37  MQTT example

37.1 Intro

Each FireBeetle board connects to Wi-Fi and subscribes to an MQTT topic. Whenever a new message is published to the topic, the board receives it and changes the color of its built-in RGB LED accordingly.

37.1.1 MQTT Topic

The board listens to the following topic:

agrotech/mqtt_tutorial/LED

You can publish messages to this topic using an MQTT client, such as the MQTTX Web Client. Make sure to connect to the broker broker.emqx.io on port 1883.

37.1.2 Supported Commands

You can send color commands in various formats:

37.1.2.1 🔤 Named Colors

You can use full names or single-letter shorthands (case-insensitive):

Command	Resulting Color
red or r	🔴 Red
green or g	🟢 Green
blue or b	🔵 Blue
white or w	⚪ White
yellow or y	🟡 Yellow
cyan or c	🟦 Cyan
magenta or m	🟣 Magenta
off or black	⚫ LED Off

37.1.2.2 🎨 Custom RGB Triplets

You can also send a custom color as a comma-separated RGB value, e.g.:

255,100,0

This would set the LED to an orange-like color. The values should range from 0 to 255.

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This setup is ideal for remote visual feedback or synchronized color indicators across multiple ESP32 boards on the same MQTT topic.

37.2 LED subscribe

Download code

#include <Arduino.h>
#include <WiFi.h>
#include <PubSubClient.h>
#include <Adafruit_NeoPixel.h>

#define LED_PIN    5  // built-in WS2812 RGB on FireBeetle 2 = GPIO5 (D8)
#define NUM_LEDS   1
#define BRIGHTNESS 50

const char* ssid = "erez";         // <-- change this
const char* password = "arduino1"; // <-- change this
const char* mqttServer = "broker.emqx.io";  // <== NEW BROKER
int mqttPort = 1883;
const char* mqttTopic = "agrotech/mqtt_tutorial/LED";

WiFiClient wifiClient;
PubSubClient mqttClient(wifiClient);
Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);

String msgString;

void setColor(uint8_t r, uint8_t g, uint8_t b) {
  strip.setPixelColor(0, strip.Color(r, g, b));
  strip.show();
}

void parseColor(String color) {
  color.trim();
  color.toLowerCase();

  // named or shorthand colors
  if (color == "r" || color == "red") setColor(255, 0, 0);
  else if (color == "g" || color == "green") setColor(0, 255, 0);
  else if (color == "b" || color == "blue") setColor(0, 0, 255);
  else if (color == "w" || color == "white") setColor(255, 255, 255);
  else if (color == "y" || color == "yellow") setColor(255, 255, 0);
  else if (color == "m" || color == "magenta") setColor(255, 0, 255);
  else if (color == "c" || color == "cyan") setColor(0, 255, 255);
  else if (color == "off" || color == "black") setColor(0, 0, 0);
  else if (color.indexOf(',') != -1) {
    // RGB triplet: "100,200,30"
    int r = color.substring(0, color.indexOf(',')).toInt();
    int g = color.substring(color.indexOf(',') + 1, color.lastIndexOf(',')).toInt();
    int b = color.substring(color.lastIndexOf(',') + 1).toInt();
    setColor(r, g, b);
  }
  else {
    Serial.println("Unknown color command");
  }
}

void callback(char* topic, byte* message, unsigned int length) {
  msgString = String((char*)message, length);
  Serial.print("MQTT message received: ");
  Serial.println(msgString);
  parseColor(msgString);
}

void setupMQTT() {
  mqttClient.setServer(mqttServer, mqttPort);
  mqttClient.setCallback(callback);
}

void reconnect() {
  Serial.println("Connecting to MQTT Broker...");
  while (!mqttClient.connected()) {
    String clientId = "ESP32Client-" + String(random(0xffff), HEX);
    if (mqttClient.connect(clientId.c_str())) {
      Serial.println("Connected to MQTT.");
      mqttClient.subscribe(mqttTopic);
    } else {
      Serial.print(".");
      delay(1000);
    }
  }
}

void setup() {
  Serial.begin(115200);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nConnected to WiFi.");

  strip.begin();
  strip.setBrightness(BRIGHTNESS);
  strip.show(); // off

  setupMQTT();
}

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