I am looking at a new project which involves controlling an MP35SP-7N stepper motor rescued from an old scanner. I know I need to control it via a darlington array such as the ULN2003 but I do not know which of the wires on the stepper motor to connect to what!
I don't know if this is a unipolar or Bipolar stepper.
There are Red, Orange, Yellow, Brown & Black wires. I assume the Red is power and the others are the coils and are therefore connected to the outputs of the ULN2003. Is this correct?
I assume the Red is power and the others are the coils and are therefore connected to the outputs of the ULN2003.
Why are you making this assumption? Is it just a guess you pulled out of a hat?
If you don't have a datasheet for the motor (or can't find one), then you will have to use a multimeter to ohm-out the coils. Since you have five wires, it is likely a 5-wire unipolar stepper:
You need to figure out which wire is the common wire using a multimeter; measure the resistance between pairs of wires; when you find one wire that gives the same resistance reading when the other four wires are probed, that is your common wire (could possibly be the black wire, but not always). Any other combination will give you a resistance reading that should be around double that of the reading for when you find the common (because those combinations will be a resistance reading across two coils, instead of a single coil).
Right, I have rang it out with my meter and the Red appears to be the common. I have based this on the fact that the readings for red to any other wire are approximately 47 ohms whereas all other readings are approximately 95 ohms.
I did find a datasheet for the motor but it did not give any indication of which wire was which. It also lists 2 different voltages for the supply, 6v and 24v. Both are under the same part number heading and it appears that the only differences are torque, current consumption and the maximum "pull-in" and "pull-out" pulse rates.
The power supply for the scanner was 7.5V so I presume the figures in the 6V column of the datasheet are the ones to note.
Another (possibly dumb) question. Can you reverse a stepper motor. Is it as simple as energising Coil1, coil2, coil3, coil4 for one direction then coil 4, coil 3, coil 2, coil 1 for the reverse?