Display and Touch Technology Choices

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

2. Elements of a Touchscreen System • Hardware • Touchscreen • Controller • Cables • Software • Drivers for standard OSs, or • Touch processing code in the application D S S

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 doesn’t apply in a stand-alone product… D S S

4. Display Technologies • “Standard” display panels --Most common is transmissive AMLCD • Limited availability of reflective/transflective panels—usually smaller sizes • Emissive panels • Plasma • VF • AMOLED becoming available in small sizes • System processor may dictate display type and size/resolution D S S

5. Display Technologies, cont’d • Display/touchscreen interactions can affect display AND touchscreen choice. Things to consider will largely be in the areas of: • Optics • EMI • Environment D S S

6. Touchscreen Technologies • Commercially available touchscreens: • Analog resistive—four 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 resistive—analog and digital • “In cell” touch (several variations) D S S

7. Touchscreen Technology Descriptions • Resistive • Concept: a two axis voltage divider • Two major types—four and five wire • 4W—a dedicated conductive sheet for each axis D S S

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 D S S

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 D S S

10. Touchscreen Technology Descriptions • Resistive important details • “Separator dots” between the two active sheets: • Hold the sheets apart except when touched • ~100-200um (0.004-0.008 “) diameter • ~10-40um height • Screen or foil printed • Construction can be “film-film” laminated to rigid backplate, film-glass, or glass-glass D S S

11. Touchscreen Technology Descriptions • Resistive important details • “Construction can be “film-film” laminated to rigid backplate, film-glass, or glass-glass • Typical cross section: Plastic (Coversheet) Adhesive Spacer ITO Coating Glass 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 interface—USB, RS232 for PNP, I2C, SPI, etc. for embedded D S S

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. D S S

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 1 4 Resistive Network Touchscreen Glass 2 5 D S S

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. • 15-30% 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 transmission—typ 80%--and very reflective • OK for many indoor apps, poor in direct sunlight. • Standard 5W does not support multi-touch D S S

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 D S S

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 D S S

19. Touchscreen Technology Descriptions • Why consider Surface Capacitive in a new design? • Established technology in gaming, kiosks and some ATMs—customer 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 D S S

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 capacitance—measured to a common electrode for both axes • Mutual capacitance—measured between a given electrode and nearby electrodes in the 2nd axis array. Supports multi-touch. • Measurement not a trivial issue—capacitance 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. D S S

21. Touchscreen Technology Descriptions • Projected Capacitive • Features • Many different glass and/or film constructions possible—can 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 sizes—for cell phones and tablets • Availability of larger sizes as component limited • Few third party controllers available in any form D S S

22. Touchscreen Technology Descriptions • Projected Capacitive • Features, cont’d • Excellent finger sensitivity • But poor gloved hand/stylus sensitivity • Good portable/mobile performance—none 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 requirements—less 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 finish—no CP filters D S S

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. D S S

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 Piezo-electric transducers (4) YR YT XR Y Axis 5.53MHz“burst” signal from XT, YT Return signal from XR, YR XT D S S X Axis ~5 Time in usec 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 46”diagonal • Desktop+ sizes cost competitive with other technologies

26. Touchscreen Technology Descriptions • SAW Features, cont’d • Good EMI performance • Vandal resistant--adapts to surface scratches • Finger or soft stylus touch only • “Point and shoot” touch excellent • Dragging may produce skips—glass finish, finger moisture, stylus type, etc. • Some issues with environmental sealing and contamination sensitivity • Similar to PCAP re optical enhancements—no 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) D S S

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. D S S

29. Touchscreen Technology Descriptions • APR (Elo) and DST (3M) • Features • Plain glass with backside piezo-electric pickups • Excellent optics—no conductive coatings • Very up scalable—large touch monitors available • Works with fingers and most stylii—may be some issues with rubber gloves • Easy environmental sealing • No touch and hold capability (no signal after initial touch) D S S

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 D S S

31. Touchscreen Technology Descriptions • Optical Touchscreens—Scanning 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 IR Diode Photo transistor D S S

32. Touchscreen Technology Descriptions • Optical Touchscreens—Scanning Infrared, cont’d • Features • Scalable, but cost increases with size/component count • Few standard designs—most 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 D S S

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? • Cost—needs large quantity to overcome NRE • Speed, resolution • Some sunlight de-sense issues D S S

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 D S S

35. Touchscreen Technology Descriptions • Why consider Camera-based IR in a new design? • Cost vs other large format touch—SAW, 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? D S S

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 D S S

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 can’t handle • Why avoid an electronic digitizer in a new design? • Because you don’t need any of this • Will your supplier be there tomorrow? D S S

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 fail—don’t be one of those customers! D S S

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 aren’t too far off • Fixing failed touchscreens in the field is a potential economic disaster • Be wary of the opinions of one technology touchscreen vendors—they only have one thing to sell you. D S S

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 D S S