[HN Gopher] A CD Spectrometer (2006)
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A CD Spectrometer (2006)
Author : wcrossbow
Score : 192 points
Date : 2023-09-13 08:26 UTC (14 hours ago)
(HTM) web link (www.cs.cmu.edu)
(TXT) w3m dump (www.cs.cmu.edu)
| msk-lywenn wrote:
| Does using a DVD or Bluray instead of a CD improves the result?
| The angle might have to be different?
| userbinator wrote:
| Here's a video showing the construction of one based on the same
| principle, but using a camera for wavelength measurement:
|
| https://www.youtube.com/watch?v=p3MzQ1OF3lk
| 1-6 wrote:
| I've been checking the quality of my light sources for years
| using a CD (florescent vs LED vs incandescent). Didn't DIY'ers
| know this technique for years?
| crazygringo wrote:
| Using a 0.2 mm slit? Or do you have an easier way that uses
| just the CD?
|
| First I've ever heard of it, and I went pretty deep into the
| rabbit hole of spectrum when I switched to LEDs in my home.
| Don't think this is very common knowledge.
| TacticalCoder wrote:
| How does that work? Are you using a CD to tell if one
| fluorescent bulb is better than another? Or to tell if one bulb
| is LED or incandescent or ...?
|
| > Didn't DIY'ers know this technique for years?
|
| I used to live in a rural area (fixing everything in the house
| by myself) so I'm quite the DIYer but I don't know anything
| about that!
| jonhohle wrote:
| I've been wanting to check my lights and didn't know about
| this.
|
| A few years ago we had several cans replaced with solid state
| LED fixtures and my wife has had a lot of trouble with sleep
| which roughly correlates. It may be placebo, but it seems like
| she also may get better sleep when watching an OLED TV vs an
| LCD iPad. It made me wonder if we should put 460nm filters on
| our ceiling lights.
| tecleandor wrote:
| Oh, for a while Public Lab's Paper Spectrometer [0] was very
| popular in "citizen science" workshops or forums. It was made
| peeling the diffraction grating of a DVD-R (not a +R) disc.
|
| It's a fun thing to do in an afternoon. 0:
| https://publiclab.org/wiki/papercraft-spectrometer
| anfractuosity wrote:
| I recently got a spectrometer with a fibre input from fleabay,
| which I've been enjoying playing with.
|
| I got a tiny ruby stone and shone a tungsten halogen light behind
| it - https://www.anfractuosity.com/files/ruby.png I could see a
| dip around 694nm like someone else's spectrum -
| https://en.wikipedia.org/wiki/Ruby_laser#/media/File:Ruby_tr....
| This is the same wavelength that ruby lasers emit light
| apparently.
|
| I'm planning on using it to try to measure ABV of beer/spirits. I
| noticed some of the cuvette holders with fibre inputs seem to be
| crazy expensive though, so probably need to DIY that!
|
| A while ago I got a little spectroscope that looked a bit like -
| https://shop.wf-education.com/science/op66595.html. And simply
| attached to a camera, to generate graph from.
| HerculePoirot wrote:
| A $500 DIY near-IR spectrometer that would sell for $10,000
|
| https://caoyuan.scripts.mit.edu/ir_spec.html
| anfractuosity wrote:
| Looks very impressive!, thanks
| qwertox wrote:
| Current discussion:
| https://news.ycombinator.com/item?id=37498142
| OJFord wrote:
| What sort of wavelength of sensor do you need for ABV
| measurements? Size of ethanol particle? Half it because of
| Nyquist? Or what does it have to relate to?
|
| I'm just wondering how fancy vs. DIY you need for that sort of
| purpose basically.
| anfractuosity wrote:
| This is the paper I've been looking at -
| https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356901/ they
| make use of a tungsten lamp and IR leds, I tried with just a
| tungsten lamp and only really saw a plateau around 900nm when
| ethanol was present. Their spectrometer goes further into IR
| than mine, mine tops out around 1000nm, but hopefully I'll
| still be able to get some results when I add IR LEDs.
|
| I'm not sure what the peaks correspond to regarding the
| ethanol molecule though afraid. It's been a while since I
| read the paper, but maybe that indicates this.
|
| I believe my spectrometer just has a linear CCD sensor.
| qwertox wrote:
| FYI, the ruby.png image is 19200 x 14400 pixels big. Luckily
| it's mostly white.
| anfractuosity wrote:
| Thanks for the heads up, just regenerated the graph
| kurthr wrote:
| Hey, try heating up that ruby! It'll turn darker as the bandgap
| moves toward the IR. You can shift your dip with a hair drier.
|
| It should move from ~1.15eV at room temp 75F/25C to ~1.10eV at
| 120F/50C, which should be about 35nm longer.
| anfractuosity wrote:
| Ooh, cool! Will definitely have to give that a shot.
| isoprophlex wrote:
| And here I was, thinking this was about circular dichroism!
|
| Cool article nonetheless..!
| higginsc wrote:
| same! I was excited to see something so esoteric from my grad
| school days come up
| dang wrote:
| Related:
|
| _Constructing a spectrometer using a CD_ -
| https://news.ycombinator.com/item?id=10285117 - Sept 2015 (9
| comments)
| symmetricsaurus wrote:
| In my high school physics class we measured the pitch between the
| tracks of a CD using the same principle. You just need a light
| source with a known wavelength, like a laser. It was a pretty
| cool experiment!
