While VIN is more sharply centered, it has outliers in the range of 1200 to > 8200. The 3V3 is more spread (higher IQR) but outliers only between 3200 to 6200.
Yes, I think this data is convincing. Then indeed it is unclear which one is better - the one more compact but with larger outliers or the one that has larger spread, but smaller outliers. At least, I don’t have a clear answer.
On the topic of shorting 3V3 + VIN. From the ADXL345 datasheet (from Analog devices):
A 1 μF tantalum capacitor (CS) at VS and a 0.1 μF ceramic capacitor
(CI/O) at VDD I/O placed close to the ADXL345 supply pins is
recommended to adequately decouple the accelerometer from
noise on the power supply. If additional decoupling is necessary,
a resistor or ferrite bead, no larger than 100 Ω, in series with VS
may be helpful. Additionally, increasing the bypass capacitance
on VS to a 10 μF tantalum capacitor in parallel with a 0.1 μF
ceramic capacitor may also improve noise.
Looking at Adafruit adxl345 schematics, it seems that it has only 0.1 uF capacitor on VS+VDD. If you short 3V3 pin with VIN on the board, you add 10 uF capacitor in parallel to that. As per datasheet, it may improve the noise. So, maybe there’s that. And according to the schematics of some Chinese adxl345 boards they have better capacitor schemas for filtering (whether those schematics are trustworthy is a different story, plus the stepdown converters could be different on different boards).
What are the likely resonant frequencies for a given structural architecture, e.g., simple bed slinger, delta, etc?
The sampling rates I’m seeing here may be a potential contributor of the noise. I am just now coming onboard with both Klipper and the use of ADXL as a test sensor so this thread is intriguing. I’m many years away from my former elex schooling so take what I say with a grain of salt. More data doesn’t necessarily translate to better information. As is common knowledge in science the item being observed often changes as a direct function of the observation. With each reading the impedance of the circuit changes transmitting ripples back thru the system; ripples that may still be active by the time the next reading begins. Thus, my intro question above is trying to discover the expected resonance bands so that an appropriate sampling rate based on the Nyquist rate can be determined.
