external power supply for arduino/ driving motors?
I need to use an external dc power supply for arduino. I have the male jack for the power jack on the arduino (that is what the black round jack next to the usb jack on arduino uno is right?) but, given the power supply from the usb is 5v, should I use 4.5v or could I use 6v? I also need to run two 1.5-3v motors on it. I read that because the arduino digital pins have a total output of about 20 ma, and if you plug something larger into it, it could fry the processor, and that you should use mosfet transistors to connect the larger items. but could you just use NPN transistors rather than the mosfet transistors?