ULN2003 and ARDUINO UNO Wiring and Simple Example Code

Below is the connection diagram for the ULN2003 and Arduino UNO.

Simple example code:

#include <Arduino.h>
#define IN1 5        // Pin naming  
#define IN2 4
#define IN3 3
#define IN4 2
void setup()
{
    pinMode(IN1,OUTPUT);   //Set the pin as an output pin  
    pinMode(IN2,OUTPUT);
    pinMode(IN3,OUTPUT);
    pinMode(IN4,OUTPUT);
}
void loop()
{
    Phase_A();         //Set phase A
    delay(2);         //Changing the delay can change the rotation speed 
    Phase_B();         //Set phase B
    delay(2);           
    Phase_C();          //Set phase C
    delay(2);           
    Phase_D();         //Set phase D
    delay(2);
}
void Phase_A()
{
    digitalWrite(IN1,HIGH);    //ln1 pin high level
    digitalWrite(IN2,LOW);
    digitalWrite(IN3,LOW);
    digitalWrite(IN4,LOW);
}
void Phase_B()
{
    digitalWrite(IN1,LOW);   
    digitalWrite(IN2,HIGH);     //ln1 pin high level
    digitalWrite(IN3,LOW);
    digitalWrite(IN4,LOW);
}
void Phase_C()
{
    digitalWrite(IN1,LOW);   
    digitalWrite(IN2,LOW);
    digitalWrite(IN3,HIGH);      //ln1 pin high level
    digitalWrite(IN4,LOW);
}
void Phase_D()
{
    digitalWrite(IN1,LOW);   
    digitalWrite(IN2,LOW);
    digitalWrite(IN3,LOW);
    digitalWrite(IN4,HIGH);     //ln1 pin high level
}

Updated on: 07/08/2025