The touch-sensor technology is about using our fingers or some other pointer, to view and manipulate information on a screen. On a conventional system, with every mouse click, the operating system registers a mouse event. With a touch-screen system, every time your finger touches the screen, a touch event is registered.
A basic touch-screen system is made up of three components:
1. A touch sensor
3. Software driver
The touch-sensor is a clear panel, which when touched, registers a voltage change that is sent to the controller. The controller processes this signal and passes the touch event data to the PC through a bus interface. The software driver takes this data and translates the touch events into mouse events.
A touch-screen sensor any of the following five mechanics: resistance, capacitance, acoustics, optics and mechanical force.
1. Resistance-based sensors.
A resistant sensor uses a thin, flexible membrane separated from a glass or plastic substance by insulating spacers. Both layers are coated with ITO (Indium-tin-oxide). These metallic coatings meet when a finger or stylus presses against the screen, thus closing an electric circuit.
2. Capacitance-based sensors.
Here voltage is applied to the corners of the screen with electrodes spread uniformly across the field. When a finger touches the screen, it draws current from each current proportionately. The frequency changes are measured to determine the X and Y coordinates of the touch event.
3. Acoustic sensors.
These sensors detect a touch event when a finger touches the screen resulting in absorption of sound energy. Bursts of high frequency (5-MHz) acoustic energy are launched from the edges of the screen. Arrays of reflection at the edges divert the acoustic energy across the screen and redirect the energy to the sensors. Because the speed of sound in glass is constant the energy arrival time identifies its path. A touch causes a dip in the received energy waveform for both axes. The timing of dips indicates the X and Y touch point coordinates.