Repeaters

(For creating repeaters, see *Redstone Dust crafting combinations)

Redstone repeaters have three main fuctions. They act as a repeater, a diode and a delayer. They can be used to delay the charge given off from a button, they can also be used for pulse generator or clocks (see Pulse Generators for more information). They are the simplified and compact version of NOT gates, which have the same uses. Repeaters can be set to 4 different delays: 1 to 4 ticks. Each tick represents 0.1 seconds, so 1 tick = 0.1 seconds, 2 ticks = 0.2 seconds, and so on. Repeaters are generally used to "refresh" a current, allowing it to travel another 16 pieces of wire.

(Click for larger Image)
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 neighbouring spaces. This makes it quite useful in tightly packed circuits.

Any of the following can serve as an input to a repeater when placed dirrectly behind it:
-A piece of redstone wire, which will automatically attach itself to the repeater (as of 1.7)
-A redstone torch
-A block charged by wire or any other method
-Any type of switch (See Switches)
-Another repeater pointing in the same direction

Any of the following can serve as an output to a repeater when placed dirrectly infront of it:
-A piece of redstone wire, regardless of the orientation
-Any type of block that can be charged
-Any device that can be controlled by redstone
-Another repeater pointing in the same direction

As delayers

As mentioned above, repeaters can be used as a delayer for redstone current. They have 4 different presets, each adding 0.1 seconds to the delay, and can be chained to provide longer delays.

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 redstone 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.

-Joshua Richardson