Hi!
In the attached folder there is everything you are looking for Fourier series, and much more; The main worksheet is "Waveforms' Spectra" which takes, maybe, half an hour to analyze and graph about forty signals. But there is also a second one apart, which produces the graphs of some signals. The operation is not immediate because first of all you have to adapt the references of the single worksheets to the folder where the files are copied, it doesn't take much time. Regarding the references, see the example in the following photo:
