#define RED_LED    PA5
#define YELLOW_LED PA6
#define GREEN_LED  PA7

void setup(void)
{
  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
}

void loop(void)
{
  // RED light
  digitalWrite(RED_LED, HIGH);
  digitalWrite(YELLOW_LED, LOW);
  digitalWrite(GREEN_LED, LOW);
  delay(5000);   // 5 seconds

  // YELLOW light
  digitalWrite(RED_LED, LOW);
  digitalWrite(YELLOW_LED, HIGH);
  digitalWrite(GREEN_LED, LOW);
  delay(2000);   // 2 seconds

  // GREEN light
  digitalWrite(RED_LED, LOW);
  digitalWrite(YELLOW_LED, LOW);
  digitalWrite(GREEN_LED, HIGH);
  delay(5000);   // 5 seconds
}