The New Arduino MEGA has lots of pins and so it will be easer to draw too much current out of it. We are often asked what is the maximum, well this time it is not too easy with the current limits of groups of pins needing to be within limits.
Therefore I have done a spread sheet to allow you to calculate the current an power of a design and see if you are exceeding any limits. I would be grateful if you could check this out and see if there are any mistakes in it before putting it in a more permanent place.
http://www.thebox.myzen.co.uk/temp/Calc1.xls
Hi,
I read a lot about the "driving tons of leds" with the MEGA, so I checked the datasheet right now.
Maybe I'm misunderstanding it, but when you read, under "absolute maximum ratings" the following:
DC Current VCC and GND Pins... 200.0 mA
doesn't this mean that the TOTAL current going IN the chip (and so, out of its pins) is limited to 200mA?
After of course there are also other limitations (40mA each pin, and the group limitations that Grumpy_Mike reported on his .xls file) but this seems to me the biggest of all.
[edit] also the atmega168 has the same total current limit!
However if you are crafty you can have 200mA of current being sourced by the pins, that goes through the Vcc.
AND
200mA of current being sunk by the pins, that goes through the GND.
So the chip could (subject to other considerations) power 400mA of Pin current.
I think the spread sheet needs to get a bit more complex to deal with this.
However if you are crafty you can have 200mA of current being sourced by the pins, that goes through the Vcc.
AND
200mA of current being sunk by the pins, that goes through the GND.
So the chip could (subject to other considerations) power 400mA of Pin current.
I think the spread sheet needs to get a bit more complex to deal with this.
That sounds more like a Wall Street Lawyer looking for a loop hole in a contract. 
Not sure it's factual, but I like your attitude!
Lefty