multi-touch resistive Archives

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?

September 30, 2011/in Ask Touch Guy

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 wants 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

My engineers claim gestures on multi-touch resistive do not work nearly as well as they do on projected capacitive (PCT) used in a variety of consumer devices, like the iPhone – why is this? Have there been any recent breakthroughs with resistive multi-touch? I would appreciate any new input on this subject.

September 30, 2011/in Ask Touch Guy

Hi Alex:

When you are comparing iPhone/iPad projected capacitive (also called PCT or P-Cap) to any other (even identical) projected capacitive sensors, you may not find the performance to be as good as Apple ’s product. How can this be? It is because Apple has had a really big head-start (as in years). You and yours are playing catch-up, and it will take a while for you to integrate the prior art (yes, Apple did not invent multi-touch) with the new, to achieve the same thing.

Here is a good example: Using a multi-touch demo, you can use the pinch gesture to make the picture really small….so small, that you will not be able to “catch” the corners and expand it…it will stay really small until you reset the program. Apple has anticipated the picture getting too small, so their software will accept nearby fingers and “guess” that the user wants to expand that photo, and it will. There is a lot of anticipation in the iXX software that makes it better than your stuff. Touch Guy is a hardware person, so you can guess that he will point the blame finger at the software folks.

Now to your original question… MARS is different only in the pressure required to enable the gestures. Otherwise, the gestures should be the same and the performance the same as projected capacitive and better, of course, with input from pens and pencils. Keyboard entry is noticeably better with sure-footed MARS than with projected capacitive, which seems to often “guess” wrong at which key you wanted (auto correct to the rescue).

For more info on multi-touch, check out Touch International’s Putting the ‘Touch’ in Multi-Touch White Paper.

Touch Guy

I’m kind of new to the touch screen world and am trying to figure out why it is so difficult to get large (over 22”) multi-touch resistive and projected capacitive touch screens. Also, what are the big advantages and performance differences between the competing multi-touch technologies?

September 30, 2011/in Ask Touch Guy

Hi Jim:

So you want to know about big ‘uns?

Projected capacitive, our favorite multi-touch technology, has pretty much topped out at 32 inch diagonal sizes. There are bigger ones available, but they have those annoying little wires that nobody likes to see.

In the realm of large format multi-touch, we find that infrared, camera (often called optical) and DST are the most commonly used touch technologies for large sizes (+32”), however IR and DST only support two touches. The mainstream projected capacitive and multi-touch resistive technologies are capable of unlimited touches, but are not as easily scalable (note that unlimited touch is controller-dependent, not sensor-dependent). So if you fancy yourself as Tom Cruise on a big 60 inch display, you will probably have to wait for projected capacitive to make it big.

So, what are we waiting for? We are waiting for transparent low ohm conductors. You will recall that projected capacitive is an X-Y scanned technology, using ITO for that purpose. But, white paper fans amongst you will recall that ITO has a relatively high resistance when compared to something like a copper wire. As the touch sensor gets bigger, the ITO resistance gets higher, and eventually, too high for the electronics to work. So, what is to be done?

TA DA! Debuting now, for your viewing pleasure, are nano-wires (think a Chinese population of angels on the head of a pin) and super-fine line copper webs. Both of these sport the required low resistivity, and only the most critical alien-eye can see them…. we can even coax them into rows and columns. Expect the electronics to grow as well, but, hey, what is an extra multiplexer or two…

So, Mr. Proctor, looks like your wait is over. Technology is getting bigger, not smaller, this time.

For even more info on multi-touch, check out Touch International’s Putting the ‘Touch’ in Multi-Touch White Paper and refer to the graph below.

– Touch Guy