so that means that I should be able to interact with it as long as I can bring a small current to the screen where I want to touch.
No. You don't "bring" current to the device. These devices measure capacitance, not current or voltage. The additional capacitance thru your body back to ambient or circuit ground is detected by looking at how the capacitive pad responds to some specifically chosen signals.
I've actually made some progress with this method I have found the problem to be the parasitic, or static capacitance of whatever I stick to the screen. It is enough to bring the base level reference at that sensor up too high to consider anything else a touch.
If I stick the foil with a 5 inch strand of hair-width wire, and pinch the end of the wire, it will work for about 30 seconds then stop working. If I leave it for 10 minutes it still won't work, nor will touching the foil itself. If I clip the strand of wire to maybe 3 inches, and pinch the end, it will start working after 30 seconds. Leaving it again for 10 minutes, it still works.
So really the question is, if I have a piece of foil on the screen with a 2 inch strand of wire, how do I electrically connect something to that for a moment, without adding any parasitic capacitance to it in the mean time. A transistor by itself was ok, pinching the wire would still get a touch but as soon as I solder something to the emitter of the transistor the foil would stop working after 30 seconds. A relay also has too much metal inside the terminal, causing the same problem after 30 seconds.
I am pretty sure I have the problem pinned down, as with both of these situations, if I clip what I have soldered off, after 30 seconds or so the foil begins working again if I pinch the little strand.
EDIT
So the problem was a thick tempered glass screen protector I had on the phone. I removed that and the amount of material able to be connected to the foil increased substantially. It works perfectly with a relay for hours. I tried with a transistor it works for a while but eventually becomes 'numb' to it so I guess the minuscule current across the 'off' transistor is enough to cause the foils capacitance to increase.
Thanks for the comments
Best Answer
I've worked a few years in a company making touch controller ICs for large size Touch Panel. According to my knowledge of these product (world leader in their market segment), I can tell you that:
there are high-pass filters in the data acquisition chain, that will prevent you to measure signals below 1~10 kHz.
The touch sensors must be able to detect touch in many different conditions (size of the finger, temperature, humidity etc...). I think such sensors are not able to measure fine local variations of the body part, because these signals are much much lower than the inherent noise of the touch system.
Depending on the touch system solution, the data post processing may be different, and you solution may work on one type of touch panel, and not on another type.
I would be you I would search for specific sensors, and forget the touch panel.