Circuit Documentation

Summary

This circuit is designed to monitor environmental conditions using an MQ2 gas sensor and a DHT11 humidity and temperature sensor. It also includes an HC-05 Bluetooth module for wireless communication, a buzzer for alerts, and three LEDs (yellow, red, and green) for visual indicators. The circuit is controlled by an Arduino 101 microcontroller.

Component List

MQ2 Gas Sensor

• Pins: VCC, GND, AOUT, DOUT
• Description: The MQ2 gas sensor is used to detect the presence of gases such as LPG, i-butane, propane, methane, alcohol, hydrogen, and smoke.

DHT11 Humidity and Temperature Sensor

• Pins: VDD, DATA, NULL, GND
• Description: The DHT11 sensor measures both humidity and temperature.

HC-05 Bluetooth Module

• Pins: Key, VCC, TXD, RXD, State, GND
• Description: The HC-05 module is used for wireless communication via Bluetooth.

Arduino 101

• Pins: A5/SCL, A4/SDA, AREF, GND, D13/SCK, D12/MISO, D11 PWM/MOSI, D10 PWM/SS, D9 PWM, D8, D7, D6 PWM, D5 PWM, D4, D3 PWM, D2, D1/TX, D0/RX, AIN, ioref, RESET, 3V3, 5V, VIN, A0, A1, A2, A3, ICSP MISO, ICSP SCK, ICSP MOSI
• Description: The Arduino 101 is the main microcontroller used to control the circuit and process sensor data.

Buzzer

• Pins: PIN, GND
• Description: The buzzer is used to provide audible alerts.

LED: Two Pin (Yellow)

• Pins: Cathode, Anode
• Description: A yellow LED used as a visual indicator.

LED: Two Pin (Red)

• Pins: Cathode, Anode
• Description: A red LED used as a visual indicator.

LED: Two Pin (Green)

• Pins: Cathode, Anode
• Description: A green LED used as a visual indicator.

Resistor (220 Ohms)

• Pins: Pin1, Pin2
• Description: Resistors used to limit current to the LEDs.
• Properties: Resistance: 220 Ohms

Wiring Details

MQ2 Gas Sensor

• VCC: Connected to Arduino 101 5V
• GND: Connected to Arduino 101 GND
• AOUT: Connected to Arduino 101 A0

DHT11 Humidity and Temperature Sensor

• VDD: Connected to Arduino 101 5V
• DATA: Connected to Arduino 101 D2
• GND: Connected to Arduino 101 GND

HC-05 Bluetooth Module

• VCC: Connected to Arduino 101 5V
• TXD: Connected to Arduino 101 D0/RX
• RXD: Connected to Arduino 101 D1/TX
• GND: Connected to Arduino 101 GND

Buzzer

• PIN: Connected to Arduino 101 D8
• GND: Connected to Arduino 101 GND

LED: Two Pin (Yellow)

• Anode: Connected to Arduino 101 D7
• Cathode: Connected to one end of a 220 Ohm resistor
• Resistor: Other end connected to Arduino 101 GND

LED: Two Pin (Red)

• Anode: Connected to Arduino 101 D6 PWM
• Cathode: Connected to one end of a 220 Ohm resistor
• Resistor: Other end connected to Arduino 101 GND

LED: Two Pin (Green)

• Anode: Connected to Arduino 101 D5 PWM
• Cathode: Connected to one end of a 220 Ohm resistor
• Resistor: Other end connected to Arduino 101 GND

Code Documentation

#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT11
#define BUZZER_PIN 8
#define ALERT_LED_PIN 7
#define CONTROL_LED_PIN 6
#define CONTROL_LED2_PIN 5
#define MQ2_PIN A0
#define THRESHOLD 600

DHT dht(DHTPIN, DHTTYPE);

void setup() {
    Serial.begin(9600);
    dht.begin();
    pinMode(BUZZER_PIN, OUTPUT);
    pinMode(ALERT_LED_PIN, OUTPUT);
    pinMode(CONTROL_LED_PIN, OUTPUT);
    pinMode(CONTROL_LED2_PIN, OUTPUT);
    Serial.println("Type 'on' or 'off' to control the first LED, and 'on2' or 'off2' for the second LED.");
}

void loop() {
    int mq2Value = analogRead(MQ2_PIN);
    if (mq2Value > THRESHOLD) {
        digitalWrite(BUZZER_PIN, HIGH);
        digitalWrite(ALERT_LED_PIN, HIGH);
    } else {
        digitalWrite(BUZZER_PIN, LOW);
        digitalWrite(ALERT_LED_PIN, LOW);
    }

    if (Serial.available() > 0) {
        String command = Serial.readStringUntil('\n');
        command.trim();
        if (command == "on") {
            digitalWrite(CONTROL_LED_PIN, HIGH);
            Serial.println("Control LED 1 turned ON");
        } else if (command == "off") {
            digitalWrite(CONTROL_LED_PIN, LOW);
            Serial.println("Control LED 1 turned OFF");
        } else if (command == "on2") {
            digitalWrite(CONTROL_LED2_PIN, HIGH);
            Serial.println("Control LED 2 turned ON");
        } else if (command == "off2") {
            digitalWrite(CONTROL_LED2_PIN, LOW);
            Serial.println("Control LED 2 turned OFF");
        } else {
            Serial.println("Invalid command. Type 'on', 'off', 'on2', or 'off2'.");
        }
    }

    float humidity = dht.readHumidity();
    float temperature = dht.readTemperature();
    if (isnan(humidity) || isnan(temperature)) {
        Serial.println("Failed to read from DHT sensor!");
    } else {
        Serial.print("Humidity: ");
        Serial.print(humidity);
        Serial.print("% Temperature: ");
        Serial.print(temperature);
        Serial.println("°C");
    }
}

This code initializes the DHT11 sensor, sets up the pins for the buzzer and LEDs, and continuously reads the gas sensor value. If the gas concentration exceeds a threshold, the buzzer and alert LED are activated. The code also listens for serial commands to control two additional LEDs and prints the humidity and temperature readings to the serial monitor.