Introduction

Modern climate control systems must be smart, efficient, and connected. This ESP32 climate controller using the SHT40 sensor demonstrates how microcontrollers can monitor environmental conditions and automate temperature regulation.

The system:

Reads temperature and humidity from SHT40
Displays real-time data on OLED
Hosts a web dashboard over Wi-Fi (AP mode)
Allows user to set a target temperature
Controls a relay for heating
Uses RGB LED for visual status indication

This project reflects real-world IoT thermostat systems.

How the ESP32 Climate Controller Works

ESP32 reads temperature and humidity every minute
Displays data locally on OLED
Hosts a web interface
User sets a target temperature
ESP32 compares ambient temperature with target
Relay and RGB LED respond accordingly

System Logic

No target set → System idle (Green LED)
Temperature < Target → Heating ON (Orange LED)
Temperature > Target → Heating OFF (Cyan LED)
Temperature within ±0.5°C → Idle

This ensures stable control without rapid switching.

Components Used

ESP32

Provides:

WiFi connectivity
Web server hosting
Decision logic

SHT40 Sensor

High-accuracy temperature and humidity sensor using I2C communication.

OLED Display

Shows:

Temperature
Humidity
Target temperature

Relay Module

Controls external heating or cooling appliances.

WS2812 RGB LED

Visual status indicator:

Green → Idle
Orange → Heating
Cyan → Cooling

Circuit Diagram

Code

#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_SHT4x.h>
#include <FastLED.h>

// ========== DISPLAY CONFIG ==========
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ========== SENSOR ==========
Adafruit_SHT4x sht4 = Adafruit_SHT4x();

// ========== WEB SERVER ==========
AsyncWebServer server(80);

// ========== PINS ==========
#define RELAY_PIN 5
#define LED_PIN 18
#define NUM_LEDS 1
CRGB leds[NUM_LEDS];

// ========== VARIABLES ==========
float temperature = 0.0;
float humidity = 0.0;
float targetTemp = -1;   // -1 means not set
unsigned long lastRead = 0;
const unsigned long readInterval = 5000;  // 5 seconds

// ========== SETUP ==========
void setup() {
 Serial.begin(115200);
 Wire.begin(21, 22);

 // Sensor init
 if (!sht4.begin()) {
   Serial.println("SHT40 not found!");
   while (1);}
 sht4.setPrecision(SHT4X_HIGH_PRECISION);
 sht4.setHeater(SHT4X_NO_HEATER);

 // OLED init
 if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
   Serial.println("OLED failed");
   while (1);}
 display.clearDisplay();
 display.display();

 // Relay
 pinMode(RELAY_PIN, OUTPUT);
 digitalWrite(RELAY_PIN, LOW);

 // RGB LED
 FastLED.addLeds<NEOPIXEL, LED_PIN>(leds, NUM_LEDS);
 FastLED.setBrightness(100);
 FastLED.clear();
 FastLED.show();

 // Start WiFi AP
 WiFi.softAP("ClimateController");
 Serial.println("Access Point Started");
 Serial.println(WiFi.softAPIP());
 setupWebServer();
}

// ========== MAIN LOOP ==========
void loop() {
 if (millis() - lastRead > readInterval) {
   readSensor();
   updateDisplay();
   updateClimateControl();
   lastRead = millis();
 }}

// ========== SENSOR READING ==========
void readSensor() {
 sensors_event_t temp, hum;
 sht4.getEvent(&temp, &hum);
 temperature = temp.temperature;
 humidity = hum.relative_humidity;
 Serial.print("Temp: ");
 Serial.print(temperature);
 Serial.print("  Hum: ");
 Serial.println(humidity);
}

// ========== DISPLAY ==========
void updateDisplay() {
 display.clearDisplay();
 display.setTextSize(1);
 display.setTextColor(SSD1306_WHITE);
 display.setCursor(0, 0);
 display.print("Temp: ");
 display.print(temperature, 1);
 display.println(" C");
 display.print("Hum: ");
 display.print(humidity, 1);
 display.println(" %");
 display.print("Target: ");
 if (targetTemp >= 0)
   display.print(targetTemp, 1);
 else
   display.print("--");
 display.println(" C");
 display.display();}

// ========== CLIMATE CONTROL ==========
void updateClimateControl() {
 if (targetTemp < 0) {

   // No target set
   leds[0] = CRGB::Green;
   digitalWrite(RELAY_PIN, LOW);
 }
 else if (temperature < targetTemp - 0.5) {

   // Heating ON
   leds[0] = CRGB::Orange;
   digitalWrite(RELAY_PIN, HIGH);
 }
 else if (temperature > targetTemp + 0.5) {

   // Cooling / idle
   leds[0] = CRGB::Cyan;
   digitalWrite(RELAY_PIN, LOW);
 }
 else {

   // Stable zone
   leds[0] = CRGB::Green;
   digitalWrite(RELAY_PIN, LOW);}
 FastLED.show();
}

// ========== WEB SERVER ==========
void setupWebServer() {
 server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
   String html = "<!DOCTYPE html><html><head>";
   html += "<meta name='viewport' content='width=device-width, initial-scale=1'>";
   html += "<meta http-equiv='refresh' content='5'>";
   html += "<title>ESP32 Climate Controller</title></head><body>";
   html += "<h2>ESP32 Climate Controller</h2>";
   html += "<p>Temperature: " + String(temperature, 1) + " C</p>";
   html += "<p>Humidity: " + String(humidity, 1) + " %</p>";

   if (targetTemp >= 0)
     html += "<p>Target: " + String(targetTemp, 1) + " C</p>";
   else
     html += "<p>Target: Not set</p>";
   html += "<form action='/set'>";
   html += "Set Temp: <input type='number' name='temp' step='0.5' min='10' max='40'>";
   html += "<input type='submit' value='Set'>";
   html += "</form>";
   html += "</body></html>";
   request->send(200, "text/html", html);
 });

 server.on("/set", HTTP_GET, [](AsyncWebServerRequest *request) {
   if (request->hasParam("temp")) {
     targetTemp = request->getParam("temp")->value().toFloat();
     Serial.print("New Target: ");
     Serial.println(targetTemp);
   }
   request->redirect("/");
 });
 server.begin();}

Connectivity Features

The system runs in Wi-Fi Access Point (AP) mode:

Creates its own network
Hosts a web dashboard
Allows temperature target setting

This enables future upgrades like:

Mobile app integration
Cloud data logging
BLE automation

Results

Sensor provides stable readings
OLED updates every minute
Web interface refreshes automatically
Relay switches accurately based on target
RGB LED indicates system state clearly

The system performs reliably for indoor climate monitoring and control.

Applications

Smart thermostat systems
Portable temperature monitoring
Greenhouse climate control
Server room monitoring
IoT-based environmental automation

Conclusion

This ESP32 climate controller with SHT40 sensor demonstrates real-world IoT implementation. It combines sensing, connectivity, user interface, and automation in one compact system.

It is an ideal embedded systems project for students interested in IoT, smart homes, and automation.

ESP32 Climate Controller with SHT40 Sensor

Introduction

How the ESP32 Climate Controller Works

System Logic