A little more than a year ago, one of my first columns here at Design News was the EyeWriter. This is a brilliant way for people who have been afflicted with ALS and are completely paralyzed with the exception of being able to move their eyes, can interact with a computer and use it to communicate with others.
The original Eye Writer uses an IR LED and a cheap webcam to track the pupil as the eye moved. The LEDs are mounted around the periphery of the webcam, which is modified to remove any IR filter. The whole thing is mounted on an arm that is attached to a pair of Cheap Sunglasses. Software translates the motion of the eye into mouse cursor movements, allowing the user (the system was originally designed to allow graffiti artist TEMPT1 to continue to produce artwork) to draw, type, and otherwise make use of the computer.
The new version, EyeWriter 2.0, draws on techniques used by commercial systems, but implements them using open source software and simple hardware that can be duplicated for a couple hundred dollars. The advantage compared to EyeWriter 1.0 is that the hardware is not mounted on the head, it is mounted on the computer or monitor. This allows it to be used by people who wear glasses, and allows it to compensate for small movements of the head.
The hardware consists of a PlayStation Eye camera, modified to remove the IR filter and to bring the vertical sync pin outside the camera. The face of the user is illuminated by IR LEDs. Some LEDs are mounted directly adjacent to the camera lens, while others are located at the edge of the monitor. The LEDs are synchronized to the vertical framing signal such that the face is illuminated by the center LEDs on even frames, and by the side LEDs on odd frames. The clever result of this is that on even frames the pupil appears bright because of the IR bouncing off the retina(like red eye), and on odd frames the pupil appears dark. Software takes a difference of the two frames in realtime and is able to track the location of the pupil.
The remaining hardware is an Arduino that drives the illuminating LEDs synchronously with the vertical sync signal. It would be neat if a more powerful microcontroller could be used to do the pattern recognition and present a simple USB HID/mouse interface to the PC, but that would be more expensive and it would be harder to do the initial calibration.
The software is all open source and includes calibration screens, an on screen typewriter, drawing program, and pong game.
In my original post I wrote that the original EyeWriter was “another example that the internet can enable truly profound collaboration to improve the human condition”. EyeWriter 2.0 is ditto, only more so.
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