Name: PlantHolder
short-description: USB MIDI host and Placeholder-style reverb — built for the Instruo Pocket Scion, happy with any USB MIDI device.
Language: C++ (Pico SDK + ComputerCard)
Creator: Phil Miller
Version: "0.2.0"
Status: Beta
License: MIT
date-created: 2026-05-17
date-updated: 2026-08-06

contact:
  website: https://github.com/philmillman
  social:
    instagram: https://www.instagram.com/nauticalartifacts/

tags:
  - effect
  - reverb
  - midi-host
  - midi-to-cv

# Pinned rather than auto-discovered, so a local build/ directory never adds a
# second download tile alongside the committed firmware.
uf2:
  - path: UF2/plant_holder.uf2
    name: PlantHolder 0.2.0

summary: |
  Originally a companion for the [Instruo Pocket Scion](https://instruomodular.com/product/pocket-scion/),
  now a generally fun stereo reverb that's also a **USB MIDI host**. Plug in the Scion or any USB MIDI
  device — the Computer will power it — and break MIDI channels **1** and **2** out as v/Oct + gate
  (route voices in the Scion companion app, or your device's MIDI Settings).

  The reverb is modelled on the Fairfield Circuitry **Placeholder (EB)** — three cross-coupled delay
  lines with a tone-tilted feedback path. **DECAY self-oscillates around 2–3 o'clock**, highly
  interactive with Size, Tone, LPF, and Mix.

  The name nods to the Scion's plant-biosonification heritage and to the Householder reflection
  matrix at the heart of the Placeholder's feedback delay network.

  Requires a **Rev1_1** board (Q2 2025 or later) for USB host mode.

panel:
  inputs:
    - id: AudioIn1
      name: Audio Left
      type: audio
      description: Left channel audio input
    - id: AudioIn2
      name: Audio Right
      type: audio
      description: Right channel audio input
    - id: CVIn1
      name: Decay CV
      type: cv
      description: Bipolar trim added to the DECAY knob; full scale covers the whole range
    - id: CVIn2
      name: Size CV
      type: cv
      description: Bipolar trim added to the SIZE knob; full scale covers the whole 12–160 ms range
  outputs:
    - id: AudioOut1
      name: Reverb Left
      type: audio
      description: Left channel reverb output
    - id: AudioOut2
      name: Reverb Right
      type: audio
      description: Right channel reverb output
    - id: CVOut1
      name: Pitch Ch 1
      type: cv
      description: v/Oct for MIDI channel 1, A4 = 0 V, with ±2-semitone pitch bend
    - id: CVOut2
      name: Pitch Ch 2
      type: cv
      description: v/Oct for MIDI channel 2, A4 = 0 V, with ±2-semitone pitch bend
    - id: PulseOut1
      name: Gate Ch 1
      type: pulse
      description: Gate for MIDI channel 1, last-note priority
    - id: PulseOut2
      name: Gate Ch 2
      type: pulse
      description: Gate for MIDI channel 2, last-note priority

controls:
  switch:
    up:
      name: Size / Ratio
      description: X and Y set reverb SIZE and the length ratio between delay lines
    middle:
      name: Decay / Tone
      description: X and Y set reverb DECAY and the TONE tilt
    down:
      name: Mod Page
      description: >-
        Hold Down for 1 s to latch the MOD page (LED 5). Main becomes the wet
        hi-cut and X/Y become MOD depth and type, until you hold Down again.
        While Down is held unlatched, the knobs keep their Middle meanings.
  knobs:
    - main:
        name: Mix
        description: Dry/wet balance. Held at its stored value while the MOD page is latched
    - when: { z: up }
      x:
        name: Size
        description: Delay-line length, 12–160 ms
      y:
        name: Ratio
        description: Scales the length of delay lines 2 and 3 relative to line 1
    - when: { z: middle }
      x:
        name: Decay
        description: >-
          Feedback amount, from a single reflection up into self-oscillation
          around 2–3 o'clock. Highly interactive with Size, Tone, LPF, and Mix
      y:
        name: Tone
        description: >-
          Shelving tilt around 500 Hz, with a detent at noon. CW cuts lows and
          lifts highs. Sits inside the feedback path as well as on the wet
          output, so it doubles as a damping control
    - when: { z: down }
      main:
        name: Wet Hi-Cut
        description: >-
          1st-order low-pass on the wet output, sweeping 1 kHz to fully open.
          This is the pedal's F switch, which lives in its output section. MIX
          keeps whatever value it had before the page was latched
      x:
        name: Mod Depth
        description: >-
          Depth of the delay-time modulation, up to about 4 % of the delay
          length. Deliberately subtle, as on the pedal
      y:
        name: Mod Type
        description: None / cyclical / random / both, in four steps across the knob
  leds:
    - display: list
      items:
        - id: "0"
          name: Host Status
          description: Solid when a USB MIDI device is mounted. Blinks when the board is older than Rev1_1 and cannot run USB host mode
        - id: "1"
          name: MIDI Activity
          description: Flashes on incoming note and pitch-bend messages
        - id: "2"
          name: Gate Ch 1
        - id: "3"
          name: Gate Ch 2
        - id: "5"
          name: Mod Latched
          description: Lit while the MOD page is latched

host:
  usb:
    - name: USB MIDI device
      role: host
      description: >-
        Plug the Instruo Pocket Scion or any USB MIDI device into the Computer's
        USB port (the port will also power the Scion). Notes and pitch bend on
        MIDI channels 1 and 2 drive the two CV/gate pairs — route voices in the
        Scion companion app, or your device's MIDI Settings.
  notes: |
    USB host mode requires a **Rev1_1** board (Q2 2025 or later). On earlier hardware the host is
    never started and LED 0 blinks to say so; the reverb still runs.