Peripherals/Touch Screen

Technology

Different touch screen technologies:

4-Wire Resistive
5-Wire Resistive
Capacitive
Surface Acoustic Wave
Infrared
Strain Gauge technology
embedded ccd in panel - can't find link but light detectors can be intermixed with light generators, maybe on an oled display, so the computer can detect when light reflected
A simple light sensor could also work as a display pointer. A tethered pen could detect flashed target boxes, like the old Nintendo Light Gun. For continuous drawing, the screen could flash through a series of patterns where the pen either sees light or dark. Each screen location would thus have a unique binary code flash through it, which would be reported by the pen's narrow light sensor. This screen scan will start in a small box near where the pen was last to reduce search time, and the eyesore of flickering. -- Nintendo wii remote has been hacked to provide multi touch interface-- http://gizmodo.com/gadgets/clips/wiimote-hack-is-wireless-multitouch-tv-321329.php

Apparently most PDA’s use 4-Wire Resistive touch screen technology. However I am not positive on this.