WAM

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WAM

• Chapter 4
• Controlling Motion

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Controlling Motion with a Microcontroller

• Microcontrollers control the motion of many
  things in our daily lives
• Printer head movement.
• DVD and VCR mechanisms.
• Grocery store automatic doors.
• Robotic movement.

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• Instead of being simply ON or OFF, many of these
  motion devices require a variety very fast pulses
  of signals for position control or movement.
  These pulses must occur much faster than the
  rates at which we turned LEDs on and off

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• The PULSOUT duration is a command that sends
  pulses to the servo in 2 uS (microsecond)
  increments.
• 1 ?S .000001 seconds.1 mS 1000?S
• For a command of PULSOUT 14,750
• This would be sending a pulse that lasts750 x 2
  ?S 1500 ?S or 1.5mS out to the servo on pin 14.

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TIMING DIAGRAMS
PULSOUT 14,1000
1000 x .000002sec 0.002 sec 2ms pulse
PULSOUT 14,500
500 x .000002sec 0.001sec 1 ms pulse
PULSOUT 14,750
750 x .000002sec 0.0015 sec 1.5 ms pulse
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THIS IS CALLED PWM

• Analyze each signal on Data Studio Scope

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• Example Code
• If ran, the pulse of 750 is sent 150 times with
  20mS pauses.
• TOTAL TIME SPENT ON THIS POSITION 2 us x 750
  1500 us 1.5ms20 ms 21.5 ms
• 21.5 ms X 150 loops 3225 ms 3.2 seconds

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Activity 1 Connecting and Testing the Servo

• Servo Parts

Servo Connector Black Vss Red Vdd
or Vin White Signal
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• Circuit to be built
• Connecting to the servo to the board depends on
  which board you have.

The servo can be damaged with voltages above 9V.
A wall-transformer may be stated to be 9V, but
output 12V. If using anything but batteries,
verify the supply is no more than 9V. See your
text.
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Servo on Board of Education Rev. C
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Centering the servo

• Enter and run this code
• Put a straw or a piece of tape on the horn
• Unscrew and reset horn so straw is in the middle
• RIGHT TIGHT
• LEFT LOOSE

DO NOT OVERTIGHTEN
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Enter, run, and save this code as servotest.bs2
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Adjusting position and hold timeREMEMBER

• PULSOUT and PAUSE controls where

• Loop controls how long servo is working on
  achieving a given position.

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Save ServoTest.bs2 as ServoTestYourTurn.bs2

• Modify all for next loops so they execute half as
  many times
• FOR counter 1 to 75
• See if this works
• Modify all for next loops so they execute twice
  as many times as the original
• FOR counter 1 to 300
• See if this works

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Now lets change position

• Modify PULSOUT in the second loop to
• Pulsout 14,650
• What change occurs
• The servo goes to about 1 Oclock instead of
  about 2 Oclock
• Modify PULSOUT in the second loop to
• Pulsout 14,850
• What change occurs
• The servo goes to about 11 Oclock instead of
  about 10 Oclock

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ACTIVITY 2 Controlling Position With Your
Computer

• Automation of a factory involves
• Microcontrollers reading sensors
• Sending data about the sensors to a computer
• Computer operator interprets sensor data
• Computer operator sends information back to the
  microcontroller using the computer
• Update conveyer belt speed
• Change position of factory welder
• IN THE NEXT EXERCISEYOU ARE THE COMPUTER OPERATOR

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• The DEBUG window allows the user
• to enter the number of pulses and the
• duration.
• Once prompted, the user enters the data
• The BS2 waits for your reply and then stores your
  input for later usage.

