Page 28 · SumoBot – Mini Sumo Robotics
The technique for converting the raw sensor reading to a bit value takes advantage of the
{optional} comparison parameter with the
LOOKDOWN
function. Without the comparison
parameter,
LOOKDOWN
uses equality to scan its table for a value match. By using the
comparison parameter, we can test a range of values with a single table entry.
This line:
LOOKDOWN lLine, >=[1000, 0], lbLeft
will put 0 into
lbLeft
if
lLine
is greater or equal to 1000, otherwise it will but 1 in
lbLine
(
lLine
is between 0 and 999). This works because the comparison parameter is >= and
the first table entry [index 0] is 1000.
LOOKDOWN
will transfer the index to the output
variable as soon as a match is found. If the sensor value is less than 1000 (as when on the
border), the index value of 1 is moved into
lbLeft
.
We could use an
IF-THEN-ELSE
coding technique to accomplish the same thing:
Left_Conv:
IF (lLine >= 1000) THEN
lbLeft = 0
ELSE
lbLeft = 1
ENDIF
As you can see, using
LOOKDOWN
with the comparison parameter is the more elegant
approach. You may be wondering why the value 1000 was used as the black level
threshold. It was selected to allow the QTI to be affected by external light and still return
an accurate reading. Extra light falling on the playing surface will reduce the QTI output
values. By using a value about one-fourth the normal black reading, the program has
plenty of margin for lighting variability. Now let's examine what happens with the output
values.
The bit variables
lbLeft
and
lbRight
are aliased into
lineBits
– this means a change in either
will cause a change in
lineBits
. We will use this variable with the
SELECT-CASE
structure to determine and display which action to take based on the QTI sensor values.
Summary of Contents for Boe-Bot
Page 1: ...SumoBot Mini Sumo Robotics Assembly Documentation and Programming VERSION 2 1...
Page 4: ......
Page 9: ...Preface Page ix...
Page 10: ......
Page 20: ......
Page 32: ......
Page 54: ......
Page 74: ......
Page 76: ......
Page 77: ...Appendix D SumoBot PCB Schematic Page 67 Appendix D SumoBot PCB Schematic...
