Uno voltage minimum

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 )

http://www.atmel.com/devices/ATMEGA328.aspx

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:

http://www.gammon.com.au/forum/?id=11497

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.

[quote author=Nick Gammon link=topic=101146.msg758638#msg758638 date=1334271297] I have a speed/voltage table here:

http://www.gammon.com.au/forum/?id=11497

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. [/quote] 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!