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JamesF

A DIY Stevenson screen

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Now the observatory is up and running my mind has turned to wiring up my weather station kit again and getting it all working as I can now connect it all to the PC in the observatory and have some records of conditions when I've been observing/imaging.  I dismantled everything some time back when my last bodged-together screen gave up the ghost, so this time I thought I'd do a bit better job though most of the materials will be stuff I have sitting around the place.

Initially I had considered 3D printing the louvred sides, but I discovered that Screwfix sell vents about 200mm square with built-in insect screens (I'm not desperately keen on it becoming a home for bees/wasps/hornets) for about £1.40 each and anything else looked rather too much effort at that point, so I bought four of them, one for each side and two for the door:

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A hunt about in the stack of wood "that may come in useful one day" turned up some 30mm square softwood, a bit of T&G and a few offcuts of ply and I also found some galvanised mesh I could use for a floor, so I set to with the tools and made up a box and frame for the door:

stevenson-screen-02.jpg

The wooden floor section is to allow me to drill holes for feeding cables in.

The next steps are to make up a second roof (apparently a second roof with an air gap underneath is desirable, presumably to reduce the effect of the Sun) and to paint everything so I can finish assembling it all.  I was contemplating covering the second roof with an offcut of EPDM, but I'm not sure at the moment.  It might well defeat the object of having a second roof in the first place.  On the other hand, this will be going on the north east wall of the observatory, so shouldn't really get any significant heating from the Sun anyhow.

James

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My latest weather station will use all electronic components for measuring temperature, humidity etc. using an Arduino with shield so I'll be using a simple small 3D printed Stevenson screen.

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Looking good.  Just one thing about the vents, you will probably need to vacuum clean quite frequently.  Once the spiders find it, it will be heaven for them.

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25 minutes ago, Oldfort said:

Looking good.  Just one thing about the vents, you will probably need to vacuum clean quite frequently.  Once the spiders find it, it will be heaven for them.

Perhaps they'll move out of the observatory then :)

James

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51 minutes ago, Gina said:

My latest weather station will use all electronic components for measuring temperature, humidity etc. using an Arduino with shield so I'll be using a simple small 3D printed Stevenson screen.

Mine is going to be electronic too, but I want enough space inside to be able to get my hands in and fiddle about with stuff, especially as I might also use it as the main connection point for external sensors such as a rain gauge, anemometer and perhaps a sky quality meter.

James

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I didn't have much time today, but managed to get a fair bit of the painting done.  Hopefully I can finish it during the week ready for installation next weekend.

James

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The painting I did yesterday didn't feel particularly dry today (perhaps not surprising given the temperatures), so I thought I'd dig out some of my old 1-wire kit and have a tinker this evening.  What a bundle of joy that has been!

First I found that my 1-wire hub wouldn't power up.  It looks as though the 15V PSU has died.  I reckon I might be able to feed it from the 12V supply for the observatory though, so perhaps all is not yet lost (or at least waiting for me to buy another PSU) there.

I downloaded the last release of OWW, the software I used using to read the 1-wire devices and just couldn't get it to build properly.  After a lot of faffing about I tried the previous version and that seems to be fine.

The next step was to plug in the 1-wire controller device and a few sensors and see what happened.  Well, nothing much happened at all because it seems the way the controller interfaces with Linux has been completely changed in the intervening years and OWW can't find any of the devices.

I discovered that I might need to load some additional driver modules to get the devices to be recognised, so I tested with a few of those.  I've crashed my desktop twice so far (the first time I've managed that in years).

Everything is now plugged into my laptop instead so I don't need to reboot my desktop again...

James

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Oh dear!!!  That doesn't sound very good news for when I resurrect my weather station project.  Hope you can get it sorted out, James.  Good luck.

Actually, thinking about it, I have a slightly different setup with an Arduino Uno and shield.  The Arduino acts as the 1-wire controller.

