Playing around with the STM32, I wanted to test if the electret was capable of listening to 18 to 20kHz sounds... Indeed! I've created 18kHz and 20kHz wav files on the repo, then played those and tested with the FFT capacity: the two peaks are very well resolved ! You can see the jupyter notebook for the experiment.

The peaks correspond the beacons are using. This proves that it'd definitely be possible to have a small device tracking the ultrasound beacons on the road!

Next steps.. having a better looking GUI on the small system OLED =)