Plotter

Web UI for controlling a 3D printer (Marlin firmware) as a pen plotter over serial.

Plotting a multi-color topographic map

• Serial console with real-time output from the printer
• Pen up/down control with adjustable Z heights
• SVG file import with preview, scaling, and fit-to-bed
• Handles large/complex SVGs (100K+ paths) — server-side preprocessing, spatial-grid path optimization, batched command sending
• Circle drawing with G2 arc commands
• Real-time serial throughput stats (TX/RX bytes/sec, saturation, RTT, commands/sec)
• Emergency stop and serial reset
• Command queue with Marlin ok-based flow control
• Fill/shading support for closed paths (hatch, crosshatch, dots) with brightness-based density

Web UI showing serial console and SVG import

python3 -m venv .venv
.venv/bin/pip install -r requirements.txt

.venv/bin/python server.py

This starts the server on port 8000 with auto-reload — any changes to .py, .html, .js, or .css files will restart the server automatically.

Open http://localhost:8000

Edit server.py to change:

• SERIAL_PORT — defaults to /dev/ttyUSB0
• BAUD_RATE — defaults to 115200

.venv/bin/pytest
node tests/test_plotter.js

Tests cover:

• API endpoints (tests/test_api.py) — SVG preprocessing endpoint (parsing, transforms, simplification, bounding boxes, error handling), static file serving, and port listing API
• SVG processing (tests/test_svg_processing.py) — unit tests for parse_svg_path_to_subpaths (line/curve/arc commands, relative coordinates, implicit repeats, subpaths), apply_transform (translate, scale, matrix, combined), and douglas_peucker path simplification
• Client-side plotter logic (tests/test_plotter.js) — path optimization (simplify, sort, merge), coordinate transforms, bounds checking, G-code generation, and SVG element conversion

The tools/ directory contains standalone generators and utilities for creating plotter-ready SVG artwork (Perlin landscapes, typography posters, calibration grids, map conversion). See tools/README.md for details.

Developed for a Creality CR-10S Pro (300x300mm bed) but should work with any Marlin-based printer. A 3D-printed pen holder replaces the hotend nozzle and holds standard pens or pencils. The 3D models made in OnShape are available to clone or export as STL files for printing.

Pen holder mounted on the printer