Instructor: Nachiket M. Kharalkar

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Introduction to Microcontrollers

• Instructor Nachiket M. Kharalkar
•  
• Lecture 18
• Date 07/18/2007
• E-mail knachike_at_ece.utexas.edu
•  

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Todays Agenda

• Exam 2 coming Monday (7/23/07)
• Lab 6 demo
• Stepper motor interfacing
• Lab 7 discussion
• Quiz 2

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Stepper motor output sequence

• Full-step sequence 5,6,10,9,...
• Half-step sequence 5,4,6,2,10,8,9,1,...

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• Two Stepper Motors Control Robot Motion
• PT7-PT4 Right Track Stepper Motor
• PT3-PT0 Left Track Stepper Motor

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Driving the stepper motor

• Forward stepping causes the motor to spin forward
• Full-step sequence 5,6,10,9,...
• Half-step sequence 5,4,6,2,10,8,9,1,...
• Backward stepping causes the motor to spin
  backward
• Full-step backward sequence 9,10,6,5,...
• Half-step backward sequence 1,9,8,10,2,6,4,5,..

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Stepper motor controller
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• org 3800
• Pt rmb 2 pointer to current state
• org 4000
• out equ 0 8-bit output
• next equ 1 4 pointers to next state
• S55 fcb 55 8-bit output
• fdb S55,S69,S66,S96 next for each in
• S66 fcb 66
• fdb S66,SAA,SAA,S55
• SAA fcb AA
• fdb SAA,S99,S99,S69
• S99 fcb 99
• fdb S99,SAA,S55,SAA
• S69 fcb 69
• fdb S69,SAA,S55,S55
• S96 fcb 96
• fdb S96,S55,SAA,SAA

FSM implementation
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Bottom view of the robot car
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The 24 possible motions of the robot car
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One possible way to configure the stepper motor
car
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Sensors on the robot car

• Front bumper will be active PM4
• Back bumper will be active PM3
• Right slot sensor PM1 (20 rising falling
  edges)
• Left slot sensor PM0 (20 rising falling
  edges)
• ADC channel 0, will give a number from 0 to 255
  representing the X coordinate (0 on the left, 255
  on the right)
• ADC channel 1, will give a number from 0 to 255
  representing the Y coordinate (0 on the top, 255
  on the bottom)
• ADC channel 2, will give a number from 0 to 255
  representing the heading coordinate (0 is right,
  64 is down, 128 is left and 192 is up)

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Plot window showing one of the mazes. The red
line is the robot car.
X Y 0
Y Actual field 0999
Y 255
X 255
X 0
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Wall-following solutions may not work
http//www.astrolog.org/labyrnth/algrithm.htm
Does not work
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Grading policy

• -30 solves the maze with friction off
• -10 solves the maze, but doesnt stop at the end
• -10 gets stuck, or lost so that a reset is
  required to try it again (solves it on the second
  try)
• -20 gets stuck, or lost so that a reset is
  required to try it again (solves it on the third
  try)
• No 4th try
• Questions style graded as usual