Status: First prototype tested successfully, in refinement.

Update: Before I left Denver, I did build a prototype interface and test it with three of the four major American power wheelchair brands (Quantum/Pride, Quickie, and Invacare).  Because the fourth brand (Permobil) uses the same system of electronics as Quickie (R-Net), I'm fairly sure that it will work with Permobil chairs as well.  The new design uses Bluetooth, rather than USB, so it can be controlled wirelessly from nearly any Bluetooth enabled computer, tablet, or smart phone.  Unfortunately, I am extremely busy with classes now, and haven't found time to refine this design and post it here.  I will do so eventually, but if you need the information sooner, please feel free to email me.  I can give you what I have and point you in the right direction.  It's really not a very complicated design.

In designing the eye-controlled wheelchair, it was necessary to reverse engineer the available power wheelchair and hack into its proprietary circuitry.  This process took quite a while, and has been repeated by many other researchers around the world.  This seems like a waste of time that could be better spent developing improved input methods, control algorithms, environmental sensors, and so on.  No one likes reinventing the wheel.

In order to alleviate this issue, I am developing a universal computer-wheelchair interface, which would handle that part of the puzzle and allow researchers to focus their time on more important endeavors.  In addition, this will allow users to take advantage of currently existing computer access methods, such as head trackers, specialized mice, keyboards, joysticks, touch screens, single or double switch scanning, etc.  Combining such a tool with preexisting eye trackers (like those from Tobii and Dynavox) would result in an improved alternative to my previous eye-controlled wheelchair.  Finally, the use of a common PC as a controller (as opposed to one or more microcontrollers) would make software development more accessible, opening doors for work in self-localization, mapping, obstacle avoidance, semi-autonomous navigation, docking, input smoothing/correction, and other avenues of smart wheelchair research.

USB and BlueTooth are obvious choices for connection to a computer, but selecting the proper connection to the wheelchair is more difficult.  The four major power wheelchair brands in the U.S. (Invacare, Pride/Quantum, Quickie, and Permobil) use different, proprietary connections to interface with specialized drive controls.  Some developers (like Adaptive Switch Labs) produce products that interface with these connections, but these are generally brand-specific.  I have, however, discovered that nearly any power wheelchair accepts a 9-pin D-sub connection (with the same pin-outs as an old Atari joystick), though occasionally an ASL adapter is required.  This connection is utilized by a variety of drive controls, such as wafer boards and external switch scanning systems.  I am worried that, if this connection really mimics Atari-style pin-outs, it will only allow digital control of the chair.  However, some proportional touch pads also use this connection, which makes me think that proportional control is possible.  I need to do some more testing to clear this up.

My current concept includes: