Daniil Guitelson’s BGI library was also used for the graphics.
Here is the output showing the DC, 3300 Hz, 5700 Hz and 25700 Hz signals:
The next step is to port the code to a suitable Arduino board and to show the results physically. Thus, he used a MicroView OLED display and here it is listening to a 3v 1kHz square wave:
He then updated the project to work with Nokia LCD, here it is showing the 0-3v 1 kHz square wave signal:
Amazing ideas and projects can be inspired by this project. You can download these files to start your own spectrum analyser!
The full project and detailed information are available at the project page on Hackaday. You can follow it to keep updates with the latest versions.