12-OBD-Speed: battery voltage arc and idle/screen-off mode

- ATRV every 2 s; voltage arc in the bottom gap (11-15 V) + number,
  colored by state (low / weak / resting / charging / overcharge)
- idle after Off/2/5/10 min without speed data (settings page, NVS):
  screen off, GIF paused, OBD polling stopped, ATRV every 30 s;
  wakes on touch (swallowed by a top-layer overlay) or > 13.2 V
- status pill moved up to make room for the voltage

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -79,7 +79,7 @@ Display color format is `RGB565_SWAPPED` (ST77916 byte order, set in `lv_conf.h`
 | `1-Instructions` | Spec PDF (duplicate), AIDA64 remote-sensor layout `aida_remote_1.85.rslcd`, MJPEG conversion tool (Windows .NET, converts video to 360×360 MJPEG 25 fps) |
 | `2-Program Example/Demo_Arduino` | **Vendor only:** `library/` (3 libs), `lv_conf.h` (vendor original), `sd/` (SD listing example; its lv_conf.h has FATFS edits), `docs/` (setup screenshots + compile instructions). The vendor's original LVGL demo sketch no longer exists unmodified. |
 | `shared` | **Shared code for all JC3636W518 projects:** `jc3636w518.ini` (PlatformIO base config), `include/lv_conf.h` (LVGL 9.6), `lib/JC3636W518` (board library). See its `README.md` |
-| `12-OBD-Speed` | **The new program — working in the car (2026-10-23):** speed from the ELM327 over BLE as big number + arc gauge on a GIF background; swipe left for the adapter menu (scan, select → remembered in NVS, auto-reconnect every 3 s). See its `README.md` |
+| `12-OBD-Speed` | **The new program — working in the car (2026-10-23):** speed from the ELM327 over BLE as big number + arc gauge on a GIF background, battery-voltage arc in the bottom gap; swipe left for the adapter menu (scan, select → remembered in NVS, auto-reconnect every 3 s), again for settings (rotation, idle/screen-off timeout). See its `README.md` |
 | `10-GIF-Tests` | **GIF playback experiments** (was `10-OBD-Display-2024`): `display_gif_embedded`, `display_gif_sd`, `assets/gifs`. The 2024 bridge/ELMulator/WiFi speed sketch, the broken LVGL 9 archive and the BLE scanner tool (`11-BLE-Scanner`: on-screen scan, GATT listing, ELM test, LittleFS log) were removed 2026-10-23 — all in git history |
 | `3-Specification` | Spec sheet (factory firmware features, interface photo) |
 | `4-Chip manual` | ESP32-S3R8 datasheet, PCM5100A datasheet |
@@ -93,6 +93,9 @@ Display color format is `RGB565_SWAPPED` (ST77916 byte order, set in `lv_conf.h`
 AIDA64 secondary screen (18 styles), mic spectrum, MP3 player (`/music` on SD), photo frame (`/pic`, 360×360 JPEG), MJPEG player (`/mjpeg`), weather, theme clocks, WiFi provisioning AP "My App"/12345678 + web config at device IP.
 Re-flash it with Flash Download Tool: ESP32-S3, `1.85_demo.bin` @ 0x0.
 
+## Car battery / idle
+Cheap ELM327 clones draw ~20–50 mA permanently (OBD pin 16 = always 12 V); the display ~180 mA if its USB stays powered. `12-OBD-Speed` idle mode stops OBD polling after N min without data so the car's ECUs can sleep; `ATRV` (adapter-internal) every 30 s detects an engine start (> 13.2 V).
+
 ## OBD adapter (user's)
 AliExpress "ELM327 Mini V2.1 Bluetooth OBD **Dual Mode** 5.1" — dual mode = Bluetooth Classic SPP **and BLE**, so the ESP32-S3 should be able to connect directly over BLE (no bridge ESP32).
 **Verified in the car (2026-10-23, with the since-removed BLE scanner tool; log in `12-OBD-Speed/docs/2026-10-23_ble_scanner_car_test.txt`):**
@@ -123,5 +126,6 @@ AliExpress "ELM327 Mini V2.1 Bluetooth OBD **Dual Mode** 5.1" — dual mode = Bl
 - BLE (NimBLE) in the user's home: ~12 devices visible within 10 s.
 - Big fonts: generate with `npx lv_font_conv` (Node 22 installed) from `lvgl/scripts/generators/built_in_font/Montserrat-Medium.ttf`; `-DLV_LVGL_H_INCLUDE_SIMPLE` (in shared ini) makes the generated `#include` work.
 - Binary assets (GIFs): `board_build.embed_files = data/x.gif` → `extern const uint8_t x_start[] asm("_binary_data_x_gif_start")` (no huge C arrays).
-- Serial output right after a reset can be lost/garbled (USB-CDC re-enumeration, prints from two cores interleave) — don't conclude a task isn't running from a missing early line.
+- Python edit scripts: never pass C strings containing `\n` through a bash heredoc into Python — it turned into a real line break twice; write the script with the Write tool instead.
+- Serial output from the background task (core 0) is often lost, not only right after reset; don't rely on it as proof. Serial output right after a reset can be lost/garbled (USB-CDC re-enumeration, prints from two cores interleave) — don't conclude a task isn't running from a missing early line.
 - `Preferences` prints `nvs_open failed: NOT_FOUND` the first time a namespace is read before it was written — harmless.