...by any other means than madly pulsing their input?

The picture illustrates my problem.

Piston blocked The piston was powered up when both spaces between it and the obsidian block were filled with cobblestone. This is perfectly expectable. Now I broke the second piece of cobble, and I'd expect the piston to move the other block. It does not.

How can I get the piston to act in this situation?

(This is a reduced testcase. In my case the situation is more complex; there is a queue of stones blocked, waiting until needed. A piston pushes a block out of the front of that queue on demand, and the location after the removed block should immediately fill as soon as the "on demand" piston retreats. This doesn't happen because the queue even stopped momentarily, is stuck forever.)

  • Instead of a lever make a clock mechanism. Note that this will keep pushing until the limit of the piston, which I believe is 7 or 8 blocks.
    – Batophobia
    Jul 30, 2013 at 19:56
  • You can not make pistons retriggerable in this way, as it would cost tons of processor time, and therefore the game does not support it. If you could describe your general situation, though, we could try to think of something else...
    – Orc JMR
    Jul 30, 2013 at 20:18
  • Orc: Actually, it would cost only a little more memory and very little more CPU time. Mark the blocks as "pending move", once any of them is moved/removed re-check all pending move.
    – SF.
    Jul 30, 2013 at 22:08

1 Answer 1


There is a way you can detect if a block is missing using a repeater and redstone current.

The further stone-block is destroyed in between the images. As far as I know, this is the only way to do it without clocks (pulses). The piston itself does not keep itself triggered, but that can be implemented with memory cells if need be (See 3rd image).

Figure #1 Figure #2 Figure #3

  • This is fine but becomes unpleasantly big especially if there's a bunch of pistons getting blocked, each working autonomously, self-triggered.
    – SF.
    Jul 31, 2013 at 7:42
  • @SF. That is indeed a problem. It's possible to make this smaller than it is in the pictures, but not by much.
    – 3ventic
    Jul 31, 2013 at 8:10

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