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25 novembre 2010 4 25 /11 /novembre /2010 02:29

touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus       (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk/ .

The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a cursor controlled by a mouse or touchpad. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand. Such displays can be attached to computers, or to networks as terminals    (Dell Studio XPS 1340 Battery)      .

They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices, mobile phones, and video games      (Dell Studio XPS 1640 Battery)       .


The prototype x-y mutual capacitance touchscreen (left) developed at CERN in 1977 by Bent Stumpe, a Danish electronics engineer, for the control room of CERN’s accelerator SPS (Super Proton Synchrotron). This was a further development of the self capacitance screen(right), also developed at CERN in 1972        (Dell Vostro 1710 Battery)      .

In 1971, the first "touch sensor" was developed by Doctor Sam Hurst (founder of Elographics) while he was an instructor at the University of Kentucky. This sensor, called the "Elograph," was patented by The University of Kentucky Research Foundation. The "Elograph" was not transparent like modern touch screens; however, it was a significant milestone in touch screen technology    (Sony VGP-BPS13 battery)     .

In 1974, the first true touch screen incorporating a transparent surface was developed by Sam Hurst and Elographics. In 1977, Elographics developed and patented five-wire resistive technology, the most popular touch screen technology in use today  (Sony VGP-BPS13/B battery)    .

Touchscreens first gained some visibility with the invention of the computer-assisted learning terminal, which came out in 1975 as part of the PLATO project. Touchscreens have subsequently become familiar in everyday life. Companies use touch screens for kiosk systems in retail and tourist settings, point of sale systems        (Sony VGP-BPS13/S battery)      ,

ATMs, and 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 acceptance of, touchscreens  (Sony VGP-BPS13A/B battery)          .

From 1979–1985, the Fairlight CMI (and Fairlight CMI IIx) was a high-end musical sampling and re-synthesis workstation that utilized light pen technology, with which the user could allocate and manipulate sample and synthesis data, as well as access different menus within its OS by touching the screen with the light pen        (Sony VGP-BPS13B/B battery)       .

The later Fairlight series III models used a graphics tablet in place of the light pen.

The HP-150 from 1983 was one of the world's earliest commercial touchscreen computer. It did not have a touchscreen in the strict sense; instead, it had a 9"Sony Cathode Ray Tube (CRT) surrounded by infrared transmitters and receivers, which detected the position of any non-transparent object on the screen     (Sony VGP-BPS13B/B battery)      .

Until recently, most consumer touchscreens could only sense one point of contact at a time, and few have had the capability to sense how hard one is touching. This is starting to change with the commercialization of multi-touch technology         (Sony VGP-BPL9 battery)          .

Touchscreens are popular in hospitality, and in heavy industry, as well as kiosks such as museum displays or room automation, where keyboard and mouse systems do not allow a suitably 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  (Sony VGP-BPL11 battery)     .

Display manufacturers and chip 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     (Sony VGP-BPL15 battery)      .


There are a variety of touchscreen technologies.


A resistive touchscreen panel is composed of several layers, the most important of which are two thin, metallic, electrically conductive layers separated by a narrow gap          (Dell Inspiron E1505 battery)        .

When an object, such as a finger, presses down on a point on the panel's outer surface the two metallic layers become connected at that point: the panel then behaves as a pair of voltage dividers with connected outputs. This causes a change in the electrical current, which is registered as a touch event and sent to the controller for processing     (Dell Latitude E6400 battery)        .

Surface acoustic wave

Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touchscreen 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      (HP Pavilion dv6000 Battery)        .

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 touchscreen of a mobile phone      (Sony Vaio VGN-FZ31S battery)

A capacitive touchscreen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide (ITO). As the human body is also a conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance       (Sony VGN-FZ31S battery)          .

Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing.

Surface capacitance

In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field      (Hp pavilion dv6000 battery)      .

When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution          (SONY VGN-FZ38M Battery)       ,

is prone to false signals from parasitic capacitive coupling, and needs calibration during manufacture. It is therefore most often used in simple applications such as industrial controls and kiosks       (SONY VGN-FZ31z Battery)     .

