Introduction of Touch Technologies EE174 – SJSU Tan Nguyen

Touch Technologies Introduction Brief History Market and Trends Touchscreen Technology Resistive Capacitive Surface Acoustic Wave (SAW) Infrared LED or Optical Touchscreen System Applications

Introduction An electronic visual display that locates the coordinates of a users touch within display area Works independently of what is being displayed on screen Allows a display to be used as an input device, removing the keyboard and/or the mouse as the primary input device for interacting with the display's content Can be used without any intermediate device Being used in a wide variety of applications to improve human-computer interaction. Because of its convenience, touchscreen technology solutions has been applied more and more to industries, applications, products and services, such as modern smartphones, video games, kiosks, navigation systems, POS, tablets, etc...

Invented by E.A. Johnson (Royal Radar Est.) around 1965 for air traffic control First "touch sensor" was developed by Dr Sam Hurst in HP-150 home computer using infrared technology in Apple’s Newton and IBM’s Simon 2002 Microsoft’s Windows XP Tablet 2007 Apple’s iPhone (Multi-touch) Brief History

Overall Touchscreen Market Compound Annual Growth Rate

Touchscreen Market by Technology (Units)

Touchscreen Technology There are four different technologies used to make touchscreens today: Resistive Sensing Capacitive Sensing Surface Capacitance Projected Capacitance (Self and Mutual Capacitance) Surface Acoustic Wave (SAW) Infrared LED or Optical

The Big Three of Touchscreen Technology Resistive Touchscreens are the most common touchscreen technology. They are used in high-traffic applications and are immune to water or other debris on the screen. Resistive touchscreens are usually the lowest cost touchscreen implementation. Because they react to pressure, they can be activated by a finger, gloved hand, stylus or other object like a credit card. Surface Capacitance Touchscreens provide a much clearer display than the plastic cover typically used in a resistive touchscreen. In a surface capacitive display, sensors in the four corners of the display detect capacitance changes due to touch. These touchscreens can only be activated by a finger or other conductive object. Projected Capacitance Touchscreens are the latest entry to the market. This technology also offers superior optical clarity, but it has significant advantages over surface capacitive screens. Projected capacitive sensors require no positional calibration and provide much higher positional accuracy. Projected capacitive touchscreens are also very exciting because they can detect multiple touches simultaneously.

Resistive Technology 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 Any material can trigger sensors Indium Tin Oxide (ITO) Polyethylene (PET) PET: Polyethylene Terephthalate

4-Wire Analog Resistive Touch Screen: How does it work?

Types: 4-wire (low cost, short life) is common in mobile devices 5-wire (higher cost, long life) is common in stationary devices 6-wire & 7-wire, 8-wire = replacement only Constructions Film (PET) + glass (previous illustration) is the most common Film + film (used in some cellphones) can be made flexible Glass + glass is the most durable; automotive is the primary use Film + film + glass, others… Size range 1” to ~24” (>20” is rare) Analog Resistive Technology Controllers Many sources Single chip, embedded in chipset/CPU, or “universal” controller board Suppliers Young Fast, Nissha, Nanjing Wally, Truly, EELY, Mutto, J-Touch… 60+ suppliers Applications Mobile devices (shrinking) Point of sale (POS) terminals Automotive Industrial Wherever cost is #1

Disadvantages Not durable (PET top surface is easily damaged) Poor optical quality - The flexible top layer has only 75%-80% clarity If the ITO layers are not uniform, the resistance will not vary linearly across the sensor. Measuring voltage to 10 or 12-bit precision is required, which is difficult in many environments. No multi-touch Require periodic calibration to realign the touch points with the underlying LCD image. Analog Resistive Technology Advantages Works with finger, stylus or any non-sharp object Lowest-cost touch technology Widely available (it’s a commodity) Easily sealable to IP65 or NEMA-4 Resistant to screen contaminants Low power consumption Market trends Analog resistive is shrinking in units and revenue ● P-cap dominates in most consumer applications Analog resistive is still significant in commercial applications ● Especially POS and industrial-control terminals

