Circuit Documentation

Summary

This circuit is designed to monitor gas levels, temperature, and humidity using an MQ-2 gas sensor and a DHT11 humidity and temperature sensor. The circuit includes an Arduino Nano microcontroller, a red LED, a buzzer, and a resistor. The system triggers the buzzer and LED when gas levels, temperature, or humidity exceed predefined thresholds.

Component List

1. LED: Two Pin (red)

   • Pins: Cathode, Anode
   • Description: A red LED used to indicate when thresholds are exceeded.

2. Arduino Nano

   • Pins: D1/TX, D0/RX, RESET, GND, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11/MOSI, D12/MISO, VIN, 5V, A7, A6, A5, A4, A3, A2, A1, A0, AREF, 3V3, D13/SCK
   • Description: The main microcontroller used to read sensor data and control the LED and buzzer.

3. MQ-2

   • Pins: GND, VCC, ANALOG, Digital
   • Description: A gas sensor used to detect gas levels.

4. DHT11 Humidity and Temperature Sensor

   • Pins: VDD, DATA, NULL, GND
   • Description: A sensor used to measure humidity and temperature.

5. Buzzer

   • Pins: PIN, GND
   • Description: A buzzer used to provide an audible alert when thresholds are exceeded.

6. Resistor

   • Pins: Pin1, Pin2
   • Description: A 220 Ohm resistor used to limit current to the LED.
   • Properties:
     • Resistance: 220 Ohms

Wiring Details

LED: Two Pin (red)

• Cathode: Connected to GND of Arduino Nano.
• Anode: Connected to Pin1 of the Resistor.

Arduino Nano

• A0: Connected to ANALOG pin of MQ-2.
• D9: Connected to Pin2 of the Resistor.
• D8: Connected to PIN of the Buzzer.
• D7: Connected to DATA pin of DHT11 Humidity and Temperature Sensor.
• 5V: Connected to VDD pin of DHT11 Humidity and Temperature Sensor.
• GND: Connected to:
  • Cathode of LED
  • GND of Buzzer
  • GND of DHT11 Humidity and Temperature Sensor
  • GND of MQ-2

MQ-2

• GND: Connected to GND of Arduino Nano.
• VCC: Not connected in this circuit.
• ANALOG: Connected to A0 of Arduino Nano.
• Digital: Not connected in this circuit.

DHT11 Humidity and Temperature Sensor

• VDD: Connected to 5V of Arduino Nano.
• DATA: Connected to D7 of Arduino Nano.
• NULL: Not connected in this circuit.
• GND: Connected to GND of Arduino Nano.

Buzzer

• PIN: Connected to D8 of Arduino Nano.
• GND: Connected to GND of Arduino Nano.

Resistor

• Pin1: Connected to Anode of LED.
• Pin2: Connected to D9 of Arduino Nano.

Documented Code

Arduino Nano Code

#include <DHT.h>

#define GAS_SENSOR_PIN A0
#define BUZZER_PIN 9
#define LED_PIN 8
#define DHT_PIN 7           // DHT sensor connected to pin 7
#define GAS_THRESHOLD 400    // Gas threshold value
#define TEMP_THRESHOLD 45.0  // Temperature threshold in Celsius (example)
#define HUMIDITY_THRESHOLD 80.0  // Humidity threshold in percentage

// Initialize DHT sensor
DHT dht(DHT_PIN, DHT11);  // DHT11 sensor type

void setup() {
  pinMode(GAS_SENSOR_PIN, INPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  
  // Initialize DHT sensor
  dht.begin();
}

void loop() {
  // Read gas level from MQ-2 sensor
  int gasLevel = analogRead(GAS_SENSOR_PIN);

  // Read temperature and humidity from DHT11 sensor
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();  // Temperature in Celsius

  // Check if readings are valid
  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT sensor!");
    return;  // Stop if there's an error in reading from the sensor
  }

  // Print sensor readings to Serial Monitor
  Serial.print("Gas Level: ");
  Serial.println(gasLevel);
  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.print(" °C, Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");

  // Check if gas level exceeds threshold
  if (gasLevel > GAS_THRESHOLD || temperature > TEMP_THRESHOLD || humidity > HUMIDITY_THRESHOLD) {
    Serial.println("Gas or temperature/humidity threshold exceeded! Triggering buzzer and LED...");
    tone(BUZZER_PIN, 1000);  // Trigger buzzer with 1kHz tone
    digitalWrite(LED_PIN, HIGH);  // Turn on LED
  } else {
    noTone(BUZZER_PIN);  // Turn off buzzer
    digitalWrite(LED_PIN, LOW);  // Turn off LED
  }

  delay(500);  // Delay to make readings easier to observe
}

Additional Code for Arduino Nano

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

This documentation provides a comprehensive overview of the circuit, including a summary, detailed component list, wiring details, and the code used in the microcontroller.