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The Older MP3 Player Design

Making Your Own High Capacity MP3 Player

I got tired (impatient) of waiting, so I rolled my own. Here's a photo.

It's actually not all that difficult to make your own player. The MAS3507D decoder chip does all the hard work of turning a MP3 bitstream into the decoded audio. A CS4327 DAC provides the audio output, though many other audio DAC chips will work. One of my 8051 development boards reads the hard drive and pumps the bitstream into the MP3 decoder chip. The decoder only runs on 3 volts, so there are a couple logic level conversion issues.

Here is a larger photo of just the player. The hard drive is in the middle, the 8051 development board with IDE interface, MP3 decoder, and audio output is on the top, and a power supply board is located on the bottom. Vent holes allow the power supply and hard drive to keep cool.

Cool Stuff

• Plays for a long time. I used a spare 1.2 gig hard drive and loaded it with 17 hours of MP3s, but the design can easily handle any modern IDE drive. I'll probably buy a 20 gig drive for this thing someday soon.
• It sounds great. The MP3 decoder chip and DAC are really quite easy to use and they sound great. Both manipulate 20 bit data.
• Reasonably small size. About half of the box is the power supply, which was a spare one laying in my junk drawer. Most of the development board circuitry is not necessary for playback. The design could be much smaller.
• The top and bottom pushbuttons jump to the next or previous track.
• The middle pushbutton pauses and restarts playback.
• I can keep listening while rebooting between Linux and Windows, or while playing games, or in my car!

Things To Improve Upon

• The 8051 can't play 256k and 320k bitrates. Bitrates 192k and lower work fine, and variable bitrates work fine.
• There is currently no buffering, beyond a single 512 byte sector.
• If you shake it (fairly hard), the drive will have higher read latency, and without much buffering, little gaps in the playback can happen. Walking with it is no problem, but jogging won't work. Works fine in my car on the front seat, but probably would need shock mounting if it were bolted down.
• The firmware requires the MP3 files to be written directly to the drive, with a table in the first several sectors to indicate where each track begins. I wrote a little program to copy the files to the drive, but it requires all of them to be copied at once. You can't easily add and remove files. The program runs in Linux. There is currently no windows version.
• Power supply needs 120 volts AC. I've used it in my car with a small inverter. Should really design a 10-15 volt input supply for use in my car.
• There is no display and no support for playlists, categories, etc.
• The drive always spins, so it uses too much power to run from any small-size battery.
• Plastic enclosure looks nice, but it's a pain to remove the drive for loading new data.

Design Info (For Free)

Disclaimer: This code and design data is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.

The circuit board shown is the newer 8051 development board. The schematic and layout are available. Wrote a detailed page about the IDE interface, which is the circuitry on the right side of the photo, partially hidden by the ribbon cable. The circuits on the left side are the MAS3507D, a crystal oscillator for it, a Cyrstal Semiconductor DAC, and a couple chips to do the 5 volt to 3 volt logic level conversions. There is now schematic for this circuitry. The 8051 sends data to the MAS using its serial port, configured in "mode 0" (sync serial). See the 8051 datasheets for more info. I did not actually draw a schematic, but you can view Originally I did not have a nice schematic drawn, just these hand-drawn notes and sketches that I used when I built the player. Some close-up photos of the point-to-point wiring are available, in case I've forgot to document something.

Here is a copy of the firmware source code (assemble with as31). This code is intended to be used with my Paulmon2 monitor. To get a group of MP3 files onto the hard drive, you will need to use this little perl script that generates the raw hard drive image, in the linear sector format that the firmware uses, with a list of the starting sector addresses in the first 256 sectors of the drive. It's ugly, I know, but it does work, and unlike a lot of the other players you'll find on the net (see below), I am actually distributing the design data for free.

Future Plans

If you're interested in this project and/or want to have one of your own, please contact me. I'm interested in any feedback or ideas you may have.

Other Homebrew Players

• MP3 Projects Dot COM - A very nice site with links to many home built players -- Use This Link... this list is old and not maintained anymore.
• H-Mpeg, Der Player vor der Uberholsur - CDROM based, very nice looking hardware, pages in German
• SoundBastard public domain mp3 decoder - Photo of a nice-looking board.
• OSCAR (formerly at http://www.oscar-mp3.com)
• ELM Player - Flash memory based player
• MP3mobile
• EloLand
• Inmotion (formerly at http://www.jarcom.com/inmotion)
• carmp3
• MP3 CDPlayer (disappeared, was at http://www.zottl.com/)
• The KrazyKarl.com Car MP3 Player - PC Computer, Linux
• LCDAT - Linux Compressed Digital Audio Transport - PC Computer, Linux
• MP3 Discman - Student project, no visible results (9/Apr/2000) - Isn't Discman a registered trademark of Sony? (formerly at http://seniord.ee.iastate.edu/may0017/homepage.html)
• Portable MP3 Player - Student project, no visible results (9/Apr/2000).
• Hardware Assisted Playback