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.
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in a 1990 Electronics World magazine. The circuit can be mounted today by...