MQ-7 Carbon Monoxide Gas Sensor [Arduino Sensors for Everyone]

This chapter explains how to use the MQ-7 sensor. You will learn its features, operating principles, specifications, connection pin arrangement, output values, and connect Arduino and the sensor together to measure the air around you easily using the library.

 

Contents

 

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MQ-7 Carbon Monoxide Gas Sensor

 

 

 

 

 

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Effects on the human body

Carbon monoxide is called the death gas or the silent killer. When carbon monoxide is generated, it is difficult to know at first, and even a small amount of inhalation can lead to fatal consequences. Once inhaled, carbon monoxide binds to hemoglobin instead of oxygen and causes hypoxia. It lowers the blood's oxygen capacity and causes permanent brain damage.

When the carbon monoxide exposure concentration is low, even healthy people complain of fatigue, and heart disease patients experience chest pain. As the exposure concentration increases, symptoms of angina pectoris, impaired vision, decreased brain function, disorientation, headache, dizziness, confusion, nausea, impaired consciousness, and flu symptoms appear.

In particular, people with heart disease can have pain or heart attack in the chest area, which is commonly referred to as carbon monoxide poisoning. Poisoning with high levels of carbon monoxide can lead to loss of consciousness or serious damage to brain tissue and nervous system, leading to death. Chronic growth disorders and chronic respiratory problems (pneumonia, bronchitis, asthma) appear when in an environment that is constantly exposed to carbon monoxide. 

 

 

 

 

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MQ-7 Sensor?

The MQ-7 gas sensor is a gas sensor that detects carbon monoxide (CO). It is inexpensive and suitable for other applications.

 

MQ-7_Hanwei.pdf

0.08MB

  

 

According to the MQ7 sensor data sheet, the structure and configuration of the sensor is a sensor micro aluminum oxide (AL2O3) ceramic tube, a tin oxide (SnO2) fixing layer, and the measuring electrode and the heater are fixed with a plastic and stainless steel mesh cluster.

 

 

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[MQ-7 sensor configuration]

According to the MQ7 sensor data sheet, the structure and configuration of the sensor is a sensor micro aluminum oxide (AL2O3) ceramic tube, a tin oxide (SnO2) fixing layer, and the measuring electrode and the heater are fixed with a plastic and stainless steel mesh cluster.

 

 

 

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[MQ-7 sensor specifications ]
The specifications of the MQ-7 sensor are as follows.

 

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[MQ-7 sensor sensitivity curve ]
The sensitivity curve of the sensor is as follows.

 

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[Typical temperature/humidity characteristics of an MQ-7 sensor ]
  
• Ro: sensor resistance of 100 ppm CO in the air at 33% RH and 20 degrees 
• RS: sensor resistance of 100 ppm CO at various temperatures and humidity

 

 

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[MQ-7 sensor operating principles ]

According to the MQ7 sensor data sheet, the surface resistance of the sensor Rs is obtained through the effective voltage signal output of the load resistance RL, and the series resistance is as follows.

 

 

• Vc: Loop voltage, always supplied voltage, DC 10V or less 
• VH: Heater voltage, DC 5.0V (60 seconds) and 1.4V (90 seconds) alternately supplied 
• VRL: Displayed as a voltage value according to the sensor amount 

  
The MQ7 sensor operates by alternating the two power sources VH 5.0V and 1.4V for 60 seconds and 90 seconds. When the power is first on for 60 seconds, error data is generated due to the nature of the carbon monoxide sensor, so accurate information can be read only after 60 seconds have elapsed.

 

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[Sensitvity Adjustment ]

The resistance values of the MQ7 are different for different types and concentrations of gases. Therefore, sensitivity adjustment is very necessary when using this component. It is advisable to calibrate the detector for 200 ppm CO in air and use a RL (load resistance) value of about 10 KΩ (5 KΩ to 47 KΩ). When making an accurate measurement, after considering the temperature and humidity effects, an appropriate alarm point for a critical concentration should be determined. 
 
Sensitivity adjustment program:
-Connect the sensor to the application circuit
-Turn on the power and preheat for 48 hours
-Adjust the load resistance RL until you get a signal value that responds to the specific carbon monoxide concentration at the end of 90 seconds. 
-At the end of 60 seconds, adjust the other load resistance RL until a signal value responsive to the CO concentration is obtained.

