The Lowspec spectrometer

[drjolo]

I use LowSpec spectrometer in the (mostly) remotely controlled roll-off shed and also I plan to use 1800 lpmm grating, so I decided to automate the device. The automation covers such functions:

• moving Relco starter in and out of optical train
• adjusting grating angle
• adjusting focus
• switching on/off Relco starter
• regulating 0-100% slit LED iluminator
• perform all the tasks above from the dedicated small software

The components that were used:

• three small 12V BYJ28 stepper motors with integrated gear box
• Arduino Nano
• two ULN2803 universal drivers
• universal PCB, two 5.5/2.1 DC sockets, 5 and 2 pin JST XH connectors, some cables and wires
• 5mm red LED with 15 degree light angle as slit iluminator
• M5x100 bolt that replaces M5X80 bolt in focuser
• M6x40 bolt with M6x20 cylindrical nut that replaces micrometer screw to regulate grating angle
• 3D printed elements - casing, gears, etc

 

  

  

All gears and software were developed and assembled step by step, so actually there was no serious problems during whole process. Currently Relco starter is controlled with small relay, but it will be replaced with 12V inverter, so no 230V will be supplied to spectrometer. After one and half night session all worked well, and I didn't need to visit my shed to refocus or change spectrum range. And that was the idea behind it

If someone is interested in this solution please let me know, so I clean up all files and share STL objects to print, schematic, Arduino sketch and control panel software. Panel is for windows system only, but the communication protocol with Arduino is pretty simple, so it can be rewritten to other systems as well. Or it can also be controlled using serial port terminal as well. 

RR Her spectrum below - captured already with modified LowSpec spectroscope:

[ejp1684]

Wow, I'm impressed! Not sure I'd be capable of doing all that even if I had all the 3d files and instructions. I'd be interesting in seeing them, though.

Eric.

[Jagho]

1 hour ago, ejp1684 said:

Wow, I'm impressed! Not sure I'd be capable of doing all that even if I had all the 3d files and instructions. I'd be interesting in seeing them, though.

Lukas, maybe you could offer these accessories in your Astrojolo shop.

[Thalestris24]

I've had enough trouble just trying to focus mine manually... Also, was testing it out last Friday and had a bit of a disaster. The whole assembly fell off the scope and crashed to the floor 😮. The Atik broke off (the pla T2 insert came out). I put it all back together ok (though it's now nicknamed 'Humpty'). I couldn't get a spectrum out of it It was only later that I realised that the grating assembly had jumped out of place. Fortunately, it was easy enough to push the grating assembly back in place but I've had trouble getting a sharp focus on a starter bulb. I have recorded spectra of the cloudy sky, the Moon and a floodlight. Will have a go at processing them in BASS Project when I can.

Louise

[Paul Gerlach]

9 hours ago, drjolo said:

If someone is interested in this solution please let me know

Uhh yes please!! Great work Lucas!
I'm a bit of a noob when it comes to electronics but I'm eager to learn. I can make out the Arduino Nano but I can't place the other components (ULN2803) and a capacitor. Is that for controlling the stepper motors? I would like to see more of your design. I think most observers will eventually want to control things remotely.
A while ago a LOWSPEC user in Spain came up with something similar (link) but I find your use of 3D printed gears much more appealing. I'm not so sure about sticking the Relco bulb directly in front of the slit. I think It's better to do it via a diffuser (e.g. reflecting it of a white surface).

Regards,
Paul

[drjolo]

11 hours ago, Paul Gerlach said:

(...) I'm not so sure about sticking the Relco bulb directly in front of the slit. I think It's better to do it via a diffuser (e.g. reflecting it of a white surface).

Yeah, I already have problems with such solution - I wrote about it at separate thread https://stargazerslounge.com/topic/348122-relco-sc480-starter-lines-position-depends-on-bulb-orientation/ . I need to redesign it to use some diffuser. 

[Paul Gerlach]

On 12/02/2020 at 11:28, Thalestris24 said:

The whole assembly fell off the scope and crashed to the floor 😮. The Atik broke off (the pla T2 insert came out)

Ohw my! That terrible! Was it PLA glued onto PLA? What glue did you use?
I had mine LOWSPEC attached to the telescope for weeks and did not have any problems. But that was printed in ASA and the threaded inserts we glued with a fair amount of two component epoxy glue.
How's you camera? Hope it survived this ordeal.

