Receveur sans porte 2.0

local modem = peripheral.find("modem")
rednet.open("top")

while true do
    local id, message
    id, message = rednet.receive()
        if message == "N4" then
        redstone.setOutput("back", true)
        sleep(0.4)
        redstone.setOutput("back", false)
        end
end