This circuit was found in a 1965 General Electric manual. It is intended for cars that have negative ground. At the time there were vehicles with positive mass.
Suggested by Texas Instruments in 1980s documentation, this circuit uses a component of the era....
The idea of this simple circuit is to use a tape recorder to key a transmitter in code emission....
This relay circuit with a dual channel MOSFET (not very common today) was found in an old American...