Smartphones, it seems everyone has one these days. But how do they actually work? How is it possible that this device, by just touching it, knows what you want to do? Most people claim it is because of the heat of your finger. But honestly, do you think this is true? ;-)

The truth is that there are 3 types of technologies used in modern smartphones.

The first one is the “resistive” touchscreen. You may notice on some smartphones, if you hold the screen to the light, you can see a lot of small dots.
These dots separate multiple layers of material that are in fact transmitting currents. When the top, more flexible, layer of the screen is pushed into the lower layer, the electrical current changes and the location of the impact is calculated.
This type of screen can be operated by your bare fingers, but also if you are wearing gloves (really, it has nothing to do with heat) or a pen will work as well.
Basically anything that can apply pressure.

There are some disadvantages to this type of touchscreen. However it is rather cheap to produce it has some limits. The most obvious one is the visibility, if you are outdoors and are using this type of screen, you will have some trouble seeing what is going on. The visibility is rather poor. Also, no “multi-touch” actions can be done. 1 impact, 1 action.

Another type of touch screen is called the “capacitive” screen. This works somewhat different. However, there is also a current involved, this current is broadcasted from the corners of the screen. When a finger touches the screen it changes the current and the location is calculated.
This screen shows much better performance outdoors, even in broad daylight you will have a fairly good idea of what is showing on your screen and it also allows multiple touch commands. It is somewhat more expensive than the resistive screen.
This screen can only be used with your bare fingers. (for the record, this is the type of screen used for the iphone)



The last screen available is the “infrared” screen. And this can work 2 ways. The first one is, believe it or not, heat. This is the only screen that detects heat. Needless to say, you can only use this with a warm, bare finger.
But there is another way in which infrared screens are used. This is the optical way. Sensors are used to shoot a grid of invisible beams just above the screen. The point where the x/y axis is interrupted by an object will be calculated.

If your phone has an infrared screen, it’s obvious that you can only use your (warm) finger to operate the phone.
Optical doesn’t have this problem. Some object that can interrupt the beams can operate the screen. It probably is needless to say, but this is the most expensive way of building a screen. This screen provides great visibility outdoors.



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