You won't be disappointed with the performance of this sensitive ultrasonic receiver. It can let you listen to bugs, bats, engines, and virtually any other source of ultrasonic sounds. The circuit uses a piezo tweeter as an ultrasonic microphone, amplifier stages Ql, Q2, and an LO using a 567 IC. Q3 is a mixer that heterodynes the ultrasonic sounds down to the audible range. U2 is an amplifier that will drive a pair of headphones.
U2 is an amplifier that will drive a pair of headphones.