PSOC5 floppy disk imaging interface
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FluxEngine is a very cheap USB floppy disk interface capable of reading and writing exotic non-PC floppy disk formats. It (should, this bit's not done yet) allow you to use a conventional PC drive to accept Amiga disks, CLV Macintosh disks, bizarre 128-sector CP/M disks, and other weird and bizarre formats.

a FluxEngine attached to a floppy drive

Big warning. Right now it is a hacked together prototype. It is not ready to use. Unless you eat and breathe embedded systems code and were born with a soldering iron in your mouth (hopefully, turned off) then this is not for you. If you were... please, give it a try!

Infrequently asked questions because nobody's got round to asking them yet

Q. Why not just use a USB floppy drive? There are lots and they're cheap.

A. Because USB floppy drives typically support a very limited set of formats --- typically only IBM 1440kB and 720kB. The FluxEngine should work on (almost) anything.

Q. But aren't floppy disks obsolete?

A. Absolutely they are. That doesn't mean they've gone away. Good luck with any old hardware, for example; a classic Mac won't boot without a classic Mac boot disk, and you can't make them on PCs (because they're weird). This is where the FluxEngine comes in.

Q. But how can you read and write non-PC formats on a PC floppy drive?

A. Because the FluxEngine hardware simply streams the raw magnetic flux pulsetrain from the drive to the PC, and then the analysis is done off-line in software. It doesn't rely on any floppy disk controller to interpret the pulsetrain, so we can be a lot cleverer. In fact, the disk doesn't even have to be spinning at the same speed.

Q. That's awesome! What formats does it support?

A. I'm glad you asked the question. Not a lot, currently.

Formats that it supports

Currently, not a lot.

  • IBM MFM 1440kB and 720kB formats, a.k.a. standard PC floppy disks; read only (I haven't got round to writing the write support)

  • Brother 240kB word processor disks; read and write

...aaaand that's it. If you want more, please get in touch; I need samples of floppy disks to scan and play with.



The system is based around a Cypress PSoC5LP CY8CKIT-059 development board, which is a decently fast ARM core wrapped around a CLDC/FPGA soft logic device. You can get one for about $15.

You need no extra components --- my current prototype (pictured above) has a 17-way header soldered to one side of the board; it then pushes directly onto the floppy drive connector. Then you plug it into your PC via USB and you're ready to go.

(Disclaimer: you do, however, need to remove four components from the board. I'm looking into moving the pinout to avoid this.)

Bill of materials

So you've decide to go against my advice and attempt to build on of these suckers. Well, good luck, that's all I can say.

Here's the physical stuff you need.

  • one (1) CY8CKIT-059 development board. See above. If your soldering is like mine, you may potentially need more, but I managed to construct the thing without frying it so it's not too hard.

  • one (1) standard PC floppy disk drive. You'll have to search around as they're increasingly hard to find. The FluxEngine should work with any standard 3.5" drive. It's theoretically capable of supporting 5.25" drives too but I'd need to modify the firmware timings. If you want this, get in touch.

  • some way of connecting the board to your drive. My prototype above uses a set of headers to let me attach the board directly on the back of the drive; this works fine, but the geometry's kind of awkward as part of the board covered the power socket and I had to modify it. (Which is why the programmer is hanging off the back.) I'd probably recommend soldering on pins instead, and using a traditional floppy cable. That'd let you attach two drives, too (although this is currently unsupported in the firmware; if you want this, get in touch.

  • decent soldering iron skills and an iron with a fine tip --- the pads on the board are very small.

  • a Windows machine to run the Cypress SDK on. (The FluxEngine client software itself will run on Linux, Windows, and probably OSX, but you have to build the firmware on Windows.)

  • optional: a floppy drive power cable. You can cut this in half, solder the raw end to the FluxEngine board, and power the drive off USB --- very convenient. This only works for drives which consume less than 500mA. Check before trying (5.25" drives need not apply here). Otherwise you'll need an actual power supply.

Assembly instructions

closeup of the board

(In the picture above, the extra two wires are the serial port and go off to the programmer. Normally that's attached on the left but I had to cut it off to make it fit. If you use pins rather than a header you won't need to do this.)

  1. Very carefully remove C7, C9, C12 and C13 from the top of the board. It's not hard; use tweezers or fine needle-nosed pliers to lift the component, apply heat to one end, wait for a few seconds and as the heat soaks through the solder will soften and it'll come away. Be careful; they're incredibly small. (I'm looking at changing the pinout to avoid needing this step, which is first so that if you ruin your board you don't waste time.)

    They're the circled components in this image. (They are actually clearly labelled but my circles have obscured the labels.) Note that the middle circle contains two capacitors side-by-side.

    which capacitors to remove

  2. If you're using a header: solder your 17-way header to the bottom of the board, from 0.2 to 3.0 inclusive. (It has to be the bottom because there are components that stick out on the other side and the bottom needs to go flush against the drive.)

  3. If you're using pins: solder your 17-way pins to either side of the board, from 0.2 to 3.0 inclusive.

  4. Optional: solder the ends of your floppy drive power supply cable to any convenient VDD and GND pins on the board. Remember to check the polarity.

And you're done!

Building the firmware

On your Windows machine, install the Cypress SDK and CY8CKIT-059 BSP. This is a frustratingly long process and there are a lot of moving parts; you may need to register. You want the file from the above site marked 'Download CY8CKIT-059 Kit Setup (Kit Design Files, Creator, Programmer, Documentation, Examples)'. I'm not linking to it in case the URL changes when they update it.

