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.
When the sensor, an ordinary photo-transistor, receives light, the relay closes its contacts. The...
This circuit consists of a bass filter that can be used as a subwoofer in a sound system. The...
This circuit has a traditional configuration often found on this site. The transistor must be...