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floppy drive music player

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.

Reply to
jesrandall
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Given the type of head used your best bet is to use either a digital or an FM version of your audio signal to record.

I suppose FM will be easier.

An HD floppy drive is 300 RPM and 100 kbits per track. A bit is a flux reversal with MFM so your carrier should be somewhere between 250 and

500 KHz.

Just hope that the drive doesn't do any 'signal alignment' for you...

Thomas

Reply to
Zak

thanks thomas, your suggestions are very helpful, i hope it works. Are there any sites or books that I can learn more about floppy drive details such as the bits/track you posted.

You suggested I use a digital signal, but I actually already am... I havn't tried using analogue audio yet...I'm just trying to record digital tones produced by 555 timer, right now. The FM idea sounds good... but why can't I use the low frequency (2000-3000hz) audio sound im using write now... is there a physical attribute with the floppy drive heads that prevents this.... I don't mind using FM but I'd like to understand why I have to. Also, the strange effect I got... when I held the write input low but still got a tone on the read pin. I know according to MFM format all zeros are mixed with a clocking signal (explainging the tone I got), but does the drive automatically convert incoming signals into MFM format??? Thanks a lot for helping me...

-Jesrandall

Reply to
jesrandall

Are

details

digital

but why

write

why I

input low

all

but

format???

I faintly recall that floppies had a very simple write circuit- don't recall the part-number, but the read circuit companion was the Motorola

3470. The head was center-tapped and the two-phase drive was generated by the 34???. Even after floppies' electronics were reduced to One Big Chip, the original parts' functionality was kept. Sorry.... it's been a while. Wade
Reply to
wade_h

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
Reply to
Michael A. Terrell

playback of

modulated

is

my

the

cassette

formats

using

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after a

disk

26-27

for

I've

however I

it.

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write

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is

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able to

hissssssssss-pop-----hisssss....etc.

noice.

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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.

Reply to
worldcitizen

Look for floppy controller data sheets. The Western Digital WD1770 and similar (1771, 1791, etc) are early models, and with early technology the sata sheet may give a bit of an explanation.

I guessed you want to keep the drive electronics intact. That said the rotationa speed is too high and the head is too small to give appreciable bass response. Actually I thing the drive acts as a differentator: you feed it a signal which it will record, but it will respond with a pulse for every transition that you sent it.

No, you have to send data and clock yourself and separate them on the controller.

FM would write the clock, then a data (or not), another clock, another data and so on.

MFM would double the speed and leave out the clock is a data was just written if I remember correctly, thus keeping the frequency reasonable.

But the drives are made to read and write digital signals only -this is why I suggested FM.

Thomas

Reply to
Zak

thanks everyone for your suggestions. I will try encoding the sound through fm with a carrier frequency of 40-70khz... hopefully it works. I havn't picked up any "noticable" cross talk between the tracks. Since I have been able to record "pulses" and hear them on one track, but hear nothing on the adjacent track... hopefully I won't have any problems with interference.

Reply to
jesrandall

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