| The technology used to read barcodes is | | | | So by noting the locations of the guard bars, the |
| relatively simple, but there is little information | | | | scanner can actually combine scans of the left |
| available for the novice. This is intended to be an | | | | and right sections to make a complete code. |
| introduction to the scanning, processing and | | | | Once the type of barcode has been identified, the |
| presentation of barcode information. | | | | pulse string is broken into groups of bars that |
| Scanners | | | | form characters. When decoding a UPC, each |
| A scanner is a device that converts the image of | | | | character is four bars: 2 black, 2 white. |
| a barcode into electrical pulses. There are four | | | | Once each character has been identified, there |
| basic ways of doing this: contact wands, active | | | | might be a check sum calculation to verify the |
| non-contact (AKA laser scanners), and passive | | | | complete code is valid. The UPC barcode |
| non-contact, which can be cameras or linear CCDs | | | | performs a calculation determined by each digit's |
| (charge coupled devices). All of these devices | | | | position and compares that to the last digit of the |
| have similar outputs, strings of electrical pulses | | | | code. |
| that mimic the white/dark and width of the bars. | | | | |
| With the exception of cameras, a scanner will | | | | Data to information |
| always include a light source, either LED or laser. | | | | The converted data is now in a digital form. This |
| Wands are the simplest, but have the most | | | | may be a coding pattern like ASCII or it might be |
| limitations. A wand has a light source, focusing lens | | | | keyboard codes. The former is standard for |
| and a light detector. It has no moving parts, which | | | | stand-alone readers, the latter more common in |
| makes it the most rugged of scanners, but it also | | | | point-of-sale or office use. |
| means the operator must move the wand over | | | | Keyboard wedges that connect scanners to |
| the code. This takes some practice. The second | | | | computers will use keyboard codes, so the |
| major limitation: the wand must touch the | | | | computer accepts the input as if someone were |
| barcode. A barcode under a plastic case or an | | | | typing the code. |
| overly-thick wrapper cannot be read by a wand. | | | | A wireless reader can either store the digital |
| | | | codes or transmit them to a central system. |
| Laser scanners have moving parts that are easily | | | | Many handheld, portable readers contain small |
| damaged. They consist of a laser light, a set of | | | | amounts of memory that can store 100-150 |
| mirrors and a detector. At least one of the | | | | barcodes before they need to be connected to a |
| mirrors moves, which allows the laser beam to | | | | computer to download. Connections can be via |
| scan a code. Multiple mirrors can redirect the | | | | USB or a serial port. In almost all cases, specialized |
| beam in many directions. A laser beam is very | | | | software is required to read the data. Wireless |
| thin and this allows the scanner to read barcodes | | | | readers that transmit to a central system do not |
| at long distances. They can also make multiple | | | | need data storage, but they are limited in their |
| scans of the same code in very short periods. | | | | range. This is most useful within a warehouse or a |
| These properties make them ideal for retail | | | | factory. |
| stores and factory use where the distance | | | | |
| between the barcode and the scanner can very | | | | Making use of the data |
| from scan to scan. | | | | If a barcode is not routed to a central computer, |
| | | | it needs to be displayed in a human-readable |
| CCD scan engines will contain a light source (most | | | | format. Devices that can do this are called |
| often LED), lenses and a linear CCD. The barcode | | | | portable data terminals (PDT).This is a bad term, |
| is illuminated and the lenses focus the image on | | | | because only the portable part is true. A portable |
| the CCD. Scanning is performed by reading the | | | | data terminal is a free-standing barcode-reading |
| reading the charge levels on each of the CCD | | | | system. |
| elements. CCD detectors can have 1024, 2048 or | | | | A PDT will contain a scanner, a processor, |
| even more elements. Like a wand, a CCD scanner | | | | memory, storage and a display. Often, they are |
| has no moving parts. These scanners do not | | | | actually laptop or palm computers to which a |
| make contact with the barcode, so they can | | | | scanner has been added. A few are purpose-built |
| work at a distance. Because of the need to focus | | | | and optimized to read barcodes and translate that |
| the barcode's image on the CCD strip, the | | | | to useful, human-readable form. A PDT can |
| distances within which a CCD scanner works is | | | | contain tables or databases which allow it to look |
| much more limited than for a laser scanner. | | | | up scanned codes and tell the user what they |
| | | | represent and how many there are. |
| Camera scanners use an array of CCDs and | | | | A PDT tends to be very expensive, because it |
| lenses, and some them include a light source. | | | | has so many capabilities. Those based on laptops |
| They have lower-resolution detectors, which limits | | | | can cost several thousand dollars. Even palm |
| their use to special 2D matrix barcodes, unless | | | | devices can be $600-$1000 dollars once the |
| close-up focusing is an option on the camera. | | | | scanner has been added. Businesses can integrate |
| Webcams and cellphones can be used in this way. | | | | PDTs into their inventory systems, and some of |
| | | | the lower-cost devices can be placed in the hands |
| Light to data | | | | of all of their field personnel. Items used while |
| The output of a scanner is a string of electrical | | | | servicing customers' equipment can be scanned |
| pulses. Generally two voltages are used for the | | | | on site and the information loaded into the main |
| pulses, a high-state and zero. If viewed with the | | | | inventory system later for billing and inventory |
| right equipment, the high & low states would | | | | management. |
| map directly to the black & white bars of a | | | | Some purpose-built PDTs are small enough and |
| code. The conversion is done by part of the | | | | inexpensive enough to be used as consumer |
| reader, or in some applications by a keyboard | | | | devices. Given a scanner, storage and a display, |
| wedge. | | | | consumers can use these devices to inventory |
| The pulse string is processed in several ways. The | | | | their music, movie and book collections. |
| first is a look at the lengths of the pulses. Many | | | | The inventories can be stored on their home |
| barcodes use constant width bars and spaces, but | | | | computers or stored remotely, or both. Websites |
| the most common barcode, the UCC/EAN code, | | | | that cater to collectors can frequently convert |
| uses four widths. Each barcode type has a font. | | | | barcodes to more useful information like titles, |
| Most of them also have guard bars, which indicate | | | | authors and composers. Small, pocket-sized |
| where the code starts and stops. The guard bars | | | | devices designed for portability can actually be |
| may also give a clue as to the direction of the | | | | carried at all times, and used to check new |
| scan. The UPC barcode uses three bars at the | | | | purchases against items already collected, just by |
| ends and five in the middle. The guard bar | | | | scanning codes. |
| patterns are not used for numbers or characters. | | | | |