discrete

31 Articles

A CPU-Less Computer With A Single NOR-Gate ALU

November 23, 2020 by 13 Comments

We see a lot of discrete-logic computer builds these days, and we love them all. But after a while, they kind of all blend in with each other. So what’s the discrete logic aficionado to do if they want to stand out from the pack? Perhaps this CPU-less computer with a single NOR-gate instead of an arithmetic-logic unit is enough of a hacker flex? We certainly think so.

We must admit that when we first saw [Dennis Kuschel]’s “MyNor” we thought all the logic would be emulated by discrete NOR gates, which of course can be wired up in various combinations to produce every other logic gate. And while that would be really cool, [Dennis] chose another path. Sitting in the middle of the very nicely designed PCB is a small outcropping, a pair of discrete transistors and a single resistor. These form the NOR gate that is used, along with MyNor’s microcode, to perform all the operations normally done by the ALU.

While making the MyNor very slow, this has the advantage of not needing 74-series chips that are no longer manufactured, like the 74LS181 ALU. It may be slow, but as seen in the video below, with the help of a couple of add-on cards of similar architecture, it still manages to play Minesweeper and Tetris and acts as a decent calculator.

We really like the look of this build, and we congratulate [Dennis] on pulling it off. He has open-sourced everything, so feel free to build your own. Or, check out some of the other CPU-less computers we’ve featured: there’s the Gigatron, the Dis-Integrated 6502, or the jumper-wire jungle of this 8-bit CPU-less machine.

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Discrete-Logic UART Keeps 8-Bit TTL Computer Connected

August 26, 2020 by 18 Comments

Pity the poor TTL computer aficionado. It’s an obsession, really — using discrete logic chips to scratch-build a computer that would probably compare unfavorably to an 80s era 8-bit machine in terms of performance. And yet they still forge ahead with their breadboards full of chips and tangles of wire. It’s really quite beautiful when you think about it.

[Duncan] at Shepherding Electrons has caught the TTL bug, and while building his 8-bit machine outfitted it with this discrete logic UART. The universal asynchronous receiver-transmitter is such a useful thing that single-chip versions of the device have been available since the early 1970s. [Duncan]’s version makes the magic of serial communications happen in just 12 chips, all from the 74LS logic family.

As if the feat of building a discrete logic UART weren’t enough, [Duncan] pulled this off without the aid of an oscilloscope. Debugging was a matter of substituting the 2.4576 MHz crystal oscillator clock with a simple 1 Hz 555 timer circuit; the reduced clock speed made it easier to check voltages and monitor the status of lines with LEDs. Once the circuit was working, the full-speed clock was substituted back in, allowing him to talk to his 8-bit computer at up to 38,400 bps. Color us impressed.

For more TTL computer goodness, and to see where [Duncan] got his inspiration, check out [Ben Eater]’s many discrete logic projects — his scratch-built 6502, a low-end video card, or even his take on serial communications.

Homebrew 16-Bit Computer Is A Wire-Wrapped Work Of Art

July 24, 2020 by 9 Comments

Breadboard 8-bit computer builds seem all the rage these days, and with good reason: building your own CPU from the board up using discrete logic chips is a great way to really learn how microprocessors work. Not to mention that it’s an incredible flex. But once you’ve conquered the eight-bit, what do you do? Easy: build a 16-bit computer from 74HC logic chips.

Attentive readers will likely remember this computer’s builder, [Paulo Constantino], from his previous work on 8-bit breadboard computers. As gloriously entropic as that tangled mass of wires was, it must have been a nightmare for [Paulo] to maintain. And so when the time came to upgrade, he wisely chose a more integrated construction method. The construction method is wire-wrapping, with multiple cards plugged into backplane and connected by ribbon cables. The whole card cage is far neater than the previous build, and seems to lend itself to rapid modifications. The top card in the cage acts as a control panel for now; eventually, [Paulo] planes to put a real front panel on the cage to support all the switches and blinkenlights such builds demand. Stretch goals include supporting audio and video and getting the machine online so anyone can log in.

The video below is an overview of the current state of the machine; earlier videos in the playlist cover the design and build in more detail. We hope to see schematics soon, and we’d love to know where to get some of those wire-wrap PCBs for projects of our own.

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The Descendants Of Ancient Computers

May 31, 2020 by 13 Comments

Building computers from discrete components is a fairly common hobby project, but it used to be the only way to build a computer until integrated circuits came on the scene. If you’re living in the modern times, however, you can get a computer like this running easily enough, but if you want to dive deep into high performance you’ll need to understand how those components work on a fundamental level.

