Icne555 cofig. Prob.

Discussion in 'The Projects Forum' started by sammmm, Apr 5, 2014.

  1. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    please help me
    this circuit is not working prperly
    the output at pin 3 is not getting high when input at pin2 is getting low
    ICNE555 is configured in monostable mode.
     
  2. nerdegutta

    Moderator

    Dec 15, 2009
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    785
    Hi, Sammmm.

    Explain what you expect the circuit to to. Are you expecting the relay to be energized when the IR sensor is not receiving IR?

    Explain the whole setup.
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Pin 2 won't get low!

    The 3-pin IR sensor has an open-collector output pin, that pulls LO when IR is present. Your diode stops it from being able to pull pin 2 low.

    Also, since the pin is open-collector it cannot source a + voltage, so you need a pullup resistor from the IR output pin to +5v. 10k should be fine but some IR modules need a high value like 27k.
    :)
     
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  4. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    hieee nerdegutta,
    this is the circuit diagram of automatic tap
    in which we have used TSOP1738 IR sensor whose output get low when the IR RAYS falling on it get interrupted.
    and this is connected to IC555 PIN2 which is configured in monostable mode. the output of this IC GET higher when trigger at pin 2 get lower .
    this is the whole procedure to energise relay but this is not happening really
    can u help me to detect the problem????
     
  5. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    I can't understand wht are u exactly trying to saying

    can u please elaborate????
     
  6. nerdegutta

    Moderator

    Dec 15, 2009
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    Have you read the datasheet for the IR sensor?

    Page 2, Application Circuit.
     
  7. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    yes I have read it but there is no problem in the sensor
    the whole problem is about ic555 which I think not config properly
     
  8. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    thanks for ur help
    but can u suggedt something elese
     
  9. nerdegutta

    Moderator

    Dec 15, 2009
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    This document says something about how to trigger a 555 with a LOW.

    I've not tested it , so I have no idea if it works or not.
     
  10. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    Thnks
    I think i will surely get something from this
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The solution is in post #3. Try to understand it.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    You don't have a diode across the relay coil. Without a diode there, the current from the relay coil won't have a place to go when the transistor turns OFF, and the transistor will be destroyed due to the high voltage pulse. Connect a diode across the coil, with the cathode (band) towards the normally more positive side of the coil.
     
  13. sammmm

    Thread Starter New Member

    Apr 5, 2014
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    Hey , THE_RB
    I have tried what you said. And it works but there is another problem. The relay connected in this circuit requires 7A,6v parameters which is not possible in this circuit as it works on 5mA current . Can u suggest me how to drive relay without affecting current circuit .
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If your circuit runs from a PSU that only has enough power to run the 555 timer, then to drive the relay you need another power source. One that has enough power to drive the relay coil.

    What other power sources do you have?

    You need to provide more information, like an "overview" of the entire project, not just the 555 circuit.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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