NXT-G Programming Guide

Welcome to the wonderful world of graphical programming for Lego Robotic Systems! Before you are introduced to any actual code, it is necessary to settle a few fundamental questions regarding this new language you must be so eager to tackle.

What is NXT-G? If you don't know, don't worry. The language itself is rather uncommon outside of circles that deal directly with the Lego NXT Block on a regular basis. Now let's establish the correct terminality from the beginning:

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Do other languages exist? Yes. NXT-G is not the only way to program a robot using the Lego NXT Module, however it is the easiest to learn for an inexperienced programmer, as well as the easiest to understand. The two other languages which are commonly used are called RobotC and LabView. NXT-G, although it's own language, is built on top of LabView which is also a graphics based language. RobotC however, is entirely code based. Only NXT-G will be further addressed after this point.

Why NXT-G? So, there are other languages, huh? Even as an experienced programmer, it is necessary to understand the learning curve of a language and the amount of time necessary to gain experience using it. NXT-G is easy to grasp, therefore it can be implemented quickly to solve a variety of programs. Unlike LabView or RobotC, errors are easy to find and correct due to a unique Lego-like layout. Building a program (in theory) is just as easy as building with Legos.

This is NXT-G. It is a graphics based language developed by National Instruments and Mindstorms to allow novice users to develop and implement simple robotic systems. Don't let my description fool you though, the language is quite capable of handling moderately complex designs, especially at a low level. It is a common issue to confuse the two terms. NXT-G is a Language, while "the brick" (NXT Module) is a physical Lego piece

This is an NXT Module. It is the metaphorical brain of any system you could conceive for your Legos. The unit is responsible for receiving signals from your sensors, performing calculations based on input, and moving motors and servos accordingly. The unit can be attached to four sensors and three motors; more than enough for a truly amazing system!

Introduction: What is NXT-G?Saturday, August 22, 200911:59 PM

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In this chapter you will:

Build a small robot-

Learn the basics of the NXT-G Interface-

Learn to manage memroy-

Program your robot to move-

Resources you will need:

Your orange box of Legos-- Contains all parts necessary for building a robot-

An NXT Brick-

A USB cable for your NXT-

An install CD for NXT-G-

Chapter One: Getting StartedSunday, August 23, 200912:40 AM

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This is a guide on teaching you to program robots in a proprietary language. That's great and all, however it seems you may b e missing one thing. A robot… Before programming is addressed, it will be necessary to fabricate a small drive train and space to mount sensors. Don't worry, it's not terribly difficult and it will give you a good idea of how to physically design the systems you will later provide logic to. It always pays to be well rounded!

It is necessary however, to tell you that Lego includes a guide on programming as well as building right in it's software. I f you have ever put together furniture from IKEA, you know that sometimes having words, or at least part numbers can be helpful. The following instructions have been inc luded in this document for your convenience, however they can be accessed directly from NXT-G if you so desire.

Building the Robot--Just follow these directions before you continue any further.

1.

Aha! This is one of those times it helps to be able to comment! You may notice there is an eight next to the black shaft. Th at is to denote it's length in "Lego units". The piece displayed is just as long as the width of eight single units, meaning it could span eight blocks side by side. The circle denotes length of the unit, while a square would represent width.

2.

3.

Disoriented? Make sure you flipped your motor over. Also, the square with the thirteen in it is used to show the widths or length of a piece with holes in it. I must admit, counting the holes is much easier than trying to understand how long those black and grey shafts are.

Chapter One: Before you beginSunday, August 23, 200912:43 AM

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admit, counting the holes is much easier than trying to understand how long those black and grey shafts are.

4.

TIP: its usually easier to build the unit in yellow separately and then attach it to the larger unit than to build both simul taneously.

5.

6.

7.

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8.

9.

10.

11.

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12.

Great Job! You just built the mount for your NXT to sit on! Now for the other components...

This wheel will be built separately, and then attached once you are finished.

13.

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14.

15.

16.

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17.

NOTE: Make sure you have your motor-unit turned to the orientation in the diagram. The round end of the motor should be facing up.All that is left is mounting the NXT.

18.

NOTE: Although pictured, you do not need to use the rechargeable battery as shown in the diagram.

19.

It goes up!

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20.

21.

IMPORTANT!!: When looking at the unit shown with the NXT directly facing you, make sure the RIGHT motor is connected to port C, and the LEFT on port B. If this is incorrect your programs will not work. Period.

22.

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Congratulations! You just built a robot! In it's current state, you creation just stands as a trophy to your [perhaps] newly acquired engineering skills with Legos. Let's make it do something worthwhile!

Again, before we start with programming it is necessary to introduce to you the NXT -G interface, seeing as you will be using it extensively from now on. To begin, launch NXT-G.

When you begin, you will be greeted by a screen giving you a few options, much like other GUIs.

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As a new project, your canvas will be blank. You should see a starting block

Note: The program itself is not directly labeled by the language it is used as an interface for. Nowhere in the name is NXT-G. Funny, huh?

For this lesson, you are going to create a new program called "Move Forward". Go ahead and use the program creation menu to do so.This project will be the name of the file stored on your NXT device, so make sure to make it descriptive. If you are going to make changes to something that currently works, it's often a good idea to save it as a new file first. File versions are also often helpful to include in a file name, especially for large projects.

Think of this as the beginning of a word document. What makes NXT-G somewhat different from other languages is that it is represented in linear fashion, meaning data is read from left to right.

Start ---> [function] ---> [function ]---> end

Most languages are read from top to bottom or bottom to top.

Start FunctionFunctionEnd

Chapter One: Getting to know the NXT-G interfaceSunday, August 23, 20091:28 AM

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The Three Function Menus

To add different "blocks" to create your program, take a look at the left hand side of the screen.

Common Complete Custom There you should find a menu looking like one of the tree seen here. Toggle between these windows by using the tabs at the bottom:

Each of the tabs is called a "palette", and just like an artists palette it contains an array of different formulas used to create something larger.

NXT-G offers three palettes: common, complete, and custom. For the purpose of this guide, we will always be using the complete palette with the occasional use of the custom one. The common palette is a small collection of very basic functions that you will outgrow rather quickly.

The complete palette contains several menus for users to use.

The Common menu: You don't quite escape the common palette by switching to the complete menu. This collection of functions are the basic workings of any program. From this menu you can access functions available from other menus, however it is the only place you can access the Move function, which as the name states, allows you robot to move.

The Action menu: From here you have access to functions that cause your robot to DO something, such as moving a motor or emitting a sound. This menu is for when you want something physical to happen within your program.

The Sensor menu: As the name implies, the sensor menu is were one would go to access functions dealing with sensors. The functions created by this menu are primarily used to interface with the sensor directly. For example, you would use a function from here with an Ultrasonic sensor to see the distance the sensor was currently reporting.

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The Flow menu: This is were the majority of your program's structure will come from. If you have had any experience with programming before, you will know the necessity of loops and switch statements, however an interesting concept called "wait" has been added, which pauses the continuation of the program till the statement has been met.

The Data menu: Although for extremely basic programs this menu is unnecessary, it is used in more complex situations to perform calculations as well as create and store variables. Functions found here can be used to test if a situation is true or false, perform basic arithmetic, and compare values.

The Advanced menu: Although it is called "advanced", this menu might as well be called miscellaneous, seeing as it’s contents have no relative correlation and really nowhere else to go. There are only a few functions in this menu you will use to begin with, however keep it in the back of your mind.

The NXT Control Panel

Found on the lower right hand corner of the screen , the small collection of buttons allows you to control the NXT while it is connected to the computer.

The Download and Run key: This key is used to compile, download, and execute the current program on the currently running NXT. The program will start soon after you press this button, so be careful if your robot is still plugged in!

The Stop key: Used to stop the current program running on the NXT. This only works if the NXT is connected to the computer.

The Download key: Unlike the download and run key, this will just download the current project to the NXT. This is often helpful if you want to start the program after you have moved your robot away from the computer, or have unplugged it.

The Download and Run Selected key: Do not use this key. It is used to change only parts of the code that you specify and can lead to problems later on. If you want to make changes to only part of the code, save it as a new file and download it as a new program.

The NXT Window key: This is an important button to keep in mind. From this you can access information about the currently connected NXT device.

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Finally! Time to get into the real portion of this guide. In the following lesson, you will be programming your robot to go forward, as well as understanding what is happening when you do so. A good programmer understands what he is engineering, just as a good pharmacist understands the disease they are treating. Without a fundamental understanding of engineering AND programming, developing competent systems can be quite a challenge.

Your first task will be to start a new program. If you created a project called "Move Forward" previously, then you are where you need to be, otherwise create that file now.