Projected capacitance

Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation, by etching the conductive layer     .

An X-Y grid is formed either by etching a single layer to form a grid pattern of electrodes , or by etching two separate    (Sony VGN-FZ31Z Battery)   ,

perpendicular layers of conductive material with parallel lines or tracks to form the grid (comparable to the pixel grid found in many LCD displays).

The greater resolution of PCT allows operation without direct contact, such that the conducting layers can be coated with further protective insulating layers, and operate even under screen protectors, or behind weather and vandal-proof glass    (SONY VGN-FZ31E Battery)     .

Due to the top layer of a PCT being glass, PCT is a more robust solution versus resistive touch technology. Depending on the implementation, an active or passive stylus can be used instead of or in addition to a finger. This is common with point of sale devices that require signature capture        (SONY  VGN-FZ31J Battery)       .

Gloved fingers may or may not be sensed, depending on the implementation and gain settings. Conductive smudges and the like on the panel surface can interfere with the performance. Such conductive smudges come mostly from sticky or sweaty finger tips, especially in high humidity environments       (SONY VGN-FZ31M Battery)       .

Collected dust, which adheres to the screen due to the moisture from fingertips can also be a problem. There are two types of PCT: Self Capacitance and Mutual Capacitance.

Mutual Capacitance

In mutual capacitive sensors, there is a capacitor at every intersection of each row and each column        (SONY VGN-FZ31B Battery) .

A 12-by-16 array, for example, would have 192 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field which reduces the mutual capacitance. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis        (SONY VGP-BPS13 Battery)        .

Mutual capacitance allows multi-touch operation where multiple fingers, palms or stylus can be accurately tracked at the same time.

Self Capacitance

Self capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently    (Dell Inspiron 1320 Battery)        .

With self capacitance, the capacitive load of a finger is measured on each column or row electrode by a current meter. This method produces a stronger signal than mutual capacitance, but it is unable to resolve accurately more than one finger, which results in "ghosting", or misplaced location sensing    (Dell Inspiron 1320n Battery)         .


An infrared touchscreen uses an array of X-Y infrared LED and photodetector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch       (Dell Inspiron 1464 Battery)      .

A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. It is generally used in outdoor applications and point-of-sale systems which can't rely on a conductor (such as a bare finger) to activate the touchscreen   (Dell Inspiron 1564 Battery)         .

Unlike capacitive touchscreens, infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system.

Strain gauge

In a strain gauge configuration, also called force panel technology, the screen is spring-mounted on the four corners and strain gauges are used to determine deflection when the screen is touched       (Dell Inspiron 1764 Battery)  .

This technology has been around since the 1960s, but new advances by Vissumo and F-Origin have made the solution commercially viable. It can also measure the Z-axis and the force of a person's touch. Such screens are typically used in exposed public systems such as ticket machines due to their resistance to vandalism    (Dell Studio 1450 Battery)    .

Optical imaging

This is a relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch or even measure the size of the touching object (see visual hull)      (Dell Studio 1457 Battery)         .

This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.

Dispersive signal technology

Introduced in 2002 by 3M, this system uses sensors to detect the mechanical energy in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch   (Dell Latitude D610 Battery)         .

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 stylus     (Toshiba NB100 Battery)          .

A downside is that after the initial touch the system cannot detect a motionless finger.

Acoustic pulse recognition

This system, introduced by Tyco International's Elo division in 2006, uses piezoelectric transducers located at various positions around the screen to turn the mechanical energy of a touch (vibration) into an electronic signal       (Toshiba Satellite M65 battery)   .

The screen hardware then uses an algorithm to determine the location of the touch based on the transducer signals. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy     (Toshiba Satellite M60 battery)      .

The technology is also well suited to displays that are physically larger. As with the Dispersive Signal Technology system, after the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects       (Dell Latitude D830 Battery)      .


There are several principal ways to build a touchscreen. The key goals are to recognize one or more fingers touching a display, to interpret the command that this represents, and to communicate the command to the appropriate application.

