The barcode is made by the US N. T. Woodland first proposed in 1949. In recent years, with the increasing popularity of computer applications, the application of bar codes has been greatly developed. Bar code can indicate the country of manufacture, manufacturer, product name, date of manufacture, book classification number, start and end of mail, category, date, etc., so it is available in many fields such as commodity circulation, book management, post and telecommunications management, banking system, etc. A wide range of applications. Bar codes are composed of lines and digital symbols of a certain length, width and width. It is a computer graphics language that is printed by ordinary printing methods and read by photoelectric scanning reading devices. Barcode is a data input technology and automatic identification technology researched and developed in recent decades. It can reflect many types of information such as the category of the product, the manufacturer, the weight, the amount, the date of manufacture, and the circulation time.
　　   Since objects of different colors have different wavelengths of visible light, white objects can reflect visible light of various wavelengths, and black objects absorb visible light of various wavelengths. Therefore, when the light emitted by the bar code scanner light passes through the aperture and the convex lens 1, When irradiated onto the black and white bar code, the reflected light is focused by the convex lens 2, and then irradiated onto the photoelectric converter, so that the photoelectric converter receives the reflected light signals different in intensity from the white bars and the black bars, and converts them into corresponding The electrical signal is output to the amplification shaping circuit. The width of the white strip and the black strip are different, and the duration of the corresponding electrical signal is also different. However, the electrical signal corresponding to the bar code and the space of the bar code output by the photoelectric converter is generally only about 10 mV, and cannot be directly used. Therefore, the electric signal output from the photoelectric converter is first sent to the amplifier for amplification. The amplified electrical signal is still an analog electrical signal. In order to avoid the error signal caused by defects and stains in the barcode, a shaping circuit is needed after the amplifying circuit to convert the analog signal into a digital electrical signal so that the computer system can accurately interpret the signal. .
　　   The pulsed digital signal of the shaping circuit is translated into digital and character information by the decoder. It identifies the code system and scanning direction of the bar code symbol by identifying the start and end characters; it determines the number of bars and spaces by measuring the number of pulse digital electrical signals 0, 1. Determine the width of the strip and the space by measuring the duration of the 0 and 1 signals. In this way, the number of bars and spaces of the bar code symbols to be read and the corresponding width and the code system used are obtained. According to the coding rules corresponding to the code system, the bar symbols can be replaced with corresponding numbers and character information. The interface circuit is sent to the computer system for data processing and management, and the whole process of bar code reading is completed.