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I just want to confirm something before I wire up my first ever Arduino project and fry all the stuff I just spent money on.

It is my understanding that the Vin power input will tolerate a 9V battery and use voltage regulators to pare it down to either 3.3V or 5V (as different parts of the board require). So it is then my assumption that if I have a 9V battery running to Vin, that I could then connect a power wire to the 3.3V connector, and reliably get a 3.3V signal (and ditto for 5V), yes?

Or, is it that they are input jacks expecting either 3.3V or 5V signals? I guess I'm confused over this:

  • Will Vin then power the 3.3V and 5V inputs, giving me access to voltage at that level; or
  • Do I have to choose between 3.3V, 5V or Vin, and only use one of those to power my board (with the appropriate voltage level)
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    Have you checked the schematic yet? – Ignacio Vazquez-Abrams Jun 8 '15 at 16:07
  • If you can provide a schematic I'll check it out and maybe it answers my question, but I'm so new to electronics, I may not even be able to make sense of it. – smeeb Jun 8 '15 at 16:09
  • All Arduino product pages link to a schematic for the board. – Ignacio Vazquez-Abrams Jun 8 '15 at 16:09
  • Then I would assume this is what you mean, in which case, I cannot at this exact moment make sense of it. And although I think I can guess your next argument, which is probably "Well then you need to learn how to read schematics, otherwise get out of electronics", I would counter-argue that Arduino is from the ground-up aimed at complete electronics newbies like myself. And that this is a basic usage question that should be answer-able without a moderate understanding of EE/ECE. – smeeb Jun 8 '15 at 16:16
  • And yes, in time, I will learn this stuff, but I shouldn't have to be able to read that diagram and fully comprehend it to understand how to connect my board to a battery. – smeeb Jun 8 '15 at 16:17
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DC Jack is connected, through a diode, to Vin.

Vin is stepped down to 5V on-board.

5V is stepped down to 3V3 on board.

Thus you can do any one of the following numbered items.

  1. Connect a 7-12V supply to the DC Jack; thus:

    • use Vin as a supply @ DC - 0.7V for off-board peripherals, and
    • use 5V as a supply for off-board peripherals, and
    • use 3V3 as a supply for off-board peripherals.
  2. Connect a 6-12V supply to Vin; thus:

    • use 5V as a supply for off-board peripherals, and
    • use 3V3 as a supply for off-board peripherals.
  3. Connect 5V supply to the 5V; thus:

    • use 3V3 as a supply for off-board peripherals.

The above is only guaranteed for boards that follow the reference schematic, as plenty of clone/compatible boards do. If you buy a cheap Chinarduino and something doesn't work, or the thing breaks, after following anything above then that's your tough luck.

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Yes your assumption is correct you can power 3.3v and 5v items from those pins as long as you don't take more current than the onboard regulator(s) can supply

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