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Arduino Mega · 28BYJ-48 Stepper

Arduino Mega 28BYJ-48 Stepper Simulator: Wiring, Code and a Live Circuit

This is a 28BYJ-48 stepper motor on its ULN2003 driver board, wired to an Arduino Mega 2560 and turning live in your browser: a quarter turn forward, a quarter turn back, with the shaft angle drawn as it goes.

Four control wires to 8, 9, 10, 11, and the motor’s power from 5V. It uses the stock Stepper library.

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  • 5 V logic
  • Library: Stepper.h
  • IN1 to IN4 on 8, 9, 10, 11
  • 2048 steps a turn
Arduino Mega · 28BYJ-48 Stepperlive0.000 s 0.00x
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The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the 28BYJ-48 Stepper to the Arduino Mega

Every connection in the circuit above, with the board’s own pin names.

28BYJ-48 Stepper pinArduino Mega pinWhy
IN1pin 8Coil A, through the ULN2003’s first Darlington.
IN2pin 9Coil B.
IN3pin 10Coil C.
IN4pin 11Coil D.
VCC (+)5VThe motor’s 5 V supply: a couple of hundred milliamps, more than USB likes to spare.
GND (-)GNDCommon ground.

The ULN2003 board carries the coil current, so the Arduino Mega’s pins only drive its inputs. The motor’s 5 V comes from the 5V pin here; on a real bench a separate 5 V supply with the grounds joined keeps the board from resetting.

Pins to leave alone on the Arduino Mega

Pins 14 to 19 are the three extra serial ports and 20 and 21 are I2C, so keep them free if you will need those. An Uno shield’s I2C on A4 and A5 is not connected to anything on a Mega.

On a real bench

The Mega is long, so put the breadboard beside its double row of pins 22 to 53 and leave the left-hand headers free. The 28BYJ-48 Stepper uses only a few of its 54 pins; a Mega earns its size when one sketch drives a keypad, a display and several sensors at once.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

28BYJ-48 stepper on Arduino Mega
#include <Stepper.h>

// The 28BYJ-48 through its ULN2003 board: 2048 full steps a turn.
const int STEPS_PER_TURN = 2048;

// Note the order: IN1, IN3, IN2, IN4. The Stepper library's sequence
// matches the motor's coils that way.
Stepper motor(STEPS_PER_TURN, 8, 10, 9, 11);

void setup() {
  Serial.begin(9600);
  motor.setSpeed(12);               // rpm; the 28BYJ-48 tops out near 15
  Serial.println("Stepper ready");
}

void loop() {
  Serial.println("Quarter turn forward");
  motor.step(STEPS_PER_TURN / 4);
  delay(300);
  Serial.println("Quarter turn back");
  motor.step(-STEPS_PER_TURN / 4);
  delay(300);
}

Stepper motor(2048, IN1, IN3, IN2, IN4) is the line everybody gets wrong. The library energizes its four pins in a fixed sequence, and for this motor the middle two have to be swapped, or it buzzes in place instead of turning.

setSpeed(12) sets the step rate for 12 revolutions a minute. step(512) blocks until a quarter turn is done, about 1.25 seconds at that speed, then step(-512) comes back. Nothing else in the sketch runs while it steps; AccelStepper.h is the library for moving without blocking.

Serial.begin(9600) opens the serial monitor. Serial is the USB port; Serial1 to Serial3 are on pins 18 and 19, 16 and 17, and 14 and 15.

Common mistakes with the 28BYJ-48 Stepper on the Arduino Mega

The pin order in the constructor

Stepper(steps, IN1, IN2, IN3, IN4) makes the 28BYJ-48 vibrate without turning. The order has to be IN1, IN3, IN2, IN4, as in the sketch.

Asking for more than 15 rpm

The gearbox makes this motor slow. Above about 15 rpm it skips steps or stalls, and because nothing reports the shaft’s position, the sketch never knows. Keep setSpeed() low.

Assuming the motor knows where it is

A stepper has no sensor: the sketch counts the steps it sent. After a stall or a power cycle that count is wrong, which is why real machines home against a limit switch at start-up.

Questions and answers

Can I simulate a 28BYJ-48 stepper with an Arduino Mega 2560?

Yes. The circuit at the top of this page is an Arduino Mega 2560 with a 28BYJ-48 stepper and ULN2003 driver, running in your browser on a simulated ATmega2560. The simulated motor follows the coil sequence on the four pins, so a wrong order makes it stall on the drawing too. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

How many steps is one turn?

2048 in full-step mode and 4096 in half-step mode, because of the motor’s 64 to 1 gearbox. The Stepper library uses full steps.

Can I run two steppers at once?

Not with Stepper.h, whose step() blocks. AccelStepper.h moves several motors at once by calling run() for each in loop().

What about a NEMA 17?

A NEMA 17 needs a current-limiting driver such as the A4988, driven with STEP and DIR pins. The simulator has both, and the A4988 tutorial covers it.

Build your own 28BYJ-48 Stepper project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

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