Generating a series of n pulses

Discussion in 'The Projects Forum' started by Llamarama, Jul 11, 2014.

  1. Llamarama

    Thread Starter Active Member

    Feb 1, 2010
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    Hello everyone, I'm trying to find a circuit that will generate n pulses if I send a single momentary pulse.

    Can anyone think of a way of doing it other than gating an oscillator for a pre-determined length of time?

    Many thanks, Mike
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    On the trigger input you load a counter and generate one pulse each time the counter is grater than 0. Each time you generate a pulse you decrement the counter. It is a straightforward state machine.
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    And, you don't really need a physical counter, per se. You could build a synchronous state machine using just logic.
     
  4. Papabravo

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    Feb 24, 2006
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    Any circuit that keeps track of the current state is in effect a counter. It may not be a binary counter, but it is still a counter.
     
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    That's why I prefaced the word "counter" with the word "physical". But, thanks for the clarification.
     
  6. Papabravo

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    Feb 24, 2006
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    Any collection of memory devices (aka flip-flops) is in effect a state counter. I don't have any clue about what a non-physical counter would look like.
     
  7. joeyd999

    AAC Fanatic!

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    Semantics.

    I was referring to a discrete solution, say, built with NAND gates as opposed to a dedicated, integrated, counter.

    But, whatever.
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    You call it semantics and express irritation, but precise communication is important. Lack of it is what leads to Martian probes crashing into the surface instead of landing softly. Feet, Meters it's just semantics!! Harumpff
     
  9. Llamarama

    Thread Starter Active Member

    Feb 1, 2010
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    I'd prefer a system based on a counter of flip flops rather than a state machine, purely because I feel more confident with counters and disctere systems than I do with state machines.

    I have an idea that uses a couple of 4017s, but I'm going to have a bit more of a think, dig out my Digital Logic Systems notes and have a read

    Thanks for the ideas so far though :)
     
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    How about some additional information:

    How many pulses?
    What frequency / duty cycle is the output?
    A fixed or adjustable number of pulses?
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    If you make a ripple counter out of flip-flops then the propagation delay through the carry chain will limit the speed of the clock. If you implement a synchronous counter you will be using lots of AOI gates if you go much beyond 4 or 5 stages.

    Five stages will get you any n from 1 to 31.

    BTW - a binary counter is a state machine in case you did not know that, so you are familiar with them. :)
     
  12. tindel

    Active Member

    Sep 16, 2012
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    Another approach is to use a micro controller - An MSP430 launchpad is $10 and is very versatile for little projects - you can use it for all sorts of stuff. With an external crystal you can get very accurate timing - and the launchpad comes with a 32kHz crystal. It does take some time to learn the architecture of your desired uC and how to program it, but once you do - you can do stuff like this very quickly - in a few hours.

    If timing accuracy and power isn't a concern you can go all the way up to 16MHz with the MSP430.
     
  13. Llamarama

    Thread Starter Active Member

    Feb 1, 2010
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    Frequency: about 5-10Hz

    Duty Cycle: Not really too much of an issue, anything will do but I guess either 25% or 75% ish just to put a number on it.

    Ideally adjustable, I was going to use this circuit to form a simple switching scheme similar to old style telephone dials, except with an adjustable number of "commands" or pulkse train lengths.

    Hope this is of help, I know it's vauge, but it's the best I can come up with at the minute, going through a rough patch.
     
  14. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Just for laughs- an analog approach would be to use a charge pump to act as a "counter"- each pulse injects a bit of charge into a capacitor, feed that voltage into a comparator to gate the oscillator off and reset the capacitor. This would work ok for small numbers of pulses.
     
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