How to Implement Wi-Fi Remote Logging with Zephyr RTOS and MQTT over TLS

Introduction

Implementing Wi-Fi-based remote logging with Zephyr RTOS using MQTT over TLS is a powerful way to transmit sensor data securely. This tutorial will guide you through the steps to set up your environment, configure MQTT over TLS, and send sensor data remotely.

Prerequisites

• Basic knowledge of embedded programming and C language
• Familiarity with Zephyr RTOS
• MQTT protocol understanding
• A compatible Wi-Fi module (e.g., ESP32)
• MQTT broker (e.g., Eclipse Mosquitto) configured for TLS
• Development environment set up with Zephyr SDK

Parts/Tools

• Development board (e.g., ESP32)
• Computer with Zephyr SDK installed
• MQTT broker with TLS capability
• Wi-Fi access point
• Sensor (e.g., temperature sensor)

Steps

1. Set Up the Development Environment
   1. Install Zephyr SDK from the official Zephyr website.
   2. Clone the Zephyr repository:

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

   3. Set up your environment variables:

   export ZEPHYR_BASE=/path/to/zephyr

2. Create a New Zephyr Application
   1. Navigate to your Zephyr workspace:

   cd ~/zephyrproject/zephyr/samples

   2. Create a new directory for your application:

   mkdir mqtt_tls_logging

   3. Copy an existing sample as a starting point:

   cp -r mqtt_publisher mqtt_tls_logging/

3. Configure MQTT over TLS
   1. Edit the prj.conf file to add necessary configurations:

   CONFIG_MQTT_LIB=y
   CONFIG_MQTT_LIB_TLS=y
   CONFIG_NETWORKING=y
   CONFIG_WIFI=y

   2. Include certificate files for TLS in your project.
4. Implement Sensor Data Reading
   1. Include necessary headers in your source file:

   #include 
   #include 

   2. Initialize your sensor (example for a temperature sensor):

   struct device *sensor_dev = device_get_binding("TEMP_SENSOR");
   if (!sensor_dev) {
       printk("Sensor not foundn");
   }

5. Setup MQTT Client
   1. Initialize the MQTT client:

   struct mqtt_client client;
   mqtt_client_init(&client);

   2. Set client configurations including broker address and port:

   client.broker = "mqtt.example.com";
   client.port = 8883;

6. Implement Data Transmission
   1. Create a function to publish sensor data:

   void publish_sensor_data(float temperature) {
       // Prepare payload
       char payload[50];
       snprintf(payload, sizeof(payload), "{"temperature": %.2f}", temperature);
       mqtt_publish(&client, "sensor/data", payload, strlen(payload), MQTT_QOS_1);
   }

   2. Call this function after reading the sensor data:

   float temperature;
   sensor_sample_fetch(sensor_dev);
   sensor_channel_get(sensor_dev, SENSOR_CHAN_TEMP, &temperature);
   publish_sensor_data(temperature);

Troubleshooting

• MQTT Connection Issues: Ensure your broker is running and accessible. Check firewall settings.
• TLS Handshake Failures: Verify that the certificates are correctly installed and configured.
• Sensor Not Found: Check the device binding string and ensure the sensor is connected properly.

Conclusion

In this tutorial, you learned how to implement Wi-Fi-based remote logging using Zephyr RTOS and MQTT over TLS. By following these steps, you can securely transmit sensor data to a remote MQTT broker. Experiment with different sensors and data formats to expand your application’s capabilities.