Drive a physical LED from Minecraft
This beginner experiment demonstrates the route redstone → SerialCraft I/O Module → USB serial → Arduino Uno R3 → LED.
Hardware
You need an Uno R3, one ordinary LED, a 220–330 Ω resistor, breadboard, jumper wires and a USB data cable.
Connect Uno D9 → resistor → LED anode, then the LED cathode to GND. Do not connect mains-powered devices or motor loads directly to D9.
Configure the game
- Install the version-compatible Minecraft 26.2, Java 25, Fabric Loader, Fabric API and SerialCraft.
- Connect the Uno at 115200 baud.
- Place an I/O Module, open Boards → Configuration, set the Channel to
led_verde, and choose Minecraft → Hardware. - In the world, right-click one of the module's terminals to set it as a green input face and connect a lever or redstone line. The Diagnostics tab does not edit terminals.
- Choose DIGITAL for on/off; ANALOG for values proportional to the received redstone strength.
With full redstone, the expected message is led_verde:255; with no redstone, led_verde:0. An Uno sketch can read complete lines and apply the value with analogWrite(9, value).
For working firmware and the entire connection procedure, use the maintained Uno R3 example. Reading only part of a line or using a different baud rate causes confusing failures.
Debug it in layers
First verify the serial connection, then the I/O Module channel and mode, then the redstone face, and finally LED wiring and polarity. Avoid opening Arduino IDE's serial monitor while SerialCraft is already holding the same USB port.
Important: an Arduino can retain the last LED level after a hard disconnect. Hardware-side watchdog logic is appropriate when an output must return to a safe state.