SIM820X sends data to Alibaba Cloud IoT Platform via MQTT

MQTT is a message protocol based on the publish/subscribe programming mode of binary messages; due to its simple specification, it is very suitable for IoT scenarios that require low power consumption and limited network bandwidth, such as smart homes, smart cities, and medical care; it is widely used by children’s shoes. Favored and loved. Let’s take SIM820X as an example to implement MQTT communication:

Hardware

• SIM8200EA-M2_5G_HAT
• Raspberry Pi 4 Model

Sofeware

• minicom

sudo apt-get install minicom 

• Alibaba Cloud IoT Platform

Communication steps

1.Hareware connection

• Connect the NB card and antenna to SIM8200EA-M2_5G_HAT
• Connect Raspberry Pi 4 Model and SIM8200EA-M2_5G_HATvia USB cable
  

Configure Alibaba Cloud (it is recommended to change SIM7020 to SIM8200)

• Enter the Alibaba Cloud IoT platform. If you have not purchased the product, you need to purchase the product. The enterprise version is free for the first month.
  

• Create a product
  

• Set DeviceName, check the device after completion, check the DeivceSecret of the device, and change these values to the values for the MQTT code
  
  

• Triple preparation, the following steps are useful to copy and paste directly in the past

{
  "ProductKey": "a1mQpKOF9hp",
  "DeviceName": "7600",
  "DeviceSecret": "8f663b388dee796b931ebcb789b75a39"
}

• To register a topic, click Products–>View 7020_test–>Topic Categories–>Edit Topic Category–>Select Publish and Subscribe
  

• The triplet gets the password through the Password Tool

Analysis of key instructions

• Open mqtt service

at+cmqttstart

• Apply for a client

at+cmqttaccq=0,"7600|securemode=3,signmethod=hmacsha1|"

• Connect to mqtt server

at+cmqttconnect=0,"tcp://a1zjhbLfSbW.iot-as-mqtt.cn-shanghai.aliyuncs.com:1883",60,1,"7600&a1mQpKOF9hp","D48150E8D550607B15C667E100635EE96EA7D512"

• Subscribe

AT+CMQTTSUB=0,27,1,1

• After the prompt > appears, enter:

/a1mQpKOF9hp/7600/user/7600

• Enter the subject of the message to post

AT+CMQTTTOPIC=0,27

• After the prompt > appears, enter:

/a1mQpKOF9hp/7600/user/7600

• Post a message (send a 5-character message to)

AT+CMQTTPAYLOAD=0,5

• After the prompt > appears, enter:

hello

• Complete sending

AT+CMQTTPUB=0,1,60

• Unsubscribe from topic

AT+CMQTTUNSUB=0,28,1

• Disconnect from the server

AT+CMQTTDISC=0,60

• release a client

AT+CMQTTREL=0

• Close the mqtt service

AT+CMQTTSTOP

Sample program

• Key code

#!/usr/bin/python

import serial
import time

ser = serial.Serial("/dev/ttyUSB2",115200)
ser.flushInput()

rec_buff = ''
mg1='/a1mQpKOF9hp/7600/user/7600'
mg2='/a1mQpKOF9hp/7600/user/7600'
mg3='hello'

def send_at(command,back,timeout):
        rec_buff = ''
        ser.write((command+'\r\n').encode())
        time.sleep(timeout)
        if ser.inWaiting():
                time.sleep(0.01 )
                rec_buff = ser.read(ser.inWaiting())
        if back not in rec_buff.decode():
                print(command + ' ERROR')
                print(command + ' back:\t' + rec_buff.decode())
                return 0
        else:
                print(rec_buff.decode())
                return 1
def MQTT():

# connect to Ali cloud
        send_at('at+cmqttstart','OK',1)
        send_at('at+cmqttaccq=0, \"7600|securemode=3,signmethod=hmacsha1| \"', 'OK', 1)
        send_at('at+cmqttconnect=0, \"tcp://a1zjhbLfSbW.iot-as-mqtt.cn-shanghai.aliyuncs.com:1883 \",60,1, \"7600&a1mQpKOF9hp\",\"D48150E8D550607B15C667E100635EE96EA7D5$
        send_at('AT+CMQTTSUB=0,27,1,1','OK',1)
        ser.write(mg1.encode())
        send_at('AT+CMQTTTOPIC=0,27','OK',1)
        ser.write(mg2.encode())
        send_at('AT+CMQTTPAYLOAD=0,5','OK',1)
        ser.write(mg3.encode())
        send_at('AT+CMQTTPUB=0,1,60','OK',1)
        send_at('AT+CMQTTUNSUB=0,28,1','OK',1)
        send_at('AT+CMQTTDISC=0,60','OK',1)
 #Stop MQTT   
        send_at('AT+CMQTTREL=0','OK',1)
        send_at('AT+CMQTTSTOP','OK',1)

try:
#       print('Sending  Message Test:')
        MQTT()

except :
        if ser != None:
                ser.close()

• Operation result