Does anybody here know a great tutorial or sample sketch for fft? I tried the Arduino FFT but I only get gibberish. Would like to find out if its my wiring or something.
That is, exactly the library I tried and the outcome seems to be just random values
The only way to test FFT routines is to inject pure spot frequencies and check the expected bin for a coresponding high value.
The best way is to preload your sampling data with your spot freqency and check. If you inject into the audio input and your audio circuit is full of noise, then the FFT will be full of noise and thus random numbers.
You need to work back from the FFT routines stage by stage and see where it falls over.
Inject spot frequencies into the FFT, then multiple frequencies, then equivalent signals and so on until you are back to the original analogue input point. If these test frequencies produce the FFT you expect then it is working. Tie the input to ground to see if all the bins are zero would also be a simple test and needs nothing special.
Without good test gear, like: oscilloscope, signal generators and ideally arbitary waveform generators, it will be very difficult to fault find the analogue parts that maybe injecting/generating noise into your FFT calculations.