Simple proof of concept wind meter using your phones compass. The spinning magnets change the magnetic field around the phone which is picked up by your phones magnetometer.
Check out vavuud website to look at real deal which you can purchase to support the application. They have tested their one in a wind tunnel so it's quite accurate.
Step 1: Shopping
From you local dollar shop you should be able to get most of the stuff you need.
2 sets of measuring spoons, I used 2 x 5ml spoons.
Neodymium magnets (the shinny strong ones) I got mine out of a fishing game
Small bearings, I got mine for a couple of dollars from a model shop, but you can get them from some toys as well.
A few old pens.
3.5mm headphone jack ( cheap headphone will work)
Other tools you need are scissors, soldering iron, small hack saw.