Specification:

This circuit is based around two 555 astables. One low frequency astable sets the tempo and enables a second astable which produces a tone but for a very short time. Adjusting the second astable using PR1 will alter the pitch of the beat.

The sound changes greatly with pitch and is worth experimenting with. It is worth using a speaker of at least 66mm in diameter. An 8 ohm type will do but a 16 ohm is better.

A word of warning, after prolonged use the case of T3 (BFY51) does get quite hot. The peak current through the speaker and the transistor is quite high - around 800mA, so take care when testing.

The circuit works with a 9v PP3 battery which will gives many weeks of operation. The peak current is quite high (few hundred mA's) but this occurs on each beat. The normal operating current is around 12mA. Diode D3 prevents the circuit from being damaged if the battery is momentarily connected the wrong way.

Download PCB and circuit details

A diagram of the PCB showing how the VR1 can be PCB mounted if required.

A new version PCB has been developed. The circuit is almost identical and has the same operating parameters. The new PCB is shown left and is amost identical size

A kit is available including PCB, components from our shop.