Slides for the 2012 OregonFIRST LabView Training class

1. FRC LabVIEW INTRODUCTION
Homework exercises for 2012
summer FRC LabVIEW class series
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2. Overview
• By completing these exercises the student will
become familiar with the mechanics of the
LabVIEW programming.
• Each exercise demonstrates the use of digital
logic and analog numerical conversion commonly
used in robotic system design
• A typical FRC robot program will use a
combination of many of these examples.
• From “Getting Started” screen. programs start
with a New BLANK.vi and can be run on a stand
alone PC without a cRIO
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3. General guidelines
• Construct each program inside a “WHILE
loop”
• Put a control STOP button in WHILE loop
• Put a 100ms TIME DELAY in each WHILE loop
• (Stop button allows us to an easy way to stop
the program execution.
• The time delay will keep simple LabVIEW
program from taking ALL compute bandwidth
from your PC.
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4. WHILE LOOP
Control for
WHILE loop
Time Delay
THIS IS LABVIEW BLOCK DIAGRAM
SCREEN
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5. Use ‘Context Help’
• The best tutor to get more information about
any parts of LabVIEW is ‘Context Help’
• From tool bar (top of Block Diagram screen) ,
click on Help – Show Context Help.
• Then Cusor will display more information on
LabVIEW details.
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8. 01 Digital to Analog conversion
• The robot ‘s ball lift mechanism has two motors. Each
needs an analog (numeric) signal of .5 to run at the
correct speed. WE want the ball lift to turn on when
the a Digital (boolean) switch is TRUE. LabVIEW has
two convenient methods for D/A conversion : the CASE
struct and the ‘Select’ icon on the comparison palette.
• Drive both motors from one button.
• Use numeric meter indicator.
• Change meter properties –scale from 0-1.
• When button – switch is off, motor control should be
0.
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9. Control
for
while Edit
loop properties
Scale
0-1
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10. Click on
down arrow
to display
FALSE Case
What
value
goes in
FALSE
Case?
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11. QUESTIONS?
• How would you drive the each motor at
different speeds?
• How would you add a third motor control to
this program?
• We are using NUMERIC CONSTANTS in this
program. If we want to add a BOOLEAN
(digital) constant to control an LED indicator,
how would you add it to your program?
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13. 02 Analog signal inversion
(convert 0-1 v signal to 12 -0 v signal)
• Use a Control knob to produce analog signal 0 – 1
• Motor (meter indicator) control needs inverted
analog signal 12 volts – 0 .
• When knob is 0 (minimum signal), motor (meter)
should indicate 12 volts
• When knob is 1 (full scale), motor (meter) should
indicate 0 volts.
• Use two stage numeric signal conversion to change
signal
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14. Labview block diagram
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15. Does it run correctly? Click on white arrow
to run LabVIEW vi
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16. QUESTIONS
• If we add a second METER indicator outside
of the WHILE loop, what happens?
• Does it work as you expect?
• Any “output” from a WHILE loop will not be
‘active’ until WHILE loop completes
operation!!!
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18. FAQ
• “Jim, why don’t we just change the properties
on the knob to give us the signal range that is
needed?”
• The knob is a virtual control so we can make it
produce any signal we want. In the real
world however, the sensors will produce
signals as described by the data sheet. We
use LabVIEW to convert the signals to match
what is needed by the rest of the program.
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19. 03 Analog with Gate enable
• The ‘gyro compass’ is a sensor which will tell us
which direction robot is facing. We want ball
launch to only be allowed when gyro signal is
between 100 and 200 degrees.
• Use Knob to simulate analog signal from gyro
• Use LED to simulate digital Ball Launch Signal
• Use Boolean push button to simulate ball launch
button on joystick
• Use comparison IN RANGE function and Boolean
AND to GATE digital signal to only reach LED
when Gyro signal between 60 and 85.
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20. Change ‘property –scale’ to
be 0 - 360
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21. From Boolean
pallete
From NUMERIC pallete
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22. QUESTIONS
• We want to add an LED indicator that shows
when button is pressed.
• Can you add it to the program and make it’s
color properties RED?
• How does the operation of the program
change?
• What happens to the program operation if
you change the time delay constant to 1000??
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24. 04 Nested CASE structs
• Robot control panel has three push buttons for drive speed
control because operator needs 3 specific speeds for
different zones on the field
• Analog motor (meter indicator) is 0 when no button
pressed
• Button A pressed motor control = 3
• Button B pressed motor control = 5.5
• Button C pressed motor control = 7.3
• Use nested CASE structs to generate signal…
• Hint ‘nest’ inside FALSE case
• Hint2 button properties..mechanical action.. “switch until
released”
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27. QUESTIONS
• We want an indicator to show which gear we
are in.
• Can you add a Numeric Indicator which shows
a number (0,1,2, 3) for what ‘gear’ we are in?
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29. 05 counters & shift registers
• Increment by one each time the WHILE loop runs
will create a counter.
