Author: Dan Maloney

3300 Articles

A Deep Dive Into A 1980s Radio Shack Computer Trainer

February 26, 2024 by 17 Comments

For those of us who remember Radio Shack as more than just an overpriced cell phone store, a lot of the nostalgia for the retailer boils down to the brands on offer. Remember the Realistic line of hi-fi and stereo gear? How about Archer brand tools and parts? Patrolman scanners, Micronta test instruments, and don’t forget those amazing Optimus speakers — all had a place in our development as electronics nerds.

But perhaps the most formative brand under the Radio Shack umbrella was Science Fair, with a line of kits and projects that were STEM before STEM was a thing. One product that came along a little too late for our development was the Science Fair Microcomputer Trainer, and judging by [Michael Wessel]’s deep dive into the kit, we really missed the boat. The trainer was similar to the earlier “100-in-1”-style breadboarding kits, with components laid out on a colorful cardboard surface and spring terminals connected to their leads, making it easy to build circuits using jumper wires. The star of the show in the microcomputer trainer was a Texas Instruments TMS1100, which was a pretty advanced chip with a 4-bit CPU with its own ROM and RAM as well as a bunch of IO lines. The trainer also sported a peppy little 400-kHz crystal oscillator clock, a bunch of LEDs, a seven-segment display, a speaker, and a rudimentary keyboard.

The first video below is a general introduction to the trainer and a look at some basic (not BASIC) programs. [Michael] also pulls out the oscilloscope to make some rough measurements of the speed of the TMS1100, which turns out to be doing only about 400 instructions per second. That’s not much, but in the second video we see that it was enough for him to nerd-snipe his collaborator [Jason] into coding up an 80-nibble Tower of Hanoi solver. It’s a little awkward to use, as the program runs in spurts between which the user needs to check memory locations to see which disc to move to which peg, but it works.

It looks like people are rediscovering the Microcomputer Trainer all of a sudden. It might be a good time to pick one up.

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Op-Amp Drag Race Turns Out Poorly For 741

February 23, 2024 by 32 Comments

When it was first introduced in 1968, Fairchild’s 741 op-amp made quite a splash. And with good reason; it packed a bunch of components into a compact package, and the applications for it were nearly limitless. The chip became hugely popular, to the point where “741” is almost synonymous with “op-amp” in the minds of many.

But should it be? Perhaps not, as [More Than Electronics] reveals with this head-to-head speed test that compares the 741 with its FET-input cousin, the TL081. The test setup is pretty simple, just a quick breadboard oscillator with component values selected to create a square wave at approximately 1-kHz, with oscilloscope probes on the output and across the 47-nF timing capacitor. The 741 was first up, and it was quickly apparent that the op-amp’s slew rate, or the rate of change of the output, wasn’t too great. Additionally, the peaks on the trace across the capacitor were noticeably blunted, indicating slow switching on the 741’s output stage. The TL081 fared quite a bit better in the same circuit, with slew rates of about 13 V/μS, or about 17 times better than the 741, and nice sharp transitions on the discharge trace.

As [How To Electronics] points out, comparing the 741 to the TL081 is almost apples to oranges. The 741 is a bipolar device, and comparing it to a device with JFET inputs is a little unfair. Still, it’s a good reminder that not all op-amps are created equal, and that just becuase two jelly bean parts are pin compatible doesn’t make them interchangeable. And extra caution is in order in a world where fake op-amps are thing, too.

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Your Noisy Fingerprints Vulnerable To New Side-Channel Attack

February 23, 2024 by 28 Comments

Here’s a warning we never thought we’d have to give: when you’re in an audio or video call on your phone, avoid the temptation to doomscroll or use an app that requires a lot of swiping. Doing so just might save you from getting your identity stolen through the most improbable vector imaginable — by listening to the sound your fingerprints make on the phone’s screen (PDF).

Now, we love a good side-channel attack as much as anyone, and we’ve covered a lot of them over the years. But things like exfiltrating data by blinking hard drive lights or turning GPUs into radio transmitters always seemed a little far-fetched to be the basis of a field-practical exploit. But PrintListener, as [Man Zhou] et al dub their experimental system, seems much more feasible, even if it requires a ton of complex math and some AI help. At the heart of the attack are the nearly imperceptible sounds caused by friction between a user’s fingerprints and the glass screen on the phone. These sounds are recorded along with whatever else is going on at the time, such as a video conference or an online gaming session. The recordings are preprocessed to remove background noise and subjected to spectral analysis, which is sensitive enough to detect the whorls, loops, and arches of the unsuspecting user’s finger.

