A 1-bit Full Adder is a basic circuit used to add three input bits: two data bits (A and B) and a carry-in bit (Cin).
It produces two outputs:
- Sum: The result of the addition.
- Carry (Cout): The carry passed to the next bit in case of multi-bit additions.
This circuit plays an important role in digital electronics and serves as the foundation for larger systems like multi-bit adders used in microprocessors.
At first, I followed the typical textbook design, which uses:
-
2 XOR gates
-
2 AND gates
-
1 OR gate
This approach worked, but it required more transistors than I expected. Every gate used multiple transistors, so the total count grew quickly.
To make it simpler, I tried using only NOR gates. This reduced the number of components, and I was able to build the adder using just 9 transistors. It was a good way to explore how small changes can make a big difference in circuit design.
Sum: A ⊕ B ⊕ Cin
Carry (Cout): (A · B) + (Cin · (A ⊕ B))
| A | B | Cin | Sum | Cout |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
I first got the idea for this project in my Digital Logics class, where we learned about logic gates and how they are built. I thought it would be fun and helpful to build a real circuit and see how the gates work together. I had already made a schematic of the prototype earlier, but the final version came together during Workshop 101 by LAB448 at Pashchimanchal Campus.
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After the success of the prototype, I decided to make a PCB for the adder. This pcb is designed to be used as a module to make the student understand the concept of full adder.
This repository not only tracks the 1-bit Full Adder but also keeps a record of my progress and future updates. It will serve as a reference for new experiments and improvements.