The discrete fourier transform (DFT), and the related fast fourier transform (fft) are staples of signal processing, and have many important applications in electrical engineering. As such, a thorough mathematical understanding of the DFT is very helpful to the aspiring engineer or serious hobbyist. Reader James sent in a tip to a well-written free online version of the book shown above. Check it out!

I was working downstairs in the engineering library at Purdue today when a book on one of the bookshelves caught my attention.

Pulling the books off the shelf, I found these:

I checked the Library of Congress numbers given in the books and found that they were, regrettably, out of print. However, I was lucky enough to find both books available for free online at NASA’s website. Go check them out! Definitely a worthwhile read for the space enthusiast!

Biomedical Results for Apollo
Biomedical Results for Skylab

Not long ago, reader Zelimir read our announcement post of our original PWM Operating Theory tutorial, and in the comments tipped us off to what appears to be a fantastic resource on PWM Control System Theory. There are 2 documents available for download from the site, and both appear to be engineering textbook-quality write-ups on the subject. It should be noted that these write-ups are well beyond amateur-hobbyist level tutorials, requiring advanced training in math and science, so keep this in mind before you get started. Very impressive!