2025 Component Abuse Challenge: Digital Logic With Analog Components

[Tim] noticed recently that a large number of projects recreating discrete logic tend to do so with technology around 70 years old like resistor-transistor logic (RTL) or diode-transistor logic (DTL). To build something with these logic families nowadays requires an intense treasure hunt of antique components bordering on impossible and/or expensive. Rather than going down this rabbit hole he decided to invent a somewhat new logic system using analog components in this entry in our Component Abuse Challenge.

The component in question here is an analog multiplexer, which is normally used to select one of two (or several) signal lines and pass them through to an output. Unlike digital multiplexers which only pass 1s and 0s, analog multiplexers can pass analog signals since the transistors aren’t driven to saturation. He has come up with an entire system of logic gates using these components, with trickier devices like latches eventually implemented with help from a capacitor.

The first attempt at using this logic system had a small mistake in it which caused these latches to behave as oscillators instead, due to a polarity mistake. But a second attempt with simplified design and reduced component count ended up working, proving out [Tim]’s concept. Not only that but his second prototype is functioning at an impressive 15 MHz, with a possibility of an even higher clock speed in future designs. Not bad!

Should’ve Used A 555 — Or 276 Of Them

When asked to whip up a simple egg timer, most of us could probably come up with a quick design based on the ubiquitous 555 timer. Add a couple of passives around the little eight-pin DIP, put an LED on it to show when time runs out, and maybe even add a pot for variable timing intervals if we’re feeling fancy. Heck, many of us could do it from memory.

So why exactly did [Jesse Farrell] manage to do essentially the same thing using a whopping 276 555s? Easy — because why not? Originally started as an entry in the latest iteration of our 555 Contest, [Jesse]’s goal was simple — build a functional timer with a digital display using nothing but 555s and the necessary passives. He ended up needing a few transistors and diodes to pull it off, but that’s a minor concession when you consider how many chips he replaced with 555s, including counters, decoders, multiplexers, and display drivers. All these chips were built up from basic logic gates, a latch, and a flip-flop, all made from one or more 555s, or variants like the 556 or 558.

As one can imagine, 276 chips take a lot of real estate, and it took eleven PCBs to complete the timer. A main board acts as the timer’s control panel as well as serving as a motherboard for ten other cards, each devoted to a different block of functions. It’s all neat and tidy, and very well-executed, which is in keeping with the excellent documentation [Jesse] produced. The whole thing is wonderfully, needlessly complex, and we couldn’t be more tickled to feature it.

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VGA From Scratch On A Homebrew 8-bit Computer

[James Sharman] has built an impressive 8-bit homebrew computer. Based on TTL logic chips, it has a pipelined design which makes it capable of Commodore-level computing, but [James] hasn’t quite finished everything yet. While it is currently built on its own custom PCB, it has a limiting LCD display which isn’t up to the standards of the rest of the build. To resolve this issue, he decided to implement VGA from scratch.

This isn’t a bit-bang VGA implementation, either. He plans for full resolution (640×480) which will push the limits of his hardware. He also sets goals of a 24-bit DAC which will allow for millions of colors, the ability to use sprites, and hardware scrolling. Since he’s doing all of this from scratch, the plan is to keep it as simple as possible and make gradual improvements to the build as he goes. To that end, the first iteration uses a single latching chip with some other passive components. After adding some code to the CPU to support the new video style, [James] is able to display an image on his monitor.

While the image of the parrot he’s displaying isn’t exactly perfect yet, it’s a great start for his build and he does plan to make improvements to it in future videos. We’d say he’s well on his way to reproducing a full 8-bit retrocomputer. Although VGA is long outdated for modern computers, the standard is straightforward to implement and limited versions can even be done with very small microcontrollers.

Thanks to [BaldPower] for the tip!

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Project Egress: Two Ways To Latch The Hatch

With July slipping away and the deadline approaching, the Project Egress builds are pouring in now. And we’re starting to see more diversity in the choice of materials and methods for the parts being made, like these two latches made with very different methods by two different makers.

For the uninitiated, Project Egress is a celebration of both the 50th anniversary of Apollo 11 and the rise of the maker movement. Spearheaded by [Adam Savage], the idea is to engage 44 prominent makers to build individual parts from the Unified Crew Hatch (UCH) from the Apollo Command Module. The parts will be used to create a replica of this incredibly complex artifact, which will be assembled by [Adam] before a live audience at the National Air and Space Museum next week.

