Arduino Internals. Dale Wheat

Transcription

1 Arduino Internals Dale Wheat

2 Arduino Internals Copyright 2011 by Dale Wheat All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior written permission of the copyright owner and the publisher. ISBN-13 (pbk): ISBN-13 (electronic): Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, logos, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. President and Publisher: Paul Manning Lead Editor: Ralph Moore Technical Reviewer: Sam Kelly, Jordi Muñoz Editorial Board: Steve Anglin, Mark Beckner, Ewan Buckingham, Gary Cornell, Morgan Ertel, Jonathan Gennick, Jonathan Hassell, Robert Hutchinson, Michelle Lowman, James Markham, Matthew Moodie, Jeff Olson, Jeffrey Pepper, Douglas Pundick, Ben Renow-Clarke, Dominic Shakeshaft, Gwenan Spearing, Matt Wade, Tom Welsh Coordinating Editor: Corbin Collins Copy Editors: Tiffany Taylor, Heather Lang Production Support: Patrick Cunningham Indexer: SPi GlobalArtist: SPi Global Artist: SPi GlobalArtist: SPi Global Cover Designer: Anna Ishchenko Distributed to the book trade worldwide by Springer Science+Business Media, LLC., 233 Spring Street, 6th Floor, New York, NY Phone SPRINGER, fax (201) , orders-ny@springersbm.com, or visit For information on translations, please rights@apress.com, or visit Apress and friends of ED books may be purchased in bulk for academic, corporate, or promotional use. ebook versions and licenses are also available for most titles. For more information, reference our Special Bulk Sales ebook Licensing web page at The information in this book is distributed on an as is basis, without warranty. Although every precaution has been taken in the preparation of this work, neither the author(s) nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in this work. Any source code or other supplementary materials referenced by the author in this text is available to readers at For detailed information about how to locate your book s source code, go to

3 To my wife, Anne. Her love, patience, faith, trust and support are what made this book even remotely possible. While she has her own area of technical expertise (she is a Registered Nurse), this is perhaps the only part of this book that she is ever going to read. And that's fine with me. Thank you, beloved.

4 Contents at a Glance About the Author... xv About the Technical Reviewers... xvi Acknowledgments... xvii Preface... xviii Chapter 1: Hardware... 1 Chapter 2: Software Chapter 3: Atmel AVR Chapter 4: Supporting Hardware Chapter 5: Arduino Software Chapter 6: Optimizations Chapter 7: Hardware Plus Software Chapter 8: Example Projects Chapter 9: Project Management Chapter 10: Hardware Design Chapter 11: Software Design Chapter 12: Networking Chapter 13: More Example Projects Index iv

5 Contents About the Authors... xv About the Technical Reviewers... xvi Acknowledgments... xvii Preface... xviii Chapter 1: Hardware... 1 What Is an Arduino?... 1 The Arduino Uno... 2 Processor... 3 Serial Port... 5 Power Supply... 5 Expansion Connectors... 6 Shields... 9 The Arduino Mega Previous Hardware Arduino Serial Arduino USB Arduino Extreme Arduino Nuova Generazione (New Generation) Arduino Diecimila Arduino Duemilanove Arduino Mega v

6 CONTENTS Who Makes Arduinos? Officially Licensed Products Everybody Else Build Your Own Arduino Printed Circuit Boards Breadboard Arduinos Summary Chapter 2: Software Hosts and Targets Step by Step Step 1: Write Some Code Step 2: Compile the Code Step 3: Program the Device Step 4: Test and Debug Step 5. Repeat Semiautomatic Blinking in C Going Further Summary Chapter 3: Atmel AVR Origins AVR Device Families When in Doubt: Product Datasheets Device Packaging Through-Hole DIPs Surface-Mount Devices (SMDs) Extra Pins vi

7 CONTENTS Pin Descriptions Power Pins AVR Core Clock Sources Address Spaces Instruction Set Internal Peripherals General Purpose Input/Output (I/O) External Interrupts Timer/Counters USART Two-Wire Serial Interface (TWI), a.k.a. I 2 C Analog Inputs Summary Chapter 4: Supporting Hardware Schematic Diagrams Component Types Reference Designators Component Values Component Value Tolerances Other Component Parameters The Connections Getting Power to the Board The Barrel Connector Input Power Conditioning Voltage Regulator Power Circuit Evolution vii

