Relay Digital Clock


Ok, this has nothing to do with Tube audio, but I don’t have any other place that might be a good spot to put this project.

Years ago at Disneyland they had a hall sponsored by the Bell System. It featured 360 Vision where you could watch a movie with a 360 degree screen. They had the Bell picture phone, but the most interesting thing they had was a ‘Computer’ that was made from relays that played Tic-Tac-Toe. I always dug that, more so as I became computer literate.

So now many years later I have decided to make a digital clock with relays. I had my share of digital logic courses over the years and have forgotten most of what I had learned. With some false starts I’m back on this project.

I found some very nice software to help with some of the non-sequential logic, basically truth tables and such. It’s called Logic Friday, and it based on some underlying logic software created by academia. That being said it’s a fantastic tool to keep me from having to re-learn optimizing K-Maps.

The software basically lets you enter in a truth table and it outputs the logic! It’s does even better then that, you can select the type of gates you want to implement it. And finally the money feature (well it’s free software) is the ability to optimize the logic to reduce gate count. This is important when dealing with old school chip based logic element (ie, 7400 series logic blocks) to build something. It’s even more important when using relays as they are large and costly vs the logic chips.

Logic Friday does not help with sequential logic so much, for example it won’t help design a decade counter or flip flops, that’s really not it’s purpose. But I’ll leave that mess after I get something simple working.

Also you can find some very nice examples of programmable relay computers if you look hard enough, even some nice videos on YouTube of them in operation. They offer some interesting circuits related to the Flip-Flop which is needed to do counting and state related logic. More on that later.

For now it’s back to basics. I’ll begin posting ideas and simple circuits as I do them. This is a fun project and hopefully one that gets completed or what the hell am I going to do with 550 SPDT relays.

Welcome! If you are following along and feel free to comment!



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