Android companion app for the micrOBU; a compact V2X on-board unit developed by HAW Hamburg and consider it GmbH for vulnerable road users (cyclists, e-bike riders, pedestrians).

The app serves as the HMI for the micrOBU hardware, handling V2X message display, sensor data collection, trip recording, and OBU communication over USB-C, Wi-Fi (dev), and Bluetooth (upcoming).

Platform: Android (Kotlin) · Min SDK: 29 (Android 10) · Target SDK: 36

What it does

Real-time V2X monitoring; subscribes to the OBU's MQTT broker and displays live CAM, DENM, SPAT, MAP, and CPM messages grouped by topic with pretty-printed JSON and TX/RX badges.

DENM transmission; triggers DENM use cases (e.g. stationary vehicle warning hln-sv) on the OBU via the consider it Use Case API (v2x-uca/input/denmtrg) with a single tap.

Sensor monitoring; live readout of phone GNSS, accelerometer, gyroscope, magnetometer, and barometer alongside OBU GNSS for cross-reference.

Trip recording; foreground service records all sensor streams and detects cycling events (braking, turning, stopping) using orientation-independent signal processing. Works fully offline with no OBU connected.

Trip review; past trips displayed on an OpenStreetMap layer with detected events overlaid as coloured pins. Tap any pin for event details.

CSV export; every sensor sample written to a timestamped CSV in real time during a session. Shareable via the standard Android share sheet.

Architecture

MVVM with Repository pattern throughout. Jetpack Compose for all UI (no XML layouts). Hilt for dependency injection.

ui/screens/         Compose screens (Dashboard, V2X Monitor, Sensors, Recording, Trip History, Settings…)
ui/navigation/      Navigation graph and bottom nav bar
viewmodel/          MqttViewModel, SensorViewModel, TripRecordingViewModel
data/mqtt/          MQTT repository, Paho client, exponential-backoff reconnection
data/transport/     USB tethering detection and gateway IP resolution
data/db/            Room database (sessions, trips, detected events)
data/               SensorRepository, TripRepository, CsvExporter
domain/detection/   EventDetector, RunningStats sliding window (orientation-independent)
service/            TripRecordingService (foreground service)

Connectivity

The app uses a phased transport strategy. The MQTT client, topic subscriptions, and all UI are identical across transports; only the underlying network path changes.

Phase	Transport	Status
Phase 01	Wi-Fi	Complete
Phase 02	USB-C tethering	Active
Phase 03	Bluetooth BLE	Future

The MQTT broker runs on the OBU hardware (Mosquitto 2.0.11, port 1883). In Phase 02, Android USB tethering exposes the OBU as a virtual Ethernet interface at 192.168.42.x. The app auto-detects the gateway IP on plug-in.

Key dependencies

Library	Purpose
Jetpack Compose + Material3	UI
Eclipse Paho MQTT	OBU communication
Room	Local database
Hilt	Dependency injection
OSMDroid	Trip review map
DataStore	Settings persistence
FusedLocationProviderClient	GNSS

Getting started

Open in Android Studio (Hedgehog or newer).
Connect a device running Android 10+ (API 29).
Build and run the app module.
For Phase 02 testing: plug the phone into the OBU via USB-C, enable USB tethering on the phone, and the app will detect the interface and connect automatically. Broker IP can be overridden manually in Settings → Connection.
For standalone trip recording: no OBU required. Go to the Record tab and tap Record.

The Wi-Fi transport (Phase 01 broker at 192.168.3.202) remains available in developer builds and can be toggled in Settings → Developer.

Project context

The micrOBU project is funded under the ZIM program (BMWK) and targets micromobility users in Hamburg. The companion app offloads processing from the compact OBU hardware to the smartphone; GNSS fusion, event detection, and future antenna coordination all run on the phone to keep the OBU lightweight and power-efficient.

V2X communication uses ITS-G5 (IEEE 802.11p / DSRC) at 5.9 GHz. The app communicates with the OBU exclusively via the consider it MQTT API v6 (processed JSON messages); no ASN.1 encoding in the app.

Owner: HAW Hamburg