This circuit was found in an American documentation of the 90s. Optical resources with the LDR as a lens can help in obtaining directivity and sensitivity.
This detector uses an unusual sensor today. The circuit is from an 80s documentation. Its...
This circuit was found in the December 1976 issue of Radio Electronics magazine. The circuit...
For inductive loads we have the configuration shown in the figure. Note that the opto-coupler...