Because a voltage divider is a very bad idea for power.
I’m not sure I understand why.
In this case it is a spectacularly bad idea because that power is used as an analog reference.
Isn’t using the voltage for the ADXL337 as analog reference an advantage?
My thinking: If the voltage fluctuates due to fluctuations in the ADXL337’s power consumption, then the voltage on AREF will fluctuate accordingly. In other words, the ratio of g/AREF will stay the same, and I will get consistent measurements.
OK below you write that the fluctuations can be at high frequency. If that is the case, and if AREF cannot keep up, then I understand that there is an issue. But is it the case?
If the chip being powered uses a variable amount of current then the voltage at the divider will vary. This will be unpredictable and possibly quite high frequency, so impossible to measure and correct for.
Concerning current, the ADXL337 spec sheet only states:
Supply Current: 300 μA (at 3 V)
With the 300 μA, I did some calculations. For a voltage divider with two 100 Ω resistors, I get a supply voltage of: 2.485 V
Now – although there is no mention of that in the spec sheet – let’s assume that the current fluctuates by ±50%. The corresponding fluctuation of the supply voltage is negligible at: 2.485 V ± 0.3%
This looks OK.
I think it is time to design your own PCBs.
At the current state, I don’t think it makes sense. I would need to manufacture all 22 nodes again, which takes a lot of time. And then maybe it doesn’t work as I want, and I would need to choose a different accelerometer, etc.
But there are ADXL335/337 breakout boards with voltage regulators on them. Guess I’ll get some of these, just to be on the safe side.
If anything, it rigidly fixes your tilt sensor relative to the outside casing.
The tilt sensor in the first image in my second post is rigidly fixed to the outside casing: It is glued to the Arduino Pro Mini with double sided tape, and the Arduino Pro Mini sits firmly in the casing.