Placing a button on a touch screen?

Question

First off, I know nothing about electrical engineering. So please bare with me.

I'm designing a faceplate for a moto360 smart watch that has a small area that overlays the bottom edge of the screen. Set into that area is 3 buttons made from a clear orange resin that act as a stylus.

These buttons correspond to tabs programmed into the on screen watch face. Pressing these buttons should trigger the software to switch to the corresponding tab and cause a patch of the screen that is hidden by the plate to turn bright white just below the contact point. This illuminates the clear resin button, giving the illusion of a tiny LED.

As you may have guessed, I didn't realize that simply adding a drop of rubber from an old stylus to the bottom of the button wouldn't be enough to trigger it.

I've done some reading and I feel confident enough to know why. Basically, not enough of a draw to pull any electrons from the screen? (Not really the point of this post either way.)

Anyways, my question is, is there a type of affordable space age material that I could attach to the bottom of the 2mm diameter button that would work? Or maybe some kind of clear conductive resin or additive that my caster could use?

Here is a picture of the tiny tiny button assembly as currently planned. The orange pieces are the clear resin and slide into the green pla section. The black dots represent the now useless stylus material.

http://puu.sh/iwnnB/b586ae5189.jpg

This is a very rough picture of how the final plate should look when assembled. This is not an item I have made, but it is a decent representation of how the item should sit around the watch.

https://goo.gl/photos/E2dc9jmBQumnRcdcA

Answer 1

It depends on the kind of touchscreen it is. At this point, I think most technology is based on capacitance, and not multi-layer resistance. If this is the case, you might want to look into how those touch-screen capable gloves work. These are gloves that have a finger and a thumb covered in some material that works with modern touchscreens.

There is also apocryphal evidence that a hotdog, cold out of the fridge, works on these screens. Make of that what you will.

Answer 2

At a guess, what you want to do is simply not possible. As a check, try this: make a stylus out of metal (preferably not aluminum - copper would be better) which ends in a point which is about the same area as the area of your buttons where they contact the face plate. See if using that stylus activates the touch area on some existing app. I suspect it won't, and I can't explain why without getting into questions of capacitive coupling which you won't understand.

If a conductive material producing a small contact area doesn't work, there is no way you can get your buttons to work.