Tech Term of the Week #7: Touchscreens at 7:09 PM

Touchscreens have always been used to provide a intuitive interface that any user can learn to use. Since the iPhone's release back in July of 2007, touchscreens has been more and more prevalent especially in the cellphone market, where keypad phones are now a rarity.

Now many of you might be wondering how this seemingly devil magic works and today hopefully I can explain them before my brain decides to stop functioning.

There are 3 general kinds of touchscreens, resistive, capacitive, and infrared.

Resistive touch screens work due to the pressure of you fingers making electrical contacts on the screen

As you can see from the picture a resistive touchscreen has two conductive layers separated by a minuscule gap. When you finger pushes on the screen the two membranes come into contact and a voltage can be detected by the screen controller and the x and y coordinates can be pinpointed by seeing where the voltage came from. These types of touchscreens were the first to be utilized in mass production, and are characterized by a slight squishiness of the screen. An example of a resistive screen is the Nintendo DS

The next and more recent type is capacitive touchscreens. Almost all modern touch screens use this technology for touch. Capacitive screens use the conductivity of you human flesh to detect motion. The actual scientific explanation is quite confusing and long so I'm going to skip it and give a gross oversimplification. Actually this is totally an excuse because I actually have no idea how it actually works down on the technical level

Basically a current is fed through a conductive panel. When you finger touches it it alters the flow of the current enough so that a receiving electrode can detect it. Based on where you touch the current will be different to the receiver and this is how the touch is detected. This technology can be used to detect multiple touches by having the receiver look for different patterns of the received current. The downside to this is that only conductive materials can be used as pointers, so for example if you had gloves, you could not use your laptop touchpad, your Apple scroll wheel, or your iPhone screen.

Last we have infrared touch screens. How this works is having a grid of infrared lights.

So you have at one end a row of diodes and at the other detectors. Same thing with the columns.
When you touch the screen you finger blocks the light from reaching the detector in both the x and the y axis. Using this information the controller can tell the device where the touch has occurred.







So these are the three main forms of touch screens with capacitive screens being most common followed by resistive and infrared. Hopefully this is explained  how you snazzy new cellphone can tell that you touched the take call button instead of hanging up on person on your phone.