ok, and another question... I don't want to spam the board, so I'll ask here:
Is there an easy way to calculate the approximate time arduino runs on battery?I'll use around 50 leds. I remember there was some kind of a formula. I should
be able to calculate this if I know what kind of battery I'll use and how much the
LEDs need, right?
It depends on the batteries as well as what's being powered.
For AA recharable NiMH batteries, you have around 2 amp-hours. An LED takes about 20 mA and the Arduino takes about 20mA. So if you had all 50 LEDs on at once, you'd be using about 1000mAh, and the batteries would last about 2 hours.