| SamBam wrote:
| What's the pitch between tracks?
| tmearnest wrote:
| 1.6 mm
| SamBam wrote:
| Ah, I see. Multiple meanings of both "pitch" and "tracks"
| on a music CD.
| anfractuosity wrote:
| That sounds a fun project :) I tried a little peeling of a CD-R
| under a microscope, where can see the tracks, I should try and
| measure the pixel distance and convert to track width -
| https://www.anfractuosity.com/files/cd-r.JPG
| dylan604 wrote:
| what microscope are you using? i've been itching to get into
| microscope photography for a new hobby, but because i know
| myself, it'll be a fun but expensive rabbit hole. i've been
| deliberately putting off on researching because i also know
| myself and will be just as likely to be shopping than
| researching
| anfractuosity wrote:
| It's an Olympus BHM that I got cheaply from ebay. It's a
| trinocular metallurgical microscope, that I added an old
| SLR to, for that photo. I noticed the semi-silvered mirror
| seems rather scratch though, so might need to look at
| replacing that.
| dylan604 wrote:
| are you attaching the camera directly with an adapter, or
| is it projecting on to whatever lens you are using? i
| guess i'm coming at this thinking of it in terms of
| astrophotography using T-adapters to connect in place of
| on eyepiece vs taking an image from the eyepiece
| dekhn wrote:
| Either works, but trust me, the trinocular part is far
| superior, ergonomically. You do need to know whether you
| want a metalurgical scope or a compound light
| transmission scope. The former is good at looking at
| opaque samples, the latter for transparent samples
| (biological stuff mostly).
| dylan604 wrote:
| that is something i have considered, but not known what
| terms to use to look it up. i would love to be able to
| look at opaque things in a highly magnified way, so the
| lighting issue is something i had in the back of mind. i
| do like the biological stuff in hopes of possible
| timelapse to show growth.
| dekhn wrote:
| This is what I have for general opaque and transparent
| stereo viewing: https://www.amazon.com/AmScope-
| SM-4TZ-144A-Professional-Trin...
|
| then I get this illuminator:
| https://www.amazon.com/AmScope-LED-6W-Powerful-Gooseneck-
| Ill... for top-down viewing, and it can be adjusted for
| bottom-up illumination.
|
| Then you can buy samples- microscope slides, petri dishes
| and samples,f rom places like Carolina Biological.
| dylan604 wrote:
| You're my hero!!! I hear Santa's sleigh bells now!
| anfractuosity wrote:
| In the trinocular port, there's an eyepiece, which I
| forget the magnification of afraid. And to that port I
| added this - https://www.alanwood.net/olympus/photomicro-
| adapter-l.html and then used an OM to EF mount converter,
| which the Canon camera directly attached to.
|
| I've since bought a microscope imager, that provides an
| output over USB. But I think I need to remove the OM
| converter, and get a shorter adapter to successfully
| attach to the microscope C-Mount.
| dylan604 wrote:
| Thanks for that. I was hoping that would would be
| possible. I think I now know what to ask Santa for xmas!
| chankstein38 wrote:
| This is an awesome picture! Forgive me if this is a stupid
| question but are we seeing 0s and 1s here? Is that what the
| black is? Kind of the equivalent to a morse code dit (0) and
| dah (1)?
| andruby wrote:
| That not a stupid question. It's a bit (ha!) more complex.
| These are called pits and lands.
|
| > The pits and lands do not directly represent the 0s and
| 1s of binary data. Instead, non-return-to-zero, inverted
| encoding is used: a change from either pit to land or land
| to pit indicates a 1, while no change indicates a series of
| 0s. There must be at least two, and no more than ten 0s
| between each 1, which is defined by the length of the pit.
| This, in turn, is decoded by reversing the eight-to-
| fourteen modulation used in mastering the disc, and then
| reversing the cross-interleaved Reed-Solomon coding,
| finally revealing the raw data stored on the disc.
|
| https://en.wikipedia.org/wiki/Compact_disc#Physical_details
|
| These encoding types are used to improve the "tracking" of
| the laser head, and to keep the timing consistent. We want
| the medium to regularly have changes between pits and lands
| to synchronise the timing and speed of the disc. The
| encoding scheme enforces this.
|
| https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI
|
| https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation
| peter_d_sherman wrote:
| Absolutely and utterly brilliant!
|
| I would have never in a million years thought of this use for a
| plain old CD... but yes, after reading this article, yes, I now
| see how a CD Spectrometer could indeed work!
|
| Again, absolutely and utterly brilliant!
|
| Upvoted and favorited!
| wcrossbow wrote:
| At my current company we build satellites with imaging
| spectrometers as payload and wanted to propose building a bunch
| of this on our upcoming team day. I was hoping for the non-
| technical team to get a better feeling of what is that we are
| trying to sell.
| diracs_stache wrote:
| Can you give a hint without doxxing yourself?
| lasermike026 wrote:
| Oh my word, that's awesome!
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