Self Drive Piezo Buzzer

Why do some piezo elements have three wires?

img_20180113_164753_6ognnO4myR

Most piezos have two connections, but this type has three. They are called self drive types, and they’re meant to be used as part of the oscillator.

The piezo effect works both ways: if you apply a voltage the piezo stretches, but also if it stretches it creates a voltage. This principle is used to create a feedback signal which drives the oscillator.

The advantage of the self drive is that it will automagically work at its resonance frequency, where it produces the loudest sound.

kuvatommis_2018-01-13_17-03-00_VSoimqFXwo

You need:

  • Piezo
  • 2N2222A transistor (or some other NPN transistor)
  • 150K ohm resistor
  • 3.9K ohm resistor
  • 620 ohm resistor

2n222-npn-transistor-pinout_HutZsVSBJk

kuvatommis_2018-01-13_16-05-12_6tfVkBpk9u

Demo:

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