OtterVIS LGL spectrophotometer

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This is a 3D-printable spectrophotometer based on a TCD1304 linear CCD and standard 35mm camera optics. The resolution is ~1nm, with the Na-doublet at 589nm being just exactly not resolvable. The total price of the components depends on how cheaply you can scavenge them on that auction site, but expect to pay something like this: Optics: 2x $10, CCD: $10, MCU: $15, Grating: $3, A few $$ for misc. parts. Total: ~$60. The design is a lens-grating-lens design. The diffraction grating is a cheap transmission grating slide. Both lenses are Pentax SMC-M 50mm f/2, which are easy to find and cheap. The grating constant is 1000 lp/mm and the lower wavelength is chosen to be 380 nm as the lenses start absorbing here. From 760 nm second order diffraction starts to overlap so 760 nm is chosen as the upper limit for the spectrum. Inserting these values into the diffraction equation gives angles of diffracted light from 22.3°-49.5°. The center angle is 35.9°, which is the angle between the two optical axes of the lenses. The CCD (TCD1304) is 29.1 mm long and with a bit of trigonometry we end up with an ideal focal length of 60mm for the focusing lens. A bit higher than the 50mm actually used, so a part of the CCD remains unused. How to construct the spectrophotometer Step 1: Print Download .scad files. If you have a different grating calculate the center angle and modify the parameter 1st in the file poly-definitions.scad. Modify the files slit-holder.scad, and magnet.scad to fit your magnets. Make sure that the CCD-PCB matches the holes in the spectrometer box. Print everything. Mind you that the spectrometer box will take ~18 hours to print. Lenses Strip the lenses. Unscrew and remove the bayonett. Unscrew and remove the aperture coupling together with any screws you find. Unscrew front ring. Again remove any screws you come by. Remove the front lens group. Remove the aperture iris. Remove the lens barrel from the focusing helicoid. Reassemble the front and back lens groups. They should now look like this: Insert the lenses in the lens holders and secure them with some of the left-over screws. The linear CCD module The spectrometer uses a TCD1304 linear CCD driven by a ST Micro Nucleo F401. The firmware can be found here https://tcd1304.wordpress.com/. A small assortment of magnets is also required. A DE-razor blade and diffraction grating slide (1000 lines/mm) are needed for the spectrophotometer. Software Linux (any distro will do), macos (Sierra works, probably others as well. You can even use windows with Jens-Ulrich Fröhlichs java-based GUI.), TCD1304 driver firmware for STM32F401RE (UART), GUI or CLI (UART), and Both are available from tcd1304.wordpress.com. For an Octave extended GUI visit http://science.jefro.de/.