Author Topic: 24 hours alarm clock  (Read 835 times)
sol
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24 hours alarm clock « on: November 15, 2020, 09:47:07 PM » Author: sol
Since we have a very vast knowledge base here, I thought I'd ask here first. I am looking for a standard red LED alarm clock that uses 120V 60Hz but displays time in 24 hour format. I have found some with varying reviews on Amazon, and I have no desire to order only to return or keep units I don't want. I'd order from overseas, but most of these use the 50 or 60Hz as the periodic timing element, so a 50Hz clock on 60Hz mains with only voltage converter won't keep time and defeats the purpose. Setting up a Hz converter is way too much trouble for this project.

Alternatively, is there an easy way to hack one to change to 24 hours ? I'm not a solder person, and I have very limited knowledge of the inner workings of electronic appliances.

Many thanks.
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Binarix128
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220V AC 50Hz, NTSC


GoL UCOUT2noI2R__jgPSJUjGRtA
Re: 24 hours alarm clock « Reply #1 on: November 15, 2020, 10:01:53 PM » Author: Binarix128
Most digital clocks even the cheapest you can find will show the hour in a 24 hours format or can be configured. Using the mains as timing is practically obsolete nowadays, because it will only work on an specific voltage and frequency and, and you will need to design the clock for every single mains standard, instead you put a switching power supply that can work on 100-250V 50-60Hz and then you use an internal quartz oscillator, it keeps the things simple and cheaper, almost all devices nowadays that work in all mains voltages and frequencies.

So don't worry much while searching, the clock that you liked is likely to work with all mains standards and it's also likely to show the hour in a 24 hour format.
« Last Edit: November 15, 2020, 10:04:35 PM by Binarix128 » Logged
Medved
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Re: 24 hours alarm clock « Reply #2 on: November 16, 2020, 02:32:43 AM » Author: Medved
If the clock is based on the LM8560 (most LED clock radios with analog tuning; uses 9V backup vattery), you may switch the display to 24 hour format by letting the pin 28 open. Of course, the clock has to have the full "24hour" display board. It is quite common for tye clock radio makers to use the same design, just different transformer and two configuration solder bridges being the only difference among versions of different markets.

Newer clocks (mainly where the radio has digital control using the same display; uses 3V 2xLR03 or LR6 as backup battery) are quartz controlled, so you may buy the EU version and suffice with replacing the transformer for the 120V one (or just modify it to run from 5VDC from an old phone charger).
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