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Electronic Sound of Chirping Canary

2018-05-01 16:10  
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Figure 1 

The circuit aims to imitate a chirping canary made of electronic circuit components such as the Hartley Oscillator.

Hartley Oscillator – a variable frequency oscillator circuit where a center tapped inductor is connected in parallel with a tuning capacitor

Designing this circuit does not require much complicated connections. It can be powered by a 9 V battery source while the modification and adjustment being made to the circuit output may be controlled by the tank circuit utilizing the benefits of the Hartley oscillator. The loudspeaker is being driven and coupled to the circuit by the miniature audio transformer LT700 having a frequency of 1 kHz. Since it is small, some of it will only have a dimension of 16 X 16 X 20 mm and weighs around 0.02 kg. The impedance of 8 ohms is rated on the secondary coil while an impedance of 1K ohm is center tapped on the primary winding.

The feature of producing and imitating the chirp sound of a canary is the made possible by the oscillation done by resistor R1 and capacitor C1. The capacitor, having a capacitance value of 100 uF, is charging through the resistor, having a resistance of 4.7 K ohms. During this stage, R1 is the bias for the transistor making it operate in the cut off. When the transistor is in cut off mode, the base-emitter voltage is very minimal for any considerable current to flow. This mode triggers the oscillation to end but will start again once the capacitor discharges across the transmitter’s base-emitter circuit.

The frequency of the chirp may be modified by changing the values of the resistor and capacitor. The charging of the capacitor occurs when operating the push button switch. By releasing the button, the chirping runs faster while the oscillation weakens.

The advantages of using Hartley oscillators is the constant feedback ratio between the two conductors; constant amplitude output when tuned to the proper frequency range; and simple variation of the frequency by adjusting the value of the tuning capacitor in the circuit. Due to these features, Hartley oscillators are widely used on FM band as well as all broadcast bands. Scott 310E RF oscillator is being used for its FM division.

This circuit can be utilized as a replacement for doorbells, creator of sound effect, as an alarm or may be built as a decoration.


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