ESP32 RS485

This tutorial instructs you how to use RS485 communication with ESP32. In detail, we'll learn the following aspects:

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×USB Cable Type-C
1×TTL to RS485 Module
1×Jumper Wires
1×(Optional) RS485 to USB Cable
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 RS485 Module

When utilizing serial communication on the ESP32 with functions such as Serial.print(), Serial.read(), and Serial.write(), data transmission occurs via the TX pin, while data reception happens through the RX pin. These pins operate at TTL level, meaning they handle signals with a limited range. Hence, for serial communication over extended distances, converting the TTL signal to RS232, RS485, or RS422 signal standards becomes necessary.

In this tutorial, we'll explore the utilization of RS485 (also referred to as RS-485) with the ESP32 by employing a TTL to RS485 module. This module facilitates the conversion of TTL signals to RS485 signals and vice versa.

Pinout

The RS485 to TTL module features two interfaces:

  • TTL Interface (connected to ESP32):
    • VCC Pin: This power pin should be connected to VCC (5V or 3.3V).
    • GND Pin: This power pin should be connected to GND (0V).
    • RXD Pin: This data pin should be connected to a TX pin of the ESP32.
    • TXD Pin: This data pin should be connected to an RX pin of the ESP32.
  • RS485 Interface:
    • D+ (A or TR+) Pin: This pin facilitates data communication.
    • D- (B or TR-) Pin: This pin is utilized for data transmission.
    • GND Pin: While optional, including this pin is strongly recommended to mitigate noise interference, ensuring optimal performance.
    RS-485 module Pinout
    image source: diyables.io

Wiring Diagram

ESP32 TTL to RS485 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.

How To Program ESP32 to use the RS485 module

  • Initializes the Serial interface:
Serial2.begin(9600);

ESP32 Code

/* * 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-rs485 */ void setup() { // start communication with baud rate 9600 Serial.begin(9600); // Serial Monitor Serial2.begin(9600); // RS485 // 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 do a test by sending data from your PC to ESP32 via RS-485 and vice versa. To do it, follow the below steps:

  • Connect ESP32 to your PC via RS485-to-USB cable as below:
ESP32 RS485 to PC communication
  • 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 ESP32.
  • If successful, you will see the echo data on the Serial Terminal.

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