In the most popular techniques, the capacitive or resistive approach, there are typically four layers     (Dell Studio 1735 Battery)  ;

  1. Top polyester layer coated with a transparent metallic conductive coating on the bottom
  2. Adhesive spacer
  3. Glass layer coated with a transparent metallic conductive coating on the top
  4. Adhesive layer on the backside of the glass for mounting      (Dell Latitude D620 Battery)         .

When a user touches the surface, the system records the change in the electrical current that flows through the display.

Dispersive-signal technology which 3M created in 2002, measures the piezoelectric effect — the voltage generated when mechanical force is applied to a material — that occurs chemically when a strengthened glass substrate is touched     (Dell Inspiron Mini 10 Battery)     .

There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting light beams projected over the screen. In the other, bottom-mounted infrared cameras record screen touches.In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch      (Sony VGN-FW11S Battery)        .


Virtually all of the significant touchscreen technology patents were filed during the 1970s and 1980s 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     (Sony VGN-FW11M Battery)       .

The development of multipoint touchscreens facilitated the tracking of more than one finger on the screen, thus operations that require more than one finger are possible. These devices also allow multiple users to interact with the touchscreen simultaneously   (Dell Studio 1555 battery)    .

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    (Dell Latitude E5400 Battery)     ,

touchscreen hardware and software has sufficiently matured and been perfected over more than three decades to the point where its reliability is proven. As such, touchscreen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances, and handheld display devices of every kind     (Dell Latitude E4200 Battery)       .

With the influence of the multi-touch enabled iPhone, the touchscreen market for mobile devices is projected to produce US$5 billion in 2009.

The ability to accurately point on the screen itself is also advancing with the emerging graphics tablet/screen hybrids   (Dell Vostro A840 Battery)     .

Ergonomics and usage

Finger stress

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 can be required for certain types of touchscreen      (Dell Inspiron 300M Battery)           .

As the touch screen craze continues to grow society is experiencing a lot more finger stress . This can be alleviated for some users with the use of a pen or other device to add leverage and more accurate pointing. The introduction of such items can sometimes be problematic, depending on the desired use (e.g., public kiosks such as A.T.M.s)       (Dell Studio 1737 battery)       .

Also, fine motor control is better achieved with a stylus, because a finger is a rather broad and ambiguous point of contact with the screen itself.

Fingernail as stylus

Pointed nail for easier typing. The concept of using a fingernail trimmed to form a point, to be specifically used as a styluson a writing tablet for communication, appeared in the 1950 science fiction short story Scanners Live in Vain    (Dell Inspiron E1505 battery)      .

These ergonomic issues of direct touch can be bypassed by using a different technique, provided that the user's fingernails are either short or sufficiently long. Rather than pressing with the soft skin of an outstretched fingertip, the finger is curled over, so that the tip of a fingernail can be used instead       (Dell Latitude E6400 battery)      .

The thumb is optionally used to provide support for the finger or for a long fingernail, from underneath. This method does not work on capacitive touch screens.

The fingernail's hard, curved surface contacts the touchscreen at one very small point      (Dell RM791 battery)         .

Therefore, much less finger pressure is needed, much greater precision is possible (approaching that of a stylus, with a little experience), much less skin oil is smeared onto the screen, and the fingernail can be silently moved across the screen with very little resistance , allowing for selecting text, moving windows, or drawing lines      (Dell XPS M2010 battery)     .

The human fingernail consists of keratin which has a hardness and smoothness similar to the tip of a stylus (and so will not typically scratch a touchscreen). Alternately, very short stylus tips are available, which slip right onto the end of a finger; this increases visibility of the contact point with the screen    (Dell XPS M1530 battery)      .


Touchscreens can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coatings designed to reduce the visible effects of fingerprint oils, such as the oleophobic coating used in the iPhone 3G S, or by reducing skin contact by using a fingernail or stylus    (Dell Vostro 1000 battery)        .

