Touch Screen Computer Displays


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Introduction

When most people think about a computer display, many may develop a mental
picture of an output device. However a computer display can function as both an input
device and an output device. A touch sensitive screen provides a computer user with an
input interface that doesn’t require extensive computer skills or literacy. This interface,
operates as a pointing device, much like a mouse or an input device much like a
keyboard. Touch screen add-ons and displays with integrated touch screen technology
are widely available and in use in many facets of society.
During a recent visit to the Bob Bullock State History Museum I had the pleasure
of watching a small child of about four years of age explore Texas history with the use of
a touch screen computer display. He easily explored and navigated through the screens
without needing mouse or keyboard skills. The following week as I moved about the
University of Texas at Austin campus I noticed the use of touch screen computer displays
and my interest in this technology was triggered. Even the state government has begun
making use of kiosks with touch screen computer displays. As part of the National
Partnership for Reinventing Government’s Hassle-Free Communities Initiative, the State
of Texas has installed interactive kiosks that provide over 150 government services with
a quick touch. The kiosks, which are installed in malls, community centers and in
government buildings, are an effective method of bringing government services to the
people of Texas in an easy to use interactive format without the need for computer
literacy. Liz Salih a regional coordinator for the initiative reports that the system
receives hit at all hours of the night and that kiosks systems have far exceeded
expectations.
This technology was originally developed and invented for use by physicians whose
keyboarding skills were lacking. However, touch screen computer displays are now
found throughout society. They can be found in use as public information displays, retail
and restaurant systems, computer-based training systems, customer self-service aids,
control and automation systems, assistive technology for the disabled, and as tourism
kiosks.

Significance

With the higher cost, when compared to standard computer monitors, their need
for special software and their vulnerability to outside element damage, what are the
advantages of using a computer display touch screen system? Touch screen systems are
easy to use for the non-computer literate, and are easy to see for the visually-impaired.
For the motor-impaired, a touch screen may be the gateway to communication skills. To
accommodate the limitations of a touch screen system, changes must be made to the
appearance of screens. Often button sizes must be increased to insure successful
targeting of the touch event. Additionally active regions of the buttons are expanded so
to dead space exists. Font size is typically also increase to accommodate reduced light
transmission present in some systems. Toggle buttons are favored over check or radio
buttons to avoid confusion over where to touch the screen. Finally a delay is built into
button responses to that multiple touches are treated as single touches. A forced delay
after a touch event causes the program to ignore multiple touches.
With each advantage of using a touch screen system, a disadvantage also exists
and a purchaser must carefully weigh the pros and cons for the system in question. The
following discussion provides a brief insight into the technical aspects of each of the
three types of touch screen systems followed by a brief comparison.

Discussion

Touch screen computer displays are available in three basic systems that allow the
monitor to detect a person’s touch: resistive, capacitive, and surface acoustic wave. A
resistive system consists of a several layers that detect and register the location of the
touch. The outermost layer is a durable hard coating to protect the more delicate touch
sensors and is followed by a glass plate that contains both resistive and conductive
properties. This semi-flexible glass plate that is coated with a metallic layers to provide
conductance and resistance, each metallic layer is separated with spacers. When the
screen is touched, the touch pushes the conductive layer against the resistive layer
making and electrical contact. Voltages are then produced as the analog representation of
the position touched
Therefore registering the location of the
touched position on an x and y coordinate
system. A touch can be made by fingers, a
stylus, fingernails, or any pointing device as
long as the conductive and resistive layers are able to make contact. An averaging
algorithm is present in the driving software to eliminate noise from contact bounce and
produce a clear, detectable signal. Personal digital assistants (PDAs) commonly utilize
resistive technology.
Capacitive systems also operate through a systems of layers on the display screen.
The layering system is one in which electrical charge is stored. When a use touched the
display screen, some of the charge is transferred to the user therefore decreasing the
charge on the capacitive layer. The computer software driving the touch screen system
calculated the position of the touch from relative differences in charge at each corner.
The capacitive system produces a clearer picture over the resistive system due to the
decreased number of required layers over the actual screen. The capacitive system can
transmit 90% of the light while the resistive system only transmits 75%. The decrease in
light transmission is the result of metallic resistive and conductive coatings. A
conductive input must be used to touch the screen and register a location. Fingers are
ideal.