This might seem like a really stupid question but I'm a noob at electronics. I managed, through process of elimination, many tutorials and some guidance on these forums, to program an ATtiny85 microcontroller to light a blue LED and power a piezo to make a buzzing sound. Everything works perfectly when the breadboard is hooked up to the 5v plug on the Arduino Uno board, but when I hook the contraption up to a 6v battery supply, it doesn't work. Am I missing something that 5v is enough to power everything but 6v is not? I'm using a set of 4 button-cell batteries for the power.
Four button cells may not be able to supply enough current. Measure how much current it's drawing from the 5V (It's from the USB I assume) and see how much it is from the batteries.
I figured it was an amperage issue. I'm using my multimeter but can't seem to get a good reading from the Arduino Uno. Does anyone happen to know off hand the tech specs of the Arduino 5v supply? Obviously, 5v, but what's the amperage (I'll also take it in milliamps).
DoctorOctoroc: Obviously, 5v, but what's the amperage (I'll also take it in milliamps).
The current rating of the power supply has nothing to do with the Arduino. It'll provide whatever current its power supply will provide.
In order to measure current, you must break the circuit. A current measurement is made in series with what you want to measure. (Unlike measuring voltage which is done in parallel.)
FYI, Button cells can only provide 2-3mA in a surge. That's probably not enough to power your circuit.
If the cells are feeding the 5V regulator, the one volt difference may not be enough for the regulator to function. IIRC the regulator needs a minimum of about 7V.  If you add another button cell to bring it up to 7.5V that should do it but then you'll into the problem that they can't provide enough current anyway. My Duemilanove uses around 30ma when working and still uses 10ma when in power down mode. [/edit] Pete
I figured it was an amperage issue. I'm using my multimeter but can't seem to get a good reading ...
Here's a simple experiment -
Measure the battery voltage without the Arduino connected. Then, plug-in the Arduino and see if the voltage drops.