Redstone circuits/Transmission

A transmission circuit allows signals to move from one place to another.

Transmission types
For simple redstone structures, digital ("on/off") transmission will be sufficient.

For complex redstone structures, with banks of inputs or outputs, more sophisticated forms of transmission may be required, such as analog, binary, or unary transmission.

When numbers are represented by different types of transmission, they are said to be encoded.

Digital
A digital transmission is a transmission where all that matters is whether it is on or off.


 * Redstone wire


 * 1-wide, flat, silent
 * circuit delay: 1 tick per 18 blocks
 * A line of redstone dust is a simple and flexible transmission method.


 * "Smart wire"


 * 1-wide
 * circuit delay: none (rising edge) and 3 ticks per repeater (falling edge)
 * 'tl;dr: good for long distances, not good for fast pulses
 * Moving an entity (such as a minecart) into a tripwire line can activate a tripwire hook up to 40 blocks away.
 * While a piston moves a block, it effectively doesn't exist for redstone purposes (it won't provide or conduct power, etc.). However, when a piston moves an entity (like a minecart), the entity is moved at each game tick the piston is moving. Because of this, the minecart in smart wire moves up into the tripwire immediately, instantly activating the far tripwire hook, so there is no circuit delay on the input's rising edge. However, when the piston retracts, the minecart isn't pulled by it, but simply falls due to gravity, thus imposing a 3-tick delay per minecart to the input's falling edge. This difference between rising edge and falling edge behavior can cause on-pulses to lengthen and off-pulses to shorten, possibly even erasing short off-pulses over a number of smart wire repeaters. This makes smart wire less useful for rapidly changing states.
 * Smart wire should be built where it won't be triggered by mobs or other undesired entities: in the air, below ground, etc.
 * Earliest Known Publication: March 28, 2013

Numerous other methods exist for moving a redstone signal from one place to another. These methods may not be efficient or appropriate over long distances, but can be useful in compact redstone structures as their interaction with other components differs from redstone dust and smart wire.
 * Sticky pistons pushing blocks of redstone, or pushing regular blocks into a powered state, or pushing blocks between containers and comparators
 * Droppers pushing items into hoppers facing back into the droppers, with comparators to detect the item pushed into the hopper
 * Moving items through hopper pipes and reading locations with comparators

Transmission crossing
Tripwire circuits can cross each other without affecting each other, but redstone wires must be kept isolated so they don't interfere with each other.


 * Redstone bridge


 * silent
 * circuit delay: none
 * The fastest method for crossing wires is by building a bridge to take one wire over the other.
 * Variations: A common variation is to drop the center block one level, and cut a three-block passage into the ground under it for the north-south wire.


 * Repeater bridge


 * silent
 * circuit delay: 1 tick
 * A repeater bridge takes up less vertical space than a redstone bridge, but it adds 1 tick of delay to both wires.

Analog
An analog transmission (a.k.a. "hex line") is a transmission which outputs the same signal strength it receives as input. Because power levels can vary from 0 to 15, an analog transmission can convey 16 states in a single line.


 * Analog comparator line


 * flat, silent
 * circuit delay: 1 tick per 4 blocks
 * tl;dr: best option for short distances and tricky turns
 * The simplest analog line is a line of redstone comparators. However, like repeaters, comparators can draw a signal from an opaque block and push a signal into an opaque block, thus it is usually more efficient (in resources, and in signal delay) to place comparators every four blocks.
 * The signal strength of an analog comparator line (ACL) can be reduced or suppressed at some point along its length by feeding another signal into one of the comparators in subtraction mode. The signal can be overridden by feeding a stronger signal into one of the opaque blocks.
 * Because the redstone dust is not adjacent to any power or transmission components, only opaque blocks, it will not configure itself to point in any particular direction. This will cause the dust to also power any opaque blocks or mechanism components to the side of the analog line. Transmission components (redstone dust, redstone comparators, etc.) should not be placed adjacent to the line's dust because that would cause the dust to configure itself in a way where it doesn't power the rest of the analog line.
 * Earliest Known Publication: January 9, 2013.


