As the title says, I want to build a clock using the mains frequency (50Hz). I only want to use digital integrated circuits from the CD4xxx series or something similar. (no microcontroller or do-it-all IC)

I plan on using a transformer and a comparator to generate the clock from the mains frequency and 6 CD4511 each connected to 6 common-anode 7 segment displays for HH:MM:SS.

My question is how to build the circuitry. I was thinking of using an 8 bit counter to count at 100 and when the output is 0110 0100 (100 deca) using AND/NAND gates to build a new clock which goes positive only at 100 deca. Next one CD4510 for every digit and make them reset at different values with AND/NAND gates again. This seems a bit cumbersome. Is it an easier way to hook the counters up?

  • 3
    \$\begingroup\$ In order to get a review of a design you need to provide the design in a conventional readable form (schematic). \$\endgroup\$
    – Eugene Sh.
    Jan 19, 2018 at 16:17
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    \$\begingroup\$ I'd go for the tradtional count-to-60 method. \$\endgroup\$
    – Andy aka
    Jan 19, 2018 at 16:19
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    \$\begingroup\$ It is indeed cumbersome and uses a lot of ICs. But that's the criteria you have set yourself, so unfortunately you have made a rod for your own back. Hey, you could compromise your rules here a bit to remove all that aggravation. If you'd use a cheap CPLD, you could still do your design in the schematic entry tool, gate by gate, but not have the trouble of making a big circuit and the difficulty in changing it as you debug. \$\endgroup\$
    – TonyM
    Jan 19, 2018 at 16:22

1 Answer 1


You will find it a lot easier to use two 4-bit counters for each pair of digits. One will divide by 10 (0..9) and the other 0..4 (mains) or 0..5 (minutes, seconds). The hours pair may count 1..12 or 0..23.

Basically, it's easier to count directly in BCD rather than trying to use binary.

The old classic part was the single SN7490 biquinary counter with its non-standard power pins. You can still buy dual divide-by-10 counters (74HC390).

The 74HC163 is nice for the non-divide-by-10 counters- it has synchronous reset and load so you only need to NAND together the '1' bits of the final count for an up-counter to get it to go back to 0 or to load a 1 on the next clock edge.


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