ESP32 RS232

In this tutorial, we are going to learn how to use RS232 communication with ESP32. In detail, we will learn:

How to connect ESP32 to the TTL to RS232 module
How to program ESP32 to read data from the TTL to RS232 module
How to program ESP32 to send data to the TTL to RS232 module

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-A to Type-C (for USB-A PC)
1	×	USB Cable Type-C to Type-C (for USB-C PC)
1	×	TTL to RS232 Module
1	×	Jumper Wires
1	×	Breadboard
1	×	Optionally, USB to RS232 Cable
1	×	Optionally, USB to RS232 Converter
1	×	Optionally, RS232 Gender Changer
1	×	Recommended: Screw Terminal Expansion Board for ESP32
1	×	Recommended: Power Splitter for ESP32

Or you can buy the following kits:

1	×	DIYables ESP32 Starter Kit (ESP32 included)
1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links in this section are Amazon affiliate links, meaning we may earn a commission at no additional cost to you if you make a purchase through them. Additionally, some links direct you to products from our own brand, DIYables .

Introduction to TTL to RS232 Module

When you use the serial communication by using Serial.print(), Serial.read(), Serial.write() ... functions on ESP32, ESP32 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 ESP32) 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 ESP32
TXD pin: data pin, needs to be connected a TX pin of ESP32

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

Wiring Diagram

How to connect ESP32 and RS232 to TTL module using breadboard

This image is created using Fritzing. Click to enlarge image

How to connect ESP32 and RS232 to TTL module using screw terminal block breakout board

This image is created using Fritzing. Click to enlarge image

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: The best way to Power ESP32 and sensors/displays.

How To Program ESP32 to use the RS232 module

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduini IDE.
Initializes the Serial interface:

Serial.begin(9600); // Serial Monitor Serial2.begin(9600, SERIAL_8N1, 16, 17); // RS232

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

ESP32 Code for RS232

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-rs232 */ void setup() { // start communication with baud rate 9600 Serial.begin(9600); // Serial Monitor Serial2.begin(9600, SERIAL_8N1, 16, 17); // RS232 // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on Serial if (Serial2.available()) { char data = Serial2.read(); // read the received character Serial.print(data); // print the recived data to Serial Monitor } }

Testing

You can conduct a test by transmitting data between your PC and ESP32 via RS232 in both directions. Follow the steps outlined below:

Connect the ESP32 to your PC using an RS232-to-USB cable, as illustrated in the image below:

The real connection to RS232-to-USB cable is shown as below:

Install a Serial Terminal Program such as Tera Term or PuTTY.
Open the Serial Terminal Program and configure the Serial parameters (COM port, baud rate, etc.).
Enter some data in the Serial Terminal to transmit it to the ESP32.
If the test is successful, you will observe the echoed data on the Serial Terminal.

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