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.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...