The coolest application of an FFT I implemented was for a custom oxygen sensor for a wearable breath measuring device. The sensor would flash a blue light at about 40 kHz, and there was a phosphorescent dye which would flash orange with a phase lag that changed based on temperature and oxygen level.
Using an FFT we could get that phase lag at 40 kHz and back out the % oxygen in exhaled breath! Typical oxygen sensors at the time were not anywhere near fast enough to do that.
Using an FFT we could get that phase lag at 40 kHz and back out the % oxygen in exhaled breath! Typical oxygen sensors at the time were not anywhere near fast enough to do that.