The Decoders

A project log for Relay Logic Clock

A digital 24 hour clock using only relays and diodes for the counting logic.

Dave GönnerDave Gönner 12/30/2015 at 14:105 Comments

Today my latest shipment of relays got in from Hong Kong, so I can finally finish one of the decoders. I am just posting some pictures for now, but I promise to add a complete description later. The decoder shown here is the first of four. It is the single-minutes decoder. It has five inputs, from the first five flip-flops and it drives one single seven-segment display. At the bottom you see the array of diodes that decode the ten different digits. The five relays at the top are responsible for the AND operations to detect the correct state of the flip-flops.


Dave Gönner wrote 12/31/2015 at 13:32 point

Oh by the way, do you know about this clock design:

If you want to build a transistor clock, this is still the best example I know. Even though he sells a kit, the freely downloadable manual contains a full schematic and detailed explanation of how it works. This was one of the sources I used for info when designing my relay clock.

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Yann Guidon / YGDES wrote 01/02/2016 at 12:38 point

Fabulous !

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Dave Gönner wrote 12/31/2015 at 09:50 point

Thanks for the tip, I did not know about this technique. Not sure however that this will work in my case. The diodes are actually conducting the current that lights the LEDs to ground, not just providing a logic level. I think one would require buffers to make the inverted logic work.

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Yann Guidon / YGDES wrote 01/02/2016 at 12:36 point

There must be a way to make it work with relays :-) I'm just too lazy to think about it right now.

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Yann Guidon / YGDES wrote 12/30/2015 at 19:17 point

Awesome !

You can save diodes by using inverted logic, look at

Keep hacking ! I'd love to make a clock in this fashion but with transistors.

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