This simple bridge circuit can be used for impedance or resistance measurement using a high impedance earphone as an indicator. The circuit is from an American 80's documentation.
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...