I've asked this before, but knew less about the tech and didn't word the question properly. I know other people have asked similar questions and knew little, so let me be as specific as possible here:
What I want to do is make a fine-tipped stylus for my iPad so that I can write and draw without an awkward clunky stylus that may as well be another finger.
I know there are fine-tipped styli out there, but I dislike all of them as they either do not work as advertised, scratch the screen, or are to flimsy.
But most importantly: I like making things.
The sensor array in the iPad is mutually capacitive. A grid of capacitors is laid out under the glass. A constant voltage is passed through one axis of the grid. The other axis waits and detects changes in the voltage. So to trip a sensor, an object such as a human finger or stubby capacitive stylus must be brought close enough to change the voltage of one of the capacitors with its local electric field. When that field covers a wide enough area, the device registers it as input and decides where the center point is. This is how it maintains accuracy while being so low-definition.
So to reiterate: how can I make a device that generates the same electric field as a human finger over a ~5mm radius from a much finer tip? It can be ugly, hooked up to wires, even grounded to human skin with a wrist strap. I don't care about form. Just function.
Best Answer
I've been wanting to find out info about this subject my self and also don't have much in the way of electronics background. I believe that Raiden wants to create his own DIY fine point stylus like the Nota stylus (http://hex3.co/products/nota) which is described as electronically activated. There are also others which are coming to market in the near future.
As far as I understand they work by increasing the capacitance of the stylus point. So I've looked into what can be done to increase capacitance of the stylus.
Formulas
If i understand correctly when you touch the screen you make a sort of capacitor due to the layer of insulating film /glass and the change in voltage at that point is the detected. (May be completely wrong about this). So in the 2nd equation if you reduce the surface area you will reduce the capacitance. So in order to increase the capacitance we need to change the dielectric constant of the material being used.
Here is an example of a fine point stylus that uses foam and water https://www.youtube.com/watch?v=alrweIVt2RQ . The Constant of water is ~80 compared to rubber of ~3 and i believe that is why this example of a fine point stylus works. Unfortunately it is inconsistent and water doesn't play nice with touch screens. I would theorise that using a material with a high constant would help reduce the size of a stylus point. For example Graphite has a constant of ~ 36.
My other thoughts are to try using an electronic circuit to add voltage to the stylus point. But thats well out of my range of understanding.