Bar Code Basics
How does a bar
code work?
Actually, a bar code works in much the same way as an ordinary flashlight
-by reading the reflected light from a surface. The process begins when a
device directs a light beam through a bar code. The device contains a small
sensory reading element. This sensor detects the light being reflected back
from the bar code, and converts light energy into electrical energy. The
result is an electrical signal that can be converted into data.
Bar codes are
measured by the width of the narrow bar and are recorded in mils, or 1/1000
inch. A 15 Mill bar code, for instance, has a narrow bar that is 15/1000
inches wide. Further, "quiet zones," or blank spaces to the left
and right of bar code symbols, are included to insure the bar code can be
read.
How do you read a
bar code?
It's a three-step process. First, an input device must convert light energy
into electrical energy. There are a variety of input devices, each with its
own unique characteristics.
Input Devices
 The "wand" is the
simplest and least expensive input device available. It is durable and
contains no moving parts. It must, however, come into contact with the bar
code, which can present a challenge. If a bar code must be read more than
once, it may become smeared or damaged and, in essence, unreadable. Also, a
wand is "human powered," which means it must be held at the
proper angle and moved at the proper speed. For these reasons, a wand is
the best choice when cost is the largest determining factor.
 The CCD, or "Charge
Couple Device," is another common input device. A CCD is a very
"aggressive" instrument, with a high ability to read bar codes
quickly and easily. But it has two primary limitations. First, it has a
short "read" range, and must be held no more than 1 to 3 inches
from the bar code. Further, the CCD has a limited width, and will not read
bar codes that are wider than the face of the input device. It is largely
popular for use in point of sale applications.
 The laser scanner is perhaps
the most popular bar code input device. A laser scanner need not be close
to the bar code to do its job. A standard range laser scanner can read a
bar code from about 6 to 24 inches away, and a long range scanner can read
one from perhaps 2 to 8 feet away. An extra long-range device can even read
a bar code 30 feet from the device. Laser scanners vary in price from $200
to $2,000 and come in a variety of models.
Decoders
 Step two involves converting
the electronic signal into data, which is accomplished with a decoder. The
decoder is an electronic device serving three functions:
- It automatically
discriminates between the various bar code types, which are known as
symbologies.
- It decodes the electronic
signal into information.
- It translates the
information into data for the host.
A decoder may be
located inside or outside the input device. An internal decoder takes up
less space and is less expensive, but it is also less functional. An
external decoder is a bit more expensive, but is also more functional, with
the capabilities to manipulate data and accommodate multiple input devices
on a single port.
Host Connection
Finally, bar codes are used to input data into a host computer system, and
can dramatically improve both the accuracy of the data and the speed with
which it is entered. The keyboard "wedge" is the most common
method of host connectivity for bar code equipment. In this configuration,
the decoder is "wedged" between the PC or terminal and its
keyboard, allowing users to input bar code data without changing existing
applications. The serial "wedge," which utilizes the connection
of a dumb terminal with an RS-232 interface, is another connectivity
method, and it is also possible to use a direct connection to a serial
port.
Reading a bar code
is as easy as 1-2-3
Step One: Carefully choose an input device
Step Two: Decide whether you need an internal or external decoder
Step Three: Attach equipment to the host computer
How do you print
Bar Code Labels?
 Bar codes can be printed with
existing dot matrix or laser printers, but with varying results. Thermal
label printers, on the other hand, were designed specifically for the job
and are built to produce high-quality text and graphics. They print at fast
speeds and can be used to print one label at a time or an entire roll.
There are two basic
thermal printing methods:
Thermal transfer
printing
In this method, the print head transfers ink from a ribbon onto standard
paper. The thermal transfer printer brings greater consumable costs because
it utilizes a ribbon, but there is less wear and tear on the print head.
Thermal direct
printing
In this method, the print head is in direct contact with treated paper, and
no ribbon is used. As a result, consumable costs are smaller, but the print
head undergoes substantially more wear and tear. A ribbon produces less
friction than paper, so a print head lasts approximately four times longer
when printing in thermal transfer mode than in thermal direct mode. Print
heads are considered consumable items and must be included in the overall
cost of operation.
Further, the width of
the print head determines the maximum width of printed labels. Print heads
are generally 2,4,6 or 8 inches wide.
Every thermal label
printer is driven by a proprietary programming language, which can make the
bar code printing process challenging. However, bar code label software can
make it easier by allowing you to create labels on the screen and print
labels with data from various sources. Label software can be generic to all
printers or specific to one manufacturer.
What's A Portable
Data Terminal?
 Sometimes you must bring the
computer to the bar code, particularly to handle jobs such as warehouse
inventory control or freezer applications. A portable data terminal (PDT),
a fully programmable hand-held computer, is necessary in such instances.
Choosing the correct PDT is very important, and consists of a four-step
process.
1. Scanner Option:
First, you must choose a scanner option. The bar code input device can be
integrated into the unit or attached externally by a cable. The most common
implementation is an integrated laser scanner.
2. Display Unit: You
should also choose a display unit. Character-based terminals use text to
prompt the operator for data input, which can come from the bar code
scanner or the keyboard. Some applications may require a graphical user
interface, and a stylus (or pen) is used to operate the application
software. These pen-based solutions are useful for filling in forms or
applications that require signature capture.
3. Communications:
Collected data must be transferred back to the host computer from the PDT,
which can be accomplished in one of two ways. A wireless communications
link provides online real-time data communications, immediate updates to
databases and feedback to the operator. However, this solution could
require a complex connection to the host, and you may need a less difficult
or expensive method. Mobile data collection is a simpler and easier
process. In this method, data is collected in small batches and transferred
from the portable into the host computer by a cable connection.
4. Operating System:
The operating system of the portable data computer determines the method of
programming. Proprietary operating systems usually require knowledge of a
proprietary programming language. Other units may use a common operating
system such as DOS or Microsoft Windows, allowing for programming with a
more common language such as BASIC or "C." Most applications will
be unique to the user and are likely to require customer programming.
Programs may be written in a common language, or a program generator may be
used to cut development time.
For more information
on Bar Code Technology contact T&W Enterprises Technical
Support.
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