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5.15 comprehensive case 2.0 - gas detection system

2022-05-15 07:47:41Zhiyunfu

brief introduction

Natural gas is the main fuel for household cooking and heating , Its main component is methane (CH4), It also contains a small amount of propane , Ethane 、 Butane and other small amounts of gas . Natural gas itself is colorless and tasteless , Less dense than air . Natural gas leakage is difficult to detect , Its concentration in the air reaches 5%~15% when , It will explode in case of open fire . The popularity of household natural gas , Every year due to improper use 、 Human factors cause gas leakage and explosion accidents one after another .
This case is to teach developers to build a gas leakage detection system step by step against this background .

MQ2 Gas sensors

MQ-2 Gas leakage monitoring devices commonly used in homes and factories , Suitable for liquefied gas 、 benzene 、 Alkane 、 alcohol 、 hydrogen 、 Detection of smoke, etc . So ,MQ-2 To be exact, it is a multi gas detector .

MQ-2 The smoke sensor belongs to tin oxide semiconductor gas sensing material , It belongs to surface ionic formula N Type semiconductor . be in 200~300 Degree Celsius , Tin dioxide adsorbs oxygen in the air , Form negative ion adsorption of oxygen , Reduce the electron density in semiconductors , So as to increase its resistance value . When in contact with smoke , If the potential barrier at the grain boundary changes due to the adjustment of smoke , It will cause the change of surface conductivity . Using this, we can obtain the information of the existence of this kind of smoke , The higher the concentration of smoke , The greater the conductivity , The lower the output resistance , The larger the output analog signal .


  • MQ-2 The sensor is sensitive to natural gas 、 Smoke such as liquefied petroleum gas has high sensitivity , Especially sensitive to alkane smoke , It has good anti-interference , It can accurately eliminate the interference information with irritating non combustible smoke .
  • MQ-2 The sensor has good repeatability and long-term stability . Initial stability , Short response time , Good working performance for a long time . It should be noted that : It must be heated for a period of time before use , Otherwise, the output resistance and voltage are not accurate .
  • The detection range of combustible gas and smoke is 100~10000ppm(ppm Is the volume concentration . 1ppm=1 Cubic centimeter /1 Cubic meters )
  • The circuit design has a wide voltage range ,24V Any of the following , Heating voltage 5±0.2V

Be careful : If the heating voltage is too high , It will cause excessive input current , Fuse the internal signal wire , Thus, the device is scrapped .

Get ready

The hardware required for this case

equipment Number
HaaS506 Development board 1
MQ2 Gas sensors 1
SIM card 1
DuPont line A number of

Hardware connection diagram

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Code flow

1、 Connect to Alibaba cloud platform .
2、 Duplicate read MQ2 Gas voltage sensor , Upload data to Alibaba cloud .
3、 Use Mobile application function , Show weather 、MQ2 Gas sensor voltage change 、 Equipment alarm .

Function realization

1、 Internet of things platform development

Readers who use the Internet of things platform for the first time , You need to use the Internet of things platform function after opening the instance . You can also use free public instances for development , stay Alibaba cloud Internet of things platform in , In the upper left corner, choose ‘ East China 2- Shanghai ’, Click on ‘ Public examples ’, It can be opened .

1、 Platform product creation can refer to haas506 2.0 Development tutorial -aliyunIoT
2、 Create product attributes ( Additive model )

  • Choose products Function definition Edit draft
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  • Add custom features
  • add to identifier And data type ( The identifier should be consistent with the code )
  • Click on Published online
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  • Click ok
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2、 Device side development

  • Readers who use the development board for the first time can follow haas5062.0 Development tutorial - Introduction Build development environment .
  • Copy the following code to Visual Studio Code, Copy the product certificate to the corresponding location of the code .
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# coding=utf-8
from driver import ADC
from driver import GPIO
import network
import ujson
import utime as time
import modem
from  aliyunIoT import Device
import kv

# When iot Triggered when the device is connected to the Internet of things platform 'connect'  event 
def on_connect(data):
    global module_name,default_ver,productKey,deviceName,deviceSecret,on_trigger,on_download,on_verify,on_upgrade
    print('***** connect lp succeed****')
    data_handle = {
    data_handle['device_handle'] = device.getDeviceHandle()

# When the connection is disconnected , Trigger 'disconnect' event 
def on_disconnect():
    print('linkkit is disconnected')

# Upload alarm light status 
warning_data = {
# When iot When setting the cloud distribution properties , Trigger 'props' event 
def on_props(request):
    warn = params["alarmLight"]
    warning_data["alarmLight"]= warn

# When iot Cloud call device service when , Trigger 'service' event 
def on_service(id,request):
    print('clound req id is {} , req is {}'.format(id,request))
# When the device follows iot When an error is encountered during platform communication , Trigger 'error' event 
def on_error(err):
    print('err msg is {} '.format(err))

# Callback function of network connection 
def on_4g_cb(args):
     global g_connect_status
     pdp = args[0]
     netwk_sta = args[1]
     if netwk_sta == 1:
         g_connect_status = True
         g_connect_status = False

# network connections 
def connect_network():
     global net,on_4g_cb,g_connect_status
     #NetWorkClient This class is a singleton class , Realize the functions related to network management , Include initialization , Connected to the Internet , Status information, etc .
     net = network.NetWorkClient()
     g_register_network = False
     if net._stagecode is not None and net._stagecode == 3 and net._subcode == 1:
         g_register_network = True
         g_register_network = False
     if g_register_network:
    # Register the callback function of network connection on(self,id,func); 1 For connection ,func  Callback function  ;return 0  success 
         print(' Network registration failed ')
     while True:
         if g_connect_status:
             print(' Network connection successful ')

