[solved] Serial to TTL receive issue

I used Serial - TTL converter to Arduino uno pin 2 (RX) and Pin 3 (TX).

Then I use softwareserial, open Serial (uno) and mySerial (soft) began to communicate.

It is normal to send messages from Serial to mySerial.

But when I send a message from mySerial to Serial, it will automatically receive the message.

(EX:MySerial sends “a” messages, and Serial receives “a”, but mySerial also receives “a”, mySerial should not receive any messages)

The situation is

  1. PC → send a → Arduino (PC and Arduino both receive a) (issue)
  2. Arduino → Send a → PC (PC receives a, Arduino does not have any message (fine)

PC (RS232) →RS232 to TTL →Arduino.

What can I do?


What can I do?

Step 1: Post your code. Obviously, it is your code that is causing the problems.

Sorry, simple code.

#include <SoftwareSerial.h>

SoftwareSerial MySerial(2, 3);

void setup() {

Serial.begin(9600); //Arduino to PC
MySerial.begin(9600); //PC to Arduino


void loop() {
if (MySerial.available()) {
char my = MySerial.read();
Serial.print(my); //MySerial also receives the sent value

if (Serial.available()) {
char real = Serial.read();


Can you post a picture of the MySerial object that is connected to the pins? If what is connected to the pins is NOT a MySerial, why is the instance named that?

Thank PaulS !!

Sorry, I found the problem, Is a fool's mistake, jumpers T / R short circuit, resulting in data back.