remember them all or look them up, I have a laminated double-sided table in my drawer. P. S., I am not an Apple user; I don’t know if that makes a difference. Ron Walker, King Creek, NSW. Comment: We also use the ALT+number pad codes, but they have several drawbacks. For one, many keyboards these days lack the number pad, making them almost impossible to use. Also, as you imply, this method is DOS/Windows specific and does not work on other systems (although Macs have a similar system using different keys). Another topic you raise is that many of the characters we want to type, such as most of the Greek letters, are not part of regular ASCII but are Unicode characters. There are ways to type Unicode characters in Windows, but you must enable it. There are thousands of codes, and again, the input method is platform-specific. It just isn’t practical. Having commonly used symbols on the keyboard must be the easiest solution. There just needs to be a single symbol modifier key, which could replace a useless key like pause/break. Pitfalls of mail delivery I have just read your December 2023 editorial and was prompted to write. I have been buying your magazine for over 20 years and thoroughly enjoy reading it. I have even built a few of your projects including, most recently, your 50MHz Frequency Counter and GPS Analog Clock Driver. Those two were my first foray into surface mount technology, and I built both successfully despite my eyesight not being what it used to be. Australia's electronics magazine siliconchip.com.au Introducing ATEM Mini Pro The compact television studio that lets you create presentation videos and live streams! Now you don’t need to use a webcam for important presentations or workshops. ATEM Mini is a tiny video switcher that’s similar to the professional gear broadcasters use to create television shows! Simply plug in multiple cameras and a computer for your slides, then cut between them at the push of a button! It even has a built in streaming engine for live streaming to YouTube! Live Stream to a Global Audience! Easy to Learn and Use! Includes Free ATEM Software Control Panel There’s never been a solution that’s professional but also easy to use. Simply press ATEM Mini is a full broadcast television switcher, so it has hidden power that’s any of the input buttons on the front panel to cut between video sources. You can unlocked using the free ATEM Software Control app. This means if you want to select from exciting transitions such as dissolve, or more dramatic effects such go further, you can start using features such as chroma keying for green screens, as dip to color, DVE squeeze and DVE push. You can even add a DVE for picture media players for graphics and the multiview for monitoring all cameras on a in picture effects with customized graphics. single monitor. There’s even a professional audio mixer! Use Any Software that Supports a USB Webcam! You can use any video software with ATEM Mini Pro because the USB connection will emulate a webcam! That guarantees full compatibility with any video software and in full resolution 1080HD quality. Imagine giving a presentation on your latest research from a laboratory to software such as Zoom, Microsoft Teams, ATEM Mini Pro has a built in hardware streaming engine for live streaming to a global audience! That means you can live stream lectures or educational workshops direct to scientists all over the world in better video quality with smoother motion. Streaming uses the Ethernet connection to the internet, or you can even connect a smartphone to use mobile data! ATEM Mini Pro $495 Skype or WebEx! Learn more at www.blackmagicdesign.com/au Here’s a small slice of the technologies that we offer at Quest Semiconductors: ● SiC High Voltage Wafers When I built the fence across the front of our property here in Otago, I went to a great deal of trouble and expense to build into the wall a large letter box with a 330mm wide slot so that the postman could deliver oversized items flat. However, for reasons known only to themselves, they seem hell-bent on folding everything in half and ruining them. I get a monthly newsletter from a car club and the HRSA’s Radio Waves; both invariably turn up with folds down the middle. This is very annoying and is why I will always buy Silicon Chip from the newsagent, rather than subscribing, so that I get a mint copy. I am sure I would not be the only disappointed reader if you went to an online-only version. I would also like to convey my appreciation to you and your staff for what is no doubt the finest electronics magazine on the planet. Ron Barnes, Otago, Tas. Comment: we understand your desire to receive a pristine magazine, so your situation is frustrating. We know that mail delivery doesn’t suit everyone. You could consider renting a large PO Box as magazines delivered to our PO Box are not folded. As stated in a previous editorial, we have no plans to discontinue the printed edition, although it’s hard to say what will happen in the distant future. ● SiC Mosfets & Membranes ABC News article on dark patterns We are Australia’s only power semiconductor manufacturer based in Queensland. We offer ASIC designs for OEMs as well as off-theshelf devices for distributors. ● SiC Homogeneous SBDs (Schottky barrier diode) ● Solar diodes ● Australian SiC Diode Fabrication and Technology ● IGBTs & TCIGBTs (trench clustered insulated gate bipolar transistor) ● Power Modules ● Sensors and JFETs ● ASICs Quest Semiconductors Pty Ltd Unit 1, 2-8 Focal Avenue, Coolum Beach, QLD 4573 email: sales<at>questsemi.com Tel: +61 (07) 3132 8687 8 Silicon Chip On the topic of your January editorial, there is an article regarding dark subscription patterns in this week’s ABC RN Newsletter. When PCs fail, virus and tune-up subscriptions carry on that are specific to that failed PC. Some tune-up programs don’t have an obvious subscription cancel method. See: siliconchip.au/link/absb Adrian Tyler, Wahroonga, NSW. The fate of our prototypes As yet another long-time reader of Silicon Chip, I would like to congratulate you on producing such a first-class magazine and, in particular, the quality of your projects. Like many of your readers, I have an ever-expanding library of your printed magazine along with EA, ETI, Wireless World and others going back to the fifties and beyond. I have not yet reached the stage of having to scale back my library, and often just pick a year and flick through, looking at the projects and technical advancements of yesteryear. Back in the halcyon days of electronic magazines (late sixties, early seventies), there appeared to be a much greater number of short technical articles covering electronics in all sorts of disciplines. Although you continue to produce great technical articles, they are typically larger and more comprehensive but at the expense of shorter ones like EA’s technical review section of many years ago. I suppose the internet has a lot to do with that. Still, to be honest, I find a 1970s edition of EA a more comprehensive and satisfying coverage of the world of electronics (albeit with much simpler projects) of its day. Finally, I have one burning question that I have always wanted to ask. What do you do with all your completed project hardware? You would have produced hundreds of completed projects over the years. Sadly, I think many no longer exist due to space limitations, but they would have made a great contribution to a technical museum or similar. Clive Allan, Glen Waverley, Vic. Australia's electronics magazine siliconchip.com.au A selection of our best selling soldering irons and accessories at great Jaycar value! 25W Soldering Iron TS1465 $22.95 Build, repair or service with our Soldering Solutions. We stock a GREAT RANGE of gas and electric soldering irons, solder, service aids and workbench essentials. ESD Safe Tweezer Set TH1760 $24.95 Solder Flux NS3070 $21.95 Precision Angled Cutters TH1897 $27.95 1.5 to 3mm Desolder Braid NS3026-NS3028 $9.95EA 0.71mm & 1mm Solder NS3001-NS3096 FROM $4.55 240V Fume Extractor TS1580 $79.95 PCB Holder with LED Magnifier TH1987 $41.95 48W Soldering Station TS1564 $149 160pc Heatshrink Pac k WH5524 $29.95 Shop at Jaycar for soldering essentials: • Battery, gas and electric soldering irons & stations • Wide range of solder • Desoldering braid & tools Explore our great range of soldering gear, in stock on our website, or at over 115 stores or 130 resellers nationwide. • Soldering iron stands, cleaners & PCB holders • Heatshrink tubing • Tools & service aids jaycar.com.au Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 1800 022 888 Comment: there are a variety of reasons articles have grown longer. For one, readers expect articles to be comprehensive, and we are more likely to receive complaints about some specific information that’s missing if we try to be brief. We may be able to publish more articles like that; it depends on finding someone who can write them and finding topics that haven’t already been covered extensively (or are worth revisiting). The completed project prototypes are mostly accumulating in a pile at our office. We have most prototypes going back about 15 years and some older ones. Occasionally, we must dig one out to look into a reported problem or update it. Sometimes, a member of staff will take one home. Some of them are in frequent use, such as the Ultra-LD Mk.3 stereo amplifier, the CLASSiC DAC prototypes, the latest Bass Extender, the Majestic loudspeakers and a few others. Information on mains slave switch project On page 112 of your August 2023 edition, in the “Ask Silicon Chip” section, G. M. of North Epping, NSW, asked about a “load-controlled mains switching box” project they had lost all information on. They may have been talking about a project I had built a few years ago but accidentally ‘cooked’ by thoughtlessly running a 1kW fan heater through it! The project was called “PowerUp”. Mine worked perfectly until I grossly overloaded it. I used it to switch my PC monitor, printer, and speaker system on and off automatically, controlled by my PC’s power switch. The overload fried the main Triac, charred the PCB and melted the plastic case before I realised my stupid mistake. I can’t remember if it was an EA or Silicon Chip project, as I was buying both at the time. Hopefully, this may be of some help. Neville Goddard, Blue Haven, NSW. Comment: Thanks for the information. PowerUp was published in Silicon Chip in the July 2003 issue (siliconchip. au/Article/3905), although it doesn’t match G. M.’s description. PowerUp has a transformer mounted on the PCB, while his PCB has little more than a relay, a 10W resistor, six diodes and two transistors. We suspect it was an EA or ETI project similar to the PowerUp but published earlier. Objections to the term “renewables” Further to your response to the letter from Rex Mower in the November 2023 issue, I take exception to the use of the term “renewables” when referring to electricity provided by wind turbines and solar panels. Undoubtedly, the sun is an energy source of essentially infinite duration. Therefore, the term “renewables” would be seen by most as appropriate for the sun itself. However, when used in reference to electricity produced by wind turbines and solar panels, the term “renewables” must be seen as a fraud. That is because the technology needed to generate the electricity is not of infinite duration (it breaks) – and given the ongoing lack of recycling (back into a form where it can be reused for the same purpose – as opposed to the pretence of recycling which is more-correctly called “repurposing”), the raw-materials will inevitably run out. So the technology will cease to be available in something in the order of decades to half a century. It is long 10 Silicon Chip Australia's electronics magazine siliconchip.com.au past time that the finite nature of the so-called renewables was recognised – at least in respectable technical forums. It is also long past time that Australia started applying intelligence and planning to what is so far a piecemeal and highly inefficient transition to a technology that, so far at least, is far more finite than coal and that (when whole-oflife is taken into account) is not nearly as low-polluting as is portrayed. Australia needs a thorough analysis of our demand for electricity on a minute-by-minute basis (particularly given the very short duration of some of the electricity storage mediums) throughout the year, and an analysis of the current and planned infrastructure that is supposed to replace our generators. It seems we are changing over to a less-than-efficient network – with generators placed wherever is best for the owners of those generators and mostly not “firmed”, and the hook-up is paid for by the taxpayer in the form of network links that are far more expensive (and damaging to those who own the land) than they would otherwise need to be due to both length and capacity. While we are at it – we could also look at the masses of rooftop solar that is totally under the manufacturer’s control (via networking back to the manufacturer) and could easily be weaponised to destabilise our grid. I invite Silicon Chip to do an expose on the current and imminent situation in Australia. It is long past time that intelligent analysis was performed on this escalating disaster. John Evans, Macgregor, ACT. Comment: while you have a point, we aren’t likely to run out of silicon (or the required dopants, used in minuscule quantities) any time soon. That isn’t to say that manufacturing and recycling/disposing of solar panels and wind turbines is not environmentally damaging. We think what you have stated applies more to batteries, which is why pumped hydro is so attractive for grid-scale energy storage. Working around generic email blocks In the January 2024 issue, J. S. of Avondale, Qld, complained about the SendGrid and SMTP2GO services not accepting his email (Gmail) address (Ask Silicon Chip, page 100). A good workaround is to get your own domain name, in my case via VentraIP. When asked for a ‘business’ email address, I can use a custom address at my domain. An added advantage is that you can get a personalised address. For the above case, he could have a domain name of, say, avondale.net or whatever, and his email address could be js<at>avondale.net. It is relatively cheap, around $10-20 per year. You can also have more than one email address in the domain. I have me<at>mydomain, wife<at>mydomain and daughter<at>mydomain addresses. Paul Cahill, Balgal Beach, Qld. Comment: this is a good idea, but be careful because many scam emails are currently trying to trick VentraIP customers. Electronics History articles enjoyed The articles about the History of Electronics (October to December 2023) are quite fascinating. I initially thought they would be boring, but not at all. There were so many little-known contributors who built on each other’s work to bring electronics to where it is today. Paul Howson, Warwick, Qld. 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Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. jaycar.com.au 1800 022 888 Data Storage Systems Part 1: by Dr David Maddison My articles on Computer Memory last year concentrated on ‘ephemeral’ storage such as RAM. I also mentioned more permanent storage systems like punch cards, magnetic drums and core memory. These two articles take a more complete look at permanent and semipermanent data storage of today, the future and the past. T hose two earlier articles on Computer Memory were in the January & February 2023 issues (siliconchip. au/Series/393). There is some overlap between this series and that one because computers didn’t always distinguish between temporary and permanent storage, especially in the early days. Partly, that was because RAM was so expensive per kilobyte, and it was necessary to use slower but cheaper storage to ‘swap out’ the contents of RAM. That allowed the computer to work with more data without needing a lot of expensive memory chips. We refer to the more permanent storage systems as ‘secondary storage’; this is long-term data storage, which retains its state when the system power is off. It is typically used to store an operating system, programs and (of course) for data storage. In contrast, ‘primary storage’ is volatile memory the computer uses during operation as programs run. An example of secondary storage is a hard disk or solid-state drive (SSD). By definition, it is a permanent part of the computer. A hierarchy of computer storage is shown in Fig.2. Offline storage is much like secondary storage but is removable, transportable media such as a USB flash drive or an optical disc like a DVD. Once connected to the computer, it behaves much like secondary storage. It is typically used for transporting data 14 Silicon Chip between computers without a physical connection, or for backing up data, including off-site backups. With some offline storage, the recording medium is kept in longterm physical storage, for backups of important information such as bank records. Being completely offline means it cannot be accessed or damaged without authorisation. Such storage might be for historical and archival records, such as old government census data. Tertiary storage is where the data is accessible to a computer, but not permanently connected to it. An example is a large tape library requiring a robotic arm to retrieve and insert a tape into an appropriate reading mechanism. This is also called nearline storage; it is almost online, but retrieving the data storage medium takes time. Cloud storage might be considered a form of secondary storage that a third party manages. It is located remotely from the user and may span multiple servers. Its main advantage is that it is more convenient, as it can be accessed from various locations. Disadvantages include an unknown risk of unathorised access (it depends on many factors such as the company managing it), an unknown risk of data loss (it has happened...) and the fact that the cloud storage company could go out of business and cut you off from your data. Therefore, cloud data still needs to be backed up like any other data. There are and have been many different secondary storage technologies; this article focuses on the more Fig.1: a blue IBM-style 80-column card encoded with almost the full Extended Binary Coded Decimal Interchange Code (EBCDIC) character set, shown at the top. Source: https://w.wiki/8R5y Australia's electronics magazine siliconchip.com.au significant ones, as well as some of the more unusual and interesting systems. We won’t go into as much detail on systems that were already covered in the aforementioned Computer Memory article. Technologies covered The entries below are arranged chronologically, based on the earliest use of the technology. There will be some overlap between the later versions of one technology and the earlier versions of its replacement. Entries marked with an asterisk (“*”) were covered in some detail in the Computer Memory article. In this first article, we have details on: • Punched cards* • Paper tape* • Drum memory* • Core memory* • Rope memory* • Magnetic tape* • Magnetic cards • Floppy disks • Bubble memory* • Optical discs • Magneto-optical discs The follow-up next month will concentrate on: • Hard disks • Flash memory* • Solid-state drives (SSDs) Plus the following possible future technologies: • 5D optical storage • Holographic storage • DNA storage Fig.2: ways that memory and storage can attach to a computer. Fig.3: a Canon Canola 167P calculator/computer (1971) with punched card program storage. Similar machines were used in NSW high schools in the early 1970s. Image courtesy of John Wolff, www.johnwolff.id.au Punch(ed) cards Punched cards are pieces of cardboard with holes in them representing the data – see Fig.1. The most recent and common form of punched card was the IBM 80-column card at 7⅜ × 3¼ inches (187 × 83mm). They were introduced in 1928 for tabulating machines. Not all modern punch cards were in IBM format, though; the Canon Canola 167P (Fig.3) would be familiar to many readers who were NSW high school students in the early 1970s. Fig.4: durable Mylar replaced paper in punched tape for industrial use, such as machine control. This tape was among the last to be produced in 1979. Source: https://w. wiki/8R62 (CC BY-SA 3.0). Punched paper tape Punched paper tape is similar to punched cards, except it is continuous; see Fig.4. This format has been obsolete since the early 1980s. Drum memory Drum memory was invented by siliconchip.com.au Australia's electronics magazine February 2024  15 Austrian Gustav Tauschek in 1932. Data was recorded on a drum coated in magnetic material. It was invented much earlier than the modern computer because it was used to record and tabulate data from punched card machines. The original device could store 62.5kB of data. Drum memory was used as RAM on some early computers but also as secondary storage in the 1950s and 1960s. It was the first type of secondary storage for computers – see Fig.5. The ERA 1101, renamed UNIVAC 1101, was built by Engineering Research Associates in 1950 and was one of the first stored program computers (ie, it was not programmed by rerouting wires). Programs were stored Fig.5: an early drum drive, circa 1951, at the Computer History Museum, Mountain View, California. The scratches on the drum surface are damage due to misaligned heads. Source: https://w.wiki/8R63 (CC BY 2.0). on a drum system of about 48kB. The drum was 22cm in diameter, spun at 3500 RPM and had 200 read-write heads. One of the last drum memory devices created was the IBM 2301, introduced in 1968 for the System/360 mainframe. It cost US$80,000 and had a storage capacity of about 4MB. It had an access time of 8.6ms, a transfer rate of 1.2MB/s and was used for memory paging (supplementing main memory to create a virtual memory extension). The drum was about 60cm high and 30cm in diameter, and the entire cabinet was about 2m tall and had a 1 × 2m footprint. Drum memory was not manufactured after the 1970s, although as late as 1980, PDP 11/45 computers that used drum memory and ran Unix were still in use. US Minuteman ICBM missile “Launch Control Centers” used drum memory until the mid-1990s. Perhaps the ultimate development of magnetic drum storage was the Univac FASTRAND, a giant 2.4m-long machine weighing about 2276kg. FASTRAND II stored the equivalent of 99MB (8-bit bytes). The FASTRAND III (Fig.6) had a higher data density, holding about 50% more data. Both the II and the III models had two counter-rotating drums, as the model I with a single drum had serious gyroscopic precession problems; only a few were made. Drum memory was the forerunner of hard disk drives and was eventually replaced by them. You can watch a video titled “1963 Sperry Rand UNIVAC FASTRAND Magnetic Drum, Computer History Archives, Unisys Educational” at https://youtu.be/luPM6XaKZuU The video mentions that such drives were used in OTC’s automatic message relay system in Paddington, Sydney, which was decommissioned in 1988. For further information on that, see siliconchip.au/link/abrn Another video about a 1960s-era minicomputer with drum storage titled “Meet my new Litton Minicomputer (it has Drum Memory)!” is at https://youtu.be/2yRcyQUIA5g Magnetic core memory Fig.6: a FASTRAND III drum drive from 1969 at https://gwdg.de/ – Source: https://www.radiomuseum.org/museum/d/rechnermuseum-der-gwdggoettingen/.html 16 Silicon Chip Australia's electronics magazine This memory was commonly used from around 1955 to 1975 as the main memory in computers, but it was also a form of non-volatile memory as it would retain its data when the power siliconchip.com.au Fig.7: an IBM core memory from the 1950s or 1960s. Source: https:// collections. museums victoria. com.au/ items/394677 (CC BY). was off. It comprised a grid of toroidal cores, which could be individually magnetised to store bits of information (see Fig.7). The YouTube video “Building the Core64 Interactive Magnetic Core Memory Kit” at https://youtu. be/7K6Qu-mNDms might interest our readers. Also see www.core64.io/ Besides covering core memory in the Computer Memory article last year, we also had a dedicated article on it in the March 2014 issue (siliconchip. au/Article/6937). Core rope memory Rope memory is a fascinating type of ROM (read-only memory) using magnetic cores with multiple sense, set/ reset and inhibit wires going through (or bypassing) them. This type of memory was used in the Apollo Guidance Computer. It had a much higher density than erasable magnetic core memory, which could only store one bit per core. With rope memory, up to 192 bits could be stored per core. The precise way it worked is very complicated. The best way to understand it is to watch these videos: • “Apollo Core Rope Memory (Apollo Guidance Computer Part 30)”: https://youtu.be/hckwxq8rnr0 • “Core Rope Memory Built and Explained - F-J’s Physics - Video 169”: https://youtu.be/WBHdNpAC7X4 • “DRUM MACHINE USING NASA TECHNOLOGY - Rope Core Memory Sequencer”: https://youtu.be/ zytjONYkU94 (also see Fig.8). Magnetic tape Magnetic tape was a common method of data storage on earlier computers, and it is still used today for backups and archival storage. Earlier tapes used ‘open reels’, but modern tapes are contained with cartridges. Today, magnetic tape is generally cheaper per gigabyte than other storage media but also slower, so it is used where speed is not so important. Magnetic tape was first used on the UNIVAC I computer on half-inch (12.7mm) metal tapes. There were eight tracks of data. Six tracks contained 128 characters per inch; one was for parity (error checking), and one was a clock signal. Those tapes were heavy and cumbersome. IBM computers from the 1950s used half-inch (12.7mm) wide plastic tape siliconchip.com.au Fig.8: the top of this device has an eightcore core rope memory, made with large cores as it is a demonstration unit. Source: https:// youtu.be/ zytjONYkU94 Storage capacity units The following are standard SI units for storage capacity. These measurements are often applied to the capacity of storage and networking capacity. ● 1 kilobyte = 1000 bytes (103) ● 1 megabyte = 1,000,000 bytes (106). ● 1 gigabyte = 1,000,000,000 bytes (109) ● 1 terabyte = 1,000,000,000,000 bytes (1012) ● 1 petabyte = 1,000,000,000,000,000 bytes (1015) ● 1 exabyte = 1,000,000,000,000,000,000 bytes (1018) A byte usually contains 8 bits. Similar terms can be used to refer to storage by number of bits (kilobit, megabit, gigabit etc). When referring to RAM, the same terms are sometimes used to refer to numbers based on the powers of two. For example, a kilobyte can sometimes refer to 1024 bytes (210), a megabyte to 1,048,576 bytes (220) etc. To reduce confusion, per the IEC, they are now called kibibyte (KiB, 210 bytes), mebibyte (MiB, 220 bytes), gibibyte (GiB, 230 bytes), tebibyte (240 bytes) etc. The names may seem strange, but the motivation is that “bi” are the first two letters of the word “binary”. Unfortunately, you sometimes see the use of mixed bases, eg, one “megabyte” may refer to 1000 × 1024 or 1,024,000 bytes. Thankfully, that is relatively uncommon. Australia's electronics magazine February 2024  17 ◀ Fig.9: the IBM 729 tape drive was popular in the 1960s. This bank of 729s is at the Computer History Museum in Mountain View, California. Source: Ken Shirriff, https://ibm-1401.info/729-Info.html ◀ Fig.10: the last nine-track, half-inch tape drive produced, the Qualstar 3400. It could be attached to a PC. Source: www.bitsavers.org/pdf/ qualstar/Qualstar _3400_Brochure.pdf coated with ferric oxide, much like audio tape. Lengths of 1200ft (365m) and 2400ft (730m) became standard. A tape reel size of 10.5 inches (267mm) was used, although smaller reels and shorter lengths were available. Earlier IBM tapes, introduced in 1952, used seven tracks (six data bits and one parity across the tape), while later ones, introduced in 1964, had nine tracks (eight data bits and one parity). Seven-track tapes had a recording density of 100, 200, 248, 556 or 900 characters per inch, while nine-track tapes stored 800, 1600 then 6350 characters per inch. Thus, the shortest tapes at the lowest recording density had a capacity of about 1.44MB. The longest tapes at the highest recording density had a capacity of around 182.88MB (but due to block size considerations, more like 170MB). During the late 1950s to the 1960s, the IBM 729 Magnetic Tape Unit (seven tracks) was a common tape unit in various versions – see Fig.9. The last half-inch nine-track tape drives were the Qualstar 3400 series from the USA in 2003; see Fig.10. Such drives interfaced with PCs and were presumably used to transfer data from old tapes. The nine-track format dominated offline tape storage until the early 1990s. Another type of tape was DECtape (Fig.12), introduced in the 1960s and used with many Digital Equipment Corporation computers such as the PDP-8 and PDP-11. These tapes were ¾-inch wide (19mm) and 260ft (79m) long. Each tape could store 184,000 12-bit PDP-8 words. DECtape had six data tracks, two mark tracks, two clock tracks and 18 Silicon Chip a data density of about 350 bits per inch. The tape system was considered highly reliable and durable. DEC­ tape is derived from LINC tape (1961), which was a public domain technology as the US taxpayer had funded its development. DECtape II was introduced in 1978, with very narrow (3.8mm) tape in a cartridge, giving a 256kB capacity. At the time, DECtape was considered a major advance for storing a computer’s operating system over the alternative of paper tapes, which could not support time sharing. The drum and disk drives of the time were expensive, unreliable and of limited capacity. Many early home computer systems used audio cassettes (Compact Cassettes) to store data. Some Compact Cassette tapes had a special formulation for digital data, and the tape length was usually shorter than audio tapes. Computers that used (or could use) cassettes included various Commodore computers (VIC-20, C64, C128 etc), ZX Spectrum, Sony MSX, Amstrad CPC 464, BBC Micro and various Ohio Scientific computers, among others. “Pocket computers” like the Sharp PC-1211 (TRS-80 Pocket Computer PC-1) and PC-1500 (TRS-80 Pocket Computer PC-2) also used cassette tapes. The Commodore computers used the Datasette (Fig.13), which was considered reliable but slow. It used a digital recording scheme on standard tape and transferred data at around 50 bytes per second. Various vendors developed ‘fast loader’ software to load data from cassettes much faster than the default methods used by computer manufacturers. Formats for cassette data storage Australia's electronics magazine included Frequency Shift Keying (FSK), first developed by RCA for their prototype home computer of the early 1970s. It was called FRED or Flexible Recreational Educational Device and had a built-in cassette drive. The Hobbyist Interchange Tape System (HITS) was introduced in 1975 by Jerry Ogdin for general hobbyist use. It used Pulse Width Modulation (PWM). The original article on HITS can be downloaded from siliconchip. au/link/abrt The Kansas City Standard (KCS) was introduced in 1975 by S-100 bus computer manufacturers and used FSK. KCS and its variations were used for numerous computers, including the Acorn Electron, BBC Micro, Dick Smith Super-80, Exidy Sorcerer, Microbee, MITS Altair 8800, Ohio Scientific, Sega SC-3000, Sony MSX and various Casio calculators. Particularly interesting variations of KCS included the encoding of software on a flexible vinyl 33⅓RPM record distributed in the May 1977 issue of Interface Age. KCS was also used to Fig.12: DECtape and DECtape II (lower right). Source: https://w. wiki/8R6W (CC BY-SA 3.0). siliconchip.com.au distribute software over the air in 1979 or 1980 via the Dutch broadcaster Nederlandse Omroep Stinging. The Apple I and ][, Atari computers and the TI-99/4 had their own versions of cassette interfaces. A ZX81 computer could load from tape at 300 baud (bits per second), while the ZX Spectrum could load at 1500 baud without speed loader software. The 1982 Dick Smith Wizzard computer used cassette tape, as demonstrated in the video titled “The Dick Smith Wizzard - Part 2 - Cassette Storage Module” at https://youtu.be/ bXKFag4x6EU The D/CAS (Data/CASsette) or streamer cassette was a professional form of Compact Cassette for digital recording. It used media optimised for data, and there was a notch in the case to identify this special format. Storage capacities started at 200kB; 600MB was possible by 1990 (see siliconchip.au/link/abru). It wasn’t only personal computers that used Compact Cassette for storage. The Burroughs B1700 mainframe of the 1970s could be booted from Compact Cassette tape! The DC100 (Data Cartridge 100) by HP and 3M was released in mid-1976. It was originally used in the HP9820 calculator and a range of other HP calculators, terminals and computers, such as the HP85. It had a formatted storage capacity of 560kB on 140ft (43m) of tape. The format was available for other companies, but the take-up rate was poor. It was a scaled-down version of 3M’s DEC300 cartridge, which had 300ft (91m) of tape and 2.5MB capacity. A variation of the DC100 cartridge, the DC150, was used for DECtape II, mentioned above. The ZX Microdrive (Fig.11) was introduced by Sinclair Research for use with the ZX Spectrum home computer in 1983. It was an endless loop tape drive containing 5m of 1.9mm-wide magnetic tape. It could store around 85kB, taking into account bad sectors. Video tape was also used for backups. The Danmere Backup was introduced in 1996 and could store between 750MB to 4GB on a video cassette, depending on the settings and model. There was also the Magurex Video Backup System for the Commodore Amiga and the Russian ArVid (2GB of data on an E180 tape). These systems were in use from about 1992 to about 1998 but had limited popularity. See the video titled “LGR Oddware - Danmere Backer VHS Hard Drive Backup System” at https:// youtu.be/TUS0Zv2APjU I recall Dick Smith Electronics selling one of these systems, possibly the Danmere. QIC tape (Quarter Inch Cartridge) Fig.13: the Commodore Datasette. It could store about 100kB per 30-minute side on standard audio cassette tape, but with special speed loading software, that could be extended to 1MB per 30-minute side. Source: https://w.wiki/8R6X Fig.14: the internals of a Sony LTO-3 cartridge. Note the RFID chip in the lowerleft corner. Source: https://w.wiki/8R6Z (CC BY-SA 4.0). Fig.11: a ZX Microdrive (opened) in comparison to Compact Cassette tape. Both hold about the same amount of data (about 100kB nominal), but the cassette takes 20 minutes to load fully, and the Microdrive 10 seconds. Source: https://w.wiki/8R6Y siliconchip.com.au Australia's electronics magazine was introduced by 3M in 1972. The tape is ¼-inch (6.35mm) wide, and the cartridges are very robust, with a heavy aluminium baseplate. The original tape cartridge was the DC300, which held 200kB on 300ft (91m) of tape and formed the basis of the DC100 tape and the DECtape II formats. Other formats were QIC-11 (20MB), QIC-24 (45MB or 60MB), QIC-120 (125MB), QIC-150 (150MB), QIC525 (525MB) and QIC-1350 (1.35GB), among others. Travan was another derivative of the QIC format intended for PC backup use, with 8mm-wide tape. Tape types included QIC-80 (80MB-500MB), TR-1 (400MB), TR-1EX (500MB), QIC3010 (340MB), TR-2 (800MB), QIC3020 (670MB), TR-3 (1.6GB), TR-3EX (2.2GB), QIC-3080 (1.2-1.6GB), TR-4 (4GB), QIC-3095 (4GB) and TR-5 (10GB). Linear Tape-Open (LTO) or Ultrium (Fig.14) is a successful and popular attempt to make a universal, open standard for tape for backups, archives and data transfer. It is under the control of Hewlett Packard Enterprise, IBM and Quantum via the LTO Consortium (www.lto.org). The original version, LTO-1, was released in 2000 and had a native capacity of 100GB. The current (2021) version is LTO-9, with a native capacity of 18TB per cartridge (advertised by its compressed capacity of 45TB). Future versions of LTO are planned with native capacities as follows: LTO-10 (36TB), LTO-11 (72TB), LTO12 (144TB), LTO-13 (288TB) and LTO14 (576TB). LTO tape is 12.65mm wide (‘½in’). The length was 609m for LTO-1, increasing to 1035m for LTO-9. Each tape has a passive RFID non-contact February 2024  19 memory chip inside that stores various identification information about the tape and user data. There is also a bar code specification for LTO tapes, for use in a tape library or for general identification. LTO is designed with a certain amount of compatibility with older versions. Generations 1 to 7 can read tapes from two generations prior and can write to tapes of the previous generation. LTO-8 can also read and write LTO-7 tapes, while LTO-9 can also read and write LTO-8 tapes. Otherwise, older tapes need to be migrated to newer versions. As with all other media formats, given that the earlier LTO tapes can be up to 24 years old, it is essential to migrate old data to newer versions as older media may degrade. Manufacturers specify that LTO tapes will retain their data for between 15 and 30 years. Tape libraries are a convenient way to store large collections of tapes. They may stored on shelves for manual retrieval or, more likely today, in automated systems with robotic media retrieval – see Figs.15 & 16. Card Random Access Memory (CRAM) CRAM was a product of NCR Corporation and became available for their NCR Century series computers in 1962 (see Fig.17). It comprised cartridges with either 256 or later, 512 plastic cards with a magnetic recording surface, each 3in x 14in (76 × 356mm). Each card had a unique notch pattern at one end by which it was suspended by rods. By rotating the suspending rods, an individual card could be selected. It was released from the cartridge and then read, after which it was returned. The capacity was either 5.5MB or 11MB per cartridge. CRAM was quite successful, according to the document at siliconchip.au/link/abro: “NCR was the first company to incorporate bulk storage as an integral element of online inquiries. Bulk storage provided accessibility to a larger capacity than could be cost-justified on secondary storage devices such as disk drives. The cost/bit was reduced by using removable media, transport mechanisms, and read/write stations.” So, it was cheap enough to enable the storage of online data for purposes such as bank balance enquiries. Such a machine is in the Museums Victoria Collections (siliconchip.au/link/ abrp). The original CRAM product brochure can be seen at siliconchip. au/link/abrq Other magnetic cards The HP-65, introduced in 1974, was the first calculator to use a magnetic card for storage. The card would store 250 bytes per side – see Fig.18. Another calculator that used magnetic cards was the Texas Instruments TI-59, which was introduced in 1977. Shown in Fig.19, it was also the first calculator series to use removable ROM modules with pre-written applications containing up to 500 steps. The card would hold 240 bytes per side for a total of 480 bytes, and the calculator itself had a memory of 960 bytes. There was a ROM module for a US Marine Corp version of the related TI-58C for Harrier ‘jump jet’ takeoff and landing calculations; siliconchip. au/link/abrr Fig.15: an LTO tape library with a robotic arm to store and retrieve tapes automatically. Source: Fujifilm (www.techradar. com/news/heres-the-cheapest-way-to-store-a-huge-1000tb-ofdata-online). 20 Silicon Chip Fig.17: an NCR CRAM unit. Source: NCR product brochure (https://archive.computerhistory. org/resources/text/NCR/NCR. CRAM.1960.102646240.pdf, p27). In 1969, IBM introduced the Magnetic Card Selectric Typewriter, an early word processor that could record, store and play back keystrokes. It used magnetic cards for storage (see Fig.20). They were like a combination of a punched card and a floppy disk. Each card could store about 5000 characters, compared to a punched card with just 80. There is a video of it titled “1969 IBM Mag Card Selectric Typewriter MC/ST Electronic Word Processing Magnetic Storage automation” at https://youtu.be/bW_jJjUarp0 Floppy disks A floppy disk is a flexible disc with a magnetic coating within a protective sleeve (usually square). The name ‘floppy’ was used because those sleeves were originally flexible, although rigid housings were used Fig.16: the IBM TS4500 Tape Library at KEK, Japan’s “High Energy Accelerator Research Organization”. Its capacity is 100 petabytes (100PB). Source: https://w. wiki/8R6a (CC BY-SA 4.0). Australia's electronics magazine siliconchip.com.au Fig.18: an HP-65 calculator with a magnetic card that passes through the machine as the program is loaded or stored. Source: https://w. wiki/8R68 (CC BY 2.0). Fig.19: a TI-59 calculator with magnetic card storage. Source: https://w. wiki/8R69 (CC BY-SA 4.0). starting with the 3.5in version. They were a common storage medium from the 1970s to the 1990s. Development of the floppy disk was started by IBM in 1967, and the first 8in (20cm) floppy was introduced in 1971 as the IBM 23FD, called the Minnow, with ~80kB (81,664 bytes) of storage, equivalent to over 1000 punch cards. The drive was read-only and was used to load microcode onto System 370 mainframe computers. The first 8in floppy drive with read/ write capability was the Memorex 650, which had a capacity of 175kB and was introduced in 1972. In 1973, IBM introduced the 8in Diskette 1 as part of its 3740 data entry system (Fig.22), which popularised the floppy disk. It had a capacity of 242,944 bytes formatted. There is an interesting related IBM document, “IBM 3740 Data Entry System System Summary and Installation Manual Physical Planning”, available from siliconchip.au/link/abrs The 8in floppy disk was developed to a peak capacity of around 1.2MB in 1977. A 5.25in (13⅓cm) disk and drive was introduced in 1976, the Shugart SA-400 Minifloppy, with a nominal capacity of 110kB (formatted capacity 87.5kB). This product became extremely popular. By 1978, Tandon introduced a 360kB double-sided, double-density format and, in 1979, the TM-100 drive (Fig.21). It appears that it wasn’t immediately used by any of the popular PC manufacturers. The original Apple ][ of 1978 used SA-400 drive mechanisms and had a capacity of 113kB. Atari released a similar 90kB drive in Fig.20: the IBM Selectric MC-82 with a magnetic card reader. Source: https://w.wiki/8R6A (CC BY-SA 3.0). 