power via batteries (no regulator)

Most likely a dumb question but,

If I were to make a bare bones setup could I supply power to the atmega168 with only two or three 1.5v batteries or three 1.2v rechargeables? Would I even need filtering caps or a diode?

I know the operating voltages of the atmega168 is 2.7v to 5.5v per the data sheet however I have no idea how smooth or stable dc current from a battery is.

P.S. I typically use a 7805 voltage regulator, caps, and a diode however I am trying to reduce both size and power consumption of a couple of smaller projects.

Thanks for your time.

I don't think you can get any smoother DC then from a battery! I don't see any stability issues either.

I would only use a diode if I was worried about hooking it up accidently with reversed polarity. A diode in series will cost you some volts. (~.7)

You might wait for other answers, but I think you're fine with say 3xAA.

It appears to me that brown out detection on the chip is set for 2.7V, so you should be in good shape as the batteries weaken. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1218505929/9#9

three AAs work fine, with two caveats: don't try to burn a program (won't be reliable, could hose the chip requiring a programmer to correct), and the ADC will be pretty useless, as Vref will be floating along at the battery voltage (unless you add an external reference that's below the battery voltage).

-j

Thanks... Thats exactly what I needed to know.