We found this circuit in the 1983 Radio Electronics Special projects magazine. The components are common, and the circuit drives a relay. The power supply must be isolated.
An advanced motor control software plug-in for Microchip’s MPLAB® X Integrated Development...
This relay without lock uses a general-purpose transistor. The relay is according to the supply....
This signal follower is from a 1970's documentation. So it uses the traditional configuration at the time...