Building an ESP32 Smart Room Weather Logger with DHT11 and OLED

Monitoring room temperature and humidity is the cornerstone of home automation. In this guide, we will connect a sensor and display to the ESP32 and program it to serve stats on a local website.

Introduction & Concept

By pairing the dual-core ESP32 microcontroller with a DHT11 temperature and humidity sensor, we can create a powerful local weather node. We will read the ambient values, display them locally on a 0.91" OLED screen, and initialize a basic HTTP web server that allows any smartphone connected to the same Wi-Fi network to view the logs.

Required Electronic Components

Component Name	Store Link
ESP32 WROOM-32 NodeMCU Development Board	Buy ESP32 Board
DHT11 Temperature & Humidity Module	Buy DHT11 Module
0.91 inch I2C OLED Display Module	Buy 0.91 OLED Screen

Wiring Connections Diagram

     [ESP32 Development Board]
     +-----------------------+
     |                       |
     |                  3.3V |------------+------------+ (VCC)
     |                   GND |------------|------------| (GND)
     |         GPIO21  (SDA) |------------|----> SDA   | 
     |         GPIO22  (SCL) |------------|----> SCL   | [0.91" OLED]
     |         GPIO4  (Data) |------->    |            |
     +-----------------------+       |    +------------+
                                     |
                                     v
                                   [DATA] ---> [DHT11 Sensor]
          

Wiring Table

OLED / DHT11 Pin	ESP32 Pin	Description
OLED VCC / DHT11 VCC	3.3V	Power Source
OLED GND / DHT11 GND	GND	Ground Reference
OLED SDA	GPIO 21	I2C Data Line
OLED SCL	GPIO 22	I2C Clock Line
DHT11 Data	GPIO 4	Digital Signal Data

Program Sketch

#include <WiFi.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <DHT.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 32
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
DHT dht(4, DHT11);

const char* ssid = "Your_WiFi_Name";
const char* password = "Your_WiFi_Password";
WiFiServer server(80);

void setup() {
  Serial.begin(115200);
  dht.begin();
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("SSD1306 allocation failed");
    for(;;);
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
  server.begin();
}

void loop() {
  float t = dht.readTemperature();
  float h = dht.readHumidity();
  
  display.clearDisplay();
  display.setCursor(0,0);
  display.printf("IP: %s\nT: %.1f C | H: %.1f %%", WiFi.localIP().toString().c_str(), t, h);
  display.display();
  delay(2000);
}