The Public Lab Desktop Spectrometer 3.0 is an open-source optical spectrometer kit released under the CERN Open Hardware License 1.2. The system builds an optical bench enclosure from folded cardstock to capture, calibrate, and analyze visible light emission and absorption spectra. The design features a precision 0.2 mm entrance slit aperture, internal light baffling, a 200 mm optical bench path length, a 35 mm focal centerline height, and an internal mounting bracket that holds a transmission diffraction grating and a focus-adjustable camera at an angle of 45° or 65°. The physical apparatus contains no custom printed circuit boards; all electronic hardware consists of an off-the-shelf USB webcam module powered directly from a host computer via a standard 5 V DC USB bus rail (nominally 5 V, ≤ 500 mA). Captured spectra are digitized by the camera and transmitted over USB to a host PC running the Spectral Workbench web platform (either locally or via spectralworkbench.org).

Bill of Materials

• Focus-Adjustable USB Webcam Module

  • Identity: Commercial off-the-shelf UVC-compliant USB webcam or bare camera module with manual focus adjustment (historically generic Syba or Vimicro-based CMOS webcam modules).
  • Quantity: 1
  • Footprint/package: Compact chassis-mount or bracket-mount camera module fitting within a 35 mm optical center enclosure compartment.
  • Electrical constraints: 5 V DC supply voltage powered via USB 2.0 bus (current draw ≤ 500 mA).
  • Mechanical/optical constraints: Lens assembly must have a manual focus ring capable of focusing closely at a 200 mm object distance. Must possess a visible-light CMOS/CCD image sensor (wavelength response approximately 400 nm to 700 nm); any factory IR-blocking filter must permit visible light transmission.
  • Substitution latitude: Any standard USB Video Class (UVC) webcam module can substitute, provided the outer housing fits inside the cardstock compartment or can be removed, and the lens can be manually refocused down to 200 mm.
  • Operated control: Yes. The manual focus ring on the lens is an operated control adjusted by the user during initial setup and calibration to sharpen spectral line images (referenced as lens focus: /n/7226).
  • Sourcing plan: retail shopping search: manual focus USB webcam module UVC 720p

• Transmission Diffraction Grating

  • Identity: Linear transmission diffraction grating; either a commercial holographic diffraction grating film sheet or a peeled recording layer from a blank DVD-R disc (approx. 1350 grooves/mm).
  • Quantity: 1 piece (approximately 20 mm × 20 mm square).
  • Footprint/package: Thin-film optical square mounted directly over the webcam lens aperture.
  • Optical constraints: Linear transmission diffraction grating with groove density between 800 lines/mm and 1350 lines/mm. Mounted at an orientation angle of 45° or 65° to diffract the 1st-order spectrum across the camera image sensor.
  • Substitution latitude: A standard 1000 lines/mm linear holographic diffraction grating sheet or a clean, separated DVD-R polycarbonate data layer can be substituted (as documented in Public Lab research notes /n/5964 and /n/5892).
  • Operated control: No. Set-once alignment held fixed by internal angle brackets.
  • Sourcing plan: retail shopping search: 1000 lines/mm transmission diffraction grating film sheet

• Precision Slit Card (0.2 mm Aperture)

  • Identity: Public Lab 0.2 mm removable slit card (documented in community research /n/11246 and cut plans).
  • Quantity: 1 (cut plans include templates for 4 interchangeable slit cards).
  • Footprint/package: Cardstock card insert (approx. 35 mm × 35 mm square) with a 0.2 mm wide centered slit aperture.
  • Optical constraints: Slit width strictly 0.2 mm. Material must be completely opaque to ambient light to prevent light leakage around the aperture.
  • Substitution latitude: Any rigid opaque substrate (heavy black cardstock, laser-cut plastic, or razor blade edges) providing an optical slit width of 0.2 mm can substitute. Slit width determines the tradeoff between light throughput and spectral line resolution.
  • Operated control: Yes. Removable and swappable during operation to exchange apertures or sample holders.
  • Sourcing plan: general web research: Public Lab 0.2 mm spectrometer slit card cut template

• Spectrometer Enclosure Base (Bottom Chassis)

  • Identity: Public Lab Spectrometer 3.0 Bottom Enclosure Cut Sheet (vector drawing: spec-box-bottom.pdf).
  • Quantity: 1 sheet.
  • Footprint/package: Die-cut or laser-cut cardstock / corrugated paperboard sheet (~430.0 mm × 305.9 mm flat size). Folds into a rectangular optical bench bench box with a 200 mm path length and 35 mm height.
  • Mechanical/optical constraints: Interior surfaces must be non-reflective matte black to prevent internal optical reflections and light contamination. Features an entry slit holder and light baffle slots.
  • Substitution latitude: Can be fabricated from 80 lb to 100 lb matte black cardstock, chipboard, or thin cardboard using a laser cutter or craft cutting plotter following the vector plans.
  • Operated control: No.
  • Sourcing plan: general web research: Public Lab Spectrometer 3.0 spec-box-bottom cut file

