How Barcode Reader works

Bar coder readers decodes a bar code by scanning across the bar code and measuring the intensity of the light reflected back. The light variation is converted into digital signal. Due to barcode design, it does not matter you scan from the left to right or from the right to left.

A barcode reader contains two parts. The first part is the scanner that scans the image and coverts into digital representation (01111000). The second part is the decoder which combines the binary digital signals into a series of characters. The decoded information is sent to the computer via keyboard or serial interfaces.

Input Device

An input device accepts the reflected light and converts the optical reflection into digital/analog signals. There are two major methods used for input, laser beam and CCD (charge-coupled device). CCD scanners can be very small, but they have less depth of filed than laser scanners.


A decoder decodes the symbol’s information and passes to the host computer or stores in the memory. A decodes accepts the digital signal from the input device, and converts the signals into bar and spaces. Then it quantify the element width, decode the signal based on the quantified widths. Finally, it performs some other check such as check characters. After the decoding process is complete, it transmit the data into host computer.

Decoders can be divided into two categories: on-line decoders and portable decoders. The on-line decoders use the power from AC adapter or from the computer, and the latter uses the battery.

Symbology Identifier (SI)

A barcode reader usually accepts inputs of multiple symbologies. For some applications it is usually nice to know what kind of symbology the data is encoded. For this reason AIM has published a standard of prefix to describe the symbology. The prefix takes the form ]cm, where:


the symbology identifier flag


the code identifier character


additional options

Currently the hardware support for this feature is somewhat limited. If your application does use this filed, you need to contact the vendor before your purchase the hardware.