Buzzer inside details

tpetar said:

Usually buzzer is piezoelectric element.

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betwixt said:

A Piezo element will not produce a tone by itself. The older mechanical buzzers used a switch and coil rather like a relay but the switch was in series with the coil and normally closed. When voltage was applied, the current flowed through the switch, energized the coil and opened the switch. Without power, the coils magnetic field collapsed, the switch closed again and started the cycle over again. A diaphragm was attached to the switch to make the sound of of it opening and closing louder.

In modern electronic buzzers there is usually a piezo element and a small transistor oscillator. The oscillator pulses voltage across the piezo elelment making it flex back and forth to produce the sound. The casing and outlet hole is tuned to the oscllator frequency to make it resonate and sound louder.

Brian.

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betwixt said:

Sorry, I can't draw schematics while connected to Edaboard on a mobile phone!

Designs vary but many use a tapped inductor. The tap goes to the positive pin, collector directly to one end and the base through a resistor to the other. The piezo goes across the collector to tap side of the inductor and a capacitor goes from the base to emitter. The emitter is the negative pin. So it uses the inductor and capacitor to provide the necessary phase shift for it to oscillate.

Brian.

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Audioguru said:

Here is the schematic of a modern piezo beeper. It uses a piezo with 3 wires because one wire provides positive feedback to the transistor's input to make an oscillator:

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