draft: false
Name: Cathode Ray
short-description: Composite video synthesiser (PAL + NTSC builds) — oscilloscope, etch-a-sketch & spectrum analyser, greyscale via dithering, performance effects, 8 alt-boot screensaver/game modes
Language: C++ (Pico SDK + ComputerCard)
Creator: Andy Jenkinson (uglifruit)
Version: 1.2.0
Status: Released
License: MIT
date-created: 2026-06-30
date-updated: 2026-07-02
Repository: https://github.com/TomWhitwell/Workshop_Computer/tree/main/releases/96_cathode

tags:
  - video
  - composite
  - oscilloscope
  - visualiser
  - performance

summary: |
  Cathode Ray turns the Workshop Computer into a 1-bit composite video synthesiser.
  Wire a two-resistor DAC from Pulse Out 1 (1kΩ) and Pulse Out 2 (220Ω) into an RCA
  centre pin (grounds common) and connect to any composite-input TV/monitor. PAL by
  default; flash cathode_ray_ntsc.uf2 for NTSC (US) displays.

  The Main knob picks the mode across three zones: lower = etch-a-sketch (draw with
  CV In 1/2 as X/Y), middle = oscilloscope (Audio In 1 traces, sweep speed slow→fast),
  upper = spectrum analyser (24-band, Audio In 1). Greyscale (5 levels) is produced by a
  2×2 spatial dither into the 1-bit picture.

  Switch MIDDLE = phosphor fade / persistence, UP = static / clean. Knob X/Y are
  multi-function (CV scale / position offset / scope gain & baseline / spectrum gain &
  rotate) with pickup hysteresis.

  Three independent performance-trigger sources — Switch DOWN, Pulse In 1, Pulse In 2 —
  each runs a configurable behaviour (invert, clear, cycle/random effect, or one fixed
  effect: strobe / fade / fade-to-white / snow / swap / corrupt / roll). Hold Switch
  DOWN and twist Main/X/Y to open the on-screen config menu and assign each source.

  Hold Switch DOWN at power-on for ALT-BOOT mode: a selector of screensaver / performance
  hybrids that also protect a CRT from burn-in. Switch UP shows the selector (Main knob
  scrolls through the modes, with on-screen input/output help); Switch MIDDLE or DOWN
  plays the shown mode. Modes:
   • COMET — a round comet with a phosphor tail (Main/CV1 = speed, Y/CV2 = tail length).
   • PATCHTEROIDS — patch-controlled Asteroids. Main (+ CV In 1) steers, PU1 / Switch DOWN
     fire. CV Out 1 = pitch (+1 semitone per hit, arpeggiates down on a crash), CV Out 2 =
     gate per hit.
   • BOING — Amiga-style tilted rotating checkered ball. Knob X / CV1 = spin & kick impulse,
     Main / CV2 = bounce efficiency, Knob Y = horizontal speed, PU1 / DOWN = kick.
     CV Out 1 = height, CV Out 2 = trigger on each floor bounce.
   • STARFIELD — fly through space. Main = speed, X/CV1 = horizontal turn, Y/CV2 = vertical.
   • RADAR — a radar scope. Main aims a turret, PU1 / DOWN fires a ballistic missile (hold =
     range); PU2 (CV1 sets radius) drops fading target blocks. CV Out 2 = pulse on a hit.
   • LUNAR — Lunar Lander. Main / CV1 rotate, PU1 / DOWN thrust; land gently on the pad
     (narrows each stage) avoiding drifting UFOs. CV Out 1 = altitude, CV Out 2 = crash.
   • 3DMAZE — first-person wireframe maze. Main turns, PU1 / DOWN walks; Knob X / CV1 =
     hands-free auto-run. Find the glowing white EXIT panel on a wall (reaching it flashes and
     generates a new maze). CV Out 2 = pulse when you reach the exit.
   • FOURTRIG — a trigger-driven visual drum machine. Audio In 1, Audio In 2, Pulse In 1 and
     Pulse In 2 are all triggers; each stamps a decaying "thing" (thick 2×2 strokes) into one
     screen quadrant. Knob X = bank (icons first, words last: shapes / music-hits / symbols /
     words / emphasis), Knob Y (+ CV In 2) = the set of four, Main (+ CV In 1) = CHAOS (jitter/
     swap placement, grow + vary size, and past ~50% a rising chance of a per-hit random VFX from
     the full set incl. flip-180). Hold Switch DOWN for a momentary held VFX. CV Out 2 = pulse on
     every trigger.

