Two-Tube Spy Transmitter Fits In The Palm Of Your Hand

March 29, 2023 by Dan Maloney 13 Comments

It’s been a long time since vacuum tubes were cutting-edge technology, but that doesn’t mean they don’t show up around here once in a while. And when they do, we like to feature them, because there’s still something charming, nay, romantic about a circuit built around hot glass and metal. To wit, we present this compact two-tube “spy radio” transmitter.

From the look around his shack — which we love, by the way — [Helge Fykse (LA6NCA)] really has a thing for old technology. The typewriter, the rotary phones, the boat-anchor receiver — they all contribute to the retro feel of the space, as well as the circuit he’s working on. The transmitter’s design is about as simple as can be: one tube serves as a crystal-controlled oscillator, while the other tube acts as a power amplifier to boost the output. The tiny transmitter is built into a small metal box, which is stuffed with the resistors, capacitors, and homebrew inductors needed to complete the circuit. Almost every component used has a vintage look; we especially love those color-coded mica caps. Aside from PCB backplane, the only real nod to modernity in the build is the use of 3D printed forms for the coils.

But does it work? Of course it does! The video below shows [Helge] making a contact on the 80-meter band over a distance of 200 or so kilometers with just over a watt of power. The whole project is an excellent demonstration of just how simple radio communications can be, as well as how continuous wave (CW) modulation really optimizes QRP setups like this.

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Magic 8 Ball Provides Tech Support

March 28, 2023 by Bryan Cockfield 15 Comments

ChatGPT might be making the news these days for being able to answer basically any question it’s asked, those of us who are a little older remember a much simpler technology that did about the same thing. The humble “Magic 8 Ball” could take nearly the same inputs, provided they were parsed in simple yes/no form, and provide marginal help similar to the AI tools of today. For a toy with no battery or screen, this was quite an accomplishment. But the small toy couldn’t give specific technical support help, so [kodi] made one that can.

The new 8 Ball foregoes the central fluid-filled chamber for an STM32 Blue Pill board with a few lithium batteries to power it. The original plastic shell was split in two with a hacksaw and fitted with a 3D printed ring which allows the two halves to be reconnected and separated again when it needs to charge. It uses a circular OLED to display the various messages of tech support, which are displayed when an accelerometer detects that the toy has been shaken.

Granted, most of the messages are about as helpful to solving a tech support issue as the original magic 8 Ball’s would have been, but we appreciate the ingenuity and carefree nature of a project like this. It also did an excellent job at operating in a low-power state as well, to avoid needing to charge it often. There have been a few other digital conversions of these analog fortune tellers as well, like this one which adds GIFs to each of the original answers.

Recreating One Of History’s Best Known Spy Gadgets

March 25, 2023 by Al Williams 22 Comments

[Machining and Microwaves] got an interesting request. The BBC asked him to duplicate the Great Seal Bug — the device the Russians used to listen covertly to the US ambassador for seven years in 1945. Turns out they’re filming a documentary on the legendary surveillance device and wanted to demonstrate how it worked.

The strange thing about the bug is that it wasn’t directly powered. It was actually a resonant cavity that only worked when it was irradiated with an external RF energy. Most of the video is background about the bug, with quite a few details revealed. We particularly liked the story of using a software defined radio (SDR) to actually make the bug work.

As you might expect, things didn’t go smoothly. Did they ever get results on camera? Watch the video, and you can find out. This is just the first of six videos he plans to make on the topic, and we can’t wait for future videos that cover the machining and more technical details.

We’ve examined the Theremin bug before. There’s a definite cat-and-mouse dynamic between creating bugging devices and detecting them.

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Vintage Tektronix Virtual Graticule

March 22, 2023 by Al Williams 5 Comments

Oscilloscopes are great for measuring the time and voltage information of a signal. Some old scopes don’t have much in the way of markings on the CRT, although eventually, we started seeing scales that allowed you to count squares easily. Early scopes had marks on the glass or plastic over the CRT, but as [Vintage TEK Museum] points out, this meant for best accuracy, you had to look directly at the CRT. If you were at an angle horizontally or vertically, the position of the trace would appear to move concerning the lines on the screen. You can see the effect in the video below.

The simple solution was to mark directly into the phosphor, which minimized the effect. Before that was possible, [Bob Anderson] invented a clever solution, although Tektronix didn’t produce any scopes using it for some reason. The idea was the virtual oscilloscope graticule, and it was quite clever.

The idea was to put the graticule on a semi-reflective mirror. Looking through the assembly, you would actually see the trace and the reflection of the graticule in the mirror. The resulting image is perfectly aligned if the assembly is constructed properly. You can, at some angles, see both the front and reflected graticules.

According to the video, management was not impressed because someone other than [Anderson] showed a poor-quality prototype to them. By 1962, the graticule in the phosphor took over, and there was no need for [Anderson’s] clever invention.

