Panel led de 4 módulos: MAX7219

Esquema de conexión:

^  LED  ^  ESP32  ^
|  VCC  |  3V3  |
|  GND  |  GND  |
|  DIN  |  G23  |
|  CS  |  G5  |
|  CLK  |  G18  |


Utilizaremos la biblioteca (que no librería) md_max72xx

https://www.arduino.cc/reference/en/libraries/md_max72xx/

La podemos instalar con el manager de arduino, en tools > Manage Libreries

Yo he instalado MD_Parola que te deja hacer efectos. Te dirá que tiene dependencias y le decimos que instale todas.

====== Mensaje sencillo ======

<code>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <WiFi.h>       
#include <AsyncElegantOTA.h>


// Uncomment according to your hardware type
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
//#define HARDWARE_TYPE MD_MAX72XX::GENERIC_HW

// Defining size, and output pins
#define MAX_DEVICES 4
#define CS_PIN 5

const char* ssid     = "mi_red_wifi";
const char* password = "mi_contraseña_wifi";

IPAddress ip(192,168,1,69);     
IPAddress gateway(192,168,1,1);   
IPAddress subnet(255,255,255,0); 
IPAddress dns(8,8,8,8);

AsyncWebServer server(80);

MD_Parola Display = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);

void setup() {
 
  Display.begin();
  Display.setIntensity(0);
  Display.displayClear();
  Serial.begin(115200);
  delay(10);
  Serial.println('\n');
  
  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet, dns);
  Serial.print("Connecting to ");
  Serial.print(ssid);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print('.');
  }

  Serial.println('\n');
  Serial.println("Connection established!");  
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());

  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "V1.0 Prueba Panel Led");
  });
  
  
  AsyncElegantOTA.begin(&server);
  server.begin();
  Serial.println("HTTP server started");
  Display.print("V 1.0");
  delay(1000);

}

void loop() {

    Display.setTextAlignment(PA_LEFT);
    Display.print("Hola");
    delay(10000);
}
</code>

Explicación código:

Número de paneles:
  #define MAX_DEVICES 4
Alineamiento y lo que queremos escribir.
    Display.setTextAlignment(PA_LEFT);
    Display.print("Hola");


====== SCROLL ======
Escribe lo que le pongas en el serial:
<code>
// Use the Parola library to scroll text on the display
//
// Demonstrates the use of the scrolling function to display text received
// from the serial interface
//
// User can enter text on the serial monitor and this will display as a
// scrolling message on the display.
// Speed for the display is controlled by a pot on SPEED_IN analog in.
// Scrolling direction is controlled by a switch on DIRECTION_SET digital in.
// Invert ON/OFF is set by a switch on INVERT_SET digital in.
//
// UISwitch library can be found at https://github.com/MajicDesigns/MD_UISwitch
//
// NOTE: MD_MAX72xx library must be installed and configured for the LED
// matrix type being used. Refer documentation included in the MD_MAX72xx
// library or see this link:
// https://majicdesigns.github.io/MD_MAX72XX/page_hardware.html
//

#include <MD_Parola.h>
#include <MD_MAX72xx.h>



// Define the number of devices we have in the chain and the hardware interface
// NOTE: These pin numbers will probably not work with your hardware and may
// need to be adapted
#define MAX_DEVICES 4
//#define CLK_PIN   13
//#define DATA_PIN  11
#define CS_PIN    5
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW

// HARDWARE SPI
MD_Parola P = MD_Parola(HARDWARE_TYPE,CS_PIN, MAX_DEVICES);
// SOFTWARE SPI
//MD_Parola P = MD_Parola(DATA_PIN, CLK_PIN, CS_PIN, MAX_DEVICES);



uint8_t scrollSpeed = 25;    // default frame delay value
textEffect_t scrollEffect = PA_SCROLL_LEFT;
textPosition_t scrollAlign = PA_LEFT;
uint16_t scrollPause = 2000; // in milliseconds

// Global message buffers shared by Serial and Scrolling functions
#define  BUF_SIZE  75
char curMessage[BUF_SIZE] = { "" };
char newMessage[BUF_SIZE] = { "Hello! Enter new message?" };
bool newMessageAvailable = true;



void readSerial(void)
{
  static char *cp = newMessage;

  while (Serial.available())
  {
    *cp = (char)Serial.read();
    if ((*cp == '\n') || (cp - newMessage >= BUF_SIZE-2)) // end of message character or full buffer
    {
      *cp = '\0'; // end the string
      // restart the index for next filling spree and flag we have a message waiting
      cp = newMessage;
      newMessageAvailable = true;
    }
    else  // move char pointer to next position
      cp++;
  }
}

void setup()
{
  Serial.begin(115200);
  Serial.print("\n[Parola Scrolling Display]\nType a message for the scrolling display\nEnd message line with a newline");


  P.begin();
  P.displayText(curMessage, scrollAlign, scrollSpeed, scrollPause, scrollEffect, scrollEffect);
}

void loop()
{


  if (P.displayAnimate())
  {
    if (newMessageAvailable)
    {
      strcpy(curMessage, newMessage);
      newMessageAvailable = false;
    }
    P.displayReset();
  }
  readSerial();
}

