Love the PublicLab's enthusiastic embrace of open source hardware and software licenses. If you don't want to 3d-print your own, you can get an awesome bluray laser spectrometer + webcam at their Kickstarter. https://www.kickstarter.com/projects/publiclab/the-homebrew-...
This is neat, but I wonder what the actual resolution of this device is (and how stable are the measurements)? Is it useful for anything other than just novelty?
Not sure that I really see the point of 3d printing the parts (although scratching many geek itches, yes) when your optics are going to be a much larger cost than the mechanical mounts, and the quality of the mechanical mount is so very important.
"when your optics are going to be a much larger cost than the mechanical mounts"
It would be nice if that were always the case. I suspect this is very much like my electronics stuff, a $2 MMIC amp mounted in a $30 aluminum diecast box. You can blow a lot of money on chassis and component mounting.
Also, speed. Could print something where an exact model just drops in place with superglue and a perfect fit. I could probably replicate their chassis in aluminum by hand in a days work, but I'd much rather go lazy and print one. Also each engineering revision drops from "days work" to "hit print and come back later"
Very good point, I would think before making a fancy case and adding useless colorful LED rings, you would try to prove the actual detection concept, which hasn't been shown by the maker.
Ordinarily, an expensive notch filter would be used which is cost prohibitive for most average people. My system avoids this cost by using two less expensive edge filters which when combined in the correct manner provide the same benefit as the notch filter...at the minimal cost of a little extra computing time.
If the goal is to cancel the incident light "carrier" frequency, couldn't this also be done interferometrically, just using mirrors and beam splitters?
I'm not a physics grad, but I'm curious: can one predict the Raman response of a molecule? For example: suppose I'm interested in detecting molecule X. I have a laser of frequency f. Given these two, can I predict that the reflected light (after Raman effect) will definitely be of frequency f' ?
More or less, you start with a quantum chemical DFT calculation, the Raman frequencies are associated with the vibrations of the molecule (second derivatives of the energy, once you're at the relaxed potential energy state). Raman frequencies are shifts (Stokes and anti-Stokes) relative to the laser frequency.
For medium sized molecule, a hybrid DFT calculation (which scales in computational time with N_eletrons^3 ) would cost a few CPU days of time, giving pretty accurate frequencies (there are known correction factors of ~0.95x to compensate for systematic failings in the theories).
What we are very bad at is predicting the Raman intensity from theory.
But you get the frequencies in the correct order, and can use this to assign observed peaks to particular vibrations within the molecule.
In principle, yes. The relevant equations can't be solved exactly for any non-trivial molecules. But there are a large number of different approximation methods, which boil down to a numerical optimization problem that converges on a bounding value.
These methods generally don't scale well, however, so as the size of the system grows, the approximations that can be successfully solved quickly grow too coarse to be useful.
There are also a lot of simple heuristic methods that a chemist can employ that don't require collaboration with a theorist, e.g. particlar chemical "motifs"/"functional groups" generally have a Raman resonance at a consistent frequency that is affected only slightly by the surrounding parts of the molecule (and the general direction and order of magnitude of that shift can also be approximated heuristically).
Finally, there are enormous catalogs of recorded spectra for a huge range of molecules at e.g. the NIST webbook (http://webbook.nist.gov/chemistry/).
They are opposites, in that the vessyl site strictly discusses apps and salesmanship without mentioning how it works whereas this project is strictly how it works and what it does and you figure out what to do with it.
I enjoyed reading the vessyl site because it explained nothing at all about how it works, so I immediately applied my engineering gut sense to trying to figure out how I'd make one if I wanted to. Small scale calorimetry heating and cooling with a peltier device a couple degrees at a time? That works for metals and phase transitions but probably not enough to tell diet sodas apart. Some kind of high res ultrasound to analyze waves and thus viscosity and thus density/composition? Personally I'd go all EE on it and shove a modest AC signal thru a big capacitor and get the dielectric constant of the "stuff" in the cup. A really accurate capacitive sensor to tell exact volume with a really accurate force sensor on the base to read weight/mass and a decent thermistor to calibrate for temp and you've got density at a specific temp. Once the raw data is in there, I'm guessing its all just lookups and best fits and the like.
