# Ardiuno voltages - Beginner

Discussion in 'Microcontrollers, Programming and IoT' started by 8bit, Mar 22, 2017.

1. ### 8bit

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Oct 30, 2013
I just wondered why the Uno board has a 3.3v input plus a 9v input, seems a rather big variation in range(?)

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,299
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Jan 21, 2010
Isn't the Uno 5V?

One input (the lower one) is the voltage the microcontroller runs from. You must supply the correct voltage here.

The other one (the higher one) is an input to a voltage regulator. This will provide the lower voltage to for the microcontroller from a less accurate but higher voltage. If using this, the lower voltage pin can be tapped for a small amount of current.

3. ### Austin Clark

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Aug 29, 2016
The Uno doesn't really have a 3.3V input. That's an OUTPUT, coming from an on-board 3.3V regulator. It's just convenient to have, since many electronics that you will likely use with the Arduino run at 3.3V.

The microcontroller on the Arduino can technically run at either 3.3V or 5V, but is usually 5V (as is the case with the Arduino, which also has a 5V regulator for this purpose). The "9V" input provides power to the 5V and 3.3V regulators (should you choose to use them).

4. ### 8bit

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Oct 30, 2013
Many thanks for the info. So anything higher than 9v would burn the board out?

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
No, I think they recommend 7 to 12V with 6 to 20 bring acceptable (check that though)

At higher voltages the regulator will get quite hot.

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6. ### 8bit

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Oct 30, 2013
Thanks. The reason I ask is that I am building a project that I would like to run with rechargeable AA batteries. The problem is the battery packs I have hold 8 batteries. 8x 1.5v would be around 12V and I was worried it would burn the board.

7. ### Bluejets

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Oct 5, 2014
Arduino have a "raw" input that will take up to 12v. Either use nicads or nimh as dry cells will go over this level when new and arduino will be damaged. I'd be investing in a smaller holder and run the uc from a lower level.

Last edited: Mar 23, 2017
8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
From the Arduino web site:

One final note. The Arduino's on-board regulator can actually handle up to 20V or more, so you can actually use an adapter that puts out 20V DC. The reasons you don't want to do that are twofold: you'll lose most of that voltage in heat, which is terribly inefficient. Secondly, the nice 9V pin on the Arduino board will actually be putting out 20V or so, which could lead to potential disaster when you connect something expensive to what you thought was the 9V pin. Our advice is to stick with the 9V or 12V DC adapter.
If you're powering it with batteries, keeping it between 9 and 12V is a good aim, but if new alkaline cells take it to 13.5V, you'll be fine.

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9. ### Bluejets

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Oct 5, 2014
Thanks Steve, I stand corrected.
Trouble is many times when one reads entries on the forums, some come up with figures that support my statement, and they are well known pro's at the game too.
Still, overall it seems a bit over the top to want to supply a uc with 12v when it mostly runs on 5v.
Guess one must provide for all users.
For one, the battery is too large, for others they can't get it big enough, can't win.
Bit like the three bears.

10. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Other than is really hard to get a 7*AA cell holder, 7 cells would be near perfect.

I guess you could make a dummy battery to fill the 8th slot...

But then the batteries tend to come in 2's, 4's, 8's, etc., so you'd always have one battery left over.

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11. ### 8bit

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Oct 30, 2013
Thanks all. Yes the battery holders do come in rather odd configurations. I have one that holds 3 AA, one that holds 2 and another that holds 8. :s

12. ### 8bit

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Oct 30, 2013
Actually I have dug out a battery holder that takes 8 AAs. It would add up to 12v but I guess the rechargeable batteries won't be that efficient so the final voltage will be a little less(??)

13. ### BobK

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Jan 5, 2010
NiMH are nominally 1.2V, so you will get about 9.6V typically. But they do charge to about 1.4V so you will get 11.2V when they are freshly charged.

Bob

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14. ### 8bit

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Oct 30, 2013
Appreciate the info. Thanks Bob.