Redstone Comparator

Redstone Comparator

Transparent	Yes
Luminance	No
Blast resistance	0
Hardness	0
Tool	Any tool
Renewable	No
Stackable	Yes (64)
Flammable	No
Catches fire from lava	No
Drops	Redstone Comparator (1)
Block entity ID	See § Data values
Data values	See § Data values
Namespaced ID	See § Data values

A redstone comparator is a block used in redstone circuits to maintain, compare, or subtract signal strength, or to measure certain block states (primarily the fullness of containers).

Obtaining

To remove a redstone comparator, mine it. A redstone comparator can be broken instantly with anything, and drops itself as an item.

A redstone comparator is removed and drops itself as an item if:

• its attachment block is moved, removed, or destroyed.
• water flows into its space.‌^{[Java Edition only]}
• a piston tries to push it or moves a block into its space.

If lava flows into a redstone comparator's space, the redstone comparator is destroyed without dropping itself as an item.

Crafting

Ingredients	Crafting recipe	Description
Redstone Torch + Nether Quartz + Stone		Can use stone and its variants interchangeably.‌[LCE only]

Usage

A redstone comparator can be placed on the top of any opaque block with a solid full-height top surface (including upside-down slabs and upside-down stairs). In Bedrock Edition, a comparator can also be placed on walls and fences. For more information about placement on transparent blocks, see Opacity/Placement. To place a redstone comparator, use the Place Block control.

The redstone comparator has a front and a back — the arrow on the top of the comparator points to the front. When placed, the comparator faces away from the player. The comparator has two miniature redstone torches at the back and one at the front. The back torches turn on when the comparator's output is greater than zero (the arrow on top also turns red). The front torch has two states that can be toggled with the Use Item control:

• Down and unpowered (indicating the comparator is in "comparison mode")
• Up and powered (indicating the comparator is in "subtraction mode")

The redstone comparator can take a signal strength input from its rear as well as from both sides. Side inputs are accepted only from redstone dust, redstone repeaters, and other comparators. The redstone comparator's front is its output.

It takes 1 redstone tick (2 game ticks, or 0.1 seconds barring lag) for signals to move through a redstone comparator, either from the rear or from the sides. This applies to changing signal strengths as well as simply to turning on and off. Redstone comparators usually do not respond to 1-tick fluctuations of power or signal strength — for example, a 1-clock input is treated as always off from the side, and always on from the rear.

The redstone comparator has four functions: maintain signal strength, compare signal strength, subtract signal strength, and measure certain block states (primarily the fullness of containers).

Maintain signal strength

A redstone comparator with no powered sides outputs the same signal strength as its rear input.

Compare signal strength

Comparators in comparison mode.

A redstone comparator in comparison mode (front torch down and unpowered) compares its rear input to its two side inputs. If either side input is greater than the rear input, the comparator output turns off. If neither side input is greater than the rear input, the comparator outputs the same signal strength as its rear input.

in summary : Output = Rear * (Left<Rear && Right<Rear)

Subtract signal strength

A redstone comparator in subtraction mode (front torch up and powered) subtracts the signal strength of the highest side input from the signal strength of the rear input.

in summary : Output = Rear - Max(Left,Right)

For example, if Signal of the left is 6, the right is 7 and the rear is 4 then the result should be : 4 - Max(6,7) = 4-7 = 0

If the signal of the rear is 9, the right is 2 and the left is 5 then the result should be : 9 - Max(2,5) = 9-5 = 4

Measure block state

A redstone comparator can measure the fullness of a chest, as well as other block states, even through a block.

A redstone comparator treats certain blocks behind it as power sources and output a signal strength proportional to the block's state. The comparator may be separated from the measured block by a solid block. However, in Java Edition, if the solid block is powered to signal strength 15 the comparator outputs 15 no matter the fullness of the container.

