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JANUARY 2024 ISSN 1030-2662 01 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST Raspberry Pi Clock Radio A digital clock and Bluetooth media player in one USB to PS/2 Keyboard Adaptors Home Automation without the cloud Keep your electronics operating with our wide range of replacement Power Supplies Don't pay 2-3 times as much for similar brand name models when you don't have to. Bring in your device and we'll help you find the right power supply for your needs. 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Explore our full range of replacement power supplies, in stock at over 115 stores and 134 resellers or on our website. jaycar.com.au/replacementpsu 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.01 January 2024 14 Smart Home Automation Home automation can be very convenient, but it does come with major security and privacy concerns. We detail many of the home automation systems that are currently available and whether they will work without third-party ‘cloud’ services over the internet. By Dr David Maddison Internet of Things (‘IoT’) Raspberry Pi Clock Radio 44 WiFi Relay Modules We take a look at two relay modules based on the ESP-01, one from Jaycar (XC3804) and the other from Altronics (Z6427). Both can be remotely controlled over WiFi. By Tim Blythman Using electronic modules 64 4-digit, 14-segment LED Module Instead of the common seven segments per character, this LED module has 14 segments per character, letting it display a greater range of letters, numbers and symbols. By Jim Rowe Using electronic modules Page 28 USB to PS/2 Keyboard Adaptor 92 Restoring the Vintage QUAD 303 The Quad 303 amplifier and Quad 33 preamplifier from 1967 were a ‘treat’ to refurbish and compare well to other valve amplifiers from the same period. The design is similar to a modern ‘blameless’ amplifier. By Jim Greig Vintage hifi system 28 Raspberry Pi Clock Radio, Pt1 A modern alarm clock can take the trouble out of alarm setting and time keeping. This clock runs off most of the common models of Raspberry Pi (3, 4, Zero 2W etc) and can act as a Bluetooth media player. By Stefan Keller-Tuberg Clock/media player project 52 USB to PS/2 Keyboard Adaptors Although USB keyboards are plentiful, there are still devices that only have a PS/2 connector. This project makes it simple to connect a USB keyboard (and mouse!) to devices with a PS/2 connector, like the VGA PicoMite. By Tim Blythman Computer add-on project 68 Secure Remote Switch, Pt2 The Secure Remote Switch is designed to control low-voltage appliances such as a garage door controller. In this second and final part, we show you how to build and use it. By John Clarke Remote control/security project 74 Multi-Channel Volume Control, Pt2 Control the volume of up to 20 channels using this Volume Control. All that’s left to cover is construction and getting it running. By Tim Blythman Audio project Page 52 2 Editorial Viewpoint 4 Mailbag 41 Circuit Notebook 84 Serviceman’s Log 90 Online Shop 99 Subscriptions 1. ePaper clock and calendar 2. Semiconductor curve tracer 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata Ordering made easy Tools to search, check stock and purchase au.mouser.com/servicesandtools 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”. Configuring motors for different speeds Regarding the enquiry about the GMF Cadet two-speed electric motor by B. P. from Dundathu on page 101 of the December 2023 issue, I do not have specific information on that particular motor. However, I am using a two-speed single-phase motor, and the following information on it may be helpful. The inbuilt centrifugal start switch is more complicated than a standard single-speed start switch. It has two contacts that are normally-closed when stationary, and one normally-­open contact. The motor always starts in high-speed mode using the four-pole windings. For high-speed operation, the motor starts, and at about 70% of synchronous speed, the centrifugal switch opens the four-pole start winding. The rotor then continues to run up to its four-pole speed. For low-speed use, the motor accelerates to about 70% of its four-pole speed, then the centrifugal switch disconnects both four-pole windings and energises the six-pole winding. The motor then settles to its six-pole speed. Once running, the motor can be switched between speeds without stopping. In the accompanying figures, red indicates wires from the windings to the terminal strip, which is usually part of the switch mechanism. Different manufacturers have different termination layouts and numbering/identification/ colour methods for the various terminals and connections – the owner will have to verify this. I have shown the connections for a non-reversible motor on the left. There are typically only four wires from the stator. If the motor is reversible, both ends of the start winding will be available, as shown on the right, meaning that five wires come from the stator winding. Reverse rotation is achieved by swapping the two start winding wires on the common terminal and the centrifugal switch connection. It will then run in reverse at both speeds. I hope this helps. Ashley Smith, Flagstaff Hill, SA. long boozy lunches (this was the 1980s, remember) while seeing who could eat the most spicy curry. Professionally, it was an excellent lesson in the economics of magazine publishing. If I remember the numbers, in the decade between 1975 and 1985, the circulation of the two electronics magazines, Electronics Australia and ETI, halved from about 120,000 to about 60,000 copies, then halved again as the decade wore on. There were good practical reasons for that. Staple kit products such as hifi amplifiers were replaced by mass-­ produced shop-bought products that sold for half the price. We produced some kit computers, but once again, they were obsolete within a few years. People who might once have built computers got more fun out of programming them. Advertising was also a problem. Electronics hobby stores faced the same declining revenue base as the magazines. They were making less money and so were advertising less. I remember that, editorially, we twisted and turned, looking for a formula that would bring readers back. We never found it at ETI or Electronics Australia, but obviously, a new generation of magazine people has discovered the same passion we once had. Silicon Chip is not ETI, but I recognise the pedigree. Jonathon Fairall, Journalist and Author, Sydney, NSW. AI sometimes gets things wrong I am designing my own energy meter with sensing hardware based on the Silicon Chip Touchscreen Appliance Energy Meter published in August 2016 (siliconchip.au/ Series/302). The description of the measurement process indicates that true and apparent power are both calculated from the voltage and current measurement recordings. This concept was new to me, as I was of the understanding that one needs to know the power factor (PF, or phase angle difference) to derive true power. Investigation of the source code confirmed that there is no phase angle detection Comments on ETI Magazine by ex-editor I came across your June 2023 issue in my favourite electronics store and was amazed to see Peter Inhat’s article on the History of ETI Magazine. What a blast from the past! It was my first editing job and, like Peter, I remember those times with a great deal of affection. We worked big hours and were often in the office until late at night. I can never drive past the Agincourt Hotel without remembering the Sri Lanka Room, where we used to have 4 Silicon Chip 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! www.blackmagicdesign.com/au Learn More! in the software; the PF is derived directly from the ratio between true and apparent power. To aid in designing my firmware, I turned to ChatGPT and posed several questions on this subject. After a few replies, I finally asked this question: “Without knowing the power factor, and with a power factor other than 1, can I calculate true power from the voltage and current curves?” It solicited the following reply: If you don’t know the power factor, and it’s not equal to 1 (indicating a purely resistive load), you cannot directly calculate the true power from just the voltage and current curves. ChatGPT is telling me that the Energy Meter design is simply impossible. It appears to me that, whilst ChatGPT can pass the US bar exam and perform various other tricks, when it comes to matters of electronic and software design, it is a long way behind the brain power of Jim Rowe and Nicholas Vinen, who designed the Energy Meter published in Silicon Chip. Could the authors of the original article elaborate on the theory behind the implementation of the true/apparent power calculation? Thank you for an excellent magazine; keep up the great work. Erwin B, Wodonga, Vic. Comment: like a person, an AI can only draw on the knowledge it has experienced (or, in this case, been trained on). The current problem with AI and electronics is that AIs have only been trained with fairly basic electronics knowledge. Another problem with AIs (possibly the most significant problem at the moment) is that they are overly confident. Rather than answering a question with “I don’t know”, they will instead make things up to make it sound like they do know. That is why, even though an AI can be very helpful, you should always verify that its output is correct before using it. The phase angle difference for the power factor only works with sinusoidal voltages and currents because you can’t calculate the phase angle between two arbitrary (and probably different) waveforms. The load current will only be sinusoidal if it is purely reactive (restive, capacitive, inductive or some combination). That rules out anything with a bridge rectifier, for example. Also, the mains waveform is often far from sinusoidal, with significant distortion and clipped peaks. There is a simple method that works for any waveform shape. You take a series of voltage and current measurements to calculate the real power. At each point, you take the product of the two and keep a running total; negative results reduce the total, while positive results increase it. The signs should be such that in-phase voltages and currents increase the total. Ultimately, you divide by the number of samples (more samples will give greater accuracy). The resulting value is the real power consumption. For the apparent power (VA), you can calculate the RMS voltage and RMS current from the same readings, then multiply them. The power factor is then the real power (in watts) divided by the VA figure. Note that the real power calculation takes into account power flowing from the mains into the load and also power flowing out, which can happen in cases like a motor running down or a capacitor-rectifier-zener power supply during the part of the mains cycle where the capacitor is discharging. 6 Silicon Chip The real power could even be negative in cases like fast motor braking, with power returned to the grid! In contrast, if the calculations have been performed correctly, the VA figure is always positive and should always be the same as or greater than the real power. Using hot water as energy storage In the last round of electricity price rises, I noticed that the electricity for my controlled load (storage hot water service) had increased by 35%, while the general power rate had risen by around 20%. Some suppliers don’t even provide a controlled load rate. That indicates to me that the government is trying to get rid of these systems. In the recent past, the logic was that they had to replace these systems to reduce base load power consumption so they could close coal-fired power stations. This was particularly important for off-peak hot water, where the power was controlled by a time switch in the meter box, which switched on the power at night when there was excess power from the generators. The rate was quite cheap, to encourage the installation of these systems. In later years, this has been replaced by a “controlled load” rate, where the power can be switched on by a signal sent over the mains at any time, day or night, by the provider. I thought this controlled load could be used to switch on the power to hot water systems at any time, particularly when there is excess power coming from solar panels and wind turbines. That is, in effect, an energy storage system to store excess energy from renewable sources. Surely, that would be preferable to sending the power to a battery or pumped hydro and then to my hot water service later. I wrote to the previous energy minister about this, and he replied that he thought it was a good idea and that an energy company was having a trial using people with smart meters installed. I wondered why they had to have smart meters instead of just using the existing controlled load system. I concluded that the energy companies probably could see no benefit to them in this change and thus were not keen on pursuing the idea. I have noticed the government is pushing heat pump HWS to replace existing storage tanks, with heavily subsidised ($99) units available. The problem is that they do not last all that long and are costly to replace. They are also being pushed in the UK, where they have performed poorly when the outdoor temperature is low. We all use hot water, and I would have thought that if these systems were encouraged rather than discouraged, they would provide substantial energy storage and save on expensive batteries and pumped hydro. In any case, I was contemplating a workaround for the high power charge and thought of connecting my storage HWS directly to solar panels. There are plenty of cheap second-hand panels available now. I realise it would need a different thermostat and a DC relay. I have noticed that these things are available in the USA as a plugin replacement, as solar panels heating water are readily available there. Still, I haven’t seen much information in Australia. I spoke to a few people about this, including an installer, who have the same idea. Brian Day, Mount Hunter, NSW. Comment: your idea about off-peak hot water systems being an energy storage system for solar/wind power is Australia's electronics magazine siliconchip.com.au good. Logically, off-peak systems should be encouraged and operated at the required times to take advantage of excess power. Commercial solar power diverters are probably the best option to use excess solar power to boost your hot water system. For example, see www.powerdiverter.com The DIY version has some non-obvious pitfalls, and we have discussed it several times in the past, eg, in the Mailbag column, December 2017 (pp4-5) and April 2016 (pp12). For example, applying DC to a water heating element will cause electrolytic corrosion, so it would be necessary to reverse the polarity periodically. It would work best with water heaters with a second ‘booster’ element. Explanation for flashing mains LED lights Regarding Keith Bennett’s letter on page 10 of the December issue, perhaps you are over-thinking it. The age of the wire in installations, especially with CFLs, does not seem to matter. What is more likely (and I have measured it) is that by having a long run of parallel wire, you have the powered one inducing current into the one parallel with it by mutual capacitance. With a CFL or similar device, because the switch is single-pole, the induced voltage climbs, and you have a relaxation oscillator. That does not happen with incandescent lamps, as they present a resistive load. A lot of CFLs will fire at around 30V. On one circuit (open) with a DVM, I measured 145V AC. Marcus Chick, Wangaratta, Vic. Glowing LED lamps can be a benefit I thought I would mention our situation after reading Keith Bennett’s letter on glowing LED lights. When our house was built in 1994, we had two hallway lights with three switches wired so you could turn the lights on or off with any switch. We had neon indicators in series with 100kW resistors wired across each switch to show where the light switches are at night. Back then, we had incandescent globes, and everything worked as planned, Times changed and so did light globes. When LED globes came out, we fitted 5W globes in the hallway, and we found that they glowed faintly at night. Rather than seeing this as a problem, we found it very useful in providing a light level similar to a full moon. This allows walking through the hallway on the darkest night without needing to turn on the lights. Our back door has a light above it on the verandah with two-way switching. Once again, these two switches have the neon indicator and 100kW resistor across the switch, which had the same effect on the outside light. This is a real bonus because it dimly lights the verandah area near the back door. I have found that not all LED lights glow in these situations, so I have selected globes that do glow to provide the benefits mentioned above. It’s somewhat surprising that the small current drawn by two or three neon indicators will make some brands and wattage LED globes glow. Bruce Pierson, Dundathu, Qld. Reminiscing about colour measurement Many thanks for the article on colour measurement (Linshang LS172 Colorimeter review, October 2023 issue; siliconchip.au/Article/15972). 8 Silicon Chip Australia's electronics magazine siliconchip.com.au BEST COMPATIBILITY WITH SHIELDS, SENSORS & MODULES BEST SELLER BREADBOARD FRIENDLY FOR EASY PROTOTYPING ARDUINO® COMPATIBLE NANO ONLY ARDUINO® COMPATIBLE UNO XC4414 OUR MOST POPULAR DEVELOPMENT BOARD. 45 $ COMPACT DESIGN WITH SIMILAR FEATURES TO THE UNO 95 FROM 3895 $ XC4410/11 FOR MORE ADVANCED PROJECTS THAT REQUIRE MORE I/O & PWM PINS EMULATE A USB KEYBOARD, MOUSE, JOYSTICK, ETC. 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Shop at Jaycar for: • Arduino® Compatible Development Boards • Great Value Starter Kits • Wide range of Shields, Modules, and Sensors • Great range of Breadboards and Prototyping Accessories Explore our great range of Arduino® compatible products, in stock on our website, or at over 115 stores or 134 resellers nationwide. jaycar.com.au/devboards 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. It took me back to the days when I implemented threedye fully decoupled colour control on several paper machines in Tasmania in the early-to-mid 1980s. From what I understand, it was probably the first continuously operating implementation of paper machine colour control globally, running 24 hours a day, seven days a week, 365 days a year. I worked for a Silicon Valley company (Measurex Inc) that specialised in the measurement and control of various quality parameters for paper manufacturing. Through fortuitous timing, Measurex had developed a colour sensor (in fact, a colour spectrophotometer) for paper machine applications. At the same time, Australian Newsprint Mills (ANM), through their research & technical department, had developed the means to manipulate the colour of manufactured paper in the 3D colour space using three dyes. The project’s primary objective was to produce “Yellow Pages” paper such that there was no quality difference between the printed entries in a bound volume. One might remember that the edge of the Yellow Pages bound book sometimes showed a huge array of yellows. For competing businesses, the inconsistent paper colour could make entries on opposing pages look very different, causing discontent. At the time, the standard laboratory instrument was a HunterLab D25 Tristimulus Colorimeter, which was used for the ANM three-dye colour-control trial. Paper samples were taken at regular intervals, manually checked and the dye delivery pump settings were altered to correct any colour errors. A Hewlett Packard model 9830 desktop ‘calculator’ was used to perform the necessary computations. Hats off to the research team and their dedication to the development and the trial. If memory serves me correctly, the trial ran for 24 hours in very hot and humid conditions. My job was to implement the software within the Measurex “Quality Control System” that would integrate the colour sensor readings and automatically make adjustments to the dye pumps every 30 seconds. Standard control algorithms that Measurex had developed for the paper process were used. Fundamental to this was the “gain matrix” provided by the research team. It was a huge leap for all the uninitiated to come to terms with colour measurement and control. The Measurex Colour Sensor was a 45° illumination/normal observation device that held the moving sheet of paper against a backing mechanism. This differed from the HunterLab D25, which used diffuse lighting and an ‘infinite pad’ measurement. Never the measurement twain shall meet! We seemed to quite quickly come to terms with the names of Kulbelka-Munk and Eugene Allen, as well as other terms such as metamerism etc. The Measurex Colour Sensor used a holographic diffraction grating to focus the reflected light spectrum onto a 32-element photodiode array at 10-nanometre wavelength centres from 385nm to 705nm. The sensor was ‘smart’ (with an Intel 8088 CPU) and communicated with the host via a duplex serial link using current loops. Sheet (object) illumination was by a combination of quartz-halogen and mercury lamp sources, each with engineered filters to achieve optimal light quality. 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Jaycar reserves the right to change prices if and when required. The sensor dissipated 75W, which in a hot and humid paper machine environment necessitated water cooling, temperature control and purges of dry compressed air to clean the optics. Dry nitrogen gas was used to prevent corrosion within the electronics (edge connectors, multiple 250MW resistors etc). Accuracy and repeatability were typically significant challenges for colorimeters – even more so for a spectrophotometer. The beauty of a ‘smart’ sensor and its backing mechanism was that standards could be rotated into place every 20 minutes to measure and then compensate for dirt, electronic and thermal drift. As neither the light source nor the sensor was perfect (as compared to the “Northern Sky”), multiple standards were used to apply correction factors (all arrays of 32 elements) for a reliable and workable solution. In the mid-1980s, a novel way of measuring and controlling the addition of optical brighteners (fluorescent whitening additives or FWAs) was implemented. FWAs were getting into the feedstock via an uncontrolled recycled product stream and size press upsets. These required responses outside the dye addition process. The mercury lamp could be strobed at 20Hz to measure the effect of ultraviolet illuminant induced fluorescence within the visible spectrum. This allowed the computation of two sets of measurements: CIE (D65) Fluorescence Corrected L*, a* & b* and Fluorescence Suppressed L*, a* & b*. A Fluorescence Index was calculated from the ratio of these two measurements, which allowed decoupling at the measurement input to the controls. Fluorescence Suppressed L*, a* & b* values were used to control the addition of three dyes using the fully decoupled 3×3 strategy. At the same time, the Fluorescence Index operated as a single-loop controller regulating the addition of FWAs at the size press. Other Observations The Delta E (RMS Error) method of colour matching seemed to disappear as soon as reliable, high-accuracy process measurements went online. Colour measurement (and control) gets much easier the darker the measured object is (smaller L* values). Nearwhite shades are the most difficult to control, as adding any dye (or pigment) lowers the L* value. There is no “negative L* dye” to increase the feedstock L*. The whiter the feedstock, the more expensive it is. < Electronic & Mechanical Design > PCBWAY’s 6th Project Design Contest Up to $6000 in cash prizes! Participate and get a free Raspberry Pi Pico! Enter by the 15th of January 2024 WWW.PCBWAY.COM/ACTIVITY/6TH-PROJECT-DESIGN-CONTEST.HTML 12 Silicon Chip Fortunately, substrate compensation (or even preprinting in white) is available for most types of offset and photographic printing. The Measurex colour sensor had a measurement dynamic range of 200%. This proved very useful when some dyes were discovered to be ‘reflecting’ more than 100% in the red-yellow region. The dye was blue/violet light fluorescent. I’m unsure if this is still the case, but reliable long-life fluorescent standards were not available then. The Elrepho 2000 soon became the testing standard, displacing the much-loved HunterLab D25 because of its CIE D65 measurement credentials. That is probably because many dye manufacturers used it for dye characterisation, but I’m sure it too has been superseded by now. As is common these days, web searches for “Measurex” and “HunterLab” lead to many other vendors. Finally, I would like to acknowledge the excellent optical physicists and software engineers responsible for developing the Measurex Colour Sensor (Model 2250). We received excellent technical support from the factory, as well as ‘first line’ technical support from the dedicated Measurex field service technicians in Tasmania. One has to admire all parties that were prepared to embrace the risks and see the project through to success. Mark Schijf, Doncaster East, Vic. Not too many historical articles, please Firstly, thanks and praise for producing an interesting magazine every month! Are you interested if readers produce software for, say, the Raspberry Pi Pico LCD BackPack (March 2022 issue; siliconchip.au/Article/15236)? A little feedback: personally, I find historical articles interesting for the occasional segment, but please, it’s not a history magazine! The slogan used to be “Australia’s dynamic electronic magazine” or similar. How about some “Future of” articles? Stuart Oliver, Sydney, NSW. Comment: By all means, if you come up with interesting or useful software for one of the BackPacks, send it in. We might run it in Circuit Notebook. We are conscious of the need to balance historical, current and forward-looking articles. For example, see the Editorial in the October 2020 issue, which was on this very topic (siliconchip.au/Article/14593). If you look at the magazine over the last couple of years, you will find plenty of articles on current/future technologies like IC fabrication, heat pipes, the James Webb Space Telescope, computer memory, new aviation technology, Starlink, EV charging, HAPS, Home Automation (in this very issue) and many more. We decided to run the series on the History of Electronics when we realised that, despite being published for over 35 years, Silicon Chip had not yet gone into any great detail about how the field of electronics came about, despite that being the very topic of the magazine! It was a story that deserved to be told. Now that the series has finished, we’ll follow with different topics. The problem with articles about future technologies is that so many are overhyped pie-in-the-sky concepts that will likely never eventuate. That and, as Yogi Berra once said, “It is difficult to make predictions, especially about the future.” SC Australia's electronics magazine siliconchip.com.au PCBWay PCBWay is a fully-featured PCB production service. We have turnarounds as quick as 24 hours, with real-time tracking of your orders. New customers get a $5.00 credit to go towards their first order! 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We offer a Design Service using our team of professionals to produce your own custom PCB, software, 3D enclosures and more: www.pcbway.com/design-services.html Start manufacturing with www.pcbway.com Home Automation without the cloud by Dr David Maddison Home automation can bring significant benefits and convenience, but it comes with major concerns over security and privacy. Regardless of whether you own your home, you should control it, not someone else. So it’s vital when setting up a ‘smart home’ to do your homework and choose a secure solution that will work in the long term. H ome automation allows lights, heating, cooling and various appliances to be operated by a central controller or hub. These may operate according to a pre-programmed schedule, using sensors (eg, to detect the presence or absence of a person in a room), by voice control or remote control, such as with a smartphone. For example, you can turn on a heater or an air conditioner before you get home so the house is comfortable when you arrive. That sounds great, but many home automation products are ‘cloudbased’, and there is some truth to the saying that “the cloud is just someone else’s computer”. Most home automation jobs can be performed entirely within your home and without using proprietary, closed solutions with unknown security. The “Internet of Things” (IoT) and home automation are closely related. IoT devices connect directly to the internet, while home automation devices usually communicate with each other and can be part of a closed system if no internet access is enabled. However, some devices like voice assistants, Ring cameras and video doorbells are IoT devices that can also be part of home automation systems. Home automation can also be used in mobile homes or caravans. Fig.1 shows a screen from a Home Assistant in a caravan. A little history The history of home automation goes back much further than many would think. Any domestic labour-saving device could be considered home automation. We might not think of the following as home automation because they are ubiquitous, but examples include washing machines, dishwashers, water heaters, sewing machines, motorised lawnmowers, clothes dryers and Fig.1: Home Assistant set up in a caravan. Source: ArsTechnica – siliconchip.au/link/ abqz 14 Silicon Chip Australia's electronics magazine siliconchip.com.au electric irons. They all save a tremendous amount of labour compared to earlier methods. The modern twist is that computerisation makes it easy to change programming without, for example, changing an electromechanical timer in a switchboard. You can even control many appliances now from a smartphone or similar device; sometimes via the internet, when not at home. Devices can also be made responsive to the environment, such as switching on an irrigation system when conditions are dry, turning on interior lighting at night when someone enters the room and automatically turning lights off when they leave. Some home automation products available today are shown in the panel on the right. Two main approaches There are two main approaches to central control. One is via a third-party cloud-based system such as Google Home, Amazon Alexa or Apple Homekit over the internet. The other is a system that uses control hardware located within the home, with or without an optional connection to the internet. One concern about cloud control is the possibility of losing control of your own home, as you are at the mercy of the company that operates the service. For example, in the United States recently, a delivery driver misheard a ‘smart’ doorbell greeting and complained to the company, which consequently shut the owner out of the home’s smart system for a week while the mess was sorted out. You can read about that in the NY Post article at siliconchip.au/link/abq5 Another concern is that the provider could go out of business and shut down the cloud services. Many cloud-controlled devices are propriety and locked to the specific company, meaning that the devices (which can cost thousands of dollars in total) become useless. That happened with Insteon products (www.insteon.com). Cloud services became unavailable, although local control of devices was still possible in that case. Fortunately, the company was purchased by a group of “passionate users” who reactivated the cloud services. Also, Home Assistant integration was developed for Insteon products, ensuring they could still be used regardless (see www.home-assistant. siliconchip.com.au io/integrations/insteon/). We will discuss Home Assistant later. A further example is Philips Hue light globes, which started as locally controllable, but after purchase, the terms were changed, making them cloud-dependent (see the panel for more details). Similarly, TP-Link made Smart Plugs that once worked without the cloud, but now require a cloud connection for their Tapo device (see www.tp-link.com/au/support/ faq/3417/#A11). Insteon users were lucky, but events such as the above mean it would be wise to retain full control over smart home devices. In this article, we will explore home automation options that don’t rely on a connection to ‘the cloud’, or at least where such a connection is optional. We will also give a brief overview of cloud-connected options, which might be required for certain services, such as voice control. There are also privacy problems with any cloud-based home automation; for example, see siliconchip.au/ link/abq6 Ideally, a smart home product should be directly controllable and usable without having to give your personal details to a third party or fees beyond the purchase price. Most should not even require an active internet connection, although it’s fine to have internet connectivity as an option, so you can make an informed choice about whether to use it. Communications protocols Home automation devices such as lighting systems and temperature sensors need to communicate with each other. All devices used will need to be compatible with your controller system. Most devices connect wirelessly, although some can be wired. Some smart devices can be controlled directly from a smartphone, tablet or laptop computer via their inbuilt protocols, such as Bluetooth or WiFi. However, to support a broader range of protocols like Thread, Zigbee, Z-Wave and LoRaWAN, a central controller, known as a hub (or server), is needed. We have an overview of various protocols used in home automation in the dedicated panel (on page 24). Controlled indoor items • Heating, ventilation and air conditioning • Air purifiers • Lighting • Motorised window blinds, curtains, shutters and external shades • Chain pullers for blinds • Curtain activators • Door openers • Domestic robots like vacuuming, sweeping and mopping systems • Pet feeders • Motorised button pushers • Smart TVs • Smart washing machines, dryers and dishwashers • Smart audio systems • Remotely switched power points and ‘smart plugs’ Indoor sensors and controls • • • • Occupancy sensing Temperature and humidity meters Voice control Internet control Home security devices • Indoor and outdoor cameras • Access control (smart locks), including garage doors • Fingerprint scanners and keypads • Door/window open/close sensors • Intercoms with cameras • Alarms (burglar, fire) and sirens • Detection of gas or water leaks • Smoke sensors Garden devices • • • • • • • • • Irrigation Automated greenhouse Robotic lawnmower Swimming pool control (heating, filtering, cleaning etc) Weather station Water control valve Rain gauge Soil condition sensor (moisture, nutrition, light and temperature) GPS tracker for pets “Integrations” An “integration” allows smart home Australia's electronics magazine January 2024  15 The Philips “Hue” light globe letdown Philips Hue light globes can have their on/off state, brightness and colour controlled via Bluetooth. One of their main attractions was that they did not require the creation of an account with Philips to use them. But now, their terms of service have changed, or soon will. Philips has told users who had purchased these lights hoping for accountfree (local) operation that they will need to have a Hue account to control their own lights; see https://twitter.com/tweethue/status/1704535648437256657 For further details, see www.androidpolice.com/the-philips-hue-app-­ require-log-in-account/ and the Louis Rossmann video titled “Philips changes terms AFTER the sale: requires data-sharing account to use a light bulb” at https://youtu.be/vR2j-r3pmng hardware or software from different organisations, companies or software suppliers to work together. An example is how the IKEA DIRIGERA smart hub provides integrations so that voice assistance and control by Amazon Alexa, Apple Home and Google Home work with the IKEA system. Another is that there are over 2500 integrations available for Home Assistant. If buying a device you wish to control via your home automation system, make sure it works with the system or has vendor or third-party integrations available. Systems that require an internet connection The following systems require a cloud connection but are mentioned here to give a more complete overview of home automation. Many local home automation systems like Home Assistant can have integrations for voice assistant products. Access to voice assistant products like Alexa, Google Assistant and Siri, plus IFTTT and Ring products, are among the reasons that internet access might be desirable for an otherwise offline home automation system. These are examples only; we can’t possibly cover every manufacturer or type of system. Amazon Smart Home and Thread, to ensure compatibility with a wide variety of devices. Many smart devices can be controlled without needing a hub; you just need your home WiFi, with an internet connection, and the app. Google Assistant https://assistant.google.com/ Google Assistant is an AI-based virtual voice assistant that can also perform home automation tasks or answer inquiries by voice command. It is used via the Google Nest (hub) smart speaker on Android, Chrome OS and iOS devices. Homekit www.apple.com/au/home-app/ Homekit is Apple’s home automation system. Some devices within the system require an active internet connection, but others may not. Siri can now work (with some restrictions) without an internet connection for iOS 15 and later with certain iPhones, as voice recognition is now done on the phone, not in the cloud. IFTTT (If This, Then That) https://ifttt.com/ IFTTT is an internet-based service that allows users to program conditional statements with “applets” (like programming macros) for a home automation system. The applets can be used to change the colour of a light at sunset, have a porch light turn on when you arrive home or synchronising an Amazon Alexa to-do list with Google Calendar etc – see https:// youtu.be/Y3u6rsXJas4 A huge number of applets are available, or you can make your own. Zapier (https://zapier.com/) and Microsoft Power Automate (siliconchip. au/link/abq8) are similar services for businesses. Ring https://ring.com/au/en Ring makes a variety of security cameras, doorbells and home automation devices. The devices require an active internet connection, plus a subscription to record video. Amazon Fig.2: the SmartThings Station hub and smartphone app. Source: Samsung – siliconchip.au/link/abqw www.amazon.com.au/b?ie=UTF8&node=5425665051 Amazon Smart Home comprises Alexa and Echo. Alexa is the artificial intelligence (AI) service, while Echo is the physical device, the hands-free speaker unit. It requires an active internet connection. There are many Alexa-compatible smart home devices, such as smart lighting, switches, thermostats, cameras (including Ring) etc. Google Home siliconchip.au/link/abq7 Google Home is based on Matter 16 Silicon Chip Fig.3: the structure of the cloud-dependent SmartThings automation system. Australia's electronics magazine siliconchip.com.au owns Ring; it has been the subject of controversy, as they were handing private videos over to police without warrants or owner consent. SmartThings of devices via Zigbee, Z-Wave Plus, Matter, Thread and WiFi. Aeotec also produces its own devices. www.smartthings.com/ SmartThings is a powerful home automation system based upon the SmartThings Station hub, shown in Fig.2 (which doubles as a wireless phone charger). It is Matter compatible, so it supports any device with the Matter logo. It also supports IFTTT style conditional automations. The Station does not support Z-Wave. An active internet connection is always required for SmartThings – see Fig.3. There is an Android and an iOS App to interact with it. A supported devices list is at www.smartthings. com/supported-devices Home automation systems that may work offline The following smart home systems can work without an active internet connection but may require an internet connection for