Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
This circuit was found in the January 1989 issue of Radio Electronics magazine. The circuit sends...
We found this TTL power supply circuit in the December 1972 issue of Radio Electronics magazine. The...
This circuit was found in an American documentation from the 1980s. The sensitivity ranges from...