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DIY Sky Quality Meter(s)

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#1 RDBeck

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Posted 03 March 2019 - 09:42 AM

I have designed and tested two versions (handheld and USB) of lensed DIY Sky Quality meters using Arduino Leonardo and TSL2591 light sensor.  The heavy lifting for the light sensor was done by astrogabe.

 

DIY SQM Handheld USB

 

The code for the Arduinos is at https://github.com/beckrd/DIY_SQM

 

The enclosures and parts descriptions are at:

Handheld -- https://www.thingive...m/thing:3465650

USB -- https://www.thingive...m/thing:3465665

 

The USB version uses the SQM-LU protocol and only responds to information requests (ix) and reading requests (rx or Rx).  Testing has only been performed using INDI.


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#2 mosentos

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Posted 03 March 2019 - 09:53 AM

Very cool, thanks for sharing.  

 

BTW, what display did you use for the handheld version?  I see that the SSD1306 128x64 comes in different sized packages. 

Thanks!


Edited by mosentos, 03 March 2019 - 10:08 AM.


#3 RDBeck

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Posted 03 March 2019 - 11:25 AM

Very cool, thanks for sharing.  

 

BTW, what display did you use for the handheld version?  I see that the SSD1306 128x64 comes in different sized packages. 

Thanks!

The display I used was the ~35mm (1.38") wide version https://www.adafruit.com/product/938.

 

I also have not gotten the red plexiglass I put over it properly cut and mounted yet frown.gif.


Edited by RDBeck, 03 March 2019 - 11:27 AM.

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#4 Arjan

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Posted 03 March 2019 - 01:50 PM

Interesting, I have components ready but am stuck with some questions:
How did you make the optical front-end?
Do you know the angular response?
How did you calibrate the meter?

#5 AstroGabe

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Posted 03 March 2019 - 02:02 PM

Excellent work Richard!  I’m glad that you were able to use the code and it works well for you.  I love seeing great new DIY designs like this.  Well done!!

 

Gabe


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#6 kb58

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Posted 03 March 2019 - 04:17 PM

I guess I'll ask an ignorant question: In what situation is this used, and how are the results used? Reason I ask is, if a telescope is hauled out to a "dark" site, it won't be used there (will it?). I mean, if you just drove out there, are you going to turn around if it says "bad sky tonight?" I would assume that the scope would be used anyway.

 

Is it intended to be used at home in the backyard, where you're basically asking the sky, "are you good enough to look at tonight, and that I should haul out the scope, or should I watch TV instead?"

 

Lastly, has it demonstrated itself to be better than the Clear Sky website?


Edited by kb58, 03 March 2019 - 04:18 PM.


#7 AstroGabe

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Posted 03 March 2019 - 04:32 PM

I use the readings at home to gauge when the sky darkness saturates. You can wait till astronomical dusk, but often the LP is strong enough that the sky darkness saturates well before dusk.  That’s one possible usage.  If there’s LP around, the presence of clouds will also affect the reading and show up as a brightening.  

 

I also like data ;)


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#8 Arjan

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Posted 03 March 2019 - 04:35 PM

It will give you an estimate on transparency, through the amount of reflected light, and based on this (and experience) you may decide to do a photo session or not.

It will also serve to compare sites, so you can plan your future journeys based on actual data.

 

Edit: this is why it should be calibrated, so you can compare your data to what others have measured on different sites.


Edited by Arjan, 03 March 2019 - 04:36 PM.


#9 RDBeck

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Posted 03 March 2019 - 05:53 PM

Interesting, I have components ready but am stuck with some questions:
How did you make the optical front-end?
Do you know the angular response?
How did you calibrate the meter?

As explained at the Thingiverse pages, I used 60 degree LED lenses I purchased on e-bay.

 

Nothing was done for either the angular response or calibration.  Astrogabe's code allows for a calibration adjustment.  I took some readings with the handheld about 3 hours after sunset and 2 hours before moonrise.  The average result was 18.55 for my location, and Clear Outside estimates 18.54.  This seems to be "good enough" for me.


