CPU Built From Discrete Transistors

September 30, 2023 by Bryan Cockfield 29 Comments

We all know, at least intellectually, that our computers are all built with lots of tiny transistors. But beyond that it’s a little hard to describe. They’re printed on a silicon wafer somehow, and since any sufficiently advanced technology is indistinguishable from magic, they miraculously create a large part of modern society. Even most computers from 40 or 50 years ago were built around various inscrutable integrated circuits. On the other hand, this computer goes all the way back to first principles and implements a complete processor out of individual transistors instead.

The transistor computer uses over 2000 individual transistors to implement everything comprising the 11-bit CPU. The creator, Reddit user [ Weekly_Salamander_78] also has an online interactive book that walks through each of the steps that is required to get to the point of having a working computer like this. Starting with a guide on building logic gates from transistors it will eventually cover the arithmetic logic unit, adders, memory, clocks, and everything else that is needed for the complete CPU to get up and running. The design does rely on an Arduino for memory to simplify some things, and in the end it’s able to run a Hello, World! program and play a simple dinosaur game as well.

Building a computer out of discrete components like this is an impressive accomplishment, although we might not envy the creator of it when it comes time for troubleshooting or maintenance of all of those individual components. Presumably it would be much easier to work on than something like a relay computer, but for now we’ll all take a moment to be thankful that almost no one needs to work on debugging vacuum tube computers anymore.

A close-up view of surface-mount components on a circuit board

Smaller Is Sometimes Better: Why Electronic Components Are So Tiny

November 8, 2021 by Robin Kearey 34 Comments

Perhaps the second most famous law in electronics after Ohm’s law is Moore’s law: the number of transistors that can be made on an integrated circuit doubles every two years or so. Since the physical size of chips remains roughly the same, this implies that the individual transistors become smaller over time. We’ve come to expect new generations of chips with a smaller feature size to come along at a regular pace, but what exactly is the point of making things smaller? And does smaller always mean better?

Smaller Size Means Better Performance

Over the past century, electronic engineering has improved massively. In the 1920s, a state-of-the-art AM radio contained several vacuum tubes, a few enormous inductors, capacitors and resistors, several dozen meters of wire to act as an antenna, and a big bank of batteries to power the whole thing. Today, you can listen to a dozen music streaming services on a device that fits in your pocket and can do a gazillion more things. But miniaturization is not just done for ease of carrying: it is absolutely necessary to achieve the performance we’ve come to expect of our devices today. Continue reading “Smaller Is Sometimes Better: Why Electronic Components Are So Tiny” →

Op Amps Before Transistors: A 600V Vacuum Tube Monster

August 9, 2018 by Ben James 11 Comments

Op amps. Often the first thing that many learn about when beginning the journey into analog electronics, they’re used in countless ways in an overwhelmingly large array of circuits. When we think about op amps, images of DIPs and SOICs spring to mind, with an incredibly tiny price tag to boot. We take their abundance and convenience for granted nowadays, but they weren’t always so easy to come by.

[Mr Carlson] serves up another vintage offering, this time in the form of a tube op amp. The K2-W model he acquired enjoyed popularity when it was released as one of the first modular general purpose amplifiers, due to its ‘compact form’ and ‘low price’. It also came with large application manuals which helped it to gain users.

In order to power up the op amp and check its functionality, +300V and -300V supplies are needed. [Mr Carlson] is able to cobble something together, since it’s very apparent that he has an enviable stash of gear lying around. A 600V rail to rail supply is not something to be taken lightly, though it does give this particular model the ability to output 100V pk-pk without any distortion.

The op amp is set up as an inverting amplifier, and once powered on proves to work flawlessly. As always, the video is an entertaining watch, stuffed full of retro electronics trivia. We’re big fans of [Mr Carlson]’s work, and have previously written about his adventures with a colossal walk-in AM radio transmitter, as well as his restoration of a 1930s oscilloscope and subsequent transformer de-potting.

Continue reading “Op Amps Before Transistors: A 600V Vacuum Tube Monster” →

Biasing That Transistor: The Common Base Amplifier

May 11, 2018 by Jenny List 31 Comments

We’ve previously remarked upon a generation lucky enough to be well-versed in microcontrollers and computersised electronics through being brought up on the Arduino or the Raspberry Pi but unlucky enough to have missed out on basic electronics such as how to bias a transistor, and to address that gap we’ve taken a look at the basics of transistor biasing.

