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Low Voltage PIR speaker switch

Discussion in 'General Electronics Discussion' started by tommyleinen, May 11, 2013.

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  1. tommyleinen


    May 11, 2013
    I am looking for advice as someone who is intested in electronics and home projects but has very basic knowledge:

    I am putting in a set of ceiling speakers in the bathroom, which are connected to an amp next door.

    My theory is that i could use a couple of low voltage PIR sensors, each between one of the speakers and the amp on the speaker cable.

    The sensors I have in mind are:

    Operational Voltage: 0.8V-9V
    Static Power Consumption: 50 microampere
    Detecting Range: 3-5 meters, <140 degrees
    Operating Temperature: -15 to +70 deg C
    Trigger Method: L unrepeatable trigger / H repeatable trigger

    Can anybody tell me whether this would work, if it would work with a tweak or two, or if it is just plain daft or indeed dangerous?

    I am thinking that there might be enough voltage to power these without the need for an additional power supply...

    The amp runs at 20RMS per channel... but can easily power a pair of 100Watt speakers. It would in theory be left on all the time, with the PIRs acting as speaker switches.

    Thanks in advance :p
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    These sensors are not suited for direct insertion into the speaker wires. These sensors output a logic level signal that can then be evaluated by other circuits to produce the appropriate action.
    A typical setup using these sensors would be to have the sensors sense the presence of a person. The logic signal is amplified and controls a relay which in turn can turn on the speakers (or off, as you like).
    You will need a separate power supply for this. Although you may be able to re-route some power from the speaker wires to supply that kind of circuit, the cost is reduced fidelity of the audio signal.
    You could also tap into the audio amplifier and find a spot where you can attach the logic signal from the sensor to mute the amplifier. But that requires good knowledge of the workings of the amplifier (and ideally a schematic diagram, which nowadasy may be hard to come by).
  3. tommyleinen


    May 11, 2013
    Thankyou Harold for your informative response, I think I will have to can the idea, though I am sure it would make a good project for someone!
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