This circuit is from an American documentation from 1975. The circuit uses components of the time which can be replaced by modern equivalents. The coupler is homemade with a lamp and a photocell.
This circuit was suggested by Popular Electronics from the 90s. The circuit is quite simple using...
We found this circuit in Motorola's Circuit Applications for the Triac 1971 manual. The circuit is for ½...
In the figure we have a second order filter with very high input impedance, using an operational...