Ultrasound Detector with 567PLL and LM386 ICs

The bat ultrasounds are picked up by the microphone SPKR1 and go through two stages of amplification at Q1 and Q2. Separately, a tunable (R12) single frequency is produced by the LM567 oscillator U1. The LM567 is a tone decoder but here its input is grounded and its voltage controlled oscillator is used as a precision oscillator.

The oscillator frequency is given by f = 1/(1.1*C4*(R10 + R12)) = 1/(1.1*0.0022*10-6*(4.7 + [0-50])*103) = [88-7.5] khz The two signals are mixed at Q3 to produce both a signal in the audio range and higher frequencies that are the

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