Stepper Motors (28BYJ-48)

A stepper motor moves in precise, discrete steps rather than spinning freely like a DC motor. This makes it ideal for applications where you need exact positioning -- think 3D printers, CNC machines, camera sliders, and automated blinds. The 28BYJ-48 is an inexpensive, widely available stepper motor that comes paired with the ULN2003 driver board. It is the go-to starter stepper for learning the fundamentals.

This guide uses the ESP32-WROOM-32 DevKit. Pin labels and GPIO numbers may differ on your board -- always check your board's pinout diagram.

🔗Key Specs

Note: There is some confusion online about the exact step count. The 28BYJ-48 is commonly reported as 2048 steps per revolution in half-step mode. You may need to calibrate by running a full revolution and observing the result.

Which motor type? Steppers move in precise, discrete steps. Need continuous rotation with speed control? See DC motors. Need to hold a specific angle? See servo motors. Our motor comparison guide explains the differences.

🔗What You'll Need

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🔗Wiring

The ULN2003 driver board acts as an interface between the ESP32 and the motor. It contains Darlington transistor arrays that can handle the motor's current.

🔗ULN2003 Driver to ESP32

🔗Power

The motor connects directly to the ULN2003 board via its white 5-pin connector -- just plug it in.

Warning: Do not power the stepper motor from the ESP32's 3.3V or 5V pin. The motor draws around $240\,\text{mA}$, which can overload the ESP32's voltage regulator. Use a separate 5V supply and connect the grounds.

🔗Required Libraries

The Stepper library comes built into the Arduino IDE -- no installation necessary.

🔗Code Example: Basic Rotation

This sketch rotates the stepper motor one full revolution in each direction.

#include <Stepper.h>

#define STEPS_PER_REV 2048  // 28BYJ-48 in half-step mode

// Note: the pin order matters for correct stepping sequence
// ULN2003 IN1, IN3, IN2, IN4 mapping for the 28BYJ-48
Stepper stepper(STEPS_PER_REV, 25, 27, 26, 14);

void setup() {
    Serial.begin(115200);
    stepper.setSpeed(10);  // RPM (keep low for 28BYJ-48, max ~15 RPM)
    Serial.println("Stepper motor ready.");
}

void loop() {
    Serial.println("Rotating clockwise...");
    stepper.step(STEPS_PER_REV);   // One full revolution CW
    delay(1000);

    Serial.println("Rotating counter-clockwise...");
    stepper.step(-STEPS_PER_REV);  // One full revolution CCW
    delay(1000);
}

Important: Notice the pin order in the Stepper() constructor: 25, 27, 26, 14 (IN1, IN3, IN2, IN4). The 28BYJ-48's internal coil arrangement requires this non-sequential order. If you use 25, 26, 27, 14, the motor will vibrate but not spin properly.

🔗Code Example: Rotate by Degrees

This helper function lets you command the motor in degrees rather than steps.

#include <Stepper.h>

#define STEPS_PER_REV 2048

Stepper stepper(STEPS_PER_REV, 25, 27, 26, 14);

void rotateDegrees(float degrees) {
    int steps = (int)(degrees / 360.0 * STEPS_PER_REV);
    stepper.step(steps);
}

void setup() {
    Serial.begin(115200);
    stepper.setSpeed(10);
}

void loop() {
    Serial.println("Rotate 90 degrees CW");
    rotateDegrees(90);
    delay(1000);

    Serial.println("Rotate 90 degrees CCW");
    rotateDegrees(-90);
    delay(1000);

    Serial.println("Rotate 180 degrees CW");
    rotateDegrees(180);
    delay(2000);
}

🔗How It Works

🔗Stepping Sequence

A stepper motor has multiple coils arranged around a rotor with permanent magnets. By energizing the coils in a specific sequence, you create a rotating magnetic field that pulls the rotor from one position to the next. Each switch in the sequence moves the rotor by one "step."

The 28BYJ-48 is a 4-phase unipolar motor. In half-step mode (which the Stepper library uses), it energizes the coils in an 8-step sequence:

The internal gear train multiplies the number of steps needed for one output shaft revolution, which is what gives the motor its fine positioning ability.

🔗Speed Limits

The 28BYJ-48 is a geared motor designed for precision, not speed. Setting setSpeed() above approximately $15\,\text{RPM}$ will cause it to skip steps or stall. For reliable operation, keep the speed at $10$--$12\,\text{RPM}$.

🔗Troubleshooting

Tip: To prevent the motor from overheating when idle, set all motor pins to LOW after completing a movement. Add this function and call it when the motor should be at rest:

void disableMotor() {
    digitalWrite(25, LOW);
    digitalWrite(26, LOW);
    digitalWrite(27, LOW);
    digitalWrite(14, LOW);
}

Note that this releases the holding torque, so the shaft can be turned manually.

🔗Next Steps

• Build a motorized camera slider or turntable
• Create an automated window blind controller
• Use a stepper for precise fluid dispensing (peristaltic pump)
• Explore the AccelStepper library for acceleration/deceleration profiles and non-blocking movement