AVR Noise Toys

Noise Toys

To turn a blinky LED program into a simple square-wave synthesizer, plug a speaker into PB4 and ground (where you had the LED before), then turn up the frequency.

The code is largely the same, just toggling a pin on and off, but now we do it at different speeds (for different tones) and for differing time periods (notes duration).

squareOne.c

/* Makes a quick square wave for noise-making experimentation. */

#include <inttypes.h>
#include <avr/io.h>
#define F_CPU 16000000L         /* really?  tested with the scope */
#include <util/delay.h>

void init(void){
  DDRB |= _BV(PB4);
}

int main(void){
  uint8_t i, j, k;
  uint16_t wavelength;

  init();
  
  while(1){
    for (k = 10; k > 3; k--){   /* pitch multiplier: makes different notes */
      wavelength = 20*k;
      
      for (j=0; j < 200/k; j++){ 
        /* number of cycles at each pitch: controls speed of loop */
        
        PORTB |= _BV(PB4);
        for (i=0; i < wavelength; i++) /* on for 20*wavelength microsecs */
          _delay_us(20);               /* loop needed b/c each call to
                                          the delay function can't
                                          delay all that long before
                                          it overflows */
        
        PORTB &= ~_BV(PB4);     /* off for 20*wavelength microsecs */
        for (i=0; i < wavelength; i++)
          _delay_us(20);

      } 
    }    
  }
}

spacePhaser.c

/* Starts with a very short pulse (high-frequency) and drops rapidly. */ 

#include <inttypes.h>
#include <avr/io.h>
#define F_CPU 16000000L         /* really?  tested with the scope */
#include <util/delay.h>

void init(void){
  DDRB |= _BV(PB4);
}

int main(void){
  uint8_t i, j, k;
  uint16_t wavelength;

  init();

  while(1){
    for (k = 3; k < 120; k++){  /* pitch multiplier: makes different notes */
      wavelength = k;

      for (j=0; j < 200/k; j++){
        /* number of cycles at each pitch: controls speed of loop */

        PORTB |= _BV(PB4);
        for (i=0; i < wavelength; i++) /* on for 20*wavelength microsecs */
          _delay_us(20);               /* loop needed b/c each call to
                                          the delay function can't
                                          delay all that long before
                                          it overflows */
        PORTB &= ~_BV(PB4);     /* off for 20*wavelength microsecs */
        for (i=0; i < wavelength; i++)
          _delay_us(20);

      }
    }  
    for (j=0; j < 60; j++){     /*  with delay between shots  */
      for (i=0; i < 250; i++)
        _delay_us(200);
    }
  }  
}    

chaosEngine.c

/* Now the frequency of the wave is a crazy function. */         

#include <inttypes.h>
#include <avr/io.h>
#define F_CPU 16000000L         /* really?  tested with the scope */
#include <util/delay.h>

void init(void){
  DDRB |= _BV(PB4);
}

int main(void){
  uint8_t i, j, k;
  uint16_t wavelength;

  init();

  while(1){
    wavelength = (13 * wavelength + 1) % 123 + 100;

    for (j=0; j < 30; j++){
      /* number of cycles at each pitch */

      PORTB |= _BV(PB4);
      for (i=0; i < wavelength; i++) /* on for 20*wavelength microsecs */
        _delay_us(20);         /* loop needed b/c each call to
                                  the delay function can't
                                  delay all that long before
                                  it overflows */
      PORTB &= ~_BV(PB4);       /* off for 20*wavelength microsecs */
      for (i=0; i < wavelength; i++)
        _delay_us(20);
      
    } 
  }   
  for (j=0; j < 60; j++){       /*  longer delay between shots  */
    for (i=0; i < 250; i++)
      _delay_us(200);
  }
}