How Does a Grocery Store Barcode Reader Work?

In "simple" terms, you have the reading part correct. Your shortfall occurs in assuming the sensor "reads" the bar code and it does not. Rather it relays the reflected pattern information to a computer which then interprets the information from the scanned pattern. Since a bar code pattern is a series of light and dark lines arranged in a parallel manner the processor can determine its orientation linearly. As a serial digital (binary) signal has start and stop bits to bracket the packet of information, so has a bar code, but arranged spatially rather than temporally. The relative spatial interval is also similarly obtained. Using this information the processor can now scale and properly orient the pattern and proceed to read each bit. Keep in mind that at this point, like a series of 1's in a digital byte, a wide line encompasses a series of 1's in adjacent "spaces", while a double width space would represent two sequential zeros for instance. In my analogy, while a serially sent byte contains an alternating signal of high and low voltages that are read at predetermined interval (or baud rate) a decoded image of a byte in a bar code is read by a processor calculated spatial interval.

I hope this conceptual explanation helps.

Greg

I understand the reading bars and white space, but I still have trouble (even though I've done quite a lot of research) on the 'refected' laser back to the reader. I have used a hand-held scanner and it works at extreme angles, none of that can be reflected back into the reader head!

I just need to lead a little more on the physical reading part...

www.barcode.com helped, but I need more!!!

Thanks!! ss

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If guns kill people - I can blame mispelled words on my pencil!

Larry the Cable Guy

The laser is used to illuminate the bar code.

You are interpreting reflected in the classical sense, as in "the angle of reflectance equals the angle of incidence". Think of the sensor as an adjustable focus (or wide depth of field) "camera' that is photographing the bar code illuminated by the laser. The image processing by the computer uses pattern recognition techniques (it knows what it is looking for) to distinguish the image of the bar code from the included background "noise".

Also, some bar code are "company own", meaning some company will have bar code that starts with 123, let say, while other company will start their bar code 456. This way, the scanner will be able to find which manufacture made that product. It's kind of like a telephone number, sore of speak.

MidniteFighter

Silly Rabbit. It's MAGIC.

The only code that is 1's and 0's is a binary code, also known as phama code which you might see on pharmacuetical literature inside a pill carton, which as expected, is grows larger in length for the amount information to be contained. All bar codes have specific dimensional specifications (called the "x" dimension) which is the smallest white space or dark line. Depending on the bar code symbology, these spaces and lines are grouped into modules, pairs, etc. That is why you see spaces and bars different in size. For example, in some codes, by pairing modules, numbering from 00 to 99 can be done with less bars, which saves label space. Some symbologies usually have a start and stop bar, symbology identifier, etc, besides the actual information. This way the interpreting system will understand the code. Other symbologies are bi-dierectional, inwhich read direction does not matter. The reader is just that...a reader. The dark and white reflected contrast cause a voltage or signal change which is then interpreted in software. All bar codes must be read at a consistent scan rate due to this "x" dimension constant or a unreadable code would occur. The reason that grocery codes sometime do not read very well is usually the print is blurred (ruining the x dimension constant) or the sticker has wrinkles. Codes on can labels or boxes are rarely problematic unless dirty. Most codes seen on connsumer items are linear or 1D codes. You have probably seen on letters a differnt code, or on autoparts, ICs, and other items other types of codes in a square or rectangular format with what looks like random squares. These are 2D codes and are able to contain large amounts of information. A good source of bar code information is GS1-US (formerly the uniform code council). The UPC (universal product code) symbol on most consumer items is one of the code standards managed by this organization. Also EAN or AIM organizations. See GS1 and AIM links below:

http://barcodes.gs1us.org/About/BarCodesandeComFAQs/tabid/142/Default.aspx - sorry, link no longer available

http://www.aimglobal.org/technologies/barcode/linear_symbologies.asp - sorry, link no longer available

dberts:

I was only attempting to give a simple, conceptual overview of how the scanner reads the UPC code used on retail products, based on the wording of the original question. Having dealt with scanners and their software, I am well aware of the many standards, complications and nuances.

While you gave an interesting overview on barcodes, you muddied the water somewhat with your statement that:

"The only code that is 1's and 0's is a binary code, also known as the pharma code …."

Later you go on to say:

"The reader is just that...a reader. The dark and white reflected contrast cause a voltage or signal change which is then interpreted in software."

