user8044: I am trying to design a bicycle LED lighting system, and for that I bought an Arduino yesterday (so very beginner with Arduino).
My final system will operate at 6V, so I plan to put everything on a breadbord and tune everything (blinking times, resistor values, etc.) and for that I want to keep my Arduino plugged to USB during development.
So my question is:
How should I connect USB-powered Arduino to a higher-voltage-powered breadbord (between 6 and 12V) safely?

user10201: I think as far as i understood the problem, the system or whatever you call is will run on what ever power as long that power is not fed to the arduino that will not be a problem, just connect the two grounds together and power the arduino through the computer and connect the pins to the system accordingly. i think this will solve thus the trivial problem.

8044: <p>I am trying to design a bicycle LED lighting system, and for that I bought an Arduino yesterday (so very beginner with Arduino).</p>

<p>My final system will operate at 6V, so I plan to put everything on a breadbord and tune everything (blinking times, resistor values, etc.) and for that I want to keep my Arduino plugged to USB during development.</p>

<p>So my question is:</p>

<p>How should I connect USB-powered Arduino to a higher-voltage-powered breadbord (between 6 and 12V) safely?</p>
 10201: <p>I think as far as i understood the problem, the system or whatever you call is will run on what ever power as long that power is not fed to the arduino that will not be a problem, just connect the two grounds together and power the arduino through the computer and connect the pins to the system accordingly. i think this will solve thus the trivial problem.</p>
