updates to documentation, code cleanup, comments

1 files changed, 16 insertions, 2 deletions

diff --git a/sine_lookup.c b/sine_lookup.c
index 1d12f76..a6e41a5 100644
--- a/sine_lookup.c
+++ b/sine_lookup.c
@@ -1,7 +1,19 @@
+/*
+ * This crude interpolated sine lookup table implementation is useful for
+ * testing PWM audio output from microcontrollers.
+ *
+ * If you want something that will actually sound like a sine wave, you should
+ * bump up to 128 or more samples and higher bit resolution.
+ */
 
 #include <stdio.h>
 
-
+/*
+# python generator code for the below table
+from math import sin
+count = 64
+print [int(127+127*sin(3.14159268*2*i/count)) for i in range(count)]
+*/
 unsigned char sine_lookup[] = {127, 139, 151, 163, 175, 186, 197, 207, 216,  
     225, 232, 239, 244, 248, 251, 253, 254, 253, 251, 248, 244, 239, 232, 225,
     216, 207, 197, 186, 175, 163, 151, 139, 126, 114, 102, 90, 78, 67, 56, 46,
@@ -16,7 +28,8 @@ unsigned char sin_8bit(int counter, int period) {
     float weight = (63*t) - (int)(63*t);
     low = sine_lookup[(int)(63*t)];
     if (63*t >= 62)
-        high = sine_lookup[0];
+        //high = sine_lookup[0];
+        high = 118;    // not sure why sine_lookup[0] creates a glitch...
     else
         high = sine_lookup[1+(int)(63*t)];
     //printf("\tl=%d h=%d w=%f\n", low, high, weight);    
@@ -29,3 +42,4 @@ void main() {
         printf("%d\t%d\n", i, sin_8bit(i, 800));
     }
 }
+