Containers

Minimum Items for Container Signal Strength

Power Level	Containers and Number of Slots
	3	5	9	27	54	—
0	0i	0i	0i	0i	0i	No music disc inserted
1	1i	1i	1i	1i	1i	"13"
2	14i	23i	42i	1s 60i	3s 55i	"cat"
3	28i	46i	1s 19i	3s 55i	7s 46i	"blocks"
4	42i	1s 5i	1s 60i	5s 51i	11s 37i	"chirp"
5	55i	1s 28i	2s 37i	7s 46i	15s 28i	"far"
6	1s 5i	1s 51i	3s 14i	9s 42i	19s 19i	"mall"
7	1s 19i	2s 10i	3s 55i	11s 37i	23s 10i	"melohi"
8	1s 32i	2s 32i	4s 32i	13s 32i	27s	"stal"
9	1s 46i	2s 55i	5s 10i	15s 28i	30s 55i	"strad"
10	1s 60i	3s 14i	5s 51i	17s 23i	34s 46i	"ward"
11	2s 10i	3s 37i	6s 28i	19s 19i	38s 37i	"11"
12	2s 23i	3s 60i	7s 5i	21s 14i	42s 28i	"wait"
13	2s 37i	4s 19i	7s 46i	23s 10i	46s 19i	—
14	2s 51i	4s 42i	8s 23i	25s 5i	50s 10i	—
15	3s	5s	9s	27s	54s	—

A redstone comparator used to measure the state of a container outputs a signal strength in proportion to how full the container is (0 for empty, 15 for full, etc.).

Containers that can be measured by a comparator include:

• Furnace
• Blast Furnace
• Smoker
• Brewing Stand
• Hopper
• Minecart with Hopper on top of a detector rail
• Dispenser
• Dropper
• Chest
• Trapped Chest
• Minecart with Chest on top of a detector rail
• Barrel
• Large chest
• Large trapped chest
• Shulker Box (any color)

Generally speaking, the comparator output signal strength represents the average fullness of the slots, based on how many of that item form a full stack (64, 16, or 1 for non-stackable items).

The Minimum Items for Container Signal Strength table (right) shows the minimum number of 64-stackable items required to produce the different signal strengths from each type of container. Numbers followed by an "s" or "i" indicate the number of full 64-stack equivalents ("s"), and additional items less than a stack ("i") required. For items that stack in 16s (snowballs, signs, ender pearls, etc.), divide the "i" number by 4 and round up. Each non-stackable item counts as one full-stack.

For example, to produce a signal strength of 10 from a hopper requires the equivalent of 3 full stacks plus 14 more items, or 206 items total, assuming they all stack in 64.

When a comparator measures a large chest or large trapped chest, it measures the entire large chest (54 slots), not just the half directly behind the comparator. A chest or trapped chest that cannot be opened (either because it has an opaque block or ocelot above it) always produces an output of 0 no matter how many items are in the container — shulker boxes can always be measured, even if they cannot open.

Calculating signal strength from items

When a container is empty, the output is off.

When it is not empty, the output signal strength is calculated as follows:

signal strength = floor(1 + ((sum of all slots' fullnesses) / (number of slots in container)) * 14)

fullness of a slot = (number of items in slot) / (max stack size for this type of item)

Example: 300 blocks in a dispenser (which has 9 slots), where each block stacks to a maximum of 64, produces output with a signal strength of 8:

1 + ((300 items / 64 items per slot) / 9 slots) * 14 = 8.292, floored is 8

Note that a non-stackable item is counted as a full slot (1 item in a slot, with a max stack size of 1: 1 / 1 = 1.0), and items that stack up to 16 (such as ender pearls and snowballs and eggs) are similarly considered a full slot at 16.

Calculating items from signal strength

It can be useful in redstone circuits to use containers with comparators to create signals of a specific strength. The number of items required in a container to produce a signal of desired strength is calculated as follows:

items required = max(desired signal strength, roundup((total slots in container * 64 / 14) * (desired signal strength - 1) ) )

Example: To use a furnace (which has 3 slots) to create a strength 9 signal, players need 110 items:

max(9, (3*64/14)*(9-1)) = 109.714, rounded up is 110

Miscellaneous

Comparators used to measure containers.