• Spectrometer Enclosure Lid and Angle Brackets

  • Identity: Public Lab Spectrometer 3.0 Top and Angle Brackets Cut Sheet (vector drawing: spec-box-top+angles.pdf).
  • Quantity: 1 sheet.
  • Footprint/package: Die-cut or laser-cut cardstock sheet (~367.9 mm × 278.9 mm flat size). Folds into the light-tight enclosure lid and two angled internal mounting brackets (45° and 65°).
  • Mechanical/optical constraints: Must rigidly position the webcam and grating at a 45° or 65° angle relative to the 200 mm optical axis. Interior must be matte black.
  • Substitution latitude: Can be cut from cardstock or substituted by 3D-printed 45° and 65° camera/grating mount brackets.
  • Operated control: No.
  • Sourcing plan: general web research: Public Lab Spectrometer 3.0 spec-box-top+angles cut file

• Light-Blocking Assembly Tape

  • Identity: Opaque matte black adhesive tape (photographic paper tape, black gaffer tape, or electrical tape).
  • Quantity: 1 roll (used as needed for assembly).
  • Footprint/package: Roll tape, width 12 mm to 25 mm.
  • Optical constraints: 100% light-blocking opacity to seal paper enclosure joints, corners, and seam folds against ambient light contamination.
  • Substitution latitude: Any completely opaque black tape or opaque craft adhesive.
  • Operated control: No.
  • Sourcing plan: retail shopping search: black light blocking photographic paper tape

• USB Interface Cable

  • Identity: USB 2.0 Type-A male to camera interface cable (typically captive/integrated on the webcam module, or standard USB-A to mini/micro-B).
  • Quantity: 1.
  • Footprint/package: Standard shielded USB cable assembly (length ≥ 1 m).
  • Electrical constraints: 4-conductor shielded cable carrying 5 V DC power (VBUS, GND) and USB 2.0 differential data (D+, D-).
  • Substitution latitude: Any standard USB 2.0 data cable compatible with the chosen webcam.
  • Operated control: No.
  • Sourcing plan: distributor lookup (representative example — sources give spec only): Tensility 10-00648

Software and network dependencies

• Host Operating System / Environment:

  • Platform: Debian / Ubuntu Linux (Ubuntu 18.04 LTS or compatible environment recommended in documentation; macOS via Homebrew and Fedora/CentOS also documented).
  • Version: Stated in documentation (Ubuntu/Debian recommended).
  • Version pinning: Unpinned.
  • Check plan: support-status lookup: Ubuntu 18.04 LTS

• Ruby Language Runtime:

  • Name: Ruby
  • Version: 2.6.6 (specified as "Ruby 2.6.6 up to Ruby 2.6.x").
  • Where version came from: Stated in documentation (spectral-workbench_README.md).
  • Version pinning: Stated in documentation as 2.6.6.
  • Check plan: support-status lookup: Ruby 2.6.6

• Bundler:

  • Name: Bundler (Ruby gem dependency manager)
  • Version: 1.17.2
  • Where version came from: Pinned in Gemfile.lock (line 274: "BUNDLED WITH 1.17.2").
  • Check plan: vulnerability lookup: bundler / rubygems / 1.17.2

• System Image Processing Libraries:

  • Name: ImageMagick and development headers (imagemagick, ruby-rmagick, libmagickwand-dev, libmagick++-dev on Debian/Ubuntu; ImageMagick-devel on Fedora).
  • Version: Not stated (system package manager install: apt-get install imagemagick ruby-rmagick libmagickwand-dev libmagick++-dev).
  • Where version came from: Stated in documentation without version constraint.
  • Version pinning: Unpinned in spectral-workbench_README.md.
  • Check plan: not checkable: system library packages unpinned

• Node.js, NPM, and Yarn:

  • Name: Node.js (nodejs-legacy, npm) and Yarn static asset manager (npm install -g yarn).
  • Version: Not stated.
  • Where version came from: Stated in documentation (spectral-workbench_README.md).
  • Version pinning: Unpinned.
  • Check plan: not checkable: npm and yarn installations unpinned

• Database Engine:

  • Name: MySQL Server (mysql-server) or SQLite3.
  • Version: Not stated.
  • Where version came from: Stated in documentation (spectral-workbench_README.md).
  • Version pinning: Unpinned.
  • Check plan: not checkable: database server version unpinned

• Spectral Workbench Core JavaScript Module:

  • Name: spectral-workbench.js (https://github.com/publiclab/spectral-workbench.js)
  • Version: Not stated (cloned/included submodule).
  • Where version came from: Stated in documentation (spectral-workbench_README.md).
  • Version pinning: Unpinned.
  • Check plan: not checkable: external JavaScript repository unpinned

• Web Application Framework and Server:

  • Ruby on Rails: version 5.2.4.6, pinned in Gemfile.lock (Gemfile declares ~> 5.2.4.3). Check plan: vulnerability lookup: rails / rubygems / 5.2.4.6
  • Phusion Passenger: version 6.0.14, pinned in Gemfile.lock. Check plan: vulnerability lookup: passenger / rubygems / 6.0.14
  • Puma: version 5.6.4, pinned in Gemfile.lock. Check plan: vulnerability lookup: puma / rubygems / 5.6.4

