Sparkfun has an interesting article on some considerations to keep in mind when working on an Extreme Low Power Microcontroller Design. When you have a design that will be running on battery power it is important to keep power consumption in mind so that the system will work for days and not hours on battery power. I was quite impressed to read that the cheap Sparkfun meter has a uA mode that my much more expensive Fluke meter did not have. I might have to get one of these cheap meters or one of Dave Jones uCurrent device to measure some of these low currents on future projects.
“My overall goal was to get an ATmega328 to go to the deepest sleep possible, waking up only with an external INT button interrupt or with a 32.768kHz TMR2 overflow interrupt (for an RTC). To make this happen you’ll need to tweak the bootloader and some other settings.
In the end I was able to get a ATmega328 to run at room temperature at about 1uA with an active 32kHz RTC and external interrupts enabled. This is fairly phenomenal. Atmel has engineered the ATmega328 to the point that rubbing your fingers together produces more electrical power than a computer capable of 8MIPS on the fly.”