The author’s eldest son built a single-bit computer using discrete transistors. Inspired by this, the author helped his younger son build a relay-based calculator. Though not 100% relay-based due to cost and time constraints, relays were used for the math operations. The author explains the construction and implementation of a full adder circuit using relays and Boolean logic. They also discuss the advantages and disadvantages of relay-based logic. The author used Omron’s G6C relays for their project and shares the details of the relay-based OR, AND, and XOR gates they implemented. The author also mentions the use of an 8-bit microcontroller for auxiliary tasks. The calculator can perform addition, subtraction, multiplication, and division, and includes a display module driven entirely by relays. The author mentions the complexity and cost of implementing multiplication and division compared to addition and subtraction. They estimate that around 500 relays would be needed for a complete relay-based calculator. The final price tag would be under $1,000 using subminiature signal relays. The author concludes by mentioning their interest in exploring a 100% relay-based calculator in the future.
https://lcamtuf.substack.com/p/now-youre-thinking-with-relays