I should also add that the spectrometer connected to the MacBook, so checking how to control the USB webcam settings (hopefully for free, as some people suggest to buy this app https://itunes.apple.com/gb/app/webcam-settings/id533696630?mt=12).

Also worth noting that when I press on "Settings" here, nothing happens:

Also tried both Safari and Firefox (while having Chrome closed). In both cases, there was a request for the permission to use the USB webcam, but nothing is displayed on the screen at all.

OK well if I remember rightly Settings as you show above doesn't change the camera settings. It allows you to select your sample slice through the spectrum, if necessary to reverse the image and other stuff to do with the SW web interface. The SW pages can sometimes be a bit slow to respond making it hard to follow what is supposed to happen. Once the spectrometer is fully assembled there is often very little light coming through that slit. The dynamic range of the web cam is not that big so it can be essential that exposure and gain are controllable. Also things like white balance and or colour temperature will have an effect on your results. For calibration start with a CFL lamp really close to the slit and wobble the spectrometer back and forth to see if you get any kind of image. Usually with the lamp close you will get an overexposed image and need to either preset the gain and exposure or move the lamp away. If you still can't get an image either camera is faulty, is getting pre-set to low values of gain and exposure or the geometry of the parts inside your spectrometer is way, way off.

Hmmm, I wonder if I need to install any special drivers for the camera for the Mac OS...?

I don't know the Mac OS well but I'd guess there is a thing somewhere to manage devices and that should show your cameras. If you see two cameras then you have both a web cam and the spectrometer web cam connected and there will be an option to select between them. On my system SW and Firefox were not happy with having two cameras and tended to default to the wrong camera. So I unplugged my web cam.

OK, I'll resume tomorrow, but feels like I'm on the right track. Thanks a lot for the help so far!

Hi, what operating system do you use? There's some guidance on webcam selection here:

https://publiclab.org/wiki/spectral-workbench-usage#Webcam+selection

Thanks, Warren it MacOs and I'm looking at changing camera setting. I hope something like this might help:

https://github.com/HBehrens/CamHolderApp

For what it is worth, I just dug out and hooked up my prototype of the Public Lab Spectrometer 3 and, without fiddling around, got exactly the same result you have - black screen. I don't remember what slit size I have in there, but with any of the relatively small slits and given the degree of collimation along the length of the spectrometer there is a lot of attenuation. You really have to get the thing lined up with the light source and use a bright light source to get an image (as well as adjust the camera settings). It took a high intensity LED torch right up against the slit to get an instant and obvious image.You might try using the widest slit, I think that is a 0.4mm, or just cut a wide slit in a piece of card until you get the thing working and get used to how to set it up.

Pupshaw, thanks I tried that, it made no difference. I'll try to get the camera setting changed. Didn't have much time in the last few days, but this is what I'm looking at:

https://github.com/HBehrens/CamHolderApp

Tried building CamHolderApp from source, but had to download QTKit later, found that QuickTime has been removed from Xcode, etc.

Finally found a binary app: http://camholder.org/download/CamHolderApp.zip

Downloaded it, starts fine. Will try later tonight to connect to the camera and see if I can change the settings. I don't have the camera with me now.

This is the screenshot of CamHolderApp:

CamHolderApp didn't detect the camera. So these are my next steps: 1. Connect the camera to Raspberry Pi Zero and access via VNC Connect: https://www.realvnc.com/en/connect/docs/raspberry-pi.html 2. Explore the idea of using Raspberry Pi Zero with its camera inside the original public lab enclosure (potentially with some 3D printed part).

Also tried to build this app😀 https://github.com/valgit/uvc_scanner/tree/master/UVCCap

The app starts but doesn't detect any UVC devices connected.

Quick update:

Followed this: https://www.youtube.com/watch?v=2iVK8dn-6x4

And this: https://www.raspberrypi.org/forums/viewtopic.php?t=173181

And got spectralworkbench.org capturing images on Raspberry Pi Zero W with Chromium browser.

Next steps: 1. Ordered a micro USB to USB cable, so I can try attaching the original camera to Raspberry Pi 2. Ordered a micro USB cable with 90 degrees up connector so I can fit the Raspberry Pi in the original Public Lab spectrometer box.

Umm... It's quite a while since I fired up my Raspberry Pi but as far as I recall it has a couple of activity LEDs plus two status LEDs on the network connector. You really don't want a load of LED's flashing inside the spectrometer housing. I think you will have to mount it to one outer side of the spectrometer.

Hmm! Interesting point. I didn't think about the flashing LEDs! But thinking about this, it should be possible to put some black tape on the LED. I'll try it. Talking about Chromium+VNC there's nothing special about it. It's just starting VNC server and then instaling an launching Chromium browser. The main issue is speed. It takes type to start the browser and it's not comfortable to work with. I'll try if I can access via Raspberry Pi via HomeKit/Wifi from my Macbook. It should be possible.

My experience is that blocking all the light from a LED indicator is a lot harder than you might think. Other than disconnecting the LED's almost nothing will guarantee no light escapes. You could try smearing a blob of plasticine or blutack over them, but you still tend to get diffused leakage (from the PCB mounted LEDs) through the PCB itself.

