Picture of Digital Anemometer (wind meter)
Build your own digital Anemometer by using a bike speedometer and other inexpensive parts.
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Step 1: Parts

Picture of Parts
Major parts needed:

Wind cups, part #7903 from Davis Instruments (, cost around $15.
Bike speedometer from any bike shop
2 ball bearings, 1/8" ID from any hobby shop (used in radio control models)

Once you have the parts, this project should take less than three hours to construct I think.

Notes on the parts:

For the Anemometer head we use the "wind cups" from Davis Instruments. This is a significant time-saver over constructing your own wind cups! Davis sells anemometers and weather stations, their complete devices cost around $200 i think. So if you'd rather just buy a nice anemometer, i'd highly recommend theirs. The wind cups we are using are considered "replacement parts", you might need to tell them you have one of their weather station products but you broke the wind cups. I don't think they really care though. Anyway, the wind cups are a nice plastic assembly, about 6 inches in diameter with three cups attached to a central hub. The hub has a 1/8 inch hole for a shaft, and it has a magnet embedded in it for use with a magnetic reed switch for detecting rotation. They have a photo on-line of their entire wind-assembly, the wind-cups you'll be getting are just the piece at the bottom of this assembly.

In a future version of this project I hope to make my own wind cups. I've tried a couple designs out of cut-up beer cans and soda bottles, but have not gotten anything that works well enough...

It's quite convenient to use a bike speedometer here, because they detect bike speed using a magnetic reed switch. On a bike, you attach a magnet to one of your front wheel spokes and then you attach the reed switch to the front fork. Every time the magnet on the spinning wheel passes the reed switch, the switch pops closed and then open again. The speedometer detects the open-close-open of the switch, and speed is computed by how often the switch is activated.

You can also find the relation between RPM and wind speed in the specification guide of the Davis anemometer (where the cups come from)

1600 rev/hr = 1 mph

V = P(2.25/T)

V = speed in mph

P = no. of pulses per sample period

T = sample period in seconds

Then if you know the wheel diameter used by your bike meter, you have everything to deduce the wind speed, you don't need to calibrate it.

rgerber13 years ago
while it looks fun to build I bought one from Ebay and it was 20 bucks. I love to tinker but sometimes you just cannot beat the Chinese for price...

ckgreenman4 years ago
I had another thought.  I read elsewhere that after a while the reed switches will wear out especially if you leave the sensor up all the time and live in a windy area.  Seems to me it might be possible to use a magnet and a hall effect sensor. 
dsnevin5 years ago
Good project!
The bearings are called: Sealed Bearings -- consisting of numerous ball bearings, encased in a metal cartridge.
trisampson5 years ago
You could also... duh... use another bike computer and ride around the block and compare the values. GPS is also a possibility in that regard. On the other hand to average out any values to account for any wind, using cruise control in the car might be helpful, but using GPS to nail your speed would probably be best.
Hello, I am interested in making this anemometer, but i was looking on the Davis site, and they have 4 differnt wind cups. 2 different sizes for the part #07903, but small size or large?
static7 years ago
Out here where the owls get the chickens. Some build whirligigs out of bike wheels a cream separator plates. I have toyed with the idea of using a bike wheel and axle for the rotor. That way the digital read out could be used as is, using no math.
Marcos8 years ago
When counter-boring holes, if you drill the larger holes first, it's a snap to have the smaller one be concentric, as you'll still have the bottom of the hole, and it will have the center point ready-marked and "center punched." But you knew that already, yes?
dan (author)  Marcos8 years ago
you need to drill the small hole all the way through first. if you drill the two large holes part way, then try to drill the small one from one end, it is never going to end up at the exact center of the big hole on the other end.
Marcos dan8 years ago
Aha, looks like I was not paying enough attention. I was thinking of drilling from one side only. I figured you knew better. ;-)
bubbagump8 years ago
Ummm, "Ball" bearing? You sure about that?
Very cool, elegant in it's function & simplicity. This would go well with a digital weather vane a friend built using a nifty bcd encoder (to support the vane & read it's position) feeding a bcd-to-octal or -hex decoder which lit LEDs set in the compass rosette pattern. (Sadly, I've been living vicariously through other peoples projects, that's why I was so happy to stumble on this site.)
Hammer71379 years ago
An idea for home-made wind cups...those plastic easter eggs that break in half have a nice parabolic shape that could work. Their strength and durability might be questionable, and I haven't come up with a mounting design yet but it might be a start. Actually, it would probably be easier to use a more durable plastic ball. I plan on doing a quick test using plastic "k-nex" toys or legos.
Pauwcarn9 years ago
This is a great idea! I have found that a wealth of miniature ball bearings can be had from salvaging discarded VCR's and hard disk drives.