A hand holding the circuit in its active state

2025 Component Abuse Challenge: A Self-Charging LED Flasher By Burkhard Kainka

[Tito] entered a Self-Charging LED Flasher into the Component Abuse Challenge. It’s a simple re-build of a design by the unstoppable [Burkhard Kainka], and while [Tito] doesn’t explain its workings in detail, it’s a clever experiment in minimalism, and a bit of a head-scratcher at the same time.

You press a button and an LED flashes.  But there is no battery, so how does it work? Maybe the schematic to the right here will help. Or does it confound? Look at it yourself before reading on and see if you can figure out how it works.

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2025 Component Abuse Challenge: An LED As A Light Dependent Capacitor

The function of an LED is to emit light when the device is forward biased within its operating range, and it’s known by most people that an LED can also operate as a photodiode. Perhaps some readers are also aware that a reverse biased LED also has a significant capacitance, to the extent that they can be used in some RF circuits in the place of a varicap diode. But how do those two unintentional properties of an LED collide? As it turns out, an LED can also behave as a light dependent capacitor. [Bornach] has done just that, and created a light dependent sawtooth oscillator.

The idea is simple enough, there is a capacitance between the two sides of the depletion zone in a reverse biased diode, and since an LED is designed such that its junction is exposed to the external light, any photons which hit it will change the charge on the junction. Since the size of the depletion zone and thus the capacitance is dependent on the voltage and thus the charge, incoming light can thus change the capacitance.

The circuit is a straightforward enough sawtooth oscillator using an op-amp with a diode in its feedback loop, but where we might expect to find a capacitor to ground on the input, we find our reverse biased LED. The video below the break shows it in operation, and it certainly works. There’s an interesting point here in that and LED in this mode is suggested as an alternative to a cadmium sulphide LDR, and it’s certainly quicker responding. We feel duty bound to remind readers that using the LED as a photodiode instead is likely to be a bit simpler.

This project is part of the Hackaday Component Abuse Challenge, in which competitors take humble parts and push them into applications they were never intended for. You still have time to submit your own work, so give it a go!

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An LED Sphere For Your Desk

The Las Vegas Sphere is great and all, but few of us can afford the expense to travel to out there to see it on the regular. If you’re looking for similar vibes you can access at home, you might enjoy the desk toy that [AGBarber] has designed.

The scale is small — the sphere measures just 98 mm (3.6 inches) in diameter — but that just means it’s accessible enough to be fun. The build is based around various sizes of WS2812B addressable LED rings, and contains 120 individual RGB LEDs in total. They’re wrapped up in a 3D printed housing which does a great job of diffusing the light. Transparent filament was used to print parts that light up with a richly-saturated glow with few visible hotspots. Commanding the LEDs is an ESP8266 microcontroller in the form of a Wemos D1 Mini, which provides plenty of grunt to run animations as well as great wireless connectivity options. [AGBarber] relied on their own Pixel Spork library to handle all the cool lighting effects. Files are on GitHub for the curious.

Maybe you don’t like spheres, and icosahedrons are more your speed. Well, we’ve featured those too—with 2,400 LEDs, no less.

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2025 One Hertz Challenge: Blinking An LED With The Aid Of Radio Time

If you want to blink an LED once every second, you could use just about any old timer circuit to create a 1 Hz signal. Or, you could go the complicated route like [Anthony Vincz] and grab 1 Hz off a radio clock instead. 

The build is an entry for the 2025 One Hertz Challenge, with [Anthony] pushing himself to whip up a simple entry on a single Sunday morning. He started by grabbing a NE567 tone decoder IC, which uses a phase-locked loop to trigger an output when detecting a tone of a given frequency. [Anthony] had used this chip hooked up to an Arduino to act as a Morse decoder, which picked up sound from an electret mic and decoded it into readable output.

However, he realized he could repurpose the NE567 to blink in response to output from radio time stations like the 60 KHz British and 77.5 KHz German broadcasts. He thus grabbed a software-defined radio, tuned it into one of the time stations, and adjusted the signal to effectively sound a regular 800 Hz tone coming out of his computer’s speakers that cycled once every second. He then tweaked the NE567 so it would trigger off this repetitive tone every second, flashing an LED.

