This circuit, which uses a quadruple comparator, was found in old American documentation. The response curve is shown next to the diagram and can be adjusted in the trimpots.
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...