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/*
* 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,
37, 28, 21, 14, 9, 5, 2, 0, 0, 0, 2, 5, 9, 14, 21, 28, 37, 46, 56, 67, 78,
90, 102, 114};
unsigned char sin_8bit(int counter, int period);
unsigned char sin_8bit(int counter, int period) {
int high, low;
float t = (counter % period) / (float)period;
float weight = (63*t) - (int)(63*t);
low = sine_lookup[(int)(63*t)];
if (63*t >= 62)
//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);
return (int)(high * weight + low * (1.0 - weight));
}
void main() {
int i;
for(i=0; i<800;i++){
printf("%d\t%d\n", i, sin_8bit(i, 800));
}
}
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