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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 Hot Water System Solar Diverter questions I enjoy all your articles and projects, with their explanations. I was very interested in the Hot Water System Solar Diverter project in the June 2025 edition (siliconchip.au/Series/440). However, this project has left me with questions that other readers may also be wondering about. 1. The diverter is supposed to obtain power export data from the inverter. How does an inverter ‘know’ how much of its power output is being self-consumed and how much is being exported? I understand that the inverter measures the energy it produces. However, is it able to differentiate between its energy that is self-­ consumed and that which is exported to the grid? 2. The graph in Fig.1 on page 37 shows consumption/self-­consumption rising and falling sharply during daytime. Consumption loads during the day are typically lower than in the evenings. Unless the household is frequently switching big loads on and off, consumption would not swing as the graph suggests. The consumption seems to follow the pattern of the clouds that affect solar production. Is there more explanation for this graph? 3. The ‘diverter’ is just a switch that turns the hot water heater on and off, even with the smarts in the software. I had imagined the diverter would have a changeover capability, so the heater can be fed from the mains or solar (or neither in the case of batteries). 4. If the diverter simply supplies power to the hot water heater only when there is excess solar output, Why is the RGB LED ‘Analog’ Clock PCB round? I built the Mesmeriser LED clock from one of your kits in 2005/2006. I had much joy building the clock (my background is in electronics), and it ran faithfully on my office wall for nearly twenty years. It failed about a year ago. I don’t remember exactly what happened to it, but I decided it was ‘time’ to retire it. So, I am excited to see Nicholas Vinen’s ‘timely’ new version in Silicon Chip’s May 2025 issue, and I’ll have to buy that kit and start all over. But it occurred to me that as well as a typical round clock face, why not a square clock face, or tilt the square 45° for a diamond shape? Why stop there? Pick almost any shape you can think of: oval or rectangle (horizontal or vertical), triangle etc. A square or vertical rectangular shape could be built into a proportionately sized grandfather clock case to sit on a hall table. I have no idea of the cost to make a different shaped PCB, that may make the options prohibitive. But if it can be done cheaply, LEDs chasing around a non-round shape could appeal to some, myself for one. Hell, I might have to buy a different shape for every room in the house! Alternatively, I could make my own odd-shaped clock face and extend the relevant LED connections from the supplied round PCB. Some of the more urgent jobs around the house might just have to wait! Keep up the great work. (G. M., Pukekohe, New Zealand) ● The cost is generally based on the area of the rectangle that the PCB fits inside, so a square clock PCB that’s 200 × 200mm would cost the same as the 200mm diameter circular one we decided on. Essentially any PCB shape is possible, but the design would have to be redone in the new shape, with the LEDs painstakingly arranged and wired up. Still, a skilled PCB designer could probably redo it in a few hours. Ordering large PCBs is expensive, so we have to pick the shape that most people would want for a clock. We figured, given the option, most people would choose the circle, so that’s what we stuck with. Ordering two or three different batches of boards in different shapes would have increased the amount of work and cost substantially. 100 Silicon Chip Australia's electronics magazine wouldn’t there be cold water on low-solar days? Am I missing something here? (N. K., Kedron, Qld) ● Our replies below: #1. A typical grid-feed inverter has a current transformer in its grid interface. It measures the energy flowing into or out of the grid from the premises the same way an electricity meter would. Inverters that lack such a transformer will calculate local consumption as production minus export. #2. The consumption follows the production in this case because that is the purpose of the HWS Solar Diverter. It determines how much excess solar generation is available and adjusts the average HWS element power to use as much of it as possible without drawing from the grid. So the plot shows it doing its job, despite the constantly varying generation levels during that day. #3. The heater can be fed by mains or solar, since the two are merged at the grid-tied inverter. If the heater is switched on when there is excess solar production, it’s powered by solar. If it’s switched on when there’s little to no solar production, it’s powered by the grid. That’s the same as any appliance in a home with a grid-tied inverter. #4. The unit has a HWS temperature sensor and can command the unit to draw power from the grid if necessary. This is the feature described on the first page of the article as “Automatic override if the HWS temperature is still cold by the end of the solar day”. RGB LED Clock time zone is set manually I have almost completed the RGB LED ‘Analog’ Clock project (May 2025; siliconchip.au/Article/18126); I just need to get the Raspberry Pi Pico W time source working properly. I previously set up one of these for my Compact OLED Clock and Timer project without any difficulty. This time, the unit sets the time at GMT, 10 hours behind the correct time. I set the latitude/longitude to my siliconchip.com.au location, and although the info from the NTP insists