Touch Screen Technology

Dr. S S Verma
Electronic visual displayed has been revolutionized by the use of touch screen technology.  We see these in devices like such as mobiles/smartphones, game consoles, all-in-one computers, tablet computers, Televisions, ATMs, etc. Touch screens are everywhere. Industrial control systems, consumer electronics, and even medical devices are commonly equipped with touch-screen input. We use touch screens every day without even thinking about it. You might get cash at your ATM, sign for a package, check in for your flight, or look up a telephone number all by using a touch screen. A touch screen 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 and can also sense other passive objects. The touch screen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a pointer 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 (other than a stylus, which is optional for most modern touch screens). Touch screens 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.
Touch screens have several advantages over other pointing devices:
*    A touch screen is very intuitive easy to use ( as the user simply touches what he or she sees on the display.
* Save space as no keyboard or mouse is required.
* Touch monitors can even be mounted on the wall.
* Touching a visual display of choices requires little thinking and is a form of direct manipulation that is easy to learn.
*   Touch screens are the fastest pointing devices.
* Touch screens have easier hand eye coordination than mice or keyboards.
* No extra work space is required as with other pointing devices.
* Touch screens are durable in public access and in high volume usage
The first touch screen was a capacitive touch screen developed by E.A. Johnson at the Royal Radar Establishment, Malvern, UK. The inventor briefly described his work in a short article published in 1965 and then more fully – along with photographs and diagrams – in an article published in 1967. A description of the applicability of the touch technology for air traffic control was described in an article published in 1968. Touch screens have subsequently become familiar in everyday life. Companies use touchscreens for kiosk systems in retail and tourist settings, point of sale systems, ATMs, and PDAs, where a stylus is sometimes used to manipulate the graphical user interface (GUI) and to enter data. An early attempt at a handheld game console with touchscreen controls was Sega’s intended successor to the Game Gear. Touchscreens would not be popularly used for video games until the release of the Nintendo DS in 2004. 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.
The popularity of smartphones, tablet computers, portable video game consoles and many types of information appliances is driving the demand and acceptance of common touchscreens, for portable and functional electronics. With a display of a simple smooth surface, and direct interaction without any hardware (keyboard or mouse) between the user and content, fewer accessories are required. Touchscreens are popular 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. 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 touchscreens into the fundamental design of their products.
Types of touch screen
There are three basic systems that are used to recognize a person’s touch:
* Resistive
* Capacitive
* Surface acoustic wave
The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole setup. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse’s movements into a click or a drag.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor’s glass plate. Also placed on the glass are reflectors– they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity). Another area in which the systems differ is in which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn’t matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object — except hard and small objects like a pen tip.

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