Minecraft – Two short pulses generated when input goes high

Mob traps built close to the sky limit have been known to end up not being completely loaded by the engine in some situations. The way to test for this is to open the F3 screen and look at the 'lc' value. This number is the highest Y-level that is currently loaded. If it's lower than the top of your mob trap then you would need to add some blocks above the trap to force the entirety of it to be loaded. This youtube video shows how you can fix the problem if it happens

It's also worth mentioning that the high altitude mob traps are (all other factors being equal) always going to be at least somewhat slower than low altitude mob traps simply because there ends up being more blocks for the spawning algorithm to check

I have invented a solution to this problem using a mechanism to apply one tick of lava damage. It occurred to me that a tripwire could be placed immediately above lava in order to remove it (using a dispenser) as soon as a mob hits it, thus preventing the mob from continuing to swim in it. Doing this for the water as well as the lava means that no acceleration is needed to make sure the mob will fall down, so the whole mechanism is only a little bit of extra height above a standard fall-damage trap.

Build details, from top to bottom:

• The zombies are pushed by water into the drop pipe. I don't know how important the length of the upper section is.

• The water and lava mechanisms are identical:

  • Each dispenser contains an empty bucket.

  • All pistons are sticky.

  • The tripwire above the fluid is the input to the left (in first image) piston monostable (rising edge detector), which causes the dispenser to remove the fluid into the bucket. The monostable ensures that the tripwire input will not interfere with the second fluid-restoring pulse.

  • Behind the dispenser is a comparator followed by 2 blocks of redstone wire; this detects the dispenser having a lava bucket (which counts as 1 stack) instead of an empty bucket (which counts as 1⁄16 stack), and triggers the right piston monostable to remove the fluid. In the event that the state of the dispenser gets reversed, this circuit will simply not generate a pulse, thus correcting the problem.

• Below the water block is exactly 19 ½ blocks of empty space (counting the sign) down to the fall-damage landing platform.

Results: When the zombies hit the platform, a few still take 2 punches, but most of them take 1 punch to kill. I have successfully operated this mechanism in my survival world fed by two zombie spawners.

Glitches:

• The amount of damage done is not completely reliable.

• It is possible for the dispensers to get inverted (resulting in zombies falling on fire, without taking any lava damage, or from the wrong height). This latest revision with comparators can self-correct this problem, but it still may result in an occasional zombie with the wrong amount of health. (I have also seen a dispenser completely fail to respond to pulses, so I suspect there is a Minecraft bug involved.)

I know it can be hard to build mechanisms from screenshots, so if you would like any further explanation of other camera angles, feel free to ask me to add them.