initial setup or to update software. They could also require an optional internet connection to support voice assistant or other services. Our research shows that the most popular and well-supported offline home automation systems are Home Assistant and Hubitat. Readers should make up their own minds, but they are great starting places. No one wants to buy a smart device and discover that the company has gone out of business, and your device is no longer supported. That is much less likely to happen for open-source devices since others can easily take them over. Both Home Assistant and Hubitat are open-source. Note that not all home automation systems will support everything, but it is possible to connect two systems if one does not support particular devices. In fact, we have heard of Home Assistant and Hubitat being joined, to name one example (an integration exists for that). These are examples only; we can’t cover every manufacturer or type of system. There are simply too many. Aeotec https://aeotec.com/ Aeotec can work without the internet except for voice control via the app – see Fig.4. It supports a wide variety siliconchip.com.au Fig.4: the Aeotec Smart Home Hub and related devices. Aqara www.aqarastore.com.au Aqara uses Zigbee and will work without an internet connection as long as remote access, updates and thirdparty cloud services such as voice assistant aren’t used. A wide variety of products are offered. C-Bus A cautionary tale If you install a proprietary home automation system, you might end up having to pay a lot for a contractor to alter it in future, as the original installer may lock the code. I have a friend with a C-Bus system but the original installer is unknown, the system is passwordlocked and he would have to pay another installer a lot to reprogram the system to add to or alter it. Make sure any installer gives you the password if they use one. We can’t see any reason why it shouldn’t be written on a label on the system itself; if someone has access to the hardware, they can do whatever they want anyway. www.clipsal.com/products/c-bus C-Bus is an Australian-developed system for professional installation. Components must be connected to the main electrical distribution board, and expensive training courses are needed to become qualified for its installation and programming (see Fig.5). It is mainly used for luxury homes and commercial and industrial applications. It can operate without an internet connection, depending on the configuration and options. DIRIGERA siliconchip.au/link/abq9 DIRIGERA is a smart home hub from IKEA (Fig.6) that can operate without an internet connection. It supports a variety of IKEA smart home devices. DIRIGERA uses the Matter standard and supports Thread, WiFi & Zigbee wireless protocols. It has iOS and Android apps and supports integrations with Amazon Alexa, Apple Homekit and Google Home via the cloud. Domoticz Fig.5: an example C-Bus installation. Various “output units” are available, such as relay modules, analog outputs, current measurement units etc, all designed for a standard DIN rail. Source: Clipsal – siliconchip.au/ link/abqu www.domoticz.com/ Domoticz is a lightweight opensource home automation system that can interface with lights, switches, environmental sensors, electricity, gas & water meters and more. It can run on various hardware including the Raspberry Pi and integrates with MQTT and Apple Homekit. Once set up it does not need an internet connection (unless using specific integrations). Australia's electronics magazine Fig.6: the IKEA DIRIGERA smart hub. Source: IKEA – siliconchip.au/link/ abqv January 2024  17 Fhem https://fhem.de/ Fhem is an open-source system using Perl scripts that can run under Windows, macOS and Linux. It supports numerous protocols but seems to be for advanced users. Fibaro www.fibaro.com/en/ Fibaro is a Polish company making smart home devices (siliconchip.au/ link/abqa). The system uses Z-Wave and will work without an internet connection. Home Assistant www.home-assistant.io/ Fig.7: one of a large variety of Home Assistant dashboards, this one showing a floor plan. Source: Home Assistant – siliconchip.au/link/abr2 Home Assistant is a popular opensource home automation system for the enthusiast that can be run on a Raspberry Pi, under Windows, Linux or macOS, on an Odroid or ASUS Tinker Board single board computer (see Figs.7 & 8). Home Assistant supports a vast number of integrations, currently 2577 (see siliconchip.au/link/abqb). Note that depending on the platform chosen, you may need to purchase USB dongles or modules to support Zigbee, Z-Wave and Thread. There is a subscription fee payable if remote access is required. Home Assistant Green is a readyto-go product that comes with Home Assistant already installed, available from their website. The Yellow version has Zigbee and Thread built-in and is more extendable. See siliconchip.au/ link/abqc for setup instructions, and the video guide at https://youtu.be/ Y38qRYYAwAI HomeGenie https://homegenie.it/ Fig.8: another Home Assistant dashboard. Source: Home Assistant – siliconchip.au/link/abr3 YouTube videos with more information ● https://youtu.be/hAdDtbNMYPM – “How to Install Home Assistant on a PC (Easy!)” ● https://youtu.be/FXkkytHSTcI – “No Raspberry Pi For Home Assistant? No Problem!” ● https://youtu.be/cVWVr_T7kQ0 – Creating a weather dashboard with Node-RED ● https://youtu.be/_FktMQSD5LE – “Building my PERFECT Smart Home Control Panel!” ● https://youtu.be/cSzuWKsyuKI – Opinion: “The TRUTH About Home Assistant [Vs SmartThings]” ● https://youtu.be/3xMvjOig8J4 – Opinion: “SmartThings to Home Assistant: Joining the Dark Side” ● https://youtu.be/Q10nVFbP0ME – Opinion: “Hubitat vs Home Assistant – Best Smart Home Hub 2023” ● https://youtu.be/c5MF3MnMmJw – “Smart Home Automations 101 – The Ultimate Guide to Build Better Automations” 18 Silicon Chip Australia's electronics magazine HomeGenie is an open-source system that runs on Windows, Mac, Linux and ARM-based computers such as the Raspberry Pi – see Fig.9. It requires a certain level of Linux expertise. It can run without an active internet connection. HomeSeer https://homeseer.com/ HomeSeer is a mostly closed-source system that does not require an active Internet connection for automation, but one is needed for registration and updates – see Fig.10. HomeSeer supports a wide variety of products and integrations. It runs on a Raspberry Pi or one of the HomeTroller products. A list of compatible devices is at siliconchip.au/link/abqd while integrations are listed at siliconchip. siliconchip.com.au Fig.9: an example of a HomeGenie control panel that includes security features (alarm settings and a camera feed) plus an energy usage monitor. au/link/abqe (Android and iOS apps are available). HomeSeer products can be purchased from Black Cat Control Systems (siliconchip.au/link/abqf). Homey Pro https://homey.app/en-au/ Homey Pro claims to control any smart device and has a wide variety of features. It supports WiFi, Bluetooth, infrared (eg, for TVs and air conditioners), Z-Wave Plus and Zigbee. It can work partially without an active internet connection, but it requires periodic connection over the internet to receive an ‘access token’. So, without an available internet connection, it will eventually stop working (see siliconchip.au/link/abqg). Hubitat https://hubitat.com/ Hubitat is based on open-source software but requires the purchase of a proprietary hub. It can work without an internet connection if remote access, voice assistants and other cloud-connected services are not needed. It can control most smart home appliances and is programmed via an app or internet browser such as Firefox or Chrome – see Fig.11. The Hubitat hub (shown in Fig.12) connects to your home network WiFi router. It is compatible with Alexa, Google Assistant, Zigbee, Z-Wave, Lutron, LAN and cloud-connected devices. Fig.10: a sample HomeSeer app screen. Source: Google Play Store – siliconchip.au/link/abr0 Hubitat can optionally be integrated with Google Home, Home Assistant, Amazon Echo and numerous other devices. There is no subscription for basic remote access, but there is a fee for full remote administrative access. Insteon www.insteon.com.au/ Insteon uses power line and wireless RF to create a dual mesh network. Available products include a hub, motion sensor, remote control, door open/close sensor, thermostat, LED bulbs, relay (wired or plug-in), wired dimmer, cameras etc. Insteon devices will work without an active internet connection, although setup and certain actions Fig.12: the Hubitat Elevation C8 hub. Source: Smart Guys – siliconchip.au/link/abr7 Fig.11: an example of a Hubitat dashboard. The screens displayed can be customised. Source: Hubitat – siliconchip.au/link/abr4 siliconchip.com.au Australia's electronics magazine January 2024  19 may require an internet connection (Insteon didn’t respond to our email inquiry to clarify). Jeedom www.jeedom.com/en/ Jeedom is an open-source system that runs on Raspberry Pi and Linux systems. It has mobile apps for Android and iOS. LinuxMCE (Media Centre Edition) www.linuxmce.org LinuxMCE is an open-source home automation suite that also controls media and allows it to be distributed to any room. Unfortunately, it appears to no longer be under active development. MisterHouse https://misterhouse.sourceforge.net/ MisterHouse is one of the oldest home automation software suites, started in 1998 – see Fig.13. It is opensource and uses Perl scripts. It supports many platforms, including the Raspberry Pi and operating systems such as Linux, Unix, Windows and macOS. It can execute events at certain times or via web control, email messages, instant messages, socket messages, voice commands, serial data, Bluetooth proximity, infrared signals, X10 and Insteon powerline signals, and more. It is very versatile but requires knowledge of Perl scripting and is not recommended for beginners. It has been described as being “entirely geeky”. It supports X10, Z-Wave, MQTT, Insteon, XPL, XAP and other protocols. MyController Linux and the Raspberry Pi Zero, 1, 2, 3, and 4. Mycroft MyController is a privacy-focused open-source system that runs locally, so no internet connection is required, even for setup. It works on Windows, openHab is an open-source Linux system that can run on a Raspberry Pi – see Fig.14. It supports various technologies and devices. www.mycontroller.org/ https://mycroft.ai/ Mycroft is an open-source hardware/software platform that was crowdfunded with a privacy-based voice assistant and natural language interface. It is capable of running without an internet connection. Unfortunately, the project ceased development in 2023 (siliconchip.au/ link/abqh). However, OpenVoiceOS (https://openvoiceos.org/) appears to have taken it over. OpenVoiceOS provides a voice interface for controlling smart home devices, playing music, setting reminders and more. openHab www.openhab.org/ Fig.15: the OpenMotics “Brain” module. Fig.13: a screenshot of MisterHouse. Fig.14: a sample openHab page. In this example, data is derived from Google Calendar, an Autelis pool interface, Wemo (Coffee Maker), Z-Wave Sensors (garage and front gate), EcoBee (heating/cooling), a CCTV system and a custom pool filter pressure sensor. Source: openHab – siliconchip.au/link/abr5 20 Silicon Chip Australia's electronics magazine Fig.16: an arrangement of hardwired modules in the OpenMotics system. Source: OpenMotics – siliconchip.au/ link/abqx siliconchip.com.au OpenMotics www.openmotics.com/en/ OpenMotics is an open-source commercial platform that automates a house, building or more. It uses opensource hardware and software: • siliconchip.au/link/abqi • https://github.com/openmotics It features various extensions and integrations with products like Google Assistant for voice control, Philips Hue, OpenWeather, Siemens PLC for industrial systems, Mitsubishi heat pumps and many others; Android and iOS Apps are offered. The system is capable of operating without an internet connection. OpenMotics focuses on hardwired control of appliances rather than wireless communications, which makes it more suitable for new buildings or renovations. It uses hardware control modules based on open-source designs, such as the Brain module (Fig.15), the system’s foundation. The Brain connects to other modules such as an analog control module, relay module, CAN control module, energy module (to monitor power consumption), bus extender module and a P1 concentrator module to read smart meters via the P1 port – see Fig.16. OpenMotics has a YouTube channel (www.youtube.com/<at>Openmotics). SwitchBot www.switch-bot.com/ SwitchBot is a series of automation products, including battery-powered products that attach to existing rocker switches (such as lights or power points) to turn them on and off, a similar device for door locks, plus a variety of typical home automation products. SwitchBot uses Bluetooth in Connecting an Arduino to a smart home Enthusiasts can build their own home automation devices. For example, the Arduino Cloud commercial service (https://cloud.arduino.cc/) lets you connect your Arduino project to Amazon Alexa. There are also open-source libraries to connect your Arduino project to Home Assistant: ● www.arduino.cc/reference/en/libraries/home-assistant-integration/ ● https://github.com/dawidchyrzynski/arduino-home-assistant some low-power products, with WiFi for other devices like cameras. The Bluetooth products can connect directly to your phone; a hub is also available. SwitchBot hubs can also operate infrared remote-­ controlled appliances. An internet connection is needed for third-party cloud services to provide remote access. X10 www.x10.com/ X10 is both a home automation control protocol (see the panel on “Standards, Protocols and Certifications” on page 24) and a complete home automation system (siliconchip.au/ link/abqj). It was one of the first such systems that were commercially available. As early as 1979, Radio Shack in the USA was selling X10 products under their own “plug ‘n power” brand (see Fig.17). They also sold a controller for the TRS-80 computer to control up to 256 lights and appliances. Many X10 products are still available and in use today. Advantages of X10 include ease-ofuse because the system consists only of individually addressable receivers and senders, with no software needed, the use of existing mains wiring for transmission of signals (or wireless), no internet requirement, and an affordable, modular design. Disadvantages of X10 include a low data rate (over power lines) and susceptibility to interference. X10 can be controlled from a PC, Android, iOS device or simply from a handheld or benchtop controller. Its basic commands are fairly simple such as ON, OFF, DIM, BRIGHT etc. Australia/NZ standard light controllers and appliance modules are available from Envious Technology (siliconchip.au/link/abqk); they are no longer importing them, although they still have stock. Cloud-based devices and local alternatives Two important device types that are generally cloud-dependent are video doorbells and cameras. Noncloud alternatives for video doorbells include the LaView Halo One and DB5, Hikvision DS-HD2 and Doorbird. Noncloud smart cameras include the Wyze Cam v3, Wyze Cam Pan V2, SV3C WiFi and IP cameras, and Amcrest cameras. In each case, you should check their compatibility with any proposed home automation system. Other systems of interest We found the following systems interesting but did not include them in the other sections for reasons such as a lack of information, slow development, lack of documentation in English or being for advanced users only. Calaos https://calaos.fr/en/ Calaos is an open-source home automation system that runs on a Raspberry Pi, other single-board computers, Intel platforms, Android, iOS or Linux. It can run as a server, on the web or via a touchscreen interface. Some of its documentation is in English, but much is in French. ioBroker www.iobroker.net/ Fig.17: Radio Shack “plug ‘n power” products from 1981 that used the X10 system. Source: Radio Shack – siliconchip.au/link/abr6 (p138). siliconchip.com.au Australia's electronics magazine ioBroker is an open-source IoT platform written in JavaScript. It supports a wide variety of devices and protocols. It is a German project and very January 2024  21 See the video “What is Node-RED and How Can I Use it to Create IoT Applications?” at https://youtu.be/ pVb6Vq84ovg OpenNetHome https://opennethome.org/ OpenNetHome is a framework to integrate functions like lamp control, temperature measurements and audio/ video equipment control. It is open source and runs on Windows, Linux, macOS and Raspberry Pi. It has not seen much development work lately. Some instructions can be found at: siliconchip.au/link/abqm Pimatic https://github.com/pimatic/pimatic Pimatic is an open-source Raspberry Pi home automation project that is no longer maintained. Plasma Bigscreen https://plasma-bigscreen.org/ Fig.18: a sample ioBroker screen (in German). Source: https://w.wiki/7ovi popular there; much of the documentation is in German – see Fig.18. It requires an internet connection. For more details, see the video at https:// youtu.be/tepIlQtxVuQ MajorDoMo https://majordomohome.com/ MajorDoMo is an open-source system that works under Linux and Windows and has multi-brand and multi-protocol support. It is a Russian project and most documentation is in Russian. MyPi https://github.com/sujaymansingh/mypi MyPi is an Android and iOS app that controls a Raspberry Pi GPIO port for driving relays. See the video “Home Automation with Raspberry Pi and iPhone or iPad” at https://youtu.be/ yNSkWW9n_dA and the web page at siliconchip.au/link/abql Node-RED https://nodered.org/ Node-RED is an open-source graphical “flow-based programming tool” for connecting hardware, APIs and online services. It provides browser-based editing to create run-time libraries for event-driven applications – see Fig.19. It is based on JavaScript. IBM originally developed it, but they opensourced it in 2016. This tool is more for advanced users and developers rather than someone looking for a turnkey solution. Nevertheless, it is widely supported in industry and by other user groups. Plasma Bigscreen turns a ‘dumb TV’ into a smart TV using a Raspberry Pi or similar single-board computer – see Fig.20. It provides voice control via Mycroft AI. However, as mentioned above, that is no longer under development. QIVICON www.qivicon.com/en/ QIVICON is an alliance of companies founded by Deutsche Telekom that produces various home automation products integrated via their Home Connect platform (hub) and app. Smart switches that are suitable for Australia & NZ Here are some examples of smart switches and related products that comply with AU/NZ standards and can be controlled by various home Fig.19: a Node-RED system. Source: Home Assistant – siliconchip.au/link/abqy 22 Silicon Chip Australia's electronics magazine siliconchip.com.au automation suites. Some may require an internet connection, depending on how they are set up. These companies also usually offer other home automation products as well. You will need to do some research to determine if these devices are compatible with automation controllers other than those recommended by the manufacturer. Clipsal-Wiser siliconchip.au/link/abqn Clipsal-Wiser includes smart switches, dimmers and blind controllers using Zigbee and BLE (Bluetooth Low Energy), plus other smart home products. Deta Grid Connect siliconchip.au/link/abqo Deta Grid Connect products are available at Bunnings, use WiFi and are controllable by Grid App, Google Home and Alexa. For the technically adept, there is a way to connect them to Home Assistant documented at: siliconchip.au/link/abqp IKEA TRÅDFRI www.ikea.com/au/en/cat/smart-lighting-36812/ The IKEA TRÅDFRI wireless control outlet (Fig.21) also works with Home Assistant (see siliconchip.au/ link/abqq). Mercator Ikuü www.ikuu.com.au Mercator Ikuü devices use WiFi and Zigbee and are controllable via their app, Google Assistant and Amazon Alexa. Once set up, they should work without internet access, with some limitations. Shelly www.shelly.com/en Shelly offers a range of Australian-­ Fig.22 (left): a Shelly WiFi relay switch module. Fig.23 (right): a Zimi Powermesh Smart Switch. approved products from various distributors (see Fig.22): • siliconchip.au/link/abqr • siliconchip.au/link/abqs • siliconchip.au/link/abqt Shelly products connect to a local WiFi network and can operate without a hub, cloud connection or active internet connection. They are compatible with most home automation platforms, protocols and voice assistants. Zimi https://zimi.life/ Zimi is an Australian company that makes home automation devices such as light switches, power points, fan controllers, blind controllers and garage door openers – see Fig.23. They are AU/NZ standard types, so retrofitting is simple (although a licensed electrician will be required in Australia). They are controlled via a smartphone or tablet app. Devices communicate with each other via Bluetooth and create a mesh network. The Zimi app lets you control and schedule appliances via WiFi. A Zimi Cloud Connect device is used for control from outside the home and requires an internet connection, as does Google or Alexa voice control. The Home Assistant community Fig.20: Plasma Bigscreen is an open-source user interface for TVs, it is based on a Linux distribution. siliconchip.com.au Australia's electronics magazine is developing integrations for Zimi devices, but they may require an internet connection. Conclusion The home automation field is vast, so we can only give an overview. If you are interested in home automation but unsure where to begin, check out Home Assistant and Hubitat. Home automation is not required, nor is it for everyone. You may be unable to justify the expense or effort of automating devices like lights that are not difficult to switch manually. When choosing home automation devices, consider the benefits of having manual overrides. For example, a door lock should be operable by a key or by pressing non-electronic buttons if its battery or WiFi connectivity fails. A thermostat should be adjustable by a secondary means, for example, if the internet goes down or your home automation hub fails. While most smart locks have physical keys as a backup, often those keys are the weakest part of the system; many use cheap cylinders that are easily picked or even raked open. When it comes to security devices like smart locks, it really pays to do your homework. Fig.21: the IKEA TRÅDFRI smart plug sells for $20. January 2024  23 Standards, Protocols and Certifications ANT & ANT+ www.thisisant.com ANT & ANT+ are low-power proprietary wireless protocols primarily used for activity and environmental sensors. Bluetooth Low Energy (BLE) https://w.wiki/7pRp Bluetooth Low Energy is a protocol used by some home automation devices. It supports wireless mesh networking over the 2.4GHz ISM band and can be used for indoor device location services (presence, distance and direction of another device). A data rate between 125kbits/s and 2Mbits/s is supported, with a range of up to 100m. Philips Hue light globes are an example of smart home products that use this protocol. One of its disadvantages is a somewhat limited range and relatively low data rate. C-Bus (Clipsal Bus) www.clipsal.com/products/c-bus C-Bus is a home and building lighting and automation protocol developed in Australia by Clipsal, now part of the French company Schneider Electric. It uses low-voltage Cat5 cabling to control appliances. Lighting and appliances are controlled by dimmer or relay boards near the electrical distribution board. CEBus (Consumer Electronics Bus) https://w.wiki/7pRu CEBus (or EIA-600) is a 1992 set of standards and protocols automating homes, offices and lighting. It evolved out of a need recognised in 1984 for a more advanced system than X10. It is an open architecture and standards are defined for transmission over power lines, twisted pairs, coax, IR, RF and optical fibre. CSA (Connectivity Standards Alliance) https://csa-iot.org/ Connectivity Standards Alliance is the new name for the Zigbee Alliance. The CSA maintains standards for Matter and Zigbee. Dash7 www.dash7-alliance.org Dash7 is an industrial IoT protocol based on ISO 18000-7. DigiMesh www.digi.com/ DigiMesh is a proprietary shortrange 2.4GHz wireless mesh network communications system. EnOcean www.enocean.com/en/ EnOcean is a technology that harvests energy from the environment, such as from vibration, temperature differentials or light for wireless, batteryless devices such as switches, controls and sensors. IoTivity https://iotivity.org/ IoTivity is an open-source connectivity framework for IoT (Internet of Things) devices that may form part of a home automation system. It is a ‘reference implementation’ of OCF (Open Connectivity Foundation) standards. It is referred to as ‘middleware’ and is aimed at developers and highly advanced users. KNX https://knx.org.au/ KNX is an open standard for building automation and control. It is covered by the SA/SNZ ISO/IEC TS 14543.3.1-6:2018 specification. LoRaWAN (Long Range Wide Area Network) https://lora-alliance.org LoRaWAN is a spread-spectrum wireless communication technique. It can have a range of up to 10km or more under good conditions, at a low bit rate. Matter https://csa-iot.org/all-solutions/matter/ Matter is a new interoperability standard from the Connectivity Standards Alliance supported by Amazon, Apple, Google, LG, Samsung, TP-Link and smaller companies like Eve and Nanoleaf. Its purpose is to unify the best smart home technologies via the internet. A Matter certification allows support for a wide variety of systems and voice assistants. It was called Project CHIP (Connected Home over IP) while under development. Matter can communicate via WiFi, Thread and Ethernet. MQTT (Message Queue Telemetry Transport) https://mqtt.org MQTT is a device-to-device IoT connectivity protocol. It is the defacto protocol for IoT devices in home automation. NB-IoT https://w.wiki/84S NB-IoT is a narrowband IoT connectivity framework. NFC (Near-Field Communication) https://nfc-forum.org/ NFC is a short-range protocol for communication between a device such as a smartphone, electronic tag or card and a base unit. It is related to RFID. Such devices can be used for functions like opening an electronic door lock. Two-way communication is possible. OCF (Open Connectivity Foundation) https://openconnectivity.org/ OCF is an industry organisation that develops standards, interoperability guidelines and certification for IoT devices. It has numerous members, including ASUSTeK, Cisco Systems, Comcast, D-Link, Hisense, Huawei, Hyundai Telecom, IBM, Intel, LG, Lenovo, MediaTek, Microsoft, Netgear, Nokia, Realtek, Samsung, Sharp, Silicon Labs, ZTE and ZyXEL. PLC-BUS https://w.wiki/7pSA PLC-BUS is a powerline communications protocol similar to X10. It appears to be obsolete. RFID (Radio Frequency Identification) https://w.wiki/3opp RFID is related to NFC but it is oneway communication over longer distances. SigFox www.sigfox.com SigFox is a proprietary LPWAN (Low Power Wide Area Network) designed for low power consumption and massive IoT connectivity. Its range is up to 10km at tens of kilobits per second. Thread www.threadgroup.org Thread is a wireless mesh networking standard that uses 6LoWPAN (IPv6 over Low-Power Wireless 24 Silicon Chip Australia's electronics magazine siliconchip.com.au Personal Area Networks), which in turn is based on existing IEEE 802.15.4 radio technology. It works with other standards such as: Matter HomeKit (Apple) Weave (Google) DALI (www.dali-alliance.org) The KNX open standard for building control (https://knx.org.au/) BACnet (https://bacnet.org/) OCF (Open Connectivity Foundation) As a protocol, Thread competes with other mesh networks, such as Z-Wave and Zigbee IP. Thread can be incorporated into battery-powered sensor devices such as for temperature, humidity etc, although there are relatively few such devices currently on the market. Tuya ▪ ▪ ▪ ▪ ▪ ▪ ▪ www.tuya.com Tuya is a Chinese cloud-based AI IoT developer and management platform that collaborates with companies like Microsoft, Apple, Google, Amazon, Samsung, Schneider Electric, Lenovo, Philips and others. It is a member of the Connectivity Standards Alliance and supports the Matter standard. They provide a basic free app. Smart products supported by Tuya carry a PBT label (Powered By Tuya). UDP (User Datagram Protocol) https://w.wiki/3qsK UDP is a basic internet protocol used by some home automation devices. UPB (Universal Powerline Bus) https://pcswebstore.com/ UPB is a proprietary peer-to-peer communications protocol developed by Powerline Control Systems for transferring data over household wiring in home automation systems. It is supported by Home Assistant, openHAB, HomeSeer, and both Alexa and Google Assistant via a controller, among others. WiFi https://w.wiki/3jLG WiFi forms the backbone of most home and many office networks. It typically operates at data rates from a few Mbits/sec to many Gbits/sec on the 2.4GHz and the 5GHz bands. Its range varies, but it can typically cover the area of a conventional home without repeaters. The lower siliconchip.com.au frequency gives a better range, especially through walls and floors, but at a lower maximum data rate. Devices such as cameras are often connected via WiFi. It is important that your WiFi router can handle an adequate number of WiFi devices for a home automation system (some cheaper types supplied by ISPs may not be up to the task). Note that a Smart Hub is required to connect to devices using other non-WiFi protocols, as typical WiFi routers only support that one protocol. xAP Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P https://w.wiki/7pSH xAP is an open protocol for home automation similar to xPL. xPL https://w.wiki/7pSL xPL is an open protocol for controlling devices in a home automation system over UDP. X10 www.x10.com X10 is possibly the oldest home and commercial automation communications protocol, conceived in 1975 and first released to the public in 1979 (many sources say 1978). X10 transfers data over either household electrical wiring, or wirelessly at 433MHz (plus other frequencies like 310MHz in the USA). Zigbee https://csa-iot.org/ Zigbee is a protocol with faster transmission than Z-Wave, defined by the IEEE 802.15.4 standard. It is designed for low-power mesh networking and operates in the ISM band (2.4GHz in Australia) at up to 250kbits/s. Its range is 10-100m. Many Zigbee sensors (eg, temperature, humidity, motion, rain etc) can be battery-operated due to their low power consumption. Z-Wave https://z-wavealliance.org/ Z-Wave is a mesh networking protocol operating below 1GHz, thus avoiding busy spectrum space around 2.4GHz used by Thread and Zigbee. It has a data rate of up to 100kbit/s over a range of 100-800m, or 1600m+ for Z-Wave LR. Z-Wave products run on a different frequencies in different countries so make sure your devices are compatible. As with Zigbee, many Z-Wave senSC sors can be battery-powered. Australia's electronics magazine 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. January 2024  25 Explore our GREAT RANGE of Filament 3D Printers Create amazing 3D prints with our great selection of 3D printers. The best brands at great prices, stocked with spare parts, great service and advice. 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Part 1 by Stefan Keller-Tuberg A modern alarm clock can sound great, keep precise time and support multiple alarms. Alarm settings should include the day(s) of the week as well as the time, and you should be able to decide what sound each alarm plays, for how long, at what volume, and whether it’s a one-off or will repeat indefinitely. There’s no longer any reason you should need to set the clock’s time. It can be accurately fetched over the internet, with daylight savings and leap seconds adjustments applied automatically. Also, if the clock has speakers and a wireless connection, why not support streaming audio from a LAN, the internet or a smartphone? This project is based around a Raspberry Pi and supports all of these ‘dream’ features and many more; it 28 Silicon Chip can even snooze or cancel the alarm on your partner’s clock! The Raspberry Pi is a great platform because many of the required capabilities are already built in. Also, many of us already have a Raspberry Pi or two gathering dust and waiting to be put to good use! The custom hardware can interface with any Pi that runs Linux with a network connection and a 40-pin expansion connector. It has been tested to work with the Pi 3, Pi 4 and Pi Zero 2W models. It should also work with a Pi 2 or Pi Zero W, but they haven’t been tested yet. The newly released Raspberry Pi 5 is not suitable as it lacks an analog audio output. The Pi 3 and Pi 4 have the most capable processors and are therefore the best options, especially for media Australia's electronics magazine streaming. They also have Bluetooth, so you can stream audio to the Clock from a smartphone or similar. The slower Pi variants may be suitable if you plan to integrate a traditional overthe-airwaves radio as the audio source. In general, we recommend using a Pi 3 at the minimum. Hardware features The design uses two PCBs: a display board and a main board. The clock hardware and the Pi are powered from the same 5V DC source. The Pi connects to the main board and receives power via a short ribbon cable. I have used plugpacks for the four clocks I built for myself, but if you have the space, you could integrate a power supply inside the enclosure. The display comprises large 20mm-tall hours and minutes digits with 15mm-tall seconds digits that will be prominent anywhere in the room. The minimum and maximum LED brightness range is configured via the clock’s web interface, with the brightness automatically adjusted within the set range in response to changes in ambient light conditions. At its brightest, the display can be read in a sunlit room; at its dimmest, it is unobtrusive at night. The physical user interface comprises six switches: three centre-off toggle switches and three momentary contact push buttons. The switches replicate the features commonly found on clock radios, including snooze and media player controls, but there are too many features to control with six switches alone. All features are accessible using a web browser, so you can control the clock from a computer, phone or tablet connected to WiFi. A built in stereo amplifier with digital volume control can drive internal or external speakers according to your construction preferences. The Pi is the primary audio source, but you can integrate an alternative source, such as a traditional radio, if you want to. While the Raspberry Pi analog audio is not quite hifi quality, it is not to be scoffed at. I used a pair of bookshelf speakers with one of my clocks; the sound quality far exceeds typical commercial clock radios. If you have an old pair of speakers gathering dust, why not recycle them and put them to good use with this project? A switched power output for an siliconchip.com.au external audio source is enabled when the radio is selected; you could also integrate other audio sources into the enclosure alongside the clock hardware and Raspberry Pi. The switched power output can drive a 5V-powered device directly, feed an external regulator for a lower-voltage device, or act as an open-drain switch to control higher-voltage devices. Software features The clock supports many more features than a typical commercial clock radio. Up to twenty alarms can be configured at the same time. The first four alarms can be accessed via the clock’s switches, while all alarms can be managed via the web interface. For each alarm, you set the days of the week, time, duration, media source and relative volume. Any combination of days can be specified, from a single day to all seven. For example, you can set different alarms for weekdays and on the weekend. Alarms can be configured as oneoffs or to repeat indefinitely. One-offs may be defined up to seven days in advance and, if you like, you can set a one-off to occur on all or any of the seven upcoming days. After the one-off trips, it will not recur. I use these when I need to get up early for a work trip. To confirm you’ve set your alarm correctly, simultaneously press two alarm selection switches to display the remaining time until the next scheduled alarm. The countdown to the next alarm is displayed for as long as you hold the two alarm selection switches. An alarm can have a fixed volume, as you’d have with a regular alarm clock, or it can gradually ramp the volume up (or down) in one-minute steps so that you’re gently awakened. When the media or an alarm is playing from a playlist file, the clock will remember the last track so that it continues from the following track next time. While playing, the playlist’s contents are visible via the web interface, so you can jump tracks by clicking. One of the more novel capabilities of this project is its ability to cluster multiple clocks into one system. Clustered clocks share their alarm settings via WiFi, and changes made on one clock will be reflected soon after on the other clustered clocks. Many button press events are also shared in realtime amongst clustered clocks. siliconchip.com.au The button on the top of the case is for snooze mode, the red button is for duration while the black button is media. The switch at top right is plus/minus, while the two switches below it handle alarm 1/2 and alarm 3/4 respectively. The big knob in the centre is for radio tuning. With clocks on either side of the bed, either person can invoke snooze, change volume, modify an alarm etc. You can even use clustering to coordinate clocks in different parts of the home. Circuit protection features The circuit includes reverse polarity and overvoltage protection. Raspberry Pis have an absolute maximum supply limit of 6V, beyond which they will be damaged. At our house, we have a box of spare 5V and 12V plugpacks to draw upon for our various devices, and they all share the same style of coaxial connector. If you accidentally plugged a 12V plugpack into this project, that would instantly destroy it and the Raspberry Pi. The protection circuit was included to guard against that possibility. Because the circuit mostly follows a 5V design but the Raspberry Pi expansion interface uses strictly 3.3V logic, the clock includes series protection resistances for all general purpose I/O (GPIO) lines to guard against inadvertent shorting to a 5V source. I accidentally did this when prodding around a prototype and was glad for the protection. Trying the software You may be interested to try the software, even if you’re not yet ready to WiFi can interfere with Bluetooth Bluetooth operates in the same 2.4GHz band as WiFi and different devices in that band can interfere with one other, especially when a nearby device is using a lot of bandwidth. Bluetooth interference can cause audio stutter and spontaneous disconnections. If the interference becomes annoying, reassigning the Bluetooth channel by forgetting all Bluetooth pairings and starting over can help temporarily, as can changing the access point’s WiFi channel. However, these strategies may not be effective in the long term. The Raspberry Pi 4 supports the 5GHz WiFi band, so if Bluetooth audio streaming is an important feature for you, you’ll get the best results using a Pi 4 and ensuring there are no 2.4GHz WiFi devices or access points in the same or adjacent rooms as the clock. You could also disable the 2.4GHz band in all nearby access points and WiFi extenders. However, as most of us have legacy 2.4GHz-only WiFi devices, and sometimes 2.4GHz is the only usable spectrum, implementing this drastic strategy may be difficult (5GHz WiFi doesn’t penetrate walls very well). You can avoid severe interference if your home WiFi is based on recent access point technology supporting both 2.4GHz and 5GHz WiFi bands and band-steering. Configure the band-steering to force 5GHz-capable devices to use 5GHz WiFi channels for the fullest practical signal strength range and check that your 5GHz capable devices have switched over. Also, if possible, use wired Ethernet instead of 2.4GHz backhaul for any WiFi extenders you may have deployed. Another thing to consider is that microwave ovens operate at around 2.4GHz, so if a kitchen is nearby, an operating microwave oven can interfere with WiFi and Bluetooth in that band. Australia's electronics magazine January 2024  29 commit to the construction. The software can be installed onto any Linuxbased Raspberry Pi with a 40 pin expansion connector (the GPIO library currently does not support the Pi 5). Without the clock hardware, you can use the web GUI to set up and configure alarms, watch the alarms trip, pair your phone or tablet with the ‘clock’ to use it as a Bluetooth speaker 30 Silicon Chip or play media from the Pi’s flash card, an attached USB drive, a network share or from the internet. A script simplifies installing and configuring the Pi. It fetches the required libraries, installs them, then configures the clock, a file server, web interface, media player, automatic updates, NTP and time monitoring processes. Australia's electronics magazine You can optionally enable a firewall so the clock cannot be accessed from outside your home network and/or turn off the Pi’s power and activity LEDs so they don’t keep you awake at night. You can download the ZIP file from siliconchip.au/Shop/6/278 containing a Linux ‘tarball’ of the software and a PDF document explaining how to prepare the SD card, copy the tarball and siliconchip.com.au Fig.1: the clock display includes three dual-digit seven-segment displays (hours, minutes and seconds), two colon LEDs, eight ICs to drive the LEDs and Mosfet Q2 for PWM display brightness control. IC4-IC9 are seven-segment display drivers, while IC11 is an eight-bit latch that drives the decimal points and colons. run the installation script. There are also notes about software debugging modes for testing. See the panel on page 36 of this article for instructions on installing the software. Circuit details The Clock Radio circuit diagram is shown in Figs.1 & 2. Fig.1 is the display siliconchip.com.au section with the LED arrays and their drivers. That section is driven by the control section shown in Fig.2, which also has the audio, user interface (switch/button) and power portions. The 5V and 3.3V power rails for the display circuitry shown in Fig.1 come from the Raspberry Pi controller in Fig.2, along with the following digital data lines via 1kW resistors: Australia's electronics magazine an 8-bit data bus (D0-D7), a two-bit address bus (A0 & A1), a latch signal (EN) and a PWM brightness control line (DIM_PWM). By setting the eight data lines and the address, then ‘strobing’ (pulsing) the latch, the software on the Pi can update the digits for the hours, minutes and seconds, the six decimal points and two colon LEDs. January 2024  31 Fig.2: the Raspberry Pi connects to the display circuitry shown in Fig.1 using 12 digital lines that go via 1kW resistors. The switches and buttons also connect to the Pi’s digital I/O pins with pull-up resistors, while the ambient brightness monitoring and audio amplification circuitry are at upper right. The section at bottom left protects against power supply over-voltage and reversed polarity. 