Problem: So I’ve been taking walks with my dog, Marcus and my Arduino pedometer.
Out here in the high desert in January, it gets cold and a little wind creates a cold wind chill factor. I’m a LAZY OLD GEEK and would like to know what the wind chill factor is.

Solution: I’ve always wanted to build a weather station so I decided to make an Arduino wind anemometer to measures wind speed and a thermometer. An instrument that measures wind speed is called an anemometer. Then the Arduino can calculate wind chill.

Wikipedia Definition: Wind chill (often popularly called the wind chill factor) is the felt air temperature on exposed skin due to wind. It measures the effect of wind on air temperature.

LAZY OLD GEEK ‘facts’: Any object, e.g., a car is not affected by wind chill. If the temperature is 10F, it doesn’t matter if the wind chill is 10F or -40F. Wind chill is the apparent temperature felt by humans and animals. Or I should say some animals. My dog, Marcus has a nice fur coat and is part husky. He doesn’t feel it. He doesn’t care if it’s -40F wind chill and seems to prefer it. Now, I, on the other hand won’t venture out if the wind chill is -40F. But if it’s -10F, I might wear my full face mask (see picture) and venture out. I don’t like to wear it because it’s uncomfortable after a while so it’s helpful to know what the wind chill is.

So that’s not a great reason to build a wind chill machine but I’ve always wanted a weather station and this is a good starting point. My weather station is designed for the U.S., so I use Fahrenheit and MPH.

Attention Readers: If you want to duplicate this project, you will need a laptop with a USB port and a motor vehicle to calibrate the wind speed. Another problem is finding the cups for the anemometer. Many Instructables readers seem to be good at improvising. Aluminum is preferred but plastic should work also. For the innovative readers, I’ve provided some hardware and software tips on how to design your own anemometer. For example, the software could be adapted to an LED or LCD display for a standalone instrument.

Step 1: Parts List

Here’s a list of the parts I used:

USB Freeduino kit (Arduino-clone) $22.50
AdaFruit DIY shield $6.00

1/2” right angle
1/2” T
10 feet 1/2” PVC
2” PVC end cap

5-16 x 3” bolt
5-16 nuts and washers
8-32 x 4” bolts
8-32 nuts and lock washers

2 small magnets (10 for $1 at Harbor Freight)
1 Inline skate bearing(Size 608Z)($1.36@)
3 Aluminum balls SuperBubble, LemonHead
Honeywell SS461C Hall Effect IC($1.86 Digikey)
50 feet Telephone cable ($3.00 4 or 6 wire)
1 MCP9701 Temperature sensor($0.30 DigiKey)
2 telephone couplers ($1.00@ dollar store)

Prices US dollars February 2011
The total is about $15 plus Arduino stuff.

