Taking an example of a Raytheon operative as uncommon today, the circuit applies to other operational amplifiers. The formulas are given next to the diagram.
This application is from a circuit manual from the 90s and only works with incandescent lamps. The triac...
This circuit was found in an American magazine in 1978. It activates a relay when the speed of a...
This circuit is from 1976 documentation, but it can be assembled with more modern transistors like...