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Switches a redstone output on and off every half second, forever. It is the "hello world" of automation: the same loop drives a warning light at a train crossing, a flashing beacon on a tower, or the pulse that keeps a contraption moving.

#What to build

Put a Redstone Lamp on top of the computer. Anything that reacts to redstone works in its place: a piston, a door, a note block, a Create Redstone Link set to transmit.

Run it with blink, stop it with Ctrl+T or the Stop button. When it stops, the output keeps its last value: the lamp may stay lit until another program changes it or the computer reboots or is switched off.

#How it works

local side = "top"
local on = false

The side is kept in a variable, so changing it means changing one word: "bottom", "left", "right", "front" or "back" (left and right as seen facing the screen). on remembers the current state of the lamp.

while true do
  on = not on
  rs.set(side, on)
  sleep(0.5)
end

while true do repeats forever. not on flips the state: false becomes true and back. rs.set() accepts true (full power, 15) or false (0), or a number from 0 to 15. With half a second on and half a second off, the lamp blinks once a second.

#Ideas

• Blink faster or slower: change 0.5. Use two different delays for a short flash and a long pause: rs.set(side, true) sleep(0.1) rs.set(side, false) sleep(1.9).
• Blink two lamps in turn, like a level crossing: set "left" to on and "right" to not on.
• Blink only while a lever on the back is on: wrap the body in if rs.get("back") > 0 then ... end, as in step 10 of the tutorial.

• Blink a set number of times, then stop:

  for i = 1, 5 do
    rs.set("top", true)
    sleep(0.5)
    rs.set("top", false)
    sleep(0.5)
  end
  print("Blinked 5 times")

  Screen

  Blinked 5 times

• Send a strength instead of on and off: rs.set(side, 7) gives a signal of 7, which goes 7 blocks along redstone dust and which a Create Nixie Tube shows as a number. See rs and the redstone guide.

#The program

-- Blinks a redstone output. Put a redstone lamp on top of the computer.
-- Stop it with Ctrl+T or the Stop button.
local side = "top"  -- also: bottom, left, right, front
local on = false
while true do
  on = not on
  rs.set(side, on)  -- true = 15, false = 0
  sleep(0.5)
end