Heather, Zach and myself created a two-bit adder using laser-cut foam core board, wire and marbles. We initially tried a “boat” design similar to the one used in our one-bit adder. The boats didn’t quite come together properly, so we decided to try Zach’s secondary design that was cut at the same time. It worked beautifully, as long as we tilted the board back to at least a 75 degree angle so that the marbles didn’t fall off the front of the flip-flop gates.
The right side of the adder is the least significant bit. The top flip-flops indicate binary zero or one. The bottom ones are carry bits, and each one is intended to drop a marble onto the next most significant top flip-flop, thereby carrying the product of adding one to one up to the next place.
This design can be extended to any number of bits. Currently the marbles fall off the board or stay on the flip-flop levers. A future version could include holes in the board and a collection system that returns the marbles to the top of the adder, for reuse. It would be fun to add bells to give an acoustic bling to the project. Maybe whistles and a music box too.
2 Bit Adder
Bit for Ones Place
Carry from Ones Place to Twos Place
Twos Place Bit and Carry Bit
MOVIE!