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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
 

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OK here are the quick and dirty answers:


beginer electroner said:
1- what would happen if we replace the 7493 with a 7490 counter
The circuit would count from 0 to 9 instead of 0 to 15

beginer electroner said:
2- what would happen if we replace the 74121with a 555 monostable
Assuming that it was wired correctly, the circuit would still work.

beginer electroner said:
3 - how I can use this circuit to count from 00 to 99
Use two 7490 stages. Connect the "D" output of the first 7490 to the "A clock" of the second 7490.

JimB

PS your scanned schematic is a bit difficult to read.
 
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:mad:
Les
 

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beginer electroner said:
but what did you mean in "D" output?
and do I need two 7447 ??
The 7490 has 4 outputs labelled A, B, C & D.

You will need two 7447 ICs, one for each 7490 if you want to drive 7 segment displays.
 
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