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243_MasterPieces_02b.qxd 4/18/03 6:59 PM Page 96

96 Masterpiece 2 • The Learning Brick Sorter

}

// if not, define a new range
if (range>top_range) {
top_range++;
// if all ranges have been used, beep for error
// and terminate program
if (top_range>=RANGES) {
PlaySound(SOUND_DOWN);
StopAllTasks();
}
range=top_range;
min[range]=light_value-RANGE_WIDTH;
max[range]=light_value+RANGE_WIDTH;
}
// look for a positive value in the knowledge base array
for (bin=0;bin<BINS;bin++)
if (kb[range*BINS+bin]==KB_YES) return;
// otherwise, look for an "unknown" value in the knowledge base array
for (bin=0;bin<BINS;bin++)
if (kb[range*BINS+bin]==KB_UNKNOWN) return;
// this point shouldn't ever be reached, unless the user provided some
// inconsistent replies. If this happens, the program makes a random
// choice.
bin=Random(BINS-1);
}
You probably remember that one of the touch sensors of the switchbox shares the
same Input Port as the light sensor. Because of this, we must be sure that the lever has
been released before taking a reading from the light sensor.The purpose of the constant
LITE_THRSHLD is to be able to distinguish when the touch sensor is closed.
#define LITE_THRSHLD 98

Under normal conditions, the light sensor never returns a value even close to 100. On
the contrary, the touch sensor returns 100.This simple test against LITE_THRSHLD
allows us to identify whether the touch sensor is pressed or not.
The routine continues with the code searching and assigning the ranges that define
colors, and finally starts looking up the knowledge base. First, it scans the row correspon-
ding to the given range for a positive value; that is. a cell assigned to the KB_YES value.
If it finds one, the range has already an assigned bin and the routine can return the global
variable bin, which contains the number of the bin to put the brick into.