I frequently have laser-cut acrylics made, in lots of several hundred, and the simplest ones are still about $3.50 each -- the process is not cheap.

Thanks, Dave - actually, that sounds reasonably cheap vs. quotes we get for wood manufacturing, but I wonder if you'd be willing to share where you get acrylic cut, and/or if you know of places that do affordable wood manufacturing?

I've been starting to think of a possible design in three parts:

1. rigid base-and-optics interior
2. paper housing for light
3. rigid exterior

I think the rigid interior could be built inside the existing device, and a pretty affordable exterior enclosure could fit outside. Obviously we could simplify the paper if it's just light-blocking, but I'd like to keep thinking about how new designs could be upgraded-to by folks who have the current kit. Not a hard constraint, but unless there's a solid reason to abandon that as a constraint, it's nice to have.

So, I was thinking -- could we post a "spec for the spec" as a kind of challenge -- using the steps Dave outlined in the comments on his post a couple days ago. That is, whatever designs people post (and/or collaborate on) would have to be run through a simple test, and to meet these specific empirical specs, to "pass" as a design. Another constraint could of course be cost, though we can pool resources/knowledge on manufacturing processes and vendors to keep that low.

If you're interested, it'd be nice if @stoft could post it, since he enumerated the "first draft" of the specs. We could iterate on the specs as well, of course, and I'm happy to post it as well. I think it'd need a clear "testing methodology" that people could follow, and a numbered set of "specs" it'd have to meet. Thoughts?

The little thing with the hole in front of your DVD - is this for preventing stray light coming in?

@viechdokter, yes, it was just an experimental baffle for stray light. Keeping reflections low inside the space between slit and grating is necessary as the slit can let in light from any angle. While the only light we care about is that which is inline with the grating, that doesn't mean that will be the only light traveling inside the enclosure. But, no, the baffle doesn't require rigid mounting in the way that the camera does -- using the same style mounting parts was simple the easiest thing to do and the rigid mount doesn't hurt.

Also see some of the suggestions here, which experiment with interior rigidity as well: https://publiclab.org/notes/ygzstc/08-19-2015/some-suggestions-for-spectrometer-v3-0-and-oil-testing-kit-otk-attachment

Jeff, I have a local supplier call Tap Plastics but I assume laser-cut plastics are now available in most metropolitan areas.

Ok, that's fine to keep the previous version in mind. In fact, my basic proto spectrometer module does fit that paper housing. I just abandoned it when I discovered there are simpler ways to cover and there remained the issue that that paper housing decoupled the base optics from the user's mounting -- i.e. the user can hold / mount the paper but that doesn't actually control the mechanics of the base optics. That ends up adding mechanical motion to the optics which is only indirectly related to the housing. Sorry, but there is just no substitute for rigid mounting -- either it is or it is not.

Yes, the idea of a measurement reference test is a good one. Actually, I'd previously suggested that a CFL signature might form such a reference. While I'm not finished decoding the SWB 'quality' rating code and implementing some comparative testing, I don't think that value is the correct one. I think a check of several specific factors of a CFL signature might provide better analysis of spectrometer performance -- like how well the double-green peak is resolved. That said, I'd still suggest that work on both such a qualification test and work on a replacement product design continue together. Many design concepts can be analyzed just through thought experiments w/o building hardware or involved testing. In parallel, if users are to be able to test and qualify their spectrometers, than those algorithms need to be implemented in whatever software is commonly available -- SWB for now it seems.

I'd suggest 3 things are required: 1) a list of what is to be tested and the basis of the criteria for passing the tests, 2) three lists of specifications, a) the measured (so far) spec limits under the best of conditions and b) the specs that we'd expect a product to pass in the hands of the user and c) a slightly tighter manufacturing spec (i.e. a 'professionally built kit will pass'), and 3) a set of specs the mechanical design must meet and the reasons those specs were selected (eg, materials cost, assembly tools, rigidity, light-tight qualities, assembly compatibility, legacy options, modularity (i.e. adaptability for an OTK, etc.). Should also keep in mind that some might be willing to pay extra to get a fully assembled version.

Might need 3 dedicated spaces for these topics to evolve.

Warren,

I know that the spectrometer that I have built is extremely rigid, but it is not made of cardboard, It is made from square black plastic rainwater down-pipe. If you look back through some of my submissions you will see photos of it. Is black plastic rainwater down-pipe available in the USA? If it is, I will gladly describe how I made my rigid and opaque spectrometer.

Guillaume851

Thanks, Guillaume851 - I've seen yours and it does look very rigid, thank you! Part of the design I'm prototyping in my note here is a design we could lasercut from acrylic and sell with our current kit, and that is easy to make from materials available everywhere in the world, even without a lasercutter.

Hi, everybody!!! We've finally developed a new approach to posting/sharing/collaborating, and are looking at how this extends into hardware modifications as well.

You can read a bit about the Questions system and the Activities system on these posts: #activity-grids

But, following up on this series of ideas, a few questions and one "Upgrade" have been posted which I hope will help us to take steps forward:

https://publiclab.org/notes/stoft/09-16-2016/stability-upgrade-mockup-for-plab-spectrometer-3-0 (which riffs on ideas here and in other notes)

And one "replication" or "build" of that documented upgrade: https://publiclab.org/notes/warren/09-20-2016/building-the-stoft-stability-upgrade-for-desktop-spectrometry-starter-kit-3-0

Formulating a question about light leaks/ambient light: https://publiclab.org/questions/warren/09-19-2016/how-can-i-reduce-ambient-light-inside-the-desktop-spectrometry-starter-kit -- I imagine this may lead to another "upgrade" or two, which others could replicate.

I encourage folks to:

1. try out the upgrade and report back with results (replication!!!)
2. pose clear "answerable" questions which could lead to, or justify, new upgrades (i.e. define the specific problem the upgrade would solve, and how to measure it)
3. post your own upgrades with clear instructions and invite others to replicate (and help them if they have trouble!)

Thanks!!!

warren awards a barnstar to viechdokter for their awesome contribution!