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Simple Lie Detector with Digital Panel Meter

Discussion in 'Electronic Basics' started by Markan, Jan 21, 2005.

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  1. Markan

    Markan Guest


    I am looking for a simple lie detector cicruit for my son's science
    project. We have a Digital Panel Meter with a 0-200Mv range. The resistance
    we would like to measure would be about 0.2 - 2Mohms.

    This does not need to be accurate. Help would be appreciated on how to find
    a suitable circuit diagram.


  2. If you put a 10M resistor in series, and use a 1.2V source (actually, a
    1.5V battery would work fine), you'll get 200mV when the resistance is
    2M, and about 23mV when it's at 200k ohms. That sounds about right.

    However, your digital panel meter may have a low resistance itself, thus
    messing with the reading. Hopefully, it will have a 10M or higher
    resistance, so it won't interfere too much. If it interferes too much,
    come back and somebody will help you build a buffer to measure the
    voltage with.

    HOwever, I think this circuit will be fine. Use courier font, or other
    monospaced font to view.

    ___ +
    .--|___|---o------o Probe1
    | |
    | |
    | |
    | / \ Meter
    1.5V --- (_/_)
    - \_/
    | | -
    '----------o------o Probe2

    (created by AACircuit v1.28 beta 10/06/04

    If you need to power the meter, use separate batteries.

    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
  3. Markan

    Markan Guest


    Thank you this works great!

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