The need for energy efficiency may not spring to mind when creating general Arduino-based projects as a fair amount of them may not leave the comfort of USB power. However if you're designing remote data-logging devices running from solar-charged batteries, or placing the device in a somewhat inaccessible location - the longer it can run from a set power source the better.
For some interesting experiments in running an Arduino-compatible circuit for longer, the people behind the "heliosoph" site have demonstrated various methods of using sleep mode, experimenting with the AVR fuses and also disabling various I/O functions of the microcontroller to bring the current draw down to the micro-ampere level.
Their series of articles has a variety of interesting tips, and even shows how long you can run a circuit from some capacitors. To find out more, visit their interesting website. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're wanting to experiment with low-power Arduino-compatible circuits, then you'll need a an ATmega328P MCUs with Arduino Uno bootloader:
This is the same Atmel AVR ATmega328P microcontroller used in the official Arduino Uno, as well as our Eleven, EtherTen, USBDroid, and other boards. Perfect for building your own Arduino-compatible project directly on a breadboard or on a custom PCB, or for replacing the MCU in an existing board. Comes with the Arduino Uno bootloader pre-installed. Better still, it even has a special label stuck on top with details of the pinout, so you don't even need to look up the datasheet when connecting it up in your project! For more information and to order, click here!