NodeRED

MQTT with ESP32 + DHT22 on Node‑RED (Wokwi)

In this quick hands‑on post, you’ll simulate an ESP32 with a DHT22 sensor in Wokwi, publish temperature and humidity via MQTT, and build a simple Node‑RED Dashboard to see live updates — inspired by the IoT Frontier video linked below.

Overview

Simulate ESP32 + DHT22 entirely in Wokwi.
Publish readings over MQTT (e.g., temperature and humidity topics).
Subscribe in Node‑RED and visualize on a Dashboard.

Prerequisites

Wokwi account (free) to simulate ESP32 + DHT22
Node‑RED installed locally (or hosted)
An MQTT broker like Mosquitto (local or cloud)

Steps at a glance

Wokwi setup: Add ESP32 and DHT22. Connect data to a GPIO (e.g., GPIO 15), power to 3.3V, and ground to GND.
Publish to MQTT: ESP32 sends JSON or plain text to topics like home/dht22/temperature and home/dht22/humidity.
Subscribe in Node‑RED: Use MQTT‑in nodes for each topic and wire them to gauges/charts on the dashboard.
View Dashboard: Open the Node‑RED dashboard to watch live updates from the simulator.

Resources

npm install -g --unsafe-perm node-red

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#include 
#include 
#include "DHTesp.h"

const int DHT_PIN = 9;

DHTesp dhtSensor;

const char* ssid = "Wokwi-GUEST";
const char* password = "";
const char* mqtt_server = "broker.hivemq.com";

WiFiClient espClient;
PubSubClient client(espClient);
unsigned long lastMsg = 0;
#define MSG_BUFFER_SIZE  (50)
float temp = 0;
float hum = 0;
int value = 0;

void setup_wifi() {

  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

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

  randomSeed(micros());

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

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();

  // Switch on the LED if an 1 was received as first character
  if ((char)payload[0] == '1') {
    digitalWrite(2, LOW);   // Turn the LED on (Note that LOW is the voltage level
    // but actually the LED is on; this is because
    // it is active low on the ESP-01)
  } else {
    digitalWrite(2, HIGH);  // Turn the LED off by making the voltage HIGH
  }

}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str())) {
      Serial.println("Connected");
      // Once connected, publish an announcement...
      client.publish("iotfrontier/mqtt", "iotfrontier");
      // ... and resubscribe
      client.subscribe("iotfrontier/mqtt");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup() {
  pinMode(2, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
  dhtSensor.setup(DHT_PIN, DHTesp::DHT22);
}

void loop() {

  if (!client.connected()) {
    reconnect();
  }
  client.loop();

  unsigned long now = millis();
  if (now - lastMsg > 2000) {
    lastMsg = now;
    TempAndHumidity  data = dhtSensor.getTempAndHumidity();

    String temp = String(data.temperature, 2);
    Serial.print("Temperature: ");
    Serial.println(temp);
    client.publish("iotfrontier/temperature", temp.c_str());
    
    String hum = String(data.humidity, 1);
    Serial.print("Humidity: ");
    Serial.println(hum);
    client.publish("iotfrontier/humidity", hum.c_str());
  }
}

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