SparkFun Forums

[Pumpkin]

I am using the OLA with DMP logging enabled and got raw accelerometer measurements. How do I convert these to acceleration expressed in g or do you have a user guide for this? Thanks.

[TS-John]

I am assuming you are using the Razor 9DoF IMU M0 board?

Our hook-up guide has libraries and code that should allow you to read the data in g's:

https://learn.sparkfun.com/tutorials/9d ... e-firmware

[Pumpkin]

Hi. I am using the SparkFun OpenLog Artemis board (https://www.sparkfun.com/products/16832).

I enabled DMP option in the IMU logging config menu and here is a sample from a logging file collecting with the board just resting upright on a table:
Q9_1 Q9_2 Q9_3 HeadAcc RawAX RawAY RawAZ
-0.001 -0.001 0 448 552 -422 7534
-0.002 -0.001 0 448 518 -410 7494
-0.002 -0.001 0 448 518 -410 7494
-0.002 -0.001 0 448 476 -462 7612
-0.002 -0.001 0 448 476 -462 7612

I want to convert the raw acceleration to g. I tried dividing the raw measurement by the sensitivity number, which is 2048 according to the spec https://invensense.tdk.com/products/mot ... icm-20948/, and got almost 4g in the z-axis. I am expecting around 1 g in z-axis. I must be doing something wrong?

[PaulZC]

Hi Pumpkin,
There is not a simple answer to this... There are still many things about the DMP that we do not understand. You are also not the only person to notice this. There is useful background information in the open and closed issues in the ICM-20948 GitHub repo:
https://github.com/sparkfun/SparkFun_IC ... is%3Aissue
https://github.com/sparkfun/SparkFun_IC ... s%3Aclosed
It may indeed be a scaling issue. If you want to try some experiments, please try Example10_DMP_FastMultipleSensors. You can edit the code to change the rate and scaling:
https://github.com/sparkfun/SparkFun_IC ... #L370-L379
https://github.com/sparkfun/SparkFun_IC ... #L400-L407
https://github.com/sparkfun/SparkFun_IC ... #L459-L475
If you work out the answer to this, please tell us!
Good luck!
Paul