Edited by Gina

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I didn't have a lot more time left last night, but out of lack of other ideas tried it out on an RPi where it seems to work much more reliably.  I wonder if the drivers aren't stable on 64-bit environments or something like that.  As I was quite probably going to end up with an RPi in the screen anyhow, that may not be the end of the world and it does have the advantage that all the 1-wire cabling can be short.

However, I think I might be able to get it to work a different way on my desktop and laptop if I blacklist the standard 1-wire drivers.  It looks as though OWW can talk to the USB device directly and control everything from there.

James

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I'm making progress.

After blacklisting all the 1-wire modules on my desktop and making a udev rules script that allows non-root users access to the USB device, I've plugged in the circuit board of my AAG weather station, a pressure sensor and a combined solar/temperature sensor and fired up oww.  It lives, Igor!

oww-01.png

The software is whining about an error reading the wind direction ADC, but I think that's because I dismantled the weather station so I could remove one of the 6P6C plugs (the entire unit was blown down in a storm a few years back and the cable tore out of the plug) and replace it.  I've not reassembled it yet.  I'm actually half-tempted to try to 3d print an entire new housing as the original has somewhat degraded in the sunlight.

Getting this bit of software working is actually more than I need in fact.  There's a non-GUI version that can just log the data to a database which means it can be pulled out to be used however I want.

I also have a combined temperature/RH sensor that I want to try out (need to make up a cable for that, but it shouldn't take long) and some loose DS18B20(?) temperature sensors I can test.

James

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Oh!  I nearly forgot!  I also have a rain gauge that needs a bit of a clean-up.  Given that it was only rain falling inside it's incredibly filthy.

James

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Progress is slow, largely due to the colder weather meaning paint drying times have increased, but also I was waiting for some stainless screws to arrive.  Today however I fitted the door and all the vents.

stevenson-screen-03.jpg

The upper roof section is also in progress, but I'm quite tempted to try to fit this in position tomorrow anyhow and fit the additional roof section when it is ready (probably next weekend).  It's not like it needs much protection from the Sun at the moment, after all.  I just need to add two or three rails across the back so I can fix sensors etc. in place.

James

Edited by JamesF
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This week I have completed the painting and finished fitting the roof.  I also nipped into Screwfix on the way to a meeting at school and picked up some elbows and clips for the 20mm conduit that I found stashed in the ceiling of the workshop.

Today I fitted the screen to the north-east wall of the warm room and ran three cat5e cables (one 1-wire, one ethernet, one spare) and a 12V power connection through the conduit into the warm room, which meant I could plug in the 1-wire hub/power injector and a couple of the 1-wire devices that I've cleaned up since their last outing.  They're "casually abandoned" inside the housing for the time being.  I'll fit them more neatly when I have the other devices ready to go.

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Quite pleased with  the project so far.

The computer end of the 1-wire network is plugged into a DS2490 (I think that's the one) USB interface and I'm working on getting the software side of that up and running at the moment.  I also need to work out where and how I'm going to fit the rain gauge and the original AAG weather station that has the anemometer and wind direction meter. (both of which need some repair work first).

Which reminds me... Today I found my copy of a paper documenting the design of a solid-state combined anemometer and wind direction meter using some ultrasonic transceivers and a single-board computer.  It was published in 2006, so before the advent of the RPi and Ardiuno, but I imagine either would be suitable these days.  In fact I bet someone's already done it.  I quite fancy having a go at building one at some point.

James

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That's interesting though I already have a magnetic transducer arranged for the wind vane and simple Hall device for the anemometer.  1-wire instruments connect to an Arduino Uno plus data logging shield which also has the pressure sensor on.  It all works basically - I just have to get round to finishing it.

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The AAG weather station uses magnets on the end of a spindle to trip reed switches as a means of calculating wind speed (count the number of times the reed switch is tripped per minute, I guess) and direction (eight more reed switches arranged at N, NE, E, SE, S, SW, W, NW).  It's actually a bit of a mess now -- I guess UV has taken a bit of a toll on the plastic.  It's just occurred to me that I could paint it all gloss white and perhaps get a bit more life out of it whilst I design a replacement to 3D print.  The vane for the direction is dead though -- all the actual vane has gone.

I could start work on the painting and whilst that is drying get the rain gauge up and running again.  It really requires a new base to allow the water to drain out, but I could 3D print something suitable pretty quickly I reckon.  A longer cable would be good, too.

James

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Mine is all home built.  The wind vane uses a magnetic field direction sensor in an SMD chip.  Measures in degrees - not that it needs anything like that level of accuracy.  I must take the thead (assuming I can find it) and convert it to a Blog.

Edited by Gina

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I think it's high time I resurrected this project though I might finish my ASC first.  BTW the rotary encoder chip is MLX90316.

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I'm still working on this, though like everything else in my life it's taking a little longer than I hoped :)

Today I thought I'd take a look at the rain gauge which isn't working.  I opened it up and had to drill out one of the screws to get at the electronics as it had rusted too much to come undone.  It appears that the unit uses a reed switch that is activated by a magnet on the tipping system that collects the rain:

rain-gauge-02.jpg

The battery has clearly expired, so I thought I'd pop it out and replace it, but that's proving a little more awkward than I expected.  It seems the battery is somehow welded to the contacts.  Not ideal :(

rain-gauge-01.jpg

I guess I have a few options at this point.

I could attempt to unsolder the contacts from the PCB, add a new battery holder either on the PCB or on the end of some wires, and then fit a new battery.  But that still leaves me having to replace the battery every so often.

Although there are only two wires connecting to the board to connect it to the 1-wire hub, the main cable has four cores and the hub supplies 5V on one of the "spares".  I'm wondering if I dare attempt to re-wire it to provide power from that instead of the battery (and whether I actually need to step the voltage down as it might run quite happily on 5V anyhow).  Given the amount of hot-melt used it's quite hard to make out what the other components are.  Ultimately though I think it uses the same 1-wire counter components as the weather station anemometer (which also works using a reed switch) and that runs off 5V.

I don't feel I have much to loose at this point though.  If I unsolder the wires from the board so I can remove it I can perhaps get a better look at it.

Unfortunately I've not yet been able to find much information about the rain gauge on the web.

James

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I think I have most of my other sensors up and running now.  I have owfs running to get the sensor values with a script that displays them every thirty seconds or so.  Clearly there's some tweaking to be done.  I have four temperature sensors, one in the AAG anemometer, one in the solar sensor, one in the RH sensor and one in the barometer.  This is the data I'm seeing:

21:17:22 AAG: -0.19, SOL: 1.62, BAR: 1.54, RH: -0.53 degC, 1024.0 mb, 102.2% RH
21:17:58 AAG: -0.19, SOL: 1.56, BAR: 1.53, RH: -0.62 degC, 1023.9 mb, 102.5% RH
21:18:31 AAG: -0.25, SOL: 1.56, BAR: 1.53, RH: -0.66 degC, 1023.9 mb, 102.7% RH
21:19:07 AAG: -0.19, SOL: 1.56, BAR: 1.52, RH: -0.56 degC, 1023.9 mb, 102.5% RH
21:19:42 AAG: -0.25, SOL: 1.56, BAR: 1.51, RH: -0.53 degC, 1024.0 mb, 102.8% RH

Obviously they can't all be right.  As the dew is already freezing, I'm inclined to think that the AAG and RH values are probably nearer the mark.  Atmospheric pressure looks about right.  Perhaps a little optimisitic, but not too bad.  I assume it's telling me that the RH is over 100% because we're below  the dew point.  I'll have to work that one out.  owfs gives me access to the raw data from the sensor so I can recalculate it myself to check.

James

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