Touch screen is a type of display screen that has a touch sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or a device pen, you can use your finger to point directly to objects on the screen. Although touch screens provide a natural interface for computer novices, they are unsatisfactory for most application because the finger is such as large relatively large object. It is impossible to point accurately to small areas of the screen. In addition, most users find touch screens tiring to the arms after long use.
The basic touch screen has three basic systems.
- Resistive System
- Capacitive System
- Surface Acoustic Wave (SAW)
The resistive system consists of a normal glass panel or a touch screen sensor is a clear glass panel with a touch responsive surface,that is covered with a conductive and a resistive metallic layer.The sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. This voltage change is used to determine the location of the touch to the screen.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the screen with his finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases and this decrease is measured in circuits located at each corner of the screen. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software.
- Surface Acoustic Wave (SAW):-
Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touchscreen panel. This technology came in the late 90′s, and uses sound waves to calculate where you have pressed. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touch screen panels can be damaged by outside elements.The screen is covered by a special glass,called as Small transducers, marked as transmitters in the green on the image, it sends out sound waves. Using the small “mirror” which are then reflected those beyond the screen surface. When you press on the screen, the recipients by means of reflections and delays calculate where you have pressed.
The sound waves are sent out from the transmitters, and for every mirror they pass is a small part reflected over the surface, while the rest continue on to the other mirrors. Since sound beam lose strength, are the mirrors at the end of the range set closer together. In the same way the waves are reflected back to the receiver on the opposite side of the glass.
