PLOTS SPECTROSCOPE webcam + DVD + slit + case + software = Digital Spectroscope
Jul 03, 2015
PLOTS SPECTROSCOPE
webcam + DVD + slit + case + software
=
Digital Spectroscope
Clip on device for smartphone ($10)
Desktop kit uses a webcam ($40)
Public Laboratory (and kickstarter)
Spectral Workshop
•Online (share camera)•Offline (no longer supported, but available)
•Allows calibration of spectra captured by camera•Uses CFL spectra (mercury lines)
CFL spectrum overlaid with intensityCALIBRATION
436nm blue line 546nm green line
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)
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
Beer’s Law
Does coffee obey Beer’s Law (500nm absorbance)http://publiclaboratory.org/notes/akjeff91/3-28-2013/does-coffee-obey-beers-law-spectrometric-investigation
http://publiclaboratory.org/notes/cfastie/3-2-2013/fraunhofer
Fraunhofer’s Lines in Solar Spectrum
http://publiclaboratory.org/notes/straylight/10-14-2012/classroom-flame-spectroscopy
Flame Emission Spectrography
Injecting metal salt solutions into bunsen venturi and analysing the spectra
Wine Analysis By Absorption
http://publiclaboratory.org/notes/warren/1-19-2012/wine-spectroscopy-adam-hasler
Wine in petri dish over incandescent light source baseline, analysed for absorption characteristics
Energy Drink Artificial Colouring
http://publiclaboratory.org/notes/natalieorms/3-28-2013/qualitative-comparison-percent-transmittance-three-energy-drinks-do-conc
More Applications
• Black Body Radiation• LED colour analysis
• Halogen vs Incandescent vs LED lighting
• Stage 2 physics (Balmer Series)
• Stage 2 chemistryhttp://publiclaboratory.org/wiki/spectral-analysis
Sample Spectra
http://www.ausetute.com.au/emissions.html
(not from spectral workbench)
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
DVD Plastic Diffraction GratingThe 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 middle of the camera field of view.
The DVD “grooves” run vertically
The Slit• Aluminium Foil stuck
to a microscope slide
• Sticky tape !
• Smaller slit = better resolution
• 0.5mm is good
• Any old slit works !
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
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
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)\QuickTime\QTSystem\QTJava.zip to C:\Program Files (x86)\Java\jre6\lib\ext\QTJava.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
WinVDIG - QTCap
Source should be “USB Video Device WDM”
Preview should be “compressed”
The webcam video should come up in the boxes
Run Spectral Workbench
• “Spectral workbench master/spectrometry_kit/application.windows/spectrometry_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
Getting The Picture
Adjust sample row by click and drag vertically. It is clumsy !
Getting a Nice Spectra
• Two green lines + sharp blue + many reds• No overexposure• Small slit = good resolution
Mercury Discharge Lamp
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
•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
Want to Know More ?
• http://spectralworkbench.org/capture
• https://github.com/jywarren/spectral-workbench