Touch screen interfaces have now become very common and even toddlers are seen meddling around with touch screen phones etc. There are three basic systems – Resistive, Capacitive and Surface acoustic wave which acts as the user interface.
Resistive interfaces consist of two metallic sheets or layer with an electrically resistive coating. There is a separation between these two sheets. When the device is in ‘on’ state current passes through these two layers.
When pressure is applied on the top sheet of the display, it bends back towards the second sheet. When the two sheets come in contact, there is a change in electric field. This change is interpreted and information is displayed accordingly. This kind of display needs only pressure to register your touch. So you can use anything sensible to apply pressure.
Capacitive interface consists of a layer that is placed on the glass panel of the monitor. This layer stores electrical charge. When we touch the panel, some of this charge is transferred to the user. Now the charge on the capacitive layer decreases. This decrease is calculated and information is accordingly displayed. A capacitive system gives a much clearer picture than the resistive system.
Surface acoustic wave systems consist of two transducers (one receiving and one sending) on the glass plate. Also placed on the glass are reflectors. These reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics.
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