 * Analog repeater line


 * flat, silent
 * circuit delay: 1 tick per 14 blocks
 * tl;dr: fastest option for long distances
 * Signal strength can also be retained by using repeaters to repeat every possible signal strength at the correct distance from the output to convey the correct signal strength.
 * A single segment of analog repeater line (ARL) consists of exactly 15 repeaters connecting an input line to an output line. To connect multiple segments together without additional comparators, the segments must be arranged so that the output dust of the last repeater is the same as the input dust of the next segment (i.e., block B of the previous segment is block A of the next segment). This causes the segments to overlap in distance by one block and causes each segment to be offset to the side from the previous segment by two blocks.
 * Variations: To keep the segments in-line, use a comparator and an opaque block between the segments, and alternate the direction the repeaters are facing. However, this increases the circuit delay to 2 ticks per 17 block.
 * Earliest Known Publication: November 21, 2012.


 * Analog subtraction line


 * flat, silent
 * circuit delay: 1 tick per (18-N) blocks (see below for N)
 * tl;dr: complicated, infrequently useful
 * If fewer than 15 states need to be transmitted, it may be more efficient to encode those N states in the higher levels of signal strength, and then repeatedly subtract the transmitted value from 15 after (17-N) dust, an even number of times.
 * Variations: The chests can be replaced with any other full container. The chests can also be replaced with regular power components (redstone torches, powered levers, etc.) if the redstone dust next to them is raised or lowered by one block, or if the subtraction comparator and its power source are moved so that the redstone dust runs straight into the comparator's side with the comparator perpendicular to the line still facing into the same block.
 * Earliest Known Publication: January 26, 2013

Binary
A binary transmission consists of multiple digital lines run in parallel, with each line representing a different digit in a single binary number. For example, three lines might individually represent binary 001 (decimal 1), binary 010 (decimal 2), and binary 100 (decimal 4) -- allowing them together to represent any value from decimal 0 to 7 (by summing the represented values of the powered lines). An individual digital line of a binary transmission is referred to by the value it can add to the total number (for example, the 1-line, the 2-line, the 4-line, the 8-line, the 16-line, etc.)

When a binary transmission is intended to output a decimal value (such as with a 7-segment display), it is known as "Binary-Coded Decimal" (BCD).


 * 4-bit binary encoding
 * A 4-bit binary encoding contains the same amount of information as an analog line. …

8-bit (a.k.a "byte bus") and 16-bit binary encodings are also used in the construction of computer recreations.

Unary
A unary transmission consists of multiple digital lines run in parallel, where a value is represented by which line is on (for example, the number 5 might be represented by having only the fifth line on). Unary encoding is rarely used for transmitting values, but may be used for inputs (e.g., which lever is turned on) or outputs (e.g., which dispenser is triggered), with conversion to or from a more efficient transmission method in between.


 * 16-state unary encoding
 * A 16-state unary encoding contains the same amount of information as an analog line. …

Vertical transmission
While horizontal transmission can be relatively straightforward, vertical transmission requires trade-offs.

Vertical digital transmission
Tripwire is incapable of transmitting signals vertically, but there are many other options for vertical digital transmission.


 * Redstone staircase


 * 1xNxN, 1-wide, silent
 * circuit delay: 1 tick per 15 blocks
 * Redstone dust will propagate a signal to adjacent redstone dust one block up as long as no opaque block "cuts" the signal. This allows "staircases" of blocks to carry redstone signals up (actual blocks of stairs aren't required, but can be used if placed upside-down).
 * Variation (Circular Staircase): By turning 90 degrees in the same direction each time the wire goes up a block, a "circular" staircase can be created in a 2x2 footprint. This variation is 2-wide tileable in both horizontal directions as long as the rotation direction is alternated in each direction (clockwise, anticlockwise, clockwise, etc.).


 * Redstone Ladder


 * 1x2xN, 1-wide, silent
 * circuit delay: 1 tick per 15 vertical blocks
 * Transparent blocks which support redstone dust do not "cut" redstone dust, so "ladders" of these blocks can be made zig-zagging back and forth upwards. Glowstone and upside-down slabs are the most commonly used supporting blocks, but upside-down stairs and hoppers also can be used.
 * Redstone ladders can transmit signals up but not down.


 * Torch tower


 * 1x1xN (upwards) or 1x2xN (downwards), 1-wide, silent
 * circuit delay: minimum 1 tick per 2 vertical blocks
 * Redstone torches can power blocks above them or redstone dust beneath them, allowing towers to be built going upwards or downwards.


 * Piston tower


 * 1x1xN, 1x1-tileable
 * circuit delay: 2 ticks per 5 vertical blocks (rising edge) and none (falling edge)
 * Piston towers can only convey signals downwards.
 * Because of the difference in rising and falling edge behavior, on-pulses are shortened by 2 ticks per piston and may possibly be erased altogether. This makes piston towers less useful for rapidly changing states.

