Thank you very much for your answers!
One last question about the battery, if you are speaking of them.
I would like to power the whole circuit from a 2.1mm DC jack like the one that the UNO has.
In my theory it will work with 7-12V DC adapters, with 9V batteries (six AA or even "PP3"), etc (everything 7-20V or so).
Is there anything wrong with PP3, or why have you mentioned it?