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[Tutorial] Using the Observer Block

Mojang introduced the oddly unique observer block a whole month ago in the 0.15.0 “Friendly” update, and it has so many uses already.

The whole purpose of this block is to detect when a block is updated, like when a door opens, or a block is removed or placed. PC users can make fancy redstone contraptions to achieve this, but with MCPE’s optimised redstone, the developers needed a replacement for this feature. Enter observer blocks!

Crafting

The observer block is quite easy to craft, with simple ingredients.

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The block only takes 6 cobblestone, 2 redstone, and 1 piece of quartz- all stuff you’ve used to make redstone components before.

Usage

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Smaller hole side

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Big scary red eye side

The observer block is quite simple. The first thing you should notice is that one side has a big red scary sensor, and the other side has a smaller friendlier hole.

The side with the big scary eye (left) is used to detect the block updates.

In a contraption, this should directly face the block you want to monitor, like it’s trying to physically feel the change.

Unfortunately it’s not the prettiest side, so if your contraption’s supposed to look good on this side… it won’t once this block is installed.

The other side (right), the one with the little hole, is the side that provides the redstone output.

You could put a repeater or a lamp here, and that would get powered everytime a block update happens on the other side.

But what can it detect?

Well, it’s quite a long list. The Minecraft Wiki lists over 20 different types of block updates it can detect (though some may not work anymore).

  1. Block placement
  2. Block destruction
  3. Re-flowing of water/lava
  4. Water freezing
  5. Ice melting
  6. Gravel/sand landing from a fall
  7. Movements of blocks by pistons
  8. Movements of pistons
  9. Endermen stealing a block
  10. Endermen placing a block
  11. Growth of plants
  12. Leaf growth and decay
  13. Growth and death of grass blocks
  14. Anything happening to farmland
  15. Fire igniting or dying
  16. Redstone ore glowing
  17. Changes in redstone state or power level
  18. Repeater delay being changed
  19. Rails changing direction
  20. TNT igniting
  21. Cake being eaten
  22. Activation of a tripwire (even if disconnected from hooks)
  23. Changing water level in cauldron

There’s probably even more that we haven’t found yet- correct this list in the comments!

Cool Contraptions

Automatic sugarcane farm

OMGchad from the OMGcraft channel made this cool autoamtic sugarcane farm using observer blocks. It works by detecting when the sugarcane has grown really tall, before using a piston to break the sugarcane so it can be collected in a chest.

Flying machines?

Overly excited MCPE Youtuber AdventureGamingHQ built a cool super compact flying machine that takes him all the way into the sky. It uses the observer block to detect when a piston moves, so it can activate the next piston, pushing the platform even further. With a little bit of work, you could create a whole spaceship!

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