4 ms·

RamanPi – The 3D Printable Raspberry Pi Raman Spectrometer

63 points by MichaelAO 12y ago

jlev 12y ago
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-oil-testing-kit https://www.kickstarter.com/projects/publiclab/the-homebrew-... Participatory citizen-science FTW!
discardorama 12y ago
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' ?
- gipp 12y ago
  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/ http://webbook.nist.gov/chemistry/).
  - discardorama 12y ago
    Thanks. Followup question: does the light source have to be a laser? I read on the Wiki that CV Raman demonstrated the phenomenon with sunlight. So would it be possible to just observe the reflected light from an object and determine the molecules on it that are lighting up? If so, can (someday) someone come with a Star Trek-style tricorder that you look through and figure out the molecular composition of an object? Maybe at a distance of 100 meters?
- jarvist 12y ago
  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. http://www.gaussian.com/g_tech/g_ur/k_freq.htm http://www.gaussian.com/g_tech/g_ur/k_freq.htm
0xdeadbeefbabe 12y ago
How does this compare to vessyl[0]? Is building one of these harder than building a radio kit? [0] https://www.myvessyl.com/ https://www.myvessyl.com/
- VLM 12y ago
  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.
  - fhnjh 12y ago
    I'd do all of it, and then pull it apart with machine learning.
- frontline 12y ago
  it differs in that it's not an obvious scam
- ibisum 12y ago
  .. or how about a Spectruino: http://myspectral.com/ My big question is - what can these be used for? What are they actually useful for? I guess .. gardening? Medicine?
  - 12y ago
mcmancini 12y ago
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.
- VLM 12y ago
  "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"
  - mcmancini 12y ago
    A custom housing could certainly be on the order or more expensive than the optics, but if you were using catalog parts the mechanics should not be the largest cost. For example, a "cheap" 1" notch filter from Thor would run about $500, whereas a kinematic mount would be somewhere closer to $40.
    - ycui1986 12y ago
      For Raman spectroscopy, a "cheap" notch filter won't even work. a 0.5" long pass filter made for Raman can easily cost $2000. When you have a $2000 filter, you have to use temperature stabilized laser, otherwise the laser wavelength shifts, thus, spectrum shifts. Grating and concave mirror can also cost a fortune. Also, Raman typically is very weak, roughly 10^-6 of the laser intensity. The CCD/CMOS has to be low dark count. The things is, if you have spent $5000 on components, why should you save couple hundreds of dollar on good optical mounts? This 3D printed plastic base/structure will never have good stability and precision for any serious scientific application.
CamperBob2 12y ago
From the article: 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 12y ago
  That's exactly what expensive notch filters do.
  - CamperBob2 12y ago
    Cool. I guess it was naive of me to visualize a piece of colored glass. :)
flatCat1597 12y ago
Hey, I just want to thank everyone for the kind words I've been getting..! I'd love to hear any suggestions or comments anyone has on my project..! Take a look if you're interested at the project page on hackaday.io... hackaday.io/project/1279

63 points by MichaelAO 12y ago

jlev 12y ago

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-oil-testing-kit https://www.kickstarter.com/projects/publiclab/the-homebrew-... Participatory citizen-science FTW!

discardorama 12y ago

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' ?

gipp 12y ago
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/ http://webbook.nist.gov/chemistry/).
- discardorama 12y ago
  Thanks. Followup question: does the light source have to be a laser? I read on the Wiki that CV Raman demonstrated the phenomenon with sunlight. So would it be possible to just observe the reflected light from an object and determine the molecules on it that are lighting up? If so, can (someday) someone come with a Star Trek-style tricorder that you look through and figure out the molecular composition of an object? Maybe at a distance of 100 meters?
jarvist 12y ago
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. http://www.gaussian.com/g_tech/g_ur/k_freq.htm http://www.gaussian.com/g_tech/g_ur/k_freq.htm

0xdeadbeefbabe 12y ago

How does this compare to vessyl[0]? Is building one of these harder than building a radio kit? [0] https://www.myvessyl.com/ https://www.myvessyl.com/

VLM 12y ago
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.
- fhnjh 12y ago
  I'd do all of it, and then pull it apart with machine learning.
frontline 12y ago
it differs in that it's not an obvious scam
ibisum 12y ago
.. or how about a Spectruino: http://myspectral.com/ My big question is - what can these be used for? What are they actually useful for? I guess .. gardening? Medicine?
- 12y ago

mcmancini 12y ago

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.

VLM 12y ago
"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"
- mcmancini 12y ago
  A custom housing could certainly be on the order or more expensive than the optics, but if you were using catalog parts the mechanics should not be the largest cost. For example, a "cheap" 1" notch filter from Thor would run about $500, whereas a kinematic mount would be somewhere closer to $40.
  - ycui1986 12y ago
    For Raman spectroscopy, a "cheap" notch filter won't even work. a 0.5" long pass filter made for Raman can easily cost $2000. When you have a $2000 filter, you have to use temperature stabilized laser, otherwise the laser wavelength shifts, thus, spectrum shifts. Grating and concave mirror can also cost a fortune. Also, Raman typically is very weak, roughly 10^-6 of the laser intensity. The CCD/CMOS has to be low dark count. The things is, if you have spent $5000 on components, why should you save couple hundreds of dollar on good optical mounts? This 3D printed plastic base/structure will never have good stability and precision for any serious scientific application.

CamperBob2 12y ago

From the article: 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 12y ago
That's exactly what expensive notch filters do.
- CamperBob2 12y ago
  Cool. I guess it was naive of me to visualize a piece of colored glass. :)

flatCat1597 12y ago

Hey, I just want to thank everyone for the kind words I've been getting..! I'd love to hear any suggestions or comments anyone has on my project..! Take a look if you're interested at the project page on hackaday.io... hackaday.io/project/1279