A barcode reader (or barcode scanner) is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones. Additionally, nearly all barcode readers contain decoder circuitry analyzing the barcode’s image data provided by the sensor and sending the barcode’s content to the scanner’s output port.
Methods
Scanning methods are distinguished by the amount of operator manipulation required:

Pen or wand-type readers: requires the operator to swipe the pen over the code.
Semi-automatic handheld readers: The operator need not swipe, but must at least position the reader near the label
Fix-mount readers for automatic reading: The reading is performed laterally passing the label over the reader. No operator is required, but the position of the code target must coincide with the imaging capability of the reader and ll
Reader gates for automatic scanning: The position of the code must be just under the gate for short time, enabling the scanner sweep to capture the code target successfully.

Types Of Technology
The reader types can be distinguished as follows:
Pen Type Readers
Pen type readers consist of a light source and a photodiode that are placed next to each other in the tip of a pen or wand. To read a bar code, the tip of the pen moves across the bars in a steady motion. The photodiode measures the intensity of the light reflected back from the light source and generates a waveform that is used to measure the widths of the bars and spaces in the bar code. Dark bars in the bar code absorb light and white spaces reflect light so that the voltage waveform generated by the photo diode is a representation of the bar and space pattern in the bar code. This waveform is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.

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Laser Scanners
Laser scanners work the same way as pen type readers except that they use a laser beam as the light source and typically employ either a reciprocating mirror or a rotating prism to scan the laser beam back and forth across the bar code. As with the pen type reader, a photodiode is used to measure the intensity of the light reflected back from the bar code. In both pen readers and laser scanners, the light emitted by the reader is tuned to a specific frequency and the photodiode is designed to detect only this modulated light of the same frequency.
CCD Readers
CCD readers (also referred to as LED scanner) use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. Each sensor measures the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a bar code is generated in the reader by sequentially measuring the voltages across each sensor in the row. The important difference between a CCD reader and a pen or laser scanner is that the CCD reader is measuring emitted ambient light from the bar code whereas pen or laser scanners are measuring reflected light of a specific frequency originating from the scanner itself.
Camera-Based Readers
2D imaging scanners are the fourth and newest type of bar code reader currently available. They use a small video camera to capture an image of a bar code. The reader then uses sophisticated digital image processing techniques to decode the bar code. Video cameras use the same CCD technology as in a CCD bar code reader except that instead of having a single row of sensors, a video camera has hundreds of rows of sensors arranged in a two dimensional array so that they can generate an image.
There are a number of open source libraries for barcode reading from images. These include the ZXing project, which reads one- and two-dimensional barcodes using Android and JavaME, the JJIL project, which includes code for reading EAN-13 barcodes from cellphone cameras using J2ME, and Zebra (Changed name to ZBAR), which reads various one-dimensional barcodes in C. Even web site integration, either by image uploads (e.g. Folke Ashberg: EAN-13 Image-Scanning and code creation tools) or by use of plugins (e.g. the Barcodepedia uses a flash application and some web cam for querying a database), have been realized options for resolving the given tasks.
Omni-Directional Barcode Scanners
Omni-directional scanning uses “series of straight or curved scanning lines of varying directions in the form of a starburst, a lissajous pattern, or other multiangle arrangement are projected at the symbol and one or more of them will be able to cross all of the symbol’s bars and spaces, no matter what the orientation.”
Omni-directional scanners almost all use a laser. Unlike the simpler single-line laser scanners, they produce a pattern of beams in varying orientations allowing them to read barcodes presented to it at different angles. Most of them use a single rotating polygonal mirror and an arrangement of several fixed mirrors to generate their complex scan patterns.
Omni-directional scanners are most familiar through the horizontal scanners in supermarkets, where packages are slid across a glass or sapphire window. There are a range of different omni-directional units available which can be used for differing scanning applications, ranging from retail type applications with the barcodes read only a few centimetres away from the scanner to industrial conveyor scanning where the unit can be a couple of metres away or more from the code.
Omni-directional scanners are also better at reading poorly printed, wrinkled, or even torn barcodes.
Housing Types
The reader packaging can be distinguished as follows:
Handheld scanner: with a handle and typically a trigger button for switching on the light source.
Pen scanner (or wand scanner): a pen-shaped scanner that is swiped.
Stationary scanner: 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.
Fixed position scanner: an industrial barcode reader used to identify products during manufacture or logistics. Often used on conveyor tracks to identify cartons or pallets which need to be routed to another process or shipping location. Another application joins holographic scanners with a checkweigher to read bar codes of any orientation or placement, and weighs the package. Systems like this are used in factory and farm automation for quality management and shipping.
PDA scanner: a PDA with a built-in barcode reader or attached barcode scanner e.g. Grabba.
Automatic reader: a back office equipment to read barcoded documents at high speed (50,000/hour) e.g. Multiscan MT31
Methods Of Connection
Early Serial Interfaces
Early barcode scanners, of all formats, almost universally used the then-common RS232 serial interface. This was an electrically simple means of connection and the software to access it is also relatively simple, although needing to be written for specific computers and their serial ports.{10}
Proprietary Interfaces
There are a few other less common interfaces. These were used in large EPOS systems with dedicated hardware, rather than attaching to existing commodity computers.
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.{11}
Keyboard Wedges
With the popularity of the PC and its standard keyboard interface, it became ever easier to connect physical hardware to a PC and so there was commercial demand similarly to reduce the complexity of the associated software. “Keyboard wedge” hardware plugged between the PC and its normal keyboard, with characters from the barcode scanner appearing exactly as if they had been typed at the keyboard. This made the addition of simple barcode reading abilities to existing programs very easy, without any need to change them, although it did require some care by the user and could be restrictive in the content of the barcodes that could be handled.
Later barcode readers began to use USB connectors rather than the keyboard port, as this became a more convenient hardware option. To retain the easy integration with existing programs, a device driver called a “software wedge” could be used, to emulate the keyboard-impersonating behaviour of the old “keyboard wedge” hardware.
PS/2 Port
Most barcode readers now use a PS/2 or USB cable for output: PS/2 cables are connected to the host computer in a Y formation, the 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 decoded and converted to keyboard input within the scanner housing. This makes it easy to interface the bar code reader to any application that is written to accept keyboard input
USB is supported by many newer scanners. In many cases a choice of USB interface types (HID, CDC) are provided. Some have Powered USB.
Wireless Networking
Modern handheld barcode readers are operated in wireless networks according to IEEE 802.11g (WLAN) or IEEE 802.15.3 (Blueooth). However, such configuration limits the time of operation from battery or rechargeable battery and required recharging at least after a shift of operation.
Resolution
The scanner resolution is measured by the size of the dot of light emitted by the reader. If this dot of light is wider than any bar or space in the bar code, then it will overlap two elements (two spaces or two bars) and it may produce wrong output. On the other hand, if a too small dot of light is used, then it can misinterpret any spot on the bar code making the final output wrong.
The most commonly used dimension is 13 mils (0.3302 mm). As it is a very high resolution, it is extremely important to have bar codes created with a high resolution graphic application.
While cell phone cameras are not suitable for many traditional barcodes, there are 2D barcodes (such as Semacode) which are optimized for cell phones. These open up a number of applications for consumers:

