ComputerCraft

Control redstone with a computer

Read and write redstone signals from Lua. Build automatic doors, alarms, or any redstone contraption driven by code.

Category: ComputerCraft Difficulty: Beginner Time: ~15 min

What you will end up with

A CC:Tweaked computer that detects a redstone signal on one side and toggles a signal on another side — essentially a programmable repeater, timer, or gate. The same technique is used to build automatic doors, alarms triggered by pressure plates, and timed pulse generators.

What you need

A Computer (from CC:Tweaked)
Any redstone input device — a lever, button, or pressure plate
Any redstone output device — a door, lamp, or piston
Redstone dust to connect them to the sides of the computer (optional if placed directly adjacent)

Each face of the computer corresponds to a direction string in Lua: "top", "bottom", "left", "right", "front", "back". Place your devices on the matching side.

Step by step — automatic door

Place a Computer in the world.
Place a pressure plate touching the left side of the computer (or connect it with redstone dust).
Place an iron door touching the right side of the computer.
Right-click the computer and create a new program:
edit door.lua
Type the following program:
-- door.lua -- Opens the door when pressure plate is triggered while true do local signal = redstone.getInput("left") redstone.setOutput("right", signal) os.sleep(0.1) end
Save and exit (Ctrl → Save → Ctrl → Exit), then run the program:
door
Step on the pressure plate — the door opens. Step off — it closes.

How the redstone API works

CC:Tweaked exposes the redstone API for reading and writing signals on each face:

redstone.getInput("side") — returns true if the side is receiving a signal
redstone.setOutput("side", true/false) — turns the output signal on or off
redstone.getAnalogInput("side") — returns signal strength 0–15
redstone.setAnalogOutput("side", strength) — sets analog output strength

Example — timed alarm

This script pulses a bell or alarm for 2 seconds whenever the input is triggered, then resets — regardless of how long the input stays on.

-- alarm.lua
-- Pulses output for 2 seconds when input is triggered

while true do
  -- Wait for a rising edge on the "back" side
  os.pullEvent("redstone")
  if redstone.getInput("back") then
    redstone.setOutput("front", true)
    os.sleep(2)
    redstone.setOutput("front", false)
  end
end

os.pullEvent("redstone") pauses the script until any redstone input changes — this is more efficient than polling in a tight loop with os.sleep().

Troubleshooting

Output not working — make sure the device is on the correct side. Use redstone.getSides() to list all side names.
Signal fires multiple times — use os.pullEvent("redstone") instead of a polling loop to detect edge transitions cleanly.
Door opens but does not close — check that you are setting the output to false when the input drops.

← Back to Tutorials