Soldering tools
DMM Recommended
Drill/drill press
Socket wrenches
<p>Shouldn't MPH or KPH be determined by taking the circumference of the outside of the cups - call CUPC and use below:</p><p>CUPC = pi * Diameter of circle (either inches or centimeters)</p><p>CUPC * RPM * 60 / (5280 * 12) or (1000) depending on whether you want MPH or KPH?</p><p>Why would the car calibration method be needed? Or is the above formulate not accurate?</p>
<p>I am not a physicist but I'm pretty sure that wouldn't work. As I see it some of the problems are that the wind is not blowing on the cup at right angles most of the time. Sometimes the wind is actually blowing on the back of the cups. So this suggests that the shape of the cups must also be a factor. </p><p>Also the length of the arms will make a difference. I am also pretty sure that the number of cups (2, 3, 4) makes a difference. </p><p>I tried to find some formulas for calculating this but what I did find, I couldn't understand.</p><p>Also, it seems like the rotational friction is a factor. If the friction was higher it would take higher speed wind to get it moving. </p><p>Anyway, that's why I used the car calibration.</p><p>LOG</p>
I realize the arm length will factor in, as that will determine the radius of the circle for computing the circumference.<br><br>The way I see it, the distance one ball will travel in one revolution would be the circumference of its circle, making it linear. If you know how many revolutions in one minute, you can calculate distance traveled x 60 to get the distance traveled in one hour then divide by 5280 to covert the number of miles per hour. If your circumference was in inches, then divide again by 12 for 12 inches in a foot.<br><br>Curious now, if you apply this to your model at a specific RPM will the above formula come close to your car calibration?<br><br>Rotational friction, guess you could calculate that based on a difference between the car calibration and the math formula, which expects no friction. But i would think it wouldn't make a big difference especially with the bearings.<br><br>One thing that is difficult is that counting the revs in one minute can be scewed in that the wind speed won't be the same for the whole minute. Kind of like looking at a heart monitor, it really only shows the pulse at that exact second, it bases it's rate on the previous beat and the current beat, as if it were like that for a minute. 60 divided by the Number of seconds between beats is what is displayed. <br><br>It might work since all three arms are the same angle of the circle, if you had a magnet on each of the arms, thus each revolution would trigger 3 hits on the Hall effect. Now take 60 / time in seconds between 2 hits / 3 since your now getting triggers from each arm this will give you an Estimated RPM based on the last partial revolution, which would show varying wind speeds better.<br><br>I'll be working on my model over the next couple months, so I'll have to update you on what I find using both calibration methods.
<p>Just wondering if you figured out the 3 magnet variation of your anemometer project. I am building one myself using the HDD drive motor as the bearing unit and I 3d printed a 3 cup anemometer thingy. I am still waiting on my hall effect sensor but thought I would ask before hand to see if you had any more input.</p>
<p>I don't think you need three magnets. You only need to count the revolutions of the anemometer and one magnet would be enough. I mostly used two magnets so that the weight was balanced.</p><p>LOG</p>
<p>I did a little more internet research and it seems some people agree with you. But I have one question which was better stated by someone else:</p><p>&quot; I would imagine that your anemometer will give significantly low values. Note that when the wind is pushing on one of the cups to make it rotate counterclockwise, say, then the wind is simultaneously pushing on a cup on the other side trying to make it rotate clockwise. The only reason the thing rotates is because the cup is more streamlined in one orientation compared to the other. Even without any friction in the system, I don't see how it would ever rotate at a speed such that the cups are moving at the wind speed.&quot;</p><p><a href="http://www.physicsforums.com/showthread.php?t=653605" rel="nofollow">http://www.physicsforums.com/showthread.php?t=6536...</a></p><p>As a theoretical example, if the cups were replaced with flat disks, the anemometer wouldn't move at all.</p><p>So in the cup design, how do you calculate in the wind force blowing on the rounded side of the cup??</p><p>Anyway, it might be fun to do some experimentation with this. Unfortunately, I'm too LAZY and OLD.</p><p>LOG </p>
<p>I thought about the opposite cup issue as well, which is why I think they go with cup shape, or at least sphere shape, which should be aerodynamic enough to have the air go around it , similar that bullets and such are that shape as well. But you think a pointed shape like a rocket would be best, but it might be a safety issue. That may also be a basis on why you read odd number of cups was better than even, so one cup is never 180 degrees from the other. I thought it was interesting that you wrote that, as when I was looking into wind turbines, I had read the same thing about even number of blades vs odd number; also read it didn't matter, but I don't think I've ever seen a fan with even number of blades. </p>
