Trying a PWM audio application. I can't figure out why I'm getting a loud beep overlapping my sound












2














I want to play some short audio clips (they range from 50ms to 100ms) from my atmega168 microcontroller and output it to a cheap speaker.



I was following this tutorial but because I'm using a atmega168 and not a atmega2560, I had to modify my code as well as replaced the sound.



Like in the tutorial, I'm using a 8MHz internal oscillator (I set LFUSE = 0xE2 in the Makefile) and all the PWM settings are the same...which means




  • Using a 16 Timer/Counter1 with 8-bit PWM resolution

  • Set OC1A on compare match (and clear on bottom)

  • No prescaling


As for the sound clip, I sampled it at 15.625 kHz and exported it to a 8-bit PCM wav file. I then get a hex dump via xxd -i which gives me the output c file. I didn't remove the header as I figured I can just skip it by just going to the 44th position of the output array as it is the data position.



The problem I'm having is that while I do get my (distorted and soft) sound, there is this loud beeping noise that is overlapping with my sound and I have no idea what is causing it.



Unfortunately I don't have access to an oscilloscope, so I can't really nail down if it is the way I sampled my sound, or if my sound is way too short or something that's beyond my current understanding.



Main.c



#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include <avr/power.h>
#include <util/setbaud.h>
#include <avr/interrupt.h>

#include "switch.h"
#define WAV_DATA_POSITION 44
#define BASE_LEVEL 0xff

unsigned int count=WAV_DATA_POSITION;;
volatile uint16_t timerOverflowCount;
unsigned char sample_count =2;

// This interrupt service reads new data,
ISR(TIMER1_OVF_vect){

sample_count--;

if(sample_count ==0)
{
sample_count = 2;
if (count < switchResampled_len){
OCR1A= pgm_read_byte(&switch_raw[count]);
count++;
}
}
else{
OCR1A= BASE_LEVEL;
}
}

void pwm_init()
{

SREG |=0x80;

//select Fast PWM with 8-bit resolution,set OC1A on compare match and clear at bottom
TCCR1A|=(1<<COM1A1)|(1<<COM1A0)|(1<<WGM10);

//No prescaling therefore timer frequency = 8 MHz and PWM frequency = 31250 Hz
TCCR1B|=(1<<WGM12)|(1<<CS10);

TCNT1=0x00;

OCR1A=BASE_LEVEL;
//Enable the timer interrupt
TIMSK1 |= ( 1 <<TOIE1);

//Clear all interupt flags
TIFR1|=(1<<ICF1)|(1<<OCF1B)|(1<<OCF1A)|(1<<TOV1);

//Enable interrupts
sei();

}


int main(void)
{
//PB1 is OC1A. Use this for output
DDRB |= (1 << PB1);
pwm_init();

/* insert your hardware initialization here */
for(;;){

/* insert your main loop code here */
}
return 0; /* never reached */
}


Switch.h (Sound file)



