Bar Codes

It has become the most popular method of automatic identification in retail sales & in factory data collection. A typical bar code comprise a sequence of thick & narrow colored bars separated by narrow and thick spaces separating the bars. The pattern of bars & spaces is coded to represent alphanumeric characters. Bar code readers interpret the code by decoding and scanning the sequence of bars. The reader consists of the decoder and scanner.

The scanner emits a beam of light that is swept past the bar code either by automatically or manually and senses light reflections to distinguish among spaces and bars. The light reflections are sensed by a photo decoder which converts the spaces into an electrical signal and the bars into absence of an electrical signal. The width of the bars & spaces is shown by the duration of the corresponding signals. The decoder analyzes the pulse train to validate & interpret data.