Synthesis

Begin forwarded message:

Subject: Re: Touch sensing traces

If you want proximity it has to be capacitive/e-field.
e-fields are non-linear so you will have to linearize the values.
Paper is environmentally sensitive especially to humidity. Some kind of calibration/compensation might be needed.

This ink works on most paper: http://www.electroninks.com/faq/
Here is that pen in action by yours truly: https://www.youtube.com/watch?v=ytDGMQSrJJ0

I am also exploring aginc that only works on certain coated papers.

As for the exact layout, I can't help you yet. My conductive ink jet printer hasn't arrived yet so I have done
0 experiments.

I can tell  you that the most efficient tiling for uniformly samping the plane is the triangular not the square one (by roughly 30% as I recall). This tiling may be harder to wire up than a square tiling though. I like to ground all the traces I am not sensing with and then read capacitance from each sensor area in turn. The keyboard patterns in the e-field sensing
article I circulated are pretty well thought out and a good starting point.

You can prototype this patterning problem with a sharp knife and conductive tape.  
I try to make it look easy in that video but it isn't unless you have good penmenship, lots of paper to experiment with
and quite a few pens. Mistakes are a challenge to deal with.

The main contribution of my video is to show that you can use connectors designed for flat cable in these paper applicaitons.
You may have to reinforce the paper with card stock if you expect to pull the paper in and out of the connector often.



On Sep 29, 2014, at 8:35 AM, Assegid Kidane <Assegid.Kidane@asu.edu> wrote:

Dear Adrian and Natalie,
we have a need for interdigitized traces on paper on an area of about 6 inch by 6 inch that would be divided into four quadrants of equal size. We need to sense each quadrant with very high sensitivity so I need help in terms of what conductive material or paint to use, what distance to use between the interdigitized fingers and in what shape. The patterns need to  provide as much information as possible regarding the proximity and position of the hand and fingers, and since you have already done a lot of research in this area we are hoping to save ourselves much time. So each quadrant of the 6 by 6 area needs to be three by 3  and we need to know what type/brand of conductive paint to use, the spacing between the interdigitized traces, the width and length of the traces,  and the shape of the traces to achieve maximum sensitivity when a finger or a hand approaches the paper.  also hopefully the sensing data generated will be linear in terms of distance of the hand or fingers.

Thank you for your help.


Assegid

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