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• The DEBUGIN command is used to send
• data from the computer to the
• BASIC Stamp when it is entered in the text
• box.Here is the syntaxDEBUGIN DEC Pulses
• We will be sending two values
• Pulse width or duration
• Number of pulses

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Enter, run, and save the code found on the next
slide (pg 122 in text), but stay withing 500
1000 pulse widths!!
If you make a mistake entering a number, press
the reset button on the board. The backspace key
sends data which the BASIC Stamp uses the same as
the Enter key.
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Stay within 500 and 1000...You can damage the
servo!!
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TRY THE FOLLOWING

• Try an experiment
• Put in a 2 for the number of pulses
• Put in a 1000 for the duration
• RUN THE PROGRAM AGAIN
• THIS TIME
• Put in a 150 for the number of pulses
• Put in a 500 for the duration
• RUN THE PROGRAM ONE LAST TIME
• Use the same numbers as your first trial, but use
  150 instead of 2what is your conclusion about
  the purpose of the loop

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Limiting the Software

• THE PROBLEM
• REMEMBER
• stay within 500 1000 pulse widths!!
• What if the user ignores this warning?

• THE FIX
• Resave your code as
• servocontrolwithdebugyourturn.bs2
• As the next slide states
• Replace 2 lines of code with a special
  replacement

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THE FIX

• REPLACE

WITH
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Save and Run this program and verify that it is
working properlyyour new code should look like
that on the next slide
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Activity 3 Converting Position to
Motioncontrolling servo velocity

• By changing the horn's position each pass through
  a loop, you can get motion. The STEP part of the
  FORNEXT defines how much to add to each
  repetition.
• By modifying the STEP value, the velocity of the
  servo can be controlled.

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Why the DEC5 instead of DEC

• Look at the debug terminal while this code is
  running (crsrup.bs2)
• Monitor the terminal again with the DEC 5
  replacing the DEC
• Now see what happens when the CR before CRSRUP is
  taken out

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Turning the opposite direction at various speeds

• A loop can also count down such as
• FOR counter 1000 to 500
• This would make the servo turn in the opposite
  direction

• A step could be added to this to make the servo
  turn this way faster
• FOR counter 1000 to 500 STEP 20

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1-Enter, run, and save ServoVelocities.bs2
on the next slide (page 126 in text)
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How ServoVelocities.bs2 works

• Rotate clockwise
• DEC5 means the number to be displayed will be
  five digits longwithout this the number
  displayed will appear to exceed 1000 TRY IT BY
  LEAVING OUT THE 5 IN DEC5
• CRSRUP must follow CRstands for cursor
  up..allows the pulse width display to be
  constantly updated in the same spot

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How it works contd

• Rotate counter clockwise
• BUT AT A FASTER RATE
• Repeat program

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THIS IS CALLED CODE OVERHEAD
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Make some adjustments

• Try different STEP values and observe the new
  turning rates
• Experiment with different PAUSE command Durations
  (between 3 and 12)find the value that gives the
  servo the smoothest motion

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Activity 4 Servo Control with Pushbuttons

• The servo can also be controlled by receiving
  inputs from a button instead of a the debug
  terminal
• Add two pushbuttons to the circuit to control the
  Servo's position.

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The goal will be to make each button activate a
different direction of rotation
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Write a program to do the following

• When the button on pin 3 is pressed, a 1 should
  be reported, otherwise a 0 should be reporteddo
  this using IF THEN and ENDIF
• Revise the program, so it is receiving input from
  the button on pin 4 instead.
• Again, test to see that the program is operating
  correctly

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In the next sample program

• IFTHEN code blocks are used to check the
  pusbutton states and either add or subract from
  the DURATION variable
• DURATION will be used in the pulsout command
• This will have the effect of making the servo
  turn one way or the other
• A nested IFTHEN statement will decide whether or
  not the DURATION value is too large or too small

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ENTER, RUN, and SAVE servocontrolwithpushbuttons.b
s2 on the next slide (page 132)

• Verifty that the servo turns counterclockwise
  with pin4 button held
• Verify that if duration exceeds 1000 the servo
  stops
• Do the same test for the pin3 button with a
  clockwise rotation

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Mechanical stoppers and software stoppers

• The servo has a mechanical stopper, that will not
  allow the servo to rotate past a certain position.

• Your program can be modified to narrow this range
  of motion even further.
• Change the limits, so they are between 650 and
  850 instead of 500 and 1000
• Run the program and note the differences

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Rotation rates

• Adjust the software imposed rate so that the
  duration variable is incremented or decremented
  by 10 instead of 25
• Run the program and notice the differences
• Now try 50 istead of 10
• Run the program and notice the differences