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<pre>void dir(void (*callback)(char *));</pre>  
 
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Output the directory of the SD card. A pointer to a callback  
 
Output the directory of the SD card. A pointer to a callback  
function must be provided.  
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function must be provided. The callback function is called once for every file found in the root directory of the card. The strings contain zero-termination but no linefeeds.
  
 
Usage example:
 
Usage example:

Version vom 29. Juni 2012, 22:40 Uhr

About

Play audio files with your Arduino in decent quality from SD card, only very few additional hardware required.

Features

  • 8-Bit PWM output - no external DAC required
  • 62.500 kHz (fullrate) / 31.250 kHz (halfrate) sampling rate @ 16 MHz
  • 31.250 kHz (fullrate) / 15.625 kHz (halfrate) sampling rate @ 8 Mhz
  • PWM output is operating always at fullrate for easier filtering
  • Mono, bridge and stereo mode
  • RAM usage ~1.3 kByte
  • ROM usage ~6.1 kByte
  • Integrated SD library (minimal FAT only, optimized for low RAM usage and high performance)
  • Works with most SD card shields that are hooked to SPI port
  • Easy to use API: 1. init library, 2. select audio file, 3. call play, 4. call worker while audio is playing
  • Supports SD and SDHC cards formated with FAT16 or FAT32

Restrictions

  • Audio file must be converted prior use
  • Audio files must reside in root directory of card
  • File name of audio file must be in 8.3-format
  • Audio file must reside completely non-fragmented on card
  • Fullrate and stereo actually leads to buffer underruns
  • Minimum controller required: ATmega168. ATmega8 is too low on RAM.

Usuage

Quickstart guide

  • Install library: Unzip all to your /libraries/ folder.
  • Copy the file /libraries/SimpleSDAudio/examples/example.raw to root folder of a freshly formated SD card (don't use quick format!).
  • Connect SD card to your Arduino board (using shield or whatever, SD card's chip select should go to pin 4, all other to SPI pins).
  • Connect a speaker or headphone via 100 ohm resistor in series to audio output pin (pin 9 on Arduinos with ATmega168/328, pin 44 on Arduinos with ATmega1280/2560). Connect other end of speaker to GND.
  • Launch Arduino IDE and try example "BareMinimumWithDebug" first.
  • You should hear the audio (plays just a few seconds). Activate serial monitor to find some information if it does not work. Maybe you have to adjust SD cards CS pin in sketch.

Software installation guide

Browse to your sketchbook location (see Arduino - File - Preferences). There should be a folder called /libraries/, if not, create a folder and name it exactly like that. Then extract the zip-file preserving the folders and put all into the "libraries" folder that you end up with a structure where the "example" folder is located here: /libraries/SimpleSDAudio/examples/. Now you can start Arduino IDE and find examples for the library under File - Examples - SimpleSDAudio.

To convert audio files for usage with this library read the next paragraph.

Preparation of SD card and conversion of audio files

The audio library uses a very trimmed SD library that uses the FAT only to find the start sector of the files. Therefore the file must be completely non-fragmented on the SD card. The best way to ensure this is to do a fresh and full format of the card (don't use quick format!). After formating the SD card, only copy new files on it. Don't delete files and avoid rename operations that creates file names that doesn't fit into 8.3 format (see http://en.wikipedia.org/wiki/8.3_filename ). All files must placed in root directory as folders are not supported by the audio library.

To convert audio files I suggest the use of SoX from http://sox.sourceforge.net .

Windows users

Windows users should download from there the ZIP distribution and unzip it to the libraries/SimpleSDAudio/tools folder. Afterwards they can drag and drop .wav files to the appropriate batch files to start the conversion. The converted files will end up in folder "converted".

Linux users

Linux users should compile SoX from source or use their favorite package manager to install SoX. I recommend to use the following line for conversions:

sox inputfile.wav --norm=-1 -e unsigned-integer -b 8 -r 31250 -c 1 -t raw outputfile.raw

Change the following according to your needs:

  • For stereo change -c 1 to -c 2
  • For full rate use -r 62500 @ 16MHz, -r 31250 @ 8 MHz
  • For half rate use -r 31250 @ 16MHz, -r 15625 @ 8 MHz

The option --norm=-1 is used to avoid bad sounding clipping effects.

Hardware setup

The SD card should be connected to the SPI port of the controller. The chip select pin from the card can be connected to any free digital pin, but if pin 4 is used on Arduinos you don't have to adjust the source code. Many shields with SD card support like Ethernet-Shield will work.

According your mode configuration, one or two pins are used for audio output. This pins can not be changed and are different between different Arduino boards. For ATmega168/328 based plattforms those are pins 9 and 10. For ATmega1280/2560 those are pins 44 and 45. For other plattforms look into the file SimpleSDAudio.h.

