The electromechanical relay clock project is complete!



After years of waiting to find the right hardware, I have finally found the time and the opportunity to build my own digital mechanical clock that uses absolutely no transistors or ICs. Its technology is reminiscent of the early relay computers from many decades ago. It uses 67 relays arranged in such a way to create 21 identical flip-flop logic circuits.

All of this logic works together to accurately keep track of the time 24 hours a day. A synchronous motor and gearbox references the 60Hz main frequency in such a way to deliver a 1PPS signal to the logic gates. From here, a 6-bit binary “register” increments up by one unit each second. Once it reaches 60, an additional flip-flop circuit simultaneously clears this register and adds one unit to the minutes row.

A similar process also happens between the minutes, hours, and AM/PM bit.

How to read this clock

Don’t know how to read binary? It’s easy! A numerical guide is given below the display area to signify the decimal value of each column.


Take this image above for example. If the blue light is on, it means its currently PM. The red, yellow, and green lights signify hours, minutes, and seconds respectively.

The hours row currently has the binary value 1010. To convert that to decimal, add 8+2. This gives you 10 for the hours.

The minutes row has the value 001001. If you add up the bits that are on, you get 9 for the minutes.

So the time seen in the picture above is 10:09pm. The seconds row is insignificant for most cases, still we can read that too. It shows a binary value of 111011. Follow the columns down and you’ll see that you’ll have to add 32+16+8+2+1, which equals 59.

Would you look at that, it’s 10:10! Do you ever notice that every watch and clock ad, regardless of the company or model always shows the time as 10:10? It’s true! Take a look next time you see one of those ads.

4 thoughts on “The electromechanical relay clock project is complete!”

  1. OMG!!!!!
    That is amazing!
    I too love electromechanical systems and this is the kind of thing i would like to build.
    In my line of work, i have a steady stream of replacee Paragon defrost timers i keep thinking im going to create something with.
    Sadly, with 2 jobs, time is rather tight.
    But, thank you for the inspiration!

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