Touch Screen Technology

What is a touch screen?An electronic visual display that locates the coordinates of a users touch within display areaWorks independently of what is being displayed on screen

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When is it Applicable?It allows users to interact directly with what is being displayed, rather than indirectly using a mouse or keyboardCan be used without any intermediate device Found in modern smartphones, video games, kiosks, navigation systems, etc. . .

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Brief HistoryInvented by E.A. Johnson (Royal Radar Est.) around 1965 for air traffic controlHP-150 home computer using infrared technology in 19831993 Apples Newton and IBMs Simon2002 Microsofts Windows XP Tablet2007 Apples iPhone (Multi-touch)

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Touch Screen TechnologyFour different technologies used to make touch screens today:ResistiveCapacitiveSurface Acoustic Wave (SAW)Infrared LED or Optical

Resistive Touch ScreensTwo layers of conductive materialTouch creates contact between resistive layers completing circuit

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Resistive Touch ScreensVoltage in circuit changes based on positionController determines location based on voltagesAny material can trigger sensors

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Why Resistive?Advantages:Cost-effective and low power RequirementsActivated by any objectAccurate Disadvantages:Polyester surface can be damagedOnly 75% light transmissionLower endurance (~35 million touches)

ResistiveSummary8 resistive touch screen will cost about $604 and 5 wire touch screens dont need controllersFor those that do, they cost less than $5Any object can be used to activate the screenNot able to register multiple touches~75% of light is transferred through (12.5% per layer)

Capacitive Touch ScreensGlass panel with conductive layer (Indium Tin Oxide)Small amount of voltage applied to four corners of touch screen

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Capacitive Touch ScreensTouch draws minute amount of current creating voltage dropCoordinates of point of contact calculated by controller

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Why Capacitive?Advantages:Durable surface materialHigh endurance (~255 million touches)Very accurateGood optical qualityDisadvantages:Triggered only by bare finger or active stylus

CapacitiveSummary8 capacitive touch screen costs about $100Controllers can be bought for less than $5Only conductive objects can be used to activateAble to register multiple touches~88% of light is transferred through

Surface Acoustic Wave Touch ScreensSurface consists of glass overlay with transmitting and receiving transducers

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Surface Acoustic Wave Touch ScreensElectrical signals sent to the transmitting transducers converts to ultrasonic waves Waves are directed across screen by reflectors then directed to receiving transducers

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Surface Acoustic Wave Touch ScreensWhen finger touches screen it absorbs wavesReceived values are compared to stored digital maps to calculate x and y coordinates

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Why SAW?Advantages:Best optical qualityHigh surface durability and sealActivated by multiple sources Disadvantages:ExpensiveContaminates on screen can cause false-touches

Surface Acoustic WaveSummaryWe were not able to find prices for individual screensAny object can be used to activate the screenAble to register multiple touches~100% of light is transferred through

Uses infrared LEDs and matching photodetectorsTouching screen interrupts LEDs

Infrared/Optical Touch Screens[2]

Infrared/Optical Touch ScreensCameras detect reflected LED caused by touchController able to calculate coordinates from camera data

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Infrared/Optical Touch ScreensAdvantages:High optical clarityDurable surfaceSupports multi-touchCan scale to large sizesDisadvantages:ExpensiveCameras can get out of alignment

Infrared/OpticalSummary8 infrared touch screen costs about $160Any object can be used to activate the screenAble to register multiple touches~100% of light is transferred through

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TypeExamplesPrice (DigiKey)Tool for InputMulti-touchResistive$10 (3.5)$60 (8)$150 (19)Any object NoCapacitive$100 (8)$160 (19)$310 (32)Finger or active stylusYesSAW $500 (15)$850 (19)*includes touch screen and LCD monitorAny object YesInfrared/Optical$130 (8)$250 (19)$320 (26)Any object Yes