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Bar Coding Basics
Bar codes provide a simple and inexpensive method of encoding
text information that is easily read by inexpensive electronic
readers. Bar coding also allows data to be collected rapidly and
with extreme accuracy. A bar code consists of a series of parallel,
adjacent bars and spaces. Predefined bar and space patterns or "symbologies" are
used to encode small strings of character data into a printed symbol.
Bar codes can be thought of as a printed type of the Morse code
with narrow bars (and spaces) representing dots, and wide bars
representing dashes. A bar code reader decodes a bar code by scanning
a light source across the bar code and measuring the intensity
of light reflected back by the white spaces. The pattern of reflected
light is detected with a photodiode which produces an electronic
signal that exactly matches the printed bar code pattern. This
signal is then decoded back to the original data by inexpensive
electronic circuits. Due to the design of most bar code symbologies,
it does not make any difference if you scan a bar code from right
to left or from left to right.
The basic structure of a bar code consists of a leading
and trailing quiet zone, a start pattern, one or more data characters,
optionally one or two check characters and a stop pattern.
There are a variety of different types of bar code
encoding schemes or "symbologies", each of which were
originally developed to fulfill a specific need in a specific industry.
Several of these symbologies have matured into de-facto standards
that are used universally today throughout most industries. The
symbologies supported by B-Coder, The TAL Bar Code ActiveX control
and the TAL Bar Code DLLs are those most commonly used across all
industries.
The different symbologies have different capabilities for encoding data. For
example the UPC symbology used to identify retail products always contains
12 numeric digits whereas the general purpose Code 39 or Code 128 bar code
symbologies can encode variable length alphanumeric data up to about 30 characters
in length. These types of bar codes are called "linear symbologies" because
they are made up of a series of lines of different widths. Most commercially
available bar code scanners are able to read all of the different linear bar
code symbologies therefore you do not need different readers for different
types of bar codes.
New "2-Dimensional" bar code symbologies like PDF417, Aztec Code
and Data Matrix are also now available that can encode several thousand bytes
of data in a single bar code symbol including text or binary data. The newer
2D bar code symbologies typically require special bar code readers that are
designed specifically for reading them.
The primary purpose of a bar code is to identify
something by labeling the item with a bar code containing a unique
number or character string. Bar codes are typically used with a
database application where the data encoded in the bar codes is
used as an index to a record in the database that contains more
detailed information about the item that is being scanned. For
example, when a checkout clerk scans a bar code on a product in
a grocery store, the bar code data is fed to a computer that looks
up the information in a central database and returns more detailed
information about the item that was scanned including possibly
a description of the item and a price. By using bar codes, the
grocery store does not need to put a price tag on each item in
the store and they can also change the price for a particular item
by modifying a single entry in the central database. They can also
track how much of a product is currently in stock so that they
know when to re-order more of each item as the number of items
in stock falls.
Bar codes also provide a quick and error free means
for inputting the data into an application running on a computer.
By using bar codes, the potential for errors from manual data input
is eliminated. Another typical application for bar codes is therefore
for inputting data without having to type. For example you could
encode name or address data in a bar code on an ID badge and then
scan the ID badges to input a persons name into a computer program
instead of typing the information.
The different bar code symbologies support different
types and amounts of data therefore you normally choose a particular
symbology based on the type and amount of data that you want to
encode in your bar codes.
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Symbology
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Data Capacity
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UPC-A
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12 numeric digits - 11 user specified and 1 check digit.
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UPC-E
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7 numeric digits - 6 user specified and 1 check digit.
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EAN-8
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8 numeric digits - 7 user specified and 1 check digit.
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EAN-13
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13 numeric digits - 12 user specified and 1 check digit.
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Code 39
Code 93
Code 128
EAN-UCC 128
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Variable length alphanumeric data - the practical upper
limit is dependent on the scanner and is typically between
20 and 40 characters. Code 128 is more efficient at encoding
data than Code 39 or Code 93. Code 128 is the best choice
for most general bar code applications. Code 39 and Code
128 are both very widely used while Code 93 is rarely used.
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I 2 of 5
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variable length numeric data - the practical upper limit
is dependent on the scanner and is typically between 20 and
50 characters.
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Data Matrix
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Data can consist of any type of data including binary or
alphanumeric and be up to 3116 bytes in length.
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Aztec
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Data can consist of any type of data including binary or
alphanumeric and be up to 3750 bytes in length.
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Maxicode
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Maxicode can hold up to 93 alphanumeric characters or 138
numeric digits. Maxicode is used almost exclusively for United
Parcel Service package identification.
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PDF417
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PDF417 is a little more complex and it is difficult to say
exactly what its capacity is because it depends greatly on
the type of data that you encode in a PDF417 symbol as well
as the amount of error correction capacity that you choose
to use in a PDF417 symbol.
For general binary data with no error correction enabled,
a single PDF417 symbol can hold up to 1108 bytes. If the
data consists of all numeric digits, then a single PDF417
symbol can hold up to 2725 digits. If the data consists of
alphanumeric data, you can encode a maximum of 1850 bytes.
If you have a mix of alphanumeric and binary data, the capacity
will be somewhere between 1108 and 1850 bytes and will depend
on the content of the data.
All of our bar code software products use an extremely efficient
encoding algorithm that will squeeze the maximum number of
bytes possible into a PDF417 symbol however it still must
work within the limits of the symbology specification.
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You are generally free to use any type of bar code
that you like and encode whatever data that you like for applications
in a closed system.
If you want to place bar codes on retail items that will be commercially distributed
(i.e. UPC or EAN bar codes), you will need to apply for a manufacturer number
from the Uniform Code Council in
the USA, Tel: 937-435-3870. If you plan to distribute your products outside
of the United States then you need to apply for a manufacturer code from EAN
International in Belgium. Tel: 011-32.2.227.10.20
See Also:
How a Bar Code Reader Works
Bar Code Symbology Descriptions
Printing Perfect Barcodes from ANY Printer |
