Brad Ormand - First Embedded Fourier Transform

11.16.2014 – Fourier Test & Guitar Practice

Well, during my tests of the real-time FFT on the embedded system with the SSD1306 as the display, I blew the Atmel chip out. Ugh.  At least I think so.  No smoke released, no smells, no heat – it just won’t program anymore.  It’s done.  And, I think I know what I did to brick it.

I’m running the chip with an ADC reference of 3.3v, and while using my iPhone as a signal source, I probably drove about 1.8v + 1.8v (peak-to-peak) = 3.6v+ into it (or more), to my estimate.  It’s stated max *is* at 3.6v.  I built a front-end circuit for it to all be positive voltage, so no negative voltage passed through, but had no input peak protection at all.  I measured the signal on the oscilloscope beforehand, and it was lower than the 3.3v, but it was turned down, and it was voiceover instead of mastered music, and there may have been transients and all that…  Ugh.  Basically, I just spaced and didn’t pay attention to currents.  I would never have even hooked it up with it turned up if  I had been really thinking.  I was in a hurry to do the tests, I guess.  Fools rush in. 🙂

So, anyway, I’ll build some input protection on there and re-consider, twice, what signals I feed in next time.  The good thing is…  I have a few more of those chips, soo…  I’ll drop another in and carry on.

But, during the tests, I was actually able to make a real-time-updating waveform display on the SSD1306, which looked soooper cool.  I did do a static test of the FFT implementation on the system and snapped a pic – it’s kind of a crappy pic, but you can see the peak and a few harmonics.  It was a really low sample rate.  However, never got to the part where I enabled the FFT per frame before the system stalled during my ADC tests…  So, I’m really looking forward to doing that, later.  Will it work?  Will it be super slow?  IDK.  When I get more time, I’ll restart.

Brad Ormand - First Embedded Fourier Transform

And, in other news, I re-strung my guitar with those 10’s and tuned it up.  It sounds pretty great.  I set up a comfortable station with an amp and a chair between the kitchen and the living room.  I then began practicing some scales at the level I left off a few months ago.  Breaking off rust, right now.  My goal is to play the “Kitchen” solo, at speed.