I never had an idea what to do with something like a Raspberry (I have my NAS server) or an Arduino device. But somebody told me about his Weather station project and that finally brought me on track, And therefore I proudly present my first ESP8266 microcontroller based prototype of a temperature/humidity sensor, reporting to Openhab where the data is presented nicely via web browser.
For easier prototyping the tiny ESP8266 I used a NodeMCU board, did some minimal C programming using Arduino-IDE and connected that to Openhab running in a docker container on the Diskstation.
Final goal: have three of those things (the plain ESP chip + sensor + some power supply) soldered properly on a small PCB that can be hidden in a wall outlet
observer language filtered content at https://firstname.lastname@example.org