Spectrometer is device that analyzes spectrum of incoming light beam. We illuminate a sample and analyze spectrum of the light coming out vs. the spectrum of the light coming in. The difference is absorption spectrum of the sample and from that we can deduce its chemical composition!
A box with tiny hole at one end, and tilted piece of CD, which acts as a diffraction grating. Incoming beam is diffracted from the grating and dispersed light is captured by a webcam at the other side of the box.
Basic processing of the webcam picture, and histogram based on rainbow intensity.
The basic construction and software is done by TomSuch and ATA. Better software needs to be built now that will be able to derive some useful information from the measured spectrum now.
However, current hardware has some major issues, e.g. chromatic aberration of used lens affects measurement (this could be fixed by using mirrors instead of lens, see Czerny-Turner monochromator design).