[Tim] and [Yann] have been working on replicating circuitry found in the CDC6600, the first Cray supercomputer built in the 1960s. Part of what made this computer remarkable was its insane (for the time) clock speed of 10 MHz. This was achieved by using bipolar junction transistors (BJTs) that were capable of switching much more quickly than typical transistors, and by making sure that the support circuitry of resistors and capacitors were tuned to get everything working as efficiently as possible.

The duo found that not only are the BJTs used in the original Cray supercomputer long out of production, but the successors to those transistors are also out of production. Luckily they were able to find one that meets their needs, but it doesn’t seem like there is much demand for a BJT with these characteristics anymore.

[Tim] also posted an interesting discussion about some other methods of speeding up circuitry like this, namely by using reach-through capacitors and Baker clamps. It’s worth a read in its own right, but if you want to see some highlights be sure to check out this 16-bit computer built from individual transistors.

Building Video Pong With Discrete Components

September 17, 2019 by 19 Comments

Pong is a classic from the very dawn of the video game era. Recreating it remains a popular exercise for those new to coding. However, its simple logic makes this game particularly suited to an all-hardware build; something which [Glen] tackles with aplomb.

Not content to take the easy way out, [Glen] went for a particularly hardcore method of construction. The game uses absolutely zero integrated circuits in its construction. Instead, it relies upon the services of 431 bipolar transistors, 6 JFETs and 826 diodes. Everything is laced together on protoboard, connected with a neatly organised nest of colored wires. Schematics are available for the curious.

It’s a full featured build, too. Video output is in color, scores are displayed at the top of the screen, and there’s even stereo panning for the sound effects. It just goes to show what some humble components can do when put to work in the right way. We’ve seen some of [Glen]’s work before too, for example in this op-amp bouncing ball device. Video after the break.

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Logic And EEPROMs Bring VGA To Life, Sans Microcontroller

July 1, 2019 by 9 Comments

For whatever reason, the Video Graphics Array standard seems to attract a lot of hardware hacks. Most of them tend to center around tricking a microcontroller into generating the signals needed to send images to a VGA monitor. We love those hacks, but this one takes a different tack – a microcontroller-free VGA display that uses only simple logic chips and EEPROMs.

When we first spied this project, [PH4Nz] had not yet shared his schematics and code, but has since posted everything on GitHub. His original description was enough to whet our appetite, though. He starts with a 27.175-MHz clock and divides that by 4 with a 74HCT163, which has the effect of expanding the 160×240 pixels image stored in one of the EEPROMs to 640×480. Two 8-bit counters keep track of horizontal and vertical positions, while the other EEPROM takes care of generating the Hsync and Vsync signals. It’s all quite hackish, but it works. [PH4Nz] tells us that the whole thing is in support of a larger project: an 8-bit computer made from logic chips. We’re looking forward to seeing that one too.

This isn’t the first microcontroller-less VGA project we’ve seen, of course. Here’s a similar one also based on EEPROMs, and one with TTL logic chips. And we still love VGA on a microcontroller such as the ESP32; after all, there’s more than one way to hack.

Thanks to [John U] for the tip.

Discrete Pong Project Goes Big, Adds A Player

February 7, 2018 by 13 Comments

Some projects just take on a life of their own. What started as a pleasant diversion or a simple challenge becomes an obsession, and the next thing you know you’ve built a two-player color Pong game with audio completely from discrete components.

If this one seems familiar, it’s because we were dazzled by its first incarnation last year. As impressive as version 1.0 was, all the more so since it was built using the Manhattan method and seemingly over the course of a weekend, it did have its limitations. [GK] has been refining his design ever since and keeping accurate track of the process, to the tune of 22 pages on the EEVblog forum. We haven’t pored through it all yet, but the state of the project now is certainly worth a look. The original X-Y output to an oscilloscope was swapped out to composite video for a monitor, in both mono and color. This version also allows two people to play head-to-head instead of just battling the machine. It looks like [GK] had to add a couple of blocks worth of real estate to his Manhattan board to accommodate the changes, and he tidied the wiring significantly while he was at it.

It’s a project that keeps on giving, so feast your eyes and learn. We suspect [GK] doesn’t have any plans to finish this soon, but if he does, we can’t wait to see what’s next.

Thanks to [David Gustafik] for reminding us to check back on this one.