const unsigned char switch_raw PROGMEM = {
0x52, 0x49, 0x46, 0x46, 0x0d, 0x04, 0x00, 0x00, 0x57, 0x41, 0x56, 0x45,
0x66, 0x6d, 0x74, 0x20, 0x10, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
0x09, 0x3d, 0x00, 0x00, 0x09, 0x3d, 0x00, 0x00, 0x01, 0x00, 0x08, 0x00,
0x64, 0x61, 0x74, 0x61, 0x4b, 0x03, 0x00, 0x00, 0x80, 0x7f, 0x7f, 0x7e,
0x7f, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7f, 0x80, 0x7f, 0x7e, 0x7e,
0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7d, 0x7f, 0x81, 0x7e, 0x7e, 0x7f, 0x7f,
0x7e, 0x7e, 0x7f, 0x7f, 0x7f, 0x7d, 0x80, 0x81, 0x7e, 0x7b, 0x7e, 0x7f,
0x7f, 0x81, 0x7e, 0x7e, 0x7d, 0x80, 0x80, 0x7e, 0x7e, 0x7e, 0x7d, 0x7e,
0x80, 0x80, 0x7e, 0x7c, 0x7d, 0x7f, 0x81, 0x7f, 0x7e, 0x81, 0x7d, 0x7b,
0x80, 0x7f, 0x7f, 0x83, 0x7f, 0x7b, 0x7f, 0x80, 0x7f, 0x82, 0x7f, 0x7e,
0x80, 0x7e, 0x81, 0x7f, 0x7f, 0x81, 0x7d, 0x7e, 0x80, 0x7e, 0x80, 0x7e,
0x7f, 0x85, 0x80, 0x83, 0x7b, 0x77, 0x83, 0x81, 0x86, 0x7e, 0x7b, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x7f, 0x81, 0x82, 0x7f, 0x7e, 0x7e, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x80, 0x80, 0x81, 0x7e, 0x7e, 0x80, 0x83,
0x7f, 0x7d, 0x7b, 0x80, 0x80, 0x94, 0x79, 0x68, 0x87, 0x75, 0x98, 0x87,
0x6e, 0x7f, 0x8c, 0x81, 0x54, 0x7c, 0xc4, 0x8a, 0x46, 0x31, 0x72, 0xe2,
0xc1, 0x8a, 0x41, 0x2f, 0x71, 0xb3, 0xc8, 0x96, 0x51, 0x41, 0x67, 0x9c,
0xb1, 0x98, 0x74, 0x57, 0x5f, 0x76, 0x99, 0xa8, 0x96, 0x72, 0x5b, 0x64,
0x7e, 0x97, 0xa1, 0x8f, 0x6f, 0x56, 0x66, 0x89, 0xa0, 0x9d, 0x7e, 0x62,
0x5c, 0x78, 0x93, 0x9d, 0x90, 0x70, 0x58, 0x68, 0x88, 0x9c, 0x95, 0x7c,
0x66, 0x64, 0x7c, 0x90, 0x95, 0x82, 0x6f, 0x6b, 0x75, 0x86, 0x8e, 0x88,
0x79, 0x72, 0x75, 0x80, 0x88, 0x89, 0x81, 0x78, 0x74, 0x78, 0x84, 0x85,
0x84, 0x7d, 0x7b, 0x7c, 0x7b, 0x80, 0x85, 0x87, 0x81, 0x76, 0x74, 0x7e,
0x82, 0x89, 0x84, 0x7c, 0x77, 0x78, 0x84, 0x83, 0x84, 0x7c, 0x78, 0x7b,
0x83, 0x83, 0x80, 0x83, 0x80, 0x7d, 0x7a, 0x7e, 0x83, 0x87, 0x82, 0x79,
0x78, 0x7e, 0x87, 0x8b, 0x80, 0x76, 0x79, 0x7e, 0x87, 0x87, 0x80, 0x7a,
0x7a, 0x80, 0x82, 0x84, 0x81, 0x7f, 0x7e, 0x7d, 0x7a, 0x82, 0x88, 0x7f,
0x7a, 0x79, 0x7f, 0x85, 0x85, 0x7f, 0x7d, 0x7a, 0x7d, 0x83, 0x87, 0x7e,
0x78, 0x7e, 0x7d, 0x83, 0x7e, 0x81, 0x81, 0x80, 0x7f, 0x81, 0x81, 0x7c,
0x7e, 0x7a, 0x81, 0x82, 0x81, 0x84, 0x82, 0x79, 0x78, 0x84, 0x86, 0x7d,
0x7b, 0x7e, 0x7f, 0x7c, 0x7d, 0x7d, 0x82, 0x80, 0x80, 0x7e, 0x7d, 0x85,
0x84, 0x7b, 0x75, 0x7c, 0x7d, 0x84, 0x88, 0x84, 0x7b, 0x7b, 0x7d, 0x7c,
0x88, 0x88, 0x7b, 0x78, 0x78, 0x78, 0x88, 0x8d, 0x80, 0x78, 0x7f, 0x86,
0x86, 0x83, 0x7c, 0x71, 0x76, 0x84, 0x97, 0x93, 0x70, 0x6d, 0x68, 0x78,
0xc5, 0xb6, 0x5f, 0x37, 0x2a, 0x69, 0xc1, 0xc9, 0xa0, 0x7a, 0x52, 0x50,
0x71, 0x8a, 0x9d, 0xa0, 0x8b, 0x69, 0x67, 0x68, 0x79, 0x94, 0x96, 0x87,
0x7b, 0x81, 0x84, 0x7e, 0x7d, 0x7e, 0x75, 0x72, 0x89, 0x8e, 0x88, 0x86,
0x6d, 0x6d, 0x7a, 0x82, 0x8d, 0x8e, 0x78, 0x76, 0x7f, 0x7d, 0x7e, 0x82,
0x80, 0x7b, 0x7d, 0x7a, 0x7b, 0x86, 0x89, 0x80, 0x7b, 0x75, 0x77, 0x7f,
0x83, 0x84, 0x86, 0x81, 0x81, 0x7e, 0x73, 0x7c, 0x83, 0x7f, 0x85, 0x82,
0x7d, 0x83, 0x7d, 0x7d, 0x80, 0x7b, 0x7c, 0x86, 0x85, 0x7e, 0x7b, 0x74,
0x7d, 0x86, 0x85, 0x8b, 0x81, 0x76, 0x78, 0x78, 0x7e, 0x89, 0x83, 0x7e,
0x80, 0x78, 0x7f, 0x84, 0x81, 0x84, 0x7a, 0x77, 0x7f, 0x81, 0x84, 0x81,
0x78, 0x7a, 0x7e, 0x84, 0x8e, 0x81, 0x72, 0x75, 0x77, 0x83, 0x8b, 0x84,
0x84, 0x7b, 0x72, 0x7a, 0x83, 0x84, 0x85, 0x7e, 0x78, 0x7e, 0x7d, 0x7f,
0x82, 0x80, 0x7f, 0x7e, 0x7f, 0x81, 0x7e, 0x7b, 0x80, 0x85, 0x84, 0x82,
0x7d, 0x7a, 0x7d, 0x7f, 0x84, 0x84, 0x7f, 0x79, 0x7b, 0x82, 0x80, 0x80,
0x81, 0x80, 0x81, 0x81, 0x7f, 0x7e, 0x79, 0x79, 0x81, 0x86, 0x85, 0x82,
0x7d, 0x77, 0x7a, 0x7e, 0x86, 0x8b, 0x84, 0x7a, 0x7a, 0x7d, 0x7e, 0x83,
0x83, 0x80, 0x7e, 0x7c, 0x7c, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x80, 0x7e,
0x7f, 0x80, 0x7f, 0x7c, 0x80, 0x7d, 0x7e, 0x85, 0x81, 0x7c, 0x7d, 0x7b,
0x7c, 0x81, 0x80, 0x7d, 0x7f, 0x80, 0x7d, 0x82, 0x84, 0x7e, 0x7a, 0x7e,
0x7e, 0x7f, 0x82, 0x7d, 0x7e, 0x81, 0x7f, 0x7d, 0x7e, 0x81, 0x83, 0x83,
0x80, 0x79, 0x77, 0x7c, 0x83, 0x87, 0x86, 0x7f, 0x75, 0x79, 0x7e, 0x85,
0x86, 0x80, 0x7a, 0x78, 0x7c, 0x7f, 0x83, 0x81, 0x82, 0x7d, 0x7a, 0x7f,
0x81, 0x80, 0x80, 0x7c, 0x7b, 0x80, 0x7e, 0x80, 0x85, 0x84, 0x7d, 0x7b,
0x7a, 0x7f, 0x83, 0x82, 0x80, 0x7c, 0x7e, 0x7e, 0x80, 0x81, 0x7f, 0x7f,
0x7e, 0x7f, 0x82, 0x7f, 0x7c, 0x7b, 0x7b, 0x82, 0x84, 0x83, 0x7e, 0x7c,
0x7b, 0x7e, 0x83, 0x81, 0x7f, 0x7d, 0x7e, 0x7f, 0x83, 0x81, 0x7e, 0x7d,
0x7b, 0x7d, 0x80, 0x82, 0x81, 0x80, 0x7f, 0x7d, 0x7f, 0x80, 0x7f, 0x80,
0x81, 0x80, 0x7f, 0x7d, 0x7d, 0x7e, 0x81, 0x82, 0x80, 0x7d, 0x7f, 0x81,
0x80, 0x7f, 0x7d, 0x7c, 0x7e, 0x80, 0x80, 0x80, 0x80, 0x80, 0x7e, 0x7f,
0x7d, 0x7e, 0x80, 0x81, 0x80, 0x7f, 0x7e, 0x7c, 0x7f, 0x81, 0x80, 0x80,
0x80, 0x7f, 0x7e, 0x7e, 0x7f, 0x7f, 0x80, 0x80, 0x80, 0x81, 0x80, 0x7d,
0x7c, 0x7f, 0x80, 0x83, 0x81, 0x7c, 0x7b, 0x7c, 0x7f, 0x82, 0x82, 0x7f,
0x7d, 0x7c, 0x7e, 0x80, 0x81, 0x81, 0x7f, 0x7f, 0x7d, 0x7d, 0x80, 0x82,
0x7f, 0x7e, 0x7d, 0x7d, 0x80, 0x83, 0x82, 0x7f, 0x7f, 0x7a, 0x7d, 0x80,
0x81, 0x81, 0x80, 0x7e, 0x7f, 0x80, 0x7e, 0x7e, 0x7f, 0x80, 0x7f, 0x80,
0x7f, 0x7e, 0x7d, 0x7f, 0x7e, 0x80, 0x81, 0x81, 0x80, 0x80, 0x7e, 0x7e,
0x7e, 0x7d, 0x80, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7e, 0x7c, 0x7f, 0x82,
0x7f, 0x80, 0x7f, 0x7d, 0x7d, 0x7f, 0x7f, 0x80, 0x80, 0x7f, 0x7e, 0x7f,
0x7f, 0x7f, 0x80, 0x7e, 0x7f, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7d, 0x7d,
0x81, 0x82, 0x80, 0x7e, 0x7d, 0x7e, 0x80, 0x81, 0x7f, 0x80, 0x80, 0x7f,
0x7f, 0x7d, 0x7f, 0x81, 0x80, 0x7f, 0x80, 0x7f, 0x7e, 0x7d, 0x7e, 0x4c,
0x49, 0x53, 0x54, 0x48, 0x00, 0x00, 0x00, 0x49, 0x4e, 0x46, 0x4f, 0x49,
0x43, 0x52, 0x44, 0x12, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31, 0x36, 0x2d,
0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32, 0x37, 0x00,
0x00, 0x49, 0x53, 0x46, 0x54, 0x22, 0x00, 0x00, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x20, 0x28,
0x6c, 0x69, 0x62, 0x73, 0x6e, 0x64, 0x66, 0x69, 0x6c, 0x65, 0x2d, 0x31,
0x2e, 0x30, 0x2e, 0x32, 0x34, 0x29, 0x00, 0x69, 0x64, 0x33, 0x20, 0x46,
0x00, 0x00, 0x00, 0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x3c, 0x54, 0x58, 0x58, 0x58, 0x00, 0x00, 0x00, 0x17, 0x00, 0x00, 0x00,
0x53, 0x6f, 0x66, 0x74, 0x77, 0x61, 0x72, 0x65, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x54, 0x44,
0x52, 0x43, 0x00, 0x00, 0x00, 0x11, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31,
0x36, 0x2d, 0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32,
0x37

};

const long switchResampled_len = 1045;









share|improve this question






















  • That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
    – analogsystemsrf
    4 hours ago










  • 1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
    – brhans
    4 hours ago










  • By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
    – Nayuki
    6 mins ago
















2














I want to play some short audio clips (they range from 50ms to 100ms) from my atmega168 microcontroller and output it to a cheap speaker.



I was following this tutorial but because I'm using a atmega168 and not a atmega2560, I had to modify my code as well as replaced the sound.



Like in the tutorial, I'm using a 8MHz internal oscillator (I set LFUSE = 0xE2 in the Makefile) and all the PWM settings are the same...which means




  • Using a 16 Timer/Counter1 with 8-bit PWM resolution

  • Set OC1A on compare match (and clear on bottom)

  • No prescaling


As for the sound clip, I sampled it at 15.625 kHz and exported it to a 8-bit PCM wav file. I then get a hex dump via xxd -i which gives me the output c file. I didn't remove the header as I figured I can just skip it by just going to the 44th position of the output array as it is the data position.