32 Silicon Chip Australia's electronics magazine siliconchip.com.au The seven-segment displays are driven by six BCD-to-seven-segment display drivers, IC4 to IC9, and the dots and colon from IC11. IC4 to IC9 convert binary numbers to segment patterns on the seven segment displays and can deliver the necessary LED drive current. IC11 works like a one byte (eight bit) memory to remember which dots are turned on. These chips have 3.3V-compatible inputs, suiting the Pi’s GPIO bus, and 5V outputs that can draw from the higher-current 5V supply rail. It is important to use 74HCT chips rather than 74HC because the latter are marginal at recognising 3.3V as a high level while the former have a maximum high threshold of 2V. Decoding the address bus and latching of the data is performed by IC10. As the decoding logic is all at the same level (3.3V), IC10 can be of the 74HC variety. IC4 to IC9 and IC11 drive all the LED display anodes via nominally 430W resistors while the LED display cathodes all go to the drain of N-channel Mosfet Q2. A PWM signal applied to Q2’s gate therefore determines the overall brightness of all the LEDs. A 1MW resistor holds it off whenever the Pi is not actively driving it, so the display is blank when the Pi software is not running. The software cannot determine whether all LEDs are present because the display section is a ‘write-only interface’. If you don’t need them, you could leave off the seconds LEDs and associated BCD driver chips, and no software changes will be required. Matching LED brightness Theoretically, identical displays from the same vendor should have the same brightness. As the project uses a combination of 0.8-inch 7-segment displays, 0.56-inch 7-segment displays and discrete LEDs, they might not all be the same efficiency. In that case, they can be equalised by adjusting the values of the 430W current-­ limiting resistors. Four of the five clock prototypes used Lumex 7-segment displays, and both sizes produced identical brightnesses. One prototype used Multicomp Pro devices, resulting in the smaller digits being slightly brighter than the larger digits. The larger Multi-comp Pro displays were slightly less bright siliconchip.com.au Australia's electronics magazine January 2024  33 than the equivalent Lumex devices, but the clock’s brightness adjustment had the headroom to compensate. To equalise the Multicomp Pro display intensities, I changed the smaller display’s current limiting resistors to 820W on that Clock Radio. If you construct the board using Multicomp Pro parts, we suggest not populating the small display’s current limiting resistors until you’ve built and tested your clock and can determine the optimal resistance. If constructing with Lumex, as Dirty Harry said, you’ve got to ask yourself a question: “Do I feel lucky?”. You can populate the 430W resistors for the small display as we did, but there’s a chance you might need to adjust them if they don’t match adequately (we didn’t need to). The two discrete 3mm LEDs that make up the colon (“:”) have characteristics independent from the 7-segment displays. For the devices specified in the parts list, we found 1.3kW series resistors illuminated the colon about the same as the 7-segment displays Fig.3: you can add a radio receiver board, which will only be powered on when needed, via CON5. Here are three ways to connect it depending on its power requirements. 34 Silicon Chip from either vendor. Any 3mm LEDs will work in this design, but be prepared to experiment with those resistor values if you use different parts. Dimming The dimming function of the circuit comprises an ambient light level monitor and the PWM control mentioned above. The ambient light level is sampled by a light-dependent resistor (LDR), which forms a voltage divider with a 10kW resistor across the 3.3V rail. The brighter the ambient light level, the lower the LDR/resistor junction voltage. IC12 is an MCP3201 12-bit analog-­ to-digital converter (ADC) used to measure this voltage. The raw number read from the ADC becomes smaller as the ambient light level increases; the software processes it into a value with 0 indicating darkness and 4095 being the maximum measurable brightness, as shown on the web setup page. The MCP3201 comes in two versions with different accuracies labelled B & C. You can save yourself a dollar because the cheaper, less-accurate part (C) works fine in this circuit. The parts list specifies two LDRs that will work well. Ideally, the LDR dark resistance should be at least 10 times its light resistance. The setup page on the web GUI includes four sliders for adjusting the minimum and maximum LED brightness and specifying the corresponding LDR levels. The sliders provide a lot of flexibility to adjust for minor differences in LDR characteristics so that the display achieves the full range of potential LED brightness. If you choose a different LDR and can’t get the dimming to work over the whole range, the 10kW resistor value will need to change. In response to the ambient light level, the software generates a 50Hz PWM waveform that drives the gate of Mosfet Q2 and continuously updates the PWM duty cycle according to the ambient light measurements. Although the Pi has two high-­ resolution timers that could be used for hardware PWM timing, neither is available in this design. One is used for the Pi’s analog audio output, while the other is commandeered by the Pi’s GPIO daemon (service). The LED brightness PWM is therefore generated in software by the GPIO daemon. You’re unlikely to notice that; the worst case is when the display is at its dimmest and the CPU is heavily loaded, such as when an alarm has tripped and it is downloading, decompressing and playing a media file. In that case, the software reduces the PWM frequency to minimise the jitter induced in the PWM signal. The two PCBs for the Raspberry Pi Clock Radio are mounted perpendicular to each other and then soldered together. Australia's electronics magazine siliconchip.com.au Audio The audio section includes the amplifier that drives the speakers and an audio input for an external radio. The amplifier (IC13) is a PAM8407 Class-D low-distortion filterless amplifier chip. At typical listening volumes, it has a distortion below 0.1% across most of the audible band. It is more than adequate for a clock radio and media player and comparable with the Pi analog audio output quality. Three GPIO pins are dedicated to putting the amplifier into and out of standby and adjusting its volume. The audio source is selected by DPDT relay RLY1, driven by Mosfet Q4. The GPIO line that drives Q4 also operates a second Mosfet, Q3, to act as a power switch for the external audio source. The switched external power is available at three-pin header CON5. Fig.3 shows three possible ways to power an external radio from CON5. Q3 has a maximum voltage rating of 30V so, if using an external power source, do not exceed that. If you don’t plan to integrate an external radio or audio input, you could omit Q3 and Q4, the associated resistors, PCB headers and the relay, and fit wire links to the relay pads on the PCB to connect the Pi’s audio output to the amplifier permanently. User interface Each switch pole or button has a 10kW pull-up resistor to the 3.3V rail and is connected to one of the Raspberry Pi’s GPIO pins that’s configured as a digital input. Therefore, when a button is pressed or a switch is toggled, the corresponding pin goes low and is detected by the software. Power supply and protection The reverse polarity and overvoltage protection section consists of diodes D1 & ZD1, SCR1, Mosfet Q1 and associated passive components. It protects the Clock Radio from an incorrect power supply that could otherwise damage it. D1 protects against reverse polarity by effectively short-circuiting the supply rail if power is applied with the wrong polarity. It will get hot, but it gets the job done. A switch-mode plugpack will enter overcurrent shutdown if shorted by D1, and your Clock Radio will not power on, allowing you to discover siliconchip.com.au Parts List – Raspberry Pi-Based Clock Radio 1 instrument case, 200 × 155 × 65mm [Jaycar HB5912, Altronics H0480F] 1 Raspberry Pi (model 3, 4, Zero 2W or similar) 1 sheet of green acrylic/Perspex, sized and shaped for the front panel 1 double-sided PCB coded 19101241, 150 × 83mm 1 double-sided PCB coded 19101242, 150 × 44mm 1 5V DC 2A+ plugpack 1 16-33kW light-dependent resistor (LDR1) [DigiKey PDV-P8103-ND, element14 3168335] 3 panel-mount SPDT centre-off momentary toggle switches (S1, S5, S6) 3 panel-mount SPST momentary pushbuttons (S2-S4) 1 J104D style 5V DC coil, 2A DPDT relay (RLY1) [DigiKey 2449-J104D2C5VDC.20S-ND, element14 1652604] 1 2×20-pin header, 2.54mm pitch 1 2.5mm chassis-mounting DC barrel socket (CON1) [Jaycar PS0524] 1 2-way right-angle pluggable terminal block, 5.08mm pitch 6 3-way, 2.54mm pitch polarised headers with matching plugs and pins 5 2-way, 2.54mm pitch polarised headers with matching plugs and pins 2 40-pin IDC line sockets 1 20-pin DIL IC sockets 7 16-pin DIL IC sockets 1 8-pin DIL IC sockets 1 panel-mount barrel socket to suit plugpack 2 red panel-mount banana socket 2 black panel-mount banana socket 1 short stereo audio cable with a 3.5mm jack plug at one end 1 15cm length of 40-way ribbon cable 1 50cm length of figure-8 speaker cable 1 1m length of 3-way ribbon cable 2 M3 × 32mm panhead machine screws 10 M3 × 6mm panhead machine screws 2 M3 hex nuts and flat washers 6 12mm-long M3-tapped Nylon spacers 2 short lengths of medium-duty hookup wire (red & black) Semiconductors 6 74HCT4511 7-segment display driver ICs, DIP-16 (IC4-IC9) 1 74HC139 dual 2-to-4 decoder IC, DIP-16 (IC10) 1 74HCT374 8-bit parallel latch IC, DIP-20 (IC11) 1 MCP3201-CI/P 12-bit ADC, DIP-8 (IC12) 1 PAM8407DR filterless Class-D stereo amplifier IC, SOIC-16 (IC13) 3 IRLB4132PbF 30V 78A N-channel Mosfets, TO-220 (Q1-Q3) 1 2N7000 small signal N-channel Mosfet, TO-92 (Q4) 1 C106D1G sensitive-gate SCR, TO-126 (SCR1) 2 0.8in/20.3mm green dual 7-segment display, eg, LDD-C812RI or LD0805GWK [DigiKey 67-1473-ND, element14 2627654] 1 0.56in/14.2mm green dual 7-segment display, eg, LDD-C512RI or LD0565GWK [DigiKey 67-1459-ND, element14 2627648] 2 green diffused 3mm LEDs (LED1, LED2) [DigiKey 754-1609-ND, element14 2112096 or equivalent] 1 5.1V 1W zener diode (ZD1) 2 1N4004 400V 1A diodes (D1, D5) Capacitors 2 470μF 16V electrolytic (2.5mm lead pitch) 1 47μF 16V electrolytic (2mm lead pitch) 2 1μF 50V (multi-layer) ceramic 4 470nF 50V (multi-layer) ceramic ● values may need to vary to match 10 100nF 50V (multi-layer) ceramic or MKT the display segment brightness. 1 10nF 50V (multi-layer) ceramic or MKT Resistors (all 1/4W 1% axial unless noted) 2 1MW 2 1.3kW SMD M3216/1206 1% ● 1 470W 1/2W axial 10 10kW 1 1.3kW 48 430W SMD 1206 1% ● 1 2.7kW 26 1kW 2 390W Australia's electronics magazine January 2024  35 Installing the software on a Raspberry Pi You will need an SD card with at least 4GB capacity. Larger is fine; you can use the extra storage to hold your media library. With Raspberry Pis, the read/write speed and quality of the SD card make a difference. Cheap SD cards often perform poorly. The SD card must be loaded with either the Debian Bullseye Lite or Debian Bookworm Lite operating systems. Debian images older than Bullseye are not suitable. The easiest way to prepare the SD card is with “Raspberry Pi Imager”, freely available for Windows, macOS and Linux. Launch Raspberry Pi Imager, insert the SD card into your computer (via a card writer if it doesn’t have a slot) and click the CHOOSE DEVICE button, then select “No Filtering”. For a Pi 4 or Pi Zero 2W, choose Raspberry Pi OS (Other) → Raspberry Pi OS Lite (64-bit). For other models, select Pi Raspberry OS (Other) → Raspberry Pi OS Lite (32-bit). Then click CHOOSE STORAGE to select the SD card, click NEXT, pick EDIT SETTINGS and fill out the form: 1. Set a unique hostname for your clock (“clock” if you can’t think of anything else). 2. Enable SSH using password authentication. 3. Set a username and password for logging in via SSH. 4. Enter your wireless LAN details (SSID, password and country). 5. Set the locale settings for your area. 6. Deselect the option to eject media (the SD card) when finished, as you’ll also be copying the clock software to the SD card before ‘ejecting’. Write down the hostname, username and password so you can log into the Pi later. Next, click SAVE, then YES then WRITE. When the card has been written, download the clock software zip file from the Silicon Chip website. Inside the zip file is a file named “alarm-clock_v01.tgz” that you need to copy onto the SD card. Copy the TGZ file from the ZIP archive to the root of the “bootfs” directory on the SD card the same way you transfer files to a thumb drive. The v01 number could increase in future if there are updates to the software. Finally, eject the SD card, insert it into the Pi and apply power. The ZIP archive also contains a PDF document with screenshot of the installation, and post-publication notes. Connecting to the Pi Because there’s no video output, the only way to know the Pi is ready to proceed is to connect to it over your network (wired or WiFi). The first time a Pi boots, it could take a few minutes longer than usual. To avoid frustration, apply power and make a cup of tea or coffee. You will need an SSH client to connect to the Pi. In Windows, you can use PuTTY or OpenSSH; macOS and Linux have ‘ssh’ command line tools. You can connect using its IP address or the hostname specified when you prepared the SD image. Most home routers generally publish local hostnames using a “.local” suffix, as suggested in Raspberry Pi Imager. So you can try to connect to “clock.local” (or whatever other name you chose). If that does not work, consult your router’s documentation or look at the router’s DHCP leases table to find the IP address allocated to the Pi. When you connect, the Pi will prompt for the username and password that you specified during the SD card setup. Enter them to log in and get the remote command prompt. Finishing the clock software installation On the Pi, the file you copied to the SD card earlier is available within the bootfs partition at /boot. You can now extract the contents using the command: tar zxf /boot/firmware/alarm-clock_v01.tgz tar zxf /boot/alarm/alarm-clock_v01.tgz ← for Bookworm OS ← for Bullseye OS This command creates a subdirectory called “alarm-clock” containing the source code and will also leave an installation script in your current directory. The last stage in the software installation is to run that installation script (you must copy this exactly, including the letter case): sudo ./Install_Clock.sh The installation script asks for your password twice, whether you would like to install firewall rules that prevent access from IP addresses originating on a different subnet (you will probably want to say yes) and then asks if you would like to attempt to disable the power and activity LEDs. Web-based configuration To reach the web interface, open a browser and surf to http://clock.local or whatever system name or IP address you used to ssh into the clock. You’re 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. We’ll have more information on configuring the clock in part two next month, along with instructions on updating the software, using it as a Bluetooth speaker, testing and more information on the clock software. If you run into trouble during installation you should check the instructions included with the software download, as steps may have changed after publication. These instructions are for the 1.8.1 version of Raspberry Pi Imager, but earlier versions will work with slight changes. 36 Silicon Chip Australia's electronics magazine the mistake without losing any smoke. The over-voltage protection isolates the rest of the circuit from the supply if the supply voltage exceeds about 5.7V. With a normal supply of around 5V, zener diode ZD1 does not conduct, so the gate of SCR1 remains at 0V. The 2.7kW pull-up resistor pulls the gate of Mosfet Q1 up to +5V, switching it on and connecting circuit ground to the incoming supply’s negative terminal. If the supply voltage exceeds 5.7V, there is around 0.6V at the gate of SCR1, so it switches on, pulling the gate of Mosfet Q1 to 0V. That switches Q1 off, allowing the circuit ground to rise to the positive supply rail, leaving no voltage to power the remainder of the circuit. The potential for damage to the Pi starts at around 6V, so the SCR trigger voltage is just slightly below that. SCRs behave a little like bipolar NPN transistors acting as switches, except that SCRs latch themselves on after their trigger voltage has been reached. This way, Q1 remains off until the offending power supply is disconnected, at which point it resets. Component selection When purchasing components for this project, note that electrolytic capacitors come in all shapes and sizes. The hole spacing for the two 470μF electrolytics is 2.5mm, while the 47μF electrolytic holes are spaced at 2mm. Most 16V rated capacitors will have similar lead spacings but higher-­ voltage electros may not fit well. If possible, measure the actual component or check the catalog or data sheet to find a good match. The clock will work with higher-voltage or larger components, but they may not fit as neatly on the board. Sockets are recommended for the DIP ICs. If ever you need to replace a chip, extracting the IC from a socket will be much easier than desoldering it from the joined main and display board assembly. However, sockets can slowly oxidise over time and eventually cause problems; soldered chips are generally more reliable in the long term. Removing the chip from its socket and then reinserting may be all that’s required to re-establish good contact. The second article next month will have all the construction details, usage instructions and information on updating the firmware. SC siliconchip.com.au HAPPY NEW Build It Yourself Electronics Centres® NEW! 69.95 $ GEAR! T 2125 NEW! 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Mail Orders: mailorder<at>altronics.com.au Victoria Western Australia » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 » Auburn: 15 Short St 02 8748 5388 » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 New South Wales Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 » Prospect: 316 Main Nth Rd 08 8164 3466 South Australia © Altronics 2023. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0001 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. ePaper ‘analog’ clock and calendar ePaper displays can still be read when the power supply is removed and they have a 180° viewing angle. Also, they don’t need a backlight. That results in an extremely low power consumption. One significant disadvantage of ePaper is that its refresh rate is rather slow, taking 3-8 seconds for a full update. That is why they are mostly limited to book readers and clock displays without second hands. This project uses a 190mm black & white ePaper display made by Waveshare with 800 × 480 pixels to show an analog clock view with a second hand. Circuit Ideas Wanted siliconchip.com.au The second hand cannot move every second; instead, it updates every 2-3 seconds. You can see a video of it at https://youtu.be/nD0xoOV_DkY The entire circuit will draw about 60mA from a 3.7V lithium-ion cell and can run for well over two days with an 18650 cell of modest capacity, although it is shown here running from a USB 5V power supply. The ePaper screen is driven by an ESP32 microcontroller module. However, driving an ePaper screen is a bit different than other screens. The ePaper display is divided into two pages: firstPage and nextPage. You have to write in both the pages in reverse colour so that when firstPage expires and nextPage starts, the reverse colours will cancel each other, and it will update the display properly. On the first page, if you write white on black, on the next page, you must write the same pixels with black on white. If you do not, you will have a flickering ghost image that changes continuously! When connecting the HAT, ensure the SPI connection switch is towards the “4 wire” SPI side, and the display configuration switch is towards the B side. The ribbon cable between the ePaper display & the HAT is delicate. Try not to move this cable much, or it could be damaged. The Arduino software can be downloaded from siliconchip. com.au/Shop/6/326 The library files are to be installed in the Arduino libraries directory. There are two sketches, one for the clock by itself and one for the clock with calendar. For easy understanding, or if you want to use an ePaper that Waveshare doesn’t make, I have retained the commented-out lines of the sketch. One can uncomment them and change to the correct display driver if required. The clock’s low power consumption means you could replace the power supply with a Li-ion battery and a small solar panel. The ePaper display is visible under broad daylight or indoor light. However, the ePaper will not be visible in the dark as it needs incident light to work, like regular paper. Bera Somnath, Kolkata, India. ($100) 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 January 2024  41 ESP32-based semiconductor curve tracer This circuit forms a simple and inexpensive semiconductor curve tracer. It graphs some characteristics of bipolar transistors, Mosfets, diodes, LEDs and low-voltage zener diodes. It allows the comparison of devices of the same type and will also show whether a device is faulty or out of specification, such as having a low gain. The software is contained in an Arduino sketch, and the device uses an ESP32 30-pin ‘DevKit’ microcontroller module. The micro includes WiFi, and the user interface is a web page served by a web server to avoid the expense of an LCD touchscreen. Web Socket technology eliminates page refreshes and provides rapid screen data updating. I housed the prototype in a small 3D-printed box with a 14-pin ZIF socket mounted on the lid to connect the device under test (DUT). The base current for an NPN bipolar 42 Silicon Chip transistor or the gate voltage for an N-channel Mosfet comes from the 8-bit DAC1 analog output of the ESP32 microcontroller (DAC stands for digital-to-analog converter). It is amplified by op amp IC1c, which has a gain of about 2.8 times. Its output is applied to the DUT via a 22kW resistor. The high side of this resistor is connected to a 56kW/27kW voltage divider and then to analog input pin 33 of the micro, which feeds its internal ADC (analog-to-digital converter). The voltage dividers keep the ADC input voltage below the 3.2V limit. The low-side (base or gate) voltage is buffered by a unity-gain op amp IC1a that feeds another ADC channel on pin 32 of the ESP32 via another voltage divider. The base current or gate voltage can be varied and measured by stepping the DAC output over its range. The collector current for an NPN Australia's electronics magazine bipolar transistor or the drain current for an N-channel Mosfet is provided by the ESP32’s DAC2 analog output, amplified by op amp IC1d. This op amp output is applied to the base of 2N5551 NPN transistor Q1 via a 1kW resistor. Q1’s collector is connected to a regulated 9V supply, while its emitter feeds a 100W resistor to the collector or drain of the DUT. Q1 works as an emitter-follower so that as the DAC2 output voltage increases, the voltage at the emitter of Q1 increases, as does the voltage applied to the DUT. The voltages at either end of the 100W resistor are measured so that the current can be measured along with the collector or drain voltage. To create the device curves, the DAC1 output is set to a low value while DAC2 is swept low-to-high across the range and the current, while the voltage readings are saved siliconchip.com.au The curve tracer is controlled from a web page. siliconchip.com.au Australia's electronics magazine to RAM. At the end of DAC2’s sweep, DAC1 is stepped up to a higher value, and the DAC2 sweep starts again. This continues until DAC1 is at its highest value. At the end of the test, the data is placed on the web page and plotted on a graph. The ESP32 ADCs are non-linear and do not work below about 400mV or above about 2.5V. Diode D1 (1N4004) is used to lift all measured voltages into the operating range, with a bias current provided by a 1kW resistor. ADC calibration data is loaded from the defaults.txt file, but a default set is loaded if it is missing. If the default calibration is unsatisfactory, the calibration routine can be run. For P-channel/PNP devices, a complementary circuit based around PNP transistor Q2 operates similarly to Q1 for N-channel/NPN devices. DAC1 and DAC2 are swept in reverse. That is, maximum base and collector currents are achieved with the DACs at zero. For diodes, including LEDs and zeners diodes, the collector and emitter pins of the N-type DUT are used with no connection to the base terminal. In this case, DAC2 sets the current through the device. Power is from a 12V plugpack that supplies the op amps directly. A 7809 linear regulator provides the test voltages and the micro via its VIN pin. Please confirm that your micro has a 3.3V onboard regulator as well as a blocking diode to prevent the direct connection of the VIN pin and the USB 5V terminal. Some ESP32 modules have a 0W resistor connecting the USB 5V pin to the VIN pin. If this is the case and you connect the VIN pin to 9V and the USB socket to your computer, you will most likely damage your computer's USB ports. To avoid this possibility, do not connect both unless you have confirmed the blocking diode's presence. As the test voltage is limited to 9V, the DUT base current is limited to about 350µA, collector and drain currents are limited to about 60mA, and gate/diode voltages must be under 9V. Consequently, only the device's lower voltage and current characteristics can be tested. You can download a full manual for the device as a PDF and the ESP32 firmware from siliconchip.com.au/ Shop/6/328 Phillip Webb, Hope Valley, SA. ($125) January 2024  43 Feature by Tim Blythman WiFi Relay Modules Connecting a microcontroller to a WiFi network is something we almost take for granted today, but 10 years ago, it was more expensive and difficult. This article examines two relay modules based on an ESP-01 module that can be controlled remotely over WiFi. T he Espressif Systems ESP8266 is a 32-bit microcontroller incorporating a WiFi radio. Initially, it came with firmware that included a TCP/IP stack. It could be controlled via a serial interface that allowed commands to be sent similarly to an old Hayes-­compatible phone-line modem. The ESP-01 is a minimalist standalone ESP8266 module that we reviewed in April 2018 (siliconchip. au/Article/11042). We also used the ESP-01 to create the Clayton’s GPS Time Source (April 2018; siliconchip. au/Article/11039). Its relatively simple circuit is shown in Fig.1. It wasn’t long before it became possible to program the various ESP8266 modules directly. The possibility of doing this with the Arduino IDE, and later the Python language in the form of MicroPython, meant that working with WiFi suddenly became very easy. Indeed, the ESP8266 is one of the main reasons the Arduino IDE has been updated to support so many different processor architectures and board types. The two WiFi relay modules covered in this article are based on the ESP8266 processor and both contain a removable ESP-01 module. That means both are programmable with the Arduino IDE, among other methods. They both come loaded with functional firmware, which means that they can be used without having to be programmed. We’ll look at their design and operation, then describe how they can be controlled. We’ll also look at the benefits of reprogramming them. Why WiFi? There are numerous possible applications for a WiFi relay, especially for things like home automation, as WiFi networks can easily cover the average home (or be expanded to do so). While the relays on both modules are rated for switching mains, you should not use them to switch mains directly. That’s because the modules are so compact that it’s impossible to ensure safe separation of the mains Fig.1: the ESP-01 module circuit is pretty simple, with the ESP8266 IC being connected to an antenna, crystal, serial flash memory chip (IC2), power LED, plus 8-pin connector CON1 for power and communications. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.2: the Z6427 has about the minimum circuitry needed for an ESP-01 module to control a relay. Several pullup resistors set the correct operating mode for the microcontroller, and a power LED and a reset button are provided. A high-side PNP transistor drives the relay. The module has no onboard voltage regulator and requires a 3.3V supply. and low-voltage parts of the circuit. You could easily use them to trigger a safer external mains relay, though. On the other hand, out-of-the-box, they are ideal for controlling things like low-voltage (eg, 12V LED) lighting, DC motors and other decorative applications. The Altronics Z6427 The Altronics Z6427 is a compact module measuring 36 × 24 × 16mm. It has a 4-pin right-angle header overhanging one end and a three-way screw terminal at the opposite end. The ESP-01 module sits over the relay and is attached to the module using a 2×4 pin socket. It’s very neatly laid out and there are mounting holes in each corner. Fig.2 shows the schematic diagram of the module. As you can see, there is not much to it. The header has connections for 3.3V power, ground and serial UART lines. These four pins connect directly to their corresponding pins on the ESP01 module. A red LED indicates when 3.3V power is applied, while the tactile switch can be used to reset the microcontroller on the ESP-01 module. Some of the ESP-01’s pins are pulled up to 3.3V by either 1kW or 4.7kW resistors. One of the ESP-01’s I/O pins, GPIO0, drives a high-side PNP transistor. When GPIO0 is driven low, the transistor conducts and powers the relay coil. A diode is provided to quench the coil voltage generated when the transistor switches off. The relay has 3A-rated contacts. The module was designed by Keyestudio, and more information about siliconchip.com.au the module can be found at (including a link to download a binary image of the firmware and software tools): siliconchip.au/link/abpv Firmware The firmware tries to connect to an access point named “KeyesWifi_S” (with the password “KeyesWifi”) if such an access point is present. If that doesn’t work, after a short while, the firmware on the Z6427 sets up a WiFi access point called “KeyesWifi_A”, with the same password. In either case, the firmware opens TCP port 8080 for incoming connections. The relay contacts will close if the string “PIN00=0” is received on that port. If “PIN00=1” is received, the relay contacts will open. This corresponds to the inverted logic that the circuit presents. The GPIO0 pin (Pin 5) that is used to drive the relay is also used to set the boot mode of the processor; that is probably the reason for the somewhat unusual PNP transistor drive circuit. This pin is also driven low as the processor boots, causing the relay to close briefly. Such behaviour may not be desired in your application! The Keyestudio web page also provides a “NetAssist” Windows PC program that can be used to test the module's operation. We have also written some Arduino sketches that can be used to test and control the relays, The Altronics Z6427 WiFi Relay Module is compact, with mounting holes being a handy touch. The detachable ESP-01 module sits over the 3A sugarcube-sized relay. 3.3V power and ground can be connected at one end, with the relay contacts available at the other end. which will be described shortly. Since the header on the Z6427 also carries serial data lines, we hooked up a serial-USB adaptor to see if anything was being sent. Fig.3 shows how you can connect this module to a CP2102 USB-serial module. There is diagnostic data at the unusual rate of 74,880 baud, which can be seen in Screen 1. The Jaycar XC3804 The Jaycar WiFi Relay is a bit larger at 45 × 28mm and has a more complex circuit; in fact, there is another microcontroller on the main module, aside from the ESP8266 on the attached ESP01 module. Fig.4 shows its schematic. There are three external connections equivalent to those on the Altronics unit. A threeway screw terminal presents the relay contacts, while a four-way pin header provides serial data and power, in this case, 5V. Another two-way screw terminal parallels the 5V and ground connections, which may be preferred for some applications. The XC3804 also hosts an AMS1117 3.3V regulator to power the 3.3V ESP-01 module. The Jaycar unit uses a low-side NPN transistor to drive the coil of a 5V relay. There is also a quenching diode. An indicator LED and its ballast resistor are in parallel with the coil, so the LED illuminates when the coil is powered. This relay has 10A contacts. Fig.3: connecting the Z6427 to a CP2102 USBserial converter module allows the diagnostic boot data to be viewed at the unusual baud rate of 74,880. Australia's electronics magazine January 2024  45 ◀ Screen 1: the Z6427’s data includes information about the access point it creates, as well as its progress in connecting to other access points. Screen 2: the XC3804 produces data about the access point and URL you need to connect to. The accented characters are actually binary commands to the STC15F104W chip that are also echoed to the external serial lines. Interestingly, the transistor is controlled by an 8-pin STC15F104W microcontroller. This micro is powered from the 5V rail and is also connected to the serial UART lines of the ESP-01 and the four-way header. There are unofficial reports that the ESP8266 processor has 5V-tolerant inputs, allowing the direct connection of the nominally 3.3V ESP8266 to a 5V microcontroller. The ENABLE pin of the ESP-01 is pulled up to 3.3V, and our module had several unpopulated component footprints too. The data sheet for this module includes the Arduino source code (siliconchip.au/link/abpw). The code is straightforward and contains elements from Arduino example sketches. The XC3804 creates an open access point named “Duinotech WiFi Relay” and also sets up a DNS responder for the “relay.net” hostname. This means that the Relay can be accessed via this host name as well as its IP address. There is also a web (HTTP) server hosting a page that provides a pair of links to control the relay remotely. The links point to the URLs relay.net/open and relay.net/close According to both the source code and the behaviour we saw, the “open” command sets the transistor’s base high, energising the relay, while “close” de-energises the relay. That is opposite to what we expected. Otherwise, the XC3804 worked as expected and was perhaps slightly easier to operate due to its inbuilt HTTP server rather than a raw TCP server. Despite the extra microcontroller, the relay on the XC3804 occasionally chattered when powered on but less often than the Z6427. Also, the relay status LED (as fitted to the XC3804) is more useful than the power LED on the Z6427; the ESP-01 module already has a tiny red LED that lights up when it is powered. This module can be wired up to a CP2102 USB-serial module, as shown in Fig.5. There is little diagnostic data available from the XC3804, apart from an instructional boot message at 9600 baud, shown in Screen 2. Further binary data (the line of accented characters) is sent whenever the URLs are requested. This data appears to be the commands to the STC15F104W for it to drive the relay. Demonstration software We have written software demonstrating how to control these modules over WiFi. Naturally, we needed a WiFi-capable microcontroller, and we have chosen to use the Pico W as it can be programmed with either the Arduino IDE or with BASIC using the WebMite firmware. Since the Pico W’s UF2 firmware files are easy to upload, we have also provided those as downloads, so you can try out our examples without even having the Arduino IDE installed. You will just need a serial terminal program, such as TeraTerm on Windows or Minicom on Linux. For the Arduino IDE, we’ve used the arduino-pico board profile version 3.1.0 from siliconchip.au/link/abpx Some of the Arduino sketches have also been tested to work with the D1 Mini ESP8266-based boards. Fig.4: the XC3804 includes an AMS1117 voltage regulator, so it will work with a 5V DC supply. It has a second microcontroller in addition to the ESP8266 on the ESP-01 module, which receives commands over a serial pair and activates the relay via a standard low-side NPN transistor arrangement. 