Photosensitive resistor is used as signal acquisition device, which is a photoelectric device based on photoconductive effect. When there is no light, the value of photosensitive resistor is very large, but the value of circuit is very small. When exposed to light, the conductivity of semiconductor material increases, the resistance decreases, and its resistance decreases with the intensity of light. Choose photosensitive resistors to collect illumination signals, and convert different illumination intensities into different resistance values. Different resistance values can be converted into different voltage values by connecting photoresistors in series in DC circuit. The photoelectric signal processing is transformed into the voltage signal processing.