[Swlug] An interesting time with an accelerometer

[Rhys Sage]

After hunting around a bit I found some C++ code that uses accelerometer data (but curiously not gyroscopic data) to produce roll and pitch data. I had to convert from C++ to Python which was not that challenging. I can't test  the original as I have Python on my Pi Pico and not C++. I really don't want to have to rig up a Pi Pico with C++ as it's a little out of the scope of what I'm doing so I'm presuming the C++ code actually works. Having said that I'm skeptical because my conversion produced angles in the tens of thousands. This is the original...

https://github.com/mahengunawardena/BeagleboneBlack_I2C_ADXL345/blob/master/ADXL345Accelerometer.cpp
  
My Python conversion is

from imu import MPU6050
from time import sleep
from machine import Pin, I2C
import math

i2c = I2C(0, sda=Pin(0), scl=Pin(1), freq=400000)
imu = MPU6050(i2c)

while True:
   #input('rotate some, hit enter')
   ax=round(imu.accel.x,2)
   ay=round(imu.accel.y,2)
   az=round(imu.accel.z,2)
   AccelerationX = ax * 3.9
   AccelerationY = ay * 3.9
   AccelerationZ = az * 3.9
   Pitch = 180 * math.atan (AccelerationX/math.sqrt(AccelerationY*AccelerationY + AccelerationZ*AccelerationZ))/math.pi;
   Roll = 180 * math.atan (AccelerationY/math.sqrt(AccelerationX*AccelerationX + AccelerationZ*AccelerationZ))/math.pi;
   print("Roll", int(Roll), " Pitch", int(Pitch),end="\r")
  
I don't see obviously any difference - I think I have encompassed all the necessary code which in C++ looked like this section:

accelerationX = (signed int)(((signed int)rawData_X) * 3.9);
        accelerationY = (signed int)(((signed int)rawData_Y) * 3.9);
        accelerationZ = (signed int)(((signed int)rawData_Z) * 3.9);
        pitch = 180 * atan (accelerationX/sqrt(accelerationY*accelerationY + accelerationZ*accelerationZ))/M_PI;
        roll = 180 * atan (accelerationY/sqrt(accelerationX*accelerationX + accelerationZ*accelerationZ))/M_PI;

The output is not within the anticipated range and looks to be somewhat strange....

MicroPython v1.19 on 2022-06-16; Raspberry Pi Pico with RP2040
Type "help()" for more information.
>>> %Run -c $EDITOR_CONTENT
Roll -1.067217e-07  Pitch 80.44571
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
MicroPython v1.19 on 2022-06-16; Raspberry Pi Pico with RP2040
Type "help()" for more information.
>>> %Run -c $EDITOR_CONTENT
Roll 0  Pitch 80977

Has anybody any suggestions? I rather suspect the original github code might be bad since there's no inclusion of gyroscopic data and nothing that looks particularly Kalman.

Rhys Sage