A high-precision GPS-based lap timer and data logger designed for motorsports and track day enthusiasts. Features 25Hz logging, sector timing, RPM monitoring via tachometer, and multiple customizable display pages.
- 25Hz GPS Logging - High-frequency data capture straight to SD card
- Accelerometer - On-board 6-axis IMU when using Seeed XIAO nRF52840 Sense, +/-16g
- RPM Monitoring - Tachometer input with noise filtering for ignition systems
- "Just Drive" Mode - Automatic track detection, course detection, and lap timing — no manual selection needed
- Sector Timing - Optional 2 and 3-sector support for detailed performance analysis
- Lap Anything - Automatic waypoint-based lap timing when no track files match or no sectors configured
- Lap Timing - Current lap, best lap, last lap, and optimal lap calculation
- Pace Comparison - Real-time pace difference vs. best lap
- Lap History - Session-based lap history (up to 1000 laps)
- Speed Display - Large, easy-to-read speed display
- Sleep Mode - Low-power sleep with display/GPS/IMU off (~2-4 mA), instant wake on button press or engine start
- DOVEX Format - Crash-safe logging with reserved header for instant replay
- Review Data - Instant replay of DOVEX session headers on-device
- Bluetooth Downloads - Can now download files directly to HackTheTrack.net
- Configure settings - none of us want to fill in text with three buttons
- Track Sync - Update on-device track library via the webapp
- Update GPS Tray - Matek now wants $50 per module, when they are $15 from digikey, doesn't require any supporting circuitry
- External Sensors - Add thermocouple sensor / m8 circle connector
- Tachometer - I have a working tachometer... it's not easy to replicate, I need to fix that
- Pin Lock - require pin to pull logs from device
- GPS Statistics (battery, satellites, HDOP, logging status)
- Speed (with current lap number)
- Tachometer (RPM with max RPM tracking)
- Current Lap Time
- Pace Off Best Lap (visual indicators when beating best)
- Best Lap Time
- Optimal Lap (combined best sectors with lap numbers)
- Lap History (paginated list)
- GPS Debug (distance to line, crossing status, etc.)
- Loads track layouts from JSON files on SD card
- Support for forward/reverse direction selection
- Optional sector timing lines (2 and 3 sectors)
- Easy to add new tracks - just add a JSON file
- MCU: Seeed XIAO nRF52840 Sense (64MHz ARM Cortex-M4 with FPU + BLE 5.0 + 6-axis IMU)
- ~120 mA active draw with 2.45" screen, ~2-4 mA sleep
- Built-in battery charging circuit (BQ25101)
- GPS: u-blox SAM-M10Q (Matek SAM-M10Q recommended, found from most RC hobby shops)
- Configured for 25Hz UBX binary (PVT) update rate
- GPS-only constellation for maximum nav rate
- TODO Update GPS tray to use bare $15 GPS module, battery backup is optional
- Display: 2.45" 128x64 OLED (SH110X or SSD1306 compatible)
- I2C interface (address: 0x3C)
- Software sleep/wake via I2C commands (~10uA when off)
- SD Card: Standard SD card module
- FAT16/FAT32 formatted
- 1 MHz SPI for EMI resistance
- Battery: 1500mAh 103050 LiPo
- ~12.5 hours active, ~15-30 days in sleep mode
- Buttons: 3x momentary pushbuttons for navigation
- Left, Select/Enter, Right
- RC low-pass filters recommended (10K + 100nF) for EMI rejection
- Tachometer Circuit: Inductive pickup for RPM sensing
- Input on pin D0
- Noise filtering for ignition systems
- Circuit diagram:
tachometer-circuit.jpg(README coming soon) - diagram is missing required optocoupler and isolated dc-dc power supply
- Active draw: ~120 mA with 2.45" OLED display
- Active battery life: ~12.5 hours continuous on 1500 mAh
- Sleep draw: ~2-4 mA (display, GPS, IMU off)
- Sleep battery life: ~15-30 days on 1500 mAh
- Battery percentage and voltage displayed on stats page and charging screen
The system loads track configurations from JSON files stored on the SD card. Each track file can contain multiple layouts (e.g., "Full Course", "Short Course", "Chicane Bypass").
SDCARD/
└── TRACKS/
├── OKC.json
├── BMP.json
├── PIQUET.json
└── [your-track].json
Two formats are supported. The device auto-detects which format is used.
