# A Discrete Logic Word Clock

Self-acclaimed computer nerd [Kevin Koster] was tired of designing new TTL-logic clocks before finishing his previous designs. So he finally buckled down and completed this unique word clock, which uses only a handful of TTL chips. We can’t disagree with his friends who complained that they can’t read [Kev]’s handwriting, so perhaps this diagram will make it clearer.

Besides being a nice logic-only project, this will give an example to younger folks how much effort went into things which are so simple to implement today. We don’t see a Karnaugh map on the project page for sorting out the logic diodes driving the minutes LEDs. If [Kev] did it on the fly, as the rat’s nest of diodes on the schematic would suggest, we’re not sure whether to scold him or be impressed (he does redraw that logic very neatly on a separate sheet).

No worries about high speed wiring on this project. The main oscillator derives time from the 50 Hz AC transformer power supply, and outputs a reference clock signal of 16.7 mHz (not MHz), or once per minute. This is divided down to 3.3 mHz for the 5-minutes counter and again to 277 uHz for the hour counter. If you live in a 60 Hz power mains country, you’d have to modify the oscillator section. Or you could contact [Kev] on his site, as he is considering making this available as a kit worldwide. If you like word clocks, we’ve covered quite a few of them before, including this crazy-complex rear-projection one.

# Another 74XX Series CPU

[Jack Eisenmann] is no stranger to building impressive DIY CPU’s on vast stretches of breadboard. This time [Jack] has done away with the seventeen breadboards he used in his last 8-bit computer and instead has gone a step further and designed a set of generously utilised PCB’s for the CPU. The result is the DUO Enterprise.

The CPU design is based around an 8-bit data bus and a 24-bit address bus. As usual, a minimal yet carefully chosen instruction set allows [Jack] to do all the heavy lifting in software as part of the compiler and operating system he is working on. There is no sign of a display yet, instead the computer communicates via a dumb terminal. We love the aluminum foil for shielding! Check out the video, below, to see what we mean.

Over the years, we have seen many of [Jack]’s other CPU builds featured on Hackaday. One of his first designs was a 4-bit CPU that could play many games on a LED matrix.Later he did a much more impressive 8-bit CPU along with analog video output and an OS ofcourse. It could even play pong. He even built a Single Instruction Set Computer (SISC).

His final goal with DUO Enterprise is to allow anyone to utilise its computing power by submitting programs and calculations. Heads up [Jack], our neural net needs training soon.

# Homebrew TTL Logic Computer

Although [Jack] just graduated High School and doesn’t have much experience with electronics, that didn’t stop him from building the DUO Adept, a homebrew computer built entirely out of TTL logic chips.

The DUO Adept has 64k of memory, 6K of which is dedicated to the video ram that outputs a 240×208 black and white image onto a TV. Bootstrapping the computer to it’s current state was quite a challenge, as an entire OS was put into th system one bit at a time though DIP switches. After the OS was written to the computer, [Jack] was able to connect a keyboard and started programming. [Jack] programmed a hex editor and a few games of his own design. If all that wasn’t impressive enough, [Jack] also programmed an assembly compiler and emulator for his homebrew system.

We’ve seen a a few homebrew computersbefore, but not many of them are laid out on 17 breadboards like the DUO Adept. With skills like these, we can’t wait to see what [Jack] comes up with next. Check out the video after the break for a walk-through of the build.