Barcodes and barcode scanners
by Chris Woodford. Last updated: September 14, 2014.
Blip! Blip! Blip! Buying things at a grocery store has never been
easier or quicker thanks to barcode technology. You must have seen the
black-and-white zebra stripes on everything from cornflake packets to
library books and the laser wands that are used to read them. But have
you ever stopped to think how they work?
Photo: An electronic zebra? A barcode represents the line of numbers printed underneath it with a pattern of black and white bars. Barcodes are designed for computers to read quickly by scanning red LED or laser light across them.
What are barcodes used for?
If you run a busy store, you need to keep track of all the things
you sell so you can make sure the ones your customers want to buy are
always in stock. The simplest way of doing that is to walk around the
shelves looking for empty spaces and simply refilling where you need
to. Alternatively, you could write down what people buy at the
checkout, compile a list of all the purchases, and then simply use that
to reorder your stock. That's fine for a small store, but what if
you're running a giant branch of Wal-Mart with thousands of items on
sale? There are many other difficulties of running shops smoothly. If
you mark all your items with their prices, and you need to change the
prices before you sell the goods, you have to reprice everything. And
what about shoplifting? If you see a lot of whisky bottles missing from
the shelves, can you really be certain you've sold them all? How do you
know if some have been stolen?
Using barcode technology in stores can help to solve all these
problems. It lets you keep a centralized record on a computer system
that tracks products, prices, and stock levels. You can change prices
as often as you like, without having to put new price tags on all your
bottles and boxes. You can instantly see when stock levels of certain
items are running low and reorder. Because barcode technology is so
accurate, you can be reasonably confident that any items that are
missing (and don't appear to have been sold) have probably been
stolen—and maybe move them to a more secure part of your store
or protect them with RFID tags.
A barcode-based stock system like this has three main parts. First, there's a central
computer running a database (record system) that keeps a tally of all the products you're selling, who makes it, what each one costs, and how
many you have in stock. Second, there are the barcodes printed on all
the products. Finally, there's one or more checkout scanners that can
read the barcodes.
How barcodes represent the numbers 0-9
A barcode is a really simple idea: give every item that you want to
classify its own, unique number and then simply print the number on the
item so an electronic scanning device
can read it. We could simply print the number itself, but the trouble
with decimal numbers is that they're easy to confuse (a misprinted
eight could look like a three to a computer, while six is identical to
nine if you turn it upside down—which could cause all sorts of chaos at
the checkout if you scanned your cornflakes the wrong way up). What we
really need is a completely reliable way of printing numbers so that
they can be read very accurately at high speeds. That's the problem
that barcodes solve.
If you look at a barcode, you probably can't make head or tail of
it: you don't know where one number ends and another one begins. But
it's simple really. Each digit in the product number is given the same
amount of horizontal space: exactly 7 units. Then, to represent any of
the numbers from zero through nine, we simply color those seven units
with a different pattern of black and white stripes. Thus, the number
one is represented by coloring in two white stripes, two black
stripes, two white stripes, and one black stripe, while the number two
is represented by two white stripes, one black stripe, two white
stripes, and two final black stripes.
Photo: Each digit in a barcode is represented by seven equal-sized vertical blocks.
These are colored in either black or white to represent the decimal
numbers 0-9. Each block has been designed so that, even if you turn it upside down,
it can't be confused with any other.
You've probably noticed that barcodes can be quite long and that's
because they have to represent three different types of information.
The first part of a barcode tells you the country where it was issued.
The next part reveals the manufacturer of the product. The final part
of the barcode identifies the product itself. Different types of the
same basic product (for example, four-packs of Coca-Cola bottles and
six-packs of Coca-Cola cans) have totally different barcode numbers.
Most products carry a simple barcode known as the UPC (universal
product code)—a line of vertical stripes with a set of numbers
printed underneath it (so someone can manually key in the product
number if the barcode is misprinted or damaged in the store and won't scan through the
barcode reader). There is another kind of barcode that is becoming increasingly common and its
stores much more information. It's called a 2D (two-dimensional) barcode) and you sometimes see it on things like self-printed postage stamps.
How does a barcode scanner work?
It would be no good having barcodes if we didn't have the technology
to read them. Barcode scanners have to be able to read the
black-and-white zebra lines on products extremely quickly and feed that
information to a computer or
checkout terminal, which can identify them immediately using a product
database. Here's how they do it.
For the sake of this simple example, let's assume that barcodes are simple on-off, binary
patterns with each black line corresponding to a one and each white line a zero. (We've already
seen that real barcodes are more sophisticated than this, but let's keep things simple.)
- Scanning head shines LED or laser light onto barcode.
- Light reflects back off barcode into a light-detecting electronic component called a
photoelectric cell. White areas of the barcode
reflect most light; black areas reflect least.
- As the scanner moves past the barcode, the
cell generates a pattern of on-off pulses that correspond to the black and white stripes.
So for the code shown here ("black black black white black white black black"), the cell
would be "off off off on off on off off."
- An electronic circuit attached to the scanner converts these on-of pulses into binary
digits (zeros and ones).