OK! Maybe it's possible to just disable LED via software:

https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi

I can confirm that this tuned activity LED on Pi Zero off:

#echo none | sudo tee /sys/class/leds/led0/trigger none

echo 1 | sudo tee /sys/class/leds/led0/brightness

1

I can't edit the previous comment, I get an error when I try. This is what I wanted to post:

echo none | sudo tee /sys/class/leds/led0/trigger none

echo 1 | sudo tee /sys/class/leds/led0/brightness 1

Quick update😀 1. I got the USB cable for the Raspberry Pi Zero delivered, however it doesn't fit into the original Public Lab enclosure. 2. I now installed Ubuntu VM via VirtualBox and posting this message from Linux. I'll try attaching USB camera to my Macbook and make it visible to Ubuntu.

Update: got the camera to work on Ubuntu!. The issue was fixed by installing VirtualBox extension pack and choosing USB 3.0 (instead of USB 1.0 )

I'm now able to control UVC Camera settings, however, the images are still dark when I close the list. I was hoping to be able to set Auto Focus to on or off, but I can't find such setting.

These are the settings I can change:

uvcdynctrl -d video0 -c Listing available controls for device video0: Brightness Contrast Saturation Hue White Balance Temperature, Auto Gamma Power Line Frequency White Balance Temperature Sharpness Backlight Compensation

Thanks! Warren maybe you can post the settings that you use so that I can try them tomorrow?

I actually usually use default webcam settings! So going back to the original question, I believe there may be an issue with the angle or the orientation of the DVD... sorry, it's getting quite difficult to follow all the threads on this page --

In this comment: https://publiclab.org/questions/Tomas0413/06-16-2018/dark-images-can-t-get-spectrometer-to-work#a1034

You had a perfect image, so I don't believe there is a problem with the camera itself.

But I don't see any spectra even in that image, where we should. Can you upload a new picture similar to this one but clearly showing the DVD orientation?

Thanks for the response, I’ll upload tve image tomorrow. But aa far as I remember even if I leave only the camera inside the box the moment lid closed - it’s complete darkness. I saw somewhere on PublicLab that cameras were out of stock and then new ones arrived. Could it be that the model is slightly different? Could it be that the camera you use has AutoFocus off by default and the one I have AutoFocus on without an option to turn it off?

For example threre’s a similar camera on AliExpress and the description says that it’s AutoFocus and that this can’t be changed : Look what I found on AliExpress http://s.aliexpress.com/yEJbInIn

Great, i look forward to seeing the photos. Please also upload one of the front slit of your box!

I don't think autofocus would cause complete darkness! I'm eager to see how the grating is aligned and hope we'll solve this that way. Fingers X!

And this example says FixedFocus:

Look what I found on AliExpress http://s.aliexpress.com/yiIBvmiy

Your Guvcview control panel looks much like mine running on a real Ubuntu PC (If I understand you correctly you are running it in a virtual machine). Camera settings persist after I close Guvcview. Not sure why you mention auto-focus, you don't want it and I'm pretty sure the camera that ships with the spectrometer doesn't have it. Spectral workbench and /or the browser can be very picky about accessing the camera. When you run Guvcview do you see a spectral image in the viewing window? If not something is wrong with your slit or your diffraction grating.

Pushpaw, thanks for the reply.

Not sure why you mention auto-focus, you don't want it, and I'm pretty sure the camera that ships with the spectrometer doesn't have it.

I mentioned Auto-Focus, just guessing what if the camera model I received is not correct and what with I received a model with Auto-Focus. I took a picture of the camera and it says "NB23 S2", and the model I found on AliExpress (https://bit.ly/2m2ezVf) says it's fixed focus. So maybe this isn't a problem. I also removed the grating completely. So when the lid is lifted, I can get a good picture. When I close the lid, the image turns completely dark.

Warren, for now, I just completely removed the grating. And actually, I no longer use a slice of DVD, I bought a set of gratings (an upgrade). When I had grating installed, I noticed that part of the image is covered, so I need to check why. But still after having the entire grating removed, still have 100% dark images when the lid is closed.

OK - that's OK, the camera should be looking at the dark inside surface of the lid. The grating or DVD should bend/refract the light downward into the lens -- this is why i'm concerned about the orientation of the grating.

For a DVD, it's easy to see when the curved outer edge of the disc is at the top of the box. For film gratings, this is harder to determine, but you can try rotating it 90° and trying it both ways -- it has a directionality, basically.

I would try with the DVD first just because it's easier to know when it's properly aligned. Then upon confirming nothing else is wrong, and it's working, switching over to the grating again.

Can you upload a picture with the DVD in place? Thanks!

Thanks for prompt replies. I'm travelling now without access to the spectrometer, I'll share new photos on Mon/Tue next week.

The grating orientation might be the thing. I somehow didn't think about it before. I do have a laser pointer, and when I tried a few weeks ago, I was able to get something when pointed to the slit. It's just that "something" didn't look right. I think I have to check what about doing with that grating... I feel the "aha moment" is getting closer :D

Just tried it and it is important to note that what you will see is 3 dots once the laser beam has passed through the diffraction grating. One is where the beam passes straight through and then there are two diffracted beams one below the main beam and one above. And you can see the direction of the track / lines on a DVD by just reflecting some daylight off it. You will see a reflected spectrum at right angles to the lines. I'd assume the same was true for any diffraction grating. But note that the diffraction angle is dependant on the LPI of the grating. If you are using a piece of commercial grating that is not as fine as a DVD the light may not be bending far enough to hit the camera.

Quick update:

The grating orientation might be the thing.

I tried 4 * 2 = 8 combinations for the grating, and it didn't make any difference - in all cases, the camera gets entirely dark once I close the lid. I'll have to step read all the comments once again and think about what to do next...

I have also a spectrometer version for the mobile phone, so I'll what are the results with it and maybe it will help to figure out what is wrong.