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 state
int led_red_interval = 1000;
int led_yellow_interval = 2000;
int led_green_interval = 500;
//ON for 1000ms
//OFF for 1000ms



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 >= led_red_interval)
{
  led_red_previous_millis = current_millis;

  //now reversethe led 's state
  if (led_red_state == LOW);
  led_red_state == HIGH;
}
  else
  led_red_state = LOW;

  //control the led accordingly
  digitalWrite(led_yellow, led_yellow_state);
  if (current_millis - led_yellow_previous_millis >= led_yellow_interval)
{
    led_yellow_previous_millis = current_millis;

    // now reverse the led's state
    if (led_yellow_state == LOW)
      led_yellow_state = HIGH;
    else 
      led_yellow_state = LOW;

    // control the led accordingly
    digitalWrite(led_yellow, led_yellow_state);

  }
}