Hi,
I am developing BLE sensors and after working with the nRF54L15DK boards, I have now bought 5 XIAO boards to integrate everything in a smaller form factor. With these boards I noticed that I have noise in my ADC readings, which corresponds to the BLE connection interval (50 ms in my case, but I have chagned it and the noise changed accordingly). The attached image shows the values sampled at 1 kHz with 3 different XIAO boards, using AIN2 and AIN3, which were shorted together on the header. I have tried different combinations of TACQ and TCONV but they don’t any effect on this noise.
Interestingly, some boards show less noise, but FFT analysis confirms that the noise is present in all of them. FFT analysis of the DK boards shows no such noise at all (at 20 Hz/50 ms the signal is in the noise floor). I have even tried swapping the nRF54L15 chip from a XIAO board with low noise to a board with high noise and the noise stayed with the board not the chip, though they both changed a bit, so it seems to be a board design issue rather than a faulty chip.
Could someone at seedstudio confirm my observations and maybe suggest a fix?
Thank you and best regards
Sašo