The working principle of bar code recognition is mainly because when objects of different colors reflect, our visible light wavelength will be different. Among them, white objects can reflect various wavelengths of visible light, and black objects can absorb various wavelengths of visible light. Therefore, the light from the light source of the barcode scanner passes through the diaphragm and the convex lens 1, and then shines on the black and white barcode. The reflected light is focused by the convex lens 2 and then irradiated on the photoelectric converter.

Therefore, the photoelectric converter receives reflected light signals with different intensities corresponding to white bars and black bars, and converts them into corresponding electrical signals to be output to the amplification and shaping circuit, which converts analog signals into digital electrical signals, and then translates them into digital character information through the decoding interface circuit.

Due to the different widths of black and white bars in bar codes, the duration of corresponding electrical signals is also different. But with the output of photoelectric converter, the signal corresponding to bar code and space is only about 10mV. Can not be used directly, you need to put the photoelectric output electrical signal in the amplifier to amplify, in order to see the information of the goods.