How do I get an On/Off output from piezoelectric sensor?

[badger_]

I need to get an on/off signal (like a switch) from a piezoelectric sensor, that gives me variances in voltage. Any ideas?

Here's why:

I Make Projects - How To Make Dual Bass Drum Pedals Work in ROCK BAND

This circuit takes an off/on signal from two Rock Band drum pedals and, essentially, allows them to NOT block one another if one of the pedals is down. These pedals work by magnetic switch.

Unfortunately, I need this circuit to work with the Guitar Hero pedal, which works with a piezoelectric sensor which, from what I can tell, outputs a voltage spike when the pedal is pressed.

Does anybody have any idea how I can modify the circuit to accept the sensor inputs?

OR

Can I change the sensor output to create an on/off signal the circuit can use?

 

[MikeMl]

Likely the sensor puts out one polarity when the pedal is depressed, and the opposite polarity when the pedal is released?

 

[SABorn]

A little circuit i used recently to detect a light tap on a piezo sensor was this one and the signal was fed to a picaxe microcontroller as a trigger input from the circuit.

In my case i needed the signal to be present for about 1/2 a second so the program had time to loop back and check the input and not miss the signal.
If a faster signal response time is needed then the capacitor (C.1)would need to be reduced in value or R.3 resistor reduced in value.

The actual sensitivity of the piezo input can be adjusted by R.1 trimpot.

Pete.