Bruce,

This is similar to a voltage doubler.  The Piezo is 0.01uf or so.  You
charge it up then change the polarity of the output and slam it the
other way.

What does it look like on a scope, single ended?  One output to Piezo
other Piezo terminal to gnd or Vdd?

If the output exceeds Vdd or gnd by 0.7v and current exceeds 20ma,  the
internal protection diodes are in danger.

Don

Bruce Cannon wrote:
>
> Don:
> When I feed it my square wave, at the resonant frequency I see some
> oscillation at each edge, but very low voltage, seems nothing to worry
> about.  I did notice that at one or two other frequencies I saw a spike of a
> half a volt or so at the edge, which I could eliminate with a series
> resistor.  Is this what you were referring to?
> Thanks,
>
> Bruce Cannon            Style Management Systems
> bcannon@jps.net         http://www.jps.net/bcannon
> (510) 787-6870          1228 Ceres ST Crockett CA 94525
>
> Remember: electronics is changing your world...for good!
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Donald Riedinger
> > Sent: Sunday, July 25, 1999 5:04 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: piezo audio transducer driving
> >
> >
> > Bruce,
> >
> > Have you looked at it with a scope?  You'll see what they're talking
> > about.
> >
> > Don
> >
> > Bruce Cannon wrote:
> > >
> > > Hello all:
> > > I've been developing a device which includes a piezo element driven
> > > differentially by two IO lines, no other components.  It works great and
> > > draws very little power for so much sound.  Too easy, I wonder?
> >  I've looked
> > > over past PICLIST discussions of driving piezo elements with
> > the PIC (and
> > > have searched the web for other info as well to no avail), and have seen
> > > mention of a series resistor, annd occasionally external
> > protection diodes.
> > > 1. Can anyone give me a nutshell explanation of why these
> > elements might be
> > > neccessary?  I understand that there is an average current at the given
> > > frequency, but is there also an instantaneous (or do I mean periodic?
> > > inrush?) current and/or voltage which I must consider as well
> > (and which is
> > > dangerously higher)?
> > > 2. Can anyone recommend a source for additional reading to help
> > reduce my
> > > ignorance?
> > > Thanks,
> > >
> > > Bruce Cannon            Style Management Systems
> > > bcannon@jps.net         http://www.jps.net/bcannon
> > > (510) 787-6870          1228 Ceres ST Crockett CA 94525
> > >
> > > Remember: electronics is changing your world...for good!
> >