Phase Accumulator DDS
Alwyn Nixon-Lloyd.
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#include "mbed.h"
DigitalOut myled(LED1);
DigitalIn pushButton(p23);
DigitalIn rotaryA(p21);
DigitalIn rotaryB(p22);
AnalogIn pressure(p20);
AnalogIn pos1(p17);
AnalogIn pos2(p16);
AnalogOut signal(p18);
Ticker sampleClock;
// 16 entry sinewave table.
char sineWave[]={127,175,216,244,255,244,216,175,127,78,37,9,0,9,36,78};
char sawWave[]={0,16,31,47,64,79,95,111,127,143,159,175,191,207,223,255};
unsigned int counter;
unsigned int counterSum;
unsigned int counterLimit = 2147483647; //31 bits 2^31 - 1
char temp;
float byteToFloat(char in){
float i = in;
return (i/255.0);
}
void sample2(){
}
void sample(){
//useing a 31 bit counter.
counter = counter + counterSum;
if(counter > counterLimit){
//wrap the counting.
counter = counter - counterLimit;
}
//Fout = CounterSum*Fclk/MaxCount
temp = counter>>27; //shift the top 4 bits down.
//float x = temp;
//signal.write(x/16.0);
//write the output out
signal.write(byteToFloat(sineWave[temp]));
}
int read_encoder()
{
int8_t enc_states[] = {0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0};
static char old_AB = 0;
/**/
old_AB <<= 2;
char x = rotaryA.read();
x<<=1;
x = x+rotaryB.read(); //remember previous state
old_AB |= ( x & 0x03 ); //add current state
return ( enc_states[( old_AB & 0x0f )]);
}
int main() {
//setup variables.
counter = 0;
counterSum = 302365697;
counterSum = 18897856;
//counterSum = 1181116;
//18897856.1
//hook up sample() to the ticker. run the counter at 50kHz
sampleClock.attach_us(sample,20);
while(1){
myled=1;
wait(0.5);
myled.write(0);
wait(0.5);
}
}
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