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Observer

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Observer
Observer.png

Transparency

Partial

Luminance

No

Blast resistance

17.5

Tool


Renewable

No

Stackable

Yes (64)

Flammable

No

Drops

Itself

Data values

dec: 251 hex: FB bin: 11111011

Name

observer

An observer is a block that emits a redstone signal when an adjacent block is updated.

Obtaining[edit]

An observer requires a pickaxe to be mined. When mined without a pickaxe, it will drop nothing.

Block
Observer
Hardness 3.5
Tool
Breaking time[note 1]
Hand 17.5
Wooden 2.65
Stone 1.35
Iron 0.9
Diamond 0.7
Golden 0.45
  1. Times are for unenchanted tools in seconds.

Crafting[edit]

Ingredients Crafting recipe
Cobblestone +
Redstone Dust +
Nether Quartz











Usage[edit]

An observer is placed similarly to a piston, and will observe the block that it is placed against. The texture of the detecting side is that of an 'observing' face. As observers can detect the state of other observers, placing two adjacent observers, each watching the other, can make a fast and compact redstone clock.

Behavior[edit]

In Java Edition, until 1.13 where it would appear that all block states are saved and metadata is removed entirely, an observer will detect changes in its target's block ID or data value, or the breaking or placing of a block (i.e. changes in its basic block state, but not its extended/actual block state). This means that changes like the age of crops will be detected, since they are part of the basic block state that is converted to metadata when the world is saved; however, changes such as the shape of a fence will not be detected, since those are part of the extended block state, which is not saved when the world is saved.

In Bedrock Edition, an observer acts as a block update detector, and detects anything that causes a block update in that edition.

Note that what causes a block update and how they propagate is very different between Java Edition and Bedrock Edition. As a result, each can detect some kinds of changes that the other can't. See the table below for a comparison.

When it detects something, the observer emits a redstone pulse of strong power at level 15 for 2 game ticks (1 redstone tick). The pulse can power redstone dust, a redstone comparator, a redstone repeater, or any mechanism component located at its opposite end.

In the Java Edition, the pulse is emitted with a delay of 1 redstone tick. In Bedrock Edition, it is supposed to be delayed by 1 tick as well, but is actually delayed 2 redstone ticks due to MCPE-15793, a bug causing redstone delays to be incorrect when components are activated by world changes (which, in the case of the observer in Bedrock Edition, is the only way it can be activated), as opposed to pure redstone components ticking.

It also counts as a block change/block state change/block update when the observer itself is moved by a piston. When this happens, an observer emits a pulse after being pushed or pulled, but not beforehand.

Though they block light, observers behave as transparent blocks do in one sense: they cannot be powered by an external power source, nor power themselves with their own output.

Because observers in Java Edition detect changes in the basic block state, and not block updates, they can detect a wider range of phenomena than a block update detector (BUD) circuit in Java Edition can detect (as some block state changes don't cause block updates). However, they do not detect client-side block state changes that do not change the block data value, such as a fence reshaping or redstone dust rerouting. Observers in Bedrock Edition do detect block updates (but not block state changes), and so they detect the exact same things that any other BUD would detect in that edition.

Limitations[edit]

Detected in
Kind of block update Bedrock Edition Java Edition Legacy Console Edition

Changes to the data value of fire that signifies flammable surfaces surrounding fire
No Yes No



Opening and closing shulker boxes, chests & ender chests
No No No

Changes to inventory of any blocks that comparators measure as containers
No No No

Activating / deactivating a beacon
No No No

Success of a command block
No No N/A

Activation / deactivation of a hopper
No No Yes

Dry farmland changing among its six dry-looking hydration stages
No Yes Yes

Farmland going between dry and humid
Yes Yes Yes


Activation of a dropper or dispenser
Yes Yes Yes

Activation / deactivation of redstone ore
Yes Yes Yes

Spread of grass to dirt, or decay of grass into dirt
Yes Yes Yes



Aging of saplings, sugar canes or fire
Yes Yes Yes

Moving potions and other items to / from a brewing stand
Yes Yes Yes

Activation / deactivation of a dragon head
Yes No Yes

Placing / removing an item frame, adding / rotating / removing an item in an item frame
Yes No Yes

Teleporting something by the end gateway
Yes No Yes

Adding / removing contents from a flower pot
Yes Yes Yes

Locking / unlocking a redstone repeater
Yes Yes Yes









Changes in the shape of walls, fences, iron bars, glass panes, stairs, tripwire, redstone dust, vines, melon stem or pumpkin stem
No Yes Yes



A grass, mycelium, or podzol block becoming snowy or not snowy
Yes Yes Yes

Playing a note block
Yes Yes Yes

Forced growth of sugar canes by bone meal
Yes N/A No
All other block / block state changes Yes Yes Yes

Data values[edit]

Block data[edit]

See also: Data values

In Bedrock Edition, observers use the following data values:

Bits Values
0x1
0x2
0x4

Three bits storing a value from 0 to 5:

  • 0: Observer facing down
  • 1: Observer facing up
  • 2: Observer facing north
  • 3: Observer facing south
  • 4: Observer facing west
  • 5: Observer facing east
0x8 If set, the observer is powered.


