Two arduinos one power source I was surprised that this question had no answer on Stack Exchange and I can't find much about it elsewhere so, in the hopes that it will be useful to people other than myself, I'd like to ask:
How can one power two arduinos using the same power source? Such that the first is connected by barrel jack to a 12v transformer.
I saw this youtube video which very briefly mentions doing this by make the connections:

Ardu1 --&gt; Ardu2
5V --&gt; 5V
GND --&gt; GND

This surprised me as I was not aware the 5V could operate as a power input. I was expecting the use of the VIN pin somewhere along the line.
Am I correct in thinking that the second arduino would take power on it's VIN pin from 5V on arduino one?
If so, where should the second arduino ground to?
You could put the 12v from the barrel jack on both Arduninos Vin pins by jumpering the Vin pins together instead of the Vin->+5 or +5->+5.  Then they'd have independent protection and regulation of 1A, 5V through their NCP1117ST50T3G chips.