New spectrometer
I have had some ideas for a new spectrometer.
Instead of just one angular adjustment that I have made so far; have a
separate angular adjustment oriented at 90° from the first one so that,
with another slit, I can scan across the two spectra. I don’t think that I
shall need this, I think that to scan across the spectrum can be done with
the same angular adjustment that I already have.
This might mean that I can use two light sensors instead of a camera, and
then quickly select the frequencies that I am interested in for soil analysis.
Two light sensors and their output into a computer will give me
numerical results.
Using lasers with “through the sample” beams; I might have to offset the
beams a little so that the direct laser beams don’t go to the sensors. But an
extra slit near the camera should prevent this problem. I’m not sure that
this will work.
I can use different light sources, including sunlight, lasers of different
frequencies, UV, IR, LEDs, different types of bulbs, etc. With some bulb
light sources I can adjust the intensity with a potentiometer. Perhaps I
could adjust the intensity of the lasers by varying the supply voltage.
I hope that I will be able to compare different solvents and soil solutions.
I will be able adjust the slit gaps and measure the gap using car
mechanic’s feeler gauges. I have made the slit to be adjustable with a
screwdriver. I shall have to calibrate the slit width with turns of the
screwdriver.
I can adjust the various lengths in the spectrometer.
I can assess different diffraction gratings and prisms.
I can change the orientation of the gratings by 90° intervals. I still haven’t
determined the correct orientation of the slits, the cuvettes, the diffraction
grating and the camera.
I can change the angle of the tube that is positioned after the diffraction
grating; but it seems that I need the camera very close to the diffraction
grating, so I am stuck with having the diffraction grating close to the
camera and changing the angle of the “diffraction grating – camera”
combination relative to the incoming beam.
I can change the camera, to include a good quality camera as well as
cheaper webcams.
I hope that I can use light sensitive sensors instead of a camera. I can then
feed the two sensor outputs into an operational amplifier to get the
difference of the two readings.
I can feed the operational amplifier output into a computer. If I fit
potentiometers onto the angular adjustments I can also feed the
potentiometer outputs into a computer or an Arduino.
With the spectra from two samples, I can superimpose them and visually
compare them.
I can superimpose a standard of any element and compare a sample with
the element standard; but this will involve making the two images the
same scale. That should enable me to look at more than one spectrum
frequency of each element in the soil.
I can make a table of spectrum frequencies and angles on my new
spectrometer. I can get the angles on my new spectrometer for each of the
lasers etc that I know the frequency of. I can relate colours to angles of
my new spectrometer.
I should be able to recognise an element from its primary colour
(frequency), and then confirm it from its secondary and tertiary colour
(frequency).
I shall have to make the lasers directional adjustable and also the Stanley
blades. I will need to adjust them first with the laser displayed on paper at
the camera position, without the diffraction grating; then add the
diffraction grating.
The adjustment for the Stanley blades is best made by soldering brackets
for two threaded bolts onto each blade.
I will have to solder an extra plate onto a shortened bracket, then drill
2.5mm holes through 4 flattened brackets clamped together, then tap the
holes, then bend the brackets at the edge of the extra soldered plates, then
make some sort of jig to be able to solder the brackets onto Stanley blades
so that the screwed rod in the tapped holes are aligned correctly. Then I
can drill the holes in the down-pipe plastic plates to take the 3mm bolts.
I can put a pair of 3mm nuts inter the head of the 3mm bolts to hold the
bolts in place. By turning the 3mm bolts, I can move the Stanley blades
which act as a narrow slit. I should be able to also adjust the two Stanley
blades relative to each other to get a parallel slit.
I think that I need a pair of cross-wires somewhere for alignment. I
haven’t decided where to put the cross-wires.
The deflection angle for 405 nm, 532 nm & 650 nm laser through a glass
prism is 50°. The deflection angle for a 650 nm laser through diffraction
grating is 40°. I am surprised that the same angle was recorded for the
three laser beams!
Things don’t seem to be working out as I expected with spectra.
I hope to be able to compare the spectra of identical samples in two
adjacent cuvettes and then use this to adjust the program to get zero
output; but first I have to get two spectra.
It seems as though if the slit is vertical and the axis if the diffraction
grating is vertical then the spectrum will be deflected to the right or left.
The camera should also be vertical with the operating buttons on the top.
The spectrum can be moved across the screen by sliding the camera
across the viewing frame which is not of much benefit; what will be of
more benefit is to change the angle of the camera, together with the
diffraction grating which is outside of the lens and is perpendicular to the
beam entering the camera. This will allow me to position the spectrum
relative to the centre-line of the image and read off an angle from a n
attached protractor. I can then calibrate the protractor angle against the
spectrum frequency. But I will need a cursor line on the image that tells
me where the centre of the image is. Perhaps another slit near the camera
will work. It should work as the second slit will move with the camera
across the spectrum and should give me a restricted portion of the
spectrum viewed by the camera. I think that this second slit will need to
be parallel to the first slit.
This should allow me to view a restricted portion of the spectrum where a
dominant line on the spectrum appears for a given soil element.
I have tried putting a slit before the diffraction grating but it does not
seem to be effective. I will have to try a slit or a thin wire after the
diffraction grating. I think perhaps the wire will be better than a slit.
I don’t seem to have much success with the laser pens shining into the
slit. The bright light seems to swamp everything and I can’t see a
spectrum.