Forgot to update the file.

CPX_Compass/CPX_Compass.ino

@@ -1,3 +1,15 @@
+/* Circuit Playground Express compass. */
+
+/* Adafruit invests time and resources providing this open source code. */
+/* Please support Adafruit and open source hardware by purchasing */
+/* products from Adafruit! */
+
+/* Written by Dave Astels for Adafruit Industries */
+/* Copyright (c) 2018 Adafruit Industries */
+/* Licensed under the MIT license. */
+
+/* All text above must be included in any redistribution. */
+
 #include <Wire.h>
 #include <Adafruit_NeoPixel.h>
 #include <Adafruit_Sensor.h>
@@ -7,12 +19,12 @@
 /* Assign a unique ID to this sensor at the same time */
 Adafruit_LSM303_Mag_Unified mag = Adafruit_LSM303_Mag_Unified(12345);
 
-float raw_mins[3] = {1000.0, 1000.0, 1000.0};
-float raw_maxes[3] = {-1000.0, -1000.0, -1000.0};
+float raw_mins[2] = {1000.0, 1000.0};
+float raw_maxes[2] = {-1000.0, -1000.0};
 
-float mins[3];
-float maxes[3];
-float corrections[3] = {0.0, 0.0, 0.0};
+float mins[2];
+float maxes[2];
+float corrections[2] = {0.0, 0.0};
 
 
 // Support both classic and express
@@ -27,6 +39,7 @@ float corrections[3] = {0.0, 0.0, 0.0};
 // example for more information on possible values.
 Adafruit_NeoPixel strip = Adafruit_NeoPixel(10, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);
 
+// Map direction pie slices (of 30 deg each) to a neopixel, or two for the missing ones at USB & power.
 int led_patterns[12][2] = {{4, 5}, {5, -1}, {6, -1}, {7, -1}, {8, -1}, {9, -1}, {9, 0}, {0 -1}, {1, -1}, {2, -1}, {3, -1}, {4, -1}};
 
 #define BUTTON_A 4
@@ -39,6 +52,9 @@ void fill(int red, int green, int blue) {
 }
 
 
+// Do some initial reading to let the magnetometer settle in.
+// This was found by experience to be required.
+// Indicated to the user by blue LEDs.
 void warm_up(void)
 {
   sensors_event_t event;
@@ -50,10 +66,14 @@ void warm_up(void)
 }
 
 
+// Find the range of X and Y values.
+// User needs to rotate the CPX a bunch during this.
+// Can be refined by doing more of the saem by pressing the A button.
+// Indicated to the user by green LEDs.
 void calibrate(void)
 {
   sensors_event_t event;
-  float values[3];
+  float values[2];
 
   fill(0, 128, 0);
 
@@ -103,10 +123,12 @@ void setup(void)
 }
 
 
-float normalize(float value, float in_min, float in_max, float out_min, float out_max) {
-  float mapped = (value - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
-  float max_clipped = mapped <  out_max ? mapped : out_max;
-  float min_clipped = max_clipped > out_min ? max_clipped : out_min;
+// Map a value from the input range to the output range
+// Used to map MAG values from the calibrated (min/max) range to (-100, 100)
+float normalize(float value, float in_min, float in_max) {
+  float mapped = (value - in_min) * 200 / (in_max - in_min) + -100;
+  float max_clipped = mapped <  100 ? mapped : 100;
+  float min_clipped = max_clipped > -100 ? max_clipped : -100;
   return min_clipped;
 }
 
@@ -123,20 +145,22 @@ void loop(void)
 
   float x = event.magnetic.x;
   float y = event.magnetic.y * -1;
-  float z = event.magnetic.z * -1;
 
   if (x == 0.0 && y == 0.0) {
     return;
   }
 
-  float normalized_x = normalize(x - corrections[0], mins[0], maxes[0], -100.0, 100.0);
-  float normalized_y = normalize(y - corrections[1], mins[1], maxes[1], -100.0, 100.0);
+  float normalized_x = normalize(x - corrections[0], mins[0], maxes[0]);
+  float normalized_y = normalize(y - corrections[1], mins[1], maxes[1]);
 
   int compass_heading = (int)(atan2(normalized_y, normalized_x) * 180.0 / 3.14159);
   // 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;
 
+  // We add 15 to account to the zero position being 0 +/- 15 degrees.
+  // mod by 360 to keep it within a circle
+  // divide by 30 to find which pixel corresponding pie slice it's in
   int direction_index = ((compass_heading + 15) % 360) / 30;
 
   // light the pixel(s) for the direction the compass is pointing