Let’s say you want to blink an LED. You might grab an Arduino and run the Blink sketch, or you might lace up a few components to a 555. But you needn’t go so fancy! [The Design Graveyard] explains how this same effect can be achieved with a single transistor.

The circuit in question is rather odd at first blush. The BC547 NPN transistor is hooked up between an LED and a resistor leading to a 12V DC line, with a capacitor across the emitter and collector. Meanwhile, the base is connected to… nothing! It’s just free-floating in the universe of its own accord. You might expect this circuit to do nothing at all, but if you power it up, the LED will actually start to flash.

The mechanism at play is relatively simple. The capacitor charges to 12 volts via the resistor. At this point, the transistor, which is effectively just acting as a poor diode in this case, undergoes avalanche breakdown at about 8.5 to 9 volts, and starts conducting. This causes the capacitor to discharge via the LED, until the voltage gets low enough that the transistor stops conducting once again. Then, the capacitor begins to charge back up, and the cycle begins again.

It’s a weird way to flash an LED, and it’s not really the normal way to use a transistor—you’re very much running it out of spec. Regardless, it does work for a time! We’ve looked at similar circuits before too. Video after the break.

[Thanks to Vik Olliver for the tip!]

Beehives are impressive structures, an example of the epic building feats that are achievable by nature’s smaller creatures. [Full Stack Woodworking] was recently building a new work desk, and decided to make this piece of furniture a glowing tribute to the glorious engineering of the bee. (Video, embedded below.)

The piece is a conventional L-shaped desk, but with a honeycomb motif inlaid into the surface itself. [Full Stack Woodworking] started by iterating on various designs with stacked hexagons made out of laser cut plywood and Perspex, filled with epoxy. Producing enough hexagons to populate the entire desk was no mean feat, requiring a great deal of cutting, staining, and gluing—and all this before the electronics even got involved! Naturally, each cell has a custom built PCB covered in addressable LEDs, and they’re linked with smaller linear PCBs which create “paths” for bees to move between cells.

What’s cool about the display is that it’s not just running some random RGB animations. Instead, the desk has a Raspberry Pi 5 dedicated to running a beehive simulation, where algorithmic rules determine the status (and thus color) of each hexagonal cell based on the behavior of virtual bees loading the cells with honey. It creates an organic, changing display in a way that’s rather reminiscent of Conway’s Game of Life.

It was a huge build, but the final result is impressive. We’ve featured some other great custom desks over the years too. Video after the break.

[Thanks to J. Peterson for the tip!]

Glasses are perhaps the most non-invasive method of vision correction, followed by contact lenses. Each have their drawbacks though, and some seek more permanent solutions in the form of laser eye surgeries like LASIK, aiming to reshape their corneas for better visual clarity. However, these methods often involve cutting into the eye itself, and it hardly gets any more invasive than that.

A new surgical method could have benefits in this regard, allowing correction in a single procedure that requires no lasers and no surgical cutting of the eye itself. The idea is to use electricity to help reshape the eye back towards greater optical performance.

The Eyes Have It

Existing corrective eye surgeries most often aim to fix problems like long-sightedness, short-sightedness, and astigmatism. These issues are generally caused by the shape of the cornea, which works with the lens in the eye to focus light on to the light-sensitive cells in the retina. If the cornea is misshapen, it can be difficult for the eye to focus at close or long ranges, or it can cause visual artifacts in the field of view, depending on the precise nature of the geometry. Technologies like LASIK reshape the cornea for better performance using powerful lasers, but also involve cutting into the cornea. The procedure is thus highly invasive and has a certain recovery time, safety precautions that must be taken afterwards, and some potential side effects. A method for reshaping the eye without cutting into it would thus be ideal to avoid these problems.

Enter the technology of Electromechanical Reshaping (EMR). As per a new paper, researchers at the University of California, Irvine, came across the idea by accident, having been looking into the moldable nature of living tissues. As it turns out, collagen-based tissues like the cornea hold their structure thanks to the attractions between oppositely-charged subcomponents. These structures can be altered with the right techniques. For example, since these tissues are laden with water, applying electricity can change the pH through electrolyzation, altering the attraction between components of the tissue and making them pliable and reformable. Once the electric potential is taken away, the tissues can be restored to their original pH balance, and the structure will hold firm in its new form.

Researchers first tested this technique out on other tissues before looking to the eye. The team were able to use EMR to reshape ears from rabbits, while also being able to make physical changes to scar tissue in pigs. These efforts proved the basic mechanism worked, and that it could have applicability to the cornea itself.

