ESP32 IoT Weather Logger

📡 Project Overview

In this project, we build on the basic ThingSpeak account setup from the previous tutorial and create a real IoT application: an ESP32 board reads temperature and humidity values from a DHT22 sensor and uploads them to a ThingSpeak channel every 15 seconds, where they can be visualized as live charts.

The ESP32 connects to a local Wi-Fi network, reads sensor data, and sends it via an HTTP GET request to the ThingSpeak API.

🧰 Requirements

Required Library

Only one external library is required for this project — the DHT sensor library. No HTTP or ThingSpeak-specific library is required because we send data manually using simple HTTP GET requests.

🔌 Wiring Diagram

The DHT22 sensor requires only 3 connections to the ESP32: power, ground, and one data pin.

☁️ ThingSpeak Channel Setup

Before uploading the code, prepare your ThingSpeak channel:

This project uses only Field 1 (Temperature) and Field 2 (Humidity), even though a channel can support up to 8 fields.

🧑‍💻 Code Explanation — Step by Step

1. Including Libraries

Three libraries are used: Wi-Fi connectivity, HTTP requests, and DHT sensor communication.

#include <WiFi.h>
#include <HTTPClient.h>
#include "DHT.h"

2. Defining the Sensor

We specify which GPIO pin the sensor's data line is connected to, and which DHT model we're using (DHT22).

#define DHTPIN 27
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

3. Wi-Fi Credentials & ThingSpeak URL

The SSID and password connect the board to your local network. The serverName string is the ThingSpeak "update" endpoint containing your unique Write API Key.

const char* ssid = "Robotics Lab";
const char* password = "Robotics@321";
String serverName = "https://api.thingspeak.com/update?api_key=XXNUJDNUCHY4FTYU";

4. setup() — Connecting to Wi-Fi

The board attempts to connect repeatedly until successful, printing dots to the Serial Monitor as feedback, then prints the assigned local IP address once connected.

Serial.begin(9600);
WiFi.begin(ssid, password);
while(WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
}
Serial.println(WiFi.localIP());
dht.begin();

5. loop() — Reading Sensor & Sending Data

Inside the main loop, the program checks the Wi-Fi status. If connected, it reads temperature/humidity, builds the request URL, and sends it via HTTP GET.

if(WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    float h = dht.readHumidity();
    float t = dht.readTemperature();

    String url = serverName + "&field1=" + t + "&field2=" + h;
    http.begin(url.c_str());
    int httpResponseCode = http.GET();

    if (httpResponseCode > 0) {
        Serial.println(httpResponseCode);
    }
    http.end();
    delay(15000);
}

6. The 15-Second Rule

7. Handling Disconnection

If Wi-Fi is not connected, the board prints a "WiFi Disconnected" message with a short 1-second delay, rather than the full 15 seconds, so reconnection status feedback still refreshes at a fast pace.

else {
    Serial.println("WiFi Disconnected");
    delay(1000);
}

📄 Complete Source Code

// Import necessary libraries
#include <WiFi.h>
#include <HTTPClient.h>
#include "DHT.h"
#define DHTPIN 27 // dht connection
#define DHTTYPE DHT22   // DHT 22  (AM2302), AM2321
DHT dht(DHTPIN, DHTTYPE);

// Set our wifi name and password
const char* ssid = "Robotics Lab";
const char* password = "Robotics@321";

// Your thingspeak channel url with api_key query
String serverName = "https://api.thingspeak.com/update?api_key=XXNUJDNUCHY4FTYU"; // please replace with your write API Key

void setup() 
{
  Serial.begin(9600);

  WiFi.begin(ssid, password);
  Serial.println("Connecting");
  while(WiFi.status() != WL_CONNECTED) 
  {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to WiFi network with IP Address: ");
  Serial.println(WiFi.localIP());
  delay(2000);
  dht.begin();
}

void loop() 
{
    if(WiFi.status()== WL_CONNECTED)
    { 
      HTTPClient http;
      float h = dht.readHumidity(); 
      float t = dht.readTemperature();
      Serial.print("Temperature = "); Serial.println(t);
      Serial.print("Humidity = "); Serial.println(h);
      Serial.println("*****************************************");
      String url = serverName + "&field1=" + t + "&field2=" + h;
      http.begin(url.c_str());
      int httpResponseCode = http.GET();
      if (httpResponseCode > 0)
      { 
        Serial.print("HTTP Response code: ");
        Serial.println(httpResponseCode);
      }
      else
      {
        Serial.print("Error code: ");
        Serial.println(httpResponseCode);
      }
      http.end();
      delay(15000);  
    }
    else 
    {
      Serial.println("WiFi Disconnected");
      delay(1000);
    }
}

🚀 Upload & Test Instructions

Follow these steps in the Arduino IDE:

Expected Serial Monitor Output

Connecting.....
Connected to WiFi network with IP Address: 192.168.1.45
Temperature = 26.70
Humidity = 58.30
*****************************************
HTTP Response code: 200

📊 Visualizing Data on ThingSpeak

Once data starts arriving, ThingSpeak automatically generates two default charts — one per field — labeled "Field 1 Chart" and "Field 2 Chart". You can rename these fields (e.g. "Room Temperature" and "Room Humidity") and customize each chart's appearance from the channel settings.

Customizable Chart Settings

🔮 Next Steps

This project can be extended further, such as: