This is the simple instruction on how to send data from a MCU(eg. Arduino Nano) to a MQTT broker for the 2024 Spring Energy class in NYU ITP’s solar project.

Prerequisites

Libries

MQTT Arduino Library: ArduinoMqttClient

And any library you need to read sensor data. In my case, it’s DHT11 for temperature and humidity data.

Also, preventing your Arduino from hanging, it’s recommended to install this

Define the topic name and what data you are storing and sending

• Topic name: the topic you are going to subscribe/ publish to for your sensor data, for example /energy_solar_project/group5
• The data you want to collect, for example:
  • temperature
  • humidity
• Send these data to networking team member, and they will make sure your data shows on the panel

Arduino Sample Code

old example (with subscribing topics)

// Include the library to read sensor data
#include <DHT11.h>

// Include mqtt client library
#include <ArduinoMqttClient.h>
#if defined(ARDUINO_SAMD_MKRWIFI1010) || defined(ARDUINO_SAMD_NANO_33_IOT) || defined(ARDUINO_AVR_UNO_WIFI_REV2)
#include <WiFiNINA.h>
#elif defined(ARDUINO_SAMD_MKR1000)
#include <WiFi101.h>
#elif defined(ARDUINO_ARCH_ESP8266)
#include <ESP8266WiFi.h>
#elif defined(ARDUINO_PORTENTA_H7_M7) || defined(ARDUINO_NICLA_VISION) || defined(ARDUINO_ARCH_ESP32) || defined(ARDUINO_GIGA) || defined(ARDUINO_OPTA)
#include <WiFi.h>
#elif defined(ARDUINO_PORTENTA_C33)
#include <WiFiC3.h>
#elif defined(ARDUINO_UNOR4_WIFI)
#include <WiFiS3.h>
#endif

// define pin for sensor data read
DHT11 dht11(2);

// Don't need to change
char mqtt_user[] = "energy";
char mqtt_pass[] = "password";

// Don't need to change
const char broker[] = "9.tcp.ngrok.io";  //IP address of the EMQX broker.
int port = 24004;

// The SSID and password we are going to use in NAVY YARD, if you want to test, use your own wifi ssid and password
char ssid[] = "NewLabMember 2.4GHz Only";  // your network SSID (name)
char pass[] = "!Welcome2NewLab!";      // your network password

// Set up topics, you want to publish,
// For instance:
const char publish_topic[] = "/energy_solar_project/group5";

WiFiClient wifiClient;
MqttClient mqttClient(wifiClient);

void setup() {
  // Create serial connection and wait for it to become available.
  Serial.begin(9600);
  while (!Serial) {
    ;
  }
  // Connect to WiFi access point.
  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  delay(1000);

  WiFi.begin(ssid, pass);
  delay(2000);

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

  Serial.println("You're connected to the network");
  Serial.println();

  // You can provide a username and password for authentication
  mqttClient.setUsernamePassword(mqtt_user, mqtt_pass);

  Serial.print("Attempting to connect to the MQTT broker.");

  if (!mqttClient.connect(broker, port)) {
    Serial.print("MQTT connection failed! Error code = ");
    Serial.println(mqttClient.connectError());

    while (1)
      ;
  }

  Serial.println("You're connected to the MQTT broker!");

  Serial.print("Subscribing to topic: ");
  Serial.println(subscribe_topic);

  // initiate watchdog timer with a 8sec count down
  // you can look up differnt duration here: <https://github.com/gpb01/wdt_samd21>
  wdt_init ( WDT_CONFIG_PER_8K );

}

void loop() {
  int temperature = 0;
  int humidity = 0;

  // Attempt to read the temperature and humidity values from the DHT11 sensor.
  int result = dht11.readTemperatureHumidity(temperature, humidity);

  // Check the results of the readings.
  // If the reading is successful, print the temperature and humidity values.
  // If there are errors, print the appropriate error messages.
  if (result == 0) {
    Serial.print("Temperature: ");
    Serial.print(temperature);
    Serial.print(" °C\\tHumidity: ");
    Serial.print(humidity);
    Serial.println(" %");

    // send message, the Print interface can be used to set the message contents
    // notice the way we structure data here, 
    // we are making a JSON like string for the server to parse and store into the database
    // the data below will look like this {"temperature":24,"humidity":18}
    
    mqttClient.beginMessage(publish_topic);
    mqttClient.print("{\\"temperature\\":");
    mqttClient.print(temperature);
    mqttClient.print(",\\"humidity\\":");
    mqttClient.print(humidity);
    mqttClient.print("}");
    mqttClient.endMessage();

    // if you only have one data to send, you can comment the code above and use this instead
    // mqttClient.beginMessage(publish_topic);
    // mqttClient.print("{\\"temperature\\":");
    // mqttClient.print(temperature);
    // mqttClient.print("}");
    // mqttClient.endMessage();

  } else {
    // Print error message based on the error code.
    Serial.println(DHT11::getErrorString(result));
  }

  delay(3000);
  
  // reset the watchdog timer, or the watch dog will trigger the MCU to restart
  wdt_reset();
}

You should see something like this if your code works correctly