Summary

https://www.youtube.com/watch?v=iFnLUQjlFxI

This anemometer is intended to be used with an android phone.
It is mounted on its base via a balls bearing.
It's a 11x7x3 mm bearing extracted from the heads coil of an old HDD disk. Consequently it's a high quality bearing with a very small friction.
At the base of the rotor are inserted two rare earth magnets (4mmx2mm)
These magnets when rotating induce a variation of the magnetic field which can be sensed by the magnetometer of your smartphone.

I have also developed an android App which is able to detect the rotation speed using Fast Fourrier Transform.
It also allows to calibrate the anemometer using your GPS in an almost automatic way. You just have to attach the device to an electric bike and to drive at various (constant) speeds. Then data are captured together with quality indicators. You can then fit a curve with excel to get an almost perfect calibration.

This anememeter is nice but needs quite a lot of wind to start rotation...
A new one will soon be posted with a classical 3 cups shape.

Stay tuned !
it there : https://www.thingiverse.com/thing:2527455

This idea is not mine, Vaavud company sells this kind of anemometers : https://vaavud.com/products/wind-meters/

The red filament is provided by ArianePlast : http://www.arianeplast.com/
A really good quality one !