Combined with haptics

The user experience with touchscreens without tactile feedback or haptics can be difficult due to latency or other factors. Research from the University of Glasgow Scotland [Brewster, Chohan, and Brown 2007] demonstrates that sample users reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%) when touchscreens are combined with haptics or tactile feedback,   (Acer Aspire One battery)          .

Gorilla arm

The Jargon File dictionary of hacker slang defined Gorilla Arm as the failure to understand the ergonomics of vertically mounted touch screens for prolonged use. The proposition is that human arm held in an unsupported horizontal position rapidly becomes fatigued and painful, the so-called "gorilla arm"      (Toshiba Satellite P10 Battery)     .

It is often cited as a prima facie example of what not to do in ergonomics. Vertical touchscreens still dominate in applications such as ATMs and data kiosks in which the usage is too brief to be an ergonomic problem.

Discomfort might be caused by previous poor posture and atrophied muscular systems caused by limited physical exercise    (SONY VGN-FZ210CE Battery)   .

Fine Art Painters are also often subject to neck and shoulder pains due to their posture and the repetitiveness of their movements while painting.

Mobile Devices With Touch Displays

Some mobile devices [cell phones, handheld game devices] are Apple iPhone      (Dell Precision M70 Battery)       ,

Apple iPod Touch, Google Android OS Powered Phones, Palm WebOS devices, some of LG [with Verizon stock OS] phones have a touch screen [some of the most popular are the LG enV Touch, LG Dare, LG Voyager], Apple iPod Nano, Apple iPad, UMPCs, and many more       (Toshiba Satellite L305 Battery)      .


touchpad (also trackpad) is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce     (Toshiba Satellite T4900 Battery)     .

Touchpads vary in size but are rarely made larger than 40 square centimeters (6.3 x 6.3 cm or about 6 inch²). They can also be found on personal digital assistants (PDAs) and some portable media players, such as the iPod using the click wheel.

A touchpad is perhaps the most common kind of tactile sensor     (Toshiba PA3399U-2BRS battery)        .

Operation and function

Touchpads operate in one of several ways, including capacitive sensing and conductance sensing. The most common technology used as of 2010 entails sensing the capacitative virtual ground effect of a finger, or the capacitance between sensors   (Toshiba Satellite A200 Battery)         .

Capacitance-based touchpads will not sense the tip of a pencil or other similar implement. Gloved fingers may also be problematic.

If the computer is powered by an external power supply unit (PSU), the detailed construction of the PSU will influence the virtual ground effect     (Toshiba Satellite 1200 Battery)        ;

a touchpad may work properly with one PSU but be jerky or malfunction with another (this does not imply any electrical risk whatsoever, a delicate capacitative ground, not a contact ground, is at issue). This has been known to cause touchpad problems when a manufacturer's PSU, which will have been designed to work with the touchpad, is replaced by a different type   (Toshiba Satellite M300 Battery)       .

This effect can be checked by touching a metallic part of the computer with the other hand and seeing if operation is restored. In some cases touching the (insulated) power supply with some part of the body, or using the computer on the lap instead of on a desk, while working can restore correct operation    (Dell Latitude XT2 Tablet PC Battery)      .

While touchpads, like touchscreens, by their design are able to sense absolute position, resolution is limited by their size. For common use as a pointer device, the dragging motion of a finger is translated into a finer, relative motion of the cursor on the screen, analogous to the handling of a mouse that is lifted and put back on a surface     (Toshiba Portege 335CT Battery)        .

Hardware buttons equivalent to a standard mouse's left and right buttons are below, above or, to reduce the depth of the pad in compact devices such as netbooks, beside the pad.

On some touchpads and associated device driver software tapping the pad may be interpreted as a click, and a tap followed by a continuous pointing motion (a "click-and-a-half") can be used for dragging         (Dell Vostro A90 Battery)       .

Touchpad drivers can also allow the use of multiple fingers to facilitate the other mouse buttons (commonly two-finger tapping for the center button).

Some touchpads have "hotspots", locations on the touchpad used for functionality beyond a mouse     (Toshiba Satellite P15  Battery) .