1979, while Commodore had a 170kB drive, also in 1979. The original IBM PC from 1981 had an optional floppy disk drive with 160kB per side. Support for 180kB per side (360kB total) was not offered until 1983. The TRS-80 Model III (1980) used Tandon TM-100 drives with a total capacity of 360kB. 5.25in floppies reached a maximum capacity of 1.2MB by 1982. In 1982, the Microfloppy Industry Committee (MIC) released the 3.5in (8.9cm) disk specification. A single-­ sided disk was released in 1983 with a formatted capacity of 360kB, or 400kB on the Apple Macintosh, followed by a double-sided disk of 720kB or 800kB on the Mac, and 880kB on the Amiga. In 1986, a 3.5in floppy was released with a formatted capacity of 1.44MB or 1.76MB on the Amiga. A 2.88MB “Extra High Density” (ED) 3.5in floppy disk was introduced in 1987. The Video Floppy (VF) disk was a 2in (50mm) floppy disk for recording analog video, usually as a series Fig.21 (left): a Tandon TM100-2A 5.25in floppy disk drive, as used on the original IBM PC, with an initial capacity of 320kB (increased to 360kB with DOS 2.0). Source: https://w. wiki/8R6D Fig.22 (right): the IBM 3740 Data Entry System popularised the floppy disk. On top of it are four 8in floppy disks, a Diskette 1 box and an oddly shaped CRT monitor. Source: https://w.wiki/8R6C (CC BY-SA 2.0). siliconchip.com.au Australia's electronics magazine February 2024  21 Floppy disk hacks Some early 5.25in floppy disks were sold as single-sided, and the “writable” side was indicated by a notch on one side. However, the media was actually writable on both sides. Some people used a paper hole puncher or special punch to make a notch on the other side so they could turn the disk upside-down and write data on both sides. This trick worked only with single-sided drives, such as for the Apple ][ or Commodore 64. Similarly, the capacity of single-density 720kB 3.5in floppy disks could be increased to 1.44MB by using a special punch to tell the drive it was a double-density disk. 3.5in, 5.25in & 8in floppy disks. Source: Eric Chan – www.flickr.com/photos/186773210<at>N06/52405767023 of separate independent still images. It was introduced in 1981 by Sony for the original Mavica “still video” cameras, which stored images in analog rather than digital format. It was also later used by Canon, Minolta and Panasonic. The disk had multiple medical and industrial imaging applications throughout the 1980s and 1990s. A data variant called the LT-1 was also produced that could store 793kB of data. Iomega introduced the Bernoulli Box floppy disk in 1982. The original disks were rather large at 21 × 27.5cm. Capacities of 5MB, 10MB or 20MB were initially available. It was discontinued in 1987. Bernoulli Box II was released later in a smaller 5.25in form factor with capacities of 20MB, 35MB, 44MB, 65MB, 90MB (late 1980s), 105MB, 150MB, and in 1993, 230MB. At the time of its introduction, standard floppy disks had a capacity of 1.2MB and hard drives around 30MB. Disk-ruining head crashes were still a problem with floppy and hard disks at the time. However, the Bernoulli principle enabled the head to be drawn toward the fast-spinning disk without touching it, so theoretically, it was impossible for the head to hit the media. Several ‘bump tests’ by reviewers confirmed this. Floptical disks were high-capacity floppy-like disks introduced in 1991 that used optical tracking with magnetic read/write. They were intended to replace conventional floppy disks. Their formatted capacity was 20.3MB in the same 3.5in form factor as a standard floppy disk. They contained an optical track for accurate read/write head tracking, but the data was still written and read magnetically. The drive could also read standard 720kB and 1.44MB standard 3.5in floppy disks. The Iomega Zip drive was introduced in 1994 (Fig.23), initially with a capacity of 100MB, then 250MB and 750MB. It became the most popular of the high-capacity floppy products but was eventually displaced by cheaper CD-R and CD-RW drives and media, then later, USB flash drives. ZIP disks were a different form factor to 3.5in floppies and incompatible with them. By 2003, the sales of ZIP disks and drives had declined dramatically. The Iomega Jaz was sold by Iomega from 1995 to 2002, initially with a 1GB capacity, increased to 2GB in 1998. However, like the PocketZip, they never became very popular. The Imation LS-120 SuperDisk had a capacity of 120MB, doubled with the subsequent LS-240. They were sold from 1997 to 2003 and were conceptually similar to the Flopticals mentioned above. They were intended as a replacement for the 3.5in 1.44MB floppy disk and had the same form factor. The SuperDisk drives could also read and write regular 3.5in floppy disks and could format such a disk to 32MB, although any alteration to the data required the whole disk to be rewritten. The SuperDisk had limited success, partly because Iomega’s ZIP disk had been on the market for several years at the time of SuperDisk’s release. Also, Fig.24: the Japanese Fujitsu FM-8 computer from 1981 had optional bubble memory storage, originally 32kB but later 128kB. It was the first PC with such an option. Source: https://w. wiki/8R6F (CC BYSA 4.0). Fig.23: an Iomega ZIP drive and 100MB disk. This is the external model; internal versions were also made. Source: https://w.wiki/8R6E (CC BY 2.0). 22 Silicon Chip Australia's electronics magazine siliconchip.com.au USB flash drives were becoming available and popular, and the cost of CD burners and media was falling. Caleb Technology released the UHD144 in 1998. It could read and write conventional 3.5in floppies and its own 144MB disks. Compared to other high-capacity disks, the disks were inexpensive, but the product did not survive competition from the Iomega ZIP, the Imation LS-120 and the CD-ROM. The company went bankrupt in 2002. The Iomega PocketZip or Clik! was introduced in 1999 as a small 40MB disk but never became popular and, like other floppy disk technologies, was replaced by flash memory devices. The Sony HiFD was released in 1998, and like some others, could read and write conventional 3.5in floppies. It had a capacity of 200MB. Unfortunately, the product suffered many problems, such as head crashes. It was re-released in 1999, but its reputation meant it was doomed to failure. Bubble memory We mentioned this type of memory in Part 2 of our article about Computer Memory. Briefly, individual bits of data are kept in the form of magnetic domains or ‘bubbles’ in a thin film of a substance such as gadolinium gallium garnet. The bubbles remain even when power is removed. It was introduced commercially in 1977 (see Fig.24) but became obsolete in the 1990s. It was once seen as a rugged alternative to hard drives, with a similar storage density to early drives, but that was quickly surpassed. Optical discs The idea of the modern optical disc came from David Paul Gregg in 1958. He was awarded US Patent 3,350,503 on it in 1967. The patent mentions the ability to record digital data. This invention and several related ones led to the development of the LaserDisc for analog data, the CD (Compact Disc), MiniDisc, DVD, Blu-ray and many derivatives. Optical discs store data in the form of pits and lands in the substrate. They are read by a laser, as shown in Fig.25. For writable media, the pits are also made by a laser. For mass production, the data is written all at once with a stamping machine rather than a laser. LaserDiscs were launched in 1978, storing video and audio data as analog signals (later versions included digital audio). Despite being analog, fundamentally, the information was still stored on the disc as a series of pits and lands like later fully digital CDs and DVDs. LaserDiscs were not generally used as a data storage medium, although in 1984, Sony produced a little-known digital LaserDisc format that could store 3.28GB of data per disc. The extent to which it was commercially used is not clear. There is a reference to it in the video titled “The Computer Chronicles - Japanese PCs (1984)” at https://youtu.be/rbh1XP4kCT4?t=954s LaserDiscs were officially discontinued in 2009, but had failed to be popular long before that, unlike the physically smaller DVD format, which was wildly successful. The Compact Disc (CD) was invented by Sony and Philips and released in 1982 as the Digital Audio Compact Disc for sound recordings. The CD-ROM (ROM = read-only memory) was announced in 1984 for data storage, but a suitable file format specification was not released until 1986. That was the “High Sierra” format, developed by Microsoft, Philips, Sony, Apple and DEC. Standard CD-ROMs have a capacity of 650-700MB, depending on how close to the edge the data is written. If some of the ‘rules’ are ignored (eg, lower data integrity), capacities of up to 900MB per disc are possible. One of the first products on CD-ROM was the Grolier Academic Encyclopedia. These discs were widely used for distributing software and in game consoles in the 1990s and early 2000s. They were also used for data backups of hard disks and for making copies of audio CDs. Regular CDs were 12cm in diameter, although mini 8cm CDs came along later, with a significantly reduced capacity. Eventually, people realised they didn’t have to be round, and all sorts of oddly shaped mini CDs were made for promotional purposes. However, ‘slot loading’ type compact disc drives only supported the full-size 12cm CDs, limiting the usefulness of the smaller versions. Besides audio discs and CD-ROMs, CDs were produced in many other versions. The CD-R became available in 1990 and could be written once and read many times (WORM), according to a specification released in 1988. The CD-RW was introduced in 1997 and could be written to, read and erased many times. Fig.25: a comparison of how data is stored on CDs, DVDs, HD DVDs and Blu-ray discs. Legend: track pitch (p), pit width (w), minimum length (l), laser spot size (⌀) and laser wavelength (λ). siliconchip.com.au Australia's electronics magazine February 2024  23 Fig.26: an IBM 3363, an early WORM drive with a formatted capacity of 200MB. Source: www. ardent-tool.com/docs/pdf/brochures/ ibm-3363-opticaldrive&cartridge.pdf CD-MO used magneto-optical technology, similar to the MiniDisc, but was never released commercially. Another CD format was Kodak’s (initially proprietary) Photo CD, introduced in 1991 and designed to contain 100 high-quality photos for display on the CRT TVs of the day. However, the format failed to gain widespread market acceptance and was discontinued around 2004. Picture CD was another Kodak product that followed Photo CD. DVDs (Digital Versatile Discs) were released in Japan in 1996 and other countries from 1997-1999. They can store any digital data, but video was initially the primary use. A standard non-rewritable DVD-ROM with one side and one layer can store 4.7GB of data (DVD-5); a single-sided, duallayer disc 8.5GB, and with two sides and dual layers, 17GB (DVD-18). As with CDs, commercial prerecorded discs are stamped rather than “burned”. Prerecorded movie discs are typically in either DVD-5 (single-side, single-­ layer) or DVD-9 (single-side, dual-layer) format. Single-side, dual-layer discs use Reverse Spiral Dual Layer (RSDL), a technique where the data is first written from the inside of the disc outwards. The laser wavelength is then changed to penetrate the first layer, and read the second layer. The second layer of data is written from the outside of the disc inwards. This allows a seamless change of layers for movies or other continuous data streams. As for writable DVDs, there are two write-once versions (DVD+R, DVD-R) and two rewritable versions (DVD+RW, DVD-RW). The less common DVD-RAM was designed to act like a removable hard disk. The difference between the “+” and 24 Silicon Chip “-” formats is that DVD-R was developed by Pioneer in 1997 and approved by the DVD Forum (www.dvdforum. org), while DVD+R was developed by Sony and Philips in 2002. There are technical differences in the method of recording and reading data. Both have compatibility problems with some drives, although the “+” versions are slightly better. Another type of DVD is HD DVD (High-Density DVD), with around triple the capacity of a regular DVD (15GB instead of 4.7GB per side and layer), up to 60GB for dual side, dual layer. This format was on the market from 2006 to 2008 but was supplanted by Blu-ray. Regular DVDs are the same size as standard CDs at 12cm in diameter, but there were also 8cm diameter mini DVDs with reduced capacity. Blu-ray was introduced in 2006 and is the same diameter as CDs and DVDs at 12cm. It has a capacity of 25GB (single layer), 50/66GB (dual layer), 100GB (triple layer) or 128GB (quad layer) for the BDXL write-once variant (specification released 2010). Blu-ray is mainly used for video and games. Standard Blu-ray discs only support a video resolution of up to 2K (1080p), so Ultra HD Blu-ray was introduced in 2016 to support 4K (3840 × 2160 pixels). BDXL and HD Blu-ray discs are incompatible with standard Blu-ray players and with each other for reading and writing. Optical Disc Archive (https://pro. sony/en_AU/products/optical-disc) is a proprietary Sony product introduced in 2012 and marketed as an alternative to Linear Tape Open (described earlier) with greater durability and a longer life – see Fig.27. It uses a cartridge containing 11 optical discs with three layers on each side for a capacity of 5.5TB in the largest cartridge. Australia's electronics magazine Fig.27: a 5.5TB Optical Disc Archive cartridge. The discs themselves are similar to, but not the same as, Blu-ray discs; they are Archival Discs (AD), which were jointly developed by Sony and Panasonic and designed to last at least 50 years. There were other optical disc formats that did not become popular, such as GD-ROM (Gigabyte Disc Read-Only Memory), a special format developed by Yamaha and used in Sega game consoles from around 1999 to 2006. Its purpose was to make copying the discs more difficult, but it also offered increased capacity compared to standard CDs of about 1GB. UDO (Ultra Density Optical) discs are a WORM technology intended for archival use with an expected life of 50 years, introduced by Sony and Plasmon in 2003. UDO 2 discs were released in 2007 with a capacity of 60GB. The discs are still available, although the format is not widely supported. M-DISC is a technology for DVD, Blu-ray and Blu-ray BDXL designed for extreme longevity, claimed to be up to 1000 years. They are readable by standard DVD players from 2005 Fig.28: a Sony MDW80 MiniDisc. Source: https://w.wiki/8Uen siliconchip.com.au and by standard Blu-ray and Blu-ray BDXL players. They are writable by most drives made since 2011. Other optical and magneto-optical systems An early example of an optical WORM drive for PCs that preceded the widespread adoption of CDs was the IBM 3363 (Fig.26). It was introduced in 1987 and intended for use with the IBM Personal System/2. It used a polycarbonate optical disc in a 5.25in cartridge and had a formatted capacity of 200MB. The MiniDisc (MD) was introduced by Sony in 1992 (see Fig.28) and discontinued in 2013. It was an erasable 65mm magneto-­optical disk in a caddy, meant for audio recording and intended to replace cassette tape. MiniDiscs could record 60, 74 or 80 minutes of audio using unique digital compression developed by Sony. To write data, a laser would heat a spot on the disk, altering its magnetic characteristics and allowing it to be magnetised, after which a magnetic head would write to it. To read the data, a laser sensed the altered polarisation of light due to the magnetic field of the spot. MD Data was a magneto-optical medium introduced in 1994. It used the same technology as the audio MiniDisc, although the caddy was slightly different to prevent insertion in a MiniDisc player. The disks stored 140MB, more than the 100MB of Iomega’s Zip drive, which was released at about the same time. However, MD Data was regarded as slow and discs were expensive. They were primarily used in Sony’s digital cameras, some other Sony products and a Sharp camera. The last product to use it was introduced in 1997. In 1999, MD Data2 (also called MDView) was released. This could hold 650MB of data but was only used in one Sony camera and some audio products. MiniDisc’s successor was Hi-MD, released in 2004, intended for data storage. It could store 1GB but was discontinued in 2011. Next month The second and final article in this series next month will continue where this one left off, covering the more modern storage technologies mentioned in the introduction. SC siliconchip.com.au The first terabit storage system – on photographic film! The IBM 1360 was the first computer storage system to store one terabit of data (125GB). It evolved from a mid-1950s CIA requirement to store vast numbers of printed documents. A system called “Walnut” was produced and delivered to the CIA in 1961 that could store 99 million photos of documents. 200 small boxes each contained 50 pieces of photographic film, each holding 99 photos in a 3×33 array for a total of 990,000 photos. Each set of 200 boxes was kept in a “document store”, and there could be up to 100 of those. Individual pieces of film were retrieved by an automated process. This system was developed into “Cypress”, using a superior film type, and IBM tried to commercialise it as the 1350 Photo Image Retrieval System. The same basic system was developed into the 1360 Photo-Digital Storage System (see Fig.29). It stored digital data on 35 × 70mm photographic film in a black and clear pattern, as shown in Fig.30. Each piece (or “chip”) had 32 data frames in a 4 × 8, holding a total of 6.6Mbits. 32 chips were held in a box called a cell. Data was written to unexposed film using an electron gun; it was then automatically developed. If data had to be updated, a chip was removed and replaced by a new one. There was extensive data redundancy, so there were 4.7Mbits of usable space per 6.6Mbit chip. There were 75 “trays” holding 30 cells each for a total of 2250 cells per “cell file unit” for half a terabit of data. Systems with more than one cell file unit achieved one terabit of storage or greater. The system at Lawrence Livermore National Laboratory kept one terabit. Only five 1360 machines were delivered in 1967 and 1968; the last system was shut down in 1980. No 1350 machines were delivered. The original IBM manual is available from siliconchip.au/link/abrv and there are videos titled “The First Terabit Server -The 1967 IBM 1360” (https://youtu.be/ twso8Nj7fLI) and “IBM 1360 Photostore Cell” (https://youtu.be/4-Jvd7lOjWA). Fig.29: the IBM 1360 PhotoDigital Storage System, circa 1965. It was the first secondary storage system to store one terabit of data. Source: https://w.wiki/8R6G Fig.30: a piece of photographic film from an IBM 1360 showing the data storage pattern, with a sewing needle for scale. Source: IBM press kit (https://w.wiki/8R6V). Australia's electronics magazine February 2024  25 Multi-function Weather Stations GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. FROM 8995 $ • Indoor & outdoor temperature • Temperature alert alarm • 12 Hour weather forecast XC0366 $89.95 A GREAT PRICE FOR A 7 MODELS PRINTER / ENGRAVER / GREAT VALUE! LASER ETCHER ALL OF THE WEATHER DATA AT THE BUDDING METEOROLOGIST'S FINGERTIPS 7" Colour Touchscreen with 5-Way Long Range Transmitter • Indoor & outdoor temp • Wind speed with direction • Dew point & heat index • Rain gauge with rate • 12 Hour weather forecast XC0432 $239 • Indoor & outdoor temperature • Wind speed with direction and chill • Dew point & heat index • Rain gauge with rate • 12 Hour weather forecast XC0434 $369 Our stylish weather stations are feature rich with useful atmospheric measurements such as temperature, humidity, barometic pressure, moon phase, rainfall plus data logging, alarms, time, calendar and more. T GRE A GIEFATS! ID From simple forecast displays to detailed modelling we have a model to suit any budget. Shop Jaycar for environmental meters: • Desktop Thermometers • Light, Wind and Sound Meters • Digital Multimeters & Data Loggers AUTOMATICALLY UPLOADS WEATHER DATA TO ONLINE WEATHER SERVICES 5.4" Colour Screen & Wi-Fi 5.4" Colour Screen & Wi-Fi • Indoor & outdoor temperature • Wind speed with direction and chill • Dew point & heat index • Rain gauge with rate • Upload data via Wi-Fi to Weather Underground & Weathercloud • Indoor & outdoor temperature • Wind speed with direction and chill • Dew point & heat index • Rain gauge with rate • Supports ProWeatherLive, Weather Underground, Weathercloud & more with separate Temp/Humidity Sensor XC0440 Model Comparison with 4 Day Forecasting JUST 349 $ 449 $ XC0450 ENTRY LEVEL MID JUST PROFESSIONAL XC0366 XC0412 XC0400 XC0432 XC0434 XC0440 XC0450 Indoor Thermometer √ √ √ √ √ √ √ Outdoor Thermometer √ √ √ √ √ √ √ Min/Max Records √ √ √ √ √ √ √ Hygrometer √ √ Touchscreen √ √ √ √ √ √ √ Wind Speed √ √ √ √ √ Wind Direction √ √ √ √ √ Wind Chill √ √ √ √ √ Dew Point √ √ √ √ √ Rain Gauge √ √ √ √ √ Rain Rate √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ Barometric Pressure √ √ √ √ Time/Date Display √ √ √ √ √ √ √ √ √ Transmitter Power 2 x AAA 2 x AA 2 x AA 3 x AA 3 x AA 7 x AA 3 x AA √ √ √ √ Transmission Range 30m 30m 100m 150m 150m 150m 150m $89.95 $129 $159 $239 $369 $349 $449 Moon Phase High/Low Alarms Colour Screen Price √ √ Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Explore our full range of weather stations, in stock at over 115 stores, or 130 resellers or on our website. jaycar.com.au/weather-stations 1800 022 888 Phil Prosser’s compact and high-quality Microphone Preamplifier If you use microphones for stage, recording or testing, you will be familiar with the need for a preamp to get a usable signal. Many microphones also need ‘phantom power’. This small box runs from a plugpack and offers a flat frequency response, very low distortion, low noise and adjustable gain. Background image: https://unsplash.com/photos/ALM7RNZuDH8 T his small microphone preamp is ideal for use in the studio, workshop or on the stage. It allows you to boost the gain of your microphone to line level and delivers a balanced or single-ended signal. The main version of this Preamp fits into a small, standard-sized enclosure that is widely available, as shown in the photos. This diecast aluminium case makes it tough enough to survive the worst abuse. If you want to integrate this design into a larger project, we have a version of the board that omits the cutout for the XLR connectors and drops one of the switching regulators, making it easy to run it from existing ±15V DC rails. That would make sense if integrating it into a power amplifier, preamplifier, mixer or similar. When built as a standalone unit, it runs from 9V DC, as widely used on stage. Those plugpacks generally have 2.1mm plugs with a positive ring and negative tip. We have included reverse polarity protection, so no damage will occur if the wrong plugpack is used. We set this requirement as it is a fair bet that things will get mixed up on the stage. You don’t want to be fiddling with equipment while the crowd waits for the concert to start! Therefore, it should ‘just work’. Performance The performance of the Microphone Preamplifier depends on various factors. Having low noise is important; the noise level is significantly affected by the source impedance and gain setting. For a source impedance of 560W with 50dB gain and a 1V RMS output, the signal-to-noise ratio is 70dB. At the same output voltage but a gain of 20 times, the SNR is 85dB. Features & Specifications Operates from a 9-15V DC plugpack (9V DC is common for stage equipment) Fits in a compact 120 × 93.5 × 35mm diecast enclosure Adjustable gain from -15dB to +50dB Switchable 20dB attenuator for high-level sources Switchable 48V phantom power Drives in excess of 5V peak-to-peak (1.75V RMS, 13dBu) into a 600Ω load Balanced or single-ended output Frequency response: ±0.1dB, 12Hz to 20kHz (gain=26dB/20×) (see Fig.1) Signal-to-noise ratio (SNR), Zi = 560Ω, Vout = 1V RMS: 85dB (gain=26dB/20×), 70dB (gain=50dB/320×) » Total harmonic distortion (THD): <0.002% (see Fig.2) » Built-in power protection, including reverse polarity » Inputs and output protection against most abuse » » » » » » » » » 28 Silicon Chip Australia's electronics magazine The frequency response with a gain of 20 times (26dB) is within 0.1dB from 12Hz to 20kHz – see Fig.1. As shown in Fig.2, the distortion (THD+N) is entirely determined by noise. The underlying distortion is significantly lower, in the region of -95dB (0.0018%) to -105dB (0.0006%). There is some evidence of noise from the switch-mode regulator at the output, but it is 70-80dB down, depending on the gain setting. That is a low enough level that it is not a concern. Given that the distortion is so low, it’s the SNR that’s going to be the performance limit. 70dB is pretty much the worst you can expect as long as your input signal level is sufficient to achieve at least 1V RMS output at the maximum gain setting of around 50dB. As you reduce the gain to 26dB, it will improve to 85dB, and it should improve further at even lower gain settings, exceeding 90dB. That’s assuming your microphone/signal source is high enough in level to still provide a useful output with less gain. Some challenges This design is a little tricky because microphone phantom power needs to be 48V DC to be universal. That is a lot higher than 9V DC. To provide users with headroom of 10-15dB over 0dBu, we want to be able to deliver an output signal with peaks above ±8V. That is needed for people using the mic closer than expected and to deal with loud passages. Stage equipment must have headroom; the siliconchip.com.au sound engineer can deal with levels at the mixing desk. That means we need supply rails of 48V DC plus dual rails sufficient to get this ±8V from an op amp. We want this in a small box and for the circuit to be as tough as a cheap steak. If we start with 9V DC and drop 0.5V across a reverse polarity protection diode, then budget another 0.5V for the plugpack output drooping, we only have a poorly-regulated 8V supply to work with. We considered using switched capacitor inverters/doublers using 555s but found that gave marginal supply rail headroom. After some thought, we decided to take a more industrial strength approach, using two LM2577 boost regulators and a cunning trick to sneak in a negative rail. These regulators are more powerful than we need, but they are widely available and can handle 60V on their output, enough for the phantom power rail. The resulting power supply fills a significant proportion of the PCB, as we shall see in more detail later. While this solution is hefty, it is very tolerant of input supply variation; even if the output is loaded with a very low impedance, the rails will stay up. If you are wondering if this could be run from a 9V battery, the answer is not for any length of time. The current draw is far too high to expect a decent lifespan from the battery, and it will go flat exactly when you don’t want it to. Full load current draw is about 120mA, which will flatten a 9V battery in short order. Don’t think that all this talk about the power supply means we’ve forgotten that the preamp part must also have decent performance. We’re using the same hybrid transistor/op amp balanced microphone preamp found in the Loudspeaker Test Jig (June 2023; siliconchip.au/ Article/15821), developed by audio guru Douglas Self. It gives excellent performance with low distortion and noise, plus a wide range of possible gain settings. Fig.1: we had to make the vertical scale very small to see the variations in frequency response as it is so flat. Fig.2: any distortion produced by the circuit is well and truly buried in the noise. Thus, the SNR is the primary determinant of the performance at any given gain setting. Circuit description Fig.3 is the block diagram for the Preamp, while the main (analog) part of the circuit is shown in Fig.4. S1 switches phantom power for the microphone via header CON10. Noise is filtered out of the 48V DC supply by a 100W/220μF low-pass filter (LPF). We siliconchip.com.au Fig.3: the Mic Preamp block diagram shows the somewhat complicated power supply at the top, with the superficially simple attenuation and preamplification circuitry below. Australia's electronics magazine February 2024  29 have used 6.8kW resistors for the two bias resistors; these should be matched as close as possible. We selected two resistors that measured within 0.1% from our collection of 6.8kW 1% resistors. You could buy 10 resistors and choose the bestmatched pair. The 47μF/100nF parallel capacitor pairs block DC from the microphone signal as it’s fed into the attenuator. These prevent the full 48V phantom power from being applied to the attenuator when the microphone is unplugged, so they must be rated at a minimum of 63V. This Preamp has a 20dB pad at the front end. It can be switched in to avoid the Preamp clipping with higher-­ level input signals. The pad uses two 1.8kW resistors in series with the input signals and a 430W resistor connected between the terminals of RLY1. Fig.4: the main analog section of the Preamp circuit. It is based on two dual op amps and two transistors; the transistors lower the noise floor substantially. The second op amp drives the balanced and unbalanced outputs. Relay RLY1 switches in a resistive attenuator so it can handle higher level input signals. 30 Silicon Chip Australia's electronics magazine siliconchip.com.au When the attenuator is switched out, the relay shorts out the 1.8kW resistors, and the 430W resistor is out of the circuit. When switched in, the 430W resistor is connected between the downstream ends of the 1.8kW resistors, forming a voltage divider. These relatively low values minimise additive noise from the attenuator and keep the impedance driving the following preamplifier low. To calculate the attenuation of this stage (when activated), add a mental ground connection in the middle of the 430W resistor, splitting it into two 215W resistors. These resistances are in parallel with the 4.7kW resistors to ground, so the dividers are formed with resistances of 1.8kW plus the microphone source impedance and 205.6W. Assuming a low source impedance, the resulting attenuation is -19.8dB. Note that we need closely-matched values for the 1.8kW and 4.7kW parts to ensure good common mode rejection performance when the attenuator is switched in. We have used a relay for this job as our experience with switching small signals with miniature toggle switches wired to the board is not great. A telecom relay gives better long-term reliability and lower noise for a modest increase in cost. The 6.8V zener diode across the relay protects it in case someone runs the Preamplifier from a higher voltage than expected. The series resistor will get quite warm, but it should survive, provided this abuse is not continuous. Preamp gain We have provided a variable gain Two versions of this project allow it to fit into a small box (as shown) or a larger chassis with dual-rail power available. that allows you to set the level from a range of microphone types and situations. When VR1 is set to minimum resistance, the gain is 47.8dB, calculated as: G = 1 + 2.7kW ÷ (10kW || [22W ÷ 2]) G = 1 + 2.7kW ÷ 10.98W G = 247 (47.8dB) When VR1 is set to its maximum of 10kW, the gain is 5.1dB: G = 1 + 2.7kW ÷ (10kW || [(10kW + 22W) ÷ 2]) G = 1 + 2.7kW ÷ 3338W G = 1.8 (5.1dB) Using a reverse log taper potentiometer for VR1 results in the attenuation being ‘linear’ in dB terms as the potentiometer is rotated. Otherwise, most of the potentiometer’s range will result in relatively low gain, with the last fraction of the rotation ramping the gain over 20dB or so. So make sure the pot you choose has a ‘reverse log’ or ‘reverse audio’ (C) taper. The small signal diodes in the preamplifier (D4-D8) ensure the op amp inputs are not overdriven. We have included a buffer following the preamplifier that also produces an inverted Calculating the total current draw The phantom power supply needs to provide about 10mA to the LM317HV (REG1) and a maximum of 14.1mA into the 6.8kW resistors if they are shorted to ground. That is 24mA at 55.3V, which will require ~166mA (55.3V ÷ 8V × 24mA) at the input of the REG3. The dual rail power supplies must supply up to about 40mA to the NE5532 op amps and input circuit and about 10mA each for REG3 and REG4. That is a total of 100mA, given there are positive and negative rails, meaning a draw of up to about 225mA (18V ÷ 8V × 100mA) at the input to REG4 in the worst case. That means the Preamp could draw something in the region of 350mA, although that would only happen if it were driving a shorted load. Most 9V plugpacks can supply this, but most 9V batteries can’t. The most we saw in our tests was 150mA from 9V. Note that the worst case current is at startup, when the switch mode regulators are charging the 56V and ±18V supply filtering capacitors. We have included a power LED, powered from the negative rail. We chose this rail because if a user connects the Preamp to an 18-24V DC plugpack, the boost regulator for the positive rail will likely shut down, and the negative rail will not be generated. No damage should occur, but the user will be informed that it is not operating by the power LED being off. siliconchip.com.au Australia's electronics magazine output. This allows the output to be single-ended or drive a balanced line at a high level. We have also added small signal diodes to the positive and negative rails on the outputs (D14-D17) so that if someone inadvertently connects this to a piece of equipment with a large DC offset on its input, they will protect the NE5532 (IC1). We have incorporated 100W series resistors on the outputs to ensure the op amp remains stable even when driving difficult loads or long cables. Those will also help to limit the current flow in the case of a misconnection. You can use the positive buffered output at pin 2 if you only need a single-­ended output. Power supply The power supply portion of the circuit is shown in Fig.5. The overall design comprises two switch-mode pre-regulators that drive LM317/337 linear regulators. This generates very clean power rails, including the phantom power rail. The phantom power supply uses the LM2577 (IC3) in a textbook configuration. Its input is bypassed with a 220μF low-ESR capacitor and a 100nF capacitor. 220μF is quite low, but the maximum current we need to supply is less than 30mA. That is little more than idling for the LM2577. We have increased the compensation capacitor in series with the 2.7kW resistor at its pin 1 from a suggested value of 1μF to 10μF. That slows the startup of the boost regulator. Our small 500mA switchmode plugpack went into current limiting without February 2024  31 this; that would not be a problem with a larger plugpack (or a linear type). The output voltage is set by the resistors connected to the feedback pin (pin 2). With the 33kW/750W feedback divider and IC3’s internal 1.23V reference, the result is an output of 56.25V (1.23V × [33kW ÷ 750W + 1]). A 10W/10μF low-pass RC filter on the output reduces the remnants of the 52kHz switching frequency. The following LM317HV-based linear regulator drops the output close to the 48V required for phantom power while removing most of the remaining switch-mode noise. The 330W and 12kW feedback resistors set its output to 46.7V (1.25V × [12kW ÷ 330W + 1]). Switch-mode regulator IC4 produces the +18V rail (dropped to +14V by linear regulator REG3) and is set up similarly to REG3. It uses the recommended 1μF compensation capacitor rather than the higher 10μF value used for REG3 to reduce its startup current. A lower value inductor of 100μH is used due to the much lower boost ratio required, under 2:1. You must use toroidal inductors. Its output voltage is set by 33kW and 2.4kW resistors to about 18.4V (1.25V × [33kW ÷ 2.4kW + 1]). It also has a 10W/10μF low-pass RC filter on its output, and the following LM317based linear regulator has its output voltage set by 3.9kW and 390W resistors, resulting in about 13.75V (1.25V × [3.9kW ÷ 390W + 1]) for the positive op amp rail. Now to the cunning trick. Being a boost regulator, LM2577 (IC4) switches its pin 4 to ground to establish a current in L1. When pin 4 subsequently goes open-circuit, that current continues to flow and charges the output capacitor to our target of 18V DC. That is repeated at 52kHz by this device. Therefore, we have a node at pin 4 switching between about 18.7V and ground. Our trick is to generate the negative rail is piggybacking off this node using a 2.2W resistor, 47μF capacitor and ultrafast diode D9. When the output of IC4 reaches 18.7V, that capacitor is charged to around 18V via D9. When IC4 switches pin 4 to ground, the positive end of that capacitor is pulled to 0V, so the negative end goes to about -18V. That charges the following 47μF capacitor via diode D3, creating our negative rail. The negative rail is not directly regulated, but the positive rail regulation will ensure the negative rail is about right. LM337 linear regulator REG4 has its output set to -13.75V, so even if its input is a little lower in magnitude Fig.5: the power supply circuitry uses two switch-mode regulator ICs, one charge pump and three adjustable linear regulators to generate a 48V DC phantom power rail plus regulated ±14V rails for the op amps. Those are all derived from a single 9V DC input. 32 Silicon Chip Australia's electronics magazine siliconchip.com.au than that of REG3, the final regulated rails will still be close to ±14V. While the negative rail can only provide a modest current, we only need about 40mA total to power a few op amps. PCB layout INPUT INPUT PROTECTION PROTECTION AND A ND A TTENUATOR ATTENUATOR MICROPHONE MICROPHONE PPREAMPLIFIER REAMPLIFIER OUTPUT OUTPUT BUFFERS BUFFERS + + + + DC 48V DC 48V LINEAR LINEAR R EGULATOR REGULATOR + Australia's electronics magazine + +56V DC DC +56V BOOST BOOST REGULATOR REGULATOR + + + + ±18V ± 18V DC DC BOOST BOOST REGULATOR REGULATOR ±14V ±14V DC DC LINEAR LINEAR REGULATOR R EGULATOR + + Fig.6: how the various circuit sections have been arranged on the PCB. This configuration allows it to fit in a compact case while keeping the noisy switchmode ICs away from the sensitive analog preamplifier circuitry. + siliconchip.com.au + + + The Microphone Preamp is built on a double-sided PCB coded either VR1 XLR MIC OUTPUT SOCKET XLR MIC INPUT SOCKET + Construction The ‘box’ version of the PCB requires some more components due to the dual-rail generation circuitry. In our prototype, we used bobbin-style inductors, but we found that toroidal inductors provided such a great improvement in performance that we had to change them to the design presented. COIL We have laid the board out so that it is a neat, if tight, fit into a standard 120 × 93 × 35mm diecast aluminium enclosure. It is just large enough to accommodate the PCB, two XLR connectors and the switches, but small enough not to get in your way in use. The aluminium is tough enough to take some abuse without getting ratty or cracking. Due to the fairly packed board, it was important to put the switch-mode regulators at one end and the preamp circuitry at the other and use extensive ground planes to keep the noise down. The resulting board configuration is shown in Fig.6. To get it to fit, we had to lay the board out with cutouts for the integral pillars in the corners of the enclosure and a cutout into which the XLR connectors sit. That allowed us to use through-hole parts exclusively, so it’s straightforward for anyone to build. Suppose you are integrating this into a larger enclosure, such as an existing preamp. In that case, we have designed a separate ‘embedded’ version of the board without the LM2577 that generates the positive and negative rails (IC4). That means you can run it from external ±15V rails instead. At the same time, we filled in the cutout as it would serve no purpose in such an application. Everything else is basically identical, so you can use the same overlay diagrams regardless of which version you build. Just leave out the parts that don’t exist on the embedded version (in case that is not obvious!). When buying your board, make sure you choose the version that suits your needs. The only other difference in components is that the 150W resistor next to CON10 is increased to 330W and two of the 3.9kW resistors have been reduced to 3.0kW so that the LM317/337 regulators will not go into dropout with their inputs at ±15V rather than the ±18V generated by the switching regulator in the other design. February 2024  33 VR1 VR1 Mic In 34 Silicon Chip G ND − 15V +15V CON 1 UF4002 + 220mF 2 5V 220mF 63V 22pF 2.2kW 4148 D6 4148 D4 100n F 100n F D26 47mF + 10mF 3.0kW 10mF 10mF 33kW 750W + 1 00n F R E G3 D28 10 0n F 4148 4148 4.7kW D7 D8 R E G4 390W 47mF LM317 390 W 100nF + 10W LM337 100n F D27 3.0kW 2.7kW 100nF IC3 LM2577T D13 10 W + Q1 BC559 10kW 1 00 W D1 5 47mF 10 W 47mF 4.7kW 1nF 1nF 100nF D29 IC2 NE5532 + 10W 1 D23 47mF + 47 m F 4148 4148 4148 D17 4148 GND 47mF D16 CON4 10 0n F 47 k W 10W 1 00 W 10 W Mic Out R E G1 330W 63V 4.7kW 10k W ZD4 ZD3 ZD2 47kW ZD1 1nF 4 30 W CON3 Atten. LM317HV 3.0kW A K 6.8kW 100nF 6.8kW 100nF 22pF 2.2kW 4148 D6 4148 D4 ZD5 10 0 W CON10 3 30 W 10mF 63V 22pF D14 22kW Q2 B C 559 2.7kW 10 0n F 22kW 1 0m F D22 100nF IC3 LM2577T Fig.7: this version of the PCB suits the diecast metal case, with a cutout at the top for the XLR sockets to fit. The diodes, electrolytic capacitors and ICs are all polarity sensitive, so make sure they are orientated as shown here. 01110231 (full version) or 01110232 (embedded version) and measuring 85 × 110mm in either case. The two layouts are shown in Figs.7 & 8. The main difference is the omission of the dual rail generation circuitry in the ‘embedded’ version. Most other parts and locations remain the same. We will describe building the full PCB that fits in the small case. You simply skip the missing parts for the embedded version that operates from dual rails. The only added part is the three-pin header for power input CON1 rather than the barrel socket. Start by fitting all the resistors. The pairs of 6.8kW, 4.7kW and 1.8kW resistors in the input section at upper left, need some care. These parts should ideally be matched to better than 1%; we bought 10 of each and chose the two that measured the closest for each pair. That improves the common mode (noise) rejection. Now move on to the diodes. There are five different diode types, so don’t get them mixed up and ensure that the cathode stripes are orientated as Phantom Power 63V + 22k W 2.7kW UF4002 6 3V 2.7kW 47mF 10 W 220mF 25V 220mF D27 3.9kW 63V LED CON5 22pF IC1 NE5532 1.8kW 220mF 4.7kW 10m F UF4002 33kW 750W 1mF LM317 390W RLY1 5V 4.7kW 100nF D7 4.7kW 4148 100nF + 10mF 3.9kW 10mF 10mF 100nF IC4 LM2577T 100nF REG3 47mF 10m F D13 100nF 220mF 25V + D26 D28 10mF 47mF 100nF REG4 390W 4.7kW 1.8kW 100nF 4148 4.7kW D8 10W L2 330mH + LM337 UF4002 2.4kW 33kW 3.0kW A K 100W D15 D29 10W 10W D2 Q1 BC559 10kW 4.7kW 10kW 1nF 1nF 100nF L1 100mH 2.2W D3 U F 4002 + 1N5819 or 100nF 47mF 100W 10W + 47mF + 10W 1 2.7kW U F 4002 1N5819 or 220mF 63V 100nF 47mF 1N5819/UF4002 D9 10W 220mF 63V + 47mF 4148 4148 4148 D17 4148 GND 47mF D16 CON4 D23 CON1 D1 1N5819 ZD3 ZD 4 47kW REG1 330W 63V 9V DC IN 47kW 10W LM317HV Mic Out 100nF 10mF Phantom Power 63V D22 12kW 150W 6 3V ZD2 ZD 1 1nF 430W + 47mF D14 10mF + 100W CON10 + 63 V CON3 Atten. 