Regards,
Paul

[Thalestris24]

Just now, Paul Gerlach said:

Ohw my! That terrible! Was it PLA glued onto PLA? What glue did you use?
I had mine LOWSPEC attached to the telescope for weeks and did not have any problems. But that was printed in ASA and the threaded inserts we glued with a fair amount of two component epoxy glue.
How's you camera? Hope it survived this ordeal.

Regards,
Paul

It wasn't glued - since I'd had so much trouble with the threads. It is glued in place now! If I were building it now I'd use a metal t2 insert. I've had trouble with the slit holder also and wondering whether to reprint it. It's difficult to keep the slit aligned. At the moment I can't get a sharp focus - not sure if that's something to do with the slit. The camera is ok. It fell out of the scope because thumbscrews on the scope must have come slightly loose. I'm double checking, now, when the Lowspec is attached.

Louise

[saac]

On 12/02/2020 at 08:50, drjolo said:

If someone is interested in this solution please let me know, so I clean up all files and share STL objects to print, schematic, Arduino sketch and control panel software. Panel is for windows system only, but the communication protocol with Arduino is pretty simple, so it can be rewritten to other systems as well. Or it can also be controlled using serial port terminal as well. 

RR Her spectrum below - captured already with modified LowSpec spectroscope:

 

Lucas (drjolo) that is an amazing upgrade you have made, I can imagine these mods make it a joy to operate remotely. I'm just about to start testing my optics on my Low Spec but just to echo what Eric said; if you were ever to make your plans/code available then it would be gratefully received. I would also be keen to see and hear how you  get on with using the LowSpec , I really want to understand how this amazing spectrometer can be exploited. 

Jim 

Edited February 13, 2020 by saac

[drjolo]

Thanks Jim! 

I will do some final tweaks and clean up, and also need to add some small diffuser to Relco starter to make calibration more reliable. Then I will post or link whole project here.

At this moment I am very happy with LowSpec results. Resolution is pretty high (over 1500 at the red part with 600 lpmm gratning), it is fairly easy to setup and calibrate. I use QHY163M as main camera, ASI290MM as guider, all is attached to 10" SCT and there is IMX224 camera with 50mm guider as electronic viewfinder. One tricky part (for me at least) was to align guiding optical path. Guiding lens is fast and needs to be set very precisely to avoid coma and/or astigmatism. Now it is time for me to decide what kind of work it should do. I am not yet 100% sure, but I ordered 1800 lpmm grating to check it out  

I already had few nights with LowSpec (with and without Moon), and my almost all spectra are at my blog https://astrojolo.com/spectra/ 

Edited February 14, 2020 by drjolo

[ejp1684]

1 hour ago, drjolo said:

One tricky part (for me at least) was to align guiding optical path.

Same here. I've now used a laser to try and align the mirror, waiting for miserable UK skies to clear so I can try it out.

Eric.

[Thalestris24]

Hi

I'm thinking of swapping over my Atik383l+ with a qhy183m. The Atik has been driving me nuts - it takes about 12 secs to download a full frame so trying to focus it, is difficult and frustrating. The 183 has a smaller sensor so won't cover as much of the spectrum in one go. The big Atik covers 4037-6963A, the 183 only covers 4416-6584A (SimSpec v4.3). But the 183 is a lot more sensitive, lower noise, a lot quicker - and a lot quieter! Am I right in thinking I'd just take two exposures with rotation of the grating position using the micrometer? Plus calibration exposures for each position? Presumably I'd also have to adjust focus for each position, but maybe that's really a good thing, if a bit of a pain.

Louise

[Merlin66]

Louise,

Yes, use the micrometer to change the wavelength, take a reference image, use this to adjust focus, best FWHM (if necessary).

BASS can join the calibrated sections together.....

 

[Thalestris24]

Just now, Merlin66 said:

Louise,

Yes, use the micrometer to change the wavelength, take a reference image, use this to adjust focus, best FWHM (if necessary).

BASS can join the calibrated sections together.....

 

Oh ok, thanks Ken! I knew there had to be a way of doing it as lots of people seem to use cameras with smaller sensors. I'll give it a try sometime this week 🙂 

Louise

[andrew s]

16 hours ago, Thalestris24 said:

Hi

I'm thinking of swapping over my Atik383l+ with a qhy183m. The Atik has been driving me nuts - it takes about 12 secs to download a full frame so trying to focus it, is difficult and frustrating. The 183 has a smaller sensor so won't cover as much of the spectrum in one go. The big Atik covers 4037-6963A, the 183 only covers 4416-6584A (SimSpec v4.3). But the 183 is a lot more sensitive, lower noise, a lot quicker - and a lot quieter! Am I right in thinking I'd just take two exposures with rotation of the grating position using the micrometer? Plus calibration exposures for each position? Presumably I'd also have to adjust focus for each position, but maybe that's really a good thing, if a bit of a pain.

