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Advertising Index Altronics.................................39-46 Blackmagic Design....................... 7 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................ 4-5 Jaycar..................IFC, 10-11, 27, 67 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia.......................... 9 PCBWay....................................... 13 PMD Way................................... 103 SC Battery Checker..................... 65 SC USB-C Power Monitor......... 103 SC Keyboard Adaptors............. 100 Silicon Chip Shop.................90-91 Silicon Chip Subscriptions........ 99 The Loudspeaker Kit.com.......... 87 Wagner Electronics..................... 12 Errata and on-sale date High power H-bridge uses discrete Mosfets, Circuit Notebook, November 2017: the PCB design is missing a connection between pin 3 of IC1 and the pad of the 3.6kW resistor immediately next to pin 5 of IC1. This can be fixed by adding a short length of insulated wire. Next Issue: the December 2025 issue is due on sale in newsagents by Thursday, November 27th. Expect postal delivery of subscription copies in Australia between November 25th and December 12th. 104 Silicon Chip is damaged. Have you tried our DCC_ Programmer_Shield_V2.ino sketch? It is a much simpler way of testing the hardware. We would be interested to see waveforms (or AC/DC voltages) on IC1’s pins 5 and 9; they might indicate which of the out-of-phase signals has the problem. If you have any photos of your construction/arrangement, please send them to us so we can look for any obvious problems. Options for making a Driveway Monitor The driveway to our house is about 50m long. I would like to detect a car coming when it’s within about 20m from the house; there is a convenient garden to install a sensor there. A signal would go to the house to switch a light on for a prescribed time. A standard IR sensor mounted at the house does not have this range. Can I use John Clarke’s Driveway Monitor project from the July & August 2015 issues (siliconchip.au/ Series/288) to do this? Are the parts still available 10 years later? If not, perhaps I could run a solar-powered IR motion sensor in the garden and communicate to the house via WiFi to switch the light on. That’s all I really need. (R. W., King Creek, NSW) ● For a while, it was difficult to find the main detector IC used in the 2015 Driveway Monitor (the HMC1021S) at a reasonable price. However, DigiKey has recently obtained a very large number (over 10,000) and they are selling them for $11.58 each (siliconchip.au/ link/ac85). So for now, at least, it is still possible to build our 2015 design. Still, Jaycar sells a wireless driveway sentry that flashes LEDs and plays a ‘ding dong’ tone when a vehicle is detected. Its output could be adapted to switch on a light. See www.jaycar. com.au/p/LA5178 Synchronising older clocks to GPS time Some time ago I built a couple of your Big Digit 12/24 Hour LED clocks, as described in the March 2001 issue (siliconchip.au/Article/4235). The clocks work well and have been put into service in a couple of our local churches. However, they still need to be manually adjusted from time to time to keep the clocks accurate, and also Australia's electronics magazine when daylight saving begins and ends. I notice that you have presented many clocks in Silicon Chip over the ensuing years and have more recently also presented enhancements to many of them, enabling them to be GPS synchronised. That seems a very worthwhile exercise, and I wonder whether John Clarke’s design I mentioned above could be modified simply to improve its accuracy. If so, how could I interface a GPS module, and where would it connect in the circuit? I know I could probably build one of your more recent designs, but seeing as I have already built otherwise good clocks, I wonder whether they could be improved with the addition of a GPS module. (N. A., Canberra, ACT) ● The Big Digit 12/24 Hour LED Clock uses a 4MHz crystal for timekeeping (and also to run the microcontroller), so you would need a way of producing a GPS-locked 4MHz signal to do what you suggest. We have published several circuits that can provide a 10MHz reference locked to satellite signals, such as the May 2023 GPS-Disciplined Oscillator (siliconchip.au/Article/15781). So it could be done if we can find a way to convert a 10MHz signal to 4MHz. While you can certainly do that with a phase-locked loop (PLL), there is a simpler method that may work. Build the GPSDO and feed its 10MHz output to a decade counter like the 74HC4017. That chip can run from 5V, operates to over 70MHz and has 10 outputs that go high in sequence, numbered Q0 through Q9. If you then connect the Q0, Q2, Q5 and Q7 outputs to the four inputs of half of a 74HC4002 dual 4-input NOR gate, you should get a 4MHz square wave at the corresponding output. It will have significant jitter, but we don’t see why that will matter in this application, since the PIC16F84 is rated to run up to 10MHz, and the shortest pulses in this scheme are only equivalent to a 5MHz clock. Note that you could pick any four non-consecutive outputs from the 74HC4017, where Q0 and Q9 are considered consecutive. If you can’t easily get a 74HC4002 (they are still available in DIP & SMD packages), you could use a 74HC32 quad 2-input OR gate, with two of the outputs fed to one pair of inputs, making a 4-input OR gate with SC one spare 2-input gate. siliconchip.com.au