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Modifying x10 motion sensor to trigger halloween props

Discussion in 'Sensors and Actuators' started by jamescl, Sep 11, 2013.

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  1. jamescl


    Sep 10, 2013
    Halloween is coming up and I'd like to trigger some of my props with a battery operated motion sensor. I'm new to electronics so I'm not to sure I'm going about this the right way.

    I bought a MS16A X10 motion sensor which runs on 2 AAA batteries (3V). Using a schematic I found online (thanks Ed Cheung!), R3 is the place where the motion signal is sent. My multimeter sees approx 1.5V appear here when it trips.

    The props have a footpad or "try me" button that connects via a plain mono-plug. When I cut the wire to one, and touch the 2 wires inside the cable together, the prop triggers.

    I'm hoping I can connect a transistor (NPN222A) to the motion sensor trigger spot (as base), and connect the mono-plug wires to the emitter/collector pins.

    I'm not sure if I have the right transistor or if I'm going about this all wrong. Any advice is much appreciated.

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    If it sees 1.5V, then what is being sent is a coded sequence, not a logic level (if so, it would read 3V).

    Yes, you could use this to switch a transistor, but it would turn on and off rapidly.

    As an alternative, you can filter the output of this point so that the transistor stays on. The simplest method would be to use a circuit like this:


    The load needs to be quite light. For loads heavier than maybe 100mA, I would place a relay here (not forgetting the catch diode).

    The capacitor charges fairly quickly through R1 and D1, and discharges much more slowly through R1 and R2. This keeps it well charged during the pulse train.

    The capacitor provides current to the transistor via resistor R3.

    I have just picked "reasonable" values. Some tuning may be required depending on the exact nature of the pulse train and the load you're switching.

    Attached Files:

  3. jamescl


    Sep 10, 2013
    I was wondering why I was only seeing 1.5V there. That makes sense. I'll give your suggestion a whirl. I knew it couldn't be that simple. Thanks!
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