SFH4232_ 查看數據表（PDF） - OSRAM GmbH
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SFH4232_ Datasheet PDF : 14 Pages
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Fig. 2: Reflection type principle of a camera-
based touchscreen. The influence of a stylus
in the light path on the cell’s signal of the line
scanning sensor is sketched in the graph.
2.2 Camera-based Touchscreens
Very recent developments are camera-
based touchscreen setups. This technology
is growing in popularity, due to its scalability,
versatility and affordability, especially for
larger units. One typical setup is presented
in Fig. 2.
The system usually consists of two or more
IR line-scanning optical sensors, like used in
barcode or flat-bed scanners. Each one is
mounted in the upper left and right corner of
the screen bezel. The sensors monitor the
complete screen which is illuminated with
infrared light.
The infrared illumination of the screen area
is done by IREDs positioned in the upper left
and right corners, next to the line scanning
sensors, but optically isolated to avoid
crosstalk. Each of these IRED assemblies
illuminates the complete 90° angular range
of the screen.
The reflection of a stylus or object (e.g.
finger) triggers a rise in the signal of the
relevant detector cells. By special
Fig. 3: Camera-based touchscreen
realization with an edge emitting light guide.
The light guide provides a diffuse
illumination of the screen.
computational algorithms (e.g. triangulation)
based on the readout of the two line
scanning sensors the exact coordinates and
even the size of the touching object or finger
tip can be calculated via software.
2.3 Camera-based with Light Guide
In a different arrangement, a light guide
based infrared lighting system is mounted at
the cameras opposite field of view, inside
the bezel (see Fig. 3). Practical realizations
of this backlighting system include high
power IREDs which couple light into both
ends of an edge emitting optical light guide
element. This light guide is mounted around
the screen and provides an IR light curtain.
In this case the touch of a stylus or object
shows up as a shadow generating a drop in
the relevant detector cells’ signal. Again,
special computational algorithms are needed
to do the calculation of the location resp.
size of the object.
August 13, 2010
page 3 of 14
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