Momentary contact during power On and Off.

Discussion in 'General Electronics Chat' started by sangeetk, May 27, 2009.

  1. sangeetk

    Thread Starter New Member

    May 27, 2009
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    0
    I am new to this forum and my knowledge about electronics is very basic. I am planning to add a laptop in my car which will be used as a carputer.

    My requirement is to make momentary contacts for the power switch both during the power (12 VDC) ON and OFF (to switch on and switch off the laptop).

    I am able to find some circuit diagram which gives momentary contact during power on in the following link
    http://www.the12volt.com/relays/page5.asp

    But not able to find something which also gives momentary contact during power OFF.

    Any help will be really appreciated.
     
    Last edited: May 27, 2009
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    The circuit you want is referred to as an "edge detector". The attached are examples.

    Ken
     
  3. sangeetk

    Thread Starter New Member

    May 27, 2009
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    0
    In the 2nd circuit diagram, instead of reed relay, can we normal SPDT relay?
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Sure. That's just what I had used to get a long pulse period. The length of the pulse depends on the size of the capacitor and the resistance of the relay coil...mostly. About C (in farads) x R (in ohms) = T (in seconds).

    Ken
     
  5. sangeetk

    Thread Starter New Member

    May 27, 2009
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    0
    I am facing a problem with the above circuit (with relay), the fuse is keep on blowing.
    The relay which I am using is similar to http://www.blueseaele.com/showprod.asp?id=170 and capacitor is of 470uF. The input volt is 12 vdc. Is there anything wrong with the circuit diagram.

    SangeetK.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    The schematic is correct. Re-check your wiring.

    Ken
     
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