Conceptually the circuit there is simple, consisting of the ultrasonic receiver, followed by a transistor amplifier for the modulated wave, then a diode for demodulation, another transistor ...

Microchip’s rfPIC microcontroller family includes the 18-pin rfPIC12C5O9AG which features an integrated 315/433MHz ASK transmitter, and the 20-pin rfPIC12C5O9AF which features an integrated 315/433MHz ...

But this time the receiving side was swapped out, as [GreatScott] built a basic circuit around a TA7642 AM amplifier/demodulator IC, with only six passive components and a hand-wound coil.

The receiver is equally simple and also based on a CMOS 555. As long as the sensor picks up infrared light from the transmitter, the reset input of the 555 IC is held low and the buzzer is silent.

Electronic Circuits and Tubes By the Electronics Training Staff of the Cruft Laboratory, Harvard University. Pp. xxiv + 948. (New York and London : McGraw-Hill Book Co., Inc., 1947.) 45s.