Stiebel Eltron LWZ 130 and Home Assistant

I have a LWZ 130 ventilator that I’d like to hook up to Home Assistant to control the fan speed and to get other metrics like the inlet and inside temperature. The ventilator communicates with the display over I2C and, based on my previous investigation and the good work at https://github.com/kdarnok/lwz180, it looks straight forward. It’s I2C, but any device can broadcast at any time.

The bus runs at 5V, so my plan is to use a 5V-tolerant CH32V006, run Zephyr, implement a LWZ to MODBUS interface, and then use a ESP32 ESPHome device to bridge between MODBUS and Home Assistant. Adding a 5V tolerant interface directly to the ESP32 would be simpler but less fun.

I’ll also investigate using the CH32V006 internal bootloader to support remote updates.