12-OBD-Speed/README.md

# OBD Speed (JC3636W518)

Vehicle speed from an ELM327 over BLE, shown as a big number + arc gauge on top of an animated GIF.
Uses the shared board library and LVGL 9.6 (`../shared`), NimBLE-Arduino 2.5.1.

## Use
- **Speed page** — speed in km/h (`--` = no data: not connected, or ignition off), arc gauge 0–200 km/h,
  status at the bottom (adapter name when running, otherwise what it is doing).
- **Swipe left → adapter menu** — scans while open. OBD-like adapters (name OBD/ELM/…, or service FFF0/FFE0/18F0)
  are listed first in green. **Tap one** to select it: it is remembered (NVS) and connected immediately.
  **Forget** clears the remembered adapter, **Done** (or swipe right) returns to the speed page.
- On power-up the remembered adapter is connected automatically; if the link drops or the adapter is not
  there (car off), it retries every 3 s. With no adapter remembered, the device starts on the menu page.

## How it talks to the ELM327
Service `FFF0`, notifications + commands on `FFF1` (verified with the user's "OBDII" adapter, see
`docs/2026-10-23_ble_scanner_car_test.txt`, made with the BLE scanner tool that was removed afterwards — in git history); other adapters: first notify+write pair.
Init: `ATZ`, `ATE0`, `ATL0`, `ATS0`, `ATH0`, `ATSP0`, `0100`; then `010D` (speed) is polled continuously.
Serial (115200) prints status changes as `[obd] ...`.

## Files
| File | What |
|---|---|
| `src/main.cpp` | LVGL UI (tileview: speed page + menu page) |
| `src/obd_link.cpp/.h` | BLE scan, connect/reconnect, ELM327 init and speed polling (background task on core 0) |
| `src/font_speed_120.c` | Montserrat Medium 120 px, digits and `-`, 4 bpp (generated with `lv_font_conv`, see header) |
| `data/bg.gif` | Background (`ezgif-5-cb56986bc7.gif`, 360×360), linked into the firmware via `board_build.embed_files` |

Replace `data/bg.gif` with any 360×360 GIF to change the background (keep it under ~3 MB).