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

October 16, 2025 by 15 Comments

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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Three Years In, JawnCon Continues To Grow And Impress

October 16, 2025 by 5 Comments

Make no mistake, just getting a hacker con off the ground is a considerable challenge. But the really hard part comes after. To be more than a one-off success story, you’ve got to expand the event year after year in a manageable way. Go too slow, and attendees might lose interest. Move too fast, and you run the risk of going broke if your ticket sales don’t keep up with your ambitions.

Luckily for hackers living in the Philadelphia area, the folks behind JawnCon have once again demonstrated they’re able to thread the needle. While the ticket price remained the same as in 2024, this year an additional track of talks was introduced as well as expanded activities throughout the con. Even though it only wrapped this past weekend, there’s already buzz about what the event will look like in 2026.

Until then, let’s take a look at some of the projects that were on display at this year’s JawnCon. If it’s the talks you’re after, they’ll be edited and uploaded to the event’s YouTube page in the near future. In the meantime, the Friday and Saturday live streams are still available.

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Live Coding Techno With Strudel

October 16, 2025 by 15 Comments

The super talented [Switch Angel] is an electronic music artist, with a few cool YouTube videos to show off their absolute nailing of how to live code with Strudel. For us mere mortals, Strudel is a JavaScript port of TidalCycles, which is an algorithmic music generator which supports live coding, i.e. the music that is passed down to the synthesizer changes on-the-fly as you manipulate the code. It’s magical to watch (and listen!) to how you can adapt and distort the music to your whims just by tweaking a few lines of code: no compilation steps, hardly any debugging and instant results.

The traditional view of music generators like this is to create lists of note/instrument pairs with appropriate modifiers. Each sound is specified in sequence — adding a sound extends the sequence a little. Strudel / Tidalcycles works a little differently and is based on the idea of repeating patterns over a fixed time. Adding an extra sound or breaking down one sound slot into multiple sounds squeezes all the remaining slots down, causing the whole pattern to repeat in the same period, with the sounds individually taking up less space. This simple change makes it really easy to add layer upon layer of interest within a sequence with a few extra characters, without recalculating everything else to fit. On top of this base, multiple effects can be layered—more than we can mention here—and all can be adjusted with pop-in sliders directly in the code.

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A Tale Of Two Car Design Philosophies

October 16, 2025 by 123 Comments

As a classic car enthusiast, my passion revolves around cars with a Made in West Germany stamp somewhere on them, partially because that phrase generally implied a reputation for mechanical honesty and engineering sanity. Air-cooled Volkswagens are my favorites, and in fact I wrote about these, and my own ’72 Super Beetle, almost a decade ago. The platform is incredibly versatile and hackable, not to mention inexpensive and repairable thanks to its design as a practical, affordable car originally meant for German families in the post-war era and which eventually spread worldwide. My other soft-spot is a car that might seem almost diametrically opposed to early VWs in its design philosophy: the Mercedes 300D. While it was a luxury vehicle, expensive and overbuilt in comparison to classic Volkswagens, the engineers’ design choices ultimately earned it a reputation as one of the most reliable cars ever made.

As much as I appreciate these classics, though, there’s almost nothing that could compel me to purchase a modern vehicle from either of these brands. The core reason is that both have essentially abandoned the design philosophies that made them famous in the first place. And while it’s no longer possible to buy anything stamped Made in West Germany for obvious reasons, even a modern car with a VIN starting with a W doesn’t carry that same weight anymore. It more likely marks a vehicle destined for a lease term rather than one meant to be repaired and driven for decades, like my Beetle or my 300D.

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EmuDevz Is Literally A Software Game

October 16, 2025 by 7 Comments

The idea of gamifying all the things might have died down now that the current hype is shoving AI into all the things — but you’ve probably never seen it quite like EmuDevz, a game in which you develop an 8-bit emulator by [Rodrigo Alfonso].

