Low-power bicycle GPS tracker with BLE sync. Records GPS coordinates during rides and syncs to a phone app via Bluetooth Low Energy. No cellular, no SIM card, no third-party cloud — fully open source.
- Attach the tracker to your bicycle
- Start riding — the tracker detects motion and begins logging GPS every 5 seconds
- Stop riding — after 30 seconds of no motion, tracking stops
- Your phone app auto-syncs the ride data via BLE
- The tracker goes to deep sleep until the next ride
- Automatic motion detection (wake on movement, sleep when idle)
- GPS logging at 5-second intervals
- BLE sync to phone (auto-sync or manual)
- AES-128 encrypted data — only your paired phone can read it
- Flash storage — ride data survives reboots and battery swaps
- Factory reset via BOOT button (5 second hold)
- Deep sleep with 30-second periodic wake for motion check
| Component | Description | Est. price |
|---|---|---|
| ESP32-C3 dev board | Microcontroller with BLE (e.g. XIAO ESP32-C3, Super Mini) | ~€2-5 |
| ATGM336H GPS module | UART GPS with ceramic antenna included | ~€3-9 |
| ADXL345 accelerometer | I2C motion detection for wake/sleep | ~€2-4 |
| 3x AA battery holder | Power supply (4.5V via onboard regulator) | ~€0.50-1 |
| Total | ~€8-19 |
Optional: TP4056 USB-C charger module + Li-Po battery instead of AA.
See docs/bom.md for detailed bill of materials.
| Module | Pin | XIAO ESP32-C3 |
|---|---|---|
| ATGM336H | TX | D7 (GPIO20/RX) |
| ATGM336H | RX | D6 (GPIO21/TX) |
| ATGM336H | VCC | 3V3 |
| ATGM336H | GND | GND |
| ADXL345 | SDA | D4 (GPIO6) |
| ADXL345 | SCL | D5 (GPIO7) |
| ADXL345 | VCC | 3V3 |
| ADXL345 | GND | GND |
| Battery holder | + (red) | 5V |
| Battery holder | - (black) | GND |
See docs/wiring.md for more detail.
- Arduino IDE
- ESP32 board support: add
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.jsonto Board Manager URLs - Board: XIAO_ESP32C3
- Libraries: TinyGPSPlus, Adafruit ADXL345, Adafruit Unified Sensor
- Open
firmware/gps_tracker/gps_tracker.inoin Arduino IDE - Select board and port
- Upload
| Characteristic | UUID | Type | Description |
|---|---|---|---|
| Point | beb5483e-... |
Read | Returns one AES-encrypted GPS point per read, "DONE" when finished |
| Count | 8ca20d91-... |
Read | Number of stored points |
| Clear | 9da30e02-... |
Write | Write any value to clear all points |
| Pair | a1b2c3d4-... |
Write | Write 16-byte key to pair (first time only) |
| Status | b2c3d4e5-... |
Read | "SETUP" or "PAIRED" |
| State | c3d4e5f6-... |
Read | "IDLE" or "TRACKING" |
Service UUID: 4fafc201-1fb5-459e-8fcc-c5c9c331914b
The companion app is part of the Bike Data Project app (.NET MAUI, Android). See the feature/ble-tracker-sync branch.
Estimates with 2500mAh battery, optimized firmware:
| Usage | Battery life |
|---|---|
| 2 x 1-hour rides/day | ~25 days |
| 5 x 10-min rides/day | ~52 days |
Main drain is the GPS module (~25mA active). Deep sleep current is ~5µA.
Hold the BOOT button for 5 seconds. This clears the encryption key and all stored data. The device returns to "Setup" mode for re-pairing.
MIT