Will it still run on less than 5 volts? Will it break?

  • 4
    Can you be more specific? Are you talking about the power supply voltage, a digital input pin, an analog input pin?
    – jfpoilpret
    Commented Feb 25, 2014 at 6:22

1 Answer 1


Will it break at < 5V? Not likely.

  • Check the datasheet for the IC's on the board and find the minimum power supply voltage the device works at.
  • At typical ATmega328 Safe Operating Area (under "Speed grades" in the datasheet) specifies approximately 4.1V for 16MHz.
  • If you require to use the USB interface, you'll have to check the datasheet for that chip too.

Will it run at < 5V? Maybe.

  • If the supply voltage gets below the minimum operational voltage, the controller may behave erratically. That means it can do anything (un)expected. This value is in the datasheet and probably somewhere around 2.7V.
  • If the Brown Out circuit is configured (in fuses), then the controller will switch itself off when supply voltage gets too low to prevent undefined situations. Once the supply voltage returns, it restarts.

Will it break at > 5V? Depends on where you apply it.

  • V(IN) should work fine for 7-20VDC as it is fed through an on board regulator. Notice though that the regulator has to dissipate the excess voltage and can get pretty hot when you draw a fair bit of current. The regulator will fail if the voltage goes over 20V or gets too hot too often;
  • +5V should work fine up to 5V, and I personally wouldn't worry if an external supply delivers up to 5.5V unloaded. Above that 5.5V you will probably release the magic blue smoke.
  • 2
    Whilst outside of technical specs, I have not encountered a single ATmega328 that fails to run at 16MHz at 3.3V. Commented Feb 25, 2014 at 11:19
  • You also have to take care of the Brown Out Detection fuses that will put the ATmega328 into sleep mode whenever it gets below a given level (cf the datasheet).
    – zmo
    Commented Mar 1, 2014 at 15:53
  • @zmo, the question was if it breaks. Answer is no, not likely. If the question is "will it stop working as intended?" then the brown out detection comes into play.
    – jippie
    Commented Mar 1, 2014 at 16:10
  • 1
    @zmo You are right. Edited my answer
    – jippie
    Commented Mar 1, 2014 at 16:24
  • 1
    One point you might want to note is that if you supply a voltage <5V, you should feed it to the +5V pin, not VIN, to bypass the voltage regulators (Conversely, as you note, voltages >5V must be fed to VIN). Commented Mar 2, 2014 at 19:35

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