Beeper/FSR testing circuit
A simple way to get playing around with a force-sensitive resistor. When you change the resistance by tapping on the FSR, the piezo beeps.
See the Fritzing sketch for details, it's essentially two modules: An op-amp comparator with a pot, whose output is connected to the reset pin on a 555 timer that's outputting a ~4khz square wave into the piezo. When the FSR voltage divider gows above the comparator voltage, the reset line goes high, and the piezo sounds.