The PLOTS spectroscope is a cheap ($10) device that boasts good resolution, is easy to buld and has applications in a number of areas. This slide show was put together for a workshop at the South Australian Science Teachers annual conference 2013. It details how to build the spectroscope, install the software and outlines many uses for it in education. It provides links to the main PLOTS site, where a non-profit version of the scope is being sold and the software developed.
2. Desktop kit uses a webcam ($40)
Clip on device for smartphone ($10)
Public Laboratory
(and kickstarter)
3. Spectral Workshop
•Online (share camera)
•Offline (no longer supported, but available)
•Allows calibration of spectra captured by camera
•Uses CFL spectra (mercury lines)
4. CALIBRATION
CFL spectrum overlaid with intensity
436nm blue line 546nm green line
5. Some Captured Spectra
Calibration using CFL – standard spectra Mercury discharge lamp
Solar spectrum Green laser 484nm
Osram Biolux lamp Halogen
Strontium chloride Red Bull (for absorbance)
6. Photosynthetically Active Radiation (PAR)
http://publiclaboratory.org/notes/cfastie/3-16-2013/par
Absorbance using halogen
(probably) as source lamp
(baseline) and subtracting light
transmitted by chlorophyll solution
7. Beer’s Law
Does coffee obey Beer’s Law (500nm absorbance)
http://publiclaboratory.org/notes/akjeff91/3-28-2013/does-coffee-obey-beers-law
8. Fraunhofer’s Lines in Solar Spectrum
http://publiclaboratory.org/notes/cfastie/3-2-2013/fraunhofer
9. Flame Emission Spectrography
Injecting metal salt solutions into bunsen venturi
and analysing the spectra
http://publiclaboratory.org/notes/straylight/10-14-2012/classroom-flame-spectroscopy
10. Wine Analysis By Absorption
Wine in petri dish over incandescent light source
baseline, analysed for absorption characteristics
http://publiclaboratory.org/notes/warren/1-19-2012/wine-spectroscopy-adam-hasler
11. Energy Drink Artificial Colouring
http://publiclaboratory.org/notes/natalieorms/3-28-2013/qualitative-comparison-
percent-transmittance-three-energy-drinks-do-conc
12. More Applications
• Black Body Radiation
• LED colour analysis
• Halogen vs Incandescent vs LED lighting
• Stage 2 physics (Balmer Series)
• Stage 2 chemistry
http://publiclaboratory.org/wiki/spectral-analysis
13. Sample Spectra
(not from spectral workbench)
http://www.ausetute.com.au/emissions.html
14. Building The Spectroscope
• Make a slit for the end of the box
• Put some DVD plastic over the camera lens
• Put the camera in the box, opposite the slit, at
about 45°
• Install the software, plug in the camera
• Select view
• Calibrate
• Use
15. DVD Plastic Diffraction Grating
The DVD plastic from a blank
DVD (+/- R) has almost parallel
lines printed at 740nm spacing.
These provide a cheap and
effective transmission diffraction
grating. First order maxima of
interference pattern is at around
60 degrees.
The camera and DVD are
angled around 50 degrees to
introduce an incident angle,
which makes the pattern
asymmetric. One side of the
pattern is now centred in the
The DVD “grooves” run vertically middle of the camera field of
view.
16. The Slit
• Aluminium Foil stuck
to a microscope slide
• Sticky tape !
• Smaller slit = better
resolution
• 0.5mm is good
• Any old slit works !
17. Camera and Slit
Arrangement
Cover is off the box
The slit to camera distance is
dependant on the minimum
focusing range of the camera.
The longer the distance, the
better the resolution
18. Camera Angle
•About 45-60 degrees
works well
•Align with slit opening
•Blu Tak is your friend
•Reversing the angle
reverses the spectrum
order
•Changing the angle also
spreads out the spectrum
a bit
19. Spectral Workbench - Offline
• Windows Installation Instructions
• You need
Spectral Workbench Master (folder 35MB)
Apple Quicktime (Quicktime Installer – Use default settings)
WinVDIG_101 (installer – Use default settings note that only
version 1.01 works, not newer versions)
• After installing quicktime, you need to:
copy C:Program Files (x86)QuickTimeQTSystemQTJava.zip
to C:Program Files (x86)Javajre6libextQTJava.zip
• After Installing WinVDIG_101 run QTCap, which is a video or webcam
stream that allows spectral workbench to capture your webcam through
quicktime (QTCap)
• Follow the instructions for QTCap on the next slide, this gets you a webcam
feed
20. WinVDIG - QTCap
Source should be “USB Video Device WDM”
Preview should be “compressed”
The webcam video should come up in the boxes
21. Run Spectral Workbench
• “Spectral workbench
master/spectrometry_kit/application.windows/sp
ectrometry_kit.exe”
• You should see a grey screen and the QTCap
window again
• Select the webcam source and preview
“compressed”
• Click 'OK'.
• In a few seconds, spectral workbench will fire up
23. Getting a Nice Spectra
• Two green lines + sharp blue + many reds
• No overexposure
• Small slit = good resolution
24. Troubleshooting
•Grey Screen of Death means WinVDIG or
quicktime aren’t set up properly
•Try using the ‘scope with a big slit to get
an idea of where the spectrum lies
Mercury Discharge Lamp
•Don’t clean the DVD plastic, the purple
layer has the lines on it !
•Use the “Adjust Sample Row” to see
everything the camera sees, then angle the
camera to get the image.
•Reducing reflections inside the box helps
the camera auto exposure work
•Don’t be afraid to play with the apparatus,
turn the camera or move stuff around
25. Want to Know More ?
• http://spectralworkbench.org/capture
• https://github.com/jywarren/spectral-
workbench
