How to Implement Wi-Fi MQTT Logging in Zephyr on nRF52840 with JSON Payload

Implementing Wi-Fi-based MQTT Logging in Zephyr using the nRF52840 with a JSON Payload Format

This tutorial will guide you through the process of implementing Wi-Fi-based MQTT logging in the Zephyr RTOS using the nRF52840 development board. We will focus on sending data in a JSON format, which is popular for its lightweight structure and ease of use. By the end of this tutorial, you will have a working example of an MQTT logger that can send JSON payloads over Wi-Fi.

Prerequisites

• Basic understanding of C programming and embedded systems.
• Familiarity with Zephyr RTOS.
• nRF52840 development board.
• Wi-Fi network credentials.
• MQTT broker (e.g., Mosquitto) set up and running.
• Development environment for Zephyr (e.g., VS Code or command line with Zephyr SDK).

Parts/Tools

• nRF52840 Development Board
• USB cable for programming
• Computer with Zephyr SDK installed
• MQTT broker (e.g., Mosquitto)

Steps

1. Set Up Your Development Environment
   • Install the Zephyr SDK and ensure that the toolchain is configured correctly.
   • Clone the Zephyr repository:

     git clone https://github.com/zephyrproject-rtos/zephyr.git

   • Navigate to the Zephyr directory:

     cd zephyr

2. Configure the nRF52840 Board
   • Set up your board configuration by creating a new application directory:

     mkdir my_mqtt_app && cd my_mqtt_app

   • Create a new `prj.conf` file and add the following configurations:

     CONFIG_MQTT_LIB=y
     CONFIG_WIFI_NRF7002=y
     CONFIG_NET_MQTT_CLEAN_SESSION=y
     CONFIG_NET_DEBUG_MQTT=y
     CONFIG_JSON=y

3. Implement the Application Code
   • Create a `src/main.c` file and include necessary headers:

     #include 
     #include 
     #include 
     #include 
     #include 

   • Define the MQTT client and connection parameters:

     static struct mqtt_client client;
     static struct sockaddr_storage broker; // Fill with your broker details

   • Implement the JSON payload creation function:

     char* create_json_payload() {
         cJSON *root = cJSON_CreateObject();
         cJSON_AddStringToObject(root, "sensor", "temperature");
         cJSON_AddNumberToObject(root, "value", 23.5);
         char *json_string = cJSON_Print(root);
         cJSON_Delete(root);
         return json_string;
     }

   • Set up the MQTT connection and publish the JSON data:

     void publish_data() {
         char *json_payload = create_json_payload();
         mqtt_publish(&client, "sensors/data", json_payload, strlen(json_payload), 0);
         free(json_payload);
     }

4. Build and Flash the Application
   • Use the following commands to build your application:

     west build -b nrf52840dk_nrf52840

   • Flash the application to your nRF52840 board:

     west flash

Troubleshooting

• If you encounter issues connecting to the MQTT broker, check your Wi-Fi credentials and ensure the broker is running.
• For JSON parsing errors, validate your JSON structure using tools like JSONLint.
• Check the Zephyr logs for any error messages by enabling logging in your `prj.conf`:

  CONFIG_LOG=y
  CONFIG_LOG_DEFAULT_LEVEL=3

Conclusion

In this tutorial, you have successfully implemented Wi-Fi-based MQTT logging in Zephyr using the nRF52840. You learned how to create a JSON payload and send it to an MQTT broker. This setup can be expanded for various applications, such as IoT devices that require remote monitoring and data logging.