WiFi Pen Plotter

A WiFi-enabled pen plotter with an MS Paint-style web interface. Draw on your phone or tablet and watch it plot!

Full writeup and 3d print files here https://hackaday.io/project/204593-pen-plotter-esp32

Features

• WiFi Control - No USB connection needed, control via web browser
• Touch-Friendly Interface - Draw with your finger on phone/tablet
• Multiple Drawing Tools - Freehand, lines, rectangles, and circles
• Real-time Preview - See your drawing before plotting
• Custom Motor Control - Direct stepper motor control without external firmware

Quick Start

1. Upload the Firmware

cd plotter_sketch
pio run --target upload

2. Connect to PlotterBot WiFi

• SSID: PlotterBot
• Password: plot2025

3. Open Web Interface

Open your browser to: http://192.168.4.1

4. Draw and Plot!

• Select a drawing tool (Draw, Line, Rectangle, Circle)
• Create your design on the canvas
• Click "Send to Plotter" to start plotting
• Watch your creation come to life!

Hardware Requirements

Components

• ESP32 DevKit (38-pin recommended)
• 3x 28BYJ-48 stepper motors (5V unipolar)
• 3x ULN2003 driver boards (Darlington transistor arrays)
• Power Supply - 5V DC (1-2A recommended)
• Pen holder mechanism - For Z-axis
• Frame/Rails - For X and Y movement

Wiring

See HARDWARE_SETUP.md for detailed wiring diagrams.

GPIO Pin Assignments:

• X-Axis Motor: GPIO 13, 14, 27, 26
• Y-Axis Motor: GPIO 16, 17, 5, 18
• Z-Axis Motor: GPIO 19, 21, 22, 23

Calibration

The plotter includes calibration settings in plotter_sketch/src/motor_control.h:

#define STEPS_PER_MM_X 52    // Adjust for your X-axis mechanical setup
#define STEPS_PER_MM_Y 40    // Adjust for your Y-axis mechanical setup
#define STEPS_PER_MM_Z 50    // Adjust for pen lift height

To calibrate:

1. Draw a known size (e.g., 100x100px square)
2. Measure the actual plotted size
3. Adjust STEPS_PER_MM_X/Y proportionally
4. Higher values = smaller movements, Lower values = larger movements

Axis Inversion: If your plotter is mirrored, change the inversion settings:

#define X_INVERT -1  // Change to 1 if X-axis is backwards
#define Y_INVERT 1   // Change to -1 if Y-axis is backwards

Architecture

Built with custom firmware (no GRBL/FluidNC dependency). See PROJECT_PLAN.md for architecture details.

Key Components

• motor_control.h - Direct stepper motor control using half-step sequences
• gcode_parser.h - Simple G-code interpreter (G0, G1, G28, M3, M5)
• web_interface.h - Embedded HTML/CSS/JS interface
• main.cpp - WiFi AP and web server setup

Development

Built with PlatformIO for ESP32.

Build Commands

cd plotter_sketch

# Build only
pio run

# Build and upload
pio run --target upload

# Monitor serial output
pio device monitor

Project Structure

pen_plotter_esp32/
├── plotter_sketch/          # Main PlatformIO project
│   ├── src/
│   │   ├── main.cpp         # Entry point, WiFi & web server
│   │   ├── motor_control.h  # Stepper motor control
│   │   ├── gcode_parser.h   # G-code interpreter
│   │   └── web_interface.h  # Embedded web UI
│   └── platformio.ini       # PlatformIO configuration
├── HARDWARE_SETUP.md       # Hardware assembly guide
├── README.md               # This file
├── LICENSE                 # GNU AGPL v3.0
└── PROJECT_PLAN.md         # Architecture decisions

Web Interface

The web interface is fully embedded in the ESP32 firmware (no SPIFFS required).

Drawing Tools:

• ✏️ Freehand Draw - Touch/click and drag
• 📏 Line - Click start and end points
• ⬜ Rectangle - Click and drag corners
• ⭕ Circle - Click center and drag radius

Controls:

• 🚀 Send to Plotter - Execute your drawing
• 🏠 Home - Return to origin (0,0) with pen up
• ⬆️ Pen Up - Lift pen manually
• ⬇️ Pen Down - Lower pen manually
• 📊 Status - View current position
• 🗑️ Clear - Erase canvas

Troubleshooting

Plotter doesn't move:

• Check power supply to motors
• Verify GPIO pin connections
• Check serial monitor for errors

Drawing is mirrored:

• Adjust X_INVERT or Y_INVERT in motor_control.h

Drawing is wrong size/shape:

• Calibrate STEPS_PER_MM_X and STEPS_PER_MM_Y
• Check mechanical setup (belts, pulleys, etc.)

Pen doesn't touch paper:

• Adjust STEPS_PER_MM_Z value
• Check Z-axis motor connection
• Verify pen mechanism height

WiFi doesn't appear:

• Wait 10-15 seconds after power-on
• Check serial monitor for "AP started" message
• Try rebooting ESP32

G-Code Support

Supported G-code commands:

• G0 - Rapid positioning (pen up)
• G1 - Linear move (pen down)
• G28 - Home all axes
• G90 - Absolute positioning mode
• G91 - Relative positioning mode
• M3 - Pen down
• M5 - Pen up
• M114 - Report current position
• M18/M84 - Disable motors

Attribution

This project has 3d parts and inspiration from:

https://www.thingiverse.com/thing:4637226/files

https://www.thingiverse.com/thing:4607077#google_vignette

https://www.pcbway.com/project/shareproject/Build_a_simple_3D_Arduino_Mini_CNC_Plotter_e2c3f905.html