Preparing SD Card for DFPlayer Mini

The first step in using the DFPlayer Mini is preparing an SD card that can be read by the module.

By the end of this article, you will have a compliant SD card with audio files on it, ready to be recognized by the DFPlayer Mini.

Overview

The primary audio source for the DFPlayer Mini is its internal SD card reader. The Micro SD card inserted into the reader must meet a few requirements for the DFPlayer Mini to recognize it:

• Size: DFPlayer Mini supports Micro SD cards with a maximum capacity of 32GB. If your SD card is larger than that, DFPlayer Mini cannot read it.
• Format: The Micro SD card must use the FAT16 or FAT32 file system. If the card is formatted with a different file system, such as the popular exFAT, DFPlayer Mini won’t be able to read it.
• Audio Format: DFPlayer Mini supports three audio file formats: MP3, WAV, and WMA. However, your audio files must also use the correct bit rates and encodings. Otherwise, DFPlayer Mini will not be able to process the audio files.
• Structure: Audio files must be organized in a specific folder structure on the Micro SD card. If this structure is not followed, DFPlayer Mini may fail to find your audio files or may not play the correct files.

1. Health-Checking the SD Card

If you purchased a brand-new Micro SD card, chances are you are already set to go: most Micro SD cards come pre-formatted with FAT32.

However, if your SD card has been used before in other projects, it may be configured in a way that prevents DFPlayer Mini from recognizing it. It could be using an incompatible file system, or its storage space may have been partitioned into multiple separate drives.

To reset an SD card to factory defaults, follow these steps:

1. Insert the Micro SD card into your PC. If the Micro SD card doesn’t fit, use an SD card adapter. If your PC doesn’t have an SD card reader slot, you can use an external SD adapter connected via USB.

   

2. Open Windows Explorer and identify the drive corresponding to your SD card.

   

Remove Partitions

If you see multiple new drives after inserting the SD card into your PC, the card has been partitioned. Even if you see just one drive, additional (hidden) partitions might still exist.

One simple way to ensure there are no partitions on your SD card is to use the free SD Card Formatter from the SD Card Consortium.

This tool is legitimate and comes from a trusted authority, but it lacks a valid digital signature and requires a full Windows Installer installation.

Changing drive partition configuration requires Administrator privileges.

Once the SD Card Formatter has formatted the drive, it will contain just a single partition. However, the SD Card Formatter won’t let you choose the file system it uses. On SD cards larger than 4GB, it defaults to exFAT, which is unsuitable for DFPlayer Mini.

Switch to FAT32 File System

To check the current file system used by your SD card, right-click its drive icon in Windows Explorer and choose Properties.

Verify that the SD card is using the FAT32 file system. If it shows exFAT (like in the picture), you need to reformat the SD card with the FAT32 file system. DFPlayer Mini (like most DIY components) cannot read exFAT.

SD Cards Up to 4GB

SD cards up to a size of 4GB can be directly converted to FAT32 using the built-in tools in Windows:

1. Open Windows Explorer. Identify the drive that represents your SD card. Right-click on the SD card drive in File Explorer and select Format...:

   

2. Select FAT32 as the File system, check the box for Quick Format, and then click Start. The formatting begins, and after a few seconds, the SD card is initialized with the FAT32 file system.

SD Cards Larger Than 4GB

SD cards with a capacity greater than 4GB cannot be converted to FAT32 using the native Windows system tools. You are then limited to the options exFAT and NTFS.

There is no technical reason for this limitation, so you can work around it with third-party tools (e.g., fat32format). In my tests, however, all tools I found were unreliable and did not work on my machine. I was unable to find the reason.

As a solution, I created a new PowerShell command named Show-Fat32Converter that opens a graphical dialog and lets you quickly format any removable drive of any size with the FAT32 file system in just a few seconds:

1. Get DoneLandTools:
   Download the free PowerShell module DoneLandTools:

   Install-Module -Name DoneLandTools -Scope CurrentUser
   

2. Re-Format SD Card:
   Open a PowerShell console, then run this command:

    Show-Fat32Converter
   

   This opens a dialog that lets you convert any SD card media to FAT32.

   

3. DoneLandTools can be removed as easily as it was added:

    Uninstall-Module -Name DoneLandTools
   

   Testing SD Card

The final step should be a quick test to ensure it works correctly. This test is important: SD cards can wear out over time, and it is not uncommon for older or low-quality SD cards to malfunction.

1. On your PC, copy a number of files (e.g., images, videos, or audio files) onto your SD card.
2. Eject the SD card, wait a moment, and then re-insert it.
3. Copy the files from your SD card into a temporary folder. Open the files to ensure they are intact.

2. Copying Audio Files Onto the SD Card

Next, copy the audio files you want DFPlayer Mini to play to your Micro SD card. You have several options for naming and organizing them.

File Naming

Audio file names must start with a three- or four-digit number:

• Prefix: DFPlayer Mini only looks at the file name prefix, which must be numerical. The remainder of the file name is ignored.
• Number of Digits: DFPlayer Mini expects either three or four digits, depending on where you store the file.
• Extension: DFPlayer Mini automatically looks for the file extensions mp3, wav, and wma. So, a file can be named 0001.mp3, 0023.wav, 1097 my song.mp3, 0345 another song.wma, and so on.

PS C:\> dir f:\ -Recurse -File


    Directory: F:\MP3


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a----          9/6/2022   2:30 AM        2415454 0001_fir1.wav
-a----         3/22/2024   3:41 AM         243488 0002_pressluft.wav
-a----         3/22/2024   3:41 AM         285662 0003 624 Land.wav
-a----         3/22/2024   3:41 AM         286826 0004 624 Stadt.wav

$sfs = New-Object -ComObject Scripting.FileSystemObject

Get-ChildItem -Path f:\ -Recurse -File | 
ForEach-Object {
  [PSCustomObject]@{
    'Long Name' = $_.Name
    '8.3 Name' = $sfs.GetFile($_.FullName).ShortPath | Split-Path -Leaf
  }
}

Long Name          8.3 Name    
---------          --------    
0001_fir1.wav      0001_F~1.WAV
0002_pressluft.wav 0002_P~1.WAV
0003 624 Land.wav  000362~1.WAV
0004 624 Stadt.wav 000462~1.WAV

Files can be stored at these locations on your SD Card:

In a nutshell:

• use the folder \MP3 by default if you plan to control DFPlayer Mini via microcontroller and UART.
• switch to numbered subfolders ( \00-\99) if you have a large number of files that you’d like to better organize into categories.

When you use push buttons to control DFPlayer Mini directly (without microcontroller), the folder structure is irrelevant. The buttons play all audio files - regardless of storage location - in the order in which they were originally copied to the SD card.

Get-ChildItem -Path c:\path_to_audio_files -File |
  Sort-Object -Property Name |
  Copy-Item -Path e:\  # adjust drive letter of SD Card

3. Verifying Audio File Formats

With the SD Card prepared and audio files copied onto it, you are ready to test-drive DFPlayer Mini.

Before you do, you may want to ensure that the audio files on your SD Card are using supported codecs and formats.

Supported Audio Formats

DFPlayer Mini can play back audio files in the formats MP3, WAV, and WMA provided they are encoded in the correct way:

So it is not sufficient to just select any .mp3, .wav, or .wma audio file. You must also ensure it uses the correct codec and is within supported bit rates.

This is especially important with .wav audio files: most use uncompressed PCM which is not supported by DFPlayer Mini due to its small buffer and the large audio file sizes. .wav files must use ADPCM which is a compressed format that reduces 16-bit uncompressed PCM to 4-bit compressed files, conveniently cutting down file sizes to 25%.

Examining Audio File Format

To ensure your audio files match the appropriate formats, you can use Get-AudioFileInfo from the PowerShell module DoneLandTools (see above). This tool internally uses the free open-source ffprobe.exe utility. On Windows, this utility is automatically downloaded if it is missing. On other operating systems, you can download it manually.

