Piezo Element as Digital Input


I am working on a project where I have already max'd out the analog ins with capacitance sensors and I'm wanting to use the digital inputs for collecting tapping on piezo elements. I know I need to produce a 5volt spike to register a digital on.. and i know its possible to boost the output of the piezo to 5 volts with an op amp, but I have 8 of these piezo triggers so I was wondering if anybody had a better idea?

Thanks! J

tapping a a piezo will actually produce very high voltages that are way above 5V. So the problem is not how to get the voltage up, it's how to keep it at 5V or below.

Try just putting a 5.5V rated zener diode and a 100K or 1M ohm resistor across the Arduino input that the piezo is connected to.

PS: there have been lots of threads on this... try searching the forum with google.