Ashin Walpola
f1770e11dd
UI: - Top bar shows a USB glyph reflecting the serial link on the ESP32-C5 path, instead of a Wi-Fi glyph driven by an MQTT state that is permanently disconnected there. - Recording screen's OBU stream row follows whichever transport the selected hardware uses. It previously read as offline throughout a recording that was actively beaconing CAMs. - Live map uses distinct markers: a centred dot for own position (a fact about the viewer, not a tracked object) and a teardrop pin for remote stations, tinted by alert severity. Both were osmdroid's identical default pin before, and severity required tapping a marker to read its label. - Sensor Monitor moves out of the bottom nav to Settings > Developer. A live phone-sensor feed is a bench tool; the Dashboard already reports GNSS/IMU health. Screen and route are unchanged, just not in the rider's way. Detection engine on the ESP32 path: - Seed our own StationID from the persisted value CamTransmitLoop transmits. It was null here (the CiT One learns it from v2x/rx/obu_gnss, which doesn't exist on this path), so the self-heard-TX filter never fired: the ESP32 runs promiscuous for raw TX to work at all, hears our own CAMs back off the air, and they were tracked as a remote station - a ghost vehicle on top of the ego position, fed to the engine as a collision partner for itself. RSSI: - The firmware has always sent per-frame RSSI in byte 0 of every CAM_RX frame; the app discarded it. Now carried on Cam, persisted per V2X message, shown per station in the received-CAM list, and exported. Null for own CAMs and the whole CiT One path, neither of which has a measurement. Trips, CSV and export (schema v3 -> v4): - trips.sessionId links a trip to the CSV session recorded alongside it. The two are written by independent subsystems that the Recording button happens to start together; without the link, deleting a trip orphaned its CSV forever. Timestamp matching was rejected - close recordings would delete the wrong file. - Deleting a trip now removes the CSV file AND its sessions row, so it stops appearing in the Session Log pointing at nothing. - Per-trip combined CSV export: GPS track, detected events, V2X messages (with RSSI) and the raw sensor samples in one file, keyed by a leading type column. One file rather than a zip of tables because the point of the export is correlating those streams, and splitting them pushes the join downstream. - Export takes the Activity context. Sharing from the ViewModel's Application context threw AndroidRuntimeException on startActivity - this crashed on the first tap of the share button. Trips recorded before v4 have a null sessionId, so their exports omit raw sensor rows and their CSVs still need clearing by hand once.
MicrOBU Android App
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
appmodule. - 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