A4988 stepper driver with Arduino Nano — NEMA 17 on STEP/DIR

The A4988 drives the NEMA 17 steppers used in 3D printers, CNC machines and camera sliders. The Nano only sends two signals: a pulse on STEP for each step and a level on DIR for the direction.

The motor runs from its own 12 V supply on VMOT, while the A4988’s logic runs from the Nano’s 5V. Set the current limit with the trimmer first — it is the one step that decides whether the driver survives.

Wiring

Board quirks

• Set the current limit before connecting the motor: turn the small pot until Vref (pot wiper to GND) = motor current × 8 × Rsense. With 0.1 Ω sense resistors and a 1 A motor, Vref ≈ 0.8 V; with 0.05 Ω (some clones), 0.4 V.
• Never unplug the motor while VMOT is powered — the voltage spike kills the A4988.
• MS1–MS3 left open = full steps (200 per turn). Tie all three to 5V for 1/16 microsteps (3200 per turn) and raise the speeds.
• Find the coil pairs with a multimeter: two wires with a few ohms between them are one coil (1A/1B).
• The Nano’s STEP pulses are fast enough for ~4000 steps/s with AccelStepper; beyond that use a timer-based library.

Code

// A4988 stepper driver on an Arduino Nano with AccelStepper: one revolution each way.
// STEP → D3, DIR → D2, EN → D4 (LOW = enabled), SLP and RST → 5V, VDD → 5V, GND → GND,
// VMOT → 12 V supply (+), supply (−) → GND. MS1-MS3 open = full steps (200/rev for a NEMA 17).
#include <AccelStepper.h>

const uint8_t STEP_PIN = 3;
const uint8_t DIR_PIN = 2;
const uint8_t EN_PIN = 4;
const long STEPS_PER_REV = 200;

AccelStepper stepper(AccelStepper::DRIVER, STEP_PIN, DIR_PIN);

void setup() {
  Serial.begin(115200);
  stepper.setEnablePin(EN_PIN);
  stepper.setPinsInverted(false, false, true);  // EN is active-LOW on the A4988
  stepper.enableOutputs();
  stepper.setMaxSpeed(400);       // steps/s
  stepper.setAcceleration(800);
  stepper.moveTo(STEPS_PER_REV);
  Serial.println(F("Driver enabled - one turn forward"));
}

void loop() {
  if (stepper.distanceToGo() == 0) {
    Serial.print(F("At step "));
    Serial.println(stepper.currentPosition());
    delay(500);
    stepper.moveTo(-stepper.currentPosition());
  }
  stepper.run();
}

// A4988 stepper driver on an Arduino Nano with AccelStepper: one revolution each way.
// STEP → D3, DIR → D2, EN → D4 (LOW = enabled), SLP and RST → 5V, VDD → 5V, GND → GND,
// VMOT → 12 V supply (+), supply (−) → GND. MS1-MS3 open = full steps (200/rev for a NEMA 17).
#include <AccelStepper.h>

const uint8_t STEP_PIN = 3;
const uint8_t DIR_PIN = 2;
const uint8_t EN_PIN = 4;
const long STEPS_PER_REV = 200;

AccelStepper stepper(AccelStepper::DRIVER, STEP_PIN, DIR_PIN);

void setup() {
  Serial.begin(115200);
  stepper.setEnablePin(EN_PIN);
  stepper.setPinsInverted(false, false, true);  // EN is active-LOW on the A4988
  stepper.enableOutputs();
  stepper.setMaxSpeed(400);       // steps/s
  stepper.setAcceleration(800);
  stepper.moveTo(STEPS_PER_REV);
  Serial.println(F("Driver enabled - one turn forward"));
}

void loop() {
  if (stepper.distanceToGo() == 0) {
    Serial.print(F("At step "));
    Serial.println(stepper.currentPosition());
    delay(500);
    stepper.moveTo(-stepper.currentPosition());
  }
  stepper.run();
}

Library: AccelStepper (Mike McCauley) — compiled with AccelStepper 1.64.

Expected serial output

Driver enabled - one turn forward
At step 200
At step -200
At step 200

Driver enabled - one turn forward
At step 200
At step -200
At step 200

Common errors