We had tried tilt switches that functioned like a joystick and then a program converted this to mouse movement. This method didn't work very well and there was the problem of how to produce mouse clicks. At first we thought of a bite operated switch, but there was a major problem : a mouse has two buttons but our bite-switch could only emulate one. Then the friend of mine who was doing all this (Stephen Hall) had the brilliant idea of using a small laser mounted on an old pair of spectacles and a target-board with 6 Light Dependant Resistors (LDR's) - 4 for direction and 2 for mouse buttons. These worked as a joystick and the rest was done by software to convert it to mouse movement. This worked quite well but it was slow and I could only move the mouse in 4 directions (NSEW) so if (for example) I wanted to go to the bottom left of the screen and the cursor was in the middle of the screen, I would first have to go to the extreme left or down followed by down or extreme left. Then there was the disadvantage that I had to look at the target-board while using it, making me loose focus of the screen. When I needed letters I would use an on-screen keyboard called Click' N' Type (available free - www.lakefolks.org/cnt ). This setup (although quite slow) allowed me to do just about anything on my computer, which is (by the way) a standard laptop. Then we were having a few problems with the laser : we were using cheap keychain lasers, but these lost power after a week - we needed something more reliable. Eventually two were ordered from England, and these have proved very reliable .
We then found the SmartNAV(www.naturalpoint.com/smartnav/ ) it looked suspiciously good : it was cheap and seemed to do exactly what I wanted. It has 4 infra-red Light