Touch Screen Displays
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Touch screen displays are the most user-friendly PC interface. They are input devices, a way to communicate with the PC. The user touches the screen to select options presented on the screen. Associated hardware and software are used to determine the location of the press. 

There are five basic types of touch screen technology: resistive, capacitive, infrared, surface acoustic wave (SAW) and strain gauge. Resistive and capacitive are the most commonly implemented although all the technologies are viable and suited to different applications.  Resistive touch technology consists of a glass or acrylic panel that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots. When operating, an electrical current moves through the screen. When pressure is applied to the screen the layers are pressed together, causing a change in the electrical current and a touch event to be registered.  A capacitive touch screen consists of a glass panel with a capacitive (charge storing) material coating its surface. Circuits located at corners of the screen measure the capacitance of a person touching the overlay. Frequency changes are measured to determine the X and Y coordinates of the touch event.  Infrared is similar to resistive, infrared screens project horizontal and vertical beams of infrared light over the surface of the screen. When a finger or other object breaks those beams, the X/Y coordinates are calculated.  Surface Acoustic Wave technology is one of the most advanced touch screen types. It is based on sending acoustic waves across a clear glass panel with a series of transducers and reflectors. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point.  In a strain gauge configuration the screen is spring mounted on the four corners and strain gauges are used to determine deflection when the screen is touched. This technology can also measure the Z-axis.

The major difference between products is that some offer "continuous" touch areas while others offer "discrete" touch areas. With continuous screens, buttons can be placed in any location and made any shape and size. With discrete touch screens, the shape and size of touch-sensitive areas are pre-determined. In practical terms, however, many of these discrete touch areas are about one-quarter the size of a finger, allowing relatively flexible positioning of buttons.

Touch screen displays can be either internally mounted, or externally mounted on an existing screen.  An internally mounted screen is a touch screen input device that is designed to be installed on the inside of a PC monitor. It is commonly a touch sensitive glass panel that uses a touch screen controller and a software driver to interface with a PC system. The internal touch screen requires a sometimes-technical installation, as the monitor needs to be opened and in some cases the touch screen controller needs to be wired to a power source inside the monitor.  An external touch screen panel is a touch screen input device that is designed to mount on the outside of a PC monitor. The external touch screen does not require any difficult installation or opening of the monitor. It is commonly a touch sensitive glass panel that uses an external touch screen controller and a software driver to interface with a PC system.  Touch screen displays are generally LCD or CRT.

Important performance specifications to consider when searching for touch screen displays include number of touch points, actuation force, pixel pitch, response time, operating life or number of touches, and image resolution.  Screen dimensions are also important to consider.  Generally screen dimensions are given as one value, the diagonal, but effective screen width and effective screen height can also be specified.  Other advanced parameters to consider when specifying touch screen displays include external connections, mounting options, features, and environmental operating parameters.
There are five basic types of touch screen technology: resistive, capacitive, infrared, surface acoustic wave (SAW) and strain gauge. Resistive and capacitive are the most commonly implemented although all the technologies are viable and suited to different applications.

The major difference between products is that some offer "continuous" touch areas while others offer "discrete" touch areas. With continuous screens, buttons can be placed in any location and made any shape and size. With discrete touch screens, the shape and size of touch-sensitive areas are pre-determined. In practical terms, however, many of these discrete touch areas are about one-quarter the size of a finger, allowing relatively flexible positioning of buttons.
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