To program your robot to go forward, grab the "move" block from the common menu, dragging it onto the square labeled "start".

Now that you have placed the block on the beginning of your "program timeline", click on your newly placed function and look at the bottom of your screen to find a menu like the one shown below.

The Move block is a unique function that allows you to control multiple motors simultaneously, often with the intent of driving or steering a robot. Within the menu you will come across multiple options to control the speed and direction of the motors, a few of which are briefly outlined in the following section. Each of these will be covered more in depth in later lessons.

Port: Selects the motor/s that are to be controlled by the function. Up to two can be selected . Motors correspond with the port letters they are plugged into on the top of the NXT unit.

Direction: as the name implies, the radio button array can be used to select the direction a motor goes in. There is one button however, that is used for braking. Using this setting will cause the motors to LOCK, meaning they will not slow down to a stop, but rather stop immediately.

Steering: This is a setting unique to the Move block, seeing as it can be used to determine the direction of two motors, whereas the Motor block can only be used to control one. Use the slider to determine the direction you want your robot to go in.

Power: this particular type of power determines the speed of the motor, not it's strength.

----Drag---->

Chapter One: Programming Your RobotSunday, August 23, 20096:04 PM

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Time: Motor turns for a specified unit of time.Degrees: The motor itself turns a select number of degrees. Please note that this does not cause the robot to rotate that exact distance, just the motor.Rotations: Motor/s turn a specified number of times.Unlimited: The motor turns until it is told to stop by another function, or not at all.

Duration: Within duration you can select four methods to determine the length of time the motor should turn.

Next Action: Used only if duration is not unlimited, the next action is used to determine if the motors are locked or not after they turn their specified distance.

Finalizing your program and putting it on the robot

Now that you understand a bit about how the Move block works, it's time to compile the program and execute it. Start by setting the "rotations" setting to 5. At the moment, your program should look like this:

Here's the big surprise: that's all you need! Plug in your NXTUnit to the computer and turn it on.

NOTE: It is always a good idea to have a long cord and set your robot on the ground, as the program will start as soonas soon as it is downloaded.

In the lower right hand corner of the screen, press the Download and Run key (center) from the NXT controlpanel.

At this point you should feel giddy with joy as you watch your robot move forward a foot or so and then stop. The best part? You did that.

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There are times when there may be too much content on your NXT device to load a program onto it. You can easily manage and delete files from your NXT from the memory window.

There are also buttons which allow you to control how programs on the NXT are dealt with. Interestingly enough, you can actually upload from the NXT a program you might not have saved on your computer.

To access the memory window, first open the NXT screen window from the control station in the lower right hand corner of the screen. This will bring up a menu showing the name of your NXT and the type of connection you currently have established.

A few other interesting things such as battery life and remaining memory can be found from this menu, however to direct man age memory, go to the memory tab.

The menu is composed to two different elements. There is the memory usage graph, which is to the right, and there is the program menu, which shows all of the components currently on the NXT. From the graph, select different types of programs to see the files of their type on the NXT.

Chapter One: Memory ManagementMonday, August 31, 20093:34 PM

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In hindsight, this will prove to be useful if you understand how it is done before you encounter a problem. If you are using the new NXT-G 2.0 software, as you most likely are, it may be necessary to update the firmware of your NXT Device to load programs onto it.

You will know if you need a firmware update if you press the download and run button and get an error message. Such as the one shown to the left.

Don't worry, fixing this isn't difficult at all, however you will need an active network connection to download the new files.

NXTFirmwarePC

For your convince, I have included a file with an update to version 1.05. This may not help you if you are using NXT-G 2.0 however, so know there is another way to access the files. Although you can find firmware updates online at : http://www.lego.com/education/school/default.asp?locale=2057&pagename=softu&l2id=3_2&l3id=3_2_4&l4id=3_2_4_2 , there exists a better way to get files.

To get the latest firmware automatically, first go to the "tools" menu on the file bar and then go to update NXT-G Firmware. This will open up a menu much like the one shown.

Shown here, my NXT has firmware version 1.21 currently installed. NXT-G 2.0 uses firmware 1.25 and above.

To check and see if there is a new version of firmware available for download, press the "Check" button at the top of the menu.

To install firmware, select the version you would like to use (the latest version of course) and press the download button below.

If everything downloads correctly, the progress bars should fill up as shown below.

Chapter One: Firmware UpdatesTuesday, September 01, 20094:35 PM

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http://www.lego.com/education/school/default.asp?locale=2057&pagename=softu&l2id=3_2&l3id=3_2_4&l4id=3_2_4_2




Learn to use the Display of the NXT Module -

Learn to put out sound through the NXT Module.-

Learn about wait function-

You will need:

Your NXT Device-

A USB cable-

Chapter Two: NXT Related Functions and Wait StructuresSunday, August 23, 200911:16 PM

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If you have ever programmed before, chances are that using NXT-G is somewhat different than anything you have experienced before. By programming a robot, you loose the familiar interface of a computer screen and instead see the results of your code through physical movement.

The NXT Brick allows you to show functions on it's screen and NXT-G provides an easy way to "print" the image or text you want to the screen.

To begin, we will print a simple diagram to the screen. Open up NXT-G and create a new program called "Print_To_Screen"'

Displaying an Image

Select Display from the Action menu and drag it onto the main timeline

If you were to export this now, the screen would display the image for a fraction of a second and then exit.Consider the way the code is built:

Start ---> Display ---> End

When run, the current program will do everything you tell it to, however it will not necessarily do what you WANT it to do.

What you want is for the NXT screen to display your image long enough for you to read it, or until some other stimulus gets rid of it. What you are looking for is for the program to wait till you are ready for it to continue. Fortunately, such a structure exists.

Using the Wait Structure

Using your current program, you will introduce the Wait Structure from the Flow menu.

Once you have the function on the timeline, click on it to get to it's properties. From here you will change the image to the checkmark below.

Chapter Two: The NXT Display and Wait StructuresThursday, August 27, 200912:45 PM

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Place the structure after the display function, seeing as you are waiting before going on to the next piece of the program (which in this case is the end.)

Go ahead and run this function on your NXT. Your screen should display the following for five seconds:

Displaying Text

In retrospect, I realize it may be helpful to demonstrate how to display text through the Display function. Go ahead and change the "action" in the display panel from image to text.

If you notice, the default setting for the Wait structure is for it to be used with a touch sensor. Although that could work for this program, it is easier to just set the structure to wait for a period of time.

Go to the function properties (bottom of the screen), and change the "control" of the function from sensor to time. Set the number of seconds to 5.

After it does this, the program ends.

Using the textbox provided, write what you would like to be displayed.

NOTE: You are limited to 15 characters.

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Although sound may not play a huge part in the actual logic in a system, it can help developers know what stage of a program is currently executing, or if the robot is encountering something unexpected.

To start, create a program called "Sound"

Take the Sound function from the Action menu and drop it onto the starting square.

Using Sound Files

The difference in the two is the fact that a sound file takes up a lot of memory. The NXT device has less memory than a floppy diskette. Much less. A tone however, requires no legitimate memory at all, seeing as the capabilities are already built into the device. To select which you would like to play, look at the properties menu for the sound function.

By default, NXT-G has the sound function play "Good Job" . Download and Run the current program as it is, and listen to the sound file it plays.

At this point it may be necessary to point out a key difference in the use of a Sound Function over that of a Display Function. If you notice, a Sound function waits until it has played it's sound to move on to the next part of the program. This is an optional piece that builds in a wait function.

It is helpful to recognize that you don't need to add a wait function on top of a sound function to get the desired result.

Using Tones

Like sound files, tones have a built in wait function as well.

From here, it is necessary to explain the two different types of sound that can be played. The NXT can play a sound file, which can be anything from a number to a phrase such as "hello"; and the NXT can play a Tone, which is just a note.

Chapter Two: Using Sound Saturday, August 29, 200910:52 PM

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Like sound files, tones have a built in wait function as well.

You can select the note you would like the NXT to play, as well as the length of time you would like to play it.

Note: When a program starts on the NXT, it plays a tone automatically. If you play a tone at the beginning of your program, you will hear both tones.

Create a program

To illustrate the difference between the built in wait functions and the real ones, build a program that plays a note, displays what note is playing, and then waits a second to play the next, higher note.

If you need some help, look at the following model:

Sound

If you are using Microsoft One Note to view this, you can right click the file to the right and save it to your computer or double click to open it in OneNote. It contains the above code. If you are not a OneNote user, then all that is an image.

