Thumper

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

Features

• Heart rate monitoring via any Bluetooth Low Energy HR strap (auto-reconnects to last device)
• 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 Room
• TCX export of individual or all workouts to Downloads (compatible with Garmin, Strava, etc.)
• Adjustable sensitivity for jump detection threshold

Requirements

• Android 12+ (API 31)
• BLE-capable device (for heart rate)
• Microphone permission (for jump detection)

Build

./gradlew assembleDebug
adb install -r app/build/outputs/apk/debug/app-debug.apk

Requires JDK 17. Android Studio's bundled JBR works:

export JAVA_HOME="/Applications/Android Studio.app/Contents/jbr/Contents/Home"

Architecture

Single-activity Compose app, MVVM pattern.

com.tejaswin.thumper/
  MainActivity.kt             Navigation, permissions, keep-screen-on
  viewmodel/
    WorkoutViewModel.kt        State: timer, HR collection, TCX export, summary
  ui/
    WorkoutScreen.kt           Main screen + settings/scan/summary dialogs
    HistoryScreen.kt           Past workouts list + TCX export buttons
  ble/
    HrmBleManager.kt           BLE scan, connect, HR notifications
  audio/
    JumpAnalyzer.kt            Pure amplitude/cooldown logic (no Android deps)
    JumpDetector.kt            Mic recording, delegates to JumpAnalyzer
  data/
    WorkoutDatabase.kt         Room DB (v4, with workout samples)
    WorkoutDao.kt              Queries
    WorkoutEntity.kt           Workout schema
    WorkoutSampleEntity.kt     Per-workout trackpoint samples (HR, jump count)

Testing

JAVA_HOME="/Applications/Android Studio.app/Contents/jbr/Contents/Home" ./gradlew testDebugUnitTest

Pure business logic is extracted into Android-free functions/classes for JUnit testing:

• JumpAnalyzerTest - amplitude threshold, cooldown, reset
• HeartRateParserTest - BLE heart rate byte parsing (8-bit, 16-bit)
• WorkoutSummaryTest - avg HR, jump count, jumps-per-minute math
• TcxExportTest - TCX XML structure, timestamps, trackpoints

Privacy

Thumper is entirely offline and makes zero network connections. See PRIVACY.md.

Tech

Kotlin, Jetpack Compose, Material3, Room, BLE GATT, AudioRecord, MediaStore for TCX export.