Floppy drive selector board

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Joined: Sun Sep 09, 2012 5:46 am
Location: Australia

Floppy drive selector board

Post by spags » Mon Apr 25, 2016 2:24 pm

This isn't really a feature request but I have this crazy idea of an add-on board (actually, more like a controller board) for Kryoflux but have neither the time, resources or knowledge to implement it. I suspect it may be quite costly as well, but I'm documenting it here for anyone to pursue should they feel so inclined.

I would guess that most Kryoflux owners have several drives in their collection. Whenever I find the need to use my Kryoflux, I pull out the bunch of drives I think I might need to use, connect everything up and use. Afterwards, I then disconnect it all and pack it away. I take care with plugging in and removing the floppy cable, but there will only be so many times that it can be used in this fashion before it starts failing.

My idea was to connect all of my drives to the Kryoflux and never need to disconnect them again. I wondered if there was such a thing as a floppy drive selector (like the old parallel printer selector boxes). I don't think there is and it would need to be a magical board where you feed it the 34-pin floppy cable with the 4-pin floppy power, and then it fans both of these to all the drives you have connected to it.

I realised that it wasn't going to be easy. There would be a set of drive selector buttons (so that you could pick which drive to use), but this board would need to be smart to make sure that it connects and disconnects the selected drive in the correct manner. It would need to have an onboard micro controller to handle this, as well as the Kryoflux USB connect/disconnect as well.

To control the connection for a single drive, this board would need to be able to control 17 (maybe 18 - don't know why pin 33 in the KF circuit diagram is not ground) data lines and 4 power lines for each drive (of course, with both sizes of connectors as well). Possibly the same types of buffer drivers could be used as found on the Kryoflux itself, but the power lines would probably need to be controlled by 2A relays. The 17/16 ground pins would be constantly connected between the board and the drives, so only the remaining 17/18 + 4 would need controlling. No ridiculous power supply would be required because only the board itself and the selected drive would be actively powered.

Such a board would be intended to operate the Kryoflux in single-drive mode. It would probably also be designed to switch up to 8 devices (for simplicity sake, say 1 Kryoflux board and 7 drives). If designed correctly, it could have its own type of daughter boards that allows for daisy chaining of those 7 drives to another set of 8 drives - one board could switch up to 57 devices. This would allow for advanced users or institutions to modularly upgrade their board to cater for the number of drives in their collection.

Disadvantages/Possible problems:
Noise - the use of the tri-state buffers should reduce this but with such a complex setup, noise seems likely especially towards the most distant drives in the topology.
Size/cost - the base board would probably be a little deeper than the Kryoflux and definitely much wider (one drive needs 3 buffers, the 34-pin connector, 2 or 4 relays and 2 different sizes power connectors - multiply all that by seven) - plus a bus to handle all that, then circuitry for the micro controller and selector buttons. The daughter boards would be slightly smaller, but at least since they would be the same they would be cheaper to produce in quantity.

Enclosures - home users could mount almost everything in a full-size ATX tower, pros could make huge dedicated drive enclosures/walls - one mains power in and one USB in.
Set and forget - no need to worry about connecting/disconnecting in the correct order.
Cost - while this would probably rival the cost of a Kryoflux itself, it means only one Kryoflux is required (as opposed to having multiple Kryoflux boards embedded in multiple different enclosures).
Double up - while it is intended for the Kryoflux to be used in single-drive mode, it may be possible to still use two drives per cable.

I'm sure there are things I have missed or show-stoppers, but that is the general idea.

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Re: Floppy drive selector board

Post by SomeGuy » Mon Apr 25, 2016 5:42 pm

You are over thinking it a bit. The Kryoflux already supports up to two floppy drives connected via a "standard" IBM PC twisted floppy cable.

Because the Kryoflux is generally treated as an archival tool for games, rather than an interoperability tool, I suspect many, including the developers, are happy with simply a 1.44mb 3.5" drive and a 1.2mb 5.25" drive. And because there are few copy protected titles on 3.5", even just a 1.2mb may be enough for most.

Although the way I use mine, it would be handy to have a 1.44mb 3.5, 1.2mb 5.25" and 360k 5.25" drive, all mounted in a mini ITX case like this: http://www.newegg.com/Product/Product.a ... 6811147131

That way the only time I would have to reconfigure anything is when I need to hook up my 8" drive. I'm not aware of any current enclosures that could fit that. :)

At any rate, all you would need to control are the drive select lines. The original Shugart floppy interface actually supports up to four floppy drives on one flat cable. (IBM gimped that) The Kryoflux hardware might technically be able to operate in that mode, but as far as I know the software does not support that. And most 3.5" drives are not designed to operate in that mode.

You would not need to switch power, just plug all of the drives in to their own power supply.

Beyond that, all you would need is a physical switch for the drive select or perhaps a couple of simple TTL logic chips if you wanted to do some fancy trickery.

On a Kryoflux, when a drive type is changed the only thing that needs to be reconfigured is the maximum number of tracks. So using a physical switch to switch between a 1.44mb and 1.2mb drive would be easiest.

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Re: Floppy drive selector board

Post by ChrisCwmbran » Mon Apr 25, 2016 9:35 pm

I like this idea. Sometimes I do actually use my KryoFlux to write an image to media for a disk I need.

I have four drives I connect though: 5.25" 40 track, 5.25" 80 track, 5.25" HD and 3.5" HD.

I'd buy something along these lines.

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Location: Australia

Re: Floppy drive selector board

Post by spags » Tue Apr 26, 2016 11:46 pm

@SomeGuy You are too kind for suggesting I was only "over thinking it a bit".

I was aware that the original Shugart interface supported four drives but it was my understanding that the Kryoflux only supported the IBM PC interface (hence the two-drive jumper on the board).

In some ways I can understand your statement that only the Drive Select line needs switching. Thinking about a standard twist cable, both drives will be receiving the same signals (the cable wires don't magically separate with the corresponding DS signals), so obviously that scheme works. However in other ways that would seem to be a potential source of noise (or signal attenuation). Is that why single-drive mode is suggested in the Kryoflux quick start guide?

In that case, why is the Kryoflux using tri-state buffer drivers on all but the ground lines? Okay - obviously there is the concern that the micro controller may not be able to sink/source the current, but why not just use standard buffer drivers (without tri-state)? Looking at the Kryoflux circuit diagram, it certainly seems to use the tri-state ability to disconnect those lines.

I'm also unsure about the suggestion that the power lines wouldn't need switching. Is that because you are suggesting virtually all of the signal and ground lines would already be connected together anyway (and therefore no concern about disparate grounds).

Personally, I probably have a mix of about 8 different drives (3.5 and 5.25), which I find give varying levels of performance over different disks (although I have a few favourites). I find it somewhat surprising that you can have a single dedicated drive for a given medium and just rely on that single drive to get "the" dump.

Based on the comments here so far, it sounds like the daughter board idea would be overkill anyway.

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