Specifications

16
Scanning Infrared
Scanning infrared (IR) technology relies
on the interruption of an IR light grid in front
of the display screen. The touch frame or
opto-matrix frame contains a row of IR-light
emitting diodes (LEDs) and photo
transistors, each mounted on two opposite
sides to create a grid of invisible infrared
light. The frame assembly is comprised of
printed wiring boards on which the opto-
electronics are mounted and is concealed
behind an IR-transparent bezel. The bezel
shields the opto-electronics from the
operating environment while allowing the IR
beams to pass through.
The IR controller sequentially pulses the
LEDs to create a grid of IR light beams.
When a stylus, such as a finger, enters the
grid, it obstructs the beams. One or more
photo transistors detect the absence of light
and transmit a signal that identifies the x and
y coordinates.
Surface Acoustic Wave
Surface acoustic wave technology is
based on transmitting acoustic waves across
the surface of a glass overlay placed over the
display surface. A transducer mounted on
the edge of the glass emits the acoustic wave,
which travels on the surface of the glass
overlay and is reflected back across the
overlay. Since the speed of the wave is
known and the size of the glass overlay is
fixed, the first reflector will send the first
signal back first, then the second, and so on.
When a stylus such as a finger comes into
contact with the wave, it attenuates the wave
motion by absorbing part of the wave. This
is detected by the control electronics and
determines the touch location.