Autocompactron

local function select_item(item, mincount)
    local mincount = mincount or 1
    for i = 1, 16 do
        local it = turtle.getItemDetail(i)
        if it and it.count and it.name and it.count >= mincount and it.name == item then
            turtle.select(i)
            return true
        end
    end
    return false
end

local function run_cycle()
    turtle.up()
    select_item "minecraft:iron_block"
    turtle.place()
    turtle.up()
    select_item("minecraft:redstone", 2)
    turtle.place()
    turtle.down()
    turtle.down()
    turtle.dropUp(1)
    sleep(5)
end

while true do
    if turtle.getFuelLevel() > 4 then
        if select_item "minecraft:iron_block" and select_item("minecraft:redstone", 2) then
            print "Running."
            run_cycle()
        else
            print "Insufficient items."
        end
    else
        print "Insufficient fuel."
    end
    sleep(2)
end