LVEE Beginners User Guide

8/8/2019 LVEE Beginners User Guide

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This User Guide is in Beta Test form. Please feel free to use it as is, and to make comments on the

effectiveness of this guide. The intention is to construct a functional document that can help new users of

the LabVIEW Education Edition programming software.

Cheers,T. Jump


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LVEE

Vocabulary

Autonomous

Block diagram

Code

Compile

Download

Direct mode

Front panel

Remote modeVirtual Instrument (VI)

Materials

Each student:

Engineers Journalw/worksheet pages

Each student group:

Challenge

Building Guide*

Programming Guide

LEGO MINDSTORMSkit

Computer withLabVIEW EducationEdition

Introduction

Introduction

LabVIEW is a programming language that uses graphics insteadof text to create computer programs. With LabVIEW you cancreate games for kids, math programs for teaching high schoolstudents, and advanced applications to control laboratoryexperiments and display results. You can also use LabVIEW tocontrol robots.

The LabVIEW Education Edition (LVEE) incorporates specialfunctions for interfacing with the LEGO NXT controller. This guideis designed to help beginners get started with LVEE and begin to

explore the world of programming robots with LabVIEW.

Copyright 2009 Timothy E. Jump 1


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The NXT also has a series of buttons that allow for

running programs and viewing data captured by the

NXT.

LVEE Introduction


As mentioned above, LVEE has built in functions to interface withthe LEGO NXT controller. The LEGO NXT controller (or brick) isessentially a small computer (microcontroller) that is an integratedcomponent in the LEGO MINDSTORMS and PITSCO Tetrix kits,and is used to interact with motors and sensors to control robotsbuilt with these systems.

The NXT brick has 3 output ports (A, B, C) on the top where

motors are attached, and 4 input ports (1, 2, 3, 4) on the bottom

where sensors are attached.

Hardware Tip

There is a rotation

sensor built into the

motors of the LEGO

NXT MINDSTORMS

kit. This embedded

rotation sensor does

not plug into the input

ports of the NXT (ports

1, 2, 3, or 4) but are

controlled through the

output ports (ports A, B

and C).


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In order to program the NXT with LabVIEW, LVEE must be

installed on a host computer that can then communicate with theNXT over a USB cable or via Bluetooth. Once a program to

control the NXT has been written (with LVEE on the host

computer) the program can be executed in either direct or remote

mode. In direct mode, the program executes on the computer

and the computer controls the NXT. In remote mode, the

program is compiled and then downloaded to the NXT where

the NXT executes the program.

LVEE Introduction


Introduction Tip

You can think of direct

mode as the computer

being the brain and

remote mode as the

NXT brick being the

brain.

Programs in remote

mode take less time to

execute than programs

in direct mode because

information does not

need to be sent backand forth between the

computer and the NXT

brick. For this reason

you will want to execute

most of your programs in

remote mode.

Direct mode is useful for

debugging a program

because you can display

output values to the front

panel. You can also plot

sensor values on thefront panel in real time.


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If you have not done so, load LVEE on to your computer. Once

loaded, access LVEE by clicking on the National InstrumentsMeasurement & Automation icon that should have loaded on your

computer desktop.

LVEE Set-Up


Set-Up Tip

A simpler process for

accessing LVEE is to

select START (bottom

left of your computer

screen if you are using

Windows), then select

All Programs, then

select National

Instruments, then select

LabVIEW 2009.

You should now be able

to see the LabVIEWicon.

Once you click the NI icon the following window will appear.

Expand the Software menu found in the panel to right by

selecting the + sign next to Software.

Right click on the icon

and select Send To. Now

select Desktop (create

shortcut) and this will

place this shortcut icon

on your desktop. Now

you can get to LVEE

directly.


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LVEE Set-Up


Set-Up Tip

Once the Software menu is expanded you should see thefollowing screen. Now select LabVIEW 2009.


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Now select Launch LabVIEW 2009 from the top of the new

window that now shows.

LVEE Set-Up


Set-Up Tip

Launch LabVIEW gets

you to the same window

as using the LabVIEW

shortcut created using

the Programming Tip

from page 4.