8 CONTENTS Serial Interface RS-232 Interface The Processor Power Consumption I/O Drive Capability The -RESET Signal The Time Base Decoupling Capacitors Blinky Lights Room for Expansion The Mechanical Form Factor Universal Serial Bus (USB): Signals Plus Power Summary Chapter 5: Arduino Software Open Source Software Multiplatform Support The Arduino Heritage Installing the Software The Process, or How to Arduino A Tour of the User Interface The File Menu The Edit Menu and the Edit Context Menu The Sketch Menu The Tools Menu The Help Menu Summary viii

9 CONTENTS Chapter 6: Optimizations How Will You Know It Worked? Shrink Blink How Blink Works Measuring Space-Saving Optimizations Code Analysis Life Without pinmode() Abbr. & Shrtcts Binary Notation Further Analysis Easy Toggling Further Reduction Wasting Time More Efficiently Using Lower-Level Code Saving Space with Simple Serial Communication What Hello, world! Does Writing to Configuration Registers Transmitting Data A String of Characters Printing Numbers Saving SRAM Measuring SRAM Requirements The Bare Minimum Memory Sections Where Variables Live Using the Appropriate Data Type Strings of Characters, Revisited Low Power or High Speed? ix

10 CONTENTS Electronic Measurements The Arduino as Test Equipment As Fast As Possible Slowing It Down Further Power Reductions Summary Chapter 7: Hardware Plus Software Available Peripherals Serial Port(s) General-Purpose Digital Inputs and Outputs Timers and Counters Pulse-Width-Modulation (PWM) Outputs Analog Inputs External Interrupts Interrupt Reference Summary Chapter 8: Example Projects Beyond the Blinking LED: Starting Simply Slow Enough Mostly Optimized Six-Channel Dimmer It s Dim, Alright Other Uses for a Blinking LED Infrared Remote Control TV-B-Gone A Lot of Blinking LEDs A Direct-Drive Example Direct-Drive with LED Drivers Multiplexing Techniques x

11 CONTENTS A Digital Clock Accuracy User Interface Additional Features Summary Chapter 9: Project Management Documentation Source-Code Comments Whitespace Code What You Mean, Mean What You Code Automated Documentation Writing For Your Audience Hardware Documentation Going Further Teamwork and Collaborative Development Blogs Forums Wikis Revision Control Systems A Note About Revision- or Version-Numbering Project-Hosting Web Sites Licensing Your Work Patents and Trademarks Copyright Open Source The Public Domain Summary xi

12 CONTENTS Chapter 10: Hardware Design Learning About Hardware Things You Must Have Things You Want Infrared Proximity Sensor A Modest Prototype Some Modest Improvements Printed Circuit Boards PCB Layout Techniques A First Attempt A More Compact Version Making the Connection Your Own Custom Arduino Compatibility with Existing Arduinos and Shields Power Supply Options Processor Selection Anything Else? Design Software CadSoft EAGLE EAGLE Tips Summary Chapter 11: Software Design Advanced Topics Within Arduino Writing Arduino Libraries Alternate Cores xii

13 CONTENTS And Without Arduino The Bare Metal, Revisited Other Development Environments Summary Chapter 12: Networking Point-to-Point Networking Talking Over the Serial Port Arduino to Arduino MIDI: Musical Instrument Digital Interface The Internet Summary Chapter 13: More Example Projects An Autonomous Robot Power Supply Motion Control Electric Motors and Actuators Sensors Light Sensors Touch Sensors Noncontact Sensors Audio Sensors Indicators, Controls, and Other Forms of Communication Control Systems Open-Loop Systems Closed-Loop Systems xiii

14 CONTENTS Example Robot Projects A Practice Robot The Next Robot Your Ultimate Robot Summary Index xiv

15 About the Author Dale Wheat is a full-time freelance writer, specializing in electronics and embedded systems. He has written several articles for technical and hobbyist magazines such as Circuit Cellar, O'Reilly's MAKE magazine, and Elektor. He teaches classes on electronics, microcontrollers, and soldering skills. He designs and sells DIY electronics kits from his website, dalewheat.com. Before becoming a full-time writer, Dale consulted as a computer programmer and systems analyst for several companies, including IBM, MCI, and GTE (now Verizon). Dale is a two-term past president of the Dallas Personal Robotics Group, the world's oldest personal robotics club. He is a member of the National Honor Society, Phi Theta Kappa, and intends to continue his education as long as they keep the doors open. He lives with his wife, Anne, near Dallas, Texas. xv

