You carry an amazing scientific instrument around in your pocket every day, using it for mundane tasks like making phone calls or listening to music. Your iPad 2 is as fast as a Cray-2 supercomputer from just a few decades ago, yet most people only use it to read books or surf the Web. What a waste.

This book is all about connecting your iPhone, iPod Touch, or iPad to the real world. You’ll start by learning how to access the sensors built right into your device. Next you’ll see how to connect wired sensors through the headphone port using a wonderful little device called HiJack. Several chapters show various ways to use Bluetooth low energy to connect to sensors, Arduino microcontrollers, motor controllers, and even other iPhones or iPads. Finally, you’ll see exactly how to use WiFi to connect to the Internet or physical devices connected to WiFi devices.

It would be pretty boring to make all of these connections just to make a few LEDs light up, so the book is organized around fun, interesting projects. The built-in sensors are used to create a metal detector. HiJack is hooked up to a simple electrical device so it can be used as a plant moisture sensor. Bluetooth low energy connects to a Texas Instruments SensorTag to detect acceleration to track the flight of a model rocket, and later to an Arduino microcontroller to hack a radio-controlled car, showing how to create robots and control them with your iPhone. Bluetooth low energy can also be used for peer-to-peer communication between iOS devices. You will learn how this is done by creating an arcade game that uses iPhones for game paddles. WiFi will be hooked up to a serial bridge to control servos, ultimately hacking a candy dispenser to give you candy under iPhone control.

Our look at each topic starts with a chapter that introduces the basic concepts using a simple project. One or more chapters follow these introductions, presenting the fun projects just mentioned. You may not want to build every one of them yourself, but reading through how they are created and how they work, you will get ideas about how to build your own projects.

You don’t need to go through this book linearly. If a project in the middle of the book seems really interesting, jump right to it. Each chapter starts with a section called “About This Chapter.” It lists the prerequisites, telling you which other chapters contain information you might need before attempting the project in the chapter you are interested in.

All of the hardware in the book is developed with electronic components you can buy from many Internet stores, but some of it is hard to find locally. Plan ahead. Glance at the parts list in a chapter a week or two before you want to get started, and order the parts you need.

Finally, the projects in this book cover several disciplines. There’s a lot of software, quite a bit of electronics, and a fair amount of mechanical engineering involved. Some of the stuff in this book is going to seem beyond your abilities. I know a few of the projects seemed that way to me as I wrote the book. After all, even though most of us have some technical ability, either through education or experience with hobbies, almost no one is fully qualified at computer science, electrical engineering, mechanical engineering, and physics.

Be brave, grasshopper.

Everything is laid out very carefully. If you don’t know much about software, start with the completely developed programs in the book, all of which are built right into techBASIC. If you don’t know one end of a battery from another, just wire stuff as you see it in the diagrams and photos that carefully document each circuit. As you learn more, you can experiment. Sure, there will be some failures along the way. I burned out a circuit or two and crashed a lot of software writing the book, and you’ll do the same as you read it. That’s how we learn.

I hope you don’t just build the projects in this book, though. The whole point is to learn how to do things, not just follow some plans. Whether you’re a professional trying to figure out how to remotely access data from a buried seismograph, a student exploring robotics for a science fair project, or an inventor tinkering with awesome ideas in your garage, I hope this book gives you some techniques and ideas that will enable you to create amazing things by combining software, electronics, and mechanics to build devices.

So, let’s go forth and control our world!

Conventions Used in This Book

The following typographical conventions are used in this book:

Indicates new terms, URLs, email addresses, filenames, and file extensions.
Constant width
Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords.
Constant width bold
Shows commands or other text that should be typed literally by the user.
Constant width italic
Shows text that should be replaced with user-supplied values or by values determined by context.


This icon signifies a tip, suggestion, or general note.


This icon indicates a warning or caution.

Using Code Examples

This book is here to help you get your job done. Where this book includes code examples, you may use the code in this book in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “Building iPhone and iPad Electronic Projects by Mike Westerfield (O’Reilly). Copyright 2013 James M. Westerfield, 978-1-449-36350-5.”

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at .

Safari® Books Online


Safari Books Online is an on-demand digital library that delivers expert content in both book and video form from the world’s leading authors in technology and business.

Technology professionals, software developers, web designers, and business and creative professionals use Safari Books Online as their primary resource for research, problem solving, learning, and certification training.

