SOLVED - SoftwareSerial : no display in Serial monitor ( Arduino UNO)

For debugging purpose , I need to use SoftwareSerial as the USB port of the Arduino UNO is connected to a controller .

For example to connect the USB PC cable to pin 10 (Rxd) , pin 11 (Txd) and GND on Arduino UNO side

 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 * The ArduinoGateway prints data received from sensors on the serial link.
 * The gateway accepts input on seral which will be sent out on radio network.
  * Wire connections (OPTIONAL):
 * - Inclusion button should be connected between digital pin 3 and GND
 * - RX/TX/ERR leds need to be connected between +5V (anode) and digital pin 6/5/4 with resistor 270-330R in a series
 * - To use the feature, uncomment any of the MY_DEFAULT_xx_LED_PINs
 * - RX (green) - blink fast on radio message recieved. In inclusion mode will blink fast only on presentation recieved
 * - TX (yellow) - blink fast on radio message transmitted. In inclusion mode will blink slowly
 * - ERR (red) - fast blink on error during transmission error or recieve crc error

// Enable debug prints to serial monitor
#define MY_DEBUG

// Enable and select radio type attached
// #define MY_RADIO_NRF24
// #define MY_RADIO_RFM69

// Set LOW transmit power level as default, if you have an amplified NRF-module and
// power your radio separately with a good regulator you can turn up PA level.
// #define MY_RF24_PA_LEVEL RF24_PA_LOW

// Enable serial gateway

// Define a lower baud rate for Arduino's running on 8 MHz (Arduino Pro Mini 3.3V & SenseBender)
#if F_CPU == 8000000L
#define MY_BAUD_RATE 38400

// Enable inclusion mode
// Enable Inclusion mode button on gateway

// Inverses behavior of inclusion button (if using external pullup)

// Set inclusion mode duration (in seconds)
// Digital pin used for inclusion mode button

// Set blinking period

// Inverses the behavior of leds

// Flash leds on rx/tx/err
// Uncomment to override default HW configurations
// #define MY_DEFAULT_ERR_LED_PIN 4  // Error led pin
// #define MY_DEFAULT_RX_LED_PIN  6  // Receive led pin
// #define MY_DEFAULT_TX_LED_PIN  5  // the PCB, on board LED

#include <MySensors.h>
#include <SoftwareSerial.h>

int LEDpin = 13;                 // LED connected to digital pin 13
SoftwareSerial mySerial(10, 11); // RX, TX

void setup() {

// set the data rate for the SoftwareSerial port
  Serial.println("Hello, Serial ready");
  mySerial.println("Hello, SoftwareSerial ready");
  pinMode(LEDpin, OUTPUT);
  // Setup locally attached sensors

void presentation() {
 // Present locally attached sensors

void loop() {
  digitalWrite(LEDpin, HIGH);  // Show activity LED 13
  digitalWrite(LEDpin, LOW);  // Show activity LED 13
     Serial.println("Hello, Serial ready");
    mySerial.println("Hello, SoftwareSerial");
  // Send locally attached sensor data here

So first I have connected an USB cable from my PC to the Arduino UNO USB port to load the sketch (MySensors serial GW) which is running fine as shown in the serial monitor

0;255;3;0;9;MCO:BGN:INIT GW,CP=R-NGA–,VER=2.0.1-beta
0;255;3;0;14;Gateway startup complete.
0;255;3;0;9;MCO:REG:NOT NEEDED
0;255;3;0;9;MCO:BGN:INIT OK,ID=0,PAR=0,DIS=0,REG=1

Then I connected the 2nd USB cable to the virtual port “software serial pin10/pin11/GND” to the Arduino UNO , with an USB to TTL serial convertor , and to the windows 10 PC … and the virtual port is recognized as a USB serial adapter.

The FOCA FTDI-based USB to Serial converter USB as per this datasheet

This USB Seral converter is connected to pin 10,11,GND on Arduino UNO side as SoftwareSerial and is connected to the PC side via the USB connector.

  1. The USB port on PC side is shown as USB Serial Converter = OK

  2. The serial GW sketch is loaded in the Arduino UNO withSoftwareSerial (9600) added but no printout in “myserial” monitor (9600) = NOK

  3. On the USB to Serial board , the LED PWR is ON

  4. The serialGW Arduino UNO is running

0;255;3;0;9;MCO:BGN:INIT GW,CP=R-NGA–,VER=2.0.1-beta
0;255;3;0;14;Gateway startup complete.
0;255;3;0;9;MCO:REG:NOT NEEDED
0;255;3;0;9;MCO:BGN:INIT OK,ID=0,PAR=0,DIS=0,REG=1

  1. The LED RX on the USB Serial adapter is flashing OK as a “SoftwareSerial.print” has been added in the loop of the sketch ( every 5s)

  2. No output on the SoftwareSerial monitor .

Please , can you advice how to track the issue between the USB Serial converter and the Arduino monitor ?

When you run into problems like this you need to remove any unnecessary complications. Use a simplified sketch that tests the problem area in the most simplified manner possible:

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

void setup() {

void loop() {
  mySerial.println("Hello, SoftwareSerial ready");

This is a very important troubleshooting technique that you will need to learn if you want to be successful with Arduino. It will also help you if you need to get help on the forum because we don’t have to look through a hundred lines of meaningless code and hunt down unnecessary libraries just to help you solve your issue. Once you get the simplified sketch working you can start adding in other code, testing after each change.

Do you have the USB-serial adapter wired to the Arduino software serial pins with RX connected to TX and TX connected to RX?

Do you have the Serial Monitor set to 9600 baud?

Thank you Pert for your reply and your advice to test a function with only the minimum code required tu run it.

I checked that RX USb serial is connected to TX on Arduino side and TX on RX and that the baud rate is 9600.

Si I ran your code and I see the LED RX flashing every 1s on the USB Serial device when receiving the softwareserial print but nothing is displayed in the "SoftwareSerial" serial monitor.

Did you select the port of the USB-serial converter that’s connected to the software serial pins from the Tools > Port menu? You may have multiple different ports, including the Uno’s onboard USB-serial port so you need to make sure you have the right one selected.

in the Arduino INDE , I see COM5 assigned to the Arduino board (used to upload the sketch) and I selected the COM3 which is knowed as the USB Serial device in Windows device manager so I think that the SoftwareSerial port is the right one selected.

Sounds like the issue is something trivial but .....

Hi ,

Found the problem .... my mistake

The Serial monitor COM port in the IDE was wrongly assigned to the USB port "USB serial converter "

The point is CLOSED