This circuit uses a contactor having been found in a 1987 publication. More modern equivalent devices may be used. The circuit has neon indicator lamps.
We found this circuit in the April 1988 issue of Radio Electronics magazine. The circuit can be...
Found in an old Radio Electronics, this circuit applies to frequency meters for frequencies up to 100 MHz....
This circuit from an American documentation from the 70s, indicates a photodiode to generate...