Digital Clock Help

Thread Starter


Joined Nov 14, 2007
I need to make a 24 hour clock with seconds using 7490's, 7447's and 7-segment displays. I have connected the SECONDS display ona breadboard. Then i built a similiar circuit for the minutes part. but when i connected the output of the seconds to the input of the minutes, the circuit doesnt seem to be working. i tried to troubleshoot and fed both circuits with the same clock input, and the display will count between 00-59. So the circuits work but how do i connect them?
pictures or circuit diagrams would be most appreciated =) thanks


Joined Apr 20, 2004
We strongly encourage you to do your own work. We can give advice, but don't think it proper to just give you the assignment.

Have you done any searching on your own? This is not the first time the subject has come up.

Other things to consider - what are you going to use as a counting source? How you you get a decade counter to stop at 6 or 2 or 1, rather than 9?


Joined Dec 23, 2006
I have the full schematic in my files somewhere..that was such a fun project to do. Anyways, if I remember right, you have to tie the trigger input of the ones minutes counter to the ANDed output of the two bits that make up the 5 value on counter, which would be the bits that represent 4 and 1. This is assuming that your counter triggers on a falling edge square wave. Basically how it works is that when the clock reaches 50, the AND gate goes high, and when the seconds resets back to 00, the AND gate goes back to low, trigger the counter. I believe you would just use a NAND gate if it's rising edge trigger. How you tied together the ones second digit to the tens second digit should be fairly similar. However, I could be wrong about it all..