HOMEBREW Wheelchair Safety System By Bryant Underwood
My daughter Katy uses an electric wheelchair
and last year she went off to college. Her mom and
I were concerned about Katy’s safety in navigating
the campus — she might get her chair stuck or have
some other type of trouble and not be able to get to
So I used a Parallax microcontroller to control
a GSM cellphone as a “telematics” system for her
wheelchair. Inside the gray box mounted on the
back of her chair, I use the phone in speakerphone
mode with an external microphone and speaker.
The way I did this was by leveraging the old modem
“AT” command set that almost any GSM phone has
for legacy control. Using a prepaid phone, I broke it
down and connected it to the Parallax Basic Stamp 2
microcontroller and a receiver with two wireless
remotes. I used an old Sony Ericsson T226 phone,
but I’ve since learned that the Motorola C168i or
T720 would have been much easier.
For operation, Katy keeps one remote in her
purse while the other one is attached to her chair.
If there’s a problem, she can push the buttons on
either remote and the device will call a local health
care provider, then my mobile phone, and then our
200 Make: Volume
home, or with another sequence of button presses it
will call campus police. When anyone is reached, the
unit acts like a standard speakerphone.
The joy for me is that it’s always on and I never
have to worry. Plus, at boot-up the BS2 sends a
command to the phone to put it in auto answer
mode. If we’re ever concerned, as a last resort we
can call the phone and it will answer in speakerphone mode without ringing (also good for Dad’s
concern of boys in the dorm room!). I thought about
adding GPS, but my daughter vetoed that idea.
Since Katy’s chair is always with her, we know
she’ll be safe. The alternatives were just not
acceptable; even pay services were little more than
remote-enabled speakerphones with a required
wired connection. With the ease of the BS2, the
whole project was assembled over a weekend,
including time for coding and debugging. So in a
very short time at home, I was able to develop and
deploy a one-of-a-kind wireless product that exactly
fits my needs!
Bryant Underwood serves as the director of supply chain for a
defense contractor and resides in the Bridgeport, Texas, area.
Photograph by Debra Underwood