Circuit Documentation

Summary

This circuit is designed to monitor gas levels using an MQ2 gas sensor and display the readings on a 16x2 I2C LCD screen. If the gas level exceeds a certain threshold, an alert is sent via the SIM800L module, and a buzzer is activated. The circuit is controlled by an Arduino UNO microcontroller.

Component List

1. 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

2. MQ2

   • Description: Gas sensor for detecting LPG, i-butane, propane, methane, alcohol, hydrogen, and smoke.
   • Pins: VCC, GND, AOUT, DOUT

3. LCD screen 16x2 I2C

   • Description: 16x2 character LCD display with I2C interface.
   • Pins: SCL, SDA, VCC, GND

4. SIM800L

   • Description: GSM/GPRS module for sending SMS and connecting to the internet.
   • Pins: NFT, RING, VCC, DTR, RST, MIC +, RXD, MIC-, TXD, SPK+, GND, SPK-

5. 3.7V Battery

   • Description: Power source for the circuit.
   • Pins: +, -

6. Buzzer

   • Description: Audio signaling device.
   • Pins: POSITIVE, NEGATIVE

Wiring Details

Arduino UNO

• 5V connected to VCC of SIM800L and LCD screen 16x2 I2C.
• GND connected to GND of Buzzer, LCD screen 16x2 I2C, SIM800L, MQ2, and 3.7V Battery.
• A1 connected to AOUT of MQ2.
• A4 connected to SDA of LCD screen 16x2 I2C.
• A5 connected to SCL of LCD screen 16x2 I2C.
• D6 connected to POSITIVE of Buzzer.
• D3 connected to TXD of SIM800L.
• D2 connected to RXD of SIM800L.

MQ2

• VCC connected to + of 3.7V Battery.
• GND connected to GND of Arduino UNO.
• AOUT connected to A1 of Arduino UNO.

LCD screen 16x2 I2C

• VCC connected to 5V of Arduino UNO.
• GND connected to GND of Arduino UNO.
• SDA connected to A4 of Arduino UNO.
• SCL connected to A5 of Arduino UNO.

SIM800L

• VCC connected to 5V of Arduino UNO.
• GND connected to GND of Arduino UNO.
• TXD connected to D3 of Arduino UNO.
• RXD connected to D2 of Arduino UNO.

3.7V Battery

• + connected to VCC of MQ2.
• - connected to GND of Arduino UNO.

Buzzer

• POSITIVE connected to D6 of Arduino UNO.
• NEGATIVE connected to GND of Arduino UNO.

Documented Code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <SoftwareSerial.h>

// Define the pins
const int gasSensorPin = A1; // MQ2 analog output connected to A1
const int buzzerPin = 6;     // Buzzer connected to D6
const int sim800lTx = 3;     // SIM800L TX connected to D3
const int sim800lRx = 2;     // SIM800L RX connected to D2

// Initialize the LCD
LiquidCrystal_I2C lcd(0x27, 16, 2); // Change the address to 0x27 if needed

// Initialize the SIM800L
SoftwareSerial sim800l(sim800lRx, sim800lTx);

void setup() {
  // Initialize the LCD
  lcd.begin(16, 2); // Specify the number of columns and rows
  lcd.backlight();
  
  // Initialize the serial communication for debugging
  Serial.begin(9600);
  
  // Initialize the SIM800L
  sim800l.begin(9600);
  
  // Set the buzzer pin as output
  pinMode(buzzerPin, OUTPUT);
  
  // Print a message to the LCD
  lcd.setCursor(0, 0);
  lcd.print("Gas Sensor Init");
  delay(2000);
  lcd.clear();
}

void loop() {
  // Read the gas sensor value
  int gasValue = analogRead(gasSensorPin);
  
  // Print the gas value to the LCD
  lcd.setCursor(0, 0);
  lcd.print("Gas Value: ");
  lcd.print(gasValue);
  
  // Print the gas value to the serial monitor
  Serial.print("Gas Value: ");
  Serial.println(gasValue);
  
  // Check if the gas value exceeds the threshold
  if (gasValue > 300) { // Adjust the threshold as needed
    // Sound the buzzer
    digitalWrite(buzzerPin, HIGH);
    
    // Send an alert message using SIM800L
    sendAlertMessage(gasValue);
  } else {
    digitalWrite(buzzerPin, LOW);
  }
  
  // Wait for a second before the next reading
  delay(1000);
}

void sendAlertMessage(int gasValue) {
  // Send SMS alert
  sim800l.println("AT+CMGF=1"); // Set SMS mode to text
  delay(1000);
  sim800l.println("AT+CMGS=\"+1234567890\""); // Replace with the recipient's phone number
  delay(1000);
  sim800l.print("Gas Alert! Value: ");
  sim800l.print(gasValue);
  delay(1000);
  sim800l.write(26); // ASCII code for CTRL+Z to send the message
  delay(1000);
}

This code initializes the LCD and SIM800L modules, reads the gas sensor value, displays it on the LCD, and sends an alert message if the gas value exceeds a specified threshold. The buzzer is also activated when the threshold is exceeded.