TeslaLED

An Android app that remote-controls an LED message panel mounted on a car, over Bluetooth. The panel itself is driven by a Raspberry Pi (3B/3B+).

Note: this app is also maintained as android/ inside romainhedouin/tesla-panel (a fork of hzeller/rpi-rgb-led-matrix), alongside the Pi-side receiver in that repo's tesla/ directory — see tesla/README.md there for deployment and a documented gotcha around Bluetooth pairing on a headless Pi. This standalone repo may drift from that copy; treat tesla-panel as the actively-maintained one if the two disagree.

How it works

• The phone pairs with the Raspberry Pi over classic Bluetooth (SPP, RFCOMM), connecting to a hardcoded MAC address (BluetoothClient.findDevice()).
• Everything the panel can show is a PanelMessage (model/PanelMessage.java): a label, a category (Greetings/Courtesy/Traffic-safety/Fun/Data/Custom), an optional language tag (fr/en/none), and either a fixed list of Frames (a ready-to-send 64×32 PPM + a display duration) or a LiveDataSource for the Data category. A single frame is a static image; multiple frames are a slideshow — there's no separate "animation" concept, it's just a PanelMessage with more than one frame.
• The Data category (data/TimeDataSource, data/SpeedDataSource) shows the current time or GPS speed, re-rendered and re-sent once a second until stopped — no fixed duration, no frame list. Labels ("Heure:"/"Time:", "Vitesse:"/"Speed:") follow the app's display language, set via the language menu (see below), not the phone's locale.
• storage/MessageStore loads the bundled defaults (assets/default_messages.json
  • the .ppm assets it references) and any user-created messages (persisted under the app's internal files dir), filterable by category/language. A message with no language tag is treated as language-neutral and matches every language filter, not just "All" — a message meant for everyone shouldn't disappear because a specific language is selected.
• MainActivity shows those messages as a thumbnail grid (MessageAdapter), filterable by category chips and an app-bar language popup (next to a brightness popup, 25/50/75/90/100%). A "now showing" bar at the top reads "Connected"/"Not connected" (polled from BluetoothClient.isConnected()) when idle and "Displaying..." with a live thumbnail while something's active, plus a Stop button — all accurate for free, since the app is the only thing that ever tells the panel what to display or when to stop. Long-press a custom message's card to delete it (built-in messages can't be deleted).
• CreateMessageActivity (the "+" button) is how you make a custom message: a label, category, language, and a list of frames. Each frame is just typed text — render/PixelFontRenderer rasterizes it using a bitmap (BDF) font bundled from the rpi-rgb-led-matrix library (assets/fonts/9x18B.bdf; Data's two-line time/speed layout uses the smaller 6x13B.bdf), blitting glyph pixels directly with no anti-aliasing, so panel text is always crisp. A frame whose text doesn't fit the panel width is auto-paginated into multiple frames by render/TextChunker (word-boundary aware) — long messages split into readable chunks rather than scrolling, since scrolling text is hard to read from a following car.
• MessageSender runs all Bluetooth I/O (which blocks - a connect can take several seconds) on a dedicated HandlerThread, never the caller's thread, and posts Listener callbacks back to the main thread for UI updates. It sends a fixed PanelMessage's frames in order, timing each client-side, or for a live-data message re-renders and re-sends every second until stop(). A monotonic generation counter (touched only on the I/O thread) lets a stop()/new send() invalidate any in-flight timers/ticks without locks.
• Messages are framed as [1 byte command type][4 bytes big-endian payload length][payload], then a single-byte status response. BluetoothClient writes the whole thing in one shot — no manual chunking or sentinel values, since RFCOMM is a reliable ordered stream that already handles fragmentation/reassembly transparently. Command types: image, kill, and set-brightness (see Settings — brightness is a persisted app setting, changeable from the app-bar dropdown, synced to the Pi before every message and pushed immediately on change if already connected).
• Traffic-safety includes generated EU-style (red circle) and US-style (portrait "SPEED LIMIT" rectangle) speed-limit sign images — see scripts/generate_speed_signs.py to regenerate or add more.

Requirements

• Android Studio (or just the command-line SDK tools + a JDK) with SDK Platform 32 installed.
• minSdk 23, targetSdk/compileSdk 32.
• A phone with Bluetooth, paired with the Pi ahead of time (pairing happens outside the app, at the OS level — see tesla-panel's tesla/README.md if pairing silently fails, since a headless Pi needs a pairing agent running to accept it).

Building

./gradlew assembleDebug

The APK lands in app/build/outputs/apk/debug/app-debug.apk. Sideload it to a phone directly (adb install, AirDrop, etc.) — it isn't published anywhere.

Known rough edges

• The target device's Bluetooth MAC address is hardcoded in BluetoothClient.findDevice(). Point it at a different Pi and you'll need to edit and rebuild.
• No error surfacing beyond System.out.println/Toast — failures don't produce a real diagnostic message.
• On Android 12+ (targetSdk 31+), BLUETOOTH_CONNECT is a runtime permission, and ACCESS_FINE_LOCATION is required for the Data category's speed reading. MainActivity requests both on launch; if you see the app silently no-op on button taps (a toast, no crash) or Speed always show "--", one of these was denied — check phone Settings → Apps → TeslaLED → Permissions.
• Multi-frame sequences are "slideshow" pacing (each frame shown for at least ~0.5-1s+), not smooth high-fps animation — each frame costs a Bluetooth round trip. Fine for paginated text, a deliberate slideshow, or the Data category's 1Hz updates; not meant for anything resembling video.
• Custom messages currently support text only (no photo import, no freehand drawing) — both would fit the same Frame model later without changing anything else.