adding compass example

examples/lis2mdl_calibrate.py

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+""" 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

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+""" Display compass heading data from a calibrated magnetometer """
+
+import time
+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).
+#
+# To get these values run the lis2mdl_calibrate.py script on your device.
+# Twist the device around in 3D space while it calibrates. It will print
+# some calibration values like these:
+# ...
+# Calibrating - X:    -46.62, Y:    -22.33, Z:    -16.94 uT
+# ...
+# Calibration complete:
+# hardiron_calibration = [[-63.5487, 33.0313], [-40.5145, 53.8293], [-43.7153, 55.5101]]
+#
+# You need t copy your own value for hardiron_calibration from the output and paste it
+# into this script here:
+hardiron_calibration = [[-61.4879, 34.4782], [-43.6714, 53.5662], [-40.7337, 52.4554]]
+
+
+# This will take the magnetometer values, adjust them with the calibrations
+# 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
+
+
+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
+
+    print("Heading:", compass_heading)
+    time.sleep(0.1)