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

• mymenu
• midihelpers
• parameters
• seqlib
• patched Encoder library
• Vortigont LinkedList library
• patched bodme/TFT_eSPI library dont think this needed anymore?
• Adafruit TinyUSB library patched with my patch from adafruit/Adafruit_TinyUSB_Arduino#238
• vscode+platformio+earlephilhower core
• the TFT_eSPI gfx library by Bodmer for fast DMA writes

Hardware/PCB wiring

• Use env:pcb with -DBUILD_PCB
• WIP PCB & panels in KiCAD and Gerber format here - don't use these yet without checking with the author for any problems/new versions!
• I'm using These small TFT screens
• And These encoders
• These +/-24v ADC breakout boards

Images

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?
  • Actually, think this is the bug in the TinyUSB library that is fixed/worked around by my simple patch mentioned in https://github.com/adafruit/Adafruit_TinyUSB_Arduino/issues/238
• 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