Re: floppy drive music player

From: Michael A. Terrell (mike.terrell_at_earthlink.net)
Date: 02/26/05 

Date: Sat, 26 Feb 2005 16:30:39 GMT

jesrandall wrote:
>
> I am trying to create a driver circuit to allow recording and playback of
> sound to a 3.5 inch floppy disk using a standard floppy disk drive...
>
> I know that normally information is recorded to the disk in a modulated
> format (specifically MFM - modified frequency modulation) and that it is
> normally stored in sectors and other logical structures. However, for my
> project, I want to record "raw" sound (no file format) directly to the
> disk (similar to the way information is stored on a record or cassette
> tape)
>
> I don't want to use exiting floppy drive controller chips, although I
> don't think these would help because they are designed around PC formats
> anyway (perhaps they could be modified), but I would like to avoid using
> them.
>
> If it helps, here is some of my current progress.
>
> I have set up a simple PIC microcontroller programmed to keep track of
> which track the drive is on and automatically increment the track after a
> revolution. This way I can record (starting on track 0 all the way to
> track 79 and then switch sides and go from 79 back to 0) Since the disk
> spins about 6 times per second (360RPM) that turns out to be about 26-27
> seconds of recording time. The microcontroller will eventually allow for
> simple control of record, pause, and playback functions. The problem I've
> run into and hopefully only, is that I am unable to record!! lol however I
> am able to "change" the information on the disk and presumably read it.
> Since I don't have an oscilloscope I have connected the read output of the
> disk drive to a piezo speaker and I listen for sound changes. The write
> process is set up like this: when the user wants to record, write enable
> is set low (which is the "go active" value (negative logic)) so then the
> drive writes to the disk whatever is on the write input pin....
>
> So....lets say I connect the write input to ground and write enable is
> enabled. It would seem like it would just record a blank space on the
> disk, wouldn't it??? But apparently this doesn't happen, instead it
> records a steady hissing noise (frequency is unknow, i don't have a
> frequency counter either...) when I connect the write data pin to positive
> the same thing happens. Using a 555 timer to generate tones I was able to
> make beat sounds during playback like hissssssssss-pop-----hisssss....etc.
> If I set the 555 timer to a very high frequency it produces almost
> complete quitness, but not quite there is still a little background noice.
> And finally, Once I have recorded that quiet space, I can tap the input on
> negative or positive while recording over it to produce clicks and pops
> that exactly match my tap rate.. similar to just connected a speaker to a
> battery. It would seem if all this happens I would be able to easily
> record music or atleast tones (faster beats/sec , thats determines the
> pitch of the tone), but it doesn't work.
>
> Does any body know anything about what actually happens when you record or
> write/read to a disk??
> I've read a lot about flux reversals and stuff like that but I was
> convinced music/sound could still be recorded in my way mentioned above.
> Has anyone else ever tried or succeeded doing this?? I would really like
> any information or suggestions.
> Thank you very much. I hope I was clear with my question. If you need any
> specifics answered about what I've already done I'd be happy to answer.

   How much recording time do you think you will get? at 300 rpm you
get 1/5 of a second per track. There are 80 tracks per side, so it
would be 16 seconds per side. You need a high frequency bias to record
low frequency audio. The bias should be 50 to 70 Khz and the level has
to match the magnetic media. You need to study the circuits in common
reel to reel or cassette recorders to wrap your mind around how analog
recording works.

   Digital recording is simpler. Saturate the magnetic media without
burning up the head then reverse polarity and repeat. After that it
becomes the problem of timing the transitions. 

-- 
Beware of those who post from srvinet.com!
Michael A. Terrell
Central Florida

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