Homebrew — Wheelchair Safety System

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 her cellphone.

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 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!