char led_red = 23;
char led_yellow = 19;
char led_green = 18;

char led_red_state = LOW;
char led_yellow_state = LOW;
char led_green_state = LOW;

long led_red_previous_millis = 0;
long led_yellow_previous_millis = 0;
long led_green_previous_millis = 0;
//this variable to store the last time
// the red led has changed store

int red_led_interval = 1000;
int yellow_led_interval = 2000;
int green_led_interval = 500;
// ON for 1000 ms
// OFF for 1000 ms

void setup() {
  // put your setup code here, to run once:
  pinMode(led_red, OUTPUT);
  pinMode(led_yellow, OUTPUT);
  pinMode(led_green, OUTPUT);
}

void loop() {
  long current_millis = millis();

  if (current_millis - led_red_previous_millis >= red_led_interval)
{
    led_red_previous_millis = current_millis;
 
   if(led_red_state == LOW)
    led_red_state =HIGH;
   
   else
    led_red_state = LOW;
   
    digitalWrite(led_red, led_red_state);

  }


  if (current_millis - led_yellow_previous_millis >= yellow_led_interval)
 
  {
   led_yellow_previous_millis =current_millis;
    

    if(led_yellow_state == LOW)
    led_yellow_state =HIGH;
  
    else
    led_yellow_state = LOW;
    

    digitalWrite(led_yellow, led_yellow_state);
    
  }

  if (current_millis - led_green_previous_millis >= green_led_interval)

  {
    led_green_previous_millis =current_millis;
 

    if(led_green_state == LOW)
    led_green_state =HIGH;
  

    else
    led_green_state = LOW;
   
    digitalWrite(led_green, led_green_state);

}
}