I am interested in creating a device with contains a multi-touch capacitive screen with many curves and bends. I am wondering if this is possible, and what the potential price range might be.

Dear Mr. Curve-A-Lot.

Needless to say, you have Touch Guy’s curiosity aroused as to what you would do with this curvy-bendy-multi-touch touch-screen. Also, he wants to make sure you need this to be transparent because that drives the touch sensing technology and ultimately the cost…..and do you need proximity sensing as well?

In the antediluvian days of CRT’s, all touch screens were curved, so we are familiar with building curved touch screens. Since then, plastic and glass forming has advanced to allow for just about any possible shape. Part of the magic is the use of transparent nano-inks to follow the contours of your crazy design and still remain conductive.

Though it is not the typical PCAP product, Touch International does build all-plastic projected capacitive touch screens for remote controls, automotive panels, and aerospace devices. The cost depends upon the materials, glass or plastic, and the tools needed form to your contour. Once the tooling is designed and proven, the cost to produce each part is not exceptionally high.

So yes, what you want to do is completely possible, but you are going to have a lot of fun interpreting the touch coordinates!

Touch Guy

I am in need of an oddly-shaped, custom projected capacitive multi-touch display that is waterproof, able to work with varying pressure, and provides maximum velocity for input acquisition and transmission to controller. The dimensions of the sensor need to be 460mm long and the widths need to be 42mm and 58mm respectively; the boarder must be narrow at 1-2mm (maybe made of plastic or aluminum). It is also important that the electronics work with Linux.

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 TouchGuy_Basicsome 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… 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

I’m working on an open source 17″ tablet for the DIY 3D printing community and am in desperate need of a 17″ – 17.1″ USB multi-touch screen overlay with a 16:9 or 16:10 aspect ratio. So far, I am only coming across single touch resistive and IR multi touch panels. We only really need dual touch panels with as good light transparency as possible, as these are graphics editing machines we are making. Projective capacitive panels would be the ideal technology I assume. How can I find such a beast?

So you want a 17 inch projected capacitive touch screen and are having a tough time finding one? You have chosen wisely, because for the printing business, you will want the super sharp image that you get using this optically clear technology.

Even though Touch International makes projected capacitive sensors up to 22 inches, I have to tell you, you are on the cutting edge of wanting the “big guns” for projected capacitive touch screens. Except under special request, all of our projected capacitive panels have to have a perfect image (no shadows), they must do multi-touch (two or more fingers, no ghosting), and they have to have a touch response of less than a 1/10th of a second (among other things). Because of these requirements, we are not always the fastest to market, but we’re sure to deliver some of the best touch screens around.

There are two key reasons that larger-sized projected capacitive is difficult to do. The first is that no-shadow touch screens require very precise manufacturing equipment of the type used to make semi-conductors or TFT displays. Most commonly available are machines that will process projected capacitive sensor sizes up to 15 inches, which is why that size is easy to find.  You may know that Touch International has just opened its new China factory, and can process up to 17 inch sensors, so you are in luck (pretty soon).  We can (and do) make 19 inch, and larger, projected capacitive panels using other methods, but they break the visible line requirement, so they will not work for you.

The second complication to making big projected capacitive panels is the speed at which the multiple touches are recognized, which is dictated by the touch electronics. As I am sure you know, having read my white papers on the subject, projected capacitive is a scanned system which means that every row and column must be “energized”, and then interpolated to get an overall resolution of 1024 by 1024, which is a lot of work for those little silicon buggers.  As the screens get bigger, there are more rows and columns to move into action. This requires multiplexing, or, most often, it takes multiple fancy projected capacitive ASICs working together in a master/slave relationship. A single ASIC, which will handle 17 inch screens, has just hit the market (two touch maximum), so, once again, you are just in time.

So, we may be your source, but you will need to hold your breath a little longer – maybe until Q2.

Touch Guy