Dr. Imre Bartfai wrote:

> at first I could not follow your arguments. The it became clearer.  However, I
> think, it is true only if the device connected between A and B has enough > ca
pacity to hold some coulombs during pin transition. On the other hand:
> the piezo devices drain not too much current, i. e. you can put a serial
> resistor between it and the PIC. Now, assuming the capacity is high enough
> to satisfy the condition described above, nothing bad will happen as the
> PIC has voltage clamping diodes. I guess 2 x 10k will work.

But the 20k will diminish the increase in sound that you were trying to achieve
by using two pins, non?  If the large R's are necessary, then you might be
better off just using one pin and ground, methinks.

I think that what David is suggesting is right.  Perhaps one could think of it
as a first approximation of a sinewave that is being sampled at the peaks and
the zero-crossings?  Since the slope of the sinewave at the zero-crossing is
more steep than the slope at the peaks, the 0-0 period could be very small in
respect to the period of the signal.

I have not used this idea, but I will incorporate it the next piezo element that
I drive.  Thank you, David.

Just my opinion.  Your mileage may vary.

Michael

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