• Core Application Ruby Gems (manifest located at Gemfile and Gemfile.lock): All 102 resolved gem dependencies are pinned in Gemfile.lock. Key direct operational and security-sensitive gems include:

  • rmagick: version 4.2.6, pinned in Gemfile.lock. Check plan: vulnerability lookup: rmagick / rubygems / 4.2.6
  • nokogiri: version 1.13.8, pinned in Gemfile.lock. Check plan: vulnerability lookup: nokogiri / rubygems / 1.13.8
  • paperclip: version 6.1.0, pinned in Gemfile.lock. Check plan: vulnerability lookup: paperclip / rubygems / 6.1.0
  • mysql2: version 0.5.4, pinned in Gemfile.lock. Check plan: vulnerability lookup: mysql2 / rubygems / 0.5.4
  • rack: version 2.2.4, pinned in Gemfile.lock. Check plan: vulnerability lookup: rack / rubygems / 2.2.4
  • therubyracer: version 0.12.3, pinned in Gemfile.lock. Check plan: vulnerability lookup: therubyracer / rubygems / 0.12.3
  • uglifier: version 4.2.0, pinned in Gemfile.lock. Check plan: vulnerability lookup: uglifier / rubygems / 4.2.0
  • recaptcha: version 5.9.0, pinned in Gemfile.lock. Check plan: vulnerability lookup: recaptcha / rubygems / 5.9.0
  • open_id_authentication: version 1.3.0, pinned in Gemfile.lock. Check plan: vulnerability lookup: open_id_authentication / rubygems / 1.3.0
  • ruby-openid: version 2.9.2, pinned in Gemfile.lock. Check plan: vulnerability lookup: ruby-openid / rubygems / 2.9.2
  • bootsnap: version 1.12.0, pinned in Gemfile.lock. Check plan: vulnerability lookup: bootsnap / rubygems / 1.12.0
  • sprockets: version 4.1.1, pinned in Gemfile.lock. Check plan: vulnerability lookup: sprockets / rubygems / 4.1.1

• Network exposure:

  • Physical device: The spectrometer hardware itself connects solely as a standard USB video device to a host workstation and carries no autonomous network interfaces.
  • Local Web Server: The host application (Spectral Workbench) launches an HTTP server listening on TCP port 3000 (http://localhost:3000) via Passenger or Puma. Test suite runs a Jasmine client-side test server on port 8888 (http://localhost:8888).
  • External Authentication / Network Connections: The application delegates user authentication via OpenID to publiclab.org; logging in redirects students to approve authentication against PublicLab.org credentials.
  • Public Cloud API: Documentation instructs users that spectra can be published and analyzed remotely by submitting JSON payloads authenticated with an API token to the public cloud service at https://spectralworkbench.org/spectrums.json.

Online Resources and URL Dependencies

• Public Lab Community Research and Calibration Documentation:

  • Lens focusing guide: publiclab.org/n/7226
  • Grating angle research: publiclab.org/n/5964 and publiclab.org/n/5892
  • Removable slit card design: publiclab.org/n/11246
  • Spectrometer development history: publiclab.org/n/10691
  • Calibration procedures: publiclab.org/n/191
  • Linearity studies: publiclab.org/n/10476 and publiclab.org/n/6225
  • General hardware wiki: publiclab.org/wiki/dsk and publiclab.org/wiki/spectrometer
  • Application use-case notes: /wiki/oil-testing-kit, /n/174 (brightening agents), /n/10015 (pesticides), /n/10955 (wine sugar), /n/10382 (olive oil), /n/10012 (milkfat), /n/9432 (lycopene), /n/6168 (atmospheric spectra), /n/7475 (Beer's Law), /n/4406 (flame spectroscopy), and /n/8995 (reference spectra).

• Source Code Repositories:

  • Web application repository: https://github.com/publiclab/spectral-workbench.git
  • Core spectral JS library: https://github.com/publiclab/spectral-workbench.js

Fabrication Specifications

• Enclosure Base Sheet (spec-box-bottom.pdf):

  • Total sheet boundary / MediaBox: 1219 pt × 867 pt (approx. 430.0 mm × 305.9 mm / 16.93 in × 12.04 in).
  • Layer content: Single-page Adobe Illustrator CS6 cut plan containing perimeter cutting vectors (red lines), interior fold score lines (blue lines), and assembly/reference alignment markings.
  • Substrate: Opaque heavy cardstock (80 lb to 100 lb) or thin corrugated e-flute board with matte black light-absorbing interior finish.

• Enclosure Lid and Brackets Sheet (spec-box-top+angles.pdf):

  • Total sheet boundary / MediaBox: 1043 pt × 790.5 pt (approx. 367.9 mm × 278.9 mm / 14.49 in × 10.98 in).
  • Layer structure: Two distinct layers / optional content groups:
    • Layer 1 (OCG /MC0): Die-cut / laser cut vector paths and fold score lines for box lid and 45°/65° mounting angle brackets.
    • printing (OCG /MC1): Silk-screen / print graphics and alignment markings.
  • Substrate: Identical cardstock or corrugated board matching the base enclosure.