Wearable F411RE Locator

This is an embedded C++ project for a wearable locator system based on the STM32F411RE microcontroller. The system uses an IMU (MPU-9250) and RSSI from LoRa modules to estimate the relative position between two devices. It runs on FreeRTOS and includes custom sensor fusion, calibration routines, and LoRa-based distance estimation.

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🛠️ Requirements

To build and run the project, you need the following:

• VS Code with STM32VSCode Extension
• STM32CubeCLT v1.17.0 – for compatibility with STM32 build tools.
• STM32CubeMX – for pin configuration and code generation.
• CMake – as the project build system (minimum 3.22).
• ST-Link driver – for flashing and debugging.
• Serial terminal app (e.g., PuTTY) – to monitor device output via the COM port (USB to UART2 through ST-Link).

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⚙️ How to Build & Run

1. Open the project folder using VS Code.
2. Ensure system paths are configured for CubeCLT and CMake.
3. Go to the Run and Debug tab.
4. Select Build & Debug Microcontroller - ST-Link.
5. Hit Run.

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🧪 Calibration Flow

1. IMU Calibration:

   • Lay the device flat until accelerometer and gyroscope calibration completes.

2. Magnetometer Calibration:

   • Rotate the device in multiple directions until completion.

3. Path Loss Exponent:

   • Choose a path loss exponent based on your environment (e.g., open field, urban).

4. RSSI Calibration:

   • Hold two devices 1 meter apart, facing each other until calibration finishes.

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🔄 FreeRTOS Task Structure

The system uses FreeRTOS for task scheduling. Task creation and flow depend on whether the device is configured as a transmitter or receiver.

📡 Transmit Device Flow

1. rssi_calibration_tx – Performs 1-meter RSSI calibration.
2. After completion, it spawns:
   • quaternion_update – Continuously updates orientation using IMU data.
   • LoRa_task_send – Sends direction and distance via LoRa.
3. rssi_calibration_tx then deletes itself to free resources.

📥 Receive Device Flow

1. rssi_calibration_rx – Performs 1-meter RSSI calibration.
2. After completion, it spawns:
   • quaternion_update – Continuously updates orientation.
   • LoRa_task_receive – Receives data from the transmitting node.
   • display_task – Outputs relative direction and distance to the terminal.
3. rssi_calibration_rx then deletes itself to free resources.

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📁 Project Structure

📂 Core

Main application logic is implemented here, split into headers (Inc/) and implementations (Src/):

Inc/

• compute_direction.h – Header for computing relative direction between two devices using IMU data.
• custom_printf.h – Lightweight formatted print utility for outputting data over UART2 (ST-Link COM port).
• FreeRTOSConfig.h – RTOS configuration file for task scheduling and memory.
• IMU_9250.h – Interface for initializing and reading from the MPU-9250 IMU.
• LoRa.h – LoRa communication interface, includes calibration task logic.
• MadgwickAHRS.h – Madgwick sensor fusion algorithm header.
• main.h – Function declarations and main setup routines.
• quaternion.h – Definitions and examples for quaternion math and operations.
• stm32f4xx_hal_conf.h, stm32f4xx_it.h – STM32 HAL and interrupt configuration.

Src/

• compute_direction.cpp – Contains compute_direction FreeRTOS task that calculates direction and prints it via terminal.
• custom_printf.c – Sends formatted data to the terminal over USB (UART2).
• freertos.c – FreeRTOS initialization and system startup logic.
• IMU_9250.c – Handles reading IMU sensor data (accel, gyro, mag).
• LoRa.cpp – Manages LoRa communication, including distance estimation and calibration for both TX and RX.
• MadgwickAHRS.cpp – Implements sensor fusion filter using Madgwick's algorithm.
• main.cpp – System entry point, initializes peripherals and starts the RTOS scheduler.
• quaternion.cpp – Contains the quaternion_update task for real-time orientation tracking.
• stm32f4xx_hal_*.c, syscalls.c, sysmem.c, system_stm32f4xx.c – HAL interface and system-level configuration for STM32F4.

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📂 Drivers

Includes CMSIS and STM32 HAL drivers for hardware abstraction.

📂 Middlewares

Contains FreeRTOS kernel source files and configuration for multitasking.

📂 RadioLib

Houses the RadioLib library for LoRa communication, adapted to use STM32 HAL SPI API.

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🔧 Build Files

• CMakeLists.txt – CMake build script.
• startup_stm32f411xe.s – Assembly-level boot code for the MCU.
• STM32F411RETx_FLASH.ld – Linker script defining memory layout.
• .mxproject, .project – STM32CubeMX project metadata.
• compile_commands.json, CMakePresets.json – Settings for code analysis and CMake build presets.

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📌 Notes

• Ensure CubeCLT v1.17.0 is used to avoid version mismatches.
• Use PuTTY or a similar tool to monitor output via ST-Link COM port.
• During RSSI calibration, maintain stable device orientation for accurate results.

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