![]() Each sensor measures the intensity of the light immediately in front of it. ![]() 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.ĬCD readers (also known as LED scanners) ĬCD readers use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. As with the pen-type reader, a photo-diode is used to measure the intensity of the light reflected back from the barcode. 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 barcode.
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