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Spectrometer

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« Back to Spectrometry

Update: pre-order a spectrometer kit (including one which attaches to your mobile phone) now at the Breadpig Store

Purpose

Chemists use expensive tools called spectrometers (there are several kinds) to analyze unknown solid or liquid samples. We are working on a cheap version which we hope to use to identify oil contamination in water and soil, as well as a range of other possible toxins.

Spectrometers can also be used to identify species of plants or crop diseases, assess plumes from smokestacks, and have many other applications.

Spectrometry diagram

spectrum

What's spectrometry?

What we perceive as a single color consists of multiple blended colors- just as green paint can be made from mixing yellow and blue paint. A spectrometer is a device that splits light into the various colors it is composed of, which we otherwise cannot distinguish with the naked eye. By viewing a substance through a spectrometer, one can distinguish the exact mixture of colors, which correspond to specific wavelengths of light, that make up the perceived color of the sample.

Spectrometer interior

Make a spectrometer

The PLOTS spectrometer is a Do-it-Yourself tool made from simple materials:

  • 4 1/8" x 8 3/8" stiff black card paper
  • a clean DVD-R
  • a webcam
  • velcro, dark tape, a box cutter/x-acto knife

The DVD's tightly packed grooves act as a diffraction grating -- basically a prism. When light enters, the different wavelengths of light are bent to different degrees, forming a rainbow -- a spectrum.

Video spectrometer construction »

The above link offers step-by-step instructions on making your own spectrometer. There is also a short tutorial on how to take out the filter on the webcam (optional). This design is released under the CERN Open Hardware License 1.1 (read agreement here). It features:

  • around 400-900 nanometer range, maybe wider (what you can see with the naked eye, plus some infrared)
  • 5-10 nm spectral resolution
  • 20-30 samples per second
  • ~ $10 in materials
  • < 1 hour construction time
  • open-source software

Though these specs look pretty good, they still need to be compared rigorously with a traditional laboratory spectrometer. Are you interested in trying it?

Using your spectrometer

One group of toxins common to fossil fuel contamination are PAHs, polycyclic aromatic hydrocarbons, which are generally carcinogenic. We're trying to develop a step-by-step experimental procedure to prepare a soil or water sample, shine a full-spectrum light (like a halogen lamp) through it, and detect the missing wavelengths.

If you're interested, please chip in to develop and document a consistent way to read samples here:

Spectrometer usage »

We're also putting together a list of research (some of it our own) to draw upon in developing spectral analysis techniques for anything from soil to grapes to coffee:

Spectral Analysis »

Spectral Workbench

Online spectral analysis

Along with the physical tool itself, the PLOTS team has also developed a software suite and online spectrum sharing website which allows anyone to upload their data and work with others to try to interpret it. These tools are early prototypes and we're looking for help developing them.

Finally, a FAQ with some insights about actually using your spectrometer can be found here:

Spectrometer FAQ

Goals

This is an early-stage, speculative project, but our goals include:

Older designs

Several older designs have been documented on this site. Guides have been made showing you how to make some of these; they include: