I just got a Duemilanove board with the ATMEGA328 chip installed, and have a rather simple question to ask...
Out of curiosity, I wanted to see the actual voltage drop across a digital pin, so I set it to high and measured 4.82V when powered via standard USB A to B cable, and measured 4.94V when powering the board via 9VDC adapter.
Is this voltage difference something that's typical or should I expect them to be pretty close? I guess I don't really know what kind of accuracy I should be expecting. Thanks for bearing with my newbie question!
That's pretty typical. USB "5V" is really loose and can be anything down to 4.4V, especially if going through a USB hub. Same thing with 5V regulators...their typical tolerance is 5% so 4.75V-5.25V is entirely reasonable.
Thats weird, I am getting 8.2v out of my digital pin. I connected a multimeter to digital pin 8 and the ground pin... Maybe I measured the wrong way? Still new.