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 instrumentation amplifier with differential inputs was found in documentation from the 90s....
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
Found in a 90s 303 Circuits, this circuit has an output power of 100 mW. L1 consists of 890 turns...