touch screen technology report and ppt

[seminar project explorer]

Touchscreen
Sudheesh.S & Dino P Ponnachan
Electronics & Communication
Mohandas College of Engineering and Technology

[attachment=10239]

Abstract
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. Although the touchscreen technology
dates back to about forty years ,it has made a revolution in the past five years with its application into
devices that we deal in our day to day life .There are basically three underlying technologies used in
touchscreens ,namely Resitive,,Capacitive and Acoustic. The latest developments in touchscreen
technology are Multitouch and Haptic Touch.

Introduction
A touchscreen is an electronic visual display that can
detect the presence and location of a touch within the
display area. The touchscreen has two main
attributes. First, it enables one to interact directly
with what is displayed, rather than indirectly with a
cursor 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. Such
displays can be attached to computers, or to networks
as terminals. They 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.

History
The prototype x-y mutual capacitance touchscreen
(left) developed at CERN in 1977 by Bent Stumpe, a
Danish electronics engineer, for the control room of
CERN’s accelerator SPS (Super Proton Synchrotron).
In 1971, the first "Touch Sensor" was developed by
Doctor Sam Hurst (founder of Elographics) while he
was an instructor at the University of Kentucky. This
sensor, called the "Elograph," was patented by The
University of Kentucky Research Foundation. The
"Elograph" was not transparent like modern touch
screens; however, it was a significant milestone in
touch screen technology. In 1974, the first true touch
screen incorporating a transparent surface was
developed by Sam Hurst and Elographics. In 1977,
Elographics developed and patented five-wire
resistive technology, the most popular touch screen
technology in use today. Touchscreens first gained
some visibility with the invention of the computer-
assisted learning terminal, which came out in 1975 as
part of the PLATO project.
The Main Components of Touch Screen
Every touch screen has three main components:

digital signal that computer can understand
Touch Sensitive Surface
The touch sensitive surface is an extremely
durable and flexible glass or polymer touch
response surface, and this panel is placed
over the viewable area of the screen. In most
sensors there is an electric signal going
across the screen, and a touch on the surface
causes change in the signal depending on the
touch sensor technology used.This change
allows the controller to identify the location
of the touch.
• The Controller
The controller is a device that acts as the
intermediate between the screen and the
computer. It interprets the electrical signal
of the touch event to. The controller can be
placed with the screen or housed externally.
• The Software Driver
The software driver is an interpreter that
converts what signal comes from the
controller to information that the operating
system can understand.

Technologies
1.Resistive
A resistive touchscreen panel is composed of several
layers, the most important of which are two thin,
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.
2.Capacitive
A capacitive touchscreen panel is one which consists
of an insulator such as glass, coated with a
transparent conductor such as indium tin oxide (ITO).
As the human body is also a conductor, touching the
surface of the screen results in a distortion of the
screen's electrostatic field, measurable as a change in
capacitance. Different technologies may be used to
determine the location of the touch. The location is
then sent to the controller for processing.The
different technologies under capacitive sensing are
Surface capacitance, Projected capacitance, Mutual
Capacitance, Self Capacitance.
3. 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


Other Technologies
An infrared touchscreen uses an array of X-Y
infrared LED and photodetector pairs around the
edges of the screen to detect a disruption in the
pattern of LED beams. These LED beams cross each
other in vertical and horizontal patterns. This helps
the sensors pick up the exact location of the touch. A
major benefit of such a system is that it can detect
essentially any input including a finger, gloved
finger, stylus or pen.Unlike capacitive
touchscreenspatterning on the glass which increases
durability and optical clarity of the overall system.

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 triangulated to locate the
touch or even measure the size of the touching
object . This technology is growing in popularity, due
to its scalability, versatility, and affordability,
especially for larger units.
Dispersive signal technology
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 fingers and stylus. A downside is
that after the initial touch the system cannot detect a
motionless finger.
Acoustic pulse recognition
This system 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. 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.

Refernces
• Shneiderman, B. (1991). "Touch screens
now offer compelling uses". IEEE Software
8 (2): 93–94, 107.
• Potter, R.; Weldon, L. & Shneiderman, B.
(1988). Improving the accuracy of touch
screen: An experimental evaluation of three
strategies. Proc. CHI'88. Washington, DC:
ACM Press. pp. 27–32.
• Sears, A.; Plaisant, C. & Shneiderman, B.
(1992). "A new era for high precision
touchscreens". In Hartson, R. & Hix, D..
Advances in Human-Computer Interaction.
3. Ablex, NJ. pp. 1–33 .
• http://en.wikipediawiki/Touchscreen"C
ategories: Touchscreens | Computer
hardware
• Howstuffworks - How do touchscreen
monitors know where you're touching?
.
• MERL - Mitsubishi Electric Research Lab
(MERL)'s research on interaction with touch
tables. .
• Jefferson Y. Han et al. Multi-Touch
Interaction Research. Multi-Input
Touchscreen using Frustrated Total Internal
Reflection