// mega-serial-esp32.ino
// 
#       ESP32 D1 R32                                     Arduino Mega Serial1()
# GPIO16 / U2RX / IO16  <---   white  <---  yellow <---    TX1 / D18
# GPIO17 / U2TX / IO17   --->  grey    ---> orange  --->   RX1 / D19

void setup() {
  Serial.begin(9600); Serial.println("\nSerial-Test ");
  Serial1.begin(115200); Serial1.println("\nSerial1-Test");
}

void loop() {
  while (Serial.available()) {
    Serial1.println(Serial.read());
  }
  Serial1.println("'Hi' from MEGA");
  while (Serial1.available()) {
    Serial.println(Serial1.read());
  }

}