How to Program an Arduino as a Modbus RS485 Master & Slave

Learn how to create your own Modbus RS485 Master and Slave Device using the Arduino Uno Development System

Created byEmile Ackbarali

Last updated 5/2026

English

What you'll learn

Understand the Arduino Uno and RS485 Shield from a Hardware persepctive
Connect an Arduino RS485 Shield to an Arduino Uno
Connect an Arduino Uno to a Hitachi HD44780 LCD display
Use the Arduino IDE to develop applications for the Arduino Uno
Write an Arduino Sketch application to display messages on an LCD display
Write an Arduino Sketch application to implement a Modbus Master
Test an Arduino Modbus master using the Modsim32 Modbus slave simulator
Write an Arduino Sketch application to implement a Modbus Slave
Test an Arduino Modbus slave using the Modscan32 Modbus master application

Course content

9 sections • 34 lectures • 2h 47m total length

Introduction4:10
Accessing Attached Resources and Setting Optimal Video Resolution2:23

The Hardware List4:36
The hardware that is used in the course is listed and their purpose given.
The Arduino Uno5:05
An overview of the Arduino Uno.
The RS485 Shield for Arduino Uno4:31
An overview of the RS485 shield for Arduino Uno.
The LCD Display and Interconnecting Hardware5:07
An overview of the LCD display and Interconnecting Hardware.
The USB-to-RS485 Converter and Connection Overview3:19
An overview of the USB-to-RS485 converter as well as the basic connection of the hardware.
Hardware Setup on my Workbench2:41
A look at the physical hardware set up.

The Arduino Programming Software2:24
This lecture shows where to go on the web to download and install the free Arduino programming software.
The Modbus Libraries3:50
Modbus Libraries are used to simplify the implementation of the Modbus protocol on the Arduino.
Modsim32 Modbus Slave Simulator2:00
Modsim32 is a Modbus slave simulation application. It will be used to provide data values that will be read by the Windows Modbus Master application.

A look at the Programming Software - Arduino IDE6:20
The Arduino IDE is briefly introduced.
Our First Program - Testing the LCD Display7:23
A built in application is used as the first application and also to test the LCD display.
Getting the LCD to display the value of a Variable8:36
The code is modified to display the value of a variable on the LCD display.
Additional LCD Code to support Modbus Master Operation9:43
Additional LCD code is added to update the LCD display only on data changes.
Adding Code to Implement Modbus Master Functionality9:11
Running our First Arduino Modbus Master Application4:14
Using the laptop with Modsim32 as a Modbus Slave, the Arduino application is run and tested.

Review of the Current Application Code6:27
Quite a bit of coding was done very quickly in the last section. This lecture reviews all of the code so as to solidify the function of the various commands.
Adding Code to Read a Holding Register6:54
Code is added and the application updated to be able to read a holding register.
Adding Code to Read an Input Status7:54
Code is added and the application updated to be able to read an input status.
Adding Code to Read a Coil5:52
Code is added and the application updated to be able to read a coil.

What we are going to do in this Section2:47
An overview of the details of the section.
How to Acquire the Sensor3:25
We have a look at the website from which the sensor was purchased.
A Look at the Datasheet for the Sensor5:47
We look at the datasheet for the sensor to determine the communication details.
The Arduino and Sensor setup on my Workbench2:53
Writing the Arduino Code to Read Data from the Temp/Humidity Sensor7:08
Testing the Arduino Program3:10
Modification of Code to Display Decimal Places3:21

Installing the Modbus Slave Arduino Library3:59
The previously downloaded Modbus Slave Library is installed into the Arduino IDE.
Implementing the Arduino Modbus Slave and Testing Read Functionality7:44
Code is written to implement the Modbus Slave in the Arduino and then Modscan32 is used to read Modbus data.
Implementing the Arduino Modbus Slave and Testing Write Functionality3:49
The code from the previous lecture is modified to test the write functionality of the slave. Modscan32 is used to write to the Arduino slave.

Requirements

Basic working knowledge of the Modbus RTU protocol.
Familiarity with the installation of software applications on the Windows OS platform
Elementary understanding of the "C" programming language
Basic understanding of elementary electronics

Description

If you work in the Automation Industry, you will know that automation equipment is very expensive. And many a time, especially for small applications, you simply cannot justify the use of very expensive equipment.

This is where the Arduino comes in!

The Arduino development board allows you to create very simple, but very powerful, Modbus master or slave devices through the use of relatively simple "C" programming. With the Arduino, you have full custom control over the program design allowing you to create very lean and very efficient devices for very specific purposes.

Put simply, mastering Modbus on the Arduino is going to take your skill level and value in the Automation Industry to a whole new level.

That is what this course is going to do. At the end of the course, you will know how to:

1. Choose the appropriate Arduino hardware.

2. Interconnect Arduino hardware with other add-on hardware.

3. Write "C" applications to implement Modbus master and slave functionality.

4. Use software and hardware to test each application that you write.

All of the programs written in the course are freely downloadable and give you a perfect starting point for further development. At the end of the course, you will have the knowledge to create your own products, your own custom Modbus master and slave hardware.

Looking forward to seeing you on the inside!

Who this course is for:

Electrical Engineers
Electrical Technicians
Electrical Tech or Engineering Students
Process Control Technicians and Engineers
Process Automation Engineers
Programmers working in the Process Automation field

How to Program an Arduino as a Modbus RS485 Master & Slave

What you'll learn

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Course content

Introduction2 lectures • 7min

The Hardware We Will Be Using6 lectures • 25min

The Software We Will Be Using3 lectures • 8min

Quick Start - Creating our First Arduino Modbus Master Application6 lectures • 45min

Extending the Arduino Modbus Master Application4 lectures • 27min

Configuring the Arduino to Read/Display Data from a Modbus Temperature Sensor7 lectures • 29min

Configuring the Arduino to Write Modbus Data to the Slave2 lectures • 9min

Configuring the Arduino as a Modbus Slave Device3 lectures • 16min

Bonus Section - How to Always get the Lowest Prices for my Courses1 lecture • 2min

Requirements

Description

Who this course is for: