startup

while true do
  local id,message = rednet.receive()
  if message=="ping" then
    sleep(1.5)
    for i =1,10 do
      sleep(0.3)
      redstone.setOutput("back",true)
      sleep(0.1)
      redstone.setOutput("back", false)
      i = i + 1
    end
  end
end