how do you craft a redstone repeater?

two more things it does that come in handy. it always puts out a full-strength signal, so if your line dies after 15 blocks, drop a repeater in and it carries on. and if you power one from the side with another repeater it locks, holding whatever state it's in. that's the basis of most simple memory circuits.

3 stone along the bottom, then torch, redstone dust, torch across the middle. has to be smooth stone, not cobblestone, so smelt your cobble once first. right-click a placed repeater to change the delay.