Using colour to determine pointer position on a screen

Thin Film Transistor (TFT) screens are becoming more common in the workplace, replacing traditional Cathode Ray Tube (CRT) screens. As the TFT screen does not generate a scan line, traditional methods of light sensing pens do not work effectively on a TFT screen. This paper describes a novel light pen type peripheral, which may be used on either a TFT or CRT screen. The peripheral is intended to replace the need to use a touch screen, mouse or keyboard. A specially designed kaleidoscope is placed on the screen; these colours are then detected using a tri-colour photodiode. The output from the sensor is filtered and transmitted via a link to the computer; the computer then translates the colour into a corresponding co-ordinate on the screen.