How do iphones detect touch

VAT number: Authorised and regulated by the FCA How does the iPhone touch screen work — and why is it made of glass? It happens to everyone: you smash the iPhone touch screen and you wonder why Apple would use a screen made of glass on a mobile phone. The answer is behind the technology used for the touch detection.

There are a few solutions for touch detection, like near-infrared light, sound waves, or cameras which monitor changes in light. But the most popular technologies used are resistive screens and capacitive screens. The iPhone's capacitive touch-screen technology means that you aren't limited to simply pressing the screen in one place. The iPhone can detect the difference between your pressing the screen with one, two, three or four fingers. It can also detect gestures such as swiping or pinching.

This sensitivity gives you a much wider range of controls for each individual application. It also helps make the user interface much more intuitive. For example, programmers can map your finger swipes to scrolling through a long page, or pulling two fingers apart to zoom in on an image. Capacitive touch screens such as the iPhone are configured to detect the conductivity level of a human finger. Instead, they work with anything that holds an electrical charge — including human skin.

Yes, we are comprised of atoms with positive and negative charges! Capacitive touch screens are constructed from materials like copper or indium tin oxide that store electrical charges in an electrostatic grid of tiny wires, each smaller than a human hair. Capacitive touch screen technology [Image credit: Electrotest ] There are two main types of capacitive touch screens — surface and projective. Surface capacitive uses sensors at the corners and a thin evenly distributed film across the surface as pictured above whereas projective capacitive uses a grid of rows and columns with a separate chip for sensing, explained Matt Rosenthal, an embedded project manager at Touch Revolution.

In both instances, when a finger hits the screen a tiny electrical charge is transferred to the finger to complete the circuit, creating a voltage drop on that point of the screen. The software processes the location of this voltage drop and orders the ensuing action. Newer touch screen technologies are under development, but capacitive touch remains the industry standard for now. The biggest challenge with touch screens is developing them for larger surfaces — the electrical fields of larger screens often interfere with its sensing capability.

Software engineers from Perceptive Pixel , which designs multi-touch screens, is using a technology called frustrated total internal reflection FTRI for their larger screens, which are as big as inches. When you touch an FTRI screen you scatter light — and several cameras on the back of the screen detect this light as an optical change, just as a capacitive touch screen detects a change in electrical current.

Allison T. McCann has a B. How does that work? Many, including the iPhone, monitor changes in electrical current. Others monitor changes in the reflection of waves. These can be sound waves or beams of near-infrared light.

A few systems use transducers to measure changes in vibration caused when your finger hits the screen's surface or cameras to monitor changes in light and shadow. The basic idea is pretty simple -- when you place your finger or a stylus on the screen, it changes the state that the device is monitoring. In screens that rely on sound or light waves, your finger physically blocks or reflects some of the waves.

Capacitive touch screens use a layer of capacitive material to hold an electrical charge; touching the screen changes the amount of charge at a specific point of contact. In resistive screens , the pressure from your finger causes conductive and resistive layers of circuitry to touch each other, changing the circuits' resistance. Most of the time, these systems are good at detecting the location of exactly one touch.