Lecture 6: Touch & Multi-Touch Interfaces

Vocabulary flashcards covering key hardware technologies, sensing methods, user-identification techniques, and interaction challenges discussed in the Touch & Multi-Touch Interfaces lecture.

Multi-Touch Interface

An interactive surface that can detect and process multiple simultaneous touch points from one or several users.

Resistive Touch Sensing

A technology that uses two flexible, conductive layers separated by a gap; a press closes the circuit, and position is derived from measured resistance.

Capacitive Touch Sensing

Touch detection that measures changes in capacitance caused by a conductive object approaching or contacting sensor electrodes.

Self-Capacitance

Capacitive technique that senses the capacitance between a single electrode and ground, enabling proximity and single-touch detection.

Mutual Capacitance

Capacitive sensing method that measures coupling between two electrodes (transmit and receive), supporting robust, high-resolution multi-touch.

Force-Sensitive Resistor (FSR)

A sensor made from conductive polymer whose resistance decreases with applied force, enabling continuous pressure measurement.

Interpolating Force-Sensitive Resistance (IFSR)

A grid of wires sandwiching a pressure-sensitive sheet that outputs a 2-D pressure image, allowing inexpensive, flexible multi-touch + pressure sensing.

CapSense Library

An Arduino software library that simplifies measuring self-capacitance via timing the RC charge/discharge cycle.

Time Constant (R × C)

The product of resistance and capacitance that determines how quickly a capacitor charges or discharges (63.2 % after one time constant).

Simple 2-D Sensing Using Interpolation

Capacitive method where four edge electrodes create fields; touch location is interpolated from the capacitance change at each electrode.

Swept Frequency Capacitive Sensing (SFCS)

Technique that excites an electrode over a range of frequencies; frequency-dependent responses are classified to identify touch context (e.g., Touché).

Touché

Disney Research system that applies SFCS to recognize complex touch gestures and object interactions on everyday conductive items.

Capricate

TU Darmstadt approach that embeds printed electrodes in 3-D-printed objects for capacitive touch detection.

Plush Game Controller

A soft toy interface that employs conductive fabric electrodes read by an Arduino for capacitive button input.

MPR121

Adafruit breakout board for self-capacitance sensing, supporting up to 12 touch pads via the I²C bus.

MTCH6303

Microchip controller that provides mutual-capacitance sensing for up to 10 concurrent touches over USB or I²C.

Multi-Touch Kit

An open-source toolkit that delivers mutual-capacitance multi-touch sensing using only a standard Arduino—no custom IC required.

Surface Acoustic Wave Sensing

Touch detection that analyzes acoustic waves propagating through a surface, captured by attached microphones.

Skinput

CMU/Microsoft research that localizes taps on the human arm by classifying body-propagated acoustic signals.

IR Grid Sensing

Optical touch method forming horizontal and vertical infrared beams; a touch breaks two beams, revealing its coordinates.

Frustrated Total Internal Reflection (FTIR)

Optical sensing where touches disturb internally reflected IR light inside acrylic, producing bright spots captured by a camera.

Diffuse Illumination (DI)

Technique that floods a rear-projection surface with IR light; cameras see reflections from touch points and objects.

Embedded Optical Sensing (ThinSight)

Grid of mini IR emitters and sensors embedded beneath an LCD, enabling thin, scalable, multi-touch detection of arbitrary shapes.

Depth-Camera Based Touch Sensing

Approach using an overhead depth sensor to track fingertip positions and distinguish contact from hover via depth thresholds.

DiamondTouch

Capacitive tabletop that identifies users by coupling AC signals from the surface through chairs to individual receivers.

HandsDown

System that recognizes users by comparing the geometric shape of their flat-laid hands on the touch surface.

Fiberio

Rear-projection display whose special diffuser lets a camera capture fingerprints, enabling touch-time user authentication.

Carpus

User-identification method that classifies visual features of the back-of-hand captured by an overhead RGB camera.

SmartSkin

Early mutual-capacitance prototype (2002) that sensed hands hovering above a table for freehand manipulation.

Multi-Touch Skin

Ultra-thin, deformable electrode array for high-resolution mutual-capacitance sensing directly on human skin.

Fat Finger Problem

Imprecision caused by the relatively large contact area of a finger, making it hard to select small UI targets accurately.

Precise Selection Techniques

Methods (dual-finger midpoint, X-Menu, stretch, rocking) devised to overcome the fat finger problem on touch screens.

Midas Touch Problem

Issue where every touch is interpreted as intentional input because standard touch lacks a hover state for disambiguation.

Buxton’s 3-State Model

Mouse input framework (out-of-range, tracking, dragging) that highlights the missing hover state in touch interaction.

Gestural Interaction

Use of multi-finger or multi-hand movements (pinch, rotate, two-hand box) to manipulate objects on touch surfaces.

Posture-Based Interaction

Technique where distinct hand shapes (one finger, fist, palm) explicitly signal modes or commands instead of motion gestures.

Field-of-View Issues

Challenge that large wall/table displays exceed a user’s visual field, complicating overview and detail work.

Reachability Issues

Difficulty touching distant UI elements on large horizontal or vertical surfaces; often mitigated with tangibles or remote gestures.

Hover State

An interaction phase where an input device is detected above the surface without activating it—present in mice, absent in basic touch.