Input Devices

Dimensions to Classify Computer Input

Sensing Method

• Mechanical (e.g. switch, potentiometer)
• Motion (e.g. accelerameter, gyroscope)
• Contact (e.g. capacitive touch, pressure censor)
• Signal processing (e.g. computer vision, audio)

Continous vs. Discrete

Degrees of Freedom (DOF)

Typewriters and QWERTY

• QWERTY is designed to space "typebars" to reduce jams and speed typing up

Problems:

• Common combinations require awkard finger motions
• Common combinations require a jump over home row
• Common combinatiosn are typed with one hand
• Most typing with left hand

• (16% lower row, 52% top row, 32% home row)

• Alternatives includes DVORAK and QWERY

DVORAK Layout

• Letteres should be typed by alternating between hands
• Most common letters and diagraphs should be easiest to type
  • about 70% of strokes are on home row
• The least common letteres should be on the bottom row, which is the hardest to reach

• The right hand should do more of the typing (most people are right handed)

• Does not significantly improve speed in comparison to QWERTY

Mechanical Design of Keyboards

• Downsized keyboards to improve portability
  • Interferes with typing

Virtual Keyboards

• Touch screen or other flat surface

Chording Keyboards

Englebart's NLS Keyboard

• Multiple keys together to produce letter
• No "targeting", potentially very fast
• Can be small and portable
• One handed

Thand Starner's Twiddler

• For wearable computing input

Text Recongnition and Gestures

• Graffiti/Unistroke Gestures
  • Map single strokes to "enter letter" commands
• Natural handwiriting recognition
  • Dictionary-based classification algorithms

Predictive Text

• Use language characteristics to predict input
  • The most likely intended character and word giving the existing input
• A variation is used for T9, nine-key text entry (traditional phones)
  • Given an ambiguous set of characters, what is the most likely word
• Potential problems
  • "Collisions" between common words
  • Entering words that's not in the dictionary is difficult
  • hard to focus on typing and monitoring prediction

Positional Input Devices

Absolute vs. Relative positioning

• Absolute - a direct mapping of input device position to a display input position

  • e.g. touchscreen

• Relative - maps changes in input device position to changes in display input position

  • e.g. mouse

Direct vs. Indirect contact

• Direct: touchscreen

• Indirect: mouse

• Absolute direct: touchscreen

• Relative indirect: digitizer

Force vs. Displacement sensing

• Force: most joysticks

• Displacement: mouse

• Also called isometric vs. isotonic

• Elastic isometric devices vs. pure isometric devices

Position vs. Rate control

• Rate: joysticks

• Position: mouse

• Force sensing (isometric) should be mapped to rate (speed)

• Displacement (isotonic) sensing should be mapped to position

DOF (dimensions) sensed

• 1 = dial, 2 = mouse, 3 = Wiimote

Control-Display Gain (CD Gain)

• Ratio of display pointer movement to device control movement
  • A scale factor
  • Usually expressed in terms of velocity
  • Works for rate/position control

$CDgain=V_{pointer}/V_{device}$

Gesture Input

• Maps movements to commands (position of body part)