Specifications

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

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