📖 Overview

This project is a universal USB-to-Serial flasher board based on the CH340C USB-UART bridge.

It is designed for ESP8266, ESP32, ESP01, Arduino, and other microcontrollers with UART bootloading.

Unlike cheap USB-to-TTL adapters, this flasher includes:

Auto-programming circuit (RTS/DTR → EN/IO0)

Reset & Boot pushbuttons for manual control

Colored silkscreen pin labels for easy connection

Status LEDs (PWR, TX, RX)

USB-C connector with ESD protection

Clean PCB layout with ground pours

This makes it a reliable, beginner-friendly, and professional-quality programmer.

⚡ Features

🔌 USB-C connector (reversible, modern interface)

⚡ CH340C USB-UART chip (stable drivers, Windows/Linux/macOS support)

🔒 ESD protection diodes on USB D+/D−

🔄 Auto-reset circuit for ESP32/ESP8266 (no need to hold BOOT manually)

⏹ Manual RESET & BOOT buttons for recovery and testing

🌈 Color-coded silkscreen pin labels for easy wiring:

3.3V (Red), 5V (Purple), GND (Black), TX (Orange), RX (Green), RST/DTR (Blue), EN/IO0 (Yellow)

💡 LED indicators:

Green = Power

Orange = TX activity

Yellow = RX activity

🛡️ SJ jumpers (SJ_RTS, SJ_DTR) to enable/disable auto-programming

📏 Compact PCB: ~62 × 27 mm

🧩 Pinout

Pin Function Color

3.3V 3.3 V output 🔴 Red

5V 5 V from USB 🟣 Purple

GND Ground ⚫ Black

TX UART Transmit 🟧 Orange

RX UART Receive 🟩 Green

RST Reset / EN 🟦 Blue

DTR Data Terminal Ready 🟦 Blue

EN Chip Enable 🟨 Yellow

IO0 Boot Mode Select 🟨 Yellow

🛠️ SJ_RTS and SJ_DTR

Two solder jumpers are included:

SJ_RTS → Connects RTS → EN (reset line).

SJ_DTR → Connects DTR → IO0 (boot line).

🔹 Why they are useful

Default = closed (auto-programming works normally).

If you cut the jumper, auto-reset for that pin is disabled.

This lets you take manual control via the pushbutton, useful for debugging or when using the board as a generic USB-UART adapter.

👉 For ESP32/ESP8266 flashing: leave both SJ closed.

👉 For Arduino or other MCUs without auto-program support: you can cut them.

📦 Bill of Materials (BOM)

Here are the key components (from your BOM):

Qty Reference Value Part No / Notes 1 U2 CH340C USB-UART bridge 1 U1 SGM2212-3.3 3.3V LDO regulator 2 Q1, Q2 MMBT3904 NPN for auto-program 2 R8, R9 100k Base pulldown resistors 2 R1, R2 10k Base resistors (RTS/DTR) 2 R4, R5 10k Pull-ups (EN, IO0) 1 R3 1k Power LED resistor 2 R6, R7 2.2k TX/RX LED resistors 3 LED1-3 Green/Orange/Yellow Power, TX, RX indicators 3 D2–D4 LESD5D5.0 USB ESD protection 1 D1 1N5819 Reverse protection 5 C1–C5 10 µF Bulk capacitors 3 C3, C5, C6 100 nF Decoupling capacitors 2 SW1, SW2 Reset/Boot buttons Tactile SMD 1 USB1 USB-C connector Receptacle (📑 Full detailed BOM available in Excel file)

🖼️ PCB Layout

Final routed PCB layout with ground pours

🖼️ PCB Schematic

Final routed PCB Schematic

🔌 How to Use

Connect the board via USB-C to your PC.

Install CH340 drivers (Windows only, Linux/macOS usually auto-detect).

Connect your target microcontroller using the 9-pin header.

ESP32/ESP8266: connect 3.3V, GND, TX, RX, EN, IO0.

Arduino: connect VCC, GND, TX, RX, RST.

Flashing ESP8266/ESP32:

Auto-programming works (no need to hold BOOT).

Use Arduino IDE / esptool.py / PlatformIO to upload code.

Flashing Arduino/AVR:

Connect TX/RX + RST.

Disable SJ jumpers if needed.

Manual boot mode:

Hold BOOT + press RESET → release RESET, then release BOOT.

LEDs:

PWR = board powered

TX = blinks when sending data

RX = blinks when receiving data

📑 Why Use This Board

🟢 Safer for ESP (3.3V regulated output, correct auto-programming circuit).

🟢 Beginner-friendly (color-coded silkscreen, clear pinout).

🟢 Robust USB-C connector with ESD protection.

🟢 Supports multiple targets: ESP32, ESP8266, ESP01, Arduino, STM32 (UART bootloader).

🟢 Debug-friendly: RESET/BOOT buttons, jumpers to disable auto-reset.

📸 Project Assets

✅ 3D Render (top view)

✅ PCB Layout (routing + pours)

✅ BOM (Excel, LCSC parts)

✅ Schematics (EasyEDA / PDF)

All files can be published on GitHub/PCBWay for sharing.

📂 Downloads

📄 Schematic (PDF)

📄 BOM (Excel)

📄 Pick And Place (Excel)

📄 PCB Layout (PNG)

📄 3D Preview (PNG)

🌐 Author & Contact

👨‍💻 Designed by ElectroIoT

🔗 Website: https://electroiot.in

▶️ YouTube: ElectroIoT-IN

📸 Instagram: @electroiot_in

📧 Email: electroiot.in@gmail.com