touch Screen

A touch screen is a computing device that combines the features of a display screen (monitor) and those of a pointing device like a mouse or trackball.
This reduces the number of devices on some systems and software to perform very well suited to ergonomic functions. Touch screens are used, for example, PDAs, GPS, MP3 players, smartphones, Nintendo DS, ticketing machines, all boxes and computers without a cashier.
A touch screen may be sensitive to more than two pressure levels with a resolution better (hybrid screen / stylus) and more than one place at one time (multitouch / Fingers)
There are several types of implementation for touch screens, each with advantages and disadvantages. The choice of either of these technologies will be based on the criteria of price, impact strength, precision or size (some are difficult to stretch big and small screen sizes).Surface Wave Technology
The technology of surface waves using ultrasonic waves traveling at the surface of the screen. These waves create an interference pattern that is modified by touching the screen. This change in the interference pattern, once detected, is processed by a controller to define a coordinate (x, y).
The major drawback of this technology stems from the fact that the slightest scratch (or even a dirt or stain) on the surface alters the interference pattern base and thus affects the accuracy of detection on the screen.Analog resistive technology [edit]Resistive touch screen
The resistive system consists of a glass plate whose surface is conductive (resistive: ITO). It is covered by a plastic film whose underside is conductive (resistive: ITO). These two layers are held apart by tiny spacers, in addition, an additional layer is added to prevent surface scratches (for example, by the pen nibs).
An electric current is induced in the two conductive faces during the operation. When the user touches with the tip of a stylus (or finger), initiate a pressure contact between the two sides electrified. The change in the electric fields of the two conductive faces to determine the coordinates of the point of contact. Once the coordinates determined by the software processing system is established.
The electrical conductivity of the two sides a little wear at each contact with each other (because of static discharge: micro sparks). Therefore, the accuracy of detecting coordinates of the hit is reduced with use. This technology requires the user to recalibrate the touch pad. This recalibration is to hide the wear of touch by spreading over its entire surface, the errors of the most used parts touch. Types of devices using this system: laptop touch screen Windows 7, the former company PALM PDA, some smartphones (HTC Tattoo, HTC TyTN II, LG Viewty ...)

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