Vertical analog transmission
The vertical options for analog transmission are similar to the horizontal options.


 * Vertical ACL
 * silent
 * circuit delay: 1 tick per 1 vertical block
 * A redstone comparator can power a block with dust on it, and that dust can power another comparator at its level, etc. Vertical ACL travels two blocks sideways for every 1 block moved upwards (or three blocks with an additional block between the dust and the comparator), but can also be bent at each block into a 3&times;3 "circular staircase".


 * Vertical ARL
 * silent
 * circuit delay: 1 tick per 14 vertical blocks
 * Vertical ARL is an analog repeater line built on redstone ladders. It only transmits signals upwards and only in segments of 14 vertical blocks (use vertical ACL to close any gaps). Like horizontal ARL, the last dust of the previous segment must be the first dust of the next segment unless a short run of vertical ACL is used to connect the two segments.

Vertical ASL basically just consists of redstone staircases or ladders with occasional breaks for subtraction.

Repeater
To "repeat" a signal means to boost it back up to full strength. When redstone signals are transmitted through redstone dust, their signal strength fades and must be repeated after 15 blocks. Repeater components and circuits keep signals going over long distances.

Basic repeaters
Some redstone components can repeat signals.


 * Redstone Repeater


 * The common method of repeating a signal is to use a redstone repeater. Using a block before and after the repeater, this method of repeating a signal averages 18 redstone used per 18 blocks (15 redstone dust, and 3 redstone per repeater) and 1 tick delay per 18 blocks.


 * Torch Repeater


 * When crossing long distances, redstone torches can also be used, simply allowing the signal to be inverted an even number of times during its journey. Torch repeaters use slightly less redstone than redstone repeaters (16 redstone per 17 blocks) but are slightly slower (1 tick delay per 17 blocks).

Instant repeater
An instant repeater is a circuit which repeats a redstone signal change with no delay. A sequence of instant repeaters and redstone dust lines is known as instawire (or "instant wire").


 * Insta-Drop Instant Repeater


 * 1&times;3&times;2 (6 block volume), 1-wide
 * circuit delay: none
 * This circuit is small and relatively resource-efficient, but it depends on some unintuitive piston behavior which might be changed in future releases.
 * Behavior (Rising-Edge): While the input is off, the block of redstone keeps the lower sticky piston activated by connectivity. When the input turns on, the upper sticky piston begins to extend the block of redstone. The instant the block of redstone starts moving, the lower sticky piston deactivates and begins to retract block A, the reason the upper piston is extending -- this turns the upper sticky piston's extension into a 0-tick extension/retraction (the "insta-drop": the sticky piston "drops" its grip on the block and leaves it behind when it retracts), leaving the block of redstone above the lower sticky piston and powering the output. All of this happens instantly (in the same redstone tick), effectively allowing a rising edge to pass through the circuit with no delay. Now that the block of redstone is above the lower sticky piston, the lower sticky piston extends again, and two ticks later block A is back in position causing the upper sticky piston to extend again, ready to retract block A when the signal turns off.
 * Behavior (Falling-Edge): When the input turns off, the upper sticky piston begins to retract the block of redstone, immediately cutting off power to the output, effectively allowing the falling edge to pass through the circuit with no delay. While the block of redstone is moving, the lower sticky piston deactivates, but then activates again when the block of redstone stops moving and can activate the lower sticky piston by connectivity again.
 * Earliest Known Publication: February 14, 2013.


 * Dust-Cut Instant Repeater


 * 1&times;5&times;4 (20 block volume), 1-wide
 * circuit delay: none
 * This circuit is a little larger than the Insta-Drop Instant Repeater, but it uses mechanics which are well understood and likely to remain intact in the game.
 * Behavior (Rising-Edge): When the input turns on, the lower sticky piston begins to extend, causing the upper sticky piston to retract, allowing the powered redstone dust below block A to connect to the output. All of this happens instantly (in the same redstone tick), effectively allowing a rising edge to pass through the circuit with no delay. The moving block of redstone also instantly depowers the dust below it, but by the time that turns off the repeater's output, the block of redstone has arrived to continue powering the output.
 * Behavior (Falling-Edge): When the input turns off, the lower sticky piston begins retracting the block of redstone, immediately cutting off power to the output, effectively allowing the falling edge to pass through the circuit with no delay. The block of redstone then arrives at its retracted state and tries to power the output dust again, but it also powers the piston above it and block A arrives to cut the output before the repeater can output the signal from the block of redstone.
 * Variation (2-Wide): The two upper levels (including the dust on top of the block the repeater is facing) can be moved one block over and down, and the last block on the lower level and its dust removed, to make a 2-wide version which is shorter in height and length (but larger in volume: 2&times;4&times;3, 24 block volume). In this version, to reduce the amount of redstone used, the block of redstone can be replaced with a regular block if redstone torches are placed under both its extended and retracted position.
 * Earliest Known Publication: January 3, 2013.

