unsigned char Red_LED = 23;

unsigned char Yellow_LED = 19;

unsigned char Green_LED = 18;


void setup() {
  pinMode(23, OUTPUT);
  pinMode(19, OUTPUT);
  pinMode(18, OUTPUT);
  }

void loop() {

 digitalWrite(23, HIGH);
 digitalWrite(19, HIGH);
 digitalWrite(18, HIGH);

 delay(2000);

 
 digitalWrite(23, LOW);
 digitalWrite(19, LOW);
 digitalWrite(18, LOW);

 delay(2000);
}