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 circuit that can be activated by light or heat was found in an old American documentation, but the...
We found this circuit in an old French documentation from the 70s, but it can be assembled using...
This circuit was obtained from Hands-On Electronics, an American magazine of January 1987. The...