Two-way repeater
A two-way repeater (a.k.a. "bi-directional repeater") is a circuit which can repeat a signal in either direction.

Two-way repeaters have two inputs that also act as outputs.

Typically the problem to be solved in design is repeating the signal in either direction without repeating the signal back into the same input which could create a clock or a permanently-powered repeater loop.

Current designs also have a reset time -- when input from one side is turned on, and then input from the other side is also turned on, then the first input turned off, there is a short time while the transmission on the first side remains off until the circuit can reset itself to allow the second input through. Thus, the reset time can be seen as a spurious off pulse in a line that should be on.


 * Repeater-Lock Two-Way Repeater


 * 3&times;4&times;2 (24 block volume), flat, silent
 * circuit delay: 1 tick, reset time: 3 ticks
 * When a signal comes in from either side, it blocks the other input with a repeater lock.
 * Variation (Offset Input): The circuit shown in the schematic to the right keeps the transmission lines in-line with each other, but reduces the signal strength by 1 in side movement in both input and output before continuing the transmission, so the circuits must be placed with only 11 dust between them to work. Placing a block behind each of the input repeaters and moving the input/output lines closer to the repeaters' outputs means that signal strength is only lost in side movement at input, allowing an additional dust between the circuits (and thus a more efficient transmission), but requires that the transmission lines alternate which side they run on.
 * Earliest Known Publication: December 21, 2012


 * Comparison Two-Way Repeater


 * 2&times;5&times;2 (20 block volume), flat, silent
 * circuit delay: 2 ticks, reset time: 4 ticks
 * When a signal comes in from either side, it blocks the other input by providing a strength 15 signal to its comparator's side.
 * It's possible to override or block this circuit with additional inputs from the comparators' other sides.
 * Variations: Opaque blocks can be placed before and after the repeaters to increase the length of the circuit (as the usual point of a repeater is to cross distance efficiently).
 * Earliest Known Publication: February 16, 2013


 * CubeHamster's Two-Way Repeater


 * 2&times;6&times;3 (36 block volume), silent
 * circuit delay: 2 ticks, reset time: 3 ticks
 * The output on each side is produced by the redstone torch under the block, held unpowered by the input torch from the other side. When the other input signal turns on, the output torch turns on -- this also turns off the input torch holding the other output torch off, but each output torch also holds the other output torch off, keeping the circuit from becoming permanently powered.
 * Variations: If it's not necessary to get the signal back to the lowest level (such as if this is built in a 1-deep hole), then this circuit can be considered to be 2&times;4&times;3 (24 block volume) and thus only four blocks long.
 * Earliest Known Publication: August 9, 2012


 * Original Two-Way Repeater


 * 3&times;4&times;3 (36 block volume), silent
 * circuit delay: 2 ticks, reset time: 4 ticks
 * This design offers few advantages over the other designs, but may be appropriate for some needs.

Diodes
Another important aspect of signal transmission is making sure a signal doesn't go the wrong way. "Diodes" are redstone components or circuits which allow signals to propagate in one direction but not the other.


 * Component diode


 * 1-wide, flat, silent
 * circuit delay: 1 tick
 * Both the redstone repeater and the redstone comparator behave as diodes, but add 1 tick of delay.


 * Transparent diode


 * 1-wide, silent
 * circuit delay: none
 * Some transparent blocks can support redstone dust: glowstone, upside-down slabs, upside-down stairs and hoppers. These blocks have the property that redstone dust on them can propagate signals diagonally upwards, but not diagonally downwards (transparent blocks which cannot support redstone dust cannot be used for this purpose). Thus, simply jumping the signal up one block to one of these transparent blocks creates a diode circuit (to get it back to the same level, run the line over an opaque block before dropping it).
 * Upside-down slabs are the transparent block most commonly used for this purpose, but glowstone is used where light would be useful (to suppress mob spawning, etc.), upside-down stairs can be used where a full-side solid surface is required without light (for example, alongside a water channel transporting items over ice), and hoppers may be used in this way where they are already being used for item transport.