</code>

===== Mensaje de **conectando a wifi** mientras conecta =====

<code>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <WiFi.h>       
#include <AsyncElegantOTA.h>


// Uncomment according to your hardware type
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
//#define HARDWARE_TYPE MD_MAX72XX::GENERIC_HW

// Defining size, and output pins
#define MAX_DEVICES 4
#define CS_PIN 5

const char* ssid     = "mi_red_wifi";
const char* password = "mi_contraseña_wifi";

IPAddress ip(192,168,1,69);     
IPAddress gateway(192,168,1,1);   
IPAddress subnet(255,255,255,0); 
IPAddress dns(8,8,8,8);

AsyncWebServer server(80);

MD_Parola Display = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);


void setup() {
  Display.begin();
  Display.setIntensity(0);
  Display.displayClear();
  Display.displayScroll("CONECTANDO WIFI", PA_CENTER, PA_SCROLL_LEFT, 25);

  Serial.begin(115200);
  delay(10);
  Serial.println('\n');
  
  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet, dns);
  Serial.print("Connecting to ");
  Serial.print(ssid);

  while (WiFi.status() != WL_CONNECTED) {
    if (Display.displayAnimate()) {
    Display.displayReset();
  } 
  }

  Serial.println('\n');
  Serial.println("Connection established!");  
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());

  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "V1.0 Prueba Panel Led");
  });
  
  
  AsyncElegantOTA.begin(&server);
  server.begin();
  Serial.println("HTTP server started");
  delay(1000);


    

}


void loop() {
}

</code>

===== Muestra la IP una vez conectado =====


<code>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <WiFi.h>       
#include <AsyncElegantOTA.h>


// Uncomment according to your hardware type
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
//#define HARDWARE_TYPE MD_MAX72XX::GENERIC_HW

// Defining size, and output pins
#define MAX_DEVICES 4
#define CS_PIN 5

const char* ssid     = "mi_red_wifi";
const char* password = "mi_contraseña_wifi";

IPAddress ip(192,168,1,69);     
IPAddress gateway(192,168,1,1);   
IPAddress subnet(255,255,255,0); 
IPAddress dns(8,8,8,8);

AsyncWebServer server(80);

MD_Parola Display = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);
String my_ip;

void setup() {
  Display.begin();
  Display.setIntensity(0);
  Display.displayClear();
  Display.displayScroll("CONECTANDO WIFI", PA_CENTER, PA_SCROLL_LEFT, 25);

  Serial.begin(115200);
  delay(10);
  Serial.println('\n');
  
  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet, dns);
  Serial.print("Connecting to ");
  Serial.print(ssid);

  while (WiFi.status() != WL_CONNECTED) {
    if (Display.displayAnimate()) {
    Display.displayReset();
  } 
  }

  Serial.println('\n');
  Serial.println("Connection established!");  
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());

  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "V1.0 Prueba Panel Led");
  });
  
  
  AsyncElegantOTA.begin(&server);
  server.begin();
  Serial.println("HTTP server started");
  delay(1000);

  my_ip = WiFi.localIP().toString();
  Serial.println(my_ip);

  Display.displayClear();
  Display.displayScroll(my_ip.c_str(), PA_CENTER, PA_SCROLL_LEFT, 25);
  
  while(true){
    if (Display.displayAnimate()) {
      Display.displayReset();
      break;
    }
  }
}


void loop() {

    Display.setTextAlignment(PA_LEFT);
    Display.print("Hola");
    delay(10000);

}


</code>

Si cambiamos la parte del while por esto, lo muestra 2 veces
<code>
  for (int muestra_ip = 1; muestra_ip <= 2; muestra_ip++) {
    while (true) {  
      if (Display.displayAnimate()) {
        Display.displayReset();
      break;
      }  
    }
  }
</code>

===== Muestra mensaje leido de internet =====
Lee el texto que le indicamos en la web que tengamos en:
  serverPath = "http://bateriaseko.lobo99.com/prueba_led";

Al leer la cadena le pone un símbolo raro al final solo en la pantalla led, en el serial monitor no.

Le quitamos el último carácter con:
  payload.substring(0,strlen(payload.c_str())-1)

<code>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <SPI.h>
#include <WiFi.h>        // Include the Wi-Fi library
#include <HTTPClient.h>
#include <ESPAsyncWebServer.h>
#include <AsyncElegantOTA.h>


// Uncomment according to your hardware type
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
//#define HARDWARE_TYPE MD_MAX72XX::GENERIC_HW

// Defining size, and output pins
#define MAX_DEVICES 4
#define CS_PIN 5

const char* ssid     = "mi_red_wifi";
const char* password = "mi_contraseña_wifi";

IPAddress ip(192,168,1,69);     
IPAddress gateway(192,168,1,1);   
IPAddress subnet(255,255,255,0); 
IPAddress dns(8,8,8,8);

AsyncWebServer server(80);

const int lectura=5;
String power="";

String serverPath = "http://bateriaseko.lobo99.com/prueba_led";

