Why can't you just use a common USB lead to communicate with the computer, like everybody else does.Leo..
What would you do to send an arduino data to the computer? (So that the arduino is connected to a voltage source (because the project is going to be implemented in real life).
The Arduino has a built in power switch.Your 7 volt to the power jack takes precedent over the USB 5v from the USB cable..
You are feeding 8V to the barrel jack, or to Vin? Both will result in Vin/2 of more than 3.3V.