This circuit was found in a Popular Electronics from the 90s. The circuit uses an ultrasonic microphone. The indicator is dual with LED and Buzzer.
The two circuits we suggest are from the book Optoeletronics - Theory and Practice by Texas...
The presented rectangular oscillator makes use of one of the four NAND ports of a 4093 integrated...
This circuit can receive the signals from CIR10466 or another like this, of the many described on this...