RISC-V Microcontroller Lights Up Synth With LED Level Meter

January 10, 2025 by 8 Comments

The LM3914 LED bar graph driver was an amazing chip back in the day. Along with the LM3915, its logarithmic cousin, these chips gave a modern look to projects, allowing dancing LEDs to stand in for a moving coil meter. But time wore on and the chips got harder to find and even harder to fit into modern projects, what with their giant DIP-18 footprint. What’s to be done when a project cries out for bouncing LEDs? Simple — get a RISC-V microcontroller and roll your own LED audio level meter.

In fairness, “simple” isn’t exactly what comes to mind while reading [svofski]’s write-up of this project. It’s part of a larger build, a wavetable synth called “Pétomane Ringard” which just screams out for lots of blinky LEDs. [svofski] managed to squeeze 20 small SMD LEDs onto the board along with a CH32V003 microcontroller. The LEDs are charlieplexed, using five of the RISC-V chip’s six available GPIO lines, leaving one for the ADC input. That caused a bit of trouble with programming, since one of those pins is needed to connect to the programmer. This actually bricked the chip, thankfully only temporarily since there’s a way to glitch the chip back to life, but only after pulling it out of the circuit. [svofski] recommends adding a five-second delay loop to the initialization routine to allow time to recover if the microcontroller gets into an unprogrammable state. Good tip.

As for results, we think the level meter looks fantastic. [svofski] went for automated assembly of the 0402 LEDs, so the strip is straight and evenly spaced. The meter seems to be quite responsive, and the peak hold feature is a nice touch. It’s nice to know there’s a reasonable substitute for the LM391x chips, especially now that all the hard work has been done.
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It’s IP, Over TOSLINK!

January 9, 2025 by 19 Comments

At the recent 38C3 conference in Germany, someone gave a talk about sending TOSLINK digital audio over fiber optic networks rather than the very low-end short distance fibre you’ll find behind your CD player. This gave [Manawyrm] some ideas, so of course the IP-over TOSLINK network was born.

TOSLINK is in effect I2S digital audio as light, so it carries two 44.1 kilosamples per second 16-bit data streams over a synchronous serial connection. At 1544 Kbps, this is coincidentally about the same as a T1 leased line. The synchronous serial link of a TOSLINK connection is close enough to the High-Level Data Link Control, or HDLC, protocol used in some networking applications, and as luck would have it she had some experience in using PPP over HDLC. She could configure her software from that to use a pair of cheap USB sound cards with TOSLINK ports, and achieve a surprisingly respectable 1.47 Mbit/s.

We like this hack, though we can see it’s not entirely useful and we think few applications will be found for it. But she did it because it was there, and that’s the essence of this game. Now all that needs to happen is for someone to use it in conjunction with the original TOSLINK-over network fiber, for a network-over-TOSLINK-over-network abomination.

All-Band Receiver Lets You Listen To All The Radio At Once

January 9, 2025 by 52 Comments

There are many ways to build a radio receiver, but most have a few things in common, such as oscillators, tuned circuits, detectors, mixers, and amplifiers. Put those together in the right order and you’ve got a receiver ready to tune in whatever you want to listen to. But if you don’t really care about tuning and want to hear everything all at once, that greatly simplifies the job and leaves you with something like this homebrew all-band receiver.

Granted, dispensing with everything but a detector and an audio amplifier will seriously limit any receiver’s capabilities. But that wasn’t really a design concern for [Ido Roseman], who was in search of a simple and unobtrusive way to monitor air traffic control conversations while flying. True, there are commercially available radios that tune the aviation bands, and there are plenty of software-defined radio (SDR) options, but air travel authorities and fellow travelers alike may take a dim view of an antenna sticking out of a pocket.

So [Ido] did a little digging and found a dead-simple circuit that can receive signals from the medium-wave bands up into the VHF range without regard for modulation. The basic circuit is a Schottky diode detector between an antenna and a high-gain audio amplifier driving high-impedance headphones; [Ido] built a variation that also has an LM386 amplifier stage to allow the use of regular earbuds, which along with a simple 3D-printed case aids in the receiver’s stealth.

With only a short piece of wire as an antenna, reception is limited to nearby powerful transmitters, but that makes it suitable for getting at least the pilot side of ATC conversations. It works surprisingly well — [Ido] included a few clips that are perfectly understandable, even if the receiver also captured things like cell phones chirping and what sounds like random sferics. It seems like a fun circuit to play with, although with our luck we’d probably not try to take it on a plane.

