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Simple LED Alarm Bell for CCTV recorder

Discussion in 'Electronic Design' started by [email protected], Mar 14, 2005.

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  1. Guest

    I'm looking to get this DVR for a new CCTV installation.
    Shown here:

    Basically, when someone walks past the sensor, it should trigger the
    alarm I wire up to the back of the CCTV DVR. I think most time lapse
    VHS recorders have sensor/alarms terminals on the back.

    On page 9 and page 10 of the above .pdf, there is a picture of the
    sensor (Dry Contact Input), a picture of a LED relay, and a picture of
    an alarm bell relay.

    Can someone tell me an easy way to hook this up so when someone
    triggers the sensor, I can get a quiet buzzer to sound and and a LED
    to flash. I want an on/off switch for each sensor, only want to buy
    one buzzer and 8 LEDs.

    I'm in the UK and has parts online for everything
    like this. I suspect I have to make my own kit as I can't find
    anything pre-built in google for CCTV alarm bells.

    The system I'm getting has 8 sensors input and 8 alarm bell 500ma, 12v
    outputs. The picture only shows 4 and 4. Should be quite simple
    though. Any ideas?
  2. Rich Grise

    Rich Grise Guest

    Should be as simple as eight resistors for the LEDs and eight diodes for
    the bell. How to connect them depends on if the 12V is high-side switched
    or low-side switched. If it's high-side, i.e., one output is "ground" and
    the other is either 0V or +12V, then use 8X 1K resistors, one from each
    output to the anode of a LED, and ground the LED cathodes. Use 8X 1N400x
    diodes, with the anodes each to one output (along with its LED resistor),
    and all of the cathodes connected to the relay coil, and the other side of
    the relay coil grounded.

    If they're low-side switched, i.e., there's a constant 12V, and the
    outputs go from floating (or maybe a 12V pullup) to a switch to ground
    (e.g., a transistor collector), then connect all 8 LED resistors (on the
    anode side) to the +12v, and each LED cathode to one of the outputs, and
    the 8 diodes' cathodes to the outputs, their anodes together to the relay
    coil, and the other side of the relay coil to +12.

    Good Luck!
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