46 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 3: our basic Z6427_CLIENT demo software for the Z6427 connects to its access point and can control the relay by sending appropriate data over the WiFi network. There are three Arduino sketches for the Z6427 and one BASIC program. There is also an Arduino sketch for the XC3804. There are some limitations to the WebMite WiFi interface that mean there are some things we cannot do with it. For each example, you can load the UF2 file by pressing the white BOOTSEL button on the Pico W while connecting it to a computer. After that, copy the appropriate UF2 file to the RPI-RP2 drive that appears and connect to the virtual USB-serial port with your terminal program. You could also compile the sketches with the Arduino IDE. Note that Arduino and the WebMite firmware use different implementations of the virtual USB-serial port, so the port name or number might differ (for the same Pico W) depending on which firmware is loaded. Z6427 remote control There are three versions of the Arduino demo software for the Z6427. One version (Z6427_CLIENT) behaves as a The XC3804 has screw terminals for power and relay contacts, plus a separate header for power and serial communications. It is larger than the Altronics unit and does not have mounting holes but the onboard relay is rated for 10A. siliconchip.com.au Screen 4: this second version of the client software can scan and connect to different Z6427 Relays. It can be pretty slow, as switching between the access points each Relay provides takes some time. WiFi station and tries to connect to the access point on a Z6427. When it does, it prints its IP address. The Relay can be controlled by typing “0” or “1” into the serial terminal; Screen 3 shows the typical output. Sometimes the connection does not work immediately, so you may need to wait up to a minute for the station to connect to the access point. It also appears that the Z6427 does not always start its access point (“KeyesWifi_A”) until it has decided that it can’t connect to any other access points (“KeyesWifi_S”). The Z6427_CLIENT_V2 sketch (or UF2 file) is designed to allow control of more than one Z6427. This sketch scans for networks with the “KeyesWifi_A” name and allocates them a letter code (A, B, C etc). Screen 4 shows its output. Entering the letter code will connect to the appropriate Relay, after which “0” and “1” will switch the specific Relay, like the previous sketch. Note that this sketch is very slow to switch between Relay access points, so it will Fig.5: the XC3804 communicates at 9600 baud, and you can see some brief debugging data output and the commands to the STC15F104W that drives the relay. Australia's electronics magazine not be suitable for practical uses of those Relays. The Z6427_AP_CLIENT demo operates as an access point and allows Relays to connect to it; its serial output is shown in Screen 5. The “0” and “1” commands are pushed out to all Relays that connect. Unfortunately, there isn’t an easy way to tell the relays apart (eg, by querying their MAC addresses) from within the Arduino code. Like the previous sketch, this version is impractical for anything but demonstration purposes, but might be handy to show how the Relays operate in these configurations. WebMite BASIC The current version of WebMite BASIC (5.07.07 at the time of writing) has some limitations that mean it is not possible to provide as many examples. Screen 5: the Z6427_AP_CLIENT sketch provides an access point to which the Z6427 Relays can connect. It shows the connected stations and sends out the same command to all the Relays it detects. January 2024  47 In particular, the WebMite cannot be configured to work with an open WiFi network, meaning that it is impossible to use it to communicate with the Jaycar XC3804, which only offers an open WiFi access point. The WebMite cannot be an access point, so we cannot create an equivalent to the Z6427_AP_CLIENT sketch. Also, the access point to which the WebMite connects is fixed as an OPTION, so it cannot be easily changed at runtime; that rules out a BASIC program like the Z6427_­ CLIENT_V2 sketch. So, our sole BASIC example for the WebMite connects it to a single Z6427 access point and allows remote control of the relay with “0” and “1” keystrokes. You can break out of the program with Ctrl-C if you want to modify it. This can be loaded by downloading the Z6427.UF2 file to a Pico W. The output is shown in Screen 6. Note that because all Z6427s use the “KeyesWifi_ A” access point, this UF2 file has OPTION WIFI set to use that access point name, so it should just work. Software for the XC3804 The XC3804 only creates an access point and does not have the option to connect to other access points, so there is only one Arduino example for it, named XC3804_CLIENT. It works in much the same fashion as the Z6427_ CLIENT software and connects to the Relay. You can then control the relay over its serial port by sending “0” or “1”. As expected, the logic is reversed, so “0” will energise the relay (and the LED will come on), while “1” will power off the relay. Screen 7 shows the serial data produced by this sketch. Improved firmware These two relays have handy features but could benefit from some improvements. In particular, neither can connect to a pre-existing WiFi network, which is what we expect most people to do, especially if they wish to interact with devices on the wider internet. The Z6427’s habit of toggling the relay as it powers up might be sufficient to rule it out of some critical Screen 6: we also created a version of the Z6427_CLIENT software in BASIC for the WebMite, which runs on the Raspberry Pi Pico W hardware. Screen 7: like the Z6427_CLIENT software, XC3804_CLIENT connects to the access point that the Relay creates. Since the XC3804 uses the HTTP protocol, it can also be operated using a computer and browser. 48 Silicon Chip Screen 8: our DUPLEX_RELAY_ FIRMWARE_MDNS firmware can be loaded onto the Z6427 or XC3804 Relays to improve the interface. Our firmware serves up the web page shown here and allows it to connect to an existing WiFi network, such as a home access point. Other information shown allows the Relay to be uniquely identified for later use. Australia's electronics magazine applications, but otherwise, its numerous interfaces are pretty handy. The XC3804’s HTTP interface is very easy to use, particularly for testing purposes, as any computer with a browser can operate it. The lack of a secure access point means it can’t be used with the WebMite. With these aspects in mind, we decided to write our own firmware to work with both module types. Our Clayton’s GPS Time Source article had details about wiring up the ESP-01 module for reprogramming. We have reproduced the figure from that article (Fig.6 here) as it shows the critical details of how to connect the USB/serial adaptor to the ESP-01 via a breadboard for programming. Our improved firmware was also written with the Arduino IDE; the sketch is named DUPLEX_RELAY_ FIRMWARE_MDNS. We have also exported a BIN file you can program directly into the ESP-01 (or other ESP8266 board) with the free ESPFlashDownloadTool software. The ESPFlashDownloadTool software can be downloaded from: siliconchip.au/link/abpv That link is also provided on the Altronics Z6427 product page. The BIN file (and any other BIN files for ESP8266 boards) should be programmed to address 0x000000. Altronics sells the ESP-01 module separately as the Z6360 (siliconchip. au/link/abpy), so you can experiment with this without modifying the ESP01 module that comes with the WiFi Relay Module if you prefer. This firmware provides the same outputs as expected by the Altronics Z6427 and Jaycar XC3804 Relays, so an ESP-01 module programmed with this firmware can be used in either. Simply remove the original ESP-01 and replace it with one programmed with our firmware. Briefly, the updated firmware adds interfaces to allow it to connect to a specific WiFi network. That will enable the relay to connect, for example, to your home WiFi network. Naturally, the selected access point is saved for automatic connection in the future. Some basic diagnostic data is now available via a serial terminal at 9600 baud. This baud rate is necessary to match the rate used by the ESP-01 when it communicates with the second microcontroller on the XC3804 module. siliconchip.com.au Fig.6: this is how you can connect a USB/serial adaptor to an ESP8266 module to reprogram it. The breadboard is mainly needed so you can connect the required pull-up resistors. Like the Jaycar XC3804, an open access point is created, this time with the name “relay”. A DNS server means you can browse to http://relay.setup to easily access the configuration. Screen 8 shows the web page that is displayed. You can test the operation of the Relay by using the OPEN and CLOSE buttons on the web page. You can also set the WiFi SSID and password using the text entry boxes. The information at the bottom of the page includes the IP address of the Relay once it has connected to another network. The HOST and MDNS fields are unique names based on the unique MAC (hardware) address of the ESP01 module. They can be used later to identify each Relay as they should never change, even if the IP address changes. A password can be entered in the LOCK password field to prevent the SSID and password from being modified by someone accessing the Relay’s access point. Re-entering the LOCK password will unlock the Relay. Like any such application, physical access to the relay means that any security measures can be broken, such as by reprogramming the module or reading out data from the flash memory. So we don’t claim that the Relay is invulnerable to security issues, but this small measure should help. The same page is also served up when the Relay has connected to another access point, so you should be able to check operation by browsing to the IP address shown (while connected to the programmed SSID) and confirming that you see the same host address and that the Relay can be controlled in the same fashion. siliconchip.com.au To configure multiple Relays, you should power on each in turn. When each one comes up, access its “relay” access point and configure it to access your preferred WiFi network. Note the IP address and HOST/MDNS fields, then set the LOCK password and power off the Relay before configuring the next. Depending on your access point’s settings, the IP addresses might change, but the HOST/MDNS will not. You can then access the Relays via the following client software. Client control A functional test can be made using the DUPLEX_AP_CLIENT sketch. This connects to the “relay” WiFi network and accesses the http://relay.setup page to control the relays. It is controlled from a serial terminal. It works in the same fashion as the XC3804_CLIENT software seen in Screen 7. Indeed, it is much the same code-wise apart from the different access point and web page addresses. For a more comprehensive control program, use the DUPLEX_STA_­ CLIENT_WEBSERVER sketch. It also has a serial control interface, allowing it to connect to your WiFi network and scan for Relays. On start-up, the sketch scans for networks and prompts you for a password to allow a connection to your home network. This network is saved in emulated EEPROM for future use. You will then see a menu like Screen 9. Both the DUPLEX_RELAY_FIRMWARE_MDNS and DUPLEX_STA_ CLIENT_WEBSERVER sketches implement the mDNS (multicast domain name server) protocol. The Relays are identified by their MDNS names which are displayed in their individual configuration web pages. After a Relay scan (triggered by the “Y” command), any Relays found are saved to emulated EEPROM and can be selected by choosing their letter code (A, B, C etc). They can be operated by typing “0” or “1”. The DUPLEX_STA_CLIENT_WEBSERVER sketch also serves up a web page at the IP address that it prints on the serial terminal. Screen 11 shows a typical display, which, as you can Screen 9: the DUPLEX_ STA_CLIENT Arduino sketch provides a much more advanced control interface. The mDNS protocol allows other Relays to be found by scanning, and individual Relays can be saved and controlled independently. Australia's electronics magazine January 2024  49 The Altronics Z6427 (left) and Jaycar XC3804 (right) shown enlarged for clarity. see, will allow you to scan and control Relays on your local network. BASIC code We’ve also provided a BASIC version (for the WebMite) of this sketch. It is called DUPLEX_STA_CLIENT and works like its Arduino equivalent, although it lacks the web server interface. The UF2 can be loaded onto a blank Pico W to turn it into a WebMite already programmed with this software. However, you will still need to manually configure the OPTION WIFI parameter to connect to your preferred network at the command prompt. Since WebMite BASIC does not implement the mDNS protocol, it has to work slightly differently. It accesses the web page that the Relay generates and looks for the “MDNS:” text to extract the unique identifier. We recommend noting the IP addresses and then using the “V” command to check the relay at that IP address. We’ve included a scan (“Y”) routine, but it is very slow and does not always work. Screen 10 shows the output from the WebMite BASIC program. It can store Relays to non-volatile memory and then control them by typing a letter (A, B, C etc) and “0” or “1”. Fixes We tried adding a capacitor to see if we could eliminate the relay toggling while the WiFi Relay Modules are booting. The capacitors are fitted between the base and emitter of the Q1 transistor in each case. For the Altronics Z6427, around 470μF was required, while the Jaycar XC3804 only required 10μF. Watch the polarity if you try this with electrolytic capacitors. Conclusion Our updated firmware offers significantly improved options for controlling these WiFi Relays, especially as it allows them to connect to a known WiFi network. This simplifies applications where you already have devices connected to an existing network. There is still the limitation of the Altronics Z6427 that the relay contacts close briefly when power is first applied; the Jaycar XC3804 also appears to do so occasionally. For these reasons, we can’t suggest these Relays for interfacing with things Screen 10: although WebMite BASIC does not support the mDNS protocol, our DUPLEX_ STA_CLIENT BASIC program provides similar features (apart from scanning) to the DUPLEX_ STA_CLIENT Arduino sketch. 50 Silicon Chip Australia's electronics magazine Screen 11: the HTTP web server incorporated into the DUPLEX_STA_ CLIENT_WEBSERVER sketch displays a page that allows you to configure and control other WiFi Relays. That means you don’t need to use a serial terminal apart from the initial setup. like automatic gates and garage door openers. A power outage might result in the garage door receiving a spurious open command in the middle of the night! Still, they would be great for controlling low-voltage lights and other decorative applications. They would probably be fine for uses where safety or security is not a concern. All the software we have written for these Relays is also available in compiled form, so you don’t need the Arduino IDE to try them out. For example, we have UF2 files that can be loaded directly onto a Pico W. These are available for all Arduino sketches (except the updated Relay firmware, which is not intended for the Pico W). Our serial control is simple and intended to demonstrate how these devices operate. We expect many readers will add interfaces such as buttons and sensors to automate the operation of the Relays further. Having said that, the web page interface might be sufficient for some readers. As well as the UF2 files for our Pico (Arduino or WebMite) programs, some of the Arduino sketches have also been exported as BIN files, which can be programmed into ESP8266-based boards or modules for testing. We used a D1 Mini for these tests as it has a built-in USB-serial interface. Jaycar sells it as XC3802. Both Relay modules are available for $17.95 at the time of writing. • Altronics Wi-Fi ESP8266 Relay Module For Arduino: siliconchip.au/ link/abpz • Jaycar Smart Wi-Fi Relay Main Board module: www.jaycar.com. au/p/XC3804 SC siliconchip.com.au ADD MOTION DETECTION TO YOUR PROJECT PIR MOTION DETECTION MODULE ADD OBSTACLE DETECTION OR AVOIDANCE DUAL ULTRASONIC SENSOR MODULE • Adjustable delay times XC4444 $6.95 • 2cm - 450cm 15° range XC4442 $8.95 Expand your projects with our extensive range of Arduino® compatible Modules, Shields & Accessories. OVER 100 TYPES TO CHOOSE FROM AT GREAT PRICES. ADDRESSABLE RGB LEDS DETECT WHEN PLANTS NEED WATERING SOIL MOISTURE SENSOR MODULE • Analogue output XC4604 $4.95 VIEW OVER 70 ARDUINO® PROJECTS YOU CAN BUILD AT: jaycar.com.au/projects Shop at Jaycar for: • Arduino® Compatible Development Boards • Display Modules • Servos, Solenoids & Motors • Wheels & Chassis 1.3" MONOCHROME OLED DISPLAY • 128x64 Pixel XC3728 $19.95 ADD AMAZING COLOUR TO YOUR NEXT PROJECT 5V LED STRIP WITH 120 ADDRESSABLE RGB LEDS HALL EFFECT SENSOR MODULE • 2m long, flexible, waterproof XC4390 $38.95 • Sense magnetic presence XC4434 $5.75 • Prototyping Hardware and Accessories • Project Enclosures • Servos & Motors • Switches & relays Explore our wide range of Arduino® compatible modules, shields and accessories, in stock on our website, or at over 115 stores or 134 resellers nationwide. 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/shieldsmodules 1800 022 888 U S B ▶ P S / 2 Keyboard Adaptor Numerous devices still use PS/2 keyboards, even though USB keyboards have been around for 20 years. That’s because PS/2 is very easy to interface with a microcontroller, so kit-built computers like the VGA PicoMite include a PS/2 keyboard interface. This Adaptor allows you to connect a USB keyboard to a VGA PicoMite or anything else that needs a PS/2 keyboard. By Tim Blythman W hile it’s still possible to buy PS/2 keyboards, they aren’t as widespread as they used to be. USB keyboards often have better features, and wireless USB keyboards are pretty cheap these days. Wireless PS/2 keyboards exist but are no longer common, making this Adaptor especially useful. We recently came across a nice design that is based on a Raspberry Pi Pico microcontroller module. It allows a USB keyboard and mouse to connect to a computer that expects a PS/2 keyboard and mouse; see https://github. com/No0ne/ps2x2pico The hardware presented there is not much more than a Pico board, a level shifter board and some flying leads. We decided to develop a slightly slicker design that would be more - VGA PicoMite version kit (SC6861, $30) - ps2x2pico version kit (SC6864, $32.50) Both kits include everything except the Jiffy box and 6-pin mini-DIN to mini-DIN cable. The mounting hardware and optional headers/sockets are present. The Pico is supplied blank and requires programming. 6-pin mini-DIN cable (SC6869, $10): 1.5m long PS/2 cable. Two cables are required if using both the keyboard and mouse. 52 Silicon Chip Image Source: https://unsplash.com/photos/ZByWaPXD2fU robust and easy to use with the VGA PicoMite (July 2022; siliconchip.au/ Article/15382). We’re presenting two designs here, with one designed specifically to work with the VGA PicoMite. It should also work fine with any computer system that expects a PS/2 keyboard, including older PCs and boot-to-BASIC computers such as the MaxiMite or Colour MaxiMite. This project was also prompted by enquiries about the USB Mouse and Keyboard Interface for Micros (February 2019; siliconchip.au/ Article/11414), asking us to add a PS/2 interface. The PS/2 keyboard protocol “PS/2” refers to the IBM Personal System/2 computer that introduced this interface. The physical side of the PS/2 protocol is quite simple and consists of two lines that are normally pulled up to 5V. The connected devices (eg, keyboard and host computer) can either leave the lines high or pull them down to 0V using a transistor collector/drain. This allows communications in both directions without conflict. Australia's electronics magazine The lines are called CLOCK and DATA, and electrically, the protocol is very similar to I2C. Each byte is sent on the DATA line as a start bit (0), eight bits, an odd parity bit, then a high stop bit. The level on the DATA line is much the same as would be seen on an asynchronous serial line using the ‘8O1’ (eight data bits, odd parity, one stop bit) setting. However, there is a CLOCK line, which is specified as operating at 10-16.7kHz, so it is a synchronous protocol. The keyboard always provides the CLOCK signal, and the only time the host controls it is to briefly pulse it low to signal that it wants to send data. When the host sends its data, it depends on the keyboard to drive the clock signal as the host drives the DATA line. Some of the commands the host can send include those to set the lock key LEDs (Caps Lock, Num Lock & Scroll Lock) and to set the ‘typematic’ rate and delay. Typematic is the term for automatic key press repeats when keys are held down. Since USB keyboards do not implement typematic, we need to emulate that feature. The host can also query the keyboard siliconchip.com.au The PCB shown at left fits into the VGA PicoMite case and replaces the PS/2 socket with its USB socket. Six pin headers connect the two PCBs. The construction is a bit fiddly, but the tidy result is worth the effort. The PCB shown at right is the ps2x2pico version and has more features such as a mouse adaptor. Due to its larger size, it needs to be fit into a UB5 Jiffy box, but it can convert a USB keyboard/mouse combo to work with two PS/2 ports and it supports wireless USB devices. about its status and identity. For the most part, though, data is sent from the keyboard to the host when keys are pressed or released. The PS/2 ‘scancodes’ that the keyboard sends do not neatly map to anything like the ASCII codes or the USB scancodes sent by USB keyboards. In fact, PS/2 scancodes correspond to the original physical location of the keys on the keyboard, as adjacent keys often have similar codes. The mapping was clearly chosen to simplify the scanning and encoding of keys by the keyboard, leaving the hard work of decoding the scancodes to software on the host computer. A PS/2 mouse works similarly, although it sends button presses and movement changes instead of scancodes. The host can command it to set parameters like sampling (update) rate and scaling. So, apart from the scancode interpretation that is needed, the PS/2 protocol is fairly simple and is easy enough to implement as it is driven by the keyboard. We can control the clock rate since we are trying to emulate a keyboard. Circuit details As mentioned earlier, the first circuit is specifically designed to work with the VGA PicoMite. A second circuit siliconchip.com.au is intended to match the circuit used by No0ne’s ps2x2pico software. PCBs are available for both. Electrically, both are very simple, and most components are present to interface a 3.3V Pico microcontroller board to the 5V levels used by the PS/2 interface. Each circuit has a corresponding PCB; we will describe their differing software and construction later. We think the first version (Fig.1) is the best choice if you want to connect a USB keyboard to a VGA PicoMite. However, if you’re going to interface to an old PC with both PS/2 mouse and keyboard connections, we recommend building the second version. VGA PicoMite version Fig.1 shows the circuit for this version of the Adaptor. It uses a Raspberry Pi Pico microcontroller board (MOD1), a pair of USB connectors (CON1 and CON2), a 6-pin mini-DIN socket (as used for PS/2), CON3, and a few other components. USB sockets CON1 and CON2 are connected in parallel. Those who know USB will realise that both connectors cannot be used simultaneously; they are alternatives, and only The Adaptor is a neat install in a VGA Picomite, replacing the PS/2 socket with a USB socket. Australia's electronics magazine January 2024  53 Fig.1: Q1 & Q2 act as voltage level converters connecting the 5V PS/2 bus to the 3.3V Pico. That allows the Pico software to convert signals from a USB keyboard to the PS/2 protocol. CON1 and CON2 give two different mounting locations for the USB socket. one should be fitted. They are the same socket type (both type A) but are in different locations on the PCB to suit various applications. The data lines from CON1 (or CON2) head via 22W resistors to consecutive pins on MOD1. Although the RP2040 chip on the Pico has native support for USB, some clever people have written a library that uses the Pico’s PIO (programmable input/output) peripheral as a USB controller. The general-­ purpose I/O pins do not have internal 22W resistors as required for USB communications, hence our adding them. Two more of the Pico’s pins (carrying the CLOCK and DATA signals) connect to a level-shifting arrangement based on 10kW resistors and Mosfets Q1 and Q2. An identical arrangement is used on the VGA PicoMite to interface the 3.3V Pico to the 5V levels used on the PS/2 bus. This configuration is well-suited to voltage level conversion on open-­ collector busses and is commonly used with I2C interfaces. The resistors pull up the lines on each side to either 3.3V or 5V. The gate is at the same voltage as the source, so the Mosfet’s channel is off, and its body diode is reverse-­ biased due to the 5V rail being higher than the 3.3V rail. If the 3.3V logic line (connected to the Mosfet source) is pulled down, the gate is at a higher voltage than the source and the Mosfet switches on, propagating the low level to the 5V 54 Silicon Chip logic side. If the 5V logic line goes low, the source is pulled down via the Mosfet’s body diode, the Mosfet switches on, and the low level is also seen on the 3.3V side. Releasing the low level allows the source to rise until the Mosfet switches off and each side returns to its initial state, with both sides pulled up by their respective resistors. One more pin of the Pico is connected to a 1kW resistor and then to ground via the LED. The latter is a status indicator, with the LED lit by bringing the digital pin high. The 5V pins of all the connectors are tied together so that any connector can supply 5V as needed. Since CON1 (or CON2) is a host USB-A port, it will power a downstream USB device like a keyboard. In normal operation, power will come from CON3, since it will be connected to a PS/2 host. If necessary, power could be provided to the circuit via the Pico’s USB socket. The Pico has an integrated 3.3V regulator, with its output available at the 3V3 OUT pin. In this case, it is only used as a reference voltage for the level-shifting circuitry. The ps2x2pico version Fig.2 shows the second circuit. It has a Pico (MOD1), USB type-A socket (CON1), two 6-pin mini-DIN sockets (CON2 & CON3) and a mini-USB socket (CON4). CON4 only has its power (VBUS & GND) pins connected. Australia's electronics magazine The ps2x2pico name has been coined for the software by its creator, No0ne. We are simply using it to identify the version of the hardware that we have developed to work with their software. The eight 10kW resistors and four Mosfets implement four logic level-­ shifting channels identically to the first circuit. The 5V sides of two channels go to CON2 for a PS/2 keyboard, while the other two connect to CON3 for a PS/2 mouse. The 3.3V sides of the level shifters connect to pins on MOD1, while CON1 connects the USB data lines to a pair of pads. These are intended to be connected to a matching pair of pads on the underside of the Pico, and thus the USB D− and D+ lines on its USB controller. Finally, LED1 and its 1kW ballast resistor connect to another of the Pico’s I/O pins. It’s possible to replace CON1 with a USB-OTG adaptor fitted into the Pico’s micro-USB socket; that is what is shown in the photos at https://github. com/No0ne/ps2x2pico We felt that having fixed sockets made for a more robust solution. The fixed socket arrangements also lend our final PCB design to being installed in a Jiffy box. Software Despite their almost identical functionality, the two circuits use vastly siliconchip.com.au Fig.2: like in Fig.1, many of the components are responsible for interfacing the 3.3V Pico with the 5V PS/2 bus. Those components are duplicated for connections to both a PS/2 keyboard and mouse. The USB data line ‘test’ pads at upper right connect CON1 to the Pico’s USB port. different software implementations. The code at https://github.com/No0ne/ ps2x2pico is built using the Pico’s C SDK (software development kit). It uses the RP2040’s internal USB controller peripheral in host mode, and implements the PS/2 interface using the PIO peripheral. We discussed the PIO peripheral in detail in our Pico review in the December 2021 issue (siliconchip.au/ Article/15125). The PIO is a programmable state machine that can be used emulate many I/O and communications peripherals. Using the internal USB controller in host mode is easier but it also means that the controller cannot operate in device mode, for example, to provide debugging data over a virtual serial port. Plus the USB data connection must be made via the test pads on the Pico, instead of standard header pins. Our software instead uses the PIO to emulate a USB host peripheral based on a library available within the Arduino IDE. Thus, we used the Arduino IDE to build our software. siliconchip.com.au The USB host implementation means that the PIO peripheral cannot provide the PS/2 interface, so we have written it to work using GPIO pins and timer interrupts instead. This timer operates at 50kHz and is divided into four phases to give a nominal 12.5kHz PS/2 clock frequency. Using the Arduino IDE also allows us to customise the code more easily, and we have ensured that it works well with the VGA PicoMite. Some key events require more than one byte to be sent on the PS/2 line, so a queue has been implemented to ensure that data moves in an orderly fashion. It should also guard against brief bursts of keyboard activity overwhelming the Adaptor. As we mentioned, the software must map scancodes from the USB scanset to the PS/2 scanset. We use what is known as Set 2, the default for PS/2 keyboards. The mapping is not quite one-toone. USB keyboards report the state of the modifier keys (Ctrl, Shift, Alt etc) as bits in a status byte rather than as scancode events. So, we have to Australia's electronics magazine convert the changes in these status bits into the key-up and key-down events that PS/2 keyboards generate. Some keys, such as Pause, have odd mappings that must be handled uniquely. That is because the Pause feature was originally invoked by the Ctrl+NumLock key combination, meaning that a single keystroke maps to eight bytes to send on the PS/2 line. The Adaptor must also send repeated key-down events to emulate the typematic feature. With USB keyboards, that is usually handled by the host computer’s software. The ps2x2pico software does not control the LED provided on the second circuit; we simply added it to the PCB in case users wish to modify or update the software to do so. Note that both versions of the software support USB hubs, so if you need to attach a separate keyboard and mouse, you only need to add a hub. If you are using a wireless keyboard and mouse, consider buying them together; in that case, both keyboard and mouse will usually share a single wireless USB receiver. January 2024  55 Parts List – VGA PicoMite USB to PS/2 Converter 1 PCB double-sided PCB coded 07111231, 42 × 66mm 1 Raspberry Pi Pico programmed with 0711123A.UF2 (MOD1) 1 UB5 Jiffy box ● 2 M3 × 10mm panhead machine screws ● 4 M3 hex nuts ● 2 M3 flat washers ● 6 header pins ♦ 1 M3 × 5mm panhead machine screw ♦ 1 M3 × 6mm tapped spacer ♦ 2 20-way pin headers (optional, for MOD1) 2 20-way female header sockets (optional, for MOD1) 1 PCB mount USB-A horizontal socket (CON1 or CON2) 1 6-pin mini-DIN socket (CON3) ● 1 6-pin mini-DIN to 6-pin mini-DIN cable ● Semiconductors 1 3mm green LED (LED1) 2 2N7002 N-channel Mosfets, SOT-23 (Q1, Q2) Resistors (all M3216/1206 SMD, ¼W) 4 10kW 1 1kW 2 22W ● only needed if installing the Adaptor in a Jiffy box ♦ only required if installing the Adaptor inside a VGA PicoMite Hardware The VGA PicoMite version PCB has been designed so it can sit directly above the main PCB of the VGA PicoMite and fit into the VGA Pico­Mite’s recommended case, as shown on page 53. In this configuration, the CON3 PS/2 connector is not fitted, and the corresponding pads on the two PCBs are directly connected with header pins or similar (shown on page 60). There is the option of fitting the USB socket where the PS/2 socket would have been, meaning that you can now plug a USB keyboard in where you would have otherwise plugged a PS/2 keyboard. You could use the other USB socket location instead, although you would need to cut a hole in the side of the VGA PicoMite case to access it. Another option is to mount either PCB inside a UB5 Jiffy box. The assembled PCB is secured to the Jiffy box’s lid. Slots for the various connectors can be made by simply cutting down from the top edge of the box, which is easier than trying to hollow out a shape in the side of the box. In this configuration, the LED should be mounted on the underside of the PCB to allow it to shine through the box lid. We’ll provide more guidance on these options later. Programming the Pico Fig.3: three 3mm holes are needed in the Jiffy box lid to accommodate the PCB coded 07111231. Two are for mounting screws and the third allows the LED to shine through. You could use the blank PCB as a jig to mark out the holes or confirm your measurements. We recommend programming the Pico before fitting it to the board, especially since the ps2x2pico version uses the USB socket normally used for program uploads. Connect the Pico to a computer, holding in the white BOOTSEL button as you do so. A drive labelled RPI-RP2 should appear. Upload the firmware by copying the respective UF2 file to that drive. Use the file “0711123A.UF2” for the VGA PicoMite version. After programming, it will reappear as a virtual USB-serial port, so you can check that such a device appears on your system. Sending a ~ character to that serial port will toggle debugging mode, but you won’t see much of note until it is connected in-circuit. The ps2x2pico version requires the “ps2x2pico.UF2” file. There won’t be any obvious clues that programming has completed except that the drive will disappear. The ps2x2pico version behaves as a USB host, so you shouldn’t see any USB devices. Australia's electronics magazine siliconchip.com.au 56 Silicon Chip That software is under active development, so keep an eye out for updates. We used version 0.7 in our testing and it is included in the software downloads. This software is copyrighted by No0ne and released under an MIT open-source license. In the software bundle, we’ve also provided a PS2_HOST sketch that we used for testing. The bundle includes the UF2 file for this sketch. It is designed to work with the VGA PicoMite version of the hardware, and simply provides a PS/2 host port on the CON3 mini-DIN socket. Communication is via a virtual USB serial port on the Pico (via the micro-USB socket). This software will report any packets received and their equivalent keys (if the device is a keyboard). Host packets can be sent by typing their hexadecimal codes followed by Enter. There is an assortment of PS/2-related links at the bottom of https://github.com/ No0ne/ps2x2pico and some of those list host commands. Construction The first circuit, the VGA Pico­Mite version, corresponds to the PCB coded 07111231 (34 × 65.5mm). The second version that supports both a keyboard and mouse uses a PCB coded 07111232 (48 × 58mm); we will refer to it as the ps2x2pico version. The Keyboard Adaptor can be fitted inside the VGA PicoMite case or a Jiffy box as shown here. This enclosure has the holes made as per Fig.3. To keep everything compact, we’ve primarily used surface-mounting components. You should have tools such as a finetipped iron, tweezers and magnifiers. Useful consumables include solder wire, flux paste and solder-wicking braid. The small PCBs can be held in place with Blu-Tack or similar while soldering (if you don’t have a PCB-holding vice). Having an appropriate solvent on hand is also a good idea, so you can clean up any flux residue left after soldering. If you are building a version to fit into a Jiffy box, you can use the bare PCB to mark out the location of the holes that are needed. That is usually easier than using our drilling and cutting diagrams, although you have that option too. There are two holes for M3 mounting screws in the VGA PicoMite version, plus a 3mm hole for the LED, as shown in Fig.3. The ps2x2pico version uses three mounting holes, plus one LED hole, although the default software does not make use of the LED, so you could omit it. Fig.4 is the cutting and drilling diagram for that version. The screw holes can easily be marked by running a pencil (the thin tip of a 0.7mm mechanical pencil is ideal) around or through the holes. The LED holes can be marked using the two holes through their pads on the PCB. Draw a line between those marks and then a smaller line across the exact middle of the one you drew to find the centre of the LED hole. There are some cuts to be made in the sides of the boxes, which are easily made by using the assembled PCBs as guides while mounted on the lids. Fig.4: the hole at centre left is only needed if the LED is fitted; the other three holes are for mounting the PCB coded 07111232. The cutout regions are necessary to accommodate the various sockets. You might find it easier to remove the red shaded region and glue the tab back in later. siliconchip.com.au Australia's electronics magazine January 2024  57 VGA PicoMite ver. assembly The PCB overlay for this version is shown in Fig.5. Use that and the photo shown opposite as a guide to fitting the parts to the PCB. Before assembling the PCB, if you are going to install it in the VGA PicoMite, carefully break off the two PCB tabs that are attached by ‘mouse bites’. Grasp the main part of the PCB with one hand, then use a pair of wide-nosed pliers to flex and break off the tabs. Do this outside to avoid inhaling any fragments of fibreglass. If you need to use a file to clean up the rough edges of the mouse bites, do that outside too. If you are fitting this PCB to a Jiffy box, one tab is used to help secure the PCB while the other fills the gap in the edge of the box adjacent to the USB socket. Neither is essential to the electrical operation of the circuit. Apply flux to the PCB for the surface mounting components. Place each in their marked locations, using the relevant overlay diagram as a guide, and tack one lead. Check that each component is within their pads before soldering the remaining lead(s). Use your solvent to clean up the PCB after the surface mounting components have been fitted and allow the PCB to dry. Solder LED1 next. There are cathode (K) markings on both sides of the PCB to allow it to be fitted to either side. If you are installing it in the Jiffy box, solder it to the back of the PCB (the side with the Silicon Chip logo). It should be flush against the PCB. If you are fitting it to the VGA PicoMite then solder it to the front of the PCB, with about 10mm of lead between the LED’s body and the PCB. Later, the LED’s leads can be bent to aim it out through the front of the enclosure near the SD card socket. Of course, you should ensure the shorter lead goes to the pin marked K. Now connect the Pico to the PCB; there are three ways to do this. Firstly, you could solder the Pico directly to the PCB. This requires no extra parts but means that the Pico needs to be accurately aligned to the pads on the PCB. You could use M2 screws in the corner holes to temporarily secure the Pico, ensuring correct alignment during soldering. Or you could instead solder pin headers to the Pico (as though you were going to use it on a breadboard). You could then solder female header sockets to the PCB and slot the Pico onto them, or solder the Pico’s headers directly to the PCB. If installing the Adaptor in a Jiffy Box, there are no height requirements that would restrict using headers. The clearance is tighter inside the VGA PicoMite case, so you need to solder the Pico directly to the PCB or use male headers only; using sockets makes the assembly too tall. ps2x2pico ver. construction Fig.6 is the PCB overlay for this Fig.5: assembly of the PCB designed for the VGA PicoMite is straightforward, as there are only 13 components. It’s important to make sure the orientation of the LED and the Pico is correct when attaching those components. 