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Wind speed and direction sensors (ec1WindSpeDirMapl.htm)

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It seems a long time I've been looking for wind speed or direction sensors, of a simple design, at a good price for the hobbyist. I want to connect them up to an Arduino, but they could be connected to a Pi, or lots of other things. There's a lot of fun in "making your own"... but if you can get the sensors made up for you, there's still lots for you to make, in the things connected to them. They are WELL worth the money. Trust me. Make your own? Been there... done that... don't want to do it again!

In April, 2016, I obtained some nice sensors from the UK electronics store "Maplin". Three windspeed sensors, with p&p came to about $15. One of the direction sensors, with p&p, about $10. Part codes: N82NF and N81NF, respectively.

Maplin only sells them for use with their weather stations (N96FY and N96GY), but both seem eminently hackable. The point of this page is to save you 15 minutes with a meter.

The two sensors mentioned here are often sold as part of a "set" of sensors... speed, direction, rainfall. But, as at Maplin, sometimes you can find individual units for sale on their own.

In the US, I have seen what looks to be the same sensors sold as part of "complete sets". These are nice, if you want to go that route. Besides the wind speed and direction sensors, you also get a rainfall measuring device, and "arms" to mount everything on. (The provision on the wind sensors for attachment to the "arms" is good... and easily adapted to other mounting choices.

At 1/17, what seems to be the same sensors, as parts of a complete kit were available from Argent ($68 plus p &p at 1/17) and Sparkfun ($77 plus p &p at 1/17) also sells what, I think, Argent created. Both sites have useful technical detail, to tell you things that I've missed or not explained successfully. Sparkfun, at 1/17, has been my main "go to" for Good Stuff for some time. They give good documentation, ship quickly, are reliable. I pay a slight premium, yes... and it is worth it. (I do tend to buy simple components, e.g. sockets for ICs from "the cheap" alternatives... and sometimes "pay" in other ways for my parsimony.) Argent has been selling the device since at least August 2011.. and they haven't raised the price since then, either! (Argent lists both the anemometer and rain gauge separately, as "replacement parts". Ask them nicely, and who knows... they might sell the wind direction sensor separately, too.)



Wind Speed Sensor

The speed sensor has a reed relay in it... you can hear it click. In early investigations, I thought, from listening to "clicks", that it opens and closes once for each full rotation of the three cups which catch the wind. Later, more thorough investigations turned up two interesting points...

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First: The switch opens and closes TWICE for one revolution of the cups, doubling the resolution of the sensor. That's four "edges" to detect, if your counter detects both rising and falling edges.

But what really impressed me is the fact that the "open" time and the "closed" times are nearly equal. This is a big help to any system that has somewhat crude electronics/software, which merely poll the state of the line from time to time. Some of my home-made sensors, while they have "worked", have switches which are only closed briefly. Without better-than-crude electronics/ software to monitor the state of the switch, some "closed" moments would be missed.



Wind Direction Sensor

The direction sensor is a LITTLE more "complex". Two wires come from it. A resistance exists between the two wires. How much depends on which way the vane is pointing. But this is not a crude, analog, "potentiometer" type sensor. It uses a clever system I first met in the AAG sensor, perhaps older than that, so that only 16 "positions" are sensed. This may seem a limitation, but what you gain for giving up resolution is robustness. The smallest "step" I could see between two positions was a bit more than 100 ohms. (Usually it is a lot more.) If you pull the signal up to 5v with a 10k resistor, the "worst" stretch of voltages as the vane swings around the positions from north to east to south... etc... is...

2.25v
0.41v
0.45v
0.32v
0.90v

Okay... the 0.41 and 0.45 positions might once in a while be confused, but at least your "direction" result will only be "out" by 22 degrees. All the other values are sufficiently far apart as to be hard to confuse. The full details are in the good technical material pdf provided by Argent. The same material is also available from Sparkfun's site.



Cables

The cables from each end in an 4 conductor RJ plug. There's a socket on the direction sensor. I believe that the design anticipates that you will plug the wire from the speed sensor into the direction sensor, and then take the two signals (speed and direction) down to the ground from the four pins on the cable leading away from the direction sensor.

I must admit: I haven't played with these yet... too busy writing this for you! But they look great- for a hobbyist's use.

If anyone knows sources, part numbers, etc, for these neat, inexpensive little sensors for hobbyists outside the UK, please contact me with those details? Having said that, I would add that they are small and light... I don't expect it would cost much to have them sent to you from the UK.

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Rainfall measurement

Water. Can't live without it. Living with it can be a pain, too. Rainfall measuring gets messy, and the equipment suffers.

I believe that the rainfall measuring device included in the "sensor sets" is one I met years ago as a stand-alone device. It is said to be of the "tipping bucket" type, which is "the way to go", as far as I'm concerned. Easy to interface to electronics. Reliable.

The "mouth" of the collector was, however, quite small... 15cm x 6cm. It "worked"... but I've been happier with a larger one (see rainfall sensors page) that I bought later. The larger one was quite expensive, though. Ah well.



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