Stepper motor interfaces

The stepper pulses are relatively slow. You should be able to do it with one micro.

There are several considerations.

If you have a unipolar motor, and want to do full stepping, using a very simple micro and n-channel MOSFETS provides a workable system.

If you have a bipolar motor, you need a bridge to drive it, and such a config argues more for a dedicated driver chip.

If you want to do microstepping, that argues even more for a dedicated driver chip.

Depends a lot on the exact type of motor you're driving. Unipolar or bipolar, what current, what voltage, etc.

I've created several projects with the 3967 from Allegro:

This is a driver chip for bipolar motors, full H-bridge, current regulators and microstepping. Driving the chip is easy : one pin for the clock for each (micro)step and one pin for the direction. It needs a few resistors and capacitors for the PWM current regulators. Be sure to provide proper thermal connections to your PCB for cooling. (I know what I'm talking about, I fried a few)

That's true, but the software and testing effort needed to get optimum performance from a particular motor can be expensive. You need to have your program control acceleration curves, watch out for resonance frequencies and a number of other functions. You still have do the tests and make the decisions with a motor controller, but you don't have to write and debug the code that implements the functions.

If you have the micro do the pulses, you are adding a somewhat demanding real-time task to the chores your micro must perform.

Mark Borgerson

I have a guess that with sufficiently small microstepping, the torque- frequency curve flattens out, and the resonant problems disappear. Smoothly commutated brushless DC motors (BLDC) have no problems with resonance. The smoother the microstep, the more the stepper motor resembles a 3 phase BLDC.

This feature alone is a strong argument for microstepping - one that had not occured to me before.

Aside : brushless DC motors should really be called brushless AC motors.