There’s a lot of learning you’ll have to do along the way, about programming and how retro systems work, including diving into 6502 assembly code. Why 6502? Well, the emulator you’re working on (it’s partially-written at the start of the game; you need only debug and finish the job) is for a fantasy system called the NEEES “an antique game console released in 1983”. It’s the NEEES and not NES for two reasons. One, Nintendo has lawyers and they really, really know how to use them. Two, by creating a fantasy console that is not-quite-a-Famicom, the goalposts for EmuDevz can be moved a bit closer in.

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RFIDisk

RFIDisk: When Floppy Drives Go Contactless

October 16, 2025 by 14 Comments

Not too long ago, part of using a computer was often finding the correct disk for the application you wanted to run and inserting it into your machine before you could start. With modern storage, this is largely a thing of the past. However, longing for some of that nostalgia, [ItsDanik] has been developing the RFIDisk, a 3D printed floppy drive that can kick off applications when their disk is inserted.

The desktop enclosure is printed to look like a standalone floppy drive, allowing use with either desktops or laptops. There’s the familiar 3.5 inch slot ready for your floppy disk, and there’s also a 1.3 in. OLED display on the front giving you feedback on the status of the RFIDisk — including telling you what’s currently inserted. Inside the enclosure is an Arduino Uno and an MFRC522 RFID reader. As the name would suggest, the way the RFIDisk enclosure reads its media is via NFC, not the traditional magnetic reader. Due to being RFID-based, the disks printed for the RFIDisk are solid without moving parts, but enclose a 25 mm NTAG213 NFC tag.

On the software side, [ItsDanik] has developed the RFIDisk Manager Python application, which is used to tie specific NFC tag IDs to commands to run when that tag is read. The application includes some nice features, such as being able to adjust the commands for both when the disk is first read and when it’s removed from the RFIDisk. You can also change what shows up on the OLED screen when the cartridge is inserted.

Using NFC to simulate physical media is a clever trick we’ve seen before, but if you’re looking for something with a bit more physical engagement, you could always put your USB devices into 3D printed cartridges.

How Bad Can A Cheap Knockoff ADS1115 ADC Be?

October 15, 2025 by 29 Comments

Although the saying of caveat emptor rings loudly in the mind of any purveyor of electronic components, the lure of Very Cheap Stuff is almost impossible to resist. Sure, that $0.60 Ti ADS1115 ADC on LCSC feels like it almost has to be a knock-off since the same part on Digikey is $4 a pop, and that’s when you buy a pack of 1,000. Yet what if it’s a really good knockoff that provides similar performance for a fraction of the price, such as with those cheap ADC boards you can get from Amazon? Cue [James Bowman] letting curiosity getting the better of him and ordering a stash of four boards presumably equipped with at least some kind of cheapo knockoff part, mostly on account of getting all boards for a mere $2.97.

The goal was of course to subject these four purported ADS1115s to some testing and comparison with the listed performance in the Ti datasheet. Telling was that each of the ADCs on the boards showed different characteristics, noticeably with the Data Rate. This is supposed to be ±10% of the nominal, so 7.2 – 8.8 times per second in 8 samples per second mode, but three boards lagged at 6.5 – 7 SPS and the fourth did an astounding 300 SPS, which would give you pretty noisy results.

Using a calibrated 2.5 voltage source the accuracy of the measurements were also validated, which showed them to be too low by 12 mV. The good news was that a linear correction on the MCU can correct for this, but it shows that despite these parts being ADS1115 compatible and having features like the PGA working, you’re definitely getting dinged on performance and accuracy.

[James] said that he’s going to run the same tests on an ADS1115 board obtained from Adafruit, which likely will have the genuine part.  We would also love to see someone test the $0.60 version from LCSC to see whether they can match the datasheet. Either way, if you are eyeing this ADC for your own projects, it pays to consider whether the compromises and potential broken-ness of the knockoffs are worth it over coughing up a bit more cash. As they say, caveat emptor.