Be careful that the audio output pins are digital ports that carry a positive voltage between 0V and 5V. It is not a good idea to have a DC voltage at line-inputs or smaller speakers as there will be a steady current flow. Therefore at least a resistor and/or a capacitor should be connected in series. For a start use at least 100 ohm or a capacitor between 100nF and 100uF. For line inputs use a voltage divider or poti to reduce the voltage.

API reference

Constants

Here is an overview of the constants used in the library.

#define SSDA_VERSIONSTRING      "1.00"

// Sound Mode Flags
#define SSDA_MODE_FULLRATE      0x00    // 62.500 kHz @ 16 MHz, 31.250 kHz @ 8 MHz
#define SSDA_MODE_HALFRATE      0x10    // 31.250 kHz @ 16 MHz, 15.625 kHz @ 8 MHz

#define SSDA_MODE_MONO          0x00    // Use only 1st PWM pin
#define SSDA_MODE_STEREO        0x01    // Use both PWM pins for stereo output
#define SSDA_MODE_MONO_BRIDGE   0x02    // Use both PWM pins for more power

// Error codes from SimpleSDAudio, see other sd_l*.h for more error codes
#define SSDA_ERROR_NULL         0x80    // Null pointer
#define SSDA_ERROR_BUFTOSMALL   0x81    // Buffer to small
#define SSDA_ERROR_NOT_INIT     0x82    // System not initialized properly

Class name and default instance

class SdPlayClass { ... }
extern SdPlayClass SdPlay;

The name of the class is SdPlayClass. One instance is already created for use and is named SdPlay.

Public class functions

init()

boolean init(uint8_t soundMode);

Call this to initialze the library and set sound mode. This function will also aquire the needed buffer (if not already set manually using setWorkBuffer), initialize SD card and sets up all used pins.

A combination of the following flags must be provided as argument (combine via or-ing):

Sample rate setting flags

  • SSDA_MODE_FULLRATE - 62.500 kHz @ 16 MHz, 31.250 kHz @ 8 MHz
  • SSDA_MODE_HALFRATE - 31.250 kHz @ 16 MHz, 15.625 kHz @ 8 MHz

Output channel configuration flags

  • SSDA_MODE_MONO - Use only 1st PWM pin
  • SSDA_MODE_STEREO - Use both PWM pins for stereo output
  • SSDA_MODE_MONO_BRIDGE - Use both PWM pins for more power

The function return true if successfull, false if an error occured. You can use getLastError() to retrieve the error code. Typical reasons for errors are wrong SD card connection or too low RAM (1k heap required) for internal buffer available.

setFile()

boolean setFile(char *fileName);

After init was successfull, call this to select audio file by providing the filename in 8.3 format.

The function return true if successfull, false if an error occured. You can use getLastError() to retrieve the error code. Typical reasons for errors are that the file was not found.

worker()

void worker(void); 

Call this continually at least as long as the audio playback is running. This function fills the internal playback buffer by reading the next sectors from SD card. You can´t call this function too often, but a buffer underrun can occur when the time between two calls are too long.

play()

void play(void);

If audio is not playing, playing will be started. If it is already playing, it will start playing from zero again.

stop()

void stop(void);

Stops playback if playing, sets playposition to zero.

pause()

void pause(void);

Pauses playing if not playing, resumes playing if was paused.

setSDCSPin()

void setSDCSPin(uint8_t csPin);

Call this before init to set SD-Cards CS-Pin to other than default.

setWorkBuffer()

void setWorkBuffer(uint8_t *pBuf, uint16_t bufSize);

Call this if you want to use your own buffer (at least 1024 bytes, must be multiple of 512). Call this before init and then init will use this buffer instead using malloc to create its own.

deInit()

void deInit(void);

Call this to free resources like buffer, release SD card pins, audio interrupts and audio pins.

dir()

void dir(void (*callback)(char *));

Output the directory of the SD card. A pointer to a callback function must be provided. The callback function is called once for every file found in the root directory of the card. The strings contain zero-termination but no linefeeds.

Usage example:

...
// setup global callback function
void dir_callback(char *buf) {
 Serial.println(buf);
}
...

   // somewhere after initialization
   SdPlay.dir(&dir_callback);

isStopped(), isPlaying(), isPaused()

boolean isStopped(void);
boolean isPlaying(void);
boolean isPaused(void);

Returns the current state of the playback.

isUnderrunOccured()

boolean isUnderrunOccured(void);

Returns if the internal underrun-flag is set and clears it. If audio sounds strange or has dropouts, test if underruns are the cause.

getLastError()

uint8_t getLastError(void);

Retrieve the last error code and clears it. To analyse the error reason, take a look also at the files sd_l1.h and sd_l2.h of the library to find the meaning of the code.