The principle of barcode identification

1. Barcode Overview

Norman Joseph Woodland from USA came up with the idea of the barcode in 1948, but it took another five years for his project to materialise.

In recent years, with the continuous popularization of computer applications, the application of barcodes has made great progress. Barcodes can store the country of production, manufacturer, product name, production date, book classification number, packaging start and end locations, category, date, and other information of goods. Therefore, they have been widely used in many fields such as commodity circulation, book management, postal and telecommunications management, and banking systems.

A barcode is a graphical identifier composed of bars and spaces of different width and reflectivity, encoded according to a certain coding rule (code system), used to express a set of numerical or alphabetical symbol information. A barcode is a set of parallel line graphics with varying thickness and spacing arranged according to certain rules. The common barcode is composed of black bars and white bars (Spaces) with significantly different reflectivity.

2. Composition of barcode identification system

In order to read the information represented by the barcode, a barcode identification system is required, which consists of a barcode scanner, amplification and shaping circuit, decoding circuit, and computer system .

3. The principle of barcode identification

Due to the different wavelengths of visible light reflected by objects of different colors, white objects can reflect various wavelengths of visible light, while black objects absorb various wavelengths of visible light. Therefore, when the light emitted by the barcode scanner light source passes through the aperture and convex lens 1 and is irradiated onto the one-dimensional barcode between black and white, the reflected light is focused by the convex lens 2 and irradiated onto the photoelectric converter. The photoelectric converter then receives reflected light signals of different strengths corresponding to the white and black bars, and converts them into corresponding electrical signals to output to the amplification and shaping circuit.

The width of the white and black bars is different, and the corresponding duration of the electrical signal is also different. However, the electrical signal corresponding to the bar and space of the barcode output by the photoelectric converter is generally only about 10mv and cannot be directly used. Therefore, the electrical signal output by the photoelectric converter needs to be amplified by an amplifier first.

The amplified electrical signal is still an analog electrical signal. In order to avoid erroneous signals caused by defects and stains in the barcode, a shaping circuit needs to be added after the amplification circuit to convert the analog signal into a digital electrical signal, so that the computer system can accurately read it.

The pulse digital signal of the shaping circuit is decoded into digital and character information by a decoder. It identifies the code system and scanning direction of barcode symbols by identifying the starting and ending characters; Distinguish the number of bars and spaces by measuring the number of pulse digital electrical signals 0 and 1. Distinguish the width of bars and spaces by measuring the duration of 0 and 1 signals.

In this way, the number of bars and spaces of the barcode symbol being read, as well as the corresponding width and code system used, are obtained. According to the encoding rules corresponding to the code system, the bar symbol can be replaced with the corresponding numerical and character information, which is sent to the computer system for data processing and management through the interface circuit, completing the entire process of barcode identification.