inexpensive webcam based spectrometer

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inexpensive webcam based spectrometer

Postby Bob Mcree » Wed Mar 26, 2014 3:24 am

The folks at publiclaboratory.org have come up with a $40 kit to build a spectrometer using an HD webcam, slice of a DVD-R, and a slit, mounted in an electrical conduit box. Using their web-based software at spectralworkbench.org, a full function spectrometer with data capture can be achieved. They make a less expensive unit that mounts on a cell phone, or custom construction can be used. The unit is based on a CERN design. The kit is a good educational tool and the idea has many applications that might interest members here. One of my pet projects is optical detection of pesticide residue by flourescent excitation. Leak detection is another idea.

The unit can only be operated online at present; there is some standalone Java software that needs work. The Google Chrome browser is required, as it is the only one that lets the software assume remote control of the webcam. There is lots of room for improvement in the design or modifications for specific applications. I invite others to suggest possible applications.

On the subject of metrology, light and color measurement has been a major part of my career and is still an interest in retirement. I have some Photo Research equipment including a 2856K black body source and a Spectra photoradiometer. I have some interest in developing an inexpensive PIC based photoradiometer, and welcome others who may have similar interest to collaborate. This is just one project of many, so there is no rush.
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Re: inexpensive webcam based spectrometer

Postby Doug Coulter » Wed Mar 26, 2014 11:24 am

This looks like something worth pursuing. Why insist that it be java/phone app, though? Why not make straight out PC software for this? Shouldn't be that hard since vid libraries etc are already there to be called, and the analysis shouldn't be that seriously hard.

There would be limits - I probably couldn't get this to resolve tight enough to see, say, Doppler shifts in the hydrogen lines due to how fast the atoms were going in a fusor (which would be nice to know, but would take etalons or something), but you could sure make a great leak detector - poor man's mass spectrometer, with it. I'd think there would be some accuracy issues vs wavelength and you'd want to calibrate the camera response some way, but that might not be that big a deal once the basic thing was working, if you had a known light source.
No shortage of data with a bright source...after all, it's a video camera, and you can average for awhile if you need to, and probably do other digital signal processing tricks since I'd bet the spectrum isn't zero-width, so you'd have more than one pixel per color (deliberate misalignment could result in effectively having pixels closer together along the spectra too).

I'm not a windows-head anymore, but I know there's considerable camera handling software libraries and video->still kinds of things available in linux that can be called from most languages to get to the basic bits you need for a spectrum, and free plotting software as well.

By the way, to put in a link here, you can use the url button. It produces this:
Code: Select all
[url][/url]


You put your url inside the initial tag like this with whatever you want to look like a link between the start and end tags, like this:

Code: Select all
[url=http://spectralworkbench.org/]Some highlighted text[/url]


Which produces this:
Some highlighted text

And oh, by the way, thanks for posting a metrology subject under the right subforum. I've got to go remind a couple of regulars here that getting a neutron tube to work is metrology, not analog electronics, so much. We try to keep this organized!
It's also part of the reason I didn't let in a huge flood of people all at once - too much work for the moderators here to keep it all straight.


FWIW, both google+ hangouts and skype work on all the major browsers, so it's not just chrome that lets you get to the vid stream. It might be a different API, but they all manage it some way.
No need for a browser at all, actually, speaking of "bloat". You can get to all this working a heck of a lot closer to the "metal" in all opsys. It's just that I'm only expert in the one (linux) right now, and not particularly expert with vid streams, but I do hardware-direct data aq no sweat with small programs in things like perl.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: inexpensive webcam based spectrometer

Postby Jerry » Wed Mar 26, 2014 4:06 pm

There was one guy who was making a open source spectrometer of much higher quality. They were designing it around a line CCD like commercial units use.

I have a scanning monochrometer that I want to get running. It has internal stepper drive electronics that drive the grating with step/dir signals. I have one of the little all in one Hamamatsu PMT modules that I plan on attaching to the output and maybe use something like an arduino to control it all.

Or just get myself one of the little ocean optics units.
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Re: inexpensive webcam based spectrometer

Postby Bob Mcree » Wed Mar 26, 2014 9:58 pm

Hey Jerry, greetings from another "webfoot" here in Oregon. I am a couple of hours from you. I am a California native who moved here 7 yrs ago so we could afford to have room for our horses to run. I worked with the early Ocean Optics spectrometers that used a Sharp fax machine detector. We worked out a way to use them for photometric and colorimetric measurements and used them to build test equipment for all the big guys like HP, Dell, Sony, etc. when they were building the first flat panels.

We used the spectrometers without a slit, and let the fiber diameter control the resolution and sensitivity. With a 200u fiber we were able to measure down to 0.1 nits or candela per meter squared. (talk about nit-picking). We measured color to within .005 in xy color space.

I am interested in helping people build real tri-corders. My short term goal is demonstrating it is possible to detect some of the pesticide residue in our food with blue leds and webcams. There are lots of surplus line detectors of various technologies that can be used to build detectors from way below vis to way above. I have lots of experience in assembler and machine language programming with 6800-z80-pic and beyond. I am interested in building a cheap accurate spectrometer to help others learn about this technology.

I am primarily a hardware guy. I would love to find others to work together on spectrometer applications as well as colorimetry and other metrology apps. I also helped some of the first companies to make CRT displays figure out how to improve line width and geometric parameters.

When I think of your home, Beaverton, I think Tektronix. The 475 scope that helped me build the first MRI prototypes at UCSF in the late 70's is still serving me well. I have only been married 30 years next month. My 475 scope was with me long before that :)

BTW did you know the ocean optics spectrometer was developed with DARPA money? It was for ocean pollution measurements at first.
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Re: inexpensive webcam based spectrometer

Postby Jerry » Thu Mar 27, 2014 2:45 am

Yeah, Tek is just down the street, maybe a 5 minute drive away. Well, at least what is left of it. It is a shell of it's former self.

I have a lot of ex-Tek equipment, one of my RGAs came from there, my big coating system, my cnc lathe, and a bunch of other misc electronic equipment like my Gigatronix RF signal generator and a whole bunch of other little things here and there. There are a lot of spin off companies around here too like Planar, Maxim, and Triquint.

I used to do service calls in Bend but I have not been over the hill in years.

I had a nice Spectrophotometer up until last year, had to sell it for money when I couldn't find a job. It was fiber coupled but it did use a slit.
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