4.7kW 220mF 22pF 63V 63V IC2 NE5532 + 47mF 12kW Mic In 6.8kW 100nF 6.8kW 100nF ZD5 10m F 1.8kW Q2 BC559 2.7kW 100nF 22kW + 47mF 22kW COIL COIL RLY1 5V 22kW 2.7kW + 10m F + 4.7kW 1.8kW 22pF IC1 NE5532 + 63V 4.7kW + 63V + + 47mF + + 47mF LED CON5 470mF L2 330mH 22W CON2 470mF + CON2 + XLR MIC INPUT SOCKET + XLR MIC OUTPUT SOCKET 22W VR1 VR1 1 Fig.8: the ‘embedded’ version of the PCB removes the split rail generators so it can run from ±15V DC rails (or similar) that might already be available within a mixer, preamplifier or power amplifier. shown in the overlay diagrams. Note that the 400mW zener diodes look similar to the 1N4148 small signal diodes, so be careful with those. While diodes D2, D3 & D9 can be either UF4002 or 1N5819 high-speed types, D13 must be a UF4002. Next, mount all the non-polarised capacitors, ie, the ceramic and plastic film types. Follow with the electrolytic capacitors, which are polarised. They all face the same way, with the positive (longer) lead to the right and the stripe on the can to the left. We have marked the 63V-rated capacitors on the PCB, although if you use the parts specified in the parts list, they will already have the correct ratings. Now install the power socket, twopin and three-pin polarised headers, the two toroidal inductors (which are not polarised) and the potentiometer. The orientations of the polarised headers are not critical, but if you use our suggested orientations, you’re less likely to make mistakes following our wiring instructions. Australia's electronics magazine We can now fit the two LM2577s and test the boost regulators. Depending on whether yours come with staggered or straight leads, you might need to bend the leads to fit the pads. Ensure that the regulators sit close to the PCB and do not hang off the edge. You can put a dab of neutral cure silicone under the inductors. Initial testing To test the switching part of the board, connect a 9V DC plugpack and check the voltages on either side of D1, the protection diode. There should be 9V on the anode and over 8.5V on the cathode. If not, check for shorts and things getting hot, and verify that your plugpack has negative on the tip and positive on the ring (the opposite of many that you’ll find). Check the voltage on either end of the 10W resistor immediately next to the 33kW resistor (it’s all by itself on the embedded version, to the left of that 33kW resistor). You should get readings at both ends of 55V ±5V. Do not touch this with your fingers as it siliconchip.com.au is a high enough voltage to bite. If that is not correct, check the parts in the lower-right corner, especially IC3, and verify the orientation of D13. For the dual rail voltage generator on the non-embedded version, measure the voltage on either end of two more 10W resistors in the power supply section. One is just to the left of D26, while the other is just above D29. These should be ±18.4V ±1.5V. Again, if these voltages are not correct, stop and work out why. The likely culprit is incorrect diode or capacitor orientation. If IC3 or IC4 is not working, put a scope probe on pin 4 of IC4. You should see a switching waveform at around 52kHz. If not, it might not be getting power. Now fit the LM317HV, LM317 and LM337 devices (REG1, REG3 & REG4). After that, check the voltage on CON10, the phantom power header. It should be 48V ±4V. Also check the voltage on pins 4 and 8 of the (still empty) IC1 and IC2 locations. You should measure +14V ±1V on pins 8 and -14V ±1V on pins 4. Again, if one of these is off, there must be a problem around the associated regulator, so check the input voltages, and the orientations of the regulators and associated protection diodes. With the power supply now fully operational, mount the relay (watch its orientation), the two BC559 transistors and the two NE5532 op amps, which can be soldered directly to the board or socketed (although using sockets could reduce its robustness). Double-check their orientation before soldering, as desoldering op amps or relays is hard. If you have to remove one, cut off all the legs and desolder them individually. Re-apply power and check that the relay works by shorting the pins of CON3; you should hear the relay click. If not, check that the relay is the right way around and that you have ZD5 orientated correctly. You can now plug in a microphone or oscillator, with a maximum input level of 100mV, to the CON2 input and check that it is amplifying the signal correctly and delivering correct output signals at the pins of CON4. If you don’t get an output, check that you have phantom power on if required. Place a shorting block across CON10 if necessary. There should be close to 48V on the CON10 pins and a siliconchip.com.au Parts List – Compact Microphone Preamplifier 10 double-sided PCB coded 01110231, 85 × 110mm 1 120 × 93.5 × 35mm diecast aluminium box [Altronics H0454, Jaycar HB5067, Mouser 546-29830PSLA] 10 9V DC 700mA+ plugpack with 2.1mm ID plug 10 100μH toroidal inductor (L1) [Altronics L6522] 1 330μH toroidal inductor (L2) [Altronics L6527] 1 9mm 10kW reverse log potentiometer (VR1) [Mouser 858-P091NFC25CR10K or 652-PTD9012015FC103] 1 knob to suit VR1 (D shaft), around 13mm in diameter 10 PCB-mounting 2.1mm inner diameter barrel socket (CON1) [Altronics P0620] 2 8-pin DIL IC sockets (optional; for IC1 & IC2) 2 3-pin polarised headers, 2.54mm pitch, with matching plugs and pins (CON2, CON4) 3 2-pin polarised headers, 2.54mm pitch, with matching plugs & pins (CON3, CON5, CON10) 1 3-pin female chassis-mount XLR socket (CON11) [Altronics P0850] 1 3-pin male chassis-mount XLR socket (CON12) [Altronics P0852] 2 SPDT chassis-mount mini toggle switches (S1, S2) [Altronics S1310] 1 5V DC coil DPDT PCB-mounting telecom relay (RLY1) [Altronics S4128B] 1 panel-mount green 3mm LED with bezel (LED1) [Altronics Z0240] 8 M3 × 16mm panhead machine screws 4 6mm-long M3-tapped Nylon spacers 10 M3 shakeproof washers 6 M3 hex nuts 4 stick-on rubber feet [Altronics H0940] 3 1m lengths of light-duty hookup wire (eg, white, red & black) 1 short length of 3mm diameter heatshrink tubing Semiconductors 2 NE5532 dual low-noise op amps, DIP-8 (IC1, IC2) 21 LM2577T integrated switch-mode regulators, TO-220-5 (IC3, IC4) 1 LM317HV or LM317 adjustable linear regulator, TO-220-3 (REG1) [Altronics Z0545] 1 LM317 adjustable linear regulator, TO-220-3 (REG3) 1 LM337 adjustable negative linear regulator, TO-220-3 (REG4) 2 BC559 low-noise PNP transistors, TO-92 (Q1, Q2) 5 6.8V 400mA axial zener diodes, DO-35 (ZD1-ZD5) [Altronics Z0320] 10 1N5819 40V 1A schottky diode, DO-41 (D1) 30 1N5819 40V 1A schottky or UF4002 100V 1A ultrafast diodes, DO-41 (D2, D3, D9) 1 UF4002 100V 1A ultrafast diode, DO-41 (D13) 8 1N4148 75V 200mA diodes, DO-35 (D4, D6-D8, D14-D17) 6 1N4004 400V 1A diodes, DO-41 (D22, D23, D26-D29) Capacitors 1 470μF 25V radial electrolytic; 5mm pitch, max. 10mm dia. & 21mm high [Altronics R5164] 42 220μF 63V radial electro; 5mm pitch, max. 10mm dia. & 21mm high [Altronics R5148] 21 220μF 25V radial electro; 3.5mm pitch, max. 8mm dia. [Altronics R5144] 10 47μF 63V radial electro; 2.5-3.5mm pitch, max. 8mm dia. & 21mm high [Altronics R5108] 87 10μF 63V low-ESR radial electrolytic [Altronics R4768] 10 1μF 50V/63V radial electrolytic [Altronics R4718] 1512 100nF 63V/100V MKT Microphone Preamp Kit (SC6784, $70): 1 10nF 63V/100V MKT includes the standard PCB plus all 3 1nF 63V/100V MKT onboard parts, switches and mounting 3 22pF 50V C0G/NP0 ceramic hardware. Case, XLR connectors, bezel low-ESR types are preferred but not required LED and wiring not included. Resistors 2 47kW 6 4.7kW 2 1.8kW 3 100W 21 33kW 20 3.9kW 1 750W 1 22W 3 22kW 13 3.0kW 1 430W 7 10W 1 12kW 10 2.4kW 2 390W 10 2.2W 2 10kW 43 2.7kW 12 330W 2 6.8kW 1 2.2kW 10 150W 🔹 🔹 🔹 For the embedded version, add: 1 double-sided PCB coded 01110232, 85 × 110mm 1 3-pin polarised header, 2.54mm pitch, with matching plugs and pins (CON1) num digit indicates how many to use for the embedded version Australia's electronics magazine February 2024  35 If you decide to build the version that suits a case (shown right), it is a neat and tight fit. Because only the pot shaft needs to go through the case, assembly is not as hard as it might look. The embedded version of the PCB is a bit simpler (shown left). ‘reasonable’ DC voltage at pins 2 and 3 of the input connector. This will vary depending on the microphone; expect it to be between about 5V and 43V. If you still have trouble, use an oscillator to drive the ‘hot’ input (middle pin of CON2) and: ● Check the input voltage with a scope. It should be set to 100mV. ● Check the voltages on the 1.8kW resistors immediately on either side of RLY1. Assuming the use of a single-­ ended oscillator, one of these should have your test voltage. Switch the attenuator in and out; you should see a 20dB (10 times) reduction in voltage level at one end. ● Check the base voltages of Q1 & Q2. They should be about 0V (a ‘touch’ above, to be precise!) ● Check the Q1 & Q2 emitter voltages; they should be about 0.6V. ● There should be about 10V across the two 10kW resistors right next to the XLR socket cutout, on either side of the 470μF capacitor, and about 4.7V across the 4.7kW resistors immediately to the right of D7 and below D8. Check the orientations of D7 and D8 if these voltages are not right. These voltages should be identical as they connect to the inverting and non-inverting inputs of the same op amp (IC2a). ● Check the voltage on pin 1 of IC2; it should be close to 0V with no signal applied to the Preamp. If it is pegged to one of the supply rails, look for something amiss in the feedback loop through IC2a, IC2, Q1 & Q2. 36 Silicon Chip If it’s working, check that the gain control provides about 48dB of range. You will need to drop the input voltage at high gain settings to avoid clipping. You should be able to achieve more than 8V RMS between pins 2 and 3 of the output connector into a 600W load. Case preparation The 120 × 93.5 × 35mm (119mm from some sources) diecast enclosure is available from a range of suppliers. All our measurements assume the use of 6mm standoffs for mounting the PCB, which provide clearance for the attenuation and phantom power switches and taller low-ESR capacitors. If you want to use different standoffs, verify that everything will fit, especially the 63V capacitors and switches. Standoffs taller than about 8mm are unlikely to work. Start by drilling and deburring the holes in the side walls of the enclosure, as shown in Fig.9; hold off on the mounting holes in the base. We used a stepped drill bit to make the XLR connector holes. These are a real boon for making larger holes. We bought several types of XLR connectors and found they were all similar Fig.9: the drilling details for the XLR sockets and holes for the potentiometer, LED, DC socket and switches. Leave the small XLR mounting holes until you have the sockets ready to install so you can position them accurately. Australia's electronics magazine siliconchip.com.au Fig.10: while you can expect the PCB mounting holes to be in these positions, you should use the PCB assembly to mark them exactly before drilling them to ensure everything will fit. Fig.11: by attaching the standoffs like this, we get a robust result while also allowing us to finagle it into the case. ◀ The PCB is designed to accommodate the XLR connectors and just fit inside the case. The board is a tight fit, but the parts are not squished together too much. ◀ but differed in the required cutout. You might need to fine-tune your metalwork for your connector. We also recommend that you hold off drilling the smaller fixing holes for the XLR connector until after you have made the main hole. Once the connector fits OK, mark and drill these holes so they are in the ideal locations. The two lower holes for the XLR connectors will need to be drilled and tapped for a 3mm thread (drill to 2.5mm first), as there is no room for nuts inside the case. An alternative is to use a long 3mm pop rivet, an approach we have tried and found to work well, especially if you get a hole slightly crooked. Once you have the side holes drilled, present the PCB to the case without the standoffs attached, and mark the locations of the mounting holes. They are shown in Fig.10 but you should use the PCB to mark them more accurately. Drill these to 3.5mm and deburr them. This method is easiest since getting those measurements perfect inside the box is not easy. Install the standoffs to the case by putting a 16mm M3 machine screw and M3 shakeproof washer through the panel from the outside, then screw the 6mm standoff onto the machine screw – see Fig.11. Do not fully tighten it, as you need to be able to jiggle the PCB onto the M3 screws. Once the PCB is in place, tighten the screws onto the standoffs. Pushing the PCB onto the standoffs will help you do that. We placed slotted holes at the connector end of the PCB so you can present the board to the case with the connector end tilted down, allowing the gain control pot shaft to go through the front panel. You can then jiggle the M3 screws through the slotted holes. Once the board is in place, use shakeproof washers and an M3 nut to secure it, as shown in the photos. Installing the XLR connectors The input connector is next to the input header, with the output XLR next to the gain control. Solder three differently-coloured 100mm wires to these and twist them together neatly. Trim these back to allow a neat installation, and crimp or solder pins to the pluggable headers. Refer to the wiring diagram, Fig.12, to connect the ground, hot and cold wires to pins 1-3, respectively. The bottom fixings for the XLR siliconchip.com.au Australia's electronics magazine February 2024  37 HEATSHRINK SLEEVES Switches and LED 10mF 220mF 25V IC4 LM2577T 2.7kW 100nF 220mF 63V 4148 4148 4148 D6 D4 100nF 4.7kW 4148 2.2kW + 47mF + LM317 390W D27 3.9kW 2.7kW 100nF IC3 Fig.12: how to wire it all up. The switches, connectors and LED all connect to the PCB via polarised headers, so you can wire each up one at a time and then plug it all together once the PCB is in the case. 100nF D26 10mF 3.9kW 10mF 10mF 220mF 25V 47mF 100nF REG3 D28 33kW 750W 1mF 100nF + UF4002 REG4 390W D7 D8 10W 100nF D13 + L2 330mH + LM337 IC 2 NE5532 4.7kW 2 2 pF UF 4002 2.4kW 33kW 3.0kW A K Q1 BC559 Q2 BC559 2.7kW 100W D15 1nF 10kW 4.7kW 10kW 1nF D29 10W 10W D2 L1 100mH 2.2W D3 U F4 0 0 2 + 1N5819 or 100nF 47m F 100W + 47mF 22kW 10W 1 100nF U F4 0 0 2 1N5819 or 220mF 63V 100nF 47mF 1N5819/UF4002 D9 10W 220mF 63V 2.7kW 47mF 4148 4148 4148 D17 4148 GND 47mF D16 CON4 D23 CON1 D1 1 N5 8 1 9 Mic Out REG1 330W 63V 9V DC IN ZD3 ZD4 47kW LM317HV 100nF 10mF Phantom Power 63V D22 12kW 63V 150W 100W CON10 + 47mF 22kW D14 10mF + HEATSHRINK SLEEVES 63V + 1S S1 CON3 Atten. 4.7kW 220mF 47kW 10W 1.8kW LED C O N5 2 2 pF 100nF 22kW 10 m F 100nF RLY1 5V 10W 430W ZD5 10m F ZD2 4.7kW 1.8kW 4.7kW IC1 NE5532 ZD1 1n F 6.8kW 6.8kW 100nF 63V + 100nF + 47mF 63V COIL 1S S2 + 47mF + BOTH SWITCHES TURNED BY 90° TO MAKE CONNECTIONS CLEARER 1 + K F 0n 2 2 pF 470mF A + LED1 INPUT 2 3 SOCKET 1 CON2 VR1 V R1 22W Mic In 1 XLR MIC OUTPUT PLUG (XCLO 2) RN M1IC OUTPUT 3 2 1 SOCKET + XLR MIC INPUT SOCKET (XCLO 1) RN M1IC socket are pretty close to the case base, so we simply drilled and tapped ours. Solder a 10nF capacitor between the case lug on one of the XLR connectors and the ground wire on pin 1. This will effectively ground the case for AC signals. The connections for the switches are made with light-duty hookup wire. Use twisted wire (any colour will do) and assemble to the two-pin pluggable headers, as shown in Fig.12. Similarly, use two pieces of twisted light-duty hookup wire for the LED. Apply heatshrink tubing over the solder connections to it. We used red for the anode and black for the cathode. These connect to pins 1 and 2 of the pluggable header, respectively. Now attach a knob for the gain control. Make it small, as it will be next to the output XLR connector. You should have tested the board already, so you will be set to go. We found that the lip of the lid hit the M3 nuts that secure the XLR connectors. To solve that, we used a file to notch the lip on the lid to clear the nuts, and the lid was then a perfect fit. You will find that the case is very full. The capacitors and TO-220 devices fit with a couple of millimetres of clearance to the lid. We think this is about as good packaging as we could have achieved. If you are using the ‘embedded’ version, we will leave it to your creativity on where and how you mount the Preamplifier. It is a relatively modest PCB, so it should fit in most places. We would supply the board with ±15V, but you could probably run it from up to ±30V without the regulators getting hot, as the current drain on the linear rails is quite low. You will need to check this detail in your application. We kept our labelling simple in line with the utilitarian intended use of this device (see Fig.13); you can be creative with this if you wish. Finally, stick some rubber feet on the bottom so it won’t damage the surfaces it’s on and won’t slide around too much. Using it Fig.13: print out and attach this lid panel artwork to the top of the box so you (or someone else) will remember what everything does. The Preamp should generally be run from a 9V DC plugpack. It will work fine from 12V DC. While it will not be damaged by a higher voltage, up to 24V DC, it likely won’t operate as the negative rail will not be generated. SC Australia's electronics magazine siliconchip.com.au 38 Silicon Chip Build It Yourself Electronics Centres® SAVE $80 719 $ K 8610 IP54 Rated with stainless hardware NEW! 29.95 $39.95 $ X 2386 4W 500 Lumen X 2387 7W 800 Lumen 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. Requires no wiring. 3 dusk activated lighting modes. 15 S 5327 Window/Door Open Alert Alerts you when a door or window opens with an alarm or chime. 4 Way USB Wall Charger 149 $ Compact DC Power Hub & Isolator Designed to manage power in your 12V or 24V vehicle. 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N 1130F SAVE 20% 34 20 $ 43 $ P 8073 Corner Mounts $ P 8067 Side Mounts P 8069 55cm End Mounts 2pcs. ABS Plastic ‘No Drill’ Solar Panel Mounts These tough surface mount brackets offer a way to mount solar panels without penetrating the roof of the caravan or boat. They can be attached using a silastic or similar adhesive. NEW! 29.95 $ X 0212A X 0204 NEW! 36.95 $ Aluminium USB Torch Durable all metal 5 Watt USB rechargeable torch. Can be used as an emergency power battery bank. 182mm long. Genlamp® Pro Head Torch A camping essential! 280 lumen spot + 220 lumen flood beam. USB C recharging. 199 $ SAVE $40 Includes canvas carry case. 130W Remote Power Folding Solar Panel Going bush this summer? Have power wherever you go on your next 4WD/camping adventure. Includes 130W panel, solar regulator, battery connection cables and canvas carry case. 3 stage solar charger. Adjustable stand for best sun placement. 664x631x75mm (folded). Vehicle & Trailer Tyre Pressure Monitor System 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. Provides high/low pressure alarms, leak detection and temperature monitoring. Optional signal booster Q 1302 $95. Your one-stop electronics shop since 1976. | Order online at altronics.com.au NEW! 175 $ Q 1300 Workbench Deals T 2651 Tool Kit SAVE $50 169 $ T 2650 Iron Only. SAVE $40 SAVE $70 129 239 $ $ Don’t forget the gas! T 2451 $9.50 per can. T 2065 T 2496 Desolder parts in seconds! SAVE 22% 62 $ High Output Blow Torch Micron® Vacuum Desoldering Station Super hot 1350°C flame with high output nozzle. Handheld or self standing design for tasks such as heatshrinking, model making, silver soldering! Designed to desolder through hole componentry, removing molten solder quickly and easily from solder pads and components. In-handle reservoir is easily removed and cleaned. Includes three desoldering tip, nozzle cleaner and filter pads. 160°-480°C. T 1528A SAVE $25 39 Repair faster with a lithium screwdriver. This USB rechargeable screwdriver has an adjustable torque drive for accurate driving of precision screws. Suits 4mm driver bits. 2 hrs use per charge. Two way control. NEW! 79 $ T 2127 .95 149 $ $ All metal with ratchet action Superb build quality! Combines a ratchet wire stripper, cutting blade & kwik crimper. Suits 10-24 AWG cable. SAVE $36 35 $ Wire Stripper & Kwik Crimper T 2196 SAVE 23% 90 $ 185W of power for both blow torch and soldering work. Powered by refillable butane cartridges (2 included). Provides 500°C soldering & 1300°C blow torch. Kit includes tips, solder sucker, flux, cutters & solder. T 1552A T 1566A SAVE 20% Iroda® Solderpro 180 Portable Gas Tool Includes case! RJ45 Pass Thru Crimper Spade, Ring & Lug Crimper Switch to Pass Thru RJ45 modular crimps and save time! Crimps and cuts in one ratchet action and works with industry standard connectors. Crimps all standard “kwik” connectors such as ring terminals, bullets and spades. Easy to identify red, blue, yellow jaws. Deutsch Connector Crimping Kit The complete suite of tools for popular multipole DC connectors by Deutsch. Suits size 12, 16 and 20 DT series pins. Included in the kit are a terminal housing release tool, pin removal tool and screwdriver. Includes 36 driver bits! SAVE 34% 30 $ SAVE 23% X 0435 35 $ Jakemy® 38 Piece Precision Driver Kit SAVE 22% T 2173A A compact and useful kit for general repairs and servicing. Great for high tech devices - including special bits for iPhone disassembly. Includes a variety of 4mm driver bits & a flexible extension. All in a neat self standing spring loaded case. 35 $ T 1461 USB 5x Magnifier Lamp Ultimate Flexible Helping Hands A handy 20 diopter magnifier powered by USB. Provides a crisp, clear view. 430mm long. The ultimate in soldering helper hands! Includes magnifier to assist with those fiddly jobs. Arm length ≈30cm. Order online at altronics.com.au | Sale pricing ends February 29th. Secure & save this month SAVE $50 Wi-Fi RGB Strip Lighting Kit 149 $ S 9843B Also includes magnetic balljoint bracket. Cable Free Wi-Fi Surveillance This handy 1080p camera can be installed just about anywhere indoors or out and has an in-built battery so you don’t need to run any cables! Offers 4-6 months of motion detect recording. When it’s flat, just take it off the wall & recharge via USB. Suits sheltered outdoor use. What is Tuya® Smart Home? X 3227* SAVE 20% This kit includes 5m of RGB strip lighting, power supply, controller unit and IR remote control allowing you to create colourful lighting effects around your home. Controller features a music sensor input allowing the lighting to trigger to music being played in the room. Great for home entertaining. 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SAVE 24% 69 $ A 1011 Two Channel UHF Switch System This 433MHz fixed code remote control switching system allows you to switch devices on and off remotely. Dual 12A relay channels .9-24V input. Build It Yourself Electronics Centres® Sale Ends February 29th 2024 Find a local reseller at: altronics.com.au/storelocations/dealers/ Makes a great baby or pet monitor, this camera features intelligent tracking of moving objects within the frame. 2-way audio with mic and speaker. 1080p HD Distributed 12V Power Supply Pan & Tilt Wi-Fi Camera Outdoor Wi-Fi Camera A sturdy outdoor wi-fi Tuya camera with two way audio and 25m night vision coverage. 1080p HD, IP66 rated for outdoor use. SAVE $70 85 $ Provides 9 dedicated 12VDC outputs for connecting low voltage devices. 7.5A max load. Individually fused outputs. Provides extra coverage with motorised pan (355°) and tilt (100°). Auto-tracks moving objects. 2-way audio. 30m IR night time coverage. 1080p HD, IP66 rated for outdoor use. Covert 1080p CCTV Recorder Great for monitoring in remote locations, temporary CCTV monitoring etc. Runs off batteries, so its quick & easy to set up anywhere. Requires 8xAA batteries & 32GB SD card. SAVE $20 S 9446D S 9753B 79 $ 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 2024. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0002 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. 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. Latching relay toggle circuit I searched the internet for a circuit that would toggle a relay on and off using a single-pole, single-throw momentary pushbutton switch. I found a circuit at www.the12volt. com/relays/relaydiagram23.html that would do what I wanted, but it used four relays. I also found a circuit from Silicon Chip (Circuit Notebook, May 2010 issue; siliconchip.au/Article/143) that would also work if I added a 30A horn relay to handle a higher current than the Jaycar SY4060 dual coil latching relay used there. However, I felt sure there was a simple way to do this with just two 30A SPDT horn relays. The circuit I developed works as follows. It starts in standby, with both relays off. Pressing the pushbutton switch (S1) turns on LAMP1 and also activates RELAY B via D1, which supplies power to the load. Diode D2 latches RELAY B on. Releasing S1 switches off LAMP1, removing the 12V at the negative side of RELAY A, energising it via D3. Both relays remain on, and power is provided to the load. Pressing S1 again switches on LAMP2, and RELAY B drops out as the coil now has 12V on both sides. Power is removed from the load plus D2 and D3, while RELAY A stays on via D4. Releasing S1 switches off RELAY A and the circuit returns to the standby condition. I used SPDT 30A horn relays from Jaycar, while the lamps are 12V 5W festoon bulbs. Each bulb fits perfectly into a single AAA cell holder, making them easy to connect. They have a very low resistance when off and act as a 5W resistor when on. Back-EMF from the relay coils is taken care of by D1, D4 and both lamps. G. G., New Zealand. ($90) DHT22-based temperature/humidity chart display This BASIC program charts the temperature and humidity from a standard DHT22 sensor on a 2.8inch Micromite LCD Backpack (May 2017; siliconchip.au/Article/10652). The chart plots both readings over a 24-hour period. That period could be easily changed to be longer or siliconchip.com.au shorter by modifying the software. By default, it shows a temperature range of 10°C to 40°C and relative humidity (RH) from 0% to 100%. The 24-hour display period starts when the program runs. The basic process is to draw a line for every reading from the ‘old’ Australia's electronics magazine reading to the ‘new’ reading for both values for every pixel across the screen. That is done 320 ÷ 24 times per hour, which equates to every 4.5 minutes. The temperature readings are displayed in white, with the humidity in yellow. At the end of the 24 hours, the display starts at the beginning of the screen again, therefore showing the difference between the reading now and the one the day before. The program is pretty simple to follow and changes can easily be made. This same program could be used with multiple DS18B20 digital temperature sensors, using different colours to distinguish between sensors. You can download it from: siliconchip.com.au/Shop/6/332 Ray Saegenschnitter, Huntly, Vic. ($75) February 2024  43 Isolated mains voltage and current monitor This configuration uses two small power transformers and a current transformer to provide high-voltage isolation when measuring the voltage applied to and current drawn by a mains-powered device, while preserving accurate current and voltage waveforms. A single power transformer will provide isolation but will have a distorted secondary waveform due to the non-­ linearity from the core magnetisation approaching saturation (see Fig.1). This is the optimal condition for a power transformer but not satisfactory for this task. The core magnetisation must be kept in its linear region to get an accurate voltage waveform. In this circuit, the primary windings of two small power transformers (Altronics M2851L, 1.8VA) are connected in series, thereby halving the primary voltage each sees. This keeps the core magnetisation in the linear region of the B-H curve (see Fig.2). However, the secondaries are wired in parallel to ensure that the currents in both transformers remain balanced. A simple divider with a 10-turn pot provides for calibrating the output; in this case, a 50V input gives a 1V output (equivalent to a ×50 oscilloscope probe). The frequency response is within 0.5dB from 50Hz to at least 20kHz. The phase shift is within 1° to 2kHz, reaching 7° by 20kHz. Figs.1 & 2: the yellow trace is the incoming mains and mauve trace is the output of the transformer, with a single transformer shown on the left (Fig.1) and two in series on the right (Fig.2). Circuit Ideas Wanted 44 Silicon Chip Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine siliconchip.com.au A 1:1000 current transformer (AX1000 or AXC100) produces 1mA per amp, which translates to 0.1V per amp with a 100W burden resistor (equivalent to a ×10 current probe). To ensure the voltage and current outputs are in phase and the ‘right way up’, apply a half-wave rectified test load to the output. The transformer windings can be swapped to achieve the correct polarities, that is, indicating current drawn on the positive-going half of the voltage waveform. With the transformers mounted in a small Jiffy box and wired with an IEC input and a GPO output, as shown in the photo, the Mains Monitor provides a quick and safe way to check AC voltage waveforms up to 300V RMS at load currents up to 10A. Mark Hallinan, Woolloongabba, Qld. ($100) The finished isolated mains voltage and current monitor can be mounted in a Jiffy box. ESP32-based AI ChatGPT terminal I wish I had access to ChatGPT during my school days. For writing small programs on platforms like Arduino, Micropython or Python, these days it’s much easier to get ChatGPT to help rather than go searching for library documentation, read programming books and so on. I even prepared the code for this siliconchip.com.au project using hints from ChatGPT! This simple console provides a keyboard and a small screen that lets you type a question and almost immediately get a (usually) helpful answer. It does this by sending what you type to the ChatGPT servers via WiFi; then, when it receives the response, it prints it on the TFT screen. You don’t need Australia's electronics magazine any elaborate computer; you just need an internet WiFi connection and a ChatGPT account. You may ask why I’m using an old PS/2 keyboard instead of a USB keyboard. The precise answer is that I could not get a USB keyboard to work with the ESP32. An advanced reader might like to see if they can it going with a Bluetooth keyboard instead. There isn’t a lot to the circuit. The February 2024  45 ESP32 is wired to a 3.5-inch TFT screen via an 8-bit parallel bus and some control lines to update the screen's contents. The PS/2 keyboard socket connects directly to the ESP32 as well. Note that the ESP32 pins IO34 and IO35 used to get data from the keyboard are inputs only. A single 5V supply powers the screen, ESP32 module and keyboard. The 5V could come from various sources, such as a USB charger or USB battery bank, although the circuit diagram shows a simple linear regulator that allows it to be powered from a source of 9-12V DC, like a small plugpack. For the software to work, it needs an API key that provides access to the OpenAI servers. For this, you need to create an Open­AI account, log in, go to your user page via the menu and then down to the API keys section. You must copy that key and put it in the provided source code, which you can download from siliconchip.au/Shop/6/272 Once you’ve put the API key in the software, use the Arduino IDE (with the ESP32 Board Profile selected) to compile and upload it to the ESP32 module and wire it as shown in the circuit. Power it up after that and it’s ready for use. Press the ‘Esc’ key on the keyboard to start a new session. That clears the screen and readies it for taking a new question. Type your question and press Enter. At the end of the question, a number indicates how many characters are in the answer text. The accompanying photo shows an example of the sort of question the unit is capable of answering. Regarding the firmware, note that the delays I’ve used inside loops are critical. You may change them, but start with my values first. Once you have got a handle on your responses, you may change them. This is really just a proof of concept to show that with a keyboard and internet connection, AI can be used by a microcontroller. In a future development, I plan to eliminate the keyboard and instead use a speechto-text interface or a ChatGPT voice interactive solution. Bera Somnath, North Karanpura, India. ($80) WiFi Night Light using a simple circuit I created this Smart Night Light for a relative who had problems with mains-powered night lights failing, as well as the inability to control their brightness. It uses an ESP8266based ESP-01S module and has the following specifications: • Drives five white 5mm LEDs or a 3V COB LED panel • Runs from a 5V USB power supply drawing less than 100mA • WiFi: 2.4GHz only with on/off control • Web-based control interface and network setup • Four-digit LED Clock display using a TM1637 I2C module • Adjustable brightness • Australian capitals location settings • Daylight saving on/off • Audible alarm on/off setting and duration • Manual on/off, settable on/off times or sunset to sunrise 46 Silicon Chip The Night Light is designed to operate in dark areas such as the passageway of new homes where traditional night lights would stay on permanently. The best feature is that the brightness can be varied to suit the location. The Night Light is powered via a 5V USB supply, commonly used to charge phones. Australia's electronics magazine The heart of the unit is an ESP-01S module that includes WiFi hardware and software so that a connection can be made to your local network and the internet. A web server is created and the Night Light control web page can be accessed via a web browser. A fixed local IP address is set on the first boot to ensure the Night Light web page IP is always the same. The web server uses web socket technology to update the web page data values without continuously refreshing the page. The unit gets the current time from a network time protocol (NTP) service and uses a library to calculate sunrise and sunset times for the set time zone. The main control loop constantly checks the time to determine whether the LED panel and alarm beeper should be on or off. PNP transistors buffer the microcontroller outputs for the buzzer siliconchip.com.au LED-based motion sensor This circuit began in my mind as a demonstration of an experimental concept: a diodic divider. In this case, it allows us to use LEDs at minuscule current as light sensors. You could compare this to a passive infrared (PIR) sensor. However, there are significant differences. This device operates in the light. It stops working after sunset or if light levels drop below about 800 lumens (eg, the light provided by a 60W incandescent bulb or a 10W LED). Unlike a PIR device, it can see through glass. It is also much cheaper to build. In good light, without any enhancement of the LEDs, this circuit picked up my movement 10m away. It will also detect LEDs switching on or off at the same distance. As an active device (for example, using a cheap laser to and the LED panel. These ensure that the GPIO pins are pulled high at boot, a requirement of the microcontroller. A 5V USB plug pack provides power. Its output is regulated to 3.3V for the microcontroller using a three-terminal AMS1117 3.3V siliconchip.com.au illuminate the LEDs), this circuit can operate at all times, potentially with a range of kilometres. The diodic divider comprises diodes D2 to D5 plus ultrabright red LEDs LED1 & LED2, which conduct a mere 2.5nA with 12V across the lot. This indicates a 1.2GW impedance due to the reverse current of 1N4148 signal diodes. You can imagine D2-D5 as resistors, conducting 10nA at 12V, with a maximum capacitance of 4pF. using four signal diodes, rather than two, reduces drift in lower light. The second part of the circuit, IC1a, is a diode pump. It produces a pulse of about four seconds when it detects motion. This can be varied by adjusting the value of the 100kW resistor or 22μF capacitor. If LED3 is not used in combination with a small piezo buzzer, low-dropout regulator module with input and output capacitors installed. For more details on the control interface, see the PDF user manual available from siliconchip.com.au/ Shop/6/334, along with the Arduino source code. Australia's electronics magazine replace the buzzer with a 1kW resistor. Ideally, one should set up this circuit during the day, at the maximum brightness the circuit would encounter (or in an enclosed space, with the lights on) by carefully turning VR1 and VR2. After adjustment, allow a minute for the circuit to settle before testing, or readjusting it. The circuit is designed so that it is well-balanced and stable if the LEDs are aimed more or less at the same light source (say, daylight behind curtains, or a well-lit wall). You can experiment with various light sources, positions for LED1 and LED2, and lenses. Without triggering, this circuit should run for about three weeks from six AA alkaline cells in series. Thomas O. Scarborough, Cape Town, South Africa ($100) That PDF also has instructions on how to build and upload the code to the ESP-01S module, which is complicated by the fact that, due to complexity, the sketch spans 19 separate files. Phillip Webb, Hope Valley, SA. ($110) February 2024  47 Part 1 of John Clarke’s Mains Power-Up Sequencer This Mains Power-Up Sequencer solves many problems caused by powering up several devices simultaneously, including circuit breakers tripping, thumps from audio equipment and modem/router overloading. The Mains Power-Up Sequencer can also power several appliances on or off when a ‘master’ appliance switches on or off. Y ou might have run into problems switching on several appliances at once, eg, using the switch on a mains outlet. You might have a bank of equipment that all needs to be powered up, but you would prefer to do it in sequence with the convenience of a single switch. Sometimes, if you switch everything on at once, it can trip the mains circuit breaker. There can also be a sudden drop in mains voltage when switching on a bank of equipment due to the high initial current draw that causes other equipment to reset or act up. Similarly, the high initial current can trip the circuit breaker when you have several personal computers that are all switched on together, such as in a school or office. Additionally, powering up several computers at one time can cause them all to try to access the network/internet at the same time, overloading the router and causing slow startups or even lockups. Staggering the powering up of each computer by a few seconds can prevent this. The Power-Up Sequencer can 48 Silicon Chip address these concerns. It includes four mains outlets that can switch on equipment sequentially, with a delay between each. If four outlets are insufficient, then a second Sequencer can be added that daisy chains from the first unit. Daisy-chained Sequencers can be powered from a separate power circuit to the first Sequencer, allowing for more devices than can be plugged into a single GPO (general purpose mains outlet). The separate power circuit can even be from a different phase. Not only does the Sequencer power up equipment in an orderly fashion but it can also be used to power down in sequence. Another feature is the ability to Warning: Mains Voltage All circuitry within the Mains Sequencer operates at Line (mains) voltages. It would be an electrocution hazard if built incorrectly or used with the lid open. Only build this if you are fully experienced in building mains projects. Australia's electronics magazine power up and down multiple devices by switching one piece of equipment on and off. That can be useful when equipment is difficult to access and a single, more accessible switch can be used for the on and off powering sequence. For example, you could have your receiver, amplifier and DVD player automatically switch on when you power up your TV by remote control. Most equipment draws a substantial current over the first few mains cycles when powering up, often described as inrush current. With some appliances, this current is because a large capacitance needs to be charged. These draw a high initial current before the capacitor voltage rises and the current reduces. In other cases, it can be due to a motor spinning up. Typically, the inrush current won’t cause a circuit breaker to trip if only one appliance is switched on at a time. However, with more devices switched at the same time, the current is multiplied. Switching them on in sequence will avoid that. It should be noted that the Sequencer siliconchip.com.au Scope 1: the mains voltage (mauve) and current (yellow) drawn by three amplifiers in parallel that was switched on just after the mains voltage peak. After a small initial current flow, it drops to zero, followed by a big spike to 182A as the amplifiers’ capacitor bank starts to charge. is not designed for electric motors such as power tools. If you need to reduce the startup current for motorised appliances, we have published soft starters that are more applicable: • Active Mains Soft Starter (February & March 2023; siliconchip.au/ Series/395). • Soft Starter for Power Tools (July 2012; siliconchip.au/Article/601). • The SoftStarter (April 2012 issue; siliconchip.au/Article/705). Peak currents As an example of the initial surge current drawn by an appliance, we measured the current initially drawn by a 25V DC power supply that uses a 125VA toroidal transformer to charge two parallel 6800μF capacitors via a bridge rectifier. We measured current using