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Touch Screen
Posted Date: 16 May 2008 Resource Type: Articles/Knowledge Sharing Category: Computer & Technology
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Posted By: Shanthi M Member Level: Diamond
Rating:  Points: 1
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Touch Screen
A Touch screen is a computer display screen that is sensitive to human touch, allowing a user to interact with the computer by touching pictures or words on the screen. Touch screens are used with information computer-based training devices, and systems designed to help individuals who have difficulty manipulating a mouse or keyboard. This allows the 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. Touch screens also have assisted in recent changes in the design of personal digital assistant (PDA), satellite navigation and mobile phone devices, making these devices more usable.
FEATURES OF TOUCHSCREEN
• Touchscreen requires special software to operate mouse and keyboard.
• The touchscreen is an input device like a mouse or track pad, and it emulates basic mouse functions. The touchscreen can emulate left-clicks, double-clicking, and dragging. When the screen is touched, it is the same as if you used your mouse to move the pointer to that spot, and then clicked your mouse button. Right-clicking can be done with additional software.
• Touch screen generally interfaces to the PC via a serial port (RS-232) connection or a USB type connection.
• We can use mouse and keyboard simultaneously along with a touchscreen since touch screen will work along with a USB, or serial connection.
• We can use finger or another pointing device depends on the type of touchscreen.
• Resistive touchscreens are pressure sensitive and will work with any type of input- finger, gloved hand, stylus, pen, or any pointing device.
• Capacitive screens will only work with finger input.
• SAW (surface acoustic wave) touch screens will work with finger input or soft-tipped stylus input. With SAW technology, a hard tipped pen will not create a touch response, but a soft-tip stylus will work.
• We can use a touch screen to browse Web site.
• We can design custom programs and applications to work with the touchscreen because the screen emulates standard mouse functions.
• Any standard glass cleaner (non-ammonia based) can be used to clean the touchscreen. Always spray the glass cleaner on the cloth or towel and then clean the touchscreen.
• When designing a touchscreen application, remember the finger is larger than a mouse pointer. Design buttons large enough and spaced apart enough for a finger to touch easily. It is also a good idea to include a graphical or audio response to each touch.
• Although most notebooks do not have space for a touch screen to be built into it, several laptops that can be purchased with built-in touchscreen interface. An external touch screen is available that will add touch input capability to any laptop system with a 12" to 14.1" display.
COMPONENTS OF TOUCHSCREEN
A basic touchscreen has three main components: a touch sensor, a controller, and a software driver. The touchscreen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.
1. Touch Sensor
A touch screen sensor is a clear glass panel with a touch responsive surface. The touch sensor/panel is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen. There are several different touch sensor technologies on the market today, each using a different method to detect touch input. The sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. This voltage change is used to determine the location of the touch to the screen.
2. Controller
The controller is a small PC card that connects between the touch sensor and the PC. It takes information from the touch sensor and translates it into information that PC can understand. The controller is usually installed inside the monitor for integrated monitors or it is housed in a plastic case for external touch add-ons/overlays.
The controller determines what type of interface/connection you will need on the PC. Integrated touch monitors will have an extra cable connection on the back for the touchscreen. Controllers are available that can connect to a Serial/COM port (PC) or to a USB port (PC or Macintosh). Specialized controllers are also available that work with DVD players and other devices.
3. Software Driver
The driver is a software update for the PC system that allows the touchscreen and computer to work together. It tells the computer's operating system how to interpret the touch event information that is sent from the controller. Most touch screen drivers today are a mouse-emulation type driver. This makes touching the screen the same as clicking your mouse at the same location on the screen.
This allows the touchscreen to work with existing software and allows new applications to be developed without the need for touchscreen specific programming. Some equipment such as thin client terminals, DVD players, and specialized computer systems either do not use software drivers or they have their own built-in touch screen driver.
TYPES OF TOUCHSCREEN
There are a number of types of touch screen technology:
1. Resistive
A resistive touch screen panel is composed of several layers. The most important are two thin metallic electrically conductive and resistive layers separated by thin space.
When some object touches this kind of touch panel, the layers are connected at certain point; the panel then electrically acts similar to two 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. When measuring press force, it is useful to add resistor dependent on force in this model -- between the dividers.
A resistive touch panel output can consist of between four and eight wires. The positions of the conductive contacts in resistive layers differ depending on how many wires are used. When four wires are used, the contacts are placed on the left, right, top, and bottom sides. When five wires are used, the contacts are placed in the corners and on one plate.
4 wire 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.
2. Surface acoustic wave
Surface Acoustic Wave (SAW) 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.
3. 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 can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive touch screens are not affected by outside elements and have high clarity.
4. Infrared
An infrared touch screen panel employs one of two very different methods. 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.
5. 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. Typically used in exposed public systems such as ticket machines due to their resistance to vandalism.
6. Optical imaging
A relatively-modern development in touch screen technology, two or more image sensors are placed around the edges (mostly 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.
7. 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 styli. A downside is that after the initial touch the system cannot detect a motionless finger.
8. Acoustic pulse recognition
This system uses more than two piezoelectric transducers located at some positions of the screen to turn the mechanical energy of a touch (vibration) 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 out of which it is made. It works with scratches and dust on the screen, and accuracy is very good. It does not need a conductive object to activate it. It is a major advantage for larger displays. As with the Dispersive Signal Technology system, after the initial touch this system cannot detect a motionless finger.
9. Frustrated total internal reflection
This optical system works by using the principle of total internal reflection to fill a refractive medium with light. When a finger or other soft object is pressed against the surface, the internal reflection light path is interrupted, making the light reflect outside of the medium and thus visible to a camera behind the medium.
OPERATION OF TOUCHSCREEN
A touch screen kit includes a touch screen panel, a controller, and a software driver. The touch screen panel is a clear panel attached externally to the monitor that plugs into a serial or Universal Serial Bus (USB) port or a bus card installed inside the computer.
The touch screen panel registers touch events and passes these signals to the controller. The controller then processes the signals and sends the data to the processor.
The software driver translates touch events into mouse events. Drivers can be provided for both Windows and Macintosh operating systems. Internal touch screen kits are available but require professional installation because they must be installed inside the monitor.
PRODUCTS OF TOUCHSCREEN
There are two main types of touchscreen products:
• Touchscreen add-ons
• Integrated touchscreen monitors
Touchscreen add-ons are touchscreen panels that hang over an existing computer monitor. Integrated touchscreen monitors are computer displays that have the touchscreen built-in. Both product types work in the same way, basically as an input device like a mouse or trackpad.
APPLICATIONS OF TOUCHSCREEN
The touch screen is one of the easiest PC interfaces to use, making it the interface of choice for a wide variety of applications. Here are a few examples of how touch input systems are being used today:
• Public Information Displays
• Retail and Restaurant Systems
• Customer Self-Service
• Control and Automation Systems
• Computer Based Training
• Assistive Technology
LATEST TRENDS IN TOUCHSCREEN
The present invention is to provide a touch screen having a bacteria inhibition layer for prohibiting bacteria from growing thereon .
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