Know Audio: Distortion Part Two

October 6, 2025 by 5 Comments

It’s been a while since the last installment in our Know Audio series, in which we investigated distortion as it applies to Hi-Fi audio. Now it’s time to return with part two of our look at distortion, and attempt some real-world distortion measurements on the bench.

Last time, we examined distortion from a theoretical perspective, as the introduction of unwanted harmonics as a result of non-linearities in the signal path. Sometimes that’s a desired result, as with a guitar pedal, but in a Hi-Fi system where the intention is to reproduce as faithfully as possible a piece of music from a recording, the aim is to make any signal path components as linear as possible. When we measure the distortion, usually expressed as THD, for Total Harmonic Distortion, of a piece of equipment we are measuring the ratio of those unwanted harmonics in the output to the frequencies we want,  and the resulting figure is commonly expressed in dB, or as a percentage. Continue reading “Know Audio: Distortion Part Two” →

A person's hand wearing a black glove is shown in the right part of the image, making a series of gestures. A representation of a hand mimics those motions on a laptop screen.

Weaving Circuits From Electronic Threads

October 6, 2025 by 5 Comments

Though threading is a old concept in computer science, and fabric computing has been a term for about thirty years, the terminology has so far been more metaphorical than strictly descriptive. [Cedric Honnet]’s FiberCircuits project, on the other hand, takes a much more literal to weaving technology “into the fabric of everyday life,” to borrow the phrase from [Mark Weiser]’s vision of computing which inspired this project. [Cedric] realized that some microcontrollers are small enough to fit into fibers no thicker than a strand of yarn, and used them to design these open-source threads of electronics (open-access paper).

The physical design of the FiberCircuits was inspired by LED filaments: a flexible PCB wrapped in a protective silicone coating, optionally with a protective layer of braiding surrounding it. There are two kinds of fiber: the main fiber and display fibers. The main fiber (1.5 mm wide) holds an STM32 microcontroller, a magnetometer, an accelerometer, and a GPIO pin to interface with external sensors or other fibers. The display fibers are thinner at only one millimeter, and hold an array of addressable LEDs. In testing, the fibers could withstand six Newtons of force and be bent ten thousand times without damage; fibers protected by braiding even survived 40 cycles in a washing machine without any damage. [Cedrik] notes that finding a PCB manufacturer that will make the thin traces required for this circuit board is a bit difficult, but if you’d like to give it a try, the design files are on GitHub.

[Cedrik] also showed off a few interesting applications of the thread, including a cyclist’s beanie with automatic integrated turn signals, a woven fitness tracker, and a glove that senses the wearer’s hand position; we’re sure the community can find many more uses. The fibers could be embroidered onto clothing, or embedded into woven or knitted fabrics. On the programming side, [Cedrik] ported support for this specific STM32 core to the Arduino ecosystem, and it’s now maintained upstream by the STM32duino project, which should make integration (metaphorically) seamless.

One area for future improvement is in power, which is currently supplied by small lithium batteries; it would be interesting to see an integration of this with power over skin. This might be a bit more robust, but it isn’t first knitted piece of electronics we’ve seen. Of course, rather than making wearables more unobtrusive, you can go in the opposite direction. Continue reading “Weaving Circuits From Electronic Threads” →

Airbags, And How Mercedes-Benz Hacked Your Hearing

October 6, 2025 by 25 Comments

Airbags are an incredibly important piece of automotive safety gear. They’re also terrifying—given that they’re effectively small pyrotechnic devices that are aimed directly at your face and chest. Myths have pervaded that they “kill more people than they save,” in part due a hilarious episode of The Simpsons. Despite this, they’re credited with saving tens of thousands of lives over the years by cushioning fleshy human bodies from heavy impacts and harsh decelerations.

While an airbag is generally there to help you, it can also hurt you in regular operation. The immense sound pressure generated when an airbag fires is not exactly friendly to your ears. However, engineers at Mercedes-Benz have found a neat workaround to protect your hearing from the explosive report of these safety devices. It’s a nifty hack that takes advantage of an existing feature of the human body. Let’s explore how air bags work, why they’re so darn loud, and how that can be mitigated in the event of a crash.

Continue reading “Airbags, And How Mercedes-Benz Hacked Your Hearing” →

GuitarPie Uses Guitar As Interface, No Raspberries Needed

October 6, 2025 by 13 Comments

We’ve covered plenty of interesting human input devices over the years, but how about an instrument? No, not as a MIDI controller, but to interact with what’s going on-on screen. That’s the job of GuitarPie, a guitar-driven pie menu produced by a group at the University of Stuttgart.

The idea is pretty simple: the computer is listening for one specific note, which cues the pie menu on screen. Options on the pie menu can be selected by playing notes on adjacent strings and frets. (Check it out in action in the video embedded below). This is obviously best for guitar players, and has been built into a tablature program they’re calling TabCTRL. For those not in the loop, tablature, also known as tabs, is an instrument-specific notation system for stringed instruments that’s quite popular with guitar players. So TabCTRL is a music-learning program, that shows how to play a given song.

