How to Implement a Zephyr Wi-Fi Logging System with MQTT for DHT22 Data

Introduction

In this tutorial, we will implement a Zephyr-based Wi-Fi logging system that utilizes MQTT to transmit temperature data collected from a DHT22 sensor. This project is ideal for anyone looking to monitor temperature remotely and is a great introduction to IoT (Internet of Things) applications using the Zephyr RTOS.

Prerequisites

• Basic knowledge of C programming
• Familiarity with Zephyr RTOS
• Access to a DHT22 temperature sensor
• A compatible development board (e.g., ESP32)
• MQTT broker (e.g., Mosquitto) set up on your local network
• Development tools installed (Zephyr SDK, CMake, etc.)

Parts/Tools

• DHT22 Temperature Sensor
• ESP32 Development Board
• Jumper wires
• Computer with Zephyr SDK installed
• MQTT Broker (e.g., Mosquitto)

Steps

1. Set Up the Hardware
   1. Connect the DHT22 sensor to the ESP32 as follows:
   • VCC to 3.3V
   • GND to Ground
   • DATA to a GPIO pin (e.g., GPIO 23)
   2. Ensure the ESP32 is powered and connected to your computer.
2. Configure the Zephyr Project
   1. Create a new Zephyr project directory:

   mkdir zephyr_wifi_logging
   cd zephyr_wifi_logging
   west init
   west update

   2. Create a new application folder:

   mkdir -p app/src
   cd app/src

   3. Set up the CMakeLists.txt file:

   cmake_minimum_required(VERSION 3.13.1)
   include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
   project(zephyr_wifi_logging)
   target_sources(app PRIVATE main.c)

3. Write the Main Application Code
   1. Create the main.c file and include necessary headers:

   #include 
   #include 
   #include 
   #include 
   #include 
   #include 
   // Other necessary includes

   2. Initialize the DHT22 sensor and MQTT client:

   void main(void) {
       const struct device *sensor = device_get_binding("DHT22");
       // Initialize MQTT client and connection parameters
   }

   3. Implement the temperature reading function:

   float read_temperature(const struct device *sensor) {
       struct sensor_value temp;
       sensor_sample_fetch(sensor);
       sensor_channel_get(sensor, SENSOR_CHAN_AMBIENT_TEMP, &temp);
       return sensor_value_to_float(&temp);
   }

   4. Publish the temperature data to the MQTT broker:

   void publish_temperature(float temperature) {
       // MQTT publish logic
       mqtt_publish(&mqtt_client, "temperature/topic", temperature);
   }

4. Configure Network Settings
   1. Set up the Wi-Fi settings in your project configuration:

   CONFIG_WIFI=y
   CONFIG_WIFI_SSID="Your_SSID"
   CONFIG_WIFI_PASSWORD="Your_Password"

   2. Ensure the MQTT broker settings are correctly set in your code.
5. Build and Flash the Application
   1. Build the application:

   west build -b esp32 app

   2. Flash the application to the ESP32:

   west flash

Troubleshooting

• If the sensor readings are incorrect, check the wiring and ensure the DHT22 is functioning properly.
• For MQTT connection issues, verify the broker is running and accessible from the ESP32.
• Check the console output for any error messages during the build or runtime to identify specific issues.

Conclusion

In this tutorial, we successfully implemented a Zephyr-based Wi-Fi logging system that collects temperature data from a DHT22 sensor and transmits it to an MQTT broker. This basic IoT setup can be expanded with additional sensors or functionalities for more complex applications. Happy coding!