If you have not done so, read over the Programming Tips in the

sidebar starting at page 4. This will lead you to a process of

creating a shortcut to Launch LabVIEW EE from an icon on your

computer desktop.


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The window shown below will now appear. Select Launch LabVIEW

to enter the LVEE programming interface.

LabVIEW EE Opening Window

LVEE Set-Up


Set-Up Tip

If you want LVEE to

launch direct from your

computer desktop and

bypass this final window

select the Do not show

this dialog again check

box in the lower left

corner.

Now, every time you

click on

LVEE will launch directly

into the programming

area of the IDE.

*IDE Integrated

Development

Environment


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Now that LVEE is open there are several key areas to which you

should become familiar.

The selections on the right

each point to differentresources for seeking help

with LVEE.

Blank VI and BlankVI Targeted to NXTare the options forstarting new oraccessing existingVIs.

LVEE Getting Familiar


Familiarize Tip

Programs written in

LabVIEW are called

virtual instruments

(VI).

Front Panel


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For learning to use LVEE with the NXT, the Using the NXT Module

link is a good resource.

Once you open the Using the NXT Module section you will

see multiple categories (on the left) to support you in learning

to use LVEE.



Familiarize Tip

Front Panel


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Here is a close-up look at the help categories inside Using the NXT

Module.

The first two pages give general information and point to

some selected resources.



Familiarize Tip

Expanding the Using Help section gives access

to information about how to use the Using the NXT Module

help guide.


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Once you are ready to explore the use of more complex functions inLVEE, the remainder of the Using the NXT Module section offersexplanations and instructions to get you on your way.

Expanding NXT Module Basics gives access

to explanations of basic LVEE structures.



Familiarize Tip

Take some time to

expand the different

guide sections and

explore the various

topics covered.

If you have experience programming the LEGO NXT

controller with either the LEGO MINDSTORMS NXT software

or RoboLab, accessing Migrating from Other Languages

will lead you through correlations between your previous

language and LVEE.


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Now lets look at the programming environment of LVEE. Access

the Blank VI Targeted at NXT.

You should see two windows appear.



Familiarize Tip

Front Panel


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The grey window is called the Front Panel.

The Front Panel is where human interface controls are assembled

and set up for ease of human control of a robot.



Familiarize Tip

Control for robots can be

either autonomous

(where the computer

controls the robot) or

teleoperative (where

humans control the

robot). In order for

humans to control robots

they must have access to

control devices such as

buttons, switches,

gauges and such.

Here is an example of aFront Panel with a buttonto turn on/off a motor, anLED to show when themotor is on/off and agauge to display themotors speed.

Front Panel

Front Panel


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Both the Front Panel and Block Diagram share almost identicaltoolbars.



Familiarize Tip

Note the hot-key

patterns given for

certain menu functions

Remove Broken Wires

is a great shortcut to

clear up wiring errors

that may be otherwise

difficult to identify.

Find and Replace is a

great function forswapping out elements

in your program. Say

you have a light sensor

and you want to replace

it with a touch sensor.

Rather than going into

the program, deleting

the light sensor,

dragging in the touch

sensor, then repairing

all the wiring you can

simply highlight the light

sensor and go into Findand Replace and

navigate to the touch

sensor and select it.

The drop-down menu and menu listings are identical. Selections that are

most useful for beginning programmers are:

File Where you can find the Open,

Save and Print functions as well as

where to start a new VI.

Edit Where you can find Undo,

Redo, Cut, Copy, Paste. More

importantly, here you can find critical

functions such as Remove Broken

Wires and Find and Replace.


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Familiarize Tip

View on the Block

Diagram will give you

access to the

Functions Palette.

View on the Front

Panel will give you

access to the Controls

Palette.

Window on the Block

Diagram will give

access to the Front

Panel.

Window on the Front

Panel will give access

to the Block Diagram.

Show Context Help is

a window that will

describe and give

examples of how to use

any programming

element the cursor

hovers over .

View Gets you access to

the palettes necessary for

writing programs.

Controls Palette

Functions Palette

Tools Palette

Window Where you can

get access to Front Panel

and Block Diagrams you

have open (i.e. all the

programs you have open atthe time).

Help Where you can get

directly into NXT Module

Help, and where to activate

Show Context Help.