that I am at a location 100km away, it is still within the correct time zone. I also set the IPAPI parameters. I can’t understand this. Have I set something wrong? Can you please assist? (D. C., Beachmere, Qld) ● The RGB LED Analog Clock doesn’t use the latitude/longitude data to set the time zone, so the location data should not matter. In fact, the same applies to the Compact OLED Clock; it defaults to GMT+10 (since that applies to the majority of our Australian readers). Having the correct time zone in this case is little more than the coincidence of the defaults matching your time zone. With that said, the RGB LED Analog Clock should default to the same GMT+10 time zone, and we are unsure why that is not the case. The time zone can be manually set and the full details are on page 75 of the project article. Briefly, a long press on the A button enters the time zone setting mode. Short presses on A or B will adjust the time zone earlier or later in 15-minute increments. A long press on B will toggle daylight savings (assuming it is a one-hour offset), while a second long press on A will exit this mode. How to retain a car CD player’s memory Discovering that our household had no working CD players, I decided to use an old car audio head unit that I had taken out of one of our many vehicles. I sourced a suitable 12V power supply, and have made a timber enclosure for it. Like all car audio units, its settings are retained by the continual presence of 12V DC. I’d prefer not to have my unit on all the time, so I decided to include some sort of battery backup to feed the ‘settings supply’. I thought at first that supercapacitors or the like might be a suitable store. The spec sheet doesn’t mention it, but testing shows the current draw when ‘off’ to be as much as 20mA. Given that, I assume that supercapacitors are out, as I was hoping for at least a few days of off-time without the settings getting lost. I looked around online, but did not find any products or circuit designs that I consider being definitively siliconchip.com.au Differential Probe capacitor confusion I’ve run into a problem with the PCB for this project (February 2025 issue; siliconchip. au/Article/17721). The pads for C16 are a short circuit. Could you please check your stock of boards for a short circuit between the pads of C16? It could be that I bridged these pads with solder. However, unlike C15’s pads which I’ve been able to clean up, I cannot remove the short between the pads of C16. I check all SMD components as I go for continuity and shorts; that’s how I found this problem. I’ve removed C16 and cleaned the pads, but still had a short. I then removed C15 as a sanity check, and it’s fine. (B. P., Jeir, NSW) ● Given this board’s relatively small clearances between tracks, or tracks and ground pours (6 thou/0.15mm), a fault isn’t completely out of the question, although it would be very unusual. This is a standard clearance required by many finepitch SMD ICs. Modern PCB manufacturing is pretty reliable, and most boards are electrically tested by the manufacturer. We wonder if you may have accidentally soldered the two capacitors horizontally rather than vertically, as shown by the red outlines in the accompanying diagram. That would be easy to do as the nearest components are also horizontal and there are no outlines marked on the PCB (since there isn’t much space). If you did that, the upper capacitor would be between two ground pads and thus would appear shorted. If that’s the case, it should be possible to carefully desolder the components, rotate them, and resolder them to the board correctly. suitable. This is probably indicative of the fact that I’m misguided in my approach! What do you recommend I use to feed the 20mA supply? (A. J., Mindarie, WA) ● A 12V sealed lead acid (SLA) battery or a compatible LiFePO4 12V battery that’s charged using a 12V battery charger would do the job. Something like a 4.5Ah rating would provide a few days of ‘settings’ storage, although a 1Ah battery should be suitable if only a couple of days without power is normal. The batteries and battery chargers are available from Jaycar and Altronics. Head units will happily run from up to 14.4V (as they would see when the car’s engine is running), so you could use a single power supply to run the player and charge the battery, although this does rely on enough active usage over time to keep the battery charged. You could use a 15V DC regulated Australia's electronics magazine supply with a single series diode to obtain ~14.3V to run the player, then another series diode to drop it to ~13.6V to float charge the battery. A low-value resistor in series with the battery can limit the initial charging current to avoid overloading the supply (eg, a 2.2W 5W resistor should keep the maximum charging current under 1A). Will the VGA PicoMite work with a Pico 2? I recently read about the VGA PicoMite and saw that you are selling a kit for it. I am wondering if the kit is compatible with Raspberry Pi Pico 2. If I use a Pico 2 instead of the included Pico, and install the latest PicoMite V6 firmware, will everything will work as expected? Also, I want to upgrade the default Pico with the latest version of the August 2025  101 PicoMite firmware. Will the kit still work? (J. C., via email) ● Geoff Graham responds: I have just updated my web page to clarify this. Yes, the VGA PicoMite hardware will work with either a Pico or Pico 2, as long as the appropriate firmware is installed (see the PicoMite 2 article from February 2025 at siliconchip.au/ Article/17729). There’s nothing stopping you from upgrading the firmware in the supplied Pico. How were EPROMs programmed in 1997? Dr Hugo Holden’s article