Found in an RF Design from the 90s, this circuit is based on components from the time. It can, however, be implemented with equivalent modern components.
This sensor was published in Radio Electronics magazine in April 1962. The two-transistor circuit...
Another of the many similar configurations we have in this section. This one is from a Radio...
This circuit like the previous one is intended for 24V x 3W solenoids being connected from the...