Signal sinusoïdal sortie PWM pour Arduino UNO

Voici un petit programme qui permet de créer un signal sinusoïdal sur la sortie PWM d'un Arduino UNO.
La fréquence de sortie est limitée.
Le signal de sortie PWM (pin 6) est filtré. Le filtre utilisé est fait avec des composants disponibles à la maison (suffisants pour les tests).

Le programme DDS_Sinewave_Generator.ino :


// Sources 
// http://web.csulb.edu/~hill/ee470/Lab%202d%20-%20Sine_Wave_Generator.pdf
// http://web.csulb.edu/~hill/ee470/sinewave_pcm.zip
// samj le 12 avril 2015



// Schema du filtre de sortie à brancher sur Pin 6 pwm Arduino UNO (fait avec des composants disponibles à la maison)
//
// Pin6____270ohms__________0.47mH__________0.47mH____________________Tension de sortie sinusoïdale
//                    |               |               |          |
//                    |               |               |          |
//                   470nF          1000nF           470nF      270ohms 
//                    |               |               |          |
//  0V________________|_______________|_______________|__________| 
//
//
// Autre schéma http://interface.khm.de/wp-content/uploads/2009/12/dds_lowpass1251.jpg



/*
* sinewave_pcm
*
* Generates 8-bit PCM sinewave on pin 6 using pulse-width modulation (PWM).
* For Arduino with Atmega368P at 16 MHz.
*
* Uses timers 1 and 0. Timer 1 reads the sinewave table, SAMPLE_RATE times a second.
* The sinewave table has 256 entries. Consequently, the sinewave has a frequency of
* f = SAMPLE_RATE / 256
* Each entry in the sinewave table defines the duty-cycle of Timer 0. Timer 0
* holds pin 6 high from 0 to 255 ticks out of a 256-tick cycle, depending on
* the current duty cycle. Timer 0 repeats 62500 times per second (16000000 / 256),
* much faster than the generated sinewave generated frequency.
*
* References:
* http://www.atmel.com/dyn/resources/prod_documents/doc2542.pdf
* http://www.analog.com/library/analogdialogue/archives/38-08/dds.html
* http://www.evilmadscientist.com/article.php/avrdac
* http://playground.arduino.cc/Code/PCMAudio
* http://www.arduino.cc/playground/Code/R2APCMAudio
* http://www.scienceprog.com/generate-sine-wave-modulated-pwm-with-avrmicrocontroller/
* http://www.scienceprog.com/avr-dds-signal-generator-v10/
* http://documentation.renesas.com/eng/products/region/rtas/mpumcu/apn/sinewave.pdf
* http://ww1.microchip.com/downloads/en/AppNotes/00655a.pdf
*
* By Gary Hill
* Adapted
*/

#include <stdint.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/pgmspace.h>


// Varie selon modèle, ici UNO, la fréquence est limitée (BF)
// #define SAMPLE_RATE 10000 // T~26 ms F~38.4 Hz
// #define SAMPLE_RATE 100000 // T~2.6 ms F~384 Hz
// #define SAMPLE_RATE 26000 // F~100 Hz
#define SAMPLE_RATE 26000 // F~100 Hz


/*
* The sinewave data needs to be unsigned, 8-bit
*
* sinewavedata.h should look like this:
* const int sinewave_length=256;
*
* const unsigned char sinewave_data[] PROGMEM = {0x80,0x83, ...
*
*/

/* Sinewave table
 * Reference:
 * http://www.scienceprog.com/generate-sine-wave-modulated-pwm-with-avr-microcontroller/
*/

const int sinewave_length=256;

