This 1 kHz circuit was found in American documentation from the 90s. The original operational amplifier consists of a double 741 at the time. The power supply must be symmetrical.
This circuit with a double-gate MOS transistor was found in a Popular Electronics from the 90's....
This photoelectric cell light relay was found in Radio Electronics magazine from April 1958. The...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...