Surface Capacitance In this technology, glass is uniformly coated with a conductive layer. During operation, a voltage signal is applied to all four corners of the panel, resulting in a uniform electrostatic field. When a human finger touches the panel, it forms a capacitance where one plate is the conductive layer and the other being the human finger. Depending upon the location of the finger touch, current drawn from the four corners will be different and thus the capacitance seen by those corners will also be different. This difference can be used to determine the exact location of the touch

Advantages: Surface capacitive technology is suitable for large size monitors. Surface capacitive sensor can respond to light touch, and no pressure force is needed for detection Visibility is high because structure is only one glass layer. Surface capacitive is structurally tough as it is made of one sheet of glass. Surface capacitive does not get affected by moist, dust, or grease. Parallax is minimized in surface capacitive. Surface capacitive has high resolution and high response speed. Highly sensitive (very light touch) Disadvantages: Surface capacitive can detect touches by fingers only nurface capacitive technology does not support multi-touch. Surface capacitive touch screen is likely to be affected by noise. Recently, tolerance for noise has been improved with various methods such as noise shielding. Surface Capacitive

Self-Projected Capacitive ● Uses rows and columns of conductors (overlayed in a grid pattern) ● One capacitor for each row and for each column ● A controller detects changes in capacitance for each row & column ● Controller determines an (x,y) coordinate based on the changes ● Self capacitance measure an entire row or column for capacitive change.

Self Capacitance The sensor forms a parasitic capacitance Cp with the surrounding ground pattern, and the electric field lines can be seen in the area above the sensor. When a conductor like a finger enters the area above this sensor, it alters the electric field lines and effectively adds a finger capacitance Cf to the sensor This results in an increase in capacitance of the sensor from Cp to Cp + Cf. Typical Capacitor Values: Cp ~ 15 pF Cf ~ 0.5 pF Finger capacitance added to the sensor

Mutual Capacitance Uses an array of capacitors (located at each intersection of conductor grid). When a finger touches the panel, the mutual capacitance between the row and column is reduced. This reduction in capacitance is used to identify the presence of a finger. As every intersection has its own mutual capacitance and can be independently tracked, this method provides a distinct advantage for detecting multiple fingers.

Self versus Mutual Capacitance Capable of recognizing multiple touches (Multitouch) Result: X3 & X0 = 0 X2 & X1 = 1 Y0 & Y3 = 1 Y1 & Y2 = 0 Conclusion: X2, Y0 = 1 X2, Y3 = 1 G X1, Y0 = 1 G X1, Y3 = = 8 Sensors Result: X2 * Y0 = 1 X1 * Y3 = 1 Conclusion: X2, Y0 = 1 X1, Y3 = * 4 = 16 Sensors Ghost points = False touches positionally related to real touches

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Surface Acoustic Wave (SAW) SAW touch screen consists of one glass sheet with transmitting transducers, receiving transducers, and reflectors. Transmitting transducers generate ultrasonic waves that travel over the panel surface. The ultrasonic waves are reflected by the reflectors and received by the receiving transducers. SAWs are sent out from the transmitting transducers, and traveling along the edge of panel. The reflectors located on the edge of the panel change directions of the SAWs at the angle of 90 degrees, thus the SAWs travel over the panel. Once the SAWs reached the other side of the panel, their directions get changed again by the reflectors located on the other side, and travel toward the receiving transducers. Once the SAWs are received by the receiving transducers, they will be converted into electric signals.

There are routes on which the SAWs travel from the transmitting transducers to the receiving transducers. Each route has its own distance. If one of the routes is touched by a finger, the pulse will be absorbed, and the SAW on the route will not be received by the receiving transducers. Thus, the sensor will recognize which route was touched, and locate the touched point. Surface Acoustic Wave (SAW)

Advantages: Visibility is excellent because it consists of one glass layer. SAW touch screen is notable for its durability. Even though the panel surface gets scratched, its sensing function will not be affected. It is relatively easy to build a large size touch screen in SAW technology. SAW touch screen does not get affected by external electric noise. Accuracy of detecting touched points does not get affected by environment nor passage of time. Thus, it is free of maintenance. Resolution is relatively high. Disadvantage: The frame areas need to be wide because transducers are located. Detecting function of SAW technology can be affected by water droplet, oil and so on. Malfunction can be caused by those factors. SAW touch screen does not detect a touch by hard materials which do not absorb pulse. Surface Acoustic Wave (SAW)

