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Touch Display-Touch Screen Mechanisms
Involved
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What is a touch screen?
An electronic visualdisplay that locates thecoordinates of a users
touch within display area
Works independently of what is beingdisplayed on screen
[7]
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Brief History
Invented by E.A. Johnson (RoyalRadar Est.) around 1965 for air traffic control
HP-150 home computer usinginfrared technology in 1983
1993 Apples Newton andIBMs Simon
2002 Microsofts Windows XPTablet
2007 Apples iPhone (Multi -touch )[6]
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Multi-Touch Architecture
to sense touch
Touch screensensor
To determinelocation
Touch screencontroller anddriver
Signal toexecute
application
Operatingsystem
Application
Capable of sensing multiplesimultaneous points
Capable of delivering sets of simultaneous points to the OS
Capable of forwarding multiplestreams of moving points (andacting on a defined subset of
them) Capable of decoding multiple
streams of moving points andtaking actions in response
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One Reason Why There Are So Many Technologies
Touch Technology
Resistive Surface capacitive
Surface acoustic wave Projected capacitive,Embedded (capacitive)
Camera-based & Infrared (allforms),
Planar scatter detection Embedded (light-sensing) Vision-based Acoustic Pulse Recognition &
Dispersive Signal Technology
Whats Being Measured
Voltage Current
Ultrasonic wave amplitude Change in capacitance
Absence or reduction in light
Presence of light Change in image Bending waves
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Resistive Touch Screens
Two layers of conductive material Touch creates contact between resistive layers completing circuit
Voltage in circuit changes based on position Controller determines location based on voltages
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Why Resistive?
Advantages: Cost-effective and low power Requirements Activated by any object Accurate
Disadvantages: Polyester surface can be damaged Only 75% light transmission Lower endurance (~35 million touches )
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Capacitive Touch Screens
Glass panel with conductivelayer (Indium Tin Oxide)
electrodes around the panel'sedge distribute low voltageuniformly across the conductivelayer creating a uniform electric
field
[2]
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Projected Capacitive
It is of two types : self and mutual capacitance.
Self capacitance:
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Self-capacitance electrodevariations
Self capacitance Multiple separate slots
in a single layer Each slot is scanned
individually
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Mutual-capacitance principle
No touch
Touch
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Mutual capacitance example (Apple iPhone)
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Surface capacitance
Touch draws minuteamount of current creatingvoltage drop
Coordinates of point of contact calculated bycontroller
[2]
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Surface capacitance
Scratch-resistanttop coat
Hard coat with AGElectrode pattern
Conductive coating(ATO, ITO or TO)
Glass
Optional bottomshield (not shown)
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Why Capacitive?
Advantages: Durable surface material High endurance (~255 million touches)
Very accurate Good optical quality
Disadvantages: Triggered only by bare finger or active stylus High cost
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Acoustic Wave Touch Screens-Surface Acoustic Wave
Surface consists of glass overlay with transmittingand receiving transducers
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[2]
Projected variation of amplitude of ultrasonic waves with time and distance
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Acoustic Pulse Recognition
Plain glass sensor with 4piezos on the edges
Table look-up of bending
wave samples (acoustic touch signatures)
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Acoustic Pulse Recognition
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Dispersive Signal Technology
Plain glass sensor with 4 piezos in
the corners
Real-time analysisof bending waves
in the glass (time of flight calculation )
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Why AWT?
Advantages: Best optical quality High surface durability and seal Activated by multiple sources
Disadvantages: Expensive Contaminates on screen can cause false-touches
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Uses infrared LEDs and
matching photo detectors
Touching screen interruptsLEDs
Optical or Infrared Touch ScreenTraditional infrared
[2]
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Waveguide Infrared
Principle
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Camera based optical
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Planar Scatter Detection Infrared (IR) light is injected in the
sensor substrate from the edges.
The IR light travels via TotalInternal Reflection within thesubstrate and is disturbed or scattered by any object touchingthe surface of the substrate.
The IR light is injected and
analyzed, scattered light from atouch points is detected at theedge of the sensor substrate andused to calculate the touch.
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Vision based When the user comes into
contact with the surface, the lightrays are frustrated, since they cannow pass through into the contactmaterial and the reflection is no
longer total at that point.
This frustrated light is scattereddownwards towards an infraredwebcam, capable of picking theseblobs up, and relaying them totracking software.
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Infrared/OpticalTouch Screens
Advantages:
High optical clarity Durable surface Supports multi-touch Can scale to large sizes
Disadvantages:
Expensive Cameras can get out of alignment
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Touch Screen Techniques-comparison
Technology MajorAdvantage
Major Flaw
Projected Capacitive Multi-touch Finger-only
Surface Capacitive Touch sensitivity High drift
Analog Resistive Low cost Low durability Surface Acoustic Wave Durability Soft touch object
Acoustic Pulse Recognition Any touch-object No touch & hold
Dispersive SignalTechnology
Any touch-object No touch & hold
Traditional Infrared Reliability High cost
Waveguide Infrared Low cost Contamination
Camera-Based Optical Scalability Profile height
Planar Scatter Detection Flush surface High cost
Vision-Based Multi-touch Rear projection
LCD In-Cell Integration Sensitivity
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Applications
Trade show displaysMuseum / tourism displaysPoint-of-sale terminalsRestaurant systemsEmployee time clocksIndustrial process controlsWorld Wide Web access kiosksHome automation systemsCasino and other gaming systemsComputer access for the physically disabled
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Latest in touch technology
Freescale is announcing a new industrial touch sensing technologythat'll even sense your swipes and prods through a film of water .itcan withstand noise, detect electrical interference and reduce falsetouches.
Chris Harrison, co-founder of a startup called Qeexo.new technologycalled FingerSense that adds a tiny acoustic sensor inside asmartphone to listen for and measure the vibrations of the object thattouches it.
The new LCD technology patent will allow Apple to fuse touchsensors into display circuitry, a change that could have a dramaticeffect on how thin smart phones or tablets can get.
Integration can further include eliminating redundant structuresand/or finding dual purposes
http://www.engadget.com/tag/freescalehttp://www.engadget.com/2012/02/21/pantech-element-review/http://www.engadget.com/2012/02/21/pantech-element-review/http://www.engadget.com/tag/freescale7/30/2019 Touchscreens Finall New
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THANK YOU
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