>I did a search thru the archives and found David Horn's 
>comments about using two pins to do a push-pull setup thru 
>some HC invertors.  I assume thats still a valid and easy 
>way to drive it.  I was hoping also to come across some 
>references to an inexpensive and small element that still 
>gives a good 'beep' when driven.  Presently the system 
>voltage is 5V but could be migrating to 3.3V soon.  So 
>anyone have some good suggestions or references to what 
>they have used in the past?

For one-offs the piezo element from a smoke alarm is a 
fairly capable sounder.
If you are prepared to use two pins then the generation of 
an arbitrarily high voltage with a small amount of extra 
hardware is easy * and allows a Piezo of any desired 
capability to be driven.

* A small inductor (eg the potted type the size of a 1/2 
Watt resistor) and any small transistor and resistor will 
allow the generation of N volts where N is too large. 
Judicious software control or a zener will limit this supply 
to a desired value. With a little skill the power generation 
pulses can probably be used to drive the piezo element 
acoustically. This gets you down to one pin, one resistor 
and one transistor. Maybe another resistor and a zener to 
round it out. If desperately unlucky a little more hardware, 
but not much.

Note that when pressed or struck a piezo element can produce 
substantial voltages. These can be enough in some cases to 
destroy the driving IC. A piezo in a case which can be 
mechanically flexed or user impacted can have this result. 
This is a known real world risk - not just a theoretical 
one.




        Russell 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist