Multi-Purpose, Daisy-Chained
Gait Detection System
By Balakumar Balasubramaniam and Wendi Dreesen
THE BASICS
Agait is defined as an ordered sequence of states that
typically result in locomotion. To measure the gait of
a person, we measure the angles of the various parts
of the body with respect to a reference at each instance of time
during the motion. The simplest reference that is available
everywhere and has the strongest effect on gait is gravity.
So, we measure the gait by strapping accelerometers to
the hands, legs, hips, neck, and so on, and calculating the
angle made by the gravity vector with the axes of the
accelerometers. Prior to data acquisition, we obtain a few
seconds of reference data in the rest position to measure
the angles made by the sensors with respect to the gravity
vector. Subsequent angles are all calculated with respect to
this reference. Of course, when the limbs are moving fast,
the accelerometers measure the centrifugal and radial
accelerations in addition to the gravity vector. So, it gets a
bit complicated. Research systems typically use gyroscopes
to measure the angular velocity and compensate for such
rotations, but gyros are expensive. To keep our costs low,
we built a system using only accelerometers. It turns out
that even such a simplified system provides remarkably
useful information (for example, even without the gyros,
we can measure the maximum forces on our joints while
running) and is routinely used in cutting-edge research
projects!
If you are looking for
an innovative science project
that contributes to gait
research, this is your starting
point. The system presented
here can also be used in
numerous other applications
like measuring the
accelerations of your
bicycles, motion tracking
of slow and controlled
movements, or even in fall
detection.
FIGURE 1: CIRCUIT DIAGRAM FOR THE SLAVE.
HARDWARE
DESIGN
The basic design of
this gait detection system
consists of one (or more)
slave nodes daisy-chained
to a single master node
by a fast I2C connection
operating at 400 kbps. The
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