Remixed this great Iris-Box to automate the ventilation in my rented place - which else is permanently on.
The Box opens after the light in the Bathroom is turned off and stays open for a limited time depending on the duration the light was on and humidity.
Arduino Nano / Mini
28BYJ-48 - Stepper Motor
ULN2003 - Driver Board
(Photoresistor, DHT11 - whatever you want as sensors)