interrupt sensing

Discussion in 'Programmer's Corner' started by satishkumili, Oct 29, 2008.

  1. satishkumili

    Thread Starter New Member

    Oct 29, 2008
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    initially i made P3=0;
    when am giving high i/p(+5v from power supply) the interrupt pin is responding( it is showing +5v on this pin
    if i give +5v through optocoupler the voltage on pin becomes 0v instead of +5v .
    why it is happening?
    optocoupler is working well.am taking output of optocoupler from emitter.
    is there any problem from microcntroller side or intialization?
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Typically optocouplings are inverting. So, if you apply the voltage to the LED, it lights up, then causes the transistor in the optocoupler to turn on. When it turns on, it pulls collector to near ground potential (assuming you have a weak enough pullup resistor).

    Your microcontroller pin should be set to interrupt on falling edge, or on a low.

    Steve
     
  3. satishkumili

    Thread Starter New Member

    Oct 29, 2008
    5
    0
    thanx steve for replying
    actually i connected optocoupler in propotional mode (am taking o/p from emitter & no resistance in collector, 100k resistyance is in emitter)
    so,whenever i/p to opto is high o/p is high & vice versa.
    now when i/p is high o/p(at INT1 pin o/p is not becoming high.it is still low only)
    why it is happening?
    as i intialized P3=0x00; IS this port pin,p3.3 (INT1) is effecting the optocoupler & making INT1 pin low.
     
  4. satishkumili

    Thread Starter New Member

    Oct 29, 2008
    5
    0
    dear steve , may be the last posting to you is not clearer.
    so,am sending this posting clearly
    actually i connected optocoupler in propotional mode (am taking o/p from emitter & no resistance in collector, 100k resistyance is in emitter)
    so,whenever i/p to opto is high, o/p of it is high & vice versa.
    now consider that optocoupler o/p is connected to INT1.
    so,if i/p is high, o/p(at INT1 pin is not becoming high.it is still low only)
    why it is happening?
    initially, i intialized P3=0x00; IS this port pin,p3.3 (INT1) is effecting the optocoupler & making o/p of optocoupler to low.
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Did you test the optocoupler unconnected? If so, then what is the input impedance of your microcontroller? 100K may be too high of a resistor to use, perhaps go a bit lower (1-10K)

    Steve
     
  6. satishkumili

    Thread Starter New Member

    Oct 29, 2008
    5
    0
    Dear steve,
    i have checked the optocoupler o/p without connecting to controller.
    with 100k in emitter, o/p is 5v.
    but when am connecting it to controller o/p becoming zero
    i wll replace dis 100k with 10k and wll inform u.
    thanks&Regards
    satish
     
  7. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Okay, great! Let us know how it works :)

    Steve
     
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