An Amiga Demo With No CPU Involved

September 2, 2025 by Jenny List 9 Comments

Of the machines from the 16-bit era, the Commodore Amiga arguably has the most active community decades later, and it’s a space which still has the power to surprise. Today we have a story which perhaps pushes the hardware farther than ever before: a demo challenge for the Amiga custom chips only, no CPU involved.

The Amiga was for a time around the end of the 1980s the most exciting multimedia platform, not because of the 68000 CPU it shared with other platforms, but because of its set of custom co-processors that handled tasks such as graphics manipulation, audio, and memory. Each one is a very powerful piece of silicon capable of many functions, but traditionally it would have been given its tasks by the CPU. The competition aims to find how possible it is to run an Amiga demo entirely on these chips, by using the CPU only for a loader application, with the custom chip programming coming entirely from a pre-configured memory map which forms the demo.

The demoscene is a part of our community known for pushing hardware to its limits, and we look forward to seeing just what they do with this one. If you have never been to a demo party before, you should, after all everyone should go to a demo party!

Amiga CD32 motherboard: Evan-Amos, Public domain.

Checking Out A TV Pattern Generator From 1981

September 2, 2025 by Donald Papp 11 Comments

The picture on a TV set used to be the combined product of multiple analog systems, and since TVs had no internal diagnostics, the only way to know things were adjusted properly was to see for yourself. While many people were more or less satisfied if their TV picture was reasonably recognizable and clear, meaningful diagnostic work or calibration required specialized tools. [Thomas Scherrer] provides a close look at one such tool, the Philips PM 5519 GX Color TV Pattern Generator from 1981.

This Casio handheld TV even picked up the test pattern once the cable was disconnected, the pattern generator acting like a miniature TV station.

The Philips PM 5519 was a serious piece of professional equipment for its time, and [Thomas] walks through how the unit works and even opens it up for a peek inside, before hooking it up to both an oscilloscope and a TV in order to demonstrate the different functions.

Tools like this were important because they could provide known-good test patterns that were useful not just for troubleshooting and repair, but also for tasks like fine-tuning TV settings, or verifying the quality of broadcast signals. Because TVs were complex analog systems, these different test patterns would help troubleshoot and isolate problems by revealing what a TV did (and didn’t) have trouble reproducing.

As mentioned, televisions at the time had no self-diagnostics nor any means of producing test patterns of their own, so a way to produce known-good reference patterns was deeply important.

TV stations used to broadcast test patterns after the day’s programming was at an end, and some dedicated folks have even reproduced the hardware that generated these patterns from scratch.

Continue reading “Checking Out A TV Pattern Generator From 1981” →

Tiny Datasette Uses USB For The Modern Day

September 1, 2025 by Tyler August 21 Comments

While you can still find tape being used for backup storage, it’s pretty safe to say that the humble audio cassette is about as out of date as a media format can be. Still, it has a certain retro charm we’re suckers for, particularly in the shape of a Commodore Datasette. We’re also suckers for miniaturization, so how could we not fall for [bitluni] ‘s tiny datasette replica?

Aesthetically, he’s copying the Commodore original to get those sweet nostalgia juices flowing, but to make things more interesting he’s not using compact cassette tapes. Instead, [bitluni] started with a micro cassette dictaphone, which he tore down to its essentials and rebuilt into the Commodore-shaped case.

The prototyping of this project was full of hacks — like building a resistor ladder DAC in an unpopulated part of a spare PCB from an unrelated project. The DAC is of course key to getting data onto the micro cassettes. After some playing around [bitluni] decided that encoding data with FSK (frequency-shift keying), as was done back on the C-64, was the way to go. (Almost like those old engineers knew what they were doing!) The dictaphone tape transport is inferior to the old Datasette, though, so as a cheap error-correction hack, [bitluni] needed to duplicate each byte to make sure it gets read correctly.

