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Buzzers / Sounders

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Many applications require an audible warning when something happens. Here are two devices that can provide that, buzzers and sounders.

The job they do is identical - produce a single tone when a voltage is applied to them. The way they do that job is different.

Buzzers are usually electromagnetic devices. When an electric current flows through a coil of wire inside the buzzer, it becomes an electromagnet, and pulls a metal plate towards it. This movement opens a pair of contacts, switching off the current. The plate springs back to its original position, causing the contacts to close and restoring the current. This sequence continues, with the result that the metal plate vibrates in and out, causing a sound wave.

Sounders use an effect known as piezoelectricity. Some crystals change shape when you apply a voltage to them. If you apply an ac voltage, then the surface of the crystal vibrates backwards and forwards, as the direction of the electric current changes. Under the right conditions, we hear this vibration as a sound. Most sounders have a built in oscillator, to generate the ac voltage when you connect the sounder to a power supply.

In using these devices, the main consideration is the current they need to operate. Piezoelectric devices usually require a lower current, typically 25mA, and so are often more suitable for portable devices.

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