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.  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. 

Types of Touch Screen Displays

There are five basic types of touch screen displays: resistive, capacitive, infrared, surface acoustic wave (SAW) and strain gauge. Resistive and capacitive touch screen displays are the most common.  Resistive touch screens consist of a glass or acrylic panel that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots. During operation, an electrical current moves through the screen. When pressure is applied to the touch 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 touch screens are similar to resistive products. Infrared touch 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 (SAW) technology sends 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 touch screen, the screen is spring mounted on the four corners and strain gauges are used to determine deflection when the screen is touched. This touch screen display technology can also measure the Z-axis.

Selecting Touch Screen Displays

Touch screen displays can use liquid crystal display (LCD) or cathode ray tube (CRT) technology. Selecting LCDs and CRTs is often a function of the application. 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 for graphic touch screen and alphanumeric touch screens are also important to consider. Generally, screen dimensions are given as one value, the diagonal; however, 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.


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