With this pairing, you can rock out to the tablature, the guitarist need never take their hands off the frets. You might be wondering “how isn’t the menu triggered during regular play”? Well, the boffins at Stuttgart thought of that– in TabCTRL, the menu is locked out while play mode is active. (It keeps track of tempo for you, too, highlighting the current musical phrase.) A moment’s silence (say, after you made a mistake and want to restart the song) stops play mode and you can then activate the menu. It’s well a well-thought-out UI. It’s also open source, with all the code going up on GitHub by the end of October.

The neat thing is that this is pure software; it will work with any unmodified guitar and computer. You only need a microphone in front of the amp to pick up the notes. One could, of course, use voice control– we’ve seen no shortage of hacks with that–but that’s decidedly less fun. Purists can comfort themselves that at least this time the computer interface is a real guitar, and not a guitar-shaped MIDI controller. Continue reading “GuitarPie Uses Guitar As Interface, No Raspberries Needed” →

ESP32 Decodes S/PDIF Like A Boss (Or Any Regular Piece Of Hi-Fi Equipment)

October 6, 2025 by 3 Comments

S/PDIF has been around for a long time; it’s still a really great way to send streams of digital audio from device A to device B. [Nathan Ladwig] has got the ESP32 decoding SPDIF quite effectively, using an onboard peripheral outside its traditional remit.

On the ESP32, the Remote Control Transceiver (RMT) peripheral was intended for use with infrared transceivers—think TV remotes and the like. However, this peripheral is actually quite flexible, and can be used for sending and receiving a range of different signals. [Nathan] was able to get it to work with S/PDIF quite effectively. Notably, it has no defined bitrate, which allows it to work with signals of different sample rates quite easily. Instead, it uses biphase mark code to send data. With one or two transitions for each transmitted bit, it’s possible to capture the timing and determine the correct clock from the signal itself.

[Nathan] achieved this feat as part of his work to create an ESP32-based RTP streaming device. The project allows an ESP32 to work as a USB audio device or take an S/PDIF signal as input, and then transmitting that audio stream over RTP to a receiver which delivers the audio at the other end via USB audio or as an SPDIF output. It’s a nifty project that has applications for anyone that regularly finds themselves needing to get digital audio from once place to another. It can also run a simple visualizer, too, with some attached LEDs.

It’s not the first time we’ve seen S/PDIF decoded on a microcontroller; it’s quite achievable if you know what you’re doing. Meanwhile, if you’re cooking up your own digital audio hacks, we’d love to hear about it. Digitally, of course, because we don’t accept analog phone calls here at Hackaday. Video after the break.

Continue reading “ESP32 Decodes S/PDIF Like A Boss (Or Any Regular Piece Of Hi-Fi Equipment)” →

Apple’s Continuing Failing Repair Score With The AirPods Pro 3

October 5, 2025 by 16 Comments

It takes quite a bit of effort to get a 0 out of 10 repairability score from iFixit, but in-ears like Apple’s AirPods are well on course for a clean streak there, with the AirPod Pro 3 making an abysmal showing in their vitriolic teardown video alongside their summary article. The conclusion is that while they are really well-engineered devices with a good feature set, the moment the battery wears out it is effectively e-waste. The inability to open them without causing at least some level of cosmetic damage is bad, and that’s before trying to glue the device back together. Never mind effecting any repairs beyond this.

Worse is that this glued-together nightmare continues with the charging case. Although you’d expect to be able to disassemble this case for a battery swap, it too is glued shut to the point where a non-destructive entry is basically impossible. As iFixit rightfully points out, there are plenty of examples of how to do it better, like the Fairbuds in-ears. We have seen other in-ears in the past that can have some maintenance performed without having to resort to violence, which makes Apple’s decisions here seem to be on purpose.

Although in the comments to the video there seem to be plenty of happy AirPod users for whom the expected 2-3 year lifespan is no objection, it’s clear that the AirPods are still getting zero love from the iFixit folk.

Continue reading “Apple’s Continuing Failing Repair Score With The AirPods Pro 3” →

splashflag iot swimming notification

Splashflag: Raising The Flag On A Pool Party

October 5, 2025 by 7 Comments

Some things are more fun when there are more folks involved, and enjoying time in the pool is one of those activities. Knowing this, [Bert Wagner] started thinking of ways to best coordinate pool activities with his kids and their neighborhood friends. Out of this came the Splashflag, an IoT device built from the ground up that provides fun pool parties and a great learning experience along the way.

The USB-powered Splashflag is housed in a 3D-printed case, with a simple 2×16 LCD mounted on the front to display the notification. There’s also a small servo mounted to the rear that raises a 3D-printed flag when the notification comes in—drawing your attention to it a bit more than just text alone would. Hidden on the back is also a reset button: a long press factory-resets the device to connect to a different Wi-Fi network, and a quick press clears the notification to return the device to its resting state.

Inside is an ESP32-S3 that drives the servo and display and connects to the Wi-Fi. The ESP32 is set up with a captive portal, easing the device’s connection to a wireless network. The ESP32, once connected, joins an MQTT broker hosted by [Bert Wagner], allowing easy sending of notifications via the web app he made to quickly and easily send out invitations.

Thanks, [Bert Wagner], for sharing the process of building this fun, unique IoT device—be sure to read all the details on his website or check out the code and design files available over on his GitHub. Check out some of our other IoT projects if this project has you interested in making your own.

Continue reading “Splashflag: Raising The Flag On A Pool Party” →