Designing my own floppy drive and controller...

Thread Starter

AnalogDigitalDesigner

Joined Jan 22, 2018
121
Hello. I am a very friendly person, and I am trying to make friends here.

I am one of those persons that needs to build their things from scratch, just for the magnificent beauty of understanding how they work, getting close to the metal, and for the satisfaction of knowing you have built it from scratch.

I want to build a floppy drive from scratch. Why ? Because I have a thing for floppy drives. I think they are magnificent inventions.

The thing is that I don't really know how they work. Just barely. What I know is that they work with flux changes. For example, to write a sequence of data, 0's, and 1's, are represented by flux reversals. But I don't know the specifics of that. Is there a reference flux at the start of the data say for a 1, and then any reversal after that is a 0, and no reversal is a 1 ?

Also I know that the clock is scrambled into the data. How does that work?

Do you know of any nice documents I could read in order to understand this stuff?

Thanks my friends

With a lot (I really mean a lot) of LOVE..................

Your friend Melfice
 

Papabravo

Joined Feb 24, 2006
15,765
I made a discrete controller once upon a time (ca. 1977) that involved using a bipolar PROM as part of a state machine for the data separator. I binned my notes and drawings in 2014 when I retired and had to downsize. Can't remember much about how I did it -- sorry.
 

MrAl

Joined Jun 17, 2014
8,149
Hello. I am a very friendly person, and I am trying to make friends here.

I am one of those persons that needs to build their things from scratch, just for the magnificent beauty of understanding how they work, getting close to the metal, and for the satisfaction of knowing you have built it from scratch.

I want to build a floppy drive from scratch. Why ? Because I have a thing for floppy drives. I think they are magnificent inventions.

The thing is that I don't really know how they work. Just barely. What I know is that they work with flux changes. For example, to write a sequence of data, 0's, and 1's, are represented by flux reversals. But I don't know the specifics of that. Is there a reference flux at the start of the data say for a 1, and then any reversal after that is a 0, and no reversal is a 1 ?

Also I know that the clock is scrambled into the data. How does that work?

Do you know of any nice documents I could read in order to understand this stuff?

Thanks my friends

With a lot (I really mean a lot) of LOVE..................

Your friend Melfice
Hello there,

I used to do stuff like that too until i realized that i was wasting a lot of time on stuff that was already built.

The last time i had direct contact with any development related to a floppy drive was back in the late 1980's so i dont remember much. I remember the software had to be timed very very carefully, with a stream of NOP's with a RET at the end and the stream length would have to change dynamically depending on the speed of the motor which meant it had to change to keep the read's synced with the turning of the disk even if the speed changed a little. So for one run you might see 50 NOP's and a RET, then the next run might be 49 NOP's then a RET, etc. The platform was a Z80 microprocessor.

Do you mean you want to design the entire box even the case and shafts and motor and even the read/write head? Or just the software?

You might start by trying to create software for a cassette tape drive, which can be an ordinary cassette recorder. Try to write data from your host computer or uC to the recorder and then read it back.
 

Thread Starter

AnalogDigitalDesigner

Joined Jan 22, 2018
121
Hello there,

I used to do stuff like that too until i realized that i was wasting a lot of time on stuff that was already built.

The last time i had direct contact with any development related to a floppy drive was back in the late 1980's so i dont remember much. I remember the software had to be timed very very carefully, with a stream of NOP's with a RET at the end and the stream length would have to change dynamically depending on the speed of the motor which meant it had to change to keep the read's synced with the turning of the disk even if the speed changed a little. So for one run you might see 50 NOP's and a RET, then the next run might be 49 NOP's then a RET, etc. The platform was a Z80 microprocessor.

Do you mean you want to design the entire box even the case and shafts and motor and even the read/write head? Or just the software?

You might start by trying to create software for a cassette tape drive, which can be an ordinary cassette recorder. Try to write data from your host computer or uC to the recorder and then read it back.

