Barcode Basics

Our customer service department is ready to help you with your bar code questions. If you need help with a bar coding application, please call us.

How does a bar code represent data?

Each character in a bar code is represented by a series of bars and spaces. The different widths of the bars and spaces are similar to the dots and dashes in Morse Code, and the pattern of differing widths determines the character represented. In some bar code symbologies (for example, Code 39), the bars are simply wide or narrow. In other symbologies (such as UPC) the bars are multiple of 1, 2, 3 or 4 times the narrowest bar. Most bar codes also have a start and stop code, and some have additional elements such as check digits or guard bars to ensure data integrity.

How are different bar code sizes specified?

The narrowest element in a bar code is often called the "X" dimension. The "X" dimension is usually given in mils, or thousandths of an inch. It is this dimension which determines the density of the bar code. Often, bar codes are described as low, medium or high density. Density can also be represented in characters per inch -the number of digits or characters which can be represented in one inch of bar code. Bar code wand resolution is defined in terms of the smallest "X" dimension the wand can read. Our standard wands are in the medium-high density range, with a resolution of 7 to 7.5 mils. A wand with a 7.5 mil resolution can read bar codes with 7.5 mil bars or larger.

What is a quiet zone?

The quiet zone is the name given to the white space on either side of the bar code. When printing bar codes, it is important to leave at least 1/4 " of white space for the quiet zone in order to interpret the bar code properly.

How small of a bar code can I use?

For many applications, space is limited, and it is necessary to use very small bar codes. There are two considerations - printing and reading. The size of the bar code is determined by the resolution of the printer. Some printers (such as dot matrix printers) also have a problem with ink spread, the tendency for ink to soak into the paper and thicken the lines of the bar code. For some, printing or photo-typesetting equipment may be necessary. It is very important to take the quiet zone into account when printing small bar codes. Be sure to allow for enough space for an adequate quiet zone. Reading small bar codes requires that the scanner be able to see the smallest bar. Therefore, if you are reading high density bar codes, you may need a high resolution wand. (Our standard wands are medium resolution, which are suitable for most applications. Other resolution are also available. Our tech support department can assist you with your special requirements - please give us a call if you have questions about printing or reading small bar codes.)

Types of readers

Barcode readers can be divided into two types: On-line and portable.

On-line readers

Often called wedge readers, are usually connected between a keyboard and a computer. Wedge readers offer the simplest interface, because in most cases they require no special software to operate.

Portable readers

The portable reader stores the barcode data for transfer to a host computer at a later time. This batch transfer process is called downloading. Connections with the host computer is usually done via a serial RS-232 connection.

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