These days, a graticule is just bits on the screen. Even if you roll your own.

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DOOM Ported To A Single LEGO Brick

March 18, 2023 by Lewin Day 18 Comments

By now you’ve all seen the tiny LEGO brick with a working screen in it. The work of one [James “Ancient” Brown], it was truly a masterpiece of miniaturization and creativity. Since then, [James] hasn’t stopped innovating. Now, he’s demoing a playable version of DOOM running on a single plastic brick.

We’ve covered the construction of these astounding screen bricks before. Long story short, [James] designed a tiny PCB that hosts an RP2040 microcontroller which is then hooked up to a tiny OLED screen. The components are placed in a silicone mold, which is then filled with transparent resin to form the brick. The screen is then powered via contacts in the bottom, much like older-style LEGO motors.

Early experiments involved running various graphics to emulate a spaceship dashboard, but [James] has now gone much further. He’s implemented RP2040-doom to run the game. It uses tilt controls thanks to an accelerometer, combined with capacitive touch controls for shooting. The monochrome OLED is driven very fast with a special library of [James’] own creation to create three levels of grayscale to make the game actually visible and (just barely) playable.

It’s a hack, of course, and the controls are far from perfect. Nobody’s speed-running E1M1 on [James’s] LEGO brick, to be sure. Perchance. With that said, it’s still a glorious piece of work nonetheless. Just imagine, sitting with friends, and announcing you’re going to play some DOOM — only to pluck a piece of LEGO out of your pocket and start blasting away at demons.

Just because [James] doesn’t know when to quit, we’re going to lay down the gauntlet. Let’s get network play happening on these things, yeah?
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Creating GIFs For The Channels Between Channels

March 17, 2023 by Matthew Carlson 4 Comments

In the United States, analog TV broadcasting officially ended in 2009. While the transition wasn’t without hiccups, we did lose something along the way. For [Emily Velasco], she misses the channels between channels — where an analog TV isn’t quite tuned right and the image is smeared and distorted. A recent bug in one of her projects led to her trying to recreate the experience of the in-between on a CRT.

One of [Emily]’s other projects involved generating composite video signals from an ESP32 microcontroller. While experimenting with adding color to the output signal, the image came out incredibly scrambled. She had made an error in the stride, which smeared the image across the screen. This immediately brought back memories of old analog TV sets. A quick potentiometer allowed her to control the stride error and she wrote some code to break the GIF up into discrete bitmaps for display since the GFX library handles GIFs differently than static images. Next up was vertical hold, which was accomplished by shifting the Y coordinates. With some help from [Roger], there was now a handy GIF library that would draw GIFs line by line with the composite video effects.

She used a Goldbeam portable CRT, soldered the tuning potentiometer to the ESP32, and set up 10 different GIFs to act as “channels” with space in between. It’s a fun and quirky idea, which is exactly the sort of thing [Emily] has been encouraging people to do.

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A Retro-Style Trainer For Motorola’s 1-Bit Chip

March 11, 2023 by Tom Nardi 6 Comments

If you want to program a microcontroller today, you pop open your editor of choice, bang out some code, and flash it over USB. But back in ancient times, when your editor was a piece of paper and you didn’t even have a computer of your own, things were a bit different. In that case, you might have reached for a “trainer”: a PCB that included the chip you wanted to program along with an array of switches, LEDs, and maybe even a hex keypad for good measure. Grab yourself the programming manual (printed on paper, naturally), and you’re good to go.

So when [Nicola Cimmino] became curious about the Motorola MC14500, a 1-bit ICU (Industrial Control Unit) from the 1970s, he could think of no more appropriate way to get up close and personal with the chip than to design an era-appropriate trainer for it. The resulting board, which he’s calling the PLC14500 Nano, is festooned with LEDs that show the status of the system buses and registers. Thanks to the chip’s single-step mode, this gives you valuable insight into what’s happening inside this piece of classic silicon.

An early breadboard version of the trainer.

But just because the board looks like it could have come from the 1970s doesn’t mean you have to live in the past. There’s an Arduino Nano on the backside of the trainer that handles communicating with a modern computer. [Nicola] even provided an assembler that lets you write your code in ASM before shuttling the binary off to the board for execution.

Interested in getting your hands on one? Not a problem. The design is completely open source for anyone who wants to build one at home. In fact, [Nicola] even got his trainer OSHW Certified. He’s also selling kits on Tindie, though at the time of this writing, they’re sold out.

This project has actually been a long time coming. We covered an early breadboard prototype of the concept back in 2015. We’re glad to see that [Nicola] was finally able to bring this one across the finish line. It’s a beautiful piece of hardware, and thanks to its open-source nature, something that the whole community can enjoy and learn from.