2.6 KiB
2.6 KiB
Programming Header Pinout
Header J2 - 2x4 Programming Header (8 Pins)
Use this header to connect an external USB-to-Serial adapter (CP2102, CH340, FT232, etc.) for flashing the ESP32.
Pinout (Top View)
┌─────────────┐
│ 1 2 3 4 │ ← Top row
│ 5 6 7 8 │ ← Bottom row
└─────────────┘
| Pin | Signal | ESP32 Connection | Description |
|---|---|---|---|
| 1 | +3V3 | +3V3 Power Rail | Optional - Power ESP32 from programmer |
| 2 | GND | GND | Ground reference |
| 3 | UART_TX | GPIO1 (UART TX) | ESP32 transmits to programmer |
| 4 | UART_RX | GPIO3 (UART RX) | ESP32 receives from programmer |
| 5 | DTR | GPIO0 | Data Terminal Ready (auto-reset for flashing) |
| 6 | RTS | EN | Request To Send (auto-reset for flashing) |
| 7 | NC | - | Not connected (spare) |
| 8 | NC | - | Not connected (spare) |
Connection to USB-to-Serial Adapter
When connecting your USB-to-Serial adapter:
| Adapter Pin | J2 Pin | Signal |
|---|---|---|
| VCC | Pin 1 | +3V3 (optional - only if powering ESP32 from adapter) |
| GND | Pin 2 | GND |
| RX | Pin 3 | UART_TX (receives TX from ESP32) |
| TX | Pin 4 | UART_RX (sends to RX of ESP32) |
| DTR | Pin 5 | DTR (auto-reset) |
| RTS | Pin 6 | RTS (auto-reset) |
| - | Pin 7 | NC (spare) |
| - | Pin 8 | NC (spare) |
Important Notes:
- Do NOT connect VCC if your ESP32 is already powered from J1 (JST connector power input)
- Always connect GND - this is critical for proper operation
- RX/TX are swapped - Adapter RX goes to ESP32 TX, and vice versa
- DTR and RTS enable automatic reset during flashing (no need to press buttons)
Optional Pull-up Resistors
For maximum reliability, add pull-up resistors:
- R5: 10kΩ between J2 Pin 5 (DTR) and +3V3
- R6: 10kΩ between J2 Pin 6 (RTS) and +3V3
Most USB-to-Serial adapters have built-in pull-ups, but adding them on the board ensures reliable operation.
Flashing Process
- Connect USB-to-Serial adapter to J2 header
- Power the board (via J1 JST connector or J2 Pin 1)
- Use
esptoolor ESPHome to flash:esptool.py --port /dev/ttyUSB0 write_flash 0x0 firmware.bin - The DTR/RTS signals will automatically put ESP32 into boot mode
Common USB-to-Serial Adapters
- CP2102: Common, reliable, good driver support
- CH340: Very common, cheap, good for Linux
- FT232: Premium option, excellent driver support
- PL2303: Older, less reliable
All of these will work with this header configuration.