Home Made Anemometer

For quite a long time I have wanted an anemometer to add to our weather station, but they all cost money, and the other day I read about  a project that used bearings from a disk drive on a low friction project.  I was wondering whether I could use the motor as a generator, but I read different things about disk drive motors. Sometimes it is said that they are dc drives, and sometimes stepper motors with three coils in a star configuration (four contacts). The unit that I have stripped down only has three contacts so I am wondering if the coils are in a delta configuration, and if that is the case , can I use a pulse from one coil to measure the rpm?

Does anybody know anything about disc drives?  The other suggestion I have seen is to use a bike speedometer hall effect sensor to capture the rpm.

I have glued 'cups' to the disk and it turns freely, I also need to find a place where the wind is constant around here.

Then I'll feed it into a R-Pi and make the output readable.

Suggestion 1 from DLUG: We used a 60 tooth wheel which makes calculation easy as it can be seconds or minutes (RPS, RPM).  Could use opto-coupler or hall effect chips.

Suggestion 2: I'd use an "Opto Interrupter", or "Beam Breaker" rather than an Opto-Coupler, this would apply to both projects. In the case of the anemometer, I'd fix an IR Receiver above the spinning cup shafts and and IR LED below them and count the number of times the beam is broken, dividing In the by the number of cup shafts if you want RPM.

A useful place to salvage opto switches and LED sources are old ball driven (not the "laser" sensor variety" computer mice. Pickup from the ball is usually via a spindle with an interrupter disk and then a quadrature detector, use one channel for a directionless speed. You'll also find similar on the scroll wheel of modern mice.

Extra points for just hacking the anemometer vane direct into the mouse scroll wheel. Then wind speed is just how fast the second scroll input to your PC is spinning.

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Thinking back to my history with bar coding, and having an old ball mouse available, I made my own bars on the bottom of the disk.

I divided a circle into segments until I felt that I had enough (32) that I could darken in easily.

I cut out the bits marked with a blue felt tip pen.

I was going to use Pritt glue to glue the template on to the disk, but then thought that I might not be able to remove it, so cut out a bit more of the centre and used masking tape. I then used the automotive touch up paint to paint in the removed squares.

Remove the paper and this is what we have. It was a difficult picture to get because of the reflections from the silver surface.

Turn it over, the 'bars' are on the underside, protected from the elements, and here are the cups. They are made from a piece of plastic pipe  cut into thirds, and stuck with contact cement on to the disk.

Now I need to take the mouse circuitry and mount it below the disk. In it's mouse configuration it shines through the wheel, I need it here in a reflective mode. I have also discovered that the phototransistor on the mouse is two transistors with a common collector.

end for now.
My intention is to feed into a Raspberry Pi and then use WebIOPi to display the results on the tablet.