How to Build a 4-Bit Computer on Breadboards Using Individual Transistors

A simple 4-bit computer is built on breadboards using individual transistors. This computer is called the GSN477. This is because it was built for the Global Science Network, is 4-bit, and contains two 7-stage counters.

Sections of the computer are the clock, program counter, ring counter, 10 bytes of memory, opcode register, opcode decoder, control matrix, data bus, accumulator register, output register, register B, and ALU.

Circuits are built using NAND digital logic gates, XOR gates, AND gates, inverters, buffers, and tri-state buffers. Larger circuits include D flip Flops, MS D flip flops, Edge triggered JK flip flops, and MS JK flip flops.

The computer shows how computers add and subtract numbers while running a simple program and this video was submitted for the #some3 competition.

0:00 Intro.
0:51 Computer overview.
1:30 Example program.
4:12 The clock
4:22 Ring Counter
4:53 Program Counter
5:33 10 Bytes of Memory
7:01 Opcode Register
7:11 Opcode Decoder
8:19 Control Matrix
9:06 Data Bus
9:44 Accumulator Register
10:21 B Register
10:51 ALU
11:15 Output Register
11:35 Building Suggestions

References:
Walker, J. S. Computer Time Travel: Building a Computer Processor from Discrete Transistors: A Look Back over 50 Years to the Beginning of Modern Computer Technology.

Oldfangled Publishing, 2017. Malvino, Albert P. Digital Computer Electronics. 1993.

[revolutionarydefeatism]

If I had watched this video as a teen, I can't imagine how it would have blown my mind! I used to spend days in our backyard, chalk in hand, sketching out ideas in front of our yard shed, trying to figure out how to make a simple calculator with gates. I never quite succeeded—and I didn't even have the internet back then! Thanks, Cody!

[ItsHaldun]

Absolutely insane, this should have millions of views!

[kirandeshpande]

Being from a civil engineering background, I'm genuinely impressed by your in-depth knowledge, Your video was not only informative but also incredibly well-expressed. Keep up the fantastic work, you've definitely gained a new admirer!"

[markgreco]

So cool, less than 1000 transistors. Hard for me to wrap my head around modern chips with 8.5 billion transistors. THANK YOU!!!

[alainrisch]

This should be teached every evening on TV for under graduate !! GREAT JOB !!

[mekafinchi]

Of all the homebrew cpu projects I've seen on youtube, this has to have the lowest transistor count by a mile. Working with transistors is a vastly different beast than ICs, and I'm quite pleased to find novel solutions like those ring counters being used to keep things as simple as possible while remaining functional. When I saw the thumbnail in the SoME3 playlist, I thought this was going to be a Ben Eater kit build or similar, so I'm really impressed you got a pure transistor build in the same form factor! Well done all around!

[furkanadak]

Transistor to Computer. This is the best explanation on Youtube. Thank you!

[Jnoel]

Really cool stuff, understanding a basic computer from scratch is where its at.

[phoenix]

I thought that breadboard computers with microcontrollers were impressive BUT THIS? AWESOME WORK!

[tbecker]

This is one of the best videos I ever watched on Youtube. Wish I had seen this back when i was studying computer architecture on college.

[Maddy.lotus]

Being an young electronics engineer myself, Just so beautiful to see, love it.

[riemanneconomy]

I really don't know why youtube algorithm doesn't boost your videos. Just look at the amount of comments/ visualizations... keep it up, great work as always...

[Enigma]

You should feel proud of the accomplishment of building a transistor computer, few people have actually done that especially these days, and its given you a deep understanding of how computers work at a very low level. Beyond that, you've done an excellent job of communicating that knowledge through your youtube channel, which is one of my favorite channels. So thank you and hats off to you! I hope you still have the completed project. If so, I have a suggestion. You can buy permanent breadboards that have the same pinout as solderless breadboards. If it were me, I think I would buy some of those and transfer your circuits to them. I would then mount them on a backing, add a frame, and plexiglass cover, and mount it on a wall to display it (perhaps running some continuous program). So not only would it be a personal achievement, but also a work of art on display.😊

[Jason]

Much respect for this build, this would rack my brain for sure.

[JonathanBrettMiller]

Unbelievable quality and clarity. Bravo!

[SciHeartJourney]

❤ this project! 👍
I'm an EE. I've been doing this since i was 16; 1982.
Back then I took correspondence courses in electronics, then digital microprocessor: Cleveland Institute of Electronics.
In one project we build a 4-bit computer using very simple ICs. We used a 4-bit ALU that greatly reduced the complexity. We used a 1kbit RAM memory chip to hold the data.
We could either single step each clock by hand switch, or use a 1Hz clock.
All that it did was add, subtract, xor and not.
It used only a few breadboards.
I would ❤ to build this huge design though! I like going down to the transistor level like this video shows.

One suggestion though: surface mount parts on a cheap PCB fab.
PCBs from China have become so cheap that it's better to do board layout.
I would still keep each block separate though.
This is perfect project for a young person wanting to learn more about how computers work.
I think this channel should write a book on this. I already want a copy! 😂👍

[AarmOZ]

I remember designing 8 bit computers in my Fundamentals of Computers course. Now I want to build this 4 bit transistor computer (or even bump it up to a full 8 bit system) as I see it as invaluable at helping you understand how computers work.

[JohnVance]

I built Ben's 8-bit breadboard computer, but I wanna go deeper. This looks like a really interesting project, I will check it out.

[dushyantpathak]

Bro you're the real men among others, this needs actual balls to make something like this, talking shit about this is easy but actually implementing it is an extraordinary skill 😊, keep it up brother ❤

[kishankumarhazari]

Bro literally did what I can't even do in my dreams 😅.. Hats off man 👏👏