Louise

Can't  you just use a sub frame during focusing? Pick a line and do a ROI round it.  

Regards Andrew 

[Thalestris24]

52 minutes ago, andrew s said:

Can't  you just use a sub frame during focusing? Pick a line and do a ROI round it.  

Regards Andrew 

Yeah, I can do a ROI but the camera itself is still slow (low qe) and noisy (db). The qhy183m will be much better, quicker, and much more sensitive 🙂. I'd really prefer to see the whole spectrum to focus on also. I'll try the qhy out tomorrow 🙂.

Louise

[Merlin66]

Louise,

Any updates???

Ken

 

[Thalestris24]

3 minutes ago, Merlin66 said:

Louise,

Any updates???

Ken

 

Hi Ken 🙂 How are you?

Um, not really. Having put the Lowspec back together after it fell off the scope, I've been struggling to get a clean calibration lamp spectrum. I changed the Atik over to a qhy183m which is much more sensitive and easier to use. But I've been getting a lot of 'ghosting' with the image. I've been trying to improve the calibration source by putting it in a holder with a slit. It doesn't seem to help if I diffuse the source. Not done anything with it today. I've been struggling with adjusting the focus also. Can you remind me how I check collimation? Is it by counting the number of pixels from the illuminated slit?

Thanks

Louise

[Merlin66]

Louise,

Collimation of the spectrograph optic is best checked using a laser collimator. Placed at the inlet port, adjust the grating angle until the beam is seen on a centre marked target (piece of paper etc.) at the camera port.

If everything is properly aligned the laser dot should sit on the centre of the target. 

Focusing: the slit gap can be measure in pixel and compared with the gap setting, minimum width = best focus. Normally this is actually done by measuring the reference lines, close to the target wavelength. The FWHM should be a minimum to achieve maximum R value.

HTH

 

[Thalestris24]

1 minute ago, Merlin66 said:

Louise,

Collimation of the spectrograph optic is best checked using a laser collimator. Placed at the inlet port, adjust the grating angle until the beam is seen on a centre marked target (piece of paper etc.) at the camera port.

If everything is properly aligned the laser dot should sit on the centre of the target. 

Focusing: the slit gap can be measure in pixel and compared with the gap setting, minimum width = best focus. Normally this is actually done by measuring the reference lines, close to the target wavelength. The FWHM should be a minimum to achieve maximum R value.

HTH

 

Um, I meant how best to adjust the collimation lens? When I try to get the best focus it's not been easy to get a sharp image so was wondering if that might be due to the position of the collimation lens? Maybe there's another reason...

Thanks

Louise

[Merlin66]

Using a guide scope, prefocussed on infinity,  positioned behind the collimator. The slit gap should be in focus and a clear narrow gap.

 

[Thalestris24]

1 minute ago, Merlin66 said:

Using a guide scope, prefocussed on infinity,  positioned behind the collimator. The slit gap should be in focus and a clear narrow gap.

 

Ok. Hmm... I'd have to take the grating out to do that - or maybe I could just use a mirror. It's 2:30 am here now so I'm turning in for the night!

Thanks 🙂 

Louise

[ejp1684]

6 hours ago, Thalestris24 said:

Ok. Hmm... I'd have to take the grating out to do that - or maybe I could just use a mirror. It's 2:30 am here now so I'm turning in for the night!

Thanks 🙂 

Louise

Or use the zero order reflected from the grating?

Eric.

[drjolo]

7 hours ago, Thalestris24 said:

Ok. Hmm... I'd have to take the grating out to do that - or maybe I could just use a mirror. It's 2:30 am here now so I'm turning in for the night!

I have used both a flat mirror from cheap 1.25" diagonal, and also zero order as Eric mentioned above - both solutions worked ok. 

As a collimation tool I used DSLR camera with 50mm lens set manually to infinity. And I have been watching slit at the Live View at 10x magnification. 

[Thalestris24]

1 hour ago, drjolo said:

I have used both a flat mirror from cheap 1.25" diagonal, and also zero order as Eric mentioned above - both solutions worked ok. 

As a collimation tool I used DSLR camera with 50mm lens set manually to infinity. And I have been watching slit at the Live View at 10x magnification. 

I have a small 45 deg mirror that I made before 🙂 I'll try a finder first and see how I get on - I'd rather do that than hunting around for the zero order. Will post my result 🙂. 

Louise