These are the only ones I have been able to find online:

I would like to find some more discrete models like these (as opposed to say, water logic gates or things like that). Not sure if there is a library of different techniques to build logic gates outside of electronics, or if not, what some other good examples are like these above, that perhaps demonstrate further their functionality.


1 Answer 1


Picture hanging can realize any monotonone boolean function.

I.e., you can hang a picture using two pins so that it falls IFF both pins are removed. This is trivial to achieve, and realizes an AND gate.

However, you can also hang it so that it falls IFF either pin is removed. Implementing this OR gate is not so trivial at first.

See the linked paper for nice pictures.

  • $\begingroup$ This is great, thanks. I will take a look. I should probably have clarified that I would like to see more discrete models, whereas a rope is curvy (though there are those nodes it's hanging on), so not sure yet if it is a discrete model-ish. By discrete model I mean the pieces are all discrete, so no ropes or water or anything like that. Marbles and solid edges is what I'm after, or unknown things of that nature. $\endgroup$ Mar 1, 2019 at 10:26
  • $\begingroup$ @user10869858 I see -- note that you mentioned pulley logic gates which do use ropes. Perhaps you could also look at the old game "Dr. Nim" which IIRC computed a kind of XOR with marbles. $\endgroup$
    – chi
    Mar 1, 2019 at 13:05

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