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Concept
Barcode reader
Summary
A barcode reader or barcode scanner is an optical scanner that can read printed barcodes, decode the data contained in the barcode to a computer. Like a flatbed scanner, it consists of a light source, a lens and a light sensor for translating optical impulses into electrical signals. Additionally, nearly all barcode readers contain decoder circuitry that can analyse the barcode's image data provided by the sensor and send the barcode's content to the scanner's output port.
Barcode readers can be differentiated by technologies as follows:
Pen-type readers consist of a light source and photodiode that are placed next to each other in the tip of a pen. To read a barcode, the person holding the pen must move the tip of it across the bars at a relatively uniform speed. The photodiode measures the intensity of the light reflected back from the light source as the tip crosses each bar and space in the printed code. The photodiode generates a waveform that is used to measure the widths of the bars and spaces in the barcode. Dark bars in the barcode absorb light and white spaces reflect light so that the voltage waveform generated by the photodiode is a representation of the bar and space pattern in the barcode. This waveform is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.
Laser scanning
Laser scanners direct the laser beam back and forth across the barcode. As with the pen-type reader, a photo-diode is used to measure the intensity of the light reflected back from the barcode. In both pen readers and laser scanners, the light emitted by the reader is rapidly varied in brightness with a data pattern and the photo-diode receive circuitry is designed to detect only signals with the same modulated pattern.
Charge-coupled device (CCD) readers 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.
Official source
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