Desktop Spectrometry Kit 3.0
The Desktop Spectrometry Starter Kit (now at version 3.0) is our most recent “reference design” incorporating some community improvements while balancing low cost and relative ease of construction. The DSSK was originally created as part of the Public Lab Spectrometry Project’s goal of identifying suspected oil residue after the BP oil spill.
We have not yet met all our intended goals for this design, which is still being refined by contributors like you. Please improve on this design by (for example) adding a sample holder or attaching a light, and contributing to the Upgrades section section of the spectrometry page.
Explore its capabilities in the Activity listing, and post your own for others to try.
- Capabilities
- Plans
- Parts list
- Limitations and goals
- Get involved in the next revision
Limitations and goals (Desktop Spectrometry Starter Kit)
Because most webcams’ exposure compensation cannot be disabled, we don’t know if or how much colors have been “boosted” between different photos. Because of this, you can compare spectra taken with the same device, but you can't necessarily between different devices -- but this is a challenge we’re working towards (see gain compensation in the Goals section).
Capabilities
Many basic improvements [link to updates] or additions can improve the capabilities of the DS3. But with the starter kit alone, you should be able to:
- Measure spectra with ~3 nanometer resolution (help refine this)
- Measure light from 400-700 nanometers (roughly the range of human vision) or more if you upgrade
Can you propose an experiment to provide a better answer?
Limitations & Goals
Add limitations here in the form of questions like "How can we correct for gain compensation in webcams?" Propose solutions, upgrades, or new features by first posing the question they address:
Ask a new question to explore further possible upgrades
Here are some which we'd like to adapt into question/answer format:
- Gain calibration: correct for the gain compensation of most webcams using a calibrated light source
- Improve the rigidity of the device: see rigidity upgrades
- Attach a light source and a sample holder to scan samples
As these upgrades mature, the Kits initiative will incorporate some into the Desktop Spectrometry Starter Kit itself (depending on cost & complexity) as part of our commitment to an open hardware design process
| Table of contents & resources |
|---|
| Spectrometry wiki page | About our overall spectrometry program |
| Development history | How our spectrometer was collaboratively developed |
| Previous versions | Background on versions 2-2.5 |
| Parts list | In case you want to to source parts on your own |
| Assembly | Instructions on putting this kit together |
| - - Bench |
| - - Assemble the box |
| - - Put it all on the bench |
Plans
instruction_booklet_1.0-print-halfpage.pdf - Print a cleaned-up version of this page from a PDF
spectrometer3.0-instructions1.0-booklet.pdf - Print a booklet-formatted version from a PDF
Parts List
- two-piece box
JDEPC-OV04 "gumstick" webcam with USB cable. (Datasheet: Spec_of_JDEPC-OV04_Ver_1.01.pdf) -- note, this is not the same "gumstick" webcam as used in the 2.5 Desktop Spectrometry Kit.
_Webcam is purchased in bulk from China. For more details E-mail kits@publiclab.org _
extra paper for modifications
- 45 degree wooden (ash) camera block, 3 cm x 4 x 4cm
wooden (ash) bench 1/4" (6mm) x 40mm x 235mm
_Wood products are sourced locally in Portland, OR at Roeder Woodworking _
one 65-degree fold up collimation angle
- one 45-degree fold-up camera angle.
- 50cm of 3/4" (2cm) width adhesive-backed loop fastener (Velcro-style)
25cm of 3/4" (2cm) width adhesive-backed hook fastener (Velcro-style)
_We buy our velcro from McMaster Carr in bulk here. The two part numbers are 9489K21 and 9489K201 _
one DVD-R
We buy ours from Amazon, choosing the cheapest option at time of purchase
photo emulsion printed slit 0.4mm wide printed on .004" acetate. (Design files on GitHub)
Acetate is something made custom for Public Lab by Eberhardt Press
6 yard roll of 1/8" Thermoweb Supertape double sided tape. (3mm wide)
- printed assembly instructions (below)
Also see this longer illustrated parts list.
Using your spectrometer
Once you've assembled your spectrometer and are ready to use it, plug it in and visit SpectralWorkbench.org to begin recording data with it. The web-based software works in the Chrome, Firefox and Opera browsers on most computers and smartphones.
(Peer) Support
Public Lab is not a corporation; we're an open community of DIY environmental science researchers which you have just joined! The best place to get help is the spectrometry mailing list; to join, sign up in the form to the left.
The spectrometry mailing list is made up of people like you, who are building and improving open source spectrometry techniques. Ask questions, look for help, and consider helping others too!
You can also post a question on this site; it helps to share some photos or screenshots of what you're trying to do:
Ask a question about spectrometry or Sign up to answer questions on this topic
Assembly
Your spectrometer is composed of three functional elements:
- a collimation slit that works as a lens, only allowing parallel light rays through its apeture.
- a diffraction grating that deflects light more the lower the light's wavelength, creating a rainbow diffraction pattern.
- a camera to capture the diffraction pattern, focused on the collimation slit.
These elements are mounted on an adjustable velcro bench in a black paper box.
Bench
Put velcro on the bench
Everything is built up from the bench, an ash board 4cm (1.75 inches) wide. We will cover it with the loop tape (fuzzy side of the velcro).
The velcro loop tape is slightly wider than half the width of the bench, two strips will hang over each edge a bit.
Assemble the camera block
You will need the camera, double-sided tape, the block, and the hook side of the velcro tape. Try to hold the camera by its edges, as it can be sensitive to electrical shorts.