For example, on certain touchpads, moving the finger along an edge of the touch pad will act as a scroll wheel, controlling the scrollbar and scrolling the window that has the focus vertically or horizontally. Apple uses two-finger dragging for scrolling on their trackpads      (Toshiba Satellite Pro M10 Battery)      .

Also, some touchpad drivers support tap zones, regions where a tap will execute a function, for example, pausing the media player or launching an application. All of these functions are implemented in the touchpad device driver software, and can be disabled.

Edge motion

Edge motion is a property of a notebook computer's touchpad which lets the user scroll the computer screen without having to move the pointer to ascrollbar      (Toshiba Portege 3110 Battery)          .

Moving the finger along an edge of the touch pad acts as a scroll wheel, scrolling the window that has the focus vertically or horizontally depending on which edge is stroked.

When the scrolling operation is complete, the cursor returns to its original position. This saves the labor of (1) moving the cursor to the scrollbar and (2) moving it back to where it was        (Toshiba Portege R600 Battery)   .

Touchpads in devices

Early Apollo desktop computers were equipped with a touchpad on the right side of the keyboard.

Touchpads are primarily used in self-contained portable laptop computers and do not require a flat surface near the machine  (Toshiba Satellite 1900 Battery)      .

The touchpad is close to the keyboard, and only very short finger movements are required to move the cursor across the display screen; while advantageous, this also makes it possible for a user's thumb to move the mouse cursor accidentally while typing. Touchpad functionality is available for desktop computers in keyboards with built-in touchpads    (Toshiba Portege R200 Battery) .

One-dimensional touchpads are the primary control interface for menu navigation on the currently produced iPod Classic portable music player, where they are referred to as "click wheels" since they only sense motion along one axis which is wrapped around like a wheel      (SONY VAIO VGN-FZ21m Battery)       .

Creative Labs also uses a touchpad for their Zen line of MP3 players, beginning with the Zen Touch. The second-generationMicrosoft Zune product line (the Zune 80/120 and Zune 4/8) uses touch for the Zune Pad.

Apple's PowerBook 500 series was the first laptop to carry such a device, which Apple refers to as a "trackpad"    (SONY VAIO VGN-FZ18m Battery)       .

When introduced in May 1994 it replaced the trackball of previous PowerBook models. Apple's more recent laptops feature trackpads that can sense up to five fingers simultaneously, providing more options for input, such as the ability to bring up the context menu by tapping two fingers    (Dell Vostro A90 Battery)      .

In late 2008 Apple's revisions of the MacBook and MacBook Pro have a different touchpad design with the button incorporated into the tracking surface.

Psion PLC's Psion MC 200/400/600/WORD Series, introduced in 1989        (Dell Vostro A860 Battery)       ,

came with a new mouse-replacing input device similar to a touchpad, although more closely resembling a graphics tablet, as the cursor was positioned by clicking on a specific point on the pad, instead of moving it in the direction of a stroke.

Theory of operation

There are two principal means by which touchpads work          (Dell Vostro 2510 Battery)          .

In the matrix approach, a series of conductors are arranged in an array of parallel lines in two layers, separated by an insulator and crossing each other at right angles to form a grid. A high frequency signal is applied sequentially between pairs in this two-dimensional grid array. The current that passes between the nodes is proportional to the capacitance      (Dell Vostro 1700 Battery) .

When a virtual ground, such as a finger, is placed over one of the intersections between the conductive layer some of the electrical field is shunted to this ground point, resulting in a change in the apparent capacitance at that location. This method received U.S. Patent 5,305,017 awarded to George Gerpheide in April 1994      (Dell Vostro 1400 Battery)        .

The capacitive shunt method, described in an application note by Analog Devices, senses the change in capacitance between a transmitter and receiver that are on opposite sides of the sensor. The transmitter creates an electric field which oscillates at 200-300 kHz        (Dell Vostro 1510 Battery)    .

If a ground point, such as the finger, is placed between the transmitter and receiver, some of the field lines are shunted away, decreasing the apparent capacitance     (HP Pavilion DV7 Battery)         .

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