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The graphical toolbars give access to Run programs as well as toDebugging Tools and options for cleaning up/neatly organizingcode.

As your experience with LVEE grows you will find greater value inthe tools available on the graphical toolbar.

* We will explore graphical toolbar items as we need them.

Now lets look at an example program and explore the steps towriting a program in LVEE.



Familiarize Tip

Allow the cursor to hover

over the different buttons

on the graphical toolbars

to see what each button

will do.

The example program at

right has a robot follow a

line with one light sensor

while searching for any

crossing lines with a

second light sensor. Line

following is accomplished

by alternating motors

on/off based on whether

the light sensor sees

white or black.


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We will start learning to program in LVEE by first looking at thevisible elements of the example program.

Motor On (All Motors On) (Functions Palette/NXT IO/Complete/ Motors/Motor On)

Light Sensor on Port 2 looking for a light levelGreater Than (>) 45 (Functions Palette/NXT IO/Complete/Sensors/Read Light (LED On))

(Functions Palette/NXT IO/Complete/Sensors/Sensor Port)

(Functions Palette/NXT Programming/Comparison/Greater Than)

(Functions Palette/NXT Programming/Numeric/Numeric Constant)

Light Sensor on Port 3 looking for a light levelGreater Than (>) 45 (Functions Palette/NXT IO/Complete/Sensors/Read Light (LED On))

(Functions Palette/NXT IO/Complete/Sensors/Sensor Port)

(Functions Palette/NXT Programming/Comparison/Greater Than)

(Functions Palette/NXT Programming/Numeric/Numeric Constant)

LVEE Beginner Programming Tutorial


Programming Tip

Take some time to start

recognizing the look of

different control

structures.

Example: The

beginning/end arrow on a

loop.

Under the Functions

Palette/NXT IO there are

direct links to Motors and

Sensors (among other

items) rather than going

through Complete.

These direct pathways

open Polymorphic VIs

(VIs that include a drop-

down menu that allows

for changes to the VI

settings directly at the

VI).

As your experience with

programming increases

you will find which

process you prefer.


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Nested Case Structures

Here are the paths of the Case Structures that are in thebackground of our example.

Note how the inner Case Structurenow shows the value as True andwhich motors are on/off havealternated.

* The outer Case Structure is still in the

True state. Otherwise the inner Case

Structure will not execute.

Note how the outer Case Structure

now shows the value as False andall motors are off.



Programming Tip

Set the value of the Case

Structure (True/False)

by toggling the

value arrow.

The ? mark at the left

edge ofCase Structures

is the Case Selector.

The Case Structure is

wired to its trigger event

via the Case Selector.

Also note the Boolean

Value (Boolean simply

means there are two

choices) that routes to

the While Loop. We will

explain this further as we

go through writing the

program.


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With all the parts of the program covered lets now walk through theprogramming process.

We will start with the Program Script.

The program instructs a LEGO NXT robot with differential drive (onemotor drives the left wheel, one motor drives the right wheel) tofollow a line and look for an end line on which to stop.

To follow the line the program references a light sensor (Port 3) setto respond to a light value of 45. If the value of the light sensor isTrue (45 or above meaning the light sensor sees white) the robotis instructed to turn left (left motor off/right motor on forward). If thevalue of the light sensor is False (below 45 meaning the lightsensor sees black) the robot is instructed to turn right (left motor onforward/right motor off).



Programming Tip

In this type of line

following routine it must

be determined which

side of the line the robot

will reside. In our

example the robot is on

the right side of the line

so the program must

instruct the robot to turn

right when it sees black

(away from the line) and

left when it sees white

(toward the line).

* The value the light

sensor looks for needs

to be determined at the

source (the actual

black line to be

followed).


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The program also instructs the LEGO NXT robot to look for acrossing line by referencing a second light sensor (Port 2) also setto respond to a light value of 45. If the value of the light sensor isTrue (45 or above meaning the light sensor sees white) the robotis instructed to proceed with the inner Case Structure (i.e. moveforward following the line). If the value of the light sensor is False(below 45 meaning the light sensor sees black) the robot isinstructed to stop all motors and end the program.

So now lets dissect the program.

