Touchscreen

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Touchscreens, touch screens, touch panels or touchscreen panels are display overlays which have the ability to display and receive information on the same screen. The effect of such overlays allows a display to be used as an input device, removing the keyboard and/or the mouse as the primary input device for interacting with the display's content. Such displays can be attached to computers or, as terminals, to networks. Touchscreens also have assisted in recent changes in the PDA and Cell-Phone Industries, making these devices more useable.

1 Applications
2 Technologies
3 Development and usage
4 Linearisation
5 See also
6 References
7 External links

[edit] Applications

Image:Nintendo DS Lite.jpg

Touchscreens have become commonplace since the invention of the electronic touch interface in 1971 by Dr. Samuel C. Hurst. They have become familiar in retail settings, on point of sale systems, on ATMs and on PDAs where a stylus is sometimes used to manipulate the GUI and to enter data. The popularity of smart phones, PDAs, portable game consoles and many types of information appliances is driving the demand for, and the acceptance of, touchscreens.

The HP-150 from 1983 was probably the world's earliest commercial touch screen computer. It actually does not have a touch screen in the strict sense, but a 9" Sony CRT surrounded by infrared transmitters and receivers which detect the position of any non-transparent object on the screen.

Touchscreens are popular in heavy industry and in other situations, such as museum displays or room automation, where keyboards and mice do not allow a satisfactory, intuitive, rapid, or accurate interaction by the user with the display's content.

Historically, the touchscreen sensor and its accompanying controller-based firmware have been made available by a wide array of after-market system integrators and not by display, chip or motherboard manufacturers. With time, however, display manufacturers and System On Chip (SOC) manufacturers worldwide have acknowledged the trend toward acceptance of touchscreens as a highly desirable user interface component and have begun to integrate touchscreen functionality into the fundamental design of their products.

[edit] Technologies

There are a number of types of touch screen technology:

Resistive: A resistive touch screen panel is coated with a thin metallic electrically conductive and resistive layer that causes a change in the electrical current which is registered as a touch event and sent to the controller for processing.; Some resistive panels can estimate the area (and hence the pressure) of a touch based on calculations from the resistances.; Resistive touch screen panels are generally more affordable but offer only 75% clarity (premium films and glass finishes allow transmissivity to approach 85%) and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected by outside elements such as dust or water and are the type most commonly used today.

Surface wave: Surface wave technology uses ultrasonic waves that pass over the touch screen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touch screen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen.

Capacitive: A capacitive touch screen panel is coated with a material, typically indium tin oxide that conducts a continuous electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes - it achieves capacitance. The human body is also an electrical device which has stored electrons and therefore also exhibits capacitance. When the sensor's 'normal' capacitance field (its reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits located at each corner of the panel measure the resultant 'distortion' in the sine wave characteristics of the reference field and send the information about the event to the controller for mathematical processing. Capacitive sensors must be touched with a conductive device being held by a bare hand or a finger, unlike resistive and surface wave panels that can use anything that can point, such as a finger or stylus. Capacitive touch screens are not affected by outside elements and have high clarity.

Infrared: An infrared touch screen panel employs one of two very different methodologies. One method used thermal induced changes of the surface resistance. This method was sometimes slow and required warm hands. Another method is an array of vertical and horizontal IR sensors that detected the interruption of a modulated light beam near the surface of the screen IR touch screens have the most durable surfaces and are used in many military applications that require a touch panel display.

Strain Gauge: 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. Typical application fails in protecting new touch-screen railway ticket machines from vandalism.

Optical Imaging: A relatively-modern development in touch screen technology, two or more image sensors are placed around the edges (usually the corners) of the screen. Infrared backlights are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.

Dispersive Signal Technology: Introduced in 2002, this system uses sensors to detect the mechanical energy in the glass that occur due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch. The technology claims to be unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and styluses.

Acoustic Pulse Recognition: Introduced in 2006, this system uses four piezoelectric transducers located at each side of the screen to turn the mechanical energy of a touch into an electronic signal. This signal is then converted into an audio file, and then compared to preexisting audio profile for every position on the screen. This system works without a grid of wires running through the screen, the touch screen itself is actually pure glass, giving it the optics and durability of the glass it is made of. It works with scratches and dust on the screen, and accuracy is very good. It does not need a conductive object to activate it.

[edit] Development and usage

Virtually all of the significant touchscreen technology patents were filed during the 1970's and 1980's and have expired. Touchscreen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the manufacturing of touchscreen-enabled displays on all kinds of devices is widespread.

With the growing acceptance of many kinds of products with an integral touchscreen interface the marginal cost of touchscreen technology is routinely absorbed into the products that incorporate it and is effectively eliminated. As typically occurs with any technology, touchscreen hardware and software, has sufficiently matured and been perfected over more than three decades to the point where its reliability is unassailable. As such, touchscreen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances and handheld display devices of every kind.

An ergonomic problem of touchscreens is their stress on human fingers when used for more than a few minutes at a time, since significant pressure is required and the screen is non-flexible. The resulting condition is labeled "gorilla arm" because it makes the user feel clumsy. This can be alleviated with the use of a pen or other device to add leverage, but the introduction of such items can sometimes be problematic depending on the desired use case.

[edit] Linearisation

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The raw output of a touch screen is generally not linear. A set of simultaneous equations is normally required to convert the raw data to display coordinates. The linearisation calculations are normally performed in B16 32 bit integer maths. The microwindows nxcal utility performs this.

These are generally of the form:

Yd = A.x + B.Y + C

Xd = D.x + E.y + F

Where Xd and Yd are display coordinates, and x and y are the raw values read from the touch screen.

[edit] See also

[edit] References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

[edit] External links

Acoustic Pulse Recognition - Acoustic Pulse Recognition technology explained.
Howstuffworks - How do touchscreen monitors know where you're touching?
MERL - Mitsubishi Electric Research Lab (MERL)'s research on interaction with touch tables.
Jefferson Y. Han et. al. Multi-Touch Interaction Research. Multi-Input Touchscreen using Frustrated Total Internal Reflection.
Engineeringtalk article discusses the effective use of a strain gauge.
GreenTouchscreen - Touchscreen Software Examples
Full Screen Keyboard for Pocket PC - Example of touchscreen keyboard for Pocket PC.
JazzMutant Lemur Gallery - Videos of a commercial multipoint touchscreen in use.
Multi touch screen - Collection of articles and links on multi touchscreen and many videos of Jeff Han.