After developing relay based logic gates and designing 1 bit full adder made from relays, the challenge was to link a few of these together to create a relay based binary adder. The overall objective was to create a relay based adder that could handle calculations of at least a moderately interesting size. A 4 bit adder seemed like a good place to start, since 4 bits is enough to express numbers higher than what I can count on one hand.
Because my full adder design can take 3 inputs (A,B and a carry) and produces a sum and carry bit, all that needs to be done is to connect them together end-on-end:
I have abstracted my adder designs into little boxes here in this schematic, but each box is just a placeholder for the adder designs I showed in the previous post.