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.
Decoders
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
quantize the element width, decode the signal based on the quantized
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
c the code identifier character
m 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. A list of symbology identifiers can be found
here. |