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At first, I thought it would be a good idea to teach about sensors in this chapter, however then I realized that the majority of new programmers reading this might want to familiarize themselves with the logicbehind programming before building anything to control robots.

In this chapter you will learn about:

Variables-

Basic arithmetic -

Advanced function controls in NXT-G (Data Wires)-

You will need:

Your NXT Device-

A USB cable-

Chapter Three: Math and VariablesSaturday, August 29, 200911:47 PM

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If you are not a programmer, chances are you have little concept of what a variable is. Within programming, there are many types of variables, however they all have one thing in common: they represent a named place to store a value. Consider them like a box. You can put things in a box, hide them away, and then take them out when you need them again. Variables are used in much the same way. You can create a variable, naming it "NUMBER" and then assign a number for it to store. When you ask what the value of "NUMBER" is, it will give you that number back.

Variables are most often used to keep track of things, and compare them to other things. An ambiguous definition, I know. It is helpful to use variables, however, because things in a program change. These things need to be kept somewhere while tests are performed on them to determine what to do with them. These "tests" are functions.

Variables in NXT-G

At this point, it will be easier to show you within NXT-G how to use variables than to give you a rant on them.

To begin, create a new program called "My_First_Logic"

From here you will need to do something that is quite unlike any other programming experience. Usually, when you write code, you create variables manually. In NXT-G, you are required to go to the edit menu (at the top toolbar) in order to create variables.

In the menu, click "Define Variables" from the options.

A menu like the one on the left will come up. This menu will allow you to create the variables you will use in your program.

Click on the "create" button to create a variable.

Call it "loop number"

Chapter Three: VariablesSunday, August 30, 200912:02 AM

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When creating a variable, make sure to set the datatype to the type of variable you want to create. For this program, "loop number" should be a number.

When you have done all of this, close the menu.

Now, get the variable block from the Data menu, and put it into your program.

The default value of a variable is one of NXT-G's predefined variables.Make sure to go into the properties of the block and change it to the variable you want it to be

In this case, we want this variable to be the one we just defined, so we select "loop number"You are also given the option to read or write and in this case we will be later reading the variable.

My_First_Logic

Before we do anything more, it is necessary to understand how to do simple math to change variables.

Attached is a copy of the program up to this point. If you are using OneNote, you can open the icon to the right directly into NXT-G.

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Unfortunately, we are not going to be flying a rocket into space, or piloting an aircraft with this system. The mathematic functions offered by NXT-G are basic arithmetic. They are most commonly used in conjunction with a variable.

Using Math

To perform a mathematic function, go to the Data menu and select Math

We will be building on top of our previous program using variables, so drag this function to the next slot in the program "timeline"

The purpose of this is going to be to add one to "loop number". The math function works by taking two numbers, A and B, and adding them together. To set a number to either A or B, click on the little wire holes next to the Pound Symbol on the Variable (#), or the letter A. End the wire by clicking on the other one.

At this point, the function will add A and B together, however you have not written anything to do with the number it produces. The sum of the two numbers can be linked to a variable by drawing a wire from this:

In this case, you want to set the new value of "Loop Number" to be the result of this equation. To do so, enter another variable block, this time setting it to "write" in the properties bar.

One of the things you may notice at this point in time that you have not yet encountered with other blocks, is the drop down menus. These menus are used for what are called "data wires". Data wires can be used to connect blocks and exchange information.

When you are finished, it should look something like this.

The next step is adding a set number (in this case 1), to the number set to A.

To do this, go to the properties menu of the math function.

O f course, this is going to be addition, however you will need to set the static value of B to 1.

Chapter Three: Basic MathSunday, August 30, 200912:31 AM

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Your final program should look like the diagram to the left.

My_First_Logic

Attached is a copy of the program up to this point. If you are using OneNote, you can open the icon to the left directly into NXT-G.

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This is more of a trivial addition to the guide, however it is important to be able to take a data value and display it on the NXT screen. You will be displaying the value of the variable "Loop Number".

To begin, select the Number to Text function from the Advanced Menu

Put this on your timeline after the last variable. In order to have a number to convert to text, you will need to read the variable "Loop Number" again. Draw a wire connection from the value of the variable, to the input on the Number to Text function. You program should look like the following:

Now, you will take the text and display it on the screen using the Display function from the Action menu.

When you add it to the timeline, click on the lower left hand corner to extend the full bank of input options.

Be sure to change the type of input to "text" from the properties bar.

As you may be able to figure out, you will be using the text output from the Text to Number function to draw a data wire to the text input on the display. Once you have drawn the wire, you can click the lower corner again to collapse all unused connectors.

Remember, this is a display function, therefore you will need a wait function after it in order to read what is going on.

The addition to the program should look like this (There is more to the left):

My_First_Logic


Run this program now. The NXT screen should display the number 1.

Chapter Three: The Number to Text FunctionSunday, August 30, 200912:54 AM

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The next logical step in establishing your foundation in computer science and program development is to explain the use of different program structures. While different languages call these "structures" different things , the concepts behind them remain the same.

In this chapter you will learn about:

Loop or repeat statements-

Switch statements-

Comparative operators-

Wait Statements (This is a type of structure, however we have already covered it)-

You will need:

Your NXT Device-

A USB cable-

Code from the previous chapter-

Chapter Four: Programming StructuresTuesday, September 01, 20099:35 PM

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Using the program we created before, we will now actually put that "Loop Number" variable to use.Open up the program "My_First_Logic" if you do not already have it open. The following chapter will use the entire program created in the previous chapter, therefore if you have not written it yet, the following code may not make sense.

Using Loop Statements:

To access loops, go to the Loop block of the Flow menu.

From here, drag the loop onto the beginning of the program "timeline"In NXT-G, anything inside of a loop will repeat until the loop no longer needs to continue. For this exercise the entire program will repeat, adding one to the variable "loop number" and then printing them out to the screen.

To put the blocks into the loop, select them all just as you would select multiple files (dragging a box around them)

Now drag the selected functions inside of the loop block at the beginning of the program.Notice how the loop expands to fit the content inside of it.

Chapter Four: Loop StatementsSunday, August 30, 20092:31 PM

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At this point, download and run this program. Your NXT screen should start counting up from one.If it takes a while to count, you can always set the wait function to 1 second in order to count faster.

If you continue to let the program run, the loop will continue till you hit the back button or the batteries die. Loop statements have something built in that is a little like a wait block. It's called a while statement.

Click on the right hand side of the loop to open up the properties bar.

Loops can end because of a time limit, a specified number of executions, when a comparative statement is true (which you will study later in this chapter), or because of sensor telling it to. We will study methods to break out of a function in the next chapter.

My_First_Logic

By default, NXT-G has loops perpetuate infinitely. If you have anything after an infinite loop it will never be executed, seeing as the loop will never end. Your other options are for the loop to exit when a certain contrition has been met.

Attached is a copy of the program up to this point. If you are using OneNote, you can open the icon to the leftdirectly into NXT-G.

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There often comes a time where you only want to do something if another something is right. Yes, this can talk about a lot of things, however it describes a situation where you are comparing two different things and determining if the result of their comparison is right (true) or not (false).

Programs have a way of doing this as well. They do so through what are called "Comparative Operators". NXT-G allows you to directly select three types of operators:

Greater than >Less than <Equals to =

Compare Functions

To use the Compare function, go to the data menu.

For this program, put the compare block at the end of the loop so that it is still inside of it.

You will be using the comparative operator to see if the variable "loop number" is greater than 10. If it is, the result will be the end of the loop.

The setup for a comparative functions is much like that of a math function. Drag the value of the variable to data connector for "A" and set "B" to (in this case) a static value.

Just as a tip, you don't have to put in a new variable block every time you need to access a variable. You can "recycle" old ones and have additional data wires come off of them.

Just as a rule of thumb, you can't "double up" data wires if one block is in a loop and another is not. Also, make sure the block you are using is a "read" function, instead of a "write" one.

Moving on, go to the properties bar for the comparative statement. From there set the value of "B" to be 10 and the operation to be greater than.

Chapter Four: Using Comparative OperatorsSunday, August 30, 20094:36 PM

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Download and run this program now. If you notice, the program will count up to ELEVIN. This is not an error. 11 is the first number greater than 10. If you want the program to end when you get to 10 you can do one of two things. First, you could change comparative statement to A = 10, with A being the value of "loop number" or set A>9, with 10 being the first integer greater than 9.

