Barcode reader
From Wikipedia, the free encyclopedia
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.
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[edit] Types of Barcode Readers
Many different types of barcode scanners are available. They can be distinguished as follows:
[edit] By technology
- 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, you drag the tip of the pen across all the bars in a steady even 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 an exact duplicate 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.
- 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. Just the same 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 same frequency light.
- 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 can be thought of as a single photodiode that 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.
[edit] By housing
- 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. Most often used on conveyer tracks to identify cartons or pallets which need to be routed to another process or shipping location.
- PDA scanner : a PDA with a built-in barcode reader or attached barcode scanner e.g. Grabba.
[edit] Types of Connectors
Most barcode readers 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 extremely easy to interface the bar code reader to any application that is written to accept keyboard input. However, this kind of direct input has some drawbacks. You cannot operate with that data, so in case you need to parse a code into several parts you will not be able, and the input will appear wherever the cursor was, so you must be sure it is set in the proper place.
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. You would then need a program called a "Software Wedge" to take the data from the bar code reader and feed it to the application where you want the data to go. Using this interface you gain much more control over how and where your data ends up when you read a bar code.
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 variety of connector types. Undecoded interface is an amplified output of the raw wave received back from the barcode and requires a decoder found, mostly used on older stand alone cash registers with a wide 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.
[edit] Resolution
Pen type readers and laser scanners have "resolution" as one of their main characteristics. 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. As it is a very high resolution, it is extremely important to have bar codes created with a high resolution graphic application.
