Touch screen report

Working of Touchscreen Amit Bhardwaj

Contents

Introduction……………………………………………………………………………..2

1.1 Four-Wire Resistive: ........................................................................................................ 7

1.2 Eight-Wire Variation: .......................................................................................... 8

1.3 Six- and Seven-Wire Variations: ......................................................................... 9

About Touch Screen Displays:.............................................................................................. 14

Pros and Cons of Touch screens: .......................................................................................... 18

Touch screen Cons: ................................................................................................................ 18

Advantages and Disadvantages:……………………………………………………………19

Hand movements (if used with keyboard):.......................................................................... 18

Size: ................................................................................................................................. 23

Sequential Input:............................................................................................................ 23

Feedback: ........................................................................................................................ 23

Drag Operations: ........................................................................................................... 23

Reference:……………………………………………………………………………………26

1


INTRODUCTION:

A touch screen is 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 screen are
used with information kiosks (an interactive computer terminal available for public use, as
one with internet access or site specific information), computer based training devices, and
system designed to help individuals who have difficulty in manipulating a mouse or
keyboard.Touch screen technology can be used as an alternative user interface with
application that normally requires a mouse, such as a web browser. Some applications are
designed specifically for touch screen technology, often having larger icon and link than
typical PC application. Monitors are available with built in touch screen kit. A touch screen
kit includes a touch screen panel, a controller, and a software driver. The touch screen panels
are is a clear panel attached externally to the monitors that plug in to a serial or a universal
serial Bus (USB) port a bus Card installed inside the computer. The touch screen panel
registers touch event and passes these signal to controller.The controller then processes the
signals and sends the data to the processor. The software driver translates the touch events
into mouse events. Driver can be provided for both Window and Macintosh operating
systems.Internal touch screen kits are available but require professional installation because
the must be installed inside the monitors.

Fig 1.1

2


HISTORY OF TOUCH SCREEN MONITORS:

Dr. Sam Hurst, founder of Elo-graphics, developed the first ―touch screen‖while he was an
instructor at the university of Kentucky in 1971.

Ten stockholders founded Elo-graphics, Inc. in March 1971, to produce Graphical data
Digitizers for use in research and industrial application, with the, principal being Dr. Sam
Hurst. He was on leave from the Oak Ridge National Laboratory to tech at the University of
Kentucky for two years, where he was faced with a need to read a huge stack of strip chart
data. It would have taken two graduate student s approximately two month to do the task. He
started to thinking of a way to read the and during the process, the ―Elo-graph‖ (Electronic
graphics) coordinate measuring system and Elo-graphics the company were born. The
University Kentucky research foundation applied for and was granted a patent on the Elo-
graph. The foundation granted an exclusive license to Elo-graphics.

The touch screen is one of the easiest to use and most intuitive of all PC interface of choices
fro a wide variety of applications. A touch interface to allows users to navigate a computer
system by touching icon or links on the screen.

WHY TOUCH SCREEN:

User interface PCs are quickly becoming the control device of choices for the plant floor,
machine control and any application where the user interface is important. This change has
not been without its difficulties. One challenge industrial PC manufacturers have faced is
simplifying the human machine interface while maintaining accuracy of input. Industrial
grade touches Screen system have quickly become the input device of choice for several
reasons. Touch systems generally have no additional hardware to mount and protect, such as
a mouse or keyboard. A flat panel display can also be sealed by the factory to prevent damage
from dust and water. The ultra thin nature of a touch screen on a LCD saves critical space,
which is a vital for most application.

Durability is tested to over 35 million finger touches with no over performance degradation.1
million-touch life max.

3


Design Flexibility: -

Advanced design allows flat and spherical design.

Touch screen are very intuitive; it is natural for people to respond to their environment by
touching. Touch screen are usually manipulated with ease and require minimal
instrumentation training for a user. Best of all, touch screens draw an operator ―into‖ the
application, improving accuracy attention span and speed of response. Although the touch
screen system for the rigors of everyday life, for rugged environments and the best solution
for your application.

Touch screen Characteristics:

Speed: high
Accuracy: low (finger), high (pen)
Speed control: yes

Continuous movement: yes

Directness: direction, distance, speed

Fatigue: high

Footprint: no

Best uses: point, select

4


The touch screen can be operated by two ways:

.1.Finger-Operated: 2.Stylus operated:

Fig 4.1 fig 4.2

Types of Touch Screen Technologies:

1. Resistive Touch Screen

2. Capacitive Touch Screen

3. Surface Acoustic Wave Touch Screen

4. Infrared Touch Screen

1. 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.

