I'm having a strange power problem with my project. It works just fine when powered over USB (using a Duemilianove), but when I try to power it with a 9V battery, it doesn't work. Has anyone run into anything like this? The project has various LEDs running off 3.3V and sinking into the digital pins, as well as an audio board and accelerometer using the 3.3V and ground as well as the analog pins for I2C. Any help would be greatly appreciated!
Likely the 9V battery cannot supply enough current to meet the demands of your project. The internal resistance of a 9V battery is quite high, so the voltage will sag dramatically if you try to draw lots of current. To replacing the 9V battery with a 9V power supply or 6AAs and see if the problem persists.
I'll give that a try. Thanks for the advice!