58 Silicon Chip Australia's electronics magazine version. You can use that and the photo shown next to Fig.6 to help you assemble the PCB. To fit out the PCB for the ps2x2pico version, apply flux to the pads for all the surface-mounting components, including CON4, the mini-USB socket. If you only plan to use the default firmware, you can omit the 1kW resistor and the LED, as that firmware will not drive them. If you want to modify the firmware to use the LED, it should be fitted to the rear of the PCB if you are using the Jiffy case. Otherwise, you might like to fit it to the top if you are using the bare board. Place CON4 first and locate it on the PCB with the pegs on its underside. Clean the iron’s tip and apply a small amount of fresh solder. Touch it to the pad on the PCB and the solder should run onto the lead. Use a generous amount of heat and solder to secure the four larger pads that connect to the shell and use the solder wick to draw away any excess solder if there are bridges between the pads. Then fit the four transistors, followed by the eight resistors. With the surface-mounted parts in place, you can clean off the excess flux and allow the PCB to dry. As with the VGA PicoMite version, you can install the Pico directly to the PCB or on headers. An important difference is that the two small pads (TP2 and TP3) on the Pico near its microUSB socket must also be connected to Fig.6: there are a total of 19 components to fit for the ps2x2pico version. The default firmware does not use LED1 and the 1kW resistor, so you can leave them off unless you plan to modify the software. siliconchip.com.au the corresponding pads on the PCB. If you are surface-mounting the Pico, it should be possible to flow solder through the PCB and onto the pads on the Pico. You could tin the pads on the PCB and Pico with a small amount of solder to ensure that surface tension pulls the solder all the way through. If you aren’t sure, the best way to guarantee a good connection is to surface-­mount some short pieces of stiff wire, such as axial lead offcuts, to the underside of the Pico. This will also need to be done if you plan to use headers to mount the Pico; it is what we did, and you can see it in the photo at upper right on page 60. If you are using headers, solder the male headers to the underside of the Pico; the female header sockets are fitted to the top of the PCB. Connect the Pico to the PCB (by soldering the bottom of the male headers or by pressing it into the female headers). The short wire leads should protrude through the pads in the PCB, allowing them to be soldered to it. When that is done, the CON1 USB socket and CON2/CON3 mini-DIN sockets can be fitted. VGA PicoMite version testing To finalise the Jiffy box version of the VGA PicoMite PS/2 Adaptor, solder the CON3 mini-DIN socket, ensuring it is down hard against the PCB. The USB socket can then only be soldered to the CON1 location. The Adaptor should be complete Parts List – ps2x2pico USB to PS/2 Converter 1 double-sided PCB coded 07111232, 58 × 52mm 1 Raspberry Pi Pico programmed with ps2x2pico.UF2 (MOD1) 2 20-way pin headers (optional, for MOD1) 2 20-way female header sockets (optional, for MOD1) 1 PCB mount USB-A horizontal socket (CON1) 2 6-pin mini-DIN sockets (CON2, CON3) 1 surface mounting mini-USB socket (CON4) 1 UB5 Jiffy box 3 M3 × 10mm panhead machine screws 6 M3 hex nuts 3 M3 flat washers 2 short pieces of wire (if mounting the Pico on headers) 2 6-pin mini-DIN to 6-pin mini-DIN cables Semiconductors 1 3mm green LED (LED1; optional) 4 2N7002 N-channel Mosfets, SOT-23 (Q1-Q4) Resistors (all M3216/1206 SMD, ¼W) 8 10kW 1 1kW (only needed it fitting LED) enough to perform a functional test at this stage. Plug a USB keyboard (or USB wireless receiver) into the USB socket and then plug the mini-DIN cable into the mini-DIN socket. Connect the other end of the miniDIN cable to the PS/2 socket of the computer and power it on. After a second or two, you should see the green LED light up. That indicates the Adaptor has recognised that a keyboard is attached. The LED will flicker if either the host computer or keyboard tries to communicate. Although the LED is programmed only to light up if a keyboard is connected, we have seen some wireless mouse receivers that also cause it to happen. We suspect this type of receiver is a generic type that supports both keyboards and mouses and thus enumerates as a keyboard, even though that is not necessary for its operation with a mouse. Jiffy box Drill the two holes in the lid of the Jiffy Box, plus the one for the LED. Thread a machine screw from the outside and secure each with a nut inside. Each nut forms a thin spacer to keep the PCB off the lid. Then thread the PCB over the screws and fasten it in place with washers and screws. ◀ The ps2x2pico version of the PCB is compact and uncomplicated. We omitted the 1kW resistor and the LED from our build as they are not driven by the default firmware. We decided to include them in the design in case constructors want to add support, which should not be too hard. ◀ This is the same VGA PicoMite version as shown on page 53, but built as a standalone board to be fitted into a Jiffy box. In this case, the USB socket can go in the CON1 position as the CON3 mini-DIN socket covers the CON2 position. siliconchip.com.au Australia's electronics magazine January 2024  59 ◀ The headers don’t protrude through the top of the PCB so that the USB socket can be soldered over the top. Using three pairs of 0.1in pin headers means that the individual pins do not come loose during soldering. The plastic has been filed down slightly on the middle pair due to the pad spacing being less than 2.54mm (0.1in) on the mini-DIN socket. We’ve also pushed the plastic shroud so that the pins are only 1.6mm (the PCB thickness) above the shroud. ◀ We used lead offcuts to directly connect the TP2 & TP3 pads on the Pico to the USB pads on the PCB underneath. Even if you are soldering the Pico directly to the PCB, we recommend soldering the two leads to the Pico. You can now make the two U-shaped cutouts in the sides of the box. Either use our cutting diagram, or place the mounted PCB against the box to mark out the sides. The easiest way to make these is to use a fine saw or very sharp knife (such as a hobby knife) to make the vertical cuts. Carefully score the horizontal cut on the outside of the box and then gently flex the tab with a pair of widenosed pliers until it snaps off. The hobby knife can then be used to neaten and fine-tune the shape of the cutouts until the lid slots fully into place. This version is completed by screwing the lid of the Jiffy box in place. Installing in a VGA PicoMite Installing the Adaptor inside the VGA PicoMite is a bit more fiddly, as it requires stacking the PS/2 and USB connectors. You should have already removed the two PCB tabs by snapping them off; do so now if you have not already. Solder the pin headers to the underside of the PCB in the six pads belonging to the mini-DIN connector. Make sure that the headers do not protrude above the PCB at all. We found the easiest way to do this was to separate the pin headers into pairs of two pins and then locate them into adjacent holes. The plastic surrounding the middle pins may need to be filed down a bit to give clearance; unfortunately, the mini-DIN socket does not have VGA PicoMite Build this amazingly capable ‘boot to BASIC’ computer, based on a Raspberry Pi Pico. It has a 16-colour VGA output, a PS/2 keyboard input, runs programs from an SD card and can be quickly built Blocks is a BASIC game that runs on the VGA PicoMite $35 + Postage ∎ Complete Kit (SC6417) ∎ siliconchip.com.au/Shop/20/6417 This kit comes with everything shown (assembly required). The PCB is available in green or blue. You will need a USB power supply, PS/2-capable keyboard (or the kit shown on page 52), VGA monitor and optional SD card. For the circuit and assembly instructions, see the July 2022 issue: siliconchip.au/Article/15367 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.7: this diagram shows modifications to the H0376 instrument case used for the VGA PicoMite. The added LED for the PS/2 Adaptor sits on the front panel near the SD card socket, while the cutout for the USB socket overlaps the original location of the miniDIN socket on the rear panel. a standard 2.54mm (0.1in) pitch between all pins. It helps to slide the pins along the plastic so that only a small amount (about the PCB thickness) protrudes. The photo opposite shows how the PCB looks with the header pins attached. Next, solder the USB socket above the PCB in the location marked CON2 and attach the 6mm spacer next to the LED. The Adaptor PCB can now be slotted onto the VGA PicoMite. Make sure that it is square and does not contact any components underneath. Solder the six pins to join it to the VGA PicoMite’s PCB. You might find that you need to slightly enlarge the back panel hole for the USB socket, since it is larger than the mini-DIN socket. You will also need to drill a hole for the LED in the front panel. Fig.7 shows the suggested panel modifications for those two holes. Connect a USB keyboard, then power on the VGA PicoMite. The LED should light up, then flicker as the PicoMite initialises. ps2x2pico version testing The Adaptor can be tested by connecting it to a PS/2-­compatible computer using a pair of 6-pin mini-DIN cables. Connect the keyboard and mouse to the USB socket using a hub, if necessary. We imagine many people will use a wireless keyboard and mouse combination, in which case a single compact receiver is all that needs to be plugged into the USB socket. The mini-USB socket is provided in case extra power is needed; the socket on the Pico cannot be used to supply power as it is working in host mode. Attach the machine screws to the lid of the Jiffy box and secure them on the inside using three of the nuts. Slide the PCB over the screws, then secure it to the lid with washers and screws. Use the Fig.4 cutting diagram to make the U-shaped slots in the side of the Jiffy box to accommodate the connectors. A sharp hobby knife or fine-toothed saw are good choices here. Finally, attach the lid to the box with its included screws. Jiffy box labels Figs.8 & 9 show panel artwork that can be applied to the lids of the Jiffy boxes. Fig.9 helpfully marks the distinction between the keyboard and mouse sockets. Conclusion We continue to be impressed by the capabilities of the Raspberry Pi Pico, and this application is a perfect use for its abilities. We’re sure there are many readers out there with PS/2 equipment who will make use of the option to use a modern USB keyboard on their legacy devices. You can find a list of helpful links listed below: • github.com/No0ne/ps2x2pico/ • wiki.osdev.org/PS/2_Keyboard • wiki.osdev.org/PS/2_Mouse SC Figs.8 & 9: this simple label (shown at left) can be affixed to the top of the Jiffy box for the VGA PicoMite Adaptor. While the label shown at right will help users differentiate between the otherwise identical mouse and keyboard sockets. We’ve omitted the hole for the LED as we expect most readers will not use it. Both labels are shown at actual size. siliconchip.com.au Australia's electronics magazine January 2024  61 Soldering Irons We stock a WIDE RANGE of gas and electric soldering irons at GREAT VALUE to suit your needs and budget. 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Jaycar reserves the right to change prices if and when required. Using Electronic Modules with Jim Rowe 4-digit, 14-segment LED module Instead of seven segments, this LED display module has 14 segments per character, so it can display letters, digits and even a few symbols. It has a built-in I2C serial interface, allowing popular microcontrollers like the Arduino Uno or Nano to drive it easily. T he module is about the same size as a 4-digit, 7-segment display at 50mm wide by 28mm high, with a total thickness of a little over 10mm. The two side-by-side dual-character LED displays have 14 segments per character, plus the usual decimal point LED. This allows them to reasonably display numerical digits, upper-case letters, many lower-case letters and a few symbols. The module (available from Jaycar) features an I2C serial interface that allows easy connection to just about any popular microcontroller unit (MCU). We will now look more deeply into the 14-segment LED displays, followed by the useful IC that drives them and provides the I2C interface. The 14-segment displays Fig.1 shows how the dual character displays used in the module have six of the seven segments used in the familiar 7-segment displays; the outer ones labelled ‘a’ to ‘f’. Instead of the single central horizontal segment, there are eight inner segments: three in the upper half labelled ‘g’, ‘h’ and ‘j’, three in the lower half labelled ‘l’, ‘m’ and ‘n’, and two in the centre replacing the original single horizontal segment, labelled ‘p’ and ‘k’. This gives 14 segments in each character, not counting the decimal point. The LEDs in these segments are connected in a common-cathode configuration, so each character (plus its decimal point LED) has a single cathode pin. The anodes are connected to the anode of the corresponding segment of the other character, eg, segment ‘1a’ to segment ‘2a’ etc. That allows the segments of both displays to share pins, as shown in the internal circuit, on the right side of Fig.1. So each dual-character display needs only 17 connection pins: 15 for the LED anodes and two for the cathodes. The displays have 18 physical pins, but one (pin 3) is not used. Two main suppliers of these dual 14-segment displays are Kingbright (PDC54-11GWA) and Lite-On (LTP3784E). The characters are 13.8mm (0.54in) high in both cases. These manufacturers also label the inner display segments differently, but the pin connections are the same. The displays used in this module have segments that emit orange-yellow light, but displays with other colours are available. Inside the HT16K33 IC Now we can look into the IC used to drive each pair of dual 14-segment displays in the module. This is the HT16K33, made by Taiwan firm Holtek Semiconductor Inc (www. Fig.1: how the LEDs are arranged in each of the 2-digit, 14-segment displays. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au holtek.com/page/vg/HT16K33A), which also provides the I2C interface. Holtek makes a range of microcontrollers, some of which are used in popular home appliances and various other ICs, including display drivers like the HT16K33. Holtek describes the HT16K33 as a 16×8 LED Controller Driver with RAM Mapping and an optional keypad scanning ability. It can be used for driving virtually any matrix of up to 16 × 8 LEDs, not just 14-segment alphanumeric displays, as in this module. It can also scan a matrix of 13 × 3 keys, although that feature is not used here. It can be powered from 4.5-5.5V DC. Fig.2 shows the basic block diagram of the HT16K33. The I2C interface controller is at lower left, with an internal RC clock oscillator to its right feeding a timing generator, and two random-access memories (RAMs) below them. The upper RAM is for the display control data, with a capacity of 16 × 8 bits, while the lower RAM is for storing the key scanning data, if that function is used. On the right-hand side are the two controller blocks. The upper one provides eight outputs (COM0COM7) for control of the ‘common’ LED lines (in this case, the cathodes of the 14-segment displays) and the key scanning outputs. The COM0 output is also used to sense the desired I 2C address for the HT16K33, as explained shortly. The lower controller block provides 16 outputs (ROW0-ROW15) for driving the rows of LEDs in a matrix or the segments in the 14-segment displays. It also provides inputs for sensing the desired I2C address, plus inputs for the key scanning function. The power-on reset (POR) block at upper left resets most of the other blocks when power is first applied. One of the functions of the HT16K33 not shown in Fig.2 is its ability to provide programmable 16-step dimming of the LED outputs. That is achieved by controlling the pulse width of the ROW outputs, with a range from 1/16th to 16/16th duty cycle. Another handy feature! Finally, the HT16K33 can be programmed to have any of eight different I2C addresses, from 70h to 77h, using three links on the circuit around the chip. We will see how this is done in the next section. siliconchip.com.au The rear of the 14-segment LED module contains just a few components and the HT16K33 IC. The module’s I2C address is set by the three links labelled A0-A2 on the PCB. Note that the HT16K33 IC is now obsolete, but Holtek still sells the HT16K33A, which is pretty similar. The module circuit As you can see from the circuit in Fig.3, there’s not much in the module apart from the HT16K33 device itself (IC1) and the two dual 14-segment displays. Two pull-up resistors are connected between its SDA and SCL lines and the VHI input, while the HT16K33 chip is powered from the VIO input from CON1, with a 10μF capacitor providing filtering. 5-pin SIL header CON1 is used to make all the power and signal connections to the module. Programming the module’s I 2 C address is achieved using diode D1, three resistors and three PCB links A0-A2, shown above IC1 in Fig.3. The anode of D1 is connected to the COM0 output (pin 2) of IC1, while its cathode connects to the three links via three 10kW resistors. The other ends of the links are connected to the ROW0, ROW1 and ROW2 lines of IC1, which are used as inputs when IC1 detects the desired I2C address. As shown in the small table at upper right in Fig.3, when no links are connected (A0=A1=A2=0), the module has an I2C address of 70h (h = hexadecimal). If only the A0 link is connected, the address is changed to 71h; if only the A1 link is connected, this changes the address to 72h etc. Fig.2: the block diagram for the HT16K33 IC which is used to drive both 14-segment displays. Australia's electronics magazine January 2024  65 An example of what the lowercase letters “qrst” and “abcd” look like on the LED module. The letters ‘q’ and ‘a’ are some of the more strange choices. This ability to set the module’s I2C address to eight different values means it is possible to connect up to eight of the modules to the same I2C port of an MCU. It also means that if you have another device on your I2C bus within the range of 70h to 77h, you can program the 14-segment display to one of the unused addresses to avoid a collision. Connecting it to a micro A nice feature of this module is that its I2C interface makes it easy to connect to most MCUs. This is illustrated in Fig.4, which shows how it can be connected to an Arduino Uno. The module’s VHI and VIO pins are both connected to the Arduino’s +5V pin, its GND pin to one of the Arduino’s GND pins, its SDA pin to the Arduino’s A4/SDA pin and its SCL pin to the Arduino’s A5/SCL pin. Note that with R3 and later versions of the Uno, the last two pins can be connected to the SDA and SCL pins at upper left on the Arduino, just to the left of the AREF pin. Connecting the module to an Arduino Nano is just as easy, as shown in Fig.5. The connections are very similar to those for the Uno in Fig.4. The only other thing you need to do to get the module to communicate with an MCU is to change its I2C address if necessary; it defaults to 70h when none of the links on the rear of the PCB are joined. You should find it just as easy to connect the module to most other MCUs, such as a Micromite, Maximite, Pico­ Mite, WebMite and so on. All that’s left then is to come up with some suitable software to drive the display. For an Arduino, as usual, that will involve finding a software library designed to communicate with the HT16K33 module, plus one or more example Arduino sketches to show how it’s done. Arduino libraries After looking around on the web for Arduino libraries written to communicate with the HT16K33 module, the best one I could find was from US firm Adafruit, called Adafruit_LED_ Backpack. This one was listed on the main Arduino Reference website but was also available on GitHub: • siliconchip.au/link/abpk • https://github.com/adafruit/­ Adafruit_LED_Backpack However, to work with the 14-­ segment displays used in this module, two other libraries must be installed: Adafruit-GFX-library and Adafruit_BusIO_library, see: • https://github.com/adafruit/­ Adafruit-GFX-library • https://github.com/adafruit/­ Adafruit_BusIO Fig.3: The full circuit of the 4x14-segment display module. The table at upper right shows how its I2C address can be set using the PCB links A0, A1 and A2. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au Once the three Adafruit libraries have been downloaded (as zip files) and installed on your PC as part of the Arduino IDE or installed via the Library Manager, you will find a “quadalphanum.ino” sketch in the Examples folder. Verify and compile this sketch, then upload it to the Arduino connected to the module, and you should find the module’s displays will spring to life. First, it will show a stream of all the characters it can display (this takes a while). Then, if you have the IDE’s Serial Monitor open, it will allow you to type in any combination of four characters you want and they will be displayed immediately. You can repeat this over and over. While doing this, I took a few photos to illustrate how the module’s displays show many of the common alphabetic characters. They should give you a good idea of what can be achieved. The upper-case characters are all reasonably clear, but the lower-case characters are less so. Some are pretty unclear, like “p” and “q”, while some of the symbols are very clear, such as “+” and “-”. Unsurprisingly, the numerals are also quite clear. It was a little disappointing to find nothing in the Adafruit libraries to show how to control the light output of the module’s displays. However, if you read Holtek’s data sheet on the HT16K33 (see siliconchip.au/ link/abpj), they provide quite a bit of information on how the PWM dimming of the displays works and can be achieved. Editor’s note: some lower-case letters could be made clearer by modifying the libraries to change which segments are used. To do this, edit the entries in the “alphafonttable” array within the “Adafruit_LEDBackpack.­ cpp” file. Examples of shapes we think would be more clear are shown in Fig.6. Figs.4 & 5: connecting the LED module to an Arduino Uno (above) or Nano (below) is simple. You just need to connect the SDA & SCL pins respectively to A4 & A5 on the Arduino. VHI then goes to 5V on the Arduino and is bridged to VIO, while GND goes to GND. Fig.6 (left): you can edit the library code to output arguably better representations of different letters. An example of what segments could be enabled for the letters ‘p’ and ‘q’ are shown here. Where you can get it The module shown in the pictures is currently available from Jaycar (stock number XC3715) for $9.95. It is also available from Core Electronics (ADA2158) for $21.15 and from AdaFruit (ID 2158) for US$10.50. Adafruit also has versions with different display colours, such as red (1911) for US$9.95. They also sell blue (1912), white (2157) or green (2160) displays, each for US$13.95. SC siliconchip.com.au Upper case vs lower case We recently came across an interesting fact about where the terms “upper case” (capital letters) and “lower case” (smaller letters) came from. In early printing presses, the “moveable type” letters were kept in cases near the press. As the smaller letters were used more often, they were kept in a box (case) closer to the worker. The capital letters were in a case that was higher and further away, above the other. Hence, “upper case” and “lower case” refer to where the letters were found in those early presses! Australia's electronics magazine January 2024  67 Part 2 of John Clarke’s Secure Remote Switch This new Secure Remote Switch uses rolling codes for high security. The DC-powered receiver fits in a compact plastic case, so it can be mounted pretty much anywhere. After explaining how the circuitry works last month, this second and final article has all the construction details. T here are two versions of the keyfob transmitter; one uses a prebuilt transmitter module from Jaycar or Altronics, while the other uses mostly discrete parts (with one extra IC) and is available as a complete kit. Up to 16 transmitters can be used with one receiver, and multiple independent receivers can be built without the risk of the transmitters accidentally triggering the wrong receiver. The receiver can be powered from 12V or 24V DC; there are slight component differences between the two options – the relay coil voltage varies, as does the value of one resistor. The receiver provides SPDT relay outputs that can switch low-voltage AC or DC up to 10A (possibly more if you choose a beefier relay). Assuming you have gathered the parts, we will get straight into construction. After that will come the testing and setup instructions. Construction Both transmitter versions are built on PCBs measuring 29.8 × 39.4mm, with some common components including the SOIC-14 microcontroller, regulator, capacitors and a resistor. They vary in the UHF transmitter section, which can either be a prebuilt 68 Silicon Chip module (for the PCB coded 10109232) or built from discrete components (PCB coded 10109233). The latter PCB includes more surface-­ m ounting parts, making assembling slightly more challenging. However, it doesn’t have any parts with particularly closely-spaced leads, so anyone with reasonable soldering skills should have a good chance of building it successfully. Transmitter construction The PCB overlays for the two transmitter boards are shown in Figs.4 & 5. Whichever transmitter you build, they are housed in a remote control enclosure that measures 37 × 63 × 17.5mm. This enclosure is designed for use with an A23 12V battery; you can also use an A27 12V battery with a smaller diameter but similar length. The PCB is positioned within the enclosure by a moulded protrusion in the base that fits into a location hole in the PCB. This hole is just at the top edge of switch S2. Take care with the locating pin in the enclosure, as it can break easily. If it is damaged, you can fix it by soldering a PCB pin into the locating pinhole on the PCB from the underside and drilling a 1mm hole into the Australia's electronics magazine keyfob base at the broken locating pin position. Trim the PCB pin at both ends so it’s flush with the PCB on top and just long enough to meet flush with the underside of the enclosure when the PCB is installed. IC1 will need to be programmed before it is soldered. This IC can be obtained pre-programmed from Silicon Chip (individually or as part of a transmitter kit), or you can program it yourself if you have a suitable programmer. We described a programming adaptor that can be used for this type of chip in the September 2023 issue (siliconchip.au/Article/15943). We’ll start with the construction steps that apply to both versions, then follow with separate UHF transmitter assembly descriptions. The common parts are in the sections at the top and bottom of the transmitter PCB, with the parts that vary all being in the middle, below the row of switches and above the through-hole diode and SOT-223 package regulator. Note that most SMD capacitors and inductors are unmarked, so you will need to rely on the packaging to show what they are and their value. Mount one component at a time to avoid mixing them up. Start by fitting IC1, making sure it is siliconchip.com.au Fig.4 (top): bend the module leads so that the pins can be soldered as shown here, with GND at the top and ANT at the bottom. The battery clips are soldered to the pairs of slots in the two lower corners of the board. Fig.5 (bottom): on the discrete transmitter PCB, the only new polarised part is the transmitter IC (IC2). When soldering the two SMD inductors, you must position them so their exposed copper leads are in contact with the PCB. the clips to be captured in moulded L-shaped corrals in the base of the enclosure. Module version parts orientated correctly. Solder pin 1 to the PCB and check the alignment to ensure the IC pins all align with the PCB pads before soldering the remaining pins. Also check that it’s sitting flat and not lifted on one side. After soldering, if any pins have a solder bridge between them, you can remove it with a dab of flux paste and some solder wick. The Identity can be set at this stage. If only using one transmitter, it can be left at the default of ‘0’ where none of the 1, 2, 4 or 8 links are made. For a different identity, connect one or more identity pins and the ground track using a solder bridge or a short wire soldered between the IC pins and the ground track. Table 5 (from last month) shows the 16 possible identity settings. Next, fit the 220W resistor and 100nF capacitor at either end of IC1. To do this, tack solder one end of the component and remelt the solder to straighten it, if necessary, before soldering the opposite end. Then add a bit of fresh solder (or flux paste) to the first joint and heat it to re-flow it so it is nice and shiny. Now install the three pushbutton switches, S1-S3. These are supplied with a kink in their leads and are more easily mounted if you straighten the siliconchip.com.au leads first with pliers, then insert the switch leads into the allocated holes, pushing each switch down so its body is in contact with the PCB. After that, install LED1, ensuring its polarity is correct (the longer lead is the anode [A]) and that the top of the LED lens is 10mm above the top surface of the PCB. Mount REG1, diode D1 and the two 1μF capacitors next. D1 is a throughhole component that needs to be inserted into the PCB holes with the correct orientation. Solder REG1 in place by one pin first, then remelt that joint if necessary to align the pins correctly before soldering the remaining pins, then the tab. The two 1μF capacitors can be soldered similarly to the 100nF capacitor and 220W resistor. The battery clips supplied with the enclosure should now be attached to the lower sides of the PCB. Solder these on both sides of the PCB, with the two prods inserted into the allocated slotted pads. Refer to our photos on page 73 to see how they should look once soldered in. Our prototype isn’t exactly the same as the final version, as we narrowed the prototype PCB slightly where the clips go. The final PCBs supplied will have a full-width PCB design that allows Australia's electronics magazine For the UHF module version (Fig.4), a 100nF capacitor needs to be soldered on the underside of the PCB; it is the only part on that side of the board. The UHF transmitter module can then be installed on the top side of the PCB, with its pins bent around the end of its PCB so it lies parallel to the main board, with a 1mm clearance between the main PCB. You can see how that was done on page 73. The module’s antenna is made from a 147mm length of 0.8mm diameter enamelled copper wire. Scrape 1mm of enamel off each end using a sharp craft knife, then close-wind seven turns on a 5.5mm diameter shaft (eg. the shank of a 5.5mm drill bit). Stretch the coil out to 13mm between the wire ends before soldering the ends to the PCB pads. The coil sits 1mm off the PCB. Discrete version parts Start with the discrete version parts by fitting IC2 – see Fig.5. Position it so the small pin 1 location dot aligns with that on the PCB. IC2 will have “F_113” etched on the top face. When it is orientated with the writing the right way up, pin 1 is at lower left. Crystal X1 can be mounted next. It is soldered at the very ends of the component. We recommend you mount the capacitors before the two inductors January 2024  69 (68nH and 470nH). Unlike the other passives, the inductors don’t have pads on all four sides. Therefore, you must ensure their exposed leads are sitting on the PCB before soldering the ends. If you can’t see this clearly, use a magnifying glass. If you want to be sure that the components have been soldered correctly, trace the connections to the other sections of the PCB to where there should be continuity. Their inductance values are low enough that they will appear as short circuits (or at least low-­resistance connections) to a multimeter. For example, pin 3 of IC1 should provide a low resistance reading to pin 6 of IC2. Additionally, check that there are no short circuits between component pins on the PCB that shouldn’t be connected. The board assembly is completed by fitting the antenna. Make it from a 167mm length of 0.8mm diameter enamelled copper wire. Strip the insulation from each end by about 1mm using a sharp hobby knife and close-wind it on a 6.5mm shaft (eg, the shank of a 6.5mm drill bit). Stretch it out to 13mm end-to-end before soldering in with a 1mm coil clearance above the PCB. Receiver construction The Secure Remote Monitor receiver PCB shown enlarged for clarity. Fig.6: the antenna wire is not shown on this diagram; refer to the photo above to see how it’s routed between the two ANT pads on either side. The polarised components on this board are IC1, REG1, LED1-LED3, D1, D2, S4, the three electrolytic capacitors and the receiver module. Match the pin markings on the receiver module with those shown here. 70 Silicon Chip Australia's electronics magazine The 70 × 96.5mm receiver PCB is coded 10109231 – see Fig.6. All the onboard components are throughhole types, giving you a break from the surface-­mounting parts that were on the transmitter. The assembled PCB fits nicely in a Ritec enclosure that measures 105 × 80 × 33mm. Install the resistors first, taking care to place each in its correct position. The resistor colour codes were shown in the parts list last month, but you should also use a digital multimeter to check each resistor before mounting it in place. Note the different R1 value for 24V use (470W 1W) compared to 12V (100W ½W or 1W). Diodes D1 & D2 are next. Make sure these are orientated correctly before soldering their leads. Then install the socket for IC1, ensuring its notched end matches the position shown in Fig.6. Wait to fit IC1 as that step comes later, after the power supply has been checked. Regulator REG1 is mounted vertically on the PCB as far down as it will go, to allow clearance for the lid when in the enclosure. siliconchip.com.au Next, install trimpot VR1, transistor Q1 and the BCD switch (S4). S4 must also be orientated as shown. Switches S2 and S3 can also be mounted now. The capacitors can then be fitted. The electrolytic capacitors are polarised and must be installed with the polarity shown (the longer lead is positive). Pay attention to the voltage ratings for the 10μF and the 100μF capacitors if you intend to use a 24V supply. For a 12V supply, 16V-rated capacitors can be used throughout. You can install the two 100nF MKT polyester capacitors either way around. LED1 mounts with the top of the lens up to 12mm above the surface of the PCB and the anode (longer lead) to the hole marked “A”. Switches S1 and S5 can be installed now, taking care to use the toggle switch at the S5 location and the pushbutton switch for S1. The two remaining LEDs (LED2 and LED3) mount horizontally with leads bent at right angles 6mm back from the rear of the package. Make sure you bend the leads so the longer anode lead is in the “A” pad. The height of the LED centres should be 5mm above the PCB’s top face. CON1 is the PCB-mounting barrel socket, while CON2 and CON3 are 2-way and 3-way screw terminals. Dovetail CON2 and CON3 together by sliding them along the side mouldings to produce a 5-way connector. Orientate all these connectors so the openings are toward the rear of the PCB, then solder them in place. Mount relay RLY1 next. Ensure you use a 24V coil relay if you will use a 24V DC supply or a 12V coil relay for 12V use. Now fit the headers for jumpers JP1, JP2 and JP3 and install the 433.9MHz receiver module. Before soldering the receiver module, compare the pin labels on the back of the module to siliconchip.com.au Fig.7: the front and rear panel drilling details. The large hole marked “C” on the rear panel is for a cable gland that secures the wires to the relay terminals. those in Fig.6 to ensure it is the right way around; there are two possible ways it could be fitted, and only one is correct. Your module might differ from ours, so don’t rely on the photos; check the pin connections. The antenna (not shown in Fig.6) is made from a 169mm length of 0.8mm diameter enamelled copper wire. It extends from the antenna pad adjacent to the UHF receiver to another pad between LED2 and LED3. We covered it with 1mm heat shrink tubing. That is not really required, but it produces smoother bends in the wire as the antenna is shaped. Make sure to scrape away the enamel insulation from both ends of the antenna wire before soldering it into position. close to 5V (4.75-5.25V). If this is correct, switch the power off and insert IC1 into the socket, taking care to orientate it correctly (with its pin 1 end at the notched end of the socket). Case preparation The front and rear panels need holes drilled to allow the LEDs and switches to protrude through and for access to the relay contact screw terminals and DC socket at the rear. Fig.7 shows all the panel drilling details. There is provision for a cable gland to secure any wires connecting to the screw terminals. Either a PG7 or PG9sized gland will fit. When using a PG9 gland, the nut that secures the gland to the back of the panel will need to have the circular fused-on washer cut Testing back to be flush with the straight sides IC1 will need to be programmed of the nut. before use. You can order a pre-­ To do that, only the washer sections programmed device from Silicon Chip on directly opposite sides of the nut (either individually or as part of a need to be brought back to the shape short-form receiver kit). You can also of the hexagonal nut so those sides of program it yourself using the hex file the nut can sit flush on the PCB and available from our website. top lid of the enclosure. This can be Before plugging in IC1, apply power done with side cutters and a file. and check that the voltage between The panel artwork (Fig.8) can be pins 1 and 20 of its socket measures downloaded from our website as a PDF file and printed onto a stickyFig.8: you can download this panel backed label. We have instructions on label artwork from the Silicon making labels at siliconchip.au/Help/ Chip website, print it onto adhesive FrontPanels stock and stick it to the front and Once made, the labels can be affixed rear case panels. Stickers are also to the panels after drilling. Cut out the supplied with the transmitter kits. holes in the label with a sharp craft knife. There is also artwork to make labels for the transmitters. The two Australia's electronics magazine January 2024  71 Rolling Code Systems – frequently asked questions One question that’s often asked about rolling code systems is what happens if one of the switches on the transmitter is pressed when the transmitter is out of range of the receiver. Will the receiver still work when the transmitter is later brought within range, and the button pressed again? This question is asked because the code the receiver was expecting has already been sent (but not received), and the transmitter has rolled over to a new code. How does the system get around this problem? The answer is that the receiver will process a signal that is the correct length and data rate, but it will not trigger the relay unless it receives the correct code. So if the signal format is valid, but the code is incorrect, the receiver then calculates the next code that it would expect and checks this against the received code. If it matches, the receiver will trigger the relay; that means it missed one button press. If the code is still incorrect, the receiver calculates the next expected code, and it will do this up to 10 times, to handle cases where there have been multiple transmitter button presses out of range. If none of these are correct, the receiver then changes its operation to allow for a possible valid signal more than 10 codes ahead. The receiver waits for two valid separate transmission codes before restoring correct operation. On the first receipt of a valid transmission, it looks ahead up to 200 codes, so it is more likely the required valid code will be found, but it doesn’t trigger the relay. The Learn LED lights during this look-ahead operation. If a valid code is found, the receiver waits for the next code sent by the transmitter. This following code must also be correct before the receiver will operate the relay. If only one or neither code is correct, the receiver will not take action. If it’s more than 200 codes ahead, the transmitter will need to be re-registered to operate the receiver. You can test this process by switching the receiver off and pressing one of the remote control switches 10 times or more. Then switch on the receiver and press one of the switches again. 