NBC_tutorial.pdf

Programming Lego Robots

using NBC

(Version 0.02, Oct 31, 2006)

by Ross Crawford

Preface

The Lego MindStorms NXT robot is a wonderful new toy from which a wide variety of robots can be

constructed, that can be programmed to do all sorts of complicated tasks. Unfortunately, the software that comes

with the robot, although visually attractive and much more powerful than the RIS software for the RCX, is still

somewhat limited in its functionality. To unleash the full power of your robot, you need a different programming

environment. NBC is a programming language, written by John Hansen, which is especially designed for the

Lego robots. If you have never written a program before, don't worry. NBC is really easy to use and this tutorial

will tell you all about it. Actually, programming robots in NBC is a lot easier than programming a normal

computer, so this is a chance to become a programmer in an easy way.

To make writing programs even easier, there is the Bricx Command Center. This utility helps you to write your

programs, to send them to the robot, and to start and stop the robot. Bricx Command Center works almost like a

text processor, but with some extras. This tutorial will use Bricx Command Center (version 3.3.7.15 or higher) as

programming environment. You can download it for free from the web at the address

http://bricxcc.sourceforge.net/

Bricx Command Center runs on Windows PC’s (95, 98, ME, NT, 2K, XP). The language NBC can also be

downloaded from the web at address

http://bricxcc.sourceforge.net/nbc/

Acknowledgements

I would like to thank John Hansen for developing NBC. Also many thanks to Mark Overmars for writing his

NQC tutorial, on which this is heavily based.

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Contents

Preface ___________________________________________________________________ 2

Acknowledgements ____________________________________________________________________ 2

Contents __________________________________________________________________ 3

I. Writing your first program __________________________________________________ 5

Building a robot ______________________________________________________________________ 5

Starting Bricx Command Center __________________________________________________________ 5

Writing the program ___________________________________________________________________ 6

Running the program __________________________________________________________________ 7

Errors in your program _________________________________________________________________ 8

Changing the speed ____________________________________________________________________ 9

Adding comments _____________________________________________________________________ 9

Summary ___________________________________________________________________________ 10

II. Using variables _________________________________________________________ 11

Moving in different ways ______________________________________________________________ 11

Displaying results on the screen _________________________________________________________ 13

Random numbers ____________________________________________________________________ 13

Summary ___________________________________________________________________________ 14

III. Flow Control __________________________________________________________ 15

The cmp and tst statements _____________________________________________________________ 15

The brcmp and brtst statements__________________________________________________________ 16

The jmp statement ____________________________________________________________________ 16

Loops – repeating code ________________________________________________________________ 18

Summary ___________________________________________________________________________ 19

IV. Sensors _______________________________________________________________ 20

Waiting for a sensor __________________________________________________________________ 20

Acting on a touch sensor _______________________________________________________________ 21

Light sensors ________________________________________________________________________ 21

Summary ___________________________________________________________________________ 23

V. Making music___________________________________________________________ 24

Playing tones ________________________________________________________________________ 24

Playing files ________________________________________________________________________ 24

Creating your own sound files __________________________________________________________ 25

Summary ___________________________________________________________________________ 26

VI. Threads and subroutines _________________________________________________ 27

Threads ____________________________________________________________________________ 27

Subroutines _________________________________________________________________________ 27

Defining macros _____________________________________________________________________ 28

Summary ___________________________________________________________________________ 29

VII. More about motors _____________________________________________________ 30

Stopping gently ______________________________________________________________________ 30

Synchronising motors _________________________________________________________________ 30

Regulating the motor speed_____________________________________________________________ 30

Rotating a specific angle _______________________________________________________________ 31

More advanced motor control ___________________________________________________________ 31

Summary ___________________________________________________________________________ 32

VIII. More about sensors ____________________________________________________ 33

Sensor type _________________________________________________________________________ 33

Sensor mode ________________________________________________________________________ 33

Sound sensor ________________________________________________________________________ 34

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Motor as a rotation sensor ______________________________________________________________ 34

Ultrasonic sensor_____________________________________________________________________ 35

More advanced sensor control __________________________________________________________ 35

Putting it all together__________________________________________________________________ 36

Summary ___________________________________________________________________________ 37

IX. Parallel threads ________________________________________________________ 38

A wrong program ____________________________________________________________________ 38

Using mutexes_______________________________________________________________________ 38

Summary ___________________________________________________________________________ 39

X. Communication between robots ____________________________________________ 40

Communication with other NXT bricks ___________________________________________________ 40

Communication with a PC _____________________________________________________________ 40

Communication with other Bluetooth devices ______________________________________________ 40

Summary ___________________________________________________________________________ 40

XI. More commands ________________________________________________________ 41

System calls ________________________________________________________________________ 41

System clock ________________________________________________________________________ 41

Arrays _____________________________________________________________________________ 42

Type declarations ____________________________________________________________________ 43

Type aliases_________________________________________________________________________ 44

Summary ___________________________________________________________________________ 45

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I. Writing your first program

In this chapter I will show you how to write an extremely simple program. We are going to program a robot to

move forwards for 4 seconds, then backwards for another 4 seconds, and then stop. Not very spectacular but it

will introduce you to the basic idea of programming. And it will show you how easy this is. But before we can

write a program, we first need a robot.

Building a robot

The robot we will use throughout this tutorial is the “Tribot”, the instructions for which are included with your

NXT set. If you are new to LEGO robotics, I recommend doing the tutorials that come with the LEGO software,

to get acquainted with what your NXT can do. Your robot should look like this:

(Note that you may already have added sensors and a grabber – if so, you should remove them temporarily, as

some of the examples may not work correctly with them attached.)

Starting Bricx Command Center

We write our programs using Bricx Command Center. Start it by double clicking on the icon BricxCC. (I assume

you already installed Bricx Command Center. If not, download it from the web site (see the preface), and install

it in any directory you like.) The program will ask you where to locate the robot. Switch the robot on and press

OK . The program will (most likely) automatically find the robot. Now the user interface appears as shown below

(without a window).

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