We found this circuit in the November 1992 Radio Electronics magazine. The circuit uses an LDR as a sensor and the transistor can be any general-purpose transistor.
Found in a 1980s English magazine, this trigger circuit can have different types of inputs...
Generating a square signal (50% active cycle), this circuit was found in Siliconix documentation from...
This current sensing circuit for applications up to 10 A has been found in a Linear Technology...