continuously polls the first byte in the transmit buffer of the
first slave for the ADC_DONE byte. Upon reception of the
response command, the master reads the response data
from each of the slaves. It should be noted that the
response command is placed into the transmit buffer after
the completion of the response data load into the buffer, so
that the master can immediately perform the data read
operation without waiting for the slave to load its registers.
This offers a reliable method of reading the slave’s responses
without additional, clock-dependent delays within the
master loop. The complete hand-shaking operation
described here is summarized in Figure 5. Finally, an
elementary time-out mechanism was incorporated into the
master routines to allow for the possibility of in-service
disconnections. The code snippet for the time-out is clock
rate dependent in its current form and should be adjusted
accordingly using the TIMEOUT variable. The source codes
for both the master and the slaves are available from
www.nutsvolts.com. The code for
each of the slaves should be compiled
separately with unique values of a
SLAVE_ADDR for the different slaves
in the chain. The same slave addresses
should also be included in the
SlaveArray variable in the master code.
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But, of course, the proof of the
pudding is in the eating! So, to test
our gait detection system, we
strapped a single slave module to
the hip in the front just below the
abdomen and performed various activities. The recordings from this test are
shown in Figure 6 with the vertical,
horizontal, and sideways accelerations
represented by red, green, and blue
colors. It is clear that our system has
the ability and speed to distinguish
between walking, running, and falling.
The system can even figure out if a
person starts running faster!
More critically, the presence of
clear fall signatures implies that the
data from the system can be used to
determine if its carrier has tripped. An
alerting system can be easily built by
strapping a Bluetooth module to our
current circuit, and we leave it to the
enterprising reader as an exercise.
Indeed, systems similar to this one
have been used to acquire data that
were then published in reputed
research magazines. We hope you’ll
use this inexpensive system to gather
data on the kinematics of motion,
among other fun things! SV
Call 1-800-831-4242 or Visit www.Jameco.com/Speed for the ride of your life!
42 SERVO 12.2008
The authors wish to thank the support
of Prof. Rajesh Gupta, University
Of California, San Diego during the
completion of this project.