Author: Lewin Day

3323 Articles

Blinking An LED With A Single Transistor

October 20, 2025 by 16 Comments

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.

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Classy Desk Simulates Beehive Activity

October 20, 2025 by 6 Comments

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.

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Reshaping Eyeballs With Electricity, No Lasers Or Cutting Required

October 8, 2025 by 36 Comments

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.

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Smart Bulbs Are Turning Into Motion Sensors

October 7, 2025 by 33 Comments

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?

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Airbags, And How Mercedes-Benz Hacked Your Hearing

October 6, 2025 by 42 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.

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

October 6, 2025 by 5 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.

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Divining Air Quality With A Cheap Computer Vision Device

October 5, 2025 by 10 Comments

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.

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