Electronic Mosquito repellant is founded on the theory that insects such as mosquitoes can be repelled by use of sound frequencies in the ultrasonic range. The circuit is nothing other than PLL IC CMOS 4047. It is wired as an oscillator and works at 22 KHz. We also use a complimentary symmetry amplifier that consists of four transistors to amplify the sound.

The Piezo buzzer is used to convert output of the amplifier to ultrasonic sound which can be heard by these insects. This repeller uses bridged push pull output. This output provides four times the normal two transistor push pull which connects through a coupling capacitor.

IC 4047 is an oscillator and has got its frequency set by R1 and C1. The complimentary output of IC which is accessible on pin number 10 and 11 are fed to the overpass output circuit. The frequency used to repel mosquitoes is available in ultrasonic range a piezo transducer.

Piezo transducer responds to ultrasonic sound better. It is therefore used to produce sound in place of standard loud speaker.

Connecting 4.7nF in parallel to C1 the oscillator frequency, will be an audible range. The audible sound is therefore an indicator that something has not been connected as it should. To rectify this problem, check whether there is any output and other components and IC pin connections.

If the audible sound is still there, remove the capacitor connected in parallel and the circuit will be ready for use. Piezotransducer will emit the audible signal of the oscillator.

Sound level indicator is an instrument used to measure the noise level (sound level) in an environment. These sound indicators operate in human audible range only.


  • Assemble its circuit on a general function PCB.
  • The circuit can be powered as from 12V DC.
  • Any general function piezo buzzer can be used as the buzzer.
  • The ICI have to be mounted on a holder.

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