Unipolar Stepper Motor (28BYJ-48)

Overview

A stepper motor moves in discrete, precise steps instead of spinning freely like a DC motor. The 28BYJ-48 is a unipolar stepper: it has four coils with one common wire, which the ULN2003 driver module switches on and off in a fixed sequence. Each step of the sequence nudges the rotor forward by a tiny angle, so the shaft position is exactly predictable. The 28BYJ-48 is rated for 5 V and comes with a 64:1 reduction gearbox, which trades almost all of its speed for torque and precision — the output shaft tops out around 20–25 RPM:

2048 steps per revolution in full-step mode
4096 steps per revolution in half-step mode
Half-step mode gives smaller, smoother steps (about 0.088° per step at the output shaft)

The motor draws roughly 100 mA per coil. A GPIO pin can neither source that current nor survive the voltage spikes a coil produces when switched off, so the coils are always driven through the ULN2003 module — seven Darlington transistor pairs with built-in flyback diodes. Its inputs are driven directly by the GLYPH board’s GPIO pins. The motor is rotated by energising the coils one after another. The half-step sequence used in this tutorial is:

Step	IN1	IN2	IN3	IN4
1	1	1	0	0
2	0	1	0	0
3	0	1	1	0
4	0	0	1	0
5	0	0	1	1
6	0	0	0	1
7	1	0	0	1
8	1	0	0	0

Repeating this table forward rotates the shaft one way; repeating it backward rotates the other way. The speed is set by the delay between rows. The rows energise adjacent coils in the motor’s physical order — the 28BYJ-48’s coils sit around the rotor in the order blue, pink, yellow, orange (IN1-IN2-IN3-IN4). A sequence that energises non-adjacent coils pulls the rotor forward, then back, so the shaft buzzes in place instead of turning. The same quirk is why the Stepper library in the alternative section below needs its pins passed as IN1-IN3-IN2-IN4.

Pin Configuration

The ULN2003 module has four logic inputs (IN1–IN4), two power pins, and a 5-pin socket for the motor’s JST plug.

ULN2003 driver module	GLYPH-C6
IN1	GPIO 14
IN2	GPIO 15
IN3	GPIO 18
IN4	GPIO 19
GND	GND
VCC	USB (5 V)

The module’s power terminals accept a 5–12 V supply — feed it 5 V, since the 28BYJ-48 is a 5 V motor. The 28BYJ-48’s 5-wire JST plug (red is the common wire, carried to +5 V by the module) goes straight into the module’s motor socket. Typical wire colours are IN1 = blue, IN2 = pink, IN3 = yellow, IN4 = orange, but many clones use different colours — if the motor vibrates instead of turning, swap the IN2 and IN3 wires.

Key Features

28BYJ-48 unipolar stepper — 4 coils + common, 5 V, about 100 mA per coil
64:1 reduction gearbox — high torque (about 34 mN·m) and self-locking output shaft
2048 / 4096 steps per revolution — full-step / half-step
ULN2003 driver module — Darlington array with flyback diodes, accepts a 5–12 V supply
Direction and speed fully software-controlled — no encoder needed for known distances

Application

Small robotics and camera pan-tilt mounts
3D printer extruder feeders
Air-conditioner louvres and automated blinds
Valve and actuator positioning
Any project needing slow, precise, repeatable rotation

Step 1: Hardware Required

Pcbcupid GLYPH-C6 board
28BYJ-48 unipolar stepper motor
ULN2003 driver module
6 × jumper wires (female–female)
USB-C cable for power and upload

Step 2: Circuit Diagram

Wire the driver module to the GLYPH-C6 as listed in Pin Configuration:

IN1 → GPIO 14, IN2 → GPIO 15, IN3 → GPIO 18, IN4 → GPIO 19
GND of the driver → GND of the board (grounds must be shared)
The driver’s power input (the + and − terminals, which accept 5–12 V) → the board’s USB pin, which carries 5 V while the board is powered over USB-C
Plug the motor’s 5-pin JST connector into the module’s socket

The two coils energised at once in half-step mode draw about 200 mA in total, which a USB port handles comfortably. If the motor feels weak or the board resets, power the driver from an external 5 V 1 A supply instead (module + → supply +5 V, and tie the supply ground to the board’s GND).

Step 3: Code Setup

Open the Arduino IDE and paste the sketch below into a new file. It rotates the shaft one full revolution in one direction, pauses, then one revolution back.

// 28BYJ-48 unipolar stepper + ULN2003 driver on Pcbcupid GLYPH-C6
// Rotates the shaft one full revolution each way, then repeats.

// ULN2003 inputs -> GLYPH-C6 GPIOs
#define IN1 14
#define IN2 15
#define IN3 18
#define IN4 19

const int motorPins[4] = {IN1, IN2, IN3, IN4};

// Half-step sequence. Columns = {IN1, IN2, IN3, IN4}
// 1 = coil energised, 0 = coil off. The rows energise adjacent
// coils in the motor's physical order so the shaft rotates smoothly.
const int halfStepSequence[8][4] = {
  {1, 1, 0, 0},   // IN1 + IN2
  {0, 1, 0, 0},   // IN2
  {0, 1, 1, 0},   // IN2 + IN3
  {0, 0, 1, 0},   // IN3
  {0, 0, 1, 1},   // IN3 + IN4
  {0, 0, 0, 1},   // IN4
  {1, 0, 0, 1},   // IN4 + IN1
  {1, 0, 0, 0}    // IN1
};

// The 64:1 gearbox turns 4096 half-steps into 1 revolution.
const int stepsPerRevolution = 4096;

// Milliseconds per half-step. Lower = faster (try 1 to 5).
int stepDelay = 2;

int currentStep = 0;

