Using a 709 integrated circuit this circuit was found in the June 1972 issue of Radio Electronics magazine. More modern operational equivalents can be used. The power supply is symmetrical.
With this circuit, a common multimeter can be used to check if there is a microwave leak in a...
This 80's circuit can be made with current comparators. Rectification accuracy is 1% DC up to 100...
This frequency meter, found in a 1987 documentation, uses indicator LEDs and can work with audio...