Decimilia on breadboard, common external PS?

I would like to mount my arduino on a breadboard and be able to power my external circuitry with an external power supply. I realize that I can power it by taking 5v off of the Arduino board but I am considering isolating the circuit draw from the Board. So, I am assuming that s common supply must supply both (my circuit and the arduino) Is this as simple as it seems to me? One big supply feeding the Decimilia board and the breadboard both? I can feed the 5v right to the board, right?

thanks

if you connect the ground lines of both boards together, you can use one big power supply or two smaller ones.

thank you for your response! I was unaware that I could use separate power supplies. So does this mean I could use an off board PS(7805) to power my breadboard circuits and the on-board power supply--under both conditions, jumper=INT or EXT as long as I took ground off of the GND pins (4,5) and connected it to the ground of my off-board supply?

if you are using an external 7805 to power your breadboard, add a few capacitors to the circuit and you can run that 5 volt input directly to the arduino 5v line. if you want a separate power supply for the arduino, you can run a 7+ volt power supply to the external power jack, or you can run another 5 volt regulated line to its 5v jack. just make sure to connect the grounds on the two power supplies.

thank you very much for the info, i really do appreciate your help