Problem when playing music with Arduino

Question

I am using an Arduino Nano in combination with a SD card to play some music. I have loaded some .wav files on my SD card, the card initializes, everything runs correctly, but on my output pin for my music I get an unstable square wave signal all the time.

I have tried to change the CS pin to pin 4 and 10 (only pin 4 works), I have tried different .wav files and a bunch of code and all of my libraries are installed. What can I do?

#include <SPI.h>
#include <SD.h>
#include <TMRpcm.h>

TMRpcm audio;

void setup() {
  audio.speakerPin = 9;

  //starting up SD
  Serial.begin(9600);
  if (!SD.begin(4)) {
    Serial.println("Initialization failed");
    while (true) {
    }
  }
  Serial.println("Initialization complete");

  audio.setVolume(3);
  audio.play("SSTC.wav");
}

void loop() {
}

Answer 1

It is (probably) working as intended. From the TMRpcm library's Wiki:

If using an amplifier, consider that the output is a choppy digital PWM signal, not a smooth analog signal.

This could be what you are seeing: the output is PWM, not analog. The PWM signal you get is supposed to be low-pass filtered by either a filter or the characteristics of the speaker you use.

If you want analog output, you need to pass the PWM through a low-pass filter, or use a microcontroller with a DAC, or use an external DAC (and a different library for the last two options).

Another possible problem is the performance of the Arduino Nano with .wav files with a high sample rate and bit depth; the library's Wiki says:

Main formats: WAV files, 8-bit, 8-32khz Sample Rate, mono.

It could be your .wav file doesn't comply with that.