ENGR 101: Robotics Lecture 5 Subprograms

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ENGR 101 RoboticsLecture 5 Subprograms

• Outline
• Subprograms
• The Infrared Sensor System
• References
• http//csserver.evansville.edu/richardson/
• PBASIC Programming Guide Setting Up
• PBASIC Programming Guide Writing Programs
• BASIC Stamp Syntax and Reference Manual

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Lecture 5 SubprogramsWhy Subprograms?

• If you have a common block of code that appears
  several times at different locations in your
  program, you may want to move that block of code
  into a subprogram (also known as subroutines,
  functions or methods).
• Splitting your program into subprograms usually
  results in better organized code that is much
  easier to maintain. It may result in smaller
  programs that use less memory (and require less
  typing) too.

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Lecture 5 SubprogramsPBASIC Subprograms

• An example that uses a subprogram
• LOW RM ' Initialization
• LOW LM
• PAUSE 100
• GOSUB GoForward
• PAUSE 1000
• GOSUB StopMotors
• END
• GoForward 'Drive Forward
• PULSOUT RM, RMFull
• PULSOUT LM, LMFull
• RETURN

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Lecture 5 SubprogramsPBASIC Subprograms

• A GOSUB statement causes program execution to
  branch to the program label that follows the
  GOSUB keyword. A subprogram should end with a
  RETURN statement, this causes program execution
  to continue at the statement following the GOSUB.
• Another advantage of using subprograms is obvious
  here, to change the way in which the Scribbler
  goes straight we need only make changes to the
  GoForward subprogram.

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Lecture 5 SubprogramsPBASIC Subprograms

• For easy code maintenance, a common rule-of-thumb
  is that any section of code that is longer than
  about 50 lines should be moved into a subprogram.
  Subprograms should not be longer than 50 lines
  either. Subprograms may call (using GOSUB) other
  subprograms.

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Lecture 5 SubprogramsObject Avoidance

• There are two IR emitters and an IR receiver on
  the front of the Scribbler.

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Lecture 5 SubprogramsObject Avoidance

• The IR detector has a filter that allows it to
  see IR light flashing at around 38,500 Hz. We
  use FREQOUT to generate the proper frequency IR
  at one of the emitters
• ObsTxRight PIN 14
• FREQOUT ObsTxRight, 1, 38500
• A short duration (1 ms) is used so that only a
  short IR burst of light is emitted.

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Lecture 5 SubprogramsObject Avoidance

• The program on the following slides alternately
  emits a short IR pulse on the right and left
  emitters. After each pulse is sent we look for a
  reflection back to the detector.
• The detector sends a low signal to PIN 6 (binary
  0) if there is reflected IR. A high signal (1)
  is sent if there is no reflected IR.
• Download (02_Eye_Test.bs2) from the web site.
  Run and then test it by holding a piece of paper
  about 6 in front of the robot.

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Lecture 5 SubprogramsObject Avoidance

• ' I/O Pin Definitions
• ObsRx PIN 6 ' IR detector
• LedRight PIN 8
• LedLeft PIN 10
• ObsTxRight PIN 14 ' RT IR emitter
• ObsTxLeft PIN 15 ' LT IR emitter
• ' Variable Declarations
• eyeRight VAR Bit
• eyeLeft VAR Bit

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Lecture 5 SubprogramsObject Avoidance

• ' Main Program
• DO
• GOSUB CheckRightIR 'Look RT
• GOSUB TestRightIR 'Set LED
• GOSUB CheckLeftIR 'Look LT
• GOSUB TestLeftIR 'Set LED
• LOOP
• END

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Lecture 5 SubprogramsObject Avoidance

• CheckRightIR
• FREQOUT ObsTxRight, 1, 38500
• eyeRight ObsRx
• RETURN
• TestRightIR
• IF (eyeRight 0) THEN
• HIGH LedRight
• ELSE
• LOW LedRight
• ENDIF
• RETURN

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Lecture 5 SubprogramsObject Avoidance

• CheckLeftIR
• FREQOUT ObsTxLeft, 1, 38500
• eyeLeft ObsRx
• RETURN
• TestLeftIR
• IF (eyeLeft 0) THEN
• HIGH LedLeft
• ELSE
• LOW LedLeft
• ENDIF
• RETURN

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Lecture 5 SubprogramsAssignment

• Modify the test program so that the Scribbler
  turns to the left if there is an object on the
  right and turns to the right if there is an
  object on the right. Otherwise the Scribbler
  should move forward. Also check for a stalled
  condition and take appropriate action.
• Add bells and whistles as desired ...

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