DTMF Decoder

1ISR(ADC_vect) { 
2  uint16_t sample = ADC;samples[samplePos++] = sample  - 400;
3  
4  if(samplePos >= N) {
5    ADCSRA &= ~_BV(ADIE); // Buffer full,  interrupt off
6  }
7}

1void goertzel(uint8_t *samples, float *spectrum) {
2  float v_0, v_1,  v_2;
3  float re, im, amp;
4    
5  for (uint8_t k = 0; k < IX_LEN; k++) {
6    float c = pgm_read_float(&(cos_t[k]));
7    float s = pgm_read_float(&(sin_t[k]));
8    
9    float a = 2. * c;
10    v_0 = v_1 = v_2 = 0;  
11    for (uint16_t  i = 0; i < N; i++) {
12      v_0 = v_1;
13      v_1 = v_2;
14      v_2 = (float)(samples[i])  + a * v_1 - v_0;
15    }
16    re = c * v_2 - v_1;
17    im = s * v_2;
18    amp  = sqrt(re * re + im * im);
19    spectrum[k] = amp;        
20  } 
21}

1void initADC() {
2  // Init ADC; f = ( 16MHz/prescaler ) / 13 cycles/conversion  
3  ADMUX  = 0; // Channel sel, right-adj, use AREF pin
4  ADCSRA = _BV(ADEN)  | // ADC enable
5           _BV(ADSC)  | // ADC start
6           _BV(ADATE)  | // Auto trigger
7           _BV(ADIE)  | // Interrupt enable
8           _BV(ADPS2)  | _BV(ADPS1) | _BV(ADPS0); // 128:1 / 13 = 9615 Hz
9  ADCSRB = 0; // Free-run  mode
10  DIDR0  = _BV(0); // Turn off digital input for ADC pin      
11  TIMSK0  = 0;                // Timer0 off
12}

1ISR(ADC_vect) { 
2  uint16_t sample = ADC;samples[samplePos++] = sample
3  - 400;
4  
5  if(samplePos >= N) {
6    ADCSRA &= ~_BV(ADIE); // Buffer full,
7  interrupt off
8  }
9}

1void goertzel(uint8_t *samples, float *spectrum) {
2  float v_0, v_1,
3  v_2;
4  float re, im, amp;
5    
6  for (uint8_t k = 0; k < IX_LEN; k++) {
7
8    float c = pgm_read_float(&(cos_t[k]));
9    float s = pgm_read_float(&(sin_t[k]));
10
11    
12    float a = 2. * c;
13    v_0 = v_1 = v_2 = 0;  
14    for (uint16_t
15  i = 0; i < N; i++) {
16      v_0 = v_1;
17      v_1 = v_2;
18      v_2 = (float)(samples[i])
19  + a * v_1 - v_0;
20    }
21    re = c * v_2 - v_1;
22    im = s * v_2;
23    amp
24  = sqrt(re * re + im * im);
25    spectrum[k] = amp;        
26  } 
27}