startup

while true do
  event = os.pullEvent()
  if(event == "redstone") then
    on = redstone.getInput("back")
  else
    on = false
  end

  if(on==true) then
    turtle.select(16)
    turtle.dropDown()
    turtle.dig()
  else
    placed = turtle.detect()
    if (placed==false) then
      turtle.select(16)
      turtle.place()
    end
    for i=1,15 do
      turtle.select(i)
      turtle.dropDown()
    end
    sleep(5)
  end
end