Add toy compass example.

Author: Mark Shannon

examples/compass.py

@@ -0,0 +1,28 @@
+from microbit import *
+
+needles = (Image.CLOCK12, Image.CLOCK1, Image.CLOCK2, Image.CLOCK3,
+           Image.CLOCK4, Image.CLOCK5, Image.CLOCK6, Image.CLOCK7, 
+           Image.CLOCK8, Image.CLOCK9, Image.CLOCK10, Image.CLOCK11)
+
+# You need to spin the microbit about a few times to help calibrate the compass
+
+# Scroll a message to encourage user to help calibrate the compass
+# "Spin" "Me!" reads better than "Spin Me!" due to lack of kerning
+display.scroll("Spin")
+display.scroll("Me!")
+
+# Start calibrating
+compass.calibrate()
+
+# Spin needle until calibrated.
+while compass.is_calibrating():
+    for i in range(12):
+        display.print(needles[i])
+        sleep(80)
+display.clear()
+
+# Try to keep needle pointed in (roughly) the same direction
+while True:
+    sleep(500)
+    needle = ((15 - compass.heading()) // 30) % 12
+    display.print(needles[needle])