Once this is done, I'd strongly recommend working through the initial tutorial and making the LED on your board flash. The FluxEngine firmware isn't nearly ready for fire-and-forget use and you'll probably need to tweak it. (If you do, please get in touch).

When you're ready, open the FluxEngine.cydsn/FluxEngine.cywrk workspace, pick 'Program' from the menu, and the firmware should compile and be programmed onto your board.

Building the client

The client software is where the intelligence, such as it is, is. It's pretty generic libusb stuff and should build and run on Windows, Linux and probably OSX as well, although on Windows I've only ever used it with Cygwin. You'll need the sqlite3, meson and ninja packages (which should be easy to come by in your distro). Just do make and it should build.

If it doesn't build, please get in touch.

Using it

So you have client software, programmed the firmware, and the hardware is all ready. What next?

  1. Attach the FluxEngine to your floppy disk drive. Pin 0.2 is REDWC and connects to pin 2 on the floppy drive. Pin 3.0 is DSKCHG and connects to pin 34 on the floppy drive. All the other board pins connect in the obvious order. Odd pins on the floppy drive are left unconnected.

  2. Important. Make sure that no disk you care about is in the drive. (Because if your wiring is wrong and a disk is inserted, you'll probably corrupt it.)

  3. Connect the floppy drive to power. Nothing should happen. If anything does, disconnect it and check step 1.

  4. Connect the FluxEngine to your PC via USB --- using the little socket on the board, not the big programmer plug.

  5. Do .obj/fe-rpm from the shell. The motor should work and it'll tell you that the disk is spinning at about 300 rpm. If it doesn't, please get in touch.

  6. Insert a standard PC formatted floppy disk into the drive (probably a good idea to remove the old disk first). Then do .obj/fe-readibm. It should read the disk, emitting copious diagnostics, and spit out an ibm.img file containing the decoded disk image (either 1440kB or 720kB depending).

  7. Success!

The programs

The FluxEngine client software is a largely undocumented set of small tools. You'll have to play with them. They all support --help. They're not installed anywhere and after building you'll find them in the .obj directory.

  • fe-erase: wipes (all or part of) a disk --- erases it without writing a pulsetrain.

  • fe-inspect: dumps the raw pulsetrain / bitstream to stdout. Mainly useful for debugging.

  • fe-readbrother: reads 240kB Brother word processor disks. Emits a 256-byte-sector FAT filesystem. (You can access this with mtools although you'll to edit them first.

  • fe-writebrother: writes 240kB Brother word processor disks.

  • fe-writeflux: writes raw flux files. This is much less useful than you might think: you can't necessarily copy flux files read from a disk, because errors in the sampling are compounded and the result probably isn't readable. It's mainly useful for flux files synthesised by the other fe-write* commands.

  • fe-readibm: reads 720kB or 1440kB IBM MFM disks. Emits a standard filesystem image.

  • fe-rpm: measures the RPM of the drive (requires a disk in the drive). Mainly useful for testing.

  • fe-seek: moves the head. Mainly useful for finding out whether your drive can seek to track 82. (Mine can't.)

  • fe-testbulktransport: measures your USB throughput. You need about 600kB/s for FluxEngine to work. You don't need a disk in the drive for this one.

Commands which take --source or --dest take a parameter of the syntax $FILENAME:$MODIFIER:$MODIFER... A blank filename refers to the physical disk; otherwise, you can specify a .flux file. The colon-separated modifiers limit which bits of the disk are accessed. To specify tracks, do :t=0-9 (or just :t=7). For sides, do :s=0-1 (or commonly just :s=0). If left unspecified, you get the default specified by the command, which will vary depending on which disk format you're using (and is usually the right one).

How it works

It's very very simple. The firmware measures the time between flux transition pulses, encodes them, and streams them over USB to the PC.

There's an 8-bit counter attached to an 12MHz clock. This is used to measure the interval between pulses. If the timer overflows, we pretend it's a pulse (this very rarely happens in real life).

An HD floppy has a nominal clock of 500kHz, so we use a sample clock of 12MHz (every 83ns). This means that our 500kHz pulses will have an interval of 24 (and a DD disk with a 250kHz nominal clock has an interval of 48). This gives us more than enough resolution. If no pulse comes in, then we sample on rollover at 21us.

(The clock needs to be absolutely rock solid or we get jitter which makes the data difficult to analyse, so 12 was chosen to be derivable from the ultra-accurate USB clock.)

Once at the PC, we do some dubious heuristics to determine the clock rate, which depends on what kind of encoding is being used, and that in turn lets us decode the pulsetrain into actual bits and derive the raw floppy disk records from there. Reassembling the image and doing stuff like CRC checking is straightforward.

Some useful and/or interesting numbers:

  • nominal rotation speed is 300 rpm, or 5Hz. The period is 200ms.
  • a pulse is 150ns to 800ns long.
  • a 12MHz tick is 83ns.
  • MFM HD encoding uses a clock of 500kHz. This makes each recording cell 2us, or 24 ticks. For DD it's 4us and 48 ticks.
  • a short transition is one cell (2us == 24 ticks). A medium is a cell and a half (3us == 36 ticks). A long is two cells (4us == 48 ticks). Double that for DD.
  • pulses are detected with +/- 350ns error for HD and 700ns for DD. That's 4 ticks and 8 ticks. That seems to be about what we're seeing.
  • in real life, start going astray after about 128 ticks == 10us. If you don't write anything, you read back random noise.

Useful links:


The FluxEngine was designed, built and written by me, David Given. You may contact me at, or visit my website at There may or may not be anything interesting there.


Everything here is licensed under the MIT open source license. Please see COPYING for the full text. The tl;dr is: you can do what you like with it provided you don't claim you wrote it.