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Page history last edited by Huda 8 years, 1 month ago


The Point of View

Loud dorm mates and a mother with great fascination of cooking inspired me to build a music player which could be controlled without the need of fingers. I initially planned to build a waterproof MP3 player that could be used in the shower, but I eventually realized that rather than being waterproof, a player that was water resistant and had relatively bigger buttons could be more versatile. So I set out with a rather basic code and a set of huge red buttons that can be clicked with elbows, nose, toes. Therefore, in a scenario where it is hard to use fingers with an iPod or iPhone (which are essentially impossible to control without hands) a player with speakers and easy navigation using buttons is more useful.



The box was designed to be rather rectangular, and lightweight since it dint need to be portable or moved around much but can still be moved from one place to another. It is connected to 2 speakers so that the player can be loud enough and the volume can even be decreased when required.


I used a thin, rectangular set of speakers that could fit into the housing. I also bought a set of bright, big buttons all from Fry’s Electronics.


The interface consisted of a simple rectangular box with buttons for control rather than knobs to enable a smooth control of music and volume. The songs playback from a removable micro SD card. The player receives power from a set of 4 batteries, placed at the bottom of the set.


The circuit consists the components of the barebones mp3 player with an addition of buttons and a speaker.





* example sketch to play audio file(s) in a directory, using the mp3 library

* for playback and the arduino sd library to read files from a microsd card.

* pins are setup to work well for teensy 2.0. double-check if using arduino.


* originally based on frank zhao's player: http://frank.circleofcurrent.com/

* utilities adapted from previous versions of the functions by matthew seal.


* (c) 2011, 2012 david sirkin sirkin@cdr.stanford.edu

* & akil srinivasan akils@stanford.edu



// first step is to include (arduino) sd, eeprom and (our own) mp3 libraries.


#include <SD.h>

#include <EEPROM.h>


#include <mp3.h>

#include <mp3conf.h>


// include the graphic lcd library. if you're using the lcd, but not graphics

// or bitmap capabilities, making these #define's will save program memory.


#include <nokia_5110_lcd.h>



#define NO_BITMAP


// uncomment this #define to print out eeprom & sram usage info to the serial

// terminal. note that doing so uses about 850 bytes of program memory.


// #define DEBUG

// uncomment this #define to search for id3 tags and (ideally) a title frame.

// note that doing so uses about 950 bytes of program memory.

#define ID3TAG


// setup microsd and decoder chip select pins, and the decoder-specific pins.


#define sd_cs 12 // 'chip select' line for the microsd card

#define mp3_cs 21 // 'command chip select' connect to cs pin


#define mp3_dcs 20 // 'data chip select' connect to bsync pin

#define mp3_rst 18 // 'reset' connects to decoder's reset pin

#define mp3_dreq 19 // 'data request line' connect to dreq pin


// now assign pins for the graphic lcd (carried over from the etch-a-sketch).


#define lcd_vcc 10 // 'vcc' connects to graphic lcd's vcc pin

#define lcd_sce 9 // 'slave chip select' connect to sce pin

#define lcd_rst 8 // 'reset' connects to graphic lcd rst pin

#define lcd_d_c 4 // 'data/command input' connect to d/c pin


// 'read_buffer' is the amount of data read from microsd and sent to decoder.

// it's probably best to keep this a factor of 2, up to about 1kb (2kb is the

// max). you might change this if you experienced skips during song playback.


#define read_buffer 512 // size (bytes) of the microsd read buffer

#define mp3_vol 175 // default volume. range min=0 and max=254


// file names are 13 bytes max (8 + '.' + 3 + '\0'), and the file list should

// fit into the eeprom. for example, 13 * 40 = 520 bytes of eeprom are needed

// to store a list of 40 songs. if you use shorter file names, or if your mcu

// has more eeprom, you can change these.


#define max_name_len 13

#define max_num_songs 40


// id3v2 tags have variable-length song titles. that length is indicated in 4

// bytes within the tag. id3v1 tags also have variable-length song titles, up

// to 30 bytes maximum, but the length is not indicated within the tag. using

// 60 bytes here is a compromise between holding most titles and saving sram.


// if you increase this above 255, look for and change 'for' loop index types

// so as to not to overflow the unsigned char data type.


#define max_title_len 60


// you can comment out the following line (and 3 lines at the end of setup())

// to save memory if you're not going to use the graphic lcd. note that doing

// so releases about 550 bytes of sram (!) and 200 bytes of program memory.


// instantiate a graphic lcd object using the pins that we #define'd earlier.


Nokia_5110_lcd lcd(lcd_vcc, lcd_d_c, lcd_sce, lcd_rst);


// 'File' is a wrapper of the 'SdFile' data type from the sd utility library.


File sd_file; // object to represent a file on a microsd


// store the number of songs in this directory, and the current song to play.


unsigned char num_songs = 0, current_song = 0;


// an array to hold the current_song's file name in ram. every file's name is

// stored longer-term in the eeprom. this array is used in 'sd_file.open()'.


char fn[max_name_len];


// an array to hold the current_song's title in ram. it needs 1 extra char to

// hold the '\0' that indicates the end of a character string. the song title

// is found in 'get_title_from_id3tag()'.


char title[max_title_len + 1];


// the program runs as a state machine. the 'state' enum includes the states.

// 'current_state' is the default as the program starts. add new states here.


enum state { DIR_PLAY, MP3_PLAY, PAUSED };

state current_state = DIR_PLAY;


const int buttonPin1 = 15;

const int buttonPin2 = 14;


int buttonState1 = 0;

int buttonState2 = 0;


// you must open a song file that you want to play using 'sd_file_open' prior

// to fetching song data from the file. you can only open one file at a time.


void sd_file_open() {

// first, find the file name (that's stored in eeprom) of the current song.