New format (recommended, can use HackTheTrack.net to update tracks on the device):
{
"longName": "Orlando Kart Center",
"shortName": "OKC",
"defaultCourse": "Normal",
"courses": [
{
"name": "Normal",
"lengthFt": 3383,
"start_a_lat": 28.4127081705638,
"start_a_lng": -81.3797326641803,
"start_b_lat": 28.4127303867932,
"start_b_lng": -81.3795704875378,
"sector_2_a_lat": 28.4119049886871,
"sector_2_a_lng": -81.3790708193926,
"sector_2_b_lat": 28.4118316342961,
"sector_2_b_lng": -81.3791856652217,
"sector_3_a_lat": 28.4115010664104,
"sector_3_a_lng": -81.3799856475317,
"sector_3_b_lat": 28.4115084390461,
"sector_3_b_lng": -81.3798064021136
}
]
}Older format (still parsed, but the device falls back to Lap Anything because there's no lengthFt for course detection to rank by):
[
{
"name": "Full Course",
"start_a_lat": 28.41270817,
"start_a_lng": -81.37973266,
"start_b_lat": 28.41273039,
"start_b_lng": -81.37957049,
"sector_2_a_lat": 28.41190499,
"sector_2_a_lng": -81.37907082,
"sector_2_b_lat": 28.41183163,
"sector_2_b_lng": -81.37918567
}
]New format fields:
longName/shortName: track display namesdefaultCourse: which course to prefer (used by CourseDetector)courses[].lengthFt: track length in feet (enables automatic course detection ranking)
Coordinate Requirements:
- Start/Finish Line:
start_a_lat,start_a_lng,start_b_lat,start_b_lng(required) - Sector 2 Line:
sector_2_a_lat,sector_2_a_lng,sector_2_b_lat,sector_2_b_lng(optional) - Sector 3 Line:
sector_3_a_lat,sector_3_a_lng,sector_3_b_lat,sector_3_b_lng(optional)
Each line is defined by two GPS coordinate points (A and B). The system detects crossing when you pass through the line segment between these points.
Getting Coordinates: Use Google Maps or your preferred mapping tool:
- Right-click on a point → Copy coordinates
- Paste into JSON (format: latitude, longitude)
- Precision: 8 decimal places recommended for racing accuracy
- Create a new
.jsonfile inSDCARD/TRACKS/directory - Use the format shown above
- Filename should be short (max 8 characters for FAT16 compatibility)
- Example:
LAGUNA.json,COTA.json,BRANDS.json
The track will automatically appear in the track selection menu on next boot.
Settings are stored in /SETTINGS.json on the SD card. The file is created automatically on first boot with random default values. Missing keys are auto-populated on boot when firmware is updated.
{
"bluetooth_name": "DovesDataLogger-042",
"bluetooth_pin": "7391",
"driver_name": "Driver",
"lap_detection_distance": "7",
"waypoint_detection_distance": "30",
"waypoint_speed": "30"
}| Setting | Description | Default |
|---|---|---|
bluetooth_name |
BLE device name visible during pairing | Random (e.g. DovesDataLogger-042) |
bluetooth_pin |
PIN displayed on device for webapp pairing | Random 4-digit |
driver_name |
Driver name logged in DOVEX session header | Driver |
lap_detection_distance |
Crossing detection threshold in meters | 7 |
waypoint_detection_distance |
Waypoint proximity zone in meters (Lap Anything) | 30 |
waypoint_speed |
Minimum speed in mph to activate lap timing | 30 |
DOVEX files (.dovex) use a reserved 1 KB header for session metadata, with GPS data streaming after byte 1024. This enables crash-safe logging and instant on-device replay.
Structure:
Bytes 0-1023: Session header (written when session ends)
Line 1: datetime,driver,course,short_name,best_lap_ms,optimal_ms (column labels)
Line 2: 2025-03-11 14:30:00,Driver,Normal,OKC,62345,61890 (session metadata)
Line 3: laps_ms (column label)
Line 4: 65432,63210,62345,64567,... (all lap times in ms)
Remaining: \n padding to byte 1024
Bytes 1024+: GPS data
Header row: timestamp,sats,hdop,lat,lng,speed_mph,altitude_m,heading_deg,h_acc_m,rpm,accel_x,accel_y,accel_z
Data rows: 1741128001234,12,0.8,28.41270817,-81.37973266,87.32,125.45,182.34,1.25,8450,0.123,-0.945,0.032
The 1 KB header fits about 100 lap times at ~8 characters per entry. If the device loses power mid-session the header is left blank but all GPS data after byte 1024 is still valid and recoverable — the metadata write is the LAST thing a clean session does, so file integrity is independent of it.
