Relays and display functions are working, let’s start with logic of the clock.
4.194304 MHz Quartz crystal oscillator and 4521 frequency divider provide accurate 1 Hz pulse. In the future pulse will be generated by OCXO with possible accuracy +\- 1 second per 3 years.
In my application, there is no need for rubidium frequency standard as second hand units from eBay are already aged and with 24/7 run would soon bring problem with jitter. Also energy consumption would be an issue for just a clock as it runs 24/7. Pulses are counted by 4017 decade logic.

I use transistor SPDT switch of my design to set time. Still this build have few issues I have to resolve before I put it on PCB’s.

Quartz board: 1 Hz pulse to run the clock, 4 Hz for time setting

Now let’s do some breadboard prototyping. Pulses are count from bottom right (1’s and 10’s seconds), bottom left (1’s and 10’s minutes),top right (1’s and 10’s hours). 24 hour cycle is achieved by resetting 10′ hours with NPN transistors.

I can reset seconds or master reset all time. Lot of debugging still needed. LED’s to visualize what’s going on as I don’t have a scope, frequency counter or signal generator 🙂

And some videos, please turn volume up if you can’t hear clicking. It’s louder than normal mechanical clock in real.

Electromechanical Relay Nixie tube digital clock prototype with accurate time

Electromechanical Relay Nixie tube digital clock prototype with 24 hour cycle reset

Testing breadboard prototype with alarm. All works. Next step put it on PCB’s
PCB to make: Seconds, Minutes, Hours, Mother board, and Alarm board

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