# Help designing the circuit

Discussion in 'Homework Help' started by nenadilic84, Jul 22, 2010.

Aug 7, 2009
62
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Hi,
can someone give me a direction in designing the circuit that is suppose have an operation drawn in the diagram.

It has one input and 4 outputs. When the input signal go high nothing happens at outputs, but when it goes low the first output is triggered and it stays high for the same period of time as the input signal was. Next on low of the output 1 the output 2 is triggered and so on. Thanks for your suggestions.

Regards,

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
This looks so much like an assignment that I am going to move it.

Hint:Use the input as a clock - look up Johnson counter.

3. ### Wendy Moderator

Mar 24, 2008
21,838
3,047
I'm thinking four monostables, each triggered by the preceding unit.

Aug 7, 2009
62
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Aug 7, 2009
62
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6. ### Georacer Moderator

Nov 25, 2009
5,154
1,281
If input is arbitrary and user defined, then how the circuit will know in advance the $t_{on}$ in order to calculate the $t_{on}/4$. Doesn't seem very feasible to me...

7. ### ozjon69 Member

Jul 19, 2010
11
1
Well, a microprocessor is probably the only simple way to do it. (first cct)

Somehow, the circuit has to remember the value Ton.
I can't figure how to do that with discretes

The second circuit is impossible!

Last edited: Jul 23, 2010

Aug 7, 2009
62
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Can you please give any suggestion for the second design of the circuit.
I think that some frequency divider will do, but how to trigger on the falling edge?
Thank you

9. ### Georacer Moderator

Nov 25, 2009
5,154
1,281
What were the problems with your design with the Flip Flops? What results didn't satisfy you?
Concerning the second circuit, understand that you ask of a circuit to calculate the one quarter of a time interval that isn't yet known. How do you expect that to happen? Or did you describe your problem poorly and what you really wanted is to give the input time interval first, let it finish, and then start the chain of pulses?

10. ### retched AAC Fanatic!

Dec 5, 2009
5,197
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If you waited 1 cycle to get $t_{on}$, then used that to trigger the 1/4t pulses for each additional cycle, that would work.

But, you will need a way to get $t_{on}$

Is $t_{on}$ a pre-defined time?

Aug 7, 2009
62
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Yes you are right. But I expect that the simple way is to use a microcontroller with analog input that is going to define a $t_{on}$ and make the pins high in the desired order. Thank you for the help.
i will post the solution here.

12. ### retched AAC Fanatic!

Dec 5, 2009
5,197
315
That is correct

You could use an analog or digital input to get the frequency of the pulse, then divide by 4.

Trigger the output of T/4 with the input rising edge of the next cycle.

13. ### big5824 New Member

Jul 15, 2010
9
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Looks just like a serial to parallel shift register to me, although youd need a clock signal that isnt displayed