draft: false
Name: Acid
short-description: A 303-style step sequencer
Language: C++ (Pico SDK + ComputerCard)
Creator: Samuel Smith
Version: 1.0.0
Status: Released
License: MIT
date-created: 2026-07-19
date-updated: 2026-07-19

contact:
  social:
    github: https://github.com/SamGSmith

tags:
  - sequencer
  - acid
  - "303"
  - cv

summary: |
  A deliberately slightly fiddly 16-step sequencer capturing some of the obtuse workflow of the
  original 303. Walk a cursor through the pattern, setting pitch and step type (rest / normal /
  accent / slide) per step. Pitch and step-type sequences can be independently phase-shifted and
  reset during playback.

panel:
  inputs:
    - id: AudioIn1
      name: Pitch Phase Offset
      type: audio
      description: Phase-shifts the pitch sequence
    - id: AudioIn2
      name: Step-type Phase Offset
      type: audio
      description: Phase-shifts the step-type sequence
    - id: CVIn1
      name: Transpose
      type: cv
      description: Global transpose across the pattern
    - id: CVIn2
      name: Portamento Time
      type: cv
      description: Increase glide time
    - id: PulseIn1
      name: External Clock
      type: pulse
      description: One step per rising edge, overrides the internal tempo. When connected, X selects Pulse Out 1 clock division from /1 (CCW) through /8 (CW); the divided pulse fires on pattern steps 0, N, 2N, etc.
    - id: PulseIn2
      name: Reset
      type: pulse
      description: Quantised reset based on selected reset-mode
  outputs:
    - id: AudioOut1
      name: Sawtooth Voice
      type: audio
      description: Internal sawtooth oscillator tracking the sequenced pitch (no envelope)
    - id: AudioOut2
      name: Gate
      type: audio
      description: ~2ms trigger for normal/accent steps, held high on slide steps
    - id: CVOut1
      name: Pitch
      type: cv
      description: Calibrated 1V/oct pitch output, quantised to semitones, with portamento on slide
    - id: CVOut2
      name: Accent CV
      type: cv
      description: ~5V on accented steps, 0V otherwise
    - id: PulseOut1
      name: Clock
      type: pulse
      description: Internal clock pulses, or a divided external clock when Pulse In 1 is connected. X selects /1 through /8; output pulses are phase-locked to pattern steps 0, N, 2N, etc., and Y sets the pulse width up to almost the full divided interval.
    - id: PulseOut2
      name: Accent Trigger
      type: pulse
      description: ~2ms trigger on accented steps. With Pulse In 1 connected, Y sets the gate width from the short trigger up to almost the external clock period.

controls:
  switch:
    up:
      name: Play
      description: Runs the sequence, looping the active steps
    middle:
      name: Edit
      description: Program the note and step type of the step under the cursor
    down:
      name: Advance / Config
      description: flick advances the edit cursor to next step; hold 1s to enter reset-mode
    tap:
      name: Advance
      description: Briefly press and release to advance the edit cursor to the next step
  knobs:
    - when: { z: up }
      main:
        name: Length
        description: Sequence length, 1-16 steps
      x:
        name: Swing
        description: Swing amount from 0% to ~33%; with Pulse In 1 connected, selects Pulse Out 1 division /1 to /8
      y:
        name: Tempo
        description: Internal tempo; with Pulse In 1 connected, sets Pulse Out 1 and Pulse Out 2 gate width
    - when: { z: middle }
      main:
        name: Note
        description: Semitone within the octave (0-11) for the step under the cursor
      x:
        name: Octave
        description: Octave offset (-1..+1, 0 = default) for the step under the cursor
      y:
        name: Step Mode
        description: Step type for the step under the cursor - rest / normal / accent / slide
    - when: { z: down }
      main:
        name: Reset Mode
        description: Held ≥1s, selects the behaviour applied by a Pulse In 2 reset
      x:
        name: Randomise Pitch
        description: Held ≥1s, a large turn randomises the pitch sequence
      y:
        name: Randomise Step Type
        description: Held ≥1s, a large turn randomises the step-type sequence
  leds:
    - when: { z: up }
      display: list
      items:
        - id: LED0-3
          name: Step Number
          description: Current step number (0-15) in binary
        - id: LED4
          name: Play Mode
          description: Lit in play mode
        - id: LED5
          name: Gate
          description: Blinks with the gate
    - when: { z: middle }
      display: list
      items:
        - id: LED4
          name: Accent / Rest
          description: Lit when the current step is accent or rest
        - id: LED5
          name: Slide / Rest
          description: Lit when the current step is slide or rest
    - when: { z: down }
      display: list
      items:
        - id: LED0-2
          name: Reset Mode
          description: Currently selected reset mode, shown in binary, while switch DOWN is held ≥1s