After testing the single modules for a sensor I finished the combination. Now the ESP8266 reads the temperature and humidity and sends them to the MQTT broker together with the actual voltage and the number of attempts to make a connection to the broker. The later is useful, because the ESP cannot reliably connect to the broker. I don’t know the reason, some investigation is necessary.
A photo and the circuit are in the earlier post.
As usual the code is on github.