I bought yesterday a ULN2003, an integrated circuit with which I plan to drive a stepper motor (controlled by the parallel port on my computer) as is shown here: a. http://electronics-diy.com/electronics/stepper_motors.php I could wire this very easily, but I don't want to do so until I have a full understanding of how its going to function. My main point of confusion is the operation of the ULN2003 itself. The following is a link to its datasheet, with a schematic on the first page: b. http://www.datasheetcatalog.org/datasheets/120/489337_DS.pdf Its an array of seven darlington pairs which I understand are each comprised of two NPN transistors and which can be used for amplifying or directing current. In the more general schematic on the left side of the page (b) are seven inverters and seven diode symbols, each of which connects to the common, which as in (a), will be connected to the cathode of my power supply. But why I ask, why? This is how I see it presently: The electrons from my power source are going to flow into pin 9 and up the line butting into each of these diodes and not making it through any of them. It will also flow into the motor and through individiual coils, take brown for instance, into pin 13. Lets say I have pulled pin 5 on my parallel port to high and now this is inverted before coming to pin 13, so the current from the cathode which has travelled through brown and into pin thirteen now goes through the diode and back to the cathode. Why does this work? It seems like my pulling of pin 5 high results only in a short circuiting of the cathode. Im rather new to working with circuitry and I know there is a flaw somewhere in how I understand this. I hope you can help, if someone could enlighten me as to the operation of this IC, or what I am misunderstanding, I would be greatly appreciative. Thank you!