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Display and Touch Technology Choices Put a Touchscreen on That! Design & Manufacturing Midwest 2011 Conference Session D301 DSS Robert Phares Display Sourcing.

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Presentation on theme: "Display and Touch Technology Choices Put a Touchscreen on That! Design & Manufacturing Midwest 2011 Conference Session D301 DSS Robert Phares Display Sourcing."— Presentation transcript:

1 Display and Touch Technology Choices Put a Touchscreen on That! Design & Manufacturing Midwest 2011 Conference Session D301 DSS Robert Phares Display Sourcing & Service LLC

2 Elements of a Touchscreen System Hardware –Touchscreen –Controller –Cables Software –Drivers for standard OSs, or –Touch processing code in the application DSS

3 Take the Easy Way Out! External display/separate enclosure? –Finished displays, open frame chassis with touch Often available unbranded –Controller usually in display housing –Some choice of touch technology usually available –Standard OS drivers provided by most manufacturers –Avoids many display obsolescence issues Usually doesnt apply in a stand-alone product… DSS

4 Display Technologies Standard display panels --Most common is transmissive AMLCD Limited availability of reflective/transflective panelsusually smaller sizes –Emissive panels Plasma VF AMOLED becoming available in small sizes –System processor may dictate display type and size/resolution DSS

5 Display Technologies, contd Display/touchscreen interactions can affect display AND touchscreen choice. Things to consider will largely be in the areas of: Optics EMI Environment DSS

6 Touchscreen Technologies Commercially available touchscreens: –Analog resistivefour wire (4W) and five wire (5W) –Surface (SCAP) and projected capacitive (PCAP) –Surface acoustic wave (SAW) –Dispersive signal technology (DST) and acoustic pulse recognition (APR) –Scanning infrared –Camera-based optical –Pen-based electronic digitizers Developing technologies –Multitouch resistiveanalog and digital –In cell touch (several variations) DSS

7 Touchscreen Technology Descriptions Resistive –Concept: a two axis voltage divider –Two major typesfour and five wire 4Wa dedicated conductive sheet for each axis DSS

8 Touchscreen Technology Descriptions Resistive –DC Bias is applied sequentially to each sheet, with the opposing sheet serving as a voltage probe –Position is proportional to voltage DSS

9 Touchscreen Technology Descriptions Resistive –Important assumptions include: Uniformity of the resistivity of the transparent conductive film High conductivity of the bass bars vs the film, to insure reasonably uniform drive potential/current on the buss bars DSS

10 Touchscreen Technology Descriptions Resistive important details –Separator dots between the two active sheets: Hold the sheets apart except when touched ~ um ( ) diameter ~10-40um height Screen or foil printed –Construction can be film-film laminated to rigid backplate, film-glass, or glass-glass DSS

11 Touchscreen Technology Descriptions Resistive important details –Construction can be film-film laminated to rigid backplate, film-glass, or glass-glass –Typical cross section: Glass Plastic (Coversheet) ITO Coating Adhesive Spacer Separator Dots

12 Touchscreen Technology Descriptions Resistive important details –Connecting cable attached to glass or film with Anisotropic Conductive Film (ACF) and essentially any length or shape can be had, for a price. Durability –4W resistive is NOT durable. ITO damage due to repeated flexure of upper film layer affects linearity Controllers –4W controllers are cheap, widely available in board or chip solutions, and most importantly, may be included for FREE in your system microprocessor. –Usually have your choice of communications interfaceUSB, RS232 for PNP, I2C, SPI, etc. for embedded DSS

13 Touchscreen Technology Descriptions Why consider 4W resistive in a new design? –Cheap and widely available. Small off the shelf touchscreen is a $5-10 solution depending on the controller Usually available up to ~19 diagonal –Least restrictive touch input--finger, glove, any stylus –Very low current requirements –Reasonable environmental performance Water resistant with proper seal Why avoid 4W resistive in a new design? –Poor long term durability –Poor visible light transmission (VLT) typ 80%--and very reflective OK for many indoor apps, poor in direct sunlight. DSS

14 Touchscreen Technology Descriptions Five wire (5W) touchscreen –Uses single drive layer to develop orthogonal position sensing planes –5W is somewhat higher current than 4W due to resistive network DSS Resistive Network 1245 XHHLL YHLHL Touchscreen Glass

15 Touchscreen Technology Descriptions 5W touchscreen –Now the upper film is always the voltage probe Uniformity of the conductive coating is less critical Results in significantly better field life than equivalent 4W touchscreen –Better candidate for optical and environmental enhancements –Basic construction very similar to 4W –Many of the design features similar to 4W also

16 Touchscreen Technology Descriptions Why consider 5W resistive in a new design? –Relatively inexpensive and widely available % premium over 4W Controller circuit seldom included in system microprocessor, but many inexpensive chip/board level solutions available –Least restrictive touch input Finger, with any type of glove, or any stylus –Reasonable environmental performance Water resistant with proper seal Why avoid 5W resistive in a new design? –Fair long term durability –Poor light transmissiontyp 80%--and very reflective OK for many indoor apps, poor in direct sunlight. –Standard 5W does not support multi-touch DSS