 

 

 

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Purchasing the MQ-7 sensor

As follows, the [MQ-7] sensor used in the book [Arduino Sensors for Everyone] can be purchased at Ali Express, Amazon.  

 

 

 

 

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Software Coding

Run the example file in Steamedu123_Sensor-master > examples.

/*
   @402 MQ-7   Carbon monoxide gas sensor
*/

#include <C402_Steam_Air_MQ7_CO.h>    // Internal library header file
#define AoutPIN A1

SteamMQ7 mq7(AoutPIN);  // Instance, pin number

void setup() {
  Serial.begin(9600);   // Start serial communication at a speed of 9600bps.
  mq7.begin();          // (1) Initialize the sensor.
}

void loop() {
  mq7.read();           // (2) Measure the value of the sensor.
  mq7.display();        // (3) Output the sensor value.
  delay(1000);          // Wait for 1 second.
}

 

 

 

 

 

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MQ-7 Arduino sensor operation check

When the hardware connection and software coding are completed, you can check the operation screen as follows.

 

------------------------------------------------------ 
Development environment: WINDOWS 10
Arduino IDE: 1.8.13
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01 library copy

You can easily check the operation by using the  library.  
The libraries \Steamedu123_Sensor-master folder is copied to the folder below.
* This folder is created automatically after installing Arduino C:\Users\s\Documents\Arduino\libraries

02 *. ino file execution
-Connect Arduino and PC
-Run Arduino IDE
-Menu → Tools → Board: Check Arduino UNO
-Menu → Sketch → Check/Compile

03 Check compilation

Select Sketch>OK/Compile (CTRL+R) to compile.

04 Arduino Uno upload

When the compilation is completed without any problems, select Sketch>Upload (CTRL+U) to upload the compiled file.

05 Operation check

You can check the operation as follows.
 

 

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Wrap-up

You can connect Arduino and [MQ-7] sensor and practice the sensor easily with simple coding.

 

In this section, the effect of carbon monoxide on the human body, the reference concentration, the measurement range of the simple measuring instruments, and the sensors used in simple measuring instruments were investigated. We also measured carbon monoxide concentration using the MQ7 sensor and Arduino. 
 
The MQ-7 sensor can be used not only outdoors, but also indoors.If your carbon monoxide level is high, you need to ventilate frequently to bring in fresh air.

 

 

 

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References

References for [MQ-7 carbon monoxide (CO2) Arduino sensor] used in the book [Arduino Sensors for Everyone] are as follows. 

 

[12] Air Korea real-time atmosphere information, 
[13] Air Korea Air Quality Standard (domestic), 
[14] Air Korea Air Quality Standard (Overseas), 
[15] Winsen ZE07-CO Datasheet, 
[16] 3SP_CO_1000 Package 110-109 Datasheet, 
[17] AliExpress MQ-7, 
[18] AliExpress ZE07, https://aliexpi.com/EYBC
[19] Spec Sensors CO, https://bit.ly/35R3Cgt
[20] A Study on the Installation of Carbon Monoxide Concentration Sensor in Buildings (Korea Gas Safety Corporation, 2007)
[21] MQ-7_Hanwei Datasheet, "SPECIFICATIONS Standard work condition", p1
[22] MQ-7_Hanwei Datasheet, "Sensitivity characteristic curve", p2

 

 

 

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Purchasing a book

[Arduino Sensors for Everyone] The book is available for purchase on Google Book and Apple Books.

In this book, you will learn how to use the PMS7003, GP2Y1010AU0F, PPD42NS, SDS011 Fine Dust Sensor, DHT22 temperature/humidity sensor, MH-Z19B carbon dioxide sensor, ZE08-CH2O formaldehyde sensor, CCS811 total volatile organic compound (TVOC) sensor , GDK101 radiation (gamma ray) sensor, MQ-131 ozone (O3) sensor, MQ-7 carbon monoxide sensor, MICS-4514 nitrogen dioxide sensor, MICS-6814 ammonia sensor, DGS-SO2 sulfur dioxide (SO2) sensor, BME280 atmospheric pressure sensor, GUVA-S12SD ultraviolet (UV) sensor, MD0550 airflow sensor, and QS-FS01 wind speed sensor.

 

[Google play book]

Arduino Sensors for Everyone, 저자: Ronnie Kim - Google Play 도서