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Arduino RS232

In this tutorial, we are going to learn how to use RS232 communication with Arduino. In detail, we will learn:

How to connect Arduino to the TTL to RS232 module
How to program Arduino to read data from the TTL to RS232 module
How to program Arduino to send data to the TTL to RS232 module

The tutorial also provides the instruction for both Hardware Serial and SoftwareSerial.

Hardware Required

1	×	Official Arduino Uno
1	×	Alternatively, DIYables ATMEGA328P Development Board
1	×	USB 2.0 cable type A/B (for USB-A PC)
1	×	USB 2.0 cable type C/B (for USB-C PC)
1	×	TTL to RS232 Module
1	×	Jumper Wires
1	×	Optionally, USB to RS232 Cable
1	×	Optionally, USB to RS232 Converter
1	×	Optionally, RS232 Gender Changer
1	×	Recommended: Screw Terminal Block Shield for Arduino Uno
1	×	Recommended: Breadboard Shield for Arduino Uno
1	×	Recommended: Enclosure for Arduino Uno
1	×	Recommended: Prototyping Base Plate & Breadboard Kit for Arduino UNO

Or you can buy the following kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some links in this section are Amazon affiliate links. If you make a purchase through these links, we may earn a commission at no extra cost to you.
Additionally, some links direct to products from our own brand, DIYables .

About TTL to RS232 Module

When you use the serial communication by using Serial.print(), Serial.read(), Serial.write() ... functions on Arduino, Arduino output data to TX pin or read data come from RX pin. The signals on TX and RX pins are TTL level. This signal cannot go far. Therefore, when you want to use the serial communication via long distance, you need to converts the TTL signal to RS232, RS485, or RS422 signal.

The TTL to RS232 module converts TTL signal to RS232 signal, and vice versa.

Pinout

The RS232 to TTL module has two interfaces:

The TTL interface (connnected to Arduino) includes 4 pins

VCC pin: power pin, needs to be connected to VCC (5V/3.3V)
GND pin: power pin, needs to be connected to GND (0V)
RXD pin: data pin, needs to be connected a RX pin of Arduino
TXD pin: data pin, needs to be connected a TX pin of Arduino

The RS232 interface: DB9 female D-Sub connector, connect this to the serial device

Wiring Diagram

Wiring diagram if using hardware serial

This image is created using Fritzing. Click to enlarge image

Wiring diagram if using software serial

This image is created using Fritzing. Click to enlarge image

How To Program Arduino to use the RS232 module

Initializes the Serial interface:

Serial.begin(9600);

If you use SoftwareSerial, you need to include the library and declare a SoftwareSerial object:

#include <SoftwareSerial.h> // Define the SoftwareSerial objects and their pins SoftwareSerial SoftSerial(7, 6); // RX: 7, TX: 6

To read data come from RS232, you can use the following functions:

To write data to RS232, you can use the following functions:

And more functions to use with RS232 in Serial reference

Arduino Code for Hardware Serial

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rs232 */ void setup() { // start communication with baud rate 9600 Serial.begin(9600); // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on Serial if (Serial.available()) { char data = Serial.read(); // read the received character Serial.print(data); // echo back to data to the sender } }

Arduino Code for Software Serial

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rs232 */ #include <SoftwareSerial.h> // define the SoftwareSerial object and their pins SoftwareSerial SoftSerial(7, 6); // RX: 7, TX: 6 void setup() { // start communication with baud rate 9600 SoftSerial.begin(9600); // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on SoftSerial if (SoftSerial.available()) { char data = SoftSerial.read(); // read the received character SoftSerial.print(data); // echo back to data to the sender } }

Testing

You can do a test by sending data from your PC to Arduino via RS232 and vice versa. To do it, follow the below steps:

Connect Arduino to your PC via RS232-to-USB cable as below:

Install a Serial Terminal Program like Tera Term or PuTTY
Open the Serial Terminal Program and configure the Serial parameters (COM port, baurate...)
Type some data from the Serial Termial to send it to Arduino.
If successful, you will see the echo data on the Serial Terminal.

Video Tutorial

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