The function of the bar code scanner is to read the image presented by the bar code. In its most basic form, the scanner sees and measures the absence or presence of light in the code's bars and spaces, and converts that information into an electrical signal that can be translated into recognizable or computer-compatible data. Common hand held scanning technologies includes wands, lasers, and CCDs. While they are all dedicated to the same task, reading a bar code, each scanner type offers both advantages and disadvantages, and none is clearly superior in all cases.
Hand held laser scanners are the most expensive of the scanning devices, but offer the largest depth of field making them an appropriate choice for a wide variety of non-contact applications. Hand held laser scanners use a laser diode to create a scan line by projecting a beam of energy off a rotating prism or oscillating mirror. The beam is reflected out the scanner window onto the bar code, where light energy from the bars and spaces is reflected back to the scanner, collected on a mirror, focused, and read by a photo detector. The resulting signal may then be read using decoding software within the scanner or at the terminal.
The light generating medium in first-generation moving beam laser installations was a Helium-Neon laser tube. In the past few years semiconductors capable of producing laser light have been incorporated in most laser products. Laser diodes, both visible and infrared, are in a package about the size of an LED. Compared to the gas tube used to create Helium- Neon lasers, the laser diode is much smaller, requires significantly less power, and is more durable. This makes these hand-held devices suitable for portable data collection terminals or for fixed-station decoders that are powered from the terminal.
Input devices can be grouped into three basic categories: fixed beam or moving beam, hand held or fixed mount, and contact or non-contact.