Once fingerprint patterns have been extracted, they’re used to synthesize a set of five similar fingerprints using MasterPrint, a generative adversarial network (GAN). MasterPrint can generate fingerprints that can unlock phones all by itself, but seeding the process with patterns from a specific user increases the odds of success. The researchers claim they can defeat Automatic Fingerprint Identification System (AFIS) readers between 9% and 30% of the time using PrintListener — not fabulous performance, but still pretty scary given how new this is.

LED Matrix Earrings Show Off SMD Skills

February 21, 2024 by 12 Comments

We’ll be honest with you: we’re not sure if the use of “LED stud” in [mitxela]’s new project refers to the incomprehensibly tiny LED matrix earrings he made, or to himself for attempting the build. We’re leaning toward the latter, but both seem equally likely.

This build is sort of a mash-up of two recent [mitxela] projects — his LED industrial piercing, which contributes the concept of light-up jewelry in general as well as the power supply and enclosure, and his tiny volumetric persistence-of-vision display, which inspired the (greatly downsized) LED matrix. The matrix is the star of the show, coming in at only 9 mm in diameter and adorned with 0201 LEDs, 52 in total on a 1 mm pitch. Rather than incur the budget-busting expense of a high-density PCB with many layers and lots of blind vias, [mitexla] came up with a clever workaround: two separate boards, one for the LEDs and one for everything else. The boards were soldered together first and then populated with the LEDs (via a pick-and-place machine, mercifully) and the CH32V003 microcontroller before being wired to the power source and set in the stud.

Even though most of us will probably never attempt a build on this scale, there are still quite a few clever hacks on display here. Our favorite is the micro-soldering iron [mitxela] whipped up to repair one LED that went missing from the array. He simply wrapped a length of 21-gauge solid copper wire around his iron’s tip and shaped a tiny chisel point into it with a file. We’ll be keeping that one in mind for the future.

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A Classroom-Ready Potentiometer From Pencil And 3D Prints

February 19, 2024 by 18 Comments

If you need a potentiometer for a project, chances are pretty good that you’re not going to pick up a pencil and draw one. Then again, if you’re teaching someone how a variable resistor works, that old #2 might be just the thing.

When [HackMakeMod] realized that the graphite in pencil lead is essentially the same thing as the carbon composition material inside most common pots, the idea for a DIY teaching potentiometer was born. The trick was to build something to securely hold the strip while making contact with the ends, as well as providing a way to wipe a third contact across its length. The magic of 3D printing provided the parts for the pot, with a body that holds a thin strip of pencil-smeared paper securely around its inner diameter. A shaft carries the wiper, which is just a small length of stripped hookup wire making contact with the paper strip. A clip holds everything firmly in place. The video below shows the build process and the results of testing, which were actually pretty good.

Of course, the construction used here isn’t meant for anything but demonstration purposes, but in that role, it performs really well. It’s good that [HackMakeMod] left the body open to inspection, so students can see how the position of the wiper correlates to resistance. It also makes it easy to slip new resistance materials in and out, perhaps using different lead grades to get different values.

Hats off to a clever build that should be sure to help STEM teachers engage their students. Next up on the lesson plan: a homebrew variable capacitor.

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Hackaday Links: February 18, 2024

February 18, 2024 by 17 Comments

So it turns out that walking around with $4,000 worth of hardware on your head isn’t quite the peak technology experience that some people thought it would be. We’re talking about the recently released Apple Vision Pro headset, which early adopters are lining up in droves to return. Complaints run the gamut from totally foreseeable episodes of motion sickness to neck pain from supporting the heavy headset. Any eyeglass wearer can certainly attest to even lightweight frames and lenses becoming a burden by the end of the day. We can’t imagine what it would be like to wear a headset like that all day. Ergonomic woes aside, some people are feeling buyer’s remorse thanks to a lack of apps that do anything to justify the hefty price tag. The evidence for a wave of returns is mostly gleaned from social media posts, so it has to be taken with a grain of salt. We wouldn’t expect Apple to be too forthcoming with official return figures, though, so the ultimate proof of uptake will probably be how often you spot one in the wild. Apart from a few cities and only for the next few weeks, we suspect sightings will be few and far between.

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