The problem I'm having is that while I do get my (distorted and soft) sound, there is this loud beeping noise that is overlapping with my sound and I have no idea what is causing it.



Unfortunately I don't have access to an oscilloscope, so I can't really nail down if it is the way I sampled my sound, or if my sound is way too short or something that's beyond my current understanding.



Main.c



#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include <avr/power.h>
#include <util/setbaud.h>
#include <avr/interrupt.h>

#include "switch.h"
#define WAV_DATA_POSITION 44
#define BASE_LEVEL 0xff

unsigned int count=WAV_DATA_POSITION;;
volatile uint16_t timerOverflowCount;
unsigned char sample_count =2;

// This interrupt service reads new data,
ISR(TIMER1_OVF_vect){

sample_count--;

if(sample_count ==0)
{
sample_count = 2;
if (count < switchResampled_len){
OCR1A= pgm_read_byte(&switch_raw[count]);
count++;
}
}
else{
OCR1A= BASE_LEVEL;
}
}

void pwm_init()
{

SREG |=0x80;

//select Fast PWM with 8-bit resolution,set OC1A on compare match and clear at bottom
TCCR1A|=(1<<COM1A1)|(1<<COM1A0)|(1<<WGM10);

//No prescaling therefore timer frequency = 8 MHz and PWM frequency = 31250 Hz
TCCR1B|=(1<<WGM12)|(1<<CS10);

TCNT1=0x00;

OCR1A=BASE_LEVEL;
//Enable the timer interrupt
TIMSK1 |= ( 1 <<TOIE1);

//Clear all interupt flags
TIFR1|=(1<<ICF1)|(1<<OCF1B)|(1<<OCF1A)|(1<<TOV1);

//Enable interrupts
sei();

}


int main(void)
{
//PB1 is OC1A. Use this for output
DDRB |= (1 << PB1);
pwm_init();

/* insert your hardware initialization here */
for(;;){

/* insert your main loop code here */
}
return 0; /* never reached */
}


Switch.h (Sound file)



const unsigned char switch_raw PROGMEM = {
0x52, 0x49, 0x46, 0x46, 0x0d, 0x04, 0x00, 0x00, 0x57, 0x41, 0x56, 0x45,
0x66, 0x6d, 0x74, 0x20, 0x10, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
0x09, 0x3d, 0x00, 0x00, 0x09, 0x3d, 0x00, 0x00, 0x01, 0x00, 0x08, 0x00,
0x64, 0x61, 0x74, 0x61, 0x4b, 0x03, 0x00, 0x00, 0x80, 0x7f, 0x7f, 0x7e,
0x7f, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7f, 0x80, 0x7f, 0x7e, 0x7e,
0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7d, 0x7f, 0x81, 0x7e, 0x7e, 0x7f, 0x7f,
0x7e, 0x7e, 0x7f, 0x7f, 0x7f, 0x7d, 0x80, 0x81, 0x7e, 0x7b, 0x7e, 0x7f,
0x7f, 0x81, 0x7e, 0x7e, 0x7d, 0x80, 0x80, 0x7e, 0x7e, 0x7e, 0x7d, 0x7e,
0x80, 0x80, 0x7e, 0x7c, 0x7d, 0x7f, 0x81, 0x7f, 0x7e, 0x81, 0x7d, 0x7b,
0x80, 0x7f, 0x7f, 0x83, 0x7f, 0x7b, 0x7f, 0x80, 0x7f, 0x82, 0x7f, 0x7e,
0x80, 0x7e, 0x81, 0x7f, 0x7f, 0x81, 0x7d, 0x7e, 0x80, 0x7e, 0x80, 0x7e,
0x7f, 0x85, 0x80, 0x83, 0x7b, 0x77, 0x83, 0x81, 0x86, 0x7e, 0x7b, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x7f, 0x81, 0x82, 0x7f, 0x7e, 0x7e, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x80, 0x80, 0x81, 0x7e, 0x7e, 0x80, 0x83,
0x7f, 0x7d, 0x7b, 0x80, 0x80, 0x94, 0x79, 0x68, 0x87, 0x75, 0x98, 0x87,
0x6e, 0x7f, 0x8c, 0x81, 0x54, 0x7c, 0xc4, 0x8a, 0x46, 0x31, 0x72, 0xe2,
0xc1, 0x8a, 0x41, 0x2f, 0x71, 0xb3, 0xc8, 0x96, 0x51, 0x41, 0x67, 0x9c,
0xb1, 0x98, 0x74, 0x57, 0x5f, 0x76, 0x99, 0xa8, 0x96, 0x72, 0x5b, 0x64,
0x7e, 0x97, 0xa1, 0x8f, 0x6f, 0x56, 0x66, 0x89, 0xa0, 0x9d, 0x7e, 0x62,
0x5c, 0x78, 0x93, 0x9d, 0x90, 0x70, 0x58, 0x68, 0x88, 0x9c, 0x95, 0x7c,
0x66, 0x64, 0x7c, 0x90, 0x95, 0x82, 0x6f, 0x6b, 0x75, 0x86, 0x8e, 0x88,
0x79, 0x72, 0x75, 0x80, 0x88, 0x89, 0x81, 0x78, 0x74, 0x78, 0x84, 0x85,
0x84, 0x7d, 0x7b, 0x7c, 0x7b, 0x80, 0x85, 0x87, 0x81, 0x76, 0x74, 0x7e,
0x82, 0x89, 0x84, 0x7c, 0x77, 0x78, 0x84, 0x83, 0x84, 0x7c, 0x78, 0x7b,
0x83, 0x83, 0x80, 0x83, 0x80, 0x7d, 0x7a, 0x7e, 0x83, 0x87, 0x82, 0x79,
0x78, 0x7e, 0x87, 0x8b, 0x80, 0x76, 0x79, 0x7e, 0x87, 0x87, 0x80, 0x7a,
0x7a, 0x80, 0x82, 0x84, 0x81, 0x7f, 0x7e, 0x7d, 0x7a, 0x82, 0x88, 0x7f,
0x7a, 0x79, 0x7f, 0x85, 0x85, 0x7f, 0x7d, 0x7a, 0x7d, 0x83, 0x87, 0x7e,
0x78, 0x7e, 0x7d, 0x83, 0x7e, 0x81, 0x81, 0x80, 0x7f, 0x81, 0x81, 0x7c,
0x7e, 0x7a, 0x81, 0x82, 0x81, 0x84, 0x82, 0x79, 0x78, 0x84, 0x86, 0x7d,
0x7b, 0x7e, 0x7f, 0x7c, 0x7d, 0x7d, 0x82, 0x80, 0x80, 0x7e, 0x7d, 0x85,
0x84, 0x7b, 0x75, 0x7c, 0x7d, 0x84, 0x88, 0x84, 0x7b, 0x7b, 0x7d, 0x7c,
0x88, 0x88, 0x7b, 0x78, 0x78, 0x78, 0x88, 0x8d, 0x80, 0x78, 0x7f, 0x86,
0x86, 0x83, 0x7c, 0x71, 0x76, 0x84, 0x97, 0x93, 0x70, 0x6d, 0x68, 0x78,
0xc5, 0xb6, 0x5f, 0x37, 0x2a, 0x69, 0xc1, 0xc9, 0xa0, 0x7a, 0x52, 0x50,
0x71, 0x8a, 0x9d, 0xa0, 0x8b, 0x69, 0x67, 0x68, 0x79, 0x94, 0x96, 0x87,
0x7b, 0x81, 0x84, 0x7e, 0x7d, 0x7e, 0x75, 0x72, 0x89, 0x8e, 0x88, 0x86,
0x6d, 0x6d, 0x7a, 0x82, 0x8d, 0x8e, 0x78, 0x76, 0x7f, 0x7d, 0x7e, 0x82,
0x80, 0x7b, 0x7d, 0x7a, 0x7b, 0x86, 0x89, 0x80, 0x7b, 0x75, 0x77, 0x7f,
0x83, 0x84, 0x86, 0x81, 0x81, 0x7e, 0x73, 0x7c, 0x83, 0x7f, 0x85, 0x82,
0x7d, 0x83, 0x7d, 0x7d, 0x80, 0x7b, 0x7c, 0x86, 0x85, 0x7e, 0x7b, 0x74,
0x7d, 0x86, 0x85, 0x8b, 0x81, 0x76, 0x78, 0x78, 0x7e, 0x89, 0x83, 0x7e,
0x80, 0x78, 0x7f, 0x84, 0x81, 0x84, 0x7a, 0x77, 0x7f, 0x81, 0x84, 0x81,
0x78, 0x7a, 0x7e, 0x84, 0x8e, 0x81, 0x72, 0x75, 0x77, 0x83, 0x8b, 0x84,
0x84, 0x7b, 0x72, 0x7a, 0x83, 0x84, 0x85, 0x7e, 0x78, 0x7e, 0x7d, 0x7f,
0x82, 0x80, 0x7f, 0x7e, 0x7f, 0x81, 0x7e, 0x7b, 0x80, 0x85, 0x84, 0x82,
0x7d, 0x7a, 0x7d, 0x7f, 0x84, 0x84, 0x7f, 0x79, 0x7b, 0x82, 0x80, 0x80,
0x81, 0x80, 0x81, 0x81, 0x7f, 0x7e, 0x79, 0x79, 0x81, 0x86, 0x85, 0x82,
0x7d, 0x77, 0x7a, 0x7e, 0x86, 0x8b, 0x84, 0x7a, 0x7a, 0x7d, 0x7e, 0x83,
0x83, 0x80, 0x7e, 0x7c, 0x7c, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x80, 0x7e,
0x7f, 0x80, 0x7f, 0x7c, 0x80, 0x7d, 0x7e, 0x85, 0x81, 0x7c, 0x7d, 0x7b,
0x7c, 0x81, 0x80, 0x7d, 0x7f, 0x80, 0x7d, 0x82, 0x84, 0x7e, 0x7a, 0x7e,
0x7e, 0x7f, 0x82, 0x7d, 0x7e, 0x81, 0x7f, 0x7d, 0x7e, 0x81, 0x83, 0x83,
0x80, 0x79, 0x77, 0x7c, 0x83, 0x87, 0x86, 0x7f, 0x75, 0x79, 0x7e, 0x85,
0x86, 0x80, 0x7a, 0x78, 0x7c, 0x7f, 0x83, 0x81, 0x82, 0x7d, 0x7a, 0x7f,
0x81, 0x80, 0x80, 0x7c, 0x7b, 0x80, 0x7e, 0x80, 0x85, 0x84, 0x7d, 0x7b,
0x7a, 0x7f, 0x83, 0x82, 0x80, 0x7c, 0x7e, 0x7e, 0x80, 0x81, 0x7f, 0x7f,
0x7e, 0x7f, 0x82, 0x7f, 0x7c, 0x7b, 0x7b, 0x82, 0x84, 0x83, 0x7e, 0x7c,
0x7b, 0x7e, 0x83, 0x81, 0x7f, 0x7d, 0x7e, 0x7f, 0x83, 0x81, 0x7e, 0x7d,
0x7b, 0x7d, 0x80, 0x82, 0x81, 0x80, 0x7f, 0x7d, 0x7f, 0x80, 0x7f, 0x80,
0x81, 0x80, 0x7f, 0x7d, 0x7d, 0x7e, 0x81, 0x82, 0x80, 0x7d, 0x7f, 0x81,
0x80, 0x7f, 0x7d, 0x7c, 0x7e, 0x80, 0x80, 0x80, 0x80, 0x80, 0x7e, 0x7f,
0x7d, 0x7e, 0x80, 0x81, 0x80, 0x7f, 0x7e, 0x7c, 0x7f, 0x81, 0x80, 0x80,
0x80, 0x7f, 0x7e, 0x7e, 0x7f, 0x7f, 0x80, 0x80, 0x80, 0x81, 0x80, 0x7d,
0x7c, 0x7f, 0x80, 0x83, 0x81, 0x7c, 0x7b, 0x7c, 0x7f, 0x82, 0x82, 0x7f,
0x7d, 0x7c, 0x7e, 0x80, 0x81, 0x81, 0x7f, 0x7f, 0x7d, 0x7d, 0x80, 0x82,
0x7f, 0x7e, 0x7d, 0x7d, 0x80, 0x83, 0x82, 0x7f, 0x7f, 0x7a, 0x7d, 0x80,
0x81, 0x81, 0x80, 0x7e, 0x7f, 0x80, 0x7e, 0x7e, 0x7f, 0x80, 0x7f, 0x80,
0x7f, 0x7e, 0x7d, 0x7f, 0x7e, 0x80, 0x81, 0x81, 0x80, 0x80, 0x7e, 0x7e,
0x7e, 0x7d, 0x80, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7e, 0x7c, 0x7f, 0x82,
0x7f, 0x80, 0x7f, 0x7d, 0x7d, 0x7f, 0x7f, 0x80, 0x80, 0x7f, 0x7e, 0x7f,
0x7f, 0x7f, 0x80, 0x7e, 0x7f, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7d, 0x7d,
0x81, 0x82, 0x80, 0x7e, 0x7d, 0x7e, 0x80, 0x81, 0x7f, 0x80, 0x80, 0x7f,
0x7f, 0x7d, 0x7f, 0x81, 0x80, 0x7f, 0x80, 0x7f, 0x7e, 0x7d, 0x7e, 0x4c,
0x49, 0x53, 0x54, 0x48, 0x00, 0x00, 0x00, 0x49, 0x4e, 0x46, 0x4f, 0x49,
0x43, 0x52, 0x44, 0x12, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31, 0x36, 0x2d,
0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32, 0x37, 0x00,
0x00, 0x49, 0x53, 0x46, 0x54, 0x22, 0x00, 0x00, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x20, 0x28,
0x6c, 0x69, 0x62, 0x73, 0x6e, 0x64, 0x66, 0x69, 0x6c, 0x65, 0x2d, 0x31,
0x2e, 0x30, 0x2e, 0x32, 0x34, 0x29, 0x00, 0x69, 0x64, 0x33, 0x20, 0x46,
0x00, 0x00, 0x00, 0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x3c, 0x54, 0x58, 0x58, 0x58, 0x00, 0x00, 0x00, 0x17, 0x00, 0x00, 0x00,
0x53, 0x6f, 0x66, 0x74, 0x77, 0x61, 0x72, 0x65, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x54, 0x44,
0x52, 0x43, 0x00, 0x00, 0x00, 0x11, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31,
0x36, 0x2d, 0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32,
0x37

