Bat’s Ear

To be precise, this ultrasonic distance measuring device is more than just an ear, since it generates pulses of sound at 40 kHz as well as listening for their reflections. The circuit is divided into two parts: a 40 kHz oscillator and a ‘push-pull’ output stage. The oscillator is switched on and off according to the 5 V logic level on a control input. A preset is adjusted to set the oscillator frequency exactly equal to the resonant frequency of the ultrasonic transducer, nominally 40 kHz.