# CLAUDE.md

ESPHome external component for a Samsung 2×20 serial VFD (5 V TTL, 9600 8N1,
write-only). It is consumed from git by an ESPHome server through
`external_components: source: github://...`, so the layout must stay
`components/samsung_vfd/` at the repo root.

## Layout

- `components/samsung_vfd/__init__.py`: config schema, codegen and the action
  registrations (`print`, `printf`, `clear`, `home`).
- `components/samsung_vfd/samsung_vfd.h`: the class, the control-byte constants
  and the templated action classes.
- `components/samsung_vfd/samsung_vfd.cpp`: the shadow buffer, word wrap,
  UTF-8 → single-byte sanitising and `flush_()`.
- `examples/samsung-vfd.yaml`: the full reference device config. It pulls the
  component from GitHub; for local work, switch to the commented
  `type: local, path: ../components` source.

## Design rules

- `lines_` is the screen as it should be, each line padded to exactly `cols_`.
  Every change goes through `flush_()`. It rebuilds the payload, returns early
  if the payload equals `last_payload_`, and otherwise sends `0B` (home) plus
  the payload. Don't clear before redrawing: that causes flicker.
- Anything that changes the display out of band (clear, init) must reset
  `last_payload_` so the next flush retransmits.
- Text sent to the display is one byte per character; always pass it through
  `sanitize_()`.
- Keep the protocol constants in `samsung_vfd.h`. Only `ESC @`, `0C` and `0B`
  are known to work.

## Checking changes

Hardware isn't available to Claude, so validate with ESPHome itself:

```
pip install esphome
cd examples
# switch external_components to the local source first
esphome config samsung-vfd.yaml     # schema check
esphome compile samsung-vfd.yaml    # full C++ build
```

`secrets.yaml` is gitignored. Copy `examples/secrets.yaml.example` to
`examples/secrets.yaml` to compile.

Follow ESPHome C++ style: `this->` on members, a trailing `_` on protected
members, and the `esphome::samsung_vfd` namespace.