Circuit Documentation

Summary

This circuit is designed to monitor environmental conditions using various sensors and provide feedback through LEDs and a buzzer. The system is built around an Arduino UNO microcontroller, which reads data from a temperature sensor (LM35), an MQ-2 gas sensor, and an MQ-135 gas sensor. Based on the sensor readings, the system controls a four-pin LED and a buzzer to indicate different environmental statuses.

Component List

1. Arduino UNO

   • Description: A microcontroller board based on the ATmega328P.
   • 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

2. MQ135

   • Description: A gas sensor used to detect air quality.
   • Pins: VCC, GND, A0, D0

3. Temperature Sensor (LM35)

   • Description: A temperature sensor that provides an analog output proportional to the temperature.
   • Pins: +Vs, Vout, GND

4. MQ-2

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

5. Buzzer

   • Description: An audio signaling device.
   • Pins: PIN, GND

6. LED: Four Pin

   • Description: A four-pin LED with red, green, and blue cathodes and a common anode.
   • Pins: red cathode, common anode, green cathode, blue cathode

Wiring Details

Arduino UNO

• GND connected to:

  • Buzzer GND
  • MQ-2 GND
  • Temperature Sensor (LM35) GND
  • MQ135 GND

• 5V connected to:

  • Temperature Sensor (LM35) +Vs
  • LED: Four Pin common anode
  • MQ135 VCC
  • MQ-2 VCC

• A0 connected to:

  • Temperature Sensor (LM35) Vout

• A1 connected to:

  • MQ-2 ANALOG

• A2 connected to:

  • MQ135 A0

• D2 connected to:

  • MQ-2 Digital

• D3 connected to:

  • MQ135 D0

• D4 connected to:

  • LED: Four Pin red cathode

• D5 connected to:

  • Buzzer PIN

• D6 connected to:

  • LED: Four Pin green cathode

• D7 connected to:

  • LED: Four Pin blue cathode

MQ135

• GND connected to:

  • Arduino UNO GND

• VCC connected to:

  • Arduino UNO 5V

• A0 connected to:

  • Arduino UNO A2

• D0 connected to:

  • Arduino UNO D3

Temperature Sensor (LM35)

• GND connected to:

  • Arduino UNO GND

• +Vs connected to:

  • Arduino UNO 5V

• Vout connected to:

  • Arduino UNO A0

MQ-2

• GND connected to:

  • Arduino UNO GND

• VCC connected to:

  • Arduino UNO 5V

• ANALOG connected to:

  • Arduino UNO A1

• Digital connected to:

  • Arduino UNO D2

Buzzer

• GND connected to:

  • Arduino UNO GND

• PIN connected to:

  • Arduino UNO D5

LED: Four Pin

• common anode connected to:

  • Arduino UNO 5V

• red cathode connected to:

  • Arduino UNO D4

• green cathode connected to:

  • Arduino UNO D6

• blue cathode connected to:

  • Arduino UNO D7

Documented Code

// Pin definitions
const int tempSensorPin = A0;      // Temperature sensor on A0
const int mq2AnalogPin = A1;       // MQ-2 analog on A1
const int mq2DigitalPin = 2;       // Changed from D2 to 2
const int mq135AnalogPin = A2;     // MQ-135 analog on A2
const int mq135DigitalPin = 3;     // Changed from D3 to 3
const int redLEDPin = 4;           // Changed from D4 to 4
const int buzzerPin = 5;           // Changed from D5 to 5
const int greenLEDPin = 6;         // Changed from D6 to 6
const int blueLEDPin = 7;          // Changed from D7 to 7

// Thresholds
const float TEMP_HIGH = 30.0;
const float TEMP_MEDIUM = 20.0;
const int GAS_THRESHOLD = 300;

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  
  // Set pin modes
  pinMode(tempSensorPin, INPUT);
  pinMode(mq2AnalogPin, INPUT);
  pinMode(mq2DigitalPin, INPUT);
  pinMode(mq135AnalogPin, INPUT);
  pinMode(mq135DigitalPin, INPUT);
  pinMode(redLEDPin, OUTPUT);
  pinMode(greenLEDPin, OUTPUT);
  pinMode(blueLEDPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
  
  // Initial LED test
  digitalWrite(redLEDPin, HIGH);
  delay(500);
  digitalWrite(redLEDPin, LOW);
  digitalWrite(greenLEDPin, HIGH);
  delay(500);
  digitalWrite(greenLEDPin, LOW);
  digitalWrite(blueLEDPin, HIGH);
  delay(500);
  digitalWrite(blueLEDPin, LOW);
  
  Serial.println("System Initialized");
}

void loop() {
  // Read temperature sensor value
  int tempValue = analogRead(tempSensorPin);
  // Modified temperature calculation for LM35 sensor
  float temperature = (tempValue * 5.0 * 100.0) / 1024.0;
  
  // Read MQ-2 sensor values
  int mq2AnalogValue = analogRead(mq2AnalogPin);
  int mq2DigitalValue = digitalRead(mq2DigitalPin);
  
  // Read MQ135 sensor values
  int mq135AnalogValue = analogRead(mq135AnalogPin);
  int mq135DigitalValue = digitalRead(mq135DigitalPin);
  
  // Print sensor values to serial monitor with better formatting
  Serial.println("--------------------");
  Serial.print("Temperature: ");
  Serial.print(temperature, 1);  // One decimal place
  Serial.println(" °C");
  
  Serial.print("MQ-2 Sensor - Analog: ");
  Serial.print(mq2AnalogValue);
  Serial.print(" Digital: ");
  Serial.println(mq2DigitalValue ? "HIGH" : "LOW");
  
  Serial.print("MQ-135 Sensor - Analog: ");
  Serial.print(mq135AnalogValue);
  Serial.print(" Digital: ");
  Serial.println(mq135DigitalValue ? "HIGH" : "LOW");
  
  // Control LEDs based on temperature with status message
  if (temperature > TEMP_HIGH) {
    setLEDs(HIGH, LOW, LOW);
    Serial.println("Status: HIGH Temperature Alert!");
  } else if (temperature > TEMP_MEDIUM) {
    setLEDs(LOW, HIGH, LOW);
    Serial.println("Status: Normal Temperature");
  } else {
    setLEDs(LOW, LOW, HIGH);
    Serial.println("Status: Low Temperature");
  }
  
  // Control buzzer based on gas detection with pattern
  if (mq2DigitalValue == HIGH || mq135DigitalValue == HIGH) {
    Serial.println("WARNING: Gas Detected!");
    // Beeping pattern
    for (int i = 0; i < 3; i++) {
      tone(buzzerPin, 1000);  // 1kHz tone
      delay(200);
      noTone(buzzerPin);
      delay(200);
    }
  } else {
    noTone(buzzerPin);
  }
  
  // Calculate gas concentrations as percentage
  int mq2Percentage = map(mq2AnalogValue, 0, 1023, 0, 100);
  int mq135Percentage = map(mq135AnalogValue, 0, 1023, 0, 100);
  
  Serial.print("Gas Levels - MQ2: ");
  Serial.print(mq2Percentage);
  Serial.print("%, MQ135: ");
  Serial.print(mq135Percentage);
  Serial.println("%");
  
  Serial.println("--------------------\n");
  
  // Main loop delay
  delay(2000);  // Increased to 2 seconds for better readability
}

// Helper function to set LED states