# Dynamically register callback functions 
def on_dynreg_cb(data):
     global deviceSecret,device_dyn_resigter_succed
     deviceSecret = data
     device_dyn_resigter_succed = True

 #  Connect to the Internet of things platform 
def dyn_register_device(productKey,productSecret,deviceName):
    global on_dynreg_cb,device,deviceSecret,device_dyn_resigter_succed
    key = '_amp_customer_devicesecret'
    deviceSecretdict = kv.get(key)
    if isinstance(deviceSecretdict,str):    
        deviceSecret = deviceSecretdict 

    if deviceSecretdict is None or deviceSecret is None:
        key_info = {
            'productKey': productKey  ,
            'productSecret': productSecret ,
            'deviceName': deviceName
        #  Dynamically register a device , Acquiring equipment deviceSecret
        # Below if Prevent multiple registrations , If you have registered once , Restart the device and re register will get stuck ,
        if not device_dyn_resigter_succed:

def upload_value(n):
    global value_data
    value_data["gasVoltage"]= n

if __name__ == '__main__':
    g_connect_status = False
    net = None
    device = None
    deviceSecret = None
    deviceName = None
    productKey = "a1JuD7ay6Pj"
    productSecret = "yV68ScGy5DgEczVx"
    device_dyn_resigter_succed = False

    #  Connect to the network 
     #  Acquiring equipment IMEI  As deviceName  Dynamic registration 
    deviceName = modem.getDevImei()
    # Acquiring equipment ICCID
    # Initialize the Internet of things platform Device class , obtain device example 
    device = Device()
    if deviceName is not None and len(deviceName) > 0 :
     # Dynamically register a device 
        print(" Get the device IMEI Failure , Unable to register dynamically ")
    while deviceSecret is None:
    print(' Dynamic registration succeeded :' + deviceSecret)

    key_info = {
        'region' : 'cn-shanghai' ,
        'productKey': productKey ,
        'deviceName': deviceName ,
        'deviceSecret': deviceSecret ,
        'keepaliveSec': 60,
    # Print device information 

    #device.ON_CONNECT  Is the event ,on_connect It's an event handler / Callback function 

    # The main program 
    # Gas sensors 
    value_data = {
    while True:


  • Use 485 Serial port read log, To configure “replPort”: 2, A serial port TTL Read to 0 .
  • board.json
    "version": "2.0.0",
    "io": {
        "ADC0": {
                "type": "ADC",
                "port": 0,
                "sampling": 12000000
        "ADC1": {
                  "type": "ADC",
                  "port": 1,
                  "sampling": 12000000
    "debugLevel": "ERROR",
    "repl": "enable",
    "replPort": 2


  • Debug serial port to use 485 port , Open the device manager to view the debugging port number .
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  • Serial port debugging tool use putty
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Debugging results

1、 Serial debugging tools log, Network connection successful Dynamic registration succeeded Print per second MQ2 Gas voltage sensor
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2、 There is data coming into the cloud , Turn on real-time refresh , The display data will be updated automatically .
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3、 Internet of things application development

The following is the Internet of things application development process , Next, the development of mobile application is introduced according to the following process .
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3.1 newly build ‘ Common projects ’

  • Use alicloud IoTStudio Create project .
  • Create a new blank project in project management
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3.2 Associated products and equipment

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3.3 newly build ‘ Mobile application ’

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Click... In the red box above ‘ Components ’, You can see the list of available components . Please refer to... For the instructions of each component Component description

3.4 Page design

The case uses three components :

  • Real time curve Display sensor real-time data
  • Indicator light Display alarm status
  • The weather Used to display destination weather

Drag the three components to the middle canvas area
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3.5 Register target objects

The associated data source is divided into the following three steps
Related products
Associated devices
Association attribute
Each component is set separately
1、‘ Indicator light ’ Component settings
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After setting it up , Set alarm
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2、 The same way to set ‘ Real time curve ’.
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3、 Set up ‘ The weather ’ Components , Choose the location you need .

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3.6 Business logic development

The main purpose of business logic is to facilitate users to set the behavior logic of Internet of things devices , Conventional Internet of things systems are fixed line behavior logic at the device end , If the equipment behavior needs to be modified after leaving the factory , You need to do OTA upgrade .
Create a new rule to alarm when the gas exceeds the threshold .
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The system automatically enters the business logic page , Click on the left side of the ‘ node ’, On the right is the introduction of business logic .
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1、 Select the target node
This logic needs to judge the gas voltage value uploaded by the equipment , When the voltage value exceeds the threshold, the alarm is turned on , Otherwise, turn off the alarm . Four nodes are required :

  • Device trigger node
  • Condition judgment node
  • Turn on the alarm lamp node
  • Turn off the alarm lamp node

Drag out the required nodes from the left .

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2、 Establish the association relationship between nodes , Drag the mouse to connect the nodes
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3、 Business logic editing

  • Device trigger node
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  • Condition judgment node
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    Device node behavior settings
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    Save and deploy business logic
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3.7 Launch preview and launch

After the business logic is set , Can be in “ Gas monitoring and alarm system ” page ‘’ preservation ‘’ And click the ‘ preview ’ To preview .
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Cell phones scan QR codes , You can view the data on your mobile phone .
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copyright notice
author[Zhiyunfu],Please bring the original link to reprint, thank you.

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