capacitivetouchscreen
So I am trying to build a capacitive touch screen in a table, but since the table is much larger then the touchscreen. I like to put something on top that not only make it easier to clean, but also avoid the feeling of the bevel between the normal table and the touchscreen within and if someone spills a drink that wouldn't be so much a problem.
Does anyone know which material I can put on top that would still allow touches to go through?
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
It just needs to be thin. The capacitors on a capacitive touch screen appear as a series of very thin (so thin you can see through them) metal contacts on the non-touched side of the screen. The change in capacitance developed by your finger in proximity to these is what it senses, so as long as the material is thin enough to not interfere with this, it should be fine. This is the principle by which screen protectors work.
It should be noted that most capacitive touch screens require a minimum finger area (to reduce false positives) which is produced by the action of squishing your finger against the screen.
I would suggest some sort of thin plastic sheet (less than 1mm thick) with an adhesive backing so that it gets really close to the screen, although in my experience the glass is easier to clean.