I am trying to use a piezo transducer as a switch with my keyboard hack.
The keyboard hack is done and works fine and I works using any of the switches that I have tried. I would like to use piezo's to trigger the switch to simulate hitting a key.

I am aware that piezos generate electricity and so first of all I am worried about blowing everything up. Also they are not necessarily a switch but are used in things like Vdrums to simulate this.

Has anyone done this or have any advice?

I'm a noobie to this and hope to share my projects later when they come together.

makes you wish you had an oscilloscope doesn't it! In general it would seem that a high pass, or maybe better a band pass filter, could be protected by a Zener diode. Or better yet you could use an opto isolator.

Thanks a lot.
I had a look at a few of these solutions and the opto isolator looks to me to be the best one.
As far as I can see I should attach one of these to either end of the piezo (so no extra charge can run in the wrong direction) and then run the wire on as if these three components were the switch.

I've never used piezo's for anything other than starting the grill, but I think they have a very high output impedence so you may need to buffer it to drive the opto. OTOH you could just give it a try to see if it works!

Combover

You can try to used an OpAmp (condition the voltage from the piezo with resistance/diodes) and then send this to a 4066 - analog switch.