The MIDIbox project is an open source modular DIY framework (hardware and software) MIDI platform built around the PIC family of microcontrollers (specifically the PIC18F452, PIC16F88, PIC18F4620 and PIC18F4685) and recently with STM32 32-bit ARM Cortex too. It can be used to build hardware MIDI control units for various synthesizers, multi-track recording software, and other MIDI devices; as well as stand-alone synthesizers, sequencers and other projects.
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The MIDIbox Hardware Platform is the continuation of Thorsten Klose's earlier work on MIDI controllers. Designs are based around a standardized environment of reusable and exchangeable modules. Soon after the release of the first modules, a small group of enthusiasts formed which grew into a thriving open source development community.
The focus of the platform is on well defined and documented modules based on small, uncomplicated circuits to allow for amateur assembly. These modules are then assembled into a complete project. All boards can be made as single-layer PCBs, and prototype boards designed with a freeware CAD program. Almost all components are through-hole for easier assembly.
The MIDIbox hardware platform runs its own open-source operating system: MIOS (MIDIbox Operating System), written in PIC assembly language for speed and accuracy. There is a C wrapper layer available for simplified coding. MIOS is designed and documented to allow simple reconfiguration, adaptation and extension by hobbyists and enthusiasts.
Currently there are about 15 separate modules available:
The MIDIbox Operating System (MIOS) has been developed to allow the design of flexible MIDI controller applications. MIOS adheres to a non-commercial, open platform as fundamental to the exchange of ideas and personal adaptations which are not possible with commercial controllers.
Most controllers built by the community are based on existing documented designs, and begin life with the feature set provided by the existing firmware. End users can enhance their devices with exchangeable program code, and customize them to suit their host application, synthesizer or other MIDI device. Users can also customize to suit their own preferred workflow, or design a new project from scratch.
Application source code, module schematics and PCB layouts are available free for non-commercial use as templates for modifications and improvements. Thus MIOS and the Hardware Platform allow an easy entry to hobbyist microcontroller development, while making possible applications outside the realms of the commercial, mainstream MIDI market.
MIOS was licensed under the GPL until version 1.8. Later versions now require Thorsten Klose's permission for commercial use.[1]
The operating system consist of a kernel that provides user hooks to hardware and software events, and functions for interaction with Hardware Platform modules.
One core module with a PIC18F452 microcontroller can handle
Background drivers are available for the following control tasks:
The whole operating system has been written in assembly language and has been optimized for speed. MIOS currently uses 8k of program memory and 640 bytes of RAM.
Only 75 µs is required to read 128 digital input pins and to write to 128 output pins. 16 rotary encoders are handled within 100 µs. Analog inputs are scanned in the background every 200 µs; changes larger than a definable minimum range trigger a user hook.
Up to 256 MIDI events can trigger dedicated functions; processing of the event list requires about 300 µS. MIDI events can also be processed by a user routine for sysex parsing or similar jobs. A user timer is available for time triggered code.
Support for other high-level languages apart from C is possible.
MIOS is a dedicated operating system for the Microchip Technology PIC18F452 microcontroller. This PIC is pin compatible to the PIC16F877 which was used in early MIDIbox projects. Thus it is backwards compatible with older MIDIbox Core modules, with one board modification.
The PIC18F452 features more internal flash, much more internal RAM, some new instructions and a better system architecture. It is available for the same price as the PIC16F877 in most countries.
At this point there are 11 fully documented projects available, as well as a large number of user projects generated by the community. The official projects are as follows:
16 Track Live Step and Morph Sequencer + advanced Arpeggiator
Hardware MIDI-controllable Synthesizer based on the MOS Technology SID (MOS6581) sound chip as shipped with the Commodore 64/128
Hardware synthesizer based on the Yamaha YMF262 sound chip (also known as OPL3) for generating the famous FM sounds known from Soundblaster (compatible) soundcards of the early 90s
Merges two separate MIDI inputs to a single output
Routes various MIDIboxes to a single MIDI port
Provides basic functionality to receive and transmit MIDI events
Provides CV and gate outputs to drive voltage controlled devices such as analog modular synthesizers
Full-fledged 64 channel MIDI controller
Extended version of the MIDIbox 64
The MIDIO128 interface is used to drive up to 128 digital output pins and to react on up to 128 digital input pins via MIDI
Alternative to the MIDIbox 64/64E
Reports events, which are transmitted over the MIDI cable, in a readable form