One ball adder - 4-bit + 4-bit


you can only use one ball, to add two 4-bit numbers.

puzzle starting configuration

hint: the interceptor acts as a 5th bit



A fast adder using minimum balls, and I've found a use for all those washers

Nice challenge. I have made a few adders and didn’t think this was possible until you posed the question. How to propagate the carry bit while adding each pair of bits was not obvious at first. I love the elegance of my final solution.

Click to Reveal Solution

The purple cogs are one input and the blue bits the other. The result goes in the blue register. The left interceptor is the 5th bit or overflow bit.

I have two videos to demonstrate 6+3=9 and 5+11=16:


that’s almost exactly how I made it.

click to reveal solution