  Millions of people around the world face motor impairments due to
Parkinson's, cerebral palsy, muscular dystrophy and other physical
disabilities. The goal of this project is to increase the usable surface-area
of devices for users with these disabilities by creating a simple, inexpensive,
and portable way to enable high accuracy touch interaction with large surfaces
such as a table or even a wall.
  This project uses a novel approach that analyzes the acoustic signals at four
piezoelectric microphones placed on the interactive surface to identify sounds
related to the same event (e.g., a finger tap) at each of the microphones. ALTo
(Acoustic Localized Touch) uses the results of this signal processing to
compute the time difference of arrival (TDOA) across the microphones. The
collected TDOA data is used to compute an approximate location of a sound
source (e.g., a finger tap) using a collection of hyperbolic equations.
  An experimental evaluation of a system prototype was used to identify a
number of software and signal processing optimizations needed to significantly
improve accuracy and create a usable system. The results of the research
indicate that it is possible to detect the location of a touch with high
accuracy. The ALTo prototype achieves an accuracy of 1.45cm in the x-direction
and 2.72cm the y-direction which is within the range for the target usage
(i.e., those with motor impairments).
