This circuit rejects frequencies around 1 kHz and can be adjusted using C1. Equivalent operational amplifiers can be used, and the power supply must be symmetrical.
This 7400 TTL circuit has a memory, keeping the LED on when a pulse is detected. The circuit must be...
This circuit is from a 1995 Electronics Now. It generates a 1 kHz sinusoidal signal. See in the...
We found this circuit in an old documentation for radio amateurs. The transistor can be any PNP of...