File naming: 20YYMMDD_HHMM.dovex (e.g. 20240115_1430.dovex)
- timestamp: Unix timestamp in milliseconds (since Jan 1, 1970)
- sats: Number of GPS satellites
- hdop: Horizontal Dilution of Precision (GPS accuracy indicator)
- lat/lng: GPS coordinates (8 decimal places)
- speed_mph: Speed in miles per hour (2 decimal places)
- altitude_m: Altitude in meters (2 decimal places)
- heading_deg: Heading of motion in degrees (0-360, 2 decimal places, from UBX headMot)
- h_acc_m: Horizontal accuracy estimate in meters (2 decimal places, from UBX hAcc)
- rpm: Engine RPM from tachometer input
- accel_x/y/z: Accelerometer g-force from onboard LSM6DS3 IMU (3 decimal places, logs
0.000if IMU not available)
DovesDataLogger/ # repo root
├── BirdsEye/ # sketch (folder name must match BirdsEye.ino)
│ ├── BirdsEye.ino # Entry point: globals, setup(), loop(), state machine
│ ├── project.h # Shared types, debug macros, constants
│ ├── display_config.h # Display driver abstraction (SH110X/SSD1306)
│ ├── gps_config.h # GPS configuration constants (baud, nav rate)
│ ├── images.h # PROGMEM bitmap data (splash, animations)
│ ├── accelerometer.{h,ino} # LSM6DS3 IMU init and g-force reads
│ ├── bluetooth.{h,ino} # BLE service (file transfer, settings, track sync)
│ ├── display_pages.{h,ino} # All page rendering functions (displayPage_*())
│ ├── display_ui.{h,ino} # Display init, button handling, menu navigation
│ ├── gps_functions.{h,ino} # GPS init, PVT callback, time conversion, logging
│ ├── replay.{h,ino} # Instant DOVEX header replay + haversine helper
│ ├── sd_functions.{h,ino} # SD init, track JSON parsing, track manifest
│ ├── settings.{h,ino} # Persistent JSON settings (/SETTINGS.json)
│ ├── tachometer.{h,ino} # Falling-edge ISR, Kalman-filtered RPM
│ ├── diagram.json # Wokwi simulator wiring
│ └── libraries.txt # Wokwi simulator library list
│
├── .github/workflows/ # CI: compile-sketch + arduino-lint
├── CASE/ # 3D printable enclosure files (STL + STEP)
├── SDCARD/TRACKS/ # Example track JSON files
├── TACHOMETER/ # Tachometer circuit documentation
├── README.md # This file
├── CLAUDE.md # AI-assistant project guide
└── LICENSE # GPL v3
| Library | Purpose |
|---|---|
| Adafruit GFX | Graphics primitives |
| Adafruit SSD1306 | SSD1306 OLED driver (if using SSD1306) |
| Adafruit SH110X | SH110X OLED driver (if using SH1106) |
| SparkFun u-blox GNSS v3 | UBX binary PVT GPS interface |
| ArduinoJson 6.x | Track file and settings JSON parsing |
| SdFat | SD card (FAT16/FAT32) |
| DovesLapTimer | Lap/sector timing |
| CourseManager | Auto course detection + Lap Anything (part of DovesLapTimer) |
| Seeed Arduino LSM6DS3 | Onboard IMU accelerometer/gyro (Sense variant) |
| Bluefruit nRF52 | BLE (built into Seeed nRF52 board package) |
Board package: Use "Seeed nRF52 Boards" (non-mbed). The mbed variant uses ArduinoBLE instead of Bluefruit and is incompatible.
