All Sky Camera/Weather Station build

[angryowl]

30 minutes ago, Gina said:

I was very interest in the MLX90316 rotary position sensor that you are using for the wind vane sensor   Nice and simple compared with my system   Where did you buy yours, please?

Reading your Arduino Based Weather Station thread I actually thought of suggesting you consider the MLX90316 as a simpler alternative. Very precise for this application with minimum external components required (only 2 capacitors) for use with Arduino.

I purchased mine from Mouser UK. It comes in 5 versions: 

xxx-000: standard

xxx-100: SPI

xxx-102: SPI75AGC

xx-200: PPA (Pre-programmed Analog)

xxx-300: PPD (Pre-programmed Digital)

Mine is the MLX90316EDC-BDG-100-SP version working flawlessly with Arduino SPI and it only needs 3 pins on the Adruino.

[Gina]

Thank you   Been on the Mouser UK site and they are in stock but there's £12 delivery fee - rather a lot for a £4.74 component.  I could order a spare at the same time - still the same delivery charge or maybe the analogue version.  With the latter I could add a low pass filter to smooth the motion and dispense with the magnetic damping.  Or I suppose I could add a digital LPF in the Arduino sketch.  The only problem I see with using analogue is calibrating the signal level to avoid a gap or overlap at 0/360 degrees.

[angryowl]

Oh, yeah, forgot about the steep delivery charge. I ordered multiple items with this so it made sense in my case.

I hadn't considered the analogue version as a viable option due to having to do a calibration and I too wasn't exactly sure how to deal with the transition from 0 to 360 degree.

I found a sketch for the chip online which simply outputs the current value over serial monitor which works great and am amazed at how precise it is!

[Gina]

VAT to add too.  If I order two SPI types and one analogue with carriage and VAT it comes to £31.68 rather more than the £4.74 I was looking at.  Still, gives me a spare and an analogue to play with and could save me quite a lot of work   And I'm not that short of funds

Yes, I agree about the analogue 0/360 problem - probably a waste of time to fix.  Think I'll dump that.  What else did you buy from them?  Anything useful for ASC or WS?

[angryowl]

A previous vane build of mine used a series of 8 LEDs and 8 LDRs which were mounted on the base of a HDD motor and the rotor, made from reflective aluminium, was partially wrapped in black felt leaving only a small portion of the aluminium visible. Most of the LDRs had separate pins on the Arduino but when I ran out of pins I had to multiplex some using different resistors thus each LDR on the multiplexed pin would output a value either between 10-100kΩ or 900k-1MΩ. This worked well but calibrating it all was a complete nightmare and in the end it turned out to be too unstable and inaccurate.

With the SPI MLX chip it really is so easy to set it up and lets me use my spare time on other things, such as 3D printing parts for the weather station 

[angryowl]

The only other components for this project I purchased then were a couple of 4N25 optocouplers which will be used for turning the PC on, and as switches for the camera fan and TEC. Reason I went with these was I wanted complete voltage protection for the sensitive PC and camera circuits. 

I did however purchase components for some of my other projects for which I never seem to find the time... 

[Gina]

Ordered a couple of the SPI types from mouser.  Should be here a bit later in the week.  This seems a much better solution than the Gray encoder with 4 bits giving 16 different angles.  I can have a nice big wall display of my weather data with a stepper motor for the wind direction.  Wind speed could be either another stepper of possibly a micro servo motor.

[angryowl]

Hmmm, a wall display with mechanical gauges sounds like a fantastic addition to a weather station. Something like this would look great on a wall somewhere. Here's a video of it.

No doubt you'd likely go the 3D printed route rather than a commercial one  which does make a lot of sense as there's so much more flexibility with 3D printing. Since I've got my printer, 3D printing has sort of taken over my life and completely revolutionised my hobbies in many aspects and breathed new life into them.

