Although many people experiment with low-power modes, reducing the clock speed and general circuit optimisation in order to minimise the current drain of their Arduino projects, the best solution will always be to have the entire thing turned off when not required. However to the untrained designed this may seem difficult to do, but it isn't. By recreating the circuit published by Instructables user "port3793" you can add a "soft latch" power switch to your Arduino (or any other microcontroller platform). This circuit gives control of the total power supply by way of a digital output that can control a P-channel MOSFET.
Then it's a simple matter of deciding when to power off in the sketch. Furthermore an external sensor, timing circuit or other trigger can also switch the circuit on - for example a solar-powered PIR can trigger the soft latch and turn on the Arduino after detecting movement in order to log the data or send a wireless signal - and then power off again. It's quite versatile and a great idea. For the circuit, example sketch and more visit the project Instructable. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
When adding external circuitry such as the soft switch described above to your project, and need to make it more permanent than using a solderless breadboard - consider our range of ProtoShields. From the tiny LeoStick to the Mega range, we offer a complete range for you to work with.
