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 '15 at 12:57
  • I have updated my question – Michael B Dec 21 '15 at 13:04

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 '15 at 13:14

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