> I have tried this quite recently, and the PIC has enough grunt to get
> reasonable volume, better if you can use two PIC pins and drive
> them in anti-phase to double the voltage swing

Ah yes, you've reminded me of some of the previous thread. I think
there was some mention of a vibrated piezo putting voltage back
into the PIC pin

I just got this from the archives, by Dave Van Horn

"Driving a piezo from a micro usually follows a pattern.. 
One lead grounded, one lead to the micro. Too soft. 

Both leads to the micro, driven in opposition. Nice and loud. 

Then the strange behaviour begins. 

After a while, you notice the similarity in the schematic between
a charge pump voltage doubler and your piezo element and port
pins, and you realize that every time you flip the piezo, you are
flirting with SCR Latchup or glitching your micro. 

Then you drive it through a pair of HC inverters at least
and get "happy beeps" "
 
> What really makes a huge difference to piezo sounders volume
> is mounting them in a resonant cavity, i.e. like the plastic
> encapsulated PCB mounted piezo elements you can get.

That's very true. The volume drops off considerably if the
element is impeded from vibrating freely

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