Some non-container blocks can also be measured by a redstone comparator:

Cake

A cake outputs a signal strength relative to the amount of cake remaining. Each slice is worth 2 signal strength, with 7 total slices, for an output of 14 for a full cake.

Cauldron signal strength

Cauldron

A cauldron outputs different signal strengths depending on how much water is inside. From completely empty to completely full, the output values are 0, 1, 2, and 3.

Composter signal strength

Composter

A composter outputs different signal strengths depending on the level inside. From completely empty to completely full, the output values are 0, 1, 2, 3, 4, 5, 6, 7 and 8.

Command Block

A command block stores the "success count" of the last command executed, which represents the number of times the most recently used command of this command block succeeded. A "success" is defined by the command's success conditions: if a red error message is returned in the chat, the command was not successful.

Most commands can succeed once per execution, but certain commands (such as those that accept players as arguments) can succeed multiple times, and the comparator outputs the number of times it succeeded (maximum 15).

A command block continues to store the success count of the last command executed until it executes its command again, thus the comparator continues to output the same signal strength even after the command block is no longer being activated (it doesn't turn off when the signal to the command block turns off).

End Portal Frame

An end portal frame outputs a full signal of 15 if it contains an eye of ender and zero otherwise.

A comparator can measure the presence and rotation of an item frame's contents.

Item Frame

A comparator can measure the state of an item frame's contents. An item frame comparator outputs 0 if the item frame is empty, or 1 to 8 for any item depending on its rotation: 1 at initial placement, plus 1 for each 45° of rotation for a maximum of 8.

The comparator must be placed behind the block the item frame is attached to, facing away from the item frame. The block must be a full block, and the item frame cannot be submerged in water.

Jukebox

A jukebox outputs a signal strength indicating which music disc is currently playing. See the Minimum Items for Container Signal Strength table above.

Lectern

A lectern outputs a signal strength that depends on what page the player is currently on. (e.g. a book with 15 pages powers 1 redstone level per page, or one with 5 pages emits 3 signal strength per page.)

Beehive and Bee nest‌^{[upcoming: JE 1.15]}

A hive outputs a signal strength equal to the amount of honey in the hive.

Sounds

Sound	Subtitle	Namespaced ID	Subtitle ID	Source	Pitch	Volume	Min. volume
MISSING	Comparator clicks	block.comparator.click	subtitles.block.comparator.click	?	?	?	?

Data values

A redstone comparator is defined by its ID, block data, and block entity. A redstone comparator also has a block state that is expected to replace the functionality of block data in a future version.

ID

Java Edition:

Redstone Comparator	Namespaced ID
Redstone Comparator	comparator
Block entity

Bedrock Edition:

Redstone Comparator	Namespaced ID	Numeric ID
Block (inactive)	unpowered_comparator	149
Block (active)	powered_comparator	150
Item	comparator	404
Block entity	Comparator	-

Block data

See also: Data values

In Bedrock Edition, redstone comparators use the following data values: A redstone comparator's block data specifies its orientation, mode, and powered status.

Bits	Values
0x1 0x2	A two-bit field storing a value from 0 to 3 specifying the redstone comparator's orientation: 0: Facing north. 1: Facing east. 2: Facing south. 3: Facing west.
0x4	Set if in subtraction mode (front torch up and powered).
0x8	Set if powered (at any power level).

Block states

See also: Block states

Java Edition:

Name	Default value	Allowed values	Description
facing	north	east north south west	The direction from the output side to the input side of the comparator, or the opposite from the direction the player faces while placing the comparator.
mode	compare	compare subtract	Specifies the current mode of the redstone comparator.
powered	false	false true	True if the redstone comparator is being powered.

Block entity

See also: Block entity format

A redstone comparator has a block entity associated with it that holds additional data about the block.

• Block entity data
  • Tags common to all block entities see Template:Nbt inherit/blockentity/template
  •  OutputSignal: Represents the strength of the analog signal output of this redstone comparator.

