Help converting long pulse to short pulse.

Discussion in 'The Projects Forum' started by Holder350, Jan 17, 2010.

  1. Holder350

    Thread Starter New Member

    Jan 17, 2010
    7
    0
    Bought an aftermarket keyless entry and currently I do not have the horn hooked up because it honks (gives about a 1 second burst) instead of the beep beep chirp you would expect.

    My question is, does anyone know of a way to use this 12v+ long pulse trigger and convert it to a short pulse?

    I'v racked my brain for a few hours thinking about it and cant think of anything....I could do it with a capacitor if I had a negative trigger, but the setup I came up with did not work well.

    Anyone have any idea how to do this short of building a 555 circuit?

    Or does anyone know of a chirp box that I could wire up instead of the horn?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    The horn is DC powered, right? Just put a large capacitor in front of it, when the capacitor charges up the horn stops sounding. Not very adjustable, but simple.

    Be careful of capacitor polarity, get it backwards and you've made a stink bomb.
     
  3. Holder350

    Thread Starter New Member

    Jan 17, 2010
    7
    0
    So I would have

    POWER - CAP - HORN - GROUND

    Correct?

    Could this also be used with a 12v relay? that way the cap would be....smaller correct?

    EDIT: Nevermind I mocked it up on my bread board and it works wonderfully, to drive a relay with a 100uf cap

    YOU sir....are wonderful!
     
    Last edited: Jan 17, 2010
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    It could, but I would keep it simple first.
     
  5. Holder350

    Thread Starter New Member

    Jan 17, 2010
    7
    0
    The only reason I'm wiring it with a relay is that I really dont want to pull the horn off of the circuity in the keyless entry box...plus I allready have the horn wired to a relay and the only thing I'll have to do is add a small capacitor and shrink wrap it all together.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    You may need to put a high value resistor across the capacitor in order to make sure it discharges.
     
  7. Holder350

    Thread Starter New Member

    Jan 17, 2010
    7
    0
    Yeah, I did. Figured that out after it would only chirp once. lol
     
Loading...