[sdiy] Found the Piezo Manufacturer!

[Ian Fritz]

At 08:51 PM 2/5/2005, Peter Grenader wrote:
> > (They have a passive Mosfet circuit inside the potted epoxy).
> >
> > Cynthia
> >
> >
>Possibly others, but not these.  There are only two leads coming from these
>switches.  An input and a normally open output.  Totally passive, no power
>required for operation.  They can pass audio if you wish them to.
>
>- P

Peter -- The data sheets indeed show just two leads.  But they also show an 
internal (mystery) circuit between the transducer and the mosfet 
gate.  This circuit is indicated as a clipper, but no details are 
given.  An internal circuit could be powered (transiently) by the piezo 
output voltage, so you wouldn't need extra power supply leads.

Nobody is questioning whether you circuit functions as you say.  But it is 
very difficult to understand how it works.  Almost sounds like a perpetual 
motion machine.  :-)

I notice that your circuit  has each switch contact connected to an op amp 
(+) input with no other connections to those inputs.  This leaves your 
switch and its wires floating at very high impedance.  My guess is that you 
are seeing some kind of pickup or leakage effects producing the dc 
output.  For grins, you might try connecting 1M resistors from the inputs 
to ground and see whether the circuit still works.  Also, does the circuit 
work if you press the switch with an insulating rod?

   Ian