C++ (Arduino/ESP8266)

Introduction

This example will send JSON over MQTT over WiFi - on Arduino Core for ESP8266.

Prerequisites

Example

#include <ESP8266WiFi.h>
#include <ArduinoJson.h>
#include "Adafruit_MQTT.h"
#include "Adafruit_MQTT_Client.h"

// WLAN credentials.
#define WIFI_SSID     = "SSID";
#define WIFI_PASSWORD = "PASS";


// The address of the MQTT broker to connect to.
#define MQTT_BROKER         "daq.example.org"
#define MQTT_PORT           1883

// A MQTT client ID, which should be unique across multiple devices for a user.
// Change some 8 bytes of random hex-value here!
#define MQTT_CLIENT_ID      "ef3423be2"

// The MQTT topic to transmit sensor readings to.
#define MQTT_TOPIC          "mqttkit-1/foo/bar/1/data.json"

// The credentials to authenticate with the MQTT broker.
#define MQTT_USERNAME       ""
#define MQTT_PASSWORD       ""

// How often to retry connecting to the MQTT broker.
#define MQTT_RETRY_COUNT    5

// How long to delay between MQTT (re)connection attempts (seconds).
#define MQTT_RETRY_DELAY    1.5f


// Connect to WiFi.
WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
Serial.print(" ");
while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.printf(".");
}
Serial.printf(" got IP-address ");
Serial.println("[wifi] connected");
// Printing the ESP IP address
Serial.print(WiFi.localIP());


// Create an ESP8266 WiFiClient object to connect to the MQTT server.
WiFiClient wifi_client;

// Setup the MQTT client class by passing in the WiFi client and MQTT server and login details.
Adafruit_MQTT_Client mqtt(&wifi_client, MQTT_BROKER, MQTT_PORT, MQTT_CLIENT_ID, MQTT_USERNAME, MQTT_PASSWORD);

// Setup MQTT publishing handler.
Adafruit_MQTT_Publish mqtt_publisher = Adafruit_MQTT_Publish(&mqtt, MQTT_TOPIC);

// Connect to the MQTT broker.
mqtt.connect();


// Prepare data, build JSON object.
StaticJsonBuffer<256> jsonBuffer;
JsonObject& root    = jsonBuffer.createObject();
root["weight"]      = 84.84f;
root["humidity"]    = 60.08f;
root["temperature"] = 28.90f;

// Debugging.
//root.printTo(Serial);
// This will print:
// {"weight":84.84,"humidity":60.08,"temperature":28.90}

// Serialize data.
char payload[256];
root.printTo(payload, sizeof(payload));

// Publish data.
if (mqtt_publisher.publish(payload)) {
    Serial.println("success.");
} else {
    Serial.println("fail.");
}

Real applications