ESP32 Air Quality Monitor with MQ Sensors

/*********************************************************************
 * ESP32 Air Quality Monitor with MQ Sensors
 * 
 * Measures: CO2, Smoke, NH3, Temperature, Humidity
 * Hardware: ESP32, MQ-135, DHT22
 * 
 * Libraries Required:
 * - DHT sensor library (Adafruit)
 * - Adafruit Unified Sensor
 *********************************************************************/

#include 
#include 
#include "DHT.h"

// ============== DHT CONFIGURATION ==============
#define DHTPIN 4        // GPIO 4
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

// ============== MQ-135 CONFIGURATION ==============
#define MQ135_PIN 34    // GPIO 34 (ADC)

// Calibration values
#define RLOAD 10.0       // Load resistance in kOhms
#define RZERO 76.63      // Calibration resistance
#define CO2_RZERO 76.63
#define CO2_SCALINGFACTOR 116.6020682
#define CO2_EXPONENT -2.769034857

// ============== WIFI CONFIGURATION ==============
const char* wifi_ssid = "YOUR_WIFI_NAME";
const char* wifi_password = "YOUR_WIFI_PASSWORD";

// ============== THINGSPEAK CONFIGURATION ==============
String apiKey = "YOUR_THINGSPEAK_API_KEY";
String server = "http://api.thingspeak.com/update";

// ============== DISPLAY CONFIGURATION ==============
#define BAUD_RATE 115200
#define READ_INTERVAL 5000  // 5 seconds

unsigned long lastRead = 0;

// ============== SETUP ==============
void setup() {
  Serial.begin(BAUD_RATE);
  Serial.println(F("\n======================================"));
  Serial.println(F("ESP32 Air Quality Monitor Starting..."));
  Serial.println(F("======================================"));
  
  // Initialize DHT sensor
  dht.begin();
  
  // Configure ADC
  analogReadResolution(12);  // 12-bit ADC (0-4095)
  
  // Connect to WiFi
  connectToWiFi();
  
  Serial.println(F("Setup complete!"));
  Serial.println(F("Reading air quality data...\n"));
}

// ============== MAIN LOOP ==============
void loop() {
  if (millis() - lastRead > READ_INTERVAL) {
    lastRead = millis();
    readSensors();
  }
}

// ============== FUNCTIONS ==============

void readSensors() {
  // Read DHT22 data
  float temperature = dht.readTemperature();    // Celsius
  float humidity = dht.readHumidity();           // Percentage
  
  // Read MQ-135 data
  int sensorValue = analogRead(MQ135_PIN);
  float voltage = sensorValue * (3.3 / 4095.0);
  
  // Calculate CO2 equivalent
  float co2 = calculateCO2(sensorValue);
  
  // Calculate resistance
  float resistance = calculateResistance(sensorValue);
  
  // Print to Serial
  Serial.println(F("========== AIR QUALITY DATA =========="));
  Serial.print(F("Temperature: ")); Serial.print(temperature, 1); Serial.println(F(" C"));
  Serial.print(F("Humidity: ")); Serial.print(humidity, 1); Serial.println(F(" %"));
  Serial.print(F("Sensor Value: ")); Serial.println(sensorValue);
  Serial.print(F("Voltage: ")); Serial.print(voltage, 3); Serial.println(F(" V"));
  Serial.print(F("Resistance: ")); Serial.print(resistance, 1); Serial.println(F(" kOhms"));
  Serial.print(F("CO2: ")); Serial.print(co2, 0); Serial.println(F(" ppm"));
  Serial.println(F("=====================================\n"));
  
  // Send to ThingSpeak
  sendToThingSpeak(temperature, humidity, co2);
}

float calculateResistance(int rawValue) {
  // Calculate sensor resistance
  float voltage = rawValue * (3.3 / 4095.0);
  return (3.3 - voltage) / voltage * RLOAD;
}

float calculateCO2(int rawValue) {
  // Calculate CO2 concentration using MQ-135
  float resistance = calculateResistance(rawValue);
  float ratio = resistance / RZERO;
  float co2 = CO2_SCALINGFACTOR * pow(ratio, CO2_EXPONENT);
  return co2;
}

void sendToThingSpeak(float temp, float hum, float co2) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    String url = server + "?api_key=" + apiKey;
    url += "&field1=" + String(temp);
    url += "&field2=" + String(hum);
    url += "&field3=" + String(co2);
    
    http.begin(url);
    int httpCode = http.GET();
    
    if (httpCode > 0) {
      Serial.println(F("Data sent to ThingSpeak"));
    } else {
      Serial.println(F("ThingSpeak connection failed"));
    }
    
    http.end();
  }
}

void connectToWiFi() {
  Serial.print(F("Connecting to WiFi"));
  WiFi.begin(wifi_ssid, wifi_password);
  
  int attempts = 0;
  while (WiFi.status() != WL_CONNECTED && attempts < 20) {
    delay(500);
    Serial.print(F("."));
    attempts++;
  }
  
  if (WiFi.status() == WL_CONNECTED) {
    Serial.println(F(" Connected!"));
    Serial.print(F("IP: ")); Serial.println(WiFi.localIP());
  } else {
    Serial.println(F(" Connection failed!"));
  }
}

// ============== END OF CODE ==============