24 Hours, Digital Clock Using 4510, 4511 and 7421

Thread Starter


Joined Jan 17, 2018
A 24 hours digital clock circuit specially for student's who like good integration of IC's.

digital clock_sandipgolani.jpg

Mods Note:
Please cut the space for the circuit.


Joined Apr 28, 2012
All these CMOS and TTL clocks on the internet are low profile, when you turn them off and on again, the memory will have some random value.

Its a detail but no commercial clock sold in shops would be like that.

I made one a long time ago, when you turned it on, you could watch zeros filling in, as well it had a blinking symbol on the LCD.

think it had some 25 ICs and worked for months on a few AA batteries.

Most real clocks dont have seconds display not the digital ones, but they do have pushbuttons to set the time (minutes and hours).
They also often have 12HR/24HR mode.


Joined Jul 12, 2016
How about a digital nixie clock, though only 12 hour:


And the hour and minutes are set by pressing their respective buttons. Advanced by one, per switch depression. Dekatron tube, optional.

Yes, as mentioned care should be taken when mixing 4000 CMOS with TTL. 4000 CMOS can't drive the load of a TTL output, but can easily drive just a single TTL input, as in this circuit. A TTL output may not have the voltage swing to properly drive a CMOS input. Pull up resistors are used when this is the case, but you will still not get the full TTL speed, since original 4000 CMOS, is much slower. Not an issue on this circuit.