How does a touch panel work?

There are three types of touch panels optical, electrical and acoustical. There is a series of LEDs in the horizontal and vertical sides of an optical touch panel. When a user touches the screen the screen position is determined by the interruption in beams of light emitted by LEDs. In electrical touch panel, two transparent sections are used in which one section is coated with conductive and other is coated with resistive material. These two sections are separated such that if one of the sections is touched, then it is forced to touch the other section too. This touch causes a voltage drop and hence by that the screen position is determined. In acoustic touch panels high frequency sound waves are put in between two sections of transparent glass. When touched, there is a reflection of waves from finger to emitter.  Time between transmission of waves and its reflection to emitter is used to determine the screen position.

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