Don:
Thank you for the info.  This is where I fall down conceptually: I can
understand that the piezo element has a capacitance and that, when I look at
the circuit at a moment in time, whenever I reverse the pins I am dumping
that charge and both pins are seeing that current (in or out) with
essentially no impedance.  But I thought that at a given freq the element
has some impedance which mitigates this flow of current?  Sorry if this is a
bonehead question.

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: Monday, July 26, 1999 9:17 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: piezo audio transducer driving
>
>
> 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!
> > >
>