[angryowl]

Gina, if you do decide to go down this route, the sensor works best with diametrically magnetised magnets(also recommended by the manufacturer). I have a spare 6mm dia x 4mm height one which I would gladly pop in the post for you as they are a bit pricey and I was only able to find them in packs of 4 minimum.

[Gina]

Thanks very much for your offer.  I have a number of 3mm cube Neodymium magnets and was thinking of using one of those but the 6mm diameter one sounds much better.  So I'll gladly accept your offer   I'll PM you.

Yes, I shall definitely 3D print any wall displays.  I might use concentric wind speed and direction displays (like as in a clock).  Also, I'm thinking of having a non-linear wind speed  display, spreading out the lower end - sort of semi-logarithmic.  I shall post everything I do on here as I do it.

One big advantage of working on weather stations is that it doesn't depend on clear night skies   I have a few ideas for additional sensors too.

[angryowl]

Look forward to seeing how the displays turn out, please keep us posted. 

Two other sensors I considered adding were  a DIY fog sensor such as this one and a visibility sensor. After some researching they both proved too difficult to construct and get accurate outputs from them.

[Dr_Ju_ju]

Haven't checked, but do Farnel \ RS do them? much cheaper on delivery....

[Gina]

They didn't show up on Google search for the MLX sensor, but haven't checked directly.

[Gina]

For the wind direction I was thinking of a NEMA 11/14/17 stepper motor.  The wind speed could use the little 28BYJ-48 stepper motor as the display never goes round and round and the weird gearbox ratio wouldn't matter - any errors would not be cumulative as might happen with the possibly continuously rotating wind direction.  The other dials could also use the 28BYJ-48 or even micro servo motors but those do not seem to be very reliable.  Arduinos are ideal for control.

[angryowl]

Would the 28BYJ-48 stepper be responsive/fast enough for displaying wind gusts?

[Gina]

That's a good point - maybe not.  Micro servers wouldn't be either.  Oh well, NEMAs then   28BYJ-48 would do for average wind speed.

[angryowl]

Could always use a galvanometer. I once built a laser projector out of two HDD heads which had mirrors glued to the ends. They weren't precise nor fast enough for the projector but I can see them working for such a display via Arduino analogue output.

[Gina]

I've added my Analogue Weather Display to my project List as it wasn't on it.

 

[angryowl]

Bought two of these (the 2mm thick version) for use as gaskets between the dome and enclosure. They are 60 shore solid silicone and just arrived today. I'll cut them to size and fit one between the ASA spacer and enclosure lid and the other between the acrylic dome and ASA spacer. I'll then do a test by submerging the whole thing in water and leave it for a couple of hours, if nothing leaks then I'll use them with generous amounts of sealant silicone all around the gaskets.

I can easily cut them to the inside and outside shape of the dome with a xacto knife, but does anyone have any suggestion as to how I could get the best/roundest holes for the eight 6mm mounting screws? From past experience trying to cut small round holes in rubbery materials usually gives awful results.

If they leak I've still got plenty of options as suggested by many in the beginning of the thread...

[Gina]

Hole punch.  As used to punch hole in things like leather belts.

[angryowl]

That did the job with nice round holes. The largest hole I cam make is roughly 4.5mm but actually I found it seals around the thread of the bolt quite nicely.

[Gina]

How close did you have the magnet to the direction sensor chip (wind vane)?  Is it critical?

[Gina]

Also, could you post the Arduino sketch you used with the MLX90316, please?

[angryowl]

1 hour ago, Gina said:

How close did you have the magnet to the direction sensor chip (wind vane)?  Is it critical?

My magnet is about 5mm away from the sensor. When I was testing the furthest I could go with the magnet and still get an accurate output was roughly 15mm. The reason my magnet is not too close to the sensor is because the soldered pins on the breakout board are ferromagnetic and would slightly affect the rotation of the magnet and ultimately the vane itself.

[angryowl]

1 hour ago, Gina said:

Also, could you post the Arduino sketch you used with the MLX90316, please?

Here it is, it's got the MLX library in but you also need the Metro one.

Mlx90316.zip