The circuit I put on in my last post was taken from the web site you quoted in your first request in this thread. I just grabbed the graphic and did a little work on it with MicroSoft Paint program. :)

By the way I am quite surprised that the stepper motor would need to have series resistors put to limit the current. Most of these I have used you simply hook them up and let the bulk DC resistance of the winding limit the current. If you try to operate any motor of this type by limiting the current significantly lower than the current allowed by the resistance of the winding then you are going to find a significant reduction in the amount of available torque from the stepper motor.

Of course you do need to evaluate the voltage you apply as well. If a stepper is designed for 12 volt operation (IE, the winding resistance limits current to a safe and reasonable value with 12 volts across the winding) then tryng to operate it at 24 volts would not be a good thing to do.

It is also sometimes done in stepper driver circuits to put a very small series resistor in each winding leg. Across the resistor the voltage drop is measured and if it gets too high then the drive circuit can be forced off. Some implementations will put these sensing circuits in the power feed lead to the stepper so that one sensing circuit can be used as opposed to four.


Michael Karas