ATmega8 (TQFP32 package) based on FFT Circuit applied the entry signals 16 × 16 led display (SCT2024 serial-interfaced LED driver 256 LEDs), you can see in the FFT circuit source C, hex codes have a parent/child schema for the printed circuit drawings a good example about the use of the SPI, ADC with atmega8
Fast Fourier transformation
A fast Fourier transform (FFT) is an algorithm to compute the discrete Fourier transform (DFT) and its inverse. Fourier analysis converts time (or space) to frequency and vice versa; an FFT rapidly computes such transformations by factorizing the DFT matrix into a product of sparse (mostly zero) factors. As a result, fast Fourier transforms are widely used for many applications in engineering, science, and mathematics. The basic ideas were popularized in 1965, but some FFTs had been previously known as early as 1805. Fast Fourier transforms have been described as “the most important numerical algorithm of our lifetime”.