5


fig 5.1

All types of resistive touch screens:

Resistive touch screens are used in more applications than any other touch technology– for
example, PDAs, point-of-sale, industrial, medical, and office automation, as well as
consumer electronics.

All variations of resistive touch screens have some things in common:

fig 5.1.1

They are all constructed similarly in layers-a back layer such as glass with a uniform resistive
coating plus a polyester coversheet, with the layers separated by tiny insulating dots. When
the screen is touched, it pushes the conductive coating on the coversheet against the coating
on the glass, making electrical contact. The voltages produced are the analog representation
of the position touched. An electronic controller converts these voltages into digital X and Y
coordinates which are then transmitted to the host computer.Because resistive touch screens
are force activated, all kinds of touch input devices can activate the screen, including fingers,
fingernails, styluses, gloved hands, and credit cards. All have similar optical properties,
resistance to chemicals and abuse.

6


fig 5.1.2

Both the touch screen and its electronics are simple to integrate into imbedded systems,
thereby providing one of the most practical and cost-effective touchscreen solutions.

1.1 Four-Wire Resistive:

Four-wire resistive technology is the simplest to understand and manufacture.It uses both the
upper and lower layers in the touchscreen "sandwich" to determine the X and Y coordinates.
Typically constructed with uniform resistive coatings of indium tin oxide (ITO on the inner
sides of the layers and silver buss bars along the edges, the combination sets up lines of equal
potential in both X and Y.In the illustration below, the controller first applies 5V to the back
layer. Upon touch, it probes the analog voltage with the coversheet, reading 2.5V, which
represents a left-right position or X axis.It then flips the process, applying 5V to the
coversheet, and probes from the back layer to calculate an up-down position or Y axis. At any
time, only three of the four wires are in use (5V, ground, probe).

fig 5.1.3

The primary drawback of four-wire technology is that one coordinate axis (usually the Y
axis), uses the outer layer, the flexible coversheet, as a uniform voltage gradient. The constant
flexing that occurs on the outer coversheet with use will eventually cause microscopic cracks
in the ITO coating, changing its electrical characteristics (resistance), degrading the linearity
and accuracy of this axis.Unsurprisingly, four-wire touchscreens are not known for their

7


durability. Typically, they test only to about 1 million touches with a finger-far less when
activated by a pointed stylus which speeds the degradation process. Some four-wire products
even specify 100,000 activations within a rather large, 20 mm x 20 mm area. In the real world
of point-of-sale applications, a level of 100,000 activations with hard, pointed styluses
(including fingernails, credit cards, ballpoint pens, etc.) is considered normal usage in just a
few months' time.Also, accuracy can drift with environmental changes. The polyester
coversheet expands and contracts with temperature and humidity changes, thereby causing
long-term degradation to the coatings as well as drift in the touch location.While all of these
drawbacks can be insignificant in smaller sizes, they become increasingly apparent the larger
the touch screen. Therefore, Elo normally recommends four-wire touch screens in
applications with a display size of 6.4" or smaller. However, the relative low cost, inherent
low power consumption, and common availability of chipset controllers with support from
imbedded operating systems, makes four-wire touch screens ideal for hand-held devices such
as PDAs, wearable computers, and many consumer devices.

1.2 Eight-Wire Variation:

Eight-wire resistive touchscreens are a variation of four-wire construction. The primary
difference is the addition of four sensing points, which are used to stabilize the system and
reduce the drift caused by environmental changes. Eight-wire systems are usually seen in
sizes of 10.4" or larger where the drift can be significant.As in four-wire technology, the
major drawback is that one coordinate axis uses the outer, flexible coversheet as a uniform
voltage gradient, while the inner or bottom layer acts as the voltage probe. The constant
flexing that occurs on the outer coversheet will change its resistance with usage, degrading
the linearity and accuracy of this axis.Although the added four sensing points helps stabilize
the system against drift, they do not improve the durability or life expectancy of the screen.

8


1.3 Five-Wire Resistive:

fig 5.1.4

As we have seen, four- and eight-wire touchscreens, while having a simple and elegant
design, have a major drawback in terms of durability in that the flexing coversheet is used to
determine one of the axes. Field usage proves that the other axis rarely fails. Could it be
possible to construct a touch screen where all the position sensing was on the stable glass
layer? Then the coversheet would serve only as a voltage probe for X and Y. Microscopic
cracks in the coversheet coating might still occur, but they would no longer cause non-
linearity’s. The simple buss bar design is not sufficient and a more complex linearization
pattern on the edges is required. In the five-wire design, one wire goes to the coversheet (E)
which serves as the voltage probe for X and Y. Four wires go to corners of the back glass
layer (A, B, C, and D). The controller first applies 5V to corners A and B and grounds C and
D, causing voltage to flow uniformly across the screen from the top to the bottom. Upon
touch, it reads the Y voltage from the coversheet at E.Then the controller applies 5V to
corners A and C and grounds B and D, and reads the X voltage from E again.So, a five-wire
touchscreen uses the stable bottom layer for both X- and Y-axis measurements.The flexible
coversheet acts only as a voltage-measuring probe. This means the touchscreen continues
working properly even with non-uniformity in the coversheet's conductive coating. The result
is an accurate, durable and more reliable touchscreen over four- and eight-wire designs.

