ESP32 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 ESP32 DevKit 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 25, 26, 27, 14, and the motor’s power from VIN (5 V from USB). It uses the stock Stepper library.
- 3.3 V logic
- Library: Stepper.h
- IN1 to IN4 on 25, 26, 27, 14
- 2048 steps a turn
Wiring the 28BYJ-48 Stepper to the ESP32
Every connection in the circuit above, with the board’s own pin names.
| 28BYJ-48 Stepper pin | ESP32 pin | Why |
|---|---|---|
| IN1 | GPIO 25 (D25) | Coil A, through the ULN2003’s first Darlington. |
| IN2 | GPIO 26 (D26) | Coil B. |
| IN3 | GPIO 27 (D27) | Coil C. |
| IN4 | GPIO 14 (D14) | Coil D. |
| VCC (+) | VIN (5 V from USB) | The motor’s 5 V supply: a couple of hundred milliamps, more than USB likes to spare. |
| GND (-) | GND | Common ground. |
The motor runs from VIN (5 V from USB), while IN1 to IN4 come from 3.3 V pins. The ULN2003 switches happily from 3.3 V, so no level shifting is needed. On a real bench, a stepper on USB power can brown out the board when it starts; a separate 5 V supply with the grounds joined is safer.
Pins to leave alone on the ESP32
GPIO 34, 35, 36 (VP) and 39 (VN) are input only: they cannot drive a pin or take an internal pull-up. GPIO 0, 2, 5, 12 and 15 are strapping pins, read at power-on, and GPIO 6 to 11 are the flash chip.
On a real bench
The thirty-pin DevKit straddles a breadboard with one row of holes free on each side, which is where the 28BYJ-48 Stepper’s jumpers go. Many ESP32 boards are wider and cover both rows; then use two breadboards side by side. Hold BOOT while uploading if the IDE cannot connect.
The code
The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.
#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, 25, 27, 26, 14);
void setup() {
Serial.begin(115200);
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(115200) opens the serial monitor. Serial is UART0 on the USB bridge. ESP32 sketches usually run it at 115200 baud, which this one does.
Common mistakes with the 28BYJ-48 Stepper on the ESP32
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 ESP32 DevKit?
Yes. The circuit at the top of this page is an ESP32 DevKit with a 28BYJ-48 stepper and ULN2003 driver, running in your browser on a simulated ESP32 (Xtensa LX6). 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.