Loop Continuously

* The Boolean Value is set to be contrary to the Case Structure Value. This is

what always pushes the program to the subsequent fork of the Case

Structure and away from the End Loop Condition thus creating the

continuous loop .



Programming Tip

Programming

instructions are

hierarchical. As the

programmer you must

determine which events

control subsequent

events. Since we want

the robot to stop when it

sees a crossing line this

action ranks higher in

status than following the

line. Therefore, the stop

event is resident in theouter Case Structure and

the line following is

relegated to the inner

Case Structure.

Note how the program

loops back and checks

the status of the stop

event light sensor before

proceeding to the check

of the line following

sensor.


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Check the Value of Light Sensor on Port 3

* The sensor on Port 3 is the trigger for the inner Case Structure.

* If the value of trigger is False the Case Structure instructions activate

(Read Sensor Port 3).

* If the value of the trigger is True the Switch Path of the Case Structure

activates and the program runs the other pathway of the Case Structure.



Programming Tip

A False reading is in

alignment with the set

value of the inner Case

Structure so a False

reading on the sensor

will run the inner Case

Structure.

Note the alternate motor

settings to switch the

direction of the robot

left/right with the

transition between the

different paths of the

inner Case Structure.


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So, let walk through the steps to write this program.

1) Open LVEE

2) Select Blank VI Targeted to NXT

3) Minimize the Front Panel or bring the Block Diagram to the front.



Programming Tip


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* A Note Regarding Tools (cont.)

However, there are those who prefer

to disengage the ATS and select tools

manually. To disengage the ATS

simply left-click on the ATS selection

button. You will know you are in

Manual Tool Selection (MTS) when

the cursor is a plus sign with no

degree sign present.

+

* For this tutorial we will make use

of the Tools Palette manually so

that you gain understanding of

the different tools on the Tools

Palette and how they are used.

Once complete, try the tutorialagain with the ATS engaged to

see how this functions.

5) Disengage Automatic Tool Selection.

* Note also how the ATS buttons

green light goes out when ATS is

turned off.



Programming Tip

You can also bring up

the Functions Palette

by right-clicking on the

Block Diagram. This only

gives temporary access

to the Functions Palette

and it will move back to

the background after

your next access of the

Block Diagram.

You can lock the

Functions Palette to thedesktop through this

process if, once you

have displayed it, left-

clicking on the Push-Pin

(upper left corner of the

Functions Palette) to Pin

the Functions Palette to

the desktop.


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12) Drag the Read Light (LED On)icon to the Block Diagram and

left-click to paste it in.

We now need to attach some Modifiers to the Read Light

(LED On) Function Block to set:

The light level to look for.

The way we want the program to manage the light

sensor data.

The Port where the sensor will be located.

13) While the Sensors menu is still

open, select and drag the Sensor

Port icon to the Block Diagram to

just above the Read Light sensor

icon.

14) Wire the Port Function Block tothe Read Light Function Block.



Programming Tip

The auto-wiring feature

should wire the two icons

together.

* The wire should appear

as a pink line between

the two icons.

It should be noted that

auto-wiring places wires

at their appropriate

Terminals on the

Function Blocks

(icons). Each Function

Block has various

Terminals depending on

what Modifiers need to

be associated with the

Function Block in order

for it to operate as

intended. If you right-

click on a Function Block

and select

Visible Items/Terminals

you will see the Function

Block change from the

icon image to the

terminals image.

The Terminals are color

coded according to the

type of Modifier theyaccept.

* See how the wire

terminals are pink.

To activate the Wiring Tool go to the Tools Palette and

select the Wiring icon.

* Or hit the spacebar on your keyboard.

To Wire, left-click on the Wiring Terminal of the Port

Function Block and then on the Wiring Terminal of the

Read Light sensor Function Block.

* With the Wiring Tool activated the terminals will appear when

the Wiring Tool cursor image hovers over the Function

Blocks.


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5) We will now set the port value by

selecting the arrow on the right of

the Port icon.

But before the arrow can be

selected the Selection Tool

(Pointing Finger) must be

activated, so go to the Tools

Palette select the Selection Tool.

Set the Read Light sensor toPort 2.

6) Double-click on the arrow next toNXT IO to minimize this menu.

