EchoWalk

EchoWalk is a phone-first acoustic sonar accessibility research prototype by Groundstate Technology LLC.

The Android prototype repeatedly emits a short high-frequency chirp from the phone speaker, records returning sound with the phone microphone, looks for a correlated echo, estimates candidate distance, and increases haptic feedback as an obstacle appears closer. The rear camera remains visible as a secondary visual aid; it is not used to fabricate distance measurements.

Prototype scope

Version 0.2 deliberately stays small:

• one screen
• automatic repeating acoustic sonar
• phone speaker + phone microphone only
• candidate distance in meters when a sufficiently confident echo is found
• escalating haptic proximity warnings
• rear-camera preview as an optional visual aid
• one Start / Stop Sonar control

LiDAR, BLE sensors, external ultrasonic hardware, maps, profiles, accounts, and cloud services are intentionally out of scope for this prototype.

Safety: EchoWalk is experimental software. It is not a certified mobility or medical device and must not replace a cane, guide dog, trained human assistance, or established orientation-and-mobility techniques.

Requirements

• Node.js + npm
• Android Studio
• Android SDK + Platform Tools (adb)
• physical Android phone with USB debugging enabled

The native sonar module cannot run in Expo Go. Build the Android development app.

Install

npm install
npx expo-doctor

Do not run npm audit fix --force on this project. React Native and Expo packages are version-coupled; forcing npm audit upgrades can replace Expo or React Native with incompatible versions.

Build and run

npx expo prebuild --clean
adb devices
npx expo run:android

After the first native build, JavaScript-only changes can usually be served with:

npx expo start --dev-client -c

Changes to modules/echowalk-sonar/android/... require rebuilding with npx expo run:android.

Using the prototype

1. Open EchoWalk.
2. Allow camera and microphone permissions.
3. Sonar begins automatically.
4. Keep the phone speaker and microphone uncovered.
5. Point/hold the phone in the direction of travel.
6. As candidate echo distance decreases, haptics become more urgent.
7. Tap STOP SONAR to pause acoustic measurements.

The screen intentionally shows NO READING when the acoustic result is weak. The app does not substitute a fake camera-derived meter value.

How the acoustic measurement works

The Android native module generates an approximately 17–20 kHz swept chirp, records a short PCM window, performs normalized correlation against the transmitted chirp, rejects the immediate speaker-to-microphone path, calculates candidate range from echo delay, and returns distance plus a confidence score to React Native.

Phone audio hardware introduces speaker latency, microphone latency, echo cancellation, filtering, frequency-response differences, and device-specific signal paths. Reliable accessibility use will require calibration and substantial real-world validation.

Near-term priorities

Signal quality comes before new features: per-device latency calibration, stronger direct-path rejection, multi-peak analysis, confidence validation, phone-model testing, handling Android acoustic echo cancellation, and user testing with blind/low-vision accessibility specialists.

Ownership and license

Copyright © 2026 Groundstate Technology LLC. EchoWalk is released under the Apache License 2.0 so people can use, study, modify, and redistribute it while retaining clear project ownership and attribution. See LICENSE and NOTICE.

Standalone-first deployment

This project does not require Groundstate Admin Center or a Groundstate account. Core operation remains local and independently deployable. See docs/STANDALONE_OPERATION.md for the product-specific identity and outage boundary.