MQ-135 Air Quality Sensor

The gas-sensitive material used in the MQ135 gas sensor is tin dioxide (SnO2), which has low conductivity in clean air. When polluting gas is present in the environment where the sensor is located, the conductivity of the sensor increases with the increase of polluting gas concentration in the air. The MQ135 gas sensor has high sensitivity to ammonia, sulfides, and benzene series vapors, and is also ideal for monitoring smoke and other harmful gases. This sensor can detect a variety of harmful gases and is a low-cost sensor suitable for various applications.

Module Source

Purchase link: https://detail.tmall.com/item.htm?abbucket=0&id=13302081252&ns=1&spm=a21n57.1.0.0.5668523c1NVcMb Materials download link: https://pan.baidu.com/s/1B8WhPIzTmWwQsFFVayRpAA?pwd=9966 Materials extraction code: 9966

Specifications

Operating voltage: 3.3V-5V Operating current: 150MA Output method: DO interface for digital output, AO interface for analog output Read method: ADC Number of pins: 4 Pin (2.54mm pitch header)

View Materials

This product has good sensitivity to ammonia, nitrogen oxides, alcohols, aromatic compounds, sulfides, and smoke over a wide concentration range, and has the advantages of long life, low cost, and simple drive circuit.

Its corresponding schematic diagram is shown in Figure 35.3-1. The AO output is the voltage directly output by the MQ-135 sensor, so it is analog; DO is the high/low level output after voltage comparison by LM393, so it is digital.

Porting Process

Pin Selection

Port to Project

Our goal is to port the example to the ESP32-S3 dev board. Complete driver code has been provided for you. Follow the steps below to complete the porting. For detailed instructions on creating folders and new .c and .h files, refer to section 1.4.2 in the [DHT11 Temperature and Humidity Sensor] chapter; we will not repeat it here. Just note that here we change the file names bsp_dht11.c and bsp_dht11.h to bsp_mq135.c and bsp_mq135.h, and the folder name to MQ135.

Write Code

In the file bsp_mq8.c, write the following code.

/*
 * LCSC-Openkits (LCKFB) software and hardware materials and related expansion board software and hardware materials are all open source on the official website.
 * Dev board official website: www.lckfb.com
 * Technical support resides on the forum; any technical questions are welcome for exchange and learning at any time.
 * LCKFB Forum: club.szlcsc.com
 * Follow our Bilibili account: [LCSC-Openkits (LCKFB)] to keep up with our latest updates!
 * We do not make money by selling boards; we take cultivating engineers as our mission.
 * Change Logs:
 * Date           Author       Notes
 * 2024-01-09     LCKFB-lp    first version
 */

#include "bsp_mq135.h"

esp_adc_cal_characteristics_t *adc_chars;

void delay_ms(unsigned int ms)
{
    vTaskDelay(ms / portTICK_PERIOD_MS);
}
void delay_us(unsigned int us)
{
    ets_delay_us(us);
}
void delay_1ms(unsigned int ms)
{
    vTaskDelay(ms / portTICK_PERIOD_MS);
}
void delay_1us(unsigned int us)
{
    ets_delay_us(us);
}
/******************************************************************
 * Function Name: ADC_Init
 * Function Description: Initialization
 * Function Parameters: None
 * Function Return: None
 * Author: LC
 * Notes: None
******************************************************************/
void ADC_Init(void)
{
    gpio_config_t flame_config = {
        .pin_bit_mask = (1ULL<<MQ135_DO_PIN),    //Configure pin
        .mode =GPIO_MODE_INPUT,
        .pull_up_en = GPIO_PULLUP_DISABLE,        //Disable pull-up
        .pull_down_en = GPIO_PULLDOWN_DISABLE,    //Disable pull-down
        .intr_type = GPIO_INTR_DISABLE            //Disable pin interrupt
    };
    gpio_config(&flame_config);

    adc1_config_width(width);// 12-bit resolution

    //ADC_ATTEN_DB_0: indicates reference voltage is 1.1V
    //ADC_ATTEN_DB_2_5: indicates reference voltage is 1.5V
    //ADC_ATTEN_DB_6: indicates reference voltage is 2.2V
    //ADC_ATTEN_DB_11: indicates reference voltage is 3.3V
    //adc1_config_channel_atten( channel,atten);// Set channel 0 and 3.3V reference voltage

