Follow these steps to assemble a Lego Spectrometer, for use with the Raspberry Pi camera.
To order a kit, visit the Public Lab Store: Order a kit
Design files (including Lego Digital Designer files and parts lists) are kept here: https://github.com/publiclab/lego-spectrometer
1. Lay out your pieces
You should have 53 parts, of 10 different types:
- Four (4) 1 x 2 bricks - 3004
- Thirty three (33) 1 x 4 bricks - 3010
- One (1) 1 x 6 brick - 3009
- Two (2) 2 x 2 corner - 2357
- One (1) 4 x 6 plate - 3032
- Four (4) 6 x 8 plate - 3036
- Two (2) 2 x 4 45 slopes - 3037
- Four (4) 1 x 2 Technic brick with hole - 3700
- Two (2) 1 x 4 Technic brick with holes - 3701
- Three (3) Technic pins with friction ridges - 2780
Here are images of all the pieces in the order above:
Also see this page for links to 3D-printable models on Thingiverse and Tinkercad.
Assemble the case
The case is made of legos, in three levels, as shown here. It's designed to be rigid but to be made of as few different types of Lego as possible, and using cheaper pieces.
Note: the basic Webcam version of the kit will have an extra layer of bricks, which can be added at the end, to the bottom of this stack. We'll mention this again later in the activity.
Start with one of the 6x8 plates and use 5 1x4 bricks to enclose all but one side. Add a sloped piece as shown.
On the other 6x8 plate, use four 1x4 bricks to line the sides only.
At what will become the "front" of the spectrometer, add one 1x4 Technic brick with holes with one peg in the middle. Behind it, place a regular 1x4 brick (to stop light leaking in).
Start with a single 1x6 brick at the "back" of the box, and then add a second sloped piece to make a ramp -- this is where your camera will go.
Use 1x4 bricks to continue the Level 2 walls to the front, but end with the L-shaped 2x2 bricks to create a narrower window at the front:
In front of the L-shaped bricks, add two 1x2 Technic bricks with holes and pegs. This forms the locking interface with the sample holder, or any other "compatible" attachments.
Now use 10 more 1x4 bricks to line the top, but leave the back open for the camera cable, and double up the front for strength.
Now take the 4x6 plate and use 3 1x4 bricks and 1 1x4 Technic brick with holes to make a first layer of walls.
Use 4 of the 1x2 bricks and 2 of the 1x2 Technics bricks with holes to complete the second layer and the negative side of the pin "interface" -- see how they line up with the pegs on the main body? A hole is left at the back for light to shine in, although if you're doing some kinds of analysis (like #fluorescence), you'll want this hole on the side instead.
Finish the 3rd level of the sample holder with 4 1x4 bricks, and snap it onto the main body.
Here it is assembled! The hole on top is for sample containers -- like cuvettes. You may want to pad it with black paper or foam core to make a tighter fit for whatever sample containers you use.
Add the slit
On the inside of the window of the main body, tape or glue the narrow slit we've printed on negative film. You can also make your own from two sheets of precisely cut paper or metal foil, or two razor blades. This ensures a sharp spectrum by only allowing a narrow beam of light into the box.
Mount the camera at an angle
You can use permanent double-sided foam tape, or hot glue, to affix the camera to the slope. Once it's in the box it won't be moved around, but you want it to be firmly attached. Be sure the camera points at about 45° upwards, not directly at the slit. The shaft of light entering the box will be redirected by the DVD piece (the diffraction grating) and so the camera needs to be looking upwards at an angle to "see" it.
If your spectrometer doesn't "see" anything, try pointing the camera further upwards towards the top of the box.
Note for basic Webcam kit assembly
If you have a webcam instead of a Raspberry Pi camera, attach it here instead, although you may need to modify the box to fit it -- our Webcam kit includes an extra row of Legos to make your kit 1 row taller to fit the webcam.
Note: For the basic Webcam kit, we've found that adding the extra Legos as the first or bottom row works best, rather than adding them on top -- that way the camera lens and the slit are at the same height!)
Here's the standard Raspberry Pi camera setup:
Cut and split a slice of DVD
The DVD will act as a diffraction grating (like a prism) to redirect the beam of light, but also to separate out the colors.
Cut out a slice of DVD, peel off and discard the opaque mirrored layer, then cut the remaining transparent piece down to size as shown here (from the papercraft spectrometer instructions)
Note: don't cut off the curved outer edge, because it will help keep the DVD oriented correctly. Read on to see why.
Attach the DVD to the camera
Tape or glue the DVD slice onto a piece of stiff black card paper (provided in our kit), or use Lego to make a frame if you like. You can even tape it directly to the camera -- just be sure it's very firmly affixed in place - I've used some very strong tape, but you can also use hot glue.
Be sure the outer edge of the DVD is at the top -- see the curvature in the image below as a guide.
Now fold up and add the black paper liner included in the kit. This is really just a simple black box to add extra light-damping protection, especially where Legos may be shiny enough to cause reflections. We've included some black paper that is roughly the right size, but you can trim it down like this (shown on a 1/2 inch gridded background) and keep only the big piece. (Read more about the liner here)
Note: This liner is helpful but not 100% necessary; also, any sheet of non-glossy black paper will work.
Now put the cover back on and seal up the end where the ribbon comes out, using some opaque tape. I could do a better job in this picture, but it's OK to illustrate the idea:
Now plug your Raspberry Pi into the camera cable and you're done with assembly! Download the camera software on our Pi Builder page or see this post by @partsandcrafts for instructions on setting up your Raspberry Pi to stream images over WiFi, or with the right cables you can plug in a monitor and keyboard and capture images that way.
If you have a Webcam kit, you can just plug in the webcam to your computer, and go to https://spectralworkbench.org/capture to begin.
There are a lot of things we could refine about this, and we're hoping you'll share your setups and any new add-ons you develop.
Upgrades and next steps
We're hoping to simplify the process of connecting to the Raspberry Pi to fetch images. There's some great challenges and next steps posted on this page -- if you can help improve this open source kit, please pitch in!
If you modify the design at all, please leave a comment. And tell us what goes well or what goes wrong! Post a comment here or use this page to post questions, and help one another out as well -- we're a peer-driven community!
Thanks and good luck!