Hey,
I acidently ordered a 3.15v stepper motor for my Aurduino, can I use a few resisters to hook it up to the 5v power out?
The full specs are:
Voltage: 3.15 V
Current/Phase: 1 Amp
Ohm/Phase: 3.15 [ch937]
Inductance/Phase: 2.8 mH
You will save me $30 if you can solve this conundrum 
Cheers!
Nick Deboar
5V power output of what ?
Surely the arduino cannot drive 1A motors directly. As for the motors, you only need to make sure you do not exceed the maximum current rating of the coils (stall current). So yes, you can add additional current limiting resistors. Make sure to get ones with appropriate ratings for max. dissipated power.
Stepper motor coil voltages don't mean what you think they mean. If you only supply the rated voltage, the motor will have low maximum speed and nonexistent torque.
Look up RL, linear, and chopper stepper drives. If you want to use resistors, you'll need at least 12V motor supply to get reasonable speed and power.
As Madworm also writes, you can not drive stepper motors (no matter what voltage they require) directly from the Arduino board. You need some kind of circuit that can handle the required current to interface the stepper motor to the Arduino board.
Here is a tutorial on driving a stepper motor from Arduino : http://www.arduino.cc/en/Tutorial/StepperUnipolar
Note that this setup only works with unipolar steppermotors, if your motors are bipolar you need to hook them up in a different way.
Hey,
Ha, sorry, silly question 
So, could I use one of these:
7-30V, so again im guessing Ill need some resisters to get it to work with my 3v motor?
Nick
This driver seems perfect. I'd buy it
If you read the data sheet you'll find information about current sensing/limiting. You'll need exactly 2 current sensing resistors and a reference voltage to set the maximum current the driver will pass to your bipolar stepper motor. The rest is done internally. Protective diodes and so forth are already built into the driver's H-bridge circuitry. As mentioned before you'll need a higher supply voltage than the voltage rating on your stepper motor to give the driver a chance to counteract the stepper's high inductance, that is make the phase current rise quickly enough to get a decent torque at higher rpm.
The data sheet is on the page you've posted.
http://greta.dhs.org/EasyDriver/
Edit: all of this stuff is already on the PCB sparkfun sells.
I'll second the vote on the easydriver - I'm currently using 3 on my project.
As madworm pointed out, you really don't need any special voltage regulation, the driver chip will do it for you.
For example, I run two arduinos and three stepper motors (rated @ 6v/0.8A each) off one 12v/3A power supply. I used the easydriver's current adjustment to tune down the motors to the exact amount of current necessary (well below the actual 800mA, which the easydriver cannot provide -- it's limited to 750mA, IIRC) to drive the load that each needs.
Be warned, the chips on the easydrivers can get quite hot, make sure to account for any ventilation needs.
!c
Fan-tiddly-tastic.
I am just really getting started on Ardunio, so this sort of "basic" help is a life saver.
Cheers, will post my little project when im done!
Nick Deboar
It's really easy to use, just hook up the A and B coils to the appropriately labeled inputs on the easydriver, the Vin and GND to the appropriate inputs, then one digital pin from the arduino to each of the STP (step) and DIR (direction) inputs.
Then, you just change the direction by digitalWrite()'ing HIGH or LOW to the DIR pin.
To make it perform one step, just write HIGH to the STP pin for about 3ms, and then bring it low. It'll only make one step for each transition from low to high.
!c
EasyDriver is really a neat solution
and if you ramp the stepper at start and stop you will get it really smooth
I use two oft them to dirve my robotic panorama head
cheers
Paul
I just found one thing out while playing around the other day.... They have NO facility built-in to prevent back-flow of energy when turned off.
So, be careful about "spinning" your stepper when power is off. It will turn into a generator and send power to your arduino through its pins. (I was checking a wobble I had in a drive shaft, and noticed my TX/RX lights coming on on the arduino board... =)
!c