};

const long switchResampled_len = 1045;









share|improve this question






















  • That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
    – analogsystemsrf
    4 hours ago










  • 1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
    – brhans
    4 hours ago










  • By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
    – Nayuki
    6 mins ago














2












2








2







I want to play some short audio clips (they range from 50ms to 100ms) from my atmega168 microcontroller and output it to a cheap speaker.



I was following this tutorial but because I'm using a atmega168 and not a atmega2560, I had to modify my code as well as replaced the sound.



Like in the tutorial, I'm using a 8MHz internal oscillator (I set LFUSE = 0xE2 in the Makefile) and all the PWM settings are the same...which means




  • Using a 16 Timer/Counter1 with 8-bit PWM resolution

  • Set OC1A on compare match (and clear on bottom)

  • No prescaling


As for the sound clip, I sampled it at 15.625 kHz and exported it to a 8-bit PCM wav file. I then get a hex dump via xxd -i which gives me the output c file. I didn't remove the header as I figured I can just skip it by just going to the 44th position of the output array as it is the data position.



The problem I'm having is that while I do get my (distorted and soft) sound, there is this loud beeping noise that is overlapping with my sound and I have no idea what is causing it.



Unfortunately I don't have access to an oscilloscope, so I can't really nail down if it is the way I sampled my sound, or if my sound is way too short or something that's beyond my current understanding.



