Is there a way I can run the Uno from a 4.3v supply? I know the AVR can be run from 5v or 3.3v, at 16 or 8 mHz, but I haven't ever heard about a voltage between.
Looks like you can run the 328 / 328p at anywhere from 1.8 to 5.5v. Not sure about the speeds you can run at various voltages, but if I had to guess I'd say you'd be safe using the internal oscillator. (Edit: looks like someone answered this question: http://arduino.cc/forum/index.php/topic,101084.0/topicseen.html )
Also, I believe the analog reference voltage can't exceed Vcc.
The Uno itself has a voltage regulator that needs 6-12v in order to output 5v.
I have a speed/voltage table here:
At 4.32V you could run at 19 MHz.
At 4.14V you could run at 18 MHz.
For 16 MHz (which a Uno uses) you only need 3.78V.
You would bypass the voltage regulator (assuming you don't exceed 5V) and just plug into the +5V pin.
Thank you both very much!
BTW, how come the regulator doesn't mind if you put 5v on it's output, when not powering the input?
I can't see it documented for this particular one but apparently there exists a "Reverse Current Protection Circuit" which "stops the reverse current if the Reverse Detector detects that the VOUT pin voltage has become higher than the VDD pin voltage.".
mattallen37:
BTW, how come the regulator doesn't mind if you put 5v on it's output, when not powering the input?
Because the schematic asked nicely.
You can actually go somewhat lower yet (around 3.2v, maybe a bit lower) at 16Mhz but it is out of spec so not recommended.
Thank you all! I only need to go down to around 4.3v (Lego NXT sensor supply), but the extra info is good to know!