byte noteON = 144; // note on command

void setup()
{
  // set "Hairless MIDI" to the same baud rate in the preferences
  Serial.begin(115200);
}

void loop()
{
  for (int i = 60; i < 60+12+12; i++) {

    MIDImessage(noteON, i, 100);   // turn note on
    delay(100);
    MIDImessage(noteON, i, 0);     // turn note off (note on with velocity 0)
    //delay(100);
  }
  while (1)delay(100);
}

void MIDImessage(byte command, byte data1, byte data2)
{
  Serial.write(command);
  Serial.write(data1);
  Serial.write(data2);
}