1.4 Six- and Seven-Wire Variations:

There are some manufacturers who claim improved performance over five-wire resistive with
additional wires.The six-wire variation adds an extra ground layer to the back of the glass. It
is not needed for improved performance, and in some cases is not even connected to the
companion controller.The seven-wire variation adds two sense lines, like with the eight-wire

9


design, to decrease drift due to environmental changes. The proprietary "Z border" electrode
pattern is a better solution to prevent drift.
2. Capacitive:

A capacitive touch-screen panel is a sensor typically made of glass coated with a material
such as indium tin oxide (ITO). 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. Capacitive sensors work based on proximity, and do not have to be directly
touched to be triggered. It is a durable technology that is used in a wide range of applications
including point-of-sale systems, industrial controls, and public information kiosks. It has a
higher clarity than Resistive technology, but it only responds to finger contact and will not
work with a gloved hand or pen stylus. Capacitive touch screens can also support Multi-
touch. Examples include Apple Inc.’s iPhone and iPod touch, and HTC’s G1 & HTC Magic.

Two types are available: Capacitive technology & Pen-touch Capacitive

Fig 5.2 fig 5.3

3. 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 the location. Surface wave touchscreen panels can be damaged by

10


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

Fig 5.4

4. Infrared touch screen:

Conventional optical-touch systems use an array of infrared (IR) light-emitting diodes
(LEDs) on two adjacent bezel edges of a display, with photo sensors placed on the two
opposite bezel edges to analyze the system and determine a touch event.

The LED and photo sensor 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 photo sensors.

The measured photo sensor outputs can be used to locate a touch-point coordinate.
Widespread adoption of infrared touch screens 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.

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. Infrared touch is capable of implementing multi-
touch, something most other touch technologies cannot easily achieve.

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Fig 5.5

12


WORKING OF TOUCH SCREEN MONITORS:

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.

fig 6.1

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.

13


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.

About Touch Screen Displays:

Touch screen displays are the most user-friendly PC interface. They are input devices, a way
to communicate with the PC. The user touches the screento select options presented on the
screen. Associated hardware and software are used to determine the location of the
press. Touch screen displays can be either internally mounted, or externally mounted on an
existing screen. An internally mounted screen is a touch screen input device that is designed
to be installed on the inside of a PC monitor. It is commonly a touch sensitive glass panel that
uses a touch screen controller and a software driver to interface with a PC system. The
internal touch screen requires a sometimes-technical installation, as the monitor needs to be
opened and in some cases the touch screen controller needs to be wired to a power source
inside the monitor. An external touch screen panel is a touch screen input device that is
designed to mount on the outside of a PC monitor. The external touch screen does not require
any difficult installation or opening of the monitor. It is commonly a touch sensitive glass
panel that uses an external touch screen controller and a software driver to interface with a
PC system. There are five basic types of touch screen displays: resistive, capacitive, infrared,
surface acoustic wave (SAW) and strain gauge. Resistive and capacitive touch screen
displays are the most common. Resistive touch screens consist of a glass or acrylic panel that
is coated with electrically conductive and resistive layers. The thin layers are separated by
invisible separator dots. During operation, an electrical current moves through the screen.
When pressure is applied to the touch screen, the layers are pressed together, causing a
change in the electrical current and a touch event to be registered. A capacitive touch screen
consists of a glass panel with a capacitive (charge storing) material coating its surface.

14


Circuits located at corners of the screen measure the capacitance of a person touching the
overlay. Frequency changes are measured to determine the X and Y coordinates of the touch
event.

