Floppyti

Type: MIDI Audio Module | Status: Completed

Floppy, fottiti!

A floppy-drive music player driven by a MIDI-IN interface.
Floppyti is a simple and funny, bare-metal hardware solution designed to transform a common 3.5-inch floppy disk drive into a monophonic musical instrument. The system receives MIDI-IN messages and translates them into stepper motor movement sequences, generating musical notes through the mechanical vibrations of the drive's head.

• MCU: 8-bit Microchip PIC16F628A.
• Input Interface: Optoisolated MIDI-IN port for real-time note reception.
• Audio Generation: Audio tones generated by frequency-controlled stepper motor movement.
• Pitch Range: Approximately 3 octaves, from octave 2 to octave 5.
• Monophonic: last-note-triggered playback.

• Design: Schematics and PCB layouts developed with ExpressPCB (using custom expresspcb-goslib assets).
• Firmware: Written in Microchip Assembler (MPASM).
• Toolchain: Microchip MPLAB X IDE + PICkit2.

The firmware uses a cooperative, timer-driven task scheduler rather than interrupt-driven timing. Each Timer0 overflow ($51.2,\mu\text{s}$) advances the MIDI acquisition, message parsing, activity indication and FDD synthesis tasks in a deterministic sequence.

The system does not read or connect the physical TRACK0 signal from the FDD interface. On startup, the firmware forces 90 steps outward (step_out) to guarantee that the drive head reaches its mechanical end-stop (Track 0 at the outer edge of the disk) regardless of its starting position. It then moves the head 40 steps inward (step_in) to land approximately at the midpoint of the 80-track physical range.

The physical timbre generated by the drive depends directly on the head carriage's movement bounds before direction reversal:

• Continuous Step Reversal (fddrange = 1): Reversing direction at every single step keeps the head oscillating locally in a steady, uniform cycle, yielding a smoother and continuous tone.

• Extended Sweep (fddrange > 1): Allowing multiple sequential steps in a single direction before reversing creates a cleaner square-wave line during the sweep, periodically broken by the higher-energy mechanical impact of the direction reversal at each boundary. This periodic interruption introduces a strong mechanical amplitude modulation (tremolo) to the emitted note.

(Note: A toggle switch or MIDI control could be used to dynamically adjust the step sweep threshold at runtime, effectively introducing an envelope/timbral control over the emitted sound. In the current build, the firmware hardcodes the threshold to 1.)

• firmware/: Contains the MPLAB X project and the .asm source files.
• hardware/: ExpressPCB schematic (.sch) and PCB layout (.pcb) files.
• resources/: Videos and images of the built device in action.

Author: Alessandro Fraschetti (gom9000).
Technical Notes: The hardware design was supported by ExpressPCB and the custom expresspcb-goslib libraries.
License: This experience is licensed under the MIT License.