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Optical Touch Technology

The conventional optical touch system uses an array of infrared light-emitting diodes (LEDs) on two adjacent bezel edges of a display, with photosensors placed on the two opposite bezel edges to analyze the system and determine a touch object. The LED and photosensor pairs create a grid of light beams across the display. An object (such as a finger or a pen) that touches the screen interrupts the light beam, causing a measured decrease in light at the corresponding photosensors. The measured photosensors outputs can be used to locate a touch point coordinate. Usually, the controller scans through the array of photosensors rather than measuring all of them simultaneously. In a more advanced version of the technology, each photosensor measures light from more than one LED, which allows the controller to compensate for light blockage caused by nonmoving debris on the screen.

The traditional type of optical touch has been used primarily in niche applications of touch market. However, its broader use has been hampered by two reasons: the primitively high cost of the touch technology compared to other competing touch technologies. The latter problem is that the background light increase the noise floor at the optical sensor, sometimes to such a degree that the touch screen’s LED light cannot be detected at all, causing a temporary failure of the touch screen. This is most pronounced in direct sunlight conditions where the sun has a very high energy distribution in the IR region.

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