    // Allocate memory
    adc_chars = calloc(1, sizeof(esp_adc_cal_characteristics_t));
    // Initialize ADC characteristics so that it can correctly calculate conversion results and compensation factors
    esp_adc_cal_characterize(unit, atten, width, DEFAULT_VREF, adc_chars);
}


/******************************************************************
 * Function Name: Get_Adc_Value
 * Function Description:
 * Function Parameters: CHx which scan data
 * Function Return: Corresponding scanned ADC value
 * Author: LC
 * Notes: None
******************************************************************/
unsigned int Get_Adc_Value(char CHx)
{
    unsigned char i = 0;
    unsigned int AdcValue = 0;

    /* Because it collects SAMPLES times, loop SAMPLES times */
    for(i=0; i< SAMPLES; i++)
    {
    /*    Accumulate    */
            AdcValue+=adc1_get_raw(CHx);
    }
    /* Calculate average */
    AdcValue=AdcValue / SAMPLES;

    return AdcValue;
}

/******************************************************************
 * Function Name: Get_Percentage_value
 * Function Description: Read value and return percentage
 * Function Parameters: None
 * Function Return: Returns percentage
 * Author: LC
 * Notes: None
******************************************************************/
unsigned int Get_Percentage_value(void)
{
    int adc_max = 4095;
    int adc_new = 0;
    int Percentage_value = 0;

    adc_new = Get_Adc_Value(channel);

    Percentage_value = ((float)adc_new/adc_max) * 100;
    return Percentage_value;
}

/******************************************************************
 * Function Name: Get_DO_value
 * Function Description: Get the level status of the pin
 * Function Parameters: None
 * Function Return: 0=No alcohol value above sensitivity detected 1=Alcohol value above sensitivity detected
 * Author: LC
 * Notes: Adjust the sliding resistor on the module to adjust the sensitivity
******************************************************************/
char Get_DO_value(void)
{
    if( gpio_get_level(MQ135_DO_PIN) == 0 )
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

In the file bsp_mq8.h, write the following code.

#ifndef _BSP_MQ8_H_
#define _BSP_MQ8_H_

#include <stdio.h>
#include <inttypes.h>
#include "sdkconfig.h"
#include "driver/gpio.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_rom_sys.h"
#include "esp_timer.h"
#include "driver/uart.h"
#include "rom/ets_sys.h"
#include "esp_system.h"
#include "driver/gptimer.h"
#include "esp_log.h"
#include "freertos/queue.h"
#include "driver/spi_master.h"
#include "nvs_flash.h"
#include "esp_adc/adc_cali_scheme.h"
#include "esp_adc/adc_cali.h"
#include "driver/adc.h"
#include "esp_adc_cal.h"


#define MQ135_AO_PIN          1
#define MQ135_DO_PIN          2

#define DEFAULT_VREF    1100       //Default reference voltage, unit mV

#define channel         ADC_CHANNEL_0               // ADC measurement channel
#define width           ADC_WIDTH_BIT_12            // ADC resolution
#define atten           ADC_ATTEN_DB_11             // ADC attenuation
#define unit            ADC_UNIT_1                  // ADC1

 //Number of samples
#define SAMPLES         30



void ADC_Init(void);
unsigned int Get_Adc_Value(char CHx);
unsigned int Get_Percentage_value(void);
char Get_DO_value(void);

void delay_us(unsigned int us);
void delay_ms(unsigned int ms);
void delay_1us(unsigned int us);
void delay_1ms(unsigned int ms);

#endif

Porting Verification

In the main.c file, write:

/*
 * LCSC-Openkits (LCKFB) software and hardware materials and related expansion board software and hardware materials are all open source on the official website.
 * Dev board official website: www.lckfb.com
 * Technical support resides on the forum; any technical questions are welcome for exchange and learning at any time.
 * LCKFB Forum: club.szlcsc.com
 * Follow our Bilibili account: [LCSC-Openkits (LCKFB)] to keep up with our latest updates!
 * We do not make money by selling boards; we take cultivating engineers as our mission.
 * Change Logs:
 * Date           Author       Notes
 * 2024-01-09     LCKFB-lp    first version
 */
#include <stdio.h>
#include "bsp_mq135.h"

void app_main(void)
{
    ADC_Init();
    printf("MQ135 demo start\r\n");
    while(1)
    {
        printf("%d%%\r\n", Get_Percentage_value() );
        delay_1ms(1000);
    }
}

Power-on effect:

Driver code:

File Download

📌 Materials Download Center (Click to Jump)

📌 In the Materials Download Center -> Module Porting Materials Download, inside the compressed package of this chapter.