Since a lot of time I have a simple question that I can`t find an answer that convince me. Basically the title, when use microcontroller, when use microprocessor and when combine both.

For example, an easy project that I want to do, a weather station. If I'm not mistaken, I can do it with both separately, therefore, which one should be used?

Something I understand (I think) is that the arduino is useful when you want to sample constantly and the RPi for specific moments.

I had other projects like, control lights remotely, know the flow of water through the pipes, water station of wells to know, temperature, turbidity, pH... I think I could do it with both options, therefore it is clear that there is some concept that I do not understand.

Sorry if is silly question but I need to clear this doubt once and for all.

For a long time I have had a simple question to which I can't find an answer which convinces me. Basically the title: when should I use a microcontroller, when should I use a microprocessor and when should I combine both.

For example, an easy project that I want to do is a weather station. If I'm not mistaken, I can do it with both separately; therefore, which one should be used?

Something I understand (I think) is that the arduino is useful when you want to sample constantly and the RPi for sampling at specific moments.

I had other projects, like controlling lights remotely, knowing the flow of water through the pipes, water station of wells to know, temperature, turbidity, pH... I think I could do it with either option, therefore it is clear that there is some concept that I do not understand.

Sorry if is silly question but I need to clear this doubt once and for all.