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| -rw-r--r-- | circuit.txt | 79 | ||||
| -rw-r--r-- | sine_lookup.c | 31 |
2 files changed, 110 insertions, 0 deletions
diff --git a/circuit.txt b/circuit.txt new file mode 100644 index 0000000..1ad056e --- /dev/null +++ b/circuit.txt @@ -0,0 +1,79 @@ + +### Circuit + +http://www.uchobby.com/index.php/2008/01/08/arduino-audio-dac-options/ + + 47kohm resistor off pin, then 0.01uF cap to ground and speaker in parallel, + optionally with a pot or pair of resistors (sum=100khom?) acting as a + voltage divider for the headphones. + +### MCU configuration + +Set interrupt timer for 8KHz. + +Set PWM period to 255, prescaler to 1; this gives a period of 3.54 +microseconds, or about 282KHz. Further filtering may not even be needed? + +### Example Code + +#define PWM_OUT_PIN BOARD_LED_PIN + +HardwareTimer pwm(1); +HardwareTimer gen(1); + +uint8_t[64] sine_lookup; +int counter = 0; + +/* +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[] __FLASH__ = {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}; + +void setup() { + // configure PWM output + pinMode(PWM_OUT_PIN, OUTPUT); + pwm.setChannel1Mode(TIMER_PWM); + pwm.setPrescaleFactor(1); + pwm.setOverflow(255); // 8-bit resolution + pwm.setCompare(1, 128); // initialize to "zero" + + // configure 8KHz ticker and interrupt handler + gen.pause(); + gen.setPeriod(125); // 8Khz + gen.setChannel1Mode(TIMER_OUTPUT_COMPARE); + gen.refesh() + + + // get things started! + gen.resume() +} + +void loop() { + // USB serial interaction code goes here... +} + +void handler_sample(void) { + pwm.setCompare(1, sin_8bit(counter, 800)); // 100Hz sine wave + // pwm.setCompare(1, execute(counter); + counter++; +} + +uint8_t sin_8bit(int counter, int period) { + int high, low; + float t = (t % period) / (float)period; + float weight = t - (t % 1); + low = sine_lookup[63*t]; + if (63*t >= ) + high = sine_lookup[0]; + else + high = sine_lookup[1+63*t]; + + return (int)(low * weight + high * (1.0 - weight)): +} + diff --git a/sine_lookup.c b/sine_lookup.c new file mode 100644 index 0000000..1d12f76 --- /dev/null +++ b/sine_lookup.c @@ -0,0 +1,31 @@ + +#include <stdio.h> + + +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]; + 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)); + } +} |