Found in an American publication from the 90s, this circuit allows the supply of 3, 6 and 9 V devices with currents up to 1.5 A in the car.
This 4-transistor signal tracer or follower was found in Radio Electronics magazine from May 1960....
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
Assembled with SMD components this circuit can be very small. The range is a few tens of meters. We...