a current transformer calibrated to produce 1V per 10A. The results can be seen in Scope 1. The cyan (channel 2) trace shows the mains voltage, while the yellow trace (channel 1) shows the current. Note that we show the current 180° out of phase with the voltage so that the two waveforms can be seen more easily, without one obscuring the other. Upon powering the 25V supply, it drew a maximum of 38A on the first half cycle, and 182A on the second half cycle. The first half cycle current is lower because the power was switched on later in the mains half cycle, but the next half cycle had the full waveform, siliconchip.com.au Scope 2: by switching the amplifiers on precisely at the zero crossing, we reduce the inrush current somewhat, to 168A. The reduction will be much greater for devices with a high power factor or power-factor correction (PFC). so the current was higher. When power is applied closer to the peak of the mains voltage, there will be a steep rise in the current drawn. If more than one of these supplies were powered up simultaneously, the current drawn from the GPO would add up. It is no wonder that a circuit breaker can trip if several appliances are switched on at the same time. For our Power-Up Sequencer, as well as staggering when power is applied to each appliance, we switch them on when the mains voltage is near the zero voltage crossing point. That allows the current to rise more slowly since the applied voltage follows the mains sinewave, instead of a peak voltage of up to about 325V applied instantaneously if power were applied at any time during the mains cycle. This is shown in Scope 2. The current rises from the start of the waveform just past the zero crossing as the mains voltage rises and results in a 168A peak. That’s still high because this appliance only really draws current near the peak of the voltage waveform. However, other appliances with a better power factor (PF) will benefit more from this zero-crossing switching. Sequencer options There are two options. The first is the master/slave feature, which involves monitoring the current drawn from the OUT1 GPO socket. The second is the Mains Detect Input, which can be used for daisy chaining. Switching on each GPO in sequence is done at an adjustable rate. The poweron and power-off sequence intervals Mains Power-Up Sequencer Features » » » » » » » » » » » » » Four independently-controlled 10A mains outputs (up to 10A total draw) Output switch on at mains zero crossing Adjustable power on & off sequence rates First on, first off (forward) or first on, last off (reverse) power-down sequence option Daisy-chaining for more outputs and extra current Master channel Current Detection option Separate Mains Input Detection option Number of outlets selection option (1-4) Relay switching for high efficiency with inrush/switch-off current spike protection Sequence indicators Multiple startup options Uses standard IEC mains cables and GPO outlets Housed in a rugged enclosure Australia's electronics magazine February 2024  49 are independent and can each be adjusted between 100ms and 23s. The order that the outputs are sequentially switched on is OUT1, OUT2, OUT3 and then OUT4. When switching off, you can select the reverse sequence order of OUT4, OUT3, OUT2 and then OUT1, or the forward sequence of OUT1, OUT2, OUT3 and then OUT4. We have provided several options so that the Sequencer can be as versatile as possible. That includes the option to build the unit with between one and four outlets, since some applications may not require four mains outlets. When the Sequencer is set up for fewer outlets, the powering sequences will be truncated to operate only over the installed number of outlets. Presentation & configurations The Sequencer comprises a rugged plastic enclosure with an IEC mains socket on the left side of the enclosure and four GPO mains sockets on the lid. The IEC mains socket provides input power using a standard IEC mains lead. A second IEC mains socket can be installed for Mains Input Detection, such as when daisy-chaining two Sequencers together. Fig.1 shows what the various inputs and outputs do. The basic configuration for building the Sequencer is without the second (lower) input, in which case, the outputs switch on in sequence when power is applied, and they all switch off at once when power is lost. It can also be built without the second input but with Current Detection for OUT1. In that case, OUT1 is the master socket and OUT2, OUT3 & OUT4 are the slaves. The slave outputs switch on in sequence when it detects the master device drawing current from OUT1. They switch off in sequence when the appliance stops drawing power from OUT1. The third configuration is with the Mains Detect Input but without Current Detection. Nothing happens when power is first applied to the unit in this case. It waits until it detects a mains voltage at the Mains Detect Input, then switches on the four outputs in sequence. If voltage is no longer detected at the Mains Detect Input, the four outputs switch off sequentially. They all switch off immediately if the main power input is lost. Note that no power is drawn from the supply fed to the Mains Detect Input. While the Mains Detect Input is primarily intended for daisy-chaining, it can also trigger switching the four outlets on in sequence when another device is switched on via a GPO switch or other mains-interrupting device. The first and most basic configuration is without the Mains Input Detect circuitry or Current Detection circuitry and is easier to build. The disadvantages are that you have to switch it on at the wall, and all the outlets switch off immediately when it is switched off, rather than in sequence. Whether or not that is a problem depends on your situation. Fig.1: the Mains Power-up Sequencer can have three primary configurations. It can be built with or without the optional Mains Detect Input that allows it to be triggered from a separate, isolated mains input (useful for daisy-chaining). It can also be built with current detection for OUT1 that will trigger the switching of OUT2-OUT4 but, in that case, the Mains Detect Input cannot be used. 50 Silicon Chip Australia's electronics magazine An example of where devices may need to be switched off in sequence is where you have an audio processor or mixer ahead of one or more power amplifiers. If the mixer or audio processor is switched on after the amplifiers or off before the amplifiers, a loud noise can be produced in the loudspeakers driven by the amplifiers. That is because the mixer or audio processor can produce a large voltage swing in the audio signal at switch-on or switch-off. So ideally, the amplifiers need to be switched on after the audio processor and off before the audio processor. Therefore, one of the options would be required. Both of the other configurations, with either the Mains Input Detect circuitry or Current Detection circuitry (but not both), offer power-on and power-off sequencing. Fig.2 shows how you can add more sequencer outputs by daisy chaining two (or more) Sequencer units. The primary Sequencer can have any of the three possible configurations. The other Sequencers need to be configured with the Mains Detect Input option. OUT4 from the primary Sequencer applies voltage to the Mains Detect Input of the second Sequencer using a piggyback mains plug lead (or double adaptor). In this way, when OUT4 of the primary Sequencer is powered, it triggers the second Sequencer to start providing power to its outputs and so on. The piggyback plug allows an appliance also to be powered from OUT4 so you don’t lose an output. A delay can be included in the second unit so that its OUT1 outlet does not switch on as soon as the OUT4 on the primary unit is powered. Note that if the primary and daisy-­ chained Sequencers are set for a forward off-sequence (OUT1, OUT2, OUT3 then OUT4), the daisy-chained off-sequence will begin after the primary sequence has finished. However, if the off-sequence is in reverse (OUT4, OUT3, OUT2 then OUT1), the daisy-­ chained off cycle will start as soon as the primary Sequencer begins its off-sequence. Besides using the forwards off-­ sequence, there are ways to deal with this. One is to set a greater delay for the daisy-chained off-sequence so that it starts after the primary sequence has finished, despite being triggered earlier. Also, if the primary Sequencer siliconchip.com.au Fig.2: this shows how to daisy-chain two or more Sequencers to give eight or more controlled outputs. There are other ways to expand it, but this is the easiest way and should suit most applications. off-rate is twice the daisy-chained Sequencer off rate, the outputs from each will switch off alternately between the two. There’s also the possibility of connecting the Mains Detect Inputs of secondary Sequencers to each of the OUT1-OUT4 outputs of a primary Sequencer if you need them to switch on and off in a neat sequence, with primary delays set to be longer than the secondaries. Circuit details Fig.3 shows the full circuit for the Power-Up Sequencer. It is based around microcontroller IC9, which monitors the Mains Detect Input or the current flow through an appliance plugged into OUT1. It also drives the circuitry that powers the four GPOs that supply power to the appliances. Other connections to the microcontroller are for setting the on and off sequence delays and other options. Switching mains to each GPO at OUT1-OUT4 is achieved using a relay and a Triac in parallel for each outlet. The Triacs are 600V bidirectional switches capable of conducting 30A continuously and up to 270A over one 20ms mains cycle. The Triac is included to protect the relay contacts from damage and a short life due to high initial surge currents drawn by appliances at power-up. So, instead of using the relay contacts directly, we first switch on the Triac and then the relay some 300ms later. This means that the initial startup current by an appliance is connected via the Triac, with the relay contact closing afterwards, once the current has dropped. siliconchip.com.au In the same way, the Triac is used to hold power on when the relay is switched off for 100ms, giving time for the relay contacts to fully open before the Triac switches off. That protects the relay contacts from voltage transients that may damage the relay contacts over time. The Triac is protected from voltage transients by a snubber circuit across it that comprises a 10nF X2 rated capacitor and 330W 1W resistor in series for the OUT2, OUT3 and OUT4 circuits. These values are labelled as R1 and C1 for OUT1 because they depend on whether this mains channel is used to detect whether an appliance is switched on or off for Current Detection. If Current Detection is being used, a 220nF X2-rated capacitor and series 470W 1W resistor are used instead of the values mentioned above. The relay and the Triac for each output are driven using separate optically-­ coupled Triac driver ICs. These incorporate lower current rated Triacs that are switched on via LEDs within the ICs. The optically-coupled Triac drivers (IC1 and IC2 for OUT1) are similar. However, IC1 will only trigger the internal Triac near the zero-voltage crossing of the mains waveform, when the instantaneous voltage is under 25V. So IC1 will only trigger TRIAC1 at the start of the mains waveform, and any surge current drawn by the appliance will be very low to begin with (since the voltage is low) and The finished Mains Power-Up Sequencer fitted into a standard ABS enclosure that measures 222 × 146 × 55mm. Australia's electronics magazine 51 only rise as the mains voltage increases over time. The inductor (eg, L1) in series with the Triac reduces the maximum current rise rate to a safe level. Driving the relay For the OUT1 mains channel, IC2 drives the relay coil directly. The snubber across the coil comprising a 10nF 52 Silicon Chip X2 rated capacitor and 1kW 1W resistor limits voltage spikes when the IC switches off and current flow through the relay coil ceases. This snubber also prevents the relay from buzzing when powered off due to current leakage through IC2’s internal Triac. In a typical circuit, the snubber would be across the Triac pins, but Australia's electronics magazine for our purposes, this would provide current through the relay coil when the Triac is off, so the relay will tend to vibrate (buzz). This leakage current is insufficient to switch the relay, but it can still cause it to vibrate. By placing the snubber across the relay coil, this current bypasses the coil. Both types of Triac drivers have siliconchip.com.au Fig.3: the complete Sequencer circuit. It consists of five main blocks: output switching (the entire right-hand page), power supply (upper-left corner), optional Mains Detect Input (below the power supply), Current Detection (lower left plus T1 at top middle) and control (IC9 and surrounding components). special voltage-clamping features that prevent them from conducting (switching on) when mains power is suddenly applied to the circuit. That can happen even with the internal opto-coupled LED off. The clamping siliconchip.com.au feature allows a voltage rise of up to 10kV per microsecond (10kV/μs) to occur without the internal Triac self-triggering. The LED drive current for the Triac drivers is low compared to many other Australia's electronics magazine similar devices, with a lower limit of just 2mA (or 5mA for entirely inductive loads) for the IL4108 (or IL410) and 2mA for the IL4208 or IL420. That means we can get away with a simpler power supply for this part of February 2024  53 the circuit that only has to deliver a modest current, even when all mains outputs (OUT1, OUT2, OUT3 and OUT4) are switched on. The IL4108 or IL410 IC used for switching the Triac is only switched on momentarily before the relay driver is switched on using the IL4208 or IL420. This means that when all outlets are on, the total drive for the opto-­ coupled Triac drivers will be around 8mA. We actually drive each at a little more than the required 2mA to allow for a safety margin. The Triac and relay driving circuitry is the same for all four channels. The only difference is the aforementioned snubber component value variation for OUT1 if current sensing is used. Microcontroller functions Digital outputs RC1 (pin 15) and RA4 (pin 3) of microcontroller IC9 drive the opto-couplers to control OUT1, while other similar digital outputs control the other three channels. A 680W resistor limits the current to IC1’s LED to a little over 5mA. For IC2, there is an indicator LED (LED1) in series with the LED within IC2, so we use a 750W resistor in series to ensure the current is at least 2mA. Switches S1 to S3 connect to the RB5, RB7 and RB6 digital inputs (pins 12, 10 & 11) of IC9, respectively, and these inputs have internal pullups. So each input is sensed as a high level when the switch is open and as a low when the switch is closed, pulling the input to the 0V rail. Switch S1 selects whether the sequencer detects appliance current or uses mains detection. When S1 is open, no current or mains detection is used, so the sequencer starts up whenever mains power is applied. Switch S2 selects whether the sequencer switches power to the first output immediately or after a delay when triggered. When S2 is closed, there is a delay before switching on or off, equal to the on/off sequence delay. When S2 is open, there is no such delay. Switch S3 selects whether VR1 adjusts the on-sequence or off-­ sequence rates. It can also determine whether the off-sequence runs in a forward direction or reverse. VR1 is connected across the 5.1V supply, so the wiper provides a varying voltage to the AN7 analog input of IC9 (pin 7). This voltage is bypassed 54 Silicon Chip Parts List – Mains Power-Up Sequencer 1 double-sided PCB coded 10108231, 203 × 134mm 1 222 × 146 × 55mm ABS or polycarbonate IP65 enclosure [Jaycar HB6130, HB6220] 1 set of panel labels (top and side panel) 1 IEC panel-mount mains input connector with integral fuse (CON5) [Altronics P8324, Jaycar PP4004] 1 10A mains IEC lead 1 10A M205 fast blow fuse (F1) 51 vertical-mounting 15A 300V two-way pluggable terminal blocks, 5.08mm pitch (CON1-4, CON6) [Altronics P2512 + P2572, Jaycar HM3112 + HM3122] 41 10A side-entry chassis-mount GPO sockets (OUT1-OUT4) ● [Altronics P8241, Jaycar PS4094] 41 28 × 14 × 11mm compressed powdered iron toroidal cores (L1-L4) [Jaycar LO1244 (two per packet)] 41 Schrack RT33473 16A NO 230VAC coil relays (RLY1-RLY4) [element14 2748015] 3 SPDT subminiature toggle switches (S1-S3) [Altronics S1415, Jaycar ST0310] 1 9mm PCB-mount vertical 10kW linear potentiometer (VR1) [Altronics R1946] 1 20-pin DIL IC socket 51 16kV isolation Fresnel 5mm LED bezels (Cliplite CLB300CTP) [element14 2748731] Wire/cable/hardware 41 50cm lengths of 1.25mm diameter enamelled copper wire (for L1-L4) 1 820mm length of blue 10A mains-rated wire 1 900mm length of brown 10A mains-rated wire 1 500mm length of green/yellow striped 10A mains-rated wire 1 75mm length of 10mm diameter heatshrink tubing 1 60mm length of 5mm diameter heatshrink tubing 1 250mm length of 1mm diameter heatshrink tubing (for LED leads) 2 M3 × 10mm Nylon countersunk head machine screws (for CON5) 4 M3 × 6mm panhead machine screws (for attaching the PCB to the enclosure) 2 M3 hex nuts 41 200mm cable ties (for L1-L4) 15 100mm cable ties Semiconductors 41 IL410 or IL4108 zero-switching Triac output opto-couplers, DIP-6 (IC1, IC3, IC5 & IC7) [element14 1045434, 1612489] 41 IL420 or IL4208 random-switching Triac output opto-couplers, DIP-6 (IC2, IC4, IC6 & IC8) [element14 1469488] 1 PIC16F1459-I/P microcontroller programmed with 1010823A.hex, DIP-20 (IC9) 41 T3035H-6G 30A Triacs (TRIAC1-TRIAC4), D2PAK [element14 2778110] 1 400V 1A W04 bridge rectifier (BR1) 1 5.1V 1W zener diode (ZD1) 51 5mm high-brightness LEDs (eg, one green and four red) (LED1-LED5) Capacitors 1 1000μF 16V PC electrolytic 1 10μF 16V PC electrolytic 1 470nF X2-rated mains capacitor 1 220nF X2-rated mains capacitor (10nF if current detect feature is not used) 2 100nF MKT polyester 71 10nF X2-rated mains capacitors Resistors (all ¼W 1% unless otherwise specified) 61 1MW 1W 5% 1 100kW 1 10kW Australia's electronics magazine siliconchip.com.au 1 1.5kW 1 1kW 5W 5% 41 1kW 1W 5% 41 750W 41 680W 72 330W 1W 5% (8 if current detection is not used) 41 300W Alternative parts instead of GPO sockets (●) 4 cordgrip grommets [Altronics H4280] 4 2m mains extension cords (or 4 mains line sockets and 8m of 10A mains cable) 5 crimp eyelets suitable for 4-6mm2 wire 1 M4 × 20mm panhead machine screw 1 M4 hex nut 1 M4 star washer Extra parts for Current Detection feature ____________________ 1 vertical-mounting 15A 300V two-way pluggable terminal block, 5.08mm pitch (CON7) [Altronics P2512 + P2572, Jaycar HM3112 + HM3122] 1 AC1010 10A current transformer (T1) 1 MCP6272-E/P dual rail-to-rail op amp, DIP-8 (IC10) 1 8-pin DIL IC socket 1 (P)4KE15CA transient voltage suppressor (TVS1) 2 10μF 16V PC electrolytic capacitors 1 200mm length of 10A brown mains-rated wire 1 200mm cable tie Resistors (all ¼W 1%) 1 30kW 1 20kW 1 18kW 1 15kW 2 10kW 1 2.2kW 1 470W 1W 5% Extra parts for Mains Input Detection feature________________ 1 IEC panel-mount mains input connector with integral fuse (CON8) [Altronics P8324, Jaycar PP4004] 1 mains IEC lead 1 1A M205 fast blow fuse (F2) 1 vertical-mounting 15A 300V two-way pluggable terminal block, 5.08mm pitch (CON9) [Altronics P2512 + P2572, Jaycar HM3112 + HM3122] 2 M3 × 10mm Nylon countersunk head machine screws (for CON8) 2 M3 hex nuts 1 75mm length of brown 7.5A mains-rated wire 1 75mm length of blue 7.5A mains-rated wire 1 40mm of 0.5mm diameter heatshrink tubing 1 4N25 phototransistor opto-coupler, DIP-6 (IC11) 1 400V 1A W04 bridge rectifier (BR2) 1 12V 1W zener diode (ZD2) Hard-to-get parts (SC6871, $95): 1 10μF 16V PC electrolytic capacitor includes the PCB, programmed micro, all 1 22nF X2-rated mains capacitor other semis and the Fresnel lens bezels. 1 1MW 1W 5% resistor Current detection add-on (SC6902, $20): 1 10kW ¼W 1% resistor includes the AC-1010 current transformer, 1 4.7kW ¼W 1% resistor (P)4KE15CA TVS and MCP6272-E/P dual rail-to-rail op amp. 1 1kW 1W 5% resistor 1 reduce quantities by one for each output not fitted 2 reduce quantity by two for each output not fitted siliconchip.com.au Australia's electronics magazine by a 100nF capacitor to present a low impedance when IC9 reads the voltage using its internal analog-to-digital converter. Any parameters set using VR1 are stored in flash memory within IC9, so they remain even if power is switched off. Reduced output channels Initially, all four outputs are active. However, if you don’t need all four, you can leave them off and tell the microcontroller not to use those outputs. The RA0 and RA1 digital inputs (pins 19 & 18) are initially tied to ground on the PCB. The small tracks connecting RA0 and RA1 to 0V can be broken and connected to the nearby track on the PCB’s top side, which joins to the +5.1V supply. A table next month will show which connections are required for any number of outputs. That changes how the output sequence operates in software. Unused output channels do not need to have their components populated on the PCB. Mains detection The separate mains presence detection is via input IEC connector CON8. A series 22nF X2 capacitor is used to apply and limit current to bridge rectifier BR2, while 12V zener diode ZD2 limits the voltage across the output of the bridge. The resulting DC supply is filtered with a 10μF capacitor. The 22nF capacitor provides an impedance of 144.7kW at 50Hz (1 ÷ [22nF × 2π × 50Hz]). Therefore, the current that can be drawn is 230V AC ÷ 144.7kW = 1.59mA. The 1kW 1W resistor in series with the 22nF capacitor limits the surge current through the capacitor when power is first applied, while the 1MW 1W resistor across the capacitor discharges it when power is off. When power is on, the DC supply drives the LED within optically-­ coupled transistor IC11 via a 4.7kW resistor. ZD2 will not normally clamp the voltage to 12V since the current drive to the LED within IC11 means that the rectified voltage is about 8.5V, ie, 1.59mA × 4.7kW plus IC11’s LED voltage of about 1V. The zener diode is included just for protection should there be an open-­ circuit condition. Without it, the 10μF capacitor could be charged to nearly the peak mains voltage (325V) with February 2024  55 We fitted both options for testing but you should pick one (or none). catastrophic results, such as the 10μF 16V capacitor exploding. Current Detection Current transformer T1 is used for the Current Detection feature of OUT1. It produces a current from its secondary winding that’s proportional to the current flow through the Active mains wire. The 10kW loading resistor gives about 4V AC output with a current flow of 1A and one turn of the Active mains wire through the current transformer core. We use four turns through the core, giving about 4V AC with 250mA of current through the primary. The transformer’s primary winding is terminated at the CON7 screw terminal socket. If Current Detection is not used, the two CON7 terminals still need to be joined so that the mains Active connects to OUT1. Current flowing through an appliance connected to the OUT1 GPO outlet also goes through T1’s primary winding, inductor L1 and the snubber comprising a 220nF X2-rated capacitor and series 470W 1W resistor. The impedance provided by the 220nF capacitor at 50Hz is around 14.5kW, allowing about 15.9mA to flow through the switched-on appliance when OUT1 is off. Once current is detected, the sequencer will switch full mains power to the appliance. While T1’s transimpedance is not very linear using a 10kW loading resistance, we use that relatively high value to improve sensitivity. A 100W loading resistor would provide a more linear relationship for accurately measuring current, but only gives a 1V output for a 10A primary current with a single turn through the transformer. We just need to sense when current flows. Voltage rectification The output voltage of T1 is positive and negative on each mains half-cycle, but we want a positive voltage to feed Fig.4: a subsection of the circuit shown in Fig.3, responsible for rectifying the output of current sense transformer T1. 56 Silicon Chip Australia's electronics magazine to the microcontroller, so we need to rectify it. But it’s a small voltage, so we must use precision rectification to avoid any diode voltage losses. A precision full-wave rectifier is used, made from dual op amp IC10 and associated resistors. The rectification is done purely by the op amps, without added diodes. The gain of this precision rectifier is 1.5 times. Transient voltage suppressor TVS1 clamps the output from T1 to about 13.8V AC. That limits the current into the following op amp inputs to a safe level. While it may seem impossible to rectify the incoming AC voltage without diodes, it is possible, provided that the op amp has specific characteristics. These include operating correctly (without output phase reversal) with input voltages below its negative supply rail. In addition, the op amp must be able to pull its output close to the negative rail (ground, in this case). To put it another way, diode junctions within the op amps perform this function without us needing to add external diodes. We use an MCP6272 dual op amp (IC10) for this full-wave rectification. One stage (IC10a) is connected as a unity gain buffer, while the other (IC10b) provides the 1.5 times gain. To understand how the rectification works, refer to Figs.4 & 5; A to E in Fig.5 correspond to the waveforms at the identically labelled parts of the circuit in Fig.4. Consider the operation using a 2V peak-to-peak sinewave at point ‘A’. This makes the description easier since the waveform has a peak voltage of 1V. Rectification of the negative and positive waveforms will be described separately. For the negative half of the cycle, the signal applied to the non-inverting pin 3 input of IC10a via the 15kW resistor will cause the voltage at that pin (point B) to be clamped at around -0.3V due to IC10a’s internal input protection diode. The output of IC10a (point C) therefore sits at 0V during negative portions of the cycle, since its negative supply rail is at 0V, and it cannot pull its output lower than that. IC10b adjusts its output (point E) so that the voltage at its inverting input pin 6 (point D) matches the voltage at non-inverting input pin 5 (point C). Since the 10kW resistor from point D to ground has no voltage across it, it siliconchip.com.au plays no part in the circuit during the negative portions of the cycle. With the 10kW resistor essentially out of the circuit, IC10b operates as a standard inverting amplifier with both inputs (points C and D) at 0V. Its gain is therefore -30kW divided by 20kW, which equals -1.5 times. So, the -1V peak of the waveform is amplified and inverted to produce +1.5V at point E. Rectifying positive voltages The way it works for a positive voltage at the input (point A) is more complicated. Firstly, the voltage at pin 3 (point B) is reduced compared to the 1V peak at the input. That is because of the divider formed by the 15kW and 18kW resistors, so the voltage becomes 0.5454V (1V × 15kW ÷ [15kW + 18kW]). Point C will also peak at 0.5454V since IC10a is working as a unity-gain buffer, producing the same voltage at its output as its non-inverting input. Once again, op amp IC10b adjusts the output voltage (point E) so that the voltage at the inverting input at pin 6 (point D) matches the voltage at the non-inverting input, pin 5 (point C). We know that point D is at 0.5454V, so the current through the 10kW resistor to ground is 54.54μA (0.5454V ÷ 10kW). With point A at 1V, there is 22.73μA [(1V − 0.5454V] ÷ 20kW) flowing in through the 20kW resistor. That leaves 31.82μA (54.54μA - 22.73μA) to flow from output pin 7 of IC1b and through the 30kW resistor. Therefore, the voltage across the 30kW resistor is 0.9546V (31.82μA x 30kW). With point D at 0.5454V, point E must be at 1.5V (0.5454V + 0.9546V). So, the circuit operates as a fullwave rectifier with a gain of 1.5. The degree of precision depends on the op amp parameters and resistor tolerances. The lower the offset voltage of the op amp and the lower the op amp input bias current, the more accurate the full-wave rectification will be, particularly at low signal levels. Fortunately, we are not overly concerned with absolute accuracy here. We just need full-wave rectification of the incoming AC signal from the current transformer that works down into the tens of millivolts range. This circuit is more than capable of that. Scope 3 shows the operation of the full-wave rectifier for a 1V peak (2V peak-to-peak) sinewave at the input to the full wave rectifier (point A) on channel one, shown in yellow. siliconchip.com.au The channel two cyan waveform is the full-wave rectified waveform (point E). That measures as a 1.48V peak output waveform at 100Hz, compared to 1V peak at 50Hz for the input sinewave. The 20mV discrepancy from the expected 1.5V is due to tolerances in the 1% resistors and the accuracy of the oscilloscope readings. A 2.2kW resistor and 10μF capacitor filter the rectified waveform to produce a smoothed DC voltage suitable for IC9 to monitor via its AN4 analog input (pin 16) and internal analog-to-digital converter (ADC). Power supply Power for circuitry is derived directly from the mains via the IEC connector, CON5. A 470nF X2 mainsrated safety capacitor transfers charge each half cycle to a 1000μF capacitor via bridge rectifier BR1. Zener diode ZD1 clamps the voltage to 5.1V. The supply can be visualised as rectifying a current-limited version of the mains waveform via the series impedance of the 470nF capacitor. The impedance at 50Hz is 6.77kW (1 ÷ [470nF × 2π × 50Hz]). The current that can be drawn is equal to the mains voltage (230VAC) divided by the impedance, or about 34mA. As mentioned earlier, it takes around 8mA to drive all four optos continuously, leaving plenty of overhead for the microcontroller and other components. The 1kW 1W resistor in series with the 470nF capacitor limits the surge current through the capacitor when power is first applied, especially if power is switched when the mains is at a high instantaneous voltage when the switch is thrown. The 1MW 1W Fig.5: the expected waveforms at points A-E on the circuit (Fig.4) for a 1V peak sinewave from transformer T1. The output (E) is a rectified version of the input (A) but 50% higher in amplitude. resistor across the capacitor discharges it when power is off. LED5 connects in series with a 1.5kW resistor to indicate when power is on. IC9 and IC10 include bypass capacitors to stabilise their 5.1V supplies, with IC9 having a 10μF & 100nF capacitor while IC10 has a 10μF capacitor. Next month Having described how the Mains Power-up Sequencer works, we have run out of space in this issue. The final follow-up article next month will cover building it, testing it and SC setting it up. Scope 3: the measured input (A) and output (E) waveforms of the precision rectifier circuitry with a resistive load, giving a sinusoidal current waveform. You can see how perfectly the input is rectified; using diodes for rectification (unless used within a precision rectifier) would not work this well (if at all) with such low voltages. 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Jaycar reserves the right to change prices if and when required. Review by Tim Blythman Altronics’ Z6387 ESP32 WiFi Camera Module It’s incredible what’s available to hobbyists these days. We have access to 32-bit microcontrollers that include features like WiFi and Bluetooth and are easy to program using the Arduino IDE. Altronics’ Z6387 is such a device but it also includes a two-megapixel digital camera. Here is what you can do with it. T his WiFi and Bluetooth capable camera development board, based on an Espressif Systems ESP32-S3 microcontroller, costs just $32.95. While the Altronics Z6387 “ESP32-CAM” can be programmed using the Arduino IDE, it can also be used out-of-the-box. The module has two 8-way pin headers and measures just 27 × 40 × 15mm. It could be reduced in thickness to 10mm if the headers were removed. The pin header rows are 0.9in (22.86mm) apart, so it will comfortably plug into most breadboards with some room to connect jumper wires. As well as looking at the camera module in detail, we have some Arduino code that can connect to its WiFi interface and fetch images. We also have some example code that can be programmed directly into the module. We’ll even show how the WebMite can pull images from the module and display them on a 3.5in LCD panel. The ESP32 The ESP32-S3 is a dual-core Tensilica Xtensa LX6 32-bit microcontroller from Espressif Systems that includes WiFi and Bluetooth radios. It is a successor to the ESP8266, which was a pioneer in low-cost WiFi microcontrollers. The dual-core processor allows the radio functions to run independently of the main application. The chip has a generous 512kB of RAM and 384kB of ROM. The ROM includes a bootloader and some low-level radio and library functions, allowing them to run more quickly than if they were loaded from external flash memory (while saving that flash space for other things). Like many ESP32 & ESP8266 based boards, the ESP32-S3 chip is fitted to 60 Silicon Chip a small surface-mounting module that includes a flash memory chip for firmware and a smattering of other parts hidden under a folded metal shield. The module also has a PCB trace antenna for the radio interface. The ESP32-S3 on the camera module appears to be identically pinned to the ESP-WROOM-32 module that is found on some other boards. The ESP32-S3 module on the Z6387 has a U.FL antenna socket, which can be used by attaching a suitable antenna and relocating the link resistor that usually feeds the PCB trace antenna. The processor module is only a small part of the WiFi camera module, so let’s look at how it works and what we can do with it. The WiFi camera module The circuit of the WiFi camera module is shown in Fig.1. It includes MOD1, the ESP32-S3 module mentioned earlier, with an onboard 32Mbit (4MB) flash memory chip. The WiFi camera module also has a serial 32Mbit (4MB) PSRAM chip that connects to MOD1 over its QSPI (quad SPI) bus. PSRAM is an abbreviation for pseudo-­ static RAM; it is actually a form of dynamic RAM (DRAM) with its own internal refresh circuitry. Since the quirks of the DRAM are handled internally, it can be treated as though it were SRAM. These are huge quantities for those used to dealing with microcontrollers that might have only kilobytes of flash memory and RAM. Of course, they are necessary for dealing with the complexities of WiFi and image processing. U2, an AMS1117 3.3V regulator in an SMD SOT-223 package, provides a 3.3V rail from a nominally 5V supply. Australia's electronics magazine The 5V supply feeds only the 3.3V regulator, so this could realistically be any voltage that the AMS1117 and its input capacitor can handle. P-channel Mosfet Q2 (controlled by one of MOD1’s digital outputs) switches power to two XC6206 voltage regulators (U3 and U1) that provide the 1.2V and 2.8V rails the camera chip needs. Naturally, the regulators are surrounded by numerous bypassing capacitors. A 24-pin FFC (flat flexible cable) socket connects to CAM1, a tiny camera module less than 1cm2 in size (apart from the cable). The camera is an Omnivision OV2640 CMOS camera chip with a resolution of 1632 × 1232 pixels or 2MP. This camera chip model is now nearly 20 years old and has long been marked as obsolete; it was one of the early camera chips used in mobile phones. It incorporates a compression engine that can directly output compressed JPEG (aka JPG) image data. The OV2640 can also perform subsampling and windowing, effectively allowing zooming and panning in software, although this naturally reduces the effective resolution. Because of its wide adoption and lengthy history, there is still stock of these parts, and clones have even appeared. Its specifications are pretty modest compared to modern equipment, but its capabilities are a good match for modern 32-bit microcontrollers. 15 digital lines go between MOD1 and CAM1. Two of these are an I2C pair carrying control and configuration commands, while the others include an 8-bit parallel bus used to transport image data, plus various clock signals. Another six digital pins on MOD1 siliconchip.com.au Fig.1: much of the circuitry connects the ESP32 module to the camera chip and other peripherals. Many components run from 3.3V, although the camera chip also needs 1.2V and 2.8V rails provided by U3 and U1, respectively. There are not many spare I/O pins; using any of them will probably require the microSD card socket to be unused. siliconchip.com.au Australia's electronics magazine February 2024  61 connect to a microSD card socket, allowing QSPI operation. One digital pin drives a small LED via a 1kW resistor to the 3.3V rail, and another pin (via another 1kW resistor) goes to the base of NPN transistor Q1 to drive a larger white LED. Notably, this LED does not have a current-limiting resistor and is only intended to be used for short periods, like a camera flash. The external connections are a pair of 8-way pin headers. CON1 has connections for 3.3V, ground, the UART pins, as well as the E32_RST and GPIO0 pins. These are all handy for communications or programming the flash memory on MOD1. Tactile pushbutton S1 can short the E32_RST line to ground to reset the processor, while the state of GPIO0 dictates whether or not the bootloader or flash memory application runs. Interestingly, the E32_RST pin on CON1 is marked GND/R. It appears that similar boards (from other suppliers) connect this pin to ground and don’t otherwise break out the E32_RST line. Since the tactile pushbutton is on the underside of the module when fitted to a breadboard, these variants appear to be difficult to program. Header CON2 breaks out 5V, ground and the six I/O lines that also go to the microSD card socket. These are about the only spare I/O pins if you want to interface other hardware to the ESP32 WiFi camera module. However, that would probably mean that the microSD socket could not be used simultaneously. The wide-angle camera lens on the Z6387 ESP32 WiFi camera module has an approximately 160° field of view. There are other versions of the camera with a more narrow field of view of around 60°. Like many such cameras, the focus is fixed by a threaded lens insert glued in place. As a point of reference, human binocular vision has a field of view of about 114°. Powering it The nominal dropout of the onboard AMS1117 regulator is 1V at 800mA, so we had no trouble operating the camera module with an input as low as 4.2V (using our Breadboard PSU from December 2022; siliconchip.au/ Series/401). So running from a battery of three series AA cells would be a viable option, but using 3.7V LiPo or similar batteries will require a boost circuit. The camera module’s current draw peaked near 500mA on startup and when there was activity, dropping to around 200mA at idle. With the supply at 7V, the regulator was noticeably warm but not worryingly so. So the camera module should also be fine if powered by a battery of four AA cells in series, which could reach 6.4V when new. Operation Fortunately, the Altronics Z6387 ESP32 WiFi camera module comes loaded with useful default firmware, so no programming is required. However, there are a few steps you need to take before it can be used. Firstly, the firmware requires a microSD card in the card socket. We tried 2GB and 8GB cards with FAT If the camera chip is not connected to the camera module, open the FFC connector by pivoting the black bar upwards, as seen here. Insert the cable and press the bar back down to lock the cable in place. Then use the attached tape to secure the camera to the microSD card socket. 