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Mini 4WD Racing Lap Timer

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.

License: MIT

Lap Timer UI Arduino & sensor on track

Features

  • 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)

Requirements

  • Go 1.22+
  • Arduino with IR sensor connected via USB serial

Hardware Setup

  1. Connect the IR receiver output to Arduino D2
  2. Flash the sketch at arduino/lap_sensor/lap_sensor.ino
  3. 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.

Running

go run ./cmd/server

Then open http://localhost:8080 in a browser.

Options

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

Session Data

Completed sessions are saved as JSON files in the sessions/ directory. The in-app session history panel loads them on demand.

Useful Links

Project Structure

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)