Safari Books Online offers a range of product mixes and pricing programs for organizations, government agencies, and individuals. Subscribers have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kaufmann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and dozens more. For more information about Safari Books Online, please visit us online.

How to Contact Us

Please address comments and questions concerning this book to the publisher:

O’Reilly Media, Inc.
1005 Gravenstein Highway North
Sebastopol, CA 95472
800-998-9938 (in the United States or Canada)
707-829-0515 (international or local)
707-829-0104 (fax)

We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at

To comment or ask technical questions about this book, send email to .

For more information about our books, courses, conferences, and news, see our website at

Find us on Facebook:

Follow us on Twitter:

Watch us on YouTube:


When I was a young nerd toting my slide rule back and forth to the library, one of my favorite books was The Amateur Scientist, a collection of articles from Scientific American. It was a remarkably diverse collection of projects. I added a significant amount of wear to that book, and eventually bought and wore out my own copy.

I hope this book is a lot like that one—it’s a book of projects, some of which you’re unlikely to take the time to build yourself. I hope you wear it out thumbing through the pages. As you do, though, keep in mind that it’s not the work of a single person. Oh, sure, I wrote it, but as Newton famously remarked, “If I have seen further it is by standing on the shoulders of giants.”

I owe a great deal to the people who educated me, both in and out of the classroom. A lot of them were in the early Apple II community. I won’t even try to name them, but you can find their footprints all through this book. Check out the KansasFest archives to meet some of these astoundingly creative people.

My wife is an amazing person. She’s my cheerleader, my critic, and the first person to read and correct each page. She watched our house as it was taken over by rockets, robot cars, and remote-controlled gadgets, encouraging me without complaining about the mess. She even pitched in on many of the projects. Among other things, the eyeball in Chapter 11 is her artwork. What an amazing best friend.

Thomas Schmid from the University of Utah took the time to answer a lot of questions about the HiJack, no doubt keeping me from frying a few. Like a lot of components, HiJack is manufactured by Seeed Studio. Leslie Liao from Seeed Studio kindly supplied the book’s reviewers with HiJacks so they could try the projects in Chapter 4 and Chapter 5.

I have some great new Internet friends at the Texas Instruments facility in Norway. Jarle Bøe was fantastic, getting me started with the SensorTag before it even came out. He also let me use some of his photos, which are credited in the text. His staff was more than just helpful—Jomar Hoensi even wrote a special version of the firmware so it could collect data up to ±8G for rocket flights, and took the time to answer a lot of neophyte questions as I came up to speed on Bluetooth low energy. The rockets you see in Chapter 7 exist because of their efforts. I’m happy to say the rockets got to go to Norway for some trade shows, even if I never made it there myself.

My reviewers patiently slogged through all or part of this book. The amazing and talented Ryan family made up most of the reviewers. Kevin Ryan, Jess Finley, and Ken Moreland spent countless hours making sure everything worked and the descriptions were clear enough to follow. They even had electronics parties where they got together to build the projects. Doyle Maleche joined, from afar, bringing his experience as an educator to bear on the book. I even got to get acquainted with a great O’Reilly author, Alasdair Allan, who took the time to review parts of the book. Their comments made this a much better book than it would otherwise have been.

I’ve done a lot of writing for magazines over the years, and published software with a number of companies. While this is my first traditional book, I’ve worked with publishers and editors for a long time. I was pretty lucky to get some early training and encouragement from the editors and writers at Call A.P.P.L.E. I had pretty much given up on finding a publisher that really cared that much about its authors and products, but O’Reilly sure seems to be another one. I’ve been fortunate to have two great editors on this book. Brian Jepson got me started, then handed me off to Courtney Nash when Make: split from O’Reilly. Finding two people of their quality in a row says a lot for this company. If you decide to write, be sure to drop them a line. They are good people.

So, to all of you, from the Apple II buds in my early years to my newest friends at O’Reilly, thanks for making me look good!


While modified for the book, Chapter 5 originally appeared in the June 2012 issue of Nuts & Volts Magazine and is reprinted by permission of T & L Publications, Inc.

The SensorTag photo from Chapter 6 is courtesy of Jarle Bøe at Texas Instruments.

The illustration of the declination of the Earth’s magnetic field in Chapter 3 is courtesy of Wikimedia Commons.

Get Building iPhone and iPad Electronic Projects now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.