17 Touchscreen Technology Descriptions Surface Capacitive –Concept: much like a 5W resistive design with no coversheet –Features Always glass-based Touch surface (usually ITO, ATO or TO) protected by SiO2 or sol-gel coating –More durable than resistive (no plastic coversheet) Better VLT than resistive unless EMI shield is needed, and always less reflective Excellent finger sensitivity DSS

18 Touchscreen Technology Descriptions Surface Capacitive –Controllers Touch detection method by ratios of AC current through the corners of the resistive network Some third party board level solutions available usually USB or RS232 Few chip solutions available Integration more difficult than resistive. Issues with: –Grounding –Cable routing –EMI DSS

19 Touchscreen Technology Descriptions Why consider Surface Capacitive in a new design? –Established technology in gaming, kiosks and some ATMscustomer familiarity –Easy environmental/contaminant sealing –Good durability in public areas Why avoid Surface Capacitive in a new design? –Cost, may be ~50% or more higher than resistive –Poor calibration stability in many designs –Limited gloved hand/stylus operation –Portable/mobile operation poor –Safety issues in some markets unless touchscreen is bonded to display DSS

20 Touchscreen Technology Descriptions Projected Capacitive –Despite similarity of name, completely different from Surface Capacitive –Concept: Finger contact or proximity to the touchscreen surface changes the capacitance between one or more electrodes of an array and its neighbors. Two types: Self capacitancemeasured to a common electrode for both axes Mutual capacitancemeasured between a given electrode and nearby electrodes in the 2 nd axis array. Supports multi-touch. –Measurement not a trivial issuecapacitance is usually in the 1picofarad range! –Apple and others have improved on very old technology from 3M/Microtouch (ThroughGlass) and 3M/Dynapro (Near Field Imaging) to make this technology the darling of the touch industry today. DSS

21 Touchscreen Technology Descriptions Projected Capacitive –Features Many different glass and/or film constructions possiblecan address many different applications Cable and EMI issues have led to chip on flex controller solutions from many vendors –Nice complete solution if it fits your design form factor Many vendors concentrating on smaller sizesfor cell phones and tablets –Availability of larger sizes as component limited –Few third party controllers available in any form DSS

22 Touchscreen Technology Descriptions Projected Capacitive –Features, contd Excellent finger sensitivity –But poor gloved hand/stylus sensitivity Good portable/mobile performancenone of the SCAP issues Multi-touch performance with mutual capacitance types Excellent VLT, and virtually invisible arrays in later generation products, especially if optically bonded to display Reasonable power requirementsless than 5W, more than 4W resistive Relatively narrow borders; EMI is the major integration issue Not amenable to top surface optical enhancements other than non-conductive coatings or AG finishno CP filters DSS

23 Touchscreen Technology Descriptions Why consider Projected Capacitive in a new design? –Multi-touch support –Excellent VLT without enhancements –Durability –Reasonably low power for portable/mobile Why avoid Projected Capacitive in a new design? –Limited component solutions in larger sizes –3-4X the cost of analog resistive, may have high design-in cost –Glove/stylus limitations –Possible EMI issues –Not compatible with some optical enhancements for outdoor use CP filters, etc. DSS

24 Touchscreen Technology Descriptions Surface Acoustic Wave (SAW) –Concept: Shear waves propagating in the surface of a piece of glass are attenuated by finger touch DSS YT YR XR XT Y Axis X Axis Piezo-electric transducers (4) 5.53MHzburst signal from XT, YT Return signal from XR, YR Time in usec ~5 100+

25 Touchscreen Technology Descriptions –SAW Features Always glass based Excellent optics--no conductive coatings Variety of medium-large sizes available –Not space efficient in smaller sizes (border) –But, chip on flex improves controller solution –Flat front surface on current product from Elo Multi-touch (2) capability from several suppliers now Scalable to at least 46diagonal Desktop+ sizes cost competitive with other technologies

26 Touchscreen Technology Descriptions –SAW Features, contd Good EMI performance Vandal resistant--adapts to surface scratches Finger or soft stylus touch only –Point and shoot touch excellent –Dragging may produce skipsglass finish, finger moisture, stylus type, etc. Some issues with environmental sealing and contamination sensitivity Similar to PCAP re optical enhancementsno add on filters, etc., to top surface

27 Touchscreen Technology Descriptions Why consider SAW in a new design? –Mature technology, many suppliers, cost competitive with other high performance touch –Multi-touch support –Excellent optics, good un-attended survivability –Overall excellent choice for interactive digital signage and other large format touch displays Why avoid SAW in a new design? –Size, integration in small enclosures –Higher relative cost in smaller sizes –Contamination/sealing –Few optical enhancements possible (outdoor) –Possible safety issues without bonding (exposed glass) DSS