My_First_Logic

Finally, you want you loop to exit when this statement is "true". Go into the properties bar of the loop and change the control to "logic"

If you notice, by changing the control the Loop block gained a data connector. Connect a data wire from the comparative statement to this connector in order to pass on the result of the comparison.If the result is true (if the number of loops is greater than ten) then the loop will exit.Otherwise it will continue.


~~~~~~~~~~~~~~~

NXT-G Page 32

It might make sense to use a comparative function if you are checking to see if something is true or false and then acting on one of the end results. What do you do if you want the program to do a certain thing in a situation and another thing in a different situation? Switch statements allow the program to execute a specified portion of code based on the value the statement is given.

We will again be working with the program "My_First_Logic". If you do not currently have it open, bring it up now.

Switch Statements

Like the other statements we have encountered in this chapter, the switch statement can be found under the Flow menu.

When you enter the block into the timeline, place it between the wait function and the comparative statement. By default, the Switch statement is set to use a touch sensor. For this part of the exercise, we will be using the numeric value of the "loop number" variable.

Again, by default, NXT-G sets a logical (true/false) action to the type of control. From the "type" menu in the properties bar, change "logic" to number.

Flat View

From the property bar, change the control from "sensor" to "value"

If you look at the program timeline, the switch block should look like the image to the left. Weird right? Even though you are telling the program you want to do different things based on numbers, you get a true or false execution method. This is what is called the "flat view" While in this view, switch statements can only have two options. A value can be equal to 0 or 1, and therefore true or false. To get out of "flat view" and add more options, first uncheck the box in the properties bar.

After being unchecked, your switch box should look like the image to the right. If you notice the tabs at the top, each one can be used to select a different value of input. At the moment you only have two. Lets add some more.

Additional Conditions

Chapter Four: Switch StatementsSunday, August 30, 20097:14 PM

NXT-G Page 33

Additional Conditions

To add additional conditions, go to the properties bar of the switch statement.

As you may have guessed, click on the "+" to add conditions to the list. Use the text box at the bottom to give a value to the new conditions.Create one new condition and set it to 9 and change the value of the second condition to 5.

You might notice that there is a check mark next to the first condition. This is because it is called the default condition. If a value does not match any of the specified conditions, it executes the code within in that part of the switch statement. You can select which value you want as default by clicking the asterisk button to the right.

Adding Code to Each Condition

Back on the timeline, you should now have three tabs on your switch statement. You can hover over each one to see what value the code inside corresponds to.

Click the second tab, which should be the value 5.Inside of the statement, print "Halfway There" to the screen. In the 9 tab, print "almost done". If you need help, it should look somewhat like this:

Remember to set the output type on the display to textAlso keep in mind that you need to include a wait function so that you can read what is on each screen.

As you are wrapping up, make sure to connect the input to the switch statement to a data wire carrying the value of "loop number". It is easiest to use the one for the comparative function.

Download and Run this program now.This program should count up to five and then display the message "halfway there", count up to nine and finally print out "almost done".

My_First_Logic


~~~~~~~~~~~~~~~

NXT-G Page 34

One of the things that makes robots unique from other types of systems is that fact that robots have the capabilities of being perceptive. This is to say that robots have hardware that allow them to measure things in their environment and respond to stimuli in a physical way.

Before you are fully introduced to sensors, let's start out with using the hardware that is built right into the NXT. The NXT buttons are some of the most basic sensors Lego includes.

In this program you will:

Use the NXT buttons to return a value -

Create switch statements to act on these values-

Use the "reset" function for the display function-

Use wait functions that rely on sensors. -

You will need:

Your NXT Device-

A USB Cable-

Chapter Five: Introduction to Sensors, the NXT ButtonsSunday, August 30, 20099:45 PM

NXT-G Page 35

You now understand the basics of logical programming and structures to implement it in NXT-G. A good robotic program however, responds to input from the user. Such input is derived from various types of sensors. In the following lesson you will be using the NXT Buttons as your first sensor input.

Sensor Blocks

Under the Sensor menu, find the NXT buttons block and drag it onto your program timeline.

In NXT-G, you can access the "value" of a sensor by using a sensor block. The value of something like a sound sensor would be the amount of sound, however buttons and touch sensors are different. They have three states "Pressed", "Released", and then "bumped"- which is pressed and then released.

What to do With Sensor Values

To be clear, there are only actually three buttons. The right arrow, left arrow, and center orange key. The bottom button is the "back" key, which if pressed will end you program.

At this point, please create a new program called "NXT_Buttons". This program will print out the name of the button you are pressing.

If you look at the properties bar for the NXT button sensor block (isn't that a mouthful of a name?), you will see these options outlined for you. From here, you can also select which button you would like this function to pertain to.

If you notice, the actual block on the timeline shows a Boolean value as it's output. For clarification, Boolean is a programming term for a true or false value. This is because when the program comes to this function, it checks to see if the conditions (currently if the enter button is pressed) are true or not and then passes them off along the data wire you would attach to the function.

The only thing is, this checks the state of the sensor once and then moves on. If you want a program testing to see if a button is pressed over a period of time, you will need to put this into a loop. For this purpose, an infinite loop will be alright, seeing as the entire program will be within it

Chapter Five: The NXT ButtonsSunday, August 30, 200910:06 PM

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Most likely, you will want your program to do something different based on the value of the input. This is the perfect time to use switch statements. In this program, you want to print out "enter button" to the screen only when the key is pressed. Although we will not finish the function in this lesson of the chapter, put in a switch statement right after the sensor block at this time.

NXT_Buttons

Surprisingly, we will not be using an NXT-Button switch statement. They are only used to discern between howthe buttons are pressed. Use a logical switch statement.The image to the left shows the program in "flat view" which is much easier to deal with in my opinion, seeing as it takes up less room and is less likely to confuse you.Note: this all should be in a loop.


~~~~~~~~~~~~~~~

NXT-G Page 37

Using the beginning of the program we created in the last lesson, we should now add the content that the NXT should display.

According to the current program, the sensor block for the NXT buttons will tell the switch statement if the enter button is pressed or not.

When you run the program, it should show the running screen until you press the "enter button".However, when you release the button….Nothing! The text stays on the screen!This is because you need to "reset" or "clear" the screen if it the value is false, and it should not be told to display anything.

Using the Reset Screen Attribute

Looking at your switch statement, if the sensor passes along a "true" value, then text is displayed, however if "false" is passed along, the program just continues. You actually want the program to do something if the button is not pressed. You want it to display nothing.

There are two locations you could logically place a new display function that would achieve the same logical effect.

If the button is pressed, we want the screen of the NXT to print out "Enter Button". Use the display function from the action menu.

Make sure you place the function in the "true" part of the switch statement. You only want this to execute if the statement is true.

Be sure to add a wait function to the end of the display function, seeing as you will need to read what is displayed.

At this point, download and run the program on your NXT device.

or

To set a display block to reset the screen, go to the properties menu and select "reset" from actions.

Chapter Five: Resetting the DisplayMonday, August 31, 200912:17 PM

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The first scenario places the reset function within the switch statement itself. With this syntax, the screen resets every time the enter button is not pressed. While this may work for this smaller program, what if you want the screen to display text when you press the right key? When the right key is pressed, the enter button is not. This causes a conflict. Part of the code says "reset the screen" and another says "display this text!" What results in both happening, and the screen flickering- constantly resetting and displaying just as you asked it to.

The second option on the other hand, executes after the switch statement has been evaluated. In a switch statement, if the timeline within it is empty, it just moves on within the program timeline. If you were to add in the scenario with the right button, the two switch statements would check to see if buttons were pressed, and otherwise continue on into the program until the screen is reset.

Multiple Scenarios

If you didn't guess before, you will have the screen display text in accordance to all three buttons on the NXT. Really, all that requires is two more copies of pieces of code you have already created.

Your code should end up looking like the image below (with an additional piece for the left button).

Download and run this code now. You may notice that there is a one second lag between the buttons you press.This will be addressed in the next lesson of the chapter.

NXT_Buttons

The shown piece of code is used to see if a button is pressed, and then displays text accordingly. Just make to more instances of this code, changing the text displayed and the buttons pressed to match the right and left buttons.


~~~~~~~~~~~~~~~

NXT-G Page 39

As the program is, if a button is pressed, it displays a message showing that the button is pressed. Wouldn't this program make more sense if it stopped having to display the message when you were no longer pressing the button?

It would be much more logical to wait until the button you are pressing is released.

