How to use 4G with the ESP32 PLC

In this blog post, we will explore how to use 4G LTE with the ESP32 PLC using the NB library from Industrial Shields, specifically designed for the SARA-R4 module. We will demonstrate how to integrate other protocol libraries like HttpClient and MQTT to create a versatile IoT device capable of communicating over a cellular network.This tutorial is designed to help you connect your ESP32 PLC to the internet using 4G.

Why use 4G with your ESP32 PLC?

While the ESP32 is equipped with Wi-Fi and Bluetooth, IoT 4G integration offers a wider range and more reliable internet connectivity for remote applications. In this guide, we’ll demonstrate how to enhance your ESP32 IoT projects with 4G connectivity.

Essential hardware for setting up 4G on ESP32 PLC

Before beginning, make sure you have the following hardware for ESP32 4G connection: 

• An ESP32 PLC from the ESP32 PLC family with 4G as an additional communications board. The 4G communications board integrates a U-Blox SARA-R412 module.
  
• A SIM card compatible with NB-IoT, LTE Cat M1 or GPRS.
• A computer with Arduino IDE and our boards package installed. Ready for programming ESP32 for 4G.

Step-by-step guide to inserting a SIM card in your ESP32 PLC

Proper installation of your SIM card is crucial for a stable ESP32 4G connection: 

1. Remove the Ethernet Port Cover:
   • Locate the Ethernet port on your ESP32 PLC.
   • Place your finger into the Ethernet port and apply upward pressure to lift the cover. Alternatively, use a flathead screwdriver to gently pry the cover from one of its sides.
2. Insert the SIM Card:
   • Once the cover is removed, you will see the SIM card slot located above the reset button.
   • Insert the SIM card into the slot with the contact side facing up.
3. Replace the Cover:
   • After the SIM card is securely in place, reattach the cover by pressing it back down until it clicks into place.

By following these steps, you ensure that your SIM card is correctly installed and ready to use for 4G connectivity with your ESP32 PLC.

Configuring the Arduino IDE for ESP32 PLC 4G communication

"How do I set up my Arduino IDE for ESP32 PLC 4g communication?" Follow these steps to configure your development environment:

1. Open the Arduino IDE.
2. Select the Industrial Shields ESP32 board family: Tools > Board > Industrial Shields ESP32 Boards > ESP32 PLC Family.
3. Select your specific model, for example, the ESP32 PLC 21: Tools > Model > ESP32 PLC 21 IO+.
4. Now you need to configure the 4G module, as this communication is optional. ​This module can be located in 2 expansion slots of the PLC, but it will usually be located in number 1. In the IDE, go to Tools > Extension Module 1, and select the type of communication to use: LTE, NB or GPRS.

With this the ESP32 PLC 4G communication is set up to work with the NB library that our boards package includes.  This library takes care of the communication with the module and also includes basic examples, which you can find in the IDE: Files > Examples > NB.

In this post examples, however, we will also use two other libraries that can work together with the NB: the HttpClient library and the PubSubClient library. Install them like this:

1. Open the Arduino IDE.
2. Go to Sketch > Include Library > Manage Libraries.
3. Search for and install the "HttpClient" library. (Required for the HTTP protocol.)
4. Search for and install the "PubSubClient" library. (Required for the MQTT protocol.)

Programming your ESP32 for 4G connectivity

In this section, we provide a simple sketch to demonstrate how to use the NB library to connect your ESP32 PLC to the 4G network and make an HTTP request. This is a crucial part of our ESP32 IoT tutorial, aimed at enabling your device to communicate over a cellular network effectively.