[+] [-] jlev|11 years ago|reply
Participatory citizen-science FTW!
[+] [-] mcmancini|11 years ago|reply
Not sure that I really see the point of 3d printing the parts (although scratching many geek itches, yes) when your optics are going to be a much larger cost than the mechanical mounts, and the quality of the mechanical mount is so very important.
[+] [-] VLM|11 years ago|reply
It would be nice if that were always the case. I suspect this is very much like my electronics stuff, a $2 MMIC amp mounted in a $30 aluminum diecast box. You can blow a lot of money on chassis and component mounting.
Also, speed. Could print something where an exact model just drops in place with superglue and a perfect fit. I could probably replicate their chassis in aluminum by hand in a days work, but I'd much rather go lazy and print one. Also each engineering revision drops from "days work" to "hit print and come back later"
[+] [-] nmz787|11 years ago|reply
[+] [-] flatCat1597|11 years ago|reply
Take a look if you're interested at the project page on hackaday.io... hackaday.io/project/1279
[+] [-] CamperBob2|11 years ago|reply
Ordinarily, an expensive notch filter would be used which is cost prohibitive for most average people. My system avoids this cost by using two less expensive edge filters which when combined in the correct manner provide the same benefit as the notch filter...at the minimal cost of a little extra computing time.
If the goal is to cancel the incident light "carrier" frequency, couldn't this also be done interferometrically, just using mirrors and beam splitters?
[+] [-] nmz787|11 years ago|reply
[+] [-] discardorama|11 years ago|reply
[+] [-] jarvist|11 years ago|reply
For medium sized molecule, a hybrid DFT calculation (which scales in computational time with N_eletrons^3 ) would cost a few CPU days of time, giving pretty accurate frequencies (there are known correction factors of ~0.95x to compensate for systematic failings in the theories). What we are very bad at is predicting the Raman intensity from theory. But you get the frequencies in the correct order, and can use this to assign observed peaks to particular vibrations within the molecule.
http://www.gaussian.com/g_tech/g_ur/k_freq.htm
[+] [-] gipp|11 years ago|reply
These methods generally don't scale well, however, so as the size of the system grows, the approximations that can be successfully solved quickly grow too coarse to be useful.
There are also a lot of simple heuristic methods that a chemist can employ that don't require collaboration with a theorist, e.g. particlar chemical "motifs"/"functional groups" generally have a Raman resonance at a consistent frequency that is affected only slightly by the surrounding parts of the molecule (and the general direction and order of magnitude of that shift can also be approximated heuristically).
Finally, there are enormous catalogs of recorded spectra for a huge range of molecules at e.g. the NIST webbook (http://webbook.nist.gov/chemistry/).
[+] [-] 0xdeadbeefbabe|11 years ago|reply
[0] https://www.myvessyl.com/
[+] [-] VLM|11 years ago|reply
I enjoyed reading the vessyl site because it explained nothing at all about how it works, so I immediately applied my engineering gut sense to trying to figure out how I'd make one if I wanted to. Small scale calorimetry heating and cooling with a peltier device a couple degrees at a time? That works for metals and phase transitions but probably not enough to tell diet sodas apart. Some kind of high res ultrasound to analyze waves and thus viscosity and thus density/composition? Personally I'd go all EE on it and shove a modest AC signal thru a big capacitor and get the dielectric constant of the "stuff" in the cup. A really accurate capacitive sensor to tell exact volume with a really accurate force sensor on the base to read weight/mass and a decent thermistor to calibrate for temp and you've got density at a specific temp. Once the raw data is in there, I'm guessing its all just lookups and best fits and the like.
[+] [-] ibisum|11 years ago|reply
[+] [-] frontline|11 years ago|reply