Electronic – Select appropriate bandwidth for sensor (MEMS gyroscope)

Consider an accelerometer experiencing a net acceleration of gx - gz.

There are an infinite possible ways to achieve this, here are few examples:

1. The sensor is oriented with z pointing towards the sky, and the user is moving it laterally relative to the ground with acceleration g.
2. The sensor is oriented x pointing towards the ground, and the user is moving it laterally relative to the ground with acceleration -g.
3. The sensor x/z plane is oriented at a 45 degree angle, and the user is moving it in a down-ward/left direction.
4. The sensor is rotating about some point, moving with a non-constant velocity such that the acceleration is gx - gz.

etc.

So a single accelerometer cannot determine its orientation if it's experiencing acceleration and gravity.

These problems are hard to diagnose. The first thing I would do is swap the level and pressure ADC inputs to make sure that there isn't some sort of software issue. Even if you've looked at the code a thousand times I would do this.

The impedance of your sensor is pretty high to feed directly to the ADC input. I think you should add a unity gain, non-inverting buffer between the sensor and the ADC input.

Bypass capacitors may be needed. There's not enough information to tell where they should be added or what their values should be. I would be sure to bypass the 5V supply for the sensor. You could add a small capacitor to the output of the sensor as well, assuming that the pressure is not changing rapidly.

You could also try slowing the ADC clock rate to give the sample-and-hold more time to charge. Sometimes putting the processor to sleep during a conversion can reduce noise as well.