The sensor of this circuit is a 2N3055 transistor from which the housing cover has been removed to expose the silicon wafer to light. When the light stops shining on the 2N3055 transistor, it switches the BD135 or equivalent, and the charge lamp is activated. The adjustment of the trigger point according to the intensity of the light incident on the sensor is determined by adjusting the trimpot of 1 M ohms. The circuit supports lamps up to 500 mA and the BD135 must be mounted on a heat radiator. The 10k ohms resistor can also be changed depending on the sensitivity.
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