- The binary digits are sent to a computer attached to the scanner, which detects the
code as 11101011.
In some scanners, there's a single photoelectric cell and, as you move the scanner head past
the product (or the product past the scanner head), the cell detects each part of the black-white
barcode in turn. In more sophisticated scanners, there's a whole line of photoelectric cells and the entire
code is detected in one go.
In reality, scanners don't detect zeros and ones and produce binary numbers as their output: they detect
sequences of black and white stripes, as we've shown here, but convert them directly into decimal numbers, giving a decimal
number as their output.
Types of barcode scanner
Different types of barcode scanners are available for all kinds of
applications. In small, convenience stores, you'll typically find a
basic wand scanner. The simplest ones look like electronic pens or
giant, oversized razors. They shine red LED
light onto the black and white barcode pattern and then read the
pattern of reflected light with a light-sensitive CCD or a string of
photoelectric cells. If you
have a pen scanner, you have to run it across the barcode so it can
reach each block of black or white in turn; with a wand scanner, the
CCD or photocells read the entire code at once.
In a busy superstore, you're more likely to see a very sophisticated
laser scanner. It'll be built into the base
of the checkout lane, under a piece of glass, and you may be able to
see the laser beam being bounced around at high-speed by a spinning wheel so it
reads products (literally) in a flash. Another technology uses a small video camera to take an instant digital photograph of the barcode. A
computer then analyzes the photograph, picking out only the barcode
part of it and converting the pattern of black and white bars into a
number. (Barcode-scanning apps that run on cellphones
work this way, using the phone's built-in camera to photograph the code.)
Scanners like this can accurately read dozens of products waved
past them each minute and are far more accurate than old-style
checkouts (where you have to key in the price of every item by hand).
The best barcode scanners are so accurate that they make only one
mistake in something like 70 million pieces of scanned information!
(Compare that to typing on a keypad, where you're typically likely to
make one error in every 100 characters you type.)
Photo: Left: A typical wand-type barcode scanner (also called a barcode reader).
Right: Scanning a barcode with Amazon's iPhone/iPod app. You find a product you like,
scan the code, and the online store pops up with the product details automatically.
Barcode scanning technology has been around since the early 1970s
but only really caught on in the 1980s and 1990s after stores started
to invest in sophisticated, computerized electronic point-of-sale
(EPOS) checkout terminals. Back then, store
checkouts cost many thousands of dollars. Today, scanners are much more
affordable. You can buy a simple, USB barcode
scanner and software and hook it up to an ordinary laptop or computer
for just a few dollars. Thanks to barcodes, even tiny convenience
stores can run as smoothly as Wal-Mart these days!
Who invented barcodes?
How did we arrive at a point where virtually everything we buy is marked with a barcode? Here are some
of the key moments in barcode history:
- 1948: Bernard Silver (1924–1963) and N. Joseph Woodland (1921–) get the idea for developing grocery checkouts that can automatically scan products. Woodland tries various different marking systems, including lines and circles, marks inspired by movie soundtracks, and dots and dashes based on Morse code. In October 1949, the two inventors refine their system to use bullseye patterns and apply for a patent (US Patent #2,612,944), which is granted on October 7, 1952. Their early barcode-scanning equipment uses a conventional lamp to illuminate product labels and a photomultiplier (a crude type of photoelectric cell) to read the light reflected off them. In 1951, Joe Woodland joins IBM to work on barcode technology, though the company declines to purchase his patent, which is acquired by Philco (and later RCA).
- 1960s: RCA develops a number of commercial applications until the patent expires in 1969. Work on bullseye barcodes continues, but they prove unreliable and gradually fall by the wayside.
- 1970: By now, grocery stores are beginning to explore the idea of using their own product coding and marking systems, but different stores are considering different systems, and this threatens to cause problems for large food manufacturers who sell branded goods to multiple retailers. Under the guidance of Alan Haberman (1929–2011), executive vice president of First National Stores in Boston, the stores come together to form the Uniform Code Council (UCC), later known as GS1 US, the organization that now manages barcode standards worldwide.
- 1971: Meanwhile, at IBM, George J. Laurer (1925–) builds on Woodland's ideas to develop the Universal Product Code (UPC)—the modern black-and-white striped barcode. (Read more about Laurer's work and IBM's contributions to barcode technology.)
- 1973: After examining a variety of different marking systems, Haberman's grocery stores committee settles on IBM's rectangular UPC as the standard grocery barcode. Although he didn't invent the barcode, Haberman is widely credited with its universal adoption.
- 1974: On June 26, the world's first grocery-store barcode scanner goes into use at Marsh's Supermarket, Troy, Ohio in the United States. The first scanned purchase, made by Clyde Dawson, is for a 10-pack of Wrigley's chewing gum.
- 1979: In the UK, a barcode scanner is used for the first time at Key Markets in Spalding, Lincolnshire.
- 2011: Joe Woodland and the late Bernard Silver are inducted into the National Inventors Hall of Fame in recognition of their brilliant invention.