Compact FFT Codes for Microcontrollers

Look at Microchip DSPic series. The have application notes for FFTs.

Disclaimer: I know nothing about this sort of thing, so, just ignore if rubbish- but:-

There was an article this morning from DSPdesignline on DSP on Intel Architecture. I see that the folder structure includes the term processors_fpga . Might be worth following up.

http://www.dspdesignline.com/howto/processors_fpga/217701677

The FFT has been used as a pre-processor to obtain 1/3 octave spectra for over 40 years. It is a non-real time solution, as the FFT must be done in multiple sample rates to achieve ANSI class 1/3 octave filter shapes. This also implies that you need programmable anti-aliasing filters to block out the higher frequencies when using the lower sampling rates.

Here is a URL for a free PC-based program that will do 1/3 octave:

Visual Sound Instrument 3.20C

I thank you for your replies.

Indeed; the chinese program for 1/3 octave compression & FFT display looks usefull.
I just have to charge the battery of my function generator to test it.
Also, MICROCHIP DSPic is a good advice: there is the code of compact FFT for the PIC 17C42.

However, I have a further question:

The 17C42 microcontroller is already obsolescent. I shall buy 3 of these to test the FFT, indeed I just want to build one or two setups, so there is no need for the supply of, says, 1000 devices for commercial purpose.
However, to you believe that it would be not too much difficult:

1)to convert from a linear frequency to a logarithmic frequency( I want to display from 1 millihertz to 10 megahertz,on powers of 2)

2)to adapt for less expensive EEROM Flash devices instead of windowed EPROMs, which are far more expensive.
Thank you.

You stopped too soon, keep looking on the Microchip website. There is application code for the DSPic30 and 33 series which is modern and uses flash program memory so there is no need to mess with windowed parts.

Can't really help you with the log issue but I believe it would require generating a non-linear array of constants that are used in the MAC calculations of the FFT.