Thumper

Try it now: nadahalli.github.io/thumper (Android + Chrome, add to homescreen for full PWA experience)

A minimal jump rope workout app with BLE heart rate monitoring and mic-based jump counting.

Features

• Heart rate monitoring via any Bluetooth Low Energy HR strap
• Jump counting using the phone's microphone to detect rope impacts
• Workout timer with 5-second countdown, pause/resume
• Workout summary dialog after stopping (duration, avg HR, jumps, jumps per minute)
• Workout history stored locally with IndexedDB
• TCX export of individual or all workouts (compatible with Garmin, Strava, etc.)
• Adjustable sensitivity for jump detection threshold

Requirements

• Android + Chrome (Web Bluetooth, Web Audio, Wake Lock)
• BLE-capable device (for heart rate)
• Microphone permission (for jump detection)
• Heart rate monitoring does not work on iOS because Safari doesn't support Web Bluetooth. Thanks, Apple.

Development

npm install
npm run dev

Architecture

Vanilla TypeScript PWA, no framework. Vite + Dexie.js + vite-plugin-pwa.

src/
  main.ts                     Entry point, hash router, screen switching
  core/                       Pure logic (zero DOM, zero Web API deps)
    jump-analyzer.ts            Amplitude detection (threshold, cooldown, gap tracking)
    hr-parser.ts                BLE HR measurement byte parsing
    tcx-builder.ts              Garmin TCX XML generation
    summary.ts                  Workout summary computation
  api/                        Web API wrappers (thin adapters)
    audio.ts                    getUserMedia + ScriptProcessorNode
    bluetooth.ts                Web Bluetooth scan, connect, HR notifications
    wake-lock.ts                Screen Wake Lock API
  data/                       Persistence
    db.ts                       Dexie database (workouts + samples tables)
    types.ts                    Workout, WorkoutSample interfaces
  state/                      Reactive state
    workout-state.ts            Workout lifecycle state machine
  ui/                         DOM rendering
    workout-screen.ts           Main workout view
    history-screen.ts           Past workouts list
    components/                 Dialogs (summary, settings)
    styles.css                  Dark theme, big typography

Testing

npm test

Pure business logic is extracted into framework-free modules for unit testing:

• JumpAnalyzer - amplitude threshold, cooldown, jump time accumulation, reset
• HeartRateParser - BLE heart rate byte parsing (8-bit, 16-bit)
• WorkoutSummary - avg HR, jump count, jumps-per-minute math
• TcxBuilder - TCX XML structure, timestamps, trackpoints
• WorkoutState - full workout lifecycle flow (countdown, active, pause, resume, stop, save, discard)

Privacy

Thumper is entirely offline and makes zero network connections. All data stays on your device in IndexedDB.

Tech

TypeScript, Vite, Dexie.js, Web Audio API, Web Bluetooth API, Screen Wake Lock API, vite-plugin-pwa.