Size range 6” to 52” Advantages Visibility is excellent because it consists of one glass layer. Finger, gloved hand & soft-stylus activation Notable for its durability; can be vandal-proofed with tempered or CS glass SAW touch screen does not get affected by external electric noise. Accuracy of detecting touched points does not get affected by environment nor passage of time. Thus, it is free of maintenance. Disadvantages Very sensitive to any surface contamination, including water Relatively high activation force (50-80g typical) Requires “soft” (sound-absorbing) touch object Can be challenging to seal

Surface Acoustic Wave (SAW) Suppliers Elo Touch Solutions and General Touch have >90% share <10 suppliers Market trends Two-touch and zero-bezel SAW should help reduce loss of share to p-cap in commercial applications SAW will continue to grow moderately through 2017 Applications SAW is usually employed for large size applications such as kiosk, arcade game, automated cash dispenser, medical equipment, office automation, factory automation, financial field, and so on.large size applicationskioskarcade gamemedical equipmentoffice automationfactory automation

An infrared touchscreen uses a grid pattern of LEDs and light-detector photocells arranged on opposite sides of the screen.infraredLEDs photocells The LEDs shine infrared light in front of the screen—a bit like an invisible spider's web. If you touch the screen at a certain point, you interrupt two or more beams. A microchip inside the screen can calculate where you touched by seeing which beams you interrupted. Since you're interrupting a beam, infrared screens work just as well whether you use your finger or a stylus. Traditional Infrared

Variations Bare PCB vs. enclosed frame; frame width & profile height; no glass substrate; enhanced sunlight immunity; force-sensing Size range 8” to 150” Controllers Mostly proprietary, except IRTouch (China) Ad vantages Scalable to very large sizes Multi-touch capable (only 2 touches, and with some “ghost” points) Can be activated with any IR-opaque object High durability, optical performance and sealability Doesn’t require a substrate

Disadvantages Profile height (IR transceivers project above touch surface) Bezel must be designed to include IR-transparent window Sunlight immunity can be a problem in extreme environments Surface obstruction or hover can cause a false touch Low resolution High cost Applications Large displays (digital signage) POS (limited) Kiosks Suppliers IRTouch Systems, Minato, Nexio, OneTouch, SMK, Neonode… 10+ suppliers Traditional Infrared

COMPONENTS OF TOUCHSCREEN A basic touchscreen system has three main components: A touch screen. A controller Software driver. The touchscreen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.

Touch Screen The touchscreen is the face of a touchsystem and the user's first contact point with the system. Its importance cannot be overstated, since it defines the quality and tactile feel of the touch system, and offers the only user interface. Key functional properties of the touchscreen are its optical transparency, its hardiness to wear and tear, and its touch accuracy. In all these areas, five-wire technology excels.

Controller The controller - essentially the brain of the touch system - contains a microprocessor, analog-to-digital converters, and microchips to enable communication with the host PC. The controller powers the touchscreen, controls the excitation, and interprets the information received from the touchscreen. The controller filters the returning touchscreen data and converts it into raw touch coordinates, which are then sent to the PC by a digital software protocol. A good controller will also perform substantial error-checking to detect abnormal or inconsistent touches and filter them out. The controller determines what type of interface/connection you will need on the PC. Controllers are available that can connect to a Serial/COM port (PC) or to a USB port (PC or Macintosh). Specialized controllers are also available that work with DVD players and other devices.

Software Driver The driver is a software update for the PC system that allows the touchscreen and computer to work together. The driver software, residing on the host PC, is required to manage the raw coordinate data coming from the controller, apply calibration algorithms, position the mouse cursor, and generate mouse clicks. Other important tasks include routines to define the video alignment parameters, and screening of incoming touch data for errors, inconsistencies, and integrity. Good driver software will also offer diagnostic information in troubleshooting situations.

Touch Technologies by Size & Application

Touch Technologies Comparisons

Touch Technologies by Materials & Process

Touch Is An Indirect Measurement

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