Power requirements for stepper

Hello, I am a novice in search of some pointers. (gee there is a new one!) I am attempting to control a stepper with the arduino. I have read all the tutorials on arduino.cc and elsewhere around the web. They all seem to agree that you should not run much more than a led from the arduino's power source. Ok, got it, I built a 5v regulated power supply that can supply 500ma and works great powering the 7474 d-flip-flop circuit that controls the stepping sequence.

I am planing on having the outputs from the control circuit flip some transistors to power the coils of my stepper. The steppers I have are:

Oriental Motor PK245-01AA Current per phase: 1.2 (Unipolar), .85 (Bipolar) Resistance per phase: 3.3 (Unipolar), 6.6 (Bipolar) Voltage: 4, (Unipolar), 5.6 (Bipolar)

The questions I have are, what do I need to do to power this thing? :-) Is the current rating on the stepper a max rating, ie Can I supply it less? Or is the motor going to draw that through the circuit and therefor the OTHER components must be able to handle this amount? (told ya I was a Novice) Also how do I take in account for the internal resistance, I understand V=IR, but not how to apply it to a motor.

If I need to supply the motor 'at least' the current rating, does anyone have a suggestion how to supply the correct amount? The small power supply I built is based off of the 7805 chip that even with heat sinking is only suppose to put out 900ma -1000ma, which sounds like cutting it a bit to close to me.

Part number answers would be helpful, but how you came up with the decision would be more helpful. I appreciate any help that the community can give.

I would build for a current AT LEAST 1.2A and the voltage can be more than rated as long as you stay close. Perhaps a 6vdc battery pack. You don't say if this needs to be self powered or if it can always be plugged in. I'd also look at a stepper motor controller board and chip, you can buy these premade or roll your own.

Thanks for the reply. The stepper will be driving a turret of sorts, and therefore could be plugged in. I have looked into different drivers and chips, but I chose this project so that I may learn some of the basics of circuit design. I have already put together a circuit that turns on the control wires in sequence on a clock pulse from the arduino. Right now this circuit is simply turning on 4 leds so that I could see the pattern. What I am looking to do now is find a way to take these four control wires and power the stepper. I know I should be looking at an h-bridge design (for bipolar) or a transistor array for a unipolar. What I am not clear on is what specific ratings these components will have to be at so that I will not blow anything up! More specifically how much current do I have to supply each phase of the stepper, and what transistors can handle this current?

thanks!

Within limits the more current the faster the motor will move to the next step and the harder it will hold that position. I'd start out with less than you plan to use, get it all working then boost the power to where you want it (without going over) you will tell when you have too much when things start getting hot. Hopefully you will check before the fire starts.

Ok, sounds good.

How do I find the current being passed to the motor? For instance if I give the motor 6vdc connected directly, would I divide the resistance of the coil, in my case 6.6, giving about .9a? And what about the fact that current will also be traveling though a resistor?

I appreciate the help, and I am pretty sure I understand the theory, but I am having trouble actually figuring out how to select components that will give me the desired results.

thanks again.

would I divide the resistance of the coil, in my case 6.6, giving about .9a?

YES

And what about the fact that current will also be traveling though a resistor?

It shouldn't be it will just be going through the transistor which is either off (very high resistance and hence no current) or on (very low resistance hence current limited only by your coil)

So you want at least an amp, therefore look for transistors that will take at least two amps maximum. (you will also need an external power supply)

Your best bet would be to use a FET, see the playground for examples.