// then open the file using the name we just found (stored in 'fn' global).

sd_file = SD.open(fn, FILE_READ);

// optionally find, and print 'current_song's id3tag title to the terminal.

// if the title is unicode (see comments in 'get_title_from_id3tag'),

#ifdef ID3TAG









// read a number of bytes from the microsd card, then forward them to the Mp3

// library's 'play' function, which streams them out to the decoder chip.


void mp3_play() {

unsigned char bytes[read_buffer]; // buffer to read and send to the decoder

unsigned int bytes_to_read; // number of bytes read from microsd card


// first fill the 'bytes' buffer with (up to) 'read_buffer' count of bytes.

// that happens through the 'sd_file.read()' call, which returns the actual

// number of bytes that were read (which can be fewer than 'read_buffer' if

// at the end of the file). then send the retrieved bytes out to be played.

// 'sd_file.read()' manages the index pointer into the file and knows where

// to start reading the next batch of bytes. 'Mp3.play()' manages the index

// pointer into the 'bytes' buffer and knows how to send it to the decoder.


bytes_to_read = sd_file.read(bytes, read_buffer);

Mp3.play(bytes, bytes_to_read);

// 'bytes_to_read' is only smaller than 'read_buffer' when the song's over.


if (bytes_to_read < read_buffer) {


// if we've been in the MP3_PLAY state, then we want to pause the player.


if (current_state == MP3_PLAY) {

current_state == PAUSED;






// continue to play the current (playing) song, until there are no more songs

// in the directory to play. 2 other sd library methods (that we haven't used

// here) can help track your progress while playing songs: 'sd_file.size()' &

// 'sd_file.position()'. you can use these to show say, the percent of a song

// that has already played.

void dir_play() {

if (sd_file) {



else {

// since 'sd_file' isn't open, the recently playing song must have ended.

// increment the index, and open the next song, unless it's the last song

// in the directory. in that case, just set the state to PAUSED.


if (current_song < (num_songs - 1)) {




else {

current_state = PAUSED;





void pause_play(){

if(current_state == DIR_PLAY || current_state==MP3_PLAY){

current_state = PAUSED;



current_state = DIR_PLAY;





void skip_backward(){









void skip_forward(){



if(current_song < (num_songs - 1)){ current_song++; }

else{ current_song = 0; }




void play(){

if(current_state = PAUSED){

current_state = MP3_PLAY; }



// setup is pretty straightforward. initialize serial communication (used for

// the following error messages), mp3 library, microsd card objects, then the

// graphic lcd. then open the first song in the root library to play.


void setup() {


// if using a graphic lcd, initialize the device now. the parameter '40' is

// the screen contrast, which ranges from min=0 to max=127.



// initialize the mp3 library, and set default volume. 'mp3_cs' is the chip

// select, 'dcs' is data chip select, 'rst' is reset and 'dreq' is the data

// request. the decoder sets the 'dreq' line (automatically) to signal that

// its input buffer can accommodate 32 more bytes of incoming song data.

// the decoder's default state prevents the spi bus from working with other

// spi devices, so we initialize it first.

Mp3.begin(mp3_cs, mp3_dcs, mp3_rst, mp3_dreq);


// initialize the microsd (which checks the card, volume and root objects).


// putting all of the root directory's songs into eeprom saves flash space.



// optionally print status info (serial terminal) before opening any files.

#ifdef DEBUG



// the program is setup to enter DIR_PLAY mode immediately, so this call to

// open the root directory before reaching the state machine is needed.



// test that the lcd still works, now that the other spi devices are setup.

//lcd.writeString(0, 0, "Barebones Mp3!", MODE_NORMAL);

attachInterrupt(0, FRWD, RISING);

attachInterrupt(1, BACK, RISING);

attachInterrupt(2, STOP, RISING);



void FRWD(){


static unsigned long last_interrupt_time = 0;

unsigned long interrupt_time = millis();

// If interrupts come faster than 200ms, assume it's a bounce and ignore

if (interrupt_time - last_interrupt_time > 200)




last_interrupt_time = interrupt_time;



void BACK(){


static unsigned long last_interrupt_time = 0;

unsigned long interrupt_time = millis();

// If interrupts come faster than 200ms, assume it's a bounce and ignore

if (interrupt_time - last_interrupt_time > 200)




last_interrupt_time = interrupt_time;



void STOP(){


static unsigned long last_interrupt_time = 0;

unsigned long interrupt_time = millis();

// If interrupts come faster than 200ms, assume it's a bounce and ignore

if (interrupt_time - last_interrupt_time > 200)




last_interrupt_time = interrupt_time;




// the state machine is setup (at least, at first) to open the microsd card's

// root directory, play all of the songs within it, close the root directory,

// and then stop playing. change these, or add new actions here.


// the DIR_PLAY state plays all of the songs in a directory and then switches

// into PAUSED when done. the MP3_PLAY state plays one specific song and then

// switches into PAUSED. this sample player doesn't enter the MP3_PLAY state,

// as its goal (for now) is just to play all the songs. you can change that.


void loop() {

buttonState1 = digitalRead(buttonPin1);

buttonState2 = digitalRead(buttonPin2);

if(buttonState1 == HIGH && Mp3.volume <= 255) {Mp3.volume = Mp3.volume + 5; }

if(buttonState2 == HIGH && Mp3.volume >= 0){ Mp3.volume = Mp3.volume - 5; }

switch(current_state) {


case DIR_PLAY:




case MP3_PLAY:




case PAUSED:

// h v pause_play();





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