A touchscreen is a display that recognizes the touch of a finger or stylus upon its surface. It is used primarily in PDA and customer-service kiosks such as an ATM, it allows a user to input data and control a computer without a keyboard.

There are several types of touchscreen:

Capacitive. A layer of conductive material in a glass sandwich carries a tiny current that leaks through the finger when touched. Busbars at the edges of the screen detect the location of the current leak, pinpointing where you are touching. The electrical field can also be created with a grid of fine wires.

Resistive. a flexible coating on a rigid transparent substrate (a piece of treated glass) creates a circuit with varying resistance when you touch it. It is also detected by busbars at the edge of the screen.

Surface-Accoustic Wave microvibrations are set up in the glass, and the finger damps them at the point of touch. This system can also detect the amount of pressure, creating z-axis input.

Optical Only used in conditions requiring extreme rugged operation, or places where the user may be wearing heavy gloves, or where you don't want the users to actually come in contact with the screen. A grid of infrared LEDs along two edges are paired with photodetectors on the other two edges, so the screen "sees" anything that breaks the beams, pinpointing its location.

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