Touchscreen Technologies – Resistive, Capacitive and Surface Acoustic

Touchscreen Technologies – Resistive, Capacitive and Surface Acoustic

A touchscreen is an electronic visual display that can detect the touch and point of a touch within the display area. Touchscreens are everywhere and they are embedded in Tablets, microwave ovens, phones, remote controls, GPS systems, access controls and almost all the portable devices. They are becoming more and more commonplace as their prices drop every day.  There are many different ways in which touchscreens are implemented and there are research works going on every minute to improve on these technologies.

 

Resistive

The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed at the outer layer. When an object, such as a finger, presses down on a point on the panel’s outer surface the two metallic layers become connected at that point so the panel then behaves as a pair of voltage dividers with connected outputs. This is registered as a touch event and sent to the controller for processing. A special driver translates the touch into coordinates that the operating system can understand, just like a mouse movements on a normal computer.

 

Capacitive

In the capacitive system, a layer that stores electrical charge is placed on the insulator such as glass panel of the monitor. Touching the screen results in a distortion of the screen’s electrostatic field measurable as a change in capacitance (since human body is also an electrical conductor). This change is measured and the controller calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touchscreen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.

 

Surface acoustic

In surface acoustic, piezoelectric transducers are used at various positions around the screen to turn the mechanical (vibration) energy of a touch into an electronic signal. One receiving and one sending transducers are placed along the x and y axes of the monitor’s glass plate. Also placed on the glass are reflectors that 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. A resistive system records a touch as long as the two layers make contact, which implies that it is not a function of your or a pen just touch. A capacitive system, unlike resistive, must have a conductive input, usually your finger, in order to record a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object. The resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.

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