panel:
  inputs:
    - id: AudioIn1
      name: Scope Input
      description: Oscilloscope trace / spectrum source (gain via Knob Y). In FourTrig alt-mode, a trigger input (top-left quadrant)
    - id: AudioIn2
      name: Trigger (FourTrig)
      description: Unused in the main synth. In FourTrig alt-mode, a trigger input (top-right quadrant)
    - id: CVIn1
      name: Draw X
      description: Etch-a-sketch X axis (scaled/offset by Knob X), sampled at 48kHz
    - id: CVIn2
      name: Draw Y
      description: Etch-a-sketch Y axis (scaled/offset by Knob Y), sampled at 48kHz
    - id: PulseIn1
      name: Trigger 1
      description: Configurable performance trigger (default cycle FX; set to CLS to clear)
    - id: PulseIn2
      name: Trigger 2
      description: Configurable performance trigger (default invert while held)
  outputs:
    - id: PulseOut1
      name: Video DAC bit 0
      description: Composite video via 1kΩ (black pedestal); summed into RCA centre pin
    - id: PulseOut2
      name: Video DAC bit 1
      description: Composite video via 220Ω (white step); summed into RCA centre pin
    - id: CVOut1
      name: Alt-boot CV
      description: Alt-boot only — mode-dependent (Patchteroids pitch / Boing height / etc). Unused in the main synth.
    - id: CVOut2
      name: Alt-boot Trigger
      description: Alt-boot only — mode-dependent event pulse (hit / bounce / crash / reached exit). Unused in the main synth.

controls:
  modes:
    - name: Etch-a-sketch
      activation: Main knob in the lower third (CCW); knob sets fade rate
      main: Fade rate (0.15s–2s)
      x: CV In 1 scale (MIDDLE) or X position offset (UP)
      y: CV In 2 scale (MIDDLE) or Y position offset (UP)
      switch:
        up: Knob X/Y offset the drawing position (drawings accumulate)
        middle: Knob X/Y scale the CV inputs (+ phosphor fade)
        down: Performance trigger / config menu
    - name: Oscilloscope
      activation: Main knob in the middle third
      main: Sweep speed (slow ~3s to fast ~0.1s per sweep)
      x: Centre-line (0V) vertical position
      y: Audio trace gain (0–2×)
      switch:
        up: Static single clean trace
        middle: Phosphor fade locked to the sweep
        down: Performance trigger / config menu
    - name: Spectrum analyser
      activation: Main knob in the upper third (CW); knob sets decay speed
      main: Bar/echo decay speed
      x: Rotate the radial blob (MIDDLE mode only)
      y: Audio gain
      switch:
        up: LED-segment bargraph
        middle: Radial pulsing blob (Knob X rotates; grey echo trail)
        down: Performance trigger / config menu
      notes: 24-band Goertzel filter bank on Audio In 1 (~80Hz–8kHz, bass left→treble right); bars decay; a SWAP trigger mirrors bass↔treble.
  leds:
    - items:
        - id: LED0
          name: Scope mode
        - id: LED1
          name: Etch-a-sketch mode
        - id: LED2
          name: Config menu open
        - id: LED3
          name: Phosphor fade / persistence active (Switch MIDDLE)
        - id: LED4
          name: Switch DOWN held
        - id: LED5
          name: Spectrum-analyser mode