arduino voltage

How much volt i must give to arduino?

7 to 12V into the barrel connector. Best DC, but as there is a simple diode you can also try 9V AC if you feel audacious:-)

You can also supply +5v on the +5V line through a regulator or regulated power supply. I would not advice putting AC in. You are fine to put 12 or 15V on the barrel connector as well, it is just the regulators will get hotter which could limit how much extra current you can draw for things like motors and LEDs.

Joking aside, there is really no reason to not apply AC.

Two things to consider: - The peak voltage must not exceed the rating fpr the capacitors. - As every other half wave is missing, the capacitors have to buffer this, limiting the regulatable current to less than I = U/10ms*C = 900 V/s*47uF = 40 mA

You are fine to put 12 or 15V on the barrel connector as well, it is just the regulators will get hotter which could limit how much extra current you can draw for things like motors and LEDs.

So much fun today! Look, Oettam, the more current you need, the lower the voltage you should apply to your board. This is not really contradictary, but electronics ;D

there is really no reason to not apply AC.

Well I would say that the smoothing capacitors on the input to the regulator are not sufficiently large to get away with AC.

the more current you need, the lower the voltage you should apply to your board

True, for a detailed look at the figures for this:- http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

can i use four AA(1.5v)batteries??? exuse my english but i am italian

Alas, neither for the 5 volts nor for the barrel input. Even italian batteries start fresh with around 1.65 volts, this adds up to 6.6 Volts which is dangerous for the chip and to low for the voltage regulator.

There are two options: (1) you can use 4 RECHARGEABLE batteries @1.2 volts (2) you can use 5 or 6 battries for the regulator input; there are harnesses for 6 packs...

Alas, neither for the 5 volts nor for the barrel input. Even italian batteries start fresh with around 1.65 volts, this adds up to 6.6 Volts

What about using diodes? They can't waste nearly as much power as the regulator...

They can't waste nearly as much power as the regulator...

Sorry they waste exactly the same amount of power as liner regulators, it's physics. The wasted energy has to go somewhere and it ends up as heat.