72 Silicon Chip The Learn LED will light, indicating that the look-ahead feature beyond the initial 10 times is activated. The selected function on the remote should operate on the next press of the switch, and the Learn LED extinguishes. While two successive transmission codes could be intercepted, recorded and re-sent in an attempt to activate the receiver, these codes will not be accepted by the receiver. That’s because they have presumably already been received and processed, and the receiver has already rolled past those codes. It will look forwards but not backwards. Another transmitter with a different identity will still operate the receiver (provided it has been synchronised in the first place). That’s because the receiver tracks each transmitter’s rolling codes separately. Calculating the code Another question that’s often asked is how the receiver knows which code to expect from the transmitter since it changes each time. The answer is that the transmitter and the receiver both use the same series of calculations to determine the next code. They also both use the same variables in the calculation; unique values that no other transmitter uses. For our Secure Remote Switch, we use a linear congruential generator (LCG) in conjunction with a 31-bit pseudo-­random number generator (PRNG). The LCG uses an initial seed value, an addition value and a multiplication factor to produce a nominally random result. For example, if consecutive codes have the number 3 added and then multiplied by 49, with the same starting number, both the transmitter and receiver will go through the same sequence. But the actual numbers used are very large, making it difficult to predict the next code by peeking at a few values in the sequence. The code is 48 bits long, with 281,474,976,710,656 possible values (that’s over 281 quintillion or 2.8 x 1014). One problem with the LCG is that it can produce recurring values; depending on the factors, it can produce the same number more than once within a Australia's electronics magazine few hundred rolling code calculations. To prevent this, we include a second layer of randomisation. So once we have the value from the LCG calculation, this value is used in the PRNG to generate a pseudo-random number for the rolling code. The PRNG randomisation runs between one and 256 times before providing the ‘random’ number for the rolling code value. The number generated is then used as the seed in the LCG for generating the next number in the sequence. Using the PRNG makes it difficult to predict the rolling code sequence even if the multiplier or addition value for the LCG is known. We throw further complications by also using code scrambling. The calculated code is not sent in the same sequence each time. There are 32 possible scrambling variations that are applied to the code, so predicting the next code becomes very difficult. What if the transmitter rolling code is identical for two consecutive codes, and the first of these identical codes is intercepted and re-transmitted to open the lock? Our system has safeguards to prevent the same code from appearing twice in succession. There is a check for the same code repeating itself for consecutive codes. If the code is the same, the duplicate is effectively skipped, preventing this possibility. Multiple transmitters Wouldn’t the receiver lose its synchronisation if several transmitters were used? No, because each transmitter operates independently. Each of the 16 possible transmitters used with a given receiver has its own different identity from one to 16. The codes sent by each transmitter are different due to the unique identifier within each transmitter IC that sets the rolling code calculation. Also, the code includes the transmitter identity value that differs between each transmitter. The receiver stores up to 16 different rolling code and calculation parameters, one for each identity, so each transmitter is treated independently. Therefore, even if one transmitter is not used for months while other transmitters are used frequently, its rolling codes will remain synchronised with the receiver. siliconchip.com.au On the transmitter, S1 is red, S2 is blue and S3 is black. variations cater for the timer options, as shown in Table 2 last month, set using JP2. Note that the rear panel artwork and the receiver PCB have square white blocks to allow you to mark the power supply voltage required. Use a marker pen to colour the squares depending on whether the board has been built for a 12V or 24V supply. Four self-tapping screws are provided with the receiver enclosure to secure the PCB to the base. Similarly, two screws are supplied to secure the two halves of the enclosure. Registering a transmitter To register the transmitter with the receiver, press the Learn switch (S2) on the receiver. The Learn/Clear LED (LED1) will light. On the transmitter, remove the battery and reinsert it while pressing and holding switch S1. This will set the transmitter to Synchronisation mode (with its Acknowledge LED lit) and send the registering code when S1 on the transmitter is released and then pressed again. The rolling code is continuously updated during the synchronisation time between when S1 is released and when it is pressed again. This randomises the rolling code generation sequence to an undetermined point, due to the rapid rate of the code recalculation. On average, it is updated around 500 times per second. The rolling code is then well into its generating sequence. This makes it hard to guess the code based on possible MUI values, even if the initial seed value for the code generation is known. siliconchip.com.au The acknowledge LED on the receiver will flash twice, and the Learn LED will extinguish once registration is complete. If it does not seem to work, try this registration procedure again. Test the transmitter and check that the receiver responds by switching the relay on and off. It will take a couple of attempts before the transmitter and receiver start working together. Deregistering a lost transmitter Any transmitter that has been registered can be prevented from operating the receiver; for example, if a transmitter is lost and you don’t want it to be used by an unauthorised person. Deregister the lost transmitter by selecting the transmitter’s Identity using BCD switch S4. The switch is labelled 0 to F, where the labels A-F correspond to identities 10-15. Then press and hold the Clear button (S3) for over one second. The Learn/Clear LED will light initially, then extinguish after S3 is released and the transmitter is deregistered. If you are unsure of the Identity of the lost transmitter, you can deregister all the registered transmitters, one at a time, then re-register the other transmitters again. Jumper options There are three jumper positions on the receiver board; Table 1 to Table 4, published last month, show what they do. JP1 selects the timer length multiplier (see Table 1). The range is 250ms to 60s with JP1 out (the ×1 range) or 60s to 4.5 hours with JP1 in (the ×255 range). Table 4 shows typical timeouts versus TP1 voltages as trimpot VR1 is adjusted. JP2 affects the function of the buttons on the remote control, as shown in Table 2. JP3 affects the function of switch S1 on the receiver, as SC shown in Table 3. The modulebased (left) and discrete (right) versions of the transmitter PCB shown enlarged for clarity. We have used an A23 12V battery, which fits snugly with the recommended battery clips. Australia's electronics magazine January 2024  73 Part 2 by Tim Blythman This Multi-Channel Volume Control can handle up to 20 independent channels, allowing you to build your own home theatre or surround system. You can use a touchscreen LCD panel, an IR remote control or an OLED Module with a rotary encoder to control it. This article has all the construction details. Multi-Channel Volume Control O ur Multi-Channel Volume Control can adjust the levels of up to 20 audio channels by touchscreen, IR remote or a rotary encoder. It’s modular, so you can build it with four or eight (or twelve or sixteen) channels if that is all you need. It’s intended to be incorporated as a part of a larger amplifier system, perhaps using several of our Hummingbird Amplifier modules (December 2021; siliconchip.au/Article/15126). But there is no reason it couldn’t be built as a dedicated unit in its own case. With the principles of operation covered last month, it’s time to commence construction. We assume you have already worked out what modules to build and have the parts at hand. We’ll describe the construction of each type of module in turn. You will need one Control and Power Supply Module and at least one Volume Module. If you want a rotary encoder volume control, you must also build the OLED Module. After that, we’ll go over testing the modules and connecting them together into your system. Since all three module types feature surface-mounting parts, check that you have the necessary tools for this sort of work. A fine-tipped soldering iron, flux paste (and a corresponding cleaning solvent), solder-wicking braid, tweezers and fume extraction are all highly recommended. Some sort of magnifier 74 Silicon Chip and a good light source are helpful for those with diminishing eyesight. We’re talking from experience here! Working outside is a good alternative to fume extraction and should also provide sufficient illumination. Enclosures If you have decided on your choice of enclosure, you can use the blank PCBs to mark the mounting hole positions. It will be easier to do this now before parts are fitted to the PCBs. Look at Figs.12 & 13 to get an idea of the cuts that need to be made for the Control and Power Supply Module and OLED Module, respectively. Control and Power Supply Module The through-hole parts on this Module are mainly in the power section, while the SMD parts are mostly related to the microcontroller. We’ll start with the SMDs. The three different SOT-23 package parts are the smallest and are all different types, so don’t mix them up. Check their orientation against the photos and PCB overlay, Fig.8. SOT-23 parts are small, but their leads are spread out, so you shouldn’t get bridges between pins. REG3 is the MCP1700-3.3 type. Apply flux paste to the three pads and hold it roughly in place with the tweezers. Tack one pin and adjust its position (melting the solder with the iron if needed) until it is square with the pads and flat against the PCB. Then apply Australia's electronics magazine solder to each of the other pins in turn. Refresh the first pin if necessary. Use the same technique to solder the two Mosfets, Q1 and Q2. Q1 is the P-channel part, while Q2 is the N-channel 2N7002 part. Follow with IC9, the 20-pin PIC16F18146 microcontroller. Check its orientation and ensure that pin 1 is located near the dot on the PCB near where the capacitor will be fitted later. Like the earlier parts, apply flux and rest the IC in place. It is larger, so it might not need to be held down with tweezers. Tack one lead and adjust the IC location until it is centred on its pads and flat against the PCB. Next, carefully solder each IC pin to its pad on the PCB. If you do form a solder bridge, leave it for now. Solder the remaining pins to secure the chip in the correct place. To fix a solder bridge, apply more flux and press the solder braid against the bridge with the iron. When it has drawn up the solder, carefully slide it away from the IC and repeat as necessary. After using the braid, surface tension should retain enough solder to form a solid joint, as long as the IC is flat against the PCB. If you’re not sure, have a close look using a magnifier and refresh the pins with the iron using some more solder and fresh flux. The remaining surface mounting parts are all M3216/1206 size (3.2×1.6mm) passives and can be fitted using similar techniques. There siliconchip.com.au Fig.8: there is a mix of SMD and through-hole parts, with components on both sides of this Module. Fortunately, none of the SMD parts are too small. Just take care not to mix up the components and watch the orientations of the IC, bridge rectifier, electrolytic capacitors and box header. are two 100nF capacitors and one 1μF capacitor, which won’t be marked, plus some resistors. Five SMD resistors are fitted to the same side of the PCB, plus three on the other side. To check the resistance codes printed on the parts, refer to Table 1 for the expected markings. Use a solvent to clean up the excess flux on the PCB. Isopropyl alcohol (isopropanol) is a suitable general-­purpose solvent for this. Wipe off as much excess as possible and then allow the remainder to evaporate. Inspect the PCB with a magnifier to ensure that your soldering looks correct. It will be much easier to make corrections now, before any other components are fitted. Through-hole parts The through-hole parts on the Control and Power Supply Module should generally be fitted from shortest to tallest, as that simplifies the process. Refer to the photos and overlay diagrams if needed. Start with the 5.6V zener diode, ZD1. Bend the leads by 90° and thread through the PCB, ensuring the cathode band matches the PCB silkscreen. Solder the leads and trim so they are neat. Follow with REG1, the sole TO-220 package regulator. Bend the leads backward by 90° at a point about 7mm from the body. Thread the leads through their PCB pads and affix the regulator with the machine screw, nut and washer. Once you are happy with the location, solder the leads and trim as needed. Fit bridge rectifier BR1 next, with the + polarity mark on the PCB matching the one on the rectifier. Push it down flat against the PCB before soldering it. Then adjust 500W trimpot siliconchip.com.au VR2 so its wiper is at its midpoint and solder it to the PCB. CON7 and CON8 are next. You don’t need to fit both, as only one is needed to supply power, but we used both on our prototype for testing. CON8 is required for a 24V AC centre-tapped supply, while either can be used with a single 12V AC tap. If you have a choice, the 24V AC centre-tapped transformer with CON8 is preferred. Install the three different regulators in TO-92 cases next, being careful not to mix them up. REG2 is the 78L12, REG4 the 79L12 and REG5 the LM317L. These are also marked on the PCB silkscreen. Now mount CON11 with the key in the box header facing away from the other components on this side. There might also be a marker on the box header indicating pin 1, which goes near the top of the PCB. The three different types of electrolytic capacitors are fitted next. There are four 100μF parts and two 220μF parts around CON11. Ensure that the polarities and values are correct before soldering, with the longer, positive leads towards the + markings on the board. The polarity of the two larger 1000μF capacitors near BR1 are reversed compared to the others. The last remaining component on this side of the PCB is the 5W resistor. Bend its leads and fit it to the PCB pads. Space the body of the resistor about 5mm clear of the PCB. You can tack one lead and adjust its position (if necessary) before soldering the other lead. Components on the other side To help align CON9 for the LCD touchscreen module, fit the four 12mm The majority of the components on this side are SMD parts related to driving the LCD module. Note the mounting for IRRx1, circled in red. Australia's electronics magazine January 2024  75 M3-tapped spacers to the Module using four M3 screws, with the latter on the same side as the through-hole components. Rest the 14-way female header (CON9) in place, then slot the LCD module into it, allowing the header to sit at right angles to the PCB. Solder CON9 to the board. You can test the arrangement for the IR receiver, IRRx1, next. We mounted it so it peeks out just above the top of the LCD (see the photos). There are many ways to mount IRRx1, but we think this method will work in most cases. Regardless of how you do it, just be sure that the correct pins of IRRx1 go to the correct PCB pads. You should also fit CON10 for in-­ circuit programming unless you have a pre-programmed microcontroller. We placed it on the top of the PCB, but it could also be fitted to the reverse if necessary. Programming the micro If you need to program the microcontroller in-circuit, use a 3.3V supply voltage. Also, detach the LCD module before programming to reduce the load on the programmer’s power source. These newer PICs can only be programmed with a PICkit 4 (or later) or a Snap; with the Snap, you will need to provide power separately. We discussed modifying a Snap to supply power on page 69 of the June 2021 issue (“PIC Programming Helper”; siliconchip.au/Article/14889). Use the IPE to upload the 0111122B. HEX file (0111122C.HEX is for the OLED Module) and confirm that you get the “Program/Verify complete” message. You won’t see anything that indicates that it is working right away. Testing Leave the LCD module off when checking the supply rails on the Control and Power Supply Module. It’s a good idea to do this with nothing attached, especially as we need to trim the 5.5V rail. You can connect a current limited DC supply (eg, a bench supply) to the CON8 screw terminals. Connect the negative supply to CON8’s centre GND connection with the positive supply to either of the remaining terminals. This will provide power to the positive regulators. Reversing the polarity will power the negative regulator, which we will do later. Set the current limit to around 100mA and slowly wind up the supply voltage. With 15V applied, we found that our prototype’s 12V, 5.5V, 5V and 3.3V rails were correct (within 0.1V), with the Module drawing about 60mA. You can access the 12V, 5.5V and 3.3V rails at pins 2, 4 and 9 of CON11, respectively. The 5V rail can be sensed at pin 1 of CON9 (where the LCD panel connects). CON8’s centre pin or REG1’s tab are good places to connect to ground for referencing these readings. Assuming there is 12V on the 12V rail, adjust VR2 to get a reading of 5.50V, or as close as possible, across ZD1. Don’t exceed 5.6V, or ZD1 will start conducting and could get warm. If you can’t trim the 5.5V rail, check the resistor values. Since the other regulators are fixed, there isn’t much else that can go wrong apart from the wrong regulator being fitted or the bridge rectifier not being installed correctly. Reverse the polarity applied to CON8 to check the -12V rail at pin 3 Table 1 – SMD resistor codes Value 3-digit code 104 1003 47kW 473 4702 22kW 223 2202 10kW 103 1002 2.2kW 222 2201 76 1kW 102 1001 910W 911 910R 680W 681 680R 560W 561 560R 110W 111 110R 100W 101 100R Silicon Chip LCD module backlight One of the problems we encountered during the design and testing of this project and the earlier Digital Preamp is that the LCD backlight has the heaviest current draw of any component. In the Digital Preamp, we applied the well-known technique of modulating that draw by applying a PWM signal to the backlight control. For this project, we wanted to tackle this in a better way, as it was apparent that the PWM signal was having a small but noticeable effect on the measured audio quality. So for this project, we have avoided using PWM control of the LCD backlight. You can see that the power section of the circuit now uses a 5W resistor instead of several 1W resistors, so it is better able to handle the full backlight current. We still found that the 5W resistor was getting warm, so we had a closer look at what we could do to reduce dissipation. While getting the Module to run cooler is always an advantage, we hoped the lower current draw would lead to less ripple on the main supply capacitors and thus better performance. The “LCD screen backlight modifications” panel explains how the backlight works on these LCD modules and discusses a minor modification that can be made to reduce its current draw. This modification is optional, so you can skip it if you like. Reattach and secure the LCD module using the four remaining machine screws. We can now test that the microcontroller is working correctly and can produce a display on the LCD screen. Screen 1: if you see this screen when you power up your Multi-Channel Volume Control, the Control Module is functional. The red circle at upper right is an IR (infrared) telltale that lights up whenever an IR remote control signal is received (whether it is recognised or not). 4-digit code 100kW of CON11. In this case, we found that the Module only drew about 30mA. Australia's electronics magazine siliconchip.com.au Using the connections you used to test the positive regulators (ie negative to GND, positive to either of the AC[~] connections), set the limit to around 300mA and wind up the voltage. You should see something on the LCD with the input at about 8V or higher. If you don’t see anything by 15V, there may be a problem. The actual current draw will depend on the type of LCD backlight and may be different if it has been modified, but it shouldn’t be any higher than 300mA. You should see a screen similar to Screen 1, and the UP/DOWN/MUTE buttons should respond to presses. That’s as much as we can test at this point. Fig.9: all parts for the Volume Module mount on the top side. Slightly smaller M2012/0805 size passives will fit the same pads. Watch the orientations of the ICs, the electrolytic (including tantalum) capacitors and the box header. Volume Module The Volume Module can be built without the last op amp stage if you want to save a bit of money and time, and that will also improve the volume control range if you don’t need the high maximum gain. All our performance specs are based on the fully populated version; performance will likely be the same or better without those extra op amps. We’ll describe the assembly for all components being fitted. If you wish to leave out the last op amp stage, omit IC3, IC7, their respective 100nF capacitors (one each) and the eight 1kW resistors in that area of the PCB. The two remaining 1kW resistors that pad VR1 are at the other end of this PCB. They are still used. If you omit IC3 and IC7, short out the four PCB jumpers pairs, JP3-JP6. Apply your iron to the pads of the jumper and feed in a generous amount of solder until a bridge forms. You can use solder wicking braid if you need to remove the bridges. Fig.9 and the PCB photos show the fully populated version that we will now assemble. The Volume Module is mostly populated with SMD components, with just a handful of through-hole parts. Start by fitting the eight dual diodes in SOT-23 packages. Apply flux to the pads and rest each diode in place, noting the orientation from the photos and overlay diagram. Tack one lead, adjust the positioning and then solder the remaining leads. Add some fresh flux and touch the iron to the first lead if you need to refresh that joint. Follow with the eight op amps, siliconchip.com.au IC1-IC8. They all face the same way, with their pin 1 facing towards the bottom of the PCB. Small parts like this may not have a dot printed on their bodies, but may have a bevel along the edge nearest pin 1. This bevel is most easily seen from the end of the chip. IC10, the 28-pin SOIC part, should be soldered next. Its pin 1 is orientated in the opposite direction from IC1-IC8. If you have any solder bridges on these parts, rectify them using more flux and solder-wicking braid. The top half of the PCB is marked with horizontal lines and values down the middle, indicating that four identical parts are fitted across. Each part corresponds to one of the four channels, hence the symmetry (Fig.9 shows the values individually for clarity). The remaining SMD parts on this PCB are two-lead passives. Fit ferrite beads FB1-FB4 next. They are identical and marked as FB on the PCB silkscreen and overlay diagram. The ferrite beads will probably be dark grey, matching the ferrite material they are made from; ceramic capacitors are usually a lighter beige/brown colour. The four tantalum capacitors are in a row near IC1 and IC5. As these are polarised, observe the polarity markings. It’s important to note that, unlike electrolytic can capacitors, rectangular moulded (as well as tag tantalum) electros have a stripe on the positive end, similar to a diode’s cathode marking! Australia's electronics magazine Also, our prototype used ceramic capacitors, which look different to the tantalum parts we will supply in kits. You could use high-value SMD ceramics if absolutely necessary, but they are generally inferior for audio signal coupling compared to electrolytic caps. After that, install the 11 100nF capacitors, the four 470pF capacitors and the 100pF capacitors. There are many SMD resistors of different values; naturally, they should not be mixed up. Fortunately, their values will be marked, so you can check them as you go (you might need a magnifier) – see Table 1. If you’re unsure of reading the codes, carefully use a multimeter to measure their resistances. You could even measure them using our Advanced SMD Test Tweezers from the February and March 2023 issues (siliconchip.au/Series/396). Cleaning and checking Now use your preferred flux cleaning solvent to remove any excess flux from the PCB and allow it to dry. It’s a good time to inspect the assembly and check that all the components look to be soldered correctly in the right spots before fitting the remaining components. For JP2, you might like to use a simple wire link if you know what your configuration will be. If so, populate the first board with a link across CS1, the second with a link across CS2 etc. January 2024  77 The Volume Control Module shown fully populated. The op amps just behind the RCA sockets can be left off if a lower maximum output signal is required. The four 1μF ceramic capacitors have been replaced with 2.2μF tantalums in the final version for improved performance. If you’re not sure, install the double-­ row pin header and place the links as described for testing. Adjust the 500W VR1 trimpot to near its midpoint, then solder it in place (or centre it after soldering). Next, fit box header CON5. Its key should be to the left, with pin 1 towards the middle of the PCB, as indicated by the arrow on the silkscreen. You could use a double-row pin header at a pinch, although that won’t guarantee the correct plug orientation. Next, mount the nine electrolytic capacitors. Watch out for the polarities (the longer lead is positive, while the stripe indicates negative) and install them as shown. The last parts to be soldered are the RCA sockets. Their pins and alignment pegs take a bit of wrangling, so ensure their bases are flush against the PCB before soldering them in place. We also suggest adding a tapped spacer to each of the bottom corners of the PCB. Secure them from above with machine screws. These are used to mount these boards to your choice of enclosure but will also keep the PCBs off your bench during testing. OLED Module The optional OLED Module is the smallest of the three. It is little more than a microcontroller, a rotary 78 Silicon Chip encoder and an OLED screen. All the components are fitted to one side of the PCB; the other side forms its front panel. You can see this in the Fig.10 overlay diagram and the photos. Fit the PIC16F15224 microcontroller (IC11) first. Add flux to the PCB pads, rest the micro in place, tack one lead and check its alignment before soldering the remaining leads. There are four 100nF capacitors and four 10kW resistors. None of these are polarised, and can be soldered next. At this stage, you should also add a solder bridge to the CS5 (bottom-most) position of JP7. Now clean off the excess flux and allow the board to dry. Inspect the solder joints of the smaller components and rectify any concerns. This will be easier before the larger parts are fitted. If IC11 is not programmed, you will need to fit CON13, the ICSP header. As you can see from the photo, we used a right-angled header fitted as a surface-­ mounted part. To program IC11, set your programmer to provide 3.3V, connect it to the ICSP header and upload the 0111122C. HEX file. Next, solder CON12, the surface-­ mounting box header. Note the pin 1 marking indicating the orientation. The key for the tab on the cable should face towards the top edge of the PCB. You could use a standard surface-­ mounting dual-row pin header if you don’t have a box header, but it will lack the keying that ensures the plug is always inserted correctly. Like any other part, apply some flux, rest the header in place and tack one lead. Adjust the position if necessary, then solder the remaining leads. Since these larger pins are at 0.1in (2.54mm) spacing, you can be pretty generous with the solder. You should be able to look at the gap between the PCB and the box to see that there are no bridges. Fit the rotary encoder (RE1) next. Mount the encoder using the supplied nut and then add short lengths of component leads to make the connections to the pads below. When fitting the encoder, ensure that the pins match the PCB silkscreen markings (two pins on one side and three on the other). Once the encoder is aligned, you can mechanically secure it using the pads on each side of the body. We used lead offcuts around 1cm long, bent about 3mm from one end. Tin the PCB pads and the ends of the leads and then solder the short end of the leads to the PCB. We used tweezers to hold the other end of the leads while soldering them, then gently bent the other ends of the leads against the pins of the rotary encoder and soldered them together. You can see this in the photo below. Similarly, the OLED uses short lead offcuts for its four electrical connections. Don’t fit the headers to the This shows how the rotary encoder and OLED are attached to the PCB. They both use short lengths of wire, such as component lead offcuts, to connect to the PCB. Note how we’ve soldered a header to CON13 to program the microcontroller in circuit. siliconchip.com.au Fig.10: to allow the PCB of the OLED Module to be used as the front panel, all the components are surfacemounted, including the usually through-hole parts. You can also see this in our photos. OLED, as we aren’t using them. If one is already fitted, desolder it and clear the pad holes of solder. Tin each of the four pads on the PCB and then solder a lead offcut vertically. Remove the protective film from the OLED and ease the OLED module down over the leads until it is flush against the PCB. Gently adjust the position of the OLED so that it is square within the markings on the PCB, then solder each of the four wires to the pads on the Module. Add two more lead offcuts to the two large bottom holes of the OLED and solder them to the PCB pads below. The OLED should light up if you apply 3.3V and GND (via the ICSP header or pins 9 and 20 of CON12). That’s about as much testing as is possible for now. length of 20-way ribbon cable and fit it with one 20-way IDC plug along its length for each module you have built. They don’t have to be in a specific order, as it is all a single bus. Pin 1 of each plug must align with the marked pin 1 of the cable (usually red). Otherwise, it doesn’t matter too much. The sockets can sit above or below the cable; the endmost sockets should have the cable looped back through their locking tabs to secure them. It’s best to use a designated IDC crimping tool such as Altronics’ T1540, but it is possible to use a bench vise with some care. Keep the cable square to the headers and use some pieces of timber on the faces of the vise spread the load. Proceed carefully to avoid cracking the IDC plugs. Ribbon cables Now connect all the modules together with your ribbon cable and wire up your AC supply of choice. A single 12V AC source can connect to CON7 or between the GND and one of the AC phases on CON8. For a 24V AC supply, connect its centre tap to the GND of CON8; the outer 12V taps go to the other terminals of CON8 (it doesn’t matter which). Now we must join all the modules with a custom 20-way ribbon cable. The exact arrangement depends on how you plan to arrange your modules within your enclosure, so we don’t have a specific assembly diagram of such a cable. Fig.11 shows how a typical cable might look. You should use a single Commissioning Fig.11: this is only an example of a possible ribbon cable; you might have different requirements depending on your choice of modules. As long as the pin 1 markings align with the same edge of the cable, the cable should work. Note how the keys on the headers on one side of the cable face the same way, opposite to the keys on the other side. siliconchip.com.au Australia's electronics magazine Power on the Multi-Channel Volume Control and verify that the LCD panel shows the expected screen. We still need to perform one last setup step for each of the Volume Modules. Take a multimeter and confirm that there is 5.5V between TP1 (GND) and TP2 (5.5V) of each Volume Module. If so, adjust trimpot VR1 on each to get 2.75V at TP3. This completes the hardware setup. We’ll now delve into the firmware settings to complete the configuration and then work through the operation of the controls. OLED Module If you have an OLED Module fitted, you should be able to operate its controls and see that both displays update together. Screen 2 shows a typical OLED Module display. There is no configuration needed for the OLED Module. The OLED Module will show three dashes when powered up until it receives data on the ribbon cable. If the dashes persist for more than a few seconds, the OLED module may not be receiving data correctly. In that case, check the ribbon cable and connectors, especially that the IDC plugs are fully clamped around the ribbon cable. Screen 2: the OLED Module display will show this on the screen (depending on the MUTE state). If you see three dashes then the OLED Module is not receiving data from the Control Module. January 2024  79 If you find that the operation of the rotary encoder is backward, reverse the connections from the two outer pins to the PCB using short lengths of insulated wire. We haven’t seen this happen, but it is an easy fix. Setup The default settings for the Multi-Channel Volume Control are to drive 16 channels with an OLED Module connected and the last op amp stages fitted to each Volume Module. If you have fewer than 16 channels, the ‘phantom’ channels will not respond, so you won’t need to change the settings even if you only have six or eight channels. The default IR code settings allow the Volume Control to respond to the Jaycar XC3718 IR remote control unit. Use the “−” and “+” buttons to change the volume and the PLAY/PAUSE button to mute and unmute. The LCD screen should show a red circle when a signal is received. If you don’t see a red circle when operating your remote control, its batteries could be flat, or the IR receiver may not be connected correctly. Screen 1 shows the IR telltale. To enter SETUP on the Control Module, press and hold the SETUP button on the LCD touch panel until the screen changes and you see Screen 3. In general, the “>” button cycles between the different settings, while the “+” and “−” buttons adjust them. The first four parameters set the IR device code and IR command codes. All the commands must correspond to the same device code. While these can be set manually, the option to ‘learn’ a code is also available. Press a button on your transmitter of choice and see that the value in brackets changes; these are the device and command codes the IR receiver detected. You might need to press another button and then your chosen button again to confirm this. Pressing this area of the screen (around the IR codes) will set the last received device code or command code as the current code. The values are stored in EEPROM and used immediately, so you can easily check that the Volume Control responds to the new IR code as expected. We have also found a set of codes that can be used with the Altronics A1012A Programmable IR Remote Control. Program the A1012A to use AUX code 0724 (which is for a Yamaha amplifier). This corresponds to device code 94 and command codes 216 (DOWN), 88 (UP) and 56 (MUTE). You could use the code-learning feature instead of having to enter these manually. Many other Japanese manufacturers use NEC codes. If the Yamaha code conflicts with existing equipment, a few other codes (from the Altronics A1012A list) that start with 07 also give valid NEC codes that the Volume Control can receive. The MAX VOLUME setting limits the highest value that the volume can be set to in dB. This can be set as high Screen 3: during setup, part of the screen is turned over to the setup parameters and buttons. Press and hold the SETUP button for five seconds to get to this screen and start the setup process. 