This circuit that generates signals between 1.5 and 2 kHz was found in a documentation from the 90's. The capacitor C1 can be changed to obtain other frequencies.
This circuit can be found in a 1970 Motorola documentation. The circuit can be implemented with general...
This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with...
This circuit is from 1977 documentation, and high current equivalent transistor must be used. The...