Push button timer switch possible?

Discussion in 'The Projects Forum' started by stanman11, Nov 15, 2012.

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  1. stanman11

    Thread Starter Member

    Nov 23, 2010
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    Hey guys. I thinking about making a timed switch or relay deal for my trucks horn. Its a dixie air horn from dukes of hazard.
    The thing is its hooked to a momentary push button that you have to hold until it sounds and is over.
    and the button location is in a strange spot on my dash.

    So is it possible to make a setup so i can press the button and let it do the rest for me?
    If its goin to take a lot of parts then we can forget it. but if the device is simple then I'd like to do this.
    What do you ponder?
     
  2. BlueRidge

    New Member

    Nov 13, 2012
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    You will want to create a time delay circuit, most easily with a capacitor. The size of the cap will determine the length of time it is on.
     
  3. stanman11

    Thread Starter Member

    Nov 23, 2010
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    Ive just done 2 circuits an neither work.
    Can any one show me an appropriate circuit?
     
  4. BlueRidge

    New Member

    Nov 13, 2012
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    Not sure what you mean...

    For some reason I can't pull the image, but go to the link below and scroll all the way to the bottom. The last image is a very basic circuit like you are after. Without specifics on usage or duration no further recommendations can be made, other than alternate options in circuitry componants or configuration.

    http://www.allaboutcircuits.com/worksheets/relay3.html
     
  5. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
    4
    Crap. I had the + - on the batt backwards STUPID!!!!

    Can I use any type of relay?
    The link you sent me is how my horn is set up now but without caps. can i just add that caps I want?
     
  6. BlueRidge

    New Member

    Nov 13, 2012
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    Any relay, so long as it is rated higher than the horn. Parts stores have them at 3-4$ for horns or lights. Common part.

    You can use any cap you want, but if it is too small it will cut out early, too large and it will play 1 and a half times, for instance.
     
  7. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
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    I just tested that out, ounce the button is let go it just turns off. it doesnt do any delay or I did it wrong. but i did it over again and still same.

    Tested .01uf, 1uf, 100uf. All did the same
     
  8. BlueRidge

    New Member

    Nov 13, 2012
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    Again, without useage specifications or duration timing I wouldn't know what you need, but that is the basic circuit design :)
     
  9. Meixner

    Member

    Sep 26, 2011
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    That circuit is totally unrealistic, you would need a capacitor the size of a car battery to get the delay you need.
    Look up a circuit for a 555 timer.
     
  10. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
    4
    3-4 seconds is all i need. 12v.
    the system is set up with push button relay and 15v 2.5amp fuse to an air compressor.
    But im tired of holding the button in
     
  11. Six_Shooter

    Member

    Nov 10, 2012
    33
    1
    IIRC, the last time I set up a delay circuit with a Bosch style 30A automotive relay (used for arming a factory security system, that required the door to be "open" when locked to activate, for use with a remote keyless entry system), I had to use a 4700μF 16V capacitor to keep the relay contacts closed for about 3 seconds. So you are probably just using too small of a capacitance.

    I don't like the idea of charging such a "large" capacitance without some sort of current limiting (resistor), but it does work. I actually had to use a second relay to trigger the relay that was triggering the dome light circuit and charging the capacitor, due to the current to charge the cap.

    I would look at using some timer circuit commercially available for this, it could be made to work much better and more accurately timed.
     
    Last edited: Nov 15, 2012
  12. Meixner

    Member

    Sep 26, 2011
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    If thats all you need then just do as six shooter suggested get a much larger cap. You can parallel caps together to get larger values.
     
  13. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
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    what is this thing?
     
  14. BlueRidge

    New Member

    Nov 13, 2012
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    50uf 50v nuetral polarity capacitor, i think.

    The issue wont be charging up the cap, it will be holding it the exact same length of time each push. A commercial timer would be easier, but that wouldn't be homebrewed.

    Isn't varying R an effective means to lengthen a delay instead of larger caps?
     
  15. Six_Shooter

    Member

    Nov 10, 2012
    33
    1
    As long as the voltage remains high enough with enough current, for the entire time period to hold the relay closed, a larger capacitor helps in this requirement. ;)
     
  16. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
    4
  17. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
    4
    is it possible to get something from the junk yard from a newer car?
    do they have timed relays in cars that I can pull out?
    but I guess I couldnt set them time then
     
  18. Six_Shooter

    Member

    Nov 10, 2012
    33
    1
    The eBay relay would likely work for you. A friend of mine used something similar for his cooling fans, I should have thought about something like that sooner.

    Most time delayed circuits in newer cars are not usually timed based on a circuit, but usually controlled by a microprocessor, as part of a larger system. I can't think of a car off hand that would provide what you want. The closest thing is the rear defrost relay in mid to late '80s GM vehicles, but were based on the high current passing through them, and set to be on for many minutes.
     
  19. stanman11

    Thread Starter Member

    Nov 23, 2010
    230
    4
    Ok I'll try that when Im not so behind on bills. Thanks mate!
     
  20. NFA Fabrication

    Member

    Aug 12, 2012
    104
    3
    Why not just do a simple 555 timer circuit? Am I missing something that is not making this the obvious choice?
     
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