Deteriorating section of the UCIL plant near Bhopal, India. (Credit: Luca Frediani, Wikimedia)

Cleaning Up Bhopal: The World’s Worst Industrial Disaster

January 7, 2025 by 44 Comments

Forty years ago, on the night of Sunday 2 December of 1984, people in the city of Bhopal and surrounding communities were settling in for what seemed like yet another regular night. The worst thing in their near future appeared to be having to go back to school and work the next day. Tragically, many of them would never wake up again, and for many thousands more their lives would forever be changed in the worst ways possible.

During that night, clouds of highly toxic methyl isocyanate (MIC) gas rolled through the streets and into houses, venting from the Bhopal pesticide plant until the leak petered out by 2 AM. Those who still could wake up did so coughing, with tearing eyes and stumbled into the streets to escape the gas cloud without a clear idea of where to go. By sunrise thousands were dead and many more were left severely ill.

Yet the worst was still to come, as the number of casualties kept rising, legal battles and the dodging of responsibility intensified, and the chemical contamination kept seeping into the ground at the crippled plant. Recently there finally seems to be progress in this clean-up with the removal of 337 tons of toxic waste for final disposal, but after four decades of misgivings and neglect, how close is Bhopal really to finally closing the chapter on this horrific disaster?

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16-bit Linux-like Goodness

January 5, 2025 by 15 Comments

We see many 16-bit retrocomputers around here based on Intel and Intel-like chips such as the 8086, 8088, V20, and similar. While they don’t seem very powerful by today’s standards, they were perfectly capable machines and, thanks to Elks (Embeddedable Linux Kernel Subset), you can run something fairly Linux-like on these devices.

The requirements are light: 512K of RAM is desirable, but you can do something with 256K. If you have ROM, you can even get by with 128K. Most importantly, the system doesn’t require a memory management unit to remap memory like many operating systems.

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3D Printed Case Turns Pixel 6 Pro Into Palmtop

January 3, 2025 by 33 Comments

Despite initial interest in the 1990s and early 2000s, palmtop computers never really took off. Realistically most consumers were probably satisfied enough with smartphones as they became more widely available, but those of us who would prefer a real keyboard on our mobile devices are still feeling the pain. Today there are still a few commercial palmtop-like machines out there, but they aren’t exactly mainstream.

Which is why this 3D printed case for the Pixel 6 Pro from [TypingCat] is so interesting. It takes a relatively popular and capable contemporary phone, pairs it with a physical keyboard, and manages to create something that looks quite practical. Thanks to Termux, you can even get a fairly usable Linux environment going on the thing.

There aren’t too many components at play here, but still, we appreciate the fact that [TypingCat] provided links for not only the specific Bluetooth keyboard used, but the fasteners required to hold the three printed parts together. A link is also provided to the Termux-Desktops project, which allows you to get a Linux X11 desktop environment running on Android. It’s not the pocket Linux computer of our dreams, but it’s pretty close.

While the Pixel 6 Pro is a solid enough choice to base this project around, we’re interested in seeing if the community will come up with variants of this case to hold other similarly sized phones. It’s interesting to note that [TypingCat] has decided to use the “No Derivatives” variant of the Creative Commons license for the bottom half of the case. But since the top half is a remix of an existing Pixel 6 Pro case from [JoshCraft3D], it carries a more permissive license and must be distributed separately. Long story short, folks can create and distribute custom versions of the phone-side of this case, but the bottom needs to remain the same.

If you’ve got filament to burn extrude and would rather have a more pure Linux experience, we saw a printable Raspberry Pi Zero palmtop a couple months back that looked quite promising.

FPV Flying In Mixed Reality Is Easier Than You’d Think

January 3, 2025 by 12 Comments

Flying a first-person view (FPV) remote controlled aircraft with goggles is an immersive experience that makes you feel as if you’re really sitting in the cockpit of the plane or quadcopter. Unfortunately, while your wearing the goggles, you’re also completely blind to the world around you. That’s why you’re supposed to have a spotter nearby to keep watch on the local meatspace while you’re looping through the air.

But what if you could have the best of both worlds? What if your goggles not only allowed you to see the video stream from your craft’s FPV camera, but you could also see the world around you. That’s precisely the idea behind mixed reality goggles such as Apple Vision Pro and Meta’s Quest, you just need to put all the pieces together. In a recent video [Hoarder Sam] shows you exactly how to pull it off, and we have to say, the results look quite compelling.

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