Just got the ICM20948 breakout, great unit! I was wondering about the axes. In the Arduino sketch “Example1_Basics.ino” the Acc_z reads 1020mg positive when the board in completely flat with the chips on top. According to the TDK Invensense data sheet the Z axis for Mag/Gyro points up so shouldn’t the Acc_z read -1020mg since the Gravity vector points down?
Many Thanks.
The accelerometer can’t measure the acceleration due to gravity, as gravity acts uniformly on all parts of the sensor. The acceleration it reports when sitting still on the bench top is due to the so-called “normal” force provided by the bench top, which prevents the sensor from falling and points up.
Fun fact: the measured acceleration is zero during free fall.
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Many thanks for getting back to me! That makes sense. If the MEMS is a finger type capacitor, then when the unit is vertical and stationary the fingers are dropping indicating acceleration up. If in free fall the fingers are weightless and when falling at 2G, then the fingers would be driven up indicating acceleration down.
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