Clock Hack Gives DEC Rainbow A New Lease On Life

September 12, 2023 by Dan Maloney 21 Comments

In retrocomputing circles, it’s often the case that the weirder and rarer the machine, the more likely it is to attract attention. And machines don’t get much weirder than the DEC Rainbow 100-B, sporting as it does both Z80 and 8088 microprocessors and usable as either a VT100 terminal or as a PC with either CP/M or MS-DOS. But hey — at least it got the plain beige box look right.

Weird or not, all computers have at least a few things in common, a fact which helped [Dr. Joshua Reichard] home in on the problem with a Rainbow that was dead on arrival. After a full recapping — a prudent move given the four decades since the machine was manufactured — the machine failed to show any signs of life. The usual low-hanging diagnostic fruit didn’t provide much help, as both the Z80 and 8088 CPUs seemed to be fine. It was then that [Joshua] decided to look at the heartbeat of the machine — the 24-ish MHz clock shared between the two processors — and found that it was flatlined.

Unwilling to wait for a replacement, [Joshua] cobbled together a temporary clock from an Arduino Uno and an Si5351 clock generator. He connected the output of the card to the main board, whipped up a little code to generate the right frequency, and the nearly departed machine sprang back to life. [Dr. Reichard] characterizes this as a “defibrillation” of the Rainbow, and while one hates to argue with a doctor — OK, that’s a lie; we push back on doctors all the time — we’d say the closer medical analogy is that of fitting a temporary pacemaker while waiting for a suitable donor for a transplant.

This is the second recent appearance of the Rainbow on these pages — [David] over at Usagi Electric has been working on the graphics on his Rainbow lately.

Hackaday Links: September 10, 2023

September 10, 2023 by Dan Maloney 17 Comments

Most of us probably have a vision of how “The Robots” will eventually rise up and deal humanity out of the game. We’ve all seen that movie, of course, and know exactly what will happen when SkyNet becomes self-aware. But for those of you thinking we’ll get off relatively easy with a quick nuclear armageddon, we’re sorry to bear the news that AI seems to have other plans for us, at least if this report of dodgy AI-generated mushroom foraging manuals is any indication. It seems that Amazon is filled with publications these days that do a pretty good job of looking like they’re written by human subject matter experts, but are actually written by ChatGPT or similar tools. That may not be such a big deal when the subject matter concerns stamp collecting or needlepoint, but when it concerns differentiating edible fungi from toxic ones, that’s a different matter. The classic example is the Death Cap mushroom (Amanita phalloides) which varies quite a bit in identifying characteristics like color and size, enough so that it’s often tough for expert mycologists to tell it apart from its edible cousins. Trouble is, when half a Death Cap contains enough toxin to kill an adult human, the margin for error is much narrower than what AI is likely to include in a foraging manual. So maybe that’s AI’s grand plan for humanity — just give us all really bad advice and let Darwin take care of the rest.

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Wien Bridge Oscillator Drives Distortion Into The Floor

September 8, 2023 by Dan Maloney 12 Comments

It’s not often that a single photo can tell you pretty much everything you need to know about a project, but the spectrum analyzer screenshot nearby is the perfect summary of this over-the-top low-distortion audio oscillator build. But that doesn’t mean there’s not a ton of interesting stuff going on with this one, so buckle up.

One spike at the fundamental and not much more.

The project is by [Basin Street Design], who doesn’t really offer much by way of inspiration for this undertaking, nor a discussion on what this will be used for. But the design goals are pretty clear: build an oscillator with as little distortion as possible across the audio frequency range.

The basic circuit is the well-known Wien bridge oscillator where the R-C pairs are switched in and out of the feedback loop to achieve frequency range control. This was accomplished with rotary switches rebuilt from their original configuration in a Heathkit IG-18 sine/square wave generator, a defunct instrument that was gutted and used as an enclosure for this build. There are a lot of other treats here, too, like the automatic gain control (AGC) that uses a homebrew voltage-controlled resistor made from an incandescent lamp and a cadmium sulfide photoresistor glued inside a piece of brake line, and an output attenuator made from discrete resistors that drops the output in 10 dB steps while maintaining an overall 75-Ohm impedance.

But at the end of the day, it all comes down to that single spike on the spectrum analyzer, with no apparent harmonics. To make sure there wasn’t something hiding down in the noise, [Basin Street] added a notch filter to lower the fundamental by 60 dB, allowing the spectrum analyzer sensitivity to be cranked way up. Harmonics were visible, but so far down into the noise — as low as -115 dBc — that it’s hardly worth mentioning.

There’s a lot more detail in this one, so dive in and enjoy. If you want another take on Wien bridge circuits, check out this recent LM386-based oscillator. Just don’t expect such low distortion with that one.

Building Up Unicode Characters One Bit At A Time

September 7, 2023 by Dan Maloney 33 Comments

The range of characters that can be represented by Unicode is truly bewildering. If there’s a symbol that was ever used to represent a sound or a concept anywhere in the world, chances are pretty good that you can find it somewhere in Unicode. But can many of us recall the proper keyboard calisthenics needed to call forth a particular character at will? Probably not, which is where this Unicode binary input terminal may offer some relief.

