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Build an 8-bit computer from scratch (2016)

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I did the whole thing, was able to get the Fibonacci numbers appear and learned a lot during the process. However, I would not recommend other people to try this today, because --

* It is not necessarily the best way to spend your time and money. You'll be looking at tens of hours on building it plus over $300 in parts, for a very slow and basic computer that you probably will forget and throw away at some point. Cutting and laying out wires are some of the most tedious and frustrating process. There are other cheaper, more efficient ways to learn how a computer works. It may or may not be worth the effort to you.

* The tutorial is really old, with some very questionable design choices and no updates from the author. Some of the designs are just plain wrong -- e.g. floating inputs or missing resistors. It is very unlikely you can reproduce it by strictly following the tutorial. You'll need to spend time debugging those issues and go to reddit to see other people's experience with this, potentially seeking help as well. No doubt debugging is an important part of designing and understanding the circuit. But only if you have the foundational knowledge and patience, of which I happened to have, but I can imagine that someone who does not understand digital electronics well enough can easily get lost and feel defeated.

* To make the previous point worse, some of the parts are hard to source, depending on where you are. (You'll likely fry or physically break a few components when building it.) Many of the parts are not very commonly used these days, and not exactly easy to acquire, if you only need 1 or 2 of them. I had to go to eBay to get some of them, which took about a week, during which I had to stop and wait for parts to arrive.

With all that said, this may still be the best resource out there that lets you build all these on a breadboard, as I am not aware of an alternative that addresses all the issues above.

19 hours agoby rs186

I always upvote Ben Eater's project(s).

I got his 6502 kit and worked through his YouTube videos to get it up and running with LCD display and all. I want to actually frame it and get it running, hanging on a wall.

If anyone is new to Ben, find a comfortable chair or couch, make some tea, take a breath, and begin your descent into his long-form breadboard series of nerd-splaining how a CPU works, beginning with basic logic gates.

His follow-on series is a little higher level. He's still at it with the breadboards but he allows that this time the CPU (a 6502) is already built for us. He then walks through how the address bus works, how to attach RAM, etc.

It makes me wish I could be transported back to the 70's when things could still be understood.

22 hours agoby JKCalhoun

Just wanted to add that there is "a homebrew computer ring" project [1] and you will be surprised how many ideas for DIY computers you can find there.

(I also made a two-breadboard CPU with ~5 instructions myself but had yet no time to finish the software)

[1] https://www.homebrewcpuring.org/

48 minutes agoby codedokode

The Ben Eater computer is an interesting starting point. With a few modifications, such as an extended program counter / address bus, a combinatorial ALU programmed in flash, and a few more registers, it can be upgraded to a more powerful, if slow, computer.

Further, these circuits can be directly simulated in an FPGA if you want to teach yourself an HDL like VHDL or Verilog. You really want to learn better and faster ways to organize a CPU, but it's a fun way for a beginner to bridge into this kind of work.

At the local hackerspace, we actually taught a class that assembled a hybrid 8-bit / 16-bit variation of this computer with 1MB of RAM, an 8-bit ALU, a 16-bit data bus / registers, and a 20-bit address bus. With this additional capability, we could program it over serial with a very basic bootloader, and it was powerful enough to compute pi to 1000 digits. Granted, this took about 18 hours, but it could have run faster with a printed circuit board and a crystal oscillator. We just never really got to that point.

As for how powerful such a computer with discrete logic can be, consider that the KB-11A CPU for the PDP-11/45 was built using 74-series logic ICs. It wasn't until after this system that DEC moved on to VSLI. So, this is a way to play with technology found in computers in 1972 / 1973.

As a stepping stone to digital logic and FPGA work, Ben Eater's tutorial isn't bad. Just get yourself a copy of Don Lancaster's TTL Cookbook or CMOS Cookbook to bring his tutorial up to best practices.

15 hours agoby nanolith

Note that even the "Update" video is nine years old.

Also note that yes it's a computer, but it has 16 bytes of memory to hold both the program and the program's variables.

BYTES. Not KB, not MB, not GB. Bytes.

The demo Fibonacci program is pretty much the most complex thing you can do with it.

But it is in fact a genuine von Neumann computer. And understandable.

20 hours agoby brucehoult

Ben's videos are fantastic, learned a lot. For HW beginners like myself I suggest to skip the computer but just build the clock - very easy and great testing tool!

Here's my question: Obviously there's tremendous interest in kits like this. Why doesn't Ben or someone else create small company to:

  * Modernize the components 
  * Update the videos
  * Add additional modules to make the computer a bit more powerful

People would pay money for this. I would.

3 hours agoby Jun8

Ben Eater's breadboard CPU is a good way to learn the basics, but since the focus is pedagogical, it's very underpowered for the quantity of chips it uses (and you better enjoy forming wires). For a much more powerful computer built around the same number of TTL chips, see the Gigatron.

21 hours agoby apricot

Building up a full CPU from logic was one of my favorite things in university! The class was digital logic in the electrical engineering department and was a lot of fun. We even got to write machine code programs for it.

20 hours agoby roland35

Always love seeing Ben Eater’s “build [X] from scratch” His YouTube is one of the best channels to understand how stuff works from fundamental building blocks.

17 hours agoby ata_aman

Wasn't there someone who did a physical discrete logic implementation of the NAND to Tetris design?

I feel like that could be a good choice for someone doing this today because there's now a kind of a large ecosystem of resources for that design (not that it's inherently better somehow).

18 hours agoby schoen

I can trace back the moment I saw YouTube as a tool for learning when I first saw your 8-bit computer series. I was honestly amazed with the quality of the videos and how clear you can explain things. Top content. I'm a subscriber and a fan to this day. Keep up the good work.

20 hours agoby atum47

I kinda judge YouTube channel by the inverse of the speed I need to scale down/up.

Ben Eater is always among the top 10.

18 hours agoby markus_zhang

It is a rite of passage, as electronics wizards say. I remember at least another good example shared in the wild: https://github.com/vascofazza/8bit-cpu

15 hours agoby giulianopz

RE "....Cutting and laying out wires are some of the most tedious and frustrating process....." I would be investigating to use wire wrap. I built some circuits using wire wrap, back in late 70s ,early 80s. I designed and built a circuit on a wire wrap prototype board to put a 68008 DIL chip on the Apple II bus. I'm not sure of the cost of wire wrap parts now - may be quite expensive , the special wire wrap sockets etc .....

13 hours agoby asdefghyk

If figuring out how computers work starting all the way from logic gates interests you, but you don’t want to start by ordering parts and soldering, check out the ”game” Turing Complete.

Of course it’s not the same thing as actually building the electronics! But it can be a nice introduction.