Touchscreens Scott Greenhorn EP413 – How Things Work Oct. 26th, 2017 – 10:00 am, Physics 127

Outline Background Software & Firmware History Types Resistive Capacitive Surface Acoustic Wave Infrared Conclusion & Summary https://www.pilkington.com/~/media/Pilkington/Site%20Content/Global%20Images/Digital%20Signage/touch%20screen.ashx

Background Method of Human-Computer Interaction Goal : Analog to Digital conversion Convert a touched point on a screen to a pair of x, y coordinates used by software Can include more advanced functions like Palm rejection Multitouch Pressure Sensitivity

Software & Firmware Hardware provides x, y coordinates, which are mapped as mouse clicks by OS Often, features like palm rejection are done in software Scrolling or dragging is accomplished by measuring an initial point of contact and computing the vector between a recent position and the initial position Software design for touchscreens is more difficult, as keyboard and/or mouse interrupts must be mapped to locations on the screen

History of Touchscreens 1965 : E.A. Johnson at Royal Radar Establishment in U.K. First touchscreen (capacitive type) Used by air traffic controllers until 1990s Limited to 1 touch and no pressure sensing 1970 : Dr. G. Samuel Hurst Used conductive paper on a grid of wires to read x, y coordinates Resistive type Became the most common type of touchscreen for several decades

History of Touchscreens 1982 : Nimish Mehta at University of Toronto First multitouch using camera and frosted-glass panel Led to use of ‘gesture’ control on touchscreens Early 1980s : HP HP-150 touchscreen desktop commercialized Ergonomic complaints arise, ‘Gorilla Arm’ coined shortly thereafter https://arstechnica.com/gadgets/2013/04/from-touch-displays-to-the-surface-a-brief-history-of-touchscreen-technology/2/

History of Touchscreens 1984 : Bob Boie at Bell Labs First capacitive multitouch overlay Allows touchscreens to work with conventional displays Early 1990s : Touchscreen devices become common IBM/BellSouth Simon Personal Communicator Apple Newton Palm Pilot

History of Touchscreens Late 1990s : Wayne Westerman’s doctoral dissertation Described the method on which modern multitouch device firmware is based Formed FingerWorks company, later bought by Apple Early 2000s : touchscreens are refined and begin appearing in more devices, including cellphones 2007 : Apple iPhone Touchscreens become ubiquitous in mobile devices https://www.technobuffalo.com/wp-content/uploads/2016/09/iphone-2007-revisited-24-470x310@2x.jpg

Types - Resistive First type to be commercialized Functionality : a multi-layer screen, with a flexible, conductive upper layer, a moving array of spacer dots, and two grids of wires (x and y) Transmits 75% of light through Different varieties with 4, 5, 6, 7, or 8 wires

Types - Resistive IC measures current along wires and calculates the location of the touch based on changes in current Works with anything that can put pressure on display : fingers, stylus, etc. Commonly used in older devices : old phones, Nintendo DS, etc.

Types - Capacitive Most commonly used today, in nearly any modern mobile device Functionality : a glass panel coated in Indium Tin Oxide (conductive), with another conductive inner layer, separated by glass. Essentially a capacitor Transmits 90% of light

Types - Capacitive The IC measures the changes in capacitance and finds the position that was touched Two different methods : Surface capacitive – measures capacitance at the four corners Projective-Capacitive, where ITO layer is etched into grid, and capacitance is measured at row/column intersections. Requires a conductive object to register a touch

Types – Surface Acoustic Wave A less common, more expensive type of touchscreen Functionality : Transmitter and Receiver transducers on x and y axes, as well as reflectors. Ultrasonic bursts are sent, and received, but are absorbed where the screen is touched Allows 100% of backlight to pass Works with any interaction, but vulnerable to contamination, which absorbs ultrasound

Types - Infrared Another less common type of touchscreen Uses a grid of infrared LEDs and photo detectors. A touch on the screen absorbs a certain amount of specific LED’s light, measured by the photodetectors, which determines the place that was touched. Transmits 100% of backlight Often used in outdoor environments due to durability

Summary Touchscreens developed from experimental devices to nearly ubiquitous in a span of under 50 years Many advances in technology, hardware and firmware, have made this possible There are a wide variety of implementations for touchscreens that have been used, each with strengths and weaknesses. https://i.ytimg.com/vi/XVbuk3jizGM/maxresdefault.jpg

References Touchscreens or Human Machine Interface (HMI) EngineersGarage - https://www.engineersgarage.com/articles/touchscreen-technology-working What Are The Different Types Of Touchscreen http://www.cammaxlimited.co.uk/what-are-the-different-types-of-touchscreen/ From touch displays to the Surface: A brief history of touchscreen technology Florence Ion - Apr 4, 2013 1:00 pm UTC - https://arstechnica.com/gadgets/2013/04/from-touch-displays-to-the-surface-a-brief-history-of-touchscreen-technology/