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INTRODUCTION TO TOUCHSCREENTECHNOLOGY

A touch screen is an input device thatallows users to operate a computingdevice by just touching the displayscreen.

The display screen has a sensitive glassoverlay and used to give the desiredinput by touching it.

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CONSTRUCTION

REQUIREMENTS: To recognize one or more fingers

touching a display.

To interpret the command that thisrepresents .

To communicate the command to theappropriate application.

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TOUCH SENSORS

A touch screen sensor is a clear glasspanel with a touch responsive surfacewhich is placed over a display screen so

that the responsive area of the panelcovers the viewable area of the displayscreen.

The sensor generally has an electricalcurrent or signal going through it andtouching the screen causes a voltage orsignal change. This voltage change is

used to determine the location of the

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Picture showing a touchscreen

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ADVANTAGES:

User friendly.

Increases input speed.

Reduces input errors.

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DISADVANTAGES:

Suffer from the problem of

fingerprints on the display.

Presence of sunlight may reduce

the efficiency of some touchscreenslike IR touchscreens.

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APPLICATIONS:

User interactive displays like ATMs.

Personal digital Assistants(PDAs).

Satellite navigation devices. Mobile phones.

Video games.

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FUTURE TRENDS (soft

touchscreen)

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OVERVIEW

A touchscreen basically comprises ofthree things.

Touch overlay on the screen Controller

Software Driver

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1. TOUCH OVERLAY

It is the sensing portion placedover the screen for detection and

is transparent covering theviewable area of the displayscreen. The sensing technique

used may vary depending uponthe technology.

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2. CONTROLLER

The controller is actually ahardware that connects between

the touch sensor and the PC. Ittakes information from the touchsensor and translates it intoinformation that PC canunderstand

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3. Software Driver

The driver is a software that allowsthe touch screen and computer to

work together. It tells theoperating system how to interpretthe touch event information that issent from the controller.

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TOUCH SCREEN

TECHNOLOGIESResistive

Dispersive Signal (DST)

Acoustic

Infrared

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RESISTIVE TOUCHSCREEN

A resistive touchscreen panel iscomposed of several layers, the mostimportant of which are two thin,

metallic, electrically conductive layersseparated by a narrow gap.

When an object, such as a finger

presses down on a point on the panel'souter surface the two metallic layersbecome connected at that point.

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The panel then behaves as a pair of

voltage dividers with connectedoutputs. This causes a change in theelectrical current which is registeredas a touch event and sent to the

controller for processing.

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LAYERS OF THE RESISTIVE

TOUCHSCREEN:

1. Polyester Film .

2. Top Resistive Layer.3. Conductive Transparent Metal

Coating.

4. Bottom Resistive Layer .5. Insulating Dots .

6. Glass Substrate

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ADVANTAGES OF RESISTIVE

TOUCHSCREEN

Activated by any stylus

High touch point resolution

Low power requirements

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DISADVANTAGES OF RESISTIVETOUCHSCREEN

Reduced optical clarity

Polyester surface can be damaged

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DISPERSIVE SIGNAL

this system uses sensors to detectthe mechanical energy in the glassthat occurs due to a touch.

Complex algorithms then interpretthis information and provide the

actual location of the touch.

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Mechanical waves created with touch

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Advantages

No need for additional elements onscreen

Provide excellent optical clarity ,since mechanical vibrations are used

Any object can be used to generatethese events, including fingers andstylus

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Continued...

Touch unaffected by surfacecontaminants, such as dirt, dust..

Operation unaffected by surfacedamage.

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Disadvantages

More expensive to integrate.

Only available for displays

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ACOUSTIC(SAW)

Surface acoustic wave (SAW)technology uses ultrasonic wavesthat pass over the touchscreen panel.

Transducers mounted at the edge ofa glass overlay to emit ultrasonic

sound waves along two sides

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Waves are reflected across thesurface of the glass and received bysensors.

A finger or stylus absorbs some of theacoustic energy and the controller

measures the amplitude change ofthe wave to determine touch location.

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Acoustic wave touch overlay

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Advantages

Good optical clarity

Z-axis capability

Durable glass front

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Disadvantages

Requires finger or sound absorbingstylus .

Signal affected by surface liquids orother contaminants.

Difficult to industrialize.

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COMPARISON OF

TOUCHSCREEN TECHNOLOGIESTECHNOLOGYRESISTIVE SAW IR CAPACITIVE

DURABILITY 5 Yr. 5 Yr. 3 Yr. 2 Yr.

STABILITY HIGH HIGHER HIGH OK

TRANSPARENCY

OK GOOD GOOD OK

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COMPARISON OF

TOUCHSCREEN TECHNOLOGIESTECHNOLOGY RESISTIVE SAW IR CAPACITIVE

TOUCH Anything Finger/Pen

AnythingConductive

INTENSE LIGHT-RESISTANT

Good Good Good Bad

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COMPARISON OF

TOUCHSCREEN TECHNOLOGIESTECHNOLOGY RESISTIVE

SAW IR CAPACITIVE

RESPONSE

TIME

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COMPARISON OF

TOUCHSCREEN TECHNOLOGIESTECHNOLOGY

RESISTIVE SAW IR CAPACITIVE

MONITOROPTION

CRT CRT CRT orLCD

CRT orLCD

WATERPROOF Good Ok Ok Good