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

2. Outline Background Software & Firmware History Types
Resistive
Capacitive
Surface Acoustic Wave
Infrared
Conclusion & Summary

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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

12. 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

13. 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

14. 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

15. 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.

16. References Touchscreens or Human Machine Interface (HMI)
EngineersGarage -
What Are The Different Types Of Touchscreen
From touch displays to the Surface: A brief history of touchscreen technology
Florence Ion - Apr 4, :00 pm UTC -