MP3 disassembly: tech for thrifty tune-toters
Prying Eyes looks inside a low-end digital-audio player.
By Brian Dipert, Senior Technical Editor -- EDN, July 6, 2006
"Free with $75 purchase." That's the coupon that, after I bought a laser-printer toner cartridge, also delivered the OD-128MP3 (also known as the MP3-818) portable digital-audio player to my door. The price sure is music to my ears, especially considering that Office Depot normally lists the player for $69.99. The features aren't too shabby either: MP3 and WMA audio-codec support, an LCD (take that, iPod Shuffle!), and even voice-recording capability. What's inside the 1.75×3×0.75-in. silver case?
Photo gallery
Click on any of the images below to see an extreme closeup. You'll also find links to the full-size images within the text of the article.
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I couldn't find any good shots of the OD-128MP3 on the Internet, so I took some myself. Here they are for your perusal; , , , and . Removing four Phillips-head screws gained me access to the unit's insides. Here's the , showing the LCD window and the backside of the front-panel button array. Turning my attention to the guts of the player, I encountered the buttons' matching contacts and was surprised to discover that the monochrome LCD is from its bright blue companion backlight. The two devices press together when the MP3-818 is assembled; in , I've simulated the mating via a piece of tape.
Removing four more screws and gingerly wriggling the minimal-trace circuit board out of the case gained me visual access to . The AAA battery bracket dominates the landscape. The microphone is in the bottom right corner of the board and, I presume, much of the circuitry above it is for mic input and headphone output filtering and amplification.
Considering the "made in China" moniker on the MP3-818's packaging, I strongly suspected I'd find homegrown silicon inside. And I was right; a 24-bit Actions Semiconductor ATJ2051, operating at 72 MIPS and based on a Z80 core, resides to the left of the battery bracket and runs the show. Members of the ATJ20xx family differ from each other via features such as multichannel recording, hardware-accelerated real-time MP3 encoding, and enhanced system connectivity.
Between the ATJ2051 and the USB connector resides the sole standalone memory chip, a 1-Gbit Hynix flash memory. I presume this device both holds audio files and the firmware image, because the ATJ2051 supports booting from NAND flash memory.
The MP3-818 presents itself as a USB memory device to a connected PC, enabling the user to use it to store general-purpose files in addition to music. This configuration decision, however, renders the MP3-818 incapable of supporting "DRM'd" WMA files (those protected by the Windows Media digital-rights-management system).
The system design is both highly integrated and quite rugged; it survived my disassembly-and-reassembly sequence with aplomb.
A quick aside: Those of you considering a flash-based portable audio player might be interested in reading through this recently-published eight-unit shootout by Ars Technica.
Author information
You can reach Senior Technical Editor Brian Dipert at 1-916-760-0159, bdipert@edn.com, and www.bdipert.com.
Editor's note
The above is an extended version of an article that appeared in shorter form in the print edition of EDN. This PDF file shows the printed version.
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I'm helping someone troubleshoot their mp3-818... i've tried it with both xp and vista, when it is plugged in via mini-usb it simply turns off, upon unplugging it turns back on! (if its in an off state it stays off and whe unplugged turns back on.) it has been tried with fresh batteries.
obviously because it is off, there is no message on the computer what-so-ever. has anyone else had this problem? any ideas? seems like a hardware issue to me. thanks!
omatzyo - 2007-12-3 08:09:00 PDT -
please help i have a mp3-818 and can not figure out how to download music from my windows media player or anything else for that matter. If anyone can help it would be greatly appreciated. thanks
Emilia Tejo - 2007-23-2 19:28:00 PST -
Well, I'm another mom that got the OD-128MP3W and I have Windows XP 2002. I was just as frustrated as y'all, until I decided to install the '98 software anyway. Guess what...it worked! Also, the manual is on the disk. I'm not saying it will work for you guys, but you might try it. I've successfully loaded the MP3 for my daughter and she's "rocking out"!
Akiko - 2007-19-2 10:38:00 PST -
I received a free MP3 OD-128MP3W. $20 from Office Depot. I understand this is a "cheap one". But still I would like to be able to use it. It didn't come with a manual. How do I get one?
Jan Bulla - 2007-17-2 18:41:00 PST -
My son received an OD-128MP3W for Christmas. I am running Windows XP and it does not recognize the device. The disk that came with it looks to be a zip drive and states on it NOT to download it unless you have Windows 98. My computer does not allow for the disc provided (being it is so small). Is there any place I can go to download the software so that it recognizes the device? I already have iTunes because my daughter has an iPod, however, I cannot export the playlist onto the new MP3 Player... UGH!!!
Bobbi Zidar - 2007-9-1 15:16:00 PST
