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Transistor switch circuit

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daviddoria

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I am trying to make 2x 4017 timers count to 20! haha i'm sure i can just get a 20 output counter IC, but this is fun hehe.

so the idea is this:
i have 2 555s and 2 4017s.

i have the last out put of the first 4017 turn off the first 555 and on the second 555. i have the last output of the second 4017 turn off the second 555 and on the first 555. make sense?

the only problem is maintaining the state (on or off of the 555) while the other chip is counting to 10. i have been reading about transistor switch circuits, but i don't understand.

anyone have a good example circuit?

thanks
david
 

Gene

New Member
Facinating logic question. You can do this with one 555 and two 4017s. Check out the circuit provided by kinalgp at http://www.electro-tech-online.com/threads/old-computer-power-suply.681/

Also check out the last post which has a few adjustments to the circuit. Of interest is that this circuit is designed to go to 12 and then reset. You will want to move the reset to a latter signal to go above 12 but I'll bet you can do it.

For what it is worth, I think you can do this with your parts and your logic but you may have to consider the operation (final state) of the 555s. You may need one for the pulse, one in monostable to trigger the first 4017, and another 555 in monostable to trigger the second 4017.
 
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