could any one please answer me these questions:
after looking at the fig bellow:
1- what would happen if we replace the 7493 with a 7490 counter
2- what would happen if we replace the 74121with a 555 monostable
3 - how I can use this circuit to count from 00 to 99
thank you very much
Nah! 7490's had their individual flip flops labelled A, B, C & D.
The 7490 is split in half internally with a separate divide by 2 and a divide by 5.
To get the 7490 to carry the count over to the next 7490, you have to connect the output D of the first one to the A Input of the next one.
I attach some circuits, I usually use the 74390 if I do not want to preset the digits to 0 or 9.
Note that the 7490 circuits shown have their flip flops numbered 0, 1, 2 & 3 instead of the usual A, B, C & D. Just proves there is no real standard around the world
Les
100 Hz counter, the 7490's can be used to drive 7447 CA or 7448 CC displays.
also before the schmitt trigger a manual pulse can be used to trigger the counter.