// libraries
#include <NB.h>
#include <HttpClient.h>

// Uncomment to automatically configure the module baud rate to 38400
//#define MAKE_AUTOBAUD

#define PINNUMBER     ""
#define APN           ""
#define USERNAME      ""
#define PASSWORD      ""

// Initialize the library instance
NBClient nbClient;
GPRS gprs;
NB nbAccess;

// URL, path, and port (for example: httpbin.org)
char server[] = "httpbin.org";
char path[] = "/get";
int port = 80; // Port 80 is the default for HTTP

HttpClient http(nbClient, server, port);

void setup() {
  // Initialize serial communications and wait for the port to open:
  Serial.begin(115200);
  while (!Serial);

  Serial.println("Starting Arduino web client.");
  
  // Connection state
  boolean connected = false;

#ifdef MAKE_AUTOBAUD
  if (nbAccess.autobaud()) {
    Serial.println("Autobaud completed with exit");
    nbAccess.shutdown();
  }
  else {
    Serial.println("Autobaud could not configure the module correctly. Trying again...");
    if (nbAccess.autobaud()) {
      Serial.println("Autobaud completed with exit");
      nbAccess.shutdown();
    }
    else {
      Serial.println("Autobaud could not configure the module correctly. Blocking...");
      while(1);
    }
  }
#endif

  // Attach to the GPRS network with the APN, login, and password
  while (!connected) {
    if ((nbAccess.begin(PINNUMBER, APN, USERNAME, PASSWORD) == NB_READY) &&
        (gprs.attachGPRS() == GPRS_READY)) {
      connected = true;
    } else {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("connecting...");

  // Make a HTTP request:
  int statusCode = http.get(path);

  if (statusCode == HTTP_SUCCESS) {
    Serial.println("connected and request sent");
  } else {
    Serial.println("connection or request failed");
  }
}

void loop() {
  // Read the response from the server and print it to the serial monitor
  if (http.available()) {
    char c = http.read();
    Serial.print(c);
  }

  // If the server's disconnected, stop the client:
  if (!http.available() && !http.connected()) {
    Serial.println();
    Serial.println("disconnecting.");
    http.stop();

    // Do nothing forevermore:
    for (;;)
      ;
  }
}

Setting up the sketch 

Learn how to configure your ESP32 to access the internet via 4G using the NB and HttpClient libraries, crucial for IoT applications requiring stable and remote communication.

Libraries and definitions

Incorporate essential libraries to facilitate cellular communication and HTTP requests:

// libraries
#include <NB.h>
#include <HttpClient.h>

// Uncomment to automatically configure the module baud rate to 38400
//#define MAKE_AUTOBAUD

#define PINNUMBER     ""
#define APN           ""
#define USERNAME      ""
#define PASSWORD      ""

These directives establish the foundation for your device to manage network interactions effectively.

Initialization

Initialize networking and HTTP client objects:

// Initialize the library instance
NBClient nbClient;
GPRS gprs;
NB nbAccess;

• These lines create instances of the necessary objects for network and client management.

Server details

Configure the server parameters for initiating HTTP requests:

// URL, path, and port (for example: httpbin.org)
char server[] = "httpbin.org";
char path[] = "/get";
int port = 80; // Port 80 is the default for HTTP

HttpClient http(nbClient, server, port);

Setting these parameters directs your HTTP client on where and how to send requests.

Setup function

Initialize the device for network communication:

void setup() {
  // Initialize serial communications and wait for the port to open:
  Serial.begin(115200);
  while (!Serial);

  Serial.println("Starting Arduino web client.");
  
  // Connection state
  boolean connected = false;

#ifdef MAKE_AUTOBAUD
  if (nbAccess.autobaud()) {
    Serial.println("Autobaud completed with exit");
    nbAccess.shutdown();
  }
  else {
    Serial.println("Autobaud could not configure the module correctly. Trying again...");
    if (nbAccess.autobaud()) {
      Serial.println("Autobaud completed with exit");
      nbAccess.shutdown();
    }
    else {
      Serial.println("Autobaud could not configure the module correctly. Blocking...");
      while(1);
    }
  }
#endif

  // Attach to the GPRS network with the APN, login, and password
  while (!connected) {
    if ((nbAccess.begin(PINNUMBER, APN, USERNAME, PASSWORD) == NB_READY) &&
        (gprs.attachGPRS() == GPRS_READY)) {
      connected = true;
    } else {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("connecting...");

  // Make a HTTP request:
  int statusCode = http.get(path);

  if (statusCode == HTTP_SUCCESS) {
    Serial.println("connected and request sent");
  } else {
    Serial.println("connection or request failed");
  }
}

• Initializes serial communication and waits for the serial port to open.
• Uses the "nbAccess" object to attempt connection to the network using the provided APN, username, and password.
• Sends an HTTP GET request to the specified server and path.