Movies: DVD/VHS movie catalogs
Music: CD catalogs, play MP3 when scanned
Book catalogs
Groceries, nutrition information, making shopping lists when the last of an item is used, etc.
Personal Property inventory (for insurance and other purposes)
Calling cards: 2D barcodes can store contact information for importing.
Brick and mortar shopping: Portable scanners can be used to record items of interest for looking up online at home.
Coupon management: weeding expired coupons.
Personal finance. Receipts can be tagged with a barcode label and the barcode scanned into personal finance software when entering. Later, scanned receipt images can then be automatically associated with the appropriate entries. Later, the bar codes can be used to rapidly weed out paper copies not required to be retained for tax or asset inventory purposes.
If retailers put barcodes on receipts that allowed downloading an electronic copy or encoded the entire receipt in a 2D barcode, consumers could easily import data into personal finance, property inventory, and grocery management software. Receipts scanned on a scanner could be automatically identified and associated with the appropriate entries in finance and property inventory software.

Code 39
Code 39 (known as “USS Code 39”, “Code 3/9”, “Code 3 of 9”, “USD-3”, “Alpha39”, “Type 39”) is a barcode symbology that can encode uppercase letters (A through Z), digits (0 through 9) and a handful of special characters like the $ sign.
A Code 39 Barcode Label
The barcode itself does not contain a check digit (in contrast to—for instance—Code 128), but it can be considered self-checking by some; on the grounds that a single erroneously interpreted bar cannot generate another valid character.
Possibly the most serious drawback of Code 39 is its low data density: It requires more space to encode data in Code 39 than, for example, in Code 128. This means that very small goods cannot be labeled with a Code 39 based barcode. However, Code 39 is still widely used and can be decoded with virtually any barcode reader. One advantage of Code 39 is that since there is no need to generate a check digit, it can easily be integrated into existing printing system by adding a barcode font to the system or printer and then printing the raw data in that font.
The name Code 39 is derived from the fact that three of the nine elements that constitute a codeword are wide elements, the remaining six are narrow. Code 39 was developed by Dr. David Allais and Ray Stevens of Intermec in 1974. It was later standardised as ANSI MH 10.8 M-1983 and MIL-STD-1189. The width ratio between narrow and wide can be chosen between 1:2 and 1:3.
The details of CODE 39 can be seen in Appendix A.