“Surely they can’t be suggesting that entering Unicode characters as a sequence of bytes using toggle switches is somehow easier than looking up the numpad shortcut?” we hear you cry. No, but we suspect that’s hardly [Stephen Holdaway]’s intention with this build. Rather, it seems geared specifically at making the process of keying in Unicode harder, but cooler; after all, it was originally his intention to enter this in last year’s Odd Inputs and Peculiar Peripherals contest. [Stephen] didn’t feel it was quite ready at the time, but now we’ve got a chance to give this project a once-over.

The idea is simple: a bank of eight toggle switches (with LEDs, of course) is used to compose the desired UTF-8 character, which is made up of one to four bytes. Each byte is added to a buffer with a separate “shift/clear” momentary toggle, and eventually sent out over USB with a flick of the “send” toggle. [Stephen] thoughtfully included a tiny LCD screen to keep track of the character being composed, so you know what you’re sending down the line. Behind the handsome brushed aluminum panel, a Pi Pico runs the show, drawing glyphs from an SD card containing 200 MB of True Type Font files.

At the end of the day, it’s tempting to look at this as an attractive but essentially useless project. We beg to differ, though — there’s a lot to learn about Unicode, and [Stephen] certainly knocked that off his bucket list with this build. There’s also something wonderfully tactile about this interface, and we’d imagine that composing each codepoint is pretty illustrative of how UTF-8 is organized. Sounds like an all-around win to us.

Mining And Refining: Quartz, Both Natural And Synthetic

September 6, 2023 by Dan Maloney 17 Comments

So far in this series, pretty much every material we’ve covered has had to undergo a significant industrial process to transform it from its natural state to a more useful product. Whether it’s the transformation of bauxite from reddish-brown clay to lustrous aluminum ingots, or squeezing solid sulfur out of oil and natural gas, there haven’t been many examples of commercially useful materials that are taken from the Earth and used in their natural state.

Quartz, though, is at least a partial exception to this rule. Once its unusual electrical properties were understood, crystalline quartz was sent directly from quarries and mines to factories, where they were turned into piezoelectric devices with no chemical transformation whatsoever. The magic of crystal formation had already been done by natural processes; all that was needed was a little slicing and dicing.

As it turns out, though, quartz is so immensely useful for a technological society that there’s no way for the supply of naturally formed crystals to match demand. Like copper before it, which was first discovered in natural metallic deposits that could be fashioned into tools and decorations more or less directly, we would need to discover different sources for quartz and invent chemical transformations to create our own crystals, taking cues from Mother Nature’s recipe book on the way.

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It’s Numbers All The Way Down With This Tape Measure Number Station Antenna

September 6, 2023 by Dan Maloney 12 Comments

For all their talk of cooperation and shared interests, the nations of the world put an awful lot of effort into spying on each other. All this espionage is an open secret, of course, but some of their activities are so mysterious that no one will confirm or deny that they’re doing it. We’re talking about numbers stations, the super secret shortwave radio stations that broadcast seemingly random strings of numbers for the purpose of… well, your guess is as good as ours.

If you want to try to figure out what’s going on for yourself, all you need is a pair of tape measures and a software defined radio (SDR), as [Tom Farnell] demonstrates. Tape measure antennas have a long and proud history in amateur radio and shortwave listening, being a long strip of conductive material rolled up in a convenient package. In this case, [Tom] wanted to receive some well-known numbers stations in the 20- to 30-meter band, and decided that a single 15-meter conductor would do the job. Unlike other tape measure antennas we’ve seen, [Tom] just harvested the blades from two 7.5-meter tape measures, connected them end-to-end, and threw the whole thing out the window in sort of a “sloper” configuration. The other end is connected to an RTL-SDR dongle and a smartphone running what appears to be SDRTouch, which lets him tune directly into the numbers stations.

Copying the transmissions is pretty simple, since they transmit either in voice or Morse; the latter can be automatically decoded on a laptop with suitable software. As for what the long strings of numbers mean, that’ll remain a mystery. If they mean anything at all; we like to think this whole thing is an elaborate plan to get other countries to waste time and resources intercepting truly random numbers that encode nothing meaningful. It would serve them right.

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Electro-Optical Control Of Lasers With A Licorice Twist

September 5, 2023 by Dan Maloney 8 Comments

You’ve got to hand it to [Les Wright]; he really knows how to dig into optical arcana and present topics in an interesting way. Case in point: an electro-optical control cell that’s powered by ouzo.

OK, the bit about the Greek aperitif may be stretching things a bit, but the Kerr Cell that [Les] builds in the video below does depend on anethole, the essential component of aniseed extract, which lends its aromatic flavor to everything from licorice to Galliano and ouzo. As [Les] explains, the Kerr effect uses a high-voltage field to rapidly switch light passing through a medium on and off. The most common medium in Kerr cells is nitrobenzene, a “distressingly powerful organic solvent” with such fun side effects as toxicity, flammability, and carcinogenicity.

Luckily, [Les] found a suitable substitute in the form of anethole — a purified sample, not just an ouzo nip. The solution went into a plain glass cuvette equipped with a pair of aluminum electrodes, which got connected to one of the high-voltage supplies we’ve seen him build before for his nitrogen laser. A pair of polarizing filters go on either end of the cuvette, and are adjusted to blank out the light passing through it. Applying 45 kilovolts across the cell instantly turns the light back on. Watch it in action in the video below.

There’s a lot of room left for experimentation on this one, including purification of the anethole for potentially better results. We’d also be curious if plain ouzo would show some degree of Kerr effect. For science, of course.

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