How Do Barcodes Work?
Since the beginning of the industrial age and the capitalistic consumption society which it spawned, people have been looking for a method of automated data collection. Even before computers, retailers kept elaborate stock number systems. Sometimes these would show up as adhesive tags on the products, but you still had to have a human read them and write them into the inventory card system. The first automated checkout system was actually to be implemented on punched cards, in 1932.
The first barcodes saw commercial usage in 1966, but only slowly gained widespread acceptance. The bar code system most readers will be familiar with is the UPC, the Universal Product Code. You find these black-and-white bars on product packages, everything from TV sets to bags of peanuts.
The UPC format is [S]NNNNN[M]NNNNN[E], where S and E are just the start and end stripes and M is the middle separating stripe. The first digit of the left number is the prefix and the last digit of the right number is a checksum digit, used only to verify that the other digits were read correctly. An interesting fact is that the prefix digit is sometimes significant:
· A 2 means that the product is sold by weight, such as with butchered meat.
· A 3 is reserved for drugs, both over-the-counter and prescription.
· A 4 is reserved for store use; it often prefixes frequent shopper discount cards.
· A 5 means it's a coupon.
The code is of course translated into those horizontal black bars, which actually correspond to a binary representation of the digits. The reader scans this by bouncing a red laser beam off of the black and white pattern, then a sensor in the scanner records the light pattern reflected back. The standard sensor is a photodiode, however, newer models have made use of a miniature video camera which literally takes a picture of the barcode, then analyzes the pixels in the image.
Variations on this theme include the pen-type laser scanner where you swipe the tip across the code, CCD readers which have an array of sensors and process the image more like a digital camera would, and the aforementioned imaging scanners. There's also the stationary scanner, which is the kind the supermarket uses, and handheld scanners.
Handheld scanners either come as an extension to a PDA or a handheld "laser gun" model that relays the data to the PDA or handheld device. Remember that a stand-alone scanner isn't made to interpret the code into meaningful data; that job is up to the inventory control software. Older scanners sent the data with a cable, plugging into a PDA with a PS/2 connector just like a computer mouse and keyboard. Newer scanners transmit the data wirelessly, either by Bluetooth or infrared signal or whatever other scheme.
Barcodes come in many more varieties than UPC. There are dozens of variations for all kinds of uses. The United States post office uses POSTNET, the UK's Royal Mail uses RM4SCC, and Canada's mail service uses CPC Binary. Pharmacies have their own code, as does the magazine publishing industry and the color print film industry.
The familiar barcade we've been thinking about so far is considered "1D", that is, it's a simple line of stripes. But there are "2D" barcodes and block (called "matrix") barcodes as well. The block barcodes look just like an image using black and white pixels. One example of 2D barcodes is the embedded sound data in 35mm film strips, used by Dolby Digital and Sony Dynamic. Microsoft has created the High Capacity Color Barcode, which uses color, and on the flip side there's a matrix-code called "Aztec code" which is formerly patented by Honeywell but now released to the public domain.
We could go on and on, but generally you get the point that there's as many ways to optically encode data onto printed media as there are ways that you can think of, and that whatever we do, we must not invent any more code systems. We have enough for every possible need. And things will be complicated enough when we all start switching to RFID tags and chips. Find a great range of Barcode Scanners from our friends over at Pressdigtial
Filed Under: Barcoding
