I have made mention of how we propeller-heads love the challenges you crazy design engineers give us. But, as exotic requests go, you have thrown us a soft ball. In the old days of resistive and surface capacitive, we have made Cartesian touch sensors that were circular, triangular, spherical, and even a hexagon or two. So your request is quite “doable”.
Recall that multi-touch projected capacitive is a digital technology that generates a high resolution analog coordinate from the row/column intersections. Within reason, the lengths of the rows or columns do not need to be the same. So making either end shorter will not change the output….just some of the coordinates will not exist where there is no sensor. Some projected
capacitive electronics work best with different (invisible) ITO patterns, so you will need to pick one that anticipates your strange-dimensions, usually streets-and-alleys, diamonds, or snowflakes…..avoid telephone poles, zigzags, triangles and rings. But odd shapes – they do not trouble us.
So much for non-uniform dimensions, but now to the bigger problem….your one or two
millimeter border. First, I need to understand if you truly have such limited space at the edge. Almost all p-cap touch sensors have a top layer, called a cover glass or cover lens, which usually has an opaque ink on the back to hide the circuitry and replace the bezel, enabling in a flush
design. The opaque ink must be at least as large as the inactive border area, and usually is much wider. For a sensor that is 460mm long, it seems unlikely that you would only be allowed such a tiny edge area. Thus, me thinks you should have a traditional bezel and allow yourself more room.
However, if you persist…..you probably know that all touch screens need a border to deliver
signals to the sensor. In the case of p-cap, there needs to be one signal delivered to each row and column, which, for a 460mm length would be about 65 signal lines in the long dimension. The minimum width of these signal lines is usually 30 microns with a 30 micron separation between the conductive traces. You do the math, but you can see that you simply cannot fit that many signal
lines in 1-2mm space. Touch-International’s solution is to put the signal lines on a flex tail and bond that tail to connecting pads at the edge of the sensor glass. Rarely, we have also drilled holes in the glass and connected via the back, but bring your checkbook for this solution.
You have me wondering what you mean by extreme velocity….here in Texas, everybody is
packing and “extreme velocity” means a bullet is headed your way. As much as I want to say PCAP will last forever… when it comes to target practice, I am lying. However, we can use up to 6mm tempered glass if you are expecting trouble.
Until Next Time,
– Touch Guy
Title: Putting the ‘Touch’ in Multi-Touch: an in-depth look at the future of interactivity
Date: Wednesday, April 20, 2011
Time: 1:00 PM – 2:00 PM CDT
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