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 aperiodic circuit was found in an old English documentation. The transistor can be any JFET...
This FM transmitter circuit was found in a Japanese publication in 1975. Equivalent transistors can be...
This circuit can oscillate at frequencies up to a few tens of megahertz depending on the crystal. The...