Minecraft wiki entry for Repeater_reboot_system, associated text: This method uses a small circular track with a detector rail, powered rails and some regular rails. The powered rails must always be powered. The detector rail should be next to some redstone going to the side of the repeater (read: not connected to the circuit). When the minecart activates the Detector Rail, it will fire the redstone signal and launch the repeater due to a block update next to it.