-
Format SD Card
- Format as FAT32 (or FAT16 for maximum compatibility)
- Create folder structure:
TRACKS/in root
-
Add Track Files
- Copy or create
.jsontrack files inSDCARD/TRACKS/ - See "Track Loading System" section above
- Copy or create
-
Flash Firmware
Option A — prebuilt release (no toolchain needed):
- Download the latest
BirdsEye.uf2from the Releases page - Double-tap the XIAO's reset button to mount the
XIAO-SENSEbootloader drive - Drag
BirdsEye.uf2onto that drive — the board reboots into the new firmware automatically
Option B — build from source:
- Install "Seeed nRF52 Boards" board package (non-mbed)
- Install required libraries (see table above)
- Select board: "Seeed XIAO nRF52840 Sense"
- Compile and upload
BirdsEye/BirdsEye.ino
- Download the latest
-
Hardware Assembly
- 3D printed case assembly instructions coming soon
- Tachometer circuit README coming soon
- STL files available in
CASE/directory - Note: Requires some glue, measuring, and jeweler's screws
Button Controls:
- Left/Right Buttons: Navigate between pages
- Middle Button: Select/Enter (in menus), Quick-jump to Pace/Best Lap (while racing)
- Hold Left + Right (5s): Enter sleep mode (from main menu)
- Hold Select + Side (5s): Reboot device (from any page)
Startup Sequence ("Just Drive" mode):
- Power on → Boot screen → Main menu
- Start driving — device auto-enters race mode at 10+ mph or 500+ RPM
- GPS fix acquired → DOVEX logging starts immediately
- Track auto-detected via GPS proximity → course detection begins
- Lap timing activates automatically (sector timing if configured, "Lap Anything" otherwise)
Ending Session:
- Auto-idle: stops automatically after 60 seconds below 2 mph
- Manual: navigate to "END RACE" page (only accessible when speed < 2 mph), confirm to stop
- Returns to main menu
Sleep Mode:
- Activates via 5-second left+right hold on main menu, or automatically after 5 minutes idle on main menu
- Turns off display, GPS (backup mode), and IMU — draws ~2-4 mA vs ~120 mA active
- Wakes instantly on any button press or tachometer pulse (engine start)
- GPS retains ephemeris in backup RAM for fast warm-start on wake (seconds, not minutes)
- Daily GPS wake keeps ephemeris fresh (~2 min every 24 hours)
- Shows charging screen with battery percentage when USB is plugged in during sleep
- Estimated sleep runtime: ~15-30 days on 1500 mAh battery
- Protocol: UBX binary (PVT messages via SparkFun callback)
- Update Rate: 25Hz (40ms between fixes)
- Mode: Automotive dynamic model
- Constellations: GPS-only (max nav rate, no multi-constellation overhead)
- Baud Rate: 57600 (auto-configured from 9600 default on first boot)
- Write Frequency: Every PVT update (~25Hz)
- Flush Interval: Every 10 seconds (prevents data loss)
- SPI Speed: 1 MHz (reduced for EMI resistance)
- Access Arbitration: Mutex prevents concurrent access from logging, replay, BLE, and track parsing
- Input Pin: D0
- Detection: Falling-edge interrupt
- Filtering: 3ms minimum pulse gap (supports up to ~20,000 RPM)
- Dead Time: Volatile flag gating prevents interrupt storms from noisy ignition pickups
- Update Rate: 3Hz with EMA filter (alpha 0.20)
- Timeout: 500ms with no pulse = engine stopped (RPM 0)
- Configuration: 1 pulse per revolution (adjust
tachRevsPerPulsefor multi-cylinder)
- Refresh: 3Hz (reduces power consumption)
- Exception: Instant refresh on button press
- Update Interval: 5 seconds
- Voltage Divider: 1510Ω / 510Ω ratio
- Display: Percentage (3.3V = 0%, 4.2V = 100%) with voltage readout
The page system is straightforward to extend. Each page needs:
-
Page Constant in
BirdsEye.ino(in the running page section):const int MY_NEW_PAGE = 13;
-
Display Function in
display_pages.ino:void displayPage_my_new_page() { resetDisplay(); display.println(F("My Custom Page")); // Your display code here safeDisplayUpdate(); }
-
Page Routing in
displayLoop()indisplay_ui.ino:else if (currentPage == MY_NEW_PAGE) { displayPage_my_new_page(); }
-
Update Page Range in
BirdsEye.ino:int runningPageEnd = MY_NEW_PAGE; // Update to new last page
Look at existing pages like displayPage_gps_speed() or displayPage_tachometer() in display_pages.ino as examples.
-
Data Viewer: DovesDataViewer
- Web-based viewer for logged data
- Preview at HackTheTrack.net
-
Core GPS Timing Library: DovesLapTimer
- Line-crossing detection
- Sector timing
- Optimal lap calculation
- Pin lock - require PIN to pull logs from device
- Additional sensor inputs (exhaust temp, water temp)
- WiFi automatic data transfer
- Real-time telemetry to pit crew
- Crossing detection threshold: configurable via
lap_detection_distancesetting (default 7m) - Maximum track locations: 1000
- Maximum layouts per track: 10
- Maximum lap history: 1000 laps per session
- GPS coordinates stored with 8 decimal places (~1.1mm precision)
- BLE disconnect triggers automatic device reboot (ensures settings changes take effect)
Contributions are welcome! See CONTRIBUTING.md for how to build the firmware, run the host tests, and the PR workflow. ARCHITECTURE.md explains how the system fits together. Found a security issue? Please follow SECURITY.md and report it privately. All participants are expected to follow our Code of Conduct.
GPL v3 — see LICENSE for details.
For issues and questions, please use GitHub Issues (search existing ones first). For security reports, see SECURITY.md.