Carrol Touch TouchSystems CarrollTouch Prog, Programmer'S Manual

Page: 21 / 274

Chapter 1 - Introduction to Infrared Touch Systems CARROLL TOUCH
1-4 Touch System Programmer’s Guide
Figure 1-3. Beam Averaging - Example 2
In Figure 1-3, beams 2, 4, 6, and 8 are interrupted on both the x- and
y-axes. The logical coordinate pair reported to the host is 5, 5.
Reporting Touch Coordinates
For a touch to be reported, at least one x beam and one y beam must be
interrupted. If no beams are interrupted in either the x- or y-axis, the
touch is ignored.
The lowest logical coordinate reported for any axis on any touch frame
is zero. The maximum logical coordinate that may be reported for a
given touch frame axis may be determined from the number of physical
beams on that touch frame axis as follows:
Maximum logical coordinate = 2 x (number of physical beams - 1)
For example, on a frame that has 40 x-axis beams and 30 y-axis beams,
the maximum logical coordinates for the frame are:
Maximum logical x coordinate = 2 x (40 - 1) = 78
Maximum logical y coordinate = 2 x (30 - 1) = 58
Therefore, the reported coordinates would range from 0 to 78 on the
x-axis and from 0 - 58 on the y-axis.
Failed Beams
Carroll Touch touch systems have incorporated into their firmware a
mechanism for detecting defective beam pairs and removing them from
consideration when determining the location of a stylus within the touch
frame. This failed beam mechanism provides a measure of fault
tolerance for the touch system so that, in the event of an opto-component
02 04 08 06 10 00
00
02
04
06
08
5,5