Thank you Udo for commenting and for the very useful information.
So I would have to get the independent source of power from somewhere else and only use the Arduino to control the Transistors.
And use a comparator to compare the value of the voltage with the potentiometer. Now you made me understand more.
anyway I am reading about "processing" now to display the data from the arduino on my computer. And hopefully to control the arduino in the future from the same user interface windows