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Giz Explains: The Magic Behind Touchscreens

Posted by Matt Buchanan at 4:00 AM on August 14, 2008

Touchscreens. They're everywhere, as if electronics makers aren't cool unless their phones or media players have them, and soon that will be true for laptops as well. Touchscreens aren't going to completely replace the mouse and keyboard in the next year or two, but we're hurtling toward a future where they're the dominant way we interact with devices. The catch is that "touchscreen" can describe a few very different technologies that all perform a similar function. Here's a breakdown of the most popular techniques for making touchscreen magic happen—and the crazy new techniques that will succumb to your caresses in years to come.


 

At a basic level, they all perform the same function--sensing a disturbance in the force when your finger or stylus or whatever pointy object you've got touches the screen, and then extrapolating that into knowing where you're touching it and relaying that to the software. The differences lie in how each screen detects a touch.

Resistive touchscreens are the ones you've probably put your greasy fingers on more than any other kind, mostly because they're the cheapest and oldest. They're in most touchscreen mobile phones, many tablets and the Nintendo DS, to name a very few.

How it works: On the bottom you've got a layer of glass, and on top of that, you've got two more: a conductive and a resistive layer. They've got a sliver of space between them. And on top of that you've got one more layer, which is the one you touch. So, when you push down on the screen, the conductive and resistive layer touch each other, which changes the electrical current running through 'em, and the device can tell from that where your finger or stylus is touching.

Good and bad: While resistive is a good deal cheaper to manufacture at the moment, one downside is that it's hard to do multitouch, because of the constraints and shortcomings of a pressure-based system. Another problem is that the multiple layers of touch technology on top of the LCD block an awful lot of light—think of how much dimmer the DS's bottom screen is than the top one.

Capacitive touchscreens are a bit fancier. They used to be really expensive, but the costs are coming down, so you're seeing them in more stuff, like this touchscreen phone from Apple you might have read about, or Dell's Latitude XT tablet.

How it works: At its most basic level, you've got a layer on top of the actual display panel that has an electrical charge running through it. Since you've got your own electrical mojo going on, when you touch the screen (presumably with your finger), it registers an electrical change. By measuring how much you're mucking up the electrical field and where the biggest disturbances are, the device can determine where you're touching it.

Good and bad: It's far easier to do multitouch with capacitive, and fewer added layers mean more light comes through for a brighter display. Still, because it's all about electrical fields interacting and conductivity and stuff, a hand with a mitten on it will have a hard time making stuff happen, and if you wanna use a stylus, you'll need a special one.

Infrared touch sensing, currently most famously used by Microsoft's Surface table, takes a slightly different approach. Because it works well with larger products, you might end up seeing this one quite a bit, especially from Microsoft.

How it works: Basically, the image on the surface is projected from underneath it, along with infrared light. Also underneath are infrared cameras that can see when the light is reflected by objects (like your fingers or mobile phones or whatever), and those images are processed and translated as you move and gesture with pictures and virtual objects.

Good and bad: The good thing about this is that it uses existing technologies that come very cheap; the bad news is that the apparatus itself can be bulky, hence the need for Surface to be hidden inside a table, or at least a large globe. Also, it's sensitive to light, so flash photography or strong sunlight can throw off its game.

More, more, more!! There are some \way more advanced touchscreen technologies that aren't yet in wide use. The surface wave acoustic system uses tranducers and reflectors that detect if the ultrasonic waves being sent between them are disturbed (absorbed, actually), meaning something is touching it. Upside is that no metal crap in the panel means 100 percent brightness and awesome clarity. But apparently dust and crud can affect it, so not good for anywhere dirty.

Sharp and others have released prototype touchscreens with optical sensing tech built directly into the display. They are sensitive enough to detect your finger rubs right down to the pixel. Besides making multitouch easy, it can also double as a scanner because of the whole optical deal. Right now it's for small screens like phones—it can scale to notebook size, but not any larger. Of course, they, like infrared, can be affected by undesired light fluxuations.

Mary Lou Jepsen—the engineering honcho behind OLPC's original XO Laptop and founder of the Pixel Qi LCD development firm—told us recently she is pushing for in-cell touchscreen tech, which would make touchscreens cost the same as regular LCDs and be the same thickness, since touch sensitivity would be part of the LCD's own matrix. The issue is that it'll only work with devices specifically coded to use it; it's not a plug-and-play touchscreen like you could order online for your home DIY fake iPhone. If you're wagering that this secret sauce will help achieve the impossibly low pricetag on OLPC's next baby, the XO-2, you win a cookie.

And that's just about everything you need to know about touchscreens to get by. Resistive and capacitive are the major two to know for now, though you might start hearing a lot more about the other ones soon enough.

Something you still wanna know? Send any questions about touching, feeling or screening to tips@gizmodo.com, with "Giz Explains" in the subject line. Top image from David Nguyen, featured in this Giz Photoshop contest.

Tags: feature | giz explains | iphone | multitouch | regulars | top | touchscreens

 

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