Here is PowerShell code which tests all your audio files on your SD Card (assuming the SD card is using drive letter F:):

Get-ChildItem -Path f:\ -Recurse -File | 
  Get-AudioFileInfo | 
  Select-Object -Property Name, CodecDisplayName, SampleRate, BitsPerSample, SizeKB |
  Format-Table

The result may look similar to this:

Name                      CodecDisplayName                SampleRate BitsPerSample SizeKB
----                      ----------------                ---------- ------------- ------
0006 AIRHORN_EQD.wav      PCM signed 16-bit little-endian      44100            16   10.4
0005 POLICE_WARNING.wav   PCM signed 16-bit little-endian      44100            16   40.7
0004 SIREN_PA20A_WAIL.wav PCM signed 16-bit little-endian      44100            16  411.6
0001 624 Stadt.wav        PCM signed 16-bit little-endian      48000            16  280.1
0002 624 Land.wav         PCM signed 16-bit little-endian      48000            16    279
0003 SIREN_2.wav          PCM signed 16-bit little-endian      44100            16   58.6

The result reveals that the audio files that I copied to my SD Card would not play in DFPlayer Mini: the .wav files use the uncompressed PCM signed 16-bit little-endian codec.

Converting Audio File Format

If you come across audio files that are incompatible with DFPlayer Mini, you can use tools to convert audio files to a more appropriate format.

For .wav files, for example, you can convert PCM signed 16-bit little-endian to ADPCM IMA WAV: while the sound quality remains the same, the now-compressed files require just 25% of their original storage space and can be played back in DFPlayer Mini.

Here is the new PowerShell command Convert-AudioWavFile from DoneLandTools that automatically converts all .wav audio files for you:

Get-ChildItem -Path f:\ -Recurse -File | 
  Convert-AudioWavFile 

This command internally uses the free open-source utility ffmpeg.exe. On Windows, this utility is automatically downloaded if it is missing. On other operating systems, you can download it manually.

WARNING: Convert-AudioWavFile is very powerful and performs an in-place conversion: any .wav files you select will be replaced with the new format. The old file is lost. If you’d like to keep the original file, add the parameter -OutPath, and specify a new file name.

F:\
└───Audio
        0002 624 Land.wav
        0003 SIREN_2.wav
        0004 SIREN_PA20A_WAIL.wav
        0005 POLICE_WARNING.wav
        0006 AIRHORN_EQD.wav
        0001 624 Stadt.wav

Get-ChildItem -Path f:\Audio -Recurse -File | 
Convert-AudioWavFile -OutPath {
  $parentFolder = $_.Directory.Parent.FullName
  $filename = $_.Name
  "$parentFolder\MP3\$filename".Replace('\\','\')
} 

F:\
├───Audio
│       0002 624 Land.wav
│       0003 SIREN_2.wav
│       0004 SIREN_PA20A_WAIL.wav
│       0005 POLICE_WARNING.wav
│       0006 AIRHORN_EQD.wav
│       0001 624 Stadt.wav
│
└───MP3
        0002 624 Land.wav
        0003 SIREN_2.wav
        0004 SIREN_PA20A_WAIL.wav
        0005 POLICE_WARNING.wav
        0006 AIRHORN_EQD.wav
        0001 624 Stadt.wav

Once the conversion is complete, you can recheck the audio files to confirm that the codec has been changed successfully. As a bonus, the file sizes will have been significantly reduced — typically to about a quarter of their original size due to the compression process, making it more efficient for playback with DFPlayer Mini.

Name                      CodecDisplayName SampleRate BitsPerSample SizeKB
----                      ---------------- ---------- ------------- ------
0006 AIRHORN_EQD.wav      ADPCM IMA WAV         44100             4    3.1
0005 POLICE_WARNING.wav   ADPCM IMA WAV         44100             4   11.1
0004 SIREN_PA20A_WAIL.wav ADPCM IMA WAV         44100             4  104.1
0001 624 Stadt.wav        ADPCM IMA WAV         44100             4   65.1
0002 624 Land.wav         ADPCM IMA WAV         44100             4   65.1
0003 SIREN_2.wav          ADPCM IMA WAV         44100             4   15.1

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