Hello there,

Sorry for jumping straight in.

Dear Mehdi,
You could use a time duration with a little experementing but this will need a really tolerant motor else you may burn the winding if you continue driving it beyond end position of the valve.

A better option is to insert a shunt in the motor path and sense the current which dramatically increases when the motor stalls.

Use the voltage drop across the shunt as a stop signal for the processor.

You might need to do a little calculation based on the hardware, the motor, you plan to use.

The easier way out is to use a motor with friction clutch more popularly called slip mechanism. You can get hold of a "Window winder motor" from one of the car accessories dealers and the 'on-time' shall do the rest for you.

Hope this helps :)

Pratik.