Help request; designing a trigger circuit

Discussion in 'The Projects Forum' started by tonyboyle, Jan 10, 2012.

  1. tonyboyle

    Thread Starter New Member

    Jan 10, 2012
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    0
    Hi,
    Can someone help me by providing a simple circuit to make a motion sensing circuit.
    Not too complex in that I wanted something which will sound a buzzer when moved roughly or sharply.
    I had though a simple manual trigger in a primary circuit with a battery could be a small metal bar on a spring which touches a contact when moved sharply. This will operate as a switch by providing a current for a short period of time.
    What I need is a circuit design which will detect this split second flow of current and switch on a secondary circuit connected to a buzzer. This must continue to sound after the initial trigger has been cut. It will also need a way of resetting it back to its original state.
    I am fairly ignorant when it comes to electronics but like a trained chimp I can make a circuit from componets given a simple diagram.
    Thanks for any help!
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    It can be an RS latch or a 555 or a thyristor or whatever you can think!
     
  3. tonyboyle

    Thread Starter New Member

    Jan 10, 2012
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    0
    Thanks. I had thought something involving a 555. But when I say I know nothing I mean I know basically nothing so what I need is a circuit diagram to work from.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    Try google and let us know your findings. ;)
     
  5. tonyboyle

    Thread Starter New Member

    Jan 10, 2012
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    Been there but I don't know enough to understand most of it so I came here hoping for a bit of guidance.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The best way probably involves an NE555 one-shot circuit, but the simplest way is a relay that latches through one set of its own contacts. You would need to choose a relay that operates on the same voltage as your buzzer and that has two sets of contacts and would be described as DPDT (double pole, double throw.)

    In the circuit attached, when S2 is closed, the circuit is ready to detect movement. Then, when S1 is closed (even momentarily,) the relay operates and feeds +V through the lower set of contacts to the buzzer, and feeds +V through the upper set of contacts to its own coil, which latches the relay in the operated state. To release the relay, you would need to disconnect the power source momentarily; you would do this by opening S2.

    The downside of a relay is that it draws current continually while it is operated and the current will drain a small battery quickly. However, if you are powering the relay with a wall wart, a small continuous power drain doesn't make much difference. In addition, there are relays with fairly high coil resistances that don't draw huge amounts of power.
     
    Last edited: Jan 10, 2012
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