A4988 stepper driver with ESP32 DevKit V1 — NEMA 17 wiring and code

The A4988 is the small red or green stepper driver used in 3D printers and CNC kits. It drives a NEMA 17 from a 12 V supply and needs only two signals: STEP and DIR.

On the ESP32 DevKit V1 power the driver’s logic (VDD) from 3V3, so STEP and DIR connect straight to GPIO26 and GPIO27. The motor supply goes to VMOT with a 100 µF capacitor at the driver. Set the current limit before the first run. The sketch uses AccelStepper’s acceleration ramps to turn the motor two revolutions forward and back.

Wiring

Board quirks

• Set the current limit before the first run. Turn the trimpot until Vref (pot to GND) is about I × 8 × Rsense — with the usual 0.1 Ω sense resistors (R100), 0.8 V for 1 A. Too high cooks the driver; too low and the motor misses steps.
• Never connect or disconnect the motor while VMOT is powered. The coil’s voltage spike destroys the A4988 instantly.
• MS1–MS3 are left open: they are pulled LOW on the board, giving full steps (200 per turn). Tie all three to 3V3 for 1/16 steps (3200 per turn) and smoother, quieter motion.
• Find the coil pairs with a multimeter: a pair shows a few ohms between its two wires. Each pair goes to 1A/1B or 2A/2B; swapping one pair only reverses direction.
• AccelStepper’s run() must be called constantly. A delay() anywhere in loop() while the motor moves stalls it. For Wi-Fi projects, run the stepper in its own FreeRTOS task.
• STEP, DIR and EN avoid the strapping pins (D2, D5, D12, D15) so the motor doesn’t jerk when the ESP32 boots.

Code

// NEMA 17 stepper + A4988 driver on an ESP32 DevKit V1 with AccelStepper.
// STEP → D26, DIR → D27, EN → D25 (LOW = driver on), VDD → 3V3, RST → 3V3 (or bridge RST–SLP).
// VMOT from a 12 V supply with 100 µF across VMOT–GND. MS1–MS3 open = full step (200 steps/rev).
#include <AccelStepper.h>

constexpr uint8_t STEP_PIN = 26, DIR_PIN = 27, EN_PIN = 25;
constexpr long STEPS_PER_REV = 200;  // 1.8° motor, full step

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(800);       // steps/s
  stepper.setAcceleration(400);   // steps/s² — ramps stop a 12 V motor stalling at start
  stepper.moveTo(2 * STEPS_PER_REV);
  Serial.println("A4988: 2 turns forward, 2 back, then rest");
}

void loop() {
  stepper.run();  // must be called as often as possible — no delay() while moving
  if (stepper.distanceToGo() == 0) {
    Serial.printf("At position %ld steps\n", stepper.currentPosition());
    stepper.disableOutputs();  // coils off while resting: motor and driver stay cool
    delay(1500);
    stepper.enableOutputs();
    stepper.moveTo(stepper.currentPosition() == 0 ? 2 * STEPS_PER_REV : 0);
  }
}

// NEMA 17 stepper + A4988 driver on an ESP32 DevKit V1 with AccelStepper.
// STEP → D26, DIR → D27, EN → D25 (LOW = driver on), VDD → 3V3, RST → 3V3 (or bridge RST–SLP).
// VMOT from a 12 V supply with 100 µF across VMOT–GND. MS1–MS3 open = full step (200 steps/rev).
#include <AccelStepper.h>

constexpr uint8_t STEP_PIN = 26, DIR_PIN = 27, EN_PIN = 25;
constexpr long STEPS_PER_REV = 200;  // 1.8° motor, full step

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(800);       // steps/s
  stepper.setAcceleration(400);   // steps/s² — ramps stop a 12 V motor stalling at start
  stepper.moveTo(2 * STEPS_PER_REV);
  Serial.println("A4988: 2 turns forward, 2 back, then rest");
}

void loop() {
  stepper.run();  // must be called as often as possible — no delay() while moving
  if (stepper.distanceToGo() == 0) {
    Serial.printf("At position %ld steps\n", stepper.currentPosition());
    stepper.disableOutputs();  // coils off while resting: motor and driver stay cool
    delay(1500);
    stepper.enableOutputs();
    stepper.moveTo(stepper.currentPosition() == 0 ? 2 * STEPS_PER_REV : 0);
  }
}

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

Expected serial output

A4988: 2 turns forward, 2 back, then rest
At position 400 steps
At position 0 steps
At position 400 steps

A4988: 2 turns forward, 2 back, then rest
At position 400 steps
At position 0 steps
At position 400 steps

Common errors