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Arduino Based Weather Station


Gina

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Hub and three cups/spokes printed and assembled.  Bearing also put in hub.  The other hole is for the magnet.  Top and skirt yet to be designed and printed.  This will keep the wet out.

One cup and spoke pushed onto hub.  This is a tight fit, no other fastening method, which works well with the ABS printed thermoplastic.

post-13131-0-73926100-1432467168_thumb.j

All three cups added to hub - bottom view.

post-13131-0-93048700-1432467176_thumb.j

Top view.

post-13131-0-98086800-1432467184_thumb.j

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But they aren't :D  It's being made from transparent ABS that makes them look delicate.  They're much stronger than the molded plastic hemispheres of the FO anemometer.

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In looking at something totally different I came across a completely different anemometer design HERE.

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Ah yes - must have a read - looks very interesting :)  Maybe a future project :D  But I'll get the simple cup anemometer and wind vane working first as I'm getting fed up with seeing my present wind stuff spoiling the view in my All Sky Camera :D  I think everyone knows I'm well up for those different and innovative projects :D

This is temporarily on hold though until I get some more acetone to unblock the nozzle of my 3D printer.  All 3D printing is suspended ATM - I can do other things in the meantime though :D

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Printer needs calibrating again - Z axis not perpendicular to the X-Y plane.  I'm a touch worried about how much longer this poor little printer will last with the pounding I give it!  With printing in Fast mode it almost shakes itself off the table :eek:   Hence I'm putting some time into the bigger one.

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Slight design change on the cup spokes and hub to provide a stronger attachment and parts printed in dark blue so that I can see the thing when it's up in the air :D  Reed switch and magnet system tested and works fine.  The magnetic attraction puts a small load on the rotation but I think it will be negligible.  If Later tests show this to affect the low wind speed readings, I'll change to Hall Effect or optical sensing.

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  • 6 months later...

I plan to resurrect this project shortly to go with my analogue weather display.  Currently I have a visual only weather vane and anemometer with one cup broken off.  The mast is bent such that the top is running at something like 15° off vertical.  On top of the mast are the remains of my Maplin Fine Offset proprietry weather staion - other parts long since defunct.

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  • 1 month later...

One part that wants replacing with a 3D printed plastic part is the mounting of the vane shaft and damping magnet to the ball bearing the vane pivots on.

post-13131-0-12670800-1452462712_thumb.jpost-13131-0-61013600-1452462713_thumb.jpost-13131-0-73202700-1452462714_thumb.jpost-13131-0-36772700-1452462716_thumb.jpost-13131-0-64282800-1452462717_thumb.j

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I've been giving some thought to the sensor system for the anemometer.  Currently the idea is a magnet on the rotor and reed switch underneath in the fixed part.  This gives two closures per revolution as the reed switch closes with either N-S or S-N magnetic field.  With one revolution per second estimated to represent 3mph this means a pulse per second for each 1.5mph.  So the wind speed reading is only resolved to 1.5mph if a period of 1s is used for counting.  I wonder if 1.5s would be short enough to detect gusts - that would give a 1mph resolution.  Average speed could have a much higher resolution by using a longer counting period.  Maybe I'll ask this question in a weather forum.

Another thing I noticed with magnetic sensing is that the anemometer rotor tends to "lock on" to the positions at either end of the reed switch due to magnetic attraction.  This reduces the wind speed at which the anemometer starts to turn so I might change over to optical sensing.  Also, I've heard of reed switches failing in this application with millions of operations a week.  Optical sensors have no such problem.

Optical sensing could use a multi-slot disc on the rotor and give faster and more accurate wind speed readings.

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I was going to put the main weather station unit in the observatory since that is where most of the data comes from but communicating the data to indoors has turned out to be more difficult than I had thought.  Now most of the sensors are 1-wire and this is a multi-device bus with a range of up to 100m and well capable of reading weather sensors from the house so it makes more sense to me to locate the main unit indoors where it acn be connected by USB to a computer for weather data processing and uploading to my weather website.  The Arduino can control the display dials on the living room wall and if the UNO hasn't got enough data pins, I can use a Mega which is also compatible with the data logging shield.

The sensors which aren't 1-wire are the DHT22 Digital Humidity and Temperature sensors and the unit which measures sky cloud and whether it's raining.  The latter uses an Arduino and I could probably use the same Arduino to connect to the DHT22s.  It then remains to arrange a way of connecting the Arduino as a slave on the 1-wire bus to collect the data.  I have a method for the water level data but that only applies to one data value which changes very slowly.  The weather data is another matter though reduced by moving the i-wire sensors directly onto the 1-wire bus

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Much of this project has been taken over by my Observatory Environment Instrumentation  thread in the DIY Obsvertories forum, as I will be reading temperature and humidity outside near the observatory and inside in both scope room and warm room plus the water level in the hole underneath.  Wind speed and direction are also highly relevant to the observatory (as is rainfall) as I have experienced many times over the years and particularly in the last couple of months!  So discussion of the weather instruments will mostly be covered in the observatory thread and this thread will deal more with data processing and upload to web site.  That will be after I get the instrumentation and communication aspects sorted out and display of the data by dials on the living room wall next to my moon phase clock.

