I have a 6-wired Unipolar Stepper Motor (KYSAN: 1124014), and I want to hook this up to an Arduino Nano ATMega328 model. I am quite new to hardware and I am mostly a developer so I don't really know how to approach setting this up, hardware wise. Things are quite expensive so I don't want anything to break by hooking it up wrongly.
I know that there are two coils (three wires for one coil) and one of the three wires is the center tap of that coil. Am I suppose to hook up the center taps to the power source (in this case a 9V NiMH battery)? The motor takes in 4V of power. Since there is a power difference, does that mean I have to use some kind of voltage regulator to step down the voltage, or no? Also can I use one 9V for 2 stepper motors and the Nano?
You can not hook a stepped directly to the arduino--not enough power available. Steppers require a certain pattern to their driver signals. A web search should turn up the details you need.
Steppers need higher voltage than the rating for good performance. A stepper like yours could be driven with 24V, maybe more, with the proper current limiting. Look for an off the shelf stepper driver. I have used some from Page Title for CNC work but I suspect they are too big for your needs.
I think I'm going to try RPCoyle's method with the transistors. It seems simple enough plus, I don't need to go order another part. Are those BJT's? And will regular diodes work here? Also, is it okay to use a mosfet if I don't have a BJT?
I just used plain old 2n222's. Works fine pulling 300 ma per transistor. The 2n222 is supposed to be rated up to about a 800 ma collector current, but I wouldn't push it that far.