bar code was first put forward by N．T．Woodland in the United States in 1949. in recent years, with the continuous popularization of computer application, the application of bar code has been greatly developed. bar code can indicate the country of production, manufacturer, product name, production date, book classification number, starting and ending place of mail, category, date and other information. Therefore, it has been widely used in many fields, such as commodity circulation, book management, post and telecommunications management, banking system, etc.

Barcodes are graphic identifiers which are composed of bars and spaces with different widths and different reflectivity and are compiled according to certain coding rules (coding system) to express a group of numbers or letter symbols. Arranging parallel line patterns at intervals according to certain rules. Common bar codes are composed of black bars (abbreviated as bars) and white bars (abbreviated as spaces) with great differences in reflectivity.

II. Composition of bar code recognition system

In order to read the information represented by bar codes, a bar code recognition system is needed, which consists of bar code scanner, amplification and shaping circuit, decoding interface circuit and computer system.

III. Recognition principle of bar code

Because objects of different colors have different wavelengths of reflected visible light, white objects can reflect visible light of various wavelengths, while black objects absorb visible light of various wavelengths, when the light emitted by the light source of the bar code scanner passes through the diaphragm and the convex lens 1 and irradiates the black-and-white bar code, the reflected light is focused by the convex lens 2 and irradiated on the photoelectric converter. Therefore, the photoelectric converter receives reflected light signals with different intensities corresponding to the white bars and black bars, and converts them into corresponding electrical signals to be output to the amplification and shaping circuit. The widths of the white bars and black bars are different, and the duration of the corresponding electrical signals is also different. However, the electrical signals corresponding to the bars and spaces of the bar code output by the photoelectric converter are generally only about 1 mV, which cannot be directly used. Therefore, the electrical signal output by the photoelectric converter should be 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 the defects and stains in the bar code, a shaping circuit should be added after the amplification circuit to convert the analog signal into a digital electrical signal so that the computer system can accurately interpret it.

The pulse digital signal of the shaping circuit is translated into digital and character information by the decoder. It can distinguish the coding system and scanning direction of bar code symbols by identifying the starting and ending characters. The number of bars and spaces can be determined by measuring the number of pulse digital electric signals and 1, and the width of bars and spaces can be determined by measuring the duration of signals and 1. In this way, the number of bars and spaces, the corresponding width and the used code system of bar code symbols can be obtained. According to the coding rules corresponding to the code system, bar symbols can be changed into corresponding digital and character information, which can be sent to the computer system through the interface circuit for data processing and management, thus completing the whole process of bar code identification and reading.

the code represented by the standard version of commodity bar code consists of 13 digits, and its structure is as follows:

Structure 1: x13x1x1 x9x8x7x5x3x2x1

where: x13 ... x7 manufacturer identification code; X6 ... x2 represents the commodity item code; X1 check code.

structure 2: x13x11x1 x9x87x6 x5x3x2x1

where: x13 ... X6 manufacturer identification code; X5 ... x2 represents the commodity item code; X1 check code.

when x13x12x11 is 69 and 691, its code structure is the same as Structure 1; When x13x12x11 is 692, its code structure is the same as structure 2.

check code calculation

refer to the method specified in the national standard of gb 1294 "General Commodity Barcode".

the shortened version of the barcode consists of 8 digits, and its structure is as follows:

x8x7x5x3x2x1

where: x8x7 X6: its meaning is the same as that of the standard version of the barcode; X5x4x3x2: indicates the commodity item code,

which is uniformly distributed by ean coding organization. In China, it is uniformly distributed by China Article Coding Center; X1: check code. When calculating,

you need to add five zeros before the shortened version of the barcode code, and then calculate according to the calculation method of the standard version of the barcode check code. Country (or region) of prefix code organization/application field Country (or region) of prefix code organization/application field

~ 19; 3 ～ 39； 6 ~ 139 USA

2 ~ 29; 4 ～ 49； 2 ~ 299 store code

5 ~ 59 coupon

3 ~ 379 France

38 Bulgaria

383 Slovenia

385 Croatia

387 Bosnia and Herzegovina

4 ~ 44 Germany

45 ~ 459; 49 ~ 499 Japan

46 ~ 469 Russia

47 Kyrgyzstan

471 China Taiwan Province

474 Estonia

475 Latvia

476 Azerbaijan

477 Lithuania

478 Uzbekistan

479 Sri Lanka

48. > 481 Belarus

482 Ukraine

484 Moldova

485 Armenia

486 Georgia

487 Kazakhstan

489 China Hong Kong Special Administrative Region

5 ~ 59 Britain

52 Greece

528 Lebanon

529 Cyprus < 53 Albania

531 Macedonia

535 Malta

539 Ireland

54 ~ 549 Belgium and Luxembourg

56 Portugal

569 Iceland

57 ~ 579 Denmark

59 Poland

594 Romania

594. p> 6、 61 South Africa

63 Ghana

68 Bahrain

69 Mauritius

611 Morocco

613 Algeria

616 Kenya

618 Ivory Coast

619 Tunisia

621 Syria

622 Egypt

624 Libya. 625 Jordan

626 Iran

627 Kuwait

628 Saudi Arabia

629 United Arab Emirates

64 ~ 649 Finland

69 ~ 695 Chinese people * * * And

7 ~ 79 Norway

729 Israel

73 ~ 739 Sweden

74 Guatemala

741 El Salvador

742 Honduras

743 Nicaragua

744 Costa Rica

745 Panama

746 Dominica < 75 Mexico

754 ~ 755 Canada

759 Venezuela

76 ~ 769 Switzerland

77 Colombia

773 Uruguay

775 Peru

777 Bolivia

779 Argentina

78 Chile

784 Paraguay. Er

789 ~ 79 Brazil

8 ~ 839 Italy

84 ~ 849 Spain

85 Cuba

858 Slovakia

859 Czech Republic

86 Yugoslavia

865 Mongolia

867 Korea

867. Netherlands

88 Korea

884 Cambodia

885 Thailand

888 Singapore

89 India

893 Vietnam

899 Indonesia

9 ~ 919 Austria

93 ~ 939 Australia

94 ~ 939. Laixi

958 China Macao Special Administrative Region

977 serial publications

978, 979 books

98 notes receivable

981, 982 general circulation coupons

99 ~ 999 coupons.