[DIYbio] Re: Does Anyone Know Of A Submersible Arduino/RaspberryPI Compatible Spectrometer?

To start, my application is not a data logger meant to sit out in a pond or swamp somewhere, it will be wired into a (hopefully PoE if I can keep the wattage low enough) connection tied directly to a server with decent storage and processing power, but am very against any form of closed hardware (not in the least of which because I use FreeBSD for servers and nobody making proprietary code likes to talk to them, but also because I've never had a pleasant experience with vendor lock-in.)

To this end I've thus far narrowed down the possible light source combination at the end of this post, which should yield a very large set of possible fluorescence spectrophotometry readings when they are switched on 1 wavelength at a time with individual snapshots taken (just listing these in case anyone else is working on a similar project, it took about a day to find a set of LEDs with fairly well-matched half-amplitude-wavelengths and similar amplitude at a 15-degree radius, the number at the start is the number needed to balance the amplitude to the others for a 15 degree angle, then what it is, then the price each, then the source.)

To get the adsorption spectra is pretty easy - just shine a light through something and see what doesn't make it.  To get the reflection spectra is a little trickier, in that you need to measure from the side you are shining the light from, and to get the fluorescence spectra you switch on 1 group at a time and see what other wavelengths you get out of it.  My best idea for this thus far is actually pretty painful to implement: take a fiber with two Y-shaped splices (so more like an X with an elongated center) and for one pair have an input going to a cavity with all the LEDs embedded in the walls pointed at a pigtailed cosine corrector (diffuser plate over top of a piece of glass which effectively opens a single mode fiber aperture to about 4mm across.)  On the other side of the input pair you would actually have your output, going to a diffraction grating with a camera pointed at it.  On the other pair you would have the sample cavity and a reference signal going back to a different y coordinate on the diffraction grating.  Then you would have 1 more fiber on the opposite side the cavity for adsorption detection which again goes to the diffraction grating - for a total of two fibers going to the probe.  This is probably really hard to decipher so I've added a diagram below (sorry for the quality of it in advance), and would welcome better ideas to achieve the same because at the moment it looks like I'll need to get a fusion splicer to make the X-shaped section and attach the components to it, plus have a cavity milled or hack one together with epoxy.

Diagram: https://i.imgur.com/52NgfBD.png