16 About the Technical Reviewers Sam Kelly is an electronic design engineer at 3D Robotics, the open-source hardware side of the DIY Drones amateur UAV community. He is a native San Diegan, but got his Electronics Engineering degree in Tijuana, Mexico in 2009, specializing in digital systems. He has been at 3D Robotics since 2010, doing PCB design for internal and community OSHW (open source hardware) projects, as well as product photography. He enjoys eating his own dog food with the rest of 3D Robotics, spending any free time flying prototype and production quadcopters and drones. Jordi Muñoz is from Ensenada, Baja California, Mexico. He grew up in Tijuana and was influenced by California in all ways, specially in technology. He spent most of his childhood building complex Lego projects and opening any electronic device in his possession. He moved to Riverside, CA in 2007 (legally) and while waiting for his residency started an Arduino aircraft autopilot project. He and Chris Anderson from the small community of DIY Drones founded 3D Robotics, an Arduinobased autopilot company. The company started in a garage, using DIY stuff and Arduino to create many products. In 2010 he and Chris won the Sparkfun UAV competition. Jordi has been featured in many newspapers and magazines in Mexico and the USA. 3D Robotics grew exponentially from a house garage to a 10,000 square-foot facility in just one year. Now the company is located in San Diego, CA close to his hometown. xvi

17 Acknowledgments You see a single name on the cover of this book. That's because I did it all myself! Bwahahahaha! Ahem. Actually, that's not entirely true. It seems I had some help. Okay, a lot of help, from a lot of people. I didn't actually invent the Arduino, myself, per se. That was actually the Arduino Team, and they keep inventing and re-inventing the Arduino. Thanks go to the Arduino Team for giving us something wonderful upon which we can build to our heart's content. Several companies and individuals contributed ideas, hardware, software, and photos to help make this book possible. I'd like to thank Marc de Vinck for giving me my very first Arduino (a Duemilanove with an ATmega328 woot!) as well as the ever-so-useful Maker Shield, which he designed. Marc also inspired me to bring my very first DIY electronic kit to market. Jimmie P. Rodgers gave me the LoL (lots of LEDs) Shield that appears in Chapter 8. Andy of Spikenzie Labs gave me the fabulous Solder : Time watch you see in Chapter 8 as well. I'd also like to make special mention of those kind folk that contributed many of the photographs, including the Arduino Team, Critter & Guitari, Seeedstudio, Gravitech, SparkFun Electronics, Fundamental Logic, Jimmie P. Rodgers, Wayne and Layne, Spikenzie Labs, and SparkFun Electronics. The crew at Apress runs a first-class operation. I'd like to thank my editorial team for their professionalism, courtesy, enthusiasm, and most of all patience in getting this book from concept to reality: Corbin Collins, Frank Pohlmann, Michelle Lowman, Ralph Moore, Jim Markham, Sam Kelly, Jordi Muñoz, and the eagle-eyed Tiffany Taylor. I'd like to thank James Floyd Kelly for his words of wisdom and encouragement, when they were needed the most. On the home front, I especially want to thank my parents and my children for their enthusiasm on behalf of this project. My wife, Anne, deserves extra special thanks for leaving me alone when I needed that and keeping me company when I needed that. xvii

