Drive a Stepper Motor with an AVR Microprocessor

Step 2 Find Common Ground

So you've got five (or four, or six) wires. Your motor's going to have two halves, and you can probably even tell just by looking which side each wire belongs to.

If you're only looking at four wires, you're in luck -- it's a bipolar motor. All you have to do is figure out which two pairs of wires go together.

If you've got a unipolar motor, or more than 4 wires, you're going to have to break out your ohmeter. What you're looking for is the common (ground) wire for each half. You can tell which is ground in a bipolar motor because it has half the resistance to either of the poles than the poles do across themselves.

Pictured is my notes from hooking up wires to wires and noting the resistance (or if they're connected at all). You can see that White is the ground for the bottom trio b/c it has half the resistance to Red or Blue that they have to each other.

(This motor's strange and doesn't have a center tap on the top magnet coil. It's like it's half-bipolar, half-unipolar. Maybe you could use this to sense rotation in the Red-White-Blue coil when the Black-Yellow coil is being driven.)