The micro cassettes only fit a laughable amount of data by modern standards this way (about 1 MB) but, of course that’s not the point. If you jump to 11:33 in the video embedded below, you can see the point: the shout of triumph when loading PacMan (all 8 kB of it) from tape via USB. That transfer was via serial console; eventually [bitluni] intends to turn this into the world’s least-practical mass storage device, but that wasn’t necessary for proof-of-concept. The code for what’s shown is available on GitHub.

If you have an old Datasette you want to use with a modern PC, you’d better believe that we’ve got you covered. We’ve seen other cassette-mass-storage interfaces over the years, too. It might be a dead medium, but there’s just something about “sticky tape and rust” that lives on in our imaginations.

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

August 30, 2025 by Tyler August 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.

Continue reading “The Qweremin Is A QWERTY Theremin With A C-64 Heart” →

A view of the schematics for each major component.

Simulating The Commodore PET

August 26, 2025 by John Elliot V 2 Comments

Over on his blog our hacker [cpt_tom] shows us how to simulate the hardware for a Commodore PET. Two of them in fact, one with static RAM and the other with dynamic RAM.

This project is serious business. The simulation environment used is Digital. Digital is a digital logic designer and circuit simulator designed for educational purposes. It’s a Java program that runs under the JVM. It deals in .dig files which are XML files that represent the details of the simulated hardware components. You don’t need to write the XML files by hand, there is a GUI for that. Continue reading “Simulating The Commodore PET” →

VIC-20 Gets ISA Slot, Networking

August 26, 2025 by Bryan Cockfield 22 Comments

There are few computing collapses more spectacular than the downfall of Commodore, but its rise as a home computer powerhouse in the early 80s was equally impressive. Driven initially by the VIC-20, this was the first home computer model to sell over a million units thanks to its low cost and accessibility for people outside of niche markets and hobbyist communities.

The VIC-20 would quickly be eclipsed by the much more famous Commodore 64, but for those still using these older machines there are a few tweaks to give it some extra functionality it was never originally designed for like this build which gives it an ISA bus.

To begin adapting the VIC-20 to the ISA standard, [Lee] built a fixed interrupt line handled with a simple transistor circuit. From there he started mapping memory and timing signals. The first attempt to find a portion of memory to use failed as it wasn’t as unused as he had thought, but eventually he settled on using the I/O area instead although still had to solve some problems with quirky ISA timing. There’s also a programmable logic chip which was needed to generate three additional signals for proper communication.

After solving some other issues around interrupts [Lee] was finally able to get the ISA bus working, specifically so he could add a 3Com networking card and get his VIC-20 on his LAN. Although the ISA bus has since gone out of fashion on modern computers, if you still have a computer with one (or build one onto your VIC-20), it is a surprisingly versatile expansion port.

Thanks to [Stephen] for the tip!

CERN’s Large Hadron Collider Runs On A Bendix G-15 In 2025

August 25, 2025 by Adam Fabio 18 Comments

The Bendix G-15 refurbished by [David at Usagi Electric] is well known as the oldest fully operational digital computer in North America. The question [David] gets most is “what can you do with it?”. Well, as a general-purpose computer, it can do just about anything. He set out to prove it. Can a 1950s-era vacuum tube computer handle modern physics problems? This video was several years in the making, was a journey from [David’s] home base in Texas all the way to CERN’s Large Hadron Collider (LHC) in Switzerland.

The G-15 can run several “high-level” programming languages, including Algol. The most popular, though, was Intercom. Intercom is an interactive programming language – you can type your program in right at the typewriter. It’s much closer to working with a basic interpreter than, say, a batch-processed IBM 1401 with punched cards. We’re still talking about the 1950s, though, so the language mechanics are quite a bit different from what we’re used to today.

To start with, [Usagi’s] the G-15 is a numeric machine. It can’t even handle the full alphabet. What’s more, all numbers on the G-15 are stored as floating-point values. Commands are sent via operation codes. For example, ADD is operation 43. You have to wrangle an index register and an address as well. Intercom feels a bit like a cross between assembler and tokenized BASIC. Continue reading “CERN’s Large Hadron Collider Runs On A Bendix G-15 In 2025” →