How to interface Arduino with RS485 protocol with example code

In this tutorial, we will explain how to communicate between two Arduino boards with the help of the RS485 serial data communication protocol. Arduino doesn’t have any peripherals for RS485 communication. We will use an RS485-based sensor module called MAX485 for communication between two Arduino boards. We will follow the RS485 master-slave communication method. For demonstration purposes, we will create a project that will ON or OFF a LED connected to a Slave Arduino from Master Arduino by sending some commands through RS485 Module.

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What is RS485?

There are different types of physical media and they are:

  • RS232: serial communication protocol
  • RS485: serial communication protocol
  • RS422: serial communication protocol
  • Ethernet: LAN (Local Area Network) Technology

RS485 is an asynchronous half-duplex serial communication protocol that communicates over devices by using the master-salve method. It can connect a maximum of 32 devices on the same line.

Figure: RS485 serial communication protocol

Most of the industry uses RS485 protocol rather than RS232 because of its longer distances (up to 1200 meters), higher data transfer rate (Up to 30Mbps), and allow for multiple devices connection on a single network by using only two wires.

MAX485 TTL to RS485 Module

MAX485 is a low-power transceiver for TTL to RS485 communication. This module needs 5V to operate and uses a 5V logic level so that it can be easily interfaced with microcontrollers like Arduino.

Key Features of MAX485:

  • It can cover longer distances of up to 1200 meters
  • Supports a higher data transfer rate of 10Mbit/s
  • MAX485 can connect a maximum of 32 devices
  • A low power consumption
  • Slew-rate limited transceiver
  • Onboard 5.08mm pitch 2P terminal for RS-485 communication wiring
Figure: MAX485 – TTL to RS485

MAX485 Module Pinout

MAX485 pin
Figure: MAX485 pin-out

RS485 communication between two Arduino boards by using MAX485 module (The project)

In this part of the article, We will explain how the RS485 communication works by doing of a simple project. We will use two Arduino Uno boards for this project. One is used as a master and another is as a slave. We will send a command “1” or “0” from the master to the slave. Slave will receive and check the value. If the value is “1” then the slave turns on a LED and prints “LED ON” on the serial monitor of Arduino IDE or if the value is “0” the slave turns off the led and prints “LED OFF” in the serial monitor of Arduino IDE.

We use a 5V Li-ion battery to power the master Arduino Board and for power the slave Arduino we use a computer 5V USB power supply.

Component List

To follow the project you will need several components and they are:

Component NameQuantityPurchase Link
Arduino development board2Amazon | AliExpress
Push button1Amazon | AliExpress
MAX485 TTL to RS485 converter module2Amazon | AliExpress
Breadboard1Amazon | AliExpress
Jumper Wire pack1Amazon | AliExpress
LED1Amazon | AliExpress
100 ohm Resistor1Amazon | AliExpress

For troubleshooting, some extremely useful test equipment

Equipment NamePurchase Link
Best Oscilloscope for ProfessionalsAmazon | AliExpress
Best Oscilloscope for BeginnersAmazon | AliExpress
Logic AnalyzerAmazon | AliExpress
Best Budget MultimeterAmazon | AliExpress

Affiliate Disclosure: When you click on links to make a purchase, this can result in this website earning a commission. Affiliate programs and affiliations include, but are not limited to

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Figure: Arduino RS485 real circuit connection

Circuit Schematics

In this article section, We will show you how to connect MAX485 module to Arduino Uno with the help of the connection diagram and pin description table.

circuit connection
Figure: Arduino RS485 circuit diagram

Connection description between Arduino and MAX485 ( master)

master table 2
Figure: Arduino RS485 master connection pin-out

We also connect a push button to pin 2 of Arduino.

Connection description between Arduino and MAX485 ( slave)

slave table 1
Figure: Arduino RS485 slave connection pin-out

We also connect a red led to pin 8 of Arduino with a 100 Ohm resistor in series.

Arduino and RS485 communication Code

We have written two Arduino sketch. One is for the master and another is for the slave. The Master will send a command and the slave will react according to the master’s command.

Arduino Code for Master

Open your Arduini IDE and go to File > new and create a new sketch. Copy the code below and paste it to the Arduino sketch and save it.

In this sketch, we will send a command “0” or “1” to the slave Arduino Board. We connect Arduino pin 2 to a push button. We configure an internal pull-up (normally high) for the push button.

.ino file for Arduino IDE

// Initialize the button state to 0
bool button_state=0;

void setup() {
  // put your setup code here, to run once:
  // arduino default baud rate for serial communication
  // DE,RE Controling pin of RS-485
  pinMode(7, HIGH);
  // pin 2 set as input with PULL-UP for button
  pinMode(2, INPUT_PULLUP);
  // DE,RE = HIGH, RS485 Transmit Enabled

void loop() {
  // put your main code here, to run repeatedly:
  // check if button is prasssed or not.
  //If digitalRead() function return 0 than the button is pressed-
  //because we use input pull-up for pin 2
  if(digitalRead(2) == 0){
    // wait 300ms to prevent debouncing
      // evry time when button pressed button state will reverse it value from 0 to 1 or 1 to 0
      button_state = !button_state;
      // print the value in serial monitor

Arduino Code for Slave

Again, open your Arduini IDE and go to File > new and create a new sketch. Copy the code below and paste it to the Arduino sketch and save it.

In this sketch, the slave Arduino receives the command from the master through the MAx485 module by using the RS485 protocol. We connect Arduino pin 8 to a LED. If the slave receives command “1” then LED will Turn ON and print “LED ON” to the Arduino IDE serial monitor or, if slave receives command “0” then LED will turn OFF and print “LED OFF” to the serial monitor.

.ino file for Arduino IDE

// Initialize the LED status
bool led_status;

void setup() {
  // arduino default baud rate for serial communication
  //DE,RE Controling pin of RS-485
  pinMode(7, OUTPUT);
  //pin 8 set as output for LED
  pinMode(8, OUTPUT);
   //DE,RE = 0, RS485 Receive Enabled

void loop() {
  // wait untill all the bytes receive from data buffer
   while(Serial.available() > 0){
    // take the integer value from buffer (0 or 1)
      led_status = Serial.parseInt();
      // delay for 10 milliseconds
      // check if command is 1
      if(led_status == 1){
        // LED pin high means LED ON
        Serial.println("LED ON");
       // check if command "0"
       if(led_status == 0){
        // LED pin low means LED OFF
        Serial.println("LED OFF");


RS485 serial data communication protocol is widely used in industries. In this tutorial, I expelled the basics of RS485 protocol and also interface it with Arduino through a TTL to RS485 module. I will write more articles about this topic soon.


Mahamudul Hasan

I hold a B.Sc degree in Electrical & Electronic Engineering from Daffodil International University, Bangladesh. I am a Printed Circuit Board (PCB) designer and Microcontroller programmer with an avid interest in Embedded System Design and IoT. As an Engineer, I love taking challenges and love being part of the solution. My Linkedin Profile Link:

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