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.
Using bipolar, FETs and unijunction this long-lasting timer can reach 10 hours with good quality...
This 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics...
We found this circuit in a 1969 General Electric documentation. The circuit uses transistors of the...