Device development based on MQTT protocol

2025-04-10

Modify configuration file

Configuration file path: code/dtu_config.json。

Based on TCP private server data transparent transmission, configure as follows:

set systemconfig.cloud configuration item as mqtt, which means MQTT transparent mode.
```
{
    "system_config": {
        "cloud": "mqtt"
    }
}
```

This experiment adopts the MQTT transparent transmission mode, and users need to set the MQTT server domain name, port, client ID, and subscription and publishing topics parameters in the mqtt_pivate_cloud_config configuration item according to the actual situation, as follows.

{
    "mqtt_private_cloud_config": {
        "server": "mq.tongxinmao.com",
        "port": 18830,
        "client_id": "txm_1682300809",
        "user": "",
        "password": "",
        "clean_session": true,
        "qos": 0,
        "keepalive": 60,
        "subscribe": {"down": "/public/TEST/down"},
        "publish": {"up":  "/public/TEST/up"}
    }
}

The configuration item uart_config is a serial port configuration parameter, which defaults to the configuration made based on the current experimental development board and cannot be changed. If users use other development boards, they need to configure according to the actual hardware.

{
    "uart_config": {
        "port": 2,
        "baudrate": 115200,
        "bytesize": 8,
        "parity": 0,
        "stopbits": 1,
        "flowctl": 0,
        "rs485_config": {
        	"gpio_num": 28,
            "direction": 0
        }
    }
}

The complete configuration file template is as follows:

{
    "system_config": {
        "cloud": "tcp"
    },
    "mqtt_private_cloud_config": {
        "server": "mq.tongxinmao.com",
        "port": 18830,
        "client_id": "txm_1682300809",
        "user": "",
        "password": "",
        "clean_session": true,
        "qos": 0,
        "keepalive": 60,
        "subscribe": {"down": "/public/TEST/down"},
        "publish": {"up":  "/public/TEST/up"}
    },
    "socket_private_cloud_config": {
        "domain": "112.31.84.164",
        "port": 8305,
        "timeout": 5,
        "keep_alive": 5
    },
    "uart_config": {
        "port": 2,
        "baudrate": 115200,
        "bytesize": 8,
        "parity": 0,
        "stopbits": 1,
        "flowctl": 0,
        "rs485_config": {
        	"gpio_num": 28,
            "direction": 0
        }
    }
}

Parameter description:

systemconfig. config: Specify the type of private cloud currently in use. Currently supports TCP and MQTT.
mqtt_private_cloud_config: MQTT private cloud configuration.
socket_private_cloud_config: TCP private cloud configuration.
uart_config: Serial port parameter configuration.

Script import and run

After downloading and installing the QPYCom tool, use the tool to download the script to the QuecPython module.

💡 Tips

QPYCom Installation and usage tutorial: https://python.quectel.com/doc/Application_guide/en/dev-tools/QPYcom/index.html

Debugging

View REPL interaction port logs

After the program runs, the log output can be seen on the REPL interaction page as shown in the following figure. There are two threads in the DTU service that process data: one is used to detect and read serial port data and forward it to the cloud, and the other is used to detect the transmission of downstream data from the cloud to the serial port, as shown in the following figure.