Click on the arrow next to NXTProgramming to expand thismenu.

Select Comparison.



Programming Tip

As you get familiar with

how the tools and

palettes work you will get

through these steps in

seconds.

What is now displayed in your Block Diagram should looksomething like this.


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When Edit/Paste is selected a copy of the selected items appears in

the Block Diagram surrounded by a flashing line. While the line isflashing move the cursor within the flashing line boundary, press andhold down the left mouse button, and move the pasted items to thedesired location in the Block Diagram.

Left-click on an open area of the Block Diagram to set the pasteditems in place.

24) Change the port on the new Read Light sensor to Port 3.

25) Select the arrow next to NXTProgramming to minimize theNumeric menu.

Select Structures.

Select While Loop and drag it tothe Block Diagram.



Programming Tip

We are using ports 3

and 2 for the Read Light

sensors as these are the

ports where the sensors

are plugged into our test

robot. If your robot has

the sensors plugged into

different inputs you will

need to adjust the port

numbers in the program

accordingly.

Likewise for the motor

ports. Our robot has the

motors plugged into the

B and C outputs with B to

the right motor and C to

the left motor.

Items can be placed in

the Block Diagram in any

order..

What is now displayed in your Block Diagram should looksomething like this.

Now lets add our first Structure.

The While Loop will surround all the programming

elements so click and hold down the left mouse buttonand stretch the While Loop across the Block Diagram sothat the elements we have created up to now are allwithin the While Loop.


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26) The Structures menu is still openso select Case Structure anddrag it to the Block Diagram.

Stretch the Case Structure insidethe While Loop and around the

Read Light sensor on Port 3.



Programming Tip What is now displayed in your Block Diagram should look

something like this.

Now lets add a Case Structure.


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Programming Tip

Note that when we add

a Case Structure it

originates in a True

state. Be sure you want

the visible items to

execute in the True

state or else they will

need to be changed.

27) Case Structures need a trigger event so wire the Greater ?

Comparison from the Read Light sensor on Port 2 (thesensor outside the Case Structure) to the Case SelectorTerminal on the Case Structure.

Also go ahead and wire the two Read Light sensorstogether.

As a Case Structure has both a True and False state we needto set the behaviors in the converse state.

28) Select the arrow in the State of the Case Structure and selectFalse from the menu that appears.


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Programming Tip The False window of the Case Structure will now show.

29) Navigate through the Functions Palette toNXT IO/Complete/Motors/MotorBrake and drag the MotorBrake icon into the Case Structure. Pull it close to the wiringnode and it should auto-wire. If not, wire it manually.

30) Drag the Loop Condition icon up next to the lower rightcorner of the Case Structure.

At some point we need to set the Loop Condition for both theTrue and False Case Structure states so lets set the Falsestate Condition now.

31) Navigate through the Functions Palette to

NXT Programming/Boolean

Drag the True Constant icon inside the Case Structure(lower right corner) across from the Loop Condition.

Wire the True Constant and the Loop Condition together.


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Programming Tip

The True and False

Constants can be

switched by simply left-

clicking on the Constant.32) Select the arrow in the State of the Case Structure and select

True from the menu that appears.

Now lets set the Boolean for the True state of the CaseStructure.

33) Navigate through the Functions Palette toNXT Programming/Boolean

Drag the False Constant icon inside the Case Structure(lower right corner) across from the Loop Condition.

Wire the False Constant and the Terminal Node that is onthe Case Structures edge together.

* The Terminal Node connects both states of the CaseStructure to the Loop Condition.


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Programming Tip

There is a difference

between Motor Port and

Motor Ports so be sure to

grab the Motor Port here.

Now that we are using

the ATS, to wire

elements together you

simply place the cursor

over the terminal of the

element until the Wiring

Icon displays. Then

left-click to paste one

end of the wire, move the

cursor to the next

element to receive the

next end of the wire, then

left-click to paste the end

of the wire.

35) Navigate through the Functions Palette toNXT IO/Complete/Motors

Select/Add a Motor Break inside the new Case Structure.

Select/Add a Motor Port above the Motor Break.

Select/Add a Motor On inside the new Case Structure.

Select/Add a Motor Port above the Motor On.

