Arduino's operating voltage

HI, which Arduino can operate with only 2 AA batteries?

There are a couple of Adrduinos that can operate of 3.3v. The most you an expect to get from a pair of AAs is 3v. Try adding one more AA.

Any of those with an 8MHz clock, e.g. Pro, Pro Mini, LilyPad, etc. To be within spec, with an 8MHz system clock, the power supply voltage should be 2.4V or greater.

Edit: Of course, a person could use a boost regulator to convert 3V to 5V, and then the answer would be "all of 'em".

The Atmega328P (and similar ones in that range) processor chips can operate down to 1.8V (depending on what speed you require).

Do you plan to use a pre-made board, are are you inquiring about the processor itself?

Thanks guys.

@Nick, I wish i could but sadly i’m only allow to use 2 AA batteries.

@Jack Christensen, i’m kinda curious about how the boost regulator works. I just Google it. LiPower - Boost Converter - PRT-10255 - SparkFun Electronics
Is that what you mean? I have a pro mini (3.3V) and a uno (5V). Is it possible to increase the batteries voltage using the boost regulator to match the voltage of either one of those?

@Nick Gammon, i’m inquiring about the pre-made board. Do you know if there’s any microcontroller that can operate below 3V?

You can use a boost converter. I used one I got from eBay for $1 in this project for a GPS clock.

I put the converter between the batteries (2 x AA) and the board, see arrow.

Device here:

Try searching for "1A 3V to 5V DC-DC Converter Step Up Boost Module" or similar.

You can also get ones which handle a lower input voltage but deliver less current. For example "1-5V to 5V 500mA DC-DC Converter Step Up Boost Module". These cost around $1.50.

Out of curiosity, I measured the performance of those two el-cheapo boost converters.

The module designed to work with lower input voltages gave me:

        voltage  current    power
input:    2.2V    140 mA   308 mW
output:   4.9V     50 mA   245 mW
efficiency: 80%

The module designed for higher voltages but higher current gave me:

        voltage  current    power
input:    2.5V    120 mA   300 mW
output:   5.1V     50 mA   255 mW
efficiency: 85%

So, assuming you can get 2.5V from your two batteries, the $1 unit should do the trick. It had 85% efficiency (ie. you lose 15% in the boosting) but delivered a full 5.1V output.

Those figures are assuming that 50 mA is enough power for your project.

I then ramped up the power consumption to see if things would, well, break. With the higher-power module things looked pretty good:

        voltage  current    power
input:    2.5V    230 mA   575 mW
output:   5.1V    100 mA   510 mW
efficiency: 89%

        voltage  current    power
input:    2.5V    480 mA   1200 mW
output:   5.1V    200 mA   1020 mW
efficiency: 85%

        voltage  current    power
input:    2.5V    740 mA   1850 mW
output:   5.1V    300 mA   1530 mW
efficiency: 82%

So even drawing 300 mA from your Arduino, you can manage with only 2.5V input. However that's drawing 3/4 of an amp from the battery, the internal resistance might be a factor there.

Freedomz_ks:
@Jack Christensen, i'm kinda curious about how the boost regulator works. I just Google it. https://www.sparkfun.com/products/10255 Is that what you mean?

That's one example, Nick showed some others.

I have a pro mini (3.3V) and a uno (5V). Is it possible to increase the batteries voltage using the boost regulator to match the voltage of either one of those?

Yes, but a 3.3V Pro Mini should do well directly with two AA cells without the need for a boost regulator.

@Nick Gammon, i'm inquiring about the pre-made board. Do you know if there's any microcontroller that can operate below 3V?

As Nick said, the ATmega328P (as in the Uno and the Pro Mini, as well as other Atmel MCUs) can operate down to 1.8V. But, the lower the voltage, the slower the system clock must be. At 1.8V, the clock should not be more than 4MHz. For details, get the datasheet and find the "Speed Grades" section.

Your 3.3V Pro Mini can in fact be operated at 5V without a problem. The main (perhaps the only) difference between a 3.3V Pro Mini and a 5V Pro Mini is the crystal (well, resonator) -- 8MHz and 16MHz respectively.

@Nick, interesting measurements, thanks for sharing. Always interesting to check things out like that. Pretty decent modules for a buck!

No, the fuses on all Arduinos are set for brown-out detection at 2.7V I believe, so you can't
run them much below 3V without editing boards.txt (although this is from a few years ago).

For the 328P the extended fuses lower 3 bits encode brown-out level, change from 5
to 6 to move BOD level from 2.7V to 1.8V. Different processors have the bits in different
places, beware!

MarkT:
No, the fuses on all Arduinos are set for brown-out detection at 2.7V I believe, so you can't
run them much below 3V without editing boards.txt (although this is from a few years ago).

Good point! And I knew that too! Of all the things I've lost ... :~