Redstone Repeater

A Redstone Repeater is a special block that interacts with Redstone. It has three main functions: acting as a repeater, a diode, and a delayer. Most likely, the reason they are called 'Redstone Repeaters' is for their primary use of repeating signals, since Redstone only travels up to 16 blocks without a signal booster. However, signals are only accepted in 3 directions: Either side (see below), front (output), or back (input). It also delays the signal by 1-4 ticks (selectable) so that long timing circuits of inverters will not be required for timed mechanisms any longer. Existing (traditional) repeaters/delayers still work.

Main uses
The repeater has multiple uses due to its complex nature. Each of the main functions are described below. For more information on the use of repeaters in circuits, see Redstone Circuits.

Repeater
The primary function of the repeater is to "refresh" a redstone signal, allowing it to travel another 15 blocks (at the cost of a minimum 1-tick delay per repeater), or 17 blocks with an opaque block before and after the repeater. Repeating signals without the delay introduced by a redstone repeater requires an instant repeater circuit (a.k.a. Instawire).

Wire/diode/amplifier
The repeater accepts input from 3 possible point: its back (the side closest to you when you place it) or the sides, but only sends output to its "front" (the opposite side). It only interacts with its sides if another repeater is placed facing that side, in which case the new repeater will "latch" the original one (see below), other signals are only accepted at its back.

Any of the following can serve as the input to a repeater when placed directly behind it:
 * A piece of redstone wire, which will automatically attach itself to the repeater
 * A redstone torch
 * A block charged by wire or any other method
 * Any type of switch (lever, button, pressure plate, etc.)
 * Another powered repeater pointing in the same direction placed at the back of it

Any of the following will receive a repeater's output when placed directly in front of it:
 * Any piece of redstone wire, regardless of orientation
 * Any type of block that can be charged
 * The block will be "strongly" charged: This means that it can pass on its charge to wire, just as when placed over a torch.
 * Any device that can be controlled by redstone (door, minecart track, note block, etc.)
 * Another repeater pointing in the same direction placed at the front of it

Note that a repeater can receive a signal from a weakly powered block (or anything else), and will boost the signal to maximum strength: A block will be strongly charged, while a wire or other device will be powered at the maximum power level of 15.

Clock/delay
By right-clicking on the repeater, you can set its delay from 1 to 4 ticks. (Each redstone tick is 0.1 seconds, or 2 game ticks.) Normally, this corresponds to a time delay of 0.1 to 0.4 seconds. Longer delays can be made with multiple repeaters; for example, a repeater set to '4' and another to '1' will give a half second delay (0.4s + 0.1s = 0.5s).

Repeaters greatly simplify the construction of delay lines and provide far more granular timing than chains of redstone torches. For example, a repeater with a long line of torches for delay would blink faster than the same design with repeaters set to four every other piece of redstone, allowing for more compact slowed down clocks.

The simplest possible clock can be implemented with only one torch and one repeater, connected in a loop, with the repeater delay set to 4 (the highest setting). Setting the delay to 3 yields a 4-clock, which requires some fancy wiring to build from torches alone. With a delay lower than 3, the torch in this circuit burns out. However, repeaters don't burn out the way torches do. If two repeaters with the same delay are connected to each other in a loop and a short pulse is introduced externally, the pulse will bounce back and forth between the repeaters indefinitely. With the delay set to 1, this circuit has a period of 2 ticks, making it a 1-clock.

The Latch


You can create a latch by combining two Redstone Repeaters: The first provides input and output, while a second, pointing into the left or right side of the first, provides the latch functionality. When the second repeater is powered, the first is "latched", and will remain on or off even if its input changes. (Visually, the latched repeater's delay switch is replaced by a crossbar.) When the second repeater is turned off, the first one will go back to repeating its input. Note that this is not simply a matter of powering the first repeater from the side, as redstone dust, levers, etc., will not latch a repeater.

This provides the equivalent of a Gated D Latch. Two such latches can also be combined to produce a "flip-flop", a.k.a. "toggle", circuit.

Note blocks
The redstone repeater is often used in combination with note blocks. In the making of a song, several repeaters are used to create rhythm in a song. It can also be used to make a device using a jukebox. Some players use redstone repeaters by linking together note blocks and buttons to make a doorbell in their homes.

Trivia

 * In the coding, it is referenced as "diode".
 * Repeaters can be used as one-way doors by placing the repeater under an arch. The arch can only passed through if there's a block overhead on the side you're trying to enter it from.
 * If the player shoots an arrow onto a repeater, every time the repeater changes state it will make the sound that arrows make as they make contact with a block.