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I'm going to continue posting ideas for the circuitry to read the wind instruments here.  The main issue is Maxim discontinuing several 1-wire devices that I was using for the weather station and not providing any replacements.  Yes, ideas as opposed to definite designs and that's why I would prefer not to clog up the Instrumentation thread in the DIY Observatories forum.

I could conrtinue to use the components as already designed but these are two of the discontinued ones with no replacements available.  I never like to design anything when I have only one of any component in case this should fail.  I think it makes more sense to redesign the circuit to use only currently available components and buy at least two of these for spares.  If an obselete component failed I would then have to redesign and rebuild the assembly maybe involving more than just a change of circuit.  Better to start with the new design I think.

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I'm going to look into using a diode pump circuit plus DS2438 to read the wind speed.  The diode pump circuit converts the pulse rate from the anemometer to an analogue voltage and the DS2438 will read this and convert it back to digital.  This sounds a bit daft but with Maxim no longer producing any form of 1-wire counter device it's either that or measure the period of the pulses which would require very fast sampling to read high wind speeds.  We 1-wire weather afficionados are very cross at Maxim drawing the mat from under our feet!!

The 1-wire device I was going to use to read the wind direction has also been discontinued :(  This is another part that will need a complete rethink.  My original idea was to use optical sensors and a Gray encoded disc to convert the wind vane angle to 16 discrete digital values.  With the optical sensors using photo-transistors with an analogue output and no hysteresis the system is very sensitive to noise if a simple logic device were used to detect the light level.  I was using a DS2450 quad A/D converter where each photo-transistor would be read as an analogue current and hysteresis applied in program code.  With the DS2450 chip being obsolete I shall need to rethink how I shall read the wind direction.

One solution would be to use a CMOS Schmitt trigger chip on the photo-transistor output and then read the digital data using something like a DS2408 8 bit PIO chip.  I'm currently investigating how these can be controlled from the Arduino 1-wire system.

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Looking at a purely digital alternative to the diode pump circuit and DS2438 A/D converter, I'll consider a CMOS counter and DS2408 8 bit PIO device. 

Pulse rates from the anemometer can vary from a pulse every couple of seconds up to 64 pps for winds of 64mph (near hurricane force).  Now the Met Ofice measure wind speed over a 3s interval and I think I'll do the same so that's a range of 1 to around 200 counts.  So 8 bits of data (256 levels) would be fine.  So one way of dealing with the anemometer would be to use an 8 bit CMOS counter and read the data with a DS2408.  This could be a viable option once I've sorted out how to use the DS2408 :D

For the counter the CMOS 4000 range, dual 4 bit counters - 4520 looks suitable.  Datasheet for MC14520B (one make)

Edited by Gina
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  • 2 weeks later...

I've been thinking about all this even though this project is on hold.  The previous circuit using obsolete 1-wire chips is AFAIK still in working order.  I shall need to do some tests to make sure but if it works is seems to make sense to use it now that the DS2408 method has ground to a halt.  Yes, I've changed my mind :happy5: There will be a couple of differences - the anemometer uses a hall effect device instead of a reed switch and the optical sensors for the wind vane will be using proper reflective optical sensors with IR LED and phototransistor in the same casing rather than separate components.  These will most likely produce a difference in the phototransistor on/off currents so different value resistors will be wanted to convert these currents to voltages.

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  • 2 weeks later...

Coming back to this project, I thought of changing from a disc wind vane encoder to a cylinder but thinking maybe a cylindrical reflector would not be as good as a flat surface.  This is the next stage of the project, at least as far as the wind is concerned.  The rain gauge is easy - I can just run a cable from the reed switch on the tipping bucket system to the indoor Arduino.  Then rain rate could be calculated from the period between bucket tips and the accumulated amount by counting switch closures.  The input to the Arduino would be on an analogue pin with and RC circuit to debounce the reed switch.

I think I shall go for a smaller Gray code disc than my earlier modified CDROM disc - I want to reduce windage to a minimum.  In those days I didn't have a 3D printer and had to bodge about with whatever I could find.  Now I can 3D print all the bits I want :)  So I shall print a smaller Gray code disc and the housing for the optical sensors.  I have already tested the reflectivity of natural ABS filament in conjunction with the optical sensor.  Next stage then is to design the Gray encoder in SketchUp ready for printing.

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Coming now to the overall design of the wind vane unit, here is a diagram of the wind vane and magnetic damping arrangement.  The vane itself is on a round aluminium tube to be seen on the right in the diagram.  The centre hub is supported on the central tube by a ball bearing.  The top part is an aluminium saucepan lid and this provides magnetic damping in conjunction with the "supermagnet" on the end of the bent arm.  The direction sensing system will be between the hub and the top pan lid.  The anemometer is attached to the top of the pan lid.

56b8ead7db95f_WindVaneMagneticDamping01.

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This next sketch shows a more practical design for the hub and bearing system with skirts to keep wind driven rain away from the ball bearing.  Rather than a central vertical aluminium tube right up through I shall use a 3D printed part that fits on top of the mast (orange), takes the bearing for the wind vane hub (yellow) and goes on up to support the pan lid in conjunction with skirted flange (blue).

56b9069750823_WineVaneBearing01.thumb.JP

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