Hello!

I am intersting is it ok to use magnetic compass shield as a simple hall sensor.
Finally I need to count RPM's of bike's wheel.

Thank you

If you're able to set up the sensor to get the maximum data output rate of 160Hz, I think it's possible for it to work, especially if the magnet is close to the hub of the wheel- you want as fast as possible so that the sensor does not 'miss' the magnet. After that, it's easy to calculate speed with a bit of math.