Time is never wasted if you are learning. Specially if you intend to work in that area. For example I study IC design. IC's are already invented and done before. But I intend to work in the industry designing IC's.
 

LesJones

Joined Jan 8, 2017
3,133
I don't think you realise how big a project this is going to be. First how do you plan to make the read/write head ?
When I was using floppy drives (In the 1980s) with a Z80 system (First 8" then 5.25" then 3.5") I would not even thought about building a controller chip from scratch. I used a WD1772 chip. This is a link to the data sheet on that chip. How many normal logic chips do you think you would need to emulate the functions of that ? Reading this data sheet you should realise how complex a project this is. If you expect someone else to google for information for you you are not prepared to put much effort in to the project.

Les.
 

profbuxton

Joined Feb 21, 2014
419
Build a floppy drive from scratch?? You haven't even said what size. But go right ahead. I would start by designing all the metalwork using Autocad or such. Once you have the metalwork sorted.you can start on the logic once you have decided on the format etc.
Do let us know when you have one made. I'm sure they will be plenty of buyers.
 

MrAl

Joined Jun 17, 2014
8,149
Time is never wasted if you are learning. Specially if you intend to work in that area. For example I study IC design. IC's are already invented and done before. But I intend to work in the industry designing IC's.
Hi,

Apparently you took my post personally. I was talking about myself and referring to my personal needs. I find now in my older age that cutting time by not repeating things that were already done in the past frees up time for me to do other things that improves my own life. There are things that either have not been done yet or have been done that are not done very well so i like to tackle those jobs. When i was younger i did repeat many things too for a learning experience. For a simple example i built my own miniature 40 position rotary switch from plain stock materials like a PC board and guitar wire and brass and plastic rod stock, and even made my own bolts from threading steel nails. I also built or improved my own test equipment, for example an 8 digit frequency counter when there were plenty of them on the market already.

That's great if you want to learn from this.
So what part of the device do you intend to design, like are you going to design the moving parts too or just electrical or ... ?
For example do you intend to design the little button that you press to eject the disk too, which is usually made of plastic?
I am trying to get an idea how much of the design you want to do yourself. Also, where you get your supplies from such as metals, electronic parts, etc., and what kind of electronic parts you would accept and not design yourself such as the controller chip that Les brought up.
 
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atferrari

Joined Jan 6, 2004
4,278
When I was using floppy drives (In the 1980s) with a Z80 system (First 8" then 5.25" then 3.5") I would not even thought about building a controller chip from scratch. I used a WD1772 chip. This is a link to the data sheet on that chip. How many normal logic chips do you think you would need to emulate the functions of that? Les.
Maybe this much, I guess:

/EDIT
Replaced the original picture with a slightly better one.

The drive is a Shugart SA410. Bought two of them when calling Newport News (or maybe Hampton Roads?).

Brand new, never used them because they were already obsolete. No guts to ditch them. :(

EDIT/

View attachment 158240

20180818_084154.jpg
 
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MrAl

Joined Jun 17, 2014
8,149
Hi,

Interesting board.
Even my old Z80 based computer used a floppy controller chip, and the DOS was floppy based (chuckle) and no hard drive. The Op Sys was about 40k bytes or something like that. The text editor i purchased, and it was about 20k bytes i think but worked very well. I used that computer for several years along with a dot matrix line printer. No mouse either, just keyboard.
My Z80 based controller board was completely home made though and was a fresh start-from-nothing design except of course for the Z80 cpu and support chips. Professionally though i was involved in a computer system design that used one FULL pc board for the CPU alone. That is one entire card for the CPU and that's not a motherboard, that is a CPU made from discrete 7400 series TTL. The other boards in the system were more or less peripherals. That was before single chip CPU's became more popular.

But i am one of the last people who would be against building your own stuff. I built my own stuff for years and years. I just recommend now that you weight the time it will take to get to the final goal with the time you nave to do other things that could be more worthwhile. For a student though repetition is probably inevitable.
 