To actually effectively reshape the cornea using this technique, a sort of mold was required. To that end, researchers created a “contact lens” type device out of platinum, which was formed in the desired final shape of the cornea. A rabbit eyeball was used in testing, doused in a saline solution to mimic the eye’s natural environment. The platinum device was pushed on to the eye, and used as an electrode to apply a small electrical potential across the eyeball. This was controlled carefully to precisely change the pH to the region where the eye became remoldable. After a minute, the cornea of the rabbit eyeball had conformed to the shape of the platinum lens. With the electrical potential removed, the pH of the eyeball was returned to normal and the cornea retained the new shape. The technique was trialled on twelve eyeballs, with ten of those treated for a shortsightedness condition, also known as myopia. In the case of the myopic eyeballs, all ten were successfully corrected the cornea, creating improved focusing power that would correspond to better vision in a living patient’s eye.

While the technique is promising, great development will be required before this is a viable method for vision correction in human patients. Researchers will need to figure out how to properly apply the techniques to eyeballs that are still in living patients, with much work to be done with animal studies prior to any attempts to translate the technique to humans. However, it could be that a decade or two in the future, glasses and LASIK will be increasingly less popular compared to a quick zap from the electrochemical eye remoulder. Time will tell.

If you’ve got an existing smart home rig, motion sensors can be a useful addition to your setup. You can use them for all kinds of things, from turning on lights when you enter a room, to shutting off HVAC systems when an area is unoccupied. Typically, you’d add dedicated motion sensors to your smart home to achieve this. But what if your existing smart light bulbs could act as the motion sensors instead?

The Brightest Bulb In The Bulb Box

The most typical traditional motion sensors use passive infrared detection, wherein the sensor picks up on the infrared radiation emitted by a person entering a room. Other types of sensors include break-beam sensors, ultrasonic sensors, and cameras running motion-detection algorithms. All of these technologies can readily be used with a smart home system if so desired. However, they all require the addition of extra hardware. Recently, smart home manufacturers have been exploring methods to enable motion detection without requiring the installation of additional dedicated sensors.

Hue Are You?

Philips has achieved this goal with its new MotionAware technology, which will be deployed on the company’s new Hue Bridge Pro base station and Hue smart bulbs. The company’s smart home products use Zigbee radios for communication. By monitoring small fluctuations in the Zigbee communications between the smart home devices, it’s possible to determine if a large object, such as a human, is moving through the area. This can be achieved by looking at fluctuations to signal strength, latency, and bit error rates. This allows motion detection using Hue smart bulbs without any specific motion detection hardware required.

Using MotionAware requires end users to buy the latest Philips Hue Bridge Pro base station. As for whether there is some special magic built into this device, or if Phillips merely wants to charge users to upgrade to the new feature? Well, Philips claims the new bridge is required because it’s powerful enough to run the AI-powered algorithms that sift the radio data and determine whether motion is occurring. The tech is based on IP from a company called Ivani, which developed Sensify—an RF sensing technology that works with WiFi, Bluetooth, and Zigbee signals.

To enable motion detection, multiple Hue bulbs must be connected to the same Hue Bridge Pro, with three to four lights used to create a motion sensing “area” in a given room. When setting up the system, the room must be vacated so the system can calibrate itself. This involves determining how the Zigbee radio signals propagate between devices when nobody—humans or animals—is inside. The system then uses variations from this baseline to determine if something is moving in the room. The system works whether the lights themselves are on or off, because the light isn’t used for sensing—as long as the bulb has power, it can use its radio for sensing motion. Philips notes this only increases standby power consumption by 1%, and a completely negligible amount while the light is actually “on” and outputting light.

There are some limitations to the use of this system. It’s primarily for indoor use, as Philips notes that the system benefits from the way radio waves bounce off surrounding interior walls and objects. Lights should also be separated from 1 to 7 meters apart for optimal use, and effectively create a volume between them in which motion sensing is most effective. Depending on local conditions, it’s also possible that the system may detect motion on adjacent levels or in nearby rooms, so sensitivity adjustment or light repositioning may be necessary. Notably, though, you won’t need new bulbs to use MotionAware. The system will work with all the Hue mains-powered bulbs that have been manufactured since 2014.

