Tracking and Characterizing Knocks Atop Large Interactive Displays
- ISSN: 02602288
- DOI: 10.1108/02602280510585727
Abstract
We describe a system that locates and characterizes knocks and taps atop a large sheet of glass using four contact piezoelectric pickups located near the sheet's corners to simultaneously record the structural-acoustic wavefront coming from the impacts. A digital signal processor extracts relevant characteristics from these signals, such as amplitudes, frequency components, and differential timings, which are used to estimate the location of the hit and provide other parameters, including a degree of confidence in the position accuracy, the nature of each hit (e.g., knuckle knock, metal tap, or fist bang - our system responds to any kind of impact), and the strike intensity. As this system requires only simple hardware, it needs no special adaptation of the glass pane, and allows all tracking transducers to be mounted on the inner surface, hence it is quite easy and inexpensive to deploy as a retrofit to existing windows. This opens many applications, such as an interactive storefront, with content controlled by knocks on the display window.
Author-supplied keywords
Tracking and Characterizing Knocks Atop Large Interactive Displays
Displays
Joseph A. Paradiso and Che King Leo
Responsive Environments Group
MIT Media Laboratory
Cambridge, MA 02142 USA
{joep,cheking}@media.mit.edu
Abstract
We describe a system that locates and characterizes knocks and taps atop a large sheet of glass using
four contact piezoelectric pickups located near the sheet's corners to simultaneously record the
structural-acoustic wavefront coming from the impacts. A digital signal processor extracts relevant
characteristics from these signals, such as amplitudes, frequency components, and differential timings,
which are used to estimate the location of the hit and provide other parameters, including a degree of
confidence in the position accuracy, the nature of each hit (e.g., knuckle knock, metal tap, or fist bang –
our system responds to any kind of impact), and the strike intensity. As this system requires only simple
hardware, it needs no special adaptation of the glass pane, and allows all tracking transducers to be
mounted on the inner surface, hence it is quite easy and inexpensive to deploy as a retrofit to existing
windows. This opens many applications, such as an interactive storefront, with content controlled by
knocks on the display window.
Keywords
touch screen, large interactive display, passive impact tracking, structural acoustics, acoustic
characterization
In Sensor Review (special issue on Vibration & Impact Sensing), Vol. 25, No. 2, pp. 134-143.
A major research thrust in HCI (Human-Computer-Interaction) is centered around investigating
large display walls [1]. When they are made interactive, large displays open up entirely new types of
group collaboration, in contrast, for example, with video kiosks, which interface mainly with single
users. Participants at interactive walls are part user and part performer – in public settings, crowds tend
to spontaneously gather to watch, contribute, and suggest choices as somebody interacts with a large
display wall. Technologies now used to track user activity atop a very large display, however, generally
involve several compromises, such as difficulty in scaling economically to large active areas, robustness
to different kinds of user input gesture, or ruggedness, especially for outdoor settings.
Glass is now a very common construction material, often used as clear walls for room dividers or
large windows bordering urban buildings. The techniques described in this paper aim at easily enabling
these large surfaces to become interactive by tracking the position of knocks atop the glass. For
example, information displayed on a projection or monitor on the inside of the glass can be determined
by knocking appropriately on the outside. A straightforward application of this niche is an interactive
storefront, where passers-by can navigate through information on the store's merchandise or explore
special offers by knocking appropriately, even when the store is closed.
This paper describes the hardware, software, and algorithms that we have developed in realizing
this capability, and presents application examples from installations that we’ve mounted in recent years
that exploit this system.
2) OTHER APPROACHES
Many techniques have been developed to track the position of hands above interactive surfaces
[2]. In general, most approaches used in conventional touch screens [3] don't scale gracefully to large
displays. Pressure-sensitive resistive sandwiches, the most common technique, aren’t made large
2
Sign up today - FREE
Mendeley saves you time finding and organizing research. Learn more
- All your research in one place
- Add and import papers easily
- Access it anywhere, anytime