This is my 10-bit relay full adder. It's composed of 6 boards, 90 relays, 96 diodes, 22 capacitors, 32 resistors and 32 LEDs. Being 10-bits, it can add and subtract any whole number between 1 and 1023. There's an extra carry bit LED to show answer larger than 1023.
For more info, check my blog at: http://usagimotors.com/2020/03/09/electronics-a-10-bit-full-adder/
