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 circuit was obtained from an American 80's documentation. The transistors can be 2N2222 and...
This low Power simple amplifier is intended to the use with high impedance phones. The circuit is...
This circuit was found in a 1963 magazine, but can still be easily assembled with some current...