Main.c



#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include <avr/power.h>
#include <util/setbaud.h>
#include <avr/interrupt.h>

#include "switch.h"
#define WAV_DATA_POSITION 44
#define BASE_LEVEL 0xff

unsigned int count=WAV_DATA_POSITION;;
volatile uint16_t timerOverflowCount;
unsigned char sample_count =2;

// This interrupt service reads new data,
ISR(TIMER1_OVF_vect){

sample_count--;

if(sample_count ==0)
{
sample_count = 2;
if (count < switchResampled_len){
OCR1A= pgm_read_byte(&switch_raw[count]);
count++;
}
}
else{
OCR1A= BASE_LEVEL;
}
}

void pwm_init()
{

SREG |=0x80;

//select Fast PWM with 8-bit resolution,set OC1A on compare match and clear at bottom
TCCR1A|=(1<<COM1A1)|(1<<COM1A0)|(1<<WGM10);

//No prescaling therefore timer frequency = 8 MHz and PWM frequency = 31250 Hz
TCCR1B|=(1<<WGM12)|(1<<CS10);

TCNT1=0x00;

OCR1A=BASE_LEVEL;
//Enable the timer interrupt
TIMSK1 |= ( 1 <<TOIE1);

//Clear all interupt flags
TIFR1|=(1<<ICF1)|(1<<OCF1B)|(1<<OCF1A)|(1<<TOV1);

//Enable interrupts
sei();

}


int main(void)
{
//PB1 is OC1A. Use this for output
DDRB |= (1 << PB1);
pwm_init();

/* insert your hardware initialization here */
for(;;){

/* insert your main loop code here */
}
return 0; /* never reached */
}


Switch.h (Sound file)



const unsigned char switch_raw PROGMEM = {
0x52, 0x49, 0x46, 0x46, 0x0d, 0x04, 0x00, 0x00, 0x57, 0x41, 0x56, 0x45,
0x66, 0x6d, 0x74, 0x20, 0x10, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
0x09, 0x3d, 0x00, 0x00, 0x09, 0x3d, 0x00, 0x00, 0x01, 0x00, 0x08, 0x00,
0x64, 0x61, 0x74, 0x61, 0x4b, 0x03, 0x00, 0x00, 0x80, 0x7f, 0x7f, 0x7e,
0x7f, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7f, 0x80, 0x7f, 0x7e, 0x7e,
0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7d, 0x7f, 0x81, 0x7e, 0x7e, 0x7f, 0x7f,
0x7e, 0x7e, 0x7f, 0x7f, 0x7f, 0x7d, 0x80, 0x81, 0x7e, 0x7b, 0x7e, 0x7f,
0x7f, 0x81, 0x7e, 0x7e, 0x7d, 0x80, 0x80, 0x7e, 0x7e, 0x7e, 0x7d, 0x7e,
0x80, 0x80, 0x7e, 0x7c, 0x7d, 0x7f, 0x81, 0x7f, 0x7e, 0x81, 0x7d, 0x7b,
0x80, 0x7f, 0x7f, 0x83, 0x7f, 0x7b, 0x7f, 0x80, 0x7f, 0x82, 0x7f, 0x7e,
0x80, 0x7e, 0x81, 0x7f, 0x7f, 0x81, 0x7d, 0x7e, 0x80, 0x7e, 0x80, 0x7e,
0x7f, 0x85, 0x80, 0x83, 0x7b, 0x77, 0x83, 0x81, 0x86, 0x7e, 0x7b, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x7f, 0x81, 0x82, 0x7f, 0x7e, 0x7e, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x80, 0x80, 0x81, 0x7e, 0x7e, 0x80, 0x83,
0x7f, 0x7d, 0x7b, 0x80, 0x80, 0x94, 0x79, 0x68, 0x87, 0x75, 0x98, 0x87,
0x6e, 0x7f, 0x8c, 0x81, 0x54, 0x7c, 0xc4, 0x8a, 0x46, 0x31, 0x72, 0xe2,
0xc1, 0x8a, 0x41, 0x2f, 0x71, 0xb3, 0xc8, 0x96, 0x51, 0x41, 0x67, 0x9c,
0xb1, 0x98, 0x74, 0x57, 0x5f, 0x76, 0x99, 0xa8, 0x96, 0x72, 0x5b, 0x64,
0x7e, 0x97, 0xa1, 0x8f, 0x6f, 0x56, 0x66, 0x89, 0xa0, 0x9d, 0x7e, 0x62,
0x5c, 0x78, 0x93, 0x9d, 0x90, 0x70, 0x58, 0x68, 0x88, 0x9c, 0x95, 0x7c,
0x66, 0x64, 0x7c, 0x90, 0x95, 0x82, 0x6f, 0x6b, 0x75, 0x86, 0x8e, 0x88,
0x79, 0x72, 0x75, 0x80, 0x88, 0x89, 0x81, 0x78, 0x74, 0x78, 0x84, 0x85,
0x84, 0x7d, 0x7b, 0x7c, 0x7b, 0x80, 0x85, 0x87, 0x81, 0x76, 0x74, 0x7e,
0x82, 0x89, 0x84, 0x7c, 0x77, 0x78, 0x84, 0x83, 0x84, 0x7c, 0x78, 0x7b,
0x83, 0x83, 0x80, 0x83, 0x80, 0x7d, 0x7a, 0x7e, 0x83, 0x87, 0x82, 0x79,
0x78, 0x7e, 0x87, 0x8b, 0x80, 0x76, 0x79, 0x7e, 0x87, 0x87, 0x80, 0x7a,
0x7a, 0x80, 0x82, 0x84, 0x81, 0x7f, 0x7e, 0x7d, 0x7a, 0x82, 0x88, 0x7f,
0x7a, 0x79, 0x7f, 0x85, 0x85, 0x7f, 0x7d, 0x7a, 0x7d, 0x83, 0x87, 0x7e,
0x78, 0x7e, 0x7d, 0x83, 0x7e, 0x81, 0x81, 0x80, 0x7f, 0x81, 0x81, 0x7c,
0x7e, 0x7a, 0x81, 0x82, 0x81, 0x84, 0x82, 0x79, 0x78, 0x84, 0x86, 0x7d,
0x7b, 0x7e, 0x7f, 0x7c, 0x7d, 0x7d, 0x82, 0x80, 0x80, 0x7e, 0x7d, 0x85,
0x84, 0x7b, 0x75, 0x7c, 0x7d, 0x84, 0x88, 0x84, 0x7b, 0x7b, 0x7d, 0x7c,
0x88, 0x88, 0x7b, 0x78, 0x78, 0x78, 0x88, 0x8d, 0x80, 0x78, 0x7f, 0x86,
0x86, 0x83, 0x7c, 0x71, 0x76, 0x84, 0x97, 0x93, 0x70, 0x6d, 0x68, 0x78,
0xc5, 0xb6, 0x5f, 0x37, 0x2a, 0x69, 0xc1, 0xc9, 0xa0, 0x7a, 0x52, 0x50,
0x71, 0x8a, 0x9d, 0xa0, 0x8b, 0x69, 0x67, 0x68, 0x79, 0x94, 0x96, 0x87,
0x7b, 0x81, 0x84, 0x7e, 0x7d, 0x7e, 0x75, 0x72, 0x89, 0x8e, 0x88, 0x86,
0x6d, 0x6d, 0x7a, 0x82, 0x8d, 0x8e, 0x78, 0x76, 0x7f, 0x7d, 0x7e, 0x82,
0x80, 0x7b, 0x7d, 0x7a, 0x7b, 0x86, 0x89, 0x80, 0x7b, 0x75, 0x77, 0x7f,
0x83, 0x84, 0x86, 0x81, 0x81, 0x7e, 0x73, 0x7c, 0x83, 0x7f, 0x85, 0x82,
0x7d, 0x83, 0x7d, 0x7d, 0x80, 0x7b, 0x7c, 0x86, 0x85, 0x7e, 0x7b, 0x74,
0x7d, 0x86, 0x85, 0x8b, 0x81, 0x76, 0x78, 0x78, 0x7e, 0x89, 0x83, 0x7e,
0x80, 0x78, 0x7f, 0x84, 0x81, 0x84, 0x7a, 0x77, 0x7f, 0x81, 0x84, 0x81,
0x78, 0x7a, 0x7e, 0x84, 0x8e, 0x81, 0x72, 0x75, 0x77, 0x83, 0x8b, 0x84,
0x84, 0x7b, 0x72, 0x7a, 0x83, 0x84, 0x85, 0x7e, 0x78, 0x7e, 0x7d, 0x7f,
0x82, 0x80, 0x7f, 0x7e, 0x7f, 0x81, 0x7e, 0x7b, 0x80, 0x85, 0x84, 0x82,
0x7d, 0x7a, 0x7d, 0x7f, 0x84, 0x84, 0x7f, 0x79, 0x7b, 0x82, 0x80, 0x80,
0x81, 0x80, 0x81, 0x81, 0x7f, 0x7e, 0x79, 0x79, 0x81, 0x86, 0x85, 0x82,
0x7d, 0x77, 0x7a, 0x7e, 0x86, 0x8b, 0x84, 0x7a, 0x7a, 0x7d, 0x7e, 0x83,
0x83, 0x80, 0x7e, 0x7c, 0x7c, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x80, 0x7e,
0x7f, 0x80, 0x7f, 0x7c, 0x80, 0x7d, 0x7e, 0x85, 0x81, 0x7c, 0x7d, 0x7b,
0x7c, 0x81, 0x80, 0x7d, 0x7f, 0x80, 0x7d, 0x82, 0x84, 0x7e, 0x7a, 0x7e,
0x7e, 0x7f, 0x82, 0x7d, 0x7e, 0x81, 0x7f, 0x7d, 0x7e, 0x81, 0x83, 0x83,
0x80, 0x79, 0x77, 0x7c, 0x83, 0x87, 0x86, 0x7f, 0x75, 0x79, 0x7e, 0x85,
0x86, 0x80, 0x7a, 0x78, 0x7c, 0x7f, 0x83, 0x81, 0x82, 0x7d, 0x7a, 0x7f,
0x81, 0x80, 0x80, 0x7c, 0x7b, 0x80, 0x7e, 0x80, 0x85, 0x84, 0x7d, 0x7b,
0x7a, 0x7f, 0x83, 0x82, 0x80, 0x7c, 0x7e, 0x7e, 0x80, 0x81, 0x7f, 0x7f,
0x7e, 0x7f, 0x82, 0x7f, 0x7c, 0x7b, 0x7b, 0x82, 0x84, 0x83, 0x7e, 0x7c,
0x7b, 0x7e, 0x83, 0x81, 0x7f, 0x7d, 0x7e, 0x7f, 0x83, 0x81, 0x7e, 0x7d,
0x7b, 0x7d, 0x80, 0x82, 0x81, 0x80, 0x7f, 0x7d, 0x7f, 0x80, 0x7f, 0x80,
0x81, 0x80, 0x7f, 0x7d, 0x7d, 0x7e, 0x81, 0x82, 0x80, 0x7d, 0x7f, 0x81,
0x80, 0x7f, 0x7d, 0x7c, 0x7e, 0x80, 0x80, 0x80, 0x80, 0x80, 0x7e, 0x7f,
0x7d, 0x7e, 0x80, 0x81, 0x80, 0x7f, 0x7e, 0x7c, 0x7f, 0x81, 0x80, 0x80,
0x80, 0x7f, 0x7e, 0x7e, 0x7f, 0x7f, 0x80, 0x80, 0x80, 0x81, 0x80, 0x7d,
0x7c, 0x7f, 0x80, 0x83, 0x81, 0x7c, 0x7b, 0x7c, 0x7f, 0x82, 0x82, 0x7f,
0x7d, 0x7c, 0x7e, 0x80, 0x81, 0x81, 0x7f, 0x7f, 0x7d, 0x7d, 0x80, 0x82,
0x7f, 0x7e, 0x7d, 0x7d, 0x80, 0x83, 0x82, 0x7f, 0x7f, 0x7a, 0x7d, 0x80,
0x81, 0x81, 0x80, 0x7e, 0x7f, 0x80, 0x7e, 0x7e, 0x7f, 0x80, 0x7f, 0x80,
0x7f, 0x7e, 0x7d, 0x7f, 0x7e, 0x80, 0x81, 0x81, 0x80, 0x80, 0x7e, 0x7e,
0x7e, 0x7d, 0x80, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7e, 0x7c, 0x7f, 0x82,
0x7f, 0x80, 0x7f, 0x7d, 0x7d, 0x7f, 0x7f, 0x80, 0x80, 0x7f, 0x7e, 0x7f,
0x7f, 0x7f, 0x80, 0x7e, 0x7f, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7d, 0x7d,
0x81, 0x82, 0x80, 0x7e, 0x7d, 0x7e, 0x80, 0x81, 0x7f, 0x80, 0x80, 0x7f,
0x7f, 0x7d, 0x7f, 0x81, 0x80, 0x7f, 0x80, 0x7f, 0x7e, 0x7d, 0x7e, 0x4c,
0x49, 0x53, 0x54, 0x48, 0x00, 0x00, 0x00, 0x49, 0x4e, 0x46, 0x4f, 0x49,
0x43, 0x52, 0x44, 0x12, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31, 0x36, 0x2d,
0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32, 0x37, 0x00,
0x00, 0x49, 0x53, 0x46, 0x54, 0x22, 0x00, 0x00, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x20, 0x28,
0x6c, 0x69, 0x62, 0x73, 0x6e, 0x64, 0x66, 0x69, 0x6c, 0x65, 0x2d, 0x31,
0x2e, 0x30, 0x2e, 0x32, 0x34, 0x29, 0x00, 0x69, 0x64, 0x33, 0x20, 0x46,
0x00, 0x00, 0x00, 0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x3c, 0x54, 0x58, 0x58, 0x58, 0x00, 0x00, 0x00, 0x17, 0x00, 0x00, 0x00,
0x53, 0x6f, 0x66, 0x74, 0x77, 0x61, 0x72, 0x65, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x54, 0x44,
0x52, 0x43, 0x00, 0x00, 0x00, 0x11, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31,
0x36, 0x2d, 0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32,
0x37

