Ashin Walpola
16998bf478
Two documents, wiki-style so they import cleanly: short titled sections, tables over prose where the content is comparative, and cross-references between sections rather than a narrative that has to be read start to end. MicrOBU-User-Guide.docx is for riders. Features, setup for both hardware paths, what each screen shows, what the five alerts mean in plain language, troubleshooting. No ASN.1, no BTP ports, no bit widths anywhere in it. The alert descriptions and the link states are taken from values/strings.xml so the guide and the interface use the same words. MicrOBU-Technical-Documentation.docx is for supervisors and stakeholders. Architecture, the message path end to end, the serial protocol, the codecs and how they are verified, the full requirements matrix, the bench results, and the decisions. Section 15 is fourteen decisions written as chosen / alternative / reasoning / cost accepted, because the alternative is the part a supervisor asks about and it was previously recorded only in commit messages. Nothing is re-derived. Every measurement is cited from 05-obu-bench-test-2026-08-25.md, 04-transmit-setup.md, asn1/README.md or the commit history. Where a claim has no evidence it is marked as unverified rather than asserted: - 11.6 Phase A success criteria is stated as not met, in its own subsection. The bench proves reception; it cannot prove the use case with two moving stations because nothing on the bench moves. This is the central claim of the project and it needs a real ride. - The tx_custom.c bypass is described as the least defensible component in the system and load bearing, with the reverse-engineered struct layouts and the skipped sanity checking spelled out. - The 5900 MHz transmit story is marked a mitigation for a hypothesis, not a diagnosis, and the isolation test that would settle it is named as not run. - The detection thresholds are presented as untuned engineering estimates in both documents, since presenting them as validated is the easiest and most damaging overstatement available here. Twenty image placeholders, none of them filled. Each is a shaded block carrying a caption and a "Must show" line. For the three screenshots that exist the line names the bench session and section they came from; for the four diagrams that do not exist yet it is a full drawing spec, so the two hardware paths, the message path, the frame layout and the verification loop can be drawn from the document without re-reading the source. references.bib collects the standards as BibTeX for a later publication: EN 302 637-2/3, TS 103 301, SAE J2735, TS 102 894-2, EN 302 636-4-1 and -5-1, TS 103 248, TS 103 097, IEEE 802.11 OCB, plus the C2C-CC white paper and the vendored parser provenance. Also tracks two documents the new ones cite that had never been committed: docs/01-requirements-traceability.md and 04-transmit-setup.md. Section 18.3 lists them as repository sources, which would have been a dangling reference otherwise. Not included, deliberately: the two consider it PDFs cited in section 18.2. They are third-party vendor documentation and redistributing them is a licensing decision, not a documentation one. Still missing: the German user guide. values-de/strings.xml already fixes the terminology for it.
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