The WiZ Kids Were Way Ahead

Philips aren’t the only ones offering in-built motion sensing with their smart home bulbs. WiZ also has a product in this space, which feels coincidental given the company was acquired in 2019 by Philip’s own former lighting division. Unlike Philips Hue, WiZ products rely on WiFi for communication. The company’s SpaceSense technology again relies on perturbations in radio signals between devices, but using WiFi signals instead of Zigbee. What’s more, the company has been at this since 2022

There are some notable differences in Wiz’s technology. SpaceSense is able to work with just two devices at a minimum, and not just lights—you can use any of the company’s newer lights, smart switches, or devices, as long as they’re compatible with SpaceSense, which covers the vast majority of the company’s recent product.

Ultimately, WiZ beat Philips by years with this tech. However, perhaps due to its lower market penetration, it didn’t make the same waves when SmartSense dropped in 2022.

Radio Magic

We’ve seen similar feats before. It’s actually possible to get all kinds of useful information out of modern radio chipsets for physical sensing purposes. We’ve seen systems that measure a person’s heart rate using nothing more than perturbations in WiFi transmission over short distances, for example. When you know what you’re looking for, a properly-built algorithm can let you dig usable motion information out of your radio hardware.

Ultimately, it’s neat to see smart home companies expanding their offerings in this way. By leveraging the radio chipsets in existing smart bulbs, engineers have been able to pull out granular enough data to enable this motion-sensing parlour trick. If you’ve ever wanted your loungeroom lights to turn on when you walk in, or a basic security notification when you’re out of the house… now you can do these kinds of things without having to add more hardware. Expect other smart home platforms to replicate this sort of thing in future if it proves practical and popular with end users.

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.

A Lot Of Hot Air

Once an obscure feature only found in luxury vehicles, airbags became common safety equipment in many cars and trucks by the mid-1990s. Indeed, a particular turning point was when they became mandatory in vehicles sold in the US market from late 1998 onwards, which made them near-universal equipment in many other markets worldwide. Despite their relatively recent mainstream acceptance, the concept of the airbag actually dates back a lot farther.

The basic invention of the airbag is typically credited to two English dentists—Harold Round and Arthur Parrott—who submitted a patent for the concept all the way back in 1919. The patent regarded the concept of creating an air cushion to protect occupants in aircraft during serious impacts. Specific attention was given to the fact that the air cushion should “yield readily without developing the power to rebound,” which could cause further injury. This was achieved by giving the device air outlet passages that would vent as a person impacted the device, which would allow the cushion to absorb the hit gently while reducing the chance of injury.

The concept only later became applicable to automobiles when Walter Linderer filed for a German patent in 1951, and John W. Hetrick filed for a US patent in 1952. Both engineers devised airbags that were based on the release of compressed air, triggered either by human intervention or automated mechanical means. These concepts proved ultimately infeasible, as compressed air could not be feasibly be released to inflate an airbag quickly enough to be protective in an automobile crash.

It would only be later in the 1960s that workable versions using explosive or pyrotechnic inflation came to the fore. The concept was simple—use a chemical reaction to generate a great deal of gas near-instantaneously, inflating the airbag fractions of a second before vehicle occupants come into contact with the device. The airbags are fitted with vents that only allow the gas to escape slowly. This means that as a person hits the airbag, they are gently decelerated as their impact pushes the gas out of the restrictive vents. This helps reduce injuries that would typically be incurred if the occupants instead hit interior parts of the car without any protection at all.

The Big Bang

The use of pyrotechnic gas generators to inflate airbags was the leap forward that made airbags practical and effective for use in automobiles. However, as you might imagine, releasing a massive burst of gas in under 50 milliseconds does create a rather large pressure wave—which we experience as an incredibly loud sound. If you ever seen airbags detonated outside of a vehicle, you’ve probably noticed they sound rather akin to fireworks or a gun going off. Indeed, the sound of an airbag can exceed 160 decibels (dB)—more than enough to cause instant damage to the ear. Noise generated in a vehicle impact is often incredibly loud, too, or course. Ultimately, this isn’t great for the occupants of the vehicle, particularly their hearing. Ultimately, an airbag deployment is a carefully considered trade-off—the general consensus is that impact protection in a serious crash is preferable, even if your ears are worse for wear afterwards.

However, there is a technique that can mitigate this problem. In particular, Mercedes-Benz developed a system to protect the hearing of vehicle occupants in the event that the airbags are fired. The trick is in using the body’s own reactions to sound to reduce damage to the ear from excessive sound pressure levels.