};

const long switchResampled_len = 1045;









share|improve this question













I want to play some short audio clips (they range from 50ms to 100ms) from my atmega168 microcontroller and output it to a cheap speaker.



I was following this tutorial but because I'm using a atmega168 and not a atmega2560, I had to modify my code as well as replaced the sound.



Like in the tutorial, I'm using a 8MHz internal oscillator (I set LFUSE = 0xE2 in the Makefile) and all the PWM settings are the same...which means




  • Using a 16 Timer/Counter1 with 8-bit PWM resolution

  • Set OC1A on compare match (and clear on bottom)

  • No prescaling


As for the sound clip, I sampled it at 15.625 kHz and exported it to a 8-bit PCM wav file. I then get a hex dump via xxd -i which gives me the output c file. I didn't remove the header as I figured I can just skip it by just going to the 44th position of the output array as it is the data position.



The problem I'm having is that while I do get my (distorted and soft) sound, there is this loud beeping noise that is overlapping with my sound and I have no idea what is causing it.



Unfortunately I don't have access to an oscilloscope, so I can't really nail down if it is the way I sampled my sound, or if my sound is way too short or something that's beyond my current understanding.



Main.c



#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include <avr/power.h>
#include <util/setbaud.h>
#include <avr/interrupt.h>

#include "switch.h"
#define WAV_DATA_POSITION 44
#define BASE_LEVEL 0xff

unsigned int count=WAV_DATA_POSITION;;
volatile uint16_t timerOverflowCount;
unsigned char sample_count =2;

// This interrupt service reads new data,
ISR(TIMER1_OVF_vect){

sample_count--;

if(sample_count ==0)
{
sample_count = 2;
if (count < switchResampled_len){
OCR1A= pgm_read_byte(&switch_raw[count]);
count++;
}
}
else{
OCR1A= BASE_LEVEL;
}
}

void pwm_init()
{

SREG |=0x80;

//select Fast PWM with 8-bit resolution,set OC1A on compare match and clear at bottom
TCCR1A|=(1<<COM1A1)|(1<<COM1A0)|(1<<WGM10);

//No prescaling therefore timer frequency = 8 MHz and PWM frequency = 31250 Hz
TCCR1B|=(1<<WGM12)|(1<<CS10);

TCNT1=0x00;

OCR1A=BASE_LEVEL;
//Enable the timer interrupt
TIMSK1 |= ( 1 <<TOIE1);

//Clear all interupt flags
TIFR1|=(1<<ICF1)|(1<<OCF1B)|(1<<OCF1A)|(1<<TOV1);

//Enable interrupts
sei();

}


int main(void)
{
//PB1 is OC1A. Use this for output
DDRB |= (1 << PB1);
pwm_init();

