The original application of this 1967 Ferranti circuit can be changed so that it functions as a pass sensor shield for gears and other moving objects.
This circuit was found in a 1973 magazine but can still be assembled using modern equivalent...
This circuit was found in an old European documentation. When R2 is cut off the circuit triggers...
We find this circuit in a Radio Electronics of July 1984. It consists of the traditional version of 1 A...