62 Silicon Chip formatting without issue. We are unsure why the card is needed, as we couldn’t see any features in the firmware that would use it. Most likely, the firmware attempts to initialise it for some reason and fails to proceed if it is absent. Also, after taking delivery of the module, you might find that the camera is not in its FFC socket. In that case, carefully pivot up the black bar on the FFC socket. The camera’s FFC cable slots in with its exposed metal contacts at the bottom. The bar rotates down to lock the cable in place. The back of the camera is also fitted with a pad of double-sided tape, allowing it to be secured to the top of the microSD card socket. This also allows the socket’s metal shell to dissipate heat from the camera, so you should adhere the camera to the microSD card socket once you are sure the cable is correctly fitted. We recommend that you connect a USB-serial converter so that you can check the module’s debugging output, including its IP address. Fig.2 shows how to wire it up. You can initially ignore the wires going to the two pushbuttons; they are only needed for programming (which we will discuss later). The USB-serial converter needs to have 3.3V logic levels, matching the camera module’s I/O levels. Set the baud rate in your serial terminal to 115,200 baud. The module briefly turns on the flash LED while powering up, so don't look directly at it. Screen 1 shows the debugging output you should see at powerup. If the microSD card is missing, you will see a “Card mount failed” message. If you don’t have a USB-serial converter then connecting a 5V supply to the 5V and ground pins on the CON2 header should be sufficient to get it to work, although you won’t have access to any diagnostic data. Screen 1: once it has successfully connected to a WiFi network, the diagnostic data from the camera module will indicate if the microSD card has been successfully mounted and the module’s IP address. The top line indicates the normal boot process when a program is run from flash memory. Australia's electronics magazine siliconchip.com.au HTTP interface The ESP32 WiFi camera module expects to connect to a network named “TEST” with the password “88888888”. It then creates an HTTP web server that provides a web page you can use to view and interact with the camera. You could temporarily change your router’s credentials to the above, or use a mobile phone’s WiFi hotspot feature to create such a network. Then use a web browser and navigate to the IP address shown in the serial terminal; Screen 2 shows what the web page looks like. With the default firmware, it’s much like a very basic wireless IP camera. It has no security features, so anyone connected to the WiFi network can access and control it. As you can see from all the settings, the camera is quite configurable. We tried the Face Detection and Face Recognition features. The camera module can detect faces, marking them with a yellow rectangle, but we can’t see how that would be usable outside of the HTTP interface. Fig.2: connecting the camera module to a CP2102 (or similar) USB-serial converter allows diagnostic data to be viewed in a serial terminal. The two pushbuttons are needed to reprogram the ESP32 chip. Pico W BackPack software We have prepared a program for the Pico W BackPack (siliconchip. au/Article/15616) that creates a suitable access point and allows the camera module to connect. The sketch is named “PICOW_BACKPACK_FOR_ ESP32CAM_SD” and there is a corresponding precompiled UF2 file. This program allows you to interact with the ESP32 WiFi camera module, including capturing and displaying images with different settings and image sizes, as well as saving and loading them to and from a microSD card. The Pico W BackPack only needs to be built with a minimal configuration, as long as it includes the 3.5in touchscreen and backlight control components. You will also need the microSD card socket components fitted (and a suitably formatted card installed) to use the microSD card related features, although the other features will work without it. To install the firmware for this, put the Pico W in bootloader mode and copy the UF2 file to the RPI-RP2 drive that appears. You can control the Pico W BackPack sketch from either the touch panel or a serial terminal. We use TeraTerm on Windows and minicom on Linux. siliconchip.com.au Screen 2: you can use a web browser on a mobile phone, tablet or computer to interface with the camera module and explore its features once it has connected to a WiFi network. Screen 3 shows the BackPack’s LCD image after booting. Power on the ESP32 WiFi camera module and, if you have a serial terminal monitoring its activity, wait until you see it indicate that it has connected (as per the end of Screen 1). Press the “Scan” button (or type “s” on the serial terminal) to allow the BackPack to find the camera module. Then use the “Capt” button or “c” followed by “d” in the serial terminal to capture and display an image. Screen 4 shows a sample image captured by the camera. The “Scan” button detects the camera by looking for its HTTP server. Don’t let too many other devices connect to the TEST access point, or the camera module might not be detected correctly. Screen 5 shows the serial terminal output for the BackPack after following the above steps, which includes a list of the other serial terminal commands. The size, quality, brightness and contrast settings are changed by sending an HTTP request to the camera, effectively clicking buttons on the web page that the camera module serves. Lower values correspond to clearer images (and larger file sizes) for the quality parameter. Numerous other settings can be accessed from the “/control” endpoint of the HTTP server on the camera module using a URL like this: http://192.168.42.16/­ control?var=framesize&val=2 The “Expt” button or “e” on the serial terminal will export (save) the currently displayed image to the microSD card (if fitted and initialised). “Next” or “n” on the serial terminal will attempt to display the next file found on the microSD card. This can be used to display JPG images captured with the camera or created on a computer and copied to the card. The sketch is intended mainly to test and demonstrate the features of the camera module. Still, it would be a good starting point if you wanted to create an M2M (machine to machine) application where a microcontroller uses the camera module to capture images for processing. You could change the sketch to periodically log photos to the microSD card, or continuously display the camera’s view as a basic remote monitor. Screen 3: the LCD screen of the Pico W BackPack after being loaded with the PICOW_ BACKPACK_ FOR_ ESP32CAM_SD firmware. It creates an access point for the camera module to connect to. Screen 4: pressing “Scan” will find the camera module on the access point’s WiFi network. Then press “Capt” to take a photo and display it on the LCD’s screen. The other large buttons save and load images to and from the microSD card. 64 Silicon Chip Australia's electronics magazine Adding a PIR motion sensor could turn it into a simple but functional security camera. Programming the camera module The Pico W BackPack makes it very easy to interface with the camera module, but you could do something more than simply displaying and saving images. Using the Arduino IDE and the ESP32 board profile, it’s possible to upload custom code to the camera module. The arrangement for programming the module is shown in Fig.2. The two momentary switches are needed to reset the processor and put it into programming download mode. If you have access to the RST button on the module, it will function the same as the RESET button in Fig.2. However, it will probably be inaccessible if the module is fitted to a breadboard. If you don’t have switches, you can use jumper wires that can temporarily be shorted to ground. You might notice that the ESP32 chips use much the same system as ESP8266 chips, and the circuit is almost the same as used for the ESP-01 modules in the WiFi Relay article from the January 2024 issue (siliconchip.au/ Article/16088). You’ll also need to install the ESP32 board profile for the Arduino IDE. You can do that by adding https:// dl.­espressif.com/dl/package_esp32_ index.json to the Board Manager URLs in Preferences. The ESP32 profile should then be available to install from the Boards Manager menu. We used the AI Thinker ESP32-CAM board setting under the Tools menu. The ESP32’s diagnostic and boot data serial rate is 115,200 baud, so set your Arduino serial monitor to that rate. The ESP32CAM_ WEBSERVER sketch The firmware loaded onto the Altronics Z6387 ESP32 WiFi camera module appears to be nearly identical to the CameraWebServer example sketch included with the ESP32 board profile. The difference is that the CameraWebServer sketch does not attempt to initialise the microSD card. We created a copy of this sketch and changed the settings to match the Altronics camera module. This is the “ESP32CAM_WEBSERVER” sketch in our software download package. siliconchip.com.au When we loaded the camera module with that sketch, it behaved almost exactly the same as when it was new. To put the processor into programming mode and allow it to download the sketch, press and hold the switch labelled RESET, then press and hold the IO0 switch. Release the RESET switch, then the IO0 switch. You should see (among other text) something like: rst:0x1 (POWERON_RESET), boot:0x3 (DOWNLOAD_BOOT) waiting for download If you instead see: rst:0x1 (POWERON_RESET), boot:0x13 (SPI_FAST_FLASH_BOOT) That means the sequencing was incorrect, and you should try again. Pressing and releasing RESET resets the microcontroller and gives the second message. You can try that if your sketch doesn’t appear to start correctly after uploading. Once it’s in the correct mode, upload the Arduino sketch using the Upload button or pressing Ctrl-U on your keyboard. You should then see output on the serial terminal like in Screen 1. If you wish to use this software with an existing WiFi network, change the SSID and password in the “Enter your WiFi credentials” section of the sketch. Then, upload the sketch with the new credentials. Screen 5: the Pico W BackPack sketch also provides a serial terminal interface and can be controlled by the commands shown here. Here, the “s”, “c” and “d” commands have been used after the menu was displayed. The ESP32CAM_PROBE_SD sketch The ESP32CAM_PROBE_SD sketch intends to show what can be achieved by code running on the ESP32 processor without WiFi. The options are similar to the Pico W sketch, although there is no LCD panel to display the images. To upload this sketch, open it in the Arduino IDE, select the AI Thinker ESP32-CAM board profile and the correct serial port at 115,200 baud. Then use the above switch sequence to select programming download mode and pick the Upload menu option from the Arduino IDE. When it runs, the sketch will show something like Screen 6 in the serial monitor. We used the “s” menu option to capture an image and save it to the microSD card, followed by the “a” option, which takes a photo and renders it as ASCII art in the terminal. The image is of a hand in front of a sheet of paper. siliconchip.com.au Screen 6: the ESP32CAM_PROBE_SD sketch shows what can be done with the camera module without requiring a WiFi interface; it can save photos to a microSD card. The ASCII art shown here is a photo of a hand above a piece of white paper. It’s intended as a way to check that the camera is working. Australia's electronics magazine February 2024  65 If you don’t have a Pico W BackPack, this is about the quickest way to see the camera generating images successfully. If you power off the camera module and put the microSD card in a card reader in a computer, you should see the photos that have been saved to the microSD card. This sketch is broken up into functions to allow you to easily modify the sketch in case you want to run custom code on the camera module. In that case, look at the files noted near the top of the sketch. They contain definitions of some other useful functions and constants (provided as part of the ESP32 board profile) that interface with the camera: sensor.h esp_camera.h img_converters.h Most of the top of the camera module is taken up by the camera chip and its FFC (flat flexible cable) connector. The chip sits on the microSD card socket and uses it as a heatsink. The LED at lower right is labelled FLASH LED in Fig.1. Both photos are shown enlarged for clarity. On our system (for the 2.0.13 version we are using), these are in “(board manager package location)\esp32\ hardware\esp32\2.0.13\tools\sdk\ esp32\include\esp32-camera”. There aren’t many spare pins available on the camera module. Most of the pins on the CON1 header are for power and serial data, while those on CON2 are shared with those used for the microSD card socket. So it is tricky to add much extra hardware to the camera module. Keep in mind that the ESP32 processors support Bluetooth as well as WiFi, so you might think of other ways to interface with it. BIN compiled binary files are also included in the software downloads. You can upload them to the ESP32 board using the ESP download tool, at address 0x000000. We won’t go into detail on how to do that as documentation is available online. WebMite software The underside carries the ESP32 module, PSRAM chip and 3.3V regulator U2. The RST button at top right is inaccessible when the module is plugged into a breadboard. The U.FL socket at lower left is for an external antenna, but the adjacent jumper resistor must be moved if using it. 66 Silicon Chip The WebMite MMBasic firmware (which also runs on a Pico W microcontroller) can interface with the camera module. We have produced software to demonstrate this, although it has few features since the WebMite cannot do everything that can be done with the Arduino IDE. The WebMite firmware is intended to be used with the Pico W BackPack hardware; it only needs the 3.5in LCD touchscreen and backlight components fitted. The program is named “WebMite ESP32-CAM.bas”. Australia's electronics magazine The easiest way to install the software is to put the Pico W in bootloader mode and copy the “WebMite ESP32CAM.UF2” file to the RPI-RP2 drive. Otherwise, the necessary OPTIONs are listed at the start of the BASIC file, if you wish to set it up yourself. If you have configured the ESP32CAM_WEBSERVER sketch to use a custom WiFi network, change the OPTION WIFI settings to match. Note that you need a WiFi router or similar to create the TEST access point, because the WebMite cannot act as an access point like the Pico W can when programmed with the Arduino IDE. You also need to manually determine the IP address of the camera module, such as by monitoring its serial output. Screen 7 shows the serial terminal output of the WebMite. Once it connects to WiFi, use the “V” option to enter the last octet of the camera module’s IP address. For example, if the camera module’s IP address is 192.168.42.16, type “16” followed by Enter. This assumes that the network uses a 255.255.255.0 subnet mask, which is typical for many home WiFi networks. If that is not the case, you can manually edit the “CAMIP” string. Screen 7 shows the output of the “G” command, which performs a GET HTTP request on the camera module and, if successful, saves the resulting JPG file to the internal A: drive of the WebMite. Finally, the “D” command displays the captured image file from the A: drive on the LCD panel. That is done by just a single line of BASIC code. The most recent captured image file remains on the WebMite’s A: drive and can be seen by using the FILES command at the MMBasic prompt. Comments Note that the camera module’s settings are shared by multiple devices trying to access it. For example, if one device changes the image size, that will be the setting used by all devices that try to capture an image with that camera module. We have also published some quite specialised Circuit Notebook items that use devices similar to the ESP32 WiFi camera module. We have not tested them with the Altronics Z6387 ESP32 WiFi camera module, but we suspect that some would work with it: • The Motion Triggered WiFi siliconchip.com.au camera from May 2022 (siliconchip. au/Article/15317) appears to use a board similar to the camera module, but has the alternative ground wiring to CON1. • The ESP32 camera sentry (November 2022; siliconchip.au/ Article/15541) and Object Recognition with Arduino and ESP32-CAM (July 2023; siliconchip.au/Article/15864) also use the alternate wiring noted above, and both require quite a bit of software set up on a second device to work. • The Automatic AI Doorman (October 2023 issue; siliconchip.au/ Article/15992) uses a different board that also includes a separate processor for AI classification of the camera images. Still, these Circuit Notebook items might inspire those looking to see what might be possible with the camera module. Conclusion The ESP32 WiFi camera module is a great entry point for those looking to incorporate a camera into a microcontroller project. Although quite an old model, the camera is configurable Screen 7: we’ve also created a simple WebMite BASIC program that can connect to the camera module over WiFi. You will need a separate WiFi access point to try this program, as the WebMite cannot create a WiFi access point. If you have a 3.5-inch LCD panel attached to your WebMite, it can also display captured photos. and handily produces compressed JPG data. Our example code means it should be straightforward to write your own software to interface with the camera module. The inbuilt WiFi interface means that just about any WiFi-capable 500 microcontroller can use the camera by connecting to the HTTP server. Alternatively, the ESP32 processor can be directly programmed with the Arduino IDE for standalone applications. The ESP32 WiFi camera module is available from Altronics (Catalog code Z6387): siliconchip.au/link/abrd SC POWER WATTS AMPLIFIER Produce big, clear sound with low noise and distortion with our massive 500W Amplifier. It's robust, includes load line protection and if you use two of them together, you can deliver 1000W into a single 8Ω loudspeaker! PARTS FOR BUILDING: 500W Amplifier PCB Set of hard-to-get parts SC6367 SC6019 $25 + postage $180 + postage SC6019 is a set of the critical parts needed to build one 500W Amplifier module (PCB sold separately; SC6367); see the parts list on the website for what’s included. Most other parts can be purchased from Jaycar or Altronics. Read the articles in the April – May 2022 issues of Silicon Chip: siliconchip.com.au/Series/380 siliconchip.com.au Australia's electronics magazine February 2024  67 Electronics Markets Sim Lim Tower & Square I can’t recall when I first heard about Sim Lim Tower, but I have long had it bookmarked for a visit. With international travel finally becoming possible for the first time in several years, I made sure to tick it off my travel bucket list. It was certainly worth it for the experience alone. We recently covered Shenzhen’s Electronics Markets in the December 2023 issue (siliconchip.com.au/Article/ 16060) and the bargains that can be had there. The prices of things (both electronic and in general) in Singapore are more closely aligned with what you might see in Australia. However, Singapore has an advantage (for us) over China in that English is one of the four official languages spoken. Many travellers know of Singapore as a stopover on the way to Europe, but I have found it an enjoyable place to visit. It is about an eight hour flight from Australia. Firstly, I’ll mention what I found at Sim Lim Tower and then Sim Lim Square. As a rough guide, Sim Lim Tower has more parts, components and the like, while Sim Lim Square has more consumer electronics. Later, I’ll note some other information that might be useful for fellow travellers. Sim Lim Tower Sim Lim Tower is seventeen stories high, but it’s the lower three floors that will interest most readers, as these are where the electronics stores are located. The upper levels are mostly offices, filled with such things as management 68 Silicon Chip consultants and insurance agencies, as well as electronics and software firms. There are several specialist stores focused on fields like marine navigation, LED lighting, digital signage, professional and ‘prosumer’ audio gear, plus industrial electric and electronic equipment. Other sellers specialise in electronic tools, equipment and supplies. Then there are the shops that are tightly packed with narrow aisles, high shelves and countless component trays. One such store would not have been much more than 50m2 in area, but I probably spent over an hour scanning the shelves to get a complete idea of what was stocked. Many shops offered a large range of constructional kits and staff could be seen putting kits together. The feel is much like a Dick Smith store from the early days, although there is no shortage of modern components and such things as Arduino boards, modules and robotics kits. Indeed, there was one small but well-laid-out shop that dealt exclusively with modules and other Arduino-related items, such as 3D printer parts. I spent quite some time in these shops. Those wanting to have a thorough look around could easily spend an afternoon within the Tower. As well as the feeling of being a ‘kid in a candy store’, I was simply interested to see if they sold anything I had not seen before. I’d heard that Shenzhen was like AliExpress in real life, but these stores were so packed with different items that Australia's electronics magazine siliconchip.com.au in Singapore with Tim Blythman Sim Lim Tower (shown at left) and Sim Lim Square (above) in Singapore are two centres full of shops crammed with all manner of electronic items. I recently had the opportunity to travel and explore both. they were more of a catalog you could peruse aisle-by-aisle. Many online stores are limited in that you can only readily find items that you know to look for. Here was a chance to literally stumble across something that I hadn’t yet thought existed. I didn’t see anything revolutionary, but there were quite a few variants of modern modules and breakout boards that piqued my curiosity. I can’t speak any of the local languages except for English, which sufficed with the help of a small amount of gesturing. I did experiment with a translation app (“Translate” In Sim Lim Tower, you will see numerous stores with eyecatching displays of all manner of LED lighting and digital signage, flashing, blinking and scrolling. You certainly won’t miss them as you walk past. The stock on display is not limited to components, with several stores having a large range of Arduino-based shields and modules, as well as Raspberry Pi boards and prototyping accessories. siliconchip.com.au Australia's electronics magazine February 2024  69 on Android, which can handle voice and text) and found this was most useful for translating signs and other written information. Purchases As I mentioned, the prices are similar to what you see in Australia. With the Singapore dollar worth about 20% more than the Australian dollar at the moment, it’s tempting to fall for the raw dollar value seen on the price tag, even if it is actually more expensive when converted. The value was in being able to buy things that I had not seen in shops back home. And unlike with online sellers, it is in your hands immediately. Some stores were happy to give me a modest discount on a cash sale. With that in mind (and the constant threat of excess baggage and creeping over the duty-free limit), I didn’t buy much. I got a handful of modules and a few cables and adaptors, all of which have worked flawlessly. I did buy a small USB programmable LED name badge that I have not been able to program. It lights up and shows scrolling text, but my Windows PC complains that the PL2303 USB-serial chip is unsupported and refuses to work with it. I suspect it is also supposed to have a rechargeable battery, which is now long dead. For the most part, the experience of being surrounded by such a novel variety of electronics outweighed the thrill of getting a bargain. However, I did not walk away empty-­ handed. Although many of the shops in Sim Lim Tower are tiny, they are crammed with a comprehensive range of components, all organised neatly into small trays. Several stock basic components like resistors, capacitors and transistors, along with a wide range of ICs. Displays like these well-stocked shelves of a broad variety of transformers are typical of Sim Lim Tower. I saw similar ranges for things like switches, connectors and even airconditioning remote controls. 70 Silicon Chip Sim Lim Square Sim Lim Square is right across the road from Sim Lim Tower. The building is newer, and several retailers moved from the older Sim Lim Tower when it opened. There are six floors of stores, as well as a basement area with a food court. Some online reviews from a decade ago indicate that scams on tourists were commonplace. It appears that there has been strong action taken against the perpetrators. I did not have any problems with pushy salesmen or the like, and the couple of small items I bought worked fine. You’ll find numerous stores selling computers, TVs, mobile phones, tablets and the like. I was not in the market for such items, so I can’t comment on them. You will find similar items at many different stores, so simply shopping around will be a good strategy. There are stores specialising in computer parts, office supplies, cameras, assorted electronic gadgets and even data recovery and device repair. In addition to a few cables and adaptors, I bought a rechargeable battery bank and a rechargeable portable fan. The fan was a welcome relief on the more humid Singapore days. None of the stores I visited at Sim Lim Square offered any cash discounts, but one offered 10% off the second item of the same type if two were bought together. Again, the novelty was the sheer variety of products available and finding things that could not easily be found in Australian stores. I only spent a few hours in Sim Lim Square. There are shops around the outside perimeter of the centre that I did not visit, as the stores inside offered an escape from the midday heat. Many appear to be open until the early evening. Getting around Sim Lim Tower is at 10 Jalan Besar, while Sim Lim Square Australia's electronics magazine siliconchip.com.au You might even see some familiar brands in Sim Lim Tower. Considering the exchange rate, these Jaycar radio modules were about the same price as in Australia. Some shops also had a very wide range of kits available for sale. These appear to be good sellers, as staff were continually putting the kits together. is at 1 Rochor Canal Road, on diagonally opposite corners of the intersection of these two roads. They are about a kilometre from the central downtown area of Singapore. With many high-rise buildings, store addresses are often given in the form #03-09, where 03 means the third floor and 09 refers to the specific store (or office or apartment). What we would call the ground floor is floor #01. Sim Lim Tower and Sim Lim Square are on the edge of the Little India precinct. The nearest MRT (subway) station is Rochor Station, almost directly in front of Sim Lim Square. Little India Station and Bugis Station are both within walking distance and, like Rochor, are on the Downtown Line. Getting off at Little India Station also allows you to try Indian cuisine at the Tekka Centre food court. Bugis Station is under a shopping centre surrounded by streets lined with market stalls. Bugis Station is also served by the East-West MRT line. Many buses also pass by on Rochor Canal Road. You can use a contactless debit or credit card for the bus and MRT by tapping on and off. Fares are pretty cheap; you can travel the breadth of the country for a few dollars (it isn’t quite as big as Australia!). None of my days’ travel exceeded 10 Singapore dollars. Sim Lim Square is aimed more at regular consumers, with stores offering device repair, gadgets and consumer electronics. There are also shops specialising in cameras and photographic supplies. The shops in Sim Lim Square have more space, but they still manage to cram in various cables, adaptors and other small devices. siliconchip.com.au Summary Unlike with Shenzhen, visiting Sim Lim Tower and Sim Lim Square probably won’t net you any massive bargains. If you are keen on electronics, though, you will enjoy seeing the sheer variety of products on offer. You might stumble on something you haven’t seen before. I bought several small items, some of which I have not come across in Australia. The prices were comparable to what I would expect to pay in Australia. I didn’t purchase expensive items such as a mobile phone or portable computer, so I can’t comment on those. If you can’t wait for the vagaries of international shipping, you might find something worth snapping up on the spot, but I mostly enjoyed being inspired by the sheer range SC and novelty of the items on sale. Australia's electronics magazine February 2024  71 Raspberry Pi Clock Radio As described last month, this new Clock Radio can also act as a media player and has many alarm options to ensure you wake up at the right time and in the manner you prefer. You can even synchronise the alarms on multiple Clock Radios. Since we’ve already explained how it works, this article will cover construction and how to use it. Part 2 by Stefan Keller-Tuberg T he major functions of the Clock Radio are handled by a Raspberry Pi (model 2, 3, 4, Zero W or Zero 2W). However, we need to add some extra hardware for the time LED display, buttons, switches, audio amplifier to drive the speakers and so on. This additional hardware is hosted on two custom PCBs that mount at right angles to each other, with a series of soldered fillets between them. The construction process will therefore be to mount the components on these two boards, join them together, wire them up to the Raspberry Pi (via a ribbon cable with IDC connectors) and then mount that assembly in the case. Once it’s in the case, it can be wired to all the external switches, connectors etc. The software will function regardless of which bits of additional hardware are connected, so any parts you 72 Silicon Chip don’t need can be left off the PCB without needing to modify the software. For example, if you don’t want the seconds digits, you don’t need to fit that two-digit LED display. Construction We suggest you start by fitting the SMD components to the Display board. This is built on a 150 × 44mm PCB coded 19101242; its overlay diagram is shown in Fig.4. Fit the 48 current-limiting resistors; if you are unsure how well the brightness will match between the larger and smaller displays, you can start by fitting just the 32 resistors associated with the 0.8-inch displays. Either way, it’s easier to solder them in groups. If you’re using different 3mm LEDs than the two options in the parts list, leave the two 1.3kW colon LED series Australia's electronics magazine resistors out for now; otherwise, add them at this stage. It’s easier to solder surface mount components by applying flux to the PCB before positioning the component. When all SMD resistors are soldered, you can clean off the residual flux with isopropyl alcohol, methylated spirits or a specific flux residue cleaner. Stubborn areas can be cleaned with a toothbrush or lint-free cloth. Do this before installing the other components, as you don’t want flux residue to be transferred onto the optical surfaces. Cleaning the board once through-hole parts have been fitted is also much harder. Move on to the 7-segment displays. Make sure you have a clean work surface, as it’s easiest to do this with the front of the displays resting on it. Mount the two 0.8-inch displays on the opposite side of the PCB than the resistors, with their decimal points towards the edge connections. Solder two opposite corner pins first, so you can adjust the displays to be tight against the PCB and nicely horizontal. When you are satisfied with that, solder the remaining two corner pins before completing the others. The 0.56-inch display has a lower profile than the others, so mount it proud of the PCB by a few millimetres to keep its front face in the same plane as the others. Insert the smaller display into its holes, check that it is correctly oriented with the decimal points towards the edge connector and then turn the whole assembly face down onto a flat surface. Press down on the assembly to ensure that the two larger displays are hard against the bench, and you will see that the legs of the 0.56-inch display barely protrude through the PCB. Solder two of its opposite corners as before, then inspect. You can use a straight edge, such as a ruler, to ensure that the front faces of all three displays are aligned in the same plane, adjusting the small one if required until you are satisfied. Then solder the remaining pins as before. Insert the 3mm LEDs into the gap between the larger displays. The cathodes (the shorter leg) are towards the edge connector. Again, place the assembly face-down onto a flat surface and solder one leg only on each 3mm LED. Adjust their angles and heights until you are happy before soldering the other leads. siliconchip.com.au Fig.4: the display board has three 7-segment displays, two colon LEDs and an LDR on the front, while the currentlimiting SMD resistors are on the back. It’s easiest to fit the resistors first, but see the comments in the text about possibly needing to change some of their values depending on which LED displays you use. The two resistors marked with a red arrow can be changed to test the colon LED and the brightness of the small 7-segment display. Fit the LDR next. The procedure is similar to the 3mm LEDs, but the LDR orientation doesn’t matter. Main board assembly The main board is coded 19101241 and measures 150 × 83mm. Fig.5 is its overlay diagram. Before fitting the components, it is worthwhile to verify that the supply rails have not been inadvertently shorted during the PCB fabrication process. Using a multimeter, check for an open circuit between pins 10 and 20 of the 74HCT374 (the diagonally opposite pins) and between pins 8 and 16 of the 74HC139 next to it (also diagonally opposite). It is rare, but if either is shorted, you just saved yourself a headache trying to find an almost impossible-to-find problem after the board is assembled! Start with the surface-mounting amplifier IC (IC13), carefully installing it with the correct orientation. Pin 1 on the chip is marked with a dot or divot and on the PCB silkscreen. Apply flux to the PCB and then position the chip. Solder just one corner pin first and then check that all of the pins align with their pads and the chip is moreor-less centred over the pad area. If not, soften the solder and nudge the chip until it’s properly aligned. When you’re happy, dab solder on the opposite corner and recheck the orientation. Solder the remaining two corner pins before completing the rest. siliconchip.com.au Clean up any bridges with solder wick, then remove any residual flux as you did with the display board. Continue by fitting the throughhole components, beginning with the lowest profile devices. Install the three diodes (watching their cathode stripe polarity) and the resistors, then the IC sockets (notched ends towards the bottom or right), followed by the ceramic or MKT capacitors, except the 100nF capacitor near the top edge of the board. Mount the electrolytic capacitors next, with their longer (positive) lead towards the + symbols. The striped side of the can is negative. Solder the relay next, followed by the transistors from shortest to tallest, except Q2, ensuring they face as shown in Fig.5. Don’t install chips into their sockets just yet, we will do that once the two boards have been joined. You can fit CON5 and the 40-pin header that will go to the Raspberry Pi now, but leave off the polarised headers around the board’s edge. That will give you reasonable access so you can join the two boards. Joining the boards If you’ve never assembled two boards using solder joints at right angles, a little planning will simplify the task. Ideally, the two boards should be aligned close to a right angle, but an error of a degree or two either way will not make much difference. I found that the easiest way to join the boards was to raise the main board above the bench using four PCB standoffs. Using a plastic right angle or similar, carefully tape the main and display boards individually to the right angle, as shown in the photo shown overleaf. Overvoltage protection can trip with poorly regulated supplies One of the 5V plugpacks I pulled from my box of spares measured 5.45V with no load. I figured this plugpack would be OK because the Clock’s protection circuit kicks in at around 5.65V – well above the supply’s no-load output. However, when I actually connected the plugpack, nine times out of ten, I could see the Pi LEDs flash briefly before turning off, a sign that the clock’s protection circuit had kicked in. An oscilloscope revealed that this dodgy plugpack was not very well regulated; at the moment a load was applied, the plugpack’s voltage would fluctuate enough to trigger the protection. I found a simple workaround with a spare 10,000μF electrolytic screwed into the terminals of the clock’s power connector, which smoothed that dodgy plugpack’s ripple enough not to reach the protection-tripping threshold. I have not had this happen with any of my other 5V plugpacks, so we recommend not using a dodgy plugpack in the first place. Australia's electronics magazine February 2024  73 Fig.5: the components on the main board are nearly all throughhole parts. The solder pads along the top of this board will connect to those along the bottom of the display board later. When assembling this PCB, watch the orientations of the ICs, transistors (including Mosfets and the SCR), diodes and electrolytic capacitors. Ensure that the display board evenly overhangs the solder side edge of the main PCB by about one millimetre for the entire length of the mating edge. The slight overhang is so you can add solder beads to the pads on either side of the main board, as there are electrical connections on both sides. That also provides extra mechanical strength. Solder the first joint on the left end of the mating edge, then the one at the right end. For these first two joints, only solder the top side of the main board. This will be fragile, but it allows you to check and easily adjust the alignment of the display board with the main board. If the alignment is imperfect, soften one joint at a time, alternating from one to the other, and make a sequence of minor adjustments until you’re happy. When satisfied, add another three or four solder joints spaced out along the top side to secure it, then flip the assembly over and work on the other side. Solder the opposite ends to shore up the mechanical strength, then solder all the remaining connections. Finally, flip it back over and finalise the original side. The boards will now be very firmly bonded, and you can remove the right angle. Complete the electronics by adding Mosfet Q2, the 100nF capacitor in the top-right corner of the main board and all the polarised headers. clock board can be made from scratch, or you can use an old IDE hard drive cable if you have one. To make it from scratch, carefully position an IDC crimp connector within a vice’s jaws and protect it using small timber offcuts. When you slide the 40-conductor cable into the connector, be careful to align it at right angles. It is easy to accidentally crimp the connector at an angle, in which case the cable probably won’t work. As you tighten the vice, you’ll hear the two ends of the crimp connector click into place, at which point you should ease off the pressure. Old IDE cables can be used for this application, but if the old cable supports two IDE drives, cut off one end of the cable using a Stanley knife. Before you do, double-check that the two crimp connectors have all 40 holes open; some IDE cables have one blocked hole, and those won’t be any good for this project. Next, you need a cable with a 3.5mm stereo plug on one end and a 3-pin polarised header plug on the other. I cut the end off an old 3.5mm headphone cable, stripped back the insulation and crimped the wires to the header pins. I then applied some flux paste, dab-soldered the signal wires and shield, then inserted the pins into their housing. Final assembly The 40-conductor ribbon cable for connecting the Raspberry Pi to the 74 Silicon Chip I found that raising the display board was helpful when joining it to the main PCB. The boards can then be taped together and soldered on both sides. Australia's electronics magazine siliconchip.com.au Because headphone conductors are fragile, I used a sparing amount of hot glue to neatly encapsulate the top of the housing, the loose conductors and the end of the headphone cable. This provides some strain relief; you could also use neutral-cure silicone sealant. Double-check the orientation of the transistors, diodes and electrolytic capacitors on the main board. When happy, carefully install the socketed ICs, noting their orientations & types, and ensuring all pins have correctly entered the sockets. The three chassis-mounting momentary pushbuttons (S2-S4) connect to the main PCB via two-way cables terminated in polarised header plugs, so solder the wires to them and crimp/ solder the plugs on the other end. Similarly, prepare three centre-off momentary toggle switches with three-way cables (that could be stripped from ribbon cable) terminated in three-way polarised header plugs. The banana sockets/binding posts for the speakers (two positive and two negative) are wired to another two polarised header plugs, this time with slightly heavier-duty wire. However, it can’t be too thick, or you won’t be able to get it into the plugs. Medium-duty hookup wire should work. Wire one red and one black terminal to each plug. The polarity doesn’t matter as long as it’s the same for both. For the external 5V supply, solder wires to the chassis socket and then screw them into the pluggable terminal. The positive input should be on the right when plugged into the PCB. If adding a radio receiver input, its audio output goes to a three-way polarised header plug that follows the same arrangement as for the Pi audio input. The GND connection is closest to the relay and the left and right channels sequentially on the other two pins. If your audio source is mono, short the left and right inputs and feed them from the mono source. Connect its power supply to CON5 as per one of the options in Fig.3 last month. Testing the Clock We recommend installing the clock software onto the Raspberry Pi (if you haven’t already) and ensuring the software works before testing the hardware, as explained last month. Commence hardware testing by repeating the earlier multimeter test to verify that the power supply rails are not shorted. The rails will not be completely open-circuit now because there are capacitors and ICs on board, but the rails should not be dead shorted either. You can test the overvoltage protection circuit if you have a current-­ limited bench supply. If you don’t, we recommend you don’t test it and assume it works because if you apply a high voltage and it doesn’t work, you will fry everything. If you have the bench supply, the test procedure is as follows. Use a voltmeter to accurately measure the applied voltage directly at the variable power supply (if it has an onboard meter, you can use that). Tenths of a When connecting the Raspberry Pi to the Clock Radio, take extra care that the polarity is correct on the ribbon cable, it should be connected as shown. siliconchip.com.au Australia's electronics magazine volt make a difference, so it is important that the voltmeter is accurate and measures to at least 100mV resolution! Use another voltmeter to monitor the voltage between the 0V power input on the board and the tab of Mosfet Q1. Starting low, ramp up the variable power supply to around 4.5V, then slow down. As the input approaches 5V, minimal voltage should be registered on the second voltmeter at the tab of Q1, indicating that the Mosfet is switched on, its default during regular operation. Continue slowly increasing the variable power supply so that its output rises just above 5V. The protection threshold voltage will depend upon the ambient temperature and idiosyncratic characteristics of the 5.1V zener diode and the SCR. When the variable input voltage reaches 5.6-5.8V (certainly below 6.0V), a voltage should develop on the Mosfet’s tab, indicating that Q1 has switched off. Don’t wind the variable power supply past 5.85V! If the SCR has not fired by 5.85V, switch off and look for a problem in the protection components above and to the right of RLY1. When satisfied that Q1 is switching off as expected around 5.6-5.8V and before powering down the variable supply, verify that the voltage across the 2.7kW resistor is about the same as the variable supply output, confirming that the SCR has fired. Finishing the wiring Now you can plug everything into the main board. That includes the buttons, switches, the audio cable from the Pi’s output jack socket to the threepin polarised header on our board, the external 5V supply, the speaker terminals and the optional radio board. Also connect the Raspberry Pi via the ribbon cable, being very careful to get its polarity right. Refer to the adjacent photo and Fig.6 to see how it’s done. Pin 1 of the Pi must be wired to the bottom-left pin of the header on the main board; use a DMM set on continuity mode to verify that before applying power. When you apply power to the assembly now, do it via the clock board only and don’t connect a separate power supply to the Pi. The Pi will receive its power via the clock assembly through the ribbon cable. When power is first applied to the February 2024  75 whole assembly, the display will start blank, and the Pi will go through its booting process. You should see the Pi’s power LED turn on as the Pi boots, but the clock display will remain blank for around half a minute. When the display eventually illuminates, it will show an incorrect time. The Raspberry Pi will be trying to connect to your home network, and when it does, it will grab the current time from the internet. The display will then jump to the correct time and will be time-locked from that moment onward. If the 7-segment displays remain blank, double-check the LED brightness and threshold settings on the web setup page. It’s possible that they have been dimmed very low and just need to be brightened. Otherwise, use ssh (eg, via PuTTY) to connect to the Pi and use the alarm clock debugging modes described in the software installation documentation to check the software’s health. The Pi installation script should have been run to completion without errors. If not, that might be a clue as to why it isn’t working. If the display is still not illuminated, but the software appears to be running, use a logic probe, oscilloscope or frequency counter to check that there is activity on the data and address bus GPIO lines between the two boards and on the PWM GPIO line to the gate of Mosfet Q2. Also check that you have used the correct Mosfet types (they must handle logic-level drive). Matching display LED brightnesses If you have not yet installed current-­ limiting resistors for the two colon (“:”) LEDs or the small display, you can start to experiment. Turn off the clock and tack-solder candidate resistors for just one each. Segments within an individual display will have the same brightness, so once you’ve matched one to the rest, that resistor value should work throughout. It is easier to use axial leaded resistors rather than SMDs for these experiments unless you have a sample book of suitable SMD resistors. Start with the default values of 430W for the display and 1.3kW for the colon or 470W/1.2kW if you don’t have those other values. A convenient resistor to choose for the small display is the top one closest to the larger digits because it illuminates a segment alongside the larger displays, making it easier to compare. Both colon resistors are convenient to access. Refer to the two resistors marked with a red arrow in Fig.4. Power on the Pi, go to the web setup page and put the clock hardware into a darkened room. Adjust the minimum brightness slider down to a level where the illuminated LED segments are just visible, then set the maximum brightness slider to midrange. Remember to save the setting using the web save button, or the next step won’t work as expected. Choose the “Start the LED brightness test” web button to turn every LED on (displaying all 8s) and force the display to the minimum brightness setting for a moment. You’ll have to judge whether the test segment and the test colon LED are the same, brighter or dimmer than the large numeric digits. The test will also go to maximum brightness for a moment for comparison. If the brightnesses aren’t even, increase the test resistance to reduce Given the height of the enclosure we recommend, it’s best to mount the Raspberry Pi as shown, so there’s enough clearance. Note that the slim radio board I added down the left-hand side, with its antenna passing through a small hole in the rear panel. Fig.6 (right): the wiring diagram for the Raspberry Pi Clock Radio. 