# Frequency Divider Circuit

Discussion in 'General Electronics Chat' started by karthickkumar, Apr 13, 2008.

1. ### karthickkumar Thread Starter New Member

Apr 13, 2008
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HI All, I want to build a Precision frequency divide by 100 circuit, to divide a 1 KHz TTL pulse to 10Hz TTL. Can any body suggest some good circuit for it.
THanks
Karthick

2. ### beenthere Retired Moderator

Apr 20, 2004
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All you need is two 7490 counters. That's not a circuit, just a bit of TTL logic. Get a data sheet and see how they work.

Jul 17, 2007
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4. ### relicmarks Active Member

Oct 13, 2006
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i thought flip flop chip circuit did frequency dividing

5. ### Ron H AAC Fanatic!

Apr 14, 2005
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Look at the datasheets. A decade counter chip contains 4 flip-flops and some logic, and they are already connected together for you! The wonders of (not so) modern technology!

6. ### relicmarks Active Member

Oct 13, 2006
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I never understood how a flip flop can take a frequency and divide it down or convert to another frequency , whats the theory behind this please?

7. ### beenthere Retired Moderator

Apr 20, 2004
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Look at a 7474 D flip-flop. If you run the not-Q output to the D input, then the flip-flop will change state every other clock. This has the effect of dividing the clock frequency by 2.

8. ### SgtWookie Expert

Jul 17, 2007
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Basically, you are "hijacking" this thread.

The original poster's request has been satisfied - this is their thread. If they have more questions, they are free to ask more, because it belongs to them.

But in brief, each flip-flop will take the input signal and divide it by two.

9. ### relicmarks Active Member

Oct 13, 2006
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sorry i didn't mean to hijack his theory

I just don't get how the flip flop divides the input by 2

And maybe others can learn from it too

10. ### Ron H AAC Fanatic!

Apr 14, 2005
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Actually, it changes state on every clock.

11. ### beenthere Retired Moderator

Apr 20, 2004
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But, RonH, if you look at the Q output, you will see that it changes at one half the clock frequency and so is performing frequency division.

12. ### Ron H AAC Fanatic!

Apr 14, 2005
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On the Nth clock, the output changes to a 1.
N+1, 0
N+2, 1
N+3, 0
N+4, 1
etc., etc.
On every clock cycle, the output changes state.
I wasn't disputing the fact that the circuit divides by two. I was disputing your terminology.

13. ### relicmarks Active Member

Oct 13, 2006
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look at the Q output, you will see that it changes at one half the clock frequency

how does it do that, i don't understand please?

14. ### beenthere Retired Moderator

Apr 20, 2004
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I was going to link you to the Ebook, but we don't seem to cover flip-flops in it.

Look up the data sheet for a 7474 (or 74LS74, 74Hc74, etc). The Q output follows the D input with each clock. With the not-Q output tied to D, then the state of D will change with each clock, so the device will have an output that changes state at half the clock frequency.

It would make existing threads run a bit better if you would post these questions as separate threads. Hijacking a thread is something like bursting into an ongoing conversation. We do discourage the practice.

15. ### Caveman Active Member

Apr 15, 2008
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Relicmarks,
It is really simple when you draw it out. Draw a square clock. Notice that a "cycle" is the clock going high, then going low. It is high for a "half-cycle" and low for a "half-cycle".
Now, the flip-flop latches its input onto the output only on the rising edge of the clock. Until the next rising edge, the output does not change. Also, at the same time, the flip-flop latches the inverse of the input onto the inverted output.
To halve the clock, just hook the inverted output to the input. Now here's the other important point. It takes time to transfer the input to the output, so what gets latched to the outputs is the input just before the rising edge of the clock.

Does that do it for you?

16. ### dragan733 Senior Member

Dec 12, 2004
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The C.I. DS8629 from National Semiconductor performs the division by 100

17. ### SgtWookie Expert

Jul 17, 2007
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Yes, unfortunately I think it's been discontinued. It's no longer listed on their website.