capacitivedrilltouchscreen
I'm thinking about using a capacitive touch screen (the touch layer only, no display) to detect the position of two moving parts. Each part would have its 'stylus' just above the screen to mark the position. Unfortunately, such a use-case would require a rather large (1.5cm hole in 7cm screen) hole in the middle of the touch screen.
Have you tried to drill a hole into a capacitive touch screen? Will it work afterwards?
The reason the stylus worked even through layers of wool is related to the very nature of capacitance: It is not about conduction (except at the electrodes themselves), it is about the insulation between the plates: Wool is about as good a dielectric as dry air, if it is not woven with some metallic fiber.
The way capacitive touch screens typically work is that they sense the change in capacitance that occurs when an earthed body - essentially any large conducting body, such as a human - comes close(r) to the surface electrode. By using a metallic stylus, that "earthed body" is being brought closer, with merely the wool in between.
This capacitance change can be measured in a number of ways. A common approach is to inject a high frequency signal between the sensing electrode and the device's own ground plane, with air (or glass, or some other material) as a dielectric between these two "electrodes". Any other conductor coming into proximity changes the dielectric (i.e. insulation) pattern, thus changing the capacitance, and thereby the pattern of load shown by the capacitor across the native capacitance.
Digitizer or touch screen/panel digitizer.
You can find them as replacements for small LCDs. For example, but these may not be suitable for your multi-touch requirement, and getting application information may be difficult.
They're typically laminated onto the LCD display, and can be removed safely with a controlled temperature hot-air gun (and care, they're usually very thin glass).
Best Answer
Most of capacitive touch screens are constructed as X,Y array of capacitive sensors.
Once You drill the hole in the middle You will open circuit some connection and might loose possibility to properly sense the touch in the rest of the touch screen. See example below:
It would be better to design custom capacitive Sensing board, that has connection the other way around.