Gas Sensor System Using 8051 Microcontroller

Introduction

Gas sensors are crucial for detecting hazardous gases in the environment and ensuring safety in various settings such as homes, industries, and laboratories. In this project, we will design a gas sensor system using the 8051 microcontroller. The system will use an MQ-2 gas sensor to detect the presence of gases such as LPG, propane, methane, and smoke. When gas is detected, an alarm will be triggered, and the gas concentration will be displayed on an LCD.

Components Required

• 8051 Microcontroller (e.g., AT89S52)

• MQ-2 Gas Sensor

• Buzzer

• 16x2 LCD Display

• ADC0804 (8-bit ADC)

• Resistors (10kΩ, 1kΩ)

• Capacitors (33pF, 100μF)

• Crystal Oscillator (11.0592 MHz)

• Breadboard and Connecting Wires

• Power Supply (5V)

Circuit Diagram

The MQ-2 gas sensor provides an analog output that needs to be converted to a digital signal using an ADC. The 8051 microcontroller reads this digital value to determine the gas concentration. If the concentration exceeds a predefined threshold, a buzzer is activated, and the concentration is displayed on the LCD.

+5V ----- +5V

          |

          |

         MQ-2

         +---+

   +5V --|VCC| 

         |    |

         |OUT |------- Vin+ (ADC0804)

         |    |

   GND --|GND | 

         +---+

ADC0804

Vin+ to MQ-2 output

VCC to +5V

GND to Ground

CS to Ground

RD to P2.0 of 8051

WR to P2.1 of 8051

INTR to P2.2 of 8051

D0-D7 to P1.0-P1.7 of 8051

Vref/2 to 2.5V (using a voltage divider)

Buzzer

Anode to P3.0 of 8051 through 1kΩ resistor

Cathode to Ground

LCD

RS to P3.6 of 8051

RW to Ground

E to P3.7 of 8051

D4-D7 to P2.4-P2.7 of 8051

Pin Connections

• MQ-2 Gas Sensor:

• VCC to +5V

• GND to Ground

• OUT to Vin+ of ADC0804

• ADC0804:

• Vin+ to MQ-2 output

• VCC to +5V

• GND to Ground

• CS to Ground

• RD to P2.0 of 8051

• WR to P2.1 of 8051

• INTR to P2.2 of 8051

• D0-D7 to P1.0-P1.7 of 8051

• Vref/2 to 2.5V (using a voltage divider)

• Buzzer:

• Anode to P3.0 of 8051 through 1kΩ resistor

• Cathode to Ground

• LCD Display:

• RS to P3.6

• RW to Ground

• E to P3.7

• D4-D7 to P2.4-P2.7

Software Implementation

The code is written in C using Keil uVision IDE. It involves initializing the ADC, reading the analog value from the gas sensor, converting it to a digital value using the ADC, and then displaying it on the LCD. If the gas concentration exceeds a threshold, the buzzer is activated.

#include <reg51.h>

#include "lcd.h"

sbit RD = P2^0; // Read signal for ADC

sbit WR = P2^1; // Write signal for ADC

sbit INTR = P2^2; // Interrupt signal from ADC

sbit BUZZER = P3^0; // Buzzer pin

void delay(unsigned int count) {

    int i, j;

    for(i=0; i<count; i++)

        for(j=0; j<1275; j++);

}

void adc_init(void) {

    WR = 0; // Start conversion

    delay(1);

    WR = 1; // End conversion

}

unsigned char adc_read(void) {

    unsigned char value;

    while(INTR); // Wait for conversion to complete

    RD = 0; // Read the value

    value = P1; // Get the digital value

    delay(1);

    RD = 1;

    return value;

}

void main() {

    unsigned char gas_value;

    float gas_concentration;

    unsigned char threshold = 50; // Example threshold value

    lcd_init(); // Initialize LCD

    adc_init(); // Initialize ADC

    BUZZER = 0; // Turn off buzzer initially

    while(1) {

        gas_value = adc_read(); // Read digital value from ADC

        gas_concentration = (gas_value * 5.0 / 255.0) * 100; // Convert to gas concentration

        lcd_cmd(0x80); // Move cursor to first line

        lcd_write_string("Gas: ");

        lcd_cmd(0xC0); // Move cursor to second line

        lcd_write_number(gas_concentration); // Display gas concentration

        if(gas_concentration > threshold) {

            BUZZER = 1; // Turn on buzzer

        } else {

            BUZZER = 0; // Turn off buzzer

        }

        delay(1000); // Update every second

    }

}

Explanation

1. Initialization:

2. LCD Initialization: The lcd_init() function sets up the LCD.

3. ADC Initialization: The adc_init() function prepares the ADC for conversion.

4. Buzzer Initialization: The buzzer is initially turned off.

5. Reading Gas Concentration:

6. The adc_read() function reads the analog voltage from the MQ-2 sensor, converts it to a digital value using the ADC0804, and returns it.

7. Gas Concentration Conversion:

8. The digital value is converted to gas concentration using the formula: gas_concentration = (value 5.0 / 255.0) 100, assuming a 5V reference voltage for the ADC.

9. Displaying Gas Concentration:

10. The gas concentration is displayed on the LCD using lcd_write_string() and lcd_write_number() functions.

11. Buzzer Control:

12. If the gas concentration exceeds the predefined threshold, the buzzer is activated. Otherwise, the buzzer is turned off.

Conclusion

This project demonstrates the use of the 8051 microcontroller to create a gas sensor system. The system is capable of reading gas concentration data from the MQ-2 sensor, converting it to a digital format using the ADC0804, and displaying it on an LCD. Additionally, an alarm is triggered if the gas concentration exceeds a predefined threshold. This project is a great way to learn about sensor interfacing, ADCs, and using microcontrollers for safety and monitoring applications.

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