adding calibration script for compass example and update compass to use calibration values.

Author: FoamyGuy

examples/lis2mdl_calibrate.py

@@ -0,0 +1,35 @@
+""" Calibrate the magnetometer and print out the hard-iron calibrations """
+
+import time
+import board
+import busio
+import adafruit_lis2mdl
+
+i2c = busio.I2C(board.SCL, board.SDA)
+magnetometer = adafruit_lis2mdl.LIS2MDL(i2c)
+
+# calibration for magnetometer X (min, max), Y and Z
+hardiron_calibration = [[1000, -1000], [1000, -1000], [1000, -1000]]
+
+def calibrate():
+    start_time = time.monotonic()
+
+    # Update the high and low extremes
+    while time.monotonic() - start_time < 10.0:
+        magval = magnetometer.magnetic
+        print('Calibrating - X:{0:10.2f}, Y:{1:10.2f}, Z:{2:10.2f} uT'.format(*magval))
+        for i, axis in enumerate(magval):
+            hardiron_calibration[i][0] = min(hardiron_calibration[i][0], axis)
+            hardiron_calibration[i][1] = max(hardiron_calibration[i][1], axis)
+    print("Calibration complete:")
+    print("hardiron_calibration =", hardiron_calibration)
+
+print("Prepare to calibrate! Twist the magnetometer around in 3D in...")
+print("3...")
+time.sleep(1)
+print("2...")
+time.sleep(1)
+print("1...")
+time.sleep(1)
+
+calibrate()

examples/lis2mdl_compass.py

@@ -1,26 +1,39 @@
-""" Display compass heading data five times per second """
+""" Display compass heading data from a calibrated magnetometer """
+
 import time
-from math import atan2, degrees
+import math
 import board
 import busio
 import adafruit_lis2mdl
 
 i2c = busio.I2C(board.SCL, board.SDA)
 sensor = adafruit_lis2mdl.LIS2MDL(i2c)
 
+# You will need the calibration values from your magnetometer calibration
+# these values are in uT and are in X, Y, Z order (min and max values)
+hardiron_calibration = [[-61.4879, 34.4782], [-43.6714, 53.5662], [-40.7337, 52.4554]]
 
-def vector_2_degrees(x, y):
-    angle = degrees(atan2(y, x))
-    if angle < 0:
-        angle += 360
-    return angle
+# This will take the magnetometer values, adjust them with the calibraitons
+# and return a new array with the XYZ values ranging from -100 to 100
+def normalize(magvals):
+    ret = [0, 0, 0]
+    for i, axis in enumerate(magvals):
+        minv, maxv = hardiron_calibration[i]
+        axis = min(max(minv, axis), maxv)  # keep within min/max calibration
+        ret[i] =(axis - minv) * 200 / (maxv - minv) + -100
+    return ret
 
 
-def get_heading(_sensor):
-    magnet_x, magnet_y, _ = _sensor.magnetic
-    return vector_2_degrees(magnet_x, magnet_y)
+while True:
+    magvals = sensor.magnetic
+    normvals = normalize(magvals)
+    print("magnetometer: %s -> %s" % (magvals, normvals))
 
+    # we will only use X and Y for the compass calculations, so hold it level!
+    compass_heading = int(math.atan2(normvals[1], normvals[0]) * 180.0 / math.pi)
+    # compass_heading is between -180 and +180 since atan2 returns -pi to +pi
+    # this translates it to be between 0 and 360
+    compass_heading += 180
 
-while True:
-    print("heading: {:.2f} degrees".format(get_heading(sensor)))
-    time.sleep(0.2)
+    print("Heading:", compass_heading)
+    time.sleep(0.1)