3- Connect ESP32 over MQTT | AskSensors Documentation

This guide explains how to use your ESP32 to publish data to the AskSensors IoT platform over MQTT.

a) Prerequisites :

Create an AskSensors account.
Setup a new sensor.
Get familar with AskSensors using this step-by-step guide.

b) Required Hardwares :

Computer running Arduino software (version 1.8.7 or higher).
ESP32 board.
USB micro cable to connect the ESP32 board to the computer.

c) Install ESP32 in Arduino IDE:

Follow the instructions below to install the ESP32 board in your Arduino IDE:

- Install the latest version of Arduino IDE software (1.8.7 or higher).
- Open the preferences window from the Arduino IDE : File> Preferences.
- Go to the “Additional Board Manager URLs” field, Enter the following URL:

https://dl.espressif.com/dl/package_esp32_index.json

https://dl.espressif.com/dl/package_esp32_index.json, http://arduino.esp8266.com/stable/package_esp8266com_index.json

Now, open boards manager (Tools > Board > Boards Manager), search for ESP32 and click the install button for the “ESP32 by Espressif Systems”.

d) Software :

Install the MQTT PubSubClient Library for the Arduino IDE.
Download this demo from the AskSensors Github page.

The provided code includes the libraries for both connecting to a WiFi network and to publish data to AskSensors using MQTT.
You need to fill the following:

- Your WIFI SSID and password.
- The Api Key In and username to set the MQTT Topic:publish/username/apiKeyIn


const char* ssid = "....."; // Wifi SSID
const char* password = ".....";// Wifi Password
const char* username = "................."; // my AskSensors username
const char* pubTopic = "publish/..../....."; // publish/username/apiKeyIn
const char* mqtt_server = "mqtt.asksensors.com";

e) Run the code

Connect your ESP32 board to the computer via serial/USB and upload the code using the Arduino IDE.
Return back to your sensor page on AskSensors, Click on’Show Graph’ and select the chart type (such as Line, Bar, Binary..) to visualize your sensor data stream in graph.
Open a serial terminal. You can cross-check the AskSensors graph readings with the values being printed on your Arduino Terminal.

f) Source Code :

A basic source code is shown below. Please refer to the AskSensors Github page to get the latest version and updates.


/*
* MQTT and AskSensors IoT Platform
* Description: ESP32 sends data to AskSensors using MQTT
* Author: https://asksensors.com, 2020
* github: https://github.com/asksensors/AskSensors-ESP32-MQTT
*/
#include <WiFi.h>
#include <PubSubClient.h>
// TODO: AskSensors MQTT user config
const char* ssid = ".................."; // Wifi SSID
const char* password = ".................."; // Wifi Password
const char* username = "................."; // my AskSensors username
const char* pubTopic = "publish/..../....."; // publish/username/apiKeyIn
const unsigned int writeInterval = 25000; // write interval (in ms)
// MQTT host config
const char* mqtt_server = "mqtt.asksensors.com";
unsigned int mqtt_port = 1883;
WiFiClient askClient;
PubSubClient client(askClient);
void setup() {
Serial.begin(115200);
Serial.println("*****************************************************");
Serial.println("********** Program Start : ESP32 publishes data to AskSensors over MQTT");
Serial.print("********** connecting to WIFI : ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.println("->WiFi connected");
Serial.println("->IP address: ");
Serial.println(WiFi.localIP());
client.setServer(mqtt_server, mqtt_port);
client.setCallback(callback);
}
void loop() {
if (!client.connected())
reconnect();
client.loop();
Serial.println("********** Publish MQTT data to ASKSENSORS");
char mqtt_payload[30] = "";
snprintf (mqtt_payload, 100, "m1=%ld&m2=%ld", random(10,100), random(10,100) );
Serial.print("Publish message: ");
Serial.println(mqtt_payload);
client.publish(pubTopic, mqtt_payload);
Serial.println("> MQTT data published");
Serial.println("********** End ");
Serial.println("*****************************************************");
delay(writeInterval);// delay
}
void callback(char* topic, byte* payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print(topic);
Serial.print("] ");
for (int i = 0; i < length; i++) {
Serial.print((char)payload[i]);
}
Serial.println();
}
void reconnect() {
// Loop until we're reconnected
while (!client.connected()) {
Serial.print("********** Attempting MQTT connection...");
// Attempt to connect
if (client.connect("ESP32Client",username, "")) {
Serial.println("-> MQTT client connected");
} else {
Serial.print("failed, rc=");
Serial.print(client.state());
Serial.println("-> try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}