blog-code/godot-arduino-1-led-first-light/README.md

Part 1 — Your First Arduino Round-Trip

Code for "Godot Isn't Just for Games: Your First Arduino Round-Trip".

A button in a Godot 4 scene reaches down a USB cable — through a Python-to-UDP bridge — and lights a real LED on an Arduino Uno.

Contents

arduino/
  LedBasics/LedBasics.ino      # reads L1/L0 off serial, drives the LED on D13
  bridge/bridge.py             # serial <-> UDP relay (run this, leave it running)
  bridge/start-bridge.bat      # Windows: double-click to start the bridge
  bridge/start-bridge.command  # macOS/Linux: double-click (or ./) to start the bridge
  bridge/ledtest.py            # standalone LED command test, no Godot (see Debugging)
godot/
  ArduinoGodot/                # Godot 4 project: one styled toggle button

Wiring

D13 → 220 Ω resistor → LED long leg (anode); LED short leg (cathode) → GND. No breadboard? The Uno's onboard LED is already on D13.

Run it

1. Flash arduino/LedBasics/LedBasics.ino to the Uno (Arduino IDE, 115200 baud).
2. Bridge: pip install pyserial, then start the relay and leave it running — either double-click arduino/bridge/start-bridge.bat (Windows) / arduino/bridge/start-bridge.command (macOS), or run python arduino/bridge/bridge.py yourself.
3. Godot: open godot/ArduinoGodot/ in Godot 4, press Play, click the button.

The bridge auto-detects the board and reconnects if the cable pops out.

Tip — one-click launch: the start-bridge.* files just run bridge.py from a double-click, so you skip the terminal each session. On Windows, right-click start-bridge.bat → Send to → Desktop (create shortcut). On macOS, if double-clicking opens it in an editor instead of running, mark it executable once: chmod +x start-bridge.command.

Debugging

If the LED won't light and you can't tell whether it's Godot or the bridge, run python arduino/bridge/ledtest.py L1 with the bridge running. It fires an L1/L0 command straight at the bridge's command port, exactly like Godot does. LED lights → the Arduino and bridge are fine, so the fault is on Godot's side. Stays dark → the problem is the bridge or the wiring, and Godot is off the hook.