[FR] 1-Wire slave output after successful HomeKey auth (Loxone iButton integration)

[MadeInHelpup]

Use case

My ESP32 HomeKey installation is mounted at a door where WiFi reception is poor. Depending on MQTT or Home Assistant automations for the actual door trigger introduces latency and a failure mode: if the broker is unreachable, the door doesn't open — even though the HomeKey tap was valid.

Loxone is a common building automation system that uses a dedicated 1-Wire Extension for iButton (DS1990A) readers. The 1-Wire bus is wired directly to the controller — no network hop, no broker, no automation rules. Everything that works with a physical iButton key fob works with a virtual one.

Proposed feature

After a successful HomeKey authentication, the ESP32 emulates a DS1990A iButton on a configurable open-drain GPIO pin for a short window (default 3 s). The Loxone 1-Wire Extension polls the bus, detects the virtual iButton, and triggers access — exactly as it would with a physical key fob.

The ROM code is derived deterministically from the HomeKey issuerId via SHA-256, so:

• No manual mapping table needed
• One Apple ID (iPhone + Watch + iPad) always maps to the same ROM
• The Loxone assignment survives firmware updates

Optionally, ROM derivation can be switched to endpointId (per device instead of per Apple ID), giving per-device access granularity — useful if different family members should have different access levels in Loxone.

Key design points

• Physical iButtons and HomeKey coexist — the virtual iButton appears on the same 1-Wire bus alongside any existing physical key fobs. No migration required.
• Access control stays in Loxone — schedules, time windows, user logs, and access logic all remain in the Loxone controller. HomeKey acts purely as a protocol converter: NFC tap → iButton presence. No access decisions happen on the ESP32.
• No dependency on MQTT or Home Assistant — the integration works standalone. If the network is down, HomeKey auth + door trigger still work.

Why not MQTT?

	MQTT/HA	1-Wire
Network dependency	Yes	No
Latency	100–500 ms	<10 ms
Broker required	Yes	No
Works without WiFi	No	Yes (auth is local)
Existing Loxone setup	Parallel system	Native integration
Access logs & schedules	In HA/broker	In Loxone (unchanged)

Implementation

Working implementation exists in a fork: https://github.com/MadeInHelpup/HomeKey-ESP32-1wire-lox

• LoxoneOneWireManager — FreeRTOS task, GPIO polling, handles reset/presence/ReadROM/SearchROM
• Disabled by default, enabled via Kconfig + Web UI
• No new library dependencies — pure ESP-IDF GPIO
• Loxone 1-Wire Extension documentation: https://www.loxone.com/enen/kb/1-wire-extension/

Happy to submit a PR if there's interest. The feature is fully opt-in and adds no overhead when disabled.