PlayerSensor

local sensor = peripheral.wrap("left")

function Get()
    local players = sensor.getNearbyPlayers(10)
    local count = 0
    for key,value in pairs(players) do
        count = count + 1
    end
    print("Found " .. tostring(count) .. " players")
    return count
end

while true do
    if Get() > 1 then
        rs.setAnalogOutput("back", 15)
    else
        rs.setAnalogOutput("back",0)
    end
end