TOUCHSCREEN TECHNOLOGY

1. TOUCHSCREEN TECHNOLOGY -nehasingh B.Tech CSE 7th semester 05170102709

2. What is a Touchscreen? • A 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. • Touchscreens are common in devices such as game consoles, all-in-one computers, tablet computers, and smartphones.

3. How Does a Touchscreen Work? A basic touchscreen has three main components: • Touch sensor; • Controller; • 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.

4. 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 can cause a voltage or signal change. This change is used to determine the location of the touch to the screen.

5. Controller • The controller 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 determines what type of interface/connection you will need on the PC. Controllers are available that can connect to a Serial/COM port (PC) or to a USB port. Specialized controllers are also available that work with DVD players and other devices.

6. Software Driver • The driver 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 as 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.

7. Touchscreen Technology • Resistive touchscreen • Capacitive touchscreen • Infrared touchscreen • Surface acoustic wave (SAW) touchscreen • Strain gauge touchscreen • Optical imaging touchscreen • Dispersive signal technology touchscreen

8. A resistive touchscreen panel comprises several layers, the most important of which are two thin, transparent electrically-resistive layers (made with ITO) separated by a thin space. These layers face each other, with a thin gap between. The top screen (the screen that is touched) has a coating on the underside surface of the screen. Just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, the other along top and bottom. Resistive Touchscreen

9. Working:A voltage is applied to one layer, and sensed by the other. When an object, such as a fingertip or stylus tip, presses down on the outer surface, the two layers touch to become connected at that point: The panel then behaves as a pair of voltage dividers, one axis at a time. By rapidly switching between each layer, the position of a pressure on the screen can be read. Resistive Touchscreen

10. Advantages: High resistance to liquids and contaminants, Low cost. Disadvantages: Risk of damage by sharp objects, poorer contrast due to having additional reflections from the extra layer of material placed over the screen. Resistive Touchscreen 4-wire resistive touchscreen

11. In this basic technology, only one side of the insulator is coated with a conductive layer. It consists of a uniform conductive coating on a glass panel. Electrodes around the panel’s edge evenly distribute a low voltage across the conductive layer, creating a uniform electric field. Surface Capacitive Touchscreen

12. Working principle:A human body is an electric conductor, so when you touch the screen with a finger, a slight amount of current is drawn, creating a voltage drop. The current respectively drifts to the electrodes on the four corners. Theoretically, the amount of current that drifts through the four electrodes should be proportional to the distance from the touch point to the four corners. The controller precisely calculates the proportion of the current passed through the four electrodes and figures out the X/Y coordinate of a touch point. Surface Capacitive Touchscreen

13. Projected capacitive touchscreens have front and back protective glass providing optical and strength enhancement options. Its middle layer consists of a laminated sensor grid of micro-fine wires, and optical enhancement options. Projected Capacitive Touchscreen

14. Working: During a touch, capacitance forms between the finger and the sensor grid. The embedded serial controller in the touchscreen calculates touch location coordinates and transmits them to the computer for processing. Projected Capacitive Touchscreen Capacitive Touchscreen Advantages:Superior optical clarity, brighter display and less surface reflection. Capacitive Touchscreen Disadvantages: Must be touched by finger, will not work with any non-conductive input.

15. Infrared (IR) technology relies on the interruption of an IR light grid in front of the display screen. The touch frame contains a row of IR-light emitting diode (LEDs) and photo transistors, each mounted on two opposite sides to create a grid of invisible infrared light. Working: The IR controller sequentially pulses the LEDs to create a grid of IR light beams. When a stylus, such as a finger, enters the grid, it obstructs the beams. One or more photo transistors from each axis detect the absence of light and transmit signals that identifies the x and y coordinates. Infrared Touchscreen

16. Advantages: A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. Clear as glass, improves reading ability. Most durable surface. Disadvantages: Sensitive to dirt/dust that can interfere with the IR beams. Suffer from parallax in curved surfaces and accidental press when the user hovers his/her finger over the screen while searching for the item to be selected. Infrared Touchscreen

17. Principle: Surface waves are readily absorbed when a soft object such as a fingertip touches the substrate. SAW Touch Screenuses pure glass with transmitting and receiving piezoelectric transducers for both the X and Y axes. The touch screen controller sends an electrical signal to the transmitting transducer, which converts the signal into ultrasonic waves within the glass. When you touch the screen, you absorb a portion of the wave traveling across it. The received signal is then compared to the stored digital map, the change recognized, and a coordinate calculate. SAW Touchscreen

18. SAW Touchscreen

19. Advantages: Durable glass construction. High optical clarity. Activated by a finger, gloved hand or soft tip. Disadvantages: Surface wave touchscreen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen. SAW Touchscreen

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