How can you run a load when a switch is open?

Discussion in 'The Projects Forum' started by Hippoman, Feb 5, 2009.

  1. Hippoman

    Thread Starter New Member

    Feb 5, 2009
    3
    0
    Hello everyone,
    I am trying to make something that will sound a buzzer or beeper when a switch is open, and remain silent when the switch is closed, and can't think of a way to do that with my basic circuitry knowledge. I'm a bit of a beginner so be as simple as possible for me :).
    Thanks,
    Evan
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    If you have a little bit of power to spare...that is, you aren't too worried about current consumption, you can put the buzzer in series with a resistor, and the switch in PARALLEL, across the buzzer. When the switch is closed, the buzzer is shorted out, when it's open, the buzzer isn't.

    By the way, this is how railroad crossing gates are activated...the train approaches a "block" and SHORTS out a section of rail, which allows a relay to open....it's a failsafe system.

    eric
     
  3. dmblfi357

    New Member

    Jan 9, 2009
    1
    0
    If you only care about the status of a specific switch you can wire load to a NC relay. When you close your switch, you will energize the coil and open the contactor and have an open circuit for your load i.e. buzzer.
    When you open the switch, your contactor will remain in the NC position and you will have a complete circuit now for your buzzer.

    Note: You can jumper your hot and neutral across the contacts so you don't have a separate source for your buzzer.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Use a switch with a normally closed (NC) and normally open (NO) contacts. If you connect the buzzer on the NC and the power supply on common pin of the switch, when the switch is at the OFF position the buzzer will be on and when the switch is at the ON position the buzzer will turn off.
     
  5. Hippoman

    Thread Starter New Member

    Feb 5, 2009
    3
    0
    Thanks for the help- I think I'm going with KL7AJ's idea- and another question: Where can I find a buzzer/beeper that can run off a watch battery directly, without a chip or anything to make the current alternate? If such a thing exists, can I just take one out of a handheld game and apply current, or is there more to it than that?
    Thanks yet again,
    Evan
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    If you connect a buzzer to a watch battery, the battery will drain in a few seconds.
     
  7. Hippoman

    Thread Starter New Member

    Feb 5, 2009
    3
    0
    Excellent, I know what my circuit will look like. Now I need a buzzer or a beeper. What would I use that can make an audible noise of some sort that can run with only direct current from a battery, and where would I find something like that? And what battery would I use for such a device? I'm going for as small as possible here.
    Thanks,
    Evan
     
  8. mik3

    Senior Member

    Feb 4, 2008
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  9. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    Ahhh! THAT's how the kids in Lindenhurst managed to drop the gates! I'd heard they dropped a metal bar across the tracks, but never figured out how that did anything! (FWIW, the tracks got elevated in the early '70's -- 1970's, not 1870's!)

    --Rich
     
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