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.

I’ll play devil’s advocate.

Following Ben’s videos and building the 8-bit CPU is the first thing that ever helped me “get” electronics and circuitry.

Honestly, way more than half of the fun has been in finding the design flaws and designing fixes for them as well as improving and expanding the design itself.

I have learned so much by going down rabbit holes. The original clock design assumes a make-before-break switch but the one shipped with the kit is the opposite, and this can put one of the flip flops into an invalid state. I switched to CMOS chips and learned why you shouldn’t drive loads like LEDs directly from digital outputs, and dove into the easiest way to power 8 LEDs off 8 IC outs without a mess of transistors. I followed another person’s expansion to a full 8-bit instruction register and a more featureful ALU (with my own changes of course). I worked to minimize power consumption. I’ve learned how to use an oscilloscope. I’ve improved upon nearly every module, and built and rebuilt them all a handful of times.

None of this has any real benefit for the CPU. It will never run anything more than toy programs. But that wasn’t ever the point.

All the flaws in the original design have been perfect as launching points for learning more and more.

I would be shocked if anyone is really looking for anything practical out of this, its more of a lab exercise that lets you learn by actually doing things. I learn best this way. It's one thing to draw a circuit, or even put it in a simulator, but the act of hooking up the chips, and watching the blinking lights really sticks with me, and far more deeply ingrains the concepts in my head. And while the 8-bit kit is expensive, and time consuming, I found it worthwhile. There is probably a lot more value to be had in the 6502 series though, if for no other reason that the 6502 is iconic, and it was something of a thrill to me to really understand at a basic level the chip that powered the NES I spent so many hours with.

Pretty strong disagree with your take (though seems like you end with "this is a bad path with no viable alternatives"?). Laying out the breadboards and wiring this has frustrations but that's part of the experience. Same with the design choices; one of the most valuable things my most-digital of minds learned was that you can never escape the analog world completely. I don't think you should be looking for cheap and efficient in this realm, but what I did to source everything was make a big ali express order about 3 months before I planned to tackle this (over a Christmas/winter break), sometimes ordering the same part from multiple suppliers, and then forgot about it, until the packages started to trickle in. You probably already have a lot of the basics, so you can do this for < $200 pretty easily. Meanwhile I completed the NAND to Tetris project, which was very complimentary. I didn't find any parts particularly hard to source and have more basic gates than all ever use.

$300 is somewhat inflated estimate - for example, the breadboard's price is estimated as $4-$9 but I usually buy breadboards at $1.5 each (well, there is a warning that they might be worse quality but I am not used to expensive breadboards so don't notice any issues and I don't care if they are slightly different shade of white).

An alternative might be to write or find a gate level simulator, then write a library for each IC like hex inverter, quad nand, etc. Then you could pick up where Ben starts at the pin level, without messing with wires and breadboards, and get much of the same understanding.

Although I haven't followed his project at all, one fully free alternative which gives similar insight (how logic gates build up to a full computer) is the nand2tetris[1] course. It starts with just a nand gate and then creates all necessary components to make a simple programmable computer, all simulated virtually so you don't need any physical components.

1. https://www.nand2tetris.org/

Speaking as a down-in-the-dirt circuit-slinger who works alongside a lot of ivory-tower engineers who couldn't diagnose a loose wire if their life depended on it, I think that's the whole point.

* Tens of hours and under $1000 is an extremely cheap route to this level of understanding if compared against university courses. I'd give my left nut to have my coworkers go through this process.

* Cutting and laying out wires is time-consuming and error-prone. Yup, hardware is like that. Sweeping out the dojo is menial but important. Developing an intuition around when a weird behavior might actually be a hardware problem, is priceless and absolutely essential for any embedded engineer. And you will never, ever get that from a simulator. (As much as I love the ideas behind nand2tetris, it's entirely done in simulation and that misses half the point, IMHO.)

* Sad to say, the outdated components thing is only getting worse as more basic stuff goes out of production in favor of more highly integrated components. (Even the epic VULCAN-74 caved and used modern RAM.) It might be possible to rework this project to use newer parts but keep the educational value. I suspect there's enough people who've pursued this project and done bits and pieces of that, someone just needs to unify it.

> tens of hours on building it plus over $300 in parts

In other words, quite inexpensive.

Yeah, I started on it and felt the same so I built

https://git.sr.ht/~vhodges/cputhing

There's

  * https://nandgame.com/
  * https://github.com/logisim-evolution/logisim-evolution 

I was going to ask, is there anything like it where you can build a physical computer out of discrete parts? but you answered that in the last remark.

I would love a physical / homebuilt computer of sorts though. Ideally with clicking switches or lights and the like.

As a side note, reading "But How Do It Know" for a total beginner like me can help to scratch the itch of understanding the basics. I really loved the book and will buy my 3rd copy (lost one and gave away another).

A game such as Turing Complete will give the same sort of understanding of the fundamentals of computing, although not a physical learning experience.

> just plain wrong -- e.g. floating inputs or missing resistors

TTL logic gates have no problem with floating inputs. Those are interpreted as logic high. [1]

This is fairly self-evident from looking at a typical TTL gate schematics. [2]

Some "TTL-compatible" CMOS parts (including 65C02) have internal pull-ups on inputs, to match this quirk. [3]

Granted, it is a bad habit to develop, given that nearly all "modern" logic (i.e. of past 30+ years) is CMOS with no "TTL compatibility", and floating inputs are a big problem there.

[1] https://electronics.stackexchange.com/questions/683051/outpu...

[2] https://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/TT...

[3] https://wilsonminesco.com/NMOS-CMOSdif/