Here's a pleasant little project to try if your Arc' is of a sufficiently old vintage to come as standard with a DD floppy drive rather than a lovely HD one. Well, it's the difference between being able to use 800k per floppy or 1600k - not to be sniffed at. I'm using an A3000 but I see no reason why it wouldn't work with an A3*0 or A4*0 series machine...
Yes, I know the vast majority of Arc' software was distributed on DD floppies even after the A5000 came out but if you've ever had to resort to transferring software by floppy you'll be glad of the extra capacity. Besides once this upgrade has been made you'll never need to feel under-endowed in the floppy department again.

So what do we need to perform this minor miracle? Well, fundamentally it revolves round making the built-in FDD controller shift twice as much data as it would normally do when dealing with HD as opposed to DD formats. That's right, yet another project that involves over-clocking something... Do you feel a there's a theme developing here?
Yes, take one 8mhz WD1772 FDD controller and try to squeeze 16mhz out of it... But it still needs to be able to do 8mhz for those times when you need to read smelly-old DD discs. Hmmm, I guess some software will be needed along with the hardware. But will a 'standard' WD1772 really take a 100% overclock? Read on...

...Well, chances are the 'standard' WD1772 attached to the A3000 won't. This probably doesn't matter as you'll need to desolder the original prior to fitting the upgrade and unless you have a proper rework station removing it will likely require cutting the legs so allowing them to be desoldered individually. Then again it might matter if you do have a 'fast' chip as the right WDC's are hard to come by.
So what FDD controller chip should you go for?
*Quite a few later AtariST-ish computers used the 16mhz-capable WDC1772's as their floppy controller. The problem Atari had even back in the day was a serious shortage of these parts so they made a pin-compatible clone to take up the slack - yes, the replacement controller for this project is quite hard to find. All the other parts should be no problem.

>The Project Files<
>Updated Project Layout<
My thanks to Boris Leppin for the originals

So let's build it:

Motherboard
First take the motherboard carefully out from the case. Write down where each wire you disconnected goes so reassembling won't be too painful.

Floppy Disc Controller
Remove old Floppy Disc Controller (FDC - 28 pins) from the motherboard. It will be labeled VLSI 1772-02 or something similar. Take care not to heat the motherboard too much if desoldering or cut the pins (fastest way) at the price of destroying the original FDC - removal without cutting pins requires special tools.

Socket for the motherboard
After removing the FDC solder a socket in it's place. You could just solder the upgrade directly to the motherboard if you're lacking room (poss the A3000) but sorting any faults will be much harder. There's lots of important tracks in this area to be careful!

Watford and Simtec 8MB Ram upgrade
(If you have one GIVE IT TO ME!!!)
With the Watford or Simtec 8MB RAM upgrades installed this upgrade probably won't fit in place. One solution is to solder a 28 wire ribbon-cable to the motherboard and the other end to the HD-upgrade. If you need to do this you won't need the connector pins on the bottom of the HD-upgrade - solder the cable straight to the PCB. You'll also need to cover the bottom of the upgrade to ensure it won't short anything.

Making the HD-Upgrade
The included files carry three different versions. Two Veroboard versions depending on what multiplexing chip you've got and a universal version for those who like to make their own custom PCB's. Needless to say I went for the latter as it's much neater, prettier, and for some reason has a nice Mouse logo on it. ;)

If you're going to go the universal PCB route some of the tracks are quite fine and close together. I strongly recommend once you've got your PCB you look very carefully for any bridged / missing tracks before soldering it up!

Do read 'How to make your own PCB'. It's really not hard and you'll end up with a much neater, and more reliable result. Also you'll have fewer space issues if fitting to an A3000. The image is NOT to scale, see the files from the link.

In true Blue Peter style, here's one I made earlier...

