#define RED    7

#define YELLOW 6

#define GREEN  5

void setup() {

   pinMode(RED, OUTPUT);

   pinMode(YELLOW, OUTPUT);

   pinMode(GREEN, OUTPUT);

}

void loop() {

   digitalWrite(RED, HIGH);

   digitalWrite(YELLOW, HIGH);

   digitalWrite(GREEN, HIGH);

   delay(500);

   digitalWrite(RED, LOW);

   digitalWrite(YELLOW, LOW);

   digitalWrite(GREEN, LOW);

   delay(500);

}