Tag Archive for: projected capacitive technology

Would an “iPad” type touch screen work in Antarctica?

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Dear Mr. Abominable,

You are not alone in the cold my friend. First, this “iPad” type touch screen you are referring to is using projected capacitive (PCAP) technology. Without diving into detail, a “touch” is sensed when you make contact with the screen, basically grounding out the circuit. That’s right, no matter what anyone has said about your personality, make no mistake that you sir are electric. The problem in Antarctica isn’t so much the temperature, it’s the fact that you certainly do not want to take off your gloves in those temperatures. Now, quite a few companies manufacture “phone friendly” gloves with a little strip of conductive material woven on the pointer finger from the inside out to bridge the gap from finger to screen. Maybe I shop at the wrong places, but most of these gloves seem a little light for sub-zero death freeze. Since that may not be an option, some PCAP screens can be tuned to handle gloves – but again, it’s the thickness of the material separating man and machine that gets in the way and can result in an overly sensitive touch screen when the gloves come off.

I apologize for throwing my “sales guy” hat on in advance, but let’s switch gears and talk new technology. For this exact reason (ok there’s a few others) the mad scientists here at TI have developed a new technology that gives your freezing fingers the freedom to be covered in any glove you choose and still get the benefits of a multi-touch interface on whatever device you’re using. It’s called PCAP Plus. I don’t want to drill down too far, but what we’ve done is combine the best of resistive touch screen technology, with the features of PCAP (multi-touch, gesture, etc) and created “Frankenscreen.” Ok well I wanted to call it “Frankentouch” but they wouldn’t let me. Now there are far more benefits than just using gloves with this new technology, especially for the military, but for you and whatever device you may be trying to develop here – this is the technology for you.

While touch may be a pita while roaming the frozen tundra, I think you may be overlooking a potentially bigger problem – the display. LCD’s and I have a lot in common – we’re square and we don’t like the cold. The colder it gets, the longer it takes for your LCD to display an image, and the dimmer your image gets. If you dip to around or below -35 degrees C, you can have permanent display damage from the liquid crystal actually freezing. Fortunately, there is a solution around this problem. Transparent heaters (sometimes simply referred to as LCD heaters) are exactly what they sound like. We take a piece of glass, coat it in a conductive material (most commonly ITO) and then give it power. You can tweak the coating depending on how much power you need and how big of a display you have. The heater is then bonded to the LCD using a UV curable, optically clear adhesive. Finally, your touch screen is attached on top of that (most likely using the same adhesive), creating a sandwich of functional touch display goodness. This will keep your display nice and toasty while you freeze to death, giving you the “instant on” that I’ll be getting from my iPad in the comfort of my living room.

So, pioneer of the great frozen unknown, I hope I answered your question and then some. Now if you’ll excuse me, I have sudden urge to make hot cocoa and s’mores.

Cheers to the good life,
-Touch Guy

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

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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’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

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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