how bar coding machines work?

Question

how does bar coding electronic machine works? what is the basic principle behind it? what type of circuitary they are using?

Answer 1

The above link is out of date. As of 01/01/2005 the manufacturer ID that makes up the first part of the barcode is variable length.

So here goes a quick primer on bar codes. The most common use for bar codes is retail item identification. In order for this to work correctly on a global scale everybody must follow the same general rules. The Uniform Code Council (UCC) was the first to publish a specification which controls the make up of the numbers that are encoded in the common bar code called a UPC-12. The European community also has a governing body called EAN International, which published the EAN-13 specification. Because both organizations work together, and due to global trade becoming the standard you can now find both specifications co-existing in the same store.

For UPC Codes each code is made up of a manufacturer ID issued by the UCC, a serialized number assigned by the manufacturer, and a MOD10 check digit. Once the number is determined it is encoded using a long and involved standard which creates vertical bars of varying widths to represent the numbers. The vertical bars are not only the contrasting color but also the background color. The width of each bar is from 1 to 4 units, each number is encoded by four bars and is a total width of seven units, as defined by the standard. The reason I state units rather than a dimension is the barcode is read as a ratio of bar sizes so as long as the ratio is intact you can still read the barcode. If you are patient enough you can decode the barcode manually, but I wouldn't recommend it, also if you do try to decode it keep in mind the standard also specifies that the barcode is bracketed by three 1 units bars.

The UCC also publishes standards about the size, placement, and quality of bar coding. Each bar code is surrounded by "quiet space" which contains no color variation from the background color. The EAN-13 process is exactly the same except for the total number of digits is 13 and the manufacturer ID is provided by a different authority. Because the reading of the bar codes depends on crisp definition of the vertical bars and high contract between the bars and spaces these are usually printed on very expensive and high quality printers whose resolution and consistency are better than most laser printers.

Reading bar codes, it's not some mystical voodoo. Bar codes are read with a laser, most readers have multiple lasers, to increase the chance or reading the barcode in a single pass. The laser scans the bar code reading the difference in the reflected light between the bars in the code. This is why most bar codes are black and white, to increase the contrast between the bars. Once the scanner has read the barcode it verifies the value by calculating the mod 10 check digit on the barcode and comparing it against the last digit it read from the barcode. If the check digits match the scanner has a valid read and the retailers software takes over and looks up the item information from their own internal applications.

Aside from retail unit marking bar codes have found acceptance in an number of applications including marking and tracking shipping cartons. In this case the numbers are longer but they usually follow a specification.

Answer 2

A linear barcode is a binary code (1s and 0s). The lines and spaces are of varying thicknesses and printed in different combinations. To be scanned, there must be accurate printing and adequate contrast between the bars and spaces. Scanners employ various technologies to "read" codes. The two most common are lasers and cameras. Scanners may be fixed position, like most supermarket checkout scanners, or hand-held devices, often used for the taking of inventories.

Answer 3

Good Q.

Answer 4

http://www.howstuffworks.com/upc.htm