Hi Paul
Your implementation looks good, and if we can squeeze 512 rather than 256 bins, then that’s great. I have one suggestion for the display that would make the NANO into a very useful tool for VLF signal displaying - that is to have a waterfall display as used in various PC programs such as Spectrum Lab. I guess this can be implemented with no additional memory requirement by writing a row of coloured pixels to the top or bottom of the screen and scrolling one row. I look forward to trying your code.
Tony