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TRANSCRIPT
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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