in the January 2025 issue about retrieving data from old microcontrollers piqued my interest. I built the colour TV pattern generator from your June and July 1997 issues. It is still working well, but it would be a shame if the EPROM failed. I am curious to know what programming setup was used at the time. I have looked on eBay etc and noticed that there are some EPROM programmers available, but they don’t appear to support the device used in the colour pattern generator. I realise that the technology is dated now, but it would be interesting to build a project that runs on modern PC software that can talk to these old chips. As mentioned in Hugo’s article, it can save some specialised gear from the scrap heap. (G. C., Toormina, NSW) ● We used a basic EPROM programmer driven by a computer programmed in BASIC. Unfortunately, the details of that setup are lost in the mists of time. The Windows-based EPROM programmer by Jim Rowe that was published in late 2002/early 2003 (see siliconchip.au/Series/110) would be able to program these devices. However, the software would need to run within a DOSBox emulator on a modern Windows computer. You would also need a USB to Centronics interface converter. An easier solution would be to purchase the XGECU T48 Universal Programmer that we reviewed in April 2023 (siliconchip.au/Article/15735). Its software runs natively on Windows 10/11. GPS Time Source not getting valid data I’m having problems with the Clayton’s GPS Time Source project (April 102 Silicon Chip 2018; siliconchip.au/Article/11039). I’m using the ESP8266 D1 Mini module, as you used in the article on page 58 of that issue. I compiled the code using Arduino IDE V2.3.5, set for an ESP8266 “LOLIN(WEMOS)D1 R1”. The code is “NTP_client_for_ ESP8266_GPS_V13skt.zip”, downloaded yesterday from the Silicon Chip site. It compiles OK and programs the ESP8266, although there are many warnings in the compile window. After programming, I managed to set it up for my home router SSID and password OK. However, the time it sends to the IDE serial port seems to be incorrect. The time was approximately 04:01 UTC according to my PC, but I got the following serial data: $GPRMC,001632.009,V,3746.000,S,14 453.000,E,0.00,000.00,010118,,,*22 $GPGGA, 001632.009,3746.000,S,1445 3.000,E,0,04,1.0,0.0,M,0.0,M,,*7B $GPGSA,A,1,,,,,,,,,,,,,,1.0,1.0,1.0,*2D $ESP82,connected,SSID Telstra****** chan 6,10.0,0.52,0,0,0*03 Do you have an idea what’s causing this? (G. P., Narre Warren South, Vic) ● The output that you’ve included looks normal, but suggests that the Time Source has not been able to acquire the time successfully through NTP. The V in the $GPRMC sentence means that the data is ‘void’ and is not yet valid. The time it is reporting is 00:16:32 on 1/1/2018, which is 16 minutes after the default time programmed into the sketch when it starts. The 010118 in the output (near the end of the $GPRMC line) is the date field. So the time is wrong because it is using a default. We suggest you start by rebooting the D1 Mini module to force it to retry. If you have another WiFi network, that might be worth trying, too. We’ve heard reports of ESP8266 modules not working in cases where there are 2.4GHz and 5GHz networks with the same name. What appears to happen is that the router kicks the modules off the 2.4GHz network to see if it will join the 5GHz network instead. Of course, the ESP8266 only has a 2.4GHz radio, so this does not work. Some readers have successfully renamed their 5GHz networks as a work-around. For example, I’ve added a ‘_5G’ suffix to the 5GHz SSID of my home network. Australia's electronics magazine We don’t think that the warnings are a concern since the project compiles successfully. We are sure that these warnings are due to changes to the board profile since the last update from a few years ago. We suggest using these versions of the board profiles: V11 should be used with ESP8266 Boards Manager Profile version 2.7.4 and earlier. V12 should be used with ESP8266 Boards Manager Profile version 3.0.0 and later (tested with V3.0.2). The newest ESP8266 board profile is version 3.1.2, which we haven’t tested, so it would be worth trying with a 3.0.x version. You can select a specific version and downgrade to it in the Boards Manager. Troubleshooting Turntable Driver I have just built the Precision Turntable Driver (May 2016; siliconchip. au/Article/9930). I tested it today and got the following very strange results. Initially, it produced 230V AC after adjusting trimpot VR1. Pins 5 and 14 of IC1 read 4.95V DC. I was able to power my turntable (with its AC synchronous motor) for a few minutes. Since my turntable runs about 5% fast (about 35.4 RPM, for some reason), I tried repeated presses of the ‘slower’ button. It did not reduce the speed back towards 33.3 RPM. However, the ‘faster’ button did increase the speed incrementally, up to nearly 40 RPM. Shortly after this, I noticed the power LED was flashing slowly, in a sort of slow pulsing fashion with the LED never completely going dark. This was accompanied by a faint tapping sound that was synchronised with the LED flashing. I plugged the turntable back in, but it appeared to get no power and didn’t spin, unlike the initial trial described above. I examined the PCB very carefully under bright light to make sure I had no solder bridges or short circuits, but of course I don’t know if all the semiconductors, capacitors etc are OK. (P. L., Kaleen, ACT) ● Based on the photo supplied, there are some long component pigtails extending from the PCB. You should check that they don’t short to the enclosure (or, even better, trim them). Otherwise, the construction looks good. continued on page 104 siliconchip.com.au