MQ-7 Carbon Monoxide Detection Sensor
The gas-sensitive material used in the MQ-7 gas sensor is tin dioxide (SnO2), which has low conductivity in clean air. It adopts a high-low temperature cycle detection method: low temperature (1.5V heating) detects carbon monoxide, and the conductivity of the sensor increases with the increase of carbon monoxide gas concentration in the air; high temperature (5.0V heating) cleans the gas adsorbed at low temperature. A simple circuit can convert the change in conductivity into an output signal corresponding to the gas concentration.
Module Source
Purchase link:
https://detail.tmall.com/item.htm?abbucket=0&id=13673403530&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 carbon monoxide 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 33.3-2. The AO output is the voltage directly output by the MQ-7 sensor, so it is analog; DO is the high/low level output after voltage comparison by LM393, so it is digital. For the specific principle, please refer to section 2.3.3.1 View Materials in the Photoresistor Light Sensor chapter.
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_mq7.c and bsp_mq7.h, and the folder name to MQ7.
Write Code
In the file bsp_mq7.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
* 2024-01-05 LCKFB-lp first version
*/
#include "bsp_mq7.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_MQ7_Init
* Function Description: Initialization
* Function Parameters: None
* Function Return: None
* Author: LC
* Notes: None
******************************************************************/
void ADC_MQ7_Init(void)
{
gpio_config_t flame_config = {
.pin_bit_mask = (1ULL<<MQ7_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_MQ7_Value
* Function Description:
* Function Parameters: CHx which scan data
* Function Return: Corresponding scanned ADC value
* Author: LC
* Notes: None
******************************************************************/
unsigned int Get_Adc_MQ7_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_MQ7_Percentage_value
* Function Description: Read MQ7 value and return percentage
* Function Parameters: None
* Function Return: Returns percentage
* Author: LC
* Notes: None
******************************************************************/
unsigned int Get_MQ7_Percentage_value(void)
{
int adc_max = 4095;
int adc_new = 0;
int Percentage_value = 0;
adc_new = Get_Adc_MQ7_Value(channel);
s
Percentage_value = ((float)adc_new/adc_max) * 100;
return Percentage_value;
}
/******************************************************************
* Function Name: Get_MQ7_DO_value
* Function Description: Get the level status of the MQ5 DO 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_MQ5_DO_value(void)
{
if( gpio_get_level(MQ7_DO_PIN) == 0 )
{
return 0;
}
else
{
return 1;
}
}2
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In the file bsp_mq7.h, write the following code.
#ifndef _BSP_MQ7_H_
#define _BSP_MQ7_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 MQ7_AO_PIN 1
#define MQ7_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_MQ7_Init(void);
unsigned int Get_Adc_MQ7_Value(char CHx);
unsigned int Get_MQ7_Percentage_value(void);
char Get_MQ7_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);
#endif2
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Porting Verification
In the main function of your project, 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
* 2024-01-05 LCKFB-lp first version
*/
#include <stdio.h>
#include "bsp_mq7.h"
void app_main(void)
{
ADC_MQ7_Init();
printf("MQ7 demo start\r\n");
while(1)
{
printf("%d%%\r\n", Get_MQ6_Percentage_value() );
delay_1ms(1000);
}
}2
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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.