16479_Bar Code Intro

8/2/2019 16479_Bar Code Intro

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Barcode Scanners


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What is a scanner?

A scanner is a devicethat uses a light

source and thenmeasures the lightreflected back to it.


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What is a bar code?

A barcode is acombination of

spaces and bar ofvarying widths thatcomprises a recordfor a computer to

decode.


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Types of Barcodes

1-d and 2-d barcodes


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How are barcodes

ordered?

The bars in a UPC symbol consist of two bars and two spaces for each digit to be

encoded. These bars and spaces fit into seven modules and are unique for each digit.

The encodation of a digit in the left half of the symbol is the logical opposite of the

encodation of the same digits in the right half of the symbol. All of the left digits have

odd parity (the sum of the bar module widths is odd) while all of the right digits have

even parity (the sum of the bar module widths is even). www.howstuffworks.com


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How are barcodes

ordered?

Diagram showingspacing and how theyare organized.


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How to decode the Bar Code:First of all, look at any 12-digit bar code. It is made up of black bars and white

spaces between the bars. Assume that the thinnest bar or space that you see (for

example, the first bar on the left) can be called "one unit wide." The bars and

spaces can therefore be seen to have proportional widths of one, two, three or four

units. If you look at any bar code you can see examples of these four widths.

The start of any bar code is "1-1-1." That is, starting at the left you find a one-unit-

wide black bar followed by a one-unit-wide white space followed by a one-unit-

wide black bar (bar-space-bar). Following the start code, the digits are encodedlike this:

0 = 3-2-1-1

1 = 2-2-2-1

2 = 2-1-2-2

3 = 1-4-1-14 = 1-1-3-2

5 = 1-2-3-1

6 = 1-1-1-4

7 = 1-3-1-2

8 = 1-2-1-39 = 3-1-1-2


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The code embedded in the bars is 043000181706:

The bar code starts with the standard start code of 1-1-1 (bar-space-bar).

The zero is 3-2-1-1 (space-bar-space-bar).

The four is 1-1-3-2 (space-bar-space-bar).The three is 1-4-1-1 (space-bar-space-bar).

The next three zeros are 3-2-1-1 (space-bar-space-bar).

In the middle there is a standard 1-1-1-1-1 (space-bar-space-bar-space), which is

important because it means the numbers on the right are optically inverted!

The one is 2-2-2-1 (bar-space-bar-space).The eight is 1-2-1-3 (bar-space-bar-space).

The one is 2-2-2-1 (bar-space-bar-space).

The seven is 1-3-1-2 (bar-space-bar-space).

The zero is 3-2-1-1 (bar-space-bar-space).

The six is 1-1-1-4 (bar-space-bar-space).

The stop character is a 1-1-1 (bar-space-bar).


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UPCs originate with a company called the Uniform CodeCouncil (UCC). A manufacturer applies to the UCC forpermission to enter the UPC system. The manufacturerpays an annual fee for the privilege. In return, the UCCissues the manufacturer a six-digit manufacturer

identification number and provides guidelines on how touse it. You can see the manufacturer identificationnumber in any standard 12-digit UPC code. The UPCsymbol has two parts:

1. The machine-readable bar code2. The human-readable 12-digit UPC number
http://www.uc-council.org/http://www.uc-council.org/http://www.uc-council.org/http://www.uc-council.org/


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The manufacturer identification number is the first six digitsof the UPC number -- 639382 in the image above. The next

five digits -- 00039 -- are the item number. A person

employed by the manufacturer, called the UPC

coordinator, is responsible for assigning item numbers toproducts, making sure the same code is not used on more

than one product, retiring codes as products are removed

from the product line, etc.


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The last digit of the UPC code is called a check digit. This digit lets the scanner determine

if it scanned the number correctly or not. Here is how the check digit is calculated for the

other 11 digits, using the code 63938200039 from "The Teenager's Guide to the Real

World" example shown above:

Add together the value of all of the digits in odd positions (digits 1, 3, 5, 7, 9 and 11).

6 + 9 + 8 + 0 + 0 + 9 = 32

Multiply that number by 3.

32 * 3 = 96

Add together the value of all of the digits in even positions (digits 2, 4, 6, 8 and 10).

3 + 3 + 2 + 0 + 3 = 11Add this sum to the value in step 2.

96 + 11 = 107

Take the number in Step 4. To create the check digit, determine the number that, when added

to the number in step 4, is a multiple of 10.

107 + 3 = 110The check digit is therefore 3.


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Barcode Scanners

Now that we knowwhat a barcode ishow do we add ascanner?


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What is a Barcode

Scanner?

A barcode scanner usually has threepieces:

Scanner - which reads or captures the codeDecoder - which translates the code

Computer Interface- Which makes use of the

code


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Types of barcode scanners

Wand Laser CCD array Camera

SCANNER TYPES


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Wand or Pen Scanner

Includes a lightsource and aphotodiode next toeach other on pen tip

Measures reflectedlight intensity and

generates awaveform accordingto bar widths


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Wand scanner pros and

cons

Pros

cheapest type

can read any size barcodesmall in size

Cons

Need steady hand when scanningNeeds to be touching the barcode


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Laser scanner

Uses a laser lightsource

Usually have mirror orprism to scan lightback and forth

Uses a photodiode as

detector


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Laser Scanner Pros and

Cons

Pros

can be used at a good distance

can read large barcodes easilyCons

High Priced


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CCD scanners

Uses CCD array

measures the

emmitted and notreflected light fromthe target


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CCD Scanner Pros and

Cons

Pros

No need to swipe barcode

Cons

Like a camera, has certain focal position, and

cannot read all sizes of barcodesNeed close proximity to the barcode


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Camera scanners

Uses small video camera to capture imageof the barcode

Employs Digital image processingtechniques also.


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Any Questions?

References www.howstuffworks.com

www.simplyscan.com

www.semicron.com

www.emediaplan.com

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