18 Preface Let's investigate the inner-workings of your Arduino. It appears to be a simple machine, but it is not. Much effort has been invested to make it easy to learn and use. Unfortunately, these good intentions can mask some of the Arduino's underlying capabilities. You suspected that there was more, much more, under the simplistic veneer. You were right. This book is about how Arduino actually works. The Arduino is a successful composite of design decisions that has evolved over time. By giving you a more in-depth understanding of the complex technologies involved, you will see the Arduino "internals" as elements to be changed and re-arranged to suit your design goals. Intended Audience This book is written for Arduino users of all stripes, from energetic newcomers to seasoned professionals. You already know what an Arduino is, and you have some ideas about what it can accomplish for you. You most likely already own one or have access to one. These are not requirements, just guesses. Your interest in Arduino and its inner mysteries is enough. We don't have to spend any time going over the very basics here; introductory Arduino tutorials are everywhere. This book both covers a lot of ground in depth and hopes to follow you on your journey; it s not meant ot be discarded and useless after you blink your first LED. What This Book Isn't This book does not attempt to teach you basic electronics in any structured manner. However, because you're an inquisitive and clever sort of person, you will probably pick up a lot of valuable electronic basics by looking at the example projects and exercises. Much effort and technical review has been invested to ensure the examples presented are based on sound design principles. This is also not an introduction to programming. It is assumed that you know how to manipulate code with an editor and follow simple instructions to accomplish specific tasks. Again, your curious nature will let you absorb "by osmosis" some of the programming examples and styles illustrated in the book, which strive to be clear and well-written. In no way do any of these chapters contain all the information available on a particular subject. Practical and useful information is presented; references to more detailed information is given. Arduino, like any other complex system, is a moving target. As Heraclitus observed more than 2,500 years ago, you cannot step into the same river twice. It was true then and it remains true today, especially with the swiftly evolving Arduino. You should know that this book is not merely a collection of technical information without a context. The shiny polish of the Arduino, as the world see it, hides layer after layer of complex solutions to complex design challenges. Revealing these layers in a meaningful and understandable order is what this book is all about. xviii

19 PREFACE Finally, this book is not just a collection of random, unrelated Arduino projects. The projects and exercises in this book are included to illustrate and reinforce important design principles, to incrementally build from simple to more complex designs, and finally to help you better imagine what is possible, both with Arduino and beyond. Chapter Overview Have a look at the table of contents and get an idea of just how far down the rabbit hole we're going to go. This book strives to be a balanced source of technical reference material, so each chapter should be able to stand on its own. It wouldn't kill you to read the chapters in the order presented. However, feel free to jump around and sample what you like. There's more here than meets the eye. As a rule, the chapters go from the general to the specific. If you skip around a lot and get stranded, try backing up a chapter or two to make sure you have the proper grounding and then proceed forward again. Chapter 1: Hardware We look at the available Arduino models and take a peek inside. Chapter 2: Software We run into software at every level of Arduino development. Here is the overview. Chapter 3: Atmel AVR The "brain" of the Arduino is a microcosm in itself. Knowing what it can and cannot do can be the difference between success and failure in your project. Chapter 4: Supporting Hardware The rest of the components play important roles, as well. Knowing what they can do and their limits helps you build a better mousetrap. Chapter 5: Arduino Software The free Arduino-provided software will get you started quickly and easily. It looks simple but it isn't. Chapter 6: Optimizations Many optimizations are possible in your sketches, and this chapter shows you how to both implement them and verify them with precise measurement techniques. Chapter 7: Hardware and Software Combined The cooperation of hardware and software, when they cooperate at all, can produce amazing results. A detailed tour of the built-in peripherals in the AVR helps you do more with less code. The general purpose I/O ports, the USART (serial port), counters. timers, PWM outputs, and analog inputs are examined in detail, with examples. The use of interrupts helps to maximize the cooperation between hardware and software. Chapter 8: Example Projects A blinking LED? Seriously? What it takes to actually blink an LED with authority. What it takes to make a more complex project: a digital clock. xix

20 PREFACE Chapter 9: Project Management Dealing with development issues, such as documentation, collaboration, and licensing. Chapter 10: Hardware Design Starting from the ground up, literally, we cover the areas of expertise needed to design your own Arduino-compatible or not-so-compatible hardware. This includes power requirements, processor selection, and shield design. Several hardware design automation tools are examined. Chapter 11: Software Design Beyond sketches: Making sound software decisions depends on knowing your options. Alternative development environments, library development and documentation, and PC-side applications are discussed. You can even design your own software tools. Chapter 12: Networking Networking your Arduino is as easy as deciding who you want to talk to and what you want to talk about; in theory, that is. In reality, it's always more complicated. Leverage the built-in communication capability of your Arduino to talk to a variety of interesting devices. Add application-specific hardware to extend your network as far as you want. Even a simple web server is possible with the addition of some inexpensive hardware. Chapter 13: More Example Projects A small autonomous robot is in reality a collection of individual projects that must work together. You'll need everything you've learned so far in this book to make this one work. Summary The goal of this book is to be an exploration, compendium, and reference for the neglected innerworkings of the Arduino architecture. Leveraging this knowledge will save you time and improve the quality of your Arduino projects. Hopefully it will also spark your interest in embedded system design and prompt you towards more ambitious projects in the future. Good luck! Don't forget to have some fun along the way! xx