ESP32 - RS232

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

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×USB Cable Type-C
1×TTL to RS232 Module
1×Jumper Wires
1×Breadboard
1×(Optional) RS232 to USB Cable
1×(Optional) RS232 Gender Changer
1×(Recommended) ESP32 Screw Terminal Adapter

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
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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)
    • 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
RS232 Pinout

Wiring Diagram

  • Wiring diagram if using hardware serial
ESP32 TTL to RS232 Wiring Diagram

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: How to Power ESP32.

  • Wiring diagram if using breadboard
ESP32 RS232 to TTL Wiring Diagram

This image is created using Fritzing. Click to enlarge image

How To Program ESP32 to use the RS232 module

Serial.begin(9600);

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); // 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:
ESP32 RS232 to PC communication
  • 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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