Thanks to everybody, who responded!!
Very interesting answers.
I will read all the things you suggested.
I am trying to power a stepper motor, that moves a certain amount of degrees every unit of time. Ideally I could do that without a computer being connected to the arduino, but rather program the arduino to do that and then let it run by itself.
If that works, I would like to add other sensors to it. Like an infrared reviever and sensor that when I interrupt the infrared beam trigger the motor to move a degree position further.
What I want to avoid is that the arduino or the motor or even worse the macintosh via the usb will take any damage, because I get the power, voltage, current whatsoever wrong.
If there are example tutorials for that I would be happy to know about them.
And one more thing i fear is that the motors might be to weak for that construction.
So the idea to control any motor, is fantastic.
But where can I get more info on how to control a powerful motor.
And even more a powerful motor that might has the appropriate libraries to control.
Thanks again..
Really great feedback