Start by putting a strip of double-sided tape on the back side of the camera:
Remove the pink protective film from the double-sided tape and attach to the center of the block's 45-degree angled side, with the white cable port on top:
On the underside of the block, attach two short strips of the hook tape (the Velcro's scratchy side).
OPTIONAL: Make the camera focus more precise. The camera's tiny lens is pre-focused to roughly 200mm at the factory, but you can do a little better. This requires twisting the lens until it is no longer held in place by the green glue on the lens, which is easiest after the camera is mounted on the block. Pliers may be needed. Once loose, point the camera at a target (like text) 200mm away and carefully twisting the camera lens until the image is in clearest focus.
See more research on lens focus.
Make a diffraction grating from a DVD
Do not touch the surface of the DVD, always hold it by the edges, fingerprints will blur this important optical component.
We are going to turn a DVD-R into a diffraction grating, a device for separating light by frequency. An ideal diffraction grating would create a straight rainbow. A DVD produces a curved rainbow, but its rigidity and consistency make it a very good grating, and the tiny webcam lens curves the spectrum anyways. Aligning your diffraction grating will take some tweaking. We’ve given you extra material to help.
We have three steps, cutting a quarter of the DVD out, peeling off the reflective aluminum side, and trimming to a small piece.
OPTIONAL: Wash the purple ink off of the DVD fragment for greater light transmission, as described in this note.
Peel apart a quarter of the DVD
Cut out a quarter of the DVD with scissors. It may take more than one try to get a good diffraction grating, so save the rest too.
Use a knife or a fingernail to dig under the corner of the DVD quarter and peel the two layers apart.
You will get two layers. We are trying to get a transparent purple piece without aluminum stuck to it. If you can’t find a good piece you may want to try another quarter DVD. You only need a 2cm (.75”) square cut from the outer edge. Trim down to a small square with roughly 2cm of the DVD’s outer edge.
Trim down to a small square with roughly 2cm of the DVD's outer edge.
Assemble the diffraction grating angle
You will need:
Overview:
When taping the three flaps together, make sure the bottom flaps are lined up. put hook tape on the bottom.
Put the outer edge of the dvd at the mid-point of the hole, and then remove the handles from the binder clip.
Put velcro on the bottom.
Put the outer edge of the DVD at the mid-point of the hole, and then remove the handles from the binder clip.
Assemble the slit card
You will need:
The collimation slit should be in the DVD sleeve.
_We will attach the slit using the tape as single sided tape-- tape it on top and DO NOT remove the backing film. _ Line up the collimation slit with the line on the slit card.
Assemble the box
Watch this step-by step video:
For the purposes of this instructional I've highlighted the edges of the box in white and used an unprinted box. Your box will have a printed and unprinted sides, and no white edges.
Place the box with the printing facing down. Pre-crease all the creases towards you. and crease the box top as well.
Fold the left side "T" shape over to the right, and insert the tab from the leftmost edge into the slot at the base of the "T", as shown here:
Lay the separate box top piece on top so that its tabs line up with the slots in the box bottom’s right side. Make sure the small rectangular holes on the top and bottom of the box line up. We will put the webcam cable through that hole later. Insert the tabs together. The box top will not lay flat-- don't worry. this is because there is extra space for the two sheets to fold together.
Now open the box back up and fold left and right side flaps to the middle to form the inner walls. They will hook together.
Fold the outer walls up and over the inner walls. Use the two circular holes in the outer walls to position the inner walls while folding the outer wall over.
Flip the box upside down and make sure the tabs have all popped out of the bottom of the box. Walk your fingers along the inside of the box and make sure all the tabs are popped out of the bottom.
Put it all on the bench
Line up the the bench with the side of the box, and align the camera's lens with the 200mm marker on the side of the box. Press the camera block down firmly.
Place the diffraction grating angle directly in front of the camera block and press it down firmly.
Slide the slit card in the front of the box. The printing is slightly off, unfortunately. level the slit card's line just above the box's line. the card should wedge in place on its bottom edge.
Push the camera cable through the cable hole in the back of the box:
You can add a knot in the cable to help stabilize it so that any pulling on the cable doesn't move the webcam:
Plug it into the camera-- it only fits one way, don't force it.
Slide the bench in at an angle, placing it down by the cable hole, and then pushing it down to the bottom.
Complete!
You're done! Your computer should recognize your spectrometer as a webcam.
Now connect to your spectrometer using the web-based software at Spectralworkbench.org
Resources
- Common hardware issues
- Using the software (including setup and software troubleshooting)
- Frequently asked questions
- Peer-contributed research on open source spectrometry
Activities
Here are the series of notes printed on the spectrometer. Notes below by: @amysoyka, @straylight, @wagnerc4, @ygzstc, @cfastie, @stoft, & @Alex-McCarthy.
- lens focus: /n/7226
- grating angle: /n/5964 /n/5892
- spectrometer development history: /n/10691
- removable slit cards: /n/11246
Spectrometer development:
Activities:
- oil testing: /wiki/oil-testing-kit
- detection of brightening agents in laundry: /n/174
- pesticides: /n/10015
- sugar in red wine: /n/10955
- olive oil adulterants: /n/10382
- milkfat concentration: /n/10012
- lycopene in tomatoes: /n/9432
- atmostpheric spectra: /n/6168
- concentration analysis (Beer’s Law): /n/7475
- flame spectroscopy: /n/4406
- importing reference spectra: /n/8995
Design Notes
Consult the following notes on development for the evolution of this design: