Oregon Robotics Tournament
and Outreach Program
Programming Techniques
Workshop for Mindstorms
NXT
2012
Opening doors to the worlds of science
and technology for Oregon’s youth
1
Instructor Contacts
Ken Cone
ken_cone@ous.edu
(503) 725-2918
Terry Hamm
terry.hamm@gmail.com
(503) 720-5157
Dale Jordan
Dale_A_Jordan@msn.com
Jim Ryan
james.r.ryan@intel.com
971-215-6087
Roger Swanson
swanson@hevanet.com
503-297-1824
2
ORTOP Project Administrator
Cathy Swider
Cathy_Swider@ous.edu
(503) 725-2920
3
Workshop Goals
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In Workshops 1 and 2 we have
introduced very basic programming to
get you started with your robots
In this Workshop we delve more deeply
into just the programming
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Introduce techniques that we think you are
likely to use sometime in your coaching
careers
Discuss the Why as well as the How
4
Agenda
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Tour the NXT software to review all the
available NXT blocks
Distinguish those with higher utility
from those with lower utility
Hands on exercises to try out the new,
higher utility blocks
5
Caveat about this Workshop
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Don’t expect to go right back to your
teams and teach them all this new stuff
you have learned.
Look for opportunities when the
youngsters are ready to pick up a new
fundamental technique
Our goal is to prepare you better so you
are ready when a new teaching
opportunity arises
And remember: “The kids do the work!”
6
NXT Block Review
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Review the NXT G Software to look at all
programming blocks that are available
7
NXT Block Summary
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High Utility
Blocks
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Move
Wait
Loop
Switch
Sensor
Blocks
Stop
Data Blocks
(variables)
My Blocks
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Low Utility
Blocks
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Useful for
Debugging
Record/Play
 Sound
Motor
 Display
Send
 Number to
Message
Text
Lamps
 Text
Mini Blocks
You should know
Random
already
Advanced
Will cover tonight
8
Simple Light Sensor Program
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Do you remember the light sensor
exercises in Workshop 1?
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Stop on black or green
Stop only on black
Difference in the two programs was
simply the trigger value used on the
light sensor.
Trigger values can be influenced by
ambient light.
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Light Sensor Calibration
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Let’s make sure each of our robots is
“uncalibrated”
Calibrating the light sensor adds more
confusion than value at this point in a team’s
development
Use the NXT’s built-in View function
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Best way to figure out how to set trigger values
for light sensors at this point.
Robot must be uncalibrated for this to work
properly
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One Note about Calibration
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With an uncalibrated light sensor
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With a calibrated light sensor
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Values read by the light sensor are 0-100
White is typically in the 60’s
Black is typically in the 20’s or 30’s
White is 100
Black is 0
Calibration spreads values over a wider range
View function is not useful once you have
calibrated your robot.
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Simple Light Sensor Program
12
Enhanced Light Sensor
Program
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Suppose that I want to use that code
sequence in lots of places in my
program.
When light conditions change, I have to
find each Wait For block and change the
trigger value.
Any ideas on what we might do to make
that easier?
13
An Answer Is in the Slides
Throughout this workshop an answer is
given in the slide set so you have
something to review when you get home.
Don’t look ahead until you have tried the
exercise yourself. 
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Use a Variable
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Variables hold values to be used elsewhere
Use Edit Menu/Define Variables to define the
variable
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Use the Variable Blocks (Data Block section) to:
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Click on Create
Give the variable a name
Set its type: logic, number, or text
Read the variable
Write the variable
Manipulate the variable with other Data Blocks
Demonstrate in the software
15
Introducing Data Hubs
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Many of the program blocks have a
capability called a “Data Hub”
These are used to set parameters of a
program block during the execution of
the program instead of during the
writing of the program.
We need Data Hubs in addition to
Variables to solve our problem.
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Data Hubs
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Look at Data Hubs in the software
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Data Wire Tips
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Easiest way to connect a data wire:
click on the port at the left end and
then click on the port on the right end
To delete a data wire: click on the right
end of the wire
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Data Wire Tips (cont.)
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You cannot connect a wire from an
output port on a data hub unless there
is a wire going into the corresponding
input port
Broken wire
Add a new variable block
in the read state
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Data Wire Tips (cont.)
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Don’t run long data wires from a
variable block to a data hub. Instead,
insert a variable block for the variable
you want to use near where you want
to use it so that the data wire is short.
Not so good
Better
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Solution?
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Can we use variables and data hubs to
solve this problem?
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How About Trying…
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Create a variable to hold the trigger
value.
Use that variable with a data hub on
the Wait For Block to set the trigger
value.
Let’s look at the NXT G software
22
There’s a Problem
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Wait For blocks don’t have data hubs.
Can we simulate a Wait For block with
another block that does have a data
hub?
Let’s look at the Light Sensor block in
the NXT G software
We also need to look at other kinds of
Loop blocks
23
Light Sensor Block
Important Notes on Data Hubs
• An input port with a
wire overrides the
parameter block
• Parameter block value
is used if no wire on an
input port
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Different Forms of Loop Block
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Look at Loop Blocks in the software
Notice the “Data Hub” on the Loop on
Logic Value block
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It’s Your Turn
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Write a program to stop on a black line,
but use the Light Sensor block instead
of the Wait For block.
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Wait For Using Light Sensor
Block
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Use a Light Sensor block, which has a data
hub, instead of a Wait For block
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Further Enhance Your Program
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Use a variable to hold the trigger value.
