I have an issue with an Arduino Nano.

I want to communicate with it through the Serial-Port. Meaning I want to send and receive Serial commands. With USB and the "Serial Monitor" this works nice. Now I have connected the COM-Port of the PC with Adruinos Digital Pins 0 and 1 (RX and TX) and a GND PIN. (3 Cables total).

Here is a minimal example of my Code:

void setup() {

void loop() {
  Serial.println("Hello World");

  delay( 1000 );

The Serial Monitor says:

Hello World
Hello World
Hello World
Hello World

Putty however says:

                                                     ▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*▒▒    ▒R▒▒▒t▒*▒▒▒R▒▒▒t▒*

Putty is connected with - BaudRate: 9600 - Data Bits: - Stop Bits: 1 - Parity: None - Flow Control: None

What is wrong here?

Update: The PC has a 9-pin D socket (Image) This is connected to a RS232 to RJ45 connector (image) From the RJ45-Cable I used the Brown, Blue, and White/Green Cable to connect with the Arduino

  • 1
    Is this a 9-pin D socket built in to the PC?
    – Majenko
    Dec 21, 2015 at 12:57
  • I have updated my question
    – Michael B
    Dec 21, 2015 at 13:04

1 Answer 1


RS232 is not TTL. You need a level converter. For more details see https://www.sparkfun.com/tutorials/215.

  • Thanks. That's it! I just found it in the documentation: "Don't connect these pins directly to an RS232 serial port; they operate at +/- 12V and can damage your Arduino board." arduino.cc/en/Reference/Serial
    – Michael B
    Dec 21, 2015 at 13:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.