How to Change Scrolling Text on MAX7219 LED Matrix Display via Bluetooth (Arduino + HC-05 Tutorial)

Introduction

In the previous tutorial, we successfully built an 8×32 MAX7219 LED Matrix scrolling display using Arduino. That display works perfectly, but there is one limitation — every time we want to change the scrolling text, we must re-upload the Arduino code. This is not practical, especially if you want to use the display in offices, shops, notice boards, or home projects.

To solve this problem, in this tutorial we will change the scrolling text wirelessly using Bluetooth. By adding just one extra component — the HC-05 Bluetooth module, we can update the scrolling message directly from a mobile phone without touching the code again.

This project is simple, beginner-friendly, and very useful for real-world applications like digital notice boards, name displays, and smart message panels.

Project Overview

Display Type: 8×32 MAX7219 LED Matrix
Controller: Arduino Nano
Communication: Bluetooth (HC-05)
Control Device: Android Smartphone
App Used: Serial Bluetooth Terminal

Components Required

Arduino Nano (or Uno)
8×32 MAX7219 LED Matrix Display
HC-05 Bluetooth Module
Connecting Wires
Type-B USB Cable
Android Smartphone

Step 1: Why Bluetooth is Needed

Normally, the scrolling text is written directly inside the Arduino sketch.
To change the text:

Modify code
Upload again
Repeat every time

This is not user-friendly. By using Bluetooth serial communication, we can send new text live from the phone, and the display will update instantly.

Step 2: Understanding HC-05 Bluetooth Module Pins

The HC-05 module has 6 pins, but we will use only 4 pins:

+5V – Power supply
GND – Ground
TXD – Transmit
RXD – Receive

The remaining pins (EN / KEY / STATE) are not required for this project.

Step 3: Bluetooth Module Connections

Connect the HC-05 Bluetooth module to the Arduino as follows:

HC-05 +5V → Arduino +5V
HC-05 GND → Arduino GND
HC-05 TX → Arduino RX
HC-05 RX → Arduino TX

⚠️ Important Rule:

TX connects to RX
RX connects to TX

This is mandatory for serial communication.

Step 4: Preparing for Code Upload

Connect the Arduino Nano to your laptop using a Type-B USB cable.
Power ON the circuit.
You will notice the Bluetooth module LED blinking rapidly, which means it is waiting for pairing.

⚠️ Before uploading the code:

Disconnect RX and TX pins of the Bluetooth module
This prevents upload errors.

Step 5: Opening the Required Arduino Example Code

Open Arduino IDE
Go to:

File → Examples → MD_MAX72xx → MD_MAX72xx_Message_Serial

This example is perfect for scrolling text via serial input.

Step 6: Modifying the Code Settings

Inside the code:

1. Select Hardware Type

Choose the correct MAX7219 hardware type used in your display.

2. Set Maximum Devices

Set how many 8×8 MAX7219 modules are connected.
For an 8×32 display, set:
MAX_DEVICES = 4

3. Adjust Scroll Delay

You can increase or decrease scroll speed as per your requirement.

4. Change Baud Rate

Find this line inside void setup():
Serial.begin(57600);
Change it to:
Serial.begin(9600);

This is required because HC-05 works reliably at 9600 baud rate.

Step 7: Uploading the Code

Go to Tools
Select correct Board Type (Arduino Nano)
Select correct COM Port
Upload the code

After successful upload:

Reconnect RX and TX pins of the Bluetooth module.

Now you will see default text scrolling on the display.

Step 8: Installing Bluetooth App on Phone

Open Play Store
Install “Serial Bluetooth Terminal” app

Step 9: App Configuration Settings

Open the app
Tap on three lines (☰) at top left
Go to Settings → Receive
Set New Line = LF

This step is very important for proper text display.

Step 10: Connecting Bluetooth Module with Phone

Turn ON Bluetooth in your phone
Open the app
Tap on ☰ → Devices
Select your HC-05 module

After connection:

App will show Connected status
Bluetooth icon appears on top right
HC-05 LED blinking will slow down (connection confirmed)

Step 11: Changing the Scrolling Text

Now the fun part

At the bottom text box of the app
Type any text, number, or symbol
Press Send

Instantly, the new text will start scrolling on the MAX7219 display.

You can send:

Text
Numbers
Special characters
Fonts supported by the library

Step 12: Using Presets (M1, M2, M3…)

The app allows preset messages:

Long-press on M1
Enter your text
Save it

Now, just tap M1 and the saved message will scroll automatically.

This is very useful for fixed messages like:

Welcome
Office Name
Alerts
Notices

Important Note (Power Loss Behavior)

⚠️ Keep this in mind:
If power is disconnected:

The display will start scrolling the default text written in the Arduino code
Bluetooth-sent text is temporary

For permanent storage, EEPROM or flash memory can be used in advanced versions.

Conclusion

By adding just one HC-05 Bluetooth module, we transformed a normal MAX7219 scrolling display into a wireless, smart, and user-friendly system. Now you can change messages instantly from your phone without touching the code or laptop again.

This project is perfect for:

Digital notice boards
Office desk displays
Shops & counters
Home automation projects