This program will display the key you are pressing, only when you are pressing it!

~~~~~~~~~~~~~~~

NXT_Buttons

The current program uses a wait function to display the name of the button pressed for one second before continuing. While this makes sense, it causes the message to display even after you have let go of the button.

Go to the wait function in the piece of code displaying the "enter button" in the properties bar of the wait function, change the type of control to "sensor", seeing as the buttons are sensors.

For the type of sensor, use NXT Buttons.

Because this function is dealing with the enter button, make sure you have it selected.

Wait functions are designed so that the function before them continues to execute until the condition of the wait function is met. We want the message to display until the button is released

At this point you wait function should look like this. It's a big change from just an hourglass, isn't it? Go ahead and make changes to all of the other button's display functions and then download and run.


Chapter Five: Wait Functions Using SensorsMonday, August 31, 20091:00 PM

NXT-G Page 40

This is the first official chapter to deal directly with offboard sensors, meaning logical hardware that exists beyond the NXT Device. Touch sensors behave like mountable buttons, and can be customized to do a number of things.


Learn how to use touch sensors to stop a robot-

Use a touch sensor to count touches-

Learn to program so that the robot can respond to multiple sensors.-

You will need:

The robot from Chapter One-

Your NXT Device-

A Touch Sensor and mount-

A USB cable-

Touch_Sensor

This is a PDF included by Lego that gives a short overview of touch sensors.

Chapter Six: Touch Sensors and the "or" opperatorMonday, August 31, 20092:46 PM

NXT-G Page 41

Time for a break from programming! Before you can truly use any sensor, you need to mount it to the robot you are planning on using it with. We will be mounting the touch sensors to the front of the robot.

Chapter Six: Building a Mount for Touch SensorsMonday, August 31, 20092:52 PM

NXT-G Page 42

NXT-G Page 43

Be sure to connect this to port one of the NXT. This is the default port for the touch sensor.

NXT-G Page 44

This very well may be the shortest lesson you will have to complete. The purpose of the following is to demonstrate the uses of the touch sensor on a small scale robot. One of the most common uses of a touch sensor is to detect an obstacle in the direct premises of the robot (touching against it).

Create a new program called: "React_to_Bump"

Seeing as this program is going to start with movement, start by adding a move block from the common menu. Place it in the start square of the timeline.

Just like in the previous program, you want the function to run until the touch sensor is pressed. Anytime you logically use anything until anything else is done, you use a wait function.

Guess what! That's it! If you download and run this program now, the robot will move forward until it hits and object and the touch sensor is pressed.

~~~~~~~~~~~~~~~

React_to_Bump

From here, go to properties and select "unlimited" for the amount of rotations. We want he robot to move until it hits an obstacle, only stopping if the touch sensor is pressed.

In this instance, the default wait function's use of the touch sensor is exactly what we are looking for. We want the robot to stop if the touch sensor in port one is pressed.


Chapter Six: Stopping Using a Touch SensorMonday, August 31, 20093:15 PM

NXT-G Page 45

The following program will require you to do a little work. First, you will need another one of the touch sensor mounts you designed for the first part of this chapter. Mount it directly to the back of the robot on the rear wheel. For this exercise, plug it into port 4 of the NXT.

In this program, we are going to do a little reworking of our previous bump reaction program. To begin, everything is going to exist within a loop.

We want the robot to move, and by extension the loop to continue, if the buttons are NOT pressed. In the properties bar of the loop statement, change the unit of repetition from "true" to "false".

At this point, you will need to remove the wait function. There is no reason to have to wait for the program to end using one of them, seeing as the program will end when the loop ends. In it's place, place two blocks for touch sensors.

You want the loop to end and the robot to stop if the front touch sensor is pressed or if the back one is pressed. Using an or statement can be achieved through the logic block under the "data" menu.

Place one of these blocks on the end of the timeline. Now look at the properties bar.

By "isolating" portions of code to a loop, you can stop the execution of entire pieces of programs based on how the loop is supposed to end. In the case of this program, the loop should be logic based.

With this, the loop will continue till the button returns that it has been pressed, a "true" value.

The touch sensors are currently be set to return the state of the touch sensor plugged into port 1. If you remember how you wired the robot, you have a touch sensor plugged into both port one and four. In the properties bar, change one of the blocks to correspond with port four.

You want the function to return a "true" value and end the loop if either touch sensor returns a "true" value. The settings shown to the left ask if they are returning "false" values. Check off the check marks to change this.

Chapter Six: Multiple Touch Sensors and the "or" StatementTuesday, September 01, 20094:56 PM

NXT-G Page 46

If you have not done so already, create data wires for your values to travel over. When you are finished, download and run the program.If you tap the front or back, the robot stops.

React_to_Bump

<---Code enclosed

NXT-G Page 47

The following lesson is more of an optional activity to further explain the uses of sensors, loops, and variables. If you feel you understand touch sensors completely, then it is alright to move on to the next chapter.

In this project you will create a short program that counts the number of times you have pressed a touch sensor. For this example, we will use both the front and back mounted touch sensor used in the previous lesson. Understand this can apply to NXT buttons as well.

First, create a new program called "Bump_Count"

Seeing as you want your program to count multiple times, the entire program will need to exist within a loop. There is really no reason for this loop to end based on any given input, so let it be infinite.

Within the loop, use the same piece of code you used from the last lesson. Two touch sensors and an "or" unit of logic. This will be used to determine if any buttons are pressed. Remember to change one of the sensor blocks to port 4, and set the values of the "or" statement to check that the sensors are "true". Also, change the buttons to being "bumped".

Instead of using this logic to end a loop, we will use it to create a switch statement. The switch statement should be logical, and a data wire should feed to it from the "or" operator.

In order to record the number of times a sensor has been pressed, the value needs to be recorded to a variable. Go to the "edit" menu in the filebar, select "Define Variables", and a menu like the one shown to the right will come up.

Create a new variable and call it "count"Make sure the variable is a number, seeing as that is the type of data counting usually deals with.

When you are done, create a variable block within the "true" section of the switch statement.

Set the action to read the variable. Make sure to select "count" as the variable that needs to be read.

Chapter Six: Counting TouchesTuesday, September 01, 20095:24 PM

NXT-G Page 48

From here, if you were to run this program in it's current state, one would be added to the value of "count" every time a sensor was pressed. This is what you wanted, right? Well, yes, but I assume you wanted to see it as well!

Download and run the program now. When you press either touch sensor and then release it, the counter on the screen should go up.

~~~~~~~~~~~~~~~

Bump_Count

Now it's time to do a little bit of math. If one of the touch sensors is pressed and the switch statement performs the code, you want to add one to the current value of "count" and then set the sum to the new value of "count". Remember to set the value of "B" to one.

When you are finished, set the sum of the variable to the new value of "count". Make sure you have the variable set to "write" and that the current variable it is setting to is "count".

Create a variable set to read the value of "count" and convert the number into text. With that text, create a display function from the action menu. Notice, that in this instance you do not need a wait function to see what is on the display. This is because the display is constantly updating due to being in a loop. Adding a wait function would cause the program to lag.


NXT-G Page 49

Sound sensors are one of the least used sensors available to the platform. The are not a "microphone" sensor as one may be compelled to believe, but rather a device used to measure the intensity of sound.

Although you may not use it, sound sensors can be used to demonstrate a few things.


Build a sound sensor mount-

Make a robot stop based on sound-

Make a robot that accelerates based on sound. -

You will need:


Your NXT Device-

A Sound Sensor and mount-

A USB cable-

Sound_Sensor

This is a PDF included by Lego that gives a short overview of sound sensors.

Chapter Seven: Sound Sensors and Acceleration Tuesday, September 01, 20096:04 PM

NXT-G Page 50

This unit plugs into port 2 by default.

Chapter Seven: Building a Mount for Sound SensorsTuesday, September 01, 20096:08 PM

NXT-G Page 51

This program is nearly identical to the one dealing with touch sensors in the previous chapter. Create a new program called: "React_to_Sound"


Guess what! That's it! If you download and run this program now, the robot will move forward until it encounters a loud sound.

~~~~~~~~~~~~~~~

React_To_Sound

From here, go to properties and select "unlimited" for the number of rotations. We want he robot to move until it hears a loud sound, only stopping if the sound is above the defined level.

Just like in the previous program, you want the function to run until the sound sensor reaches a desired level.

To set the desired level to stop at, go to the properties bar the default level of the sound being greater than 50 will work well if you are in a quiet room.


Chapter Seven: Stopping with a Sound SensorTuesday, September 01, 20096:30 PM

NXT-G Page 52

One unique thing you can do with a sound sensor is control the level of power given to the motors. With this in mind, you can create a program where a robot will move faster or slower based on the level of sound it is receiving.

To begin, create a new program called "Sound_Acceleration"

Because in this program you will be evaluating the level of sound and adjusting the speed of the motors multiple times, this entire program will need to be in a loop. This loop can be left to repeat infinitely.

Within the loop, place a sensor block to receive the level of sound from a sound sensor. By default, the sound sensors are attached to port 2.The level of sound a sensor returns as a value is a number between one and one hundred.

Now insert a move function from the "common" menu, placing it after the sound sensor on the program timeline. Click the drop down menu for data wire connectors on the move function.

The sixth connection down is the "power" level. The number that is set to this value controls the power level the motors are given, and thus the speed the robot travels at.

A higher value gives you a greater amount of power, therefore if the sound sensor reports a higher level of sound, the robot will go faster.Also, make sure to change the rotations of the motors to unlimited.

You can download and run the program at this time.

Sound_Acceleration


Chapter Seven: Sound for AccelerationTuesday, September 01, 20096:52 PM

NXT-G Page 53

Ultrasonic sensors are a bit more important than sound sensors. For some robots, the ultrasonic sensor will have the most programming out of any other system. These sensors return a value based on the distance an object is in either inches or centimeters . They work relatively like sonar.


Use ultrasonic sensors to turn a robot at a distance from an object.-

Print a distance to a screen-

Approach an object if it is within a range -

You will need:


Your NXT Device-

A Sound Sensor and mount-

A USB cable-

Ultrasonic_Sensor

Left is a PDF included by Lego that gives a short overview of sound sensors.

Chapter Eight: Ultrasonic SensorsTuesday, September 01, 20099:26 PM

NXT-G Page 54

Chapter Eight: Building a Mount for Ultrasonic SensorsTuesday, September 01, 20099:43 PM

NXT-G Page 55

Wire this to port 4 for typical programming.

NXT-G Page 56

The following use of the ultrasonic sensor is actually quite much like the programs we have created in the past that forces the program to quit when the sensors returned a true value.

Instead of quitting, this program will cause the robot to turn when it gets within a specified distance.

Start by creating a new program called "Turn_at_Distance"

Turn_at_Distance

Seeing as this program will not need to end, that is, the robot can keep driving in a square, the first thing you will need to create is a loop function for the program to go into.

As with most programs, you want your robot to move forward to begin with. You should set the rotation value to unlimited, seeing as the robot will move forward until it is within a distance of an object.

Did you catch that keyword? Use a wait function with the ultrasonic sensor to have your robot move forward until the prerequisite is met.

In the properties bar, you can set the values of the distance your robot should be within. You can also change weather they are inches or centimeters. Set it to less than 60 Centimeters.

Remember, this program is going to have the robot turn when it comes within range. To turn, create a new move block from the common menu.

To have the robot turn right sharply, drag the slider in the properties bar for steering all the way to the right.

To have the robot turn about 90 degrees, have the duration reduced to only half a rotation.

You can download and run at this time Source code ---->

Chapter Eight: Turning at a DistanceTuesday, September 01, 20099:51 PM

NXT-G Page 57

The following use of the ultrasonic sensor is actually quite much like the programs we have created in the past that forces the program to quit when the sensors returned a true value.

Instead of quitting, this program will cause the robot to turn when it gets within a specified distance.

As with most programs, you want your robot to move forward to begin with. You should set the rotation value to unlimited, seeing as the robot will move forward until it is within a distance of an object.

To have the robot turn right sharply, drag the slider in the properties bar for steering all the way to the right.

NXT-G Page 58

Sometimes it helps to know what your sensors are doing in order to create a program that works with them well, or to spot errors. Just like when we printed out the state of the NXT buttons, you can print out the distance of an object from the ultrasonic sensor.

Create a new program called "View_Distance".

If you want to use the value the ultrasonic sensor is currently returning, you need to use a sensor block, specifically that of the ultrasonic type.

If you download and run this program now, it will print out the distance from the ultrasonic sensor that an object is.

~~~~~~~~~~~~~~

View_Distance

Like most programs you have created, you want the screen to display readings constantly. Of course, this means that you have to put all of the program within a loop.

Seeing as the data wire coming off of the ultrasonic sensor is carrying a number, that is the distance from current object, you can convert this number to text by using the number to text function found under the advanced menu.

Using what you already know, it isn't difficult to see that this text is going to be output to the screen. Create a display function, make sure to switch the action to text, and create a data wire from the number to text function to it.


Chapter Eight: Print a DistanceTuesday, September 01, 200910:23 PM

NXT-G Page 59

One of the useful functions that can be used in conjunction with the ultrasonic sensor is the range function. As a logical function, it reports if a value is within two values by returning a Boolean.

To begin, create a new program called "Range_Control"

In this program you will only move forward if an object is within range. As you could imagine, this will mean you will need to check the range multiple times and therefore the program will need to be in a loop.

Of course you are going to need an ultrasonic sensor block to return the value of the distance you are currently away from an object, however to compute range you will also need a range block. They can be found under the data menu. Be sure to link a data wire between the output of the ultrasonic sensor, and the input on the range function.

As with most statements that have a logic based return, we only want the robot to accelerate if the range is within 50 and 65. Use a switch statement to set up the structure necessary to act only on a true value.

From the properties bar, set the range to be within 50 and 65. Change the sensor to that this is centimeters.

Because this is going to move until it is out of the range, place a move block within the "true" tab of the switch statement.

Chapter Eight: The Range FunctionTuesday, September 01, 200910:41 PM

NXT-G Page 60

This logic works for stationary objects of course, so if you were to download and run this code now the robot would approach an object until it got within range of it, however we want this code to work for moving objects.

Download and run the program at this time. You may notice that the robot moves forward in bursts. That is because every time the switch statement's loop is evaluated, the wheels rotate once.

~~~~~~~~~~~~~~~

Range_Control

To continually evaluate if the object has moved out of range, you will need to create a loop within the switch statement. At this point you can also get rid of the wait statement, seeing as this will be logically ended. Also, switch the move function to rotate once if it is not doing so already. From within this new function we will check again to see if after moving the values returned from the ultrasonic sensors are within the specified range.

You want this robot to move forward until it is out of range. Logically speaking, if the robot is approaching an object, the range should decrease. If the object were stationary, you could program the robot to approach it until the sensor reached the lower end of the range.

You will use the exact piece of code used before to see if you are within the range of the object. You can copy and paste if you would like.Just make sure your two range functions match in the values they are comparing.


NXT-G Page 61

Light sensors are just as important to a well working robot as ultrasonic sensors can be. A light sensor has limitations much to the same degree as the sound sensor does. Just as a sound sensor can only measure the "loudness" of sound, light sensors can only determine the intensity of the color. Light sensors can not discern colors from one another in any way beyond how dark the color is. They certainly can not be used as cameras to navigate an environment.


Use a light sensor to stop at a black line-

Use a light sensor to return a value-

Use a light sensor to follow a black line-

Use switch statements based off of light sensor's returns -

You will need:


Your NXT Device-

A Light Sensor and mount-

A USB cable-

A Black length of tape-

Light_Sensor


Chapter Nine: Light SensorsWednesday, September 02, 200912:01 AM

NXT-G Page 62

Wire this to port three by default.

Chapter Nine: Building a Light Sensor MountWednesday, September 02, 20095:57 PM

NXT-G Page 63

The following lesson is much like the ones in past chapters dealing with stopping a robot using a sensor.If you so choose, you can skip this lesson and advance to the next one. A bit of warning though, light sensors are introduced in this portion of the program.

Create a new program called: "React_to_Light"


Just like in the previous program, you want the function to run until the light sensor is activated. Anytime you logically use anything until anything else is done, you use a wait function.

With this in mind, you will need to tweak the settings of your program depending on the environment a robot will be working in. Seeing as in this program you want the robot to stop at a black line, it should return a value well over fifty. What you don't want to happen is the normal environment your robot is traveling over to be dark enough to trip a function.

You may also notice the "generate light" option. This will cause a little LED on the sensor to light up adding additional value to the return of the sensor.

If you download and run this program now, the robot will move forward until the light sensor comes over a black line.

From here, go to properties and select "unlimited" for the amount of rotations. We want he robot to move until it hits an obstacle, only stopping if the light sensor detects a high value.

In this instance, change the control of the wait function to sensor and select "light sensor" as the type of sensor. Notice that light sensors use port three as default.


If you consult the properties bar for the light sensor wait function, you will see two unique options. The first option sets the threshold for the "darkness" a color must be to trip the wait function. If you will be operating the robot on a light colored surface such as carpet, < 40 is fine.

