Chirping Bird Circuit

There are as many variations of the electronic chirping bird circuits as there are birds. And the circuits are being used for a wide range of applications, such as door bell, as horns or reverse horns in cars and scooters, and of course as bird chirps incorporated in plastic birds of a large variety.

The circuit shown here comprises two astable multivibrators the top one sets the tone of circuit and the lower one sets the rate of repetition. The two bias resistors of the tone oscillator are fed the output of rate oscillator through variable resistor VR1.

The arrangement produces a change of-tone every half cycle—the basic tone being set by the position of variable arm of VR1. With 2.2k resistors in the base and 10k variable resistor, the tone can be varied over a wide range. Change of tone is also possible with change in the collector-base coupling capacitors of tone oscillator.

The repetition rate can be varied by changing the collector-base coupling capacitors. The l0uF capacitor from the variable point of the potentiometer to ground shapes the square wave generated by the rate oscillator.

While the square wave applied to the base resistors of the tone oscillator would result in sharp tonal changes, introduction of capacitor round off the square wave produces a sort of warbling effect. Change of the supply voltage also affects the tone, but it can be reset by adjusting the variable resistor. Smooth operation is possible over a wide range of supply voltages.

Thus, it is fairly easy to obtain identical sounds for different supply voltages such as 6V for scooters or auto-rickshaws and 12V for trucks or cars. The tone oscillator produces a square wave output fed to output transistor the loudspeaker is coupled through a transformer.

The harmonics can be eliminated by a suitable capacitor across the primary of the transformer. It is much easier to manipulate this circuit to obtain the desired sound effect compared with the blocking oscillator circuit. Further, a large value capacitor across the supply charges as the supply is switched on to the circuit and it discharges through the circuit after the supply is switched off.

Thus the sound tends to decay slowly rather than being abruptly shut off. Period of decay depends on the value of capacitor and the output from the circuit.