brainwagon

Okay, it’s been a long time since I wrote anything here. Not really a lot dramatic going on in life, I just have been spending my free time writing for Quora rather than my own blog. But I still am nerding out from time to time. Last night I dusted off an old project of […]

Ken stumbled on one of my earlier posts about DTL (diode transistor logic) and was interested enough to do some basic exploration. He reduced the DTL NAND gate to a double diode, a transistor and two resistors. Ken sent me the LTSpice and EagleCAD screen dumps that fit in about .4″ square: Pretty cool. In […]

Yesterday, I mentioned Rory’s excellent introduction and exploration into DTL logic. He covers some of the basics here, including circuits for all the basic gates: AND, OR, NOT and NAND. The AND and OR gates are interesting, because they consist entirely of diodes and resistors. They do have the drawback that they are “lossy” (the […]

Previously, I had linked to Rory Mangles’ experiments with relay based computers. He had an incredible build of a relay logic computer called Tiny-8 which used paper as program mamory, inked with a pattern which could be read by photo sensors to sequence the control logic in his computer. I thought it was amazing. But […]

An anonymous commenter suggested that I look at logisim, a circuit simulator written in Java. It has many nice features. For instance, you can specify a combinatorial circuit either as a truth table or as equations, and it will convert to the other representation (in minimized forms) and will also build a circuit to implement […]

Continuing my obsession with reading up on homebrew CPU projects, I found this incredible blog. Instead of just presenting the completed design, Dawid has presented intermediate posts about his project in progress, detailing some of the choices and techniques he had to make along the way. As is true of most projects like this, it’s […]

Yep, been spending some time thinking about homebrew computer architectures. I’ve also been reading Gordon Bell’s Computer Engineering, pondering some of the older and earlier computing architectures. Caxton Foster’s Computer Architecture describes a simple computer architecture called “Blue”, which has only 16 instructions, and uses only direct addressing. It’s a pretty primitive machine (more like […]

Just another link to inspire me in my glacial moves toward designing a CPU of my own: The D16/M is a general-purpose, stored-program, single-address, 16-bit digital computer using two’s complement arithmetic. It manages subroutine calls and interrupts using a memory stack. The processor may directly address 64K words of memory or I/O. Its timing and […]

Dieter Muller has an amazingly interesting collection of interesting ideas about building homebrew cpus with TTL logic. I’m sure to old school logic designers, most of these are old hat, but to the nearly crazed home experimenter, they are quite illuminating. His hints on ALU design are what brought me to the site, so I’m […]

In a previous blog post about a year ago, I pointed you at Jack Eisenmann’s 4 bit computer built from TTL chips. It was cool, made entirely on breadboards tucked away inside a big plastic container. Or, I used to think it was cool, until I saw what he’s been up to: an 8 bit […]