Then I found a Blauber UDP -> MQTT service https://github.com/mhbosch/vent_to_mqtt - it kinda worked, but it was in German and had some bugs. So, I forked it (https://github.com/gacha/vento), translated and fixed some issues.
And at last, there is the #shelly script which reads the kitchen hood power consumption and sends commands to the fan https://gist.github.com/gacha/0e0aa95d5b69623f16f426c84c3ed5eb
Dieses Projekt kümmert sich darum, Baulberg Ventilatoren mit WLAN Schnittstelle in eine Hausautomation mit MQTT Dienst zu integrieren. - mhbosch/vent_to_mqtt
Finally, I made my Blauberg fan to automatically supply air when I turn on the kitchen hood. Before that I had to open the window a little, otherwise sometimes the draft was so strong that it pulled smoke from chimney.
The Blauberg VENTO Expert speaks only UDP, so I could not control it directly from my Shelly MiniPMG3.
Gacha
Ademant
