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This week I concentrated exclusively on the Signal Recorder and Data Analyser program. It is mostly done, in concept at least, but the Fast Fourier Transform algorithm I am using is proving to be difficult to implement and test.

I spent some time on the data visualisation and graphing, which turned out to be surprisingly easy with Qt. I still need to add some new functions, most notably the ability to save graphs and sections of graphs as image or separate text files. Saving screen out put as an image file is something I have never done before.

I did find a suitable algorithm to use for FFT, on THIS site. I also tested it’s date with some date I found HERE. My values did not match up exactly, but the output pattern of the data and expected behaviour seemed to be the same.

I need to know the Sampling Rate for some of the FFT algorithms, so I had to do some further research and experimentation into Arduino-based datalogging. I determined that the maximum rate that the Arduino serial connection seems to be capable of logging data is 62.5 Hz, which is 62.5 times a second, or once every 0.016 milliseconds. This is reasonably fast, but not really spectacular. For the FFT program to work, the sample rate has to be a power of 2, which would mean that 32 Hz is the highest sample rate that I can use.

I also spent time working on the mathematics of FFT, and making sure my understanding of it was correct. I am reasonably sure that it is at this point, and I don’t have a lot more work to do on this part of the program.