When the shape code scanner recognizes the bar code, the visible light reflected by objects of different colors has different wavelengths. For example, white objects can reflect various wavelengths of visible light, while black objects absorb various wavelengths of visible light. When the light emitted by the light source of barcode scanner shines on the black-and-white bar code through the diaphragm and the convex lens, the reflected light passes through the convex lens.
After focusing, it is irradiated on the photoelectric converter in barcode scanner. Therefore, the photoelectric converter receives reflected light signals with different intensities corresponding to white bars and black bars, converts them into corresponding electrical signals and outputs them to the amplification and shaping circuit of the bar code scanner. The widths of white bars and black bars are different, and the duration of corresponding electrical signals is also different. However, the electrical signal output by photoelectric converter corresponding to the bar and space of bar code is generally only about 10mV, so it cannot be used directly. Therefore, the electrical signal output by the photoelectric converter should be sent to the amplifier for amplification. The amplified electrical signal is still analog. In order to avoid false signals caused by defects and stains in bar codes, a shaping circuit should be added after the amplification circuit to convert analog signals into digital electrical signals so that the computer system can accurately interpret it. The pulse digital signal of the shaping circuit is converted into digital and character information by the decoder. It can identify the coding system and scanning direction of bar code symbols by identifying the start and end characters. By measuring the number of pulse digital electric signal 0, 1, the number of bars and blanks can be distinguished.
The widths of bars and spaces can be determined by measuring the duration of 0 and 1 signals. In this way, we can get the number of bars and spaces to be read, the corresponding width and the code system used. According to the coding rules corresponding to the coding system, barcode scanner converts the barcode into corresponding digital and literal information, and sends it to the computer system for data processing and management through the interface circuit, thus completing the whole process of barcode reading.
Bar code is a graphic identifier composed of bars and spaces with different widths and reflectivity according to certain coding rules (coding system), which is used to represent a group of digital or alphabetic symbol information. That is, bar code is a group of parallel lines with different thicknesses and arranged at regular intervals. Common bar codes are composed of black bars (referred to as bars) and white bars (referred to as spaces) with different reflectivity.