Loop function

void loop() {
  // Read the response from the server and print it to the serial monitor
  if (http.available()) {
    char c = http.read();
    Serial.print(c);
  }

  // If the server's disconnected, stop the client:
  if (!http.available() && !http.connected()) {
    Serial.println();
    Serial.println("disconnecting.");
    http.stop();

    // Do nothing forevermore:
    for (;;)
      ;
  }
}

• Continuous monitoring: The loop function continuously checks for data availability from the server, reads, and prints responses to the serial monitor. It also handles disconnection by stopping the client and blocking further operations if disconnected. 

Integrating MQTT with ESP32 over 4G: advanced IoT applications

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol ideal for the IoT 4G integration due to its minimal bandwidth requirements. This section covers how to use MQTT over a 4G LTE connection with the ESP32, providing real-time data transfer capabilities essential for ESP32 IoT projects.

Here’s an example of how to use the MQTT protocol with the NB library:

// libraries
#include <NB.h>
#include <PubSubClient.h>

// Uncomment to automatically configure the module baud rate to 38400
//#define MAKE_AUTOBAUD

#define PINNUMBER     ""
#define APN           ""
#define USERNAME      ""
#define PASSWORD      ""

// Initialize the library instance
NBClient client;
GPRS gprs;
NB nbAccess;
PubSubClient mqttClient(client);

// MQTT broker details
const char* mqtt_server = "broker.hivemq.com"; // Public broker example
const int mqtt_port = 1883;
const char* mqtt_topic = "test/topic"; // Topic example

void setup() {
  // Initialize serial communications and wait for the port to open:
  Serial.begin(115200);
  while (!Serial);

  Serial.println("Starting Arduino web client and MQTT.");

  // Connection state
  boolean connected = false;

#ifdef MAKE_AUTOBAUD
  if (nbAccess.autobaud()) {
    Serial.println("Autobaud completed with exit");
    nbAccess.shutdown();
  }
  else {
    Serial.println("Autobaud could not configure the module correctly. Trying again...");
    if (nbAccess.autobaud()) {
      Serial.println("Autobaud completed with exit");
      nbAccess.shutdown();
    }
    else {
      Serial.println("Autobaud could not configure the module correctly. Blocking...");
      while(1);
    }
  }
#endif

  // Attach to the GPRS network with the APN, login, and password
  while (!connected) {
    if ((nbAccess.begin(PINNUMBER, APN, USERNAME, PASSWORD) == NB_READY) &&
        (gprs.attachGPRS() == GPRS_READY)) {
      connected = true;
    } else {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("Connecting to MQTT broker...");

  mqttClient.setServer(mqtt_server, mqtt_port);
  mqttClient.setCallback(callback);

  connectToMQTT();
}

void loop() {
  if (!mqttClient.connected()) {
    connectToMQTT();
  }
  mqttClient.loop();
}

void connectToMQTT() {
  while (!mqttClient.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (mqttClient.connect("ESP32Client")) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      mqttClient.publish(mqtt_topic, "Hello from ESP32");
      // ... and resubscribe
      mqttClient.subscribe(mqtt_topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(mqttClient.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (unsigned int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();
}

Explanation of the code

Libraries and definitions

// libraries
#include <NB.h>
#include <PubSubClient.h>

// Uncomment to automatically configure the module baud rate to 38400
//#define MAKE_AUTOBAUD

#define PINNUMBER     ""
#define APN           ""
#define USERNAME      ""
#define PASSWORD      ""

• "#include <NB.h>" and "#include <PubSubClient.h>" include the necessary libraries for cellular communication and MQTT protocol.
• "#define" statements set up constants for your SIM card details.

