Hello all,

I wrote on the previous build log that we have a different flavor of HW. For now we will call it type 2. 

I was hoping that this would be just scaling the bigger footprints down and subtitling the MCU with headers, but it was not meant to be like that :)

When I got the the hardware I saw this on the scope.

I was thinking at first it is noise from the switching of the PDM and I added some RC network to each pad. This only made the thing worse. Also I was thinking that the XIAO boards are noisy. Even I striped the copper surrounding the T-scale thinking that it was picking up some noise. The problem becomes obvious once we zoom in even closer.

This is what one of those peaks look likes on the 2us scale. For the original hardware running the ST I was using port register to switch the state of the excitation pads all at once. But running the XIAO board I was switching them one by one and then we get this ladder effect. 

Now the quick solution would be to do the same for the XIAO board, but not all the pins are on the same port. Further more what happens if we put RP2040 or other controllers. We need a way of switching everything robustly and with every MCU provided. 

The solution for now would be to add a shift register like the 74HCT595D from NEXPERIA. I have some laying around and will make a test.

Also for bonus points a played around with the signal generation and I have modified the pattern a little bit so we get even nicer signals. You can get it from the repo.


Cheers,

M