Pen Plotter

Electronics

⚡ Mini Plotter V2 – Electronics Documentation

Overview

This document covers the electronics subsystem of the Mini Plotter V project.

It is intended as a reference for coworkers, fabrication, debugging, and replication of the electronics and PCB.

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Scope

Included

• PCB design reference
• Power architecture
• Microcontroller pin mapping
• Stepper driver connections
• Peripheral interfaces

Board Details

Power Architecture

Power Input

• External DC input - USB C (Power only)
• Recommended supply: 5V

Voltage Rails

• Motor Rail: Direct from input to stepper drivers
• Logic Rail: Regulated 3.3V for MCU and peripherals

Electrical Notes

⚠️ Important

• Power supply must handle motor current peaks
• Logic and motor grounds are common
• Do not connect or disconnect motors while powered

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MCU Pin Mapping

GPIO Pin Mapping (Grouped)

Motor 1 (Stepper)

Motor 2 (Stepper)

Servo Motor

Limit Switches

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⚡ ESP32-WROOM-32E – PCB Design & Boot Guidelines

This document provides electronics design guidelines for using the ESP32-WROOM-32E module in custom PCBs.

It focuses on:

• Boot and flashing requirements
• Strapping pins and default states
• Pins to avoid or use with caution
• Minimum required external circuitry
• PCB layout considerations

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ESP32-WROOM-32E Overview

• MCU: ESP32 (dual-core Xtensa LX6)
• Operating Voltage: 3.3V
• Wi-Fi + Bluetooth on-module
• Integrated antenna (keep-out required)

⚠️ All GPIOs are 3.3V only. Do NOT apply 5V.

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Minimum Circuit for Boot & Flash

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Mandatory Connections

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Boot & Flash Logic

Boot Mode Selection

To flash firmware:

• IO0 = LOW
• EN toggled LOW → HIGH (reset)

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Strapping Pins (CRITICAL)

These pins are sampled at reset.
Incorrect levels will prevent booting.

⚠️ Do not drive these pins externally at boot unless you know the impact.

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Pin Usage Guidelines

Pins to Avoid (or Use Carefully)

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Recommended Safe GPIOs

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Pull-Up / Pull-Down Requirements

Required External Resistors

⚠️ Internal pulls exist but external resistors improve reliability.

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Reset & Auto-Flash Circuit (Recommended)

For USB-UART auto programming:

This allows flashing via:

• Arduino IDE
• ESP-IDF
• PlatformIO

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Power Supply Design Notes

• Use LDO or buck regulator capable of 600–800 mA
• Place 10µF + 0.1µF decoupling capacitors close to 3V3 pin
• Keep power traces wide and short

⚠️ Brownouts are the #1 cause of ESP32 instability.

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Antenna & RF Layout Rules

⚠️ Very Important

• Keep copper clear under antenna
• No ground pours or traces under antenna area
• Follow Espressif keep-out recommendations
• Place module at PCB edge if possible

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Common Design Mistakes

❌ Powering ESP32 from 5V
❌ Using GPIO6–11
❌ Driving strapping pins at boot
❌ Weak 3.3V regulator
❌ Traces under antenna

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Recommended Bring-Up Checklist

1. Verify 3.3V rail (no load)
2. Check EN pulled HIGH
3. Check IO0 pulled HIGH
4. Reset → observe serial output
5. Pull IO0 LOW → reset → flash test firmware

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Reference

• ESP32-WROOM-32E Datasheet
• Espressif Hardware Design Guidelines

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Notes

This document is intended for PCB designers and electronics engineers working with ESP32-WROOM-32E in custom hardware.

Keep this file updated if pin usage or constraints change.