it seems that there are a few different ways to hook up those 7490 ICs
on 9XB timer pin 3 input to pin 14 on the left with pin 11 as the output of the 7490
connect 2367 &10 to ground and use pin 5 as VCC (5+)
connect 1 & 12 together and you have a divide by 10 counter
On my figure 12 simulation i used the same power and ground pins as before, but had the 555 pin 3 go to pin 14 input and used pin 11 as the output.
this time i left 1 and 12 unconnected and i got a Divide by 2 counter
Which is the best?
If both start with a center frequency of 40Khz on the 555 pot
and 9xb then gives 4Khz - 400 Hz - 40Hz as the choices
while:
fig 12 ( as a divide by 2 setup)
would give 20Khz - 10Khz and 5Khz
what is the reason behind the divide by 10 or the divide by 2 selectors in this circuit ?
DOES ANYONE HAVE THE ANSWER?









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