Godot + Arduino series: companion project code
Self-contained project code for the "Godot Isn't Just for Games" series: Arduino sketches, the Python serial<->UDP bridge, and the Godot 4 projects, one folder per article.
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tyler parker
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/*
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* LedBasics.ino — Part 1: the minimal round trip.
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*
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* Godot sends "L1" / "L0" over USB serial (via the Python bridge) and this
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* sketch toggles an LED. No sensors yet — Part 2 (JoystickBridge.ino) adds the
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* joystick telemetry going the other way.
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*
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* PROTOCOL
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* IN (host -> Uno): "L1" = LED on, "L0" = LED off (newline-terminated)
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*
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* WIRING
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* D13 -> 220 ohm resistor -> LED anode (+, long leg)
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* LED cathode (-, short leg) -> GND
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* (D13 is also the Uno's onboard LED, so it flashes during every upload —
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* a free "is this pin alive" check before you've wired anything.)
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*/
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const uint8_t PIN_LED = 13; // LED via 220 ohm resistor (also the onboard LED)
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char cmdBuf[8];
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uint8_t cmdLen = 0;
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void setup() {
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Serial.begin(115200);
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pinMode(PIN_LED, OUTPUT);
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digitalWrite(PIN_LED, LOW);
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}
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void loop() {
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// Commands in from Godot: "L1" / "L0", one per line.
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while (Serial.available() > 0) {
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char c = Serial.read();
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if (c == '\n' || c == '\r') {
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if (cmdLen >= 2 && cmdBuf[0] == 'L') {
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digitalWrite(PIN_LED, cmdBuf[1] == '1' ? HIGH : LOW);
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}
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cmdLen = 0;
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} else if (cmdLen < sizeof(cmdBuf) - 1) {
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cmdBuf[cmdLen++] = c;
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} else {
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cmdLen = 0; // overflow guard: drop the runt line
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}
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}
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}
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#!/usr/bin/env python3
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"""
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bridge.py — serial <-> UDP relay between the Arduino Uno and Godot (Main.gd)
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Godot never touches the serial port; it only speaks UDP:
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* it LISTENS on 127.0.0.1:4242 for telemetry ("x,y,btn")
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* it SENDS to 127.0.0.1:4243 for LED commands ("L1" / "L0")
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This bridge sits in the middle:
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Arduino --serial line "x,y,btn\\n"--> bridge --UDP--> Godot :4242
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Godot :4243 --UDP "L1"/"L0"--> bridge --serial--> Arduino
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Double-click friendly: with no arguments it auto-detects the Arduino port and
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keeps the window open on exit so you can read any error. Override if needed:
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python bridge.py --port COM3
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python bridge.py --port COM3 --baud 115200 # baud must match the .ino
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Requires pyserial: pip install pyserial
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"""
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import argparse
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import socket
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import sys
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import time
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try:
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import serial # pyserial
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from serial.tools import list_ports
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except ImportError:
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print("pyserial not installed. Run: pip install pyserial")
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input("\nPress Enter to close...")
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sys.exit(1)
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TELEMETRY_ADDR = ("127.0.0.1", 4242) # Godot listens here
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COMMAND_PORT = 4243 # Godot sends LED commands here
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# Substrings that identify a typical Uno / clone in the port description.
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PORT_HINTS = ("arduino", "ch340", "usb-serial", "usb serial", "wchusb", "cp210")
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def pick_port() -> str:
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"""Return a serial port: the obvious Arduino one, else the only one, else ask."""
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ports = list(list_ports.comports())
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if not ports:
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raise SystemExit("No serial ports found. Is the Uno plugged in?")
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for p in ports:
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blob = f"{p.description} {p.manufacturer or ''}".lower()
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if any(h in blob for h in PORT_HINTS):
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print(f"auto-detected {p.device} ({p.description})")
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return p.device
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if len(ports) == 1:
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print(f"using only port {ports[0].device} ({ports[0].description})")
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return ports[0].device
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print("Multiple serial ports found:")
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for i, p in enumerate(ports):
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print(f" [{i}] {p.device} {p.description}")
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choice = input("Pick a number: ").strip()
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return ports[int(choice)].device
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def run(port: str, baud: int) -> None:
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# UDP socket: sends telemetry to Godot AND receives LED commands from it.
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# Bind to all interfaces ("") not just 127.0.0.1 — on some Windows setups a
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# loopback-only bind won't see packets whose source the sender picked freely.
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udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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udp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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udp.bind(("", COMMAND_PORT))
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udp.setblocking(False)
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# Open the serial port. A short timeout keeps readline() from blocking forever.
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ser = serial.Serial(port, baud, timeout=0.05)
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time.sleep(2.0) # Uno auto-resets when the port opens; wait for the sketch to boot
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ser.reset_input_buffer()
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print(f"bridge up: {port}@{baud} -> UDP {TELEMETRY_ADDR}, <- UDP :{COMMAND_PORT}")
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print("leave this window open. Ctrl+C to quit.")
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try:
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while True:
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# 1) Arduino -> Godot: forward each complete telemetry line.
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line = ser.readline() # b"x,y,btn\r\n" or b"" on timeout
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if line:
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text = line.strip()
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if text:
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udp.sendto(text, TELEMETRY_ADDR)
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# 2) Godot -> Arduino: drain any pending LED commands, newest applied last.
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while True:
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try:
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data, src = udp.recvfrom(64)
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except BlockingIOError:
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break
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except ConnectionResetError:
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# Windows: a prior sendto hit a closed port; ICMP resets recv. Ignore.
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break
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cmd = data.strip()
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if cmd in (b"L1", b"L0"):
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ser.write(cmd + b"\n")
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ser.flush()
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print(f"cmd {cmd.decode()} from {src} -> serial")
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else:
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print(f"ignored UDP {data!r} from {src}")
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except KeyboardInterrupt:
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pass
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finally:
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ser.close()
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udp.close()
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print("\nbridge closed.")
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def main() -> None:
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ap = argparse.ArgumentParser(description="Arduino <-> Godot serial/UDP bridge")
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ap.add_argument("--port", help="serial port, e.g. COM3 (auto-detected if omitted)")
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ap.add_argument("--baud", type=int, default=115200, help="must match JoystickBridge.ino")
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args = ap.parse_args()
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try:
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port = args.port or pick_port()
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run(port, args.baud)
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except Exception as e:
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# Keep the window open so double-click users can actually read the error.
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print(f"\nERROR: {e}")
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input("\nPress Enter to close...")
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if __name__ == "__main__":
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main()
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@@ -0,0 +1,21 @@
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#!/usr/bin/env python3
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"""
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ledtest.py — isolate the bridge's receive path from Godot.
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Sends a single LED command straight to the bridge's command port, exactly like
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Godot does. If the running bridge prints "cmd L1 ... -> serial" (and the LED
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lights), the bridge's receive side is fine and any failure is on Godot's end.
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If the bridge stays silent even for this, the problem is the bridge/binding.
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Usage (with bridge.py already running):
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python ledtest.py L1 # turn LED on
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python ledtest.py L0 # turn LED off
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"""
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import socket
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import sys
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msg = (sys.argv[1] if len(sys.argv) > 1 else "L1").encode()
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sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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sock.sendto(msg, ("127.0.0.1", 4243))
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print(f"sent {msg!r} to 127.0.0.1:4243")
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