void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(12 , OUTPUT);
  pinMode(21 , OUTPUT);
 

}

void loop() {
  // put your main code here, to run repeatedly:
   digitalWrite(12 , HIGH);
  delay(1000);
  digitalWrite(12 , LOW);
  delay(1000);
  digitalWrite(21 , HIGH);
  delay(1000);
  digitalWrite(21 , LOW);
  delay(10); // this speeds up the simulation
}