8-Bit Adder Circuit - Quillan Smith

Goal

I wanted a PCB that could double as a functional circuit and a piece of wall art. Inspired by YouTube videos on transistors and computer architecture, I designed an 8-bit adder circuit, partly to build something fun to look at and partly to improve my circuit design and layout skills.

Circuit running demo

What it does

An ESP32 microcontroller generates two random 8-bit numbers, A and B, writes them to the circuit's inputs, and reads the result back from the SUM output.

Browser at adder.quillan.org showing a live sum, 59 + 79 = 138, posted by the ESP32 — Live results posted to a web page

Gate schematics

Designed in KiCad using the HierarchicalPCB plugin, breaking AND, OR, and XOR gates into reusable modular blocks. Those were assembled into a single-bit adder and finally a full 8-bit adder.

Transistor-level schematic of the AND gate — AND gate

Transistor-level schematic of the OR gate — OR gate

Transistor-level schematic of the XOR gate — XOR gate

Schematic of a single-bit full adder built from the gate blocks — Single-bit full adder

Schematic of the full 8-bit adder — eight single-bit adders chained by carry — Full 8-bit adder

This project improved my schematic and layout skills and helped me learn about computer architecture at a more fundamental level. The result is a working adder that hangs on my wall.

Project GitHub Repository →