Intro: Iphone Windmeter
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.
Step 2: Cutting and Welding
Cut the scoops off the 5ml spoons
Find a round plastic rod around the house. I used a thick spray bottle tube. Cut this about 60mm long
Using your soldering iron, weld the plastic parts together as shown. This was the first time I have tried it and it worked ok,
Step 3: Bearings
My bearings where 10mm outer diameter, 5mm internal and about 3mm high. I used an old pen as the bearing housing. It took a while to find a pen that fit well. I cut the section of pen about 15mm and inserted the bearings, then used the soldering iron to hold them in place.
Using the soldering iron I made two indents in the top of the section which the rod would locate into.
Step 4: Head Phone Jack
Cut the wire off the headset and check for fit in the bearing. If loose pack with insulation tap, if tight scrap a bit away with a knife. The bearing should sit a few mm above the phone.
Step 5: Clean and Paint
I used a dremel to tidy up the welds, then painted the whole thing it black
Step 6: Magnets
Attach the magnets to the outside of the bearing housing. They should be attracted bearings so will hold just fine. A drop of glue could be used after testing.
Step 7: Application
Download the free app from vavuud in the App Store. Plug you wind meter in the headphone jack and give it a spin. It should start displaying the wind speed. If it doesn't rotate one of the magnets and try again. My magnets sit about 5mm from the base of the phone.
Step 8: Calibration
For calibration, get someone to drive at 50kph and hold your phone out the window to check how accurate it is. Cup style anemometers are mostly linear so you should be able to apply this % change to wind speeds across the range.
Good luck, and if you can, please support the original Vavuud wind meter, they have put a lot of time and resources into developing the app.