Has anyone heard about Fourier transforms on Excel? Google didn't have any quick obvious hits.
Excel would be a cheap easy way demonstrate FFTs in the classroom.
The first column would be phase angle and 2nd column would calculate A1sin(w1*t + phi1) + A2sin(w2*t + phi2) etc. for a time domain signal.
Go down 256 cells and start something like the divide and conquer approach.
The A1, A2, A3 . . . An and phi1, phi2, phi3, . . . phin would output in the cells dedicated to various frequency ranges.
Bret Cahill