Touchscreen implementation for multi-touch

Touchscreens & Graphical User Interface

Guiding principles behind GUI
Displays relevant information
Intuitive technology
Touchscreen
Electronic

Touchscreen Technologies
Resistive
Capacitive
Surface
Projected
Optical imaging
Infrared

Resistive Touchscreen

Composed of multiple layers separated by thin spaces
Using indium tin

Resistive Touchscreen

User Presses Down
Contact is Made
Uniform Voltage on First Screen for

4-Wire design

One screen for X
Another screen for Y
Both create voltage gradient.
Uses

Advantages

Works well with fingertip or stylus input
Generally most affordable touchscreen technology
Rugged/Durable
Has

Disadvantages

Not as accurate
Multi-touch much more complex
Usually no discretion between stylus and

Capacitive Touch Technology

Consists of:
Insulator (glass or Air)
Conductive coating (ITO)
Two types:
Surface
projected

Surface Capacitance

Only one side is coated
Electrodes at the edges
Distribute voltage

Surface Capacitance Cont.

Before

After

Capacitor forms
Current flows

Determine location
Controller
Ratio of currents
,
XY coordinates

R

Projected Capacitance

Two parallel ITO layers
Two sheets of glass

Projected Capacitance

Capacitor at each point on the surface

Projected Capacitance Cont.

E Field is projected through glass
Finger couples with E

Surface vs. Projected

Limited resolution
Single touch
Operation with direct contact

High resolution
Multi

Multi-Touch Using Infrared

Frustrated Total Internal Reflection

A process by which light is trapped within

Rear Projection

Hardware
Infrared LED’s or lasers with line generator for optical

Alternative Single-Unit Design

Eliminates rear projection
Expensive
Robustness

http://wiki.fluidproject.org/display/fluid/Benchmarking+-+Touch+Screen+Options

Software

Surface Capture via Detector

Digitized View

Software Cont.

Interpret and Relay Information
Assign Objects or gestures with Unique ID#

Improving Accessibility?

Universal Design Principles
Utility for all users
Simple and intuitive
Touchscreens depend on

Pointing Device Gestures

Cursor movements as command shortcuts
Takes place of keyboard shortcuts
Useful

Implementation: Step 1

Filter Input
Sampling rate
Smooth out input data, get rid of

Implementation: Step 2

Vectorize
Separate x- and y-component
Compute dominant component and ignore smaller

Implementation: Step 3

Matching
Match captured vector array to pre-defined gesture library
If no

Example

Fig. 1 – User input

Fig. 2 – Captured/filtered pointer data

Fig. 3

Goal

Allows for a quicker and more efficient UI
Universal Design
Enhances usability for