test.ino

#include <SoftwareSerial.h>

const int MD49_RX = 8;
const int MD49_TX = 9;

SoftwareSerial md49(MD49_RX, MD49_TX);


void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  md49.begin(9600);
}

void loop() {
  if (md49.available() > 0) {
    Serial.write(md49.read());
  }
  if (Serial.available() > 0) {
    md49.write(Serial.read());
  }
}