HM-WIRED-ESP32 – ESP32 Ethernet/MQTT gateway for legacy Homematic Wired / HM485
Hi everyone,
I’d like to share a project I’ve been working on for my own Homematic Wired installation.
HM-WIRED-ESP32 is an open-source ESP32/WT32-ETH01 gateway that connects classic Homematic Wired / HM485 devices directly to MQTT and Home Assistant, without requiring a CCU or hm485d in between.
The project started because I still have a number of reliable Homematic Wired devices installed, but the original ecosystem and gateway hardware are getting older. Instead of replacing the wired installation, I wanted a small standalone gateway that speaks HM485 on one side and modern MQTT on the other.
What it currently does
- Native HM485 device discovery
- Automatic reading of device type, serial number and firmware
- Support for official HMW devices and selected HBW/Homebrew devices
- Reads channel states and HM485 status events
- Controlled write support for explicitly tested actuator profiles
- Persistent device database
- Ethernet as the primary network connection
- Wi-Fi fallback
- MQTT with retained states and availability
- Home Assistant MQTT Discovery
- Stable entity IDs based on device serial numbers
- Configurable channel names and semantic profiles such as window, door, contact, alarm or output
- NO/NC inversion per channel
- Web-based configuration
- German/English web interface
- Web OTA updates
- Configuration backup/restore
- Diagnostic/raw receive mode with transmit lockout
Home Assistant devices are created automatically through MQTT Discovery, so no custom Home Assistant integration is required.
The hardware is intentionally simple:
WT32-ETH01 + 3.3 V RS485 transceiver
The gateway communicates directly with the HM485 bus at 19200 baud.
At the moment, several original HMW devices and some HBW/Homebrew devices have been tested on real hardware. Write access is deliberately enabled only for device profiles that have actually been verified — unknown devices are never written to blindly.
The project is still evolving, and I’d especially be interested in feedback from people who still run larger Homematic Wired installations or have HM485/HBW devices that I haven’t tested yet.
GitHub:
Testing, protocol captures and additional device information are very welcome.