-Wire, Cap, then 74HC157 in place-

Do clip the 74HC157 pins so they don't protrude

-FDC socket, then connector pins-

So that's why the 74HD157 needs it pins clipping

-Crystal soldered in and FDC socketed-

All Hail Atari!
(a-hem)

Installing the HD-Upgrade to the socket
When installing the upgrade to the socket be careful not to bend the motherboard too much. Put something anti-static material under it and press down. Belting it is not a good idea - if it won't go the likely reason the pins aren't lined up well with the socket. My pins are a bit thick so do take quite a bit of (careful) force to push home - el-cheapo sockets tend to be more forgiving, like the ones Acorn uses ;-)

IOC line
(Current Turbo & HD-Floppy upgrades both use this line, sadly)
There's a wire from the upgrade to the IOC chip that also needs connecting. Locate the pull up resistor for your system and cut the wire to length. The table below details what you're looking for. (hopefully correct) Solder the wire to the end of the resistor which is the closest to the IOC chip. If you're sensible enough to check schematics take care - Acorn's 7 and 1 look similar)
Install the Floppy Disc Controller chip
Be very careful with the new FDC chip, it dosen‘t like static electricity at all! Bend it's pins against a table to 'massage' the fit for the socket on the upgrade board. (try not to handle the pins) Push the FDC chip into the socket remembering to get it the right way round!

Diode
The diode is used to fake the disc drive ready signal and connects pins 34-10. Solder a diode to the floppy cable connector on the underside of the motherboard. Pin 1 of the connector is hopefully labeled on the motherboard. If there‘s no sign try looking for numbering on the floppy drive and follow the cable to the motherboard. Details are shown in the included schematics, do solder it right way or you'll get the 'Drive empty' error when you try to access it.

Floppy cable
Floppy cable needs some modifications too. (NOTE! Some floppy drives may have weird pin numbering) Pin 2 at the floppy drive and pin 34 on the motherboard need to be disconnected. Pin 10 can also be disconnected but if you want it can be connected to the pin 12 on the motherboard which (in theory) gives you the ability to connect two disc drives. If you don‘t want to try it out then leave the pin 12 on the motherboard unconnected. All other lines remains as they are.

Floppy drive
Now connect the new HD drive. The power connector is standard one so you don‘t have to make any modifications.
NOTE! The A3000 PSU dosen‘t have 12V outputs so make sure your disc drive operates with 5V - usually but not always.

Final check
Check everything! If all's OK put it all back together and switch on. No 'magic smoke'? Good. You should be able to read DD discs with new drive but cover the extra hole on HD discs or you'll get a lot of errors. If the floppy drive dosen‘t work then recheck everything; floppy cable (and especially pin numbering of the floppy connector and floppy drive), the upgrade etc. Also try the old FDC chip if you haven‘t destroyed it. If it works with the old chip but not with the new then the new FDC chip is fritzed.

ADFS module
If all works fine with DD discs it's time to modify the ADFS module for HD support. I've included the updated version as I guess Acorn aren't about these days to complain! If you'd rather do it yourself, read on:
Check your ADFS version is 2.67 (RiscOS 3.10, not sure about 3.11 and 3.19) as the BASIC proggie which makes the patched ADFS doesn't work with other versions.

Modifying the ADFS module
Save the ADFS module from the ROM to RAM disc using !Zap (Create » Get module » ADFS) - there are other ways:

No !Zap? Try the ModuleSAVE program. It saves the ADFS module to RAM disc (you have to reserve around 60kB RAM disc before running the BASIC program).

Copy the BASIC program ADFSpt02 to RAM disc along with your saved ADFS module and change the current directory to RAM disc. The progie creates a module called HDADFS in the RAM disc. Running HDADFS should give you 1.6MB support. If all is good I'd suggest putting it in your !Boot sequence.

So there you go. HD-Floppy goodness for your older Arc'. It's a shame that for the moment this and the Turbo upgrade aren't compatible as they both use the same control line - if you have an A3000 you'll have to choose which is more important to you.
I hope to update one or the other by altering the control line used to get round this issue - the hardware shouldn't be a problem but as I'm not a software kind-of person altering that may take a bit of head-scratching.

Charlie (2009)