80 Silicon Chip as 20dB and defaults to 5dB. Disabling the OLED Module is also possible by setting the SLAVE IN USE parameter to 0. If your OLED Module is not responding, check that this is set to 1. The LEVEL OFFSET parameter provides an adjustment to the overall gain. If you have omitted the last op amp stage on the Volume Modules, set this to -6 to account for the loss of the last ×2 gain stages. The next parameter changes the number of channels in use; this is the number of channels driven by the Volume Control. This should be a multiple of four and match the number of Volume Modules you have installed. If in doubt, set it to the maximum possible. Say you have two Volume Modules and are using six channels; in that case, set it to eight to ensure the two spare channels are set to safe levels. It can’t be set higher than 16 if the OLED Module is enabled. For these settings (apart from the IR codes), the values in brackets show the lower and upper limits of what these parameters can be set to. The remaining settings are offsets (in digital potentiometer steps) that can be applied to each channel. This can be used to adjust the balance between different speakers. A short press on the SETUP button returns to the normal display. Screen 4 shows what the display looks like when MUTE is active. The EEPROM text is also yellow, indicating that the current state has not been saved to Screen 4: when MUTE is active, the screen changes to look like this. The yellow EEPROM text means that there are unsaved changes. After 10 seconds of no activity, the state (volume and mute) is saved and will be reloaded if the Volume Control is switched off and then on again. Australia's electronics magazine siliconchip.com.au LCD screen backlight modification There are two common variants of the 2.8in LCD touchscreen panels. The main difference we noted is that the touch panels register differently, requiring different calibrations. As we mentioned in last month’s installment, the Multi-Channel Volume Control is programmed to handle these variations. Another difference is in the circuitry of the LED driver for the LCD panel backlight. The two variants we have seen are marked v1.1 and v1.2, as shown in our photos (adjacent and below). Both versions have an XC6206 3.3V regulator to power the LED controller from the panel’s VCC pin and an XPT2046 touch controller IC to provide an interface to the resistive touch panel. Fig.a highlights how they differ in their connections to the LED control line (one of the pins on the 14-way header). For the v1.1 boards, this line connects directly to the LEDs and then ground via a series ballast resistor. The later v1.2 boards use the LED control line to drive a low-side NPN S8050 transistor (Q1). The LEDs are wired to the VCC line, so when the transistor switches on, current flows via a ballast resistor and the transistor to ground. The v1.1 board design lends itself to dimming by an extra series resistor in the LED line. For example, the original Micromite LCD BackPack (February 2016; siliconchip.au/Article/9812) used a trimpot for manual backlight adjustment. The v1.2 boards do not allow that, so we have tended to use it less and less. While both arrangements can be driven by a high-current PWM signal (which could be provided by Q1 and Q2 of the Control and Power Supply Module), we have avoided using PWM in this project due to the resulting digital noise. So we looked into how to modify the LCD panel to adjust the backlight current linearly. Fortunately, changing the LED ballast resistor works well enough, which is what we did. Figs.b & c show a v1.1 board before and after modification. The green circle in Fig.b shows the resistor in question, originally 3.9Ω and designated R6. The original resistor was an M1608/0603 (1.6 × 0.8mm) part, but we replaced it with a larger M3216/1206 (3.2 × 1.6mm) part by scratching back some of the nearby solder mask to allow the larger part to be soldered. This must be done carefully as the surrounding copper area is connected to ground, and a bridge here will short the incoming LED signal to ground. We used 110Ω resistors for our tests Fig.a: the LED control lines for the V1.1 and V1.2 LCD modules. Figs.d & e: for the V1.2 LCD modules, we needed to scrape some of the solder mask so we could fit a larger resistor for R5. siliconchip.com.au Figs.b & c: a V1.1 touchscreen LCD module before (left) and after (right) replacing R6 with a 110Ω resistor to reduce the backlight current. Australia's electronics magazine because we had a few left over from building our prototypes. Figs.d & e show the v1.2 LCD panels before and after the changes. Here, the resistor is marked R5 and is 8.2Ω. We did the same thing, scraping some of the solder mask back to bare copper before soldering in the replacement resistor. You might even be able to solder in an axial leaded resistor by bending its leads back until they are nearly touching. Resistor value The 110Ω resistors were great at keeping the noise and heat down but the resulting backlight brightness is too dim for a well-lit room. We suggest 22Ω as a good compromise. A 100Ω trimpot in series with a 10Ω resistor would be a good choice if you want to tweak the brightness to suit your specific conditions. Our Control Module kits will include a 22Ω M1608/0603 SMD resistor so you can make this modification with a direct resistor swap. January 2024  81 The Power Supply and Control Module mounts to the LCD module using the 14-pin header and two Nylon M3 spacers. EEPROM; that happens automatically after 10 seconds of no further activity. Installing the modules To help you fit the modules into your desired enclosures, Figs.12 & 13 are cutting diagrams of the display cutouts for the Control & Power Supply Module and the OLED Module. The cutout for the Control & Power Supply Module is essentially the same as for the 2.8in LCD module. You could even consider using one of our laser-cut acrylic lids, such as SC3456 (siliconchip.au/Shop/19/3456), as a bezel for neatly mounting the LCD panel. This acrylic piece is intended to fit onto a UB3 Jiffy box and is 68mm tall, so it will be too tall for a 3U rack unit. Otherwise, refer to Fig.12 for the dimensions of the square cutout and screw holes to suit the 2.8in LCD. You will also need to create a hole for the IR receiver if you are using it. Its exact position depends on how you have fitted it. If mounting the LCD inside a metal enclosure, we recommend using a plastic bezel or foam tape to prevent the LCD pins from shorting against anything. Fig.13 shows the outline for the OLED Module. The outermost dimensions (76.5 × 51mm) are the outline of the Module, so you can start by marking these onto your enclosure. Use something erasable or work inside the enclosure, as these will be visible once the Module is fitted. Now add another set of lines 4mm inside these and yet another set of lines 4mm inside these; thus, the second set of lines is 8mm inside the Module’s border. These twelve lines will allow you to drill four holes and cut out the panel, as shown in Fig.13. Note that the inner cutout area does not need to be precise. You should leave enough material for the screws to hold. If the panel is metal, it is worth attaching some foam tape around the perimeter at the back, where the OLED Module attaches. This will prevent the case from scraping the solder mask and possibly shorting against the PCB traces. Completion The Multi-Channel Volume Control is intended to be a ‘subsystem’ within a system such as a multi-channel amplifier, so it is up to you how you connect it to your equipment of choice. As for the RCA sockets, the white upper connections are the inputs, and the red lower connections are the outSC puts of each Volume Module. Fig.12 (left): to mount the 2.8in LCD and thus the Control Module, you’ll need a large rectangular hole and four small round holes. You might also need another small hole for the IR receiver to ‘see’ outside (like the one marked “B”). Fig.13 (right): the exact dimensions of the cutout for the OLED Module are not critical, as the shape overlaps the edge of the hole by about 4mm. Still, you might need to use foam tape or similar to protect the back of the PCB if you are using a metal enclosure. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au Huge Range of 12/24V Switches Control power to your lighting and other devices in your car, 4WD, RV or boat. SAME GREAT RANGE AT SAME GREAT PRICE. TRANSLUCENT PROTECTIVE COVERS IP67 RATED FOR USE IN DUSTY OR WET CONDITIONS ONLY 3695 $ FROM 24 95 $ SP0798 Illuminated DPDT Dust & Waterproof Pushbuttons • 12V LED illumination • On/Off or momentary options available with red, green and blue illumination. 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Jaycar reserves the right to change prices if and when required. SERVICEMAN’S LOG Getting amped up Dave Thompson Dave gives a bit of background on the various guitar amplifiers he built or bought, using the technology of the day. They evolved from valve-based designs, initially made from modified radiograms, through to solid-state hybrid and discrete amplifiers. All so that he could rock’n’roll! Years ago, when I was a little ‘un (or wee tacker, as you Australians might say), I got one of those 10-in-1 electronic sets from Dad as a present for Christmas. I loved it, and it became my favourite ‘toy’. It only had one transistor, a germanium diode (yes, I’m that old), a ferrite broadcast coil, a variable capacitor, a battery holder, a small speaker and a few resistors and capacitors. Still, I could eventually make more than the nominal 10 projects they published in the manual that came with it. These days, you can buy the same sort of thing from the local electronics shop, with 200 or more ‘projects’, but it was pretty rare back in the late 1960s. I believe that Dad purchased it in Australia, on one of his frequent trips to Melbourne to see my Uncle Roger (not the infamous orangeshirt-wearing cook/comedian, before anyone asks!). I loved that kit, but outgrew it relatively quickly. One of my favourite projects (besides the crystal radio, obviously) was the amplifier. It was nothing too fancy, but I could use it to amplify the audio from another crystal set I’d made the traditional (for that time) way. I used a multi-tapped coil wound on a cardboard toilet roll centre, with a germanium diode as a detector. The signal from that was puny, of course, although Dad had sourced me a pair of high-impedance crystal headphones (which I still have somewhere). That made a huge difference over the standard crystal earbud of the day. You know the earphone, cream-coloured case, clear plastic earpiece and a twisted-pair cord. It was precisely 84 Silicon Chip the type of thing Uncle Arthur had for his hearing aid. Fun fact: those earphones are still available from your local electronics store! So, with my crude crystal set and a substantial long-wire antenna that Dad helped me set up, I could get some quite far-off stations, but the audio was weak. Using my 10-in-1 kit set up as an amplifier (connected up using wire into the kit’s springs), I could now drive the small speaker in the kit and free myself of the clunky (and, to be honest, quite uncomfortable) Bakelite headphones. I often listened into the night with that setup, although I eventually built a much more advanced shortwave radio from one magazine project or another. I did use better mid1970s headphones with that, so I could listen late at night without disturbing anyone. I would regularly ‘skip’ the likes of the BBC World Service and Radio Luxembourg, which at that time had some excellent radio shows syndicated from around the world. Good memories. Learning to wield the axe While this was all going on, I was learning to play the guitar. I’d played the piano by this time for about six years, but guitar was what I really wanted to learn. I bought a rather dire electric example from a schoolmate and set about teaching myself. The first thing I discovered was that the sound it made was literally nothing, and I needed an amplifier. Boy, did that open up a rabbit hole of discovery and expense! As anyone who has ever bought a guitar amplifier will tell you, the choices are seemingly endless, and some manufacturers expected your pockets to be almost bottomless! The irony is that if I’d bought one at the time, it would now be ‘vintage’ and worth an absolute fortune. However, as a budding serviceman, I had to fashion my own somehow. I had seen a few related articles in some of the American magazines I was buying at the time about how people were modifying valve (vacuum tube) radiograms or lo-fi amplifiers to use as guitar amps. The main differences were the input impedances of the preamp and overall gain of the input stages; you needed enough gain to get some of that famous valve ‘crunch’. This was good news for a now-broke high school student. Home stereo systems were rapidly relegating radiograms and similar older console and mantle radios to the scrap heap. I recall often seeing them sitting on the roadside, offered for free. Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • Home-made guitar amplifiers Repairing an Icom 551-D transceiver Fixing a car head unit 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 Knowing what we know now, of course, it would be amazing to be able to pick up those antiques and use or restore them – which, let’s be honest, has since become a huge part of this hobby of ours. However, back then, they were big, timber, cumbersome lumps and simply not wanted. New-fangled solid-state hifi amplifiers and separate component systems soon superseded those in every household I visited (including ours). It was good that technology progressed so rapidly in the 1970s; that meant I had my pick of old valve amplifiers. A friend gave me the amp from his parent’s radiogram because he wanted to put a transistor amp into the case. That suited me – I’d be horrified with myself now if I had dumped some beautiful walnut cabinet. The antique radio people would blacklist me! My first guitar amp But suddenly, I had this lump of an amp. My experience with valves was watching Dad maintaining the blackand-white TV he’d built us in the 1960s. I still remember him showing me a nice fat arc when he held his Earthed screwdriver close to the flyback output. I was mightily impressed, I can tell you! Of course, he warned me never to try it myself. I’ll leave it to your imagination as to whether I followed that advice! So, this dusty old valve amp had several inputs that were no longer wired in, and I also made sure I got the speaker, which had an output transformer mounted directly onto the basket. First I ensured it was dust-free, then plugged it in and switched it on. This, of course, is against standard practice for valve amps that haven’t been used in a while. Still, I knew no different then, and I watched all the filaments glow, and a quiet hum came from the speaker. I did know enough to be too scared to go anywhere near it while it was running! I shut it down and looked at the inputs. I can’t recall if they were labelled or not, so I made up a lead with a guitar plug on one end and the older RCA-style connector this amp used on the other. I plugged the lead into the guitar and tried each of the inputs, but of course, it was either weedy and thin or grossly distorted, and not in the nice way we guitar players love. At the time, I knew much less about amplifiers than I do now; even the rare guides I discovered in magazines were vague or purposely omitted values and figures. I could see this wouldn’t fly, so I passed the whole thing on to a school chum who thought he’d like to play around with it. That left me with no amp (and, full disclosure, no real talent either at that point!). siliconchip.com.au I started looking more seriously into buying a commercial amplifier, but that was simply out of the question. I started asking around – these are the sorts of things people buy and then give up on, so some could be quite cheap. A neighbour down the street had just that: a Christchurch-­ made Abby 30, a locally produced clone of the famous Vox AC30. The guy who made them eventually moved to Melbourne, but he made a few of these and other styles of guitar amps back in the day. I wish I’d kept it, as they are now regarded as one of the best copies made, and likely worth a small fortune due to their rarity. I used it for my formative years though, so I got plenty of use out of it. When it came to touring, however, those valve amps became a real liability. The cabinet was solid timber with two heavy-duty 12-inch (30cm) Celestion speakers sitting in it and a solidly-made steel chassis sandwiched into the top; that thing soon broke my rock and roll spirit, not to mention my back! Making it more luggable What I needed was a solid-state ‘head unit’ and a single-­ speaker cabinet for playing smaller clubs and bars. Something a lot easier to lug around, that didn’t take up so much room in the small cars we had at the time (nothing like today’s monster SUVs!). By then, I had done a lot more research and read many more magazines, so I thought I could easily make one. The first one I made utilised a Sanken Hybrid SI-1050G 50W power module I had purchased a year previously. I’d been intending to make a small foldback amp/cabinet, but decided instead to use it as the power section of a guitar amp. The preamp I used was part of a project (if I recall correctly) in one of the English magazines of the day, perhaps Practical Electronics or Everyday Electronics. The power supply was part of yet another guitar amplifier project that was similar to what the Sanken module required to run it. I could have used either a ±33V split rail or a 66V single supply; I chose the latter, mainly because I had a nice beefy power transformer waiting for such a project. I had access to a transparency printer and made and etched my own PCBs, so it all ended up quite good-­looking, and I was pleased with the result. Australia's electronics magazine January 2024  85 At 50W, it seemed underwhelming compared to other 50W guitar amps I had used, so I played around a little with the gain of the preamp and got it running a bit hotter. Still, it was not cutting through the chaff on stage. Overall, a bit disappointing, then. The next build fared a little better. This time, I decided to add 50 more watts, doubling the apparent power but not the output sound level, giving little more than a nominal 3dB gain. However, it gave more punch and more headroom to play with. This module was another locally-produced product, and a kit to boot. It was a common-for-the-time push-pull power amplifier design using the perennially popular 2N3055 NPN and 2N2955 PNP general-purpose power transistors. Many well-liked guitar and hifi amplifiers utilised those robust and easy-to-source components. I used the same preamp, but as this module required a split power supply, I had to redo my 66V single supply, which was also burgled from the Sanken amp. Fortunately, the case was large enough to accommodate the new module and, with a bit of fettling, I soon had a dual-voltage power supply running at around 32V per side. That was just outside the module specs, but allowing for sag and other factors, I figured it should be OK. In use, this was a solid and reliable amplifier that really had some punch, especially after I paired it up with a tone booster, a gain/overdrive pedal and a better speaker (an Eminence driver) in the single 12-inch cabinet. I used it for many years on the circuit (pun intended!) before it was fried one night when someone hit a power pole up the road and killed the whole club’s power. I knew I had blown something, and by that time, I was in a better position to buy a commercial amplifier, which is what I did. Valve amp parts are still available I still have a love for audio amps, though, and have serviced and repaired many vastly different varieties over the years. In recent years, I’ve also re-embraced the valve amplifier scene, learning about them by building and making my own. The transformers and valves, which were always a headache for the average Joe like me to source, are now available, 86 Silicon Chip both here and overseas. While not always cheap, at least we can buy them. I also had the good fortune to stumble upon a commercial transformer winding machine that had served a local company here for decades. It sat in a friend’s garage for many more years until he passed it on to me for a peppercorn fee, and I have since tidied it up and wound several transformers with it. The different-sized cores and wire are also available (if not readily), so I’m lucky to be able to wind transformers to my own requirements and specifications. There are also many good physical schools and online classes dealing with designing and building valve amps (including an excellent one in Australia). If anyone is interested, many good books and tutorial videos are also available on the subject. Like all amplifier theory and technologies, there is often heated debate about what constitutes a good design, or even a great design. The old timers could get it right, but they also had access to high-quality, inexpensive valves and very clever people who ate, lived and breathed valve amplifier design. These days, there are still a lot of clever people about, and even those experimenting with operating valves in low-voltage applications, down to 12V, which is fantastic for the likes of stomp-boxes and portable guitar amplifiers. Editor’s note: see our ‘Nutube’ Valve Preamplifier (January 2020; siliconchip.au/Article/12217) that runs from just 9V DC! While we don’t have unlimited access to those vast quantities of valves anymore, there are still a lot of NOS (new old stock) valves available at ever-increasing prices. NOS refers to parts that have been sitting around forever, but that have never been used. As those supplies dwindle, the prices will continue to rise. While Russian and Chinese-made valves are still being manufactured, modern valve aficionados claim the quality of their valves is nowhere near as good as it was back in the days of General Electric, Philips, Sylvania and others. Sanctions are also causing supply problems for Russian-­ made valves... To take things even further, the advent of the computer and amplifier ‘modelling’ technology means that just about every ‘tone’ some legendary guitar player has come up with is now available as a patch or preset in a hardware modelling amp, selectable at the touch of a button and able to be used live at gigs, just like my own (rather crude) home-made amps. Some modellers are even built into the guitar itself! For the home recording artist, virtual instruments can be loaded into a DAW (Digital Audio Workstation), and the variety of sounds and tones available is almost limitless. Anyone with a halfway decent computer and a set of studio monitor speakers or headphones can download a free DAW and have a home studio almost more potent than many I spent time in during the ‘80s and ‘90s. It’s a whole different world in audio amplifier design and implementation now. Yet the basics remain the same – taking a signal and boosting it through several stages with minimal unwanted distortion at the output. The distortion figures on some of the amplifier designs in this magazine would have been impossible 20 years ago. I’d hate to think what that 10-in-1 amp’s figures were, all those years ago! Australia's electronics magazine siliconchip.com.au Icom 551-D transceiver repair C. K., of Mooroolbark, Vic was asked if he could repair a 50MHz all-mode transceiver, the Icom 551D, dating from the 1980s. It’s an elaborate device and capable of more than 80W output with SSB or FM and 40W with AM. I answered rather foolishly, “Yes, I can repair anything”. Little did I know what I was letting myself in for! The owner had bought it on eBay in a non-functional state. He did try to work on it, which resulted in smoke coming out. Not a very promising start. It looked like a fairly clean unit and powered up to show a display, but nothing came out of the inbuilt speaker. Also, while it showed a sensible frequency on the dial, the tuning knob did nothing. Removing a few screws allowed me to take off the top cover, revealing a large single-sided circuit board with numerous components and a rats’ nest of wires heading off to several connectors. Fortunately, I could download a full maintenance manual. After getting familiar with the various parts, I printed out the schematics on A3 paper so they were readable. All the schematics were hand-drawn; unfortunately, very few components were labelled. The diagrams of the circuit boards had all the components numbered, so together with the parts list, I could eventually identify them. I started by checking voltages. Three TO-220 NPN transistors on the main board: Q28, Q29 and Q30, in association with Q31 and Q32 plus discrete components, provide regulated supply rails. The collectors are fed by 4.7W 1/4W resistors from the 13.8V supply, which should give about 13.5V. Q28 and Q30 gave correct readings but the collector of Q29 measured about 6V (see the diagram below). On closer examination, the collector resistor looked very burnt. That must have been where the smoke came from. With the type of construction prevalent at the time, all the resistors are standing up on the single-sided board, so only one end is accessible. Replacing a resistor requires taking the board out to get at the underside. While the maintenance manual gave detailed instructions on removing the front panel, it gave no clues as to how the main board should be removed. So it was up to me to locate the many screws to be undone and all the connectors that had to be carefully unplugged. Not only were screws holding down the PCB, but two power transistors on one side were attached to heatsinks bolted to the side of the case. All the associated screws had to be removed, and I had to be careful not to damage the insulating washers between the transistors and heatsinks. Finally, after considerable time, I could ease the board out and get to the underside. If the top was a rats’ nest, the bottom was much worse! Look at all those extra components tacked on, including a 16-pin chip on a little subboard. I don’t know if these were some kind of modifications or were needed to fix design problems, but to my eye, it looked like the epitome of bad design. Editor’s note: they seem like the sort of ‘running changes’ made in a factory when they already have thousands of boards made and find that a problem needs to be addressed or an extra function included. Having located the burnt 4.7W resistor and not having that value, I replaced it with two 10W 1/4W resistors in parallel. Left: these transistors regulate the voltage rails on the main board. Below: the shaft encoder circuitry. siliconchip.com.au Australia's electronics magazine January 2024  87 After careful reassembly, I turned on the power and checked that the output on the emitter of Q29 was 9V. When I turned the volume up, hiss came out of the loudspeaker. Attaching a signal generator gave a good signalto-noise ratio with an input level well below 1μV. However, the tuned frequency was well off the indicated frequency on the dial. There is a calibration procedure in the manual that should correct this. The phase-locked loop (PLL) module has a 10.24MHz master crystal oscillator from which the VFO frequencies are generated. A trimmer capacitor on this oscillator sets the exact frequency. However, on measuring this frequency at the test point specified in the manual, I found it was too low and, even with the trimmer capacitor at its minimum value, was a long way off. The crystal had obviously aged and dropped in frequency. I decided to ignore that for now, not having a crystal with a suitable frequency in my collection. The next major problem was the tuning knob. Accessing that meant removing the front panel assembly by undoing numerous screws and carefully unplugging the many connectors. Attached to the tuning shaft is a disc with slots around the circumference. On one side are two phototransistors, and on the other side, mounted on a small subboard, are two LEDs. These are an early SMD type of LED, TLR121, made by Toshiba. They have a clear lens and provide a point source at 700nm, a red wavelength. The LEDs and phototransistors are positioned so that the outputs on the collectors are 90° out of phase, meaning the rotation direction can be ascertained by the logic. No light was coming out of either LED and, on removing the sub-board, they both measured close to a dead short. Not having any LEDs of the same size, I jury-rigged two 3mm red LEDs. It was an ugly workaround, but on reassembly, I was surprised to find that it worked; rotating the knob changed the frequency smoothly in 100Hz and 1kHz steps. Not being too happy with the long-term stability of such an arrangement, I ordered some M3216/1206-size SMD LEDs with clear lenses for a more permanent fix. They arrived a week later. Barely large enough to straddle the hole in the PCB, it was a fiddly job to fit them and I had to use solder blobs to affix them. Unfortunately, on reassembly, the tuning knob was not working correctly. It turned out that the brightness of the LEDs was insufficient to saturate the phototransistors. Reducing the LED series resistor from 560W to 330W fixed the problem. Why both LEDs had failed in such a manner was a mystery. When I mentioned the problem to another contributor to the magazine, Andrew Woodfield, he knew about this problem. Apparently, those LEDs were used in many instruments and were notorious for their failure rate. Warranty failures due to those LEDs clogged the workshop. As for the 10.24MHz crystal, local suppliers did not stock such a value, but I could get them online from the likes of AliExpress as long as I ordered a batch of ten and waited for weeks. However, an associate of mine came to the rescue and gave me a suitable crystal. Having replaced that, I could now tune it to the correct frequency. What about the transmitter? My power supply can only provide 3A at 13.8V. Also, my 50W dummy load is rated at only 15W. I plugged in the microphone, pressed the switch and whistled. This pinned the 3A supply meter, the dummy load got warm, and a pickup loop on the scope showed a clean sinewave. This gave me confidence that the transmitter part was working. Fortunately, the unit’s owner lent me a large power supply and dummy load, enabling me to check that full power was available. Repairing a car head unit These photographs show the Icom 551-D transceiver at various stages of repair. 88 Silicon Chip S. G., of Bracknell, Tasmania found that when you can’t get replacements any more, you need to have a go Australia's electronics magazine siliconchip.com.au at fixing the fault, even if it’s a bit outside of your comfort zone... One of my radio club members was selling off one of his amateur radios, a little Any Tone AT5888. This dual-band radio covered the 2m and 70cm bands, with a power output of 50W on the 2m band and 40W on the 70cm band. It was in very good nick. The price was right, so I soon struck a deal to buy it. This radio was to go into my car; one of the things I liked about it is that it had a remote head. The whole front of the radio can be removed, and one can use a Cat 5 cable to interconnect the main part of the radio and the head unit. This meant I could mount the radio in the boot and the head unit under the dash of my Ford Falcon. The antenna was mounted off the side of the boot. The whole system worked well for around 12 months until I had a car accident, and my car was written off (I was OK; it was just my pride that was hurt). It took me around a week to remove the radio; I had to go to the storage yard to remove all my belongings. I soon had a new car, a 2017 Hyundai Elantra. Mounting the main radio was not difficult, but running the power, Cat 5 cable and external speaker wiring was more challenging. I had to remove several plastic trim panels to run the cable. I ended up not mounting the head unit, as the only spot was just forward of the gear lever and under the air conditioning controls. I gave that job to the local car radio installation company as I did not want to break the plastic trim. This took the company three hours, and I paid the going price at the time, but I got what I wanted. Several weeks later, I noticed that some of the digits in the display were missing, making it hard to understand the letters. The only thing for it was to try to get a replacement head unit. This was a total waste of time; after contacting several retailers in Australia and overseas, I came up blank. It seemed like I would have to put up with the faulty LCD screen. A few months later, I thought to carefully push on the display while the radio was working, and some of the letters returned, only to go missing again once I took my finger off it. I realised the LCD’s edge connector might have gone out of alignment. I figured that taking it apart to check would be unlikely to make the situation any worse. I removed the head unit from the car mounting bracket and took it to my workshop. I soon had the unit apart and carefully removed the LCD glass and its rubber membrane. I ended up cleaning the surface edge area of the membrane with a little bit of contact cleaner, and did the same to the contact edge of the LCD glass. Putting it back together was not that hard; I just had to take my time. The actual LCD glass sits in a tin bracket that also holds in the rubber membrane that interconnects the LCD glass to the circuit board. The tin bracket has four little tabs that allow the alignment between the display and the circuit board to be adjusted, and it can also put a bit of tension on the display. Putting everything back together and reinstalling the remote head unit to the dash bracket, it was working again. The display had no more missing letters or numbers. That was nearly nine months ago, and the display has not faltered yet. SC siliconchip.com.au Australia's electronics magazine January 2024  89 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. 01/24 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 Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) GPS Disciplined Oscillator (May23) 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) 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 Flexible Digital Lighting Controller (Oct20) 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 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) COIN CELL EMULATOR (CAT SC6823) (JAN 24) $10.00 (DEC 23) - Kit: Contains all parts and the optional 5-pin header (see page 77, Dec23) - 1.3in blue OLED (SC5026) MULTI-CHANNEL VOLUME CONTROL - 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) (DEC 23) SECURE REMOTE SWITCH (DEC 23) IDEAL DIODE BRIDGE RECTIFIER (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) - 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 $30.00 $15.00 $50.00 $55.00 $25.00 $10.00 $35.00 $20.00 $15.00 $30.00 $30.00 $30.00 $25.00 $35.00 $45.00 siliconchip.com.au/Shop/ PIC PROGRAMMING ADAPTOR KIT (CAT SC6774) (SEP 23) ARDUINO ESR METER (AUG 23) CALIBRATED MEASUREMENT MICROPHONE (AUG 23) Includes all parts, except the optional USB supply (see page 71, Sept23) - 20x4 blue backlit LCD with I2C interface (Cat SC4203) - red & black PCB-mount banana sockets (two sets required; Cat SC4983) - two 1nF ±1% capacitors (Cat SC4273) 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) 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) 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) 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 (NOV 23) SILICON CHIRP CRICKET (CAT SC6620) (APR 23) PICO AUDIO ANALYSER SHORT-FORM KIT (CAT SC6772) (NOV 23) WIDEBAND FUEL MIXTURE DISPLAY (CAT SC6721) (APR 23) K-TYPE THERMOMETER / THERMOSTAT (CAT SC6809) (NOV 23) TEST BENCH SWISS ARMY KNIFE (APR 23) 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 $15.00 $6.00pr $2.50 $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 MODEM / ROUTER WATCHDOG (CAT SC6827) 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 $55.00 Complete kit: includes all parts required, except the coin cell & ICSP header $100.00 $30.00 $25.00 $25.00 Short-form kit: includes the PCB and all onboard parts. Does not include the case, O2 sensor, wiring, connectors etc (see page 47, April 2023) $120.00 Short-form kit: includes PCB, all onboard SMDs, boost module, SIP reed relay & UB1 lid. Does not include ESP32 module, case, 10A relay or connectors (Cat SC6589) $50.00 *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. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT REFINED FULL-WAVE MOTOR SPEED CONTROLLER VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE 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 DATE APR21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 PCB CODE 10102211 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 09109221 09109222 24110222 24110225 24110223 CSE220503C Price $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD 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) DATE NOV22 NOV22 NOV22 DEC22 DEC22 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 PCB CODE CSE200603 08108221 16111192 04112221 04112222 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 Price $2.50 $5.00 $2.50 $5.00 $5.00 $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 RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION JAN24 JAN24 JAN24 JAN24 19101241 19101242 07111231 07111232 $12.50 $7.50 $2.50 $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 Restoring the QUAD 303 Power Amplifier and Preamplifier A vintage hifi article by Jim Greig The QUAD 303 amplifier and associated QUAD 33 preamplifier (that they call a “control unit”) were introduced in 1967 and sold until 1985. These units belong to fellow HRSA member Ray Thomas. I was very happy to exchange some time refurbishing for a chance to listen to a classic QUAD amplifier. T he specifications of this equipment are ordinary by today’s standards but compare very well with the valve amplifiers of the time. While the output impedance is specified as the emitter resistance (0.3W), the negative feedback across these resistors will reduce it. However, the output filter and series capacitor will increase it somewhat. Power to the amplifier is from a single-ended, regulated 67V supply. Amplifier circuitry The amplifier circuit is broadly similar to a modern ‘blameless’ amplifier circuit in many ways, with a complementary emitter-follower output buffer and a ‘voltage amplification stage’ or VAS based on NPN transistor TR102 – see Fig.1. The main difference is in the input stage and feedback system, which doesn’t use the balanced, symmetrical two-transistor input that’s common today. The amplifier has quasi complementary symmetry output with transistor 92 Silicon Chip triples (TR104, TR106, TR2) to simulate a PNP transistor and provide a linear (through local feedback R120) transistor equivalent for both the PNP and NPN ‘transistors’. With this technique, ordinary 2N3055 transistors act as superior PNP and NPN devices. Diodes MR105 (NPN) and MR106 (PNP) protect the output transistors from overcurrent. On the NPN (upper) side, when the current through R123 approaches 4.3A, MR105 conducts, driving the base of TR103 more positive. As a result, the current through it decreases, cutting off TR105 and decreasing the drive to the output transistor, TR1. The VAS transistor, TR103, has a quasi constant-current load based on resistors R116 and R117 plus capacitor C106. The current available to the base of TR103 would decrease as the Any work on this unit should be done with the mains disconnected, as there are exposed mains connections when the outside cover is removed. Australia's electronics magazine output moved towards the supply voltage if not for C106. As the output moves positive, C106 also takes the junction of R116 and R117 positive, ensuring there is voltage across R117 to drive TR103. This is known as bootstrapping. The output signal from the junction of R124 and R125 idles at half the supply voltage, so a coupling capacitor (C1) is required for the speaker output. That is somewhat frowned upon today as capacitors constitute a significant source of distortion. Still, it simplifies the design and would have resulted in a relatively large cost saving at the time. The amplifier is stabilised with a Zobel network (R128/C108) and series filter (R129/L100). This must have been a very early appearance of the Zobel network in a hifi amplifier to ensure a primarily resistive load to the amplifier, regardless of loudspeaker impedance changes with frequency. The driver stages are DC-­coupled common-emitter singles where siliconchip.com.au Fig.1: one channel of the power amplifier circuit from the QUAD 303 Power Amplifier Service Data manual. differential or long-tailed pairs would be utilised today. Overall DC negative feedback is through R113 and R108, with R130, R110 and RV100 forming a voltage divider for setting the output to half the supply voltage. AC feedback follows the same path, but the gain is limited by C104 shunting R111 to ground. The overall AC gain is 82kW/2.2kW or 37 times. So 0.5V RMS at the input is amplified to 18.5V RMS at the output, giving 43W into 8W. Trimmers allow the output idle DC voltage (RV100) and standby current (RV101) to be adjusted. The standby/ quiescent current is set using the same Vbe multiplier circuit still in use today, based around TR107. Power supply circuitry The power supply (Fig.2) is interesting because the regulator is in the negative rail. The cans of filter capacitors C2 and C3 must not touch ground. The supply is referenced to zener diode MR201 (16V). The zener and associated resistor R204 are connected across the stable 67V output to keep the current through it constant, for a more stable reference voltage. A fraction of the output from the divider formed by RV200, R202 and siliconchip.com.au R203 is compared with the reference voltage. TR200 and TR201 amplify the difference; the result is applied to the emitter-follower regulator, TR3. Trimmer RV200 adjusts the output voltage. R201/MR200 ensure that TR200 is conducting at switch-on, while R200 ensures that MR200 is back-biased and not active during regular operation. The power supply can be configured for 110/120/220/240V AC mains supplies using the external selector switch. A neon indicator glows when power is applied. The chassis The amplifier is elegantly crafted with a pressed steel chassis that has the Power, Input and Output connectors on one end and a heatsink on the other. The two amplifier and power supply circuit boards fit across the bottom of the chassis, held in place with QUAD 303 amplifier weighing 8.2kg: » » » » » » » » Power output: 2 × 45W into 8Ω Frequency response: 30Hz to 35kHz +0,-1dB Total harmonic distortion at 45W: 0.03% at 70Hz and 700 Hz; 0.1% at 10kHz Output source impedance 0.3Ω (+ output capacitor & Zobel network reactance) Hum and noise: 100dB below full output Inter-channel crosstalk: better than -60dB from 30Hz to 10kHz Input sensitivity: 0.5V RMS Speaker load impedance: 4-25Ω QUAD 33 preamplifier (“control unit”) weighing 3kg: » » » » » » » » Frequency response: 30Hz to 20kHz, ±0.5dB Total harmonic distortion: 0.02%, 30Hz-10kHz at all controls level; 0.5V RMS out Input sensitivity (RMS): 2mV (moving magnet), 100mV (ceramic), 100mV (line) Signal-to-noise ratio: 70dB (moving magnet), 85dB (line) Tone control: approximately ±16dB at 30Hz and 20kHz Filter: flat to -20dB per octave at 5kHz, 7.5kHz and 10kHz Inter-channel crosstalk: better than -40dB, 30Hz to 10kHz Output level (RMS): 100mV (line), 0.5V (Pre out) Australia's electronics magazine January 2024  93 Fig.2: the regulated DC power supply circuit, again from the QUAD 303 Power Amplifier Service Data manual. plastic clips. These are easily opened to allow the boards to be removed for service, and still function without breaking. This layout is tidy but necessitates long leads from the PCBs to the output transistors. They are neatly bundled and laced, giving the amplifier a professional appearance (see Photo 1). However, compared with today’s short leads following similar paths, the layout will limit performance. Still, we are in 1967, where 0.1% distortion is considered very good. QUAD 33 preamplifier The QUAD 33 preamplifier complements the appearance of the 303 amplifier. Appearance and construction are clearly design inputs. The preamplifier is built on a steel chassis and implemented on five modules plugged into a passive motherboard and filter board (see Photos 2 & 4). The modules are the Disc Adaptor, two Preamplifiers, Tape Adaptor and Right/Left Hand Amplifier. The Disc Adaptor provides matching for Low Output Magnet (M1), High Output Magnetic (M2), Ceramic (C1) or Spare (S1) inputs by connecting different components in the preamplifier input and feedback paths. The card that plugs in from the back of the unit provides the four functions, as it is square and can plug in one of four ways – see Photo 3. The preamplifier (one channel shown in Fig.3) has two DC-coupled BC109s with R313/R314, R310 and R302 providing DC feedback to stabilise the operating point. RIAA equalisation is provided by the Disc Adaptor using connector M2 and components C104 and R110/C101 from the output to the emitter of TR301. Capacitor C308 connected to the emitter of T301 ensures that the emitter side of R302 closely follows the AC input to the base. The signal current through R302 is then minimal, greatly increasing its apparent resistance (another form of bootstrapping). The amplified disc signal may be selected along with Radio 1, Radio 2 and Tape as inputs to the Tape Adaptor board. It has an emitter follower stage, with the full output passed to the volume control and jumper selectable full or partial output to the Tape Record connector. The outputs from the volume control feed the Left and Right Amplifiers, which drive the tone controls, balance control and filters. Fig.4 shows the tone control circuit, with the output level control circuitry at lower right. The input stage is an emitter follower driving the Baxandall tone control circuit. The output passes through the filter network. There is a top cut switch with -3db points around 5kHz, 7.5kHz, or 10kHz and a slope control (RV8), varying the response from flat to a steep cut at the selected frequency. The filters can be independently set on/off, and a cancel switch bypasses the tone controls and filters. The power supply is a simple zener-­ regulated 12V configuration. A second supply connected to the output plug Photo 1: the internals of the QUAD 303 amplifier are very neat, with multiple modules built on small PCBs, wired together very neatly with loomed wiring. 