Minecraft wiki entry for Miscellaneous, associated text: Design A is the simplest form of the circuit. The hopper is initially empty so K stays low regardless of whether A is high or low. When G goes high, the item in the dropper moves to the hopper so K goes high as well. The hopper is suspended by A so as long as A is high, the item doesn't go back to the dropper so K is kept high. But there is a downside to this design. When triggered by G while A is low, a 1 tick on-pulse is emitted from K.