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#10 RDBeck

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Posted 04 March 2019 - 10:34 AM

Parts list

 

TSL2591 -- www.amazon.com/gp/slredirect/picassoRedirect.html/ref=pa_sp_atf_aps_sr_pg1_1?ie=UTF8&adId=A00433571IHZZW17TQQUW&url=%2FAdafruit-TSL2591-Dynamic-Digital-ADA1980%2Fdp%2FB00XW2OFWW%2Fref%3Dsr_1_1_sspa%3Fkeywords%3Dtsl2591%26qid%3D1551712895%26s%3Dgateway%26sr%3D8-1-spons%26psc%3D1%26smid%3DA19MRELPGC5OXX&qualifier=1551712894&id=2659017105375950&widgetName=sp_atf $12.05

 

OLED SSD1306, 1.3" -- www.amazon.com/Serial-128X64-Display-SSH1106-Arduino/dp/B075F3M44J/ref=sr_1_5?keywords=ssd1306%2B1.3%22&qid=1551711184&s=gateway&sr=8-5&th=1 $9.11

 

Leonardo -- www.amazon.com/KEYESTUDIO-Leonardo-Development-Board-Arduino/dp/B0786LJQ8K/ref=sr_1_3_sspa?crid=219TVH0P43BBA&keywords=leonardo+arduino&qid=1551713104&s=gateway&sprefix=leonardo+arduion%2Caps%2C169&sr=8-3-spons&psc=1

$12.99

 

Lenses -- https://www.ebay.com...872.m2749.l2649

$5.42 for 10 sets

 

Switch & 9V connector -- www.amazon.com/gp/product/B07JNNXC9N/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

$7.99 for pack of 20

 

Red clear plexiglass -- https://www.estreetp.../t011250612.htm

$2.99 plus applicable tax and postage ($8.75 total)

 

My total costs (purchasing light sensor and OLED from Adafruit directly):

 

Handheld -- $69.78 ($51.80 pro-rata for multiple parts, $33.45 pro-rata parts from Amazon)

 

USB -- $25.43


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#11 lambermo

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Posted 04 March 2019 - 03:11 PM

Interesting. I too built my own but used an AMS TSL237 light to frequency converter and I read it from a RPI.

My version is intended for a permanent observatory.

My code is here https://github.com/d...TSL237_pigpio.c and I plot graphs like this :

sqm_small_now-1d.png

-- Hans


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#12 calypsob

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Posted 05 March 2019 - 07:12 AM

I guess I'll ask an ignorant question: In what situation is this used, and how are the results used? Reason I ask is, if a telescope is hauled out to a "dark" site, it won't be used there (will it?). I mean, if you just drove out there, are you going to turn around if it says "bad sky tonight?" I would assume that the scope would be used anyway.

 

Is it intended to be used at home in the backyard, where you're basically asking the sky, "are you good enough to look at tonight, and that I should haul out the scope, or should I watch TV instead?"

 

Lastly, has it demonstrated itself to be better than the Clear Sky website?

I use one because I am trying to gauge how dark the sky is at a particular darksite. IMO, for imaging broadband, anything under mag 21 is unacceptable because gradients in my images become so severe and it is difficult to acquire a good snr on faint background nebula. I typically try to find that darkest locations within 1 hour of my house. I then share my recordings on this site, readings can be toggled with the SQM overlay menu https://www.lightpol...ers=B0FFFFTFFFF

By doing this, anyone can use the recordings I have made to find a darksite without much effort.

 

The only reason you would have to roll the scope inside is due to bad transparency or seeing, these meters can help you identify poor transparency if you know what the location typically averages in terms of sqm value throughout the year, of course from a light polluted area you can just look up and see bad transparency because the city lights reflect off of it.



#13 calypsob

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Posted 05 March 2019 - 07:14 AM

As explained at the Thingiverse pages, I used 60 degree LED lenses I purchased on e-bay.

 

Nothing was done for either the angular response or calibration.  Astrogabe's code allows for a calibration adjustment.  I took some readings with the handheld about 3 hours after sunset and 2 hours before moonrise.  The average result was 18.55 for my location, and Clear Outside estimates 18.54.  This seems to be "good enough" for me.

how do you focus the lens?



#14 calypsob

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Posted 05 March 2019 - 07:14 AM

I have designed and tested two versions (handheld and USB) of lensed DIY Sky Quality meters using Arduino Leonardo and TSL2591 light sensor.  The heavy lifting for the light sensor was done by astrogabe.

