We found this circuit in a 1968 Electronics World. The circuit uses a transistor of the time providing a 16 dB signal gain with a 4 V output.
The CMOS 4046 integrated circuit is not very common today, consisting of a very efficient PLL for...
In the circuit shown in the figure to the side, the relay is activated when the light stops...
With this name, the English publication where we found this circuit indicated a sensitive touch...