Retrocomputing

1584 Articles

A computer program written in basic next to a modular synthesizer with many switches and lights

Modular Synth Pairs Perfectly With The Apple II

February 4, 2022 by 4 Comments

We have a soft spot for synthesizers – seriously, who doesn’t? So when [Joshua Coleman] combined his retro-looking DIY modular synth with the equally retro Apple II computer, we just had to share it with you.

The two machines are paired using a vintage digital-to-analog logic controller pack. This DAC was originally used to control model trains using your Apple II – something that we now desperately need to see in action. The pack can output voltages between 0 and 2.55 V at 8-bit resolution (or 256 steps), which is plenty for a retro synth.

With the card installed in Slot 7 of the Apple II and the DAC wired through to the synth’s CV/gate, it’s then a trivial matter of writing POKE statements in Applesoft BASIC to control the synth. The video after the break demonstrates playing a simple melody, as well as how one might use the Apple II keyboard to ‘play’ the synth in real time.

If you’re interested in building your own, the video below has all the information needed, as well as helpful advice on where to find a DAC for your preferred model of vintage computer. If all that doesn’t tickle your musical fancy, make sure to check out our coverage on the Game Boy MIDI synth, or perhaps this peculiar synth and visualizer combo.

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Commodore Promotional Film From 1984 Enhanced

January 29, 2022 by 10 Comments

Over on Retro Recipe’s YouTube channel, [Perifractic] has been busy restoring an old promotional video of how Commodore computers were made back in 1984 (video below the break). He cleaned up the old VHS-quality version that’s been around for years, translated the German to English, and trimmed some bits here and there. The result is a fascinating look into the MOS factory, Commodore’s German factory, and a few other facilities around the globe. The film shows the chip design engineers in action, wafer manufacturing, chip dicing, and some serious micro-probing of bare die. We also see PCB production, and final assembly, test and burn-in of Commodore PET and C64s in Germany.

Check out the video description, where [Perifractic] goes over the processes he used to clean up video and audio using machine learning. If restoration interests you, check out the piece we wrote about these techniques to restore old photographs last year. Are there any similar factory tour films, restored or not, lurking around the web? Let us know in the comments below.

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An Entire Computer In ICMP Packets

January 25, 2022 by 19 Comments

The earliest stored program computer in the modern sense was not one of the names such as ENIAC or Colossus that you might expect, but the Manchester Baby, an experimental prototype computer built at the University of Manchester in 1948. Its 550 tubes gave it the multi-rack room-filling size common to 1940s machines, but its architecture makes it a comparatively simple processor by the standards of today. So simple in fact, that [Hrvoje Čavrak] has recreated it using ICMP packets as its storage, and a custom packet filter as its processor emulation. It’s a project that’s simultaneously both elegant and gloriously pointless, but as he says, “It’s still better than doing drugs or JavaScript”.

The result simulates the Baby’s combined storage and display tube in a dump of the network traffic, and gives an excellent excuse to read up about its operation. The tiny instruction set brings to mind today’s RISC architectures, but this is illusory as the designers of 1948 would have had less of an eye towards clock cycles than they would have towards the machine working at all in the first place.

If early computers tickle your fancy it may be worth taking a while to read about the UK’s National Museum of Computing, and then about Colossus, the primordial electronic computer.

Header: Geni, CC BY-SA 4.0.

When A Single Bit Was Enough, Into The Sound Of The ZX Spectrum

January 20, 2022 by 8 Comments

It’s normal for a computer in 2022 to come with a fully-featured sound card containing a complete synthesizer as well as high-quality PCM sound recording and playback. It’s referred to as a sound card after the way the hardware first appeared in the world of PCs, but in fact it’s now considered so essential as to be a built-in part of most mainboards. There was a time when computers boasted considerably less impressive sound hardware, and among the chorus of SIDs and AY chips of the perhaps the least well-featured was the original Sinclair ZX Spectrum. Its one-bit sound, a single line on an I/O port, is the subject of a thorough investigation from [Forgotten Computer]. It’s a long video which we’ve placed below the break, but for those with an interest in 8-bit music it should make a for a fascinating watch.

For Sir Clive Sinclair the 1-bit audio must have been welcome as it removed the need for an expensive sound chip and kept the Spectrum to its low price point, but on the face of it there was little more it could do than create simple beeps using Sinclair BASIC’s built-in BEEP command. The video gives us an in-depth look at how interleaving and PWM could be used to create much more complex sounds such as the illusion of multiple voices and even sampled sounds. In particular his technique of comparing the audio output with its corresponding pin on the Sinclair ULA shows the effect of the machine’s simple low-pass filter, though the music was often so close to the edge of what the interface could do that aliasing sounds are often very obvious.