/* insert your hardware initialization here */
for(;;){

/* insert your main loop code here */
}
return 0; /* never reached */
}


Switch.h (Sound file)



const unsigned char switch_raw PROGMEM = {
0x52, 0x49, 0x46, 0x46, 0x0d, 0x04, 0x00, 0x00, 0x57, 0x41, 0x56, 0x45,
0x66, 0x6d, 0x74, 0x20, 0x10, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00,
0x09, 0x3d, 0x00, 0x00, 0x09, 0x3d, 0x00, 0x00, 0x01, 0x00, 0x08, 0x00,
0x64, 0x61, 0x74, 0x61, 0x4b, 0x03, 0x00, 0x00, 0x80, 0x7f, 0x7f, 0x7e,
0x7f, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7f, 0x80, 0x7f, 0x7e, 0x7e,
0x7f, 0x80, 0x7f, 0x7f, 0x7e, 0x7d, 0x7f, 0x81, 0x7e, 0x7e, 0x7f, 0x7f,
0x7e, 0x7e, 0x7f, 0x7f, 0x7f, 0x7d, 0x80, 0x81, 0x7e, 0x7b, 0x7e, 0x7f,
0x7f, 0x81, 0x7e, 0x7e, 0x7d, 0x80, 0x80, 0x7e, 0x7e, 0x7e, 0x7d, 0x7e,
0x80, 0x80, 0x7e, 0x7c, 0x7d, 0x7f, 0x81, 0x7f, 0x7e, 0x81, 0x7d, 0x7b,
0x80, 0x7f, 0x7f, 0x83, 0x7f, 0x7b, 0x7f, 0x80, 0x7f, 0x82, 0x7f, 0x7e,
0x80, 0x7e, 0x81, 0x7f, 0x7f, 0x81, 0x7d, 0x7e, 0x80, 0x7e, 0x80, 0x7e,
0x7f, 0x85, 0x80, 0x83, 0x7b, 0x77, 0x83, 0x81, 0x86, 0x7e, 0x7b, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x7f, 0x81, 0x82, 0x7f, 0x7e, 0x7e, 0x7e,
0x81, 0x83, 0x7f, 0x7f, 0x7f, 0x80, 0x80, 0x81, 0x7e, 0x7e, 0x80, 0x83,
0x7f, 0x7d, 0x7b, 0x80, 0x80, 0x94, 0x79, 0x68, 0x87, 0x75, 0x98, 0x87,
0x6e, 0x7f, 0x8c, 0x81, 0x54, 0x7c, 0xc4, 0x8a, 0x46, 0x31, 0x72, 0xe2,
0xc1, 0x8a, 0x41, 0x2f, 0x71, 0xb3, 0xc8, 0x96, 0x51, 0x41, 0x67, 0x9c,
0xb1, 0x98, 0x74, 0x57, 0x5f, 0x76, 0x99, 0xa8, 0x96, 0x72, 0x5b, 0x64,
0x7e, 0x97, 0xa1, 0x8f, 0x6f, 0x56, 0x66, 0x89, 0xa0, 0x9d, 0x7e, 0x62,
0x5c, 0x78, 0x93, 0x9d, 0x90, 0x70, 0x58, 0x68, 0x88, 0x9c, 0x95, 0x7c,
0x66, 0x64, 0x7c, 0x90, 0x95, 0x82, 0x6f, 0x6b, 0x75, 0x86, 0x8e, 0x88,
0x79, 0x72, 0x75, 0x80, 0x88, 0x89, 0x81, 0x78, 0x74, 0x78, 0x84, 0x85,
0x84, 0x7d, 0x7b, 0x7c, 0x7b, 0x80, 0x85, 0x87, 0x81, 0x76, 0x74, 0x7e,
0x82, 0x89, 0x84, 0x7c, 0x77, 0x78, 0x84, 0x83, 0x84, 0x7c, 0x78, 0x7b,
0x83, 0x83, 0x80, 0x83, 0x80, 0x7d, 0x7a, 0x7e, 0x83, 0x87, 0x82, 0x79,
0x78, 0x7e, 0x87, 0x8b, 0x80, 0x76, 0x79, 0x7e, 0x87, 0x87, 0x80, 0x7a,
0x7a, 0x80, 0x82, 0x84, 0x81, 0x7f, 0x7e, 0x7d, 0x7a, 0x82, 0x88, 0x7f,
0x7a, 0x79, 0x7f, 0x85, 0x85, 0x7f, 0x7d, 0x7a, 0x7d, 0x83, 0x87, 0x7e,
0x78, 0x7e, 0x7d, 0x83, 0x7e, 0x81, 0x81, 0x80, 0x7f, 0x81, 0x81, 0x7c,
0x7e, 0x7a, 0x81, 0x82, 0x81, 0x84, 0x82, 0x79, 0x78, 0x84, 0x86, 0x7d,
0x7b, 0x7e, 0x7f, 0x7c, 0x7d, 0x7d, 0x82, 0x80, 0x80, 0x7e, 0x7d, 0x85,
0x84, 0x7b, 0x75, 0x7c, 0x7d, 0x84, 0x88, 0x84, 0x7b, 0x7b, 0x7d, 0x7c,
0x88, 0x88, 0x7b, 0x78, 0x78, 0x78, 0x88, 0x8d, 0x80, 0x78, 0x7f, 0x86,
0x86, 0x83, 0x7c, 0x71, 0x76, 0x84, 0x97, 0x93, 0x70, 0x6d, 0x68, 0x78,
0xc5, 0xb6, 0x5f, 0x37, 0x2a, 0x69, 0xc1, 0xc9, 0xa0, 0x7a, 0x52, 0x50,
0x71, 0x8a, 0x9d, 0xa0, 0x8b, 0x69, 0x67, 0x68, 0x79, 0x94, 0x96, 0x87,
0x7b, 0x81, 0x84, 0x7e, 0x7d, 0x7e, 0x75, 0x72, 0x89, 0x8e, 0x88, 0x86,
0x6d, 0x6d, 0x7a, 0x82, 0x8d, 0x8e, 0x78, 0x76, 0x7f, 0x7d, 0x7e, 0x82,
0x80, 0x7b, 0x7d, 0x7a, 0x7b, 0x86, 0x89, 0x80, 0x7b, 0x75, 0x77, 0x7f,
0x83, 0x84, 0x86, 0x81, 0x81, 0x7e, 0x73, 0x7c, 0x83, 0x7f, 0x85, 0x82,
0x7d, 0x83, 0x7d, 0x7d, 0x80, 0x7b, 0x7c, 0x86, 0x85, 0x7e, 0x7b, 0x74,
0x7d, 0x86, 0x85, 0x8b, 0x81, 0x76, 0x78, 0x78, 0x7e, 0x89, 0x83, 0x7e,
0x80, 0x78, 0x7f, 0x84, 0x81, 0x84, 0x7a, 0x77, 0x7f, 0x81, 0x84, 0x81,
0x78, 0x7a, 0x7e, 0x84, 0x8e, 0x81, 0x72, 0x75, 0x77, 0x83, 0x8b, 0x84,
0x84, 0x7b, 0x72, 0x7a, 0x83, 0x84, 0x85, 0x7e, 0x78, 0x7e, 0x7d, 0x7f,
0x82, 0x80, 0x7f, 0x7e, 0x7f, 0x81, 0x7e, 0x7b, 0x80, 0x85, 0x84, 0x82,
0x7d, 0x7a, 0x7d, 0x7f, 0x84, 0x84, 0x7f, 0x79, 0x7b, 0x82, 0x80, 0x80,
0x81, 0x80, 0x81, 0x81, 0x7f, 0x7e, 0x79, 0x79, 0x81, 0x86, 0x85, 0x82,
0x7d, 0x77, 0x7a, 0x7e, 0x86, 0x8b, 0x84, 0x7a, 0x7a, 0x7d, 0x7e, 0x83,
0x83, 0x80, 0x7e, 0x7c, 0x7c, 0x80, 0x7f, 0x80, 0x7f, 0x7f, 0x80, 0x7e,
0x7f, 0x80, 0x7f, 0x7c, 0x80, 0x7d, 0x7e, 0x85, 0x81, 0x7c, 0x7d, 0x7b,
0x7c, 0x81, 0x80, 0x7d, 0x7f, 0x80, 0x7d, 0x82, 0x84, 0x7e, 0x7a, 0x7e,
0x7e, 0x7f, 0x82, 0x7d, 0x7e, 0x81, 0x7f, 0x7d, 0x7e, 0x81, 0x83, 0x83,
0x80, 0x79, 0x77, 0x7c, 0x83, 0x87, 0x86, 0x7f, 0x75, 0x79, 0x7e, 0x85,
0x86, 0x80, 0x7a, 0x78, 0x7c, 0x7f, 0x83, 0x81, 0x82, 0x7d, 0x7a, 0x7f,
0x81, 0x80, 0x80, 0x7c, 0x7b, 0x80, 0x7e, 0x80, 0x85, 0x84, 0x7d, 0x7b,
0x7a, 0x7f, 0x83, 0x82, 0x80, 0x7c, 0x7e, 0x7e, 0x80, 0x81, 0x7f, 0x7f,
0x7e, 0x7f, 0x82, 0x7f, 0x7c, 0x7b, 0x7b, 0x82, 0x84, 0x83, 0x7e, 0x7c,
0x7b, 0x7e, 0x83, 0x81, 0x7f, 0x7d, 0x7e, 0x7f, 0x83, 0x81, 0x7e, 0x7d,
0x7b, 0x7d, 0x80, 0x82, 0x81, 0x80, 0x7f, 0x7d, 0x7f, 0x80, 0x7f, 0x80,
0x81, 0x80, 0x7f, 0x7d, 0x7d, 0x7e, 0x81, 0x82, 0x80, 0x7d, 0x7f, 0x81,
0x80, 0x7f, 0x7d, 0x7c, 0x7e, 0x80, 0x80, 0x80, 0x80, 0x80, 0x7e, 0x7f,
0x7d, 0x7e, 0x80, 0x81, 0x80, 0x7f, 0x7e, 0x7c, 0x7f, 0x81, 0x80, 0x80,
0x80, 0x7f, 0x7e, 0x7e, 0x7f, 0x7f, 0x80, 0x80, 0x80, 0x81, 0x80, 0x7d,
0x7c, 0x7f, 0x80, 0x83, 0x81, 0x7c, 0x7b, 0x7c, 0x7f, 0x82, 0x82, 0x7f,
0x7d, 0x7c, 0x7e, 0x80, 0x81, 0x81, 0x7f, 0x7f, 0x7d, 0x7d, 0x80, 0x82,
0x7f, 0x7e, 0x7d, 0x7d, 0x80, 0x83, 0x82, 0x7f, 0x7f, 0x7a, 0x7d, 0x80,
0x81, 0x81, 0x80, 0x7e, 0x7f, 0x80, 0x7e, 0x7e, 0x7f, 0x80, 0x7f, 0x80,
0x7f, 0x7e, 0x7d, 0x7f, 0x7e, 0x80, 0x81, 0x81, 0x80, 0x80, 0x7e, 0x7e,
0x7e, 0x7d, 0x80, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7e, 0x7c, 0x7f, 0x82,
0x7f, 0x80, 0x7f, 0x7d, 0x7d, 0x7f, 0x7f, 0x80, 0x80, 0x7f, 0x7e, 0x7f,
0x7f, 0x7f, 0x80, 0x7e, 0x7f, 0x7f, 0x80, 0x81, 0x7f, 0x7e, 0x7d, 0x7d,
0x81, 0x82, 0x80, 0x7e, 0x7d, 0x7e, 0x80, 0x81, 0x7f, 0x80, 0x80, 0x7f,
0x7f, 0x7d, 0x7f, 0x81, 0x80, 0x7f, 0x80, 0x7f, 0x7e, 0x7d, 0x7e, 0x4c,
0x49, 0x53, 0x54, 0x48, 0x00, 0x00, 0x00, 0x49, 0x4e, 0x46, 0x4f, 0x49,
0x43, 0x52, 0x44, 0x12, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31, 0x36, 0x2d,
0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32, 0x37, 0x00,
0x00, 0x49, 0x53, 0x46, 0x54, 0x22, 0x00, 0x00, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x20, 0x28,
0x6c, 0x69, 0x62, 0x73, 0x6e, 0x64, 0x66, 0x69, 0x6c, 0x65, 0x2d, 0x31,
0x2e, 0x30, 0x2e, 0x32, 0x34, 0x29, 0x00, 0x69, 0x64, 0x33, 0x20, 0x46,
0x00, 0x00, 0x00, 0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x3c, 0x54, 0x58, 0x58, 0x58, 0x00, 0x00, 0x00, 0x17, 0x00, 0x00, 0x00,
0x53, 0x6f, 0x66, 0x74, 0x77, 0x61, 0x72, 0x65, 0x00, 0x4c, 0x61, 0x76,
0x66, 0x35, 0x37, 0x2e, 0x37, 0x32, 0x2e, 0x31, 0x30, 0x31, 0x54, 0x44,
0x52, 0x43, 0x00, 0x00, 0x00, 0x11, 0x00, 0x00, 0x00, 0x32, 0x30, 0x31,
0x36, 0x2d, 0x31, 0x30, 0x2d, 0x31, 0x37, 0x20, 0x31, 0x37, 0x3a, 0x32,
0x37