Both [Joel] from the “3D Printing Nerd” channel and [Bill Doran] from “Punished Props Academy” got the nod for one of the 15 latches needed, and both played to their respective strengths. [Joel]’s latch was executed in PLA on a Prusa I3 printer. [Bill] went a different route for his latch. He used a Form 2 SLA printer to print the parts, but used them only to make silicone molds. He then cast the parts from urethane resin, which should prove much stronger than the original SLA prints. We suspect the ability to quickly cast more latches could prove handy if any of the other latch makers should fail to deliver.

The latches [Joel] and [Bill] made joins the other parts, like the wooden latch being made by [Fran Blanche] and the hatch handle [Paul] cast in aluminum. We’re looking forward to more part builds, as well as the final assembly.

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Project Egress: [Fran] Makes A Latch

[Fran Blanche] is on the team of elite hackers that has been offered a chance to contribute to [Adam Savage]’s Project Egress, a celebration of the engineering that got humanity to the Moon 50 years ago this month. By the luck of the draw, she landed a great assignment: building a replica of one of the fifteen latches that kept the Apollo Command Module hatch dogged down against the vacuum of space, and she’s doing a great job documenting her build with some interesting videos.

The first video below is mostly her talking through her design process, materials choices, and ideas about fabricating the somewhat intricate pieces of the latch. All 44 makers involved in the project get to choose what materials and methods they’ll use to make their parts, and [Fran] decided to use wood. Her first inclination was to use oak and brass, a nice combination with an 80s vibe, but in the second video, which covers more of the initial fabrication, she explains her switch to walnut. Unfortunately, the only CNC option she has is a Shaper Origin, which presents some difficulties; the handheld tool requires some complicated fixturing to safely machine the small parts needed, and its inability to read STL files means that [Fran] is stuck with a complicated software toolchain to drive the tool.

There are more videos to come as [Fran] gets further into the build, and we’re looking forward to seeing how her part and the rest of the makers’ builds come out.

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Help Solve The Single-Transistor Latch Mystery

If you’ve spent any time on hackaday.io, you may have noticed that more than a few denizens of the site are fans of “alternative” electronic logic. Aiming to create digital circuits from such things as relays, vacuum tubes, discrete transistors, and occasionally diodes, they come up with designs that use these components in either antiquated or occasionally new and unexpected ways. This is exactly what [Mark Sherman] has done with his latest project, a single-transistor latch.

If you think every design has to compete with cutting-edge integrated circuits, or even must have an immediate practical application, you might as well stop reading now — and to play on the famous Louis Armstrong quip about jazz, if you have to ask why someone would do such a thing, you’ll never know.

Given that you’ve come this far, you’ll appreciate what [Mark] has come up with. It’s semi-well-known that the collector-emitter junction of a bipolar junction transistor (BJT) can exhibit a negative resistance characteristic when reverse-biased into avalanche breakdown. It’s this principle that allows a single BJT to be used as an ultra-simple LED flasher. [Mark] took this concept and ran with it, creating a single-transistor latch that can store one bit of information. As a bonus — or is it a requirement? — the transistor also drives an LED, so that you can visualize the state. We’ve seen a one-transistor flip-flop before, but that one also required diodes and an AC bias supply. In this new device, none of this is necessary, so it’s a step up according to the unwritten, unspoken, and generally agreed upon rules of the game.

In true hacker fashion, [Mark] came up with a working device without fully understanding exactly how it works.  We, too, are a little mystified at first glance. So, [Mark] is asking for your help in replicating and/or analyzing the circuit. He explains what he has found so far in the video after the break, but the main questions seem to revolve around why the base resistor is required, and why it works with 2N4401s but not 2N2222s.

So, Hackaday, what’s going on here? Sound off in the comments below.

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Blacksmith Elevates The Craft With This Fabulous Strongbox

For most of human industrial history, the blacksmith was the indispensable artisan. He could fashion almost anything needed, from a simple hand tool to a mechanism as complex as a rifle. Starting with the most basic materials, a hot forge, and a few tools that he invariably made himself, the blacksmith was a marvel of fabrication.

If you have any doubt how refined the blacksmith’s craft can be, feast your eyes on [Seth Gould]’s masterpiece of metalwork. Simply called “Coffer”, [Seth] spent two years crafting the strongbox from iron, steel, and brass. The beautifully filmed video below shows snippets of the making, but we could easily watch a feature-length film detailing every aspect of the build. The box is modeled after the strongboxes built for the rich between the 17th and 19th centuries, which tended to favor complex locking mechanisms that provided a measure of security by obfuscation. At the end of the video below, [Seth] goes through the steps needed to unlock the chest, each of which is filled with satisfying clicks and clunks as the mechanism progresses toward unlocking. The final reveal is stunning, and shows how much can be accomplished with a forge, some files, and a whole lot of talent.

If you’ve never explored the blacksmith’s art before, now’s the time. You can even get started easily at home; [Bil Herd] will show you how.

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