Circuit Documentation

Summary

This circuit is designed to monitor environmental conditions using various sensors and an Arduino UNO microcontroller. It includes an NTC thermistor for temperature measurement, a DHT11 sensor for humidity, an MQ-2 sensor for gas detection, and a reed switch for door status monitoring. The circuit also includes LEDs for visual indication and a buzzer for audible alerts. The Arduino UNO processes the sensor data and controls the LEDs and buzzer based on predefined thresholds.

Component List

1. Analog Temperature Sensor (NTC) (Wokwi Compatible)

   • Pins: GND, VCC, OUT
   • Description: Measures temperature using a negative temperature coefficient thermistor.

2. MQ-2

   • Pins: GND, VCC, ANALOG, Digital
   • Description: Gas sensor for detecting various gases including LPG, smoke, alcohol, propane, hydrogen, methane, and carbon monoxide.

3. Door MC-38

   • Pins: S, GND
   • Description: Magnetic reed switch used for detecting door open/close status.

4. LED: Two Pin (red)

   • Pins: cathode, anode
   • Description: Red LED for visual indication.

5. Arduino UNO

   • Pins: UNUSED, IOREF, Reset, 3.3V, 5V, GND, Vin, A0, A1, A2, A3, A4, A5, SCL, SDA, AREF, D13, D12, D11, D10, D9, D8, D7, D6, D5, D4, D3, D2, D1, D0
   • Description: Microcontroller board based on the ATmega328P.

6. Buzzer

   • Pins: PIN, GND
   • Description: Buzzer for audible alerts.

7. DHT11

   • Pins: DATA, GND, VCC
   • Description: Digital temperature and humidity sensor.

Wiring Details

Analog Temperature Sensor (NTC) (Wokwi Compatible)

• GND connected to Arduino UNO GND
• VCC connected to Arduino UNO Vin
• OUT connected to Arduino UNO A0

MQ-2

• GND connected to Arduino UNO GND
• VCC connected to Arduino UNO Vin
• ANALOG connected to Arduino UNO A2

Door MC-38

• S connected to Arduino UNO D7
• GND connected to Arduino UNO GND

LED: Two Pin (red) (1)

• cathode connected to Arduino UNO GND
• anode connected to Arduino UNO D13

LED: Two Pin (red) (2)

• cathode connected to Arduino UNO GND
• anode connected to Arduino UNO D6

LED: Two Pin (red) (3)

• cathode connected to Arduino UNO GND
• anode connected to Arduino UNO D3

Arduino UNO

• GND connected to GND of all components
• Vin connected to VCC of NTC, DHT11, and MQ-2
• A0 connected to OUT of NTC
• A1 connected to DATA of DHT11
• A2 connected to ANALOG of MQ-2
• D13 connected to anode of LED (1)
• D6 connected to anode of LED (2)
• D3 connected to anode of LED (3)
• D7 connected to S of Door MC-38
• D8 connected to PIN of Buzzer

Buzzer

• PIN connected to Arduino UNO D8
• GND connected to Arduino UNO GND

DHT11

• DATA connected to Arduino UNO A1
• GND connected to Arduino UNO GND
• VCC connected to Arduino UNO Vin

Documented Code

#include <DHT.h>
#include <math.h>
#include <SoftwareSerial.h>

SoftwareSerial espSerial(10, 11);

// NTC Thermistor setup
const int ntcPin = A0;
const int ntcLedPin = 13;
const float thresholdTemp = 25.0;
const float BETA = 3950;
const float ROOM_TEMP_RESISTANCE = 10000;
const float ROOM_TEMP = 298.15;

// DHT11 setup
#define DHTPIN A1
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);
const int dhtLedPin = 3;
const float thresholdHumidity = 55.0;

// MQ2 Gas Sensor setup
const int mq2Pin = A2;
const int mq2LedPin = 6;
const int gasThreshold = 400;

// Reed Switch & Buzzer setup
const int reedPin = 7;
const int buzzerPin = 8;

// Function to read temperature from NTC thermistor
float readTemperature() {
    int adcValue = analogRead(ntcPin);
    float resistance = (1023.0 / adcValue - 1) * ROOM_TEMP_RESISTANCE;
    float temperatureKelvin = 1 / (1 / ROOM_TEMP + log(resistance / ROOM_TEMP_RESISTANCE) / BETA);
    return temperatureKelvin - 273.15;
}

void setup() {
    pinMode(ntcLedPin, OUTPUT);
    pinMode(dhtLedPin, OUTPUT);
    pinMode(mq2LedPin, OUTPUT);
    pinMode(reedPin, INPUT_PULLUP);
    pinMode(buzzerPin, OUTPUT);

    dht.begin();
    Serial.begin(9600);
    espSerial.begin(9600);
}

void loop() {
    // NTC Temperature check
    float temperature = readTemperature();
    Serial.print("Temperature: ");
    Serial.print(temperature);
    Serial.println(" °C");
    digitalWrite(ntcLedPin, temperature > thresholdTemp ? HIGH : LOW);

    // DHT11 Humidity check
    float humidity = dht.readHumidity();
    if (!isnan(humidity)) {
        Serial.print("Humidity: ");
        Serial.print(humidity);
        Serial.println(" %");
        digitalWrite(dhtLedPin, humidity > thresholdHumidity ? HIGH : LOW);
    } else {
        Serial.println("Failed to read from DHT sensor!");
    }

    // MQ2 Gas sensor check
    int gasLevel = analogRead(mq2Pin);
    Serial.print("Gas Level: ");
    Serial.println(gasLevel);
    digitalWrite(mq2LedPin, gasLevel > gasThreshold ? HIGH : LOW);

    // Reed Switch and Buzzer
    int reedState = digitalRead(reedPin);
    if (reedState == 1) { // Door is open
        tone(buzzerPin, 500); // Lower frequency
        Serial.println("Door is open! Buzzer ON.");
    } else {
        noTone(buzzerPin); // Turn off buzzer
        Serial.println("Door is closed. Buzzer OFF.");
    }
    espSerial.println();
    espSerial.print(temperature);
    espSerial.print(",");
    espSerial.print(humidity);
    espSerial.print(",");
    espSerial.print(gasLevel);
    espSerial.print(",");
    espSerial.print(reedState);
    espSerial.println();
    delay(1000); // Wait 1 second
}

This code initializes the sensors and components, reads data from the sensors, and controls the LEDs and buzzer based on the sensor readings. The data is also sent to a serial monitor and an external device via SoftwareSerial.