I have 2 hoppers with one facing a dropper completely full of the same item and the other facing into the first with every slot filled with 1 item except for the first which has 18. The idea is that when the hopper reaches 19 items in the first slot it will activate a comparator to signal strength 2 which unpowers a repeater pointed into the dropper. It should get the item unpower the repeater which pulses the hopper facing the dropper to let 1 item in then empty the single item back into it to make it full again. About 50% of the time the comparator doesnt seem to get the reading of signal strength 2 and doesnt change the torch but still unlocks the hopper and lets an item through