Making an EOS 1 Open-source Spectrometer

The EOS 1 (Erie Open Spec v1.0) is a simple, open-source, smartphone-based spectrometer designed to be used by any environment-minded person for measuring nutrient concentrations in water.

Please skip to step 5 if you have the official EOS 1 kit.

Design files (STL, DXF) are also published on our Thingiverse page: https://www.thingiverse.com/thing:3214210

Step 1: Laser-cut Acrylic Housing

skip if you have the EOS 1 kit (included in the kit)
We used a 40W Epilog Laser engraver and it worked fine.
DXF file for Laser cutting is also available on our Thingiverse page: https://www.thingiverse.com/thing:3214210
use opaque Acrylic sheet 1/8" thick ( for example, the "scratch-resistant Acrylic sheet" is a good choice: https://www.mcmaster.com/8505k741 )
do not use clear Acrylic
do not use PVC sheet (toxic fume may be produced when laser-cutting PVC)
an EOS 1 can fit in a 12" X 12" sheet
Remove cover paper on one side only

EOS1 cut pattern.dxf
Download View in 3D

Step 2: 3D-print Sample Holder and Slit

skip if you have the EOS 1 kit (included in the kit)
Use Formlabs Form 2 SLA 3D printer (https://formlabs.com/3d-printers/form-2/)
Two parts need to be 3D-printed: sample holder and slit
.form files are attached
3D design (STL) files are also available on our Thingiverse page: https://www.thingiverse.com/thing:3214210

Step 3: Clean Out Support Structures on 3D Prints

skip if you have the EOS 1 kit (included in the kit)
an exacto knife would help
don't forget the supports inside the cuvette slots, and try to make the inner surfaces as smooth as possible

Step 4: Install Reflector, LED, and Slit

skip if you have the EOS 1 kit (included in the kit)
cut a piece of Teflon sheet (1/32" - 1/16" thick) which can fit into the reflector gap
wrap a piece of Aluminum foil only on the outside (back side) of the Teflon sheet
insert Teflon+foil sheet into reflector gap
insert a bright white LED into LED hole
align the slit with guide posts on the front surface of sample holder, fix with superglue

Step 5: Assemble

attach mirror (1" square) onto the holding plate with double-sided tape
put things in place as shown in picture
Make sure the side with cover paper faces inward (anti-glaring)
secure the two side plates with screws

Step 6: Install Battery Pack

install a current-limiting resistor (10 - 220 Ohm) into one of the slots inside the battery holder, make sure it's spring-loaded
use double-sided tape to secure the battery pack onto the bottom plate (again, cover paper faces inside), make sure the switch on the battery pack is accessible from the outside

Step 7: Connect Battery Pack With LED

put two AAA batteries into the battery pack (check and make sure the polarity is correct)
install bottom plate to EOS1
connect wires from battery pack to LED (red wire to long leg on the LED, black wire to short leg)
try switching on and check that the LED lid up

Step 8: Install Diffraction Grating

$Install Diffraction Grating$ $Install Diffraction Grating$ $Install Diffraction Grating$

skip if you have the EOS 1 kit (included in the kit)
cut out a small (approx. 1cm X 2cm) piece of diffraction grating, make sure the long side align with the vertical axis of the cardboard
align the grating with the axis of the top plate (here we've come up with a simple jig with a laser pointer, see picture attached)
secure the grating on the top plate (inside, again, the side with cover paper) with Scotch tape (here we just happened to run out of Scotch tape, so we used Kapton tape)

Step 9: Install Top Plate and Cover Plate

cover plate may not be needed
here we used a piece of electrical tape as a hinge
now EOS 1 is ready
next, follow operation procedures here: https://www.instructables.com/id/Measure-Nitrate-...