savard wrote:When I replace UNO with a Arduino Leonardo (ID: 849), are the pins (5, 4, 3) in the same alignment with Leonardo as with UNO?
Yep. The mechanical layouts (where the pin headers go) are the same. The main difference is that the Leonardo uses a microcontroller that does its own USB, where older UNOs have a separate chip to handle USB. That does create some small programming issues (the serial connection disappears and reappears every time you reset the board), but for basic programming and plugging-in-shields, they're pretty much the same.
savard wrote:On the Leonardo board (ID: 849), is it possible to replace the power supply with the battery. If so – what would be required? How much voltage and how much current should I be applying to the board from the battery?
Again, yes. Running Arduinos from battery packs is common.
Your best bet is a 4-AA battery pack like this one: http://www.adafruit.com/products/830
You can even add a plug that fits the Arduino's power jack: http://www.adafruit.com/products/369
The Arduino runs at 5v and has an on-board voltage regulator. It can accept external power from supplies between 6v-20v, but prefers 7-12v if possible. A four-pack of AAs works fine. The microcontroller can supply 40mA per pin, but its upper limit is about 200mA at any one time. AA batteries usually have around 2000mA-hrs of energy, which is good for about 10 hours of continuous runtime.
If you want to be fancy, you can use the MintyBoost (http://www.adafruit.com/products/14
) which boosts the power from two AAs to 5v and supplies 500mA of current. That will power an Arduino through the USB port, just like your computer does.
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