Thread Starter

AnalogDigitalDesigner

Joined Jan 22, 2018
121
Hi,

Interesting board.
Even my old Z80 based computer used a floppy controller chip, and the DOS was floppy based (chuckle) and no hard drive. The Op Sys was about 40k bytes or something like that. The text editor i purchased, and it was about 20k bytes i think but worked very well. I used that computer for several years along with a dot matrix line printer. No mouse either, just keyboard.
My Z80 based controller board was completely home made though and was a fresh start-from-nothing design except of course for the Z80 cpu and support chips. Professionally though i was involved in a computer system design that used one FULL pc board for the CPU alone. That is one entire card for the CPU and that's not a motherboard, that is a CPU made from discrete 7400 series TTL. The other boards in the system were more or less peripherals. That was before single chip CPU's became more popular.

But i am one of the last people who would be against building your own stuff. I built my own stuff for years and years. I just recommend now that you weight the time it will take to get to the final goal with the time you nave to do other things that could be more worthwhile. For a student though repetition is probably inevitable.
what i feel is that God has a message for you through me. God says that you are a good soul and that much awaits you in heaven.

God bless MrAi.
 

AnalogKid

Joined Aug 1, 2013
9,177
Even my old Z80 based computer used a floppy controller chip,
Not the same thing. The image is the electronics in the drive, not the mating electronics in the computer. The drive electronics did not lend themselves to high levels of integration because of a) all of the analog stuff; and b) all of the patent stuff. At the all-digital, industry-standard drive/computer interface, things were much easier to compress into one chip.

The original 8" floppy disk drive was invented at IBM to take voice dictation. It was their way of getting around Philips patents for the audio cassette, also originally invented for office dictation. The System/360 mainframe guys latched on to it because they didn't want to use paper tape as the boot loader.

To the OP: The original floppy disk drive took five years to go from initial concept to production. Granted that there is no development phase for your project because all of the mechanical and electronic aspects already are standardized, but there is no way an experienced professional could do it single-handed in less than 1-2 years. BTW, how good of a machinist are you, and how good is your mill?

ak
 
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This https://en.wikipedia.org/wiki/Modified_Frequency_Modulation and it's references gets you up to speed quickly.

There were 8" hard sectored floppies and the MAC used used variable speed to write some of their disks. You can keep the bit rate constant then.

I did grow up in the ERA of removeable hard drives the size of washing machines and a "head crash" was a head crash. The drives were a little bit bigger the size of a cake dish and cover. http://www.columbia.edu/cu/computinghistory/rp04.html
 

MrAl

Joined Jun 17, 2014
8,149
what i feel is that God has a message for you through me. God says that you are a good soul and that much awaits you in heaven.

God bless MrAi.
Hello,

What a nice thing to say.
It must be the same for you too then :)

What i was trying to find out originally was how much of the total design you want to do yourself. There are so many aspects of this one.
 

MrAl

Joined Jun 17, 2014
8,149
Not the same thing. The image is the electronics in the drive, not the mating electronics in the computer. The drive electronics did not lend themselves to high levels of integration because of a) all of the analog stuff; and b) all of the patent stuff. At the all-digital, industry-standard drive/computer interface, things were much easier to compress into one chip.

The original 8" floppy disk drive was invented at IBM to take voice dictation. It was their way of getting around Philips patents for the audio cassette, also originally invented for office dictation. The System/360 mainframe guys latched on to it because they didn't want to use paper tape as the boot loader.

To the OP: The original floppy disk drive took five years to go from initial concept to production. Granted that there is no development phase for your project because all of the mechanical and electronic aspects already are standardized, but there is no way an experienced professional could do it single-handed in less than 1-2 years. BTW, how good of a machinist are you, and how good is your mill?

ak
Hi,

No problem :)
 
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