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May 12, 2009 / douglasac

Touchscreens! Part 1

Woo! Touch screens! Screens you are allowed to fondle and touch and rub and so on. You’ve probably seen them, and you may have used one. So you’re probably wondering: what’s so special about them that make them work just by touching your finger to them, and if you can get one yourself for your home computer.

So, continue forth, fine reader, and find out more.

How do they work?

Well, as there is with almost anything computer-related, there’s about four or five different technologies that all achieve the same task. These are:

  • Capacitive
  • Resistive
  • Surface Acoustic Wave (SAW)
  • Infrared
  • Multi-touch

We’ll go on a bit about each one in further detail.


Look! Pretty Picture!

So… what essentially happens with this type of screen is that a slam small amount of electrical charge is applied to the four corners of the touchscreen. Now, because you, being a human, conduct electricity, you complete the circuit. The capacitance of the circuit is then measured, and the controller card for the screen transmits the X,Y location of where you touched to your computer, hence moving the pointer to where you touched.

There are some disadvantages, however: only fingers (or other human body parts) can control it: you can’t use a coin or a stylus to move the cursor around the screen as these won’t conduct the charge. If you’re wearing gloves, then it’s not going to work both (although we have this type of screen at work, and they are more than happy to work with a latex gloved hand fondling the screen). You also need to recalibrate the screen on a regular basis: otherwise your cursor can get way, way, WAY off (and it is most irksome when this happens).


Look! Another pretty picture!

Resistive technology has a glass or acrylic panel with some electrically resistant layers, separated by invisible separator dots. As with capacitive technology, an electrical current is passed through the screen, and when you press the screen, the layers touch together, and cause a change in the electrical current. The pointer then follows your bidding and proceeds to where you touched.

As with capacitive technology, there are some disadvantages. You need to calibrate it every now and then, otherwise the cursor ends up somewhere undesirable. There are some clarity issues with these screens as well. They are also easily damaged by scratching, poking and impact (The latter two confuse me: the whole point of a touchscreen is that it is poked and impacted. So, poke gently, I guess.), and they aren’t considered suitable for public access applications. And they can wear out over time.

However, they are cheap. So, bonus.

Surface Acoustic Wave (SAW)

Yet another pretty picture! WOW!

SAW Technology sends sound waves (also known as acoustic waves) across a clear glass panel with transducers (Perhaps a Dr. Furter played a part in its creation…) and reflectors. Upon your touching of the screen, the soundwaves are absorbed, and a touch is registered. Tada!

It is quite similar to infrared technology in regards to its sophistication, and is well-suited to things such as public access terminals. However, because it is similar in sophistication to infrared with regards technology, but is more expensive than infrared, it’s not as highly recommended. It also must be touched by a finger (gloved or otherwise) or a soft tipped stylus. Anything else, i.e. coin, credit card, fingernail, pickaxe, won’t work. And it can also be affected by dirt, dust and water.


You’re probably sick of the pretty pictures, aren’t you?

Infrared technology is simple: the screen is crossed with infrared beams. Your touch obstructs two beams, and a touch is registered by the computer. Hooray!

Apart from being quite possibly the best form of touchscreen, it’s also the easiest to explain. J

As a general rule, if you can afford it, go infrared: it’ll last longer, and doesn’t need calibration, and, unlike SAW technology, isn’t really affected by dust, dirt and water.

Can I Get One?

Short answer: yes.



Really Really?

For the last time, yes.

So, I can walk into Billy’s PC Shop, and buy one right there and then, and take it home and be fondling my around Windows licketyspit?


So then I can’t buy one, then, can I?

Well, the thing is, at the moment, touchscreens are niche items and cost around about $1000 for a small screen (I’m talking 12 to 15 inches, here), and when most people see 22″ screens, they suddenly want that one.

But, wait! Something about a Touchscreen computer springs to mind!

The HP Touchsmart?


Well, that is valid. But, unfortunately, we’ll have to talk about it in the next post. Mmkay?

Oh, alright. But you better post it… or else!

I will.


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