All the circuits we worked with in the previous article had the transistor’s emitter taken to ground, took their input from the base, and their output from the collector. This configuration, called a Common Emitter amplifier is probably the most common, but it is far from the only way to use a transistor. Once you have set up the bias voltage as we described to the point at which the transistor is in its linear region, there are several other ways in which the device can be used as an amplifier. The subject of this article is one of these configurations, so described because it takes the transistor’s base to the ground instead of the emitter, as a Common Base amplifier. Continue reading “Biasing That Transistor: The Common Base Amplifier” →

Won’t Somebody, Please, Think Of The Transistors!

April 6, 2018 by Jenny List 146 Comments

At what age did you begin learning about electronics? What was the state of the art available to you at the time and what kinds of things were you building? For each reader these answers can be wildly different. Our technology advances so quickly that each successive generation has a profoundly different learning experience. This makes it really hard to figure out what basic knowledge today will be most useful tomorrow.

Do you know the forward voltage drop of a diode? Of course you do. Somewhere just below 0.7 volts, give or take a few millivolts, of course given that it is a silicon diode. If you send current through a 1N4148, you can be pretty certain that the cathode voltage will be that figure below the anode, every time. You probably also have a working knowledge that a germanium diode or a Schottky diode will have a lower forward voltage, and you’ll know in turn that a bipolar transistor will begin to turn on when the voltage between its base and emitter achieves that value. If you know Ohm’s Law, you can now set up a biasing network and without too many problems construct a transistor amplifier.

Continue reading “Won’t Somebody, Please, Think Of The Transistors!” →

42,300 Transistor Megaprocessor Is Complete

July 6, 2016 by Moritz Walter 83 Comments

As it turns out, the answer is not 42, it’s 42.3 — thousand. That’s how many discrete transistors spread across the 30 m² room housing this massive computation machine. [James Newman’s] Megaprocessor, a seriously enlarged version of a microprocessor, is a project we’ve been following with awe as it took shape over the last couple of years.

[James] documented his work in great detail, and by doing so, took us on a journey through the inner workings of microprocessors. His monumental machine is now finished, and it’s the ultimate answer to how a processor – and pretty much everything that contains a processor – works.

Continue reading “42,300 Transistor Megaprocessor Is Complete” →

How The Dis-integrated 6502 Came To Be

May 24, 2016 by Mike Szczys 43 Comments

I made a bee line for one booth in particular at this year’s Bay Area Maker Faire; our friend [Eric Schlaepfer] had his MOnSter 6502 on display. If you missed it last week, the unveiling of a 6502 built from discrete transistors lit the Internet afire. At that point, the board was not fully operational but [Eric’s] perseverance paid off because it had no problem whatsoever blinking out verification code at his booth.

I interviewed [Eric] in the video below about the design process. It’s not surprising to hear that he was initially trying to prove that this couldn’t be done. Unable to do so, there was nothing left to do but devote almost six-months of his free time to completing the design, layout, and assembly.

Unpopulated PCB

resistor fix

What I’m most impressed about (besides just pulling it off in the first place) is the level of perfection [Eric] achieved in his design. He has virtually no errors whatsoever. In the video you’ll hear him discuss an issue with pull-up/pull-down components which did smoke some of the transistors. The solution is an in-line resistor on each of the replacement transistors. This was difficult to photograph but you can make out the soldering trick above where the 3-pin MOSFET is propped up with it’s pair of legs on the board, and the single leg in the air. The added resistor to fix the issue connects that airborne leg to its PCB pad. Other than this, there was no other routing to correct. Incredible.

The huge schematic binder includes a centerfold — literally. One of the most difficult pieces of the puzzle was working out the decode ROM. What folds out of this binder doesn’t even look like a schematic at first glance, but take a closer look (warning, 8 MB image). Every component in that grid was placed manually.

I had been expecting to see some tube-based goodness from [Eric] this year. That’s because I loved his work on Flappy Bird on a green CRT in 2014, and Battlezone on a tube with a hand-wound yoke last year. But I’m glad he stepped away from the tubes and created this marvelous specimen of engineering.