MD_Parola Display = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);

void setup() {
 
  Display.begin();
  Display.setIntensity(0);
  Display.displayClear();
  Serial.begin(115200);
  delay(10);
  Serial.println('\n');
  
  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet, dns);
  Serial.print("Connecting to ");
  Serial.print(ssid);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print('.');
  }

  Serial.println('\n');
  Serial.println("Connection established!");  
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());
  
  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "V1.0 lee el valor de http://bateriaseko.lobo99.com/prueba_led");
  });
  
  
  AsyncElegantOTA.begin(&server);
  server.begin();
  Serial.println("HTTP server started");
  Display.print("V 1.0");
  delay(1000);

}

void loop() {
    AsyncElegantOTA.loop();

    Display.setTextAlignment(PA_LEFT);


    if(WiFi.status()== WL_CONNECTED){
      HTTPClient http;
      
      // Your Domain name with URL path or IP address with path
      http.begin(serverPath.c_str());
      
      // Send HTTP GET request
      int httpResponseCode = http.GET();
      
      if (httpResponseCode>0) {
        Serial.print("HTTP Response code: ");
        Serial.println(httpResponseCode);
        String payload = http.getString();
        Serial.println(String(payload.toInt()));
        
        Serial.println(strlen(payload.c_str()));

        Display.setTextAlignment(PA_CENTER);
        Display.print(payload.substring(0,strlen(payload.c_str())-1));
        delay(1000);  
      }
      else {
        Serial.print("Error code: ");
        Serial.println(httpResponseCode);
      }
      // Free resources
      http.end();
    }
    else {
      Serial.println("WiFi Disconnected");
    }

}
</code>

===== Muestra mensaje leido de internet con scroll =====
<code>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <SPI.h>
#include <WiFi.h>        // Include the Wi-Fi library
#include <HTTPClient.h>
#include <ESPAsyncWebServer.h>
#include <AsyncElegantOTA.h>


// Uncomment according to your hardware type
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
//#define HARDWARE_TYPE MD_MAX72XX::GENERIC_HW

// Defining size, and output pins
#define MAX_DEVICES 4
#define CS_PIN 5

const char* ssid     = "mi_red_wifi";
const char* password = "mi_contraseña_wifi";

IPAddress ip(192,168,1,91);     
IPAddress gateway(192,168,1,1);   
IPAddress subnet(255,255,255,0); 
IPAddress dns(8,8,8,8);

AsyncWebServer server(80);

String mensaje="";

String serverPath = "http://mensaje.lobo99.com/mensaje.txt";


MD_Parola Display = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);

void setup() {
 
  Display.begin();
  Display.setIntensity(0);
  Display.displayClear();
  String mensaje = "Conectando WIFI: " + String(ssid);
  Display.displayScroll(mensaje.c_str(), PA_CENTER, PA_SCROLL_LEFT, 25);
    
  Serial.begin(115200);         // Start the Serial communication to send messages to the computer
  delay(10);
  Serial.println('\n');
  
  WiFi.begin(ssid, password);             // Connect to the network
  WiFi.config(ip, gateway, subnet, dns);
  Serial.print("Connecting to ");
  Serial.print(ssid);

  while (WiFi.status() != WL_CONNECTED) { // Wait for the Wi-Fi to connect
    if (Display.displayAnimate()) {
      Display.displayReset();
    } 
  }

  Serial.println('\n');
  Serial.println("Connection established!");  
  Serial.print("IP address:\t");
  Serial.println(WiFi.localIP());         // Send the IP address of the ESP8266 to the 

  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
    request->send(200, "text/plain", "V1.0 http://mensaje.lobo99.com/mensaje.txt");
  });
  
  
  AsyncElegantOTA.begin(&server);    // Start AsyncElegantOTA
  server.begin();
  Serial.println("HTTP server started");
  Display.print("V 1.0");
  delay(1000);

        //Display.displayScroll(payload.c_str(), PA_CENTER, PA_SCROLL_LEFT, 25);
Display.setTextAlignment(PA_CENTER);
Display.displayScroll("hola", PA_CENTER, PA_SCROLL_LEFT, 25);
}

void loop() {
  AsyncElegantOTA.loop();
      
  if(WiFi.status()== WL_CONNECTED){

      HTTPClient http;
      
      // Your Domain name with URL path or IP address with path
      http.begin(serverPath.c_str());
            
      
      // Send HTTP GET request
      int httpResponseCode = http.GET();
      
      if (httpResponseCode>0) {
        Serial.print("HTTP Response code: ");
        Serial.println(httpResponseCode);
        String payload = http.getString();

        Serial.println(payload);
        const char* mensaje=payload.c_str();
        Serial.println(mensaje);
        Display.displayClear();
        Display.displayScroll(mensaje, PA_CENTER, PA_SCROLL_LEFT, 25);
        
        while(!Display.displayAnimate())
        {
          Serial.println("while");     
        }
      }
      else {
        Serial.print("Error code: ");
        Serial.println(httpResponseCode);
      }
      // Free resources
      http.end();
  }
  else {
    Serial.println("WiFi Disconnected");
  }
}
</code>