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‘Big Blue’ Clock


Geoff Theasby G8BMI has a couple of clock kits and also manages to squeeze in a voltmeter/ammeter.



Geoff Theasby G8BMI has a couple of clock kits and also manages to squeeze in a voltmeter/ammeter.


This comprehensive electronic clock was obtained, as were the other kits in this series, from China for less than £10. See previous articles for caveats and disclaimers.

This was the first kit I built, and with poor eyesight too. (I was awaiting a cataract operation). I caused a short-circuit by using excessive solder, letting out some resistor smoke, and I enlarged a mounting hole and cut off a supply line. This was remedied by the use of some 36-gauge wire and a magnifier. No harm was done and it worked perfectly from then on, despite the smoke. The large display is available in red, blue and green, and dims in low light but my wife said it was still too bright and she doesn’t like blue light, having heard that it interferes with sleep. I maintain that this problem refers to smartphones and tablets, not relatively low-powered LEDs, but whatever... A backup coin cell keeps time during power cuts but the display is blanked until the mains power returns. I tested the backup and it lasts for at least 40 minutes. The clock boasts an hourly chime and an alarm, and displays temperature readout, date and day of the week. I also added a false pendulum and a drawing of a bird, thus making it a ‘Cuckoo’ clock, Fig. 1. The alarm and chime or other displays can only be switched on or off, or set, when that condition is displayed, which is every 45 seconds. The microcontroller is pre-programmed so no code writing is required.

The circuit requires 5V, which I obtained from a redundant Nokia ‘wall wart’. Nokia claim a nominal 5V but the off-load supply is 8V. It is being used for a non-original purpose so I replaced the almost unsolderable fabric-based wire from the plug with copper wire. I powered the clock via a 5V regulator using an LM317 variable regulator, without a heat sink, bolted to a scrap of Veroboard and encased in a small plastic box. It has now been running for about a year with no problems. The instructions mention running it from a USB supply but no USB socket of any type is provided. It’s not an easy kit to build, being quite closely packed, but if you carefully follow the instructions and are reasonably good at soldering with a 25W iron, it will be fine. There are several YouTube videos to watch if you feel unsure. I mounted it on a piece of 1.5mm white Plastikard in order to hang it on the wall.

It keeps good time but the alarm time as set creeps backwards by one minute per day. I have no idea why but I don’t use the alarm facility.

The circuit is provided. It uses a DS1302 clock oscillator, and a 15F204EA to drive the functions and the display. Note that the third digit must be installed upside down for a correct display!

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I don’t recommend its use as a shack clock, due to the regular display of non-time-related information, when you may need an exact time for the logbook but a simpler clock follows.


Shack Clock

There is an alternative and simpler kit with only four digits and a dozen components, including a AT89C2051, costing about £5, Fig. 2. Running from 3-6V DC at 50mA, it could be battery powered but I use it as a shack clock, as suggested above. It was assembled with no problems in an hour and, as usual, it worked first time. The LH button cycles round the options, A-J, and the RH button sets the details. I run it from an old Fujifilm ‘wall wart’, giving a regulated supply of 5V. Full details of the clock at:

That’s about it really so I include a third item this time, too.

For those who like modules that work straight away, try a combined USB voltmeter/ammeter. It shows, digitally, the voltage, nominally 5V, at the USB socket, and the total current drawn by whatever is plugged in to it. Available (if you pick the right place) for under £1, Fig. 3. It’s not a lot of practical use but it’s cheap and fun!


This article was featured in the July 2018 issue of Practical Wireless