This circuit is a simple design circuit for bat detector circuit that is a frequency division type device. Frequency division type detectors allow you to hear ultrasonic sound by digitally scaling the frequency down into the human hearing range. Here’s the figure of the circuit;
Basically this circuit is essentially composed of 3 integrated circuits, or ICs. The signal from an ultrasonic transducer is fed to IC-1, an LM386 audio amplifier, which is configured to provide a signal gain of 200. The signal is coupled to IC-2, a second LM386, by a .05 uf capacitor. IC-2 is configured to provide an additional gain of 20, for a total system gain of 4,000. The output of IC-2 is direct coupled to the input of IC-3, a 7 stage CMOS digital divider circuit.
The input stage of the divider acts as a zero crossing detector, triggering on the negative transition of the signal from IC-2. The divide by 16 outputs connected to a potentiometer, which serves as an audio level control. A high impedance ceramic earphone is connected to the output of the level control. The 10K level control is a small printed circuit pot that is set and forgotten. The detector circuit is powered by a nine volt battery. (The numbers next to the IC nodes refer to the pin numbers of the IC's. Note the additional pins listed at the bottom of the schematic that need to be tied to ground).
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