Build an Arduino the Size of an AA Battery
One of the great things about Arduino is that it is completely open source, so you can create your own variations. An example is the AAduino by DIYer Johan Kanflo, the size of an AA battery.
The Kanflo project is a wireless Arduino clone that needs to work in a way that doesn’t consume a lot of battery power, so it’s pretty low power. However, there is a lot in it and it should be able to support all kinds of fun Arduino projects. It’s not easy to do it yourself by any means, but if you go to the Kanflo page on GitHub, you’ll find a complete guide to making it for you.
AAduino | Github