How to use 4G module to transmit temperature and humidity data to onenet via MQTT protocol

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This experiment uses the SIM7600CE 4G cat4 module, which supports GNSS positioning. Other 4G modules can also be used as long as they support TCP transmission. The AT commands supported by this module are quite powerful, including TCP&UDP command set, HTTP command set, and MQTT command set.

Although this module already supports the MQTT function, in actual R&D projects, in order to maintain the portability and compatibility of the project, we usually do not use the MQTT command set that comes with the module. Instead, we use code to implement the MQTT upper-layer functions and then call the module's TCP AT command set at the bottom layer.

1. Introduction to MQTT

MQTT is a client-server based message publishing/subscription transmission protocol. It is a protocol for the Internet of Things released by IBM in 1999. The MQTT protocol is lightweight, simple, open and easy to implement, which makes it widely applicable.

It is widely used in many situations, including constrained environments such as machine-to-machine (M2M) communications and the Internet of Things (IoT). It is widely used in sensors communicating via satellite links, medical devices that occasionally dial up, smart homes, and some miniaturized devices.

The design concept of MQTT is open, simple, lightweight and easy to implement. These features make it suitable for restricted environments.

For example, but not limited to: Networks are expensive, with low bandwidth and unreliable performance. Running on embedded devices with limited processor and memory resources.

The features of this agreement are:

1. Use the publish/subscribe messaging model to provide one-to-many message publishing and decouple applications;
2. Message transmission with shielding of payload content;
3. Use TCP/IP to provide network connectivity;
4. There are three message publishing qualities of service:
5. Small transmission, low overhead (fixed-length header is 2 bytes), and minimal protocol exchanges to reduce network traffic;
6. Mechanism for notifying interested parties of client aborts using the Last Will and Testament attributes.

2. ONENET Platform

OneNET is an open IoT platform created by China Mobile. The platform can help developers easily access and connect devices, quickly complete product development and deployment, and provide complete IoT solutions for smart hardware and smart home products.

OneNET has the following functions:

1. Dedicated network and dedicated number: China Mobile has built a specialized network channel based on the characteristics of the Internet of Things, providing an integrated "cloud-pipe-end" intelligent pipeline and support system, and supporting industrial-grade and automotive-grade dedicated network cards and communication modules;
2. Massive connections: Based on multiple types of standard protocols and API development to meet the high-concurrency and fast access of massive devices;
3. Online monitoring: realize monitoring management, online debugging and real-time control functions of terminal equipment;
4. Data storage: Based on distributed cloud storage, message object structure, and rich data call interfaces, high-concurrency data reading and writing operations are realized to effectively ensure data security;
5. Message distribution: All kinds of collected data are quickly notified to the business platform, user mobile phones, and APP clients through message forwarding, SMS push, and APP information push, establishing an effective channel for two-way communication;
6. Capability output: It integrates China Mobile's core capabilities such as short message, location service, video service, and public cloud, provides standard API interfaces, and shortens the development cycle of terminals and applications;
7. Event alert: Create an event trigger engine, and users can quickly implement application logic orchestration based on the engine;
8. Data analysis: Provide unified data management and analysis capabilities based on Hadoop and other platforms.

3. How to access OneNet

To access OneNet,

1. First, you need to register users, create devices, and do a series of preparations on the OneNet platform.
2. Then establish a TCP connection with the OneNet server through the network.
3. Finally, the user data is packaged and uploaded to the OneNet platform according to certain protocols (such as EDP, RestFul API, MQTT), so as to achieve device terminal access. User registration:
4. Before accessing OneNet, you need to register a user account on the platform website, log in to the URL: http://open.iot.10086.cn/, and the following interface will be displayed:

As shown above: Click the upper right corner to register.

After registration is complete, log in as follows:

As shown in the picture above, click on the MQTT IoT Suite:

As shown in the figure above, select Multi-protocol Access:

As shown in the figure above, click Add Product. The onenet platform MQTT protocol framework is divided into product ID and device ID. You can create multiple different products. Each product has different devices, and the devices are distinguished by ID numbers.

Make your selection as shown in the figure above. Next, select Linux as the operating system and China Mobile as the network operator. Because the module uses China Mobile's USIM card, you can choose according to your module card type.

As shown in the figure above, click Add Device:

Click Add Device in the upper right corner.

Click Add.

As shown in the above figure, the screenshot after the product is successfully added shows that it is in offline status. When the 4G module has data to upload, it will be displayed as online.

4. MCU & 4G module communicate with ONENET server

The following explains how to use the microcontroller to drive the 4G module to connect to the ONENET server through the serial port AT command. The microcontroller uses STM32F103RBT6 and the development environment uses MDK5.

As shown in the figure above, 606923821 represents the device ID, and PZqqtD0O=5lNOex4NshJn0RLflY= represents the API KEY

As shown in the picture above, click to view, enter your mobile phone number and send the verification code to get it. 357092 represents the product ID. The product ID in the picture above is 424250. You can fill it out according to your own situation.

CAT11 indicates authentication information, which can be obtained in the device list-device details. 183.230.40.3, 6002 indicates the server and port number of the onenet platform. With this information, you can use the 4G module to communicate with the products you create.

As shown in the figure below: You can observe the online and offline status of the device, as well as the data of the device

5. Data Acquisition and Hardware

1. Reply to mqtt in the background to get the corresponding source code function.

2. The microcontroller STM32F103RBT6 mentioned in the article can be searched on Taobao. The following are recommended:

3. The SIM card used can be a mobile phone card or an IoT card.

4. The modules common to 4g modules can be used.