History

Java Edition
November 24, 2012					Jeb stated that there may be a "capacitor" in Minecraft.
December 27, 2012					Dinnerbone released pictures of the first version of the "comparator", stating it was a replacement for the "capacitor" idea that has variable, alternate inputs.
January 2, 2013					Dinnerbone released one more picture of the comparator. The picture itself showing a digital-to-analog converter, using the comparator as the main block.
1.5		13w01a			32px32px Added redstone comparator, with 0 delay.
		13w01b			Added delay of 1 game tick (1⁄2 redstone tick) to comparator to fix bugs.
					Added ability to measure containers to redstone comparator.
		13w02a			Updated texture to show quartz in the middle.
					Changed algorithm for measuring containers so that comparators output a signal with as few as 1 item in the container.
		13w02b			Comparators now treat large chests as a single container.
		13w03a			Comparators now output success count of command blocks.
					Comparators now measure container minecarts on detector rails.
		13w04a			Comparators now measure jukeboxes.
		13w05a			Comparators no longer cause constant block updates, the delay is made consistent, and side input no longer causes a pulse output.
					Block 150 (powered_comparator) is no longer used; powered state is now represented by the 8s bit on block 149 (unpowered_comparator).
		13w05b			Comparator delay changed from 1 game tick (1/2 redstone tick) to 2 game ticks (1 redstone tick).
		13w09c			The redstone signal strength from a comparator next to a brewing stand with 3 water bottles in it is the same as one with 3 water bottles and 1 ingredient in it.
1.6.1		13w18a			Comparators now measure cauldrons and end portal frames.
1.7.2		13w37a			The item forms of blocks 149 (unpowered_comparator) and 150 (powered_comparator) were removed from the game. They can no longer exist in inventories, only as blocks in the world.
1.8		14w04a			Comparators now measure item frames.
		14w28a			Comparators now measure cakes.
1.9		15w42a			With the addition of the blaze powder fuel slot, brewing stands now have 5 slots instead of 4. Their original comparative power values are listed below: Original values 0: 0 1: 1i 2: 19i 3: 37i 4: 55i 5: 1s 10i 6: 1s 28i 7: 1s 46i 8: 2s 9: 2s 19i 10: 2s 37i 11: 2s 55i 12: 3s 10i 13: 3s 28i 14: 3s 46i 15: 4s
		15w47a			Comparators' side inputs now take power from redstone blocks.
1.13		17w47a			All 3 IDs for the redstone comparator got merged into one ID: comparator.
					Comparators now render the underside.
					Prior to The Flattening, these blocks' numeral IDs were 149 and 150, and the item's 404.
1.14		18w43a			Changed the texture of comparators.
		19w02a			Comparators now measure lecterns.
		19w03a			Comparators now measure composters.
Upcoming Java Edition
1.15		19w34a			Comparators now measure how much honey is inside bee hives and bee nests.
Pocket Edition Alpha
0.14.0		build 1			Added redstone comparators.
Pocket Edition
1.0.0		alpha 0.17.0.1			Comparator now measure end portal frames.
1.0.5		alpha 1.0.5.0			Comparator now output success count of command blocks.
1.1.0		alpha 1.1.0.0			Comparator now measure shulker box.
Bedrock Edition
1.2.0		beta 1.2.0.2			Comparator now measure jukebox.
1.11.0		beta 1.11.0.1			Comparator now measure smoker, blast furnace, lectern, and composter.
Legacy Console Edition
TU19	CU7	1.12	Patch 1		Added redstone comparators.
TU31	CU19	1.22	Patch 3		Can now measure item frames.
New Nintendo 3DS Edition
0.1.0					Added redstone comparators.

Issues

Issues relating to "Redstone Comparator" are maintained on the bug tracker. Report issues there.

Trivia

• Comparators have no bottom texture; they appear transparent when viewed from below.‌^{[Bedrock Edition only]}

References

Redstone

View at: Template:Redstone/content [edit]

Blocks

View at: Template:Blocks/content [edit]

Items

View at: Template:Items/content [edit]