As he demonstrates the various ingenious techniques that game and demo developers used to extract performance from such limited hardware that could even try to compete with the more sophisticated machines even at the same time as their code was running whatever was on the screen, it’s difficult not to come away with immense respect for their skills. If you’ve ever experimented with computer audio then you should try hardware this simple for yourself.

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An Apple I hooked up to lab power supplies and a monitor

Powering Up An Original Apple I After Three Decades In A Museum

January 10, 2022 by 27 Comments

The Apple I is the stuff of legend. Designed and marketed in 1976 by Steve Wozniak and Steve Jobs, it was the very first product released by what would become today’s multi-trillion-dollar manufacturer of iPhones and iMacs. With about 60 original ones known to exist today, prices at auction are commonly in the $300,000 range, while confirmed working ones are even more valuable.

The Heinz Nixdorf Museumsforum (HNF), a computer museum in the German city of Paderborn, is fortunate enough to have an original Apple I in its collection. Although it has been there since 1996, it was always on static display and had never been powered on. In fact, it was unknown whether it would even work, and with it being the most valuable exhibit in the entire museum, simply firing it up would be a seriously risky project.

But computers are meant to be used, so museum director [Jochen Viehoff] decided to take the plunge and attempt to get the classic Apple to run again. In the four-part video series embedded below, [Jochen] explains the history of Apple’s first product and the steps he took to bring it back to life. This began with taking it out of its bullet-proof display case and bringing it upstairs to the museum’s workshop.

In order to make a complete system, HNF staff also dug up a period-correct keyboard as well as a slightly newer Apple monitor that could display the 60 Hz composite video output. Hooking up an original power supply would have been way too risky, because a single mistake or malfunction could send their top exhibit up in flames. Instead, they used a set of lab power supplies with a programmable current limit; this way, even a dead short on the PCB would not result in any serious damage.

Not that there were any shorts: after a bit of fiddling with the keyboard and adjusting the video output level, the 45-year-old computer came to life and began to respond to commands. With just 256 bytes of ROM, its default feature set is rather limited, but the computer duly executed a simple “Hello, World” program writen in 6502 machine code. It thereby joined the elite club of confirmed working Apple I’s, of which there are thought to be about twenty.

If you haven’t got $300,000 to spare but would still like to try your hand at programming the Apple I, you’ll be happy to hear that you can get a modern copy at a far more affordable price. And if all that classic hardware is too fiddly for you, you might want to try implementing the Apple I on an FPGA.

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Blinking Cursor Turns 54, Hardly Anyone Notices

January 5, 2022 by 27 Comments

In an interesting post on Inverse, [Sarah Wells] does a deep dive into something you probably don’t think about very often: the blinking cursor. You’d assume there wasn’t much to the story. Maybe a terminal manufacturer put a toggle flip flop on the cursor output and it caught on. But the true story is much deeper than that.

We were surprised that the father of the blinking cursor was one guy, [Charles Kiesling]. In a 1967 patent, he described the blinking cursor. An ex-Navy man, [Kiesling’s] patent names his employer at the time, Sperry Rand, where he’d worked since 1955.

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Matrix Digital Rain On The IBM PC With A High Persistence Monitor

January 3, 2022 by 11 Comments

Unless you’ve been hiding under a rock for the last 20-odd years, you will have come across The Matrix series of movies, and the cool green ‘digital rain’ effect used frequently. This inspired [Oli Wright] to wonder what it would look like if instead of running the animation on a modern display, using a digitally produced phosphor persistence effect, it was implemented on some retro PC hardware, using an actual high-persistence phosphor Green Monochrome monitor. (Video embedded, below) As luck would have it, [Oli] owns a 40-year-old IBM PC 5150 as well as the matching IBM 5151 monitor, so it was a simple matter to implement the effect in 8088 assembler to create falling sequences of characters. The final binary is less than 256 bytes!

The IBM 5151’s long display persistence was intended to reduce the visibility of display flicker due to the low scan rate, but has the unfortunate side effect of smearing horribly when the image changes. This is exactly what [Oli] needed to implement this effect and we think it looks jolly fine.

[Oli] made use of the excellent PCjs browser-based emulator written by [Jeff Parsons] to demonstrate what the software is doing, without the effect being evident. If you like, you can try it out for yourselves, as the assembly listing is available on the project GitHub.

Of course, we’ve covered the digital rain effect many. many times before, for example, with this Arduino Library, and here’s a custom PC case side panel from way back in December 2021, if you can remember those days.

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