<p>What do you think about this idea:</p><p>I'm concerned about bearing friction in light wind. I am considering using an old computer fan brushless motor as the bearing system. It is almost frictionless after you get is past the very slight mag force. </p><p>I will probably remove the fan blades and mount some sort of plastic connector with super glue to accept the shaft to my wind prop. Key will be getting mount centered.</p><p>BTW: I bought a wind cup unit from a commercial marine parts department for $10. It already has the magnet mounted. </p>
<p>Would you mind sharing the source for your wind cup unit? 10 bucks sounds like a deal. What dimensions of the cups and radius?</p><p>Doug </p>
<p>I got these from my cousin but they were originally just containers for candy and I haven't seen any since. They're about 2.7&quot; diameter.</p><p>LOG</p>
<p>Sounds like a good idea. But I agree you may have problems getting it centered and balanced.</p><p>Good luck.</p>
<p>In your calibration code you're counting each time a magnet causes the sensor to go from high to low. Since there are 2 magnets why aren't you dividing the RPM count by 2? Seems like you're double counting for each revolution.</p>
<p>That is a good question. It's been a while so I had to review this Instructable. The Hall Effect I am using is a latching device and the magnets are opposite polarity. So one magnet sets the Hall Effect High and the second magnet sets the Hall Effect low. I only count the High to Low transition, so it only counts once per revolution.</p><p>LOG</p>
<p>Thanks for the Instructable! I am just starting to build my own weather station, and am using yours as the foundation. You mentioned difficulty in finding the cups. Well, after some searching online, I found the following:</p><p><a href="http://www.bakedeco.com/detail.asp?id=19654&categoryid=0#.VPNl7uH4b_x" rel="nofollow">http://www.bakedeco.com/detail.asp?id=19654&amp;catego...</a></p><p>It is a company that sells aluminum cake hemispheres in different sizes, and they are reasonably priced. Just bought 3 that are 2.75&quot; in diameter.</p>
<p>Nice find. They should work fine.</p><p>I'm still using my originals.</p><p>LOG</p>
I am new to arduino I designed anemometer cup wind vane &amp;tipping bucket.... for my project I have to get output in 16*2 LCD display can u send me complete arduino codings for it
Sorry, can't do that.<br><br>LOG
<p>If you mount it on your ROOF you will get misleading readings from it!</p><p>As the wind hits your house (Doesn't matter if flat roof or a sloped, worse on a sloped) the wind will accelerate due to hitting an immoveable object.</p><p>Best way is to mount at least 10 ft. higher than your roof and about 100 ft. from house OR mount 3 units and average the output from them.</p><p>Also if mounted high you will have very much different winds than at ground level.</p><p>A friend of mine living in NE AZ has a wind charger mounted at 30 ft. above ground, I have seen it screaming in a wind but not even a breeze at ground level, also I have seen it barely turning and you could hardly stand on the ground for the wind, and weirdest of all wind on ground coming from one direction and at 30 ft. from a completely different direction!</p>
<p>Thanks for the info. Since I'm Lazy and Old, all I care about is an approximate wind speed and and wind chill. Mostly what I use it for is to guess what I should wear when I walk my dog. </p><p>LOG</p>
<p>Can you send me arduino code for yours anemometer? I'm making my one weather station so that will help me a lot! Thanks!</p>
<p>The sketch is in Step 7:</p><p>MTSAnemometer.zip.</p><p>LOG</p>
<p>You didn't work in arduino? Sorry, I can't find code for this kind of anemometer.</p>
<p>You have to unzip the file. Then it has the PDE file which is an Arduino sketch.</p><p>LOG</p>
<p>Oh, I didn't see! Thank you very much! Can you just show me where did you put magnets? </p>
<p>Thank you very much for this instructable! I've had a ball incorporating your windspeed code into an anemometer setup I have created. The code helped me advance my knowledge of C programming for arduino also. Had fun setting up my Hall sensor too. Again - great job and thanks! </p>
<p>Glad it was helpful.</p><p>I started using the Arduino as I found it much easier to program than other microcontrollers plus there is so much support on the Internet. It's usually about the right level of difficulty for this OLD brain.</p><p>LOG</p>
<p>LZ,</p><p>How did you test the SS461C? Is it possible to attach to Arduino and pass a magnet by the chip to get some sort of reading?</p>
<p>Yes, it is. What I did was hook it up to 5V as shown in the schematic. Then I put a DMM on the output pin and watched the voltage. I passed a magnet close to the SS416C and the voltage dropped to around zero. Then I flipped the magnet over and passed it near the sensor and the voltage went back to 5V. </p><p>You can also do this with the Arduino but you'd have to write a sketch to display the output.</p><p>LOG</p>
<p>Very nice project! Just to be funny, and since you are the Lazy Old Geek, have you looked into acquiring a &quot;Weather Rock&quot; or the newer model &quot;Weather Cat&quot;? If I were to replicate this project, it would involve a dozen trips to the hardware store and 10x the money I really needed to spend. A weather rock will save you all that trouble. Cheers! :D</p>
<p>I'd never heard of Weather Rock. I like it. I couldn't find Weather Cat but maybe that's cause I'm a dog person.</p><p>I like the Weather Rock as it is scalable and portable so I could take it on dog walks. And it's so versatile, like tornado and earthquake warning.</p><p>LOG</p>
