Tue Jun 14 11:34:22 CST 2022
Several principles of common bar code scanners
Usually when we buy things in the supermarket and pay the bill, the price scanned by the salesperson is the barcode scanner. The scanner irradiates the barcode with its own light source, and then uses the photoelectric converter to receive the reflected light and convert the brightness of the reflected light into a digital signal. No matter what rules are adopted, the barcode is composed of static area, start character, data character and end character. Some barcodes also have check characters between data characters and termination characters.
▲ static area: static area is also called blank area, which is divided into left blank area and right blank area. The left blank area is to prepare the scanning equipment for scanning, and the right blank area is the end mark to ensure that the scanning equipment can correctly identify the bar code.
In order to prevent the left and right blank areas (static areas) from being inadvertently occupied during printing and typesetting, a symbol can be added to the blank area (print <; No. when there is no number on the left and >; No. when there is no number on the right). This symbol is called static area mark. The main function is to prevent insufficient width of static zone. As long as the width of the static area can be guaranteed, the presence or absence of this symbol will not affect the identification of the bar code.
▲ starting character: the first character with special structure. When the scanner reads this character, it starts to formally read the code.
▲ data character: the main content of barcode.
▲ check character: check whether the read data is correct. Different coding rules may have different verification rules.
▲ termination character: the last character, which also has a special structure, is used to inform the code that the scanning is completed, and also plays the role of verification calculation.
In order to facilitate bidirectional scanning, the start and end characters have an asymmetric structure. Therefore, the scanner can automatically rearrange the bar code information when scanning. There are four kinds of bar code scanners: light pen, CCD, laser and image
▲ light pen: the most original scanning method requires manual movement of the light pen and contact with the bar code.
▲ CCD: scanner with CCD as photoelectric converter and led as luminous light source. Within a certain range, automatic scanning can be realized. It can also read bar codes on various materials and uneven surfaces, and the cost is relatively low. However, compared with the laser type, the scanning distance is shorter.
▲ laser: scanner with laser as luminous source. It can be divided into line type, full angle and so on.