To get accurate compass readings with an AHRS filter, you'll want to calibrate your sensor. There are a few different ways to do this. The following calibrate.py code lets you do it right in CircuitPython and allows you to copy and paste the calibration values into the code.py file for this project.
You can access the calibration code and necessary libraries by downloading the Project Bundle. To do this, click on the Download Project Bundle button in the window below. It will download to your computer as a zipped folder.
# SPDX-FileCopyrightText: 2024 Liz Clark for Adafruit Industries
# SPDX-License-Identifier: MIT
#
# Adapted from Gamblor21's calibrate.py in the Gamblor21_CircuitPython_AHRS library
# https://github.com/gamblor21/Gamblor21_CircuitPython_AHRS/blob/master/examples/calibrate.py
#
# Gyro will be calibrated first, followed by magnetometer
# Keep the board still for gyro, move around for magnetometer
import time
from adafruit_lsm6ds.lsm6dsox import LSM6DSOX
import adafruit_lis3mdl
from adafruit_qualia.graphics import Graphics, Displays
graphics = Graphics(Displays.ROUND21, default_bg=None, auto_refresh=True)
i2c = graphics.i2c_bus
accel_gyro = LSM6DSOX(i2c)
magnetometer = adafruit_lis3mdl.LIS3MDL(i2c)
MAG_MIN = [1000, 1000, 1000]
MAG_MAX = [-1000, -1000, -1000]
def map_range(x, in_min, in_max, out_min, out_max):
"""
Maps a number from one range to another.
:return: Returns value mapped to new range
:rtype: float
"""
mapped = (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min
if out_min <= out_max:
return max(min(mapped, out_max), out_min)
return min(max(mapped, out_max), out_min)
def calibrate_gyro():
"""
Calibrates gyroscope
Gyroscope values are in rads/s
"""
gx, gy, gz = accel_gyro.gyro
min_gx = gx
min_gy = gy
min_gz = gz
max_gx = gx
max_gy = gy
max_gz = gz
mid_gx = gx
mid_gy = gy
mid_gz = gz
for _ in range(10):
gx, gy, gz = accel_gyro.gyro
min_gx = min(min_gx, gx)
min_gy = min(min_gy, gy)
min_gz = min(min_gz, gz)
max_gx = max(max_gx, gx)
max_gy = max(max_gy, gy)
max_gz = max(max_gz, gz)
mid_gx = (max_gx + min_gx) / 2
mid_gy = (max_gy + min_gy) / 2
mid_gz = (max_gz + min_gz) / 2
print("Uncalibrated gyro: ", (gx, gy, gz))
print("Calibrated gyro: ", (gx + mid_gx, gy + mid_gy, gz + mid_gz))
print("Gyro calibration: ", (mid_gx, mid_gy, mid_gz))
time.sleep(1)
mid_gx = float(f"{mid_gx:.4f}")
mid_gy = float(f"{mid_gy:.4f}")
mid_gz = float(f"{mid_gz:.4f}")
_CAL = [mid_gx, mid_gy, mid_gz]
return _CAL
def calibrate_mag():
"""
Calibrates a magnometer
"""
countavg = 0
x, y, z = magnetometer.magnetic
mag_vals = [x, y, z]
for i in range(3):
MAG_MIN[i] = min(MAG_MIN[i], mag_vals[i])
MAG_MAX[i] = max(MAG_MAX[i], mag_vals[i])
for _ in range(10):
x, y, z = magnetometer.magnetic
mag_vals = [x, y, z]
for i in range(3):
MAG_MIN[i] = min(MAG_MIN[i], mag_vals[i])
MAG_MAX[i] = max(MAG_MAX[i], mag_vals[i])
countavg += 1
print("Uncalibrated:", x, y, z)
cal_x = map_range(x, MAG_MIN[0], MAG_MAX[0], -1, 1)
cal_y = map_range(y, MAG_MIN[1], MAG_MAX[1], -1, 1)
cal_z = map_range(z, MAG_MIN[2], MAG_MAX[2], -1, 1)
print("Calibrated: ", cal_x, cal_y, cal_z)
print("MAG_MIN =", MAG_MIN)
print("MAG_MAX =", MAG_MAX)
time.sleep(1)
return MAG_MIN, MAG_MAX
print("Preparing gyroscope calibration. Keep board perfectly still on flat surface.")
time.sleep(5)
print("Starting gyroscope calibration..")
print()
GYRO_CAL = calibrate_gyro()
print("Gyroscope calibrated!")
print("Preparing magnetometer calibration. Move board around in 3D space.")
time.sleep(5)
print("Starting magnetometer calibration..")
print()
MAG_MIN, MAG_MAX = calibrate_mag()
print("Magnetometer calibrated!")
print()
print("MAG_MIN =", MAG_MIN)
print("MAG_MAX =", MAG_MAX)
print("GYRO_CAL =", GYRO_CAL)
Upload the Calibration Code and Libraries to the Qualia S3
After downloading the Project Bundle, plug your Qualia S3 into the computer's USB port with a known good USB data+power cable. You should see a new flash drive appear in the computer's File Explorer or Finder (depending on your operating system) called CIRCUITPY. Unzip the folder and copy the following items to the Qualia S3's CIRCUITPY drive:
- lib folder
- calibrate.py
Rename calibrate.py to code.py to run the calibration code on your Qualia S3.
Running the Calibration
Once everything is saved to the CIRCUITPY drive, connect to the serial console to see instructions and data printed out for the calibration process.
First, the gyroscope is calibrated. To do this, you need to leave your sensor still on a flat surface. Ideally, it will be mounted in the enclosure. Next, the magnetometer is calibrated. You'll need to move the sensor around in 3D space to get a full reading range for the sensor. After both calibration processes are completed, the calibration data is printed to the serial console. You can copy and paste the MAG_MIN, MAG_MAX and GYRO_CAL arrays to your code.py file.
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