[sdiy] touchplate keyboard - works!

[Ian Fritz]

At 02:01 PM 2/5/2005, Roy J. Tellason wrote:

>Eh?  A piezoelectric material is defined as one where,  when you apply a
>mechanical force you get a voltage,  and vice versa.  Same principle that's
>used in crystal-controlled oscillators,  too.
>
>They may be "capacitive" in the electronic sense,  but that doesn't change 
>the
>principle of operation...

You are wrong.

I have worked on the physics of piezoelectric materials off and on for over 
30 years.

Your definition is correct.  But the fact is that at dc there is always 
either bulk ionic or surface electrical conduction that neutralizes 
piezoelectric free surface charge and cancels the output voltage.  Any 
textbook on this topic will explain this for you in more detail.