Minecraft wiki entry for Pumpkin_and_melon_farming, associated text: This design uses a sticky piston to push the observer down to harvest a pumpkin or melon. The piston does not receive power from the direction it faces, so another route is needed to transmit the signal. A slime block is placed between the observer and piston to help extract the observer's signal. The signal is passed through a 2-tick redstone repeater that extends it enough for the sticky piston to pull the slime block and observer back to their original position.