ElevatorServer

local CurrentLevel = 0;

local GEARSHIFT = "back";
local CLUTCH = "right";

rednet.open("TOP");

while true do
    local id, message = rednet.receive();
    if message == 0 then -- if cab has reached destination
        redstone.setOutput(CLUTCH, true);
    else
        local isUp = message > CurrentLevel;
        CurrentLevel = message;

        rednet.send(id, isUp);

        redstone.setOutput(GEARSHIFT, isUp);
        redstone.setOutput(CLUTCH, false);
    end
end