cd rom as a transport?

mikk

Member
2002-01-08 12:41 am
Hi

While putting together a system for the bedroom, it seems i need another cd player. i have a few cd rom units from pc's i've upgraded over the past years, and wondered if anyone could shed some light on how to use these in standalone mode.

I know there is a very nice phillips unit people are using for diy projects, but that would be a bit of overkill for just listening to a couple of tracks before turning out the light.

I'm sure one could use a basic stamp or other pic based computer to drive the cd conventionally, but i'd like to just get some insight into how to start the unit playing, skip forward and back and so on, with out getting into IDE.

Thanks!

Michael Andersen
 
mikk, I swear I have seen a question like that just recently. I can't remember whether it was here on this forum or somewhere else. Oh well.

Using my general knowledge of PCs and peripherals, I can tell you that there is standalone circuitry inside the drive to play Redbook audio CDs. There is nearly always some small pins on the back of the drive where the the audio out lines are. You basically summarized the difficulty well when you said that the hard part is asserting some control over the play functions.

I am guessing that normally this control is sent via the IDE interface. Obviously, that is a very complicated solution in "standalone" mode. My suggestion is to pop the top off and look at the components inside. Try and cross reference the chips you see with some datasheets on the web. If you are lucky, you can find ones that have pin assignments to common audio functions, such as play, forward, back, stop, etc. You could wire contact switches to each pin to use as your controls (use current limiting resistors if you take this approach).

I don't think there exists a solution without doing some soldering. I have seen units with audio controls on the front panel, but those are rare. On the upside, I might argue that the physical transport on those drives should be quite robust, since data "jitter" requirements are more strict than most commercial audio players.

Good luck.
 

amoyan

Member
2001-12-07 12:13 pm
I use a cd-rom to drive an ART DI/O. I have not encountered a CD (redbook, ie) that will not play in this CD-ROM. All the CD-ROMs that I have will play CDs when powered. You just need 5V/12V. The buttons on the front-panel will play a CD or skip forward, general.
 
The D/A and analog circuits in a CD-ROM are not of the highest quality for high-end. Almost any cd-rom has an analog output at the back. (I havent seen any without it yet and I have seen many many CD-roms)

For best sound quality a separate D/A is neccesary. Some CD-roms have both analog and digital outputs (especially IDE-CRroms)

According to some people even the cd-transport has influence on the soundquality, despite the fact that correction circuits can provide a LOSSLESS error correction upon reading a CR-rom.

I use a cdrom in my car without any complaints though, but I have a feeling that the soundquality is a bit inferior to ordinary
cdplayers, because of the cheaper circuits probably. Mine is a SCSI-thoug, which can be used as a stand alone cd-layer with
start, stop and pause buttons. (do you use more , really ?)

/rickard
 

mikk

Member
2002-01-08 12:41 am
Wow! Thankyou all for the very rapid responses.

Looks like i'm going to take SilverPikes suggestion and see what i can find inside.

I remember i've had cdroms that had play and skip bottons, but nothing i have here now does (not even the scssi r/w).

I guess i get to learn more than i was planning on :)

The copy protection issue will be irratiating, but i guess one could write a program to bit copy the cd to the hard drive, then write back to a cr-r, ensuring a proper TOC. (i hate carrying my original cd's with me in the car, too easy to "loose").

Thankyou again all for the responses!

Michael Andersen
 
The ATAPI/IDE interface isn't *that* complicated. I think it extremely unlikely that you'll find anything on the drive which will give you a direct command interface for CD commands, though you might find an I2S bus somewhere, from which you could potentially obtain a direct PCM digital audio output. If you're willing to use a microcontroller, you can control the drive using the IDE bus. With some ambition, you can also make the thing double as an MP3 player.

Here are a few links to diy mp3 players in which a cd-rom drive is controlled by a microcontroller and an single-chip mp3 decoder is used (the best is apparently the MAS3507D):

http://www.mp3ar.com/
http://www.mp3projects.com/proj-standalone.htm

I believe the first link is a project which will play both CD-DA and MP3...

Good luck! :)
 

mikk

Member
2002-01-08 12:41 am
Thanks for the sites. This is begining to look like a project tho. Already up to my antlers in microprocessors (oopic) for an automotive based project.

I'd like to look into the mp3/cd-da player, but for the short term, looks like i'm just going to hit future shop for a player. I'll pick away at it over the winter.