Check out the Megaprocessor[0]. A guy made his own "processor" out of roughly a hundred thousand transistors, resistors, etc. Really interesting project.

[0]: http://www.megaprocessor.com/

Relatedly, a discrete 6502 built with a little over 3K transistors:

http://monster6502.com/ as seen on HN https://news.ycombinator.com/item?id=11703596

So impressive, but I am so happy to never have any reason to need to do anything like this myself. I used to fix IBM mainframes like 3033s back in the day, and debugging computers made up of gajillions of interconnected frames, boards and cards, under immense pressure, was truly the stuff of nightmares. After hours or even days, victory was finding a ringing signal with your scope, caused by a loose trilead. Then you went home and slept for a day.

"If you want to make an apple pie from scratch..."

Why stop there? From scratch should involve extracting the materials from the Earth.

Because that's the point where you take things that don't compute, and make something that computes.

>>Because that's the point where you take things that don't compute, and make something that computes.

Good point but I didn't get it quite right. What is your definition of "things that compute"? I am curious.

A device that can use a mathematical process to figure something out.

A single transistor definitely doesn't compute. A single gate? Eh, not really.

A design with a couple latches and an adder that can perform SUBLEQ? Yeah that computes if you attach a ram.

A non-turing-complete pipeline of math functions? Yes, that computes, though why make that when it takes more gates than a microprocessor needs.

You can make a razor blade diode or a pyrite diode, so I wonder if there's some way to make a make a transistor out of household junk...

Jeri Ellsworth has built working transistors at home.

Point contact germanium BJT: https://www.youtube.com/watch?v=vmotkjMSKnI

Etched silicon FET: https://www.youtube.com/watch?v=PdcKwOo7dmM

The rusty razorblade + pin point contact diode doesn't need anything special because it's a Schottky diode, with a metal/N-type semiconductor junction. If you probe lots of places you can find an N-type region where the dopant is random impurities. But the transistor needs both N and P-type regions, so I don't see any way to build one with common junk. Jeri's point contact example works by diffusing phosphorus from phosphor bronze into commercially produced N-type germanium using a high current to heat it. Phosphor bronze is arguably household junk but I don't think germanium diodes are.

I wouldn't mind actually. That toaster thing was interesting.

Yeah this is what I was expecting too