Block states[edit]

See also: Block states
Name Value Description

 facing
down
east
north
south
up
west
The direction the observer is observing. The same direction the player faces, when placing the block.

 powered
false
true
True while the observer is observing a change and emitting a pulse.

History[edit]

Java Edition
1.11 16w39a Added observer block. When first added, the observers acted as a block update detector, and would emit pulses that lasted 1 game tick (0.5 redstone ticks) and had a signal strength of 1. The observer could also power blocks (like a repeater). It also had no delay between detecting a block update and emitting a pulse, meaning that observers were essentially instant. They were also placed with the observing, or input, side facing the player.
Observer Revision 2.png Note: the "arrow" texture on the top/bottom of the observer was pointing the wrong direction (towards the input, rather than the output). This was not noticed by most people, though, since the observer in Pocket Edition had a texture bug where the top & side textures would not rotate properly (except the output/input sides), causing the arrow texture to always point in the same direction.
16w41a Observers were changed to emit 4 game tick (2 redstone tick) pulses[5], and their signal strength was changed to 15.[6][7]
Observers *appear* to no longer strongly power blocks, and now only emit activation power, like a block of redstone. (And this may have been the intended behavior for this snapshot.) However, in reality, they still strongly power blocks, but the blocks adjacent to those blocks aren't given block updates, causing weird and buggy behavior.[1]
Observers are now placed with the output facing the player.[2][3]
Fixed a bug where observers would redirect redstone dust from all 4 directions.[4] (They are only supposed to redirect dust from their output side.)
16w42a The devs attempted to make observers no longer detect block updates happening to air blocks, in order to make observer behavior more predictable.[8] In the process they broke redstone mechanics a bit, so that the block update bug from the previous snapshot now affected repeaters & comparators, too.[9]
16w43a Observer Revision 3.png Fixed the rotation of the "arrow" texture so it would point in the right direction.
General redstone mechanics work as they did before 16w42a, with the exception of the change named below.
Observers now output strong power like in 16w39a, except that they, as well as repeaters & comparators, no longer provide block updates to transparent blocks or air.
16w44a The block update changes relating to redstone from 16w42a & 16w43a were fully reverted.
Observer behavior was overhauled/redefined. The observer changed from a block update detector to a block state change detector. Observers were changed to detect when the block it was observing changed, its basic block state changed, or the block was placed/destroyed. (Note that it does not detect changes in the extended block state, AKA changes that are not saved when the world is unloaded, such as the shape of a fence, or whether or not a repeater is locked.) This change made observer behavior much more predictable, as unexpected/invisible block updates would no longer trigger observers.[10]
Observers were changed to emit a 2 game tick (1 redstone tick) pulse when activated.[11]
Observers no longer output power instantly.[12]
pre1 Observer.png Changed front (detecting side) texture to be an 'observing face'. The "arrow" texture on the top/bottom of the observer was also modified.
The redstone output side now blinks red when it outputs power.
1.13 17w47a Prior to The Flattening, this block's numeral ID was 218.
Pocket Edition Alpha
0.15.0 May 2, 2016Jeb tweeted that Daniel Wustenhoff is a working on a BUD block.[14]
ObserverRejectedGraphics.jpg
Tommaso Checchi tweeted his "rejected graphics" for the block.[13]
build 1 Observer Revision 1.png Added observer block.
0.15.3 Observers are now placed like a piston and not a log.
Bedrock Edition
1.2 build 1 Observer BE.png Updated textures to match Java Edition.
Observer blocks can now detect many more block changes.
Increased the strength of the redstone pulse outputted by Observer blocks and they no longer pulse twice when observing a retracting piston.
Opening and closing the command block screen will no longer activate an observer block
Legacy Console Edition
TU54CU441.52Patch 24Patch 4Added observers.

Issues[edit]

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

Trivia[edit]

  • When moved by a piston, an observer sends a 2 game tick (1 redstone tick) pulse after being moved, which makes it useful for slime block flying machines.
  • The current Observer texture was created because Jeb kept confusing which side was front/back. He said it was inspired by the "rejected texture" created by Tommaso Checchi.[15][16]

Gallery[edit]

See also[edit]

References[edit]