Typical Output Voltage on Digital Pins?


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!

is this voltage difference something that's typical

Yes a logic output can be anything greater than about 3.8v.

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.

Thanks for the responses. It answered my concerns perfectly.

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.

Is the pin actually driving a load? Is it this high when driving a LED through a resistor, for example?

get a new multimeter lol, and not one from radioshack.

Maybe I measured the wrong way?

Yes you did.

What voltage do you measure on the 5V pin?