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It's Magic, You Know
It all seems so simple - you take your index finger (or any of the other 4) and you start tapping away, writing emails, sending text messages, surfing the internet, but how exactly does your smartphone know where your finger is on the screen and how to respond to it? The answer may be a little more complex than you've ever imagined.
You'll probably be surprised to hear that the very first touchscreens man ever created were made in the 1960s, and their basic use was for learning-assistance. Oh, how far we've come. Today, touchscreens are used in everything from ATM kiosks to your iPhone to your tablet's screen to videogaming consoles.
There are several different technologies that power touchscreens, but they have many things in common.
For one, almost all touchscreens in use today employ a three-layered system of operating. There is the glass layer, where the user will be touching his finger to the screen in order to implement the gestures he or she wants to perform. Then, underneath the glass layer is where the tech differs, but the technology between the glass layer and the bottom layer is to interpret the finger strokes in one way or another. Finally, the bottom layer of the touchscreen serves as the final point in the relay between your finger and the screen. This bottom layer is responsible for sending information to the device in a form it can understand.
So, for our purposes, we'll be talking about the touchscreen interface that devices like the iPhone use.
First, it's important to note that touchscreens like this operate using either resistive or capacitive technologies. In a resistive technology touchscreen, the name is actually a misnomer - what happens is that the layers of the technology work essentially as voltage separators with a sensor attached. When your finger comes along and touches the screen, these two layers come closer together, and the sensor is able to detect the voltage difference, thereby detecting where your finger is.
In a capacitive system, however, the touchscreen works in a different way. This time, it relies on disturbance of an existing state of balance rather than detecting a small change in voltage. What happens is that the device generates a continual electrical current (ECE) across the screen. When your finger comes along and touches the screen this time, the sensors attached to the screen know where the disturbance in the current is thanks to the fact that your body is also a capacitor of sorts. By disrupting this current in a particular place, the sensor then relays back the information to the device to know where it was touched.
On devices like the iPhone however, you need multiple types of technology to achieve "multi-touch". You need two different perpendicular layers of materials that detect touch in order to establish "nodes" of touch, places where the device can locally detect the touch, but not devote all its capabilities to detecting that single touch. Essentially, you create a "zone" every time you touch your finger to the screen, and with advanced software and these perpendicular linings, you can achieve the sorts of multi-touch displays that Apple is quickly becoming famous for.
But that still doesn't answer exactly what happens when the touch is made onto the screen. So, to make things simple, I've taken the liberty of outlining exactly what happens (in a matter of milliseconds) inside the machine.
1. You touch the screen at a certain place.
2. Depending on the technology, you either disrupt an electrical current or you create a voltage difference, allowing an electrical signal to be generated.
3. A sensor picks up this electrical signal.
4. The original signal is collected by the sensor and sent to the processor in its raw form.
5. The processor interprets the signal as a touch and starts to clean the raw data of any "noise".
6. Once cleaned, the processor then moves on to interpret where on the screen the touch was and determine exact coordinates.
7. These coordinates are sent to the software you're trying to use to determine where the "click" will be.
And there you have it - for something that is relatively complicated, it's amazing how easily it has invaded our everyday lives, making everything from phones to refrigerators easy to manipulate.