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Published on Dec 14, 2007
A LEGO version of an old "marble logic" computer called Digi-Comp II. I set out to rebuild it from LEGO, using various tidbits and plans from the internet. More pictures of the components can be found in my Brickshelf gallery here:
I tried to recreate the original DGII design, but did make a few modifications, such as changing the "clear" switch to "clear once" style operation, & not bothering with the "auto/manual" switch (defaults to automatic) or neatly routing all the outputs back to a single collection tray (in particular, the "M/Q underflow"). It works amazingly well, and I think could be modified to essentially release four balls closely spaced in multiple mode.
I owe a debt of gratitude to the "Friends of Digi-comp" Yahoo group for advice & documentation, & to ESR & John Godfrey for making such an ingenious mechanical computer in the first place.
The finished model weighs about 10 pounds, & uses 14 simple switches, 21 flip-flops, 8 half flip-flops, and a ball release mechanism. I'm currently building a slightly improved copy at the request of a museum, for public display.