React_to_Light

~~~~~~~~~~~~~~~

Chapter Nine: Stopping Using a Light SensorWednesday, September 02, 20096:02 PM

NXT-G Page 64

Again, this lesson may sound a bit repetitive from the work you did with ultrasonic sensors, however designing a system that can return the values of an environment you are working in can be invaluable useful in setting the thresholds in values.

Sometimes it helps to know what your sensors are doing in order to create a program that works with them well, or to spot errors. Just like when we printed out the state of the NXT buttons, you can print out the value a light sensor is returning.

Create a new program called "View_Light".

If you want to use the value the light sensor is currently returning, you need to use a sensor block, specifically that of the light type.

If you download and run this program now, it will print out the amount of light a surface is currently reflecting. Note that generating light will change this.

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Like most programs you have created, you want the screen to display readings constantly. Of course, this means that you have to put all of the program within a loop.

Seeing as the data wire coming off of the light sensor is carrying a number, that is the "shade" of current surface, you can convert this number to text by using the number to text function found under the advanced menu.

Using what you already know, it isn't difficult to see that this text is going to be output to the screen. Create a display function, make sure to switch the action to text, and create a data wire from the number to text function to it.


View_Light

Chapter Nine: Print a Value from the Light SensorWednesday, September 02, 20096:44 PM

NXT-G Page 65

This is most likely one of the most common (and useful) uses of the light sensor is to cause a robot to follow a line. In many robotic competitions, there are markings on the field designed to allow users to control robots in just that way.

To begin, create a new program called "Follow_Line".

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Because want the robot to continually check to see if it is on the line, the entire program should exist within a loop. As you may have noticed by now, many programs use a loop to repeat themselves indefinitely.

Within this loop, create a switch statement with it's sensor setting set to light sensors. Switch statements for light sensors compare the level of light to a set level. If the level is true, code within this tab will execute.

To set the level of light for the switch statement to act on, use the compare option. For this lesson, set it to less than forty.

Now consider for a moment what this switch statement is doing. It is comparing two values, the current amount of light and the number 40, and then acting accordingly. This piece of code will do the EXACT same thing. In programming, there are often multiple ways to do the same thing. It takes a good programmer to decide which method to choose. For now, stick with the first switch statement we chose. Do not enter the code to the left

Logically, to follow a line you need to turn to stay on it. To help the robot stay centered, it will need to turn in both directions. For the "true" side of the statement, we will have the robot turn right until it is off of the line. For the "false" side, the robot will turn left.

The easiest way to turn in this manner is to brake one side of the robot and to give power to the other.

Chapter Nine: Following a LineWednesday, September 02, 20096:56 PM

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No switch over to the other tab in the switch statement:

As it is, this robot will only turn counter clockwise when "looking" for a line. With this in mind, you can have the robot go around a square or circle of black tape in a counter clockwise fashion. The light sensor is mounted in the center of the robot, therefore the wheels are always evenly spaced over the line even when it makes a turn.

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When you are done, download and run the program. Just know that you will need black tape or something of the like to make this program work properly.

Follow_Line

In the true portion of the switch statement, first set the motor in port B to brake by going into the properties bar and unchecking "c"

Next, set motor C to turn forward unlimitedly, till the switch statement stops.

Within this section of the switch statement (the false one), you want to brake the C motor and turn the B one. With the current setup, the robot will turn one way if it's on the line, and another if it's not.


NXT-G Page 67

Lego motors have built in sensors that are able to detect the degree the motor it turned to. In most commercially available motors, sensors such as this are called encoders and are mounted and implemented separately from the motor. Lego makes it easy for you.


Create a robot that moves and displays the rotation of the sensor. -

Reset the rotation sensors-

Commit a position to memory and have the robot turn back to that point.-

You will need:

The robot from chapter one-

Your NXT Device-

A USB cable-

Interactive_Motor


Chapter Ten: Motor EncodersWednesday, September 02, 20099:19 PM

NXT-G Page 68

In the following lesson you will be displaying the current position of the motor as a robot moves forward. When working with rotation sensors, it is important to note that the rotation of one wheel is not always exactly the same as another, especially after turning the robot. When you are dealing with rotation, typically you will only choose one motor. Be logical in your choice.

To begin, create a new program called "display_position"

Within the loop, first insert a rotation sensor block to return the current orientation of the encoder.

You can now download and run the program.

display_position

Like the programs we have created in the past, this will also exist within a loop, seeing as you will need to continually display the current rotation of the motor as well as move forward.

By default, the sensor is set to return the orientation of the motor attached to port A. In your current robot, there should not be any attachments to that port. Change the sensor to use port C, which controls the left motor. You can select the port in the properties bar for the rotation sensor block.

Like the other functions you have had print values to the screen, convert the rotation output of the sensor block to text and create a display function to print to the screen the current output of that text block.

This program would work fine as it is, however in order to actually make sense it requires the robot to move forward. Create a move function with unlimited rotations as well as a power setting of about 40.

By setting the power settings to be lower, it is easier to see the rise of the rotation sensors.


Chapter Ten: Displaying Motor PositionThursday, September 03, 20098:01 PM

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As you may notice, the sensors do not stop at 360 degrees. This can be helpful in determining the exact number of rotations a motor and wheel have turned, however it often does little help in determining direction. Luckily, you can reset the value of a rotation sensor so that it starts back from zero.

We will be using the code from the previous lesson for this one.

Download and run the program now. The display should count up to 360 as the wheels turn, and then start over a 0 when they make a complete rotation.

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display_position

To begin, place a new rotation sensor block before the existing one. Remember to change the port the sensor is monitoring the motor of to match the one in the function you were using previously.In this case, I have used C, the motor used to control the left side of the robot.

Here you will need to use a comparative operator. Remember, we only want to reset the count for rotations if the motor has turned past 360 degrees. To do so, we need to compare the current state of the rotation sensor to 360 and reset only if it is greater.

Here, insert a switch statement to act upon the comparison. The type of switch statement should be logical, seeing as comparative operators only return true or false values.

Within the "true" portion of the switch statement, place another sensor block for rotation. Just as you have with the others, make sure to adjust the port to match the motor you are monitoring. Within the properties bar, select reset as the action to act upon if the rotation is greater than 360.


Chapter Ten: Resetting the RotationThursday, September 03, 20098:46 PM

NXT-G Page 70

If you are working with the kit part number W979797, then chances are you will not have this sensor in your box. If by chance your team or instructor has purchased one, then I have included this to show the usefulness of the sensors.

Although the robot includes built in sensors on the motor, it is much easier to pass a single number into functions than it is to calculate the orientation of a robot based on both wheels.


Not do anything… After working with the sensors in NXT-G their usefulness has let me down. To truly utilize these sensors consider using LabView or RobotC. Otherwise, use the rotation sensors to accomplish the same task.

Chapter Eleven: Compass SensorsThursday, September 03, 200911:10 AM

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Okay, let's face it: you are now a programmer. As you develop more complex programs, you may start to loose track of what things are doing what. As a developer it is important to know what EVERY piece of code is doing at all times.

Take for example, the first program we created. You really don’t need to explain to a user that the code makes the robot go forward, right ? Due to it's size and relative simplicity, it is easy for another person to come and look at your program and understand what everything is doing.

In more complex programs, such as the one with the light sensor that follows a line, it is more difficult to tell what is going on. Often it is helpful to type in little comments that explain what the code is doing.

To add comments to code, change the cursor type to "comment" by clicking on the icon in the taskbar.

This will allow you to click anywhere within a program and add text.

Comments do nothing to the program structure and are entirely optional.

Also note that comments do not affect the size of the file on the NXT.If you are avoiding commenting to conserve space, it will defeat the purpose.Besides, if your program is that big, you are going to need them!

Chapter Twelve: Commenting in CodeThursday, September 03, 200911:10 AM

NXT-G Page 72

There may come a time that you need to use multiple touch sensors in conjunction with other sensors. Seeing as the robot only has room for 4 sensors, lego made a multiplexer to "split" one port into four for use by up to three additional sensors.


Display which sensor is being pressed based on touch multiplexer.-

Display multiple values simultaneously. -

Chapter Thirteen: Touch MultiplexersThursday, September 03, 200911:11 AM

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Touch multiplexers are not actually Lego products. They are produced by HiTechnic to be used with the NXT Device. To attach this to an NXT, plug in the cable to the single port on the multiplexer labeled NXT.

To begin programming, create a new program called "Mulit_Test"

If run now, your program will display text if the button is pressed. To display if multiple buttons are pressed, create another switch statement just like the one you just created, but this time do insert the value of touch sensor two from the multiplexer. Change the line of the display to line 4 as well, making sure to uncheck the "clear" box. Also make sure to reset the screen if no buttons are pressed.Download and run this program now.

