A compact BLE smart tracker that helps quickly locate misplaced vehicle keys. Includes custom PCB, firmware, enclosure, and Android BLE app. Helps quickly locate misplaced vehicle keys using BLE proximity and buzzer activation.
- Introduction
- Why This Problem Is Important
- System Overview
- Key Features
- Objectives
- Prototype Stages
- Final Design
- Power Management
- BLE Module Decision
- Deliverables
- Changes From Original Plan
- Next Steps
- Tools & Software
- Acknowledgements
This project originated from a real-world workspace problem: misplaced vehicle keys in an automotive workshop causing delays, inefficiency, and security concerns.
It is an IoT-based smart embedded system that allows workshop staff to locate keys using a smartphone app and BLE technology.
Designed and developed the entire system end-to-end, including hardware, firmware, PCB, enclosure, and mobile app.
This project was developed as part of the Design Project (EN5905) under the guidance of Dr. Samiru Gayan at the University of Moratuwa (2025).
- Workshops handle many vehicles → keys often get misplaced.
- Searching for keys wastes valuable technician time.
- Causes operational delays and customer dissatisfaction.
- Commercial trackers (Tile/AirTag) are expensive and not customizable.
This project provides a low-cost, portable, and workshop-friendly solution.
- HM-11 BLE module
- ATmega328P-AU Custom PCB (KiCad-designed PCB fabricated via JLCPCB)
- Buzzer & LED indicators
- LiPo battery (3.7V) + TP4056 charging module
- Custom enclosure
- Custom Mobile app for BLE communication (built using MIT App Inventor)
- 📡 BLE-based smartphone tracking
- 🔔 Tap-to-buzz key locator
- 🧭 Proximity detection (based on RSSI)
- 🔋 Low-power operation with sleep mode for longer battery life
- 🛠️ Fully custom PCB and enclosure
- 🧩 Compact keychain-sized form factor
- 🔒 Secure BLE pairing
- Build a BLE-based smart key tracking system
- Provide real-time proximity detection and alerts
- Design a custom SMD PCB for miniaturization
- Develop a custom mobile app interface
- Improve workshop efficiency by reducing time spent searching for keys
- Improve overall power efficiency
- Arduino Nano (3.3V)
- HM-11 BLE Module
- Buzzer + LED
- LiPo Battery + TP4056
- Firmware tested using existing BLE Scanner App
Achievements:
- Validated BLE connectivity
- Controlled buzzer/LED via smartphone app
- Measured power consumption and battery behavior
- Validated concept before PCB design
- Designed a custom SMD PCB in KiCad
- PCB fabrication done through JLCPCB
- ATmega328P-AU used as the main MCU
- Integrated HM-11, buzzer, LED, charging module pads
- Performed SMD soldering of all components
- Uploading the Code using USB to Serial (UART) TTL converter module and Tested and verified full board functionality
- Custom compact keychain enclosure
- Custom mobile app (MIT App Inventor)
- Low-power firmware with sleep mode and interrupts
Benefits:
- Significantly smaller, keychain-friendly design
- Increased reliability vs Arduino prototype
- Lower power consumption using sleep modes
- Professional and durable build quality
A complete .STL file is attached.
Soldered PCB and Final Assembly
A complete .aia file is attached.
Custom App Working
Bill of Materials (BOM)
A complete demonstration of the prototype, final PCB, enclosure, BLE functionality, and mobile app operation is included in the attached project video.
Initial Power Calculation
LiPo Battery: 3.7V, 320 mAh
Current Draw = 15.7 mA (measured from Multimeter)
Power = V × I Power = 3.7V × 15.7 mA Power = 0.058 W (58 mW)
Battery Life = 320 mAh / 15.7 mA ≈ 20.3 hours
- BLE module and MCU placed in sleep when idle
- Wake on command via BLE
- Efficient SMD layout to reduce losses
- Rechargeable via TP4056 for convenience
Power Calculation After Optimization
LiPo Battery: 3.7V, 320 mAh
Current Draw = 9.8 mA (measured from Multimeter)
Power = V × I Power = 3.7V × 9.8 mA Power = 0.036 W (36 mW)
Battery Life = 320 mAh / 9.8 mA ≈ 32.65 hours
Both regular code and power optimized codes are attached.
❌ Why Wi-Fi Was Not Suitable
- ESP8266 has a High WiFi power consumption
- Not suitable for always-on tracking
- No low-power sleep modes
✔ HM-11 BLE module
- Very low power
- Perfect for periodic wake cycles
- Small footprint → fits custom PCB
- Fully working smart BLE key tracker
- Custom SMD PCB manufactured by JLCPCB (Integrated BLE + buzzer + LED + charging)
- Mobile app for locating keys via BLE
- Reduced time searching for keys → improved efficiency
- Enhanced security for key access
- Custom keychain-friendly enclosure
- ESP8266 (Wi-Fi) → BLE (HM-11)
- Coin cell avoided due to peak current demands
- Finalize keychain enclosure
- Add app features (proximity map, last-seen location)
- Further optimize power consumption
- Arduino IDE (firmware development)
- MIT App Inventor (custom Android BLE app)
- KiCad (circuit schematic & PCB design)
- JLCPCB for PCB fabrication
- BLE Scanner App (initial BLE testing)
- Digital Multimeter
- SMD Rework Station
I would like to extend my sincere thanks to:
- My supervisor Dr. Samiru Gayan for guidance, feedback, and support throughout the project.
- My department team leader for inspiring the original idea based on real workplace challenges.
- My fellow office mate for helping troubleshoot hardware and software issues during development.