in my setup I am using EVAL-ADXL345Z connected to the GPIO Pins of a RaspberryPi via SPI. I evaluated the suitability of the setup to cable lengths up to 15 meters. Thereby I noticed that there is continuous noise. The amplitude gets bigger with increasing cable distance, up to 5 m/s² at 15m cable length (see attachment top and middle graphic).
The transformation of the recorded signal to frequency domain. showed that besides the regular noise there is some special noise that occurs at exactly 100Hz (see attachment bottom graphic). External interferences can be excluded, since the setup was tested in different environments. Different sampling and SPI frequencies were tested with the same results. Also the cable was grounded as recommended. Therefore I assume that the source of the noise is either the Raspberry, the breakout board, or the sensor itself. The 100Hz noise can also be detected on a breadboard setup, even though the peak is clearly smaller.
Now my question:
Is this a known problem? If so, are there any recommendations how to eliminate that noise?
Thank you very much in advance.
Best greetings from Germany.