Best battery for Arduino data logger?

[TomP]

I want to create a temperature and event logger that I can stick in my attic, or attach to my steam boiler, to collect data for a week or more. I have a semi-functional prototype, but so far I've been deploying it using the wall wart from ladyada's starter pack. Does anyone have any advice about the best way to power an Arduino by battery, and whether it's even practical to think about having an Arduino project run for a week or two on batteries? From what Limor wrote in the MintyBoost design article, it sounds like a 9V battery would be a poor choice for this,and that a MintyBoost with a 'B' style plug would last longer. Would that work? Are there any other alternatives worth considering?

[darus67]

Are you using any of the power management or sleep modes to conserve
power between measurements? Do the standard arduino libraries even
support this?

If not, I'd guess you're going to be hard pressed to run an arduino for a week or two
on any sort of reasonably sized battery.

If you are able to shut down the processor between measurements, then
your measurement interval will be a big factor in how long you can run on
battery.

The very first thing to do would be measure how much current
the 'duino draws when its running.

[adafruit]

you can never go wrong with a 6V lantern battery stick a 1N4001 in series and boom, now you've got it down to 5.3V...safe for your arduino.

[darus67]

Any idea what the Amp-Hour rating is for your typical lantern battery?

[timv]

http://www.google.com/search?q=alkaline+lantern+battery+amp+hours
12 or 13, depending on who you ask, for Duracell MN908

[TomP]

you can never go wrong with a 6V lantern battery stick a 1N4001 in series and boom, now you've got it down to 5.3V...safe for your arduino.

That's a nice simple idea. Thanks! A related question is, can I just attach the polarized power jack from my dead 9V battery holder to the battery/diode supply and plug it into the Arduino? I assume it's going to go through the 7805 if I do that, and I don't know whether to expect it to do anything wonky if it gets just 5V in.

Over in the Arduino forums, I just saw someone mention Rob Faludi's recent summary of Arduino battery lifetimes - using different batteries, sleeping or not, without or without a XBee, ... He apparently got 178 hours from 4 2500mAh NiMH AA batteries, even without sleeping, vs only 19hours from a 2AA MintyBoost-type supply.

[darus67]

I'm surprised by the poor showing of the boost setup with 2 AA cells.

So if 4 AA cells ran it for a week, a lantern battery should last a month.

If you can get the processor to go to sleep between measurements, it would probably last a year.

I wonder how he hooked up the 4AA pack.
Reading the power supply recommendations here: http://www.arduino.cc/en/Main/ArduinoBoardDiecimila
I see the following:
"If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable."

[TomP]

I wonder how he hooked up the 4AA pack.

Me too. Maybe he used the USB port? Otherwise, I guess you'd have to solder special power connections to the board, to bypass the regulator - personally, I wouldn't want to do that.

"If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable."

Those are restrictions created by the 7805 regulator. I hadn't looked at the datasheet before, but I see now that the output current apparently drops to zero unless there's a reasonable input-output voltage difference. So, it sounds like plugging a 5.3V supply into the power socket probably wouldn't work. It also probably wouldn't fry anything, so maybe I should just try it and see?

[TomP]

I wonder how he hooked up the 4AA pack.

I asked him He wrote back and said,

"Yes, the Arduino board needs at least 6 V to get 5 V out the other side of the regulator. However it turns out that giving it less than 5 V is just fine. The ATMEGA168 runs even if you only get it maybe 2.7 Volts,* so it's possible to use the barrel connector with lower voltages. Or you can bypass that and hook up directly to the pin labeled +5V. Just don't put anything more than 5V into that pin!"

Time to start doing some experiments...


* FWIW, I think the ATmega168 datasheet (sec 28.3) actually indicates that you need to supply at least 3.8V to run the chip at 16Mhz.