This circuit was found in a RE Experimenter Handbook from the 90's. The components are of the time, rare nowadays, except the 555 and 4017.
This 1967 Philips circuit recognizes a light signal (visible or infrared) modulated by tone. The...
This circuit turns on an old cassette recorder when the telephone rings, thus enabling the...
This is the receiver for the previous circuit transmitter. Similarly, no information about the...