This circuit was found in an Electronics World of 1968. Its purpose in triggering a relay when the circuit receives signals from a vibration sensor. The circuit is used in emergency situations.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
The adjustment of the maximum load voltage is made in the trimpot. The circuit is from 1994...
In the figure we have the conventional configuration of a differential amplifier with the...