A privacy preserving battery-powered lost-device tracker.

YouLostIt is a privacy-enabled lost-item tracker designed to help users locate misplaced belongings. The device attaches to an item (e.g., a backpack) and uses an accelerometer to detect when it has remained stationary for an extended period, signaling that it is lost. It provides:

• Visual identification via an LED indicator when in lost mode.
• Wireless alerts using Bluetooth Low Energy (BLE) to notify nearby smartphones.
• Low-power operation to maximize battery life.

• Movement Detection: Check the device movement every 10 seconds using an LSM6DSL accelerometer via I2C.
• Lost Mode Activation: If stationary for over 1 minute, the device enters lost mode and activates visual and radio notifications.
• LED Indicator: Lights up when in lost mode, providing a visual cue.
• BLE Notifications: Sends messages to nearby smartphones when lost and disconnects when found.
• Low Power Design: Utilizes STM32 Stop 2 mode to preserve energy, ensuring long battery life.

• IDE: STM32CubeIDE
• Microcontroller: STMicroelectronics B-L475E-IOT01A1 Development Board
  
• Peripherals:
  • GPIO: LED control
  • Timer & LPTIM: Accurate timing for lost mode detection
  • I2C: Communication with accelerometer(LSM6DSL)
  • SPI: Bluetooth module (BlueNRG-MS)
  • UART: Debugging
• Low-Power Techniques: Stop 2 mode, interrupt-based wake-ups

1. Normal Mode: The tracker monitors movement periodically.
2. Lost Mode Activation: If no movement is detected for 1 minute, the LED turns on, and BLE advertisements begin.
3. Notification to Nearby Phones: Nearby smartphones receive alerts via BLE.
4. Recovery: When motion is detected again, the device exits lost mode, turning off the LED and stopping BLE notifications.

• Firmware Development: Implemented low-level firmware drivers in C for STM32, including memory-mapped I/O for GPIO, Timers, I2C.
• Interrupt Handling: Implemented efficient interrupt-based event handling for movement detection and timing control.
• Sensor Integration: Wrote drivers for the LSM6DSL accelerometer to detect motion using I2C.
• BLE Communication: Added BLE communication with the BlueNRG-MS module, enabling notifications to nearby smartphones.
• Low-Power Optimization: Designed the system to stay in Stop 2 mode in most of the time, minimizing energy consumption while ensuring responsiveness.

• Embedded Firmware Development: Gained hands-on experience with low-level C firmware programming for microcontrollers.
• Using Datasheets for Hardware Integration: Learned how to implement device drivers by reading the datasheet specifications and setting register configurations.
• Peripheral Communication: Learned how to interface with hardware components using I2C, SPI, and GPIO.
• Real-Time Event Handling: Explored how to use interrupts and timers for precise control over device behavior.
• Low-Power Design Strategies: Understood how to leverage STM32 low-power modes to extend battery life.
• Debugging Embedded Systems: Improved skills in debugging embedded firmware using UART logging and logic analyzer(for I2C bus).

Here are the design notes for documenting how I built the YouLostIt project.

• GPIO and Timer Driver
• I2C and LSM6DSL Driver
• BLE Integration
• Low Power Design

• Code Sample is not available due to copyright.