But this only measures wind speed, right? Well, I discovered someone invented a way to use them to measure direction also. I think his name is Derek Weston, and he called it a Rotorvane Anemometer. Unfortunately his original web pages describing it have disappeared, but here is one of several DIY versions based on it.
The technique would involve modifying just one of the 3 cups, adding a small fin to it. This would deliberately "unbalance" the anemometer, so that it does not spin with a constant speed, even in a constant wind. As the extra fin sweeps upwind, the anemometer slows down slightly. As it then sweeps downwind, it speeds up slightly. Overall the speed of rotation is about the same, but within a single rotation there is variation.
To use this variation to resolve the wind direction, it will be necessary to measure the rotation speed in several parts (at least 3 I guess) within a single rotation. I am thinking that could be achieved using the Maplin unit by replacing the reed relay pcb with one containing 3 or more hall effect sensors at 120 degrees to each other. The time taken for the cups to rotate each 120 degrees could the separately measured.
like the concept. Should be possible. I am wondering how the natural fluctuations in wind speed will affect the measurements
iso magnets you could use a disk with holes and use (LED) light to get rotation speed. connect this to the interrupt pin of the Arduino and you can get accurate timing inthe order of 0.1 millisecond (or better). Check attachInterrupt()
Sounds dicey to me, why not play it safe with just an ordinary 4 bit, 16 direction detector?
Are you putting your life in danger with this idea?
Your sense of economy seems rather dangersous?
robwlakes:
Sounds dicey to me, why not play it safe with just an ordinary 4 bit, 16 direction detector?
I already have one of those. This is more clever and interesting.
robwlakes:
Are you putting your life in danger with this idea?
Your sense of economy seems rather dangersous?
No, I'm quite sure my life is in no danger from this idea. I think you are confusing me with Dr Frankenstein. My plan involves no lightning or grave robbing whatsoever.
I may waste a few £, but the Bank if England will be safe enough, I think.
Please allow those with more constructive opinions to respond.
PS. I don't like your picture. I hope you didn't kill that bird yourself.
I meant relying on such a system say for navigating a boat on the open sea? A bit of a fin on an anemometer does sound a bit of a flimsy system?
Ah yes the bird hit our window at full speed and was rather groggy when the photo was taken on our deck. It did fly off and I hope made a full recovery. At the time it just seemed to show its feathers off to a good angle. I had never thought people may have thought I had killed it for the photo, in fact is was the contrary, I was guarding it from any cats until it could fly off.
Nice of you to be concerned. A juvenile Crimson Rosella, the mature birds have mainly crimson and blue feathers. Probably still at the stage of figuring out what a window is.
It seems to me, even if you want to bother polling the device often enough to observe the oscillation in rotary speed of the anenometer, you will have trouble calibrating that oscillation to an actual wind direction. Particularly as any relationship you determine between the phase of the speed fluctuation, and the wind direction, will probably only apply at a particular wind speed, and will probably vary in an unknown, non-linear, way.
Determining the actual relationship between a well-balanced anemometer and wind speed is a non-trivial problem, by deliberately unbalancing the anemometer, you are making that problem worse.
robwlakes:
I meant relying on such a system say for navigating a boat on the open sea? A bit of a fin on an anemometer does sound a bit of a flimsy system?
Well, Raymarine make/made one, and they have an excellent reputation to protect.
robwlakes:
Ah yes the bird ... I had never thought people may have thought I had killed it for the photo
Sorry if I sounded a bit angry Rob, I mis-read the whole direction of your post and thought you were having a go at me. I should have a karma point deducted for that.
Nah no offence taken I could see my statement was typically vague as I am want to do ("I know what I mean like?" :|).
I think the comment of un-balancing the cups is a good comment. However in a properly designed one could the cups be balanced for weight, but have different sizes to create an asymmetric wind profile? So two thicker walled smaller ones and one bigger thin walled cup? Any unbalance, weight or profile, would also need a much better bearing to cope to with it. Also the response at slow wind speeds could be a problem, as the asymmetry would hinder the anemometer spinning up?
One way to try it would be to use an Oregon Scientific design where the wind direction vane has a magnet in it so it switches an array of 8 or 16 sensors underneath to indicate direction. Putting cups on the top of this would then have a spinning 16 sector detector where the sector of the increased speed could be detected. Obviously the original circuit could not handle this but the layout of the detectors could be interesting.
At high wind speeds the speed up / slow down will be buried in the noise, this
method only works at low wind speeds and stops the cups rotating at all in
very low speeds.
You just need a separate vane with an absolute encoder (magnetic rotary
encoder chips are available these days which would be a good match
for the task - surface mount though).
