automatic blind hooked up to existing projector screen

Hello, My name is Chipsy, I am French and have been reading instructures for at least two years, this is my first entry on this site.
The reason why I did this project: I have a small home theater system in my living room with a projector and an electric projector screen for Taiwanese businessmen.
I have a big mirror on the wall on my left that makes the room brighter, but when watching a movie you want a dark room where we can see the reflection of the movie (very annoying)
So I installed a gray/black blinds in a DIY shop, which is a good solution.
Now I have to put it down with my hands every time, so it\'s hard for me to \"why not motorize it \"?
\"Why don\'t I take the mirror off?
The mirror is embedded on the wall and it expands the living room when not watching a movie, which is good.
So I want to keep it, but can still watch a movie without seeing the mirror reflection.
The existing controller of the projector screen is the integrated circuit that drives the screen motor.
It is controlled by RF remote control.
Igrabbedmy multimeter, able to find 12 V on relay coil.
So I welded a wire on each relay coil (
When the relay is \"off\", the terminal that drops to 0 v)
Plus a wire from GND.
The idea of this circuit is to be able to \"sense\" whether the projector screen is up or down with Arduino weither.
This circuit works like this :-
When the current is provided at the bottom of the transistor, the current flows from Arduino 5 v to GND, and the Arduino input is high. -
When the current is not provided on the base of the transistor, the Arduino input is connected to the GND and then the input is low.
I used two transistors. TIP122)
, One relay per projector screen.
Now I can know when the projector screen drops and when it rises.
OK, now we can tell the blind motor to drop when the projector screen drops, and we can tell him to rise when the projector screen goes up.
But how do we know when to stop?