Redstone Repeater

The Redstone Repeater is a block added to the game in Beta 1.3. It was originally implemented by Jeb. It is designed to delay redstone signals, and right-clicking it will toggle the block through 4 possible settings; originally these settings were "1, 2, 5 and 7", but this was changed to "1, 2, 3, and 4" for simplicity's sake. Existing repeaters/delayers will still work. They were designed to save space in Redstone Circuits.

As shown in the preview video the block has three main functions: acting as a repeater, a diode, and a delayer. The block repeats signals it receives like a network bridge, so that using two not-gates every 15 blocks will no longer be necessary. Signals are also accepted only in some directions, allowing the block to function much like a diode in an electrical circuit. It also delays the signal so that long timing circuits of inverters will not be required for timed mechanisms any longer (though old timing grids will still work).

Redstone Repeater Video Tutorial - However this video makes some errors in saying there is no delay.

Uses
The repeater serves many purposes:

As Wire/Diode






The repeater only accepts input from its "back" (the side closest to you when you place it) and only sends output to its "front" (the opposite side). It does not interact with any of its other neighboring spaces. This makes it quite useful in tightly packed circuits.

Any of the following can serve as the input to a repeater when placed directly behind it:
 * A cross-shaped piece of redstone wire
 * A straight piece of redstone wire running in the same direction as the repeater
 * A redstone torch
 * A block charged by wire or any other method
 * Any type of switch (lever, button, pressure plate, etc.)
 * Another repeater pointing in the same direction

Any of the following will receive output from a repeater when placed directly in front of it:
 * Any piece of redstone wire, regardless of orientation
 * Any type of block that can be charged (which will then propagate the charge in the same way 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

As of the Beta 1.3 release, a device placed directly in front of a repeater exhibits some strange behavior. If the input to the repeater is a redstone wire or torch then the effect on the device seems to be inverted, and if the input is anything else then the device isn't affected by the repeater at all. When the repeater and device are connected by wire, everything works as expected.

Another bug in the Beta 1.3 release is that repeaters fail to update their state when their input is a block being charged by a redstone wire and the piece of wire right next to the block is destroyed. If the wire is powering the repeater when it is destroyed then the repeater will stay on until some other event triggers an update for it, like placing a block next to it.

As Repeater
...

As Clock/Delay
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Trivia

 * The block looks like two shortened redstone torches attached to a stone plate, that has the texture of the top of the old stone slab but with an arrow on it that denotes the direction of the current, for simulating diodes.
 * The particles generated when the block is destroyed look like those of a Pumpkin.
 * If a Repeater is in a 2 block high space, like a tunnel, you will crouch automatically as you walk over it. However, you will not crouch if the repeater is blocking the entrance of a tunnel.
 * A Repeater placed directly next to a redstone capable block acts as a NOT NOT gate.
 * You can link many repeaters together by placing a line of redstone on top of any block and then activating the redstone. However it will not work if you do not place the redstone on a block. As seen/used in this video Redstone arrows floor
 * If you save your world then come back to it any chains of redstone repeaters stay in the state of which was logged off. They do not change until a neighbouring block is updated.