• Set time delay for 700ms
• Starting value is “0” (constant) outside loop
• Shift registers carry value from output of the loop
around to be input when loop runs next time
• Indicator will show number changing every 700
miliseconds
• See example 5a counter wm shift reg
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30. Set
long
delay
First set up addition stage to
increment by one each time
while loop runs
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31. Right click and ‘replace with shift
register’ put second on left side
where result will be picked up for
When you RUN this it should next loop
continue to increment until
you stop it
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32. More counters & timers
• Now we want to use (Quotient-Remainder
function) to produce numbers between 0 and
9 , in one second steps
• From the counter loop we started with, add
the Quotient-Remainder function and display
the Remainder output
• Change time delay to 1000 ms.
• What happens to the read outs?
• See example 5b
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33. Does it work as you
would expect?
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34. QUESTIONS
• Right now the ‘Quotient – Remainder’ is
connected downstream (after) the
increment (+) stage.
• What happens if we change this and connect
the ‘Quotient – Remainder’ upstream
(before) the increment stage??
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36. 06 Parallel Loops
• WHILE loops can run independently
• LOCAL VARIABLES can be used to carry data outside of WHILE Loop
• Robot has ball launcher mounted on turret.
• A potentiometer rotates to tell which direction turret is pointing
and produces analog signal.
• Ball launcher will hit our own robot when potentiometer signal is
between 4 – 6.
• Put analog sensor and operator button sensor in different WHILE
loops, use Local Variables to carry data between loops.
• Put stop control button on one of inner WHILE loops, note you
need to change mechanical action of pushbutton to get program to
run.
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39. 07 timers
• Timers can be used to set activity at specific
times and for specific durations
• We want to put a blinking light on the Robot.
• The Robot Signal Light should go ON for 4
seconds and OFF for 4 seconds.
• Use an LED indicator on front panel as
simulator for RSL
• Use toggle switch for on-off control of light.
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42. questions
• Note the use of local variables
• What happens if we change the inner time
delay to 100 instead of 1000?
• Note… you may have to re-initialize variables
to default values…. From upper tool bar click
on ‘Edit -Reinitialize variables…’
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44. 08 Serial loops
• We want the program to perform several actions
but only in a specific order
• Several ways to deal with this. Start with FLAT
SEQUENCE in ‘Programming Structures’ pallete
• 8a using flat sequence struct with four frames
– Put three sec delay in first and third frame
– Then turn on an LED in second and fourth
– Does it run the way we expect??
– Hint… why does it take so long for Program to STOP
after you press the STOP button? (Reinitialize to Run
again)
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47. questions
• What happens if we use the constant in the
last frame to stop the while loop???
• We get rid of the delay for the stop
pushbutton…. Right?
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49. More questions??
• NOTICE that we can use the first Constant True
to control all the of the logic outputs because
the signal is not released until the frame is
executed….?! ?
• To test this, put another LED to display
INSIDE the frame… what happens?
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51. 08b more serial loops
• If we want to turn systems on and off, we need to
understand how to turn off the LED in previous example.
• Now we want to control a robot drive motor.
• We want it to turn on for 3 seconds, off for two seconds,
back on for 3 seconds, then stop!
• This is a place for Local variables
• Make the same 4 frame Flat Sequence Struct
• This time put the LED outside and connect it with a local
variable. And add a meter for an analog value. See next
slide
• Note I have added an indicator to see how many time the
While Loop actually runs during this program… is any one
else surprised by the number that shows up?
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54. 09 Dual motor control
• Most Robot drives have at least two motors
• To maneuver usually requires both motors be
controlled.
• The signal coming from the Joystick is an analog
signal that varies from -1 (stick pushed all the
way forward) to +1 (stick pushed all the way
back)
• Use a slider numeric control to simulate a
joystick.
• Construct a program to simulate the control of
two motors (one reversed) with one joystick
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57. 10 Simulated tank control
• Construct program with two slider controls (to simulate Joysticks) and
two Meters indicators (to simulate Left and right motor signal outputs)
• Assume the right motor is reverse mounted, so signal going to Right Motor
needs to be the opposite polarity of the Left motor control
• Change Scale Property on both controls and indicators to be Min = -1
and Max = 1
• EXTRA CREDIT construct logic
• How do the joystick controls need to be set to maneuver and turn the
Robot? Remember to move robot forward,
– Left left is greater than right
– Right right is greater than left
– Forward signals less than zero
– Backward signals greater than zero
– Straight both signals are equal
• Set up an indicator and digital logic to show direction of robot movement
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58. 11 Dead reckoning
• During Autonomous mode we may want to use Dead
Reckoning to move the robot to a specific location on the
field.
• Construct a Flat sequence with the following steps:
– Robot moves straight forward for 3 seconds (right motor
inverted)
– Robot turns right (left motor forward, right motor stopped) for
1.5 seconds
– Robot moves straight forward 3 seconds.
– Robot stops and turns on RED LED which will launch the Ball
– Note: remember to set Ball LED off when you start.
– Use Meters to show motor control signals
– Use LED to show Ball launch control signal
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61. 12 Weighted D to A
this is how MP3 players make music
• Our robot has three loads on the battery that draw
different current levels. We want to keep track of total
drain to predict how long battery will last.
• Since each load (2 fans and a motor) are controlled by a
digital switch, we can assign each switch an analog value
and add them up.
• Start with three boolean switches.
– Drive motors 10 amps
– Top Fan 3 amps
– Bottom Fan 5 amps
• Use ‘Select Function’ to add value to SUMMING Amp
• Use Meter to show analog total current on front panel,
change Max value to 20 for total current value
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