Sparkfun MP3 shield and timer interrupts

Using Arduino Audio
1

Hi,

I am trying to gradually increase volume while playing tracks from SD card.
Hardware setup: Arduino UNO R3 clone (Elegoo) + Sparkfun MP3 Player v15 shield + LED/resistor on PB5 (for troubleshooting).
I am using Timer2 overflow interrupts to increase the volume (also tried Timer1 CTC).
Problem: playing tracks from SD card seem to be interfering with the timer, i.e. timer overflow interrupt routine is not invoked.

#ifndef F_CPU
#define F_CPU 16000000UL
#endif

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

#include <TrueRandom.h>
#include <SPI.h>
#include <SdFat.h>
#include <FreeStack.h>
#include <SFEMP3Shield.h>

#if defined(USE_MP3_REFILL_MEANS) && USE_MP3_REFILL_MEANS == USE_MP3_Timer1
#include <TimerOne.h>
#elif defined(USE_MP3_REFILL_MEANS) && USE_MP3_REFILL_MEANS == USE_MP3_SimpleTimer
#include <SimpleTimer.h>
#endif

volatile char vol = 48;
volatile uint16_t tmr_count = 0;
SFEMP3Shield MP3player;
SdFat sd;

int main(void)
{

  DDRB |= (1 << 5); // Set LED on PB5 as output
  
  uint8_t result; //result code from functions, to verify success

  //Initialize the SdCard.
  if(!sd.begin(SD_SEL, SPI_FULL_SPEED)) sd.initErrorHalt();
  // depending upon your SdCard environment, SPI_HAVE_SPEED may work better.
  if(!sd.chdir("/")) sd.errorHalt("sd.chdir");

  result = MP3player.begin();  //test result here, if needed
  
  //set initial volume
  MP3player.setVolume(vol, vol);

  //set mono mode
  MP3player.setMonoMode(1);


  result = sd.begin(SD_SEL, SPI_FULL_SPEED);  //test result here, if needed


  TCCR2B |= (1<<CS20) | (1<<CS21) | (1<<CS22); // PRESCALER 1024
  TIMSK2 = (1<<TOIE2);  //enable overflow interrupt

  sei (); // Enable global interrupts
  
  for (;;)
  {
      if ( !MP3player.isPlaying() ) {
        play_tracks();
      } 
  }

}

void play_tracks()
{
  char filename[13];
  int count = 0;

  // count the files
  SdFile file;
  sd.chdir("/", true);
  while (file.openNext(sd.vwd(), O_READ)) {
    count += 1;
    file.close();
  }

  // pick a  random one
  int r = TrueRandom.random(count + 1);

  // loop over all the files agai - if our current
  // index equals the random one - play it
  sd.chdir("/", true);
  count = 0;
  while (file.openNext(sd.vwd(), O_READ)) {
    if ( count == r )
    {
      file.getName(filename, sizeof(filename));
      int8_t result = MP3player.playMP3(filename);
      if (result != 0) {
        //error - skip it
        continue;
      }

    }
    file.close();
    count += 1;
  }
}

ISR(TIMER2_OVF_vect)
{
  if(tmr_count >= 50) // gives approx. 1 sec period
  {
      if(vol <= 2)  // 2 is max volume
      {
        vol = 2;
      } else {
        vol -= 2; //decrementing vol actually increases volume
        MP3player.setVolume(vol, vol);
      }
    tmr_count = 0;
    PORTB ^= (1 << 5); // Toggle the LED
  } else {
    tmr_count++;
  }
}

Actual result: volume does not increase, LED does not blink.
If I comment out the code that initializes SD, MP3player and play_tracks(), LED blinks as expected.

Any advice would be appreciated!

2

I THINK you're on a pin that is being used by the Sparkfun MP3 player- only 2 pins on the digital side are not being used in some fashion by the player- Pin 5 and Pin 10. All the analog pins are available as well. Here's the diagram of usage by the Sparkfun MP3 player.

3

You are right @halloweenrick. After some tweaking, Analog 1 aka PC1 worked fine. Thanks!

4