36) Set the port locations for the left and right motors associatedwith the action they are to take.

* Remember, ports are relative to the robot built. Our test robothas the motors on ports B and C so these are the ones wemust choose from.

* Also remember that the action of the motor (On vs. Break) mustalign with the action needed at the robot. Our test robot isdesigned to follow the right edge of the line so when it sees theline we want it to turn away from the line (right) and when itdoes not see the line we want it to find the line (turn left). Ourrobot turns right by breaking the right motor while running the

left motor forward and vice versa for turning left. Thus, with theCase Structure in the True state (true meaning the value ofthe trigger is truein this case the Read Light sensor isGreater Than 45) then we know our robot is off the line and wewant it to turn left to find the line (left motor on Port C set toBreak, right motor on Port B set to On).

37) Wire the Motor Ports to the Motors On/Break

Wire the Motor On and Motor Break together

Wire the Read Light sensor on Port 3 to the first MotorOn/Break.

*Of course only if the auto-wire did not activate.


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Programming Tip

When you copy/paste

you often disconnect

wires. You identify

broken wires by the

Broken Wire graphic.

If you develop a Broken

Wire you can:

Left-click on it and hit

delete.

Go to Edit on the

toolbar and select

Remove Broken Wires.

Or if it is a wire that

needs to be repaired

you can use the wiringtool and wire the

broken end to the

correct location.

38) Wire the Greater ? on the Read Light sensor on Port 3 to theCase Selectorof the new Case Structure.

Your program should now look something like this.

We are almost finished. All we have remaining is to build theactions for the False state of the inner Case Structure.

As the False state uses the identical elements as the Truestate (Motor On w/Port, Motor Break w/Port):

39) Copy the contents of the inner Case Structure.

40) Select the arrow in the State of the innerCase Structureand select False.

41) Paste the copied elements into the False state of theinner Case Structure.

42) Change the Motor Ports to reverse which motor is On and

which is set to Break from the settings in the True CaseStructure state.

43) Wire the pasted elements to the Read Light sensor thattriggers this inner Case Structure.


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Programming Tip

Once you have students

writing programs it is

best to give them

independent folders to

store their programs so

that all the programs

dont get jumbled

together.

Your program will not run

if it has Code Errors.

*Code Errors deal with

errors in the software,

not with errors in theinstructions themselves.

If your robot drives in

reverse when you

wanted it to go forward

this is not considered a

Code error but a user

error.

You know if there are

Code Errors in your

program if the Run

button is a Broken Arrow.

Our program is now complete.

If you have not already done so along the way, lets save theprogram.

File/Save As

Name it what you like and select a location where you want tostore your programs

Select OK

Now we need to get our program to run on the robot.

To do this lets refer back to the Graphics Toolbar.

And specifically this section of the toolbar.


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Programming Tip

If you do end up with

Code Errors try using the

Debug Tool to help solve

the issue.

See your NXT user guide

for descriptions of all the

buttons and operating

instructions of the NXT.

This can also be

downloaded as a .pdf

and saved to your

computer from

http://cache.lego.com/do

wnloads/education/9797_LME_UserGuide_US_lo

w.pdf

If you want to run the program direct from the computerpress

And the robot will activate and follow the programinstructions.

* You must have the robot hooked to the computer via USB cableor wirelessly via the Bluetooth module if you want to runprograms direct from the computer.

If you want to download the program to the robot (to theNXT brick) press

The robot will not immediately start when a program isdownloaded to the NXT. The Run button on the NXT mustbe pressed to run programs resident on the NXT.

* You must also have the robot hooked to the computer viaUSB cable or wirelessly via the Bluetooth module todownload programs. But after the download is complete youcan disconnect from the computer as the NXT can now run

the program independent of the computer.


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Programming TipCongratulations! You have now finished this Introductionto programming with LVEE.

The more you practice the more you will develop personalpreferences on how you like to set and use the palettes, thetoolbars, and on how you like to construct your programs.Take the time to share with other programmers and connectwith LVEE and LEGO support organizations such as theCenter for Engineering Education and Outreach (CEEO) atTufts University.

http://www.ceeo.tufts.edu/

There is still much to learn about writing programs andprogramming philosophy.

Good Luck and Happy Programming!

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