Multi_Test

As with any program that will continually check the state of a sensor, you will need to create a loop to put all of your content in. Due to it's use of touch sensors, the multiplexer itself is a type of sensor.

From within the sensor menu, find the multiplexer block. It looks like a succession of four touch sensor icons. Place this within the loop.

The sensor block itself might look a little odd, seeing as the value types it returns appear to be text. Looks can be deceiving however, seeing as the value they return are actually Booleans. T1 returns the value of the button. Note that this eliminates the "bump" option, seeing a button is either pressed or it is not.

To create a function that displays the state of the button pressed on the multiplexer, create a logic based switch statement that contains a display function under it's true condition. Have it display text on line three, and turn clearing off.


Chapter Thirteen: Using a MultiplexerFriday, September 04, 200910:12 PM

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There is a feature on the NXT that allows the device to capture the motor movements and play them back in a short sequence. It's a neat feature, however it rarely comes in helpful unless you want to create a program that does not perform a predefined set of actions

In this program you will:

Record a set of movement by manually moving around the roobt-

Play back the sequence of events. -

Chapter Fourteen: Action ReplayThursday, September 03, 200911:11 AM

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The record function allows the robot to create a short recording of it's sensor readings and motor movements and then replicate them later in the program.

To begin, create a new program called "Action_Replay"

Much unlike some of the other programs we have created this far, the record function will not need to be placed in a loop, seeing as nothing is being done in repetition.

Instead, to begin this program, first place the "record and play" function from the common menu onto the timeline. Make sure the action is set to record what is happening.

Download and run the program at this time. The record as it is used in this program requires you to manually move around the robot as you would move around a toy truck or other plaything.

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Action_Replay

The function is set to record the rotations of the motors attached to ports B and C for thirty seconds. Set it to 5.

When the function is through recording, it is often helpful to notify the users so they can let go. Play a tone when the function has finished.

Instead of playing right when the function finishes recording, create a wait function so that users can put back down the robot after the tone has sounded.

Of course, now you want the robot to play back the file that you had recorded for it to follow. Switch the action to "play" in the properties bar.


Chapter Fourteen: Action ReplaySaturday, September 05, 20098:13 AM

NXT-G Page 76

One of the most important features of the NXT Devices are their ability to communicate with bluetooth devices. In my opinion, this is the BEST thing you will cover in this entire manual. Period. Having control over robots or giving robots control over one another makes things quite easy.


Learn to pair your NXT with another NXT device-

Write code that will return a value to a receiving device. -

Chapter Sixteen: Sending Bluetooth MessagesThursday, September 03, 200911:12 AM

NXT-G Page 77

In order for bluetooth to actually do anything, you have to communicate with a device. I apologize in advanced that I am unable to provide screenshots based on what is happening in my explanation. The NXT screen is easy enough to navigate, so if you do get stuck just reread where you got confused.

To begin, turn on your NXT. Press the right arrow three times until the screen shows bluetooth.

From this menu press right until you see the On/Off option. Make sure that your bluetooth has been turned on, seeing as you won't be able to connect devices if it is not.

Once your bluetooth is on, go back into the bluetooth menu and select "visibility"Make sure your NXT is set to "visible", which should look like an open eye.

Finally, from the Bluetooh menu select "search" to scan for nearby bluetooth devices. Make sure that the device you are connecting to has been set up in the same manner as the above.

Select the name of the device you would like to connect to from the menu and press enter.You will be asked which connection you want to assign this device to, make sure you select connection 1 for this lesson. The connection you select allows you to write code for multiple devices.

Once you select the connection, you will be asked for a password. Enter the same code on both devices. It is typical to use 0000 or 1234, seeing as this does not need to be extremly secure. You are building leog robots, not launching a rocket to mars.

Once you enter passwords on both devices, the NXT should beep again. If you now look up in the upper left hand corner, the bluetooth symbol should be proceeded by < >, which means it is communicating with another device.

This connection will last as long as both devices are turned on. Once you have turned one of them off, you will have to restart the connection. Restarting the connection is much easier than searching for a new one, so to demonstrate turn off both NXT's and then power them back on.

You will notice that the upper left corner now only shows < after the bluetooth symbol.

Again, go into the bluetooth menu, however this time instead of pressing "search", press "My Contacts" If you have multiple contacts, scroll through till you see the name of the device you would like to connect to. Press the orange enter key twice to connect, making sure to select connection 1.

That's it! You can connect up to four devices, just remember that you may need to remove the batteries and let the unit sit for a while after any connections. Bluetooth tends to be spotty and can get in the way sometimes, however if used correctly it can be a great tool.

Chapter Sixteen: Pairing DevicesSaturday, September 05, 20091:18 PM

NXT-G Page 78

To actually do anything with the code, you will need to write two programs. One of which will send values to control the other. The program we will create in this lesson will go onto the first NXT.

To begin, create a new program called "SEND_Message"

If you can't already tell, this is going to be the software on the SENDING end of the program. Sending a message is an action, therefore the block for it can be found under the action menu.

As it is, your program may not appear to do much, however that is because you need a back end. You can download it to the first NXT at this time, however realize that it will not do anything specific at this time. That part comes later…

SEND_Message

Because this program will be sending messages only when buttons are pressed, the entire program will need to exist within a loop so that the states of the buttons can continually be checked.

Seeing as we only want the program on the other device to react if we press a key or not, create logic based switch statements fed by button sensors.

Although only one is shown, create three of them. One for each button.

Go ahead and place the message block within the "true" portion of each of the switch statements created for each button.

When you connected the two NXTs, you assigned the contact information to connection 1. When sending messages in bluetooth, send to the connection which your back end is running on.Because we want the program to act differently based on which button is pressed, have the function send 1 for the left button, 2 for the middle, and 3 for the right.


Chapter Sixteen: Sending Messages

NXT-G Page 79

I chose to cover this in a separate chapter because this type of control requires an entire different array of functions as well as requiring developers to create new programs as well. Receiving messages from bluetooth is often much more complex than just sending them. If you are on a FTC team, a good third of your code will come from developing actions based on the input given from controllers.


Create a program to act upon the controls in "SEND_Message" -

Learn to use numerically based switch statements to streamline code.-

Chapter Seventeen: Receiving Bluetooth MessagesThursday, September 03, 200911:12 AM

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One of the most basic applications you can use to test bluetooth connections are display functions based on which key is pressed.

To begin, create a new program called "GET_Message".

Believe it or not, bluetooth messages are actually categorized as sensors. It makes sense if you think about it though, seeing as they return a dynamic value based on an external input. Put one within the loop statement and go to it's properties bar.

Thinking logically, if you press the left key in "SEND_Message" bluetooth sends the value 1 to connection 1. The receive bluetooth function acts on this and passes it on to the switch statement.

Of course, you want your robot to continually check to see if there is bluetooth action to act upon, therefore the entire program will need to exist within a loop. As you can tell from writing well over 20 programs, a good deal use loops constantly.

Change the type of message to be numeric, seeing as in the previous program we wrote a function to send a number for bluetooth.

Connect the data wire from the numeric output to a number based switch statement. Make sure to add two more conditions to the statement

In the switch function, have 1 display "Left Button", 2 "Enter Button", and 3 "Right Button". If no key is pressed, the function receives 0. Use this part of the switch statement to reset the screen if no key is pressed.If this causes the screen to flicker, do not use it.

Download and run the program on the second controller now. Connect and run both programs.

GET_Message


Chapter Seventeen: Displaying MessagesSaturday, September 05, 20092:10 PM

NXT-G Page 81

To be quite honest, I was unable to set up the Field Management System on my own computer.

The FMS is a system released by First Robotics that can be found here: http://www.education.rec.ri.cmu.edu/content/events/ftc/robotc/index.htm

It is designed to be used for FTC competitions, seeing as FFL games are nearly entirely autonomus. The system uses protocols that First added into your NXT-G program in order to allow bluetooth messages to control robots easier.

The functions above are used to receive bluetooth transmissions from a computer running the Field management system and allow you to use the input for your programs.

If you installed the NXT-G disk that came with a normal lego kit, then chances are you do not have this software. You need to use the software distributed by First in your Lego kit of parts to use the above functions and by extension the field management system.

When using controls based on the Field Management system, First requires you to abide by a template created by them that will allow the Autonomous and Manual systems to be switched over.

The templates can be found at the same address as the FMS, however for your convenience I have included one below.

TeleOp

The template allow the Field Management System to switch from autonomous and Tele-Op modes based on the part of the match that is currently going on.

Again, seeing as the FMS requires a good deal of configuration I am unable to fully explain how to use the templates at the moment. The comments in the templates, however, will be helpful should you choose to read them.

Chapter Eighteen: Using the Field Management SystemThursday, September 03, 200911:12 AM

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http://www.education.rec.ri.cmu.edu/content/events/ftc/robotc/index.htm

Documents

NXT-G Programming Guide