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Piezo vibration switch - help convert voltage to close a contact

Discussion in 'Electronic Basics' started by Timothy, Sep 18, 2003.

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  1. Timothy

    Timothy Guest

    I need a VIBRATION SWITCH. I'm trying to make one from a piezo disc
    which I got from the inside of a buzzer. When the piezo is vibrated or
    bent it creates a voltage. I need to convert this voltage to close a
    contact. I tried using an N-type FET transistor with it but the
    contacts REMAIN CLOSED for every pulse of the piezo. Maybe it's the
    transistor??? I couldn't find the one used from this schematic so I
    experemented with a few oter N type FET's.
    http://slot-tech-ftp.serveftp.com:8080/pinball/gottlieb/smart switch/gottlieb_smart_switch.htms

    Please post or email me with any helpful ideas. Thanks in advance.
     
  2. John Fields

    John Fields Guest

    ---
    Chances are the piezo film they're using is poled PVDF, which puts out a
    remarkably high voltage when it's flexed properly. If you're flexing
    your piezo disc with your finger, what's probably happening is that
    you're not flexing it fast enough to generate the voltage needed to turn
    the FET on.

    Notice that the pinball switch operates when the ball _leaves_ the
    switch, so the high voltage is generated when the switch snaps back to
    its unflexed position. What you may want to try is to tap your piezo
    disc with something hard (like a swizzle stick) and see what happens
    then.

    Also, you could use a voltage comparator to sense the voltage generated
    by the disc, and if you set it right it ought to detect it even if you
    pressed it slowly.
     
  3. Timothy

    Timothy Guest


    The piezo is generating enough voltage to turn the FET on. The problem
    is that the FET stays on. Also reversing the polarity on the piezo
    turns the FET on as it vibrates in opposite direction.
     
  4. John Fields

    John Fields Guest

     
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