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3 Owen Bishop

4 Elsevier, Inc., the author(s), and any person or firm involved in the writing, editing, or production (collectively Makers ) of this book ( the Work ) do not guarantee or warrant the results to be obtained from the Work. There is no guarantee of any kind, expressed or implied, regarding the Work or its contents. The Work is sold AS IS and WITHOUT WARRANTY. You may have other legal rights, which vary from state to state. In no event will Makers be liable to you for damages, including any loss of profits, lost savings, or other incidental or consequential damages arising out from the Work or its contents. Because some states do not allow the exclusion or limitation of liability for consequential or incidental damages, the above limitation may not apply to you. You should always use reasonable care, including backup and other appropriate precautions, when working with computers, networks, data, and files. Syngress Media, Syngress, Career Advancement Through Skill Enhancement, Ask the Author UPDATE, and Hack Proofing, are registered trademarks of Elsevier, Inc. Syngress: The Definition of a Serious Security Library, Mission Critical, and The Only Way to Stop a Hacker is to Think Like One are trademarks of Elsevier, Inc. Brands and product names mentioned in this book are trademarks or service marks of their respective companies. KEY SERIAL NUMBER 001 HJIRTCV PO9873D5FG KM8NJH2 004 BAL923457U 005 CVPLQ6WQ VBP965T5T5 007 HJJJ863WD3E GVTWMK MP5SDJT 010 IMWQ295T6T PUBLISHED BY Syngress Publishing, Inc. Elsevier, Inc. 30 Corporate Drive Burlington, MA Programming Lego Mindstorms NXT Copyright 2008 by Elsevier, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher, with the exception that the program listings may be entered, stored, and executed in a computer system, but they may not be reproduced for publication. Printed in the United States of America ISBN 13: Page Layout and Art: SPi Publishing Services Copy Editor: Judy Eby For information on rights, translations, and bulk sales, contact Matt Pedersen, Commercial Sales Director and Rights, at Syngress Publishing; m.pedersen@elsevier.com.

5 Author Owen Bishop is the author of over 80 books, mostly on electronics and computing, including the best-selling Commodore 64 Games Book. His most recent publication is the Robot Builder s Cookbook (Elsevier/Newnes, 2007). Owen s talent for introducing the world s of electronics and computing has long been proven fact with his textbooks, professional introductions and hobby guides being chosen by thousands of students, lecturers and enthusiasts. With Owen s clear program descriptions you can get your robot up and running quickly, even if you are a beginner, and have fun whilst doing so. Educated in England, at Bristol University and the University of Oxford, Owen has lived and worked in several countries as a science education adviser for UNESCO and the British Council. He is at present a freelance technical writer, living in Perth, Western Australia. v

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7 Contents Chapter 1 Robots and Programs Introduction What is a Program? Designing a Robot Specify the Robot s Environment Intelligent or Smart? Summary Chapter 2 About NXT-G Programs Introduction Creating a Program First Steps Out of Memory? Coming for a Spin? Tying it Together Chapter 3 Data Introduction Sources of Data Variables A Variable Has a Name, a Type, and a Value Arithmetic Operators Logical Operators Flag Variables Chapter 4 Loops Introduction Outside Events Time Limit Counting the Loops Dance Some More Use Loops to Make Actions Repeat Another Way to Use the Loop Counter Logical Conclusions Use a Loop (or a Wait Block) to Wait for an Event to Occur Nested Loops The Wait Block vii

8 viii Contents Chapter 5 Switches and Other Topics The Switch Block Switch Blocks Direct Execution Along Alternative Pathways Simultaneous Processing Diagnostic Programming Chapter 6 Using the Light Sensor Introduction Light Sensor Directed Downward Lined in Line Follower Edge Follower Light Sensor Directed Upward Housefly Light Sensor Directed Forward Lightfinder LightFinder Almost an Interrupt LightFinder LightFinder Summary Chapter 7 Using the Touch Sensor and the NXT Buttons Introduction Waiting for Contact Bumper Waiting for Input Scanning the NXT Buttons Entering Numbers Chapter 8 Using the Ultrasonic Sensor Introduction Avoidance Routine for Alpha Rex Ultrasonic Search Chapter 9 Sounds Received and Emitted Introduction Start and Stop Start, Stop, and Turn One Clap or Two? Playing a Tune (with a Little Dance)

9 Contents ix Choreography Song Snippets Dance Snippets Chapter 10 The Magnetic Compass Sensor Introduction Heading in the Right Direction Polygon Circle Chapter 11 More Mathematics Introduction Floating Point Arithmetic Calculating Cosines Calculating Sines Square Root Factorials Combinations X modulo Y Modulo Counting Chapter 12 Navigation Introduction Distance Traveled Magnetic Compass Edge Follower No-go Response to a Line Steering Alpha Rex Marching Orders Rex On Line Rex On Edge Pathfinder Cosine Rule Chapter 13 Games Robots Play Introduction Maze Runner Version Maze Runner Version Maze Runner Version Maze Learner Scissors, Paper, Stone

10 x Contents Signalling by Semaphore Magic The Program Chapter 14 Databases for Robots Introduction Lookup Table for Weekdays Writable Lookup Table Another Way of Using a Lookup Table Reading Data from a File Access Block Acknowledgements Index