76 siliconchip.com.au the LED brightness or decrease the resistance to make it brighter. Always power down the clock before changing resistor values, as accidentally shorting out the current limiting resistor pads can cook your 7-segment display. As you try different valued resistors, make step changes of about 25% in value, as you won’t notice too much difference when trying smaller steps. For example, change from 430W to 560W to reduce the brightness or from 430W to 360W to increase it. After determining the optimal resistances, you can source and install components for all the missing current limiting resistors, and your clock will be complete. If you don’t want to wait, you could order 16 each of the values 360W, 430W, 560W, 750W and 1kW, as it’s likely one of those will give a good match. Don’t go lower than 360W to avoid exceeding the 74HCT4511 package current limit. Testing The proper functioning of each switch is most easily tested by enabling one of the software debug modes to generate a debug log. Do this siliconchip.com.au A close-up showing the headphone cable connection to the Raspberry Pi. in an SSH session; as described in the software installation documentation, the command is “sudo alarm-clock -B”. As you press each button in the switch debug mode, a message will be logged, making it obvious that it is working. Assuming the LED displays are illuminated, if you cup your hand over the LDR (shielding its sides and the front surface) to reduce the light intake, you should see the display dim after a few seconds. LDRs can be rather sensitive to light, and the actual dimming behaviour will depend on what you’ve configured in the Clock settings. You can use the command “sudo Australia's electronics magazine alarm-clock -X” to watch as the software measures the light level. You can verify that the numbers are smaller when the LDR is dark and become larger as the LDR is illuminated more. Suppose you see this behaviour in the debug log, and there is a reasonable variation in the range between light and dark (for example, 500 counts or more). In that case, the circuit is working sufficiently well for you to be able to adjust the web sliders to achieve your desired dimming behaviour. Use the “Start the display test” button on the web setup page to exercise each seven-segment display and February 2024  77 dots. If some LED segments never illuminate, check that the series current-­ limiting resistors are adequately soldered and that the legs of the 74HCT4511 chips are all correctly inserted into their sockets. If just one of the six digits doesn’t count in the correct sequence, the problem is likely with the associated 74HCT4511. If several of the six digits count incorrectly in the same way, check for problems with the GPIOs used for the data and address bus or potentially with the 40-conductor ribbon cable. The last functions to test are the amplifier and audio inputs. Turn on the amplifier using the media player to stream local media or an internet radio site and verify that you’re getting sound from the Raspberry Pi. If your speakers are dead, plug headphones directly into the Pi to confirm that it is generating audio; if so, you’ll need to debug the amplifier section of the clock. Back on the media player web page, if you type “radio” (without the quotes) rather than entering a path to a media file or URL, you should hear the relay click, and the audio will be taken from the radio input connector. The middle pin of CON5 will be pulled to ground via Q3 when the relay is energised so the radio module will be powered. Putting it into a case You will probably want to mount the clock into an instrument case, as I did with mine. You probably shouldn’t use a metal case for this project because it will interfere too much with the Raspberry Pi’s WiFi and Bluetooth reception. If you’re capable of doing woodwork, I once saw a very cool clock idea that would turn this project into a talking piece. Timber veneer can be translucent if you shine a bright light through it from directly behind. The brightness of the clock’s LEDs can be set quite high, especially the Lumex components, and they should shine clearly through a sheet of 0.4mm or thinner light-toned veneer. You’d want to make yourself an MDF template for the front panel, possibly routing the top edge to round it off and drilling and filing out tightly fitting holes for the seven-segment displays. Mounting the front plane of the seven-segment displays immediately behind the veneer will provide mechanical backing to protect the veneer. You would also need to drill a window for the LDR or mount the LDR elsewhere in the box. I’d love to see photos of this idea if it works as well as I expect. If you choose the more conventional approach and use the plastic instrument case, I used a table saw and the finest toothed blade to cut a 3mm green Perspex sheet to the correct size to replace the front panel. Because the front panel mounting slot is 2mm wide, I firmly taped and then routed the edges of the Perspex so they fitted snugly. 2mm Perspex/acrylic is available, but I’m unsure if you can get the translucent green colour in that thickness. If you feel it’s necessary, you could mask and spray the inside of the Perspex bezel black so that only the displays show through, but I have not done this for my clocks and think they look fine. I mounted my snooze button on the top of the case and all other buttons and switches, speaker posts and the power socket onto the rear panel that came with the case. If you use the recommended While we used a Raspberry Pi model 4 to run our Clock Radio, you can also a model 2, 3, Zero W or Zero 2W. 78 Silicon Chip Australia's electronics magazine instrument case which is 160mm deep, note that the clock board assembly with mounted LEDs amounts to just under 100mm of depth, and the shorter dimension of a Raspberry Pi is 56mm, not accounting for the 3.5mm audio plug and cable which protrude further. That means there isn’t enough room to mount the Pi in the base behind the main board. I mounted the Pi partially overhanging the main board, as shown in the photo on page 76. To raise it above the main board, you can use two long M3 screws through the base of the case, secured with a nut, and M3 standoffs fitted onto the tops of the long screws secured with weak Loctite (eg, 222). Two short M3 screws will hold the Pi onto the M3 standoffs, while the two remaining Pi screw holes overhang the main board and are left vacant. It provides quite a solid mounting, provided you don’t try to insert or remove the Pi’s 40-pin expansion cable while the Pi is screwed down at only two points. I found it sturdier to elevate the Pi using the moulded standoffs in the base of the instrument case, but the hole spacing wasn’t quite right. I elongated one mounting hole to align with the Pi holes and secured the long screws with washers, nuts and Loctite 222. Then with four standoffs attached to the main board and the perspex bezel in position, I carefully positioned the PCB and epoxied the standoffs to the instrument case, saving me the hassle of precisely measuring hole locations and drilling. With the specified instrument case, there is still just enough room to squeeze a small radio board down one side if you’d like to include that option (as I did). To fit larger radio boards, you might need a larger case. The case configuration I adopted has no external access to the USB or Ethernet ports. That wasn’t a significant consideration for me, but if your case is sufficiently deep, you can rotate the Pi so that its network and USB ports are accessible through the back panel. In that case, you’ll need to fold the 40 conductor ribbon into an L-shape to facilitate the connection between the main board and the Pi. I specified a 150mm ribbon cable length and have successfully used that length with some of my prototypes. Shorter ribbons will be OK, but if you need to use a longer ribbon in yours, siliconchip.com.au be watchful for any problems when the LED display gets updated. Suppose you see digit update errors when using a longer ribbon. In that case, you can slow down the settling and latching delay from its current default of 5μs by editing the “alarm_ clock.c” source code file and changing the #defined symbol called WRITE_ BYTE_DELAY to something larger than 5000 (nanoseconds). The microprocessor on the Raspberry Pi consumes 1W, so expect the outside surface of the case in the vicinity of the Pi to be warmer than the room’s ambient temperature. That should not be a concern, but you could add some ventilation to the case if you want to keep it cooler. Using the software The Clock Radio is designed to be intuitive once you’ve logged into the web interface, with plenty of help links to guide you. Still, if you want to tinker with it ‘under the bonnet’ or fully understand how it works, you’ll want more details on how the software works. We’ll start with some of the more common features that most constructors will be interested in, then move on to the nitty-gritty of how the software works. Configuring the Clock via the web interface To reach the web interface, open a browser and go to http://clock.local or whatever system name or IP address you used to SSH into the Clock. You will be greeted by the Clock’s home page, which contains links to the various configuration and media player functions, a summary of the configured alarms, the playlist if media is currently playing, and a list of any other clocks found on the local network if any exist – see Screen 1. Screen 1 shows other clocks that have been discovered on the network. If you only have one Clock, that boxed section will not be displayed. Navigation should be reasonably intuitive. Use the Clock Setup page to configure your preferences. When you hover the pointer over some options, the browser will display hints and a description. Creating alarms is a matter of filling in details from top to bottom on the Alarm Configuration page (Screen 2): what time, how long do you want it siliconchip.com.au Using the Clock as a Bluetooth speaker Raspberry Pi models after the Pi 2 allow the Clock Radio to emulate Bluetooth speakers. Computers, phones and tablets can be paired with the Clock to play audio through its speakers. After ‘pairing’, devices only need to be ‘connected’ whenever you’d like to stream audio via the Clock’s speakers. A “Pair Bluetooth Device” icon on the Clock’s web page allows devices to ‘discover’ it for pairing; you can also enable this mode by simultaneously pressing two of the clock’s physical alarm selection switches. When activated, you’ll have three minutes to complete pairing. You can pair as many devices with the Clock as you’d like. The devices to be paired need to be in pairing/discovery mode at the same time, or they won’t see each other; you’ll need to carefully follow the documented pairing and connection process for your device. If you have difficulties pairing with the clock and are new to this process, confirm the procedure by pairing with something else. When your device is connected, audio will be played through the Clock’s speakers. Set the volume using either the physical volume up/down switch on the Clock or a slider on its web page. Bluetooth audio stutters The clock’s Bluetooth streaming has been tested with Windows, macOS, Android phones and iPhones, and it has worked well using either the Pi 3 or the Pi 4. However, there are certain circumstances where you might notice occasional audio stutter and Bluetooth disconnections. The most obvious situation is when connected Bluetooth devices move beyond their working range. A less obvious reason for Bluetooth stuttering is WiFi interference, as explained in the panel last month. Therefore, you could experience audio stuttering if you access a Pi 3 based Clock’s web interface at the same time as you’re streaming Bluetooth audio to it. Bluetooth channel assignment is typically statically allocated during the pairing process. If your Bluetooth channel experiences interference, you can try resetting pairing and starting over. There is a button on the web interface to reset all paired devices. Suppose you are streaming Bluetooth audio when you start a media player stream on the clock, including when an alarm plays a media source other than the radio. In that case, the clock will disconnect the Bluetooth devices to play the media stream correctly. You will need to reconnect your Bluetooth device afterwards if you wish to continue streaming Bluetooth audio. The finished Clock Radio connected to an iPad via Bluetooth. Australia's electronics magazine February 2024  79 adjustment is applied when the alarm first trips. Each minute after that, the digital volume control will make one step towards the target volume until it is reached (or the next chained alarm trips). So, to gently increase volume when an alarm is tripped, you could set the volume adjustment to -15 and the target adjustment to +0. The alarm will start quietly and gradually get louder until it reaches the normal (system) level. The volume adjustments are added to the current system-wide volume setting! Adjusting the alarm(s) Screen 1: the main web page shows the list of alarms and other Clock Radios on the network (if present). The buttons at the top are hopefully self-explanatory. Clicking on the link outlined in red provides information on what the six buttons/switches on the Clock Radio do. They can be used in combination, so quite a few functions are available. to run, on what days of the week and should it recur indefinitely. The alarm volume adjustment is relative to the current master volume, which is useful when chaining a sequence of alarms from different sources (where each source could have different audio levels). It can also be used to slowly increase or decrease volume with a succession of alarms. Anywhere you see a text box for entering media, you can specify a streaming radio site URL, the full Linux path to a media file or playlist, or the word “radio” (without quotes) to use the external audio input. The path to media files on USB storage devices will normally start with “/media/”. Finding internet streaming sources is easy; any internet radio station that is accessible in your country and that can be listened to with a web browser will work with the Clock. However, determining the correct URL to use with the Clock can be tricky. Instructions on how to use a browser to discover the syntax for a streaming URL are included on the Clock’s in-built web pages (also see Screen 2). Chaining alarms As I live in regional Australia, the national radio network I usually listen to inserts news bulletins from the nearest capital city. Sometimes, your ISP can allocate an IP address from 80 Silicon Chip further afield or the internet’s routing changes, resulting in you hearing news bulletins from a completely different part of the country. I realised I could use ‘chained alarms’ to work around this. When the hour ticks over and the local news commences, I configure a new alarm with its streaming media source being a local news radio station. I configured a new alarm to switch back to the original national stream after the news. The chaining trick works well, and I’ve been enjoying local news by flipping streaming sources for several months. When you chain alarms into a sequence, and a subsequent alarm trips before the timer for the earlier alarm has expired, the earlier alarm is replaced by the subsequent alarm. It will not come back even if the subsequent alarm completes. To return the first streaming source, you must chain a third alarm. Waking up gently You can use alarm chaining to be woken ‘gently’ by setting the volume adjustment low on the initial alarm, then chaining a series of subsequent alarms with progressively increasing volume. But there’s a better way to achieve the same thing. Each alarm includes a “target adjustment” setting as well as the “volume adjustment” setting. The volume Australia's electronics magazine Whenever you adjust the system-­ wide volume, the volume of all future alarms will adjust accordingly, as if you rotated the volume control knob on your traditional alarm clock and waited for the next alarm to trip. If you’ve specified any non-zero volume adjustments for any alarm, those adjustments will be applied to the current system-wide volume to maintain the volume relativity. The Clock Setup page has a “minimum alarm volume” setting. That ensures your alarms will still be loud enough to wake you if you’ve set a low system-wide volume. Alarm-specific adjustments still apply to the minimum alarm volume to maintain relativity between different alarm levels and to ensure that adjustments continue to work as you expect. However, you won’t be able to accidentally set the system-wide volume low and then sleep through an alarm. I therefore strongly recommend you check and adjust this setting during setup. Using the buttons Although there are only six buttons, they can be used in combination with each other, so you can do more with the buttons than you might think. The full description of button operation is provided in a link you will find on the Clock’s internal web page, in Screen 1. Because all functions can be reached via the web interface, it is not strictly necessary to build any or all of the buttons into the Clock. The choice is yours! 12/24 hour time display The setup web page includes a configuration option for choosing between 12-hour and 24-hour displays. This siliconchip.com.au refers to the LED display on the Clock itself, not how times are shown on the web pages. Times displayed in most web browsers are formatted according to the locale setting on the device running the web browser. That means that although you may have configured one particular format on the web settings screen, your browser might steadfastly show a different format. Automatically resuming playlists If internet streaming is not your thing, you can use a playlist of MP3 files from your own media library for your alarm. You can even chain alarms between your local playlist, the radio and internet streams. When you initially create an alarm and specify a directory as an alarm source, the Clock’s web server will build a playlist file of the underlying directory tree. Similarly, a playlist is created if you use the media player function and specify a directory. When playing a playlist, the Clock remembers the last track and will commence from the following track when it uses the same playlist again. You can therefore chain from the playlist to the news and back again, and the playlist will continue from the track after where it left off. Testing the hardware When testing the hardware to ensure the switches are being recognised and ambient light levels are correctly measured, you’ll need to use the Clock’s software debugging mode to view the debugging log. This means you’ll need to temporarily stop the operating system from managing the Clock. By default, the “alarm-clock” program runs automatically at boot time. If it ever crashes, the operating system will restart it. Usually, its text output is hidden. To reveal and watch the log, you can run the alarm-clock program from within an SSH session and enable debugging. To do this, within an SSH session, temporarily stop the alarm-clock program by issuing the command: stop-alarm-clock The Pi will revert to automatic clock management the next time you reboot. Once the program has been stopped, you can run it manually with the command “sudo alarm-clock”, or use “alarm-clock -h” to display the help options for the program. The command “sudo alarm-clock -V” will run the software with full logging. As it runs, messages and time stamps from different threads will intermix. There’s also a setting that enables logging to a file, for catching issues when you’re not around to look. The Clock’s setup file is located in “/etc/ alarm-clock/setup.conf” and you can edit it to enable file logging using the following command, which will launch a text editor: sudo nano /etc/alarm-clock/setup.conf Look for the two following lines and remove the # symbols in the first column: #VERBOSE=0x090 #LOG_FILE = “/var/log/alarm-clock.log” Screen 2: when configuring an alarm, you can choose the time, duration, which days it’s active, whether it recurs, the volume adjustments and the audio source. February 2024  81 Once you’ve made those changes, press CTRL+O to save them and CTRL+X to return to the command prompt. For more information about the configuration, compiling and playing with the code, consult the readme files in the alarm-clock directory tree you extracted from the .tgz file. Checking that the software is running To check that the alarm-clock program is running, issue the following command: ps -A | grep alarm If it is running, you’ll see a response showing how much CPU time it has used so far. If you see nothing, it is not running. Similarly, you can check for a running pigpio daemon (which must be running for us to control the Pi’s digital I/O pins): ps -A | grep pigpiod We need a Bluetooth control process and its daemon to allow us to play Bluetooth audio, so there should be two items displayed when you run this command: ps -A | grep bluetooth The web server and its workers are usually waiting to receive connections, so there should be several items displayed with the command: ps -A | grep apache To see the complete list of all the running processes along with their memory consumption, type “top” and press Enter to start a self-refreshing display (type the letter q to exit). The top command shows lots of helpful information, including how much CPU time each process is currently consuming, expressed as a percentage of a single CPU core. As there are four CPU cores on most Pis, the Pi will be fully maxed out when the sum of all current CPU utilisation reaches 400%. The largest CPU hog is the pigpio daemon [It isn’t surprising that the biggest hog starts with “pig”! – Editor]. ‘Watchdog’ reboot During the testing and running of the four prototype clocks over the past six months, I saw two of the clocks lock up after a prolonged mains power brownout. 82 Silicon Chip So, the software now incorporates several ways to determine that something has gone wrong and trigger a system reboot when it notices. A hardware watchdog will reboot the Pi if the operating system fully locks up. If just one operating system task locks up, the Clock runs a half-hourly health check, triggering a reboot if something seems amiss. The web server also triggers software checks when somebody accesses a web page. If you run “stop-alarm-clock” for debugging or testing, the health checks will eventually fail, and the automatic rebooting processes will reboot the Clock. You can prevent these automatic reboots after you’ve issued the “stopalarm-clock” command by restarting the alarm-clock program from the command line using the debugging flags you need. The health-check features will not trigger a reboot if they see the alarmclock program running. Internet stream audio delays You might notice something strange when using streaming internet radio stations for alarms. Suppose you set your alarm to trip precisely on the hour and expect the hourly news to wake you, as it would with a regular clock radio. In that case, you’ll discover that streaming radio stations can be anything from a few seconds to a few minutes behind the free-to-air version of the same radio station. The news will never start exactly on the hour with an internet stream; it will always start just a little after! A brief delay with internet streaming is to be expected, but I cannot explain why different radio stations stream with delays that change from day to day and month to month. If you notice this happening with your preferred streams, there’s nothing wrong with the Clock. It is just another artefact of the digital world we live in. If you built a traditional radio into your Clock, over-the-air broadcasts will always arrive precisely on time through that medium. That is probably the only way to guarantee your news service commences with precision. Enjoy your new clock, and if you build a couple, enjoy the liberation of both you and your partner being able to control them from either side SC of the bed! Software updates The Install_Clock script downloads and installs an automatic update client program called “unattended_upgrade” and configures it to check for updates at 3:30am every three days. If an update to any of the installed packages is released, such as a Linux security patch, the automatic updater will download and apply the change automatically. If a reboot is required because of a security patch, that will be scheduled also without human intervention. I have been running automatic updates on several Pis for years and have not struck trouble. However, if you prefer to run updates manually and at your own discretion, you can issue the following command over SSH to stop the automatic updates from occurring: sudo systemctl disable unattended-upgrades You can then manually look for and install updates using the command: sudo apt-get upgrade New versions of the Clock Radio software After installing the clock software, there are two methods you could use to install an update, if one becomes available. 1. Open up the clock, remove the Pi’s SD card, and plug it into your computer. Copy the new software .tgz file onto the SD card, put the SD card back into the Pi, exact the file contents and then rerun the Install_Clock.sh script. 2. Copy the new file into the root of your home account on the Pi over the network, using the Pi’s Samba file server. The following commands can be used to install the new software, assuming you copied the .tgz file into your Pi’s home directory (assuming the update is v02): tar zxf alarm-clock_v02.tgz cd alarm-clock make make install Australia's electronics magazine siliconchip.com.au Points Controller for Model Railways is is the sets of points, so th My layout has five with to up t and label I came control box lid layou control them. Project by Les Kerr Adding points to a model railway layout makes it a lot more fun and more realistic, too. This Controller lets you monitor and switch up to eight sets of points from a single control box with easy wiring; it could even be expanded to handle more than eight. We will also show how to make LED-based signals to go with each set of points. P oints (also known as “railroad switches”) are used where a single set of train tracks splits into two. If the points are facing one way, the train passes onto one set of tracks, while if they are facing the other way, it moves over to the others. For example, two sets of points could be used at either end of two parallel pairs of tracks to allow trains going in either direction to use either set of tracks. Points can also enable a train to move from the main tracks into a siding, or back out. Real railways have many points, especially in and around stations, so you should ideally have a few in a realistic model railway layout. So, how do you control them? siliconchip.com.au This design minimises the number of wires needed between the control unit and each set of points by using serial data. That way, you only need a few wires running around the layout, from the Controller to the first set of points, then between pairs of points, rather than the ‘spaghetti’ required if each set of points had its own set of wires. The lead photo shows my control box that supports five sets of points in my layout, while Photo 1 shows the actual layout from above. The layout has two loops, each with a siding, plus a station at the centre. Two of the sets of points allow trains to move from one loop to the other or back, while the other three allow trains Australia's electronics magazine to move between one of the loops and the sidings/station. There are two LEDs and a toggle switch on the control box for each set of points. The green LEDs show the current direction of the points, while the toggle switch allows that to be changed. The most common way to change the points on a model railway layout is to use a points motor. The insides of a typical one are shown in Fig.1. If the motor is at position X and we apply 18V to the electromagnet windings between points A & B, the magnetic field attracts the iron arm, moving the sliding bar to the right (position Y). If we then apply 18V to the winding February 2024  83 Fig.1: the basic configuration of a points motor. Depending on which side of the electromagnet is activated, the lever moves the points to one side or the other. between B & C, the points change back to their original position. The windings produce a strong magnetic field and are made of heavygauge wire, having a typical resistance of 4W. If we had a constant 18V across them, we would have a steady current of 4.5A, which would soon burn out the coil. So we need a means of applying the current for no more than 200ms. The second concern is the power supply's ability to deliver that much instantaneous power and current. That can be done using a circuit like the one shown in Fig.2. One end of the electromagnet coil is connected to the Mosfet drain while the other end connects to a 2200μF capacitor that is charged to 18V via a 47W resistor. The Mosfet acts like a switch that Fig.2: this basic circuit can switch a set of points in one direction. The Mosfet is pulsed to deliver enough current to switch it over, but not for so long that the coil burns out. Another Mosfet and diode is needed to provide switching in both directions. is off when the gate voltage is 0V. If the gate voltage is brought to +5V for 200ms, the capacitor discharges most of its energy into the electromagnet, producing a strong magnet field and a loud click as the points change. When the Mosfet switches off, the capacitor charges to approximately 18V in about 400ms, preparing it for the next pulse. A second Mosfet (not shown) is connected to the other end of the coil to switch the points back. They can share a single capacitor that’s connected to the centre tap. As mentioned earlier, this design's serial loop means you only need four wires from the control box for all the points. These are +18V, +5V, serial data and 0V. I ran a four-core alarm cable around my layout. Scope 1 shows this in action (see page 89). The cyan trace is the Mosfet gate voltage, which is high for 200ms, while the yellow trace is the voltage between the Mosfet drain and ground. You can see how the capacitor recharges over a second or so following the points motor activation. Block diagram Fig.3 shows how the modules are connected. One Receiver PCB is used for each set of points, with a single ‘Transmitter’ controlling up to eight sets (it transmits over a wire, not wirelessly). Each Receiver PCB has outputs to connect to the points motor and operate the associated signal (see Photo 2). Each Receiver is given a unique address (0-7) with the combination of three jumpers. An additional Fig.3: this system configuration keeps the wiring in the layout simple, as the Receiver modules can be mounted next to the points motors. The wiring between the Transmitter and Receivers can be daisychained or connected in any other way that provides the required four-wire bus. 84 Silicon Chip Australia's electronics magazine siliconchip.com.au Transmitter can be used if you need more than eight sets of points. The Transmitter is housed in the control box, with power for all the modules provided by a 12V AC 1A plugpack. If you have 12V AC available from a different source, you could use that instead. The complete system comprises the PCBs mentioned above, the points and motors, signals, control box wiring and layout wiring. Circuit details The circuit of the Transmitter (control box) is shown in Fig.4. Up to eight switches and sets of LEDs are wired to microcontroller IC1. Eight of its digital input pins (RA0, RC0-RC4, RA4 & RA5) are used to sense the positions of the points control switches. Each input has a 10kW pull-up, so either the switch pulls that input to GND or the resistor pulls it up to +5V. The same switch poles light one of the two connected green LEDs by pulling one of the cathodes to GND. The anodes are connected to a common 680W resistor to +5V. IC1 constantly checks the states of the eight switches and delivers a continuous serial stream at its RC5 digital output. That is fed to the eight ‘Receivers’ via a 1kW resistor, so they know which state the points need to be in. The 1kW series resistor protects the microprocessor from damage if the serial line is accidentally shorted to ground. For the power supply, the incoming 12V AC is applied to a bridge rectifier with a 2200μF smoothing capacitor to get around 18V DC. This depends on the transformer regulation and can range between 16V and 18V DC; 16V is sufficient to operate the points motor. That voltage is fed to the points motors and the input of linear regulator REG1, which produces the 5V DC supply for IC1 and the microcontrollers in up to eight connected Receivers. The 1000μF capacitor smooths out any ripple that makes its way through the 7805 regulator, while the 100nF capacitors reduce high-frequency transients from the supply and ensure stability in the linear regulator. Fig.5 shows the circuit of one Receiver. The serial data from the Transmitter goes to the RC0 digital input of IC2, which is powered by the 5V rail produced by the Transmitter. It decodes the serial stream and ignores siliconchip.com.au Photo 1 (above): a view of my layout from above. You can see how it corresponds to the diagram and controls shown in the lead photo. Photo 2 (left): a close-up of one of the signals I designed to accompany the points. They can be made using a lathe and a few bits of metal you can get from hobby shops. Semaphore Integration My design for a Model Railway Semaphore, published in the April 2022 issue (siliconchip.au/Article/15273), can be used with this Points Controller. A semaphore can be located at any set of points, with its state depending on the position of the points. Australia's electronics magazine February 2024  85 Fig.4: the Transmitter circuit consists of a microcontroller, IC8, connected to up to eight toggle switches and eight pairs of LEDs. It encodes the switch positions into a serial stream at its pin 5 digital output that’s fed to the Receivers so they can actuate the points appropriately. Fig.5: microcontroller IC2 in the Receiver decodes the serial stream and, based on its identity set by jumpers JP1-JP3, extracts the appropriate command signals and drives Mosfets Q1 & Q2 to control the points motor. It also updates the state of the signal/semaphore when the points change. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au Transmitter construction The Transmitter is built on a 74 × 47mm single-sided PCB coded 09101241 – see the overlay diagram, Fig.6. The power supply connections and four wires that go to the Receivers connect via the terminal blocks at the top of the PCB. In contrast, the off-board switches and LEDs are connected via the headers near the middle of the board. Photo 3 shows the assembled board. Fig.6: assembly of the Transmitter PCB is straightforward. The power supply inputs are at upper left, the four serial/power bus connections are at upper right, and the headers to connect up to eight toggle switches and indicator LEDs are in the middle. ► ► everything except the points position that matches its identity, 0-7, depending on the settings of jumpers JP1-JP3. Those jumpers connect to the RA5, RA4 & RC5 digital inputs of IC2. If a jumper is inserted, shorting the two header pins, it pulls the connected pin low. Otherwise, that pin is pulled high by a 10kW resistor. That means they are all at a high logic level unless a jumper shunt is added. Table 1 shows the jumper setting for each of the eight channels. When the desired points position changes, it brings one of the RC3 & RC4 digital outputs high for 200ms to drive the points motor as described earlier. It also updates the states of digital outputs RC1 & RC2 to light the appropriate LED in the signal, or change the state of the optional Semaphore with its signal input connected to SIG1 and its GND to 0V. Diodes D5 & D6 are provided because when Q1 or Q2 switches off, the magnetic field in the motor windings will collapse and cause a voltage spike at the drain of the Mosfet that was on. These diodes clamp the voltage, preventing damage to the Mosfets. The 100μF and 100nF supply bypass capacitors in each Receiver are necessary since the Transmitter that’s the source of the 5V rail could be some distance away, connected by relatively thin wires, so the supply needs local filtering. Fig.7: if using our commercially-produced Receiver PCBs, there’s no need to fit the four wire links shown here. Ensure the four bus terminals connect to the corresponding terminals on the Transmitter PCB. Start by fitting the resistors immediately on either side of IC1, followed by the IC socket with the notched end at the bottom. You can then solder the header pins, made from strips four or five pins long that can be snapped from longer headers. Follow with the capacitors, taking care with the orientation of the electrolytics (the longer lead is positive while the striped side of the can is negative). Don’t solder the PIC directly to the PCB, as there is no provision for in-­ circuit programming. Next, add the remaining resistors, which are mounted vertically, then dovetail the three terminal blocks and solder the whole lot at the top of the PCB, with the wire entries towards that edge. Solder in the 7805 voltage regulator and the 1N4004 diodes as per the layout diagram, taking care to match their orientations with what’s shown. If you have purchased the PIC16F1455 microcontroller from the Silicon Chip online shop, it will already have the firmware loaded. If you wish to do this yourself, the files can be downloaded from siliconchip. au/Shop/6/276 Check for dry joints and solder bridges and rectify them if you find any. You can then plug the header sockets onto the header pins, ready to solder the wires to the LEDs and switches. If you don’t have individual 4-pin & 5-pin strips, you can cut up longer strips with a hacksaw or side cutters. Receiver assembly The Receiver is built on a 56 × 45mm single-sided or double-sided PCB coded 09101242 – see the overlay diagram, Fig.7. The PCBs we supply will be double-sided, so they won’t need the four wire links. If you have single-sided boards (eg, you made them yourself), start by fitting the four wires shown in Fig.7. It Photos 3 & 4: the left-hand photo is the Transmitter PCB. Commercial PCBs will have silkscreened labelling. Note the headers for connecting the switches and LEDs; the extra pin is the 0V (GND) connection. The right-hand photo is the Receiver PCB. As commercially-made PCBs will have two layers, you won’t have to fit the links, saving some time. siliconchip.com.au Australia's electronics magazine February 2024  87 is advisable to use solid-core insulated wire (‘Bell wire’). You can see from Photo 4 that I used tinned copper wire; if doing the same, be careful to route the wires so they can’t short against anything. The construction procedure is the same as for the Transmitter, although all the resistors are mounted vertically on this board. Watch the orientations of all diodes, Mosfets, electrolytic capacitors and the IC socket. Also check that the terminal block wire entries are facing the nearest edge of the board. You will see that I used pieces of socket strip for CON6 & CON7, although I have specified polarised headers and matching plugs in the parts list. The advantage of the latter is that you can’t accidentally connect the points or signal backwards if you unplug and replug them later. While IC2 is the same type of chip as IC1 (a PIC16F1455), it is programmed differently, so make sure you get the right ones when purchasing pre-programmed chips. Similarly, if programming them yourself, use the HEX file ending in B for the Receiver chips and the -A file for the Transmitter chip. Check for dry joints and solder bridges, then refer to Table 1 to see which jumpers you need to plug into the headers for each Receiver based on its number. Photo 4 shows the jumper settings for points #5. Making the signals You don’t strictly need the signals, Photo 5: a points motor connected to a set of points on a small section of track for testing. but they improve the appearance and realism of the layout. Fig.8 shows how I made them. The mounting pole is made from a length of 3/32in (~2.38mm) square hollow brass tube. Cut it to size and clean up the ends using a file. The LED mounting plate is made from a piece of 0.05in thick by 0.5in wide (1.3 × 12.7mm) brass strip. Drill the 3mm diameter holes 6.5mm apart, then cut the plate to length. Use a linisher or file to round the ends to size and clean up the edges, then paint the plate matte black. For the base, place a piece of 20mm aluminium round rod into a three-jaw chuck so that 10mm protrudes. Face the end and turn it down to a 5mm diameter for a length of 3.5mm. Using a centre drill, followed by a 3mm drill, Fig.8: here are the details of the parts used to make the optional signal to go with each set of points. You could use the Semaphore described in the April 2022 issue instead. 