draft: false
Name: 8mu CV
short-description: "A playable, unpredictable Music Thing 8mu instrument: four voltages with LFOs and gesture control, plus two pulses, over USB MIDI Host"
Language: C++ (Pico SDK + ComputerCard)
Creator: Joep Vermaat
Version: "0.1.0"
Status: Beta
License: MIT
Editor: none
date-created: 2026-09-25
date-updated: 2026-10-02

contact:
  email: joep@joep-i.nl

# Vendors, unmodified and under their own MIT terms:
#   ComputerCard.h
#     (c) Chris Johnson
#   EightMU.h, which carries the rppicomidi usb_midi_host driver
#     (c) 2026 Chris Johnson; usb_midi_host (c) 2023 rppicomidi
# Their copyright headers are intact in those files.

uf2:
  - path: UF2/8mu_cv.uf2
    name: 8mu CV 0.1.0

tags:
  - midi-host
  - midi-to-cv
  - utility
  - lfo
  - controller
  - accelerometer

summary: |
  A playable, unpredictable instrument as much as a showcase for the Music
  Thing 8mu: every control it has - the eight faders, the four top buttons,
  and the accelerometer - drives the Workshop Computer's outputs. Set the LFOs
  running and latch in the accelerometer, and the controller steers voltages,
  rates and widths you didn't quite dial in - surprising, and often musical.
  It is also a way to test an 8mu channel by channel. The audio outputs are
  DC-coupled, so they carry steady voltages just as well as sound, giving four
  bipolar voltage sources rather than the usual two.<br><br>

  Faders 1-4 set the levels of Audio Out 1, Audio Out 2, CV Out 1 and CV Out
  2, each running from about -5V at the bottom through 0V in the middle to
  about +5V at the top. Faders 5 and 6 set the rates of Pulse Out 1 and Pulse
  Out 2: independent pulses from 0.1Hz to 20Hz, exponential across the fader
  so equal movements multiply the rate. Faders 7 and 8 set their widths: the
  middle is a 50% square, the way down narrows toward a sharp trigger, the way
  up widens toward a gate that stays open nearly all the time.<br><br>

  The Computer's switch picks the mode. Middle is the basic card. Up is LFO
  mode: a tap on a top button arms that output, capturing the voltage it is
  already at as the centre for a triangle LFO, with the fader then setting the
  speed. The Main knob sets how far the triangle swings, always measured to
  the nearer supply rail, so it can never clip.<br><br>

  Holding the switch Down for half a second latches the accelerometer on or
  off. When it is on, the four gesture axes take over the four voltage outputs
  and their LFO rates: Pitch and Roll (tilt), Yaw (spin), and Flip (which way
  up, unipolar so a flat 8mu reads 0). The X knob scales how far the gestures
  respond and the Y knob smooths them. The three panel knobs are otherwise
  not a fallback, since the point of the card is to drive the 8mu; unplug it
  and the outputs hold their last values.<br><br>

  The card is a pure MIDI listener: it never writes to the 8mu's LEDs or
  settings, so the controller behaves exactly as it does anywhere else. It
  needs a Rev 1.1 or later Computer, and nothing else may be in the front USB
  socket, because the Computer has to act as a USB host.

panel:
  inputs: []
  outputs:
    - id: AudioOut1
      name: Voltage 1
      type: cv
      description: >
        Bipolar voltage from fader 1, about -5V to +5V with 0V at the middle
        of the fader. Uncalibrated. The audio outputs are DC-coupled, so this
        carries a steady voltage as happily as sound. Top button 1 arms it as
        a triangle LFO in LFO mode. With the accelerometer latched on, Pitch
        drives it instead.
    - id: AudioOut2
      name: Voltage 2
      type: cv
      description: >
        Bipolar voltage from fader 2, same range as Voltage 1. Top button 2
        arms its LFO; Roll drives it with the accelerometer latched on.
    - id: CVOut1
      name: Voltage 3
      type: cv
      description: >
        Bipolar voltage from fader 3, same range as Voltage 1. Top button 3
        arms its LFO; Yaw drives it with the accelerometer latched on.
    - id: CVOut2
      name: Voltage 4
      type: cv
      description: >
        Bipolar voltage from fader 4, same range as Voltage 1. Top button 4
        arms its LFO; Flip (unipolar, flat = 0) drives it with the
        accelerometer latched on.
    - id: PulseOut1
      name: Pulse 1
      type: pulse
      description: >
        Rate set by fader 5, 0.1Hz to 20Hz with an exponential response - a
        slow LFO at the bottom of the fader, a fast rhythmic gate at the top.
        Width set by fader 7: centre is a 50% square, down narrows toward a
        sharp trigger, up widens toward a gate. Always a pulse, never dead.
    - id: PulseOut2
      name: Pulse 2
      type: pulse
      description: >
        Rate set by fader 6 and width by fader 8, independent of Pulse 1.

controls:
  switch:
    middle:
      name: Basic
      description: >
        Faders 1-4 are steady voltages and faders 5-8 are pulse rate and
        width. Any output that was oscillating in LFO mode glides back to its
        captured centre.
    up:
      name: LFO
      description: >
        Outputs armed with a top button oscillate as triangle LFOs, with their
        faders setting the rate. Outputs that are not armed stay steady
        voltages. The Main knob sets the LFO swing depth.
    down:
      name: Latch accelerometer
      description: >
        Momentary. Held for about half a second, it latches the accelerometer
        on or off. When on, the four gesture axes take over the four voltage
        outputs and their LFO rates. All six LEDs blink on the change.
  knobs:
    - main:
        name: LFO depth
        description: >
          How far the triangle LFOs swing, fully anticlockwise for no swing to
          fully clockwise for the whole distance to the nearer supply rail.
          Always measured to the rail, so an LFO can never clip. Only affects
          outputs that are armed.
      x:
        name: Gesture sensitivity
        description: >
          How far the accelerometer gestures respond, exponential from about
          0.25x to 4x across the knob. Only applies while the accelerometer is
          latched on.
      y:
        name: Gesture smoothing
        description: >
          How much the accelerometer gestures are smoothed, from barely any to
          a settled ~20ms glide. Softens a shaky hand while the accelerometer
          is latched on.
  leds:
    - display: list
      items:
        - id: LED0
          name: 8mu
          description: Lit while a USB MIDI controller is connected.
        - id: LED1
          name: Voltage 1
          description: Brightness follows the level of Audio Out 1.
        - id: LED2
          name: Pulse 1
          description: Follows Pulse Out 1 on and off.
        - id: LED3
          name: Pulse 2
          description: Follows Pulse Out 2 on and off.
        - id: LED4
          name: LFO mode
          description: Lit while the switch is up, selecting LFO mode.
        - id: LED5
          name: Voltage 3
          description: Brightness follows the level of CV Out 1.

host:
  usb:
    - name: Music Thing 8mu
      role: midi
      description: >
        Class-compliant USB MIDI controller plugged into the Computer's front
        USB-C jack. The Computer acts as USB host, which needs a Rev 1.1 or
        later board. Factory mapping, nothing to configure on the 8mu.
  notes: |
    The card only listens - it never writes to the 8mu's LEDs or settings, so
    the controller behaves exactly as it does anywhere else.