An optoelectronic switch controlled by a red laser light

An optoelectronic switch closed and opened optically has been designed. The switch has a light sensor circuit of four bipolar transistors of type BC 107 arranged as an array of 2x2 and then processed to receive light incident on it, so they were operating as phototransistors. By this switch an external electric load can get its individual operating voltage by applying a beam of visible laser on the sensor s array. A laser diode of wavelength 650nm, output power about 1mW and 5cm long has been used as the light source.