Requirements:

To assemble the mini-spectrometer, the 3D printed pirces are needed (see the model), and additional components (total cost ~9 USD):

• Optical lens of 2.5 cm of diameter with focal distance of 40 mm. You can use the lens of low-cost Google Cardboard (~6 USD, 2 lens) 
• Difraction Grating of 1000 lines/mm (~10 USD, pack of 10).
• Clip to attach to the Smartphone (~5 USD, comes with a free microscope ;-) )

The assembling steps are:

STEP 1) Prepare the following components for the assembing: the 4, 3D printed pieces, a lens and a diffraction grating.

  

STEP 2) Cut the grating of size 2cm x 2.5cm (height x width) and glue it to the base as shown in the figure. Wait the necessary time.

STEP 3) In the other side of the base, glue the lens and wait the necessary time. 

STEP 4) To build the slit, you can use a cardboard with shape borders, e.g. a visiting card. Each piece should be of 12 mm x 25mm (height x width). The sharp boders (shown with the arrows) will form the slit.

STEP 5) Fix with glue one of the cardboard pieces in the inner side of the cap as shown in the figure. Wait the necessary time.

STEP 6) Now, fix with glue the second piece of the slit, making the distance between both smallest as possible. The smaller is the distance, the higher will be the spectral resolution of the spectrometer.

STEP 7) Once the cap with the slit are ready, glue it to the tube and wait the necessary time.

STEP 8) Insert the tube to the base with the lens, without gluing them. The Tube can slide to calibrate the spectrometer.

  

STEP 9) Glue the clip to the Slider, wait the necessary time.

STEP 10) Slide the Base in the Slider piece.

STEP 11) Last step, clip the mini-spectrometer to the Smartphone, so as that the camera correctly points to the diffraction grating hole.  

 

 

The spectrometer is ready. Enjoy!!