You can hang the Weather Cat outside your window or from a clothesline by its tail, so it's more convenient. ;-)
<p>Ah, makes sense.</p><p>LOG</p>
<p>LZ,</p><p>Do you have a more complete version of the &quot;sketch' you used with anemometer?</p><p>I'm totally new to programing.</p>
<p>If you want to get real accuracy in your anemometer read this and plug in all the data: </p><p><a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3386737/" rel="nofollow">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC338673...</a></p><p>The math is mind numbing. In a nut shell I doubt that there is even 5% difference.</p><p>If I see small dogs and toupees flying by and my wind cups are a blur i will assume that the wind is blowing really really hard. </p><p>ken</p>
<p>You are right about the math but for me, also the physics terminology. So all I care about is if it's too cold for me to take my dog out for a walk and what I should wear. That has so many other subjective factors involved that wind speed is a minor factor.</p><p>By the way, I changed my temperature sensor to a DS18B20 as it seems to be calibrated over a wider range. Of course, right now I have three outdoor temperature sensors and they often vary 5-10 degrees.</p><p>LOG</p>
I trust they are all oral. :-)<br><br>Just made big change to my wind cups mount. I post photo when more complete.<br>kaw
<p>M---777</p><p>Greetings, </p><p>I'm working on building a anemometer much like the one you have built. The SS461C- DAMN it's small! </p><p>I'm thinking of isolating it in a piece of plastic tubing. At issue is how did you protect the leads from breaking? </p>
<p>You are right, they're really small. I don't remember how I did it but I think I used some electrical tape to insulate between leads and heat shrink tubing over the whole assembly. The leads are pretty firmly attached but if you're concerned, you could use hot glue or even epoxy, which I think is what most semiconductors use in their packaging. </p><p>LOG</p>
Ok, I can see if the winds are light it might be difficult but in regard to the friction if the motor you could use a small motor lets say out of a cd or DVD drive? Just thoughts here.
<p>I think cd/dvd motors are brushless. Apparently they have magnets in them so turning them with the wind should generate some voltage but I suspect it would be AC. It might be possible to make it work but it's beyond my expertise. </p><p>LOG</p>
I'm a newbie to Arduino but have always had an interest in electronics. Maybe this is a really dumb question but couldn't you also use a motor and measure the volts it generates and convert that into mph or in my case km/hr? Just working on my own weather station and am looking for ideas for an anemometer. <br><br>Thanks.
<p>A DC motor might work but I have my doubts. Two concerns I have is that you might need fairly large cups to overcome the friction of the motor. And it would be hard to measure small voltages when the wind is light. </p><p>LOG</p>
<p>Saved my frail by finding the Honeywell SS461C. I was toying with using discarded motor which added all kinds of new problems.</p><p>You've done a really good job of describing all steps in this project. </p><p>Thanks,</p><p>Ken Wood</p>
Thanks for the instructable. I'm working on a similar project, but instead of hall effect switches I'm using a home made optical encoder for the interrupt pulses, and my anemometer cups are bring printed on a makerbot by a friend. I'm going to have two 'wheels' one above the other, offest by 1/6th of a rotation and separated vertically by about 1.5 cup diameters. For the wind vane I'm also using a binary optical encoder to get 16 positions. For the wind vane I'm using the bearing from an old hard drive head assembly. The head assembly itself is going to support the bearing. and the anemometer bearing is the spindle bearing from the same HD.
Nice anemometer!<br>The way-too-high or -low temp readings you're getting might be from the sensor exposing to direct sunlight or too much wind. I've made dozens of thermometers using the LM35 series of Temperature sensors by National and I've noticed when the sun shines on the sensor, no matter how cold the air is, the reading goes up abnormally high. The same when the wind blows over the sensor. I've had readings of 50&deg;C in a fresh (16&deg;C) morning when the sun rises and reaches the sensor. Heat reflection also gives these readings. I had a sensor 2 yards from a sun-bathed wall and the thermometer went up to 36&deg;C in a 20&deg;C day. Sometimes the error is corrected encapsulating the sensor in white heat-shrink tubing. Maybe painting the sensor white works too.<br>Nice anemometer indeed!
Thanks. I've actually added two features to my weather station:<br>http://www.instructables.com/id/Arduino-Weather-Station-Part2/<br>http://www.instructables.com/id/Arduino-Weather-Station-Part3-Rain/<br><br>I don't think my readings are related to sun or wind. The ones I've noticed are just one sample where the one before and after seem to be okay so I suspect that it's either an intermittent connection or glitches in the serial communications. However since they don't happen very often and it's just for my personal use, I pretty much ignore them. <br><br>I usually leave it running 24/7. Occasionally, the Arduino stops communicating all together and I have to reset it. <br>And once, I had to replace the Atmega chip. I'm fairly certain it was lightning.<br><br>LOG
Cool project!
Thanks, I enjoyed making it.<br><br>Lazy Old Geek

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Bio: Lazy Old Geek
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