Two sensors are used in this simple remote-control circuit, one to switch on and one to switch off the relay. The circuit is from 1986 documentation. The transformer has 12 V of secondary.
The presented circuit monitors a line indicating if it is busy if there is an extension. The...
This high-powered megaphone circuit is from a Radio Electronics from December 1964. Note the use...
This linear circuit was found in a 1965 Electronic Design. The transistors are from that time....