Circuit Documentation

Summary

This circuit is designed to monitor environmental conditions using various sensors and respond accordingly. It includes an Arduino UNO microcontroller, temperature sensor (NTC), light-dependent resistor (LDR), gas sensor (MQ-2), ultrasonic sensor (HC-SR04), servo motor, piezo buzzer, and an LED. The system reads sensor values and triggers an alarm or controls the servo motor based on predefined thresholds.

Component List

Arduino UNO

• Description: 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

NTC (Temperature Sensor)

• Description: Negative Temperature Coefficient thermistor used for temperature measurement.
• Pins: A0, A1

Photocell (LDR)

• Description: Light-dependent resistor used to measure light intensity.
• Pins: pin 0, pin 1

Servo

• Description: Servo motor used for precise control of angular position.
• Pins: GND, VCC, PWM

LED: Two Pin (red)

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

Piezo Buzzer

• Description: Buzzer used for sound indication.
• Pins: pin 1, pin 2

Resistor

• Description: Resistor used to limit current.
• Pins: pin1, pin2
• Properties: Resistance: 1000 Ohms

HC-SR04 Ultrasonic Sensor

• Description: Ultrasonic sensor used for distance measurement.
• Pins: VCC, TRIG, ECHO, GND

MQ-2

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

Wiring Details

Arduino UNO

• A0: Connected to NTC (A0), Resistor (pin1), Piezo Buzzer (pin 2)
• A2: Connected to Photocell (LDR) (pin 0), Resistor (pin2)
• A4: Connected to MQ-2 (ANALOG)
• D3: Connected to HC-SR04 Ultrasonic Sensor (TRIG)
• D7: Connected to Piezo Buzzer (pin 1)
• D10: Connected to LED (anode)
• D11: Connected to Servo (PWM)
• D13: Connected to HC-SR04 Ultrasonic Sensor (ECHO)
• 5V: Connected to HC-SR04 Ultrasonic Sensor (VCC), Servo (VCC), MQ-2 (VCC)
• GND: Connected to NTC (A0), Resistor (pin1), Piezo Buzzer (pin 2), HC-SR04 Ultrasonic Sensor (GND), Servo (GND), MQ-2 (GND)

NTC (Temperature Sensor)

• A0: Connected to Arduino UNO (A0), Resistor (pin1), Piezo Buzzer (pin 2)
• A1: Connected to Photocell (LDR) (pin 1), HC-SR04 Ultrasonic Sensor (VCC), Servo (VCC), MQ-2 (VCC), Arduino UNO (5V)

Photocell (LDR)

• pin 0: Connected to Resistor (pin2), Arduino UNO (A2)
• pin 1: Connected to NTC (A1), HC-SR04 Ultrasonic Sensor (VCC), Servo (VCC), MQ-2 (VCC), Arduino UNO (5V)

Servo

• GND: Connected to Arduino UNO (GND)
• VCC: Connected to NTC (A1), Photocell (LDR) (pin 1), HC-SR04 Ultrasonic Sensor (VCC), MQ-2 (VCC), Arduino UNO (5V)
• PWM: Connected to Arduino UNO (D11)

LED: Two Pin (red)

• cathode: Connected to Resistor (pin2)
• anode: Connected to Arduino UNO (D10)

Piezo Buzzer

• pin 1: Connected to Arduino UNO (D7)
• pin 2: Connected to NTC (A0), Resistor (pin1), Arduino UNO (A0)

Resistor

• pin1: Connected to NTC (A0), Piezo Buzzer (pin 2), Arduino UNO (A0)
• pin2: Connected to Photocell (LDR) (pin 0), LED (cathode), Arduino UNO (A2)

HC-SR04 Ultrasonic Sensor

• VCC: Connected to NTC (A1), Photocell (LDR) (pin 1), Servo (VCC), MQ-2 (VCC), Arduino UNO (5V)
• TRIG: Connected to Arduino UNO (D3)
• ECHO: Connected to Arduino UNO (D13)
• GND: Connected to NTC (A0), Resistor (pin1), Piezo Buzzer (pin 2), Servo (GND), MQ-2 (GND), Arduino UNO (GND)

MQ-2

• GND: Connected to NTC (A0), Resistor (pin1), Piezo Buzzer (pin 2), HC-SR04 Ultrasonic Sensor (GND), Servo (GND), Arduino UNO (GND)
• VCC: Connected to NTC (A1), Photocell (LDR) (pin 1), HC-SR04 Ultrasonic Sensor (VCC), Servo (VCC), Arduino UNO (5V)
• ANALOG: Connected to Arduino UNO (A4)
• Digital: Not connected

Code Documentation

#include <Servo.h>

// Pin Definitions
#define LDRpin A2        // LDR Sensor Pin
#define MQ2pin A4        // MQ-2 Gas Sensor Pin
#define TEMPpin A0       // Temperature Sensor (KY-028) Pin
const int TRIG_PIN = 3;  // Ultrasonic Sensor TRIG pin
const int ECHO_PIN = 13; // Ultrasonic Sensor ECHO pin
const int SERVO_PIN = 11; // Servo Motor pin
const int BUZZER_PIN = 7; // Buzzer pin
const int LED_PIN = 10;  // LED pin

// Thresholds
const int DISTANCE_THRESHOLD = 10; // Ultrasonic Distance Threshold in cm
const int TEMP_THRESHOLD = 50;    // Temperature Threshold (raw value)
const int GAS_THRESHOLD = 200;    // Gas Threshold (raw value)
const int LDR_THRESHOLD = 100;    // LDR Threshold (raw value)

// Global Variables
Servo servo;          // Servo Motor Object
float distance_cm;    // Ultrasonic Sensor Value
float tempValue;      // Temperature Sensor Value
float gasValue;       // MQ-2 Gas Sensor Value
int LDRValue;         // LDR Sensor Value

void setup() {
  Serial.begin(9600); // Initialize Serial Monitor
  
  // Pin Modes
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  pinMode(LDRpin, INPUT);
  pinMode(MQ2pin, INPUT);
  pinMode(TEMPpin, INPUT);
  
  servo.attach(SERVO_PIN);
  servo.write(90); // Initial state: Servo closed
  
  // Ensure initial states
  digitalWrite(BUZZER_PIN, LOW);
  digitalWrite(LED_PIN, LOW);
}

void updateUltrasonic() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  float duration_us = pulseIn(ECHO_PIN, HIGH);
  distance_cm = 0.017 * duration_us;
  if (distance_cm <= 0 || distance_cm > 400) {
    distance_cm = 400; // Out of range
  }
}

void updateSensorValues() {
  tempValue = analogRead(TEMPpin);
  gasValue = analogRead(MQ2pin);
}

bool isAlarmConditionActive() {
  return (tempValue < TEMP_THRESHOLD || gasValue > GAS_THRESHOLD);
}

void playAlarm() {
  while (true) {
    digitalWrite(LED_PIN, HIGH); // Turn on the LED
    Serial.println("Alarm is active!");
    
    // Check sensor values before each pattern
    updateSensorValues();
    if (!isAlarmConditionActive()) {
      Serial.println("Conditions returned to normal - stopping alarm");
      stopAlarm();
      break;
    }
    
    // Pattern 1
    for (int i = 0; i < 80; i++) {
      digitalWrite(BUZZER_PIN, HIGH);
      delay(1);
      digitalWrite(BUZZER