};

const long switchResampled_len = 1045;






audio pwm atmega






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 5 hours ago









cheunste

634




634












  • That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
    – analogsystemsrf
    4 hours ago










  • 1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
    – brhans
    4 hours ago










  • By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
    – Nayuki
    6 mins ago


















  • That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
    – analogsystemsrf
    4 hours ago










  • 1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
    – brhans
    4 hours ago










  • By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
    – Nayuki
    6 mins ago
















That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
– analogsystemsrf
4 hours ago




That is likely the fundamental PWM rate, wherein you are modifying the DUTY CYCLE but not the repetition rate.
– analogsystemsrf
4 hours ago












1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
– brhans
4 hours ago




1045 samples at 15.625kHz is only 67mSec worth of data. How are you hearing anything in only 67mSec?
– brhans
4 hours ago












By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
– Nayuki
6 mins ago




By the way, instead of using PWM, there are cheap and accessible microcontrollers with true analog outputs (e.g. 12-bit resolution).
– Nayuki
6 mins ago










1 Answer
1






active

oldest

votes


















5














A 4MHz PWM generator (8MHz/2) At 8 bits has a 15.625kHz fundamental. If you are not filtering this out with at least a 7kHz high-order low-pass you will hear it loud and clear.



You need to bring this fundamental to at least above 20kHz or so to get it out of your hearing range, it will still annoy your dog though.






share|improve this answer





















  • Or maybe he could use a notch filter.
    – Harry Svensson
    3 hours ago











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A 4MHz PWM generator (8MHz/2) At 8 bits has a 15.625kHz fundamental. If you are not filtering this out with at least a 7kHz high-order low-pass you will hear it loud and clear.



You need to bring this fundamental to at least above 20kHz or so to get it out of your hearing range, it will still annoy your dog though.






share|improve this answer





















  • Or maybe he could use a notch filter.
    – Harry Svensson
    3 hours ago
















5














A 4MHz PWM generator (8MHz/2) At 8 bits has a 15.625kHz fundamental. If you are not filtering this out with at least a 7kHz high-order low-pass you will hear it loud and clear.



You need to bring this fundamental to at least above 20kHz or so to get it out of your hearing range, it will still annoy your dog though.






share|improve this answer





















  • Or maybe he could use a notch filter.
    – Harry Svensson
    3 hours ago














5












5








5






A 4MHz PWM generator (8MHz/2) At 8 bits has a 15.625kHz fundamental. If you are not filtering this out with at least a 7kHz high-order low-pass you will hear it loud and clear.



You need to bring this fundamental to at least above 20kHz or so to get it out of your hearing range, it will still annoy your dog though.






share|improve this answer












A 4MHz PWM generator (8MHz/2) At 8 bits has a 15.625kHz fundamental. If you are not filtering this out with at least a 7kHz high-order low-pass you will hear it loud and clear.



You need to bring this fundamental to at least above 20kHz or so to get it out of your hearing range, it will still annoy your dog though.







share|improve this answer












share|improve this answer



share|improve this answer










answered 4 hours ago









Edgar Brown

3,153425




3,153425












  • Or maybe he could use a notch filter.
    – Harry Svensson
    3 hours ago


















  • Or maybe he could use a notch filter.
    – Harry Svensson
    3 hours ago
















Or maybe he could use a notch filter.
– Harry Svensson
3 hours ago




Or maybe he could use a notch filter.
– Harry Svensson
3 hours ago


















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