Piezoelectricity

The Piezoelectric Circuit Used in the Demonstrator

The piezo disc used in the Josh's Piezoelectric Geocache demonstrator can generate a voltage as high as 18 volts with just moderate pressure. Therefore the voltage could be much too high to safely trigger the microprocessor. The input circuit was developed to remedy this problem.

Click on the diagram to enlarge it.

The diagram shows the 18 volt pulse from the piezo disc being clamped to a peak voltage of +3 volts with a 3 volt zener diode. This voltage is used to turn on the N-Channel Power MOSFET Transistor. This draws enough current through the 100 k resistor to drop the 5 volts to almost zero. The microprocessor is watching for a voltage close to zero volts to trigger the coordinates message. By the way, the output of the microprocessor drives a piezoelectric buzzer.