Is it the easiest way to flash an LED? No. It’s complicated, but it’s also creative. They say a one hertz signal is always in the last place you look.

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2025 One Hertz Challenge: Abstract Aircraft Sculpture Based On Lighting Regulations

The 2025 One Hertz Challenge is really heating up with all kinds of projects that do something once every second. [The Baiko] has given us a rather abstract entry that looks like a plane…if you squint at it under the right conditions.

It’s actually quite an amusing abstract build. If you’ve ever seen planes flying in the night sky, you’ve probably noticed they all have similar lights. Navigation lights, or position lights as they are known, consist of a red light on the left side and a green light on the right side. [The Baiko] assembled two such LEDs on a small sliver of glass along with an ATtiny85 microcontroller.

Powered by a coin cell, they effectively create a abstract representation of a plane in the night sky, paired with a flashing strobe that meets the requirements of the contest. [The Baiko] isn’t exactly sure of the total power draw, but notes it must be low given the circuit has run for weeks on a 30 mAh coin cell.

It’s an amusing piece of PCB art, though from at least one angle, it does appear the red LED might be on the wrong side to meet FAA regulations. Speculate on that in the comments.

In any case, we’ve had a few flashers submitted to the competition thus far, and you’ve got until August 19 to get your own entry in!

Raspberry Pi Pico LED display sitting in window sill

An Ode To The Aesthetic Of Light In 1024 Pixels

Sometimes, brilliant perspectives need a bit of an introduction first, and this is clearly one. This video essay by [Cleggy] delivers what it promises: an ode to the aesthetic of light. But he goes further, materializing his way of viewing things into a beautiful physical build — and the full explanation of how to do it at home.

What’s outstanding here is not just the visual result, but the path to it. We’ve covered tons of different LED matrices, and while they’re all functional, their eventual purpose is left up to the builder, like coasters or earknobs. [Cleggy] provides both. He captured a vision in the streets and then built an LED matrix from scratch.

The matrix consists of 1024 hand-soldered diodes. They’re driven by a Raspberry Pi Pico and a symphony of square waves. It’s not exactly a WS2812 plug-and-play job. It’s engineered from the silicon up, with D-latches and demultiplexers orchestrating a mesmerizing grayscale visual.

Pulse-width modulation (PWM) is the secret ingredient of this hack. [Cleggy] dims each white pixel separately, by varying the duty cycle of its light signal. The grayscale video data, compressed into CSV files, is parsed line-by-line by the Pico, translating intensity values into shimmering time slices.

It transforms the way you see and perceive things. All that, with a 1000 LED monochrome display. Light shows are all highly personal, and each one is a little different. Some of them are really kid stuff.

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Custom Bedroom Lighting Controlled By Alexa

[Arkandas] had a problem. They liked reading in bed, but their bedroom lamps weren’t cutting it—either too bright and direct, or too dim and diffuse. The solution was custom lighting, and a new project began.

The concept was simple—build a custom controller for a set of addressable LED lighting strips that would be installed in the bedroom. Specifically, in the headboard of the bed, providing controllable light directly where it was needed. The strips themselves were installed in aluminum channel with plastic diffusers to give a nice smooth light. [Arkandas] then tasked an ESP32 to control the strips, using the FastLED library to work with WS2812B LEDs, and also the Adafruit NeoPixel library for using SK6812 LEDs and their extra white channel. The ESP32 was set up to provide a web interface for direct control over the local network. [Arkandas] also made good use of the FauxmoESP library to enable the device to be controlled via Amazon Alexa, which fit nicely into their existing smarthome setup. Files are on Github for the curious.

The final build works well, creating a soft light in the habitable area of the bed that can also be readily controlled via voice commands or via web. We’ve seen the ESP32 do other great feats in this arena before, too, albeit of the more colorful variety. Meanwhile, if you’re cooking up your own smart lighting solutions, don’t hesitate to tell the tipsline!