Piezo Triggers

Ullrich Peter ullrich at kapsch.co.at
Fri Mar 8 08:08:55 CET 1996


>How do you use a piezo buzzer for a velocity sensitive trigger? 

The piezo buzzer is glued under the drum surface.

Then I use the following circuit:

         !\ !      +-----+
piezo o--+ >+------+     +-------o--------o--------o------o Analog Out 
input    !/ !      +-----+       !        !        !
                     R1          !       +++    ---+---   
        schottky              -------    ! !    !  ^     zener diode
         diode                -------    ! ! R2   / \       4V7
                                 !       +++     +---+
                                 !        !        !
                               --+--    --+--    --+--

I don´t know my actuel values but take this as guideline:

R2 = 5..10 x R1

You have to design the timeconstant of R1xC so that the C can be charged
fast enough (t about 0.3ms) and the timeconstant R2xC so that the voltage at
the output is hold as long as the following circuit (digital/analog
converter or analog gear) needs it. You can also extract an digital trigger
impuls out of the signal and sample the analog output voltage by an sample
and hold circuit.
Don´t forget the zener diode !!! The voltage of the piezo buzzer can be up
to 100 volts !!!

The output voltage is nearly the rectified positive peak voltage of the
piezo signal and so velocity sensitive.

Hope that helps !

Peter


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--oOOO--(_)--OOOo-------------------------------------------------------
                    Ing. Peter Ullrich     mailto: ullrich at kapsch.co.at 
                    Hardware & Software Developer / Electronic Musician
   .oooO            KAPSCH AG / SGB2                   Vienna / Austria
   (   )   Oooo.            Traffic Control and Transmission Technology
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