A barcode reader (or barcode scanner) is a computer peripheral for reading
barcodes printed on various surfaces. Like a flatbed scanner, it generally consists
of a light source, a lens and a photo conductor translating optical impulses
into electrical ones. Additionally, nearly all barcode readers currently produced
contain decoder circuitry analyzing the barcode’s image data provided by the
photo conductor and sending the barcode’s content to the scanner’s output port.
Types of barcode readers
Many different types of barcode scanners are available. They can be distinguished
as follows:
By Light Source
- LED scanners: also referred to as CCD scanners — even
though the CCD is in fact the photo imaging sensor, not the light source
- Laser scanners: much more expensive than LED scanners but
are generally capable of longer maximum scanning distances
- Imager scanners: These scanners take an image of the linear
barcode, generally more rugged as they have no moving parts
By Housing
- Handheld scanner: with a handle and typically a trigger
button for switching on the light source
- Pen scanners (or wand scanners): A pen-shaped scanner that
is swiped across a barcode
- Stationary scanners: Wall- or table-mounted scanners that
the barcode is passed under or beside. These are commonly found at the checkout
counters of supermarkets and other retailers.
- PDA scanners: a personal digital assistant (PDA) with a
built-in barcode reader.
Technology and engineering
Laser Scanners: typical scanners utilise a 650nm laser diode,
leveraging on the economies of scale of diodes manufactured for CD/DVD drives.
The diode is normally housed in a metal casing for heat dissipation. The laser
light emitted is focused through a lens and reflected off a rotating polygonal
mirror, or an oscillating mirror. This produces a line or raster pattern which
may be aimed at a barcode. The light reflected off the barcode is captured onto
a photodiode whereby the current is amplified and interpreted by the decoding
circuit. The signal obtained is the modulation of the laser spot (whose profile
approximates that of a Gaussian beam), over the alternating black and white
lines of the barcode. The performance of the scanner is a function of:
- the signal to noise ratio (determined by the laser power, the size of the
laser spot, refectivity/transmittivity of the optical parts, receiving light
collection area, distance to the barcode, the level of optical noise such
as sunlight, fluorescent light as well as the ability to filter out that noise,
etc). The laser power is usually limited by CDRH Class I/II safety requirements.
- The scan speed of the device. Basically a trade-off between decode speed
and the size of the decode zone.
- The barcode (determined by difference in refectance of the barcode’s alternating
black & white stripes–print contrast ratio, defects, the size of the
barcode, and the barcode’s orientation in relation to the scanner). Generally,
the laser has to pass a certain amount of the ‘quiet zone’ on the barcode
before it hits the line patterns, in order to decode.
- The decoding circuit’s ability to decode and to handle errors in the barcode,
optical noise as well as the range of frequencies at which the signal is modulated.
Types of connectors
Most barcode readers use a PS/2 wedge cable for output: This cable is connected
to the host computer’s PS/2 keyboard port with its first end, to the keyboard
with its second, and to the barcode reader with its third end. The barcode characters
are then received by the host computer as if they came from its keyboard. Many
readers can also be equipped with an RS-232 output port so that the decoded
characters arrive at the computer via one of its RS-232 connectors. USB is supported
by many newer scanners, in many cases a choice of USB interface types (HID,
CDC) are provided.
There are a few other less common interfaces. The proprietary IBM interfaces
(port 5B, port 9B and port 17) that use an SDL type connector and are based
on an RS485 protocol. OCIA is sometimes still found, mostly used on older stand
alone cash registers with a wide variety of connector types. Undecoded interface
is an amplified output of the raw wave received back from the barcode and requires
a decoder to be built into the terminal that the scanner connects to which is
more common on industrial terminals. Wand emulation is another output type that
takes the raw wave and decodes it, normalizing the output so it can be easily
decoded by the host device. Wand emulation can also convert symbologies that
may not be recognized by the host device into another symbology (typically Code
39) that can be easily decoded.
Types of symbologies
Today’s barcode scanners handle all popular barcode symbologies like EAN/UPC,
Code 39, Interleaved 2 of 5 or Code 128. A special type of barcode reader is
the area imager reader or 2D reader that typically uses LED illumination and
a CCD or CMOS imager that operates much like a digital camera. These are necessary
for decoding two-dimensional matrix codes such as Datamatrix, QR Code, Aztec
Code and MaxiCode in addition to linear and stacked symbologies.
Projectors are classified by the size of the film used, i.e. the film format.
Typical film sizes:
8 mm
Long used for home movies before the video camera, this uses double sprocketed 16 mm film, which is run through the camera twice. The 16 mm film is then split lengthwise into two 8 mm pieces that are sliced to make a single projectable film with sprockets on one side. See the 8 mm film article for more information.
Super 8
Developed by Kodak this film stock uses very small sprocket holes close to the edge that allow more of the film stock to be used for the images. This increases the quality of the image. The film is premade in the 8 mm width, not split during processing as is the earlier 8 mm. Magnetic stripes could be added to carry
encoded sound to be added after film development. See the Super 8 mm film article for more information.
16 mm
This was a popular format for audio-visual use in schools and as a high-end home entertainment system before the advent of broadcast television. It is also the smallest format that can carry an optically encoded sound track. See the 16 mm film article for more information.
35 mm
The most common film size for theatrical productions during the first half of the 20th century. In fact, the common 35 mm camera, developed by Leica was designed to use this film stock and was originally intended to be used for test shots by movie directors and cinematographers. See the 35 mm film article for more
information.
70 mm
High end movie productions are often shot using this size and some theaters are capable of projecting it. 70 mm film is also used in both the flat and domed IMAX projection system. In IMAX the film is oriented for even more effective image area than in other formats.
Some high quality productions intended for 35 mm anamorphic release are shot in and the master prints constructed using 70 mm film stock. A 35 mm print made from a 70 mm master print is significantly better in appearance than an all 35 mm process.
This article is licensed under the GNU
Free Documentation License. It uses material from the
Wikipedia article “Movie Projector”
