Circuit : Graham Maynard
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Description
A high frequency oscillator intended to repel insects from your home and garden. Notes
Repel those repugnant insects from your Garden this Summer with this insect repellent circuit. Designed by Graham Maynard the circuitry consists of a phase locked loop (CMOS 4047) wired as a 22KHz oscillator. The output is amplified by a pair of complimentary output transistors and drives a Motorola 3.25 inch Piezo. Current drain is around 120mA so an external power supply is recommended.

The piezo used was a standard 85mm square Motorola Horn, Maplin part number WF09K or WF55K. These are rated +/-3dB to 28kHz.