c64

111 Articles

A New Cartridge For An Old Computer

October 6, 2025 by 14 Comments

Although largely recognizable to anyone who had a video game console in the 80s or 90s, cartridges have long since disappeared from the computing world. These squares of plastic with a few ROM modules were a major route to get software for a time, not only for consoles but for PCs as well. Perhaps most famously, the Commodore VIC-20 and Commodore 64 had cartridge slots for both gaming and other software packages. As part of the Chip Hall of Fame created by IEEE Spectrum, [James] found himself building a Commodore cartridge more than three decades after last working in front of one of these computers.

[James] points out that even by the standards of the early 80s the Commodore cartridges were pretty low on specs. They’re limited to 16 kB, which means programming in assembly and doing things like interacting with video hardware directly. Luckily there’s a treasure trove of documentation about the C64 nowadays as well as a number of modern programming tools for them, in contrast to the 80s when tools and documentation were scarce or nonexistent. Hardware these days is cheap as well; the cartridge PCB and other hardware cost only a few dollars, and the case for it can easily be 3D printed.

Burning the software to the $3 ROM chip was straightforward as well with a TL866 programmer, although [James] left a piece of memory management code in the first pass which caused the C64 to lock up. Removing this code and flashing the chip again got the demo up and running though, and it’ll be on display at their travelling “Chips that Changed the World” exhibit. If you find yourself in the opposite situation, though, we’ve also seen projects that cleverly pull the data off of ancient C64 ROM chips for preservation.

[Linus] playing his instrument

The Qweremin Is A QWERTY Theremin With A C-64 Heart

August 30, 2025 by 5 Comments

While we have nothing against other 1980s 8-bit machines, the Commodore 64 has always been something special. A case in point: another new instrument using the C-64 and its beloved SID chip. Not just new to retrocomputing, either, but new entirely. [Linus Åkesson] has invented the QWERTY Theremin, and there’s a Commodore at its core.

If this project sounds vaguely familiar, it’s because it’s based off of the C-64 Theremin [Linus] built a couple of years back. According to [Linus], there were a few issues with the instrument. A real thereminist told him there were issues with the volume response; his own experience taught him that theremins are very, very hard to play for the uninitiated.

This model fixes both problems: first, the volume circuit now includes a pair of digital-analog-converters (DACs) connected to the Commodore’s user port, allowing smooth and responsive volume control.In this case the DAC is being used solely for volume control: SID provides the analog reference voltage, while the 12-bit digital input served as volume control. That proved noisy, however, thanks to the DC bias voltage of the audio output being scaled by the DAC even when the SID was silent. A second DAC was the answer, providing a signal to cancel out the scaled bias voltage. That in and of itself is a clever hack.

The biggest change is that this instrument no longer plays like a theremin. Pitch has been taken out of the 555-based antenna circuit entirely; while vertical distance from the spoon-antenna still controls volume as in a regular theremin and the last version, the horizontal distance from the second antenna (still a clamp) now controls vibrato. Pitch is now controlled by the QWERTY keyboard. That’s a much easier arrangement for [Linus] — this isn’t his first chiptune QWERTY instrument, after all.

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Repairing An Obscure Apple II Clone

August 3, 2025 by 8 Comments

The Apple II was made in great numbers, as was the Commodore 64. But the Mimic Spartan? It was a weird Apple II clone that you needed a Commodore 64 to use. [ARC Javmaster] has found one of these obscure machines and has set about bringing it back to life. Check out the video below.

The story of the machine has been told online by one of the developers on the project, one [Brent Marykuca]. Basically, the Mimic Spartan was an Apple II clone that was intended to take advantage of a C64 as a host machine. It came in a beige box with a bunch of edge connectors and cables sticking out, and you were intended to nest it on the back of your C64 so it could hook up to all the ports. Then, you could use your machine as a C64 or an Apple II, or sort of… both… and even exchange data between both machines in some limited ways. There are also a few details of this obscure machine that have been collated by [Mike Naberezny], who is seeking the original disk that shipped with the machine when new.

It’s early days yet for [ARC Javmaster]’s efforts to restore the Mimic Spartan. Thus far, it’s had a clean and basic test. It was able to display a short line of text on a display before ceasing activity. A full boot hasn’t been achieved just yet, but we can’t wait to see where the resurrection efforts go next.

Back in the day, there were all kinds of Frankenstein computer cards that effectively put one kind of computer inside another. These days, you can condense an entire retro machine down to run on a single microcontroller.

