TouchGuy_Basic

Do you have a question for Touch Guy?

Send him an e-mail at asktouchguy@touchintl.com.

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…..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

We are designing for an application where the customer needs to touch more than one touch screen simultaneously. We want to use projected capacitive for its scratch resistance but are not sure how to manage the interference problem when two screens are touched at the same time. Do you have any suggestions on how to solve this problem?

Hey Keith C.,

Two-timing touch on multiple displays is an old surface capacitive problem with a complicated solution. I am assuming you are using the same computer running a multi-display solution under windows. By now you know that multi-touch electronics send information to the multi-touch driver which converts it to the equivalent of multiple mice being connected to your computer. To create the actual touch, the driver takes the X-Y coordinate touch point to move touch guythe mouse pointer in the video RAM to the touch point and issues a click. So far, so good.

Now you are going to connect multiple displays, which are supported by the Windows system. Again, so far, so good. But here is the rub. The touch electronics have a USB name that tells the Windows driver that there is a multi-touch device out there. If you plug in two USB touch screens, the Windows driver will not know which touch screen is associated with which display, and, further, would be totally annoyed at you for trying to trick it with two devices with the same name.

For this application, Touch International can change the name of each of the two electronic controllers (so you can know which is which), but this would not make the Windows driver any more capable. So, now you have to call in the big-guns and get them to sell you a multi-touch-multi-display driver. This can and has been done, but get out your wallet. Touch can give you suggestions for software companies that can do this.

Till next time, Touch Guy

When evaluating a touch screen for a hardened handheld product (the system must survive a 3-5 foot drop onto cement, and cleaning with alcohol and water), how does resistive multi-touch compare with projected capacitive, particularly for gloved hand (1-2 layers of latex or nitrile), multi-touch and gesturing GUI’s?

Scott, you get one question and one bonus question all rolled into one Touch Guy answer.

With more than 50,000 iPhone touch screens being replaced per month with cracks, broken touch screens have become a big business so we kinda like the breakage. But I guess a broken screen keeping you from your Facebook page is a lot different than not being able to reprogram a defibrillator! Before Touch Guy cuts to the answer, he TouchGuy_Basicwants to emphasize that good product design means the whole assembly – touch screen, LCD, and enclosure – need to be skillfully integrated to meet the breakage requirement. And that is a good segue into reminding you that Touch International provides bonding of the touch panel to the LCD with a shock absorbing optical gel that substantially reduces breakage in mission critical devices.

The simple answer to what technology is most breakage resistant is…..it’s a tie. This is because both products can be made using all plastic components. New top level hardcoats resist scratches  and claim to have a hardness of 6H (traditional plastic touch panels have a hardness of 3H or 4H), and they have always been resistant to most harsh chemicals…alcohol is wimpy
compared to the super-hot acids and lye that these things see in processing.

All things being equal, you would pick the all plastic projected capacitive over multi-touch resistive (MARS) for optical clarity and longevity; however, while projected capacitive will perform nicely with two layers of nitrile gloves, if a doctor, soldier, or pilot wants to occasionally want to use a scalpel, thick work gloves or a pencil, you better go with MARS because it will work with absolutely anything.

As a parting shot, Touch Guy wants to say that this is a very general answer, and knowing the application and its requirements might result in a solution that uses a specialty glass like safety or bullet proof glass that might be better than an all plastic solution.

Until next time, Touch Guy