Maulik Desai 064

8/3/2019 Maulik Desai 064

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Touch Screens 2011

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Introduction

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

display as well as input devices. These are electronic visual devices that are sensitive to

pressure thus detect the presence and location of a touch within the display area. The screens

are sensitive to pressure; a user interacts with the computer by touching pictures or words on the

screen. The term "Touch" generally refers to touch or contact to the display of the device by a

finger or hand. However, if the object sensed is active, as with a light pen, the term touch

screen is generally not applicable. The ability to interact physically with what is shown on a

display (a form of "direct manipulation") typically indicates the presence of a touchscreen.


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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.


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Technologies

Various touchscreen technologies are:-

Infrared

Resistive

Surface acoustic wave

Capacitive

Optical imaging

Dispersive signal technology

Acoustic pulse recognition


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Infrared

In this technology infrared(IR) light-emitting diodes(LEDs) are placed at the

opposite edges [ aks. Bezel edges] to analyze the system and detect the touch event.The

LED and photosensor pairs create a grid of light beams across the display. An object

(such as a finger or pen) that touches the screen interrupts the light beams, causing a

measured decrease in light at the corresponding photosensors. The measured photosensor

outputs can be used to locate a touch-point coordinate.

Widespread adoption of infrared touchscreens has been hampered by two factors: the

relatively high cost of the technology compared to competing touch technologies and the

issue of performance in bright ambient light. This latter problem is a result of background

light increasing the noise floor at the optical sensor, sometimes to such a degree that the

touchscreen's LED light cannot be detected at all, causing a temporary failure of the touch

screen. This is most pronounced in direct sunlight conditions where the sun has a very high

energy distribution in the infrared region.

However, certain features of infrared touch remain desirable and represent attributes

of the ideal touchscreen, including the option to eliminate the glass or plastic overlay that

most other touch technologies require in front of the display.

In many cases, this overlay is coated with an electrically conducting transparent

material such as indium-tin oxide (ITO), which reduces the optical quality of the display. This

advantage of optical touchscreens is extremely important for many device and display

vendors since devices are often sold on the perceived quality of the user display experience.


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Another feature of infrared touch which has been long desired is the digital nature of the

sensor output when compared to many other touch systems that rely on analog-signal

processing to determine a touch position. These competing analog systems normally require

continual re calibration, have a complex signal-processing demand (which adds cost and power

consumption), demonstrate reduced accuracy and precision compared to a digital system, and

have longer-term system-failure modes due to the operating environment.

Resistive

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. 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.


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Resistive touchscreen technology works well with almost any stylus-like object. In

some circumstances, this is more desirable than a capacitive touchscreen, which has to be

operated with a capacitive pointer, such as a bare finger. The costs are relatively low when

compared with active touchscreen technologies.

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. Surface wave touch screen panels can be damaged

by outside elements. Contaminants on the surface can also interfere with the functionality of

the touchscreen.


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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. 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 nomoving parts, it is moderately durable but has limited resolution, 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.

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, perpendicular layers of conductive material with parallel lines or

tracks to form the grid (comparable to the pixel grid found in many LCD displays).


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Mutual capacitance:-

In mutual capacitive sensors, there is a capacitor at every intersection of each row and

each column. A 16-by-14 array, for example, would have 224 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. Mutual capacitance allows multi-touch operation

where multiple fingers, palms or stylus can be accurately tracked at the same time.

Self capacitance:-


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Self-capacitance sensors can have the same X-Y grid as mutual capacitance sensors,

but the columns and rows operate independently. 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.

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 pinpointed to locate the touch or

even measure the size of the touching object (see visual hull). This technology is growing in

popularity, due to its scalability, versatility, and affordability, especially for larger units.


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This technology comes as two, three or four camera solutions, providing dual and

multi-touch functionality. Optical imagingis one of the more modern touch technologies and

has substantial benefits over earlier technologies

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. 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


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fingers and stylus. 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.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.


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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.

Applications of touch screens

Computing

Personal digital assistant

Satellite navigation systems

ATM

Video games


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Microsoft Surface Computing

Microsoft Surface is an interactive table top that can do everything a network

computer can do plus more without using a keyboard or a mouse. There are four key features:

direct interaction, multi-touch ability, multi-user ability, and object recognition. Direct

interaction allows you to touch or grab digital information with your hands and use natural

gestures to open, grasp, and command virtual objects, pages and images. The multi-touch

feature enables the Surface to recognize many points of contact simultaneously so you can

enlarge an image by touching the opposite corners and dragging them outwards. Along with

the multi-touch feature, the shape and design of the Surface allows for multi-users at once,

therefore, the user sitting across from you can be doing something completely different or

independent of you. The last key feature, object recognition, enables the system to identify

physical objects just by setting them on the Surface and to respond by displaying the

appropriate software related to that item.


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Technical Aspects/Features:

These all have the same basic framework using cameras to sense objects, hand gestures, and

touch. The user input is then processed and displayed on the surface using rear projection.The following is a diagram of the Microsoft Surface and an explanation of the parts.

1) Screen: The Surface has an acrylic tabletop which a diffuser makes capable of processing

multiple inputs from multiple users. Objects can also be recognized by their shapes or reading

coded tags.

2) Infrared: Infrared light is projected onto the underside of the diffuser. Objects or fingers

are visible through the diffuser by series of infrared-sensitive cameras which are positioned

underneath the surface of the tabletop.

3) CPUThis is similar to a regular desktop. The underlying operating system is a modified

version of Microsoft Vista.

4) ProjectorThe Surface uses the same DLP light engine in many rear-projection tvs.


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Application:

The following is an example of a possible application using Microsoft Surface:

1. On the left you have your device which has stored your information.

2. On the right you have your friends device which has stored his/her information.

3. In the center its showing how you can pull the information needed from each device

and compile it to complete the final project


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Refernce

http://www.giiresearch.com/report/vd48914-screen-sensors.html

http://www.seminarprojects.com/Thread-touch-screen-technology-report-and-ppt

http://uravitam.blogspot.com/2008/08/seminar-report-touch-screen.html

http://www.microsoft.com/surface/en/us/default.aspx

http://en.wikipedia.org/wiki/Microsoft_Surface
http://www.giiresearch.com/report/vd48914-screen-sensors.htmlhttp://www.seminarprojects.com/Thread-touch-screen-technology-report-and-ppthttp://uravitam.blogspot.com/2008/08/seminar-report-touch-screen.htmlhttp://www.microsoft.com/surface/en/us/default.aspxhttp://en.wikipedia.org/wiki/Microsoft_Surfacehttp://en.wikipedia.org/wiki/Microsoft_Surfacehttp://www.microsoft.com/surface/en/us/default.aspxhttp://uravitam.blogspot.com/2008/08/seminar-report-touch-screen.htmlhttp://www.seminarprojects.com/Thread-touch-screen-technology-report-and-ppthttp://www.giiresearch.com/report/vd48914-screen-sensors.html

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