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(motorPins[i], OUTPUT);
    digitalWrite(motorPins[i], LOW);
  }
}

void setStep(int step) {
  for (int i = 0; i < 4; i++) {
    digitalWrite(motorPins[i], halfStepSequence[step][i]);
  }
}

// Move one half-step. dir: +1 one way, -1 the other.
void stepMotor(int dir) {
  currentStep = (currentStep + dir + 8) % 8;
  setStep(currentStep);
  delay(stepDelay);
}

void loop() {
  // One full revolution in one direction
  for (int i = 0; i < stepsPerRevolution; i++) {
    stepMotor(1);
  }
  delay(1000);

  // One full revolution in the opposite direction
  for (int i = 0; i < stepsPerRevolution; i++) {
    stepMotor(-1);
  }
  delay(1000);
}

How it works: halfStepSequence holds the 8 half-step states from the table above. stepMotor() walks through the rows forward or backward, and stepDelay sets how long each state is held — the smaller the delay, the faster the shaft spins.

Step 4: Upload the Code

Connect the GLYPH-C6 to your computer with the USB-C cable.
In the Arduino IDE, go to Tools → Board → esp32 → Pcbcupid GLYPH C6.

The Pcbcupid GLYPH C6 board entry only appears when the installed esp32 core version is greater than or equal to 3.1.0.

Set Tools → USB CDC On Boot → Enabled.

If USB CDC On Boot is disabled, no serial data shows up in the Serial Monitor.

Select the board’s port under Tools → Port.
Click the upload arrow button (or press Ctrl + U) and wait for the upload to finish.

Step 5: Observe the Output

Once the upload completes, the motor shaft starts turning immediately:

It spins one full revolution in one direction, pauses for a second, then one full revolution back — and repeats.
Put a small tape flag on the shaft to see the rotation more clearly.
Open the Serial Monitor at 115200 baud if you add Serial.println() calls to the sketch.

pcbcupid_unipolar_stepper_motor_rotation

Things to Try

Change the speed — edit stepDelay to 1 for faster or 5 for slower motion, and re-upload.
Find the speed limit — at stepDelay of 1 the shaft does about 15 RPM comfortably. Lower values need a smooth acceleration ramp or the rotor loses sync and buzzes — the gearbox tops out around 20–25 RPM. This motor is built for slow, precise motion, not speed.
Change the distance — replace stepsPerRevolution in the loops with 2048 for half a revolution, or 1024 for a quarter.
Go full-step — energise only rows 1, 3, 5 and 7 of the table ({1,1,0,0}, {0,1,1,0}, {0,0,1,1}, {1,0,0,1}) and use 2048 steps per revolution. More torque, but rougher motion.

Troubleshooting

The shaft vibrates but does not turn — the energising sequence does not match your motor’s physical coil order. The 28BYJ-48’s four coils sit in a fixed order around the rotor (blue, pink, yellow, orange on most units), and energising non-adjacent coils pushes the rotor forward, then back, so it buzzes in place. Swap the wires on IN2 and IN3 (or try other orders) until it turns smoothly.
The motor turns sluggishly or stalls — make sure the driver is powered with 5 V, and try an external 5 V 1 A supply with a common ground.
The revolution stops a hair short of exactly one turn — the gearbox ratio is actually about 63.7:1, not 64:1. Use 4076 half-steps for a near-exact revolution.

Alternative: Using the Arduino Stepper Library

The built-in Stepper library drives the same sequence with less code — at the cost of hiding how the motor works, and with one gotcha: the pins must be passed in the order IN1-IN3-IN2-IN4 (not IN1-IN2-IN3-IN4) to match the motor’s internal coil order, and one revolution is 2048 steps.

// 28BYJ-48 + ULN2003 using the built-in Stepper library.
#include <Stepper.h>

// With this library, 2048 steps = 1 revolution of the output shaft.
const int stepsPerRevolution = 2048;

// IMPORTANT: pin order is IN1-IN3-IN2-IN4, matching the motor's
// internal coil order — IN1-IN2-IN3-IN4 will not rotate smoothly.
Stepper myStepper(stepsPerRevolution, 14, 18, 15, 19);

void setup() {
  myStepper.setSpeed(10);  // output RPM (max about 15)
}

void loop() {
  myStepper.step(stepsPerRevolution);   // one revolution
  delay(1000);
  myStepper.step(-stepsPerRevolution);  // and back
  delay(1000);
}

Note that the library uses delay() internally, so while the motor is stepping, your sketch cannot do anything else. The manual sequence from Step 3 is the better base when you need to read sensors or run other tasks while the motor moves.

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Unipolar Stepper Motor (28BYJ-48)

Unipolar Stepper Motor (28BYJ-48)

Overview

Pin Configuration

Key Features

Application

Step 1: Hardware Required

Step 2: Circuit Diagram

Step 3: Code Setup

Step 4: Upload the Code

Step 5: Observe the Output

Things to Try

Troubleshooting

Alternative: Using the Arduino Stepper Library

​Unipolar Stepper Motor (28BYJ-48)

​Overview

​Pin Configuration

​Key Features

​Application

​Step 1: Hardware Required

​Step 2: Circuit Diagram

​Step 3: Code Setup

​Step 4: Upload the Code

​Step 5: Observe the Output

​Things to Try

​Troubleshooting

​Alternative: Using the Arduino Stepper Library

Unipolar Stepper Motor (28BYJ-48)

Overview

Pin Configuration

Key Features

Application

Step 1: Hardware Required

Step 2: Circuit Diagram

Step 3: Code Setup

Step 4: Upload the Code

Step 5: Observe the Output

Things to Try

Troubleshooting

Alternative: Using the Arduino Stepper Library