There are three basic arrangements that are used to identify touch. They are resistive, capacitive and surface acoustic wave.
The resistive system consists of a layer of glass covered with a conductive and a resistive metallic layer, which are separated by spacers. During operation an electrical currents runs through the layers and when pressure is applied to the screen and the two layers touch a change in the current is recognized and the coordinates are determined. Then a driver converts the touch into an instruction.
The capacity system has a layer of glass with a transparent metallic conductive coating. An electrode pattern distributes a low voltage field over the conductive layer. When a finger touches the screen it creates a voltage drop and the current flow is able to be measured to calculate locate the point of contact. The information is then transmitted to the computer. POS (Point of Sale), kiosks and ATMs use capacity systems.
A touch screen using a surface acoustic wave system uses a receiving and a sending transducer, which are positioned on the X and Y axes of the monitor’s glass plate. The reflectors on the glass plate reflect the electrical signal sent from one transducer to the other. The receiving transducer can instantly detect if the wave has been disturbed by a touch.
The touch screen on the iPhone has large buttons that can be pushed directly on the screen and allow the user to complete phone tasks without having to use the small buttons on a typical mobile phone. With the elimination of the keypad on a mobile phone it allows for a bigger screen without increasing the size of the phone. This has allowed for a widescreen facility to be included on the iPhone. Touch screen technology allows for easy access for consumers and businesses to use touch screen to do their banking at ATMs, get customer information from shopping centre kiosks and cash registers.
References
http://electronics.howstuffworks.com/ipod-touch.htm
http://www.ezscreen.com/capacitive_touch_screens.html
http://www.ideamarketers.com/?windows_mobile_6_sip,_windows_mobile_si&articleid=599233
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