Infrared touch screens are similar to resistive products. Infrared touch screens project
horizontal and vertical beams of infrared light over the surface of the screen. When a finger
or other object breaks those beams, the X/Y coordinates are calculated. Surface acoustic
wave (SAW) technology sends acoustic waves across a clear glass panel with a series of
transducers and reflectors.When a finger touches the screen, the waves are absorbed, causing
a touch event to be detected at that point. In a strain gauge touch screen, the screen is spring
mounted on the four corners and strain gauges are used to determine deflection when the
screen is touched. This touch screen display technology can also measure the Z-axis

15


Comparing Touch Technologies
Each type of screen has unique characteristics that can make it a better choice for certain
applications. The most widely used touchscreen technologies are the following:

4-Wire Resistive Touchscreens
4-Wire Resistive touch technology consists of a glass or acrylic panel that is coated with
electrically conductive and resistive layers. The thin layers are separated by invisible
separator dots. When operating, an electrical current moves through the screen. When
pressure is applied to the screen the layers are pressed together, causing a change in the
electrical current and a touch event to be registered.
4-Wire Resistive type touch screens are generally the most affordable. Although clarity is less
than with other touch screen types, resistive screens are very durable and can be used in a
variety of environments. This type of screen is recommended for individual, home, school, or
office use, or less demanding point-of-sale systems, restaurant systems, etc

Advantages Disadvantages
•High touch resolution
•Pressure sensitive, works with any stylus
• Not affected by dirt, dust, water, or light
• Affordable touchscreen technology • 75 % clarity
• Resistive layers can be damaged by a sharp object
• Less durable then 5-Wire Resistive technology

Touchscreen Specification
TouchType:4-WireResistiveScreen Sizes: 12"-20" Diagonal
Cable Interface: PC Serial/COM Port or USB Port
Touch Resolution: 1024 x 1024
Response Time: 10 ms. Maximum
Positional Accuracy: 3mm maximum error
Light Transmission: 80% nominal
Life Expectancy: 3 million touches at one point
Temperature: Operating: -10°C to 70°C

16


Storage: -30°C to 85°C

Humidity: Pass 40 degrees C, 95% RH for 96hours
Chemical Resistance: Alcohol, acetone, grease, and general household detergent
Software Drivers: Windows XP / 2000 / NT / ME / 98 / 95, Linux, Macintosh OS

5-Wire Resistive Touchscreens
5-Wire Resistive touch technology consists of a glass or acrylic panel that is coated with
electrically conductive and resistive layers. The thin layers are separated by invisible
separator dots. When operating, an electrical current moves through the screen. When
pressure is applied to the screen the layers are pressed together, causing a change in the
electrical current and a touch event to be registered.
5-Wire Resistive type touch screensare generally more durable than the similiar 4-Wire
Resistive type. Although clarity is less than with other touch screen types, resistive screens
are very durable and can be used in a variety of environments. This type of screen is
recommended for demanding point-of-sale systems, restaurant systems, industrial controls,
and other workplace applications.
AdvantagesDisadvantages

• High touch resolution
• Pressure sensitive, works with any stylus
• Not affected by dirt, dust, water, or light
• More durable then 4-Wire Resistive technology
• 75 % clarity
• Resistive layers can be damaged by a sharp object

17


Pros and Cons of Touch screens:

The following overview lists advantages and disadvantages of touchscreens and summarizes
their characteristics.

Touchscreen Pros:

Direct: Direct pointing to objects, direct relationship between hand and cursor movement
(distance, speed and direction), because the hand is moving on the same surface that the
cursor is moving, manipulating objects on the screen is similar to manipulating them in the
manual world

Fast (but less precise without pen)

Finger is usable, any pen is usable (usually no cable needed).

No keyboard necessary for applications that need menu selections only -> saves desk space

Touchscreen Cons:

.Dirt: The screen gets Low precision (finger): Imprecise positioning, possible problems with
eye parallaxis (with pen, too), the finger may be too large for accurate pointing with small
objects -> a pen is more accurate.

Hand movements (if used with keyboard): Requires that users move the hand away from
the keyboard; a stylus requires also hand movements to take up the pen.

Fatigue: Straining the arm muscles under heavy use (especially if the screen is placed
vertically).

Sitting/Standing position: The user has to sit/stand close to the screen

Screen coverage: The user's hand, the finger or the pen may obscure parts of the screen.

Activation: Usually direct activation of the selected function, when the screen is touched;
there is no special "activation" button as with a light pen or a mouse.

18


Uses for Touch screens:

Best Suited to Applications Where...

Opportunity for training is low
Frequency of use is low
Accurate positioning is not required
Little or no text or numerical input is required Desk space is at a premium
The environment may be chemically or otherwise "aggressive"

Not Suited to Applications...

Requiring training/trained users
With high-frequency use
Requiring accuracy
Requiring a lot of typing

Uses of touch screen in regular life: 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
Information kiosks, tourism displays, trade show displays, and other electronic displays are
used by many people that have little or no computing experience. The user-
friendly touch screen interface can be less intimidating and easier to use than
other input devices, especially for novice users. A touch screen can help make
your information more easily accessible by allowing users to navigate your presentation by
simply touching the display screen.

