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Arduino RS485

In this tutorial, we'll explore the implementation of RS485 communication with Arduino. Specifically, we'll cover the following aspects in detail:

Establishing the connection between Arduino and the TTL to RS485 module.
Programming Arduino to retrieve data from the TTL to RS485 module.
Programming Arduino to transmit data to the TTL to RS485 module.
How to send data from your PC to Arduino via RS485, and vice versa.

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

Hardware Required

1	×	Arduino UNO or Genuino UNO
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 RS485 Module
1	×	Jumper Wires
1	×	(Optional) USB to RS485 Converter
1	×	(Optional) USB to RS485 Cable
1	×	(Recommended) Screw Terminal Block Shield for Arduino Uno
1	×	(Recommended) Breadboard Shield For Arduino Uno
1	×	(Recommended) Enclosure For Arduino Uno

Or you can buy the following sensor 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 RS485 Module

When utilizing serial communication on Arduino through functions like Serial.print(), Serial.read(), and Serial.write(), the Arduino transmits data via the TX pin and receives data through the RX pin. These pins operate at TTL level, meaning the signals they handle have limited range. Thus, for serial communication over longer distances, it becomes necessary to convert the TTL signal to RS232, RS485, or RS422 signal standards.

In this tutorial, we'll delve into the utilization of RS485 (also known as RS-485) with Arduino 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 has two interfaces:

The TTL interface (connnected to Arduino) includes 4 pins

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

The RS485 interface comprises the following pins:

D+ (A or TR+) pin: This pin facilitates data communication.
D- (B or TR-) pin: This pin serves for data transmission.
GND pin: While optional, it's strongly recommended to include this pin to mitigate noise interference, ensuring optimal performance.

RS-485 module Pinout

image source: diyables.io

Wiring Diagram

Wiring diagram if using hardware serial

Arduino TTL to RS485 Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Wiring diagram if using software serial

Arduino RS-485 to TTL Wiring Diagram

This image is created using Fritzing. Click to enlarge image

How To Program Arduino to use the RS485 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 rs485(6, 7); // RX: 6, TX: 7

To read data come from RS485, you can use the following functions:

To write data to RS485, you can use the following functions:

And more functions to use with RS485 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-rs485 */ 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-rs485 */ #include <SoftwareSerial.h> // define the SoftwareSerial object and their pins SoftwareSerial rs485(6, 7); // RX: 6, TX: 7 void setup() { // start communication with baud rate 9600 rs485.begin(9600); // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on rs485 if (rs485.available()) { char data = rs485.read(); // read the received character rs485.print(data); // echo back to data to the sender } }

Testing

You can do a test by sending data from your PC to Arduino via RS-485 and vice versa. To do it, follow the below steps:

Connect Arduino to your PC via RS485-to-USB cable as below:

Arduino 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 Arduino.
If successful, you will see the echo data on the Serial Terminal.

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The Best Arduino Starter Kit

See the best Arduino kit for beginner

See Also

Arduino - SoftwareSerial

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