Using a sensor from the time, this circuit was found in the 1992 Radio Electronics Handbook magazine. The circuit uses a pair of integrated two-digit A/D converters.
This circuit can be used to recognize a tone by its frequency. When this tone is present in a...
This circuit is from a 1975 amateur radio manual. The components can be approximated to the...
This circuit is from an English publication from 1976 but can be easily assembled with BC548...