We found this circuit in the July 1992 issue of Radio Electronics magazine. An optical system produces the light beam that, when interrupted, triggers the alarm. The sensitivity is adjusted by R4.
This highly sensitive light sensor was found in a 1970 General Electric documentation. The circuit...
The given number circuit is used to activate the relay by interrupting the light beam that hits...
This alarm circuit with sensors in series was found in the Electronics Now magazine of June 1994....