Does anybody know how to make a SD-card only type mp3 player with a line out?

I'm looking for a way to play mp3's on any audio equipment that accepts aux in or something. Doesn't need to have anything flashy, just a little box, bulletproof,good sound quality, that can handle SD cards (4GB support should be enough, but more is always better). Of course it will also need the basic buttons on it for play/stop/prev/next.

How hard/expensive is this to make and how to do the actual mp3 to audio conversion? (I have no experience with chip programming)

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I know that MAKE magazine had a DIY MP3 player kit that you could buy from them, but it was very expensive compared to buying a ready made player. I have also seen other schematics out there via magazines and I also think that there was one made with one of the major microcontrollers. If you search for them, you should find them. Problem is, like the others have told you and I said above, the cost is quite a bit more than a manufactured unit.

Qa
AlexHRG (author) 5 years ago
Thanks for the replies!

I do have an additional question, i know a bit of electrics and electronics, but i'm not familiar with audio specifically. I was led to believe that the headphone out should not be used as a line out? The difference should be if there is a power source located after or not.

But yes, i'll have to concede and just get a working mp3player and use that, DIY is only effective when one cannot find exactly what one needs and most players on the market are pretty good and often have more functionality.

I'll check into the Sansa product line :-)
I have been using headphone outputs since the days of the original Walkman(s) in order to play anything from AM/FM/Tape/CD/MP3's/etc. on my stereo system(s).

There are several reasons why purists/snide professionals tell you not to use them.

1.) They are not at a constant level and you run the risk of either overdriving the input, causing distortion or maybe even damaging the input if the level is high enough, or the level is low and you may not be able to compensate enough for that low level.
2.) The impedance of the output is usually between 32 ohms and 100+- ohms while line level inputs are somewhere around 10,000 (10K) ohms. This mismatch tends to cause certain problems, such as not being able to properly drive the input (see #1 above) or coloration of the sound before it even gets to the amplification stage.

All that can be said is that if you experiment with your player, using an adapter cable (usually 1/8" (3.5mm) stereo plug to whatever your inputs are - usually stereo phono or 1/4" (6.5mm?) stereo phone plug) and starting with your player on 0 (zero) volume and slowly increasing to a level similar to a like source (actual line level source playing the same music). Once you find that matching level, write it down, memorize it, tattoo it on your forehead (nah, not really), do whatever you need to in order to have that info handy. Now switch between the player and the line level source and see if you can tell the difference in quality. If not, don't worry about it and be happy you now have your MP3 player as an additional source. If you can discern a very notable difference, then you can look for an impedance matching circuit to put between the player and the line input.

My bet is you will be just fine.

Qa
frollard5 years ago
mp3 decode/DAC is actually rather difficult as 'diy' goes; it's cheaper/easier to pick up a small mp3 player.

I know many many good reviews (from several friends) who really like the SANSA clip. It's tiny, long play time, play while charging, headphone out, small simple screen, sd support (micro I believe)...and inexpensive. 4gb internal 45 usd.

http://ca.sandisk.com/products/sansa-music-and-video-players/sandisk-sansa-clipplus-mp3-player
Burf frollard5 years ago
+1 on the Sansa. I have two Sansa Clips+ and a Sansa Fuze. I put my old iPod away because the Sansas have better sound quality than the iPod and the three of them combined cost less than 1/2 what a new iPod costs.
There are custom chips for the decoder part - look on Google for "Mp3 decoder IC", there are a lot of chinese makers. Atmel USED to do a part for it, I don't know if they still do. You need to provide some interface glue - I'm not sure if the SD card interface is provided on the decoder, or if you have to stream it yourself.

Or just do what Frollard says !