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Rising or falling edge.....

Discussion in 'Electronic Design' started by [email protected], Dec 19, 2008.

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  1. Guest

    Which would you use for pulse detection/counting?
     
  2. MooseFET

    MooseFET Guest

    It depends on a lot. In at least one case, I used both edges.
     
  3. Guest

    It depends on a lot. In at least one case, I used both edges.

    Assume noise is already filtered and you're just counting pulses with
    a MCU where just changing a bit or two determines detection on rising
    or falling.
     
  4. neon

    neon

    1,325
    0
    Oct 21, 2006
    DEFENETLY RISE TIME if it is active fall time is usualy passive and therefore longer in time.
     
  5. TTman

    TTman Guest

    both for detecting, neg for counting.In a micro, you would use (preferably)
    interrupts.
     
  6. Guest

    both for detecting, neg for counting

    So if noise is out of the picture and you have control over and set
    the inactive steady-state of the pulse source to Lo, then it's only a
    falling edge ISR that one needs to concentrate on?
     
  7. Rich Webb

    Rich Webb Guest

    Ding ding ding ding ding ... We have a winner! :)
     
  8. TTman

    TTman Guest

    Ha ha, if everything goes belly up, who cares if a pulse is missed, unless
    you're counting gold bars :)
    Happy Xmas you lot .
     
  9. Jamie

    Jamie Guest

    Hmm, sounds good for ECL, but how about CCL ?

    http://webpages.charter.net/jamie_5"
     
  10. Jamie

    Jamie Guest

    Depends on the device that is doing the pulsing?

    It's logical to use the level the device generates
    when its TRUE/ON

    For some, the raising edge how ever, this leads to
    problems where the devices must insure it does not over
    drive the unit that is receiving the pulse.

    If you use an open collector type device for example, you
    can then have the monitoring device use it's own pull up or
    what ever voltage it requires and the pulsing device won't
    care until you breach it's limits of course.

    So, with that, I would say a falling edge using an open collector
    pulser would be the ticket. And even if a totem pole/Line driver
    output device was connected for some reason, it could thus use the
    receiver device supply voltage to insure it does not get over driven.
    And with that, you still can use falling edge..

    In the case of a pulsing device that has NOT outputs with
    open-collector, you then are faced with PNP outputs on the NOT's in
    many cases and NPN on the non-NOT's
    NOT's are high side, others are low side open-collector.
    In the case of the NOT's, you would have to supply a pull down
    R. unless you design your receiver device to work with NOT/PNP sensors.
    etc..



    http://webpages.charter.net/jamie_5"
     
  11. Jasen Betts

    Jasen Betts Guest

    In an MCU you would use a hardware counter and interrupts only to
    handle counter overflows
     
  12. Jasen Betts

    Jasen Betts Guest

    it depends if you're more interested in the beginning of the
    event or the completion of the event.
     
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