94 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.3: the preamplifier front-end circuit for one channel, an extract from the QUAD 33 Control Unit Service Data manual. The Disc Adaptor shown on the left can be inserted in one of four ways, effectively acting like a four-way switch to select the S1, C1, M1 or M2 connections to suit different signal sources. is not used, other than to power the indicator. The QUAD 33’s construction is of the same high standard as the 303 amplifier. For example, the balance control is a standard potentiometer operated by a mechanical link from a slider on the front panel. The outer cover slides off on rails attached to the chassis, and the wiring is neatly loomed. Restoration These units are over 50 years old and, if untouched, require attention. Several companies offer “upgrade kits” that contain new electrolytic capacitors, resistors and transistors. There are three versions of the power amplifier, and the upgrade kit must match your model. I used a kit from Dada Electronics (https://dadaelectronics.com.au & https://dadaelectronics.eu) to restore the amplifier, while I purchased parts separately for the preamplifier. The following steps are listed in the Dada documentation for QUAD 303 power amplifiers with serial numbers above 11500, to replace: 1. The two 2000μF filter and the 2000μF output coupling capacitors with three 4700μF capacitors. 2. All electrolytic capacitors on the power supply and amplifier boards with new electrolytic capacitors (plus one 0.68μF foil type). 3. All trimmer resistors. 4. All resistors on the power supply board. 5. Both diodes on the power supply board. 6. Some power supply cabling. The existing wires from the power transformer to the rectifier and on the filter capacitors are solid 24 gauge (about 0.5mm diameter & 0.25mm2). They look good, neatly bent to follow the components, but are inadequate by today’s standards. So I replaced them with 0.7mm diameter (0.5mm2) multicore cable. Photo 2 (right): on the rear panel of the QUAD 33 preamplifier, you can see the Disc Adaptor board that plugs in at lower right, the Tape Adaptor card to its left, plus the various inputs and output connectors. Photo 3 (above): the Disc Adaptor can be plugged in on any of its four sides, setting the preamp up for one of four different input signal types. siliconchip.com.au Australia's electronics magazine 95 Fig.4: the tone control, output level control and top-cut circuitry plus the final amplification stage of the preamplifier; another extract from the QUAD 33 Control Unit Service Data manual. The power-on indicator (Photo 5) is a neon bulb connected to the incoming mains supply through a 100kW resistor. This may be faulty; the recommended replacement is a square LED with a 12kW series resistor across the DC power supply; still, a new neon indicator could be used. Along with the indicator, there are other exposed mains conductors on the fuse and voltage selector on the rear panel, near the input connector, so care must be taken to avoid contact with them. I unclipped the PCBs but did not disconnect them from the cabling. I replaced the components following Photo 4: the QUAD 33 preamplifier internals are very neatly organised and laid out, with highly organised cable routing. 96 Silicon Chip standard procedures, carefully observing the polarity of diodes and electrolytic capacitors. The PCBs are old phenolic types; care must be taken when desoldering and soldering to avoid lifting tracks. For testing, the boards must be kept away from the chassis to avoid short circuits as the chassis is Earthed. As the history of this unit was unknown, I disconnected the positive rail from both amplifier boards before power-on and added a 3.3kW 5W resistor as a load. I then used a variac to gradually apply AC voltage while monitoring the DC output volts. The power supply’s regulated DC output voltage increased slowly and stabilised at around 70V DC. Adjusting the trimmer (RV200) reduced it to the desired 67V. However, the voltage decreased further; at least 10 minutes passed before it was stable. Power amplifier testing I switched the power off and connected the first amplifier board to the supply through a 100W ½W resistor as a fuse. I also connected 10W highpower resistors across the amplifier outputs as loads. I re-applied power and monitored the amplifier DC output voltage (5 on the PCB). Fig.5: the 1kHz square wave response of the QUAD 303 amplifier is very clean. Figs.6(a) & 6(b): the leading edge (left) of the QUAD 303 amp output with a 1kHz square wave fed in. The rise time allows us to calculate the time constant of the high-pass filter formed by the coupling stages throughout the amp. The trailing edge (right) of the same waveform indicates that the response is symmetrical. It steadily increased to 29V and nothing was getting hot. I then adjusted trimmer RV100 until the output was at 33.5V. The output current can be monitored by checking the voltage across both 0.3W emitter resistors (4-6 on the PCB). I adjusted VR101 to get 8mV (allowed range 6-9mV), corresponding to 13mA. This time, both the supply voltage and the amplifier settings were drifting, so I repeated the adjustments after 20 minutes. I removed power and connected the amplifier directly to the 67V supply, then wired up the second board via the 100W resistor. After verifying that it worked, I removed that resistor and I repeated the adjustment procedure for the second board, aiming to have the standby current in both channels the same. The upgrade instructions state, “use for some hours at normal volume and repeat the calibration”, so I followed that recommendation. It is interesting to compare the procedure with the setup for the Silicon Chip Class-A 20W Amplifier that was initially designed 25 years ago (in 1998, as a 15W version) and improved to 20W in the May-August 2007 issues (siliconchip.au/Series/58). While the Class-A amplifier power supply is unregulated, the separate positive and negative supplies with the input referenced to ground ensure the output voltage is close to zero regardless of voltage fluctuations. Also, the quiescent current (1A) remained stable after setup. After monitoring voltages for a while, I ran a few simple tests. The frequency response (-3dB) was from 10Hz to over 60kHz, measured with a digital oscilloscope. It achieved 19.9V RMS output just before clipping, and with a magnified trace, crossover distortion could not be seen on an oscilloscope. A 1kHz square wave output looked good with a reasonably flat response, no overshoot and rise and fall times around 10μs (see Figs.5 & 6). A 32Hz square wave showed significant low-frequency roll-off. However, a good frequency response does not necessarily translate to a good square wave response. I measured the time constant (time for the waveform to drop to 63% of the original value) on the CRO as around 15ms. The most likely cause of this time constant is the 0.68μF capacitor 22kW resistor in series at the amplifier input. The calculated time constant is T = RC = 68μF × 22kW = 15ms, in agreement with the measurement. I connected a 22μF electrolytic capacitor across the 0.68μF capacitor, and the response improved significantly, but it still was not flat. Rather than attempt to redesign the amplifier, I left the input coupling capacitor at 0.68μF. Restoring the preamplifier Photo 5: there are exposed mains connections on the front panel, including for the neon indicator. That indicator can be replaced with a modern LED powered by the DC supply. siliconchip.com.au Australia's electronics magazine It’s important that the preamplifier has decent performance since the power amplifier will amplify any noise and distortion it introduces. In the Dada procedure, the modifications are more extensive than for the power amplifier. The following steps are recommended: 1. Replace all electrolytic capacitors. 2. Replace all BC109 transistors with lower noise BC550 types. 3. Replace some resistors with metal film types for lower noise. 4. Change some resistors to alter the gain so CD players do not overdrive it. 5. Increase the supply voltage from 12V to 16V for more headroom and lower distortion. 6. Remove the secondary power supply as it is not used. January 2024  97 Fig.7: the 1kHz square wave response of the QUAD 33 preamp (bottom) is not as good as the QUAD 303 amp, with a noticeable shift in the level during what should be flat portions. Fig.8: the 100Hz square waves response of the QUAD 33 preamplifier is noticeably triangular. Fig.9: the preamp’s 32Hz square wave response degenerates into something barely recognisable as a square wave. I changed the components as recommended and rebuilt the secondary 8V power supply that powers the indicator. The indicator bulb showed signs of heat damage, so I replaced it with a high-intensity LED soldered to the old bulb metalwork. After changing the lamp type, I moved the power supply’s yellow (indicator) lead from position 2 (AC) to 5 (8V DC). I also changed R502 to 330W to limit the LED current to 18mA. I powered the preamp on without the modules connected and measured the DC supply voltage as 15.9V. As with the power amplifier, there is exposed mains wiring that must be covered while the lid is off. I reconnected the modules and commenced testing with 1kHz sinewaves into the Radio 2 input. As the output reached around 0.5V RMS, it dropped to almost zero. The output resistances of both channels had dropped from 4.7kW to around 80W and stayed there. After some checking, I determined that the low resistance was from the metal frame of the filter switches to the output. Powering it off and pushing switches cleared the problem, but it returned as soon as the output reached the critical value. Several articles mentioned that these switches can cause problems, so I cleaned them without removing them from the PCB. Removing them would be challenging, as the spring-loaded contacts are tiny and would pop out much more easily than they would go back in (see Photo 6). Unfortunately, the problem returned after cleaning, but only in one channel this time. As the low resistance path was to the switch frame, I sprayed the gap under the switches well with contact cleaner and then washed them out with isopropyl alcohol. After that, both channels worked correctly. This would likely have cleared the faults in both channels if applied earlier. What the substance was and why it was triggered into a low resistance state depending on the signal level, I do not know. I checked the signals through the preamp from the Radio input with the filter switch in Cancel (no filter and no tone controls). The sinewave response was -3dB from 15Hz to 220kHz. The square wave response at 1kHz shows signs of poor low-frequency response (Fig.7). At 100Hz, it is obvious (Fig.8), and at 32Hz, the response is horrible (Fig.9). It is the same on both channels, so presumably the original release had similar performance as I did not reduce any capacitor values in the preamp. Examining the amplifier more closely, the signal is losing shape as it arrives at the base of the first transistor, TR400. With the preamplifier in “Cancel” mode, the output from TR400 emitter is coupled via a 2.2μF capacitor and 5.6kW resistor in series (time constant = 6ms) to the base of TR401. TR401 and TR402 constitute a high-gain amplifier with the output returned to the inverting input, making the base of TR401 a ‘virtual earth’. Investigating further would involve breaking the feedback loop. The output has another 2.2μF coupling capacitor connected to a 4.7kW load resistor. Increasing the value of capacitors in this circuit would help the square wave response, but they are not the only factor. I was reluctant to change any of those capacitor values as such changes could have a flow-on effect elsewhere. After all, this is a refit to make the best of the existing unit with minimal changes, not a redesign. Note that the measurements and comments above apply to these modified units alone. Photo 6: one of the switches that caused so many problems by intermittently shorting the signal to the case. Presumably, some kind of conductive gunk had built up; a thorough cleaning finally sorted it out. 98 Silicon Chip Australia's electronics magazine Listening tests Any comments on the sound must acknowledge that my 70+ year old ears are not in great shape. The ‘test’ was listening to Fleetwood Mac’s Rumours on a Thorens/Ortofon Blue combination played through home-built threeway Vifa Speakers. For comparison, I used the 20W Class-A amplifier I mentioned earlier, the Magnetic Cartridge Preamplifier (August 2006; siliconchip.au/ Article/2740) and a two-linear-IC tone control network. This combination is at least 30 years younger, so the comparison is unfair, but it is my reference. I found the QUAD system acceptable but not as clear as my existing system. References (www.dadaelectronics. eu/downloads): QUAD 303 Power Amplifier Service Data and Instruction Book QUAD 33 Control Unit Service Data and Instruction Book QUAD 33-303 Service Supplement QUAD 303 all versions illustrated upgrade guidelines V2.0 QUAD 33 Revision – Illustrated Guidelines V2.7 SC siliconchip.com.au Subscribe to DECEMBER 2023 ISSN 1030-2662 12 9 771030 266001 $12 50* NZ $13 90 INC GST INC GST Secure Remote Switch Control devices remotel y with up to 16 transmitters Multi-Channel Volume Control Simultaneously adjust up to 20 audio channels Six unique designs to build Australia’s top electronics magazine Ideal Diode Bridge Rectifiers Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $70 $80 $52.50 1 year $127.50 $147.50 $100 2 years $240 $275 $190 6 months $82.50 $92.50 1 year $150 $170 2 years $285 $320 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Prices are valid for month of issue. Try our Online Subscription – now with PDF downloads! The History of Electronics; Oct-Dec 23 Coin Cell Emulator; December 2023 Modem Watchdog; November 2023 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe 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 Where to get relays for Sputnik-1 Manipulator I am very interested in replicating Dr Holden’s work with the Manipulator described in his articles on Sputnik-1 (November & December 2023 issues; siliconchip.au/Series/407). Could you ask him where he obtained the PnC5 relays and if he has suggestions on obtaining some? Thank you! (W. D. R., Anchorage, Alaska, USA) ● Dr Hugo Holden replies: I could only find one seller in Ukraine that had these relays. Once I found they could substitute for the PnC4, I bought his remaining stock, about 8 or 10 pieces. I did that for experimentation, and in case I was asked by museums or others to make working replicas in future. I also had to hunt around for quite a while to find the relay sockets. None of the current Sputnik-1 replicas in museums work; they are just cosmetic mock-ups. The original units probably would work still, but there appear to be very few around. I think there is one original unit in a Japanese museum, and there will be a few original ones in Russia. There are probably more PnC5 relays in Russia (PnC4s, too), but because of the war with Ukraine, the Russians are blocking just about every electronic part export. Also, I was told that this particular part was heavily recycled because of the precious metals in the contacts. That is very worrying as it could have thinned the remaining stocks in surplus stores in Russia to near zero. When I built the transmitter replica, I had to source all of the Russian parts from Ukraine. There were some companies in Russia with them, too, but they told me the parts would likely get seized at the Russian border, and they were just as upset about that as I was. Another version of the relay, the PnC7, has completely different coils. Otherwise, it is the same as the PnC5/ C4. The coils could be re-wound fairly 100 Silicon Chip easily. They occasionally appear on eBay, usually from Ukraine. Using inverters with RCDs (safety switches) I was prompted to write in by your Editorial Viewpoint on mains safety in Silicon Chip, October 2023. We need some good advice on working with mains-voltage inverters that take low-voltage DC and step it up to 230240V AC. A faulty mains inverter can have a floating 240V AC on its low voltage DC side because it is independent of the mains and not Earthed. The Earth pin is floating free with the metal chassis. It can be in a car, caravan, part of a generator set or even an off-grid solar system. Could you publish an article on Earth leakage circuit breaker kits for mains voltage inverters? I was recently looking at adding larger lead-acid batteries to a 500W uninterruptable power supply. My concern is that the battery clamps outside the metal chassis could become mains potential if it had a fault in its power transformer. Another example is running a refrigerator from an inverter or generator set in an emergency. All the metal chassis are floating free. If the emergency is a flood, you’re going to have lots of water on the floor and extension cords running all over the place. (J. C., Mitchell Park, SA) ● Yes, an inverter’s mains output is isolated, so an RCD will not necessarily operate. The safety of these is complicated; connecting one output to an Earth will have that output nominated as Neutral and the other mains output as Active. The connection of Neutral to Earth is called the MEN (mains Earth Neutral). Once connected using the MEN system, a commercial RCD will operate as usual. More details are available from this link: siliconchip.au/link/abra By the way, mains-powered devices using transformers can also be Australia's electronics magazine dangerous if the transformer insulation breaks down, even if they are Earthed. That is why mains transformer insulation is held to very high standards. Email problems with Watering Controller I built Geoff Graham’s WebMite Watering System Controller (August 2023; siliconchip.au/Article/15899), and everything worked until I tried to set up the email. SMTP2GO doesn’t even let you start to register, saying, “emails on the shared domain cannot be used” (my address is at Gmail). SendGrid allows me to register but won’t let me continue because it isn’t a business email. I recently tried to update an HP enterprise switch, and when I tried to download the firmware, I found the same thing. I had to register with HP with a ‘business email’, which I don’t have. Previously, there were no problems downloading the firmware. As such things are security updates, I am unsure how legal this is. HP refused to provide the update. I’m not sure if it is possible, but maybe using my email provider’s SMTP server and authentication may be better. Or am I missing something? Thanks for helping. (J. S., Avondale, Qld) ● Geoff Graham responds: It is a trend; these companies are progressively blocking ordinary people from using them; first SendGrid, then SMTP­2GO. Unfortunately, most SMTP services (like Google) cannot be used because they require encryption like TLS and HTTPS, which is beyond the WebMite’s capability. I will explore some alternatives, but there may not be an easy answer. Saving Web(/Pico)Mite program to uf2 file I wrote a program on my WebMite and wanted to create a uf2 file siliconchip.com.au to make it easy for others to flash it into their Raspberry Pi Pico Ws. I installed picotool and managed to use the “save” command to extract a uf2 file from my WebMite, but when I load it into another Pico W, it just installs MMBasic and not my BASIC code. How do I save both into a single uf2 file like Geoff Graham? Also, I wanted to wipe my program to test loading it, so I installed the WebMite .uf2 file again, thinking it would give me a fresh install of MMBasic. But my program was still there afterwards! How do I wipe it and start fresh? (E. Z., Turramurra, NSW) ● Geoff Graham responds: you can save MMBasic and your program together into a .uf2 file using the following steps. 1. Download picotool from https:// github.com/raspberrypi/picotool if you don’t have it already. 2. Plug the Pico (W) into your computer while holding the white BOOT­ SEL button. 3. Install Zadig from https://zadig. akeo.ie/ then run it and use it to install the LibUSB driver for your Pico (W). You can click on Install Driver even if it shows Driver: (NONE) 4. Open a command prompt in the directory where picotool is installed (eg, via the right-click menu). 5. Run the following command: picotool save -a filename.uf2 The -a is critical; without it, it will just save MMBasic, not your BASIC program(s) and configuration options. That is probably where you went wrong. As for clearing the flash and starting fresh, there is a trick to that. Since the PicoMite and WebMite .uf2 files only contain MMBasic, loading them onto a Pico (W) generally won’t erase your BASIC code and settings. That makes it easier to upgrade MMBasic. If you need to clear the flash back to ‘factory default’, load the uf2 file at: siliconchip.au/link/abrk Soldering problems with Explore-28 I built the Explore-28 (September 2019; siliconchip.au/Article/11914) from your SC5121 kit. I have previously built nine other Micromites, including surface-mount varieties. Usually, my MacBook recognises the Microbridge (on boards so equipped) siliconchip.com.au Why Sputnik transmitter heater shunt resistors differ Regarding the article on Recreating Sputnik-1 in the December issue, in the transmitter circuit diagram on page 88, why are R15 and R16 different value resistors? Surely, that would cause the filament voltage across V3 & V2 to be significantly different. The filament resistance (hot) seems to be 22W (2.2V at 100mA). Perhaps this has something to do with the biasing, as these are directly heated valves. I would be interested if Dr Holden could explain the difference in resistance. (D. W., Hornsby, NSW) ● Dr Hugo Holden responds: The short answer is that these are directly heated valves (vacuum tubes), not indirectly heated types. The heater filaments are the cathodes as well as the filaments. So, the cathode current impacts the filament temperature. This raises two further questions that require an answer to be able to answer your question fully: 1. Why do either of the two output valves, V2 and V3, require resistors across their filament connections at all, when the other identical valve they are in series with (V1) in the oscillator section has no such resistor? 2. Why would the two resistors on V2 and V3 need to be different values? To answer question #1, in the case of the output valves, the anode (and ‘cathode’) current is not insignificant compared to the filament current. The electrons that leave the filament surface and create the plate current also heat the filament wire in addition to the filament series chain heater current. As a result, the voltage across the output valve filament and its temperature increases. Let’s say, for argument’s sake, there was just one output stage valve and one oscillator valve, with their filaments in series. It would require a resistor of some value across the filament connections of the output valve to attain the same filament voltage and filament temperature as the valve in the oscillator section, which is in a lower power situation. As for question #2, this has long been a source of confusion about the behaviour of directly heated valves compared to indirectly heated valves with a separate filament and cathode. As you suggest, it has to do with the biasing. This is because the applied voltage along the filament is not a single uniform ‘cathode voltage’ (as it is with an independent cathode in an indirectly heated valve). Instead, the filament is a physical structure acting as a ‘cathode’ with a voltage distribution, or voltage gradient, along its length. When two directly heated valves with filaments are strung in a series heater chain, and their static grid voltages are at the same potential, the valves’ effective average filament voltages (with respect to their control grids) are not matched. In other words, each valve has a different bias point. If you look at the Sputnik circuit, you will see that V3 has its filament shunted by a lower-value resistor because it is connected to the more negative side of the filament power supply. Therefore, V3 has a higher relative positive grid voltage with respect to its average filament voltage than V2. All else equal, with the same grid drive voltage, V3 will have higher plate currents and filament temperatures. The voltage across V3’s filament would climb higher than V2; hence, V3 requires a lower value resistor shunting its filament than V2 so that V2 and V3 match. and then I get the MMBasic prompt. In this case, my MacBook does not recognise the Microbridge as a valid USB device. The only response I get from the board is a steady power LED and, on pressing the programming switch, approximately three seconds later, the MODE LED flashes once only and then nothing else. Any ideas would be welcomed. (S. I., Leeming, WA) Australia's electronics magazine ● There is only one version of the Microbridge; the same chip is used with the same software, just in different physical packages. So, if it has worked for you before, it should work in this case. We’re pretty sure others have successfully used the Explore-28 with a Mac. That the LED flashes when you press the button makes it seem very likely that the Microbridge chip has January 2024  101 at least been programmed. Otherwise, it would do nothing. Have you checked that there is 3.3V between pins 1 and 14 of IC2 when it is plugged in? We know that you have successfully built others before, but this sounds like what happens when there is a soldering problem either with the socket or the Microbridge IC. Use a magnifier or take a close-up photo to check the solder joints on the socket and the IC pins, especially pins 1, 12, 13 & 14 of IC2. Look for bridges but also check that the solder has flowed from each pin down onto the pad below. The board design is tight, and access to the USB socket pins is unfortunately poor once IC1 is in place. Hopefully, you can get a good enough view in there to check if that’s the problem. It’s a pity that IC2 is on the opposite side of the board compared to the socket; otherwise, we would suggest you check the continuity of the D+ and D- lines. If the soldering is all good and the supply rails are correct, all we can think of is that the Microbridge firmware has somehow become corrupted or the chip itself is faulty, but both are unlikely. Changing motorised pot taper law I am assembling all the components to build your Low Distortion Preamp described in the March and April 2019 editions (siliconchip.com.au/ Series/333). I have managed to source every part except for the motorised 5kW dual gang log taper pot. None of the usual suppliers have a motorised log taper pot in stock for this value or even anything close. I have, however, found a supplier for either a 5kW or 10kW linear taper version. I have been toying with the idea of changing the pot ‘law’ by using a resistor across the pot output as described by Rod Elliot on his great website: https://sound-au.com/ project01.htm In this case, I am considering using a 10kW linear pot with a 1.5kW resistor. Would that work and, if so, given the note in the original article on thermal noise, what effect would it have on performance? Would using the 5kW pot with a 750W resistor be better? (K. W., Newport, Vic) ● Rod Elliot’s (Elliot Sound Products) method of adding a resistor at the wiper will work acceptably and provide better volume tracking between channels. That’s because log pots don’t track well at the lower end of the volume range. Because of the added resistor, the potentiometer source impedance will be low, so either option should provide good performance. The lower value pot (5kW) would provide less noise, so that option would be best. The NE5532 op amp can drive loads as low as 600W without significant distortion, so the low value with the resistor in parallel should not cause any problems. Another option is to replace the 5kW linear resistance in the motorised pot with a 5kW log resistance taken from a standard potentiometer. You would need to find a standard 5kW log pot with the same back shell as the motorised version. It’s a delicate procedure, but we have done it and it works. DCC Programmer needs Arduino Uno Out of curiosity, I built the DCC programmer shield by Tim Blythman (October 2018 issue; siliconchip.au/ Article/11261) from a PCB I ordered on your website, but I cannot make it work. I conducted several tests with different ICs (eg, LM556 and NE556) with and without the MOD1 onboard DC booster. I tried it with different DCC programs, but once I connected the power, the locomotive always started going forward and did not respond to any of the commands. I’ve tried all sorts of jumper setting combinations, but still nothing. Since the locomotive runs, it shows that it is partially doing its job of sending pulses to the motor, but it does not interact with the Arduino. I noticed that Tim used an Arduino Uno in his article, and I’m wondering if it may be the cause of my issue since I only have an Arduino Mega on hand. The Mega is supposed to be compatible with the Uno, but maybe there is something else I don’t see with the design. Do you have any clue of what may be wrong? I also built Tim’s DCC Booster shield from the January 2020 issue, and it works perfectly with the Mega, which is why I’m asking about a possible cause of problems with the continued on page 104 Dual-Channel Breadboard Power Supply Our Dual-Channel Breadboard PSU features two independent channels each delivering 0-14V <at> 0-1A. It runs from 7-15V DC or USB 5V DC, and plugs straight into the power rails of a breadboard, making it ideal for prototyping. Photo shows both the Breadboard PSU and optional Display Adaptor (with 20x4 LCD) assembled. Both articles in the December 2022 issue – siliconchip.au/Series/401 SC6571 ($40 + post): Breadboard PSU Complete Kit SC6572 ($50 + post): Breadboard PSU Display Adaptor Kit 102 Silicon Chip Australia's electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales Lazer Security KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware For a full list of the parts we sell, please visit www.ledsales.com.au PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au For Quality That Counts... QUALITY COMPONENTS AT GREAT PRICES Check out the latest deals this month. SMD parts and more. Go to www.lazer.com.au SILICON CHIP ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have been sold. See photos (recently updated): siliconchip.au/link/abl3 Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine January 2024  103 programming shield. Thank you for your help. (D. G., Quebec, Canada) ● According to its documentation, the TimerOne library used in the DCC Programmer sketch only works with the ATmega328 processor (ie, Arduino Uno and not Mega), so we are unsure how you got the DCC Booster Shield working. We’re assuming you are testing the Programmer with the Single Loco sketch. The Passthrough Supervisor sketch only checks the DCC and does not generate any DCC signals. The loco moving is probably due to the DCC Programmer Shield applying steady DC to the tracks. Most locos will default to ‘DC conversion’ and respond to DC signals if no valid DCC signal is present. If you can get a multimeter on the track, you should be able to confirm whether there is only DC present. DCC will manifest as an AC signal at around 6kHz. If you can send us some photos of your construction, we can look and see if you’ve missed anything. Testing with an Arduino Uno would also be a good idea, as that is what we used. Advertising Index How to reverse stepper motor drive Altronics.................................37-40 Blackmagic Design....................... 5 Dave Thompson........................ 103 Emona Instruments.................. IBC Jaycar....................IFC, 9, 11, 26-27 ....................................51, 62-63, 83 Keith Rippon Kit Assembly....... 103 Sourcing fuel injector solenoid I’m interested in building the Arduino-­ controlled Fuel Injection System for Small Engines from the January 2014 issue (siliconchip.au/ Article/5665). I have managed to find most of the parts, but I’m having trouble finding the injector solenoid valve, as no part number is mentioned in the article. Can you please tell me where I can find the part? Thank you in advance. (L. H., via email) ● The article is from quite a while back and parts can become more difficult to obtain over such time spans. There are some fuel-rated solenoids available but they are not identical to the one used in the prototype. Some that we found don’t list an operation life, so we can’t find one that is guaranteed to be suitable. The 12V version of the DN8 at the following links may be suitable: siliconchip.au/link/abr8 siliconchip.au/link/abr9 I am trying to get a stepper motor to run a ½ turn forward, then a ½ turn backward repeatedly. I am referring to Circuit Notebook for August 2011 (siliconchip.au/Article/1125), which is the only relevant article I found. I have the motor running clockwise but cannot get it to run anti-clockwise. Lazer Security........................... 103 LD Electronics........................... 103 Microchip Technology......... OBC, 7 Mouser Electronics....................... 3 PCBWay................................. 12, 13 PMD Way................................... 103 SC Breadboard PSU.................. 102 Silicon Chip Binders.................. 25 Silicon Chip PDFs on USB......... 10 Silicon Chip Shop.................90-91 Silicon Chip Subscriptions........ 99 Silicon Chip VGA PicoMite........ 60 The Loudspeaker Kit.com............ 8 Wagner Electronics..................... 89 104 Silicon Chip Errata and Sale Date for the Next Issue LEDsales................................... 103 What pin setting do I need for this? (P. C., Balgal Beach, Qld) ● You should be able to reverse the motor direction by going through the steps backwards. Instead of step 1, step 2, step 3, step 4, step 1 ... you would do step 4, step 3, step 2, step 1, step 4 ... Converting leading edge dimmer to trailing edge I built the Touch and/or Remote Controlled Light Dimmer (January & February 2002; siliconchip.au/ Series/116) back in the day, and it worked great. It is a leading-edge dimmer, suitable for incandescent bulbs but not so good for modern LEDs. The S576A chip is old and seems to have been replaced by the LS7231. Nowhere in the LS7231 data sheets does it say “leading edge” or “trailing edge”. Could the LS7231 be a direct replacement for the S576A? Do you know of a trailing edge chip that could replace the S576A? The latest Touch Dimmer that you published needed a programmed chip. (D. M., Port Melbourne, Vic) ● The LS7231 IC is not capable of trailing edge dimming. We published a remote-controlled trailing edge dimmer design in the February & March 2019 issues (siliconchip.au/ Series/332). As with virtually all of our designs, the programmed chip and PCBs are available from our Online Shop (siliconchip.au/Shop/?article =11403). We also sell some of the harder-to-get parts for that project; see the link above. SC Coin Cell Emulator, December 2023: in the circuit diagram (Fig.1) on p73, pin 2 of IC2 should only connect to the 22W resistor above and the output network below. On the PCB, it does not connect to the 10kW resistor and 100nF capacitor at its left in the circuit, nor should it. 1kW+ Class-D Amplifier Pt2, November 2023: in the Fig.15 wiring diagram on p78, the brown wires connected to the IEC mains input socket should be light blue (Neutral), and the light blue wires should be brown (Active). That means the connections to the A & N terminals of the switchmode supplies from the IEC socket should also be swapped. Modem/Router Watchdog, November 2023: the V3 software, available from our website, fixes some bugs and includes some improvements. If the first NTP check failed, it would always reboot the router, and a delay has been added shortly after booting to make it easier to break into the MMBasic command prompt using CTRL-C. A problem with the uf2 file has also been fixed. Finally, if loading the firmware manually, run the “AUTOSAVE” command before pasting the program into the terminal. Next Issue: the February 2024 issue is due on sale in newsagents by Monday, January 29th. Expect postal delivery of subscription copies in Australia between January 29th and February 16th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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