Hello there people!,
I recently thought of an idea, of designing a timer switch for my parents washroom. cuz, they leave the fan on and forget it.
Later i realized that there are switches like that in the market already! (my idea is outdated
) 
Neways, Do you guyz know how these switches are created and designed? Like can somebody tell me the theory behind this timer switch ? For ex: like this one below:
I recently thought of an idea, of designing a timer switch for my parents washroom. cuz, they leave the fan on and forget it.
Later i realized that there are switches like that in the market already! (my idea is outdated
Neways, Do you guyz know how these switches are created and designed? Like can somebody tell me the theory behind this timer switch ? For ex: like this one below: