EGR 277

1
BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering

• Navigating the BOE-BOT with whiskers
• Reference
• For more complete documentation, the following
  items are available from www.parallax.com or
  www.tcc.edu/faculty/webpages/PGordy
• Robotics with the BOEBOT Version 2.2
• BASIC Stamp Syntax and Reference Manual Version
  2.1

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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Tactile Navigation with the BOE-BOT (Wall
following using whiskers) The following is an
excerpt from Robotics, Version 2.2 Many types
of robotic machinery rely on a variety of tactile
switches. For example, a tactile switch may
detect when a robotic arm has encountered an
object. The robot can be programmed to pick up
the object and place it elsewhere. Factories use
tactile switches to count objects on a production
line, and also for aligning objects during
industrial processes. In this chapter, you will
build tactile switches, called whiskers, onto
your BOE-BOT and test them. You will then
program the BOE-BOT to monitor the state of these
switches, and to decide what to do when it
encounters an obstacle. The end result will be
autonomous navigation by touch. The whiskers are
so named because that is what these bumper
switches look like, though some argue they look
more like antennae. Whiskers give the BOE-BOT
the ability to sense the world around it through
touch, much like the antennae on an ant or the
whiskers on a cat.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Adding whiskers to the BOE-BOT If your BOE-BOT is
not already equipped with whiskers, following the
instructions shown from Robotics, Version 2.2 to
add the whiskers. If your BOE-BOT is equipped
with whiskers, skip to the next page.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Adding a whisker circuit to the BOE-BOT Shown
below is a circuit to read the status of each
whisker. It works as follows The whiskers are
connected to standoffs on the BOE which are
connected to ground (Vss). When the BOE-BOT runs
into a wall, the whisker touches a header on
the breadboard which will make a connection to a
point in the circuit below (see next page). A
whisker hitting a wall is equivalent to closing a
switch in the circuit below. In the circuit, if
the right whisker hits a wall, it makes a
connection to Vss making P7 LOW. If the whiskers
is not pressed, P7 remains HIGH. In this way we
can tell when each whiskers hits a wall by
monitoring the states of P5 and P7.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Adding a whisker circuit to the BOE-BOT Shown
below is a circuit to read the status of each
whisker. It works as follows The
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Whisker test circuit It is nice to have a test
circuit, so that we can tell if the whiskers are
working properly. An easy solution if to add two
LED (with series resistors) so that one LED
lights when the left whisker hits a wall and the
other LED lights when the right whisker hits a
wall.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Final result Whisker control circuit with LED
test circuit. Shown below is the BOE-BOT with the
whisker control circuit (see Figure 5-4) and the
LED whisker test circuit (see Figure 5-7). You
will need to add this circuit to your BOE-BOT.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Additional PBASIC Instructions Before testing the
whiskers, a few new PBASIC instructions need to
be introduced.
Inputs to the Basic Stamp The BASIC Stamp can
easily determine whether an input connected to a
pin is HIGH or LOW by checking its value. This
is done using INpin where pin can be
0 through 15 so IN3 will have the value 1
if a HIGH (5V) input is connected to P3 IN4
will have the value 0 if a LOW (0V) input is
connected to P4
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Decision structures Most programming languages
support various types of decision structures
which allows the program to branch and perform
different tasks based on some sort of logical
test. A common type of decision structure is the
IF .. THEN structure. IF (Logical Statement)
THEN statements so that the program can respond
one way when the logical statement is true and
another way when it is false. Sometimes this is
illustrated with a diagram as shown.
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
IF .. THEN statement in PBASIC IF (Logical Test)
THEN Instructions to perform if the test is
true ENDIF Or IF (Logical Test) THEN
Instructions to perform if the test is true ELSE
Instructions to perform if the test is
false ENDIF
Examples of Logical Tests X gt 2 IN3 0 IN7 ltgt 0
(not equal) A lt B AB gt CD
Example IF (X lt 0) THEN DEBUG X is
negative ENDIF
Example IF (IN8 0) THEN DEBUG P8 is
LOW ELSE DEBUG P8 is HIGH ENDIF
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Subprograms in PBASIC In order to repeat useful
sections of code, subprograms (or subroutines)
are often used. Functions are also used for this
purpose in other programming languages. For
example, suppose that at several points in a
program you wanted to cause an LED connected to
P3 to blink on and off ten times. Instead of
repeating the instructions several times, they
could be placed in a subprogram as shown below.
Main program N VAR BYTE GOSUB Blink
Call subroutine Blink Other
instructions . GOSUB Blink Call
subroutine Blink Other instructions . GOSUB
Blink Call subroutine
Blink Other instructions Other instructions . END
End of main
program -----Subroutine Blink is listed
below--------- Blink FOR N 1 TO 10 HIGH 3
PAUSE 500 LOW 3 PAUSE 500 NEXT RETURN
Note that three new PBASIC commands were
introduced in this example. Discuss each. GOSUB
Label Label RETURN
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Testing the whiskers The program below can be
used to test the whiskers. Each time a whiskers
is pressed, the input will be detected and an LED
will light. It is important to use this test
program to be sure that the whiskers are
functioning properly before navigation on a track
is attempted. This program will be used in Team
Assignment 5.
DO IF (IN7 0) THEN IN7 0
when right whisker hits wall HIGH 1
Turn on LED connected to P1
when IN7 0 ELSE LOW 1
Turn off LED connected to P1 when
IN7 ? 0 ENDIF IF (IN5 0) THEN
IN5 0 when left whisker hits wall
HIGH 10 Turn on LED
connected to P10 when IN5 0 ELSE LOW
10 Turn off LED
connected to P10 when IN5 ? 0 ENDIF PAUSE
50 Test whiskers
about every 50 ms LOOP
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering

• Sample whisker navigation program
• A whisker navigation program is provided in the
  BOE-BOT manual that could possibly be used to try
  to navigate any general maze. If a specific
  track is to be used, modifications to the program
  might be made so that it will more efficiently
  navigate that specific track.
• The program works as follows
• If neither whisker is pressed, go straight
• If the left whisker runs into an obstacle, back
  up a little bit and turn right 90º
• If the right whisker runs into an obstacle,
  back up a little bit and turn left 90º
• If both whiskers run into obstacles, back up a
  little bit and turn 180º (U-turn)
• Video a video of a BOE-BOT navigating using
  whiskers based on the sample program described
  above is available at the following URL
• http//www.parallax.com/dl/mm/video/boebot/whisk
  er.mpg

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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Sample whisker navigation program The whisker
navigation program from the BOE-BOT manual
described on the previous slide is shown below.
' STAMP BS2 ' PBASIC 2.5 ' PORT
COM1  'Sample program to navigate with whiskers
from Robotics, Version 2.2, pp.
179-180 pulseCount VAR Byte 'Loop
counter for FOR .. NEXT loops DO IF (IN5 0)
AND (IN7 0)THEN 'Both whiskers detect
obstacle GOSUB Back_Up
'Back up and do U-turn GOSUB Turn_Left
GOSUB Turn_Left ELSEIF (IN5 0) THEN
'Left whisker detects obstacle GOSUB Back_Up
'Back up and turn right
GOSUB Turn_Right ELSEIF (IN7 0) THEN
'Right whisker detects obstacle GOSUB
Back_Up 'Back up and turn
left GOSUB Turn_Left ELSE
'No contact with
whiskers GOSUB Forward_Pulse 'Go
straight forward ENDIF
'and check again LOOP ' -----
Subroutines --------------------------------------
----------- Forward_Pulse
'Go straight ahead PULSOUT 13, 850
'Left wheel full speed CCW
PULSOUT 12, 650 'Right wheel
full speed CW PAUSE 20 RETURN
Turn_Left
'Turn left about 90 degrees FOR pulseCount 0
TO 20 PULSOUT 13, 650 'Right
wheel full speed CW PULSOUT 12, 650
'Right wheel full speed CW PAUSE 20
NEXT RETURN   Turn_Right
'Turn right about 90 degrees FOR
pulseCount 0 TO 20 PULSOUT 13, 850
'Right wheel full speed CCW PULSOUT
12, 850 'Right wheel full speed
CCW PAUSE 20 NEXT RETURN   Back_Up
'Back up a little
bit FOR pulseCount 0 TO 40 PULSOUT 13,
650 'Left wheel full speed CW
PULSOUT 12, 850 'Right wheel
full speed CCW PAUSE 20 NEXT RETURN
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Modifying the whisker navigation program There
are many possible approaches to navigation by
whiskers. Some approaches might include

• Program the BOE-BOT to follow the outside (right)
  wall. Do this by giving the BOE-BOT a slight
  bias (drift) to the right. When the right
  whisker hits the wall, turn left for a short time
  and then resume the slight bias to the right.
• Same as above except follow the inside (left)
  wall. This is illustrated on the following
  slide.
• Change the program as the BOE-BOT proceeds
  through the course. For example
• The first three times that both whiskers hit a
  wall, turn right
• The 4th, 5th, and 6th time that both whiskers hit
  a wall, turn left
• Turn right for additional times.
• Note that it may be necessary to use a counter to
  keep track of the walls.
• See the example shown

Counter VAR BYTE Counter 0
Initialize counter to zero DO
IF (IN5 0) AND (IN7 0)THEN 'Both whiskers
detect obstacle Counter Counter 1
IF (Counter gt4) AND (Counter lt6) THEN
GOSUB Back_Up Back up and
turn left GOSUB Turn_Left
ELSE GOSUB Back_Up
'Back up and turn right GOSUB
Turn_Right ENDIF ELSEIF (IN7 0) THEN
'Right whisker detects obstacle
GOSUB Back_Up 'Back up and
turn left GOSUB Turn_Left ELSE
'No contact with
whiskers GOSUB Forward_Pulse 'Go
straight forward ENDIF
'and check again LOOP ' -----
Subroutines --------------------------------------
----------- Forward_Pulse
'Go straight ahead PULSOUT 13, 850
'Left wheel full speed CCW
PULSOUT 12, 650 'Right wheel
full speed CW PAUSE 20 RETURN Etc .
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BOE-BOT Lecture 4 EGR 120 Introduction to
Engineering
Possible whisker navigation program following
the outside wall