88 Silicon Chip Australia's electronics magazine bore out the hole to a depth of 5mm. Part it off to a length of 4.5mm. Fit 3mm red and green LEDs into the LED mounting plate, noting the orientation shown on the drawing. Bend, cut and solder the leads as shown to create the LED assembly. They are soldered anode-to-cathode, in inverse parallel. The LED assembly is then soldered to the post. Clean, tin and flux the mating surfaces between the LED assembly and the post. Use a soldering iron to heat the assembly until you see solder coming out of the joint. File off any excess solder. Slide the base onto the post and lock it in place 25mm from the green LED lead using Loctite GO2 (or equivalent). To get power to the LEDs, take two 300mm lengths of thin hookup wire (red & black). You can strip these out of an old USB cable. Remove about 2mm of the insulation on both ends and tin the exposed wire. Clean and tin the bottom edge of the post, then place the red wire on top and solder it to the post. Thread the black wire up the centre of the post and connect it to the LEDs, as shown in Fig.8. Attach header pins to the other end of the red and black wires, and cover the wire connections with heatshrink tubing. Cover the LED assembly with masking tape and spray the rest with silver paint. Finally, test the signal by connecting a 680W resistor in series with the positive lead of a 5V DC power supply. Connect the other end of the 680W resistor to the signal red lead and the black lead to the supply's negative. The red LED should glow. Reverse siliconchip.com.au Scope 1 (left): the Mosfet gate drive (cyan) and drain voltage (yellow) when driving one side of a points motor. After switching the points, the capacitor takes about 400ms to recover its charge. Scope 2 (right): if the Transmitter is operating correctly, the serial waveform from pin 5 of IC1 should look like this. the connections, and the green LED will light. Mounting the signal If your layout is on a timber base, drill a 3mm hole at a suitable location near the entry to the points. Insert the signal wire end into the hole first, until the base is flush with the board. Glue it in place using Loctite GO2. My layout is on a polyurethane base, so I did the same but used a 2mm drill. I enlarged the hole to 3mm from the underside with about 24mm of the hole length remaining at 2mm. Wait till you have tested the PCBs before securing the signals in place. Preparing for testing Before testing the Transmitter and Receiver PCBs, make a temporary set of points with a points motor attached, as shown in Photo 5. I mounted it on a scrap piece of 30mm polystyrene. Firstly, mount the points using 0.78 × 25mm pins. Using the points operation lever, move the points in the direction shown in the photo. Take a points motor and orientate it with its actuator down. Place the hole in the actuator directly over the pin in the point’s operation lever and pin the motor in place. Switch the points manually, checking that the point motor's actuator moves smoothly in and out. Prepare the wires on the points motor to connect to a Receiver PCB. If using the specified polarised headers, that means crimping and/or soldering them into the header plug pins, then pushing those pins into the moulded plastic block in the correct order to siliconchip.com.au mate with the header on the Receiver. I soldered the wires to header pins to match the sockets I soldered to the board, and covered the solder joints with heatshrink tubing. Transmitter testing Check the orientation of the capacitors, diodes, and the voltage regulator, then apply 12V AC to the screw terminals as shown in Fig.6 (the two at upper left). Use a DVM to check that you have +5V and between 16-18V referenced to 0V on the terminal blocks. With the DVM black lead connected to pin 14 and the red lead to pin 1 of IC1’s socket, check that you measure +5V DC. Remove power and plug in the PIC16F1455, being careful to avoid folding its legs. Reconnect the supply and, if you have an oscilloscope, check to see that serial data is being sent out from the serial screw terminal, as shown in Scope 2. Otherwise, you can use a frequency counter to check for activity. The next step is to connect the Transmitter to a Receiver but, before doing so, recheck the Receiver board to verify that the diodes, Mosfets, capacitors and IC2 are correctly orientated. Connect the points assembly, Transmitter and Receiver as shown in Fig.9. Set the jumper links for points 1 (see Table 1). Apply 12V AC to the Transmitter, and you should see the green signal LED light and the points motor switch to the left. Short pin 13 of IC1 to ground (pin 14 is ground); the red signal LED should light, and the points motor should switch to the right. Switch off the power and change the jumper settings to #2. Switching the power on will again cause the signal Fig.9: the wiring for the first set of points. It’s the same for the other seven sets of points, except that the three jumper settings change (see Table 1 below). Australia's electronics magazine February 2024  89 Fig.10: the suggested positions for the PCB mounting holes, power input socket and serial bus cable in the control box. green LED to glow and the points motor to go to the left. This time, short pin 10 of IC1 to ground; the red signal LED will glow, and the points motor will move to the right. Repeat for the remaining point channels, referring to Table 1 and Fig.4. When finished, set each Receiver to a different ID, referring to Table 1, and use a small label or marker pin to write the IDs you’ve assigned on the Receiver PCBs. Finishing the control box You will now need to create a 90 Silicon Chip suitable label for the control box. I did this on the computer, scaled it to size to fit the control box lid and printed it onto silver sticky decal paper. Remove the backing sheet and carefully fit the label to the box, avoiding any air bubbles under the surface. As every layout is different, I haven’t made a drawing of the drilling details of the lid. However, Fig.10 shows the drilling details for the base and sides of the box. Drill out the holes for the green LEDs and switches, then fit them to the case. To connect the 12V AC Australia's electronics magazine plugpack, you need to drill a hole in the back of the box for the barrel connector, plus another for the four-wire serial cable exit. The Transmitter PCB is mounted on the bottom of the box using M2.5 screws and nuts. Fig.11 shows the wiring for the first set of points, which connects to 0V, P1 and LP1. The other channels follow the same scheme; eg, for the second set of points, the wires connect to 0V, P2 and LP2. These connections can be made by soldering the wire to the socket pin, covering the solder joint with siliconchip.com.au Parts List – Model Railway Points Controller Transmitter_________________________________________________ 1 single-sided PCB coded 09101241, 74 × 47mm 1 flanged ABS plastic enclosure, 171 × 121 × 55mm [Jaycar HB6125] 1 14-pin DIL IC socket (for IC1) 1-8 SPDT or DPDT toggle switches (S1-S8) (one per set of points) 3 2-way mini terminal blocks, 5/5.08mm pitch (CON1-CON3) 1 panel-mount barrel socket to suit plugpack (CON4) 3 4-pin headers 1 5-pin header 3 4-pin female header sockets 1 5-pin female header socket 4 M2.5 × 10mm panhead machine screws 8 M2.5 hex nuts 1 long four-core wire (to connect the Transmitter to all Receivers) various lengths and colours of hookup wire various lengths of heatshrink tubing 1 12V AC 1A plugpack Semiconductors 1 PIC16F1455-I/P micro programmed with 0910124A.HEX, DIP-14 (IC1) 1 7805 5V 1A linear regulator, TO-220 (REG1) 2-16 3mm green LEDs (LED1-16; two per set of points) 4 1N4004 400V 1A diodes (D1-D4) Capacitors 1 2200μF 25V low-ESR radial electrolytic 1 1000μF 16V low-ESR radial electrolytic (5mm lead pitch) 2 100nF 50V ceramic Resistors (all 1/4W 1% axial) 9 10kW 1 1kW 8 680W Receiver (per set of points, 1-8 per Transmitter)____________ 1 single-sided or double-sided PCB coded 09101242, 56 × 45mm 1 set of points 1 PECO PL-11 points motor 1 14-pin DIL IC socket (for IC2) 2 2-way mini terminal blocks, 5/5.08mm pitch (CON5) 1 2-pin polarised header with matching plug and pins (CON6) 1 3-pin polarised header with matching plug and pins (CON7) 3 2-pin headers (JP1-JP3) 0-3 jumper shunts (JP1-JP3; number required depends on Receiver ID) various lengths and colours of hookup wire various lengths of heatshrink tubing Semiconductors 1 PIC16F1455-I/P micro programmed with 0910124B.HEX, DIP-14 (IC2) 2 IRL540N, MTP3055VL or IPP80N06S4L-07 N-channel logic-level Mosfet or similar, TO-220 (Q1, Q2) 2 1N4004 400V 1A diodes (D5, D6) Capacitors 1 2200μF 25V low-ESR radial electrolytic 1 100μF 16V low-ESR radial electrolytic (2-2.54mm lead pitch) 1 100nF 50V ceramic Resistors (all 1/4W 1% axial) 3 10kW 1 4.7kW 1 680W 2 220W 1 47W Signal (per optional signal)_________________________________ 1 50mm length of 3/32in (~2.38mm) square hollow brass tube [K&S Metals] 1 20mm length of 0.025in thick, 0.5in wide brass strip [K&S Metals] 1 20mm length of 20mm diameter solid aluminium rod 1 3mm green LED (LED17) 1 3mm red LED (LED18) siliconchip.com.au Australia's electronics magazine Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. February 2024  91 Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 92 Silicon Chip Fig.11 (above): this shows some of the wiring for the Transmitter PCB inside the control box. Additional switches and LEDs are wired similarly but to terminals with higher numbers (P2/L2, P3/L3 etc). Fig.12 (right): you will need to figure out where to position the switches and LEDs to suit your layout, but in general, this shows how they should operate. If yours does the opposite, reverse the switch or the wiring to it. heatshrink tubing and using a hot air gun to shrink it. The 12V AC comes in via its attached plug and the socket that screws into the 8mm hole on the rear of the box. The connector must then be wired to the 12V AC screw terminals on the PCB. Use four-way alarm cable or similar to make the connections between the Transmitter and the Receivers, as shown in Figs.3, 9 & 11. The cable exits the control box through the 6mm hole. Table 1 – Receiver jumper settings # A B C 1 Jumper Jumper Jumper 2 Open Jumper Jumper 3 Jumper Open Jumper 4 Open Open Jumper 5 Jumper Jumper Open 6 Open Jumper Open 7 Jumper Open Open 8 Open Open Open Australia's electronics magazine The Receiver PCBs can be mounted underneath the layout. Final testing With all the points’ switches in the up position, the green LEDs on the control box should indicate which way the points are switched – see Fig.12. Each signal should be green. Changing a switch to the lower position should cause the associated set of points to change and the corresponding signal to go red. This should be reflected on the associated control box LED. Due to the number of combinations of points types, motor positions, and signals, you may find this isn’t the case. If the problem is with the points, it can rectified by swapping the points motor's red and black wires at the Receiver PCB. If the problem is with the signal, that can be rectified by swapping the red and black wires from the signal where they connect to the associated Receiver PCB. SC siliconchip.com.au Power your projects with our extensive range of Arduino® compatible power supply modules, batteries and accessories. A GREAT RANGE AT GREAT PRICES. LED VOLTAGE DISPLAY USB OUTPUT POWER YOUR PROJECT FROM A LOWER VOLTAGE POWER YOUR 5V PROJECT FROM BATTERIES BOOST MODULE Converts 2.5-5VDC from a single Li-Po or two Alkaline cells up to 5VDC. 500mA max. XC4512 ONLY 5 $ 95 DC-DC Boost Module with Display Converts 3-35VDC up to 4-35VDC. 2A max. 2195 $ XC4609 USB OR SOLDER TAB INPUTS EASILY ADJUSTABLE BY MULTI-TURN POTENTIOMETER MAKE YOUR PROJECT BATTERY POWERED RUN ARDUINO BOARDS OFF HIGHER VOLTAGE POWER LITHIUM BATTERY CHARGER MODULE Charges a single Lithium cell from 5VDC. XC4502 ONLY ONLY 5 $ 95 DC VOLTAGE REGULATOR Accepts any voltage from 4.5-35VDC, and outputs any lower voltage from 3-34V. XC4514 ONLY 895 $ Batteries not included SINGLE 18650 BATTERY HOLDER SWITCHED 4XAA BATTERY ENCLOSURE WITH USB PORT PH9205 $3.50 MP3083 $5.95 SWITCHED 4XAA BATTERY ENCLOSURE WITH DC PLUG PH9283 $6.75 3.7V 18650 2600MAH LI-ION BATTERY SB2308 $26.95 Shop at Jaycar for: • Step Up and Step Down DC-DC Converters • Huge range of Batteries and Battery Holders • Great selection of USB and DC Connectors & Leads • Regulated DC Plugpacks & Lab Power Supplies Explore our full range of products to power your projects, in stock on our website, or at over 115 stores or 130 resellers nationwide. jaycar.com.au Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 1800 022 888 SERVICEMAN’S LOG The things we do for our pets Dave Thompson Serviceman’s log, stardate 2023.12. We have encountered strange furry creatures that are demanding to be fed. It’s almost as if they believe they are our masters. I have beamed down to the planet to see if I can open a dialog with the three famished felines. The serviceman’s curse is indeed a curse! It is, of course, tied in with our peculiarly Antipodean DIY ethos and the ‘number 8 fencing wire’ lore of Australia and New Zealand. If we think we can do it ourselves, we will at least have a good go! Still, I like to think that most of us know our limits. I, for example, would not try my own dentistry or brain surgery. For one, I’d need someone to hold the mirror and/or torch, which precludes doing most common dental and medical procedures. I think that sort of thing is better left to the professionals. With just about everything else, though, I’m willing to give it a go. Whether it is building a guitar, installing an alarm system or replacing the main bearings on my car, I’ll give it a shot. I mean, what could go wrong? The guitar could be rubbish (I have made many, but only the first one was rubbish), or the engine overhaul doesn’t go as planned. They’re all pretty minor problems in the greater scheme of things, and there’s always the option to call in a professional, hopefully without them being annoyed that I have ‘had a go’ before bringing them in. 94 Silicon Chip I encountered this all the time in my line of work. Most people would only bring their computers in for repair after they’d had a go following some ‘tutorial’ on YouTube on how to fix it themselves. When I was trying to run it on the bench, they’d often chime in to say, “I tried that” or, “I’ve already done that”. I responded that I had my own troubleshooting processes, and I might very well replicate what they’ve already done. However, as they had brought it to me to fix, we could chat about what they’ve tried, or I could get on with my process for finding the cause of the problem. As we all know, there is so much misinformation on the web that it is almost impossible to find answers to even the simplest of questions without spending hours trawling through the clickbait, scams and people posting the same old erroneous rubbish just to scrape out some ad revenue. Hard drive on the rocks As an example, once upon a time, there was a data recovery strategy that required putting dead mechanical hard drives in the freezer to rejuvenate them just long enough to get the data off. In very specific and extremely limited circumstances, that method might work if the drive motor was seized. However, the way it was promoted on hundreds of sites was as if every failed drive could be recovered by doing this simple ‘hack’. As someone who has recovered data from thousands of drives over the years, I can say that it is not a reasonable strategy for recovering data. Yet, the number of people who brought drives in saying they’d tried that method was staggering. It is just one tiny example of how misinformation can spread and how it can also dramatically reduce the success of proper data recovery by messing with things people don’t understand. Many of those doing their own computer surgery are unaware that even tipping a drive over from standing on its edge to landing flat on the benchtop could cause platter damage. Handling drives and putting them in the freezer often precluded me from recovering any data from them because those people didn’t realise how fragile the drives were. Nothing in those tutorials mentioned static protection or physical vulnerability, so often, by the time I got them, they were already ruined. One guy drove hours to get to me with his hard drive floating around unprotected in the tray of his ute! Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • What we do for our pets Repairing a Whirlpool washing machine The clock that was running fast 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 Alas, such is the DIY ethos we all have. It also encompasses devices that are often not really worth the time and effort to repair, and it is simple bloody-mindedness that keeps us trying to fix such things. I’ve spent hours repairing cat toys when it would be much more sensible to just go and buy another one. For me, it’s the principle of the thing; if I can fix it, I should. It’s my duty. And if I end up spending hours and hours on a job for someone else and can’t fix it, then I don’t charge. That’s the moral way of doing business, even if it is not a path to riches. High-tech moggie feeding solutions We have three cats, and they all eat different diets for various reasons. So we have different food bowls and feeding patterns, and this routine involves some highfalutin (read: expensive) microchip-based cat feeders for two of them. I have written about these units before. I’ve also broken one by trying to be clever; probably not the last time I’ll do something like that! These devices run on four C-sized cells, with no provision for external power. In this day and age, that’s an odd thing, or at least I thought so. I did what anyone else would do and tore it apart so I could power it with an external supply. I’ve done this with dozens of devices over the years, including guitar stomp-boxes. I have also converted primary-­cell-powered torches into rechargeable devices by switching to NiCads and adding charging sockets. It’s usually all pretty straightforward stuff. This time, however... Getting these microchip feeders apart is easy; there are no stupid security fasteners or single-use break-away clips; just good, old-fashioned screws biting into solid plastic turrets and good-quality plastic mouldings that fit together seamlessly. A long-reach Phillips screwdriver is the only special tool required, as some of the holes are deep, and the screws are beyond the reach of a standard driver. Inside, they are surprisingly complex, but there was plenty of room for adding a socket in the rear corner, and the wires to the battery bays were easy to access. I dug through my boxes of power supplies, gleaned from years of collecting them and never throwing any away, and found a 6V DC supply that would do the job. This supply would determine what type of power socket I would install, because it is far easier to get a new socket (if needed) than to change the output lead of the supply (though I have done that many times in the past). I used to watch Dad changing a supply’s lead and/or polarity by opening up the sealed plastic case. I’ve tried to siliconchip.com.au replicate what he did but have never been successful. He would sit the supply on one corner on the workshop floor and, while holding it in position with his left hand, strike the uppermost/opposite corner of the case with a hammer. Every time I saw him do it, one quick rap with the hammer and the case would just pop apart down the seams like magic. Whenever I’ve tried it, I end up with a smashed case, typically parting everywhere but the seam and with crushed corners. It can usually be glued back together, but it is highly annoying that he made it look so easy, and I’ve never been able to do it, even with him teaching me! Since then, I haven’t even tried to do it, but I can do a plug swap or add an inline switch in the wire near the supply’s output. When done properly, it looks OK and functions perfectly well. Anyway, I found a suitable socket in one of my spares boxes and installed it into a space in the back of the feeder. I re-routed the battery leads to the socket, ensuring the polarity was right, and soldered it together. I used tape tabs to hold the wiring out of the way of the door mechanism and reassembled the whole thing. I plugged the supply in, connected it and tried the feeder using one of the RFID tags that came with it. Nothing; no lights, no response to button presses or programming functions. Bupkis. Well, that was disappointing. I checked the supply’s polarity and output, and though the measured 6.5V (unloaded) was a little high, I thought it was within limits. The polarity was correct, but it didn’t work. So, I took the whole thing apart again and rewired it back to battery power. This time, I got lights, but while the door tried to open, it wouldn’t go all the way, even though the motor tried to actuate it. Australia's electronics magazine February 2024  95 Bother! (or words to that effect) Try as I might, I could not get this thing to work correctly. It was the first device in decades that wouldn’t operate after a conversion. I was gutted, especially since this thing cost 300 Kiwibucks (about 280 Aussie dollarydoos) and it had lasted less than a week. It appears that some things are not meant to be mains-powered! I was 100% sure that I’d gotten polarities and wiring correct, and I’d double-checked it half a dozen times before applying power. I guess I was trying to be too clever by half. Lesson learned! That feeder still sits in my workshop today, dead and gathering dust. While covered by a factory warranty, I’d have to ship the unit to the USA for repair and pay all shipping costs myself. That would have cost almost the same as a new unit, and I think they’d ask questions about the hole I’d bored in the back for the power socket! So, an expensive lesson then. I still don’t know why it wouldn’t power up with mains power. It was an old transformer-style supply, not a switch-mode one, so I can see no reason that wouldn’t have worked. I wasn’t going to try it again, that’s for sure! I did what any self-respecting serviceman would do and went and bought another unit! That one is still going strong today, and the four C cells last almost a year, so it was a bit of a moot exercise anyway. The pitfalls of parts swapping However, the other feeder has now developed a problem. It sounds very rough when opening and closing and sometimes stalls partway through the door-open cycle. Either the motor was getting weak, or the gearbox driving the door assembly was wearing out. Not good either way. Now, I know what you’re thinking. Did he fire six shots or only five? Sorry, wrong movie. I meant to say I have a whole new spare, non-working device sitting in my workshop that I could burgle parts from. And you’d be right, except for one tiny prob. Between the time I got these and the new one, they’d changed the model slightly, including the folding door actuator mechanism, so they look completely different on the inside. Even the PCBs are different. You can rest assured there was some blue language flying about the workshop when I discovered that! The first thing I tried was changing the batteries. Though there is a low battery indicator on the feeder (a red flashing status LED once every minute or so), I swapped them out for some new, fresh alkaline cells. There was no difference, as I suspected, so it was not caused by a lack of power. I pressed on regardless and took the covers off the grumbling feeder. It’s been opening and closing half a dozen times a day for years now, so I fully expected it to be worn out, especially given the current gear noise. The motor itself is the same in both the old and new versions, but the gearing and actuator assembly are slightly different, which is to be expected as the door opens and closes slightly differently in each version. This is a bit of a curse because swapping one assembly to the other unit would have been so easy. However, it’s rarely that easy! The only real option was to disassemble the grumbly gearbox and check it out internally for wear and tear. If anything inside the unit had totally failed and needed replacing, I’d be dead in the water, as the company does not provide spare parts. Oh, for a 3D printer! When I pulled it apart, I confirmed the motors looked the same. I guess that changing it between models would be pointless. The gearbox is a Nylon gear assembly that converts the rotary motion of the electric motor into a linear action to actuate the bi-fold door. If the door is closed, and the correct embedded microchip or RFID collar tag is detected, the motor runs in one direction to open the door. If the door is open, and the microchip or tag signal is no longer detected, after a switch-selectable preset time, the motor runs in reverse to close the door. The limits appear to be set electronically, similar to an electric window in a car, where the controller detects when the window reaches its maximum and minimum operating range by detecting the increased current drawn by the motor. This will also occur if someone gets their arm or fingers stuck in the window, or in this case, a cat gets a foot stuck in the closing feeder door. I tested it when we first got these units, and that safety feature works quite well. Fixing the feeble feline feeder In this feeder, sometimes the door won’t open more than a few centimetres. It always seems to close OK, though; it is just dodgy on opening, which likely takes more energy due to working against gravity. I guessed that something was fouling the gearing, or the grease had dried out, and the gears were binding up. In other words, I felt it was a mechanical fault rather than an electrical one. At least if the motor was failing, I have a spare one of those! I took the five screws out of the gearbox housing and carefully pulled the side clear. I’ve been caught with these sorts of things before, where some gears and shafts come out while others stay put, and half of it ends up falling onto the bench. I really didn’t want to have to work out what went where, having never seen it in place! I managed to get the case off and saw that while the gears had some noticeable wear, the light grease used was dry and crumbly and lying in the bottom of the gearbox. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au I used a contact-cleaning spray to wash the box out and mixed bearing grease and oil (all I had) to make a light composite grease. I applied it liberally over everything I could see and added drops of oil on the shafts where they engaged with the housing. I reassembled everything and inserted the batteries. Without the bi-fold door fitted, I ran the actuator forward and reverse manually several times to coat everything well. It certainly sounded better! I then reassembled the whole thing, and it has been running quietly and smoothly for a few weeks with no stoppages. If it lasts another year, I’ll be happy – who knows, maybe I’ll have a 3D printer by then! Editor’s note: I’ve sometimes had luck spraying silicone lubricant into holes in gearboxes on small pieces of equipment with similar problems. While it’s rarely a permanent solution, it can save you from having to disassemble and reassemble the lot, and sometimes you can even get away with poking the straw through a hole in the case. Repairing a retro Whirlpool washing machine D. C., of Beachmere, Qld went on quite an adventure delving into the innards of his trusty old washing machine. It is a simple and robust design that has withstood the test of time and just needed a bit of TLC... We had an older model (non-electronic!) Whirlpool 6LSS5232 washing machine for well over 30 years. It is a two-speed model with suds return, which my wife loves. Washer technicians have told us that the machine is almost indestructible and to keep it going as long as possible. These machines are direct-drive via an ingenious gearbox attached to one end of the motor, with the pump attached permanently to the other end. This turns in one direction for washing, then reverses for spinning and pump-out. The design was so successful that many other manufacturers of the time either copied the gearbox design or used Whirlpool parts in their own machines. The drive motor is an open asynchronous AC motor with high/low speed windings, plus a winding for the capacitor start, which permits rotation in either direction. The usual centrifugal switch controls the start winding disconnection. However, the centrifugal switch does not operate reliably at low speeds, so the motor is always started with the high-speed winding. After that, changeover contacts on the centrifugal switch select the low-speed winding once it is spinning. Our machine was recently showing three faults as well as quite a bit of cosmetic ageing and the usual rust from corrosive detergents, so it was time for an overhaul. The problems were timer unreliability, a leaking tub, and spinning a full tub of water while pumping out. The last one was worrying, as spinning a weight like that puts a lot of strain on the motor and clutch. To make a less rushed job of reconditioning the machine, I purchased a similar working machine, with a view to later use good parts from that machine as spares. While the spare machine was working, it had been sorely neglected and was seriously rusted, so it was of little ultimate use apart from spares. The timer is the typical rotary mechanical device of that era, with a “pull out to start” function and loads of cams and contacts to control the various functions, driven by a small timer motor. The fault turned out to be a broken siliconchip.com.au detent spring inside the timer which holds the knob in the start position. Of course, the spring is deep inside the timer mechanism, so I had to dismantle it completely. I was able to steal the spring out of the donor machine, but there were many hours of fumbling and cursing, getting all the bits back together (six hands would have been good) before I finally succeeded with repair phase one. I then started the real overhaul of the washer mechanism, learning as I went by making lots of mistakes! I managed to get it all apart and cleaned out the caked-on detergent deposits from 30 years of hard work. The tub seal is located deep inside the works and seals the agitator shaft as it enters the bottom of the tub. Amazingly, many parts for these machines are still available in the USA; some are even available in Australia, so there was no problem getting a new seal and fitting it. The spinning-while-pumping problem was a bit more involved. The gearbox allows agitation when the motor spins in one direction, and spinning and pumping out in the reverse rotation. To enable the reverse rotation to do two different jobs, spinning or pumping, the smart engineers at Westinghouse designed a device called a ‘neutral drain’. One of the ubiquitous YouTube videos helped me to understand how the neutral drain works. It is inside the gearbox and consists of a large metal wheel with several hard plastic cams and latches. The device counts up the wash agitator movements until a latch is set, and the latch prevents the drum drive dog from rotating when the motor is reversed, so the neutral drain only works immediately after a wash cycle. Thus, the water can be pumped out without the drum spinning. After a suitable time for pumping out, a short rest is included in the cycle, which allows the neutral drain latch to release, and regular spinning can resume. When the drum spins normally, the drum’s brakes are released by a cam, and the clutch allows slippage until full speed is reached. However, when the neutral drain is in, the drum is held firmly at rest by its brakes. Australia's electronics magazine February 2024  97 The Whirlpool washing machine shown with its AC motor and gearbox assembly on top. The hard plastic neutral drain components wear out with time, and a “neutral drain kit” is readily available, which completely solves the problem. I sent the required dollars, received and fitted the components, renewed the gearbox oil, then bench-tested the motor/gearbox assembly, which worked perfectly. To make bench testing easier, I built a small motor test unit that allows forward/off/reverse rotation and high/ low-speed selection. It was just a matter of mounting and wiring two switches and a start capacitor in a metal box and wiring it from the mains supply out to a motor plug. All that remained was to fit everything back into the newly de-rusted and spray-painted cabinet and do a test run with some real washing. All went well; my wife approved, and with any luck, we will get many more years out of the old machine. I learned a lot about the operation of our machine and now feel confident to solve any new problems. Finally, I dismantled the poor old donor machine, consigned useful spares to the workshop shelves and gave the remainder a decent burial at the local recycling centre. It started gaining time; after 20-odd years, you can expect some problems. Usually, when daylight saving changes, I don’t have to adjust the minutes, just the hours. However, last time, it had gained some time, then after setting it, I found it had gained again the next day. Rather than have the incorrect time showing, I switched it off, and when I got sick of walking into the bed in the dark, I decided to have a look at it. Clock radios of this era generally used the AC mains frequency as their time source, and this clock was no different. It uses an LM8560 IC as its clock driver. Plenty of data on that chip is available online, albeit as poor-quality scans. My Teac was very similar to the data sheet circuit as far as the mains cycle clock circuit goes, and the CRO showed signals that looked pretty much what you’d expect. The PSU main electro looked OK, so I rapidly came to the conclusion that the IC had probably developed a fault after 20+ years of service. I don’t blame it. I found a replacement on eBay from China for less than $2, including postage. I often wonder how they manage this – I would spend more than that on postage alone for the smallest domestic parcel, without even considering my time, packaging materials and international freight. Perhaps the Chinese Government subsidises it, or maybe its one of the reasons Australia Post is losing money. Maybe both. A month or so later, it arrived, and after walking into the bed again one night, I was inspired to fit it. It didn’t take too long, but I was both unsurprised and disappointed that the display showed gibberish with the new part. It wouldn’t respond to the time set buttons either. I checked the orientation and soldering and neither looked like the source of any problems. After muttering some profanities and vowing never to buy cheap electronic bits on eBay again, I picked it all up and unceremoniously shoved it onto the e-waste pile. A few weeks later, I saw that my son had left his Panasonic clock radio in his room when he moved out, and later that evening, it was in place next to the bed with the correct time. It wasn’t until the next day that I noticed the display was dim – so dim that I first thought it was turned off and had to shade it with my hand to read it. Ahead of its time D. T., of Sylvania Southgate, NSW has experienced that strange feeling when you manage to fix a faulty piece of electronic equipment, only to be baffled how it ever worked in the first place... I bought my Teac clock radio over 20 years ago. At the time, I wanted a combined phone-plus-clock-radio to minimise space used on the bedside table, and this Teac was the only one around. While the display was a bit bright at night when it was new, it wasn’t long before the brightness ‘wore off’, and it has been a good product overall. At night, the LED clock is easy to read; much easier than finding my smartphone and figuring out where the on button is. It is also good to navigate by – late at night, I can walk toward the display in the dark to find my side of the bed without disturbing my wife. 98 Silicon Chip This early-2000s era clock radio uses a couple of singlesided PCBs and mostly standard through-hole parts. Australia's electronics magazine siliconchip.com.au I tried it like that for a while, thinking I didn’t need to see it during the day, but I found it annoying looking over and not being able to read it. Obviously, I look at it more during the day than I thought. At least it was keeping good time. I thought this might be a case of bad electros causing the high-voltage feed to a vacuum fluorescent display to fail, but I quickly ruled that out when I opened it up and found the display used LEDs. Interestingly, I noticed it used the same LM8560 IC, with the same package and everything. I rescued the Teac from where I left it, then desoldered both ICs, and soldered the one from the Panasonic into the Teac. I gingerly switched and was greeted with a nice, clean, non-gibberish “12:00” flashing in bright green digits. I set the time and let it run. It would be great if that were the end of the story; however, I’m slightly embarrassed to say that my diagnosis of a faulty LM8560 was clearly incorrect because, by the next morning, the time was out again. So, back to the drawing board. I dug out the data sheet again. For an LM8560 to gain time, you’d think it would need to receive extra pulses, causing extra counts. Given the rate of time gain, I calculated it was receiving probably one or two additional pulses per second. I measured the main supply electro again – it was marked 470μF but measured around 350μF. It looked OK and the rail looked OK on the CRO too, but I replaced it anyway. I also checked the clock line. It was a half-wave rectified line from the transformer via a 100kW resistor and looked good. However, I noticed that while the data sheet showed a 1nF cap across the input pins of the IC, the Teac didn’t have one, nor did it have pads for one. This cap and the 100kW source impedance would have formed a simple lowpass filter with a time constant of 100μs. I thought about adding that capacitor. I don’t like second-­ guessing design engineers; I worked as one for many years, and usually, the design you choose is what’s ‘needed’. Clearly, this design hadn’t needed that capacitor for 20 years. But I was getting tired of this repair dragging on for so many months, so I soldered in a poly I had handy. It was then a matter of putting it all back together and trying it out. The initial results were promising, and I was relieved to find it still showing good time the next day, and it continues to do so. So what was it? I’d guess the main supply electro. It was definitely low in value, and perhaps something was intermittent about it, or its ESR had crept up over time. It reinforces my distrust of old electros. There could also be a latent fault somewhere else, like a shorted turn in the transformer reducing the clock voltage margin. I’m not sure. Interestingly, I note the Panasonic, like the Teac, had no capacitor on the clock input pin, so it’s probably optional. I don’t think having the poly cap there will cause any harm. I’m just glad I can find my way to bed now without injuring myself! Editor’s note: increased ESR in the power supply filter capacitor might not be obvious (unless you use an ESR meter) and could lead to reduced noise margin on the timing input. The manufacturer no doubt figured they could get away without the extra filter capacitor, and they were right, but sacrificed some reliability in saving that cent. SC siliconchip.com.au Australia's electronics magazine February 2024  99 PRODUCT SHOWCASE High-performance silicon carbide (SiC) Schottky diodes from Queensland Griffith University and Queensland Semiconductor Technology Pty Ltd (Questsemi), supported by Semefab Scotland and the Innovative Manufacturing CRC (IMCRC), are manufacturing high-performance silicon carbide (SiC) Schottky diodes, a key element in many power conversion systems. Due to their incredible thermal conductivity, high switching performance and efficiency, they are highly sought after for applications like solar inverters, motor drives, electric vehicle (EV) chargers and uninterruptible power supplies. Using SiC wafers, researchers at the Queensland Microtechnology Facility (QMF) of Queensland Micro and Nano­ technology Centre (QMNC) at Griffith University have developed a new technology that allows for more efficient and low-cost fabrication of SiC diodes. As part of the research project, a pilot production facility will be set up at QMF to support the commercialisation of the technology. Devices necessary for the initial commercial product supply will be manufactured there. Professor Sima Dimitrijev, who leads the research team, says the development and pilot manufacture of SiC diodes at QMF is an excellent example of advanced manufacturing collaboration. “We are working with local manufacturers, which enables Questsemi not only to fast-track commercialisation but also to design and manufacture semiconductor devices that meet local demand for applications such as EV battery chargers, drones, solar inverters, industrial motor drives, and high-frequency power converters,” Professor Dimitrijev said. “Manufacturing SiC diodes is complex & generally associated with high capital investment,” David Fletcher, Director of Questsemi, explained. “Unlike other SiC diode manufacturing processes, the technology developed by Griffith researchers uses steps that are common to standard silicon wafer processing and thus dramatically simplifies the manufacturing process and associated costs.” “With the funding support of IMCRC, we are able to trial production and accelerate the commercialisation of the new SiC technology, which is set to improve the overall cost of semiconductor devices used in energy-­efficient technologies,” he said. The insights and advancements made throughout the project will help Questsemi transition to volume manufacture of SiC Schottky diodes locally and overseas. IMCRC Innovation Manufacturing Manager Dr Matthew Young said Questsemi’s collaboration with Griffith University demonstrates what is possible when a business research partnership sets out to push technological boundaries to solve unmet industry needs. “SiC Schottky diodes play an important role in the semiconductor value chain, a sector often described as a global engine for technology, economic and social progress,” he said. “Questsemi and Griffith University’s SiC technology will have a flow-on effect in the design, prototyping and fabrication of other semiconductor devices, creating new business opportunities for Australia.” “With IMCRC activate funding, we are able to fast track the commercial translation of this semiconductor research into next-generation energy-­ efficient technologies.” Professor Nam-Trung Nguyen, Director of QMNC at Griffith University said, “We have a strategic line-up of projects from fundamental research to commercial development that ensures rapid transfer of technologies developed at our centre to industry partners.” Queensland Semiconductor Technologies Pty Ltd Unit 1, 2-6 Focal Avenue, Coolum Beach QLD 4573 Phone: (07) 3132 8687 sales<at>questsemi.com www.questsemi.com 100 Silicon Chip Australia's electronics magazine siliconchip.com.au Keep your electronics clean, lubricated and protected. Service Aids & Essentials. GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. 