The stapedius reflex (also known as the acoustic reflex) is one of the body’s involuntary, instantaneous movements in response to an external stimulus—in this case, certain sound levels. When a given sound stimulus occurs to either ear, muscles inside both ears contract, most specifically the stapedius muscle in humans. When the muscle contracts, it has a stiffening effect on the ossicular chain—the three tiny bones that connect the ear drum to the cochlea in the inner ear. Under this condition, less vibrational energy is transferred, reducing damage to the cochlea from excessive sound levels.

The threshold at which the reflex is triggered is usually 10 to 20 dB lower than the point at which the individual feels discomfort; typical levels are from around 70 to 100 dB. When triggered by particularly loud sounds of 20 dB above the trigger threshold, the muscle contraction is enough to reduce the sound level at the cochlea by a full 15 dB. Notably, the reflex is also triggered by vocalization—reducing transmission through to the inner ear when one begins to speak.

Mercedes-Benz engineers realized that the stapedius reflex could be pre-emptively triggered ahead of firing the airbags, in order to provide a protective effect for the ears. To this end, the company developed the PRE-SAFE Sound system. When the vehicle’s airbag control unit detects a collision, it triggers the vehicle’s sound system to play a short-duration pink noise signal at a level of 80 dB. This is intended to be loud enough to trigger the stapedius reflex without in itself doing damage to the ears. Typically, it takes higher sound levels closer to 100 dB  to reliably trigger the reflex in a wide range of people, but Mercedes-Benz engineers realized that the wide-spread frequency content of pink noise enable the reflex to be switched on at a much lower, and safer, sound level. With the reflex turned on, when the airbags do fire a fraction of a second later, less energy from the intense pressure spike will be transferred to the inner ear, protecting the delicate structures that provide the sense of hearing.

Mercedes-Benz first released the technology in production models almost a decade ago.

The stapedius reflex does have some limitations. It can be triggered with a latency of just 10 milliseconds, however, it can take up to 100 milliseconds for the muscle in the ear to reach full tension, conferring the full protective effect. This limits the ability of the reflex to protect against short, intense noises. However, given the Mercedes-Benz system triggers the sound before airbag inflation where possible, this helps the muscles engage prior to the peak sound level being reached. The protective effect of the stapedius reflex also only lasts for a few seconds, with the muscle contraction unable to be maintained beyond this point. However, in a vehicle impact scenario, the airbags typically all fire very quickly, usually well within a second, negating this issue.

Mercedes-Benz was working on the technology from at least the early 2010s, having run human trials to trigger the stapedius reflex with pink noise in 2011. It deployed the technology on its production vehicles almost a decade ago, first offering PRE-SAFE Sound on E-Class  models for the 2017 model year. Despite the simple nature of the technology, few to no other automakers have publicly reported implementing the technique.

Car crashes are, thankfully, rather rare. Few of us are actually in an automobile accident in any given year, even less in ones serious enough to cause an airbag deployment. However, if you are unlucky enough to be in a severe collision, and you’re riding in a modern Mercedes-Benz, your ears will likely thank you for the added protection, just as your body will be grateful for the cushioning of the airbags themselves.

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.

There are all kinds of air quality sensors on the market that rely on all kinds of electro-physical effects to detect gases or contaminants and report them back as a value. [lucascreator] has instead been investigating a method of determining air quality that is closer to divination than measurement—using computer vision and a trained AI model.

The system relies on an Unihiker K10—a microcontroller module based around the ESP32-S3 at heart. The chip is running a lightweight convolutional neural network (CNN) trained on 12,000 images of the sky. These images were sourced from a public dataset; they were taken in India and Nepal, and tagged with the relevant Air Quality Index at the time of capture. [lucascreator] used this data to train their model to look at an image taken with a camera attached to the ESP32 and estimate the air quality index based on what it has seen in that existing dataset.

It might sound like a spurious concept, but it does have some value. [lucascreator] cites studies where video data was used for low-cost air quality estimation—not as a replacement for proper measurement, but as an additional data point that could be sourced from existing surveillance infrastructure. Performance of such models has, in some cases, been remarkably accurate.

[lucascreator] is pragmatic about the limitations of their implementation of this concept, noting that their very compact model didn’t always perform the best in terms of determining actual air quality. The concept may have some value, but implementing it on an ESP32 isn’t so easy if you’re looking for supreme accuracy. We’ve featured some other great air quality projects before, though, if you’re looking for other ways to capture this information. Video after the break.