ULN2003 Stepper Driver with an Arduino Uno
A ULN2003 Darlington-array breakout that lets a microcontroller drive a 5V unipolar stepper motor (typically the 28BYJ-48) from four digital pins.
On an Arduino Uno the ULN2003 board's VCC goes to the 5V pin, and that 5 V feeds both its logic and the 28BYJ-48's coils, so the motor's current comes out of the Uno's own supply. IN1 to IN4 sit on D2 to D5, and the Stepper library drives them in the 28BYJ-48's swapped order.
Wiring the ULN2003 Stepper Driver to the Arduino Uno
Pin by pin.
| ULN2003 Stepper Driver | Arduino Uno |
|---|---|
| IN1 | D2 |
| IN2 | D3 |
| IN3 | D4 |
| IN4 | D5 |
| VCC | 5V |
| GND | GND |
What to know on the Arduino Uno
- The board powers the motor from the same 5 V it gets from the Uno. Over USB that 5 V is behind the Uno's 500 mA polyfuse, so run one 28BYJ-48 at a time from it and give a second motor its own 5 V supply with a shared GND.Arduino UNO R3 documentation, USB overcurrent protection
- Each ULN2003A output sinks up to 500 mA and clamps the coil with a built-in diode, so the Uno's pins only switch the Darlington inputs and never carry coil current.TI ULN2003A datasheet, p. 1
- stepper.step() blocks until it finishes: one revolution of 2,048 steps at 10 RPM keeps the Uno busy for about 6 seconds. For a sketch that must do other things meanwhile, step a few at a time in loop() or use AccelStepper.Arduino Stepper library reference
- The sketch passes the pins as D2, D4, D3, D5 (IN1, IN3, IN2, IN4). That swap is the 28BYJ-48's coil order, not a wiring mistake: wire IN1 to IN4 to D2 to D5 in order.Arduino Stepper library reference
ULN2003 Stepper Driver code for the Arduino Uno
Compiled for arduino:avr:uno on 2026-10-30.
// ULN2003 Stepper Driver on Arduino Uno: wiring and a free simulation at https://www.tinkered.ai/components/uln2003-stepper-driver/arduino-uno
#include <Stepper.h>
const int STEPS_PER_REV = 2048; // 28BYJ-48 with internal gearing
// 28BYJ-48 quirk: pass the pins as (IN1, IN3, IN2, IN4) so the coil field
// rotates in order. Wiring above on an Uno: IN1=D2, IN2=D3, IN3=D4, IN4=D5
Stepper stepper(STEPS_PER_REV, 2, 4, 3, 5);
void setup() {
stepper.setSpeed(10); // RPM
}
void loop() {
stepper.step(STEPS_PER_REV); // one full revolution forward
delay(500);
stepper.step(-STEPS_PER_REV); // one full revolution back
delay(500);
}
ULN2003 Stepper Driver on the Arduino Uno: questions
Can an Arduino Uno power a 28BYJ-48 through the ULN2003 board?
One motor, yes, from the Uno's 5V. The board feeds the coils from that 5 V, so for two motors or other heavy loads use a separate 5 V supply with its ground joined to the Uno's.
Why does my sketch freeze while the 28BYJ-48 turns on the Uno?
Stepper.step() does not return until the move ends: a full turn at 10 RPM takes about 6 seconds. Move in small steps per loop() or switch to AccelStepper.
Why are the pins given as 2, 4, 3, 5 in the Stepper constructor?
The 28BYJ-48 needs its coils energised in IN1, IN3, IN2, IN4 order with the Stepper library. The wiring stays IN1 to D2, IN2 to D3, IN3 to D4, IN4 to D5.
This guide as plain Markdown. /components/uln2003-stepper-driver/arduino-uno.md