28 Touchscreen Technology Descriptions APR (Elo) and DST (3M) –Concept: Touch position determined by analyzing time of flight (DST) or acoustic signature (APR) of bending waves at several piezo transducers attached to the back side of a piece of glass –APR = Acoustic Pulse Recognition –DST=Dispersive Signal Technology –These rather similar touchscreens offered as monitors only, at present, by Elo and 3M. DSS

29 Touchscreen Technology Descriptions APR (Elo) and DST (3M) –Features Plain glass with backside piezo-electric pickups Excellent opticsno conductive coatings Very up scalablelarge touch monitors available Works with fingers and most styliimay be some issues with rubber gloves Easy environmental sealing No touch and hold capability (no signal after initial touch) DSS

30 Touchscreen Technology Descriptions Why consider APR or DST in a new design? –Competitive solution to SAW or optical for a large finished monitor –Should be available as a component solution in the future –Good optics, good survivability in public situations Why avoid APR or DST in a new design? –Sole source –Touch hold/sensitivity/gloves potential issues DSS

31 Touchscreen Technology Descriptions Optical TouchscreensScanning Infrared –One of the earliest commercial touchscreens –Roots in the PLATO project at Univ of Illinois –Concept: Finger or stylus breaks the path of IR light between LED and photo transistor DSS IR DiodePhoto transistor

32 Touchscreen Technology Descriptions Optical TouchscreensScanning Infrared, contd –Features Scalable, but cost increases with size/component count Few standard designsmost custom Requires IR transparent bezel over optics Relatively slow Stylus independent above minimum size threshold Resolution improved with better interpolation algorithms, but still coarse Near perfect environmental seal when using display lens Contamination susceptibility (beam blocking) Now supports multi-touch from some manufacturers Some new designs decrease component count (RPO) and improve overall performance/reliability DSS

33 Touchscreen Technology Descriptions Why consider Scanning IR in a new design? –Excellent optics –Good environmental performance –Stylus independence –Supports multi-touch Why avoid Scanning IR in a new design? –Costneeds large quantity to overcome NRE –Speed, resolution –Some sunlight de-sense issues DSS

34 Touchscreen Technology Descriptions Optical Touchscreens-Camera-based Infrared –Features Many variations on this concept Fast Scales easily Low component count Potential for multi-touch Some issues with false touch Display has to be really flat! New suppliers showing up, so costs should come down DSS

35 Touchscreen Technology Descriptions Why consider Camera-based IR in a new design? –Cost vs other large format touchSAW, DST, APR, Scanning IR –Performance/speed –Stylus independence –Excellent optics Why avoid Camera-based IR in a new design? –False touches –Display flatness –Some contamination issues –Will your supplier be there tomorrow? DSS

36 Touchscreen Technology Descriptions Pen-based Electromagnetic Digitizers –Concept: Tuned circuit in the pen locally couples energy out of grid of active wires in the sensor. –Features If you must have data entry and/or annotation as well as some traditional touch function, this might be the one High resolution, good writing fidelity Pen hover function Easy to seal, so good for harsh environments Small-medium sizes available Historically, lots of manufacturers, but most have not survived High cost Pens are almost always proprietary and unique, so a lost or failed pen is at least a minor disaster in the field Some EMI issues DSS

37 Touchscreen Technology Descriptions Why consider an electronic digitizer in a new design? –Because you need it for writing, annotating, drawing or some other special purpose that the other technologies cant handle Why avoid an electronic digitizer in a new design? –Because you dont need any of this –Will your supplier be there tomorrow? DSS

38 Touchscreen Technology Descriptions And all the other not quite ready for prime time technologies: –Best of the rest, near term, is probably digital multi-touch resistive if some materials issues with top film durability can be solved. There are existing devices, but uncertain reliability Much cheaper than PCAP Stylus independent –Longer term, one of the several in cell technologies may be sufficiently matured to consider The manufacturers would really like to eliminate add-on touchscreens, allowing them to capture the additional revenue from an in-cell approach Will be largely confined to rather small displays at first Considerable danger that some approaches will faildont be one of those customers! DSS

39 Display and Touch Technology Choices Conclusions: –Display and touch selection is an interactive process –Still no perfect touchscreen Concentrate of the features that really matter –Do sanity checks on your design early An app written for mouse control can be ported to a touch computer/display for this purpose Carefully consider the application and the user when selecting the touchscreen –Many more detailed F&B analyses can be found in technical literature –The classic this touchscreen for this app tables may be biased, but usually arent too far off –Fixing failed touchscreens in the field is a potential economic disaster –Be wary of the opinions of one technology touchscreen vendorsthey only have one thing to sell you. DSS

40 Display and Touch Technology Choices Conclusions: –For further reading: Information Display from SID –http://www.informationdisplay.org/pastissue.cfm –Numerous issues featuring touch: »December 2006 »December 2007 »March 2010 »March 2011 DSS


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