I followed along this tutorial and have been trying to turn a micro bipolar stepper motor. I've successfully used this same motor on a PWM driver and the same arduino nano, so I know it's a working motor and microcontroller, but its so far motionless with this driver. I would like to avoid using 8v, and I'm not clear why it would even have a minimum voltage for motor output. I wonder if that's my problem.
Secondly, one of my motiviations was to use only two wires for step & direction and preserve pins for more motors or other modules. On that note, I noticed that they said if you only care to turn your stepper in one direction you can wire your direction pin direct to vcc. Does that mean you can drive a stepper motor with just one pin from your microcontroller? (provided you're content with one direction only?)
Please post images in a post; people don't like to go off-site.
It looks like you're using Vin as a power output. Vin on a Nano is a power input, not a power output.
It's the A4988 driver IC that requires the 8V minimum.
If you have 12V available try that.
The TB6612 can work down to 2.5V. Whay don't you just use that driver?
???
Yes.
You might consider using this driver
You need minimum of 2 wires, step and GND.
But more than one motor can share that ground wire, right? So just one control wire per motor. Also, what was the question about "micro bipolar stepper motor" is that not a thing?
As I already said yes
Just wondering about motor's voltage and current ratings.
Yea verily. 
Thanks! I'll buy some today! BTW, you suggested two- and it seems like either would be an option, but I'll probably go with your 2nd suggestion by default since it's the most recent. It helps if I can find a good tutorial or example code online, some of the driver boards seem trickier for me to code. That's one thing I like about my PWM board, it seems to always work at least, but probably just because I'm most familiar with the coding.
Thanks! Sorry about the links, and you're right about Vin- I'll change that!
I was replying to JCA34f who mentioned GND also. Sorry I guess the forum doesn't specify. (or maybe I made a mistake)Thanks for your help!
BTW, you suggested two-
I only suggested one, the MP6500
You said
I've successfully used this same motor on a PWM driver
Which is the TB6612. So I wonder why you don't continue to use that driver.
Its because that driver needs 4 wires to control it (or at least it did the way I wired it). Maybe they aren't all mandatory?
Edit: I see that yeah, you were talking about the PWM I already have. Sorry I haven't got the #'s memorized yet.
Somebody in the product comments (for this particular motor) also suggested this driver:
Geeetech-TMC2209-Stepper-Controller
Bipolar steppers don't run on PWM, they run by switching the current polarity relationship between the two phases in a 4 step sequence.
BTW- thanks again for the help, everyone! With this info I tried it out this morning and raised the motor voltage and it works. Unfortunately this motor will overheat pretty quickly at 8v (the code starts working at just over 7v) so will still be pursuing a different driver. Just wanted to note for posterity that the V was the main problem.
That's why I asked about winding voltage and resistance / current.
You never said what motor you are using, so maybe it will, maybe not but probably not if you set the current correctly
Don't forget, stepper windings are energized even though the motor is standing still and normally get pretty hot (close to 100 C, boiling point).