Demo 5: How to use Arduino ESP32 to display information on SPI LED matrix

1. Introduction
This demonstration show you how to connect a LED Matrix module to Arduino ESP32 via MAX7219 module to display information from ESP32. There are 2 ways to connect ESP32 to LED Matrix module:

• Connect directly. By using this way, ESP32 will waste many GPIO pins (at lest 8x8 for 8x8 Led matrix).
• Connect via MAX7219 module. By using this way, ESP32 will only use 3 GPIO pins which act as SPI MOSI, CLK and CS pins. MAX7219 will be responsible for converting SPI data to LED Matrix data and control signals.

 

Figure: Led matrix

2. Hardware

Connect the pins of ESP32 to the pins of LED matrix:

[ESP32 GPIO14 - LED CLK] 

[ESP32 GPIO12 - LED DIN (MOSI)]

[ESP32 GPIO15 - LED CS]
[ESP32 GND - LED GND]

[LED VCC - 5V]

or follow picture below:

Figure: ESP32 connect to LED matrix module

3. Software

We will use the library MAX7219LedMatrix that is made for Arduino but I modified a little to compatible with ESP32. You can download the library here:

https://github.com/nhatuan84/esp32-led-matrix

After downloading, unzip and copy the unzipped folder under folder:

C:/Users/[YOUR_USER_NAME]/Documents/Arduino/libraries

The library supplied some functions:

• init(): to initialize library
• setText(): set the text to print on LED Matrix
• scrollTextLeft(): scroll text to left effect
• clear(): clear the display
• drawText(): start drawing text to buffer
• commit(): commit the text from buffer to LED Matrix

In order to use these function you need to create an instance of LedMatrix with constructor: LedMatrix ledMatrix=LedMatrix(NUMBER_OF_DEVICES, CLK_PIN, MISO_PIN, MOSI_PIN, CS_PIN)

Note: NUMBER_OF_DEVICES number of cascading LED Matrix in a serial mode

Figure: 4 LED Matrix in a serial mode

Finally, you create an Arduino project and save it as esp32ledmatrix with code:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

#include <SPI.h> #include "LedMatrix.h" #define NUMBER_OF_DEVICES 3 //number of led matrix connect in series #define CS_PIN 15 #define CLK_PIN 14 #define MISO_PIN 2 //we do not use this pin just fill to match constructor #define MOSI_PIN 12 LedMatrix ledMatrix = LedMatrix(NUMBER_OF_DEVICES, CLK_PIN, MISO_PIN, MOSI_PIN, CS_PIN); void setup() { ledMatrix.init(); ledMatrix.setText("EasyIoT"); } void loop() { ledMatrix.clear(); ledMatrix.scrollTextLeft(); ledMatrix.drawText(); ledMatrix.commit(); delay(50); }

4. Result

Figure: ESP32 connect to LED matrix