 

 

 

The code for the Arduinos is at https://github.com/beckrd/DIY_SQM

 

The enclosures and parts descriptions are at:

Handheld -- https://www.thingive...m/thing:3465650

USB -- https://www.thingive...m/thing:3465665

 

The USB version uses the SQM-LU protocol and only responds to information requests (ix) and reading requests (rx or Rx).  Testing has only been performed using INDI.

Have you compared the accuracy of this unit to a unihedron sqm-L?


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#15 roscoe

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Posted 05 March 2019 - 10:12 AM

I think this is very cool. having messed with electronics since the days of vacuum tubes, what can be built by folks at home never ceases to amaze me, and a do-it-yourself SQM is right up there in the home-based wizardry category. I applaud you for figuring out how to build one, and for being generous to share your design here, well done! Amateur astronomy and Cloudy Nights members at their finest!

 

however, I find that it works ok to just look at the little dipper and see how many stars I can see, and are they twinkly or steady?  The disadvantage is that I have to wait for my eyes to become dark-adapted, but the equipment's free and the test takes seconds..... I love technology, always have, but it does worry me as an old codger that the old, simple ways are being replaced by the need to have at least one chip and one battery in everything we own.

 

Now back to the way everybody under 60 years old does it.....


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#16 RDBeck

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Posted 05 March 2019 - 05:38 PM

how do you focus the lens?

The lens I used is fixed focus.  It's actually meant to be used as a lens for an LED flashlight.

 

Have you compared the accuracy of this unit to a unihedron sqm-L?

I don't have a way to make the comparison.  My only basis to think it's OK is the combination of a friend who said his Unihedron (not sure of the model) matched Clear Outside quite well at his location and my meter matching Clear Outside well at my location.



#17 RDBeck

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Posted 05 March 2019 - 05:39 PM

Now back to the way everybody under 60 years old does it.....

Only I'm not under 60 wink.gif


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#18 AstroGabe

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Posted 05 March 2019 - 05:43 PM

Have you compared the accuracy of this unit to a unihedron sqm-L?

The version I made was quite comparable to the SQM-L model that I have.  I don't have a comparison figure available, but the times I've tested, the readings were easily w/in 0.1 mpsas of each other.  This was done after calibrating the DIY SQM.

 

Gabe



#19 roscoe

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Posted 05 March 2019 - 06:24 PM

Only I'm not under 60 wink.gif

Didn't think so, from your avatar.....  and it places you firmly in the era when it took the ol' table radio 30 seconds to make sounds after you turned it on......   the young'uns today just cannot comprehend that!


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#20 Arjan

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Posted 08 March 2019 - 12:13 PM

Looking in the TSL237 and TSL2591 datasheets, it seems that sensitivity is comparable. This is good: I expect availability of the latter is better.

#21 HyM

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Posted 27 May 2019 - 01:30 AM

Sorry about the naive question, but, wondering: if I had my imaging scope and camera setup, could I "take an SQM reading" just with that, not needing any additional hardware? I'm not sure what the conversion from ADUs would be, but I assume for a particular camera-OTA pair (e.g. arc-sec/pixel and quantum efficiency), filter bandwidth and gain setting, there would be a direct conversion from ADU values (say the median value which hopefully is the background sky's value) and the sky magnitude per square arc-second.

 

I'm sure your SQM and those that can be bought are (a) more convenient to use, (b) perhaps help you decide whether to take out the scope to begin with, and © sample a much wider patch of sky, but, perhaps the SQM values I'm most interested in are the ones nearest my targets anyway. 

 

Thanks.



#22 AstroGabe

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Posted 27 May 2019 - 11:40 AM

Yes, you definitely can.  I did the same thing a year or so ago when comparing the sky background of a few local dark sites and compared them to my hand held SQM-L.  It worked fairly well, with some small differences that could be attributed to bandwidth and fov differences between the scope + ccd and SQM. 



#23 Lacquerhead

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Posted 09 June 2019 - 07:24 AM

Perhaps I missed it somewhere in the documentation.  Is there a wiring diagram somewhere? 

 

Thanks in advance!



#24 Arjan

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Posted 09 June 2019 - 09:28 AM

Wiring of what?

#25 555aaa

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Posted 09 June 2019 - 11:30 AM

FYI you can shorten Amazon product links to amazon.com/dp/<asin> where <asin> is Amazons product code.


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