Björn Hartmann [email protected]

stanford hci group Feb 9, 2009

Björn [email protected]

Understanding & ModelingInput Devices

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Questions for today1. How do common input devices

work?2. How can we think about the larger

space of all possible input devices?3. Can we predict human input

performance?

Next class: What about uncommon input devices (music controllers, multitouch, …)?

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Today’s lecture in graph form

time

Level of abstraction

concretedetails

abstractmodels Functional

Dissection of Mouse & Keyboard

Design Space of

Input Devices Modeling

Human Performance

I spilled coffee on my keyboard. Now 25% of the keys don’t work anymore.But some of the defective keys are nowhere near the spill.What’s going on?

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Key cap

Top conductive layerBottom conductive layer

Separating layer(with hole)

Key cap

Top conductive layerBottom conductive layer

Separating layer(with hole)

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Row/Column Scanning

Q W E R T

A S D F G

Z X C V B

R1

R2

R3

R4

C1 C2 C3 C4 C59 lines

20 keys

Mouse. Engelbart and English ~1964Source: Card, Stu. Lecture on Human Information Interaction. Stanford, 2007.

A Layered Framework

12From: Hartmann, Follmer, Klemmer: Input Devices are like Onions

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Right button

Left buttonEncoder wheel for scrolling

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IR emitter IR detectorslotted wheel(between emitter & detector)

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Sensing: Rotary Encoder

High

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Sensing: Fwd Rotation

Low

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Sensing: Backwd Rotation

Low Oops!

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Solution: Use two out-of-phase detectors

HighHigh

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Sensing: Rotary Encoder

LowHigh

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Sensing: Rotary Encoder

HighLow

Coding:HH-> LH: dx = 1HH-> HL: dx = -1

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Transformationcxt = max(0, min( sw, cxt-1+dx*cd ))cyt = …

cxt: cursor x position in screen coordinates at time tdx: mouse x movement delta in mouse coordinatessw: screen widthcd: control-display ratio

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Device Abstraction Click, DoubleClick, MouseUp,

MouseDown, MouseMove …

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What about optical mice?

Source: http://spritesmods.com/?art=mouseeye

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bbbbbbbbbb

Source: http://spritesmods.com/?art=mouseeye

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Trackball, Trackpad

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Trackpoint Indirect, force sensing, velocity

control Nonlinear transfer function

Force

Velo

city

(cc) Image by flickr user tsaiid

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Joysticks

A design space of input devices…

Card, S. K., Mackinlay, J. D., and Robertson, G. G. 1991. A morphological analysis of the design space of input devices. ACM TOIS 9, 2 (Apr. 1991), 99-122.

Implicit Assumptions: Desktop-centric computing

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Which device is fastest? For what task? Pointing.

Combination of two factors: Bandwidth of human muscle group

(upper limit) Bandwidth of device itself

Bandwidth of Human Muscle Groups

Source: Card, Stu. Lecture on Human Information Interaction. Stanford, 2007.

Fitts’ Law Time Tpos to move the hand to

target size S which is distance D away is given by: Tpos = a + b log2 (2D/S)

Time to move the hand depends only on the relative precision required

Source: Landay, James. “Human Abilities”. CS160 UC Berkeley.

Mouse vs. Headmouse

Source: Card, Stu. Lecture on Human Information Interaction. Stanford, 2007.

Headmouse: No chance to win

Source: Card, Stu. Lecture on Human Information Interaction. Stanford, 2007.

Fitts’ Law in Windows & Mac OS

Windows 95: Missed by a pixelWindows XP: Good to the last drop

The Apple menu in Mac OS X v10.4 Tiger.

Source: Jensen Harris, An Office User Interface Blog : Giving You Fitts. Microsoft, 2007; Apple

Fitts’ Law in Microsoft Office 2007

                                                  Larger, labeled controls can be clicked more quickly

                            Mini Toolbar: Close to the cursor

                Magic Corner: Office Button in the upper-left corner

Source: Jensen Harris, An Office User Interface Blog : Giving You Fitts. Microsoft, 2007.

stanford hci group Feb 9, 2009

http://bjoern.org