How to Connect with MQTT Broker and Subscribe to Any MQTT Topics and Receive Updates via A9G Board using AT Commands over Cellular Internet

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A9G

Setting up A9G Board for MQTT Communication

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Configuring A9G Board for MQTT Subscription

1. Activating GPRS

GPRS (General Packet Radio Service) activation is essential for establishing cellular communication. Use the AT+CGATT=1 command to activate GPRS and enable data transmission over the cellular network.

AT+CGATT=1

2. Configuring Access Point Name (APN)

Configure the Access Point Name (APN) settings using the AT+CGDCONT command. APN settings provide the necessary connection parameters for accessing the internet via the cellular network.

AT+CGDCONT=1,"IP","CMNET"

3. Activating PDP Context

Activate the Packet Data Protocol (PDP) context using the AT+CGACT command. PDP context activation establishes a data connection, enabling internet access for the A9G board.

AT+CGACT=1,1

4. Connecting to MQTT Broker

Establish a connection to the MQTT broker using the AT+MQTTCONN command. Provide the broker address, port, client ID, and authentication credentials to establish the MQTT connection.

AT+MQTTCONN="0.tcp.in.ngrok.io",14722,12345,120,0,"",""
AT+MQTTCONN="<Host>",<Port>,<ClientID>,<KeepAlive>,<CleanSession>,"<Username>","<Password>"

Here's a breakdown of the AT+MQTTCONN command parameters:

  • <Host>: MQTT broker hostname or IP address.
  • <Port>: Port number on which the MQTT broker is listening.
  • <ClientID>: Unique client identifier for the A9G board.
  • <KeepAlive>: Keep-alive interval for the MQTT connection.
  • <CleanSession>: Indicates whether the broker should clean session state.
  • <Username> and <Password>: Optional authentication credentials.

Subscribing to MQTT Topics

  1. Subscribe Command: Use the AT+MQTTSUB command to subscribe to MQTT topics. Specify the topic to subscribe to, along with the desired Quality of Service (QoS) level. 
    AT+MQTTSUB="Test",1,0
    AT+MQTTSUB=<topic>,<QoS>,<Retain>
    • <topic>: MQTT topic to subscribe to.
    • <QoS>: Quality of Service level for message delivery.
  1. Receiving Messages: Upon successful subscription, the A9G board will start receiving messages published to the subscribed topics from the MQTT broker.
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Conclusion

By following these steps, you can configure the A9G board to subscribe to MQTT topics and receive messages over a cellular connection. MQTT subscription capabilities enable the A9G board to interact with IoT applications and receive real-time updates from MQTT-enabled devices and systems.

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