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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
Whiskers
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BOE-BOT Lecture #4 EGR 120 – Introduction to Engineering
Adding whiskers to the
Header
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
Header
When the left whisker hits a
wall, it is pushed into the
header, essentially connecting
the header to ground (Vss).
The whisker is connected to
the corner of the BOE, which
is connected to ground (Vss)
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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.
Note: Ignore the round, black buzzer
and the wire connecting it to P4. We
will not be using the buzzer.
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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 F
logical test. A common type of decision Test
structure is the IF .. THEN structure.
T
IF (Logical Statement) THEN statements
so that the program can respond one way Do this if true Do this if false
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 Examples of Logical Tests:
IF (Logical Test) THEN X>2
Instructions to perform if the test is true IN3 = 0
ENDIF IN7 <> 0 (not equal)
A <= B
Or A+B >= C+D
IF (Logical Test) THEN
Instructions to perform if the test is true
ELSE
Instructions to perform if the test is false
ENDIF
Example: Example:
IF (X < 0) THEN IF (IN8 = 0) THEN
DEBUG “X is negative” DEBUG “P8 is LOW”
ENDIF ELSE
DEBUG “P8 is HIGH”
ENDIF 11
BOE-BOT Lecture #4 EGR 120 – Introduction to Engineering
Subprograms in PBASIC
In order to repeat useful sections of code,
‘ Main program
subprograms (or subroutines) are often
N VAR BYTE
GOSUB Blink ‘Call subroutine Blink
used. Functions are also used for this
Other instructions
purpose in other programming languages.
….
GOSUB Blink ‘Call subroutine Blink For example, suppose that at several points
Other instructions in a program you wanted to cause an LED
…. connected to P3 to blink on and off ten
GOSUB Blink ‘Call subroutine Blink times. Instead of repeating the instructions
Other instructions several times, they could be placed in a
Other instructions
subprogram as shown below.
….
END ‘End of main program Note that three new PBASIC commands
‘-----Subroutine Blink is listed below---------
were introduced in this example.
Blink:
FOR N = 1 TO 10 Discuss each.
HIGH 3
PAUSE 500
GOSUB Label
LOW 3
PAUSE 500 Label:
NEXT RETURN
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/whisker.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.
' {$STAMP BS2} Turn_Left: 'Turn left about 90 degrees
' {$PBASIC 2.5} FOR pulseCount = 0 TO 20
' {$PORT COM1} PULSOUT 13, 650 'Right wheel full speed CW
'Sample program to navigate with whiskers from Robotics, PULSOUT 12, 650 'Right wheel full speed CW
Version 2.2, pp. 179-180 PAUSE 20
pulseCount VAR Byte 'Loop counter for FOR .. NEXT loops NEXT
DO RETURN
IF (IN5 = 0) AND (IN7 = 0)THEN 'Both whiskers detect obstacle
GOSUB Back_Up 'Back up and do U-turn Turn_Right: 'Turn right about 90 degrees
GOSUB Turn_Left FOR pulseCount = 0 TO 20
GOSUB Turn_Left PULSOUT 13, 850 'Right wheel full speed CCW
ELSEIF (IN5 = 0) THEN 'Left whisker detects obstacle PULSOUT 12, 850 'Right wheel full speed CCW
GOSUB Back_Up 'Back up and turn right PAUSE 20
GOSUB Turn_Right NEXT
ELSEIF (IN7 = 0) THEN 'Right whisker detects obstacle RETURN
GOSUB Back_Up 'Back up and turn left
GOSUB Turn_Left Back_Up: 'Back up a little bit
ELSE 'No contact with whiskers FOR pulseCount = 0 TO 40
GOSUB Forward_Pulse 'Go straight forward PULSOUT 13, 650 'Left wheel full speed CW
ENDIF 'and check again PULSOUT 12, 850 'Right wheel full speed CCW
LOOP PAUSE 20
' ----- Subroutines ------------------------------------------------- NEXT
Forward_Pulse: 'Go straight ahead
PULSOUT 13, 850 'Left wheel full speed CCW RETURN
PULSOUT 12, 650 'Right wheel full speed CW
PAUSE 20
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 Counter VAR BYTE
the BOE-BOT a slight bias (drift) to the Counter = 0 „Initialize counter to zero
DO
right. When the right whisker hits the IF (IN5 = 0) AND (IN7 = 0)THEN 'Both whiskers detect obstacle
wall, turn left for a short time and then Counter = Counter + 1
resume the slight bias to the right. IF (Counter >=4) AND (Counter <=6) THEN
GOSUB Back_Up ‘Back up and turn left
• Same as above except follow the inside GOSUB Turn_Left
(left) wall. This is illustrated on the ELSE
GOSUB Back_Up 'Back up and turn right
following slide. GOSUB Turn_Right
• Change the program as the BOE-BOT ENDIF
ELSEIF (IN7 = 0) THEN 'Right whisker detects obstacle
proceeds through the course. For GOSUB Back_Up 'Back up and turn left
example: GOSUB Turn_Left
– The first three times that both ELSE 'No contact with whiskers
GOSUB Forward_Pulse 'Go straight forward
whiskers hit a wall, turn right ENDIF 'and check again
– The 4th, 5th, and 6th time that both LOOP
' ----- Subroutines -------------------------------------------------
whiskers hit a wall, turn left Forward_Pulse: 'Go straight ahead
– Turn right for additional times. PULSOUT 13, 850 'Left wheel full speed CCW
PULSOUT 12, 650 'Right wheel full speed CW
– Note that it may be necessary to PAUSE 20
use a counter to keep track of the RETURN
Etc …….
walls. 16
– See the example shown
BOE-BOT Lecture #4 EGR 120 – Introduction to Engineering
Possible whisker navigation program – following the outside wall
Adding angled
Path of barriers to
robot corners may
make
navigation
Right
Place where left easier
Whisker
whisker hits the
wall
Robot naturally drives
slightly to the left and
then corrects right
after left whisker hits Areas of
the wall difficulty?
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