const unsigned char sinewave_data[] PROGMEM = {
0x80,0x83,0x86,0x89,0x8c,0x8f,0x92,0x95,0x98,0x9c,0x9f,0xa2,0xa5,0xa8,0xab,0xae,
0xb0,0xb3,0xb6,0xb9,0xbc,0xbf,0xc1,0xc4,0xc7,0xc9,0xcc,0xce,0xd1,0xd3,0xd5,0xd8,
0xda,0xdc,0xde,0xe0,0xe2,0xe4,0xe6,0xe8,0xea,0xec,0xed,0xef,0xf0,0xf2,0xf3,0xf5,
0xf6,0xf7,0xf8,0xf9,0xfa,0xfb,0xfc,0xfc,0xfd,0xfe,0xfe,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xfe,0xfe,0xfd,0xfc,0xfc,0xfb,0xfa,0xf9,0xf8,0xf7,
0xf6,0xf5,0xf3,0xf2,0xf0,0xef,0xed,0xec,0xea,0xe8,0xe6,0xe4,0xe2,0xe0,0xde,0xdc,
0xda,0xd8,0xd5,0xd3,0xd1,0xce,0xcc,0xc9,0xc7,0xc4,0xc1,0xbf,0xbc,0xb9,0xb6,0xb3,
0xb0,0xae,0xab,0xa8,0xa5,0xa2,0x9f,0x9c,0x98,0x95,0x92,0x8f,0x8c,0x89,0x86,0x83,
0x80,0x7c,0x79,0x76,0x73,0x70,0x6d,0x6a,0x67,0x63,0x60,0x5d,0x5a,0x57,0x54,0x51,
0x4f,0x4c,0x49,0x46,0x43,0x40,0x3e,0x3b,0x38,0x36,0x33,0x31,0x2e,0x2c,0x2a,0x27,
0x25,0x23,0x21,0x1f,0x1d,0x1b,0x19,0x17,0x15,0x13,0x12,0x10,0x0f,0x0d,0x0c,0x0a,
0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x03,0x02,0x01,0x01,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x02,0x03,0x03,0x04,0x05,0x06,0x07,0x08,
0x09,0x0a,0x0c,0x0d,0x0f,0x10,0x12,0x13,0x15,0x17,0x19,0x1b,0x1d,0x1f,0x21,0x23,
0x25,0x27,0x2a,0x2c,0x2e,0x31,0x33,0x36,0x38,0x3b,0x3e,0x40,0x43,0x46,0x49,0x4c,
0x4f,0x51,0x54,0x57,0x5a,0x5d,0x60,0x63,0x67,0x6a,0x6d,0x70,0x73,0x76,0x79,0x7c};



int outputPin = 6; // (PCINT22/OC0A/AIN0)PD6, Arduino Digital Pin 6
volatile uint16_t sample;
// This is called at SAMPLE_RATE kHz to load the next sample.
ISR(TIMER1_COMPA_vect) {
    if (sample >= sinewave_length) {
      sample = -1;
    }
    else {
      OCR0A = pgm_read_byte(&sinewave_data[sample]);
    }
  ++sample;
  }

void startPlayback()
  {
    pinMode(outputPin, OUTPUT);
      // Set Timer 0 Fast PWM Mode (Section 14.7.3)
      // WGM = 0b011 = 3 (Table 14-8)
      // TOP = 0xFF, update OCR0A register at BOTTOM
    TCCR0A |= _BV(WGM01) | _BV(WGM00);
    TCCR0B &= ~_BV(WGM02);
      // Do non-inverting PWM on pin OC0A, arduino digital pin 6
      // COM0A = 0b10, clear OC0A pin on compare match,
      // set 0C0A pin at BOTTOM (Table 14-3)
    TCCR0A = (TCCR0A | _BV(COM0A1)) & ~_BV(COM0A0);
      // COM0B = 0b00, OC0B disconnected (Table 14-6)
    TCCR0A &= ~(_BV(COM0B1) | _BV(COM0B0));
      // No prescaler, CS = 0b001 (Table 14-9)
    TCCR0B = (TCCR0B & ~(_BV(CS02) | _BV(CS01))) | _BV(CS00);
      // Set initial pulse width to the first sample.
    OCR0A = pgm_read_byte(&sinewave_data[0]);
      // Set up Timer 1 to send a sample every interrupt.
    cli(); // disable interrupts
      // Set CTC mode (Section 15.9.2 Clear Timer on Compare Match)
      // WGM = 0b0100, TOP = OCR1A, Update 0CR1A Immediate (Table 15-4)
      // Have to set OCR1A *after*, otherwise it gets reset to 0!
    TCCR1B = (TCCR1B & ~_BV(WGM13)) | _BV(WGM12);
    TCCR1A = TCCR1A & ~(_BV(WGM11) | _BV(WGM10));
      // No prescaler, CS = 0b001 (Table 15-5)
    TCCR1B = (TCCR1B & ~(_BV(CS12) | _BV(CS11))) | _BV(CS10);
      // Set the compare register (OCR1A).
      // OCR1A is a 16-bit register, so we have to do this with
      // interrupts disabled to be safe.
    OCR1A = F_CPU / SAMPLE_RATE; // 16e6 / 8000 = 2000
      // Enable interrupt when TCNT1 == OCR1A (p.136)
    TIMSK1 |= _BV(OCIE1A);
    sample = 0;
    sei(); // enable interrupts
  }

void setup()
  {
    startPlayback();
  }

void loop()
  {
    while (true);
  }




Le signal :