14

Interface and Application Programming

Week 14 Assignment

Assignment Overview

3D Typewriter — a small web app that sends G-code over USB to Marlin on the plotter I built for Week 12 (Mechanical Design, Machine Design): type text, preview the path, drive the XYZ steppers to write. This page is the project write-up for Week 14 (interface programming).

📋 Assignment Process

Same style as Week 1: each stage below is one step. I went through Marlin → Mega → RAMPS + power → motors → config → web app → demo.

Arduino Mega / Mega 2560 · ATmega2560 RAMPS-class shield Marlin 250000 baud

Download Marlin

Official site: marlinfw.org (documentation and download links). Source: github.com/MarlinFirmware/Marlin. Open the project in Arduino IDE and pick the configuration that matches your board (e.g. RAMPS).

Burn firmware to the Arduino Mega / Mega 2560

Board: Arduino Mega or Mega 2560, correct USB port, compile and upload so the ATmega2560 runs Marlin.

Stack RAMPS and connect 12 V

Plug the RAMPS shield onto the Mega, then connect an external 12 V supply to the RAMPS main power input (polarity and current rating must match your setup).

Arduino Mega with RAMPS shield: external 12 V power supply wiring

Connect the three stepper motors (X, Y, Z)

Each axis: 42 mm (NEMA 17) motor to the matching RAMPS driver output (A4988). Reference pinout first, then my wiring.

Reference pinout

Reference: RAMPS stepper motor connector pinout

My wiring

My build: NEMA 17 stepper motors wired to RAMPS X, Y, Z drivers

Edit Configuration.h

Set steps/mm, max feedrate, and max acceleration (see below). Set serial baud to 250000 (BAUDRATE) to match the web app.

Values I used (order X, Y, Z)

#define DEFAULT_AXIS_STEPS_PER_UNIT   { 80, 80, 400, 500 }
#define DEFAULT_MAX_FEEDRATE          { 100, 100, 10, 25 }
#define DEFAULT_MAX_ACCELERATION      { 500, 500, 50, 500 }

Tune A4988, re-flash, bench test

Adjust each A4988 VREF (output current) so motors turn reliably; together with DEFAULT_MAX_FEEDRATE and DEFAULT_MAX_ACCELERATION this fixed skipped steps and vibration. If you change microstepping jumpers, update DEFAULT_AXIS_STEPS_PER_UNIT. After edits, recompile and upload until motion is stable.

Optional bench: MINTEMP off, M211 S0, G92 for workspace zero without endstops; test with Serial Monitor before the browser.

Host computer for the web UI

macOS · Google Chrome · page served over HTTPS or localhost (required for Web Serial).

Software — 3D Typewriter

What the app does

3D Typewriter (serial-motor-web): typed text → LETTER_PATHS + Z → G-code streamed line-by-line; in-browser 3D preview of the toolpath (gray travel, blue draw).

serial-motor-web WebGL 3D preview letters.js

Paths and Z logic

Each letter is travel / draw segments in mm; words shift along X. Z only changes at travel ↔ draw (lift = pen-down Z + lift mm, then back).

Browse Web Serial (same baud as firmware)

port = await navigator.serial.requestPort();
await port.open({ baudRate: 250000 });

Busy port: close other serial apps (e.g. Arduino Monitor). Tools: Cursor / Gemini. Later: SVG paths (see canvasline.html).

UI screenshot

3D Typewriter web UI: controls and 3D path preview

Publishing

How to build the site: Week 1 — Principles and Practices

Demo

Video — software ↔ hardware

Demo below: browser / machine interaction while writing.

X / Y drive the pen in the plane; Z is only for pen up (travel) and pen down (draw)—not for drawing strokes in X/Y.