If I have a breadboard power supply that is connected to a 12v adapter on a wall outlet, and the jumper pins on this power supply are set to 5v, is it possible to use this as my only power source and have the arduino just controlling everything while it is connected to a computer via USB so I can still send my code to it?
I'm asking because I figure if my project requires say 8 servo's, 10 LED's, a stepper motor, and a few other things, I'm assuming the arduino won't be able to power all these things on it's own, so why not just use an external source right from the start.
Yes. Connect the grounds, but do not connect the power between the Arduino and the stuff it's controlling. The Arduino will be powered off USB, everything else off that power supply.
You'll damage the board if you connect the 5v on arduino to the 5v on other power supply while it's connected to USB (while it's not connected to USB, you can power an arduino through the 5v pin, but this is not recommended, because you're setting a trap for yourself - plugging the USB cable in could damage hardware)
Ok, that's what I was doing and then someone mentioned I'm still drawing power from the ground side of the Arduino which I don't understand and made me ask the question to begin with.
Another question, if I'm connecting the Arduino via USB cable but not using the 5v on the Arduino, aren't the pins still giving out some power regardless?