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garden gate sensor advice

Discussion in 'Beginner Electronics' started by Roger Taylor, Sep 1, 2005.

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  1. Roger Taylor

    Roger Taylor Guest

    I need advice for an off-the-shelf parts list, besides fine-guage wiring,
    for doing the following:
    We try to keep the dog contained in the backyard, but both gates are not
    visible from the back door. What kind of wired system can I use that would
    have two weatherproof sensors, one on each gate, and a small led-lighted
    console by the inside of the back door, that would indicate the gate is
    either open or closed?
    Should this be battery powered, and what kind of wire and batteries should I
    use? These are up to 120-foot runs, and the smaller the wire, e.g. telephone
    wire, the better, for easy installation.
    Thanks!
     
  2. Chris Head

    Chris Head Guest

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    Hi,
    I believe the standard-issue solution to this question is to place a
    magnet on each gate (on the handle end of the gate, NOT the hinge end)
    and a small reed-switch on the fence, arranged so they will almost touch
    each other when the gate is closed. Run a pair of wires to the contacts
    of the reed switch. When the gate is closed, the magnet closes the
    switch; when the gate is open, the switch will also be open. This is
    basically what security systems use to detect doors opening.

    You should be able to use very small wires for this. Since LEDs use
    little current, you should simply be able to put the power supply, the
    reed switch, a current-limiting resistor, and the LED all in series. You
    shouldn't need any transistor triggers or anything I don't think.

    Also, this system has the advantage that a broken wire or burnt LED will
    cause it to fail to the safer state: it's better to say the gate is open
    when it's closed than to say it's closed when it's open (I would imagine).

    Chris
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