Bar codes

When reading a bar code, it is required that the optical representation in the form of light and dark bars differing in width be captured, digitized, recognized by a device and provided on an interface in a machine-understandable data stream. This is performed by the bar-code reader.

One-dimensional bar code

The start code follows after a quiet zone, which usually has a length of 10 module widths. Then come the net characters, i.e. the bar code symbols containing the encoded information. In most cases, a bar code character including the information of a check digit is located behind the net characters. After a stop code, the bar code ends with another quiet zone. The quiet zone supports correct code recognition. Without quiet zones, areas and characters surrounding the bar code could be misinterpreted by the bar code reader. The narrowest occurring bar of a bar code has a width that is referred to as module width. All bars of this width can be named as modules. A module width of 0.25 to 0.6 millimeters can be found frequently in practical operation. In many cases, start and stop code consist of different bar code characters. If they consist of the same character, this character is mostly asymmetric. Due to this, the reader can detect the three-dimensional position of the bar code immediately when capturing the symbology and, if necessary, evaluate the read information rotated by 180 degrees. Different bar

codes meeting most different criteria exist and these criteria can be used to classify them into bar code families. Before deciding in favor of a specific bar code, a printing technology, a location where it is to be applied and a code size, the purpose of the symbology has to be clarified.