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I stepped on my fancy iPhone 4 and whole screen is completely cracked! I can barely see the images, but somehow it still works! How is this possible? – Astonished Jim, Little Rock, Arkansas

Dear Astonished Jim in Arkansas,

Touch guy is about to go on vacation, so thank you for an easy question! As I’m sure you know, the iPhone uses projected capacitive technology and one of the main benefits of this technology is that it will “last forever.” Touch Guy did not really mean that you could smash it, or in your case, step on it, and it would still work. But, wow, maybe you can…

So what gives? First, I want you to know that there are several ways to make projected capacitive touch sensors, but all of these methods involve putting the transparent sensing conductors, called ITO (Indium Tin Oxide), behind a protective front layer (I call this layer a lens). The lens on an iPhone is made of a thin layer of glass – you can look in the on/off hole and see how thin this glass is. Behind it is the touch sensor, which is a thicker (0.5mm) layer of glass, and is optically bonded to the thin lens. I say “optically bonded” because there is a continuous glue layer in-between that eliminates the air gap between the touch panel and the lens and is part of the reason the display looks so good.

There are a lot of ways to bond the layers together; the material used is generally known as “OCA” (you guessed it, Optically Clear Adhesive). All automotive windows are two glass layers optically bonded together, and the internal OCA, along with tempering, is what makes the glass “safety glass” with all of its protective properties. When you get a crack in your car window from “that darn rock”, only the outer layer of glass usually cracks. So Jim, that is your answer – when you klutzed the iPhone, you cracked the outer layer of thin glass, but the touch sensing layer remained intact and worked just fine through the broken lens.

But I know you want to know more! Touch International makes all plastic projected capacitive sensors which will not break (think hand-held games for children). They also use chemically strengthened glass for the lens and touch sensor to make it harder to break. There is also another type of cover glass, alumina silicate, which can increase the strength if the lens is likely to get scratched, by, say, the keys in your pocket.

Astonished-Jim-with-the-cracked screen will probably enjoy this story: the iPhone introduction was delayed for months, because the first models of the product had an unbreakable plastic projected capacitive screen. Of course, the big man himself (if you don’t know who this is then tough luck), got the first prototype. By the end of the third week, the junk in his pockets had scratched the lens, making him very, very unhappy. So the lens maker, having invested quite a tidy sum in a plastic lens making facility, had to start over with glass.

We hear that around 25,000 smart phone lenses break each month, so you are not alone. Replacement sensors are available and there you tube tutorials on how to replace them (not easy).

Whew! That was a long answer! If you still want to know more, download the Touch International white paper “Projected Capacitive Touch Screens” – it has a lot of good stuff in it!

And Touch Guy is off! (And planning to opt-out of being X-rayed at the airport)

What do you think is going to be the next “big thing” in the future of touch technology? – Paul Jones, Santa Cruz, CA

Dear Mr. Jones:

Now Touch Guy feels threatened! For many months he has been extolling the virtues of projected capacitive touch and now you think it might not be the good-for-everything solution. Ok, I will reluctantly look into the crystal ball, aka Touch International’s skunk works, to provide you the answers you seek.

In-cell technology has long been rumored to be the projected capacitive killer. With in-cell, the touch sensors are the pixels in an LCD display. By light or capacitance sensing, when the thin film transistors are not busy switching the liquid crystal material, they can sense touch and send the information back to the LCD controller. There are already two or three products using this technology but its complexities and cost have delayed large scale production.

Many people are experimenting with corner camera technology of the sort used in big touch displays. As cameras get smaller and cheaper, this technology holds promise for future use in hand-held devices. The advantage over projected capacitive is that it is better at integrating a standard pen into the system. Higher power and the need for ambient light, among other things, add to the difficulty of wide-scale integration.

Fiber bundles with one camera offer some benefit; so far, the cost of making a low profile product in volume has been evasive, but this technology offers the ability to sense a pen tip as well as two touch applications. Right now it lacks the ability to do true multi-touch, so it may lag.

You should remember that like these emerging technologies, projected capacitive is not static and may one-up itself. Pen input, proximity sensing (up to one meter) and no-touch-touch applications are on the way.

So now that you’ve seen “the future” don’t forget that Touch International’s MARS product, is available today and offers high resolution pen input and full multi-touch capabilities.

There are more than 2000 patents on touch sensing, so Touch Guy does not claim to know the future but he has no fear – projected capacitive is here to stay.

What’s the difference between resistive multi-touch and projected capacitive multi-touch and why would someone choose one over the other? – Mike Zimmerman, South Carolina

Dear Mike:

I am the long-time cheerleader for projected capacitive touch technology, so my answer may be biased, but here it is:

If you are a mechanic using a touch screen to fill out an overpriced car repair estimate, you should use resistive multi-touch touch screens (MARS); everyone else should use projected capacitive multi-touch technology (MulTI-Touch).

Touch Guy’s projected capacitive mantra is 1) it will never wear out, so it’s a better investment, 2) it has great optics and 3) it is multi-touch capable. The only downfall to projected capacitive technology is that it will not respond to every input device (i.e. pens, pencils, credit cards); only those that are conductive.

For all the mechanics out there, here is why you want to use Resistive multi-touch:

Let us assume that our mechanic, Mike, will use a torque wrench to reach over and activate the diagnostic machine’s touch screen – this requires a pressure sensing touch screen (aka resistive). Or when he fills out the repair estimate on an electronic recorder, he can use the nearby pen or pencil to input information. Mechanics will also like the palm rejection that MARS has. Palm rejection is achieved by ignoring touches in part of the screen and accepting them where the writing will occur (this is used in signature capture devices). Plus, when every nano-watt counts, resistive technology consumes less power than capacitive.

But using resistive multi-touch technology comes at a cost when comparing it to projected capacitive technology. MARS is really just a 4-wire resistive touch screen cut up into severalf small 4-wire touch screens, so it will wear out with use. And the optics are not as good as projected capacitive because it has the same reflections of a standard 4 or 5-wire resistive touch screen. MARS-groupies point out that resistive touch has worked plenty-good for the last 25 years and the benefits of multi-touch, low power and no-drift coordinates make it a long term winner. Touch Guy is not convinced but thinks multi-touch resistive is a niche product.

Until next time,
Touch Guy