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;