Found in Ferranti's 1968 documentation, this circuit uses a Darlington photo transistor to drive a 12V relay. The circuit can be implemented with modern equivalent components.
Here we show how two 4017s can be cascaded to count above 10. The circuits are driven by a square...
The circuit in the figure represents a typical application of a phototransistor exciting a relay...
This circuit, in fact, what it does is a reactivation of the batteries through a brief pulsating...