ESPHome external component for Samsung 2x20 serial VFD

Component (components/samsung_vfd), example device config, README and
CLAUDE.md.

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

README.md

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+# Samsung serial VFD — ESPHome component
+
+An ESPHome external component for the Samsung 2-line × 20-character serial VFD
+(vacuum fluorescent display) that takes 5 V TTL serial at 9600 baud, 8N1.
+
+It keeps a copy of the screen in RAM and only sends data when something
+changes. Updates overwrite the screen in place instead of clearing it first,
+so the clock doesn't flicker.
+
+```
+components/samsung_vfd/   the component (Python schema + C++)
+examples/samsung-vfd.yaml full example: clock + two Home Assistant text entities
+examples/secrets.yaml.example
+```
+
+## Using it from your ESPHome server
+
+Add this to your device YAML. ESPHome fetches the component from git when it
+compiles.
+
+```yaml
+external_components:
+  - source: github://REPO_OWNER/REPO_NAME@main
+    components: [samsung_vfd]
+    refresh: 1d
+
+uart:
+  id: uart_vfd
+  tx_pin: GPIO17
+  baud_rate: 9600
+
+time:            # needed by the component (used by samsung_vfd.printf)
+  - platform: sntp
+    id: sntp_time
+
+samsung_vfd:
+  id: vfd
+  uart_id: uart_vfd
+```
+
+For a complete device, copy [examples/samsung-vfd.yaml](examples/samsung-vfd.yaml)
+into your ESPHome config folder. Add the keys from
+[examples/secrets.yaml.example](examples/secrets.yaml.example) to your
+`secrets.yaml`.
+
+## Wiring
+
+The component only sends to the display. The ESP32's 3.3 V output is enough for
+most 5 V TTL inputs. ESP32 GPIOs are **not** 5 V tolerant, so never connect the
+display's TX back to the ESP32 without a level shifter or divider.
+
+| Display | ESP32 |
+|---------|-------|
+| RX      | GPIO17 (UART TX) |
+| GND     | GND |
+| 5 V     | external 5 V supply |
+
+The display draws more current than a dev-board regulator can comfortably
+supply. Power it from its own supply and connect the grounds together.
+
+To use GPIO1 (TX0, shared with USB logging), set `tx_pin: GPIO1` and
+`logger: baud_rate: 0` so log output doesn't end up on the display. If the
+display stays blank at 3.3 V levels, add a 74HCT125 or similar level shifter.
+
+## Configuration
+
+```yaml
+samsung_vfd:
+  id: vfd
+  uart_id: uart_vfd
+  cols: 20              # default 20 (1–80)
+  rows: 2               # default 2 (1–8)
+  send_newlines: false  # default false; send CR LF between lines
+```
+
+The UART must be 9600 baud with a `tx_pin`. The component requires a `time:`
+component in the config.
+
+## Actions
+
+| Action | Options |
+|--------|---------|
+| `samsung_vfd.print` | `text` (templatable). Optional `line:` (0-based) replaces one line. Without `line:`, the text is word-wrapped over the whole screen; `\n` forces a new line. Optional `centered: true`. |
+| `samsung_vfd.printf` | Shows the current time formatted with strftime, e.g. `format: "%H:%M:%S"`. Requires `time_id:`. Takes the same `line:` and `centered:` options. Does nothing until the clock has synced. |
+| `samsung_vfd.clear` | Clears the screen. |
+| `samsung_vfd.home` | Moves the cursor home. |
+
+```yaml
+- samsung_vfd.print:
+    id: vfd
+    line: 0
+    text: !lambda 'return "Temp " + to_string((int) id(temp).state) + " C";'
+- samsung_vfd.printf:
+    id: vfd
+    time_id: sntp_time
+    line: 1
+    centered: true
+    format: "%a %d %b %H:%M"
+```
+
+From a lambda you can call `id(vfd).print(...)`, `print_line(line, text, centered)`,
+`clear()`, `home()` and `line_text(line)`.
+
+Text is converted to one byte per character. Accented Latin-1 letters lose
+their accent (é → e), other non-ASCII characters become `?`, and control
+characters become spaces.
+
+## What the example config does
+
+- On boot: clears the screen, shows `Hello World!` for 3 s, then restores line 1.
+- Bottom line: a live clock, `%a %d %b  %H:%M:%S`, updated every second (SNTP,
+  Europe/Amsterdam).
+- Two Home Assistant `text` entities:
+  - **VFD line 1** (max 20 chars) is shown on the top line and kept across
+    reboots.
+  - **VFD status** (max 40 chars) shows a full-screen, word-wrapped, centred
+    banner for 10 s. The clock pauses meanwhile, then line 1 and the clock come
+    back.
+- Wi-Fi with a captive-portal fallback AP, OTA updates and an encrypted native
+  API.
+
+## Protocol
+
+| Bytes | Effect |
+|-------|--------|
+| `1B 40` (`ESC @`) | init / reset |
+| `0C` | clear screen |
+| `0B` | cursor home |
+| text | printed at the cursor; wraps to the next line by itself |
+
+Each update sends `0B` (home) followed by both lines, each padded to exactly
+`cols` characters.
+
+## Troubleshooting
+
+- **Line 2 lands on the wrong row, or text runs together:** try
+  `send_newlines: true`.
+- **The screen scrolls up a line after each update:** the display scrolls as
+  soon as the last cell is written. Use `cols: 19` together with
+  `send_newlines: true`.
+- **A stray character appears top-left:** the display doesn't treat `0B` as
+  home. Change `CMD_HOME` in
+  [samsung_vfd.h](components/samsung_vfd/samsung_vfd.h).
+- **Garbled characters:** check that `uart:` is at 9600 baud and that the
+  display takes 5 V TTL levels, not RS-232 levels. A real RS-232 input needs a
+  MAX232 inverter.