help, stepper motor

Thread Starter


Joined Feb 10, 2006
I just brought a L293D and has a M42SP-7 bipolar stepper motor which I take out from my old printer. This bipolar stepper motor has 4 wires ( 3 orange colour and 1 blue colour). May I know which lead wire is ( A, A bar, B and B bar) as mention in its data sheet? I know that the resistance of a same coil wire is very low. How do I know which one is A and A bar in the same coil? Can anyone tell me what is the control sequence of this bipolar stepper motor? The bioplar stepper motor data sheet I have attach it with this forum. Thank you first for your kind help. :)


Joined Aug 4, 2010
check the resistances between terminals,
ones which show finite value are A and A bar
abd respectively other set will be B and B bar
and among some u will get infinity value, leave that...


Joined Jul 17, 2007
Here is the official Mitsumi page for your stepper:

First, find your two pairs for coils A and B using a multimeter set to the 200 Ohms scale. You should measure either ~50 or ~150 Ohms on the two pairs; if 50 Ohms, it's a 12v motor; if 150 Ohms, it's a 24v motor.

The motor had a connector on it when it was installed in the printer. The orange lead is/was on one end of a connector that was keyed to only insert one way to its' mate.

You can determine how it was connected by reverse-engineering the driver board it was plugged into. However, it will probably be easier to use the trial and error method, as there are only four wires.

If the motor simply "jogs" back and fourth after connecting it to the driver, then you will need to switch the polarity of one of the coils. If it then runs backwards from the desired direction, you can either switch the polarity of both coils, or invert the logic going into the driver IC.


Joined Sep 3, 2010
Micro, you might want to find and read "Jones on stepper motors". That document has more info in it than you will ever need, but has everything in a fairly short and concise document. It has just about every possible configuration of Bi-, Uni- and Hybrid steppers and all of the basic wiring conventions as well as diagrams and coding schemes for l series and integrated driver boards. The time you spend on this doc will be well spent and return your investment many times over in good solid basic knowledge. I have a copy saved in every electronics folder on my hard drive for easy reference, no matter where I am working or what files I am currently using. It's that good....