Arduino 16 MHz with only 3.3V? Now I have these Arduino Pro Mini from Sparkfun. They are the latest version that I know (yeah, it's the one that have those horrible misaligned pins). Now they are designed around the ATmega328P and have a 16MHz crystal on them.

Now, my question is: Can I run an ATmega328 with a 16MHz crystal while supplying ONLY 3.3V.

The reason I'm doing this is because 5V / 16MHz Pro Minis from China are way cheaper then 3.3 / 8MHz.

Facts that I already know:

If I follow the datasheet to the the letter, this configuration should not work. BUT... After some test, it did work.

Also, I want an answers based on personal experience (NOT OPINIONS) and not datasheet and specs.



[EDIT] Including a way to use the internal clock (at 8MHz) of the ATmega328P would really help!
Officially, no.  Practically, often but not always.


  If I follow the datasheet to the the letter, this configuration should not work. BUT... After some test, it did work.


The data sheet does not say that it "should not" work, it says that it is that the part is not qualified for operation at 16 MHz below some voltage higher than you want to use.  That does not mean that a given chip cannot work there, it only means that a chip that fails to may not be considered "bad".  Failure may be total and obvious or subtle.

In practice I have seen it work, both on small modified import boards and those with switchable power supply voltage.  But I also recall seeing it fail to work.

Two factors that can make a theoretical difference are part-to-part manufacturing variation and operating temperature.

Note that with an ISP setup you can change the fuses to run the chip on what was sold as a 5v external crystal board, to operate from the internal 8 MHz oscillator instead, and you can do this even while leaving the crystal on the board.  If you also change the brownout detector fuse, you can lower the voltage further, for example to operate without a regulator directly on two AA cells.  Of course that applies to the ATmega itself - any other active components on the board would have to be qualified for the intended voltage too.