Optical shield (CB20698E)

This circuit was found in American documentation from the 90s. The coupler is the type that uses a photo-Darlington.

Power grid voltage failure indicator (CB7013E)
Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the...
Electric fence (CB23675E)
This circuit with SCR and Unijunction and which can be assembled today with modern equivalents was found in a...
Intermittent Defects Detector (CB17230E)
This circuit was developed to find intermittent defects in an electrical control. In the event of a...