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This work is licensed under CC BY-SA 4.0.

Microlidian / μlidian

WIP.

Project for XIAO RP2040 mcu with st7789 screen and rotary encoder. In some ways the little brother of and using components and libraries from the usb_midi_clocker project.

The aim here is to have a flexible and extensible MIDI generator based on the mutating Euclidian features from drum2musocv, but aiming to be a bit more modular and extensible.

Features

  • 8hp Eurorack panel
  • USB-Type C input for syncing to USB MIDI clock and sending out MIDI
  • 3 bipolar CV inputs (using Pimoroni ADC board)
  • TRS MIDI out for sending 16+ rhythm tracks to a MIDIMUSO-CV12 board (or other MIDI devices!).

Requirements

Hardware/PCB wiring

Images

Prototype Eurorack modules

Breadboard wiring

  • Use env:pcb with -DBUILD_BREADBOARD

Seeed XIAO RP2040 pins. Counting clockwise starting from top-right:-

  • 3.3v

  • gnd

  • 5v

  • D10/MOSI -> ST7789 SPI

  • D9/MISO -> back button (swapped with D0 on PCB version)

  • D8/SCK -> ST7789 SCK

  • D7/CS -> ST7789 CS

  • D6 -> UART MIDI out

  • D5 -> i2c scl (for adc)

  • D4 -> i2c sda (for adc)

  • D3 -> Encoder right

  • D2 -> Encoder left

  • D1 -> Encoder button

  • D0 -> ST7789 DC (swapped with D9 on PCB version)

TODO/future ideas

  • Implement a basic sequencer
    • with Euclidian stuff on top of that
    • menus for controlling such
      • modulate the parameters from cv or midi input
    • make a nice graphical display widget for it
  • 'screensaver' mode with big indicators of position and triggering notes
  • Other sequencer types
    • eg raga sequencer that loads .mid files
  • MIDI input (via USB, for setting options, clock sync, forwarding notes and drums)
    • options to enable/disable all this
  • MIDI output (via TRS/DIN, for sending clock, triggers, notes and ~triggerable envelopes/LFO~~)
    • basic hacky approach is working
    • standard gm drum machine option with assignable drum numbers
    • midimuso cv trigger+cv modes
    • nicer mechanisms for assigning outputs
    • options that would allow for modulation
    • options to enable/disable all this
  • Integrate CV inputs
    • basic cv input parameter
    • for controlling parameters
    • low-memory version of the mapping tool, since providing options for all options of 20 tracks uses 100K+ and takes us over the available RAM!
    • maybe for clock too?
    • implement CV input 'reset'
    • Setting a per-parameter range for modulation
    • Port Pitch CV->MIDI and chord quantisation stuff from usb_midi_clocker
  • MIDI inputs for controlling parameters
    • Configurable MIDI inputs for control surfaces from host USB
    • Accept baked-in CCs to configure settings (similar to how drum2musocv already does it, perhaps)
  • Figure out a way to provide storage, to save presets and templates/.mid files?
    • just save to the internal flash via LittleFS! DONE
    • rudimentary save/load of parameter mappings DONE
    • allow configuration of the output devices/channels..
    • add other settings+things to be saved/recalled..?
    • Load/save settings and presets to the flash
  • Other sequencer types
    • eg raga sequencer that loads .mid files
  • Free up pins..?
    • use an i2c rotary encoder: frees up 3(!) pins; could use the rgb encoder for extra feedback; more difficult to fit neatly under a panel due to the i2c board...
    • or, just use a Pico or Waveshare Zero instead of the XIAO and don't worry about not having enough pins!
  • Stutter/Ratchetting
  • Per-track note duration, with modulation
  • "Stick on the current pattern" control; A/B controls
  • Optional logic gates on the triggers (including 'mult-limbed-drummer' options)
  • an enhanced 'Density' control that keeps the same rhythm, but fills in gaps?
    • 'euclidian within euclidian'? so eg we fill in triggers in between other triggers?
  • rhythm-synced LFO that sets a cycle of the waveform to the length between triggers
  • Ability to boot up as a USB flash drive, for copying files to/from the LittleFS flash?
  • Allow holding a button to go into firmware update mode before running much code at all as a failsafe against bad code that won't complete setup() or first loop() DONE, hold both buttons while booting up to go straight into firmware update/uf2 mode

Known problems/gotchas

  • Trying to Serial.print() from the second core (screen+CV input) while serial is connected will hang the display!
  • Trying to Serial.print() generally seems to be unreliable and likely to cause crashes
  • Occasional glitching of output name display when on some track pages; intermittent crashes bizarrely happening when rendering output labels on pattern page; probably caused by something overwriting selected output slot or something similar? ????
    • worked around this by caching the label in OutputSelectorControl, but will probably still cause crashes if displaying a list of Output names
  • Slow loading presets causing pauses and problems
  • we don't seem to get around to doing a menu update_ticks() for every tick, so the ParameterInputDisplay graph appears very noisy unless backfilling values. even updating it from a callback for every parameter input read() didnt seem to be fast enough. so might mean that very fast changes are being missed..
  • Sometimes crashes waiting for USB MIDI or something... suspect perhaps garbled USB MIDI is cause?
  • Soft reboot when using uClock crashes/does not start up properly - works fine from cold boot/first power on though

Done

  • Basic engine for BPM and internal/external clock (based on midihelpers/usb_midi_clocker code)
  • Basic display and encoder for changing options
  • Fix redrawing problem due to no framebuffer in the TFT_eSPI library (can we just use that buffer wrapper library?)
  • Named MIDI outputs ("kick", "snare", etc, "bassline")
  • Menu options and hotkeys to force reboot + firmware update modes:
    • Hold BACK button for 4 seconds to reboot (useful if the screen hasn't started up after a cold boot, or similar)
    • Hold BACK button for 4 seconds while holding encoder button for 3 seconds to go into firmware update mode
  • FIXED: Screen doesn't turn on first time on the revision 1 hardware, don't know why. Hold the 'back' button for 4+ seconds to force a reboot and it will usually start working!
    • Tried: adding a 47k pullup resistor from CS->BLK
    • Tried: adding a delay before setup
    • Tried+fixed: added pullup resistor to display RES pin