Minecraft wiki entry for Piston, associated text: A more advanced (and much larger) circuit can double-push pistons, without extending them (and stopping the system). This circuit can also can be powered with torches from below, to hide all the wiring. Either way, input to any of the green-marked squares, so the signal reaches all the way round without needing extra repeaters. The design can be mirrored to push a pair of pistons on the same switch.