Reading floppy disk data, part 3! itsa pulse party

OK so part 1 we got our wiring worked out and found an index pulse. Part 2 is we started getting MFM data coming out. Now we’re capturing pulses with gpio bitbanging, and storing all the pulse widths in a large memory array. each track has a 500Khz signal, and outputs data every 5 Hz, so we have a max of 100K samples worst case.

since we’re using a cortex arm with 192K~256K of RAM (the RP2040 has 264K!), its no biggie to store all the pulses in an array. here we are reading track 1 and binning the pulses: we’re seeing three pulse width bins stand out, about 40 count, 62 count and 85 count. but there’s also a couple ultra short pulses (25 count) and an ultra long pulse (~200 count).

each count is about 48ns-ish so that translates to 2us, 3us and 4us bins, with a few 1us and one or two 10us+. not exactly sure whats up with those outliers. do we ignore them? are they start-of-data markers? We also noticed that track 0 has way more unusually long or unbinned pulses, like almost 100 different values. its a little mysterious, we’ll have to investigate if there’s something special about track 0!

Video.

Part 2:

Part 1:


Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.

Join 35,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Follow Adafruit on Instagram for top secret new products, behinds the scenes and more https://www.instagram.com/adafruit/

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org


Maker Business — How (some) chips get made

Wearables — Sample code is your new best friend

Electronics — Solder braid quick fix

Python for Microcontrollers — Python on Microcontrollers Newsletter: Mu 1.2.0 Released, WSL Out of Beta and so much more! #CircuitPython @micropython @ThePSF @Raspberry_Pi

Adafruit IoT Monthly — Jellyfish Lanterns, Matter 1.0, and more!

Microsoft MakeCode — MakeCode Thank You!

EYE on NPI — Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — JP’s Product Pick of the Week 11/22/22 EyeSPI Breakout @adafruit @johnedgarpark #adafruit #newproductpick

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at AdafruitDaily.com !



1 Comment

  1. I will guess that the long gaps are sector gaps/markers. If so, they will be placed at uniform intervals, and probably aligned with the index pulse.

    1.44 MB 3.5″ floppy for DOS is apparently 512Byte/sector x 18 sectors per track x 80 tracks x 2 sides. (Mac 400/800 kB drives have variable sector counts.).

    https://en.wikipedia.org/wiki/List_of_floppy_disk_formats

Sorry, the comment form is closed at this time.