How Do Bar Codes Work?

by Josh Baum

The History of Bar Codes and UPC Numbers

Applications detailing early versions of bar code scanning processes began cycling through the U.S. Patent Office in the late 1940s, but it wasn't until the mid 1970s that the bar codes and UPC numbers we know and use today found their place at the retail checkout counter. When they made their debut at grocery stores, the main idea was to provide stores with a faster way to check out customers and an easier way to keep track of inventory. The Uniform Code Council (UCC) charged product manufacturers for their UPC numbering and bar code services, and in turn, the UCC regulated the numbers, developing a sophisticated system of number assignments. Bar codes and UPC numbers now appear on almost all commercial goods sold in the United States.

Number Assignments

Every bar code has a 12 digit number printed below it. This is the UPC number, and it consists of a manufacturer ID number and an item number. The first six numbers make up the manufacturer ID number, and you'll find that same number on all of the products sold by that manufacturer. The next six numbers constitute the item number. Each item number can only be actively used on one product at a time by a single manufacturer, however the same item number may be used simultaneously on thousands of different products from manufacturers with different ID numbers.

The Bar Code

The series of lines on the bar code are simply a standardized visual representation of the 12 digit number that appears below it. Every bar code begins with the same sequence: one thin bar, one thin space and one thin bar. Some of the bars and spaces that follow may appear to be thicker, but they are actually just several thin lines or thin spaces in sequence. Each digit from 0 to 9 is assigned a distinct coded sequence of lines and spaces. Each bar code is simply the entire series, in order, of the line and space sequences of the digits that make up the UPC number. By referring to the guide of UPC digit parity patterns, you can deduce the UPC number of a bar code without the aid of a scanner. Look in the resources section for a link to a page that contains this guide.

Scanning Equipment

One of the most useful functions of a bar code is the speed by which they can be scanned and the data can be transmitted or recorded. Bar codes are often scanned using laser equipment. Laser bar code scanners work by projecting a thin, continuous, line-shaped laser beam. When a bar code is waved over the beam, the pattern of light reflection created by the bar code is reflected back toward the laser, where it is read by an infrared sensor. This sensor decodes the reflection and identifies the number. Newer bar code reading systems use small video cameras and video scanning technology to scan items faster and more reliably.

Photo Credits

  • photo_camera Image by Sergio Roberto