Robotics with the Boe-Bot text v2.2

Chapter 6: Light Sensitive Navigation with Photoresistors · Page 221
PULSOUT 13, 650
PULSOUT 12, 650
ELSE ' Go forward.
PULSOUT 13, 850
PULSOUT 12, 650
ENDIF
Here is another code block that works a little better. This code block fixes the turning
back and forth problem under certain conditions. The timeLeft variable now has to be
larger than timeRight by a margin of 15 before the Boe-Bot will apply a left pulse.
Likewise, timeRight has to be larger than timeLeft by 15 before the Boe-Bot adjusts to
the left. This gives the Boe-Bot the opportunity to apply enough forward pulses before it
has to correct with a turn, but only at certain light levels.
IF (timeLeft > timeRight + 15) THEN ' Turn right.
PULSOUT 13, 850
PULSOUT 12, 850
ELSEIF (timeRight > timeLeft + 15) THEN ' Turn left.
PULSOUT 13, 650
PULSOUT 12, 650
ELSE ' Go forward.
PULSOUT 13, 850
PULSOUT 12, 650
ENDIF
The problem with the code block above is that it works under medium dark conditions
only. If you take it into a much darker area, the Boe-Bot starts turning back and forth
again, and it never applies any forward pulses. If you take it into a brighter area, the Boe-
Bot just goes forward, and never makes any adjustments to the left or right.
Why does that happen?
Here is the answer: When the Boe-Bot is in a dark part of a room, the measurement for
each photoresistor will be large. For the Boe-Bot to decide to turn toward a light source,
the difference between these two measurements has to be large. When the Boe-Bot is in
a more brightly lit area, the measurement for each photoresistor will be smaller. For the
Boe-Bot to decide to make a turn, the difference between photoresistor measurements
also has to be much smaller than it was in the darker part of the room. The way to make
this difference respond to the lighting conditions is to make it a variable that is a fraction
of the average of
timeRight and timeLeft. That way, it will always be the right value,
regardless whether the lighting is bright or dim.