The interpretation for ("standard" bar codes) of the voltage or signal change by the processor is DIGITAL (read binary): Light or dark, "0" or "1" ! Scanning at a constant rate and applying a time based reference converts a wide space or bar into the appropriate pattern of 0's or 1's.

A barcode reader scans at a constant rate only so that the processor can interpret the barcode pattern and scale it based on the width of the thinnest bar. The UPC bar code has standards as you point out, such as to the standard aspect ratio. It is grouped into 2 groups of 6 sequential "modules" that are used to represent the digits 0-9 and separated by a divider (middle) module. The aforementioned group of 13 modules being bracketed by a start and stop module.

The digit modules are 7 bits (as in binary) wide, with the largest bar or space comprising a width of 4 bits. They are arranged in a "space-bar-space-bar" pattern to the left of the divider module and a "bar-space-bar-space" pattern to the right. If we assign a "0" to the presence of a space (absence of a bar) bit, and a "1" to a bar (presence of a bar) bit, then we see that the six "space-bar-space-bar" 7 bit long modules all start with a "0" and end with a "1", while the other six do the same when we invert the meaning of the previously defined 0's and 1's, so that a "0" represents the presence of a bar rather than its abscence. The inside 5 bits contain the information correlating to the widths of the module's spaces and bars, along with a reading error detection scheme (as in parity) bits.

For instance in the leftmost 6 modules, the module for the digit "6" consists of a space 1 bit wide, a bar 1 bit wide, a space 1 bit wide, and finally a bar 4 bits wide yielding a 7 bit pattern of 0101111, or expressed in the relative widths of spaces and bars: 1-1-1-4. Likewise, the module representing "9" is space (3bits wide) - bar (1 bit wide) – space (1 bit wide) – bar (2 bits wide) for a binary pattern of 0001011 and relative width pattern of 3-1-1-2. The same digits in the rightmost 6 modules have the same bit patterns but the expression in spaces and bars is the opposite: The "9" translating into a bar (3 bits wide) – space (1 bit wide) – bar (1 bit wide) – space (2 bits wide), again with a binary pattern of 0001011.

The choice of a 7 bit wide module was based in large part on the available processor capabilities at the code's inception and the requirement for redundant error checking.

A link I found which furnishes more relevant information on UPC codes and how to read them visually:

http://www.howstuffworks.com/upc.htm

Regards,

Greg

Hi!

1. Upper Case

2. Lower Case

3. Front Cover

4. Dust Cover

5. Mirror

6. Mirror Holder

7. Lens

8. Lens Holder

9. LED Array & board

10. CCD Sensor IC

11. CCD Sensor Board

12. Mainboard

13. Switch

14. Switch Board

15. Interface Cable

a) Keyboard Wedge or USB Cable

b) RS-232 Cable

16. Flat Cable

17. Link Cable

18. Screws

Explision Drawing:

http://images.google.com/imgres?imgurl=http://www.barcode-manufacturer.com/images/barcode/parts_explosion_chart02.jpg&imgrefurl=http://www.barcode-manufacturer.com/barcode_scanner/skd_parts.html&h=495&w=392&sz=25&hl=en&start=1&tbnid=hqW4YKdFNXWv1M:&tbnh=130&tbnw=103&prev=/images%3Fq%3Dexplosion%2Bbarcode%2Bscanner%26svnum%3D10%26hl%3Den%26lr%3D%26rls%3DWZPA,WZPA:2006-32,WZPA:en%26sa%3DX

In this case, LEDs ARRAY send the light which will be captured by the CCD sensor IC.

From here on is just data procesing. Data which comes from CCD sensor.

Saludos!

Delmar

as for the barcode reader, you just need to open it and read the barcodes.

speaking of barcode reader , i have to consider its convenience. very useful. i just had one for my iphone, maybe you can also have a try.http://www.onbarcode.com/products/iphone_barcode/

that's a good and convenient device, and as for reading barcode, i'm wondering whether the barcode scanner is good in use or the barcode reader is a better one? i only know they are all used to read barcode,

The bar code reader you asked is also a bar code scanner for .net application( just like the one I'm using now), and I've checked your scanner, it seems have a free trial, and support to read both most linear and 2d bar code, I don't know what the platform you are using, the guide on websites are clearly tell you the info, you can also download it and have a try, and then you will know if it meet your requirements.

hi,you are just expaining the manipuation of the barcode scanner, what he is asking is the internal barcode reader working process. it need someone very professional to explain barcode reader framework . thank you for the above postsm, it is what i am looking for. thank you