Retail and Restaurant Systems
Time is money, especially in a fast paced retail or restaurant environment.
Touch screen systems are easy to use so employees can get work done faster,
and training time can be reduced for new employees. And because input is

19


done right on the screen, valuable counter space can be saved. Touch screens can be used in
cash registers, order entry stations, seating and reservation systems, and more.

Customer self-services
In today's fast pace world, waiting in line is one of the things that has yet to
speed up. Self-service touch screen terminals can be used to improve customer
service at busy stores, fast service restaurants, transportation hubs, and more.
Customers can quickly place their own orders or check themselves in or out,
saving them time, and decreasing wait times for other customers. Automated bank teller
(ATM) and airline e-ticket terminals are examples of self-service stations that can benefit
from touch screen input.

Control and Automation Systems
the touch screen interface is useful in systems ranging from industrial
process control to home automation. By integrating the input device with
the display,

Valuable workspace can be saved. And with a graphical interface, operators can
monitor and control complex operations in real-time by simply touching the
screen

Computer Based Training
because the touch screen interface is user-friendlier than other input
devices, overall training time for computer novices, and therefore training
expense, can be reduced.

It can also help to make learning more fun and interactive, which can lead to a more
beneficial training experience for both students and educators.

Assistive Technology

the touch screen interface can be beneficial to those that have difficulty
using other input devices such as a mouse or keyboards. When used in
conjunction with software such as on-screen keyboards, or other assistive
technology, they can help make computing resources more available to
people that have difficulty using computers.

20


And many more uses...
The touch screen interface is being used in a wide variety of applications to improve human-
computer interaction.

Other applications include digital jukeboxes, computerized gaming,
Student registration systems, multimedia software, financial And scientific
applications, and more.

21


PROBLEM WITH TOUCH SCREEN MONITORS AND
TROUBLESHOOTING:

ATM system is one of the application of touch screen monitors.

Hardware failure can occur in touch screen monitors.

We have mentioned some of the most common hardware problems of touch screen and have
givensome of the troubleshooting’s.

Hardware problems:

 Touch screen does not respond
 Portions of the touch screen do not respond
 Touch screen is very slow to respond

Troubleshooting:

The first step in troubleshooting a touchscreen system is to determine whether the problem is
related to the display, software, or hardware:

Do not confuse display problems with touchscreen problems—the two are unrelated.
Software problems are determined by a basic hardware functionality test. If the
hardware transmits touch coordinates correctly, then the problem is with the driver or
application software.
Hardware problems may be caused by the touchscreen, controller, cabling, power
supply, or by the integration of the touchscreen components in the display.
The easiest way to verify a hardware failure is by substitution, if you have more than
one unit to try.

22


Limitations of Touchscreens:
Size:

Fingers have a certain size, So, screen elements have to have a minimum size, to ensure that
a touch screen can be operated with few errors. Even with a stylus, which makes possible to
use smaller screen elements, there are limiting factors.

Sequential Input:

Input on a touch screen is inherently sequential:

One finger is used for clicking. This slows input down compared to keyboard input where
several fingers can be used virtually in parallel.

Strain:

Keying in many numbers or letters by pointing with the finger is also very straining and
tiring. Therefore, touch screens make no sense in workplaces, where much text or number
input is required.

Feedback:

On touch screens, there is no analogue to mouse-move events. Mouse users can move the
mouse pointer over screen elements, get feedback about the selected element (e.g. by
highlighting), and may confirm the selection by clicking the mouse button.Touch screen users
directly point on a screen element.If they are lucky, they can withdraw their finger if they
touched the wrong screen element.On other touchscreens, the touch immediately initiates an
action - there is no opportunity to cancel the action.

Drag Operations:

Dragging is generally not well suited to finger-operated touchscreens,Here, pointing is the
preferred interaction. However, this is different for stylus-operated touchscreens. Here
gestures and handwriting offer promising possibilities for making interaction with
computers easier and more intuitive.But here, too is the limitation of strictly sequential
input.There are also no means to constrain drag operations to, e.g. straight lines, like with
mouse-based interfaces.

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REFERENCES

http://en.wikipedia.org/wiki/Touchscreen

http://www.buzzle.com/editorials/2-21-2005-66062.asp

http://orissa.gov.in/e-
magazine/Orissareview/jun2005/engpdf/touch_screen_system.pdfhttp://orissa.gov.in/
e-magazine/Orissareview/jun2005/engpdf/touch_screen_system.pdf

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