3- Connect ESP32 over MQTT

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

Connect ESP32 To AskSensors Over MQTT

a) Prerequisites :

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:


    • If you already have the ESP8266 boards URL, separate the URLs with a comma as show below:

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 :

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

    Now it’s time to connect your board.

  • 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.println("********** Program Start : ESP32 publishes data to AskSensors over MQTT");
Serial.print("********** connecting to WIFI : ");
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
Serial.println("->WiFi connected");
Serial.println("->IP address: ");
client.setServer(mqtt_server, mqtt_port);
void loop() {
if (!client.connected())
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: ");
client.publish(pubTopic, mqtt_payload);
Serial.println("> MQTT data published");
Serial.println("********** End ");
delay(writeInterval);// delay
void callback(char* topic, byte* payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print("] ");
for (int i = 0; i < length; i++) {
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.println("-> try again in 5 seconds");
// Wait 5 seconds before retrying

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