Is there a FFT sound grapher out there for the Peggy ? I'd like to use one but I don't know how to code it.. maybe someone has done it before ? I've made a similar one on Pure Data but can't port it to the Peggy ( lack of know-how..)
Thank you

There have been a few AVR/Arduino FFT projects; you could certainly do it on board. Although that would require some hardware to condition the audio signal such that the AVR's ADC could receive it, and the AVR ADC isn't particularly fast (15 kHz at full resolution).

Since you've got what you want in pd, would it be an acceptable solution to use the pd serial routines to stream the data to an Arduino board and then use the standard I2C "video peggy" trick?

Unfortunately, pd connects to the arduino with a pduino (firmata) sketch on the arduino and videopeggy also needs a patch on the arduino to connect to the peggy. I have no clue on how to merge the two. Challenging.

My suggestion is to skip the pduino/firmata, which is a specific means of communicating with an Arduino board, and instead to just use the *serial* routines for sending data to the Peggy; that way you can control the formatting fully.