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a Coleco Adams console on a desk

Coleco Adam: A Commodore 64 Competitor, Almost

July 21, 2025 by 65 Comments

For a brief, buzzing moment in 1983, the Coleco Adam looked like it might out-64 the Commodore 64. Announced with lots of ambition, this 8-bit marvel promised a complete computing package: a keyboard, digital storage, printer, and all for under $600. An important fact was that it could morph your ColecoVision into a full-fledged CP/M-compatible computer. So far this sounds like a hacker’s dream: modular, upgradeable, and… misunderstood.

The reality was glorious chaos. The Adam used a daisy-wheel printer as a power supply (yes, really), cassettes that demagnetized themselves, and a launch delayed into oblivion. Yet beneath the comedy of errors lurked something quite tempting: a Z80-based system with MSX-like architecture and just enough off-the-shelf parts to make clone fantasies plausible. Developers could have ported MSX software in weeks. Had Coleco shipped stable units on time, the Adam might well have eaten the C64’s lunch – while inspiring a new class of hybrid machines.

Instead, it became a collector’s oddball. But for the rest of us, it is a retro relic that invites us to ponder – or even start building: what if modular computing had gone mainstream in 1983?

The Commodore 64 Gets An HDMI Upgrade

May 25, 2025 by 39 Comments

The Commodore 64 may remain the best selling computer of all time, but it has one major flaw. It doesn’t have HDMI! That makes it a total pain to use with modern displays. Thankfully, [Side Projects Lab] has whipped up an HDMI output board to solve this concerning oversight from the original designers.

The project was inspired by work by [Copper Dragon], who whipped up a nifty RGB output board. This device worked by reading the inputs to the C64’s VIC II graphics chip, which it then used to recreate a pixel-perfect video frames to then produce a quality analog video output. [Side Projects Lab] figured the same interception technique would be useful for producing a quality HDMI output.

The result was the HD-64. It sits inside the C64 in place of the original RF modulator. It uses an interleaver socket to capture digital signals going to the VIC II. It then feeds these signals to an emulated VIC II running inside an FPGA, which creates the pixel-perfect screen representation and synthesizes the proper digital HDMI output. Meanwhile, the analog audio output from the SID chip is captured from the RF modulator’s original header, and sent out via the HDMI output as well. The default output is super-sharp, but the device can be configured to allow scanlines and anti-aliasing if that’s more to your tastes.

If you want to hook your C64 up to a modern screen, this is going to be one of the tidiest and sharpest ways to do it. We’ve seen similar hacks for other platforms before, too. Video after the break.

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C64 on desk with NFC TeensyROM and game token

TeensyROM NFC Game Loading On The C64

May 23, 2025 by 6 Comments

When retro computing nostalgia meets modern wireless wizardry, you get a near-magical tap-to-load experience. It’ll turn your Commodore 64 into a console-like system, complete with physical game cards. Inspired by TapTo for MiSTer, this latest hack brings NFC magic to real hardware using the TeensyROM. It’s been out there for a while, but it might not have caught your attention as of yet. Developed by [Sensorium] and showcased by YouTuber [StatMat], this project is a tactile, techie love letter to the past.

At the heart of it is the TeensyROM cartridge, which – thanks to some clever firmware modding – now supports reading NFC tags. These are writable NTag215 cards storing the path to game files on the Teensy’s SD card. Tap a tag to the NFC reader, and the TeensyROM boots your game. No need to fumble with LOAD “*”,8,1. That’s not only cool, it’s convenient – especially for retro demo setups.

What truly sets this apart is the reintroduction of physical tokens. Each game lives on its own custom-designed card, styled after PC Engine HuCards or printed with holographic vinyl. It’s a tangible, collectible gimmick that echoes the golden days of floppies and cartridges – but with 2020s tech underneath. Watch it here.

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LLM Ported To The C64, Kinda

May 3, 2025 by 8 Comments

“If there’s one thing the Commodore 64 is missing, it’s a large language model,” is a phrase nobody has uttered on this Earth. Yet, you could run one, if you so desired, thanks to [ytm] and the Llama2.c64 project!

[ytm] did the hard work of porting the Llama 2 model to the most popular computer ever made. Of course, as you might expect, the ancient 8-bit machine doesn’t really have the stones to run an LLM on its own. You will need one rather significant upgrade, in the form of 2 MB additional RAM via a C64 REU.

Now, don’t get ahead of things—this is no wide-ranging ChatGPT clone. It’s not going to do your homework, counsel you on your failed marriage, or solve the geopolitical crisis in your local region. Instead, you’re getting the 260 K tinystories model, which is a tad more limited. In [ytm]’s words… “Imagine prompting a 3-year-old child with the beginning of a story — they will continue it to the best of their vocabulary and abilities.”

It might not be supremely capable, but there’s something fun about seeing such a model talking back on an old-school C64 display. If you’ve been hacking away at your own C64 projects, don’t hesitate to let us know. We certainly can’t get enough of them!

Thanks to [ytm] for the tip!