Found in a Popular Electronics from the 90's, this circuit is used to recognize the frequency of a modulated infrared signal. The LM567 circuit must not be supplied with voltages above 9 V.
This circuit is from an English technical documentation and can be implemented with BC558...
This interference rejection circuit for telegraphy was found in a 1980s documentation for radio...
This circuit is suggested by Motorola, employing a photodiode with housing designed for coupling in...