How to Use a Redstone Repeater in Minecraft

Guide Java Bedrock

Quick answer: A redstone repeater does four jobs: it refreshes a fading signal back to full strength 15, works as a one-way diode (signals only pass from back to front), adds an adjustable delay of 0.1 to 0.4 seconds, and locks its output state when another repeater or comparator powers its side. Right-click it to cycle through the four delay settings.

What you need

Redstone repeater (3 stone + 2 redstone torches + 1 redstone dust)
Redstone dust and a lever for testing
Optional: a comparator or second repeater to try locking

Step by step

Craft or loot one. A repeater takes 3 stone (smelted cobblestone), 2 redstone torches and 1 redstone dust - or grab the two that generate naturally in every jungle temple.
Place it facing the right way. The arrow on top points from input to output. A repeater only accepts a signal at its back and only outputs from its front, so a backwards repeater does nothing.
Extend a dying signal. Dust fades by 1 strength per block and dies at 15. Put a repeater just before that point and it re-emits at full 15, buying another 15 blocks. Chain them for long wires.
Set the delay. Right-click (use) the repeater to move the little torches apart: the four settings are 1, 2, 3 and 4 redstone ticks (0.1, 0.2, 0.3 and 0.4 seconds). Every repeater adds at least 0.1s, so account for it in timed circuits.
Use it as a diode. Because signals only travel one way through a repeater, placing one between two circuit sections stops them back-feeding into each other - the classic fix when a piston door fires itself.
Lock it for memory cells. Power the side of a repeater with another repeater or a comparator pointing into it and it freezes in its current on or off state until the side signal stops. Two side-locked repeaters in a loop make a 1-bit memory cell.

Java vs Bedrock

Works the same in Java and Bedrock, including side-locking. The one difference to watch: Java pulses shorter than the set delay get stretched to match it, which makes some 1-tick Java circuits behave differently from Bedrock builds.

Versions: Repeaters have been in the game since Java Beta 1.3 (February 2011), and two generate in every jungle temple since 1.3.1. The four delay settings and side-locking have been stable ever since.

Frequently asked questions

How many repeaters do I need for a long wire?

One for every 15 blocks of dust. Each repeater resets the signal to full strength 15, so a 100-block run needs about 6-7 repeaters - each adding at least 0.1 seconds of delay.

Why is my repeater not powering the next block?

It is probably facing backwards - the arrow must point away from the input. Also check that you are powering its back, not its side: a side signal locks the repeater instead of passing through.

What does locking a repeater do?

A side-powered repeater freezes its output: if it was on, it stays on even when the back input turns off, and vice versa, until the side signal releases it. That is the basis of memory cells and hidden-input locks.