Re: floppy drive music player
From: worldcitizen (duncan_at_koyote.com)
Date: 02/26/05
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Date: 26 Feb 2005 10:10:31 -0800
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.
I would think that the spacing between the concurrent "tracks" would
cause considerably crosstalk between tracks. I also concur with the
person who suggested that you must use a bias signal to enable you to
record to your chosen media. This is very common practice on analog
audio recorders. You won't record squat without that bias signal.
Good luck on your project.
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