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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

I’m curious about flexible touch screens – why are there not more in the market and what are the challenges and limitations associated with them? What design considerations do I need to be aware of when integrating them?

Dear Mike:

Ancient history, my man.  Curved and flexible, I guess is the new “flat” which is what everybody has wanted in touch screens for that last ten years. If bell bottom pants can come back (they are called “flairs” now), then why not curved touch screens?  In the days of CRTs, all touch screens were formed to match the radius of the CRT tube, primarily to reduce parallax (a fancy word for your finger missing the touch target). This meant that touch screen manufacturers had the tools to precisely bend glass and plastic into most CRT sizes and radii.  We did this without damaging the integrity of the transparent ITO thin film.

Because we’ve switched to LCDs, which are flat, touch panels are now flat too. But if you need your touch panel to be bent then listen for the groans of touch screen manufacturers thinking about which storage shed is housing the forming equipment, or imagine the screams of the LCD manufacturers thinking about bending LCD mother glass. But crazy designers seem to want it
(for example, car-navigation systems are the last flat surface in most vehicles, and they are out to eliminate them), so I guess we will be forming and bending again… Shifts in the microdisplay market, especially those using projectors, might also drive the demand for curved projected capacitive touch panels, as would a flexible OLED display (yeah, yeah, we will all believe in OLED when we see it).

Touch International is getting requests for both formed (holding a shape) and flexible.  Both are possible with projected capacitive technology, which is even more forgiving than the legacy resistive or surface capacitive parts because projected capacitive starts as a digital sensor instead of an analog sensor, meaning changes in resistance (from the flexing) are not as important.

Although most projected capacitive touch panels are glass— for reasons of cost, scratch resistance, stability and optical clarity— it is only a matter of time before they are all plastic. To make a formed glass panel, because the volume is practically non-existent, it is more expensive than difficult, but you should be prepared for volume to get interest from any of us.  Formed or
flexible touch panels made from plastics, are possible in lower volumes.  And with the advent of better hardcoats, approaching the scratch resistance of glass, we are ready to start up our old furnaces again…that is, if we can find them.

To your second question, there are no special design considerations that are different from the contemporary glass panels. The most important concern is the available border area (non-visible area). The smaller (tighter) you make it, the higher the price….a tiny border can double the price over a larger boarder.  Touch Guy also wants to emphasize that software is just as important…we can make you a roll-up keyboard, but you will need to deal with the ergonomics of multiple fingers resting on the keyboards. And last, while bending and forming touch screens is old technology, it is new to all but the legacy touch companies, so some patience may be necessary.

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.

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 untilTouchGuy_Basic 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