Initialization

// Initialize the library instance
NBClient client;
GPRS gprs;
NB nbAccess;
PubSubClient mqttClient(client);

• These lines create instances of the necessary objects for network and MQTT client management.

MQTT Broker details

// MQTT broker details
const char* mqtt_server = "broker.hivemq.com"; // Public broker example
const int mqtt_port = 1883;
const char* mqtt_topic = "test/topic"; // Topic example

• Defines the MQTT broker details including server address, port, and topic.

Setup function

void setup() {
  // Initialize serial communications and wait for the port to open:
  Serial.begin(115200);
  while (!Serial);

  Serial.println("Starting Arduino web client and MQTT.");

  // Connection state
  boolean connected = false;

#ifdef MAKE_AUTOBAUD
  if (nbAccess.autobaud()) {
    Serial.println("Autobaud completed with exit");
    nbAccess.shutdown();
  }
  else {
    Serial.println("Autobaud could not configure the module correctly. Trying again...");
    if (nbAccess.autobaud()) {
      Serial.println("Autobaud completed with exit");
      nbAccess.shutdown();
    }
    else {
      Serial.println("Autobaud could not configure the module correctly. Blocking...");
      while(1);
    }
  }
#endif

  // Attach to the GPRS network with the APN, login, and password
  while (!connected) {
    if ((nbAccess.begin(PINNUMBER, APN, USERNAME, PASSWORD) == NB_READY) &&
        (gprs.attachGPRS() == GPRS_READY)) {
      connected = true;
    } else {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("Connecting to MQTT broker...");

  mqttClient.setServer(mqtt_server, mqtt_port);
  mqttClient.setCallback(callback);

  connectToMQTT();
}

• Initializes serial communication and waits for the serial port to open.
• Uses the "nbAccess" object to attempt connection to the network using the provided APN, username, and password.
• Sets the MQTT server and callback function, and attempts to connect to the MQTT broker.

Loop function

void loop() {
  if (!mqttClient.connected()) {
    connectToMQTT();
  }
  mqttClient.loop();
}

• Continuously checks if the MQTT client is connected. If not, it attempts to reconnect.
• Calls the "mqttClient.loop()" function to keep the client connected and handle incoming messages.

Connect to MQTT function

void connectToMQTT() {
  while (!mqttClient.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (mqttClient.connect("ESP32Client")) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      mqttClient.publish(mqtt_topic, "Hello from ESP32");
      // ... and resubscribe
      mqttClient.subscribe(mqtt_topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(mqttClient.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

• Attempts to connect to the MQTT broker.
• It publishes a message and subscribes to a topic, essential steps in establishing communication for ESP32 cellular projects.
• If the connection fails, waits 5 seconds and retries.

Callback function

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (unsigned int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();
}

This function is activated when a message is received on a subscribed topic, demonstrating effective data handling in ESP32 MQTT 4G setups. It prints the topic and payload to the serial monitor, providing real-time feedback crucial for debugging and monitoring ESP32 projects.

Effective debugging tips for ESP32 4G projects

If your setup is not working as expected, try the following steps:

• Uncomment the line "#define MAKE_AUTOBAUD" to configure the module's baud rate automatically.
• To enable debugging and see what the NB library is doing, change the line "NB nbAccess;" to "NB nbAccess(true);".

Maximizing IoT capabilities: leveraging 4G connectivity with ESP32

In this guide, we have shown how to connect the ESP32 to a 4G network using the Industrial Shields NB library and perform HTTP and MQTT operations. This setup enables you to create robust IoT applications with cellular connectivity. We encourage you to experiment with different protocols and explore the full potential of your ESP32 PLC 4G variant.

References and additional links

For more information, refer to the following resources:

• HttpClient Library
• PubSubClient Library for MQTT

By following these guidelines and utilizing the provided sketches and functions, you are well-equipped to develop advanced IoT solutions that leverage the power of 4G connectivity.