Touch Screen Earl

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					Introduction
Touch screen technology has found its way to many commercial applications. Due to its
versatility, they are becoming the primary user interface in many public-access system
and portable devices. This paper will look at some of the applications that touch screen
technology has been able to revolutionize. It will also look at the different type of touch
screen technology available and its basic components.


Commercial Application
Touch screen technology has found its way to many commercial application including,
but not limited to ATM’s PDA’s, POS (point of sale), and gaming with ATM being the
most common [1]. Due to the numerous advantages that it provides over other pointing
devices, touch screen is ideal in many public-access information systems [2]. In high-
volume, high-traffic public systems, touch screens offer more durability than other
external pointing devices. Instead of a vulnerable external device, a vandal proof touch
screen with an unbreakable safety glass and sensors can be used in its placed [3].


PDA’s, smartphones, and other portable devices also utilize touch screen technology.
Because touch screens eliminate the need for extra workspace, they are ideal for those
devices which require a minimal user-interface footprint. In addition, touch screen also
provides a more flexible environment which eliminates the need for applications to
design around limited function keys [4].


Underlying Technology
Currently there are few types of touch screen sensors: resistive, capacitive, and surface
acoustic wave. Resistive touch screens are force-activated which allows all types of
touch input device to be used and are the most widely used form of touch screen
technology [5]. Resistive touch screens are composed of multiple layers: a conductive
cover sheet, a resistive back sheet and a thin layer of insulating dots separating the two.
Upon touch, the two sheets come into contact and produces a change in the current.
Determining the location of the touch depends on the type of resistive touch screen being
used. Currently 4-, 5-, and 8- wire resistive touch screens are the most commonly used
[5].


Another form of touch screen sensor technology is the capacitive touch screen.
Capacitive touch screen employs only a single conductive sheet with electrodes and
sensor placed along the edges. The electrodes deliver a low voltage across to surface to
create a uniform electric field. When touched, it would draw currents from the four
corners allowing the location of the contact to be determined [5].


In a surface acoustic wave touch screen, transmitting and receiving transducers are used
along the X and Y axis. It emits waves that are transmitted across the screen’s surface
via an array of reflectors. When touched, a portion of the wave is disturbed and the
coordinates are calculated based on the change [5].


Building Blocks for Implementation
Touch screen systems consists of one of the touch screen sensors described, the proper
controller, and a processor. The system itself can either have an integrated touch screen
or have a touch screen overlay, though a majority of the commercial products will have
integrated touch screen. The controller, an analog-to-digital converter (ADC), allows the
touch screen sensors and the processor to talk, typically via a Serial/COM or USB port
[6]. Its job is to sense the touch on the touch screen, calculate the X and Y coordinates
and to scale it to match that of the display system. Additionally, the controller must also
implement calibration algorithms (3-, 5-, n- point calibration) due to the difficulty in
aligning the touch screen coordinates to the display [7].
References

[1] S. D. Desiano. “Touch Screens,” [Online], [cited 2007 Sept. 2] Available HTTP:
    http://www.bookrags.com/research/touch-screens-csci-02/


[2] B. Shneiferman, “Touch screens now offer compelling uses,” IEEE Software, March,
    pp. 93-94, 107, 1994


[3] HBM UK, (2000, Nov. 13) “Sensors help make ticket machines vandal proof,”
    [News Release]. Available: http://www.engineeringtalk.com/news/hbm/hbm111.html


[4] SDI Retail, “Summarizing the advantages of a touch screen POS solution,” [Online
    Document] Oct. 2005, [cited 2007 Sept. 1], Available HTTP:
    http://www.sdiretial.com/documents/


[5] Tyco Electronics, “Touch Technologies,” [Company Website], [2007 Sep. 1],
    Available HTTP: http://elotouch.com/Technologies/default.asp


[6] Mass Multimedia, Inc., “Introduction to Touch Screen Systems,” [Company
    Website], [cited 2007 Sep. 1], Available HTTP:
    http://www.touchscreens.com/introduction.html


[7] W. Fang and T. Chang, “Calibration in touch-screen systems,” Analog Applications
    Journal, [Application Notes] 3Q, (2007 Aug.), Available HTTP:
    http://focus.ti.com/lit/an/slyt277/slyt277.pdf

				
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