How Stepper Motors Work: Steps, Microstepping & A4988 Driver Guide

How a Stepper Motor Steps

Inside a typical NEMA 17 bipolar stepper motor are two coils (phases) wound around iron stator poles. The rotor is a permanent magnet with 50 teeth on each pole face. By alternating which coils are energized — and in which polarity — the driver creates a rotating magnetic field that the permanent magnet rotor locks onto and follows.

A standard 1.8° step motor completes 200 full steps per revolution. The sequence of coil energization for a full-step drive is:

Fig 1: Stepper motor coil sequence — stepping through the 4-step excitation cycle

Microstepping: Smooth & Silent Motion

Instead of fully energizing one coil at a time, microstepping drives both coils simultaneously with sinusoidal current waveforms. The rotor is attracted to intermediate positions between full steps, producing:

Arduino + A4988: Control Code

// Arduino NEMA 17 stepper motor with A4988 driver
// A4988 MS1=HIGH, MS2=HIGH, MS3=HIGH → 1/16 microstepping

#include <AccelStepper.h>

#define STEP_PIN 3
#define DIR_PIN  4
#define ENABLE_PIN 8

// Mode: DRIVER = step/dir interface
AccelStepper stepper(AccelStepper::DRIVER, STEP_PIN, DIR_PIN);

void setup() {
  pinMode(ENABLE_PIN, OUTPUT);
  digitalWrite(ENABLE_PIN, LOW); // Enable driver (active LOW)
  
  stepper.setMaxSpeed(1000);       // microsteps/sec
  stepper.setAcceleration(500);    // microsteps/sec²
  stepper.moveTo(3200);            // 1 full revolution at 1/16 step
}

void loop() {
  stepper.run(); // Call frequently - non-blocking
  
  if (stepper.distanceToGo() == 0) {
    stepper.moveTo(-stepper.currentPosition()); // Reverse
  }
}

NEMA Frame Sizes Compared

Frequently Asked Questions