4 2 1 5 3 BUY IN BULK & SAVE!!! 1 Isopropyl Alcohol 99.8% 250ml Spray NA1066 BUY 1+ $13.95 EA. BUY 4+ $12.45 EA. BUY 10+ $10.95 EA. 99.8% 300g Aerosol NA1067 BUY 1+ $15.95 EA. BUY 4+ $13.95 EA. BUY 10+ $12.45 EA. 70% 1 Litre Bottle NA1071 BUY 1+ $21.95 EA. BUY 4+ $19.45 EA. BUY 10+ $17.45 EA. 2 Electronic Parts Cleaning Solution 1 Litre Bottle NA1070 BUY 1+ $15.95 EA. BUY 4+ $13.95 EA. BUY 10+ $12.45 EA. 3 Liquid Electrical Tape 28g Tubes, Red or Black NM2836-NM2838 BUY 1+ $24.95 EA. BUY 4+ $22.45 EA. BUY 10+ $19.95 EA. 4 175g Aerosols Contact Cleaner Lubricant NA1012 Electronic Cleaning Solvent NA1004 BUY 1+ $13.95 EA. BUY 4+ $12.45 EA. BUY 10+ $10.95 EA. PTFE Dry Lubricant NA1013 BUY 1+ $15.95 EA. BUY 4+ $13.95 EA. BUY 10+ $12.45 EA. 5 J-B Weld Products J-B Weld Epoxy 28g NA1518 BUY 1+ $25.95 EA. BUY 4+ $22.95 EA. BUY 10+ $20.45 EA. SuperWeld Extreme 15g NA1539 BUY 1+ $14.95 EA. BUY 4+ $13.45 EA. WaterWeld 57g NA1532 BUY 1+ $23.95 EA. BUY 4+ $21.45 EA. BUY 10+ $18.95 EA. Shop at Jaycar for even more service aids & essentials: • Adhesives & Insulation Tapes • Solder & Soldering Aids • Wire & Heatshrink Tubing Explore our full range of service aids, in stock at over 115 stores, or 130 resellers or on our website. • Fasteners & Cable Ties • Ultrasonic Cleaners • Tools & Workbench Accessories jaycar.com.au Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 1800 022 888 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 02/24 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) Basic RF Signal Generator (Jun23) ATmega328P-AUR RGB Stackable LED Christmas Star (Nov20) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) 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) Railway Points Controller Transmitter / Receiver (2 versions; Feb24) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch (RX, Jul22) K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) Mains Power-Up Sequencer (Feb24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), 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) PIC16F1705-I/P Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $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 ETC MAINS POWER-UP SEQUENCER (FEB 24) Hard-to-get parts: includes the PCB, programmed micro, all other semiconductors and the Fresnel lens bezels (SC6871) $95.00 Current detection add-on: includes the AC-1010 current transformer, (P)4KE15CA TVS and MCP6272-E/P op amp (SC6902) $20.00 MICROPHONE PREAMPLIFIER KIT (CAT SC6784) (FEB 24) Includes the standard PCB (01110231) plus all onboard parts, as well as the switches and mounting hardware. All that’s needed is a case, XLR connectors, bezel LED and wiring (see page 35, Feb24) USB TO PS/2 KEYBOARD & MOUSE ADAPTOR - VGA PicoMite Version Kit: see page 52, January 2024 (SC6861) - ps2x2pico Version Kit: see page 52, January 2024 (SC6864) - 6-pin mini-DIN to mini-DIN cable, ~1m long. Two cables are required if adapting both the keyboard and mouse (SC6869) (JAN 24) (DEC 23) MULTI-CHANNEL VOLUME CONTROL (DEC 23) - Kit: Contains all parts and the optional 5-pin header (see page 77, Dec23) - 1.3in blue OLED (SC5026) 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) $30.00 $32.50 $10.00 COIN CELL EMULATOR (CAT SC6823) - 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) - 0.96in SSD1306 cyan OLED (SC6176) $70.00 (DEC 23) $30.00 $15.00 $50.00 $55.00 $25.00 $10.00 siliconchip.com.au/Shop/ MODEM / ROUTER WATCHDOG (CAT SC6827) (NOV 23) PICO AUDIO ANALYSER SHORT-FORM KIT (CAT SC6772) (NOV 23) K-TYPE THERMOMETER / THERMOSTAT (CAT SC6809) (NOV 23) PIC PROGRAMMING ADAPTOR KIT (CAT SC6774) (SEP 23) CALIBRATED MEASUREMENT MICROPHONE (AUG 23) 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 parts except the case, LCD, thermocouple probe, cable gland and switches S4 & S5. A 10A relay is included (see page 58, Nov23) $75.00 Includes all parts, except the optional USB supply (see page 71, Sept23) SMD version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6755) Through-hole version kit: same as the SMD kit (Cat SC6756) Calibrated ECM set: includes the mic capsule and compensation components; see pages 71 & 73, August 2023 issue, for the ECM options (Cat SC6760-5) DYNAMIC RFID/NFC TAG (JUL 23) RECIPROCAL FREQUENCY COUNTER KIT (CAT SC6633) (JUL 23) BASIC RF SIGNAL GENERATOR (JUN 23) SONGBIRD KIT (CAT SC6633) (MAY 23) DUAL RF AMPLIFIER KIT (CAT SC6592) (MAY 23) SILICON CHIRP CRICKET (CAT SC6620) (APR 23) Smaller (purple PCB) kit: includes PCB, tag IC and passive parts (Cat SC6747) Larger (black PCB) kit: includes PCB, tag IC and passive parts (Cat SC6748) $55.00 $22.50 $25.00 $12.50 $5.00 $7.50 Includes all parts, except the case, TCXO and AA cells (see page 57, July 2023) $60.00 $35.00 $20.00 $15.00 $30.00 $30.00 $30.00 $25.00 $35.00 $45.00 Kit: includes everything but the case, battery and optional pot (Cat SC6656) Includes all parts required, except the base/stand (see page 86, May 2023) Includes the PCB and all onboard parts (see page 34, May 2023) Complete kit: includes all parts required, except the coin cell & ICSP header *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. $100.00 $30.00 $25.00 $25.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DATE JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 PCB CODE 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 Price $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER 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 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) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION DATE DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 PCB CODE 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 01108231 01108232 04106181 04106182 15110231 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 04107231 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 Price $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $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 $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 $12.50 $7.50 $2.50 $2.50 MAINS POWER-UP SEQUENCER MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER FEB24 FEB24 FEB24 FEB24 FEB24 10108231 01110231 01110232 09101241 09101242 $12.50 $7.50 $7.50 $5.00 $2.50 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 Vintage Radio STC Radiotym model 5160 from 1956 By Assoc. Prof. Graham Parslow Clock radios from other manufacturers all followed a basic pattern of a rectangular case with a clock set where a speaker might otherwise be. However, the STC Radiotym 5160 (a modified Pixie radio, original shown above) stands out stylistically from its competitors. I n the 1950s, every major Australian radio manufacturer offered a clock radio, usually as a variant of a radioonly model. They were good in the kitchen, lounge, or bedroom to tell the time and provide entertainment. They can also be set to mechanically switch on or off at set times (eg, to be used like an alarm clock). The clocks all have synchronous motors locked to the 50Hz mains frequency and are impressively accurate. Neither the STC Pixie nor the Radiotym was a great marketing success if judged by the small number that survived in collections. I have seen several Pixies, but only the one Radiotym. I was lucky enough to purchase the one featured here from a Historical Radio Society of Australia auction (HRSA). I previously described the STC Pixie in the March 2023 issue (“Three ‘kindred’ radios from STC”; siliconchip. au/Article/15705). 104 Silicon Chip The colour choices for the Radiotym were black, cream, Chinese-red or grey. These STC radios were not styled in Australia, but in the USA by ITT, the parent company of STC. Relative to Australia, radios from the USA through the 1940s and 1950s were generally more flamboyant in style, with multiple vivid colours. For a US-designed radio, the Pixie and Radiotym are on the conservative side. Australian Pixie and Radiotym radios were made from local components in Sydney because high tariffs made it uneconomical to import assembled radios from the USA. Circuit details The Radiotym circuit and dial string arrangement details are shown in Fig.1. Many contemporary radios in 1956 featured a ferrite rod antenna. However, the front end of the Radiotym Australia's electronics magazine has a conventional aerial coil with a trimmer capacitor linking the primary to the secondary. This trimmer optimises the sensitivity to higher frequencies which would otherwise be partly shunted to earth by the 100pF capacitor in parallel with the primary winding. The secondary of the aerial coil provides tuning through the MW band by resonance with tuning capacitor C3. The 6BE6 valve (V1) designed by RCA is a commonly-encountered frequency converter in radios built from the late 1940s to the mid-1950s. The 6BE6 in this radio is branded Mullard. The local oscillator that produces the superheterodyne frequency is a Hartley circuit tuned by parallel capacitors C4 and C5. The tuned signal, converted to 455kHz (the intermediate frequency [IF]), passes through the first IF transformer for amplification by a 6BA6 valve (V2). The 6BA6 is another siliconchip.com.au Fig.1: the circuit diagram for the STC Radiotym 5160, which is a clock-controlled radio. Note that C3 & C5 are ganged capacitors, while C8, C10, C12 & C15 are valued at 75pF. RCA-designed valve released at the same time as the 6BE6. The high performance of the 6BE6/6BA6 combination contributes to the STC claim of a sensitivity of 10μV for reception across the MW (AM broadcast) band. The amplified IF signal is detected by the 6AT6 valve (V3; at pin 6) and produces an audio output at the secondary of the second IF transformer. The second diode at pin 5 in the 6AT6 generates a negative voltage proportional to signal strength. This negative voltage is fed via R3 (1MW) to the control grids of the first two valves for AGC (automatic gain control). Back-bias resistor R13 (330W) in the high tension line makes this delayed AGC, so that weak signals are not affected by AGC action. Only once signal strength crosses a certain threshold does the AGC circuit start to reduce the set’s gain. Resistor R13 is also the source of grid bias for the 6CH6 output pentode. The 6AT6 valve provides a triode section to preamplify the audio signal fed to the grid from the volume control, P1. The 6AT6 grid also receives negative feedback from the speaker via 1kW resistor R15, reducing distortion and keeping the amplifier section siliconchip.com.au stable. When reconnecting a speaker, preserving the original polarity (phase) to maintain stability is essential. Sometimes a guess has to be made during restoration – the wrong choice is given away by greatly increased distortion or howling oscillation. The 6CH6 (V4) output pentode is Photo 1: from the rear view of the chassis and case, you can just see the speaker sitting at the bottom. It is there because the normal location for a speaker is instead occupied by the alarm clock that is covered by a sheet of plastic. Australia's electronics magazine February 2024  105 Photos 2 & 3: the empty STC Pixie case, which uses the same moulding as the Radiotym model 5160. The populated case can be seen below. The two radios use identical components except for the Pixie having a mains switch in the volume control. the most unusual of the valves found in this radio. The only other radio I have encountered this valve in is a Tecnico model 1050 (the ‘fortress’). The valve was released by Brimar in 1951 as a video output pentode and can easily produce 3W of audio power due to a high anode current and heat dissipation. Brimar is a UK subsidiary of the STC-ITT group of companies, so that explains the choice. This valve has a mutual conductance (gm) of some 11mA/V, almost three times that of the more common 6AQ5 output valve (4.1mA/V). Since voltage gain depends on gm, the 6CH6 boosts the radio’s sensitivity by almost three times compared to an identical set using a 6AQ5. This gain contributes to the high sensitivity quoted for this set in the service notes. Restoration The primary of the speaker transformer in my set was open circuit, so I installed a replacement transformer. The coupling capacitor C17 was leaky, but all other components were serviceable. Many valve radios from the late 1950s have likewise mostly functional components. Adding a clock to the Pixie Photo 4: you can see the speaker grille from the underside of the model 5160 case. A downward-facing speaker is rare for vintage radios. 106 Silicon Chip Australia's electronics magazine The Pixie has a front-mounted speaker that is attached to the main chassis. The same four-inch (~100mm) speaker is used in the Radiotym. The empty Pixie case (see Photo 2) shows that the front plastic moulding inserts into the main case, leaving a vent for the speaker and a rectangle for the dial. The Pixie dial features the call signs of all Australian states, the same as for almost all Australian contemporary radios. The grille moulding for a downward-facing speaker is also included in the Pixie case (Photo 4). The Radiotym uses the same case moulding. A custom aluminium panel in the front accommodates the clock and provides a window to the dial cursor. That frequency-calibrated dial is the same as for the USA, where local station markings were impractical due to the large number of stations. The calibration numbers run from 5.5 to 16, representing multiples of 100kHz (kc/s at the time). Most Australians in 1956 would not have been familiar with locating stations by frequency. Downward-facing is the worst of siliconchip.com.au Photo 5: there is a label on the power transformer showing the valve layout. Photo 7: the Japanese Copal flip-clock radio, which was a later development in the sphere of clock-radios. all the alternative locations for a speaker. The reproduction quality then depends on the acoustic properties of the surface below. However, there is also a backwave that contributes significantly to the sound after emerging from the rear moulding of the radio. As a result, the listening quality is not great, but passable when there is nothing to compare it with. MSP speakers were made in Sydney by AWA. They used the Manufacturers Special Products label to provide original equipment manufacturers (OEMs) with items not branded with a competitor’s logo. Rola speakers were considered acceptable to use because there were no Rola radios. The chassis and component placements are identical for both the Pixie and Radiotym. In the photo showing the Radiotym components mounted below the chassis (Photo 6), the plastic shroud covering the clock against dust can be seen through the rectangular punch-hole. In the same view for a Pixie chassis, the front-mounted speaker can be seen through the rectangular hole. A simple but effective mounting to lock the downward-facing speaker to the chassis is provided by two screws tapped into the alnico (aluminium/ nickel/cobalt) speaker magnet. There is one component difference between the Pixie and the Radiotym. The Pixie has a mains switch incorporated with the volume control, while the Radiotym does not. Clock Radios use the clock to control on/off switching as well as timer functions. This can be a trap for today’s unwary collector of a clock radio. For example, a collector told me his radio was not working. I replied, “Try turning it on with the clock control knobs”. A miracle followed – it worked! Radiotym variant of the Pixie was not a huge success in Australia. However, STC also offered a locally-designed Bantam radio that was better attuned to Australian tastes in the 1950s. I also covered the Bantam radio in the article on three STC radios (March 2023; siliconchip.au/Article/15705). Before the second world war (pre1939), STC aimed for a prestige market, but after the war (post-1945), they introduced a series of Bantam radios aimed at the middle market. The Chinese-­red model Bantam is one of my favourites. For the Tymatic clock radio, STC performed a radical internal reorganisation of the Bantam to create a linear tracking dial with the speaker behind it and a clock in the usual speaker grille. I have seen several examples of the Conclusion Photo 6: the underside of the STC Radiotym model 5160 chassis, and MSP (Manufacters Special Products) speaker made by AWA. As mentioned previously, the siliconchip.com.au Australia's electronics magazine Tymatic, so this met the market more successfully than the Radiotym. I suspect that one reason is the large, clear station information on the Tymatic dial. As transistor radios displaced valve radios in the 1960s, the conventional clock radio vanished. This niche was inherited by the low-profile bedside clock radio with a digital front panel. Initially, these bedside units had a mechanical flip-over set of numerals giving a digital read-out. By this time, Australian radio manufacturing had succumbed to cheaper, wellmade imports. A photo of a Japanese Copal flipclock radio (see Photo 7) is presented above to conclude this sketch of clock radios. It shows the next step in the SC evolution of this genre. February 2024  107 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au How to program Pico for Audio Analyser Two of my Raspberry Pi Picos won’t download the Pico Audio Analyser uf2 file (0410723A.uf2), whereas they can load up the Pico­ Mite firmware (Pico­ MiteV5.07.07. uf2), after which they boot up and the LED flashes. So the BOOTSEL button, USB cable and computer interface must be working. This is when not plugged into the other board and using the 5V USB supply (November 2023; siliconchip.au/ Article/16011). Does the Pi Pico have to be connected to a completed board with an OLED screen before booting up? (G. D., Larnook, NSW) ● If, after the 0410723A.uf2 file is copied to the Pico’s RPI-RP2 drive, that drive disappears, then something has correctly downloaded to the Pico as it is no longer running the bootloader (the bootloader provides the RPI-RP2 drive). A Pico programmed with 0410723A. uf2 will ‘boot up’ regardless of whether it is connected to an Analyser PCB. However, the program does not drive the Pico’s onboard LED, so there won’t be any immediate outward signs that it is working, apart from the RPI-RP2 drive disappearing. A Pico programmed with 0410723A. uf2 provides a virtual USB-serial port, and you should be able to see that new device in your computer’s device list. Most modern operating systems don’t need special drivers for the port, so you shouldn’t need to use driver programs like Zadig. If you have a serial terminal program, you can open that port and type a question mark followed by Enter; you should see something like that shown in Screen 14 on page 45 of the November 2023 issue. You shouldn’t need to do anything with the other files to get a working Analyser. We suspect the Pico is programming correctly; you just don’t realise it because there are no obvious signs until the Pico is plugged into the completed PCB. Battery charger recommendation I am wondering if you have ever described a 12/24V mains-powered battery charger. Ideally, it could be switched between 12V and 24V volts, with MPPT charging regulation. Thank you in advance. (R. J., Kangaroo Flat, Vic) ● Our Multi-Stage Buck/Boost Charger (October 2022; siliconchip.au/ Article/15510) is quite versatile. The required power can be derived from a mains-derived source such as a 12V DC power brick, from a battery or solar system. It is based on the Buck/Boost LED Driver (June 2022; siliconchip.au/ Article/15340). We haven’t really published a more modern charger except for the 50A Battery Charger Controller (November 2016; siliconchip.au/Article/10413). That design uses a basic, low-cost mains-powered battery charger from automotive parts suppliers and adds improved charging controls to it. MPPT (maximum power point tracking) only applies when a solar panel is used as the power source. In this case, the solar panel is used in a manner that provides the maximum power output. Typically, for a 12V solar panel, the maximum power is available when the panel produces 18V at full sun. MPPT is not applicable for a mains-powered charger. Migrating assembly code to MPLAB X IDE I have MPLAB X IPE and IDE v5.40 installed. Previously, I was only using the IPE to program PICs. I got a bit more adventurous and decided to learn how to edit an ASM file and build it into a HEX file using the MPLAB X IDE. It seems to be a more difficult process than the old MPLAB IDE v8.20 I used previously. I have installed all of the XC compilers. Can you provide an example of, say, editing a line of code in John 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. 108 Silicon Chip Australia's electronics magazine siliconchip.com.au Clarke’s Thermocouple project in the November 2023 issue (siliconchip. au/Article/16013) and then the steps to compile it into a HEX file? Thanks for your help. (G. C., Toormina, NSW) ● It is not easy to learn how to use MPLAB X IDE with assembly code compared to the original MPLAB IDE. Switching is much easier if you are programming in C than in assembly language, as there are fewer differences. The syntax for assembly code has changed significantly, so you will find that if assembly code written using MPLAB IDE is loaded into MPLAB X IDE, many errors will occur when attempting to assemble it. Assembly is done using the Clean and Build Main Project icon. The Secure Remote Mains Switch (July & August 2022; siliconchip.au/ Series/383) and the Secure Remote Mains Switch (December 2023 issue; siliconchip.au/Series/408) were written in assembly language using MPLAB X IDE. We suggest you look at our example code for one of those projects. If you have questions after that, don’t hesitate to ask. Programming the chip is done using the Make and Program Device button. Once you’ve assembled your code, the hex file will be inside the project directory under the dist\default\production subdirectory within the project directory. BackPack V3 using a four-inch touchscreen I’m thinking of ordering one of your Micromite LCD BackPack V3 kits (siliconchip.au/Shop/20/5082) and replacing the touchscreen with a larger 4in LCD touchscreen like the one I found on eBay (www.ebay.com. au/itm/186133228336). I’m not sure if the software needs to change or if it would just be a direct swap. It uses an ILI9488 chip, the same as the 3.5in screen you used, has the exactly same 14-pin port and the same 480x320 pixel resolution. Do you have any knowledge about this LCD touchscreen? Your help is much appreciated. (P. C., Eastwood, NSW) ● That’s an interesting find. The eBay listing you provided doesn’t show any pin mappings (there are no photos of the back of the module). However, other listings with matching descriptions and photos do. On those other listings, it looks like the back of the PCB is almost identical (in terms of traces and component locations) to the 3.5in display around the 14-pin header. Obviously, it is larger and thus has more widely spaced mounting holes. Even the SD card socket appears to be in the same place, set back from the edge of the larger 4.0in display but flush against the edge of the smaller display boards. It’s as though they’ve just expanded the PCB to fit the LCD! We are pretty confident that this display will work without changes to the software, as long as the pin designations match those of the 3.5in LCDs we used. The mounting holes will probably be different. Also, the SD card socket holes probably won’t line up, so we don’t think the Micromite’s SD card interface will work with this panel. Temperature sensor for Temperature Switch I am interested in building the 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 February 2024  109 Temperature Switch (June 2018 issue; siliconchip.au/Article/11101), which seems to be based on the Versatile Temperature Switch (January 2017 issue; siliconchip.au/Article/2109). Can I use the Jaycar RN3440 10kW epoxy-dipped NTC thermistor for switching at around 50°C? (R. M., Melville, WA) ● Most 10kW NTC thermistors are suitable for use with the Temperature Switch. You just need to calibrate it for the switch point of 50°C. The temperature versus resistance of thermistors can differ, so the actual threshold will change when a different thermistor is used. However, there is sufficient adjustment available to set the temperature threshold accurately. What amp to use with a 66V CT transformer I’ve dug out a transformer from the back of a cupboard. I bought it some time ago for a now-abandoned project. It is a 300VA toroidal type, 66V centre-tapped, which should provide about ±46V DC rails. I want to use it for an audio amplifier, most likely an instrument amp. For comparison, I use an ETI 300W as a bass guitar amp with ±68V DC rails. My thought is for the PSU to power a stereo set-up that could be bridged for mono. A two-channel guitar amp would be great for stereo effects (or music), or BTL for a higher-power single speaker. I looked at the amplifiers Silicon Chip published recently over the weekend, noting the supply rail voltages. I also considered some hybrid ICs, like the STK range, although they may offer lower-quality sound. What do you suggest? An amplifier (or pair of amps) nominally needing >46V rails is fine, even if that means less than their full potential output, as long as the sound quality is still good and there are no other significant problems. (J. C., Auckland, NZ) ● Most of our recent amplifiers are designed for a supply of around ±57V DC, as that is a pretty good compromise for 4-8W loads, making your ±46V DC a little low. However, the SC200, Ultra-LD Mk.3/ Mk.4 and CLASSiC-D amplifiers could be used with slightly lower supply rails and still provide more power in bridge mode. No changes should be required to the circuit. In fact, your transformer and supply rail voltages should work well with 4W loads for those amplifiers, increasing efficiency and reducing dissipation compared to the original ±57V DC rails. Troubleshooting thermocouple adaptor in DIY reflow oven There is still an odd deviation in the temperature calibration settings of the DIY Reflow Oven I built (April & May 2020; siliconchip.au/Series/343). I am certain that my purple thermocouple amplifier is the right board, with an output voltage of 1.35V DC (1.25V on pin 2 of the AD8495 IC). The Vcc voltage to this board is just 3.41V DC. If I set the value to 0°C like in your article, I get the wrong ambient temperature reading of around 225°C instead of 21°C while keeping the value for tempco at the suggested 0.161. Please give some pointers as to what you based the tempco of 0.161 on and why my setting only works with a -237 offset. I also checked the output voltage of the thermocouple board with a pack of ice from my freezer at around -12°C, which gave an output voltage of 1.17V. Finally, why does “Zzzz” appear on the LCD temperature screen? (A. B., Weert, The Netherlands) ● The designer, Phil Prosser, responds: The firmware is very simple regarding how it treats the thermocouple input. It reads the DC voltage, adds the offset, then multiplies by the tempco. I note that you stated there is 1.25V on pin 2 of the AD8495 IC. The article warns that some of the boards from eBay, AliExpress etc come with the wrong reference voltage. You need to short pin 2 to ground, which is conveniently pin 3. That can be done with a dab of solder. I am confident that is your problem. The “Zzzz” is the microcontroller putting the oven into sleep mode as nothing has been done for several minutes. This turns the soak temperature down, so if you leave the oven unattended, it does not run flat out forever. The micro wakes up if you press a button or alter the set temperature. So that is normal. 110 Silicon Chip Australia's electronics magazine You should still get the full 200W per channel into 4W, although not continuously in both channels with a 300VA transformer. The power delivery into 6W loads should also be good. For 8W loads, you should get close to 100W per channel. With two channels bridged, you can expect around 250300W into 8W (with 400W+ short-term ‘music power’). Unfortunately, ±46V is too high for the Hummingbird (December 2021), which is specified for ±30-40V DC rails. The relevant amplifier module articles are as follows: • SC200 Amp: January-March 2017 (siliconchip.au/Series/308) • Ultra-LD Mk.4: July-October 2015 (siliconchip.au/Series/289) • CLASSiC-D: November & December 2012 (siliconchip.au/Series/17) • Ultra-LD MK.3: July-September 2011 (siliconchip.au/Series/286) Identifying a Thermostat project Some time ago, I built a thermostat to switch on heaters in winter and fans in summer. After a recent move, the device did not arrive at my new address. I recently gave away my past copies of Silicon Chip. Is the thermostat still available as a kit, or can you send me a copy of the article? This is a luxury device. I can’t imagine life without it. (D. V., Kirwans Bridge, Vic) ● Unfortunately, you have not provided enough information to identify a specific project. That’s because we have published at least six thermostat designs over the years. They are: • K-Type Thermocouple Thermometer/Thermostat by John Clarke (November 2023 issue; siliconchip. au/Article/16013) • Tempmaster Thermostat Mk.3 by Jim Rowe (August 2014; siliconchip. au/Article/7959) • High-Temperature Thermometer/ Thermostat by John Clarke (May 2012; siliconchip.au/Article/674) • A Very Accurate Thermometer/Thermostat by Michael Dedman/ Altronics (March 2010; siliconchip. au/Article/91) • Tempmaster Electronic Thermostat Mk.2 by Jim Rowe (February 2009; siliconchip.au/Article/1337) • A Digital Thermometer/Thermostat by John Clarke (August 2002 issue; siliconchip.au/Article/4037) siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www. ldelectronics.com.au Your unit wouldn’t be the first one, as we only just published it. The following information should help you narrow it down. The August 2014 design fits in a small box with a GPO mounted on top, roughly the same size as the box. The February 2009 version also has a small GPO socket on top, although it is in a much larger box with a clear lid (and a mostly empty PCB visible inside). None of the other versions have direct mains switching. Of the remainder, the August 2002 and May 2012 versions were housed in slim instrument cases with LCD panel meters mounted on the front (on the left for the August 2002 version and right for May 2012). Both used thermocouples as temperature sensors. That leaves the March 2010 Altronics kit, housed in siliconchip.com.au FOR SALE 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 PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. Lazer Security For Quality That Counts... QUALITY COMPONENTS AT GREAT PRICES. Check out the latest deals this month. SMD parts and more. Go to www.lazer.com.au Advertising in Market Centre Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre start at $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip. com.au and include your name, address & credit card details, or phone (02) 9939 3295. a Jiffy box with an alphanumeric LCD in the middle of the lid. Component values for Headphone Amplifier I need clarification on how to configure my Studio Series Headphone Amp (November 2005; siliconchip. au/Article/3231). I want it as versatile as possible, so I have wired in a four-way switch to switch diodes D2, D4, D8 & D10 so I can use 8W or 32W headphones. I am also going to wire in a dual 50kW log pot as a volume control. I want to be able to connect it to a CD player or a preamp. Please tell me what combination of R1, R2, R3, & C1 etc I should use and any other considerations for my configuration. I have mostly built the power supply Australia's electronics magazine board from the October 2005 issue and have heatsinks ready to fit on the regulators. I am also wondering whether the 100W and 330W 5W input current limiting resistors are required for this headphone amplifier, or are they only required for the preamp? (N. G., Blue Haven, NSW) ● To avoid high sound volumes, R3 and R6 should be 2kW for use with a directly connected CD player and 0W when connected to the preamplifier. The amplifier gain for the 8W headphones should be set with the standard values: R1 & R4 = 1kW, R2 & R5 = 1kW and C1 & C2 =1.2nF. For 32W headphones, the resulting volume may not be sufficient, so the gain can be increased. Amplifier gain can be increased to 7.2 times (17dB) to allow the full rated output power to February 2024  111 Advertising Index Altronics.................................39-42 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Jaycar....................IFC, 9, 13, 26-27 ..................................58-59, 93, 101 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 PCBWay....................................... 11 PMD Way................................... 111 Quest Semiconductors................. 8 SC GPS Analog Clock............... 109 SC Ideal Bridge Rectifiers........... 92 Silicon Chip 500W Amplifier..... 67 Silicon Chip Binders.................. 91 Silicon Chip Shop............ 102-103 The Loudspeaker Kit.com.......... 12 TME............................................. 10 Wagner Electronics..................... 99 be realised in all cases with a 1V RMS input signal. To increase the gain, use the following component values in place of those shown on the circuit and overlay diagrams: R1 & R4 = 7.5kW, R2 & R5 = 1.2kW and C1 & C2 = 100pF. If you are not using the 5V regulator, the 100W 5W resistor is not required. You probably don’t need the 330W 5W resistor that bleeds the negative supply, as this is to counterbalance the positive supply being discharged due to the load from the 5V supply. Since the 5V supply is unused when powering just the headphone amplifier board, the negative supply would be discharged faster with the 330W resistor, so it’s best to leave it off. E30 transformer for Electric Fence Driver I am building the High-Powered Electric Fence Controller design by John Clarke (April 1999; siliconchip. au/Article/4577). One of the parts is an E30 Transformer Assembly, which 112 Silicon Chip I cannot locate anywhere. I have tried major electronic components suppliers, who all say they have never heard of it. The information in the plans is not really descriptive of the voltage in and out of either transformer. Do you know where to find this transformer or any further information to help me find an alternative? (D. D., Portland, NSW) ● The E30-type transformer form factor is a standard created by EPCOS/ TDK some time ago; matching parts are still being made today. The E30 transformer bobbin is 35.4 × 35.4 × 20mm. However, the currently available parts differ slightly from those we specified in that project around 25 years ago. Instead of five pins on each side, there are seven. You may need to cut off the extra pins to fit into the PCB. RS Components (https://au.rs-­online.com) sells the cores and bobbin, but they require you to buy a minimum of 10. For this project, you will need two bobbins and four cores, so you will have eight bobbins and six cores spare. The EPCOS B66232B1114T001 bobbin is RS Stock No 125-3622, while the EPCOS B66319G0000X130 cores are RS Stock No 125-3657. The cores can be held in place with a cable tie, as shown in the article, since RS is out of stock of the clips (‘yokes’). If you particularly want to use the clips, you can get them from Mouser (Cat 871-B66232A2010X) or DigiKey (Cat 495-5379-ND). The input and output voltages are not specified for these since the transformer needs to be wound, and those voltages depend on how it is wound. The parts you buy are just the bobbin and cores, not a complete transformer with windings. Winding details are provided in the April 1999 article (siliconchip.au/Article/4577). Changing Darlington to IGBT in ignition system I realise some time has passed since you published the Programmable Ignition System (March-May 2007 issues; siliconchip.au/Series/56). Still, I believe my question should be simple to answer. I have looked at the circuit diagrams for the High-Energy Ignition System (November-December 2012), which uses an IGBT coil driver instead of the Darlington driver in the earlier design. Can I change the Programmable Australia's electronics magazine Ignition to use an IGBT coil driver by simply driving the High Energy Ignition circuit from output pin 9 of the PIC? That would eliminate the 1nF ceramic capacitor, 470W resistor and L2 and change the 10W resistor to 1kW. I have boards and most of the parts for six of these ignition units, and I thought it would be a better way to go. Does anything else need to be modified for this to work? (S. M., Leederville, WA) ● It is a simple question but not necessarily a simple answer. The IGBT coil driver may work in this case; however, we haven’t tested that change. Due to the programmable ignition advance and retard features, the microcontroller is more susceptible to electromagnetic interference (EMI), which can cause the ignition timing to become erratic if it is not managed correctly. To prevent this, there is a filter at the output of the Programmable Ignition before the coil driver. This comprises the 10W resistor and 1nF capacitor, plus inductor L2 and the 470W series resistor. The filter reduces EMI entering the Programmable Ignition microcontroller. Consequently, you should not remove those components; only the 470W resistor should be changed to 1kW to drive the IGBT. Another problem when using the IGBT is that the gate connection of the IGBT to the Programmable Ignition is at a considerable distance. That can cause the IGBT to fail due to oscillations when firing the coil or gate damage from high induced voltage. That’s due to the inductance of the wiring forming a resonant circuit with the IGBT gate capacitance. It is worth giving the IGBT coil driver a go as it reduces the number of parts in the coil driver to a minimum. However, if it doesn’t work well, you may need to revert to using the original coil driver with the Darlington. A shielded cable will be required between the Programmable ignition output and the IGBT gate to reduce voltage spikes at the gate. The shield should be connected to the IGBT emitter. SC Next Issue: the March 2024 issue is due on sale in newsagents by Monday, February 26th. Expect postal delivery of subscription copies in Australia between February 23rd and March 15th. siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! Ex GST RIGOL DS-1000E Series RIGOL DS-1000Z/E - FREE OPTIONS RIGOL MSO-5000 Series 450MHz & 100MHz, 2 Ch 41GS/s Real Time Sampling 4USB Device, USB Host & PictBridge 450MHz to 100MHz, 4 Ch; 200MHz, 2CH 41GS/s Real Time Sampling 424Mpts Standard Memory Depth 470MHz to 350MHz, 2 Ch & 4Ch 48GS/s Real Time Sampling 4Up to 200Mpts Memory Depth FROM $ 429 FROM $ ex GST 649 FROM $ ex GST 1,569 ex GST Multimeters Function/Arbitrary Function Generators New Product! 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