A real-time lap timer for Mini 4WD racing, built with Go and vanilla JavaScript. An Arduino with an IR sensor detects each car pass and triggers lap recording via serial port. Results are broadcast live to the browser over WebSocket.
| Lap Timer UI | Arduino & sensor on track |
|---|
- Real-time current lap and total race time display
- Lap history with best lap highlighted
- Pause, resume, and reset support
- Session history saved to disk
- Race sounds (countdown, GO, lap bell, best lap arpeggio)
- Go 1.22+
- Arduino with IR sensor connected via USB serial
- Connect the IR receiver output to Arduino D2
- Flash the sketch at
arduino/lap_sensor/lap_sensor.ino - Connect the Arduino to the computer via USB
The Arduino sends a TRIGGER line over serial (9600 baud) each time the IR beam is broken, with a 500 ms debounce.
go run ./cmd/server
Then open http://localhost:8080 in a browser.
| Flag | Default | Description |
|---|---|---|
-port |
/dev/ttyUSB0 |
Serial port the Arduino is connected to |
-addr |
:8080 |
HTTP listen address |
Example:
go run ./cmd/server -port /dev/tty.usbmodem101 -addr :9000
Completed sessions are saved as JSON files in the sessions/ directory. The in-app session history panel loads them on demand.
- Mini4WDGeek.com β Mini 4WD news, reviews, and resources
cmd/server/ - HTTP server, WebSocket, REST endpoints
internal/
session/ - Lap timing state machine
hub/ - WebSocket broadcast hub
serial/ - Serial port listener
storage/ - Session persistence
static/ - Frontend (HTML, CSS, JS)
arduino/ - Arduino IR sensor sketch
sessions/ - Saved session JSON files (git-ignored)