Basic Touch-Sensor Screen System
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.
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.
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.
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.
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