Posted on May 7, 2012

IC2 forms a stable oscillator whose frequency and pulse width is determined by the values of R4, R5, R6, and C4. R4 is made adjustable for precise frequency setting. The output of IC2 is pin 3, which is capacitively coupled to the base of Ql. Ll acts as a high-impedance choke to the signal, while allowing the collector of Ql to be de-biased. Ql amplifies the positive pulses from IC2 and step drives the series resonant combination ofL2 and TDl.

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Resistor RlO serves to broaden the response of this resonant circuit. L2 and the inherent capacity of the transducer, TDl, forms a resonant circuit at around 23kHz. It is usually found that most rodents are bothered when the signal is pulsed with the off exceeding the on time. This timing is accomplished via timer ICl and timer inverter Q2. ICl is free running and its periods are determined by Rl, R2, and C2 to be approximately two seconds off and two seconds on. The periods are inverted via Q2 and used to gate pin 4 of IC2, the freqoency oscillator, turning it on for two seconds and off for three seconds. The power supply is a conventional voltage doubler with a zener regulator for the oscillator voltages.

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