• http://esp8266.co.uk/tutorials/introduction-to-the-gpio-api/
• http://www.nodemcu.com/docs/gpio-module/#gpio-module-gpio-trig
• nodemcu/nodemcu-firmware#179

https://github.com/marcel12bell/feinstaub-app/blob/master/init.lua

seems wrong, because no interrupt is used. one value each second via alarm timer.