int ledpin=12;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  Serial.println("xin chao");
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(ledpin, HIGH);
  delay (1000);
  Serial.println("sang");
  digitalWrite(ledpin, LOW);
  delay(1000);
  Serial.println("tat");
//  delay(1000);// ngưng cả hệ thống
}