We found this circuit in the Radio Electronics magazine of May 1977. The circuit has the frequency given by the components according to the formula next to the diagram.
Using an operational amplifier with FET, this circuit was found in an English documentation from...
With the first project we present, a relay is activated in the presence of light. We can use it as...
This AC amplifier has a gain of 40 dB. It was found in the May 1988 issue of Radio Electronics magazine....