Book excerpt: Turn your iPhone or iPad into the hub of a distributed sensor network with the help of an Arduino microcontroller. With this concise guide, you’ll learn how to connect an external sensor to an iOS device and have them talk to each other through Arduino. You’ll also build an iOS application that will parse the sensor values it receives and plot the resulting measurements, all in real-time. iOS processes data from its own onboard sensors, and now you can extend its reach with this simple, low-cost project. If you're an Objective-C programmer who likes to experiment, this book explains the basics of Arduino and other hardware components you need—and lets you have fun in the process. Learn how to connect the Arduino platform to any iOS device Build a simple application to control your Arduino directly from an iPad Gather measurements from an ultrasonic range finder and display them on your iPhone Connect an iPhone, iPad, or iPod Touch to an XBee radio network Explore other methods for connecting external sensors to iOS, including Ethernet and the MIDI protocol