MorseRinger

An Android app that turns incoming-caller identification into a Morse code audio signal. When your phone rings, MorseRinger looks up the caller's name in your contacts and plays it back as audible Morse on your phone's ringtone audio stream.

If the caller is not in your contacts, the literal string Unknown is keyed instead.

Get the app here:

https://play.google.com/store/apps/details?id=com.uschwar.morseringer

Why does this exist?

For amateur-radio operators and Morse-code learners, the constant ringing of a phone is wasted training time. MorseRinger replaces the conventional ringtone with a short, repeating Morse transmission of who is calling, so you can practice copy in everyday situations and identify callers without looking at the screen.

How it works

Incoming call
   │
   ▼
┌────────────────────────┐
│ IncomingCallService    │  Android CallScreeningService
│ (call screening role)  │  – respondToCall(allow)
└──────────┬─────────────┘  – extracts phone number, starts foreground service
           │
           ▼
┌────────────────────────┐
│ MorseForegroundService │  – FOREGROUND_SERVICE_TYPE_MEDIA_PLAYBACK
│                        │  – keeps the process alive while the phone rings
└──────────┬─────────────┘  – delegates playback to MorseCodeAudioPlayer
           │
           ▼
┌────────────────────────────┐
│ ProcessIncomingCallUseCase │
│  ContactRepository → name  │
│  TextToMorseUseCase → dits │
└──────────┬─────────────────┘
           │  ".... .. / - .... . .-. ."
           ▼
┌────────────────────────┐
│ MorseCodeAudioPlayer   │  – TelephonyCallback observes RINGING → IDLE
│                        │  – stops playback once the call is answered
└──────────┬─────────────┘  – hard 60 s safety timeout
           │
           ▼
┌────────────────────────┐
│ MorseCodeGenerator     │  – AudioTrack (PCM 16-bit, 44.1 kHz)
│ (PCM buffer synthesis) │  – sine tone with click-suppressing fade envelope
└────────────────────────┘  – usage = NOTIFICATION_RINGTONE

The app does not reject, log, or silence calls — it only listens for the RINGING state and plays audio in parallel with the system ringer. For the cleanest experience, set the system ringtone to Silent (the in-app Ringtone Shortcut card opens the relevant Settings screen).

Architecture

The codebase follows a small Clean-Architecture-style layering inside a single Gradle module:

Layer	Package	Responsibility
domain	com.uschwar.morseringer.domain	Pure Kotlin — MorseEncoder, MorseSettings, repos, use cases
data	com.uschwar.morseringer.data	Android implementations — MorseCodeAudioPlayer, MorseCodeGenerator, repos
service	com.uschwar.morseringer.service	Telephony glue — IncomingCallService, MorseForegroundService
ui	com.uschwar.morseringer.ui	Jetpack Compose — MainScreen, SettingsViewModel
DI	MorseRingerApp.AppContainer	Manual constructor injection (no DI framework)

Key design points

• MorseCodeGenerator isolates sine-wave PCM synthesis (and the click-suppressing fade envelope) from the AudioTrack playback hardware management in MorseCodeAudioPlayer. This keeps signal generation easy to unit-test and reuse for both the looping ringtone path and the one-shot in-app preview.
• MorseSettings owns all timing / range constants (defaults, min/max for sliders, the 1200/WPM unit-duration formula). Both UI and persistence layers depend on these constants instead of duplicating numbers.
• MorseCodeAudioPlayer observes the telephony state via TelephonyCallback and cancels playback as soon as the call leaves the RINGING state (with a hard 60 s safety timeout). It is invoked from MorseForegroundService, which keeps the process alive during ringing via FOREGROUND_SERVICE_TYPE_MEDIA_PLAYBACK.
• Persistence: WPM and pitch are stored in Jetpack DataStore (morse_settings), exposed as a Flow<MorseSettings>.

Required permissions

Permission	Purpose
READ_CONTACTS	Resolve caller phone number → display name
READ_PHONE_STATE	Detect when the call is answered/declined
ANSWER_PHONE_CALLS	Required for the Call Screening role
POST_NOTIFICATIONS	System notifications (Android 13+)
MODIFY_AUDIO_SETTINGS	Configure the audio stream

In addition, the user must grant the Call Screening App role, which is requested in-app via RoleManager.

A prominent disclosure dialog explains contact data usage before the runtime permission prompt.

Privacy

Contact information is read on-device only, used solely to translate caller names to Morse code, and never persisted, logged, or transmitted off the device.

Building

./gradlew :app:assembleDebug          # debug APK
./gradlew :app:assembleRelease        # signed release APK (requires keystore.properties)
./gradlew :app:testDebugUnitTest      # JVM unit tests

Requirements:

• JDK 21
• Android SDK 37 (compileSdk) / minSdk 31 / targetSdk 37
• Android Gradle Plugin 9.2.0 · Kotlin 2.3.21

Release signing

app/build.gradle.kts reads keystore.properties from the project root if present:

storeFile=morseringer-release.keystore
storePassword=...
keyAlias=...
keyPassword=...

If the file is missing the release build is unsigned (debug works regardless).

Testing

Tooling	Where	Used for
JUnit 5 + MockK	app/src/test/java	Pure-domain unit tests
Compose UI Test	app/src/androidTest/java (future)	Instrumented UI tests

Existing unit tests cover:

• MorseEncoderTest — full A–Z, 0–9, punctuation, unmapped-fallback, word separators
• MorseSettingsTest — 1200/WPM formula, fallback for wpm <= 0, default values
• TextToMorseUseCaseTest — delegation to encoder
• ProcessIncomingCallUseCaseTest — known/unknown caller paths with mocked repository

Adding more tests

When adding behavior to the domain layer, add a JUnit 5 test alongside the existing ones — no Android dependencies required. For audio or telephony behavior, prefer Robolectric or instrumented tests in androidTest.

Project layout

app/
├── build.gradle.kts
└── src/
    ├── main/
    │   ├── AndroidManifest.xml
    │   ├── java/com/uschwar/morseringer/
    │   │   ├── MorseRingerApp.kt          ← Application + AppContainer (DI)
    │   │   ├── domain/
    │   │   │   ├── MorseEncoder.kt
    │   │   │   ├── model/                 ← MorseSettings
    │   │   │   ├── repo/ContactRepository.kt
    │   │   │   └── usecase/               ← TextToMorseUseCase, ProcessIncomingCallUseCase
    │   │   ├── data/
    │   │   │   ├── audio/                 ← MorseCodeAudioPlayer, MorseCodeGenerator
    │   │   │   └── repo/                  ← SettingsRepository, ContactRepositoryImpl
    │   │   ├── service/                   ← IncomingCallService, MorseForegroundService
    │   │   └── ui/                        ← MainActivity, MainScreen, SettingsViewModel, theme/
    │   └── res/                           ← strings (en, de), themes, icons
    └── test/java/                         ← JUnit 5 unit tests

License

This project is licensed under the MIT License. See the LICENSE file for details.