M35SP-7T stepper motor

Yesterday I unassemble an old scanner and retrieved a nice Mitsumi M35SP-7T stepper motor (datasheet: http://www.mitsumi.co.jp/Catalog/pdf/motor_m35sp_7_e.pdf).

After spending half of my day just trying to find out how to use it with the Arduino (which in my case involved learning what a stepper is and how it works and all of the different kinds of steppers), I was finally able to setup a working circuit based on Tom Igoe's explanation found here: http://arduino.cc/en/Reference/StepperUnipolarCircuit. Here is my circuit:

It is working, I would say, but the thing is that the stepper is too weak (Sorry about the lack of proper technical term). From what I've read, I believe I have to connect the stepper to an external power supply, but I could not find any reference on how to do that and I'm afraid of doing it wrong and destroying my Arduino. What I thought about doing is this:

Is this correct? Or lucky me I didn't try.

Any help is greatly appreciated.
Thanks a lot for your time,

I think you have the right idea, but the datasheet suggests there are two variations of this motor, a 6V one and a 24V one. I'd make very sure you have the 24V one. You can check by measuring the resistance of one winding. It should be 50 ohms (approximately) according to the datasheet. If it's closer to 8 ohms, you have the 6V version and should use a 6V external supply.

You are right, though, that an external supply is preferred as powering a motor directly from the Arduino is not a good idea.

I would move the external power supply ground (black) wire closer to the ground wire for the ULN2003 (near pin 8). Might as well make that path as short as possible.

Otherwise your wiring looks correct!

Hello RuggedCircuits. First of all, thanks a lot for the answer!
For some reason the topic reply email went to my spam box and I just saw your message today.
One thing that I could not quite follow was when you said:

"I would move the external power supply ground (black) wire closer to the ground wire for the ULN2003 (near pin 8)."

Could you please explain this to me again? Sorry, but I'm quite a newbie in electronics.

Thanks a lot,

This is what I mean:

Holly cow!! That was THE fastest reply ever!!! Thanks a lot!!! :smiley:

Take the black wire from the 24v supply out of the board where you have it and place it directly next to pin 8 on the darlington driver. Electrically this is the same but the current doesn't have to travel round the board through several connections to get to the pin.

So fast it beat me just writing words. I'll go and do some work now.

:wink: Nice drawings, BTW. I wish everyone took the time to explain their problems so clearly!

Hi Cassiano,

I read in your post that you are using a Mitsumi M35SP-7T stepper motor and you show in your image 5 wires from motor to circuit.

I have also a Mitsumi M35SP-7T stepper motor, but with an A extra => so M35SP-7T A. This particular motor has only 4 wires and on the label it is written 9 Ohms. So from the data sheet of Mitsumi I guess that the motor runs on 6 V. I tried 5 volts and it works fine. However, I can not find nor on the internet, nor at Mitsumi's the reason for 4 wires and the extra label A.

So at the moment I am using the motor as a bipolar one (whereas the manual says unipolar) with a puls rate of 200Hz. At what frequency are you using your motor? Do you have Mitsumi motors with 4 wires only?



Hello Guido.
Indeed mine has 5 wires. The funny thing is that it has written 140 Ohms on its label. I could not find the specs for the T model at the time, only for the M35SP-7 not the -7T. Maybe the T would explain the 140sOhms.
I also tried to google the specs on yours, but couldn't find any real reference about its existence.
Regarding the frequency, I was using the Stepper library: Stepper - Arduino Reference

Since I'm quite a beginner on all this electronics stuff, I believe I cannot help you much more than this.

Kind regards,

There are two ways of implementing a stepping motor, one uses two coils (4 wires) and the other uses four coils (5 wires)