Set it once so that the program will stop
on green or black.
Set it differently so that the program
skips green and stops on black.
Your turn to try it.
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Stop on Black with Trigger
Value in Variable
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Let’s Try Something New
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What if I wanted the robot to stop if
the touch sensor is pressed OR if
the light sensor has detected a
black line?
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Steps to Develop a Program
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Understand what is to be accomplished
Write down a list of tasks describing
how you would solve the problem
Break the tasks up into simpler subtasks
Program the subtasks, try them, and
debug them
Put the subtasks together for the final
program
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How Would You Approach
This?
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Write down a list of steps you would
take to get your robot to stop when the
touch sensor is pressed OR the light
sensor detects a black line.
Do this thought process without
thinking about the programming
ramifications.
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One List of Steps
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Start the motors to get the robot moving.
Check if the touch sensor has been pressed.
If it has, stop the robot.
If not, check if a black line has been detected.
If so, stop the robot.
Otherwise go back and repeat the above steps
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Use a Switch Block
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How will we check the touch and light sensors?
Look at Switch Blocks in the software
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Stop on Touch or Light Sensor
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You try it.
Write a program so that your robot will
stop if the light sensor detects a black
line OR if the touch sensor is pressed.
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One Answer
Note that the robot
will stop if either
the touch sensor is
pressed or a black
line is detected,
but the loop is still
going. What might
we do to continue
with something
else after the robot
stops?
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Use a Loop Controlled by a
Logic Variable
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Subroutines or My Blocks
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What if you find that you are using the
same sequence of blocks in many
places in your program?
Examples:
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90 degree spin turn
Go forward to stop on a black line
Define that sequence as a My Block and
save memory in the process
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Building a My Block
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Select the blocks from the program
Choose Make A New My Block in the
Edit menu
Give the My Block a name, fill in the
description, and build an icon (optional)
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Move in a Square
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A “primitive” way to move in a square
How big is this program?
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Use the NXT Window to manage memory
Size is 3.7KB
Demonstrate memory management in
the software
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Move in a Square with My
Blocks
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Same program with My Blocks is 2.8KB
Note that if I double click on a My
Block, it opens the code for inspection
or editing.
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Managing My Blocks
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Where does the NXT Software keep My
Blocks?
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Use Manage Custom Palette in the Edit Menu
The My Blocks sub folder has your My Blocks
You can email a file from the My Blocks
folder to share the My Block
If you receive a My Block, move it to the
My Blocks directory to make it visible in
the Custom Palette
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Build a My Block to Display a
Number
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Display Block –
displays text only
Convert number
to text
If the bounding box you use
to select the blocks for the
My Block crosses a data wire,
then that value becomes an
input or output parameter for
the My Block.
You try it
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Display Number My Block
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Note the Wait For block to wait for 3
seconds to give time to read the result
Note the number as input parameter to
the MyBlock
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Debugging Example
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Go back to your most simple Stop on Black
Program
Use your display number My Block to display
the light value when the robot stops.
Add a Move Block to move ahead a small
amount (20 degrees)
Now use your display number My Block to
display the light value.
What did you notice?
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Using the Display Number
MyBlock
Note that two blocks have been added at each point
where we want to see the light sensor value:
1.
A Light Sensor block to provide the value the light
sensor is reading
2.
The Display Number Myblock
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What Did You Notice in this
Last Exercise?
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The light sensor value when the robot
first stops will meet the trigger value
constraint.
The value 20 degrees further, however,
can be quite different.
If the light sensor senses right on the
border between black and white, the
value will be less than white but greater
than black – it might look like green. 47
Other Debugging Ideas
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I don’t know where the robot is in the
program. Use a Sound Block to just play a
tone to see if the robot has gotten to a
particular point.
What value does my variable have? “Print”
the value to the NXT screen to see the value.
Take a subtask out of a more complex larger
program and debug it separately rather than
trying to debug it in the full more complex
environment.
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Class Exercises -- Summary
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Simulate a Wait For Block – Light Sensor Block, Loop
variants, and Data Hubs.
Control Stop on Black with trigger value in a variable –
creating, reading, and writing Variables.
Stop the robot if the touch sensor is pressed OR the
light sensor detects a black line – Switch Block
Develop Display Number My Block – Number to Text,
Display Block, My Block with input parameter, and
memory management
Use the Display Number to understand why you might
be surprised with what the robot is seeing when it
stops on black – Debugging idea and using a My Block
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More Exercises for the High
Achievers or To Do at Home
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Write a program that will stop only on a
green line. (An example is attached at
the end of the slide set.)
Do a My Block that takes an integer as
input and moves that many centimeters
or inches
Use distance sensor in CanDo challenge
Use color sensor to do the stop on
green only exercise
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Contact Us
Web site: http://www.ortop.org
Email: questions@ortop.org
Phone: 503-821-1136
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Program to Stop on Green
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We did the following light sensor
exercises in Workshop 1.
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Stop on black or green
Stop only on black
Obvious follow-up is to stop only on
green
What is the list of tasks that you would
use?
52
Program to Stop on Green
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One possible list of tasks
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Go forward and stop on green or black (We
did this program in Workshop 1. No need
to reinvent the wheel.)
Decide if robot has stopped on green or
black
If green, stop the program
If black, continue the program to the next
green or black block
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Stop on Green – One Answer
Note the additions I made that were not in our steps,
which I discovered in the debugging process.
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