Book excerpt: Atmel's AVR microcontrollers are the chips that power Arduino, and are the go-to chip for many hobbyist and hardware hacking projects. In this book you'll set aside the layers of abstraction provided by the Arduino environment and learn how to program AVR microcontrollers directly. In doing so, you'll get closer to the chip and you'll be able to squeeze more power and features out of it. Each chapter of this book is centered around projects that incorporate that particular microcontroller topic. Each project includes schematics, code, and illustrations of a working project. Program a range of AVR chips Extend and re-use other people’s code and circuits Interface with USB, I2C, and SPI peripheral devices Learn to